Document Redmond_doc_d99aacfa3a

Pre-Design Report 160th Avenue NE Extension Prepared for City of Redmond November 2012 1100 112th Avenue NE Suite 400 Bellevue, WA 98004 ---PAGE BREAK--- ---PAGE BREAK--- CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT III NOVEMBER 2012 Contents Executive Summary ES‐1 Introduction ES‐1 Budget Level Costs ES‐1 Project Schedule ES‐2 Funding ES‐2 1 Introduction and Purpose 1‐1 1.1 Introduction 1‐1 1.2 Pre‐Design Report Purpose 1‐1 1.3 Project Purpose 1‐1 1.4 Existing Conditions 1‐2 1.4.1 Survey and Basemapping 1‐2 2 Alignment Alternatives Considered 2‐1 2.1 Introduction 2‐1 2.2 Alignment Alternative 1 2‐1 Reduced Right‐of‐Way Impacts 2‐1 2.3 Alignment Alternative 2 2‐2 No Regard for Existing Right‐of‐Way 2‐2 2.4 Alignment Alternative 3 2‐2 Maintains Predefined Corridor with the Least Right‐of‐Way Impacts 2‐2 3 Alternative Screening and Selection 3‐1 3.1 Overview of Public and Agency Involvement Process 3‐1 3.2 Description of Screening Process 3‐1 3.3 Recommendations and Summary of Preferred Alignment Alternative Selection 3‐1 4 Design Criteria and Assumptions 4‐1 4.1 Roadway Geometrics and Cross Sections 4‐1 4.2 Functional Classification 4‐1 4.3 Posted Speed and Design Speed 4‐1 4.4 Roadway Cross‐Section 4‐2 4.4.1 Traffic Lanes 4‐2 4.4.2 Bike Lanes 4‐2 4.4.3 Sidewalk 4‐2 4.4.4 Landscape Strip 4‐3 4.5 Maximum Grades 4‐3 4.6 Horizontal Radius 4‐3 4.7 Horizontal Tangent Runout 4‐3 4.8 Stopping Sight Distance 4‐3 4.9 Sag Curve Length 4‐3 4.10 Equestrian Facilities 4‐3 4.11 Traffic Operations 4‐4 4.12 Culvert Structures 4‐9 4.13 Retaining Walls 4‐9 4.14 Geotechnical 4‐9 ---PAGE BREAK--- CONTENTS CONTINUED CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT IV NOVEMBER 2012 4.15 Stormwater 4‐10 4.16 Utilities 4‐12 4.16.1 Existing Utilities 4‐12 4.16.2 Proposed Utilities 4‐12 5 Right‐of‐Way 5‐1 5.1 Introduction 5‐1 5.2 Parcel Table 5‐2 6 Environmental 6‐1 6.1 Summary 6‐1 7 Cost Estimates 7‐1 7.1 Budget Level Cost Estimate 7‐1 7.2 Planning Level Project Risk Assessment 7‐5 8 Redmond‐Woodinville Road Intersection Analysis 8‐1 8.1 Introduction 8‐1 8.1.1 Methods and Assumptions 8‐1 8.2 Alternatives 8‐2 8.2.1 Alternative 1: No‐Build Alternatives 8‐2 8.2.2 Alternative 2: Roundabout 8‐4 8.2.3 Alternative 3: Signalized Intersection 8‐6 8.3 Traffic Analysis 8‐8 8.4 8‐9 Appendices Appendix A Technical Memorandums A‐1 Structures Alternatives Study Technical Memorandum A‐2 Evaluation of Crossing Alternatives at Wetland 3 A‐3 Geotechnical Summary of Findings Memorandum 4‐4 Preliminary Stormwater Memorandum A‐5 Wetland and Stream Assessment Technical Memorandum A‐6 Preliminary Evaluation of Environmental Requirements Memorandum A‐7 Traffic Study and Operational Analysis Technical Memorandum Appendix B Meeting Minutes Appendix C Project Photos Appendix D Electronic Basemap and Digital Terrain Model Figures Figure 1: Vicinity Map 1‐3 Figure 2: Issues Map 1‐4 Figure 3: Alignment Alternatives 2‐3 Figure 4: Preferred Plan 4‐5 Figure 5: Preferred Typical Section 4‐6 Figure 6: Future Typical Section 4‐7 Figure 7: Preferred Profile 4‐8 Figure 8: Wetland 3 Culvert 4‐9 Figure 9: Preliminary Stormwater Design 4‐11 Figure 10: Utilities 4‐15 ---PAGE BREAK--- CONTENTS CONTINUED CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT V NOVEMBER 2012 Figure 11: Right‐of‐Way Acquisitions 5‐3 Figure 12: Planning Level Risk Assessment 7‐6 Figure 13: Year 2030 AM and PM Peak Hour Forecast 8‐2 Figure 14: Alternative 1, No Build 8‐3 Figure 15: Alternative 2, Roundabout 8‐5 Figure 16: Alternative 3, Signalized Intersection 8‐7 Tables Table 1: Geometric Design Criteria 4‐1 Table 2: Contact Information for Area Utilities 4‐14 Table 3: Parcel Table 5‐2 Table 4: Anticipated Environmental Requirements – 160th Avenue NE Extension 6‐2 Table 5: 2030 Intersection Operations at Red‐Wood Road/160th Avenue NE Intersection 8‐8 Table 6: 2030 Queue at Red‐Wood Road/160th Avenue NE Intersection for Alternative 3 8‐9 ---PAGE BREAK--- CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT ES‐1 NOVEMBER 2012 Executive Summary Introduction The purpose of this report is to provide a preliminary design concept for the 160th Avenue NE Extension Project (Project) in the City of Redmond (City) that accurately represents the current and future corridor needs of the City as well as the surrounding neighborhoods. This corridor has been analyzed previously and a final supplemental Environmental Impact Statement (EIS) was issued in 1999. Since that time, the city’s future vision for the corridor has broadened to include a greater variety of users and modes. This report provides details of the revised design and includes information on the design, costs, and environmental requirements. For the Project, three primary alternatives were developed in conjunction with design preferences from City staff and City Zoning Codes that included varying horizontal and vertical alignments, right‐of‐way footprints, retaining walls, wetland and stream crossing points, and varying cross sections. Ultimately, an alternative was selected for further evaluation that provided reduced project cost and entailed the least amount of additional right‐of‐way acquisition by making use of previously acquired city parcels, intended for the corridor. Additionally, the selected alternative provides a more direct horizontal and vertical alignment and provides a safe corridor for all users. The preferred alternative in the 1999 EIS consisted of a roadway section with five lanes. While this previous alternative more than doubles the roadway capacity of the adjacent Redmond‐Woodinville Road (Red‐Wood Road), it does not fit within the city’s current vision or the context of the adjacent roadway network and residential neighborhoods. The narrower section consisting of two traffic lanes, two bike lanes, and two sidewalks, was selected after several iterations internally within CH2M HILL and with input from City staff. This alternative reflects a design that satisfies the City’s vision of a future corridor that would reduce costs and environmental impacts resulting from a 5‐lane roadway but would still accommodate the needs of pedestrians, bicyclists, and trail users. The selected roadway section is adaptable to a future higher roadway capacity configuration including a second uphill lane with minimal changes should the city determine the necessity for this future capacity increase. After the preferred alternative and roadway section was selected, further analysis, including fieldwork to determine boundaries and categories, of the wetlands and streams and methods of crossing those critical areas was studied to minimize cost and impacts. At the largest wetland crossing immediately south of the Puget Sound Energy (PSE) transmission lines, several crossing structures were evaluated, including a bridge, precast concrete culverts, and steel culverts. A precast concrete arch culvert was selected for its simplicity, cost effectiveness, context within the Project setting, and PSE trail under‐ crossing adaptability. Additional work included consideration of slope stability and suitability of Project‐related walls, stormwater runoff processing and mitigation, and the environmental requirements including the National Environmental Protection Act (NEPA), State Environmental Protection Act (SEPA), and the required permits. Budget Level Costs A summary of the estimated budget‐level costs for right‐of‐way, Project development, and construction of the preferred alternative for 160th Avenue NE Extension is provided in this report. The estimated costs for construction were developed assuming 2012 unit prices including 30 percent contingency and were escalated to a mid‐point of construction for year 2015, assuming a 3 percent per year escalation factor. ---PAGE BREAK--- EXECUTIVE SUMMARY CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT ES‐2 NOVEMBER 2012 The estimated costs for right‐of‐way, Project development and construction management included contingencies ranging from 25 to 35 percent. The $13.4 million total cost estimated for the Project as currently envisioned is approximately 59 percent lower than the $33 million presented in the City’s 2011 Transportation Improvement Program. The primary differences are due to reducing the cross‐section from five lanes to two lanes, and crossing the existing major stream crossing with a precast concrete culvert instead of a larger concrete bridge structure. These changes have a dramatic effect on the cost of the Project when considering the steep terrain and wetland conditions that exist along the corridor. Project Schedule The overall Project schedule is dependent on the timing of available Project funding. Assuming that adequate Project funding can be obtained during the 2013‐2016 funding cycles, the following general schedule is anticipated for the Project.  Obtain full Project and/or design funding: 2013‐2014  Preliminary engineering and environmental documentation: 2014  Obtain right‐of‐way and construction funding (if necessary): 2014‐2015  Right‐of‐way acquisition: 2015  Final design and plans and specifications: 2015  Construction: 2016 Funding Due to the nature of this Project being more of a missing link connection between two residential streets, the primary funding source for this Project would most likely be the City. City sources could involve developer mitigation, stormwater and water quality, utility, and perhaps Parks and Recreation for improvements and connections related to the Powerline Trail. Other potential sources could include Transportation Improvement Board; other State funds related to water quality, stream enhancement, or wetlands; federal, or Puget Sound Regional Council funds. The traffic signal at State Route (SR) 202 could be eligible for Washington State Department of Transportation (WSDOT) funds. Project readiness is a key criterion for funding agencies. Advancing the Project to obtain environmental approvals and needed right‐of‐way are key milestones that improve the Project’s rating and scoring in a competitive grant process. Based on the schedule noted above, the City should plan to secure funds for this activity as early as 2013. ---PAGE BREAK--- CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 1‐1 NOVEMBER 2012 SECTION 1 Introduction and Purpose 1.1 Introduction The 160th Avenue NE Extension Project (Project) aims to improve the safety of all modes of travel, accommodate the increased need for additional vehicle capacity within the corridor, and provides essential arterial linkages out of Redmond’s downtown core. The Project’s solutions must balance the needs of the future vehicular traffic along with the needs of pedestrians, bicycles, and equestrians; minimize disturbance to the environment and properties; and define a solution that is practical and economically feasible for the City. The Project would extend 160th Avenue NE from its current barricaded terminus location just north of NE 98th Street to Red‐Wood Road near NE 107th Court. This extension is approximately 1,300 feet long. A vicinity map of the Project area is provided in Figure 1. Within the corridor, a number of unique aspects will need to be addressed:  Steep terrain and the presence of wetlands;  Roadway retaining walls;  Crossing of three ravines with streams and associated wetlands;  Crossing of the Seattle Public Utilities (SPU) 54‐inch water line;  Undercrossing of overhead PSE transmission lines and support towers; and  The need for a grade‐separated crossing of the Powerline Trail located within the PSE right‐of‐way. These components and key Project issues are summarized in Figure 2. 1.2 Pre-Design Report Purpose The purpose of this Pre‐Design Report is to document the alternatives development and selection process, identify design criteria, and define Project costs to support the funding application process for the final design and construction of 160th Avenue NE Extension. This report summarizes the alternative development and selection process, including:  Identification of alternatives considered  Development of the alternatives  Evaluation, screening, and selection of the preferred alternative  Development of budget‐level costs for the preferred alternative  Providing a matrix of required environmental permits 1.3 Project Purpose The 160th Avenue NE Extension Project is a necessary improvement because of limited multimodal access for all users, and site constraints to expanding Red‐Wood Road within the existing corridor. This proposed corridor would more efficiently handle congestion, increase safety, and provide multimodal access from the Downtown Redmond core to and from the north. The Project objectives have evolved from the 1999 Supplemental Environmental Impact Statement (SEIS) into the following:  Redistribute traffic flow and reduce overall congestion.  Provide a new arterial into the central business district. ---PAGE BREAK--- SECTION 1 - INTRODUCTION AND PURPOSE CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 1‐2 NOVEMBER 2012  Improve safety in the corridor.  Provide bicycle, pedestrian and equestrian facilities.  Minimize impacts to the environment.  Provide a corridor that accomplishes the aforementioned points in a cost efficient manner. This Pre‐Design phase of the Project consists of the preliminary design and feasibility of extending 160th Avenue NE. The preliminary design of the Project improvements will involve establishing a cross‐ section and optimizing a Project footprint to determine the right‐of‐way needs, environmental impacts, and estimated costs of the Project. 1.4 Existing Conditions The existing site includes a steep longitudinal cross slope with interspersed low‐quality wetlands and seasonal creeks. Vegetation is a combination of riparian grasses on the west and pockets of evergreen trees in the east. The existing hillside is unstable near the south end of the Project but becomes increasingly stable once the impacted areas extend to the north. Currently, overhead power lines and underground utility corridor crosses the proposed alignment as well as a moderately maintained, steep, multi‐use trail. There are two dwelling units in the southeast quadrant of the Project area. Photos of the existing conditions can be found in Appendix C. 1.4.1 Survey and Basemapping CH2M HILL performed a topographic survey in support of the proposed improvements for 160th Avenue NE covering the segment of undeveloped area between the northerly and southerly termini of the existing roadway. During the survey, the survey team recovered existing monuments based on a previous survey provided to CH2M HILL by the City. The map is tied to City horizontal control points "GPS903E1," "GPS903E4," "GPS903D4," and "GLO3DS and City BM # COR9177. The horizontal datum is NAD 83 (91) and the vertical datum is NAVD 88. The mapping was collected using cross‐section method at 50‐foot intervals, with grade locations at a maximum of 25‐foot spacing. It depicts existing features including roadways, right‐of‐way lines, parcel boundary lines and ownerships, easements, major utilities, walls, structures, culverts, fences, towers, trees, grade breaks, streams, and wetland flags. A digital terrain model (DTM) was generated from surveyed elevations to generate 2‐foot contours. An electronic copy of the DTM and basemap can be found in Appendix D. ---PAGE BREAK--- SECTION 1 - INTRODUCTION AND PURPOSE CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 1‐3 NOVEMBER 2012 Figure 1: Vicinity Map 160th Ave NE Extension ---PAGE BREAK--- SECTION 1 - INTRODUCTION AND PURPOSE CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 1‐4 NOVEMBER 2012 Figure 2: Issues Map ---PAGE BREAK--- CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 2‐1 NOVEMBER 2012 SECTION 2 Alignment Alternatives Considered 2.1 Introduction As shown in Figure 3, three horizontal alignments were initially considered for the City’s 160th Avenue Extension Pre‐Design Project to evaluate, select, and optimize an alignment that balances right‐of‐way impacts, environmental impacts, and earthwork and structural impacts. Field survey data of this steep and varied terrain was utilized in conjunction with the horizontal alignments to develop optimized vertical alignments. Key metrics for horizontal and vertical alignment alternative development included the following:  Economize material and construction costs.  Minimize impacts to environmentally sensitive areas (wetlands, tree strands).  Minimize right‐of‐way takes beyond existing ownership.  Adhere to City roadway standards set forth in “Construction Specification and Design Standards for Streets and Access” with additional guidance from the American Association of State Highway and Transportation Officials (AASHTO) Policy on Geometric Design Handbook.  Allow multimodal facilities within the corridor as well as crossing the corridor.  Ensure design does not preclude Americans with Disabilities Act of 1990 (ADA) design compliant trail crossing and associated approaches.  Minimize wall, structure, and earthwork costs as much as possible. The 1999 SEIS identified a preferred corridor and alignment. Based on information from City staff, an isolated parcel within the corridor was acquired during an adjacent real estate transaction sometime in the early 2000s. This parcel was located based on the preferred alignment in the SEIS. In addition to developing an alignment alternative that maintained the roadway within the limits of the parcel, two other alignment alternatives were developed that would require additional adjacent parcel acquisitions. All alignment alternatives avoided impacts to existing overhead power lines and existing underground water and gas lines while not precluding future expansions within the current utility corridor (utilidor) that the proposed roadway crosses. Each alternative was also carefully designed to allow potential at grade or grade separated crossing of the existing Powerline Trail, which crosses the site and any future improvements to the trail. Section 4 of this report details the selection process. 2.2 Alignment Alternative 1 Reduced Right-of-Way Impacts Alignment 1 (shown in orange on) utilizes direct geometry to minimize curves while avoiding wetland as much as possible. This alternative will require some realignment of the existing roadway adjacent to the Riverpoint complex and requires a steep grade exceeding 10 percent in the southern portion of the Project to minimize excessively large walls and closely follow the terrain. In the northern portion, the alignment has flatter grades that require additional walls and earthwork. Additionally, the alternative crosses the largest wetland, wetland 3A, at the widest point. Where possible, the alignment stays close to existing right‐of‐way pockets. However, the alternative would require additional “sliver” takes in ---PAGE BREAK--- SECTION 2 - ALIGNMENT ALTERNATIVES CONSIDERED CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 2‐2 NOVEMBER 2012 addition to existing city property. Parcel impacts include [PHONE REDACTED] (Veal), [PHONE REDACTED] (Veal), [PHONE REDACTED] (PSE), and [PHONE REDACTED] (King County). 2.3 Alignment Alternative 2 No Regard for Existing Right-of-Way Alternative 2 (shown in magenta on Figure 3) follows a projection of the existing alignment and then turns sharply into the hillside to gain elevation and avoid wetland 1A while minimizing the crossing length of wetland 2A and requiring large amounts of earthwork and cut walls. With a maximum grade of 8 percent, the alignment climbs up the hillside and daylights at the bottom of wetland 3A. The alignment then curves to the west to minimize the crossing length of wetland 3 (adjacent to the PSE trail crossing) followed by a right turn to re‐align with the portion of 160th Avenue adjacent to Redmond 74. The northern portion of the alignment closely follows the existing terrain. The portion would require only minimal walls and earthwork. This alignment requires require great amounts of additional right‐of‐way acquisitions due to its curving horizontal design. The alignment will affect the following parcels, [PHONE REDACTED] (Veal), [PHONE REDACTED] (Veal), [PHONE REDACTED] (PSE), [PHONE REDACTED] (PSE), and [PHONE REDACTED] (King County). 2.4 Alignment Alternative 3 Maintains Predefined Corridor with the Least Right-of-Way Impacts The main intent of Alternative 3 (shown in red on Figure 3) is to stay within the existing City right‐of‐way parcels. The alignment only features the curve just north of the Riverpoint development and affects parcels [PHONE REDACTED] (Veal), [PHONE REDACTED] (PSE), [PHONE REDACTED] (PSE), and [PHONE REDACTED] (King County). Generally, this is a straighter horizontal alignment, the maximum grade is limited to 8 percent, with only 650 feet of length greater than 5 percent, and optimizes the separation from the existing residence (Veal). Significant walls and earthwork are required along the entire length of this alignment. The crossing of wetland 3A is near the widest point, which creates the greatest impact. ---PAGE BREAK--- ---PAGE BREAK--- CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 3‐1 NOVEMBER 2012 SECTION 3 Alternative Screening and Selection 3.1 Overview of Public and Agency Involvement Process A City review team comprised of several City departments has reviewed and guided the design effort to date. There has also been contact with key utility stakeholders as well as adjacent property owners. Moving forward, a public open house should be held to inform the public and other stakeholders about the Project. 3.2 Description of Screening Process In a Project (Consultant) team meeting on April 17, 2011, the team developed screening criteria to provide a preliminary ranking of the three alternatives to focus our efforts on the most beneficial alignment. In support of this ranking, the team has considered key influences along the alignment that will drive Project costs as well as minimize impacts to the neighborhood and the environment. Ultimately, all Project attributes include an inherent cost that serves as a sufficient form of weighting and comparing Project attributes. For this particular Project, the Consultant team determined that the three top Project attributes to be examined with respect to cost are right‐of‐way impacts, environmental impacts, and earthwork and structures. During the evaluation process, the alignment alternatives were continuously compared against each other with the aforementioned attributes used to measure relative performance. Additional attributes that were used in comparison include:  Accommodation of PSE trail crossing  Roadway grade and safety criteria  Traffic operations 3.3 Recommendations and Summary of Preferred Alignment Alternative Selection As a result of the evaluation and screening process, alignment 3 is the preferred alternative for the 160th Avenue NE Extension. Alignment 3 provides a direct alignment centered in existing right‐of‐way parcels which reduces the need to acquire additional property and minimizes impacts to existing adjacent landowners. When analyzed in terms of cost with the environmental impacts of all three alignments, the cost of mitigating environmental impacts was roughly the same for all alignments whereas the right‐of‐ way impacts were quite different. Alignment alternative 3 required the least amount of additional right‐ of‐way when compared with the other alignments. While alignment alternative 3 required more earthwork and structures than alignment 1 and a longer crossing of wetland 3A than alignment 2, the relative costs of these additional expenditures were not enough to justify the additional right‐of‐way requirements for the other alignments. The maximum roadway grade and relatively simple horizontal layout of alignment 3 were also deciding factors as they were combined more desirable than either alternative alignment. Traffic operations should be nearly identical for all alignments. It is important to note that while the three alignments were thoroughly compared and contrasted, they are very similar and all provide safe mobility for all users while minimizing impacts to existing utilities, not precluding new utilities, and accommodating a trail crossing of the PSE trail. ---PAGE BREAK--- CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 4‐1 NOVEMBER 2012 SECTION 4 Design Criteria and Assumptions 4.1 Roadway Geometrics and Cross Sections Based on the City “Zoning Code, Appendix 2: Construction Specification and Design Standards for Streets and Access” the following design criteria were implemented in preliminary design. This geometric design criterion is summarized in Table 1. This is followed by additional detail regarding the basis of the selection. Table 1: Geometric Design Criteria Design Element Standard Proposed Design Functional classification Minor Arterial Minor Arterial Posted speed 30 mph 30 mph Design speed 35 mph 35 mph Number of traffic lanes 4 2 Lane width 12 feet 11 feet Bike lanes 5.5 feet 5.5 feet Sidewalk (both sides) 6 feet 6 feet Landscape strip 5 feet 4 feet to 5 feet Maximum grade 10 percent 8 percent Minimum horizontal radius 510 feet 1300 feet Minimum horizontal tangent runout 200 feet 915 feet Flat stopping sight distance 305 feet 305 feet Maximum stopping sight distance (based on maximum grade) 350 feet 350 feet Minimum sag curve length (with lighting) 165 feet 400 feet 4.2 Functional Classification Based on the City’s Transportation Master Plan the functional classification for 160th Avenue NE is a Minor Arterial. Geometric design criteria for minor arterials are shown in Table 2. 4.3 Posted Speed and Design Speed Our recommendation is to use a posted and design speed of 30 miles per hour (mph) for the Project. This coincides with the existing portion of 160th Avenue NE that is adjacent to Downtown and the Riverpoint housing development. Per the City zoning codes, stopping sight distance is computed from a speed of 40 mph for a 30 mph corridor. ---PAGE BREAK--- SECTION 4 - DESIGN CRITERIA AND ASSUMPTIONS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 4‐2 NOVEMBER 2012 4.4 Roadway Cross-Section The selection of the preferred section was an iterative one examining several interim configurations that provided flexibility for a final section. Although the preferred section does not meet all the design attributes in the City zoning code for a minor arterial, it will provide a safe and context sensitive design for the adjacent neighborhoods as well as natural areas. 4.4.1 Traffic Lanes The 33 feet of roadway width leaves two configurations for the travelled lanes while providing width for bike lanes, sidewalks, and planter strips. This two‐lane section is better aligned to the adjacent roadway network rather than a five‐lane section that was originally proposed with the 1999 SEIS. The proposed “opening day” configuration will have two 11‐foot lanes, one for each travel direction. AASHTO recommends 11‐foot lanes on arterial streets as it helps moderate speeds and, in this particular situation, reduces the amount of impervious area and right‐of‐way impacts. With 22 feet of total lane width, this will leave another 11 feet of room for bike lanes. Based on city input and citing issues related to cost and environmental impacts, a two‐lane section was selected. In the future, as travel demand increases, the roadway width can be repurposed to allow for three lanes ‐ one downhill southbound lane and two uphill northbound lanes (Figure In the three‐lane configuration, there will be no roadway width specifically purposed for bike lanes. In the southbound direction, the traveled lane will be a shared vehicle and bike lane. At the proposed 8 percent grade, it is reasonable to assume that bicycles will be traveling at the same 30 mph as the vehicles. In the northbound direction, there will be one general‐purpose lane and one shared truck climbing and bike lane. The placement of a climbing lane was evaluated; however, the AASHTO warrants and research for climbing lane placement indicate that at an 8 percent uphill grade, a speed reduction of less than 5 mph will occur over the distance of 130 feet (the length of the 8 percent grade) for a large truck with a starting speed of 70 mph. Furthermore, AASHTO indicates that a climbing lane may not be economically feasible if there is less than a 10 mph speed reduction for a heavy truck. Since the crawl speed for most trucks is between 20 and 30 mph, a truck driving up this grade will have a very small, if any, reduction in speed. Finally, the taper to add and remove the climbing lanes (300 and 600 feet, respectively, according to AASHTO) represent nearly 70 percent of the roadway length. Ultimately, if the city sees fit, the three‐lane configuration could be implemented at the roadways time of opening to mitigate effects of slower vehicles driving up the grade. 4.4.2 Bike Lanes As mentioned above in Section 4.4.1, in the proposed “opening day” configuration, there will be 11 feet of roadway width that will be utilized as bike lanes. This width allows for a 5.5‐foot bike lane in each direction. In the future configuration, the bike lanes will be eliminated and each direction will have a shared bike and vehicle lane. 4.4.3 Sidewalk In both the northbound and southbound directions of the 160th Avenue NE Extension, there will be a 6‐foot sidewalk. This sidewalk will meet all current ADA and accessibility guidelines, with a maximum cross‐slope of 2 percent. Section R302.5 of the PROWAG (Public Rights‐of‐Way Access Guide), along with WSDOT’s Field Guide for Accessible Rights‐of‐Way – 2010 Edition, provides that longitudinal grades exceeding 5 percent are permitted on facilities adjacent to a street or road with a grade equal to or ---PAGE BREAK--- SECTION 4 - DESIGN CRITERIA AND ASSUMPTIONS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 4‐3 NOVEMBER 2012 greater than the adjacent sidewalk. In addition, at the intersection of 160th Avenue NE and Red‐Wood Road, all designated pedestrian crossing locations will be appointed with ADA curb ramps and crosswalks. 4.4.4 Landscape Strip There will be a 4‐foot landscape strip located between the roadway curb and the sidewalk on the west side of 160th Avenue NE and a 5‐foot landscape strip on the east side of 160th Avenue NE. These landscape strips will not only introduce green space onto the cross‐section, but will also serve stormwater needs for the property. These landscaped strips will house stormwater filters that will infiltrate the roadway runoff as described in Section 4.15. 4.5 Maximum Grades As shown in the preferred profile in Figure 7, a maximum 130‐foot long grade of 8 percent is recommended to minimize earthwork quantities and walls. This will better align the roadway within the context of the existing topography. 4.6 Horizontal Radius A minimum horizontal radius of 1,300 feet (on centerline) provides a safe and predictable driving path that includes sufficient horizontal sight distance so that sight lines are contained within the roadway prism. 4.7 Horizontal Tangent Runout A distance of 915 feet between curves provides sufficient runout for superelevation and is long enough to prevent a condition of broken back curves. 4.8 Stopping Sight Distance Based on City Zoning Code, Appendix 2, arterial stopping sight distance was computed based on a design speed of 10 mph above the assumed posted speed (30 mph). 4.9 Sag Curve Length A 400‐foot sag curve is provided near the southern end of the Project to provide a smooth driving experience while allowing sufficient stopping sight distance and headlight sight distance for drivers. 4.10 Equestrian Facilities Based on the PSE Trail Report developed by Reid Middleton in 2009, a grade‐separated trail crossing with vertical clearance minimum of 10 feet is to be provided in the design. As shown in the roadway profile in Figure 7, the 84‐foot precast culvert at wetland 3 will allow for an equestrian crossing. The existing PSE trail will need to be realigned to descend underneath the 160th Avenue NE Extension and pass through the culvert. The 84‐foot undercrossing can accommodate a 12‐foot high by 12‐foot wide box culvert adjacent to wetland 3 for equestrian use which meets the minimum criteria set forth in the 2009 PSE Trail Report. ---PAGE BREAK--- SECTION 4 - DESIGN CRITERIA AND ASSUMPTIONS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 4‐4 NOVEMBER 2012 4.11 Traffic Operations Traffic operations along 160th Avenue NE will be influenced primarily by the major intersections at the northern terminus at Red‐Wood Road and southern end at NE 90th Street. The intersection of NE 90th Street is currently signalized, while the intersection with Red‐Wood Road is stop‐controlled. Detailed traffic operations analysis was conducted for the 160th Avenue NE/Red‐Wood Road intersection and is presented later in this report in Section 9, with the recommendation for a signalized intersection. As discussed in Section 5.4.1., there are two proposed configurations for traffic lanes. The proposed “opening day” configuration will have two 11‐foot lanes, one for each travel direction, with two 5.5‐foot bike lanes. The ultimate configuration calls for three 11‐foot travel lanes, with two northbound (uphill) lanes and one southbound lane. In the three‐lane configuration, there will be no roadway width specifically purposed for bike lanes. In the southbound direction, the traveled lane will be a shared vehicle and bike lane. At the proposed 8 percent grade, it is reasonable to assume that bicycles will be traveling at the same 30 mph as the vehicles. In the northbound direction, there will be one general‐ purpose lane and one shared truck climbing and bike lane. In addition, bicyclists traveling northbound up the hill can use the adjacent sidewalk instead of the truck‐climbing lane. The 2030 PM peak hour demand volume in the northbound direction is 815 vehicles per hour (vph). There is no existing or forecasted truck volume available for 160th Avenue NE, so 2 percent of the vehicles were assumed trucks (approximately 16 trucks). Based on methodology outlined in the HCM 2000, the arterial level of service (LOS) for northbound 160th Avenue NE is LOS C with one travel lane. Therefore, an additional climbing lane is not necessarily needed to improve traffic operational performance. Ultimately, if the city sees fit, the three‐lane configuration could be implemented at the roadway’s time of opening to mitigate effects of slower vehicles driving up the grade. ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- SECTION 4 - DESIGN CRITERIA AND ASSUMPTIONS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 4‐9 NOVEMBER 2012 4.12 Culvert Structures The proposed roadway crosses over several ravines or lowland areas that require culverts for water passage. At all but one of these locations, relatively small diameter culverts can be used. However, the ravine located immediately south of the PSE transmission lines spans approximately 150 feet from bank to bank and is about 20 feet deep at the proposed road crossing. It contains seasonal stream flow and a wetland designated as wetland 3. It is assumed that a longer span culvert or bridge is required to provide for stream flow and minimize wetland impacts. In addition, it is desired to provide for an equestrian trail crossing under the roadway along the north bank of the ravine and connect to the PSE trail on each end. These culverts can be seen in Figure 7. Several crossing structures were evaluated at wetland 3, including a pre‐stressed concrete girder bridge as well as steel and precast concrete culverts of span ranging from 48 to 100 feet. This evaluation is summarized in Appendix A‐2, and based on the evaluation performed it is recommended than an 84‐foot precast concrete culvert be used to cross wetland 3. 4.13 Retaining Walls Retaining walls for this Project include both fill and cut walls. Fill walls are mainly needed on the west side of the proposed roadway to contain the roadway embankment fill. It is assumed that structural earth walls are the most economical fill wall type when the height is greater than about 10 to 12 feet. For fill walls less than this height, rockery walls are proposed as a cost‐effective alternative. Cut walls are required at two locations on the east side of the proposed roadway where the road is benched into the hillside. Typical cut wall types include concrete cantilever walls, soldier pile walls, and soil nail walls. It is presumed that soil nail walls are the most cost‐effective choice, assuming that the soil can temporarily stand vertically several feet high to place the rows of soil nails. The cut walls can be significantly reduced or possibly eliminated if the cut slope can extend past the Veal property limit. The retaining walls are shown in Figure 4, and an evaluation of retaining walls needed for the new roadway is included in Appendix A‐1. 4.14 Geotechnical Appendix A‐3 contains a summary of the geotechnical work. It contains a geotechnical findings report summarizing field observations and a summary of work at or near this site that has been completed by others. The geotechnical work on the Project was based on field observations and review of published and existing reports. Appendix A‐3 provides a geotechnical summary of findings and provides preliminary evaluation of geotechnical conditions along the proposed alignment. The geotechnical findings report also provides recommendations for the anticipated work associated with design and construction of the new roadway and discusses areas where additional subsurface investigations will be necessary. No additional geotechnical fieldwork was completed for this phase of the Project. However, CH2M HILL noted the prior geotechnical work conducted by others along with careful field observation of site Figure 8: Wetland 3 Culvert ---PAGE BREAK--- SECTION 4 - DESIGN CRITERIA AND ASSUMPTIONS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 4‐10 NOVEMBER 2012 conditions as a basis for the decisions that form the basis of the recommendations contained in the phase of the work. As the Project moves forward in the planning and design process, additional detailed field investigations will be required to confirm foundation conditions along selected areas of the alignment as required to develop final recommendations for types of structures, foundation conditions and preparation, and other important information necessary for design development. 4.15 Stormwater Stormwater management (Figure 9) will need to address erosion and sedimentation control, pavement drainage, conveyance, water quality treatment, flow control and use of low impact development practices where feasible. Due to the steep topography of the site, both along the roadway and in the vicinity, the potential to infiltrate runoff completely within the roadway section is anticipated to be low. The current stormwater approach, as described in Appendix A‐4, integrates bioretention planters within the planter strips of the roadway to provide water quality treatment. These planter strips will be connected to infiltration trenches to maximize the potential infiltration within the site and maintain existing hydrology to streams that cross the proposed roadway alignment. Due to the close vicinity to the Sammamish River, flow control may not be required, if the Project can demonstrate adequate capacity in the conveyance system that delivers runoff to the river. As a portion of that conveyance system includes discharge through wetland 1, early design phase studies will need to evaluate the existing conditions within the wetland and the potential for the Project to affect the hydroperiod. The existing wetland is degraded and dominated by Reed Canary Grass; therefore, potential wetland restoration is included in the current design approach. Should discharge, without flow control, to the wetland not be deemed appropriate in these studies, additional flow control will likely need to be provided using underground vaults located at the southern extent of the roadway extension prior to discharge to the wetland. The pre‐design memorandum in Appendix A‐4 describes stormwater criteria applicable to the site and a proposed tiered approach to stormwater depending upon further study. ---PAGE BREAK--- ---PAGE BREAK--- SECTION 4 - DESIGN CRITERIA AND ASSUMPTIONS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 4‐12 NOVEMBER 2012 4.16 Utilities 4.16.1 Existing Utilities The following existing utilities are contained within the Project area:  Puget Sound Energy (PSE). PSE owns a 250‐foot wide corridor established for their high‐voltage transmission line and a secondary transmission line that crosses the proposed roadway alignment. Their steel tower supported transmission line supports six high‐voltage transmission cables that cross the alignment at approximately Sta 35+50. The secondary overhead power line crosses at approximately Sta 34+00. Overhead clearances are adequate for proposed traffic operations; however, when installing the 84‐foot precast, culvert construction methods will need to consider space constraints and overhead clearance restrictions by PSE.  Seattle Public Utilities (SPU). SPU operates a 54‐inch diameter water transmission main (Tolt Pipeline No. 2) that lies within a 30‐foot wide easement abutting the north margin of the PSE right‐of‐way. Cascade Water Alliance supplies water to the City from SPU’s Tolt Pipeline No. 2. Based on record drawings, the water main currently has approximately 4.5 feet of cover at the crossing of the proposed roadway alignment. The proposed roadway grade will add approximately 1 to 3 feet of fill over the existing pipeline. Special protection of the existing water main is not anticipated, but should be confirmed during the next phase of design work.  Capped Utilities. Currently both private and City utilities have been capped at both the north and south ends of the Project in anticipation of the future roadway extension. These utilities are described in Section 4.16.2. 4.16.2 Proposed Utilities Extending 160th Avenue NE provides the opportunity to connect the various existing utility systems that have been capped for future extension. It also provides utility infrastructure to support future development. Together, City and private utilities have identified the following proposed utilities for this Project (Figure 10):  City of Redmond Sewer. There is an existing sewer main capped at the southern termini of 160th Avenue NE. The City desires to extend the sewer main an additional 400 feet north, requiring two new manholes. The existing sewer is approximately 12 feet deep. Between the existing manhole and the first proposed manhole, the depth of the sewer main will range from 12 to 8 feet. The remainder of the sewer main extension between the first and second manhole will generally follow the roadway profile grade and be 8 feet deep. This sewer extension will serve the properties to the east of 160th Avenue NE south of the wetland 3. There will be no sewer line provided between the end of the 400 feet extension and the northern Project terminus (Figure  City of Redmond Water. Existing 12‐inch waterlines are capped at both ends of the Project and will be connected by the Project. The City’s standard cover requirement for water mains is 4 feet. There are four proposed culvert crossings along the roadway alignment. Three culverts are 36 inches in diameter and will be installed at depths beneath the proposed waterline and clear of any conflicts. The waterline crossing of the proposed 84‐inch culvert at wetland 3 cannot achieve the 4‐foot minimum cover requirement. To accommodate headroom for the equestrian trail, the culvert crest cannot be deeper than 4.5 feet below the roadway, resulting in only 3 feet of cover over the proposed 12‐inch water main. The proposed waterline crossing over the existing 54‐inch SPU Tolt Pipeline 2 allows the 4‐foot minimum cover to be met (Figure ---PAGE BREAK--- SECTION 4 - DESIGN CRITERIA AND ASSUMPTIONS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 4‐13 NOVEMBER 2012  Comcast. A 4‐inch conduit will be routed beneath the western sidewalk for Comcast. In addition, two new vaults will be placed in the sidewalk for maintenance access.  PSE. For electrical distribution, two 4‐inch conduits will be routed beneath the western sidewalk for PSE. PSE has indicated that they may want a future gas line installed, but it would depend on the type of future development that is expected along the corridor. There appears to be adequate space for a gas line.  Frontier. Four 4‐inch conduits are currently capped at the southern end of the Project and would be extended north throughout the length of the Project. Table 2 is a compilation of contact information for the utilities in the Project area. This contact information is subject to change. ---PAGE BREAK--- SECTION 4 - DESIGN CRITERIA AND ASSUMPTIONS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 4‐14 NOVEMBER 2012 Table 2: Contact Information for Area Utilities Utility Owner Contact Name Contact Information Water City of Redmond Jeff Thompson, PE Senior Engineer Water and Wastewater Engineering 15670 NE 85th Street Redmond, WA 98073 Phone: (425) 556‐2884 [EMAIL REDACTED] Water Seattle Public Utilities Jennyfer Jacobsen 700 5th Avenue, #4144 Seattle, WA 98104 Phone: (206) 684‐8766 Fax: (206) 233‐1532 [EMAIL REDACTED] Sewer City of Redmond Jeff Thompson, PE Senior Engineer Water and Wastewater Engineering 15670 NE 85th Street Redmond, WA 98073 Phone: (425) 556‐2884 [EMAIL REDACTED] Cable TV & Fiber Optics Comcast Jill M. Look 1525 75th Street SW Suite 200 Everett, WA 98203 Phone: (425) 396‐6032 Fax: (425) 263‐5352 [EMAIL REDACTED] Power & Gas Puget Sound Energy Kelly Purnell Municipal Construction Planner PO Box 97034, EST 11W Bellevue, WA 98009 Phone: (425) 462‐3488 [EMAIL REDACTED] Telephone Frontier Mike HaKahan Network Engineer, Outside Plant Engineering 1800 41st Street SW Everett, WA 98203 Phone: (425) 263‐4038 Fax: (425) 263‐4048 [EMAIL REDACTED] ---PAGE BREAK--- ---PAGE BREAK--- CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 5‐1 NOVEMBER 2012 SECTION 5 Right-of-Way 5.1 Introduction The right‐of‐way needs for this Project are shown on Figure 11. The existing 160th Avenue NE right‐of‐ way is 84‐feet wide through the Riverpoint residential neighborhood to the south; and is 84‐feet wide through the Redmond 74 residential neighborhood to the north. This width provides for a full five‐lane roadway with bike lanes, sidewalks, and planters; however, the existing street section is three traffic lanes, with bike lanes and on‐street parking. Based on earlier planning work to complete 160th Avenue NE, the City acquired an 84‐foot wide by approximately 270‐foot long parcel (parcel [PHONE REDACTED]) to accommodate the extension of 160th Avenue NE. The proposed roadway alignment, together with the use of retaining walls on the uphill side is designed for the improvements to fit within this existing right‐of‐way. Additional right‐of‐way is required from three parcels to complete the extension and match to the existing termini.  Approximately 31,000 square feet is required from the Veal parcel [PHONE REDACTED] to accommodate the proposed roadway, along with its cut and fill slopes. To avoid leaving the property owner with an unusable remnant, the remaining parcel area lying west of the roadway is included in the acquisition area. The right‐of‐way acquisition area includes the proposed open cut slope along the steep hillside to the east instead of retaining walls.  Approximately 20,000 square feet is required from PSE parcel [PHONE REDACTED] to accommodate the proposed roadway and stream crossing culvert. It is assumed that PSE will grant the City a permanent easement for the proposed roadway and related infrastructure. An additional easement or permit may be necessary from SPU to cross over their 54‐inch water main.  A triangular shaped 1,500‐square foot parcel is required from King County Parks parcel [PHONE REDACTED] to accommodate roadway improvements. At this time, it is unknown if this would be acquired at a fee or as permanent easement. In addition to the right‐of‐way acquisitions for roadway, additional right‐of‐way acquisitions will be required for onsite wetland buffer impacts. Based upon the roadway design and preliminary wetland work, approximately 34,000 square feet of wetland buffers would be impacted. As shown in Table 3, approximately 10,000 square feet can be used from the remnant parcel that will be acquired for roadway construction (parcel [PHONE REDACTED]). The remaining area will need to be acquired onsite as part of the right‐of‐way acquisition process to address the remaining approximately 24,000 square feet required for mitigation. Onsite wetland buffers result in the need to acquire approximately 75,000 square feet of right‐of‐way. The Project also results in wetland impacts and for the Project. It was assumed that these impacts would be addressed through the purchase of credits at an offsite mitigation bank that is currently proposed in the Project area. If credits cannot be purchased, approximately 13,770 square feet of additional right‐of‐ way would need to be acquired onsite to address the wetland impacts. ---PAGE BREAK--- SECTION 5 - RIGHT-OF-WAY CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 5‐2 NOVEMBER 2012 5.2 Parcel Table Table 3 provides a summary of the parcels that surround the Project area. Eight parcels border the Project; of those eight, only three require right‐of‐way acquisitions. Of those four parcels, two of them (owned by PSE and King County Parks) could result in an easement in lieu of an acquisition. A map of the parcels and potential right‐of‐way acquisitions can be found in Figure 11. Table 3: Parcel Table Right‐ of‐Way Purpose Property Owner Parcel ID Current Use Total Area (square feet) Acquisition Area (square feet) Net Area (square feet) Notes Roadway Good [PHONE REDACTED] Single family 84,506 ‐ 84,506 Veal [PHONE REDACTED] Single family 158,122 20,605 137,517 Veal [PHONE REDACTED] Vacant lot 134,600 ‐ 134,600 La Prete [PHONE REDACTED] Apartment 738,000 ‐ 738,000 Puget Sound Energy [PHONE REDACTED] Distribution right‐of‐way 266,151 19,750 246,401 Permanent easement King County Parks [PHONE REDACTED] Samm River trail site 968,338 1,490 966,848 Permanent easement 556962TRCT Access tract ‐ ‐ ‐ [PHONE REDACTED] Condominiums 333,880 ‐ 333,880 Roadway totals 2,683,597 41,845 2,641,752 Wetland Mitigation* Veal [PHONE REDACTED] Single family 137,517 10,000 127,517 Remnant of parcel to be used for wetland mitigation TBD 23,155 Onsite parcel to be identified Wetland mitigation totals 33,155 Project totals 2,683,597 75,000 2,608,597 * Note: assumes 13,770 square feet of credits acquired from offsite wetland mitigation bank. ---PAGE BREAK--- USE PROPERTY OWNER PARCEL ID CURRENT USE TOTAL AREA (SF) ‐ ACQUISITION AREA (SF) = NET AREA (SF) NOTES GOOD [PHONE REDACTED] SINGLE FAMILY 84,506 VEAL [PHONE REDACTED] SINGLE FAMILY 137,517 VEAL [PHONE REDACTED] VACANT LOT 134,600 LA PRETE [PHONE REDACTED] APARTMENT 738,000 PUGET SOUND ENERGY [PHONE REDACTED] DISTRIBUTION ROW 246,401 PERMANENT EASEMENT KING COUNTY PARKS [PHONE REDACTED] SAMM RIVER TRAIL SITE 966,848 PERMANENT EASEMENT 556962TRCT ACCESS TRACT ‐ [PHONE REDACTED] CONDOMINIUMS 333,880 ROADWAY TOTALS 2,641,752 VEAL [PHONE REDACTED] SINGLE FAMILY 127,517 REMNANT OF PARCEL TO BE USED FOR WETLAND MITIGATION TBD ON‐SITE PARCEL TO BE IDENTIFIED WETLAND MIITIGATION TOTALS 2,608,597 * NOTE: ASSUMES 13,770 SF OF CREDITS ACQUIRED FROM OFF‐SITE WETLAND MITIGATION BANK. 333,880 ‐ ‐ ROADWAY 2,683,597 41,845 266,151 134,600 ‐ 84,506 158,122 738,000 ‐ 20,605 ‐ 19,750 1,490 968,338 ‐ PROJECT TOTALS 33,155 WETLAND MITIGATION* 137,517 10,000 23,155 2,683,597 75,000 ---PAGE BREAK--- CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 6‐1 NOVEMBER 2012 SECTION 6 Environmental 6.1 Summary The use of federal funds will require NEPA approval, which will be conducted through WSDOT Local Programs who act on behalf of the Federal Highway Administration. NEPA documentation will consist of the WSDOT Environmental Classification Summary with any required supporting documentation attached (air quality, noise, cultural resources, and aesthetics). The NEPA documentation could be adopted to support the required SEPA approval for the Project. The Project’s impact to wetlands requires a Clean Water Act Section 404 permit from the U.S. Army Corps of Engineers and an additional state permit. Because Project effects to wetlands are anticipated to be less than 0.5 acre, a Nationwide Permit can be acquired which minimizes the review timeline. Additional state and local permits will also be required prior to construction. Overall, up to 18 months will be required to complete the necessary environmental documentation and permitting process. Table 4 provides a summary of anticipated environmental permits. Further details related to the permit matrix describing the anticipated environmental requirements are shown in Table 1 of Appendix A‐6. ---PAGE BREAK--- SECTION 6 - ENVIRONMENTAL CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 6‐2 NOVEMBER 2012 Table 4: Anticipated Environmental Requirements – 160th Avenue NE Extension ---PAGE BREAK--- CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 7‐1 NOVEMBER 2012 SECTION 7 Cost Estimates 7.1 Budget Level Cost Estimate The following estimate uses an evolved master planning cost template specifically developed for the City. The estimate shown on the following pages accounts for critical Project costs as well as identifies specific high cost items. ---PAGE BREAK--- SECTION 7 - COST ESTIMATES CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 7‐2 NOVEMBER 2012 ---PAGE BREAK--- SECTION 7 - COST ESTIMATES CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 7‐3 NOVEMBER 2012 ---PAGE BREAK--- SECTION 7 - COST ESTIMATES CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 7‐4 NOVEMBER 2012 ---PAGE BREAK--- SECTION 7 - COST ESTIMATES CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 7‐5 NOVEMBER 2012 7.2 Planning Level Project Risk Assessment The planning level risk assessment takes several factors of Project development and construction and assigns a risk level based on inputs by the design team. While the inputs are qualitative in nature, many of the factors at a preliminary level of design can be assigned risk based on engineering judgment. The assessment then creates an aggregate risk assessment that can be used to aid in the development of appropriate contingency levels for cost analysis. Each risk consideration is ranked according to the level of anticipated risk for the Project and assigned either a high, medium, or low ranking. A ranking of “high” corresponds to a large amount of risk and a ranking of “low” correlates to a small amount of risk. These risk assessment rankings are based on both the likelihood of the risk occurring as well as the impact that the risk would have on the Project. The planning level risk assessment for the 160th Avenue NE Extension Project can be found in Figure 12. Four key risk considerations were taken into account:  Environmental Permitting. This Project has four environmentally sensitive wetlands that will be disturbed temporarily or permanently during the construction of 160th Avenue NE. However, a minimal number of anticipated agency approvals will be required to build the Project. It is for these reasons that the environmental permitting risk assessment is at level medium. Section 0 provides more information on the Project’s environmental considerations.  Design and Construction. The risk assessment level for design and construction has been assessed at a medium level. Most of these risk considerations are based on structures, geotechnical data, and utilities. As mentioned in Appendix A‐3, only a limited amount of soil exploration has been performed thus far, which ranks the unknown soil conditions risk at medium. However, it is not predicted that the roadway will encounter any contaminated soils. There is currently a low level of risk assigned to utilities within the Project, because no existing utilities need to be relocated as part of the design. Because the Project is still in the pre‐design phase and concepts are still being worked through, a medium level of risk has been assigned to the Project definition.  Right‐of‐Way. Based on the proposed alignment there are four parcels that require right‐of‐way acquisition (Section 1.1). Although acquisition is required, the risk assessment for right‐of‐way has been assigned a medium score because the acquisition is small compared to the size of the parcels, and do not require the acquisition of any residential or commercial buildings or any relocations.  Other Factors. The risk assessment for other factors deals with the influence level that other neighboring projects may have on this one, how the stakeholders and public view the Project (if the Project is controversial), if the Project has any federal funding, is located within multi‐jurisdictions, and any time constraints that the Project may have. Based on the research for this Project, the risk assessment level for other factors has been ranked as none, because the other factors currently do not seem to have any adverse effects on the Project. ---PAGE BREAK--- SECTION 7 - COST ESTIMATES CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 7‐6 NOVEMBER 2012 Figure 12: Planning Level Risk Assessment ---PAGE BREAK--- CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 8‐1 NOVEMBER 2012 SECTION 8 Redmond-Woodinville Road Intersection Analysis 8.1 Introduction Three intersection configurations were evaluated for the intersection connection between the northern end of 160th Avenue Extension and Red‐Wood Road (SR 202) based on metrics of constructability, operational and multimodal safety, cost, mobility, local traffic access, and aesthetics. These alternatives included a no‐build alternative, a roundabout alternative, and a signalized intersection alternative. Methods and assumptions for the traffic operations analysis and forecasting are presented below, followed by a detailed description of each alternative. Finally, a summary of traffic operations results is presented for each alternative, followed by a preferred configuration. 8.1.1 Methods and Assumptions Intersection LOS, delays, and volume‐to‐capacity (v/c) ratios were calculated at the study intersection of Red‐Wood Road/160th Avenue NE based on methods contained in the Highway Capacity Manual 2010. (version 8.0) was used for these calculations. Appendix A‐7 contains detailed LOS worksheets for the different alternatives. Traffic forecast volumes for the year 2030 were based on information in the Summary of Traffic Operations and Forecasting – Red‐Wood Road Corridor Study, dated December 2007 by Transpo Group. The study included 2007 as the year for existing conditions and 2030 as the horizon year, based on the latest forecast year for the Bellevue‐Kirkland‐Redmond travel demand forecast model at the time the study was conducted. In that study, several alternatives were studied for the configuration of Red‐Wood Road, including three‐ and five‐lane alternatives. Based on discussions with the City, the three‐lane alternative on Red‐Wood Road was used as the basis for traffic forecasts for this traffic analysis. Recent traffic count data provided by the City was reviewed to ensure that traffic volumes near the intersection of Red‐Wood Road/160th Avenue NE have not changed significantly since 2007. PM Peak intersection counts at two locations (NE 90th Street/Red‐Wood Road and NE 109th Street/Red‐Wood Road) were reviewed for years 2007 and 2010. In both locations, total intersection entering volume was similar but lower in 2010 than in 2007:  NE 90th Street/Red‐Wood Road: 2007 volume = 2,055 vph; 2010 volume = 1,884 vph  NE 109th Street/Red‐Wood Road: 2007 volume = 1,908 vph; 2010 volume = 1,842 vph Recent volumes show that little change in traffic volumes has occurred near the Red‐Wood Road/ 160th Avenue NE intersection. Therefore, forecast volumes for the year 2030 from the Red‐Wood Road Corridor Study were assumed reasonable and conservative for estimating capacity at the Red‐Wood Road/160th Avenue NE intersection. Year 2030 PM peak hour intersection turn movement volumes for the intersection of Red‐Wood Road/160th Avenue NE are presented in Figure 13. Based on review of the existing AM and PM peak hour volumes at the two locations noted above, traffic patterns on Red‐Wood Road are highly directional relatively the same amount of traffic heading southbound in the AM period can be seen heading northbound in the PM period). Therefore, year 2030 AM peak hour volumes were estimated by reversing 2030 PM peak hour traffic flows. ---PAGE BREAK--- REDMOND-WOODINVILLE ROAD INTERSECTION ANALYSIS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 8‐2 NOVEMBER 2012 Figure 13: Year 2030 AM and PM Peak Hour Forecast Volume 8.2 Alternatives 8.2.1 Alternative 1: No-Build Alternatives The “No‐Build” Alternative (Figure 14) maintains the existing intersection configuration. The current design terminates 160th Avenue at a tee intersection with NE 106th Street. NE 106th Street then shortly connects at an un‐signalized intersection with Red‐Wood Road. The channelization from 160th Avenue NE is that of one lane in each direction. The channelization of NE 106th Street has one westbound lane, one eastbound to southbound turn lane, and one eastbound to northbound turn lane. Red‐Wood Road provides one northbound through lane, one southbound through lane, one southbound to westbound turn lane, and a middle lane that provides northbound to southbound turning traffic a refuge as well as eastbound to northbound traffic (flying  Construction Cost: minimal, configuration is currently built; some additional signage and striping may be needed.  Construction Delay and Mitigation: minimal, configuration is currently built and operating.  Safety for Vehicles: not particularly safe for traffic that is turning onto Red‐Wood Road without a protected signal. The current approach of 106th Street is up a hill to Red‐Wood Road, which likely reduces intersection sight distance coupled with Red‐Wood Road being in a horizontal curve in this area.  Safety for Pedestrians and Bicyclists: no protected crossing across Red‐Wood Road. Existing sidewalks are sufficiently wide but are steep. Marked crosswalks would need to be carefully placed in the future. Bike lanes are provided on Red‐Wood Road in this segment but no facilities are included on 106th Street.  Traffic Operations: The current configuration is not optimal and operations will quickly deteriorate because of awkward geometry requiring through movements to make several turns.  Local Traffic Access: Access will remain as it is currently. Delays from traffic congestion are likely to reduce access quality, however.  Aesthetics: the current condition of the area is landscaped providing views and open space. There is nothing particularly noteworthy or culturally significant. ---PAGE BREAK--- CITY OF REDMOND 160TH AVE NE EXTENSION FIGURE 14: ALTERNATIVE 1, NO BUILD ---PAGE BREAK--- REDMOND-WOODINVILLE ROAD INTERSECTION ANALYSIS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 8‐4 NOVEMBER 2012 8.2.2 Alternative 2: Roundabout The roundabout alternative (Figure 15) would drastically alter the existing intersection geometry and traffic configuration. Using a minimum inscribed diameter of 100 feet per WSDOT standards, combined with a 21‐foot rotary lane and sidewalks for pedestrian circulation, the roundabout alternative would occupy a substantial area of the available city right‐of‐way. Due to the sloping nature of the site, several walls are required on the south and west edges of the site to maintain a flat roundabout for traffic operational safety. Consequently, the neighborhood access at 160th Avenue would be closed and removed. With an approximate operating speed of 15 mph for vehicles up to and including WB‐40 trucks (maximum vehicle design size is estimated as a WB‐50) this configuration keeps southbound traffic moving smoothly into Downtown Redmond. Based on traffic forecasts, traffic heading northbound in a continuous stream from 160th Avenue may hinder northbound traffic entering the roundabout from Red‐Wood Road.  Construction Costs: A roundabout at this location will require a substantial amount of grading, walls, fill, new pavement, and potentially adjacent property adjustments.  Construction Delay and Mitigation: The construction of a roundabout at this location would cause major traffic detours and delays to Red‐Wood Road during construction.  Safety for Vehicles: Roundabouts drastically reduce head on collisions and are generally safer than conventional intersections while still maintaining mobility.  Safety for Pedestrians and Cyclists: Roundabouts require longer transition paths for pedestrians and have two conflict points at each leg. Either cyclists typically operate as pedestrians on paths external to the circulating roadway or speeds within the roundabout are generally low enough for cyclists to operate as traffic.  Traffic Operations: Further analysis would be required to say exactly whether a roundabout at this particular location would improve traffic flow compared to a conventional signalized intersection. There is also no way to customize traffic signal timing at various times of the day to accommodate directional commuter traffic.  Local Traffic Access: Existing access to and from the adjacent neighborhood by 106th Street would be closed and removed entirely. ---PAGE BREAK--- CITY OF REDMOND 160TH AVE NE EXTENSION FIGURE 15: ALTERNATIVE 2, ROUNDABOUT ---PAGE BREAK--- REDMOND-WOODINVILLE ROAD INTERSECTION ANALYSIS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 8‐6 NOVEMBER 2012 8.2.3 Alternative 3: Signalized Intersection The signalized intersection alternative (Figure 16) would first adjust the geometry of the existing intersection between NE 106th Street and Red‐Wood Road to make the 160th Avenue NE movement the primary movement. This alternative would maintain the existing Flying geometric configuration of Red‐Wood Road in this area but move it to the north. Separate right turn and left turn lane channelization would be provided from 160th Avenue to Red‐Wood Road. The outside northbound lane could be signalized to keep northbound traffic on Red‐Wood Road moving, while other phases of the signal are engaged. However, additional widening of Red‐Wood Road north of this intersection would probably be required for safety and to achieve maximum operational benefits. A similar present implementation of this design is at NE 51st Street and West Lake Sammamish Parkway. The future proximity of the intersection of 106th Street NE and 160th Avenue requires that access to the homes near 106th Street be restricted to a “right‐in, right‐out” configuration. Full access to 160th Avenue NE would be provided by the intersection with NE 103rd Way and 160th Avenue NE.  Construction Cost: Moderate requiring significant demolition and earthwork grading, including some walls adjacent to the properties to the west to accommodate a significant elevation differential. This could be reduced by using a terraced combination of fill walls and fill slopes.  Construction Delay and Mitigation: Constructing the intersection separate of the 160th Avenue NE extension would permit adjacent homeowners access routes without building an interim roadway. Impacts to the existing operations on Red‐Wood Road would be relatively minimal.  Safety for Vehicles: A signalized intersection could provide dedicated phases for all movement, which would reduce the likelihood of collisions.  Safety for Pedestrians and Cyclists: A signalized intersection would provide safe access across Red‐ Wood Road and provide greater neighborhood connectivity. Presently, the nearest crosswalks are 0.32 mile to the north and 0.23 mile to the south.  Traffic Operations: Given traffic predictions in the 2007 report, a signal should be seriously considered at this intersection to accommodate future traffic shifts and patterns due to the 160th Avenue Extension Project.  Local Traffic Access: Access would be restricted to one partial intersection for southbound 160th Avenue traffic only and one full intersection for safety and operational reasons.  Aesthetics: A similar landscaping style is expected. There is nothing particularly noteworthy or culturally significant about this alternative. ---PAGE BREAK--- CITY OF REDMOND 160TH AVE NE EXTENSION FIGURE 16: ALTERNATIVE 3, SIGNALIZED INTERSECTION ---PAGE BREAK--- 9 REDMOND-WOODINVILLE ROAD INTERSECTION ANALYSIS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 8‐8 NOVEMBER 2012 8.3 Traffic Analysis Results of the traffic analysis are presented in Table 5. The intersection would experience the lowest amount of delay in Alternative 3 (Signal) for both AM and PM peak hours. Despite this, the intersection would still operate at or near capacity in the Year 2030 PM peak hour, with the northbound and eastbound approaches experiencing approximately 65 seconds of control delay. Table 5: 2030 Intersection Operations at Red‐Wood Road/160th Avenue NE Intersection Northbound Eastbound Southbound Total Alternative LOS Delay (sec/veh)2 V/C LOS Delay (sec/veh)2 V/C LOS Delay (sec/veh)2 V/C LOS Delay (sec/veh)2 AM Peak 1‐No Build1 C 15.3 0.06 F >200 5.93 A 0.0 0.00 F >200 2‐Roundabout C 22.8 0.73 F 115.3 1.14 F >200 1.60 F 194.6 3‐Signal B 13.8 0.41 D 52.4 0.93 C 21.0 0.75 C 28.2 PM Peak 1‐No Build1 B 10.3 0.02 F > 200 7.28 A 0.0 0.00 F >200 2‐Roundabout F >200 1.84 F 140.3 1.24 D 27.8 0.90 F 184.4 3‐Signal E 66.2 1.01 E 64.8 1.01 C 26.6 0.55 E 57.3 Notes: 1. No Build assumes the intersection is one‐way stop‐controlled. 2. Delay values higher than 200 seconds are unreliable, and are therefore reported as >200. Based on the operational results from Table 5, Alternative 3 (Signal) was evaluated for queues to help determine storage length requirements for turn lanes. Queue for Alternative 3 are presented below in Table 6. Ninety‐fifth percentile queues are defined as the queue length that has a 5 percent probability of being exceeded during the analysis period. Fiftieth percentile queue are more typical of the driver experience, but 95th percentile queue are a conservative estimate used to help design storage for turn lanes where right‐of‐way is available. The eastbound and northbound approaches experience the longest queues in the PM peak hour, with the 50th and 95th percentile queue both exceeding the adjacent turn lane storage length. However, the eastbound right‐turn and northbound left‐turn lane demand volumes and corresponding queue length are quite low (approximately one vehicle per cycle), and should not cause an operational problem. The southbound approach experiences the longest queues in the AM peak hour, with the through lane 50th percentile queue length of 500 feet exceeding the right‐turn lane storage length of 250 feet. This means that the southbound through lane queue will periodically block entrance into the right‐turn lane, which could increase the southbound approach queue length beyond what is reported in Table 6 because right‐turn vehicles are stuck in the through lane north of the NE 107th Street intersection. The southbound approach queue would also block the northbound left‐turn lane at the NE 107th Street/Red‐Wood Road intersection. A potential mitigation to this issue is to convert the southbound right‐turn lane at the NE 107th Street/Red‐Wood Road intersection into a shared through‐ right lane that lines up with the right‐turn lane at 160th Avenue NE, as well as widen approximately ---PAGE BREAK--- 9 REDMOND-WOODINVILLE ROAD INTERSECTION ANALYSIS CITY OF REDMOND – 160TH AVENUE NE EXTENSION PRE-DESIGN REPORT 8‐9 NOVEMBER 2012 100 feet Red‐Wood Road just south of the NE 107th Street intersection. This would create approximately 725 feet of storage length for southbound right‐turn vehicles destined to 160th Avenue NE, which is longer than the 95th percentile queue length of 700 feet for the southbound through lane. Table 6: 2030 Queue at Red‐Wood Road/160th Avenue NE Intersection for Alternative 3 (Signal) AM Peak PM Peak Direction Lane Storage Length1 (ft) 50th Percentile Queue2 (ft) 95th Percentile Queue3 (ft) 50th Percentile Queue2 (ft) 95th Percentile Queue3 (ft) Eastbound Left 2,600 375 500 675 950 Right 200 0 25 25 25 Northbound Left 150 25 25 25 25 Through 2,600 200 300 675 950 Southbound Through 1,300 500 700 275 375 Right 250 0 0 0 0 Notes: 1. Through lane storage is estimated based on distance to the adjacent signalized intersection or 1/2 mile, whichever is closer. 2. The 50th percentile queue is defined as the queue length that has a 50 percent probability of being exceeded during the analysis period. 3. The 95th percentile queue is defined as the queue length that has a 5 percent probability of being exceeded during the analysis period. 8.4 Recommendation The traffic analysis and as well as the examination of constructability indicates that the signalized alternative best serves the needs of vehicles, pedestrians, and bicyclists, safely and cost‐effectively. Construction costs and impacts are minimized by the alternative being smaller than the roundabout. The signalization provides a safe connection between 160th Avenue NE and Red‐Wood Road without significantly affecting existing traffic patterns on Red‐Wood Road. The alternative also provides a safe connection for pedestrians on both sides of Red‐Wood Road and connects the existing neighborhoods better than a roundabout or the existing conditions. ---PAGE BREAK--- Appendix A Technical Memoranda ---PAGE BREAK--- A-1 Structural Alternatives Study Technical Memorandum ---PAGE BREAK--- 1 D R A F T T E C H N I C A L M E M O R A N D U M City of Redmond 160th Avenue NE Extension Preliminary Evaluation of Retaining Walls PREPARED FOR: Steve Gibbs/City of Redmond PREPARED BY: Mark Johnson/CH2M HILL REVIEWED BY: Roger Mason, Ken Green/CH2M HILL DATE: June 15, 2012 Introduction This project consists of extending 160th Avenue NE from the current terminus at NE 99th to NE 102nd Street and the intersection with Redmond-Woodinville Road. The project includes several structures, including retaining walls and a crossing structure over a ravine and wetland. A previous technical memorandum addressed the crossing structure located at the wetland south of the PSE transmission lines. This memorandum identifies and evaluates the retaining walls needed to construct the 160th Avenue extension roadway. Retaining Walls Retaining walls for this project include both fill and cut walls. Typical fill wall types include structural earth (SE) walls, cast-in-place concrete cantilever walls, and rockery walls. Structural earth walls, which consist of a select structural backfill zone reinforced with layers or mats of reinforcement, are typically faced with precast concrete panels attached to the wall reinforcement. They are an economic wall choice in locations where there is sufficient wall area to justify their use. Concrete cantilever walls are another common wall type, but are typically more expensive than structural earth walls. Rockery walls are a cost-effective alternative for relatively short walls less than 10 feet high. Typical cut wall types include concrete cantilever walls, soldier pile walls, and soil nail walls. Concrete cantilever walls are often an economical choice where there is sufficient space to overexcavate the soil to place the wall footing. Where overexcavation is not practical or cost- effective, soil nail or soldier pile walls are needed. Soil nail walls are typically used in soil conditions in which the soil can temporarily stand vertically several feet high to place the rows of soil nails. A preliminary roadway plan and profile has been developed for the project to satisfy a number of objectives, including limiting the maximum roadway grade up the hill; minimizing impacts to existing wetlands; limiting right-of-way impacts; balancing the amount of cut and fill within the project site; and minimizing the number and size of retaining walls. The site plan showing the location and extent of retaining walls is shown in Figure 1. The corresponding roadway profile is shown in Figure 1B. ---PAGE BREAK--- PRELIMINARY EVALUATION OF RETAINING WALLS 2 Wall A This tall fill wall is located on the west side of the roadway along the steep hillside at the south end of the alignment where a significant amount of fill is needed. A structural earth wall is proposed, as shown in Section A in Figure 2. At the base of the hill adjacent to Wetland 1A, it is expected that the surface soils are poor and will need to be removed prior to placing structural backfill for the wall to prevent excessive settlement and bearing failure. As the roadway climbs the hill, the wall will likely need to be benched into the hillside, as shown in Section B in Figure 2, to ensure global stability of the wall on the steep slope. Benching will require a significant amount of overexcavation of soil at the base of the wall. Walls B and C These two fill walls are located on the west side of the roadway to retain the roadway fill within the property limits. Given the length and height of the walls, structural earth walls are proposed. A typical section is shown in Section A in Figure 2. Walls D and F These two cut walls are located near the top of the steep hillside where the roadway is benched into the hill. Between the two walls, the roadway crosses over a shallow ravine and Wetland 2A, creating a short fill section retained by Wall E. The cut walls are needed to prevent the cut slope from extending past the right-of-way limit, as shown in Section B in Figure 2. Soil nail walls are proposed for these two walls, although the nails will extend into private property, requiring a permanent easement. Another option is to move the walls to the edge of the roadway so that the soil nails are mostly within the right-of-way; however, this would make it more difficult to widen the roadway or add a sidewalk to the east in the future. Another alternative is to use a concrete cantilever wall along the property line. This would require overexcavation or temporary shoring to construct the wall footing. Walls E and G These two walls are fill walls needed adjacent to wetlands to retain the roadway fill for a drainage culvert under the road. Given the short height and limited extent of the walls, rockery walls are a cost-effective choice. Summary A summary of the retaining walls is shown in the table below. Table 1 – Retaining Wall Summary WALL ID CUT/FILL WALL TYPE LENGTH (FT) AREA (SF) UNIT COST COST A FILL SE 355 7,150 $90 $643,500 B FILL SE 70 960 $50 $48,000 C FILL SE 300 3,660 $50 $183,000 D CUT SOIL NAIL 95 880 $120 $105,600 E FILL ROCKERY 50 400 $40 $16,000 F CUT SOIL NAIL 135 1,010 $120 $121,200 G FILL ROCKERY 15 150 $40 $6,000 14,210 $1,120,000 ---PAGE BREAK--- PRELIMINARY EVALUATION OF RETAINING WALLS 3 As the table shows, approximately half of the total wall cost of the project is for Wall A. The cost of Wall A could be reduced if the roadway alignment is shifted farther to the east into the hillside; however, this would likely have more right-of-way impacts than the current alignment. Another idea would be to shift the wall to the east several feet and cantilever a portion of the sidewalk past the face of the wall. This would reduce the overall wall height along the length of the wall, but would be offset by the cost of the cantilevered sidewalk. The cut walls (Walls D and F) also represent a significant portion of the overall wall cost. These walls could be significantly reduced or possibly eliminated if the cut slope could extend past the Veal property limit. The feasibility of these cost reduction measures should be explored in a subsequent phase of design to optimize the overall cost of the retaining walls. ---PAGE BREAK--- PUGET SOUND ENERGY [PHONE REDACTED] VEAL PROPERTY [PHONE REDACTED] VEAL PROPERTY [PHONE REDACTED] GOOD PROPERTY [PHONE REDACTED] CITY OF REDMOND [PHONE REDACTED] [PHONE REDACTED] PUGET SOUND ENERGY [PHONE REDACTED] 556962TRCT KING COUNTY PARKS [PHONE REDACTED] LA PRETE PROPERTY [PHONE REDACTED] EQUESTRIAN TRAIL CITY OF REDMOND 40 40 40 W W SS W E E U W W U W W W 50 50 50 50 50 SS E T 60 60 60 70 70 70 70 80 80 80 80 80 90 90 90 90 90 90 90 100 100 100 100 100 100 100 110 110 110 110 120 120 120 120 120 130 130 T TC T SS G E T WW W T G E T W W U SS 140 80 JUNE 15, 2012 1" = 100’ FILL FILL FILL FILL CUT LEGEND FILL 26+00 28+00 30+00 32+00 34+00 36+00 38+00 40+00 W W W W W PSE OHD PSE OHD FILL FILL PSE OHD SPU 54" W ATERLINE SPU WATERLINE RETAINING WALL FILL LINE CUT LINE CULVERT BUFFER CL 4 BUFFER CL 3 WETLAND ROW CONTOUR PROPOSED MINOR CONTOUR PROPOSED MAJOR CONTOUR EXISTING MINOR CONTOUR EXISTING MAJOR RETAINING WALLS FIGURE 1: 160TH AVENUE NE EXTENSION CITY OF REDMOND PSE TOWER CONCEPT APPROVAL REFINED AFTER CORRIDOR TO EXISTING TO BE TRANSITION TO MATCH WETLAND 3A 10’ SIDEWALK 6’ BIKE LANE 11’ LANE 11’ LANE WETLAND 1A RETAINING WALL A 60 70 80 90 100 110 120 130 130 RETAINING WALL B CUT CUT CUT CUT CUT FILL W CUT CUT CUT CUT FILL & WING WALLS CULVERT CROSSING RETAINING WALL F 8’ BIKE LANE RETAINING WALL C 160TH AVENUE NE RETAINING WALL D WETLAND 2A RETAINING WALL E WETLAND 4A RETAINING WALL G CONCEPT APPROVAL REFINED AFTER CORRIDOR TO EXISTING TO BE TRANSITION TO MATCH ---PAGE BREAK--- ---PAGE BREAK--- 2:1 SIDEWALK 10’ 6’ LANE BIKE 11’ LANE CL 160TH 11’ LANE LANE BIKE 2’ 0.7H H 6" CSBC 9" HMA LINE PROPERTY NOTE) (SEE 3’-4’ MIN WALL (SE WALL) FILL RETAINING 1.5:1 ZONE STRUCTURAL BACKFILL REINFORCEMENT (TYP) SOIL WALL (NAIL WALL) CUT RETAINING JUNE 15, 2012 1" = 5’ A B WALL TYPICAL SECTION WALL TYPICAL SECTION INTO HILLSIDE 3’ - 4’ MINIMUM. EXISTING HILLSIDE, BENCH WALL AT STEEP SECTIONS OF NOTE: SEE NOTE EXISTING HILLSIDE, EXISTING GROUND ZONE STRUCTURAL BACKFILL REINFORCEMENT (TYP) SOIL CL 160TH 2:1 SIDEWALK 10’ 6’ LANE BIKE LANE 11’ LANE 11’ 8’ LANE BIKE 2’ 2% 2% COMPACTED SUBGRADE H 0.7H 6" CSBC 9" HMA WALL (SE WALL) FILL RETAINING 1.5:1 EXISTING GROUND 1’ MIN 0.1H, WALL TYPICAL SECTIONS FIGURE 2: 160TH AVENUE NE EXTENSION CITY OF REDMOND ---PAGE BREAK--- A-2 Evaluation of Crossing Alternatives at Wetland 3 ---PAGE BREAK--- 1 D R A F T T E C H N I C A L M E M O R A N D U M City of Redmond 160th Avenue NE Extension Evaluation of Crossing Alternatives at Wetland 3 PREPARED FOR: Steve Gibbs/City of Redmond PREPARED BY: Mark Johnson/CH2M HILL REVIEWED BY: Roger Mason/CH2M HILL DATE: June 8, 2012 Introduction This project consists of extending 160th Avenue NE from the current terminus at NE 99th to NE 102nd Street and the intersection with Redmond-Woodinville Road. An overall site layout, roadway profile, and typical roadway section is shown in Figure 1 of Appendix A. The purpose of this phase of work is to identify alternatives to be considered, evaluate them in enough detail so a preferred alternative can be selected, and develop budget-level costs for decision-making and budgeting. The project includes several structures, including retaining walls and a crossing structure over a ravine and wetland. The crossing structure is located at Wetland 3 south of the PSE transmission lines. This memorandum identifies and evaluates several alternatives for the crossing structure, which are compared on a technical and cost basis, and a preferred alternative is recommended. Crossing Structure Alternatives The ravine located immediately south of the PSE transmission lines spans approximately 150 feet from bank to bank and is about 20 feet deep at the proposed road crossing. It contains seasonal stream flow and a wetland designated as Wetland 3. The roadway crosses the ravine on a sharp skew. One of the considerations for the crossing structure is to provide for an equestrian trail that would cross under the roadway along the north bank of the ravine and connect to the PSE trail on each end. The soils in the ravine at the wetland appear to be soft, compressive soils of unknown depth. It is assumed that the placement of structure on these soils would require deep foundations (steel piles) to support the structure. The soils along the sides of the ravine appear to be relatively dense, competent soils capable of supporting spread footings without the need for deep foundations. Several alternatives were identified for the ravine crossing, including bridge and culvert concepts. A culvert manufacturer was consulted to identify and evaluate cost-effective structure types. A plan and typical section of each alternative is included in Appendix A. The alternatives were compared using evaluation criteria that are shown in Appendix B. Planning-level comparative costs were developed for each alternative and are summarized in Appendix C. ---PAGE BREAK--- EVALUATION OF CROSSING ALTERNATIVES AT WETLAND 3 2 Alternative 1 – Single Span Bridge This alternative is considered the baseline option for crossing the ravine and is shown in Figures 2 and 3 of Appendix A. The relatively short crossing lends itself to a single span prestressed girder bridge with abutments on spread footings and wingwalls at the ends to retain the roadway embankment. A 100-foot long structure spans entirely over the wetlands and provides sufficient clearance for an equestrian trail under the structure, but is the most expensive alternative. Alternative 2 – 48’ Elliptical Steel Culvert This alternative is the longest practical steel closed-shape culvert span and is shown in Figures 4 and 5 of Appendix A. It requires over excavation of the poor, soft soils at the wetland. The advantage of this type of structure is the relatively low cost and ease of shipping and installation. However, it has significant impact to the wetland due to its relatively short span and likely does not provide enough space for an equestrian trail undercrossing. A separate culvert would be needed for the trail adjacent to the roadway crossing culvert, as shown in Figure 5. Alternative 3 – 65’ Steel Arch Culvert This alternative, shown in Figures 6 and 7 of Appendix A, provides a longer span steel culvert and consists of an arch-shaped structure on spread footings. The benefit over Alternative 2 is the longer span achieved, reducing wetland impacts. However, it requires the use of pile foundations and, as with the elliptical culvert, likely does not provide enough space for an equestrian trail undercrossing. Alternative 4 – 60’ Precast Concrete Culvert Precast concrete culvert structures were also considered for the crossing. This alternative is a 60’ precast concrete 3-sided structure, the longest span available for this type of culvert, and is shown in Figures 8 and 9 of Appendix A. Its main drawback is its limitation in accommodating the skewed crossing of the road over the ravine. As shown in Figure 8, it consists of tapered precast segments that, when assembled, form a curved structure. However, this approach requires a much wider structure than the roadway above, adding to the cost and additional wetland impacts. Alternative 5 – 84’ Precast Concrete Arch Culvert The other precast concrete alternative considered is an arch-shaped culvert that is shown in Figures 10 and 11 of Appendix A. The structure is made up of twin leaf precast panels approximately 4’ wide that are cast together at the crown of the structure during installation. This alternative is a significant improvement over the shorter span precast culvert, as it has sufficient length to span parallel to the roadway without a skew, minimizing the width of the structure. It also has sufficient headroom to accommodate an equestrian trail undercrossing. The main drawback is the overall height of the arches, which require a relatively deep excavation at the northwest corner of the structure. A variation of this structure is a flatter profile precast arch, as shown in Figure 11. This flatter arch section spans up to about 100 feet and imparts significant thrust loads into the foundations. It is expected that a thrust block could be provided at each end to distribute the forces into the sides of the ravine. ---PAGE BREAK--- EVALUATION OF CROSSING ALTERNATIVES AT WETLAND 3 3 Evaluation of Alternatives The alternatives were evaluated and compared using evaluation criteria, as shown in Appendix B. Both a weighted and unweighted screening was conducted. Construction cost was considered to be the most important criterion, and was weighted the highest. As part of the evaluation, planning-level comparative costs were developed for each alternative and are summarized in Appendix C. The precast concrete arch culvert, Alternative 5, scores highest for both weighted and unweighted screening. It is the lowest cost alternative, approximately 59% of the baseline bridge cost, and has relatively minor impacts to the wetland. It has high durability and is better able to resist corrosion and damage than the steel culvert alternatives. Due to its tall arch shape, it provides for an equestrian trail undercrossing without having to add a separate culvert structure. Summary The long span precast concrete arch culvert appears to be the best choice for this crossing due to its relative cost to the other alternatives and the minimal environmental impacts. Further refinement of this alternative, by considering flatter profile arch configurations, can be considered in a subsequent phase of design to optimize the overall cost of the crossing structure. ---PAGE BREAK--- APPENDIX A FIGURES OF CROSSING ALTERNATIVES ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- APPENDIX B EVALUATION OF ALTERNATIVES MATRIX ---PAGE BREAK--- City of Redmond 160th Avenue NE Extension Project Screening Matrix of Alternatives - Wetland 3 Crossing Revision Date: June 8, 2012 Evaluation Criteria Weighting Factor (1 - 10) Alt 1 - Bridge Crossing Alt 2 - 48' Elliptical Stl Culvert Alt 3 - 65' Steel Arch Culvert Alt 4 - 60' Precast Culvert Alt 5 - 84' Precast Arch Culvert Comments Construction Cost 10 1 3 4 2 4 Alt 1: Highest cost. Alt 2: 65% of bridge cost. Alt 3: 57% of bridge cost. Alt 4: 91% of bridge cost. Alt 5: 59% of bridge cost. Impacts to Wetlands 7 4 1 2 1 3 Alt 1: No wetland impacts. Alt 2: Impacts 1,400 SF of wetland. Alt 3: Impacts 600 SF of wetland. Alt 4: Impacts 800 SF of wetland. Structure is low and much longer than other alternatives - much less light under str. Alt 5: Impacts 600 SF of wetland. Structure provides alot of light underneath. Provides for Equestrian Trail 7 3 1 1 1 2 Alt 1: Provides for equestrian trail. Alts 2 - 4: Equestrian trail does not fit. Alt 5: Equestrian trail likely fits. Construction Impacts 4 2 3 1 2 2 Alt 1 Hauling/placement of 100' long girders. Alt 2: Some overexcavation needed. Alt 3: Pile driving likely needed for foundations, wide structural backfill area. Alt 4: Pile driving likely needed for foundations. Alt 5: Requires deep excavation for footings. Constructability 4 2 4 4 3 3 Alt 1: Requires large cranes for girder erection. Alts 2 - 3: Easy to ship, assembled onsite with small cranes. Alt 4: Heavy pieces to ship and erect. Alt 5: Heavy pieces to ship and erect. Maintenance and Inspection 6 3 2 2 4 4 Alt 1: Bridge requires biannual inspection, deck requires maintenance. Alts 2 - 3: Steel surfaces require maintenance. Alt 4 - 5: Minimal inspection and maintenance requirements. Design Life 7 3 2 2 3 3 Alt 1: Prestressed concrete long-lasting, exposed bridge deck vulnerable. Alts 2 - 3: Galvanized steel culvert shorter design life. Alts 4 - 5: Concrete long lasting. Provides for Utilities 2 4 2 2 3 2 Alt 1: Can hang utilities off superstructure. Alts 2 - 3: Can place utilities above culvert. Alt 4: More space for utilities above culvert. Alt 5: Can place utilities above culvert. Right-of-Way 3 3 2 2 1 3 Alt 1: Structure confined to roadway area. Alts 2 - 3: Have walls on each end of culvert. Alt 4: Structure much wider than roadway. Alt 5: Structure confined to roadway area. Total Score (unweighted) 25 20 20 20 26 Alternative 5 has highest score. Total Score (weighted) 131 108 117 108 153 Alternative 5 has highest score. Performance Ratings: 1 - Poor, performs worse than other alternatives 3 - Better 2 - Good 4 - Best, outperforms other alternatives ---PAGE BREAK--- APPENDIX C COMPARATIVE COST ESTIMATE ---PAGE BREAK--- 1 City of Redmond 160th Avenue NE Extension Project Comparative Cost Evaluation of Alternatives - Wetland 3 Crossing Revision Date: June 8, 2012 SUMMARY OF ALTERNATIVES No. Description Structure Cost % of Bridge Comments 1 Prestressed Girder Bridge 1,390,000 $ 100% Assume piles not needed. 2 48' Elliptical Steel Culvert 910,000 $ 65% Assume some overexcavation. 3 65' Steel Arch Culvert 790,000 $ 57% Assume supported by steel piles. 4 60' Precast Culvert 1,260,000 $ 91% Assume supported by steel piles. 5 84' Precast Arch Culvert 820,000 $ 59% Assume piles not needed. COSTS WITH EQUESTRIAN UNDERPASS TRAIL No. Description Structure Cost Equestr. Culvert Cost Total Cost % of Bridge Comments 1 Prestressed Girder Bridge 1,390,000 $ - $ 1,390,000 $ 100% Trail fits under bridge. 2 48' Elliptical Steel Culvert 910,000 $ 190,000 $ 1,100,000 $ 79% 3 65' Steel Arch Culvert 790,000 $ 190,000 $ 980,000 $ 71% 4 60' Precast Culvert 1,260,000 $ 190,000 $ 1,450,000 $ 104% 5 84' Precast Arch Culvert 820,000 $ - $ 820,000 $ 59% Trail likely fits under culvert. ALTERNATIVE 1 - PRESTRESSED CONCRETE GIRDER BRIDGE COST (SPREAD FOOTINGS): Bridge Bridge Length 100 FT Bridge Width 52 FT Bridge Deck Area 5,200 SF Square Foot Cost $200 Bridge Cost $1,040,000 Retaining Walls Location Max Ht Length Area (SF) SE Corner 14 12 101 SW Corner 18 24 259 NE Corner 15 30 270 NW Corner 8 12 58 Total Wall Area 688 Square Foot Cost $100 Wall Cost $69,000 Subtotal $1,110,000 Design Contingency 25% $278,000 Total Structure Cost $1,390,000 ALTERNATIVE 2 - 48' ELLIPTICAL STEEL CULVERT (28' RISE) No. Item Unit Quantity Unit Price Amount Comments 1 STRUCTURE EXCAV CL A INCL. HAUL C.Y. 5,500 $20 $110,000 2 ELLIPTICAL STEEL CULVERT L.F. 75 $4,500 $337,500 Installed cost 3 CULVERT HEADWALLS C.Y. 22 $600 $13,200 4 SELECT STRUCTURAL BACKFILL C.Y. 3,600 $25 $90,000 5 RETAINING WALLS S.F. 1,500 $100 $150,000 6 ROADWAY EMBANKMENT C.Y. 2,500 $10 $25,000 Subtotal $726,000 Design Contingency 25% $182,000 Total Structure Cost $910,000 ALTERNATIVE 3 - 65' STEEL ARCH CULVERT (19' RISE) No. Item Unit Quantity Unit Price Amount Comments 1 STRUCTURE EXCAV CL A INCL. HAUL C.Y. 3,400 $20 $68,000 2 STEEL ARCH CULVERT L.F. 75 $3,300 $247,500 Installed cost 3 CULVERT HEADWALLS C.Y. 16 $600 $9,600 4 CONCRETE CLASS 4000 FOR FOOTING C.Y. 67 $400 $26,800 5 FABRICATING STEEL H-PILES L.F. 480 $50 $24,000 ---PAGE BREAK--- 2 City of Redmond 160th Avenue NE Extension Project Comparative Cost Evaluation of Alternatives - Wetland 3 Crossing Revision Date: June 8, 2012 6 DRIVING STEEL H-PILES EA. 12 $2,500 $30,000 7 SELECT STRUCTURAL BACKFILL C.Y. 4,100 $25 $102,500 8 RETAINING WALLS S.F. 1,100 $100 $110,000 9 ROADWAY EMBANKMENT C.Y. 1,500 $10 $15,000 Subtotal $634,000 Design Contingency 25% $159,000 Total Structure Cost $790,000 ALTERNATIVE 4 - 60' PRECAST CULVERT (12' RISE) No. Item Unit Quantity Unit Price Amount Comments 1 STRUCTURE EXCAV CL A INCL. HAUL C.Y. 1,300 $20 $26,000 2 PRECAST CULVERT L.F. 115 $5,900 $678,500 Delivered cost 3 CULVERT INSTALLATION L.S. 1 $50,000 $50,000 4 CULVERT HEADWALLS C.Y. 13 $600 $7,800 5 CONCRETE CLASS 4000 FOR FOOTING C.Y. 102 $400 $40,800 6 FABRICATING STEEL H-PILES L.F. 760 $50 $38,000 7 DRIVING STEEL H-PILES EA. 19 $2,500 $47,500 8 SELECT STRUCTURAL BACKFILL C.Y. 1,600 $25 $40,000 9 RETAINING WALLS S.F. 600 $100 $60,000 10 ROADWAY EMBANKMENT C.Y. 1,900 $10 $19,000 Subtotal $1,008,000 Design Contingency 25% $252,000 Total Structure Cost $1,260,000 ALTERNATIVE 5 - 84' PRECAST ARCH CULVERT (22' RISE) No. Item Unit Quantity Unit Price Amount Comments 1 STRUCTURE EXCAV CL A INCL. HAUL C.Y. 1,400 $20 $28,000 2 PRECAST ARCH CULVERT L.F. 50 $6,800 $340,000 Delivered cost 3 CULVERT INSTALLATION L.S. 1 $75,000 $75,000 Need 2 cranes 4 CULVERT HEADWALLS C.Y. 27 $600 $16,200 5 CONCRETE CLASS 4000 FOR FOOTING C.Y. 44 $400 $17,600 6 SELECT STRUCTURAL BACKFILL C.Y. 1,500 $25 $37,500 7 RETAINING WALLS S.F. 1,300 $100 $130,000 8 ROADWAY EMBANKMENT C.Y. 1,400 $10 $14,000 Subtotal $659,000 Design Contingency 25% $165,000 Total Structure Cost $820,000 STEEL CULVERT FOR EQUESTRIAN UNDERPASS TRAIL No. Item Unit Quantity Unit Price Amount Comments 1 CULVERT L.F. 80 $860 $68,800 Delivered cost 2 SELECT STRUCTURAL BACKFILL C.Y. 500 $25 $12,500 3 RETAINING WALLS S.F. 700 $100 $70,000 Subtotal $152,000 Design Contingency 25% $38,000 Total Structure Cost $190,000 Notes: 1. The estimate does not include sales tax, escalation, or owner costs such as engineering, administrative, construction management, legal, or permitting. 2. This cost opinion is in June 2012 dollars. It does not include future escalation or unusual material cost increases. No potential hazardous material mitigation is included. The cost opinions shown have been prepared for guidance in project evaluation from the information available at the time of preparation. The final costs of the project will depend on actual labor and material costs, actual site conditions, productivity, competitive market conditions, final project scope, final project schedule, and other variable factors. As a result, the final project costs will vary from the costs presented above. Because of these factors, funding needs to be carefully reviewed prior to making specific financial decisions or establishing final budgets. ---PAGE BREAK--- A-3 Geotechnical Summary of Findings Memorandum ---PAGE BREAK--- TECHNICAL MEMO 5 - GEOTECHNICAL DESIGN CONSIDERATIONS/[INSERT DOCUMENT LOCATOR] 1 COPYRIGHT [INSERT DATE SET BY SYSTEM] BY [CH2M HILL ENTITY] • COMPANY CONFIDENTIAL M E M O R A N D U M - T a s k 5 G e o t e c h n i c a l D e s i g n City of Redmond 160th Avenue NE Extension Geotechnical Summary of Findings Memorandum and Preliminary Evaluation of Geotechnical Conditions PREPARED FOR: Steve Gibbs/City of Redmond PREPARED BY: REVIEWED BY: DATE: Ken Green/CH2M Hill Roger Mason, Mark Johnson/CH2M Hill August 4, 2012 Introduction This project consists of extending 160th Avenue NE from the current terminus at NE 99th to NE 102nd Street and the intersection with Redmond-Woodinville Road. An overall site layout, roadway profile, and typical roadway section is shown in Figures 1A and 1B of this report. The purpose of this project is to identify alternative roadway alignments and options to be considered, evaluate them in enough detail so that a preferred alternative can be selected, and to develop budget-level costs for decision-making and budgeting for future planning and advancement of the project. This memorandum provides a geotechnical summary of findings and provides preliminary evaluation of geotechnical conditions along the proposed alignment. This memo also provides recommendations for the anticipated work associated with design and construction of the new roadway and discusses areas where additional subsurface investigations will be necessary. No additional geotechnical field work was completed for this phase of the project; but instead prior geotechnical work conducted by others along with careful field observation of site conditions were noted as a basis for the decisions that form the basis of our recommendations contained in the phase of the work. As this project moves forward in the planning and design process, additional detailed field investigations will be required to confirm foundation conditions along selected areas of the alignment as required to develop final recommendations for types of structures, foundation conditions and preparation, and other important information necessary for design development. Existing Reports Existing reports and information pertinent to this project include the following: • USDA Natural Resources Conservation Service (NRCS), Soil Survey Data, version 7, Jul 2, 2012 • Preliminary Geotechnical Engineering Services, 160th Avenue Northeast Extension Route Location Study, Redmond, Washington, for City of Redmond, May 23, 1995, GeoEngineers. This site evaluation included field inspections, 7 test pits, and 3 hand auger borings, and hand probes in ravines. This report is attached to this memorandum. Field activities were accomplished between May 4 and May 16, 1995. Laboratory testing consisted of testing field moisture contents of a total of 20 samples obtained from field explorations and are provided in the attached report. • Selected Hand Auger Hole Logs from Report of Geotechnical Engineering Services Proposed Redmond 74 Residential Development, city of Redmond File No. PPL90-002, Redmond, ---PAGE BREAK--- GEOTECHNICAL SUMMARY OF FINDINGS MEMORANDUM AND PRELIMINARY EVALUATION OF GEOTECHNICAL CONDITIONS 2 TECHNICAL MEMO 5 - GEOTECHNICAL DESIGN CONSIDERATIONS/[INSERT DOCUMENT LOCATOR] COPYRIGHT [INSERT DATE SET BY SYSTEM] BY [CH2M HILL ENTITY] • COMPANY CONFIDENTIAL Washington, by GeoEngineers, Inc. (presumed to be about 1990). Attachment includes a total of 6 hand auger borings. • Selected Test Pit Logs from Report to Intrawest, Results of the Geotechnical Study, Proposed Townhomes on the River Trail, Redmond, Washington, Golder Associates, Inc., 1994. Attachment contains a total of 13 test pit exploration summaries. • Selected Test Pit Logs from Preliminary Geotechnical Engineering Study, Redmond 74-acre Parcel, Woodinville-Redmond Road Northeast, Redmond, Washington for Triad Associates, Earth Consultants, Inc, 1988. Attachment contains a total of 15 test pit exploration summaries. • Selected Test Pit Logs from Report of Preliminary Geotechnical Engineering Study, Maingate Shopping Center, Redmond, Washington by Earth Consultants, Inc, 1981. Attachment contains a total of 8 test pit exploration summaries. Background Information Figure 1A provides a plan view of the proposed roadway alignment illustrating the transition point at the south end of the project where the proposed roadway will connect to existing City of Redmond streets at 160th Avenue NE. The connection at the north end is at the Redmond-Woodinville road and is north of the portion of the alignment shown on Figure 1A. The new roadway will occupy the existing alignment of 156th Avenue NE and will require only slight modification between station 40+00 shown on Figure 1A and a new intersection that is proposed to be constructed near Redmond- Woodinville Road NE at the north end of the corridor. Figure 1B illustrates the conditions along the alignment in profile. Figures 1A and 1B also illustrate the generally location of existing utilities, wetlands, trail, and other existing features and provides a general location of retaining walls culverts and other structures that will be required for development of this segment of the proposed roadway. Extensive grading and new construction is required along about 1,400 lf of the alignment starting at about station 26+00 on the south end and extending to about station 40+00 on the north end. Additional road improvements and modifications are required at the north end where the new roadway will connect to Redmond-Woodinville Road NE making the length of the entire proposed roadway improvements about 2,400 lf in length. Several roadway alignments have been evaluated as part of this study and are discussed in another technical memo. The roadway generally begins at the toe of the slope next to the Sammamish River Valley at 160th Avenue NE on the south end of the corridor, and then gradually climbs up the east valley wall, crossing existing incised ravines and utility corridors along the way. The north end of the proposed corridor terminates on a broad, gently sloping plateau. Construction of road improvements will require extensive earthwork including sidehill cuts into the hillside on the east side of the new road, cuts through the high ridges that separate the ravines, and fills in many areas along the west edge of the new roadway. These cuts and fills will require the use of retaining walls in numerous areas including walls on the east side to limit the width of disturbance into private property, walls on the west side to limit the extent of filling into the wetland and onto steep slopes below the roadway alignment. Some combination of filling and use of bridges and culverts will be required to cross each of the ravines across which the new road will traverse. The roadway will need to avoid the existing overhead powerlines, poles and towers to the extent possible, and will need to avoid disturbance to the existing 54” diameter Tolt Water Supply Pipeline located near station 35+40. Fills along the west side of the road in areas near the Sammamish Valley floor are expected to range in height from a few feet to more than 20 feet. The largest fills and associated retaining walls are expected to occur between about stations 27+00 and 30+00. Fills and possible retaining walls will also likely be ---PAGE BREAK--- GEOTECHNICAL SUMMARY OF FINDINGS MEMORANDUM AND PRELIMINARY EVALUATION OF GEOTECHNICAL CONDITIONS TECHNICAL MEMO 5 - GEOTECHNICAL DESIGN CONSIDERATIONS /[INSERT DOCUMENT LOCATOR] 3 COPYRIGHT 2012 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL required at ravine crossings near wetlands 2 and 3. Small walls may be needed at wetland 4 to limit filling in the wetland and wetland buffer areas. Cuts of 10 feet or more will likely be required along the east side. These cuts, when they occur in hard silt or dense sand and gravel can be formed at 2H:1V. Where the cuts would extend beyond the property lines, small retaining walls will be required to retain a portion of the cut to control the width of the excavation. Site Conditions The proposed project extends along the east edge of the Sammamish River Valley which is characterized by its broad north-south trending orientation. The valley in this area is quite flat and generally at or below elevation 30 feet (mean sea level) in the vicinity of the proposed road corridor. The geologic conditions differ significantly along the length of the proposed road corridor. The proposed roadway starts at 160th avenue NE near the base of the slopes that define the edges of the Sammamish Valley. From there, the proposed road alignment extends to the northeast crossing along the side of steep slopes of the Valley’s sidewall and across a portion of a broad upland known locally as Education Hill. This corridor crosses three different physiographic areas each having uniquely different geologic conditions. The deeper soils along the corridor are the result of glacial activities that occurred during the advancement and retreat of ice sheets during the last period of glaciation, about 10,000 to 20,000 years ago. Shallow soils in the area of the corridor are the result of erosion and deposition that occurred from meltwater streams and lakes during the retreat of glaciers; and this erosion process continues to this day. The soils in the physiographic areas are described as follows starting from oldest to youngest: • Transitional beds are the oldest soil formation, consisting primarily of silt and sand, some gravel, with minor amounts of clay. These soils can be found in the sidehill slopes of the valley and under the broad plateau that caps the upland area. These soils were deposited in lakes and streams ahead of the advancing glacial ice. These soil deposits were later buried under advance outwash sand and gravel deposited by streams and rivers in front of the advancing Vashon glacier. The advance outwash is mapped as underlying much of the upland area west of Woodinville-Redmond Road. As the ice covered the region, it deposited Vashon glacial till over the older glacial and nonglacial deposits that currently mantle much of the higher elevations of the plateau. Till consists of a non-sorted, well graded mixture of clay, silt, sand, and gravel, is very dense and generally possess a low permeability. The till was overridden with great thicknesses of ice, compressing and compacting it as well as all underlying soils to a dense, generally high-strength condition. Although till was not observed along the proposed road corridor, it is known to mantle many areas at the higher elevations of Education Hill. It is likely that till once mantled the project area also but has since been removed by extensive scouring from glacial activities and continuing erosion, exposing the underlying outwash sand and gravel and transitional beds. This scouring and erosion has also formed stream channels and ravines which are presently being incised into the valley sidewalls forming the existing channels that are occupied by small streams that drain water from the upland areas of Education Hill. It is estimated by others that the contact between the top of the transitional beds and the overlying outwash sand and gravel occurs at about elevation 80. Outwash sand and gravel and the underlying transitional beds are the soils that most predominantly exist along the sidewalls of the Sammamish River Valley extending from about road station 27+50 to 40+00; and may extend as far as the north end of the proposed project at Redmond-Woodinville road. Because of the great length of this segment of the alignment, these soil conditions represent the predominant soils that are expected to be encountered along the proposed length of the project. Soils encountered in test pit explorations in this zone (generally below elevation 80 in the transitional beds), consists of hard silt with varying amounts of silt and gravel. The silt was encountered at depths ranging from 3.3 to 10 feet in several of the explorations. Groundwater seepage was observed in several of the test pits ---PAGE BREAK--- GEOTECHNICAL SUMMARY OF FINDINGS MEMORANDUM AND PRELIMINARY EVALUATION OF GEOTECHNICAL CONDITIONS 4 TECHNICAL MEMO 5 - GEOTECHNICAL DESIGN CONSIDERATIONS/[INSERT DOCUMENT LOCATOR] COPYRIGHT [INSERT DATE SET BY SYSTEM] BY [CH2M HILL ENTITY] • COMPANY CONFIDENTIAL ranging from 7 to 10.5 feet below the ground surface. These depths were generally found to correspond with the top elevation of the transitional beds at about elevation 80 where observed. Test pits near the tops or edges of ridges did not encounter groundwater probably because these areas are flanked by steep slopes of the ravines that allow drainage in these areas. In several areas, seepage and wet conditions can be observed in the bottom of ravines and near the base of the steep slopes and at the heads of the ravines. The general elevation at which the seepage appears to be occurring seems to correspond to the stratigraphic contact between the transitional beds and the overlying more pervious outwash sand and gravel. It appears that similar soil conditions may be encountered from station 40+00 to the north end of the project at Redmond-Woodinville Road. Previous explorations in this area indicate that the upland portion of the corridor is mantled by about 0.5 to 1.5 feet of topsoil which is underlain by medium dense to dense sand and silty sand and stiff to hard silt with varying amounts of sand and gravel, and extended to the maximum depth explored, about 11.5 feet deep. Perched groundwater was encountered in a few of test pits at a depth as shallow as about 2 to 3 feet. • The Sammamish River Valley was also formed largely during the glacial activities of the last glacial period and represents the next younger physiographic area of the project. The valley shape was formed by the thick ice sheets that occupied the area, scouring the older soil and rock and depositing soils from streams and rivers associated with glacial runoff. The Sammamish River Valley was subsequently filled with unconsolidated soils, primarily soft soils consisting of alluvial deposits of peat, silt, and sand. Other post glacial deposits include slopewash in moderately to steeply sloping areas next to the valley sidewalls and deposition from deltas that formed related stream channels and ravines that enter from the sides of the valley. These soil conditions affect the southern end of the project from about station 25+00 to 27+50 as the proposed corridor transitions from the valley bottom to the valley sidewall conditions. Soils in this area are expected to consist of topsoil underlain by deep deposits of soft silt and sand, with peat in some areas, overlying loose to dense granular soils and hard silt at depth. The thickness and extent of these surficial soils varies along this segment of the corridor. Explorations by others in this segment have encountered a topsoil layer that ranges from 0.5 to 1.5 feet in thickness, underlain by soft to medium stiff silt and peat (peat ranging from 1 to 7 feet in thickness). Next to the hillside, slopewash has resulted in soft or loose colluvial soils that mantle the older soils near the ground surface. Test pits in the area south of the end of this project encountered soft surficial soils generally extending to depths of 4 to 12 feet deep and were underlain by loose to dense sand and silty sand with varying amounts of gravel and hard silt. The hard silt unit appears to be part of the transitional beds and was encountered only in the explorations located close to the valley sidewall. It is anticipated that peat and soft soils may be encountered near station 27+50 where the proposed alignment exists at its closest point to the Sammamish River Valley wetlands (shown as wetland 1A on figure 1A). Groundwater seepage was observed at depths ranging from 3.5 to 12 feet below the existing ground surface in existing explorations in this area. Groundwater levels along the east side of the valley wall are expected to generally be closer to the ground surface at locations near the base of the slope. The water levels are expected to vary in response to seasonal levels of the Sammamish river, and to the amount of surface and subsurface water originating from the outwash and transitional beds along the valley sidewall. • The youngest soils to be encountered along the proposed corridor are found in areas of recent erosion, sedimentation and slopewash. These areas exist primarily near the bottom of several incised ravines that contain small streams. In these areas, the soils consist of topsoil and organic silt and sand. Slope wash consisting of topsoil and colluvial silt and sand also exist near the base of steep side slopes of the ravines. In the stream bottom areas, the depth of soft organic sediments is unknown but is estimated to range from less than a foot to 6 feet or more in some areas where more substantial sedimentation has occurred. Wetlands have formed and are generally associated with these small stream deposits as shown on Figures 1A and 1B as ---PAGE BREAK--- GEOTECHNICAL SUMMARY OF FINDINGS MEMORANDUM AND PRELIMINARY EVALUATION OF GEOTECHNICAL CONDITIONS TECHNICAL MEMO 5 - GEOTECHNICAL DESIGN CONSIDERATIONS /[INSERT DOCUMENT LOCATOR] 5 COPYRIGHT 2012 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL wetland 2, wetland 3, and wetland 4. Portions of wetland 1 have likely developed from similar conditions along a small stream that exists above wetland 1. At the base of the steep slopes and along the hillsides, slopewash has occurred. Several feet of loose topsoil and organic silt and sand may exist in some areas. At the mouth of the ravines containing small streams, alluvial fans have typically formed consisting primarily of loose to medium dense sand with silt and gravel. The ravines and streams that occupy the incised ravines along the valley sidewall have formed from runoff from the upper plateau of Education Hill east of the Redmond. Because much of the soils that cap the higher elevations of Education Hill plateau consist of dense till, the permeability is low. This leads to relatively low rate of infiltration resulting in increased runoff to these small streams that drain from the plateau. Since more pervious sand and gravel is sandwiched between the base of the till and the top of the transitional beds, infiltration in this zone is higher. Groundwater appears to generally be perched however at the top of the dense, low permeability transitional beds resulting in a predominate line of seepage near this contact line. This seepage is expressed by supplying water to the wetland soils in the ravines. Figure 1B shows a profile view longitudinally along most of the proposed corridor. This figure illustrates the location of incised ravines along the alignment, wetland areas, and the various physiographic regions that have been described previously. Also shown is a rough interpretation of soil types that may exist along the corridor in these various areas as described above. Conclusions and Recommendations In general, we believe that the subsurface conditions along most of the corridor are favorable for construction of the proposed roadway. Based on review of site topographic and geotechnical conditions observed in the field throughout the corridor and from existing reports, it appears that several elements of the site conditions near the south end of the project could lead to increased construction cost in this area. These conditions occur primarily in the vicinity of station 27+00 to 30+00. Several elements of the layout and design contribute to issues that must be dealt with near this location: • Presence of soft compressible soils in areas where high retaining walls are required for example under the western portion of the new road in the vicinity of Wetland 1A. • Width of the roadway overlaid on steep transverse slopes of the hillside will lead to increased height of retaining walls in this area because of the topography • Hillside stability issues although not evident in the field along this portion of the corridor, should be investigated. This concern is triggered by observation that a thick rather massive retaining wall may have been used along east side of 160th Ave NE immediately south of the beginning of the new corridor. • Seepage and groundwater are expected to be encountered in excavations near the Wetland 1A because of the relatively low elevation; and possible seepage in portions of the ravine located immediate east of wetland 1A. The above considerations within the south end of the corridor as well as other important considerations throughout the corridor are discussed in more detail later in this memorandum. These are areas that require additional investigation and more detailed understanding as the project moves forward, either because of unknown site conditions or because of potential construction cost implications to the project within these areas of the project. Soft foundation conditions are expected to be encountered in the bottom of the ravines through which the road will pass. Overexcavation and replacement with suitable foundation soils is anticipated in most locations. The ravine at Weltand 3 is expected to be the location containing the most significant widths and depths of soft sediments that will require overexcavation. ---PAGE BREAK--- GEOTECHNICAL SUMMARY OF FINDINGS MEMORANDUM AND PRELIMINARY EVALUATION OF GEOTECHNICAL CONDITIONS 6 TECHNICAL MEMO 5 - GEOTECHNICAL DESIGN CONSIDERATIONS/[INSERT DOCUMENT LOCATOR] COPYRIGHT [INSERT DATE SET BY SYSTEM] BY [CH2M HILL ENTITY] • COMPANY CONFIDENTIAL It appears that soils encountered below anticipated depths of natural topsoil and slope wash in the remaining portions of the alignment is generally expected to be medium dense to very dense and should possess good foundation characteristics for construction of roadway and structures. Conventional practices can be used in the construction of fill embankments, cut slopes, stream and trail crossing structure foundations, retaining walls, drainage and erosion control facilities and roadway pavement. Because of the proximity of steep slopes along the corridor, erosion and surface water control practices will have to be carefully constructed and monitored during construction. Removal of unsuitable soils will be required in the areas that have been described as having soft or undesirable foundation conditions. Nearly all of the soils encountered on the project are considered to be highly moisture sensitive and will require care during construction to perform work generally during non-rainy periods. Erosion Control Because of the sensitivity of soils to moisture and the erosive nature of the natural materials, erosion control during construction will be important. Best practices should be followed for all areas where vegetation is removed and areas are disturbed by the construction. Erosion control methods that should be used during construction include efficient channeling of surface water runoff, minimizing the extent of disturbed areas, use of erosion control slope cover such as straw and/or jute matting. Channel linings should be used to catch sediment and control downcutting and surface erosion; energy dissipaters should be used for trenches as required for controlling the velocity along the flow channels. The impacts of erosion should be mitigated to the extent possible by accomplishing the earthwork activities during normally dry seasons in July through early October. Long-term erosion should be mitigated by accomplishing grading to limit the concentration of runoff onto fill, cut or natural slopes and other erosion-sensitive areas, installing permanent sedimentation basins and a storm drain system. Adequate seeding to establish grass and other vegetative cover at the appropriate time of the season for planting should be used to provide permanent erosion control. Careful observation with increased monitoring and maintenance should be applied for the 1st year or until the newly graded and seeded areas become fully established. Disturbance to natural drainage courses adjacent to the alignment should be kept to a minimum so that existing erosion, sedimentation, channel stability, and flow conditions will not be appreciably changed. Undisturbed natural vegetative buffers should be protected and along natural drainage courses to help reduce impacts to the drainage courses and reduce sedimentation. Site Earthwork Activities The roadway construction will require substantial cuts and fills as discuss previously. Construction of all earthwork components of the project should be planned for only the dry summer periods, generally July through early October. It is likely that earthwork accomplished during this period will allow some re-use of excavated materials so long at the characteristics of the soils are suitable including the natural moisture content. Convention excavation and earth moving equipment can be used for the project. Imported fill will be required for construction of many of the fills. Imported materials should consist of well graded granular materials with generally less than about 10% passing the No. 200 sieve if the work is completed in the dry and away from areas of seepage. Where seepage is present or where the material could become moistened for any reason, the fill material should consist of well graded sand and gravel with less than 5 percent fines. Excavations into the natural subgrade are anticipated to encountered seepage and excess moisture in some areas. Where seepage is encountered, the water should be controlled to the degree possible by providing drains to safely allow the water to discharge from the work areas. It is recommended that a blanket drain is placed directly on the prepared roadway foundations to assure that water is drained away from the embankments. All seepage should be intercepted with such drainage blankets or ---PAGE BREAK--- GEOTECHNICAL SUMMARY OF FINDINGS MEMORANDUM AND PRELIMINARY EVALUATION OF GEOTECHNICAL CONDITIONS TECHNICAL MEMO 5 - GEOTECHNICAL DESIGN CONSIDERATIONS /[INSERT DOCUMENT LOCATOR] 7 COPYRIGHT 2012 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL chimney drains to allow free discharge from the embankment and avoid building up of water pressure behind the embankment fill. If particularly wet areas are encountered, foundation drain pipes should be incorporated in the drainage layers to assure that water can be safely discharged by gravity from the foundations. The blanket and chimney drain should consist of free-draining, well graded sand and gravel or crushed rock having less than 3 percent passing the number 200 sieve. Embankments should be placed in horizontal lifts in all areas, starting at the lowest point and working upward. Embankment lifts should tie into drainage layer or into the native soils if drainage zone is not provided. Each lift should spread to a uniform depth, not more than 10-inches in thickness prior to compaction. Where small hand- operated compaction equipment is required, lift thickness should be limited to 4-inches prior to compaction. Following the spreading of material to a uniform thickness, the soil should then be thoroughly compacted at a moisture content within 2 percent of optimum as defined by ASTM D1557. Embankment compaction should achieve a density not less than 95 percent of the maximum density in accordance with ASTM D1557. In areas where global stability is not a concern, the portion of the embankment deeper than 36 inches can be reduced to a maximum of 90 percent of the maximum density in accordance with ASTM D1557. Embankments should be kept crowned at all times to prevent the ponding of water on the embankment surfaces. If soil is placed for compaction, the lift should be immediately compacted to the required density and not left exposed to absorb moisture. Foundations for the proposed structures should be carried to a depth necessary to achieve a dense firm condition. Foundations should be proof rolled with a loaded dump truck if access if achievable and subgrade is relatively dry. In other conditions, subgrade should be tested for density and probed to determine if soft spots exist. If the subgrade condition is wet and or soft, all excavation should be accomplished using equipment working from outside the limits of the excavation. Soft areas should be removed and disposed of. As the excavation is completed and acceptable uniform foundation conditions are achieved, the foundation should be immediately covered with the specified overlying material to protect the subgrade from further disturbance. Retaining Wall Types Retaining walls will be required at selected locations throughout the project. For cost reasons, mechanically stabilized earth (MSE) walls are proposed where site conditions allow construction on a stable foundation and where global stability requirements can be met. These walls types generally result in lower unit costs for construction, are commonly designed and used by contractors, and are tolerate of minor settlement and deflections from static and seismic conditions. Other wall types that have been considered at this stage include cantilever soldier pile walls with lagging and soldier pile walls with tiebacks where improved global stability is necessary. These options are discussed and illustrated in much more detail in Technical Memorandum A-1 in Appendix A. Foundations for Structures Limited structures will be required for the proposed project. It appears from our initial assessment that foundations for most structures can be developed on spread footings. This includes the proposed arch culvert located at wetland 3. Further exploration will be required however, in order to identify the vertical and horizontal limits of soft organic materials in at this structure. Geologic evidence suggests that the depth of the soft undesirable materials are limited at this location and excavations carried to a reasonable depth below and outside the existing slopes will likely encounter competent soils consisting of outwash sand and gravel or transitional beds of hard silt and dense sand. It is important to investigate these foundation conditions well in advance since all soft and compressible materials will need to be removed and the geometry of the excavation has a significant impact on the type size and location of this structure. Memorandum A-3 in Appendix A provides additional discussion on this structure and assumed foundation configuration. ---PAGE BREAK--- GEOTECHNICAL SUMMARY OF FINDINGS MEMORANDUM AND PRELIMINARY EVALUATION OF GEOTECHNICAL CONDITIONS 8 TECHNICAL MEMO 5 - GEOTECHNICAL DESIGN CONSIDERATIONS/[INSERT DOCUMENT LOCATOR] COPYRIGHT [INSERT DATE SET BY SYSTEM] BY [CH2M HILL ENTITY] • COMPANY CONFIDENTIAL Other structures throughout the project corridor will require similar assessment of foundation conditions; however, conditions appear to generally be favorable for spread foundations in most areas. Structures located close to wetlands and on steep sideslopes where organic soils and where slope wash has occurred are areas where additional investigation and evaluation may be necessary to confirm foundation conditions. Areas of Additional Site Investigation and Analyses As stated previously, we in general, believe that the subsurface conditions along most of the corridor are favorable for construction of the proposed roadway. The south end of the project corridor is expected to require additional investigation and analysis to further define and allow consideration of the most practical options for roadway layout, configuration, and selection of design components such as types of retaining walls to be used. Without further investigation it is difficult to suggest in detail what may be the best options for the design; however, we believe that these options will become clear after conducting further investigation and analyses. Although some conditions may affect the project costs to some degree, none of these issues appear to affect the feasibility of the project. Issues at the South End of Corridor. The most difficult area geotechnically will likely be near the south end of the project. Several elements of the layout and design contribute to issues that must be dealt with near this location. These include satisfying global stability of the roadway section with 20 foot or higher retaining walls near the south end of the project where soft compressible soils are suspected to exist near wetland 1A. The underlying soils under the west side of the proposed road corridor in this area are likely to be wet, soft, and compressible and will likely possess low strength. Further analyses will be required to determine foundation conditions and options along this portion of the alignment. Options may include overexcavation to dense competent foundation soils and replacement with densely compacted, well graded granular soils placed as foundation and backfill behind (MSE) walls. Other options include cantilever soldier piles and lagging, tied-back soldier piles and lagging, and others. Global stability could also be an issue along the east side of this corridor at this location where steep transverse slopes will require deep cuts to achieve the width and grade for the road. Because of the steep slopes, the width of the roadway will lead to greater physical impact to terrain in this area than any other because of the steep existing slopes. This could lead to increased need for retaining walls as well as increased retaining wall height. Further alignment adjustments (vertically and horizontally) will help to optimize the solutions in this area of the alignment once the foundation conditions are carefully characterized in this area. The use of a massive retaining wall immediately south of the south end of the proposed corridor suggests that a careful examination is needed of the adjacent area as well as the south end of the proposed corridor to assure stability of the hillside in this area. The construction of this wall along the east side of 160th Avenue NE, immediately south of the start of this proposed project appears like it could have been because of a concern for stability of the hillside and the need to provide lateral restraint from unstable soils that may exist upslope from the wall. Obtaining further information about the design of this wall would be quite helpful in understanding the concerns and conditions in this area. Further investigation and analyses will be required near the south end of the proposed alignment to determine depth to competent soils capable of supporting walls and/or cut slopes for the proposed roadway. Issues and/or Unknown Conditions in Other Areas of the Project that Require Additional Investigation and Analysis. Seepage is presently occurring in certain areas of the corridor. These seeps appear to be concentrated near the contact between the top of the transitional beds (dense fine grained, low permeability soils) and outwash sand and gravel located in contact with the top of this formation. Prior investigations suggested that this contact may be at about elevation 80. The outwash is well graded and typically contains silt fines but is much more pervious than the underlying silt. These zones of seepage should be carefully identified and mapped throughout the project area. The seepage from these areas could lead to construction difficulties because of the characteristics of the moisture sensitive soils that surround these areas. Seepage if not controlled, also leads to ---PAGE BREAK--- GEOTECHNICAL SUMMARY OF FINDINGS MEMORANDUM AND PRELIMINARY EVALUATION OF GEOTECHNICAL CONDITIONS TECHNICAL MEMO 5 - GEOTECHNICAL DESIGN CONSIDERATIONS /[INSERT DOCUMENT LOCATOR] 9 COPYRIGHT 2012 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL increased erosion and increased incidence of required overexcavation of foundations during construction. Excessive seepage in sensitive areas can often lead to lower factors of safety of surrounding slopes. Seepage from natural groundwater can also rob the project of increased long term potential to infiltrate surface water resulting from runoff from the new roadway unless carefully collected and diverted away from these sensitive areas. For all of these reasons, it is important to further identify the zones of seepage and its seasonal variation where these conditions could affect the design and construction of new facilities. Plans should identify methods of collection and diverting the seepage to reduce the impacts to all phases of the work. Construction in each of the ravines is expected to encounter increased thickness of soft organic sediments. It appears that ravines associated with or located near with Wetlands 1 and 2 may result in minimal depth to competent foundations and associated overexcavation of these undesirable soils. However the ravine associated with Wetland 3 is more extensively underlain with these undesirable soils. It has been our assumption however, that the required overexcavation is limited to reasonable depths where dense competent foundations will be encountered. Additional exploration will be required to further identify these conditions especially at the location of proposed footings for new arch culvert structure and trail undercrossing. It is assumed that overexcavation and placement of densely compacted granular fill will provide suitable foundations for these structures. Seepage in the vicinity of these structure foundation is likely to be an issue and will need to be controlled. Additional explorations should be used to help identify the water table and seepage conditions in these areas. Care fill be required in selecting the alignment in the vicinity of the existing 54” Tolt Eastside Water Supply Pipeline. Coordination will be required with Seattle Public Utilities to assure that their future requirements for maintenance and operations are met. The depth of soft compressible soils and required overexcavation for structures at the stream associated with wetland 4 is unknown. Additional investigation is required to further define and confirm conditions in this area; however, it is likely that the depth is shallow and is probably not of significant geotechnical concern. Characteristics of the native soils including gradation and permeability should be carefully characterized throughout the length of the project, particularly at the north end. This should help in assessing areas of seepage, groundwater levels and variation, and opportunities for infiltration of stormwater. Better definition of the locations of the contact between the top of the transitional beds and the overlying granular outwash soils at selected areas of the corridor will be helpful in further understanding site conditions that will influence the design and construction. Developing adequate capacity to handle and treat stormwater runoff is an important element of the design in order to reduce impact to wetlands and reduce the cost of the project. Additional investigation should target areas where the opportunity to infiltrate water for disposal can be effective. Making efficient use of suitable soil areas for stormwater infiltration will greatly reduce the total impact to wetlands, will help reduce otherwise expensive infrastructure needed for controlling stormwater, is more environmentally friendly, and should help reduce the overall project costs. Likewise, areas where stormwater infiltration should not be considered should be identified from stability analyses and monitoring of existing groundwater conditions. Since application of additional stormwater to these areas could reduce the stability of slopes, these critical areas should be identified and application of additional stormwater to these areas should be avoided. ---PAGE BREAK--- GEOTECHNICAL SUMMARY OF FINDINGS MEMORANDUM AND PRELIMINARY EVALUATION OF GEOTECHNICAL CONDITIONS 10 TECHNICAL MEMO 5 - GEOTECHNICAL DESIGN CONSIDERATIONS/[INSERT DOCUMENT LOCATOR] COPYRIGHT [INSERT DATE SET BY SYSTEM] BY [CH2M HILL ENTITY] • COMPANY CONFIDENTIAL Figures ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- GEOTECHNICAL SUMMARY OF FINDINGS MEMORANDUM AND PRELIMINARY EVALUATION OF GEOTECHNICAL CONDITIONS TECHNICAL MEMO 5 - GEOTECHNICAL DESIGN CONSIDERATIONS /[INSERT DOCUMENT LOCATOR] 11 COPYRIGHT 2012 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL NRCS Soils Map and Legends Appendix A ---PAGE BREAK--- Sammamish River 166th Ave 95th St 104th St 99th St Sammamish River Trl 100th Ct Redmond Woodinville Rd 98th St 157th Ave 160th Ave 163rd Ave 107th St 161st Ave 108th Pl 167th Ave 161st Pl 159th Pl 163rd Pl 95th Way 162nd Ave 106th St 105th Ct 158th Ct 100th St 96th Way 97th Pl 167th Pl 95th Ct 165th Pl 103rd St 166th Pl 109th St 162nd Pl 98th Way 158th Ave 153rd Ave 101st Pl 103rd Pl 164th Pl 98th Pl 98th Ct 105th Pl 159th Ave 97th St 105th St 108th Ct 168th Pl 168th Ct 106th Pl 107th Pl 164th Ave 100th Way 168th Ave 159th Ct 107th Ct 107th Way 156th Pl 151st Ct 106th Ct 157th Ct 155th Pl 163rd Ct 160th Ct 106th Way 161st Ct 96th Pl 156th Ct 95th St 168th Ave 162nd Ave 97th Pl 163rd Pl 160th Ct 166th Pl 106th Ct 106th St 164th Ave 106th St 165th Pl 162nd Pl 105th Ct 100th St 97th St 97th Pl 167th Pl Sammamish River Trl 167th Ave Sr AmC KpB AgC PITS Ea KpD Ea AgD Sr Tu AgC EvC AgC Sr Sr W 564200 564200 564400 564400 564600 564600 564800 564800 565000 565000 565200 565200 565400 565400 565600 565600 565800 565800 566000 566000 566200 566200 5281800 5281800 5282000 5282000 5282200 5282200 5282400 5282400 5282600 5282600 5282800 5282800 5283000 5283000 0 1,000 2,000 3,000 500 Feet 0 200 400 600 100 Meters ± 47° 41' 54'' 122° 6' 54'' 47° 41' 122° 6' 55'' 47° 41' 47° 41' 55'' 122° 8' 43'' 122° 8' 42'' Map Scale: 1:10,700 if printed on A size (8.5" x 11") sheet. Soil Map—King County Area, Washington (Redmond 160th Ave Extension, Soils Map Info) Natural Resources Natural Resources Natural Resources Natural Resources Conservation Service Conservation Service Conservation Service Conservation Service Web Soil Survey National Cooperative Soil Survey 8/9/2012 Page 1 of 3 ---PAGE BREAK--- MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Units Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Gully Short Steep Slope Other Political Features Cities Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Map Scale: 1:10,700 if printed on A size (8.5" × 11") sheet. The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for accurate map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: UTM Zone 10N NAD83 This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: King County Area, Washington Survey Area Data: Version 7, Jul 2, 2012 Date(s) aerial images were photographed: 7/24/2006 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Soil Map–King County Area, Washington (Redmond 160th Ave Extension, Soils Map Info) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/9/2012 Page 2 of 3 ---PAGE BREAK--- Map Unit Legend King County Area, Washington (WA633) Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI AgC Alderwood gravelly sandy loam, 6 to 15 percent slopes 81.7 16.1% AgD Alderwood gravelly sandy loam, 15 to 30 percent slopes 29.0 5.7% AmC Arents, Alderwood material, 6 to 15 percent slopes 78.3 15.5% Ea Earlmont silt loam 55.8 11.0% EvC Everett gravelly sandy loam, 5 to 15 percent slopes 6.4 1.3% KpB Kitsap silt loam, 2 to 8 percent slopes 64.6 12.7% KpD Kitsap silt loam, 15 to 30 percent slopes 40.9 8.1% PITS Pits 49.0 9.7% Sr Snohomish silt loam, thick surface variant 77.1 15.2% Tu Tukwila muck 15.9 3.1% W Water 7.7 1.5% Totals for Area of Interest 506.4 100.0% Soil Map–King County Area, Washington Redmond 160th Ave Extension, Soils Map Info Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/9/2012 Page 3 of 3 ---PAGE BREAK--- GEOTECHNICAL SUMMARY OF FINDINGS MEMORANDUM AND PRELIMINARY EVALUATION OF GEOTECHNICAL CONDITIONS 12 TECHNICAL MEMO 5 - GEOTECHNICAL DESIGN CONSIDERATIONS/[INSERT DOCUMENT LOCATOR] COPYRIGHT [INSERT DATE SET BY SYSTEM] BY [CH2M HILL ENTITY] • COMPANY CONFIDENTIAL Existing Reports and Laboratory Analysis Appendix B ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- A-4 Preliminary Stormwater Memorandum ---PAGE BREAK--- DRAINAGE DESIGN CRITERIA TECHNICAL MEMORANDUM DRAFT 1 Technical Memorandum 160th Avenue NE Extension Project Stormwater Memorandum Prepared for: Steve Gibbs/City of Redmond Prepared by: Dustin Atchison/CH2M HILL Copies: Roger Mason P.E./CH2M HILL Project File No. 430676 Date: September 17, 2012 Introduction This memorandum describes the general criteria, preliminary analyses and recommendations for the the proposed stormwater facilities and low-impact-development features for the 160th Avenue NE Extension Project. The purposes of the memorandum are to identify drainage design criteria to be used for the development of the preliminary design and summarize preliminary stormwater design strategies and basis for the feasibility and cost of stormwater for the project. This project consists of extending 160th Avenue NE from the current terminus at NE 99th to NE 102nd Street and the intersection with Red-Wood Rd. The purpose of this phase of work is to identify the alternatives to be considered, evaluate the alternatives in enough detail so a preferred alternative can be selected, and develop budget level costs for the preferred alternative to be used for decision making and budgeting. Preliminary stormwater analysis will include determining the type, size and location of alternatives for flow control, water quality treatment, and conveyance facilities. Additionally, the feasibility of low-impact development techniques on the project site will be reviewed and a conceptual plan will be developed that outlines the suite of practices suitable to the site and locations where LID techniques are feasible. Stormwater Regulations Federal Federal stormwater regulations are contained in the Clean Water Act and typically are promulgated through local stormwater requirements. Federal stormwater-related requirements and approvals for the Renton project will need to meet the requirements of Section 7 of the Endangered Species Act (ESA), which is regulated by the U.S. Department of Interior, National Marine Fisheries Service (NMFS) and U.S. Fish and Wildlife Service (USFWS). ---PAGE BREAK--- DRAINAGE DESIGN CRITERIA TECHNICAL MEMORANDUM DRAFT 2 State If a project (new development or redevelopment on a single or multiple parcel site) has disturbed area exceed 1 acre, the project owner is required to file a Notice of Intent with the WSDOE for coverage under the National Pollutant Discharge Elimination System (NPDES) program’s General Permit for Stormwater Discharges Associated with Construction Activities. These filings would likely require the project to provide erosion control measures consistent with Ecology’s Hydraulic Permit Approvals from the Washington Department of Fish and Wildlife (WDFW) may be necessary for in-water work required. City Code requirements regarding stormwater management are in the Redmond Municipal Code, Chapter 15.24. City of Redmond’s Clearing, Grading and Stormwater Management Technical Notebook addresses technical requirements for the design, construction and maintenance of stormwater facilities. The Technical Notebook supplements and amends the 2005 Washington State Department of Ecology Stormwater Management Manual for Western Washington (2005 Ecology Manual). Minimum Technical Requirements The 2005 Ecology Manual contains 9 minimum requirements. As a new roadway extension, this project is defined as new development, large project and anticipated to exceed the thresholds requiring compliance with Minimum Requirements #1 through #9 for all new plus replaced impervious surfaces. The following paragraphs list each requirement with a discussion of how it will be addressed for this project. Minimum Requirement 1 – Stormwater Site Plans A Stormwater Site Plan following the outline provided in Chapter 3 of Volume 1 of the 2005 Ecology Manual. The Site Plan shall document the BMP selection process for the project. Minimum Requirement 2 – Construction Stormwater Pollution Prevention Plan The project will be required to provide a Construction Stormwater Pollution Prevention Plan as part of the Stormwater Site Plan. The shall be implemented beginning with initial soil disturbance and until final stabilization. The will be developed at later phases of the project. Minimum Requirement 3 – Source Control of Pollution Source control BMPs selected, designed and maintained in accordance with Volume IV of the Ecology Manual will be required. Minimum Requirement 4 – Preservation of Natural Drainage Systems and Outfalls The proposed project crosses 3 Class IV and 1 Class III (currently listed as Class IV but proposed to be re-classified) stream and will be required to maintain existing drainage patterns to the maximum extent practicable. Outfalls will require energy dissipation. ---PAGE BREAK--- DRAINAGE DESIGN CRITERIA TECHNICAL MEMORANDUM DRAFT 3 Minimum Requirement 5 – On-Site Stormwater Management Projects are required to implement on-site stormwater management BMPs to infiltrate, disperse, and retain stormwater runoff on-site to the maximum extent feasible without causing flooding, groundwater contamination, or erosion impacts. All post-construction landscaped areas within the project area are required to have compost amended soils. The project is encouraged to use runoff reduction/on-site stormwater management techniques to meet flow control requirements. A site assessment to determine the applicability and feasibility of runoff reduction techniques is required. Groundwater Protection The majority of the project area is within Wellhead Protection Zone 4, therefore, runoff from pollution generating impervious surfaces can be infiltrated without treatment provided the soil profile provides treatment per Chapter 3.3 of Volume III of the 2005 Ecology Manual. The southern extent of the project where the roadway ties into 160th Avenue is within Wellhead Protection Zone 3. Therefore, runoff from pollution generating impervious surfaces can be infiltrated with treatment prior to infiltration based on land use (see Minimum Requirement Native soils cannot be assumed to provide treatment. Minimum Requirement 6 – Runoff Treatment The project will require stormwater treatment of all pollution-generating impervious surfaces. Where discharge is to the ground, see provisions under Minimum Requirement #5 for treatment prior to discharge to native soils. Treatment Level Oil Control: Not Applicable The project will not consist of any high-use intersections, therefore Oil Control will not be required. Phosphorus Control: No Applicable The project discharges of Lake Sammamish Enhanced Treatment: Applies (assumed) The project discharges within a ¼-mile of a fish bearing stream (Sammamish River). Enhanced treatment for reduction of dissolved metals is required if the project AADT is exceeds 7,500. Basic Treatment: Applies Basic treatment is not necessary where the project infiltrates to native soils meeting treatment requirements in Wellhead Zone Minimum Requirement 7 – Flow Control The project currently discharges to the Sammamish River within a ¼-mile of the site. The currently flowpath is, however, not completely manmade as the discharges flow via streams and/or wetlands prior to discharging via a culvert beneath the Sammamish River Trails which discharges to the River. Flow control is not required if the project discharges directly, or indirectly, to the Sammamish River subject to the following conditions: ---PAGE BREAK--- DRAINAGE DESIGN CRITERIA TECHNICAL MEMORANDUM DRAFT 4  Direct discharge does not divert drainage from any perennial streams classified as Class 1, 2, 3 or 4 or from any Category I, II, or III wetland;  Flow splitting devices are provided to route natural runoff volumes to any Class 4 intermittent stream or Category IV wetland, defined as matching the durations ranging from 50% of the 2-year to the 50-year peak flow as determined using a continuous hydrologic model.  The conveyance system must be manmade and extend to the ordinary high water line of the Sammamish River; and  The conveyance system has adequate capacity and erodible elements of the conveyance system are adequately stabilized to prevent erosion. Flow Control Levels: If the requirements for direct discharge and flow control exemption, as described above, cannot be met, then the project will be subject to providing flow control to the following levels. Flow Control Duration Standard – Forested Conditions The study area is currently mapped as a forested pre-condition. Stormwater discharges shall match the developed discharge durations to forested durations for the range of pre-development rates from 50% of the 2-year peek up to the full 50-year peak flow. Alternative Flow Control – Regional Facility Areas Regional Stormwater Facility 360P is currently mapped of a portion of the study area. However, per the City of Redmond, this is a potential future facility and therefore will have no impact on the project. Minimum Requirement 8 – Wetlands Protection Much of the project site discharges to existing wetlands and will be required to meet the wetlands protection standard. The standard requires that discharges to the wetland shall maintain the hydrologic conditions, hydrophytic vegetation, and substrates necessary to support the existing and designated uses. The hydrologic analysis shall use the existing land cover condition to determin the existing hydrologic conditions unless otherwise directed. The wetlands themselves may be considered for hydrologic modification and/or stormwater treatment in accordance with Guide Sheet 1B in Appendix I-D. Wetland Buffers Stormwater treatment and flow control facilities shall not be built within a natural vegetated buffer, expect for:  Necessary conveyance systems or as allowed in wetlands approved for hydrologic modification and/or treatment. Minimum Requirement 9 – Operation and Maintenance Final design for the project will require the preparation of an operations and maintenance manual. ---PAGE BREAK--- DRAINAGE DESIGN CRITERIA TECHNICAL MEMORANDUM DRAFT 5 Approach Due to limited data and development of the preferred project alternative, the preliminary stormwater analysis focuses on identifying the site constraints and opportunities for stormwater management and recommends a tiered approach to managing stormwater as the design is developed further. Site Analysis The site is characterized by numerous critical areas that will drive the feasibility of various stormwater BMPs. Slopes The project area is dominated by steep slopes that form the Sammamish River valley wall. Soils Preliminary geotechnical investigations characterize the general physiographic and soil conditions as follows.  Sammamish Valley Wall. The existing site soils on upland areas consist primarily of highly permeable, but erosive, glacial outwash soils. It may be possible to infiltrate runoff within these soils, however, care shall be taken to minimize directing runoff that may create erosion or slope stability issues. The underlying soils or lowland portions of the site (approximately below elevation 80) on the site are characterized by a native soil consisting of transitional beds which are dominated by silts and may contain perched groundwater.  Drainage Crossings and Wetlands. Drainages crossed by the project consist primarily of of  Sammamish Valley Floor. Soils in this area at the southern extents of the project are expected to consist of topsoil underlain by deep deposits of soft silt and sand, with peat in some areas, overlying loose to dense granular soils and hard silt at depth. Streams and Wetlands Four drainages, all Class IVstreams, and four wetlands, either Category III or Category IV, were identified within the study area. It will be critical to minimize disturbance to these resources, maintain existing site hydrology and provide upstream controls to minimize the discharge of sediment, excess flow and pollutants to these resources. Preliminary Recommendations Erosion Control Due to the steep slopes and highly erosive nature of the existing site soils, erosion control during construction will be critical. To the extent practical, the limits of site disturbance shall be kept to the minimum extents necessary to complete the construction of the proposed roadway extension.  Preserve Vegetation/Mark Clearing Limits. Existing site vegetation shall be maintained and limits of work be clearly marked to minimize excessive removal of vegetation from the site.  Establish Construction Access. Due to the surrounding critical areas and difficulty of accessing the site, access to the project should be limited to discrete entrance and exit points to preserve the native soils, vegetation and critical areas surrounding the project. Construction staging should be carefully planned to minimize the necessary disturbance to accomplish site work. The access points to public roads at the north and south ends of the project should be protected with stabilized entrances, wheel washing and street sweeping as necessary. ---PAGE BREAK--- DRAINAGE DESIGN CRITERIA TECHNICAL MEMORANDUM DRAFT 6  Control Flow Rates. Construction flows from the project site should be controlled in such a manner that they do not discharge excessive flows to natural water features of the project and create the risk of erosion and turbidity.  Install Sediment Controls. All runoff from the construction site shall be directed through an approved sediment control BMP (e.g. filters, ponds, traps, silt fences, etc.).  Stabilize Soils. As noted above the site soils are highly erosive and shall be stabilized if disturbed and left unworked for an extended period. Due to the sensitivity of the site, work during the wet season should be limited.  Protect Slopes. The project will require extensive grading of site slopes. Grading work and retaining walls shall be designed to minimize erosion by directing runoff away from slopes or disturbed areas. Slope cover such as straw and/or jute matting, erosion control blankets, interceptor dikes and swales and vegetation should be used.  Protect Drain Inlets. Existing drainage inlets primarily exist at the south end of the project in NE 160th Avenue. As this is the most portion of the site, it is important to provide inlet protection at these locations.  Stabilize Channel and Outlets. Channel linings should be used to catch sediment and control downcutting and surface erosion; energy dissipaters should be used for trenches as required for controlling the velocity along the flow channels. All concentrated stormwater discharge points should be stabilized using rock pads or dispersion trenches to minimize point erosion.  Control Pollutants. Construction should design, install, implement and maintain effective pollution prevention measures to minimize the discharge of pollutants.  Control De-Watering. Due to the presence of groundwater seeps, dewatering is to be expected on this project. Dewatering water shall be controlled to discharge only clean, non- turbid de-watering water and otherwise handle and treat turbid water in accordance with standards.  Maintain BMPs. Proper erosion control requires on-going maintenance of both temporary and permanent erosion control BMPs.  Manage the Project. Erosion control on the project shall be proactively managed by maintaining an updated construction on-going inspections by a CESCL and continually manage and adapt erosion control on the project. Water Quality All stormwater runoff from pollution-generating surfaces shall be treated prior to discharge. The tiered approach below places a priority on green infrastructure or low-impact development techniques that not only provide water quality but provide additional runoff reduction and provide additional landscape benefits to the roadway. Tier 1: Where possible, final roadway sections should consider separating sidewalk and non- pollution surfaces from pollution-generating surfaces by provide onset crowns or reverse slopes. Additionally, porous sidewalks may be considered to directly infiltrate runoff into the underlying road subgrade (note: due to the steep longitudinal slope of the proposed roadway, check dams may be necessary to prevent lateral flow in the subgrade). Tier 2: The preliminary stormwater concept consists primarily of bioretention planters within the planter strips to filter and to the extent practical infiltrate runoff directly below the planters or through connection to infiltration trenches beneath the roadway subgrade. Tier 3: Where the above techniques are not feasible, the stormwater runoff may be mitigated by directing flow through Filterras or other approved proprietary tree/planter box filtration devices. Tier 4: As a last resort, runoff may be treated via underground filter cartridge vaults, catch basins or other methods. ---PAGE BREAK--- DRAINAGE DESIGN CRITERIA TECHNICAL MEMORANDUM DRAFT 7 Flow Control The proposed project will at a minimum maintain existing site hydrology to drainage crossing and adjacent wetlands. Where feasible, the project may directly discharge to the Sammamish River without flow control, provided it can be demonstrated that the conveyance system to the River is either completely manmade or has negligible impacts to the hydroperiod of existing wetlands. Tier 1: The stormwater will infiltrate runoff to the maximum extent feasible within the project area through either rain gardens or infiltration trenches located at the base of structures. Tier Where infiltration alone cannot meet the flow control requirements, the project may consider modification or modeling of the existing wetlands and conveyance system to demonstrate negligible hydrologic impact to the wetlands and suitable conveyance capacity to meet the combined requirements for direct discharge and wetlands protection. Further study for this option is required in future design development stages. Tier 3: Where infiltration and discharge to wetlands is not possible, flow control will be provided via subsurface vaults or adjacent detention ponds. References City of Redmond, Municipal Code City of Redmond, Clearing, Grading, and Stormwater Management Technical Notebook. Issue No. 6. Effective: February 23, 2012. Washington State Department of Ecology (WSDOE). 2005. Stormwater Management Manual for Western Washington August. ---PAGE BREAK--- A-5 Wetland and Stream Assessment Technical Memorandum ---PAGE BREAK--- REDMOND_160TH_WETLANDTECHMEMO_05222012.DOCX 1 T E C H N I C A L M E M O R A N D U M 160th Avenue NE Extension Project— Wetland and Stream Assessment PREPARED FOR: Steve Gibbs/City of Redmond Cathy Beam/City of Redmond PREPARED BY: Hans Ehlert, PWS No. 1165/CH2M HILL Megan Karl/CH2M HILL Randy Whitman/CH2M HILL Rob Rodland/CH2M HILL FROM: DATE: Roger Mason/CH2M HILL May 22, 2012 Purpose The purpose of this technical memorandum is to conduct a planning-level assessment of existing wetland and stream conditions for the preliminary design and feasibility of extending 160th Avenue NE from its current terminus at NE 99th northward to NE 102nd Street. This technical memorandum does not provide any information on potential impacts to wetlands or wetland buffers, or any associated mitigation. A complete wetland and stream delineation report will be prepared at a later phase of the proposed project as well as information on the impacts to wetlands, wetland buffers, streams, and stream buffers, and associated mitigation. Summary The work completed as part of this assessment did not include a complete wetland delineation. Only the boundaries of the wetlands within the study area were identified to help guide project engineers to avoid and minimize potential impacts to wetlands and streams. The study area is defined by an approximately 200-foot-wide corridor centered on the proposed roadway alignment. On March 14, 2012, biologists from CH2M HILL assessed the streams and wetlands within the project study area. Randy Whitman assessed the streams. Hans Ehlert and Megan Karl assessed the wetlands, and flagged the approximate boundaries of Wetlands 1A, 2A, and 4A. ESA Adolfson had previously delineated Wetland A (see Reid Middleton 2009), which was renamed Wetland 3A for consistency with this memo. Four drainages, all Class IV streams, and four wetlands, either Category III or Category IV, were identified within the study area. Three of the wetlands are narrow slope wetlands located within the drainages adjacent to streams. The fourth wetland is a depressional wetland that is part of the larger system located on the historical floodplain of the Sammamish River valley. Figure A provides information on the streams and wetlands identified in the study area. ---PAGE BREAK--- ---PAGE BREAK--- 160TH AVENUE NE EXTENSION PROJECT— WETLAND AND STREAM ASSESSMENT 3 Previous Studies Previous studies of wetlands in the study area were used as a starting point for the current assessment. The previous studies included:  Final Supplemental Environmental Impact Statement, 160th Avenue NE Road Extension prepared for the City of Redmond by Parametrix in 1999 (Parametrix 1999). This was a planning-level report and did not include detailed information that could be used for design and the information was developed more than 13 years ago. Residential developments have since been constructed at the north and south ends of the proposed new road extension and have likely modified the existing site conditions described in the report.  PSE Phase 3 Trail Improvement Project Sammamish River Trail to SR 202, Design Report prepared for the City of Redmond by Reid Middleton in 2009 (Reid Middleton 2009). This study includes detailed information for a portion of the project study area, such as wetland delineation, wetland rating, and stream classification within the PSE power line easement. Streams The following stream descriptions are organized geographically, starting from the south end of the alignment and proceeding northward. The four streams in the study area are summarized in Table A, and illustrated in Figure A. Stream 1 Stream 1 is a very small high gradient, intermittent watercourse. It is a Class IV stream and non-fish bearing. The watercourse drains from Redmond Woodinville Road NE westward to a drain next to 160th Avenue NE. Under extreme flow conditions, it appears that some of the flow could bypass the drain and continue flow down the hill slope where it would empty into a wetland and infiltrate into the Sammamish River floodplain. Upstream of 160th Avenue NE, the watercourse is buried under leaves and other organic debris and vegetation. Construction of 160th Avenue NE and the nearby residential development appears to have diverted the natural drainage into a pipe system that flows to an infiltration pit in the floodplain wetland at the bottom of the slope. An overflow pipe appears to have been constructed within the intermittent watercourse. Stream 2 Stream 2 is a small, high gradient, intermittent, Class IV stream and is non-fish bearing. During the stream evaluation on March 14, 2012, flow was visually estimated to be approximately 0.1 cubic feet per second (cfs) with a wetted channel width of approximately 1.0 foot. The bankfull width was estimated to be approximately 2.0 feet wide near the approximate alignment centerline. The approximate centerline of the alignment is situated at a distinct break in channel gradient, with a shallower slope immediately upstream and ---PAGE BREAK--- 160TH AVENUE NE EXTENSION PROJECT— WETLAND AND STREAM ASSESSMENT 4 steeper slope The channel also becomes confined in a ravine to the side. Channel substrate consists of gravel, sand, and organic materials. Riparian vegetation consists of reed canarygrass and blackberry upstream of the centerline, and Douglas-fir, western red cedar, big leaf maple, blackberry, and salmonberry to the side. Stream 3 Stream 3 is located in the ravine immediately to the south of the PSE powerline trail. It is a high gradient, Class IV stream and is non-fish bearing. The flow regime (intermittent vs. perennial) could not be determined at the time of the site visit. The riparian vegetation in the ravine consists of Douglas-fir, western red cedar, red alder, big leaf maple, and salmonberry. During the stream evaluation on March 14, 2012, the wetted channel width was approximately 2.0 feet with a flow estimated to be approximately 0.1 cfs. The bankfull width was estimated to be approximately 3.0 feet. Substrate consists of gravel and sand. Stream 4 Stream 4 is the largest of the four water courses within the proposed 160th Avenue NE extension alignment. It is a high gradient, Class IV stream and is non-fish bearing. The flow regime (intermittent vs. perennial) could not be determined at the time of the site visit. During the stream evaluation on March 14, 2012, the flow was approximately 0.5 cfs, having a wetted width of approximately 5 - 6 feet. Bankfull width was approximately 7.0 feet at the location examined, which was within the alignment but uncertain with regard to the centerline. Depth ranged from 2 to 6 inches deep. Substrate consists of cobbles, boulders, gravel, and sand. Sand loading appeared to be excessive. The channel had abundant small woody debris. The riparian vegetation consists of western red cedar, red alder, big leaf maple, sword fern, and salmonberry. TABLE A Streams in the Study Area Stream Name Stream Class Flow Regime Stream Buffer Width (feet) Approximate Bankfull Width (feet) Stream 1 Class IV Intermittent 25 - Stream 2 Class IV Intermittent 25 2.0 Stream 3 Class IV Indeterminant (Intermittent or Perennial) 25-36 3.0 Stream 4 Class IV Indeterminant (Intermittent or Perennial) 25-36 7.0 Source: City of Redmond 2011 a Stream buffer width required by RZC Article IV Environmental Regulations. ---PAGE BREAK--- 160TH AVENUE NE EXTENSION PROJECT— WETLAND AND STREAM ASSESSMENT 5 Wetlands The following wetland descriptions are organized geographically, starting from the south end of the alignment and proceeding northward. The wetlands are summarized in Table B, and shown on Figure A. Table C provides information on the wetland replacement ratios for the wetlands in the study area. Additional information on wetland impacts and mitigation related to replacement for any impacts will be performed at a later phase of the proposed project. The intent of this memorandum is to provide an assessment of the existing condition of wetlands in the study area. Appendix A: Wetland Photos provides photos of the four wetlands, and Appendix B: Wetland Rating Forms provides information on the wetland work completed as part of the site visit. In addition, the following available information was collected and reviewed prior to visiting the site:  Topography. Topography slopes to the west. The areas of lowest elevation onsite are located in the western portion of the study area.  Soils. Soils mapped onsite are Alderwood gravelly sandy loam, 15-30% slopes (AgD), Kitsap silt loam, 2-8% slopes (KpB), and Kitsap silt loam, 8-15% slopes (KpD). None of these are listed as hydric soils.  City of Redmond Municipal Code Chapter 21.64, Critical Areas. Chapter provides information on streams and wetlands in the City of Redmond including classification and buffer requirements.  City of Redmond Municipal Code Chapter 21.64, Critical Areas, Map 64.4 Wetlands. The map shows the entire study area as either “mixed wetland/upland” or “wetland”.  Previous studies. Parametrix (1999) shows wetlands associated with the four drainages onsite. Reid Middleton (2009) includes a delineation of the wetland within the Puget Sound Energy (PSE) power line easement, which bisects the study area.  Aerial Photography with available basemap (showing project alignment, study area limits, drainage improvements, and previously mapped streams and wetlands). Wetland 1A Wet land 1A is located at the southwestern portion of the proposed alignment (Figure It is a relatively large Category III depressional wetland that is located on the historical floodplain of the Sammamish River Valley. Wetland 1A becomes inundated from late winter through spring and drains via a culvert to the Sammamish River. Wetland 1A is dominated by emergent and scrub-shrub vegetation such as reed canarygrass, willow, dogwood, and red alder (see Appendix A: Wetland Photos). Vegetation within the within the PSE powerline easement is regularly disturbed by PSE vegetation management. This wetland is bounded by the Sammamish River Trail to the west, the PSE Powerline Trail to the north, the hillside to the east, and an apartment complex to the south. The portion of the wetland buffer that is within the study corridor is relatively well vegetated hillslope with various native trees and shrubs, and invasive blackberry vines. ---PAGE BREAK--- 160TH AVENUE NE EXTENSION PROJECT— WETLAND AND STREAM ASSESSMENT 6 Wetland 2A Wet land 2A is located just south of the center portion of the proposed alignment (Figure It is a relatively small (around 0.25 acre) Category IV slope wetland that is located on a slope and drains into Wetland 1A which is in the floodplain of the Sammamish River Valley. Wetland 2A is dominated by emergent and scrub-shrub vegetation such as reed canarygrass and salmon berry (see Appendix A: Wetland Photos). Numerous sedge plants and skunk cabbage were observed as well. This wetland is bounded by draining into Wetland 1A to the southwest, the PSE Powerline Trail to the north, and the hillside to the east. The portion of the wetland buffer that is within the study corridor is relatively well vegetated hillslope with various native trees and shrubs in the north, south and west, and invasive blackberry vines to the east. Wetland 3A The delineation and wetland rating performed by ESA Adolfson appears to be reasonably correct and was adopted for purposes of this wetland assessment. According to ESA Adolfson data, Wetland 3A is located just north of the center portion of the proposed alignment just south of the PSE Powerline Trail (Figure It is a relatively small (less than 1 acre) Category III slope wetland that is located on a slope and drains into Wetland 1A which is in the floodplain of the Sammamish River Valley. Wetland 3A is dominated by emergent and scrub-shrub vegetation such as alder, willow, reed canarygrass, salmon berry, bulrush, and stinging nettle (see Appendix A: Wetland Photos). This wetland is bounded by draining into Wetland 1A to the south, the PSE Powerline Trail to the north, and the hillside to the west and east. The portion of the wetland buffer that is within the study corridor is relatively well vegetated hillslope with various native trees and shrubs. Wetland 4A Wet land 4A is located in the northeastern portion of the proposed alignment (Figure It is a relatively small (less than 0.25 acre) Category III slope wetland that is located on a slope and has Stream 4 running through it. Wetland 4A is dominated by emergent and scrub- shrub vegetation such as reed canarygrass, alder, willow, ladyfern, and salmon berry (see Appendix A: Wetland Photos). This wetland is bounded by a disturbed area and the southern edge of 156th Ave NE to the north, the PSE Powerline Trail to the south, and the hillside to the east and west. The portion of the wetland buffer that is within the study corridor is relatively well vegetated hillslope with various native trees and shrubs in the east, south, and west, and invasive blackberry vines to the north. ---PAGE BREAK--- 160TH AVENUE NE EXTENSION PROJECT— WETLAND AND STREAM ASSESSMENT 7 TABLE B Cowardin Class, HGM Class, Category, and Buffer Width of Wetlands Located in the Study Area Wetland ID Cowardin Class HGM Class Categorya Wetland Buffer Width (feet)b Stream Present Source of Wetland Boundary Information Wetland Rated by 1A PEM/PSS Depressional 3 80 No CH2M HILL 2012 CH2M HILL 2012 2A PEM/PSS Slope 4 50 Yes CH2M HILL 2012 CH2M HILL 2012 3A PEM/PSS/PFO Slope 3 80 Yes Reid Middleton 2009 (delineated as “Wetand A” by ESA Adolfson in fall 2008) Reid Middleton 2009 4A PEM/PSS/PFO Slope 3 80 Yes CH2M HILL 2012 CH2M HILL 2012 a Category is based on Ecology’s rating system (Hruby, 2004), which the City of Redmond adopted without modification. b Buffer width required by Critical Areas Ordinance for City of Redmond. Assumes the proposed roadway is considered a high-impact land use, which has the highest buffer width. Source: City of Redmond 2011. PEM = palustrine emergent marsh; PSS = palustrine scrub-shrub; PFO= palustrine forested TABLE C Wetland Replacement Ratios for Wetlands in the Study Area Wetland Category Creation or Re- establishment Rehabilitation (Restoration) Re-establishment or Creation (R/C) and Enhancement Enhancement Only III 2:1 4:1 1:1 R/C and 2:1 E 8:1 IV 1.5:1 3:1 1:1 R/C and 2:1 E 6:1 Source: City of Redmond 2011 ---PAGE BREAK--- 160TH AVENUE NE EXTENSION PROJECT— WETLAND AND STREAM ASSESSMENT 8 References City of Redmond. 2011. Redmond Zoning Code (RZC) Article IV Environmental Regulations. Revised 12/6/2011. City of Redmond. 2011. Critical Areas Map 64.1 Fish and Wildlife Habitat Conservation Areas. City of Redmond. 2011. Critical Areas Map 64.3 Streams Classification. City of Redmond. 2011. Critical Areas Map 64.4 Wetlands. Cowardin, L. V. Carter, F. C. Golet, and E. T. LaRoe. 1979. Classification of Wetlands and Deepwater Habitats of the United States. USFWS, FWS/OBS-79/31. Parametrix. 1999. Final Supplemental Environmental Impact Statement, 160th Avenue NE Road Extension. Prepared for the City of Redmond by Parametrix (February 26, 1999). Reid Middleton. 2009. PSE Phase 3 Trail Improvement Project Sammamish River Trail to SR 202, Design Report. Prepared for the City of Redmond by Reid Middleton (November 2009). United States Department of Agriculture Natural Resources Conservation Service (USDA NRCS). Wetland Indicator Status. Accessed March 2012 online at http://plants.usda.gov/wetland.html. U.S. Army Corps of Engineers (USACE). May 2010. Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Western Mountains, Valleys, and Coast Region (Version 2.0).