Document Redmond_doc_8c2e1f5303

Downtown/Redmond Way Stormwater Trunk and Water Quality Treatment Facility Preliminary Engineering Report City of Redmond, Washington August 2009 ---PAGE BREAK--- Downtown/Redmond Way Stormwater Trunk and Water Quality Treatment Facility Preliminary Engineering Report City of Redmond, Washington August 2009 ---PAGE BREAK--- 001627\11-01231-10000 CERTIFICATE OF ENGINEER Preliminary Engineering Report: Downtown/Redmond Way Stormwater Trunk and Water Quality Treatment Facility City of Redmond, Washington August 31, 2009 The technical material and data contained in this document were prepared under the supervision and direction of the undersigned, whose seal, as a professional engineer licensed to practice as such, is affixed below. Ralph D. Nelson, P.E. ---PAGE BREAK--- 001627\11-01231-10000 Preliminary Engineering Report Downtown/Redmond Way Stormwater Trunk and Water Quality Treatment Facility Table of Contents Certificate of Engineer Table of Contents List of Tables List of Figures EXECUTIVE ES-1 Section 1 1-1 Section 2 DESIGN CRITERIA 2-1 Section 3 HYDROLOGIC AND HYDRAULIC 3-1 3.1 3-1 3.2 Hydrologic 3-1 3.2.1 HSPF/WWHM 3-1 3.2.2 Effect of Redirecting Storm Runoff from Bear 3-2 3.2.3 3-6 3.2.4 Agreement Among 3-8 3.3 Existing Conveyance 3-9 3.4 Sammamish River Water Levels 3-9 Section 4 CONVEYANCE ALTERNATIVE ANALYSES 4-1 4.1 4-1 4.2 Evaluation 4-1 4.3 Conveyance 4-3 4.3.1 Alignment Alternatives 4-3 4.3.2 Discussion of Conveyance Alternatives 4-17 4.3.3 Preferred Conveyance 4-17 ---PAGE BREAK--- Table of Contents vi R. W. Beck Preliminary Engineering Report – August 2009 Section 5 WATER QUALITY TREATMENT ALTERNATIVE ANALYSES 5-1 5.1 5-1 5.2 Evaluation 5-1 5.3 Water Quality Treatment 5-2 5.3.1 Treatment BMPs 5-2 5.3.2 Selection of Preferred Treatment BMP 5-4 5.4 Water Quality Treatment 5-5 5.4.1 Treatment Sites 5-5 5.4.2 Selection of Preferred Treatment 5-6 5.5 5-8 Section 6 OPERATION AND MAINTENANCE 6-1 6.1 6-1 6.2 Water Quality Facility 6-2 Section 7 IMPLEMENTATION 7-1 7.1 Estimated Cost of Preferred 7-1 7.2 Implementation Schedule 7-1 Appendix A. Conceptual Construction Cost Estimate Appendix B. Hydrologic and Hydraulic Models Appendix C. Sammamish River Water Levels Appendix D. Technical Studies D1. Geotechnical Memorandum D2. Environmental Sensitive Areas Memorandum D3. Diversion Memorandum D4. Cultural Resources Assessment D5. Biological Assessment D6. Preliminary Stormwater Report Appendix E. Permitting Documents E1. SEPA Checklist E2. JARPA Submittal E3. Shoreline Permit ---PAGE BREAK--- Table of Contents Preliminary Engineering Report – August 2009 R. W. Beck vii List of Tables 2-1 Design Criteria 2-1 2-2 Design Assumptions 2-2 3-1 Areas Draining to the Redmond Way Treatment Facility in the WWHM Model 3-2 3-2 Comparison of Flood 3-5 3-3 Areas Draining to the Redmond Way Treatment Facility in the Model 3-6 3-4 Peak Flows at Selected 3-8 4-1 Alternative Evaluation Criteria for Conveyance Alternatives 4-2 4-2 Traffic Evaluation 4-18 4-3 Conveyance Alternative 4-18 5-1 Alternative Evaluation Criteria for Water Quality Treatment 5-1 5-2 Water Quality Treatment Alternative Evaluation 5-4 5-3 Treatment Site Alternative 5-7 List of Figures 3-1 Redmond Way Basin and Area to Be Diverted from Bear 3-3 4-1 Existing Utilities 4-5 4-2 Redmond Way Plan and Profile Schematic 4-7 4-3 166th Ave NE Connection Plan and Profile 4-9 4-4 NE 76th Street/BNSF Right-of-Way Plan and Profile 4-13 4-5 Cleveland Street Plan and Profile 4-15 5-1 Alternative Water Quality Treatment 5-5 6-1 Estimated Annual Solids 6-2 This report has been prepared for the use of the client for the specific purposes identified in the report. The conclusions, observations and recommendations contained herein attributed to R. W. Beck, Inc. W. Beck) constitute the opinions of R. W. Beck. To the extent that statements, information and opinions provided by the client or others have been used in the preparation of this report, R. W. Beck has relied upon the same to be accurate, and for which no assurances are intended and no representations or warranties are made. R. W. Beck makes no certification and gives no assurances except as explicitly set forth in this report. Copyright 2009, R. W. Beck, Inc. All rights reserved. ---PAGE BREAK--- Preliminary Engineering Report – August 2009 EXECUTIVE SUMMARY The Redmond Way Stormwater Trunk and Water Quality Facility is one of six projects identified in the City’s Regional Facilities Plan, a large-scale effort to improve the quality of the stormwater in Redmond. Specifically, the Regional Facilities Plan intends to retrofit large portions of the City to provide flow control and water quality treatment in accordance with the City’s NPDES requirements and adopted stormwater requirements. The Redmond Way facility provides centralized treatment of stormwater before it discharges to the Sammamish River. Once constructed, it will provide treatment for over 250 acres of commercial/residential areas of the City. Included in this project are more than 5,000 feet of conveyance improvements leading to the treatment facility to be constructed in the vicinity of the Sammamish River. The purpose of this report is to document key assumptions or criteria used to develop the designs of the stormwater trunk line and treatment facility Conveyance Alternatives Alternative analyses were performed for the various conveyance and water quality treatment alternatives to assess their technical feasibility in order to help select a preferred alternative. The conveyance alignment alternatives were evaluated using various differentiating criteria to aid in the selection of a preferred alternative(s). The criteria are sorted into four major themes: cost impacts, schedule impacts, community impacts, and operations and maintenance (O&M) impacts. During the initial review of the project terrain and existing rights-of-way, three main route corridors were reviewed, and a total of 12 alternatives involving variations of the three corridors were developed. Based on the project criteria and input from the City, the BNSF railroad/NE 76th Street corridor is the recommended route. This alternative provides the following benefits when compared to the other alternatives:  Least disruptive to traffic flow in downtown core.  Least disruptive to businesses.  Collects stormwater runoff from the largest drainage area.  Least utility conflicts.  Can be easily connected to the preferred treatment sites.  Uses the existing pipe systems in Cleveland Street and Redmond Way, thus requiring the smallest new pipeline size.  Least costly of the alternatives, based on pipe size, traffic impacts, and utility conflicts. (Note: the comparative costs do not account for railroad usage of the BNSF right-of-way.) ---PAGE BREAK--- EXECUTIVE SUMMARY ES-2 R. W. Beck Preliminary Engineering Report – August 2009 Water Quality Treatment Alternatives Water quality treatment alternatives considered different treatment methodologies as well as different treatment sites. Treatment alternatives or best management practices (BMPs) were evaluated considering the treatment objectives and the potential constraints. The EcoStorm Plus system is the recommended treatment BMP for the Redmond Way water quality facility. This recommendation is contingent upon proven test results demonstrating pollutant removal effectiveness expected from the ongoing Luke McRedmond Park monitoring. The EcoStorm Plus system has the following advantages:  The system can operate in a submerged condition caused by high water levels in the Sammamish River for extended periods of time.  The system is designed for the removal of metals, which, combined with sediment pre-treatment by hydrodynamic concentrators, would meet the intent of Enhanced Treatment. (Monitoring is in progress to verify metals removal performance.)  The system provides the smallest footprint among BMPs that target metals. Among the media filtration BMPs approved by the Washington State Department of Ecology for Pilot, Conditional, or General Use Level Designation, EcoStorm Plus allows the highest treatment flow rate per filter surface area.  The system has acceptable head loss (nominally 8 to 10 inches) helping to reduce the risk of flooding along the stormwater trunk line. Treatment sites were evaluated considering their location in the basin and compatibility with urban land use. A facility site located close to the outfall would treat the largest portion of the basin. Three site alternatives were evaluated: the Triangle site, the Ben Franklin site, and the Bear Creek Parkway site. The optimal location was determined to be the Triangle site; this provides the best function while meeting the design considerations. The Triangle site is recommended because:  The presence of an existing (oil-water separator) stormwater treatment facility on this site is an established use.  It takes advantage of using an existing easement. The easement would require expansion but it would be one contiguous easement.  It is low in the basin, capturing the maximum area in a single facility.  Any of the three stormwater trunk line alternatives from the basin could be routed to this location.  It makes use of an existing 30-inch-diameter outfall.  Parking impacts during maintenance may be mitigated by using the lot at Luke McRedmond Park. ---PAGE BREAK--- EXECUTIVE SUMMARY Preliminary Engineering Report – August 2009 R. W. Beck ES-3 Permitting An aggressive permit schedule was developed due to the long lead time required by regulatory agencies. Based on a general conveyance corridor footprint and location of the water quality treatment facility on the Triangle site, permit applications for land use and in-water work approvals have been submitted to federal, state, and local agencies. ---PAGE BREAK--- Preliminary Engineering Report – August 2009 Section 1 INTRODUCTION The Downtown/Redmond Way Stormwater Trunk and Water Quality Treatment is one of six projects identified in the City of Redmond’s Regional Facilities Plan, a large- scale effort to improve the quality of the stormwater in Redmond. Specifically, the Regional Facilities Plan intends to retrofit large portions of the City to provide flow control and water quality treatment in accordance with the City’s NPDES requirements and adopted stormwater requirements. The Redmond Way facility provides conveyance and centralized treatment of stormwater before it discharges to the Sammamish River. Once constructed, the facility will provide treatment for runoff from over 250 acres of commercial/residential areas of the City (up to the design storm; the remainder of runoff will be directly discharged). The construction project will include more than 5,000 feet of conveyance improvements leading to the treatment facility to be constructed in the vicinity of the Sammamish River. The purpose of this report is to document key assumptions, decisions, or criteria used to develop the designs of the stormwater trunkline and treatment facility. The report also summarizes the different alternatives that were considered and presented at design workshops held with City staff. The recommended alternative described in this report was approved by the City Planning and Public Works Committee at an October 14, 2008, meeting. ---PAGE BREAK--- Preliminary Engineering Report – August 2009 Section 2 DESIGN CRITERIA The design criteria checklist included in Table 2-1 was prepared at the start of this project as a guide to the facilities design. Because the facilities need to be retrofitted into the existing storm drain system, the proposed solution may not meet all the criteria listed. However, the goal of the design was to meet as many of these criteria as possible. Table 2-1 Design Criteria Item Criterion Reference Capacity 50-year Return Flow (Approximately 109 cfs) Flushing Velocity Minimum 2.0 fps at 6-month Return Flow Pipe Material PVC (Sewer) for normal installation; Ductile Iron for shallow bury; Corrugated Polyethylene and Concrete may be considered Redmond Technical Notebook No. 5 Trench Backfill Native Pipe Design Match Crown King County Design Manual Minimum Pipe Slope Recommended 0.25%, absolute minimum in accordance with the Department of Ecology Orange Book Redmond Technical Notebook No. 5 Structure Spacing 200' Minimum; 400' Maximum Redmond Technical Notebook No. 5 Structure Type Manholes to avoid trapping sediment at multiple locations along the conveyance line. Sedimentation vault(s) at selected locations will be provided instead. A 0.1' drop across structure will not be provided. Easements Standard 20' wide; minimum 15' wide Redmond Technical Notebook No. 5 ---PAGE BREAK--- Section 2 2-2 R. W. Beck Preliminary Engineering Report – August 2009 In addition to the design criterion discussed above, the project team developed a list of design assumptions to be used during the design process. These assumptions are listed in Table 2-2. Table 2-2 Design Assumptions Item Assumption Sammamish River Level For conveyance and water quality system design, use design tailwater elevation of 23.5'. There have not been any 2-year or greater storms of 30- minutes or less duration that have corresponded to a river stage above this level in the 42 years of record. The Ordinary High Water Mark (OHWM) elevation is 22.5'. For comparison, the 10-year water level in the Sammamish River is 27.9’. Basin Conditions Full development with dry wells removed. Effective impervious surface based on zoning and regional values. Soils are based on assumptions by NHC for hydrologic modeling of the City (SCS data). New Development Rooftop infiltration and selected other low impact development (LID) improvements will be incentivized in upcoming revisions to the City of Redmond’s drainage standards. Existing Dry Wells Dry well systems abandoned and runoff conveyed to public storm drain system. New Public or Private Detention or Dry Wells None will be added. Railroad Rights-of-Way Design assuming that Redmond will be able to acquire the full BNSF Railroad right-of-way. State Highway Crossings Open cut; replace with 9-inch-thick asphalt and 4- inch-thick crushed surfacing top course, or match existing, whichever is greater. Existing Private Detention Vaults Assume all 25 in SWMM model will be removed as part of redevelopment in full buildout. Lane Closures on Arterials Allowable. Manholes/Catch Basins Assume channelized manholes will be used along the trunkline. ---PAGE BREAK--- Preliminary Engineering Report – August 2009 Section 3 HYDROLOGIC AND HYDRAULIC ANALYSES 3.1 Overview Hydrologic and hydraulic analyses were performed for the various conveyance and water quality treatment alternatives to assess their technical feasibility in order to help determine a preferred alternative. Hydrologic analyses determine the size and frequency of various flows while hydraulic analyses determine how the flows are conveyed through the basin. 3.2 Hydrologic Analyses Flows supporting the analyses and design were determined using three computer modeling programs: HSPF, WWHM, and HSPF, which was developed by the U.S. Environmental Protection Agency (USEPA), simulates land surface and in-stream hydrologic processes on a continuous basis. HSPF was used to develop an initial estimate of the 50-year flow rates at key points in the system and assess the possible effects of diverting runoff from portions of the Bear Creek Basin to the Sammamish River Basin. WWHM is a program commissioned by the Washington State Department of Ecology to model stormwater flows in Western Washington using the HSPF engine. WWHM was used to calculate the water quality flow rate. is an interface for the USEPA Stormwater Management Model (SWMM) program. SWMM has hydrologic and hydraulic computational blocks, and is primarily used for single-event simulation. Calculations and summary data are included in Appendix B. 3.2.1 HSPF/WWHM Predictions HSPF was used to develop planning-level flow estimates, providing a basis for the initial conveyance analyses. Fifty-year flow rates were estimated at key points in the system. This was done by generating unit area flows based on continuous simulation of the 50-year precipitation record at Sea-Tac and a conceptual pipe system. The resulting flows were applied to tributary areas draining to points of interest. The 50- year flow at the outfall was estimated to be 98 cubic feet per second (cfs) using this method. WWHM was used to develop the water quality flow rate for facility sizing. The program simulates runoff from the input land areas and determines the flow rate that would capture and treat 91 percent of the annual runoff volume. To develop land use acreages for input to HSPF/WWHM, the basin was characterized based on Natural Resources Conservation Service (NRCS) soil maps, the most recent City of Redmond zoning map, and standard assumptions about the percentage of effective impervious area associated with each zoning category. ---PAGE BREAK--- Section 3 3-2 R. W. Beck Preliminary Engineering Report – August 2009 Table 3-1 Areas Draining to the Redmond Way Treatment Facility in the WWHM Model (acres) Land Use/Coverage Bear Creek Subbasin1 Redmond Way2 Combined Pervious areas3 22.0 98.2 120.2 Effective Impervious Surfaces 32.8 109.8 142.6 Total 54.8 208.0 262.8 1 Areas currently directed to Bear Creek outfalls. 2 Areas currently directed to the Redmond Way outfall to Sammamish River. 3 Pervious areas are predominately grass covered. Water quality treatment can be provided by either an online or offline facility. An online facility receives all the runoff from the drainage basin. It becomes less efficient when flows exceed its design flow rate. An offline facility only receives flows up to the design (water quality) flow rate. Higher flows are bypassed via a flow splitter. Using the land use areas shown in Table 3-1 and Figure 3-1, water quality design flows range from 12 cfs for an offline facility to 21 cfs for an online facility, based on an hourly simulation time step. If a 15-minute simulation time step is required to size the water quality treatment facility, the water quality design flows range from 13 to 23 cfs, respectively for offline and online facilities. The water quality treatment volume is nearly 20 acre-feet. The water quality volume is used to size treatment components such as the dead storage in wet vaults The majority of the subject area lies within the City’s Critical Aquifer Recharge Area for the City’s drinking water wells. The groundwater serving these wells has a seasonal high water elevation that is very close to the ground surface. To protect this area, the City has selected a conservative approach to infiltration of stormwater. Infiltration of roof runoff and sidewalks is strongly encouraged, while runoff from pollution-generating impervious surfaces is discouraged. Zoning and development patterns within this area are such that most new impervious areas are rooftops that would be infiltrated. An increase of infiltration in the future would suggest that conveyance pipes and water quality facilities might be smaller than if they are designed for conditions as they exist today. 3.2.2 Effect of Redirecting Storm Runoff from Bear Creek A total of 54.8 acres that currently drains to outfalls discharging to Bear Creek (Table 3-1, Figure 3-1) is proposed to be redirected to the treatment system and the Sammamish River. Current land use is a mix of commercial and residential areas that are about 60 percent covered by effective impervious surfaces. Underlying soils are a mix of outwash and till-derived soils with a few small pockets of saturated soils. The subbasin is currently served by a network of inlets and storm drains that collect runoff and convey it to the outfall. ---PAGE BREAK--- ---PAGE BREAK--- This page intentionally blank. ---PAGE BREAK--- HYDROLOGIC AND HYDRAULIC ANALYSES Preliminary Engineering Report – August 2009 R. W. Beck 3-5 Not all of the area currently draining to Bear Creek in the vicinity of Redmond Way will be diverted by the proposed Redmond Way treatment facility. A small portion of the area along the eastern edge of the commercial area will continue to drain to Bear Creek because it is too low to be picked up by the proposed storm drain. There are also rooftops in the shopping center that discharge relatively clean runoff that will be infiltrated or directed to Bear Creek if practicable. Any remaining pollution- generating surface that is not captured by the project will be treated and discharged to Bear Creek as a part of redevelopment or subsequent projects under the Regional Facilities Plan. Table 3-2 provides a comparison of peak flows for storms of different predicted frequencies for both Bear Creek (draining 32,000 acres) and the 55-acre subbasin redirected to Redmond Way. The discharges from the current outfalls are small compared to corresponding flows in Bear Creek. It is expected that redirecting surface runoff away from the outfalls will cause lower flood flows in Bear Creek. Reduction of peak flood flows can be considered a positive impact given that the flows in Bear Creek have steadily increased as a result of urbanization of the watershed. Table 3-2 Comparison of Flood Flows Predicted Flows (cfs) Flow Frequency Bear Creek1 Redmond Way Outfall2 Average Annual flood 597 11 2-year 495 10 10-year 1,076 15 100-year 1,700 24 1 Based on flows recorded by King County between 1988 and 2007 at the gauging station located between the Avondale and Union Hill bridges. The largest flow recorded during the period of record is 1,572 cfs, recorded in 1997. 2 Based on a 50 year HSPF simulation for runoff from area to be redirected to Redmond Way. There could be a concern that directing surface runoff away from Bear Creek will diminish low flows during critical times of the year. The potential effect of the proposed diversion on low flows was evaluated by comparing the expected discharge from the existing outfall to the recorded in-stream flows during the low flow periods. The months of July, August and September experience the lowest in-stream flows with average daily flows in Bear Creek typically around 20 to 30 cfs. Minimum flows average between 15 to 20 cfs with the lowest recorded flows 9 to 10 cfs. For comparison, the surface runoff from the area to be directed away from Bear Creek for the same period is predicted to be less than 0.05 cfs. ---PAGE BREAK--- Section 3 3-6 R. W. Beck Preliminary Engineering Report – August 2009 The runoff in the storm drains to be redirected to Redmond Way is considered “direct” runoff, meaning that it is primarily surface runoff. Little or no interflow is captured by the storm drain system. City staff noted that there is no flow in the pipes during non- storm periods. Direct runoff occurs in response to a rainfall event and typically is of short duration. Groundwater provides the most significant source of water for base flows in Bear Creek during the summer months. Groundwater in the area tributary to the outfall does not enter the pipe system and as such would not be diverted from the basin by the proposed project. There is no persistent base flow leaving the existing outfall. Groundwater originating within the subbasin probably does contribute to Bear Creek and will continue to do so since it does not flow through to the existing outfall. Over time, as the subbasin is redeveloped, there will be opportunities to implement low- impact development (LID) practices that can reduce the volume of water directed to the Redmond Way storm trunk and increase the volume of runoff discharged to Bear Creek as groundwater. 3.2.3 Unlike the conceptual pipe system used to route flows in HSPF, the pipe system modeled in is based on the stormwater datasets maintained by the City’s GIS Services group and includes all pipes which are at least 12 inches in diameter. The event used for the model is a design storm, built to match rainfall flood frequency quantiles for durations of 0.25, 0.5, 1, 2, and 3 hours. See Appendix B for details. Preliminary design of the trunk was based on 50-year flows developed using HSPF. The model was used to validate this design. Peak outflow to the Sammamish River, including flow through the water quality facility, is predicted to be 120 cfs. This is higher than the 98 cfs predicted by HSPF because the model is based on an assumption more impervious area (Table 3-3) under future land use conditions. Table 3-3 Areas Draining to the Redmond Way Treatment Facility in the Model (acres) Land Use/Coverage Bear Creek Subbasin1 Redmond Way2 Combined Pervious areas3 12.8 58.1 70.9 Effective Impervious Surfaces 46.0 149.9 195.9 Total 58.8 208.0 266.8 1 Areas currently directed to Bear Creek outfalls. 2 Areas currently directed to the Redmond Way outfall to Sammamish River. 3 Pervious areas are predominately grass covered. ---PAGE BREAK--- HYDROLOGIC AND HYDRAULIC ANALYSES Preliminary Engineering Report – August 2009 R. W. Beck 3-7 However, validates the design by predicting no flooding along the trunk. On the existing trunks along Redmond Way and Cleveland Street, the only flooding predicted is at one manhole on Redmond Way—between 164th Avenue NE and 166th Avenue NE, where a 12-inch-diameter pipe connects the trunk to the lots along the south side of the road. The flooding is predicted to be one-half inch deep (Figure B- 5B). A lower 12-inch-diameter pipe connecting to the Cleveland Street trunk begins 60 feet south of the end of the pipe that connects to the Redmond Way trunk. Blocking the local connection to Redmond Way and connecting the two 12-inch- diameter pipes—possibly along with minor adjustments to the Cleveland Street trunk line where the 12-inch-diameter pipe ties in—would probably eliminate flooding along both existing trunks. Adding capacity to the proposed trunk would have no effect on this minor, local issue. Based on the model of future conditions, flows at the Redmond Way outfall are estimated to range up to 120 cfs (the 50-year peak flow under “future build- out” condition). For comparison, the existing conditions flow estimated using a separate model is approximately 18 cfs for the 50-year design storm. (Another 18 cfs is lost to flooding.) Future flows are expected to be higher than existing flows for the following reasons:  The addition of approximately 55 to 60 acres of area that currently drains to Bear Creek is expected to add as much as 27 cfs to the peak 50-year design flow.  The elimination of drywells (that infiltrate water from pollution-generating surfaces) is expected to increase runoff volumes by 12 percent. The use of drywells will no longer be allowed in order to protect the water quality in the City’s aquifer. Currently there are 12 acres served entirely by drywells and another 89 acres that are partially served by drywells. The areas entirely served by drywells do not contribute to the “existing conditions” flows. The areas that are partially served drain to infiltration pipes that are assumed capable of collectively infiltrating up to 8 cfs.  Impervious surfaces are expected to increase by 34 percent—almost doubling—in accordance with the City’s most recent zoning maps. Detention will not be required since the Sammamish River is a direct discharge waterbody.  Restrictions caused by the existing storm drain will be removed. The primary trunklines will be designed to convey the 50-year peak flow rate in accordance with City standards. 50-year flows at key points in the system are summarized in Table 3-4. ---PAGE BREAK--- Section 3 3-8 R. W. Beck Preliminary Engineering Report – August 2009 Table 3-4 Peak Flows at Selected Locations Element Location 50-Year/10-Minute Peak Flow (cfs) Outfall 29 Sammamish River outfall 120 Conduit TL38 Redmond Way, at confluence with new trunk 33 Conduit TL20 New trunk, at confluence with Redmond Way 88 Conduit 88069 Redmond Way, at confluence with Cleveland Street 16 Conduit 4415 Cleveland Street, at confluence with Redmond Way 14 Conduit 21858 Redmond Way, at confluence with NE 80th Street line 10 Conduit 4458 NE 80th Street line, at confluence with Redmond Way 3 Conduit 21572 Redmond Way, at confluence with Leary Way1 6 Conduit 41059 Leary Way, at confluence with Redmond Way1 8 Junction 2619 NE 83rd Street and 166th Avenue NE 51 Junction 66071 New line down 166th Avenue NE, at NE 80th Street 54 Junction 2615 Existing line down 166th Avenue NE, at NE 80th Street 3 Conduit TL33 New line down 166th Avenue NE, at confluence with Redmond Way 55 Conduit 6580 Redmond Way, at confluence with new line down 166th Avenue NE 7 Conduit TL35 New line down 166th Avenue NE, at confluence with new trunk 63 Conduit TL9 New trunk, at confluence with new line down 166th Avenue NE 28 Junction 66067 Redmond Way and 170th Place NE 28 Junction 5883 Avondale Way and 170th Place NE 11 Junction 5571 NE 80th Street and 172nd Place NE 10 1 Peaks are temporally offset. 3.2.4 Agreement Among Models The model was produced by Northwest Hydraulic Consultants (NHC), independently of the WWHM model, which was produced by R. W. Beck. Future land use in each model was based on different sets of assumptions. (See Tables 3-1, 3-3, B-1, B-2, B-3, and B-4.) To be useful, a model must generate results that drive a design which cautiously limits the likelihood of failure, but draws a line at attempting to accommodate unreasonably unlikely circumstances. Both the model and the WWHM model arrive at reasonably cautious results, though in different ways. In some aspects, the model is more conservative:  A higher percentage of effective impervious area (EIA) is assumed for each land use.  An additional 4-acre area is included in the southeast corner of the basin. ---PAGE BREAK--- HYDROLOGIC AND HYDRAULIC ANALYSES Preliminary Engineering Report – August 2009 R. W. Beck 3-9 In some aspects, the WWHM model is more conservative:  Storage in detention facilities and de facto storage due to ponding are neglected.  Attenuation due to pipe capacity and tailwater effects is not accounted for.  Timing effects due to offset peaks at different locations and travel time through the system are not included.  No water is lost to flooding. Both models are considered conservative in that they do not recognize that over time, infiltration of clean runoff from rooftops will be encouraged, thereby reducing the amount of impervious surface areas connected to the storm drain. Until full build-out is achieved in the downtown watershed, it is unknown which model produces more accurate results. Since both appear to be reasonable and conservative, was used as the basis of conveyance design—which requires spatial detail—and WWHM was used as the basis of water quality treatment design—which requires a continuous simulation. 3.3 Existing Conveyance The existing storm drain system has been evaluated using available inventory data contained within the City GIS database and survey performed by KPG. The existing storm drain along Redmond Way ranges from a 12-inch-diameter pipe at the eastern end, up to a 30-inch-diameter outfall at the Sammamish River. With current land use and drywell connections, the main trunkline is adequately sized. However, due to the changes enumerated above, the entire storm drain system in the Redmond Way basin—as well as the system along NE 79th Street, 170th Place NE, 172nd Place NE, and Avondale Way—will be over capacity. The most severe flooding is expected along the lateral which joins Redmond Way at Leary Way and continues upstream to 171st Avenue NE and NE 93rd Court, via 164th Avenue NE and then NE 83rd Street. Greatly increased flows within this area are expected because most of the area is currently served by dry wells, which will no longer be allowed (in order to protect the aquifer). Also, a large portion of the subbasin that is currently forest, open grass, and residential is assumed to be (re)developed to mixed use. See Appendix B for additional information. 3.4 Sammamish River Water Levels The proposed outfalls from the project to the Sammamish River are low enough that variation in the river elevation will have a significant bearing on the performance of the water quality facility and the conveyance system. To establish a design river elevation, the design team used a river elevation frequency plot developed by NHC (see Appendix The plot was based on U.S. Geological Survey (USGS) daily flow data from 1965 to 2005 and supported by the inclusion of additional King County data. The river elevation frequency numbers were then weighted by month based on the average rainfall, with the intention of reflecting the coincidence of high pipe flow (runoff) and high river elevation. ---PAGE BREAK--- Section 3 3-10 R. W. Beck Preliminary Engineering Report – August 2009 Based on the weighted exceedance values, a design river elevation of 21.4 feet (NGVD 29) was chosen for water quality design, which correlated to a 10 percent exceedance (90 percent of the time river levels will be less than 21.4 feet). This elevation was used to represent the tailwater for the design of the water quality facility. For purposes of establishing a design river elevation for conveyance, coincidence of 2- year storms and high river elevations was evaluated by NHC. Based on NHC’s recommendation, a design river elevation of 23.5 feet (NGVD 29) was chosen for conveyance design, as there was no coincidence of more than a 2-year or greater storm (of a 0.25-, 0.5-, or 3-hour duration) with a river elevation above 23.5 feet during the period of record. ---PAGE BREAK--- Preliminary Engineering Report – August 2009 Section 4 CONVEYANCE ALTERNATIVE ANALYSES 4.1 Overview Alternative analyses were performed for the various conveyance and water quality treatment alternatives to assess their technical feasibility in order to help select a preferred alternative. As discussed above, the intention is to convey the flow from the Redmond Way Basin as well a portion of the Bear Creek Basin to a water quality treatment facility where all but the infrequent high-flow events would be treated prior to being discharged into the Sammamish River. The project intent is to divert as much of the Bear Creek Basin flows toward the treatment facility and the Sammamish River as is feasible in order to provide service to as large an area as possible. This would eliminate the need for on-site detention and treatment in the Bear Creek Basin as the basin redevelops. Alternatives were developed by the design team and presented to the City for discussion at two workshops, the first on June 3, 2008, and the second on September 8, 2008. Information was further refined and then presented to the Planning and Public Works Committee on October 14, 2008, leading to the confirmation of a preferred alternative with the direction to proceed with design and permitting. The discussion of the alternatives below is structured around the major components of the project: the alignment of the stormwater trunkline and the water quality treatment facility. 4.2 Evaluation Criteria The conveyance alignment alternatives were evaluated using various differentiating criteria to aid in the selection of a preferred alternative(s). The criteria are sorted into four major themes: Cost Impacts, Schedule Impacts, Community Impacts, and Operations and Maintenance (O&M) Impacts. Other factors such as geotechnical or environmental impacts are generally considered to be the same regardless of the alternative, so they are not included in the comparisons. Table 4-1 provides a summary of the criteria used for comparing various conveyance alternatives. ---PAGE BREAK--- Section 4 4-2 R. W. Beck Preliminary Engineering Report – August 2009 Table 4-1 Alternative Evaluation Criteria for Conveyance Alternatives Criterion Description Cost Impacts Relative Cost Detailed cost estimates were not used as a basis of comparison between different alternatives. Rather, alternatives were compared considering factors such as difficulty of construction and need for easements and utility conflicts—each having a bearing on the expected cost of implementation. Preliminary cost estimates of conveyance and treatment were completed as a part of this Preliminary Engineering Report and are discussed in a separate section below. Utility Conflicts Costs associated with relocating or avoiding existing utilities that may be in conflict with the alternative. Railroad Requirements Impacts to cost such as required casing pipe, depth to cross tracks, and other related railroad impacts. Rights-of-Way Acquisition Costs to acquire needed rights-of-way along an alternatives route. Schedule Impacts Design Schedule Impacts due to the engineering design of the alternative, such as a longer design period for longer pipelines or more technically difficult (trenchless technology) applications. Construction Schedule Time impacts due to the length of the alternative, need to acquire right-of-way, or restrictions on when construction can occur. Environmental Constraints Scheduling impacts caused by restrictions in the permits, such as a fish window, species avoidance, wetlands, etc. Community Impacts Traffic / Transit Disruptions Likelihood of an alternative to impact the public by closing roads or restricting traffic flow. (See discussion below.) Access Disruptions Impacts based on the disruptions an alternative will cause to existing business and personal access, such as removal of sidewalks, blocking driveways, etc. Existing Utility Disruptions Extent that an alternative impacts existing utilities, either by relocation or temporary shutoff during construction. Development Intrusion Potential An alternative that requires an easement across a developable property, thus reducing the buildable lands of the parcel. Coordination with Existing CIP Ability of an alternative to coordinate with an existing project planned in Redmond. O&M Impacts O&M / Access Issues Ease of access to the pipeline access manways, safety for operators. System Performance How well does the design alternative meet the design criteria, including minimum velocities, pipeline capacity, structure surcharge, etc.? Future Expandability How easy is the alternative to connect future pipelines or upsize the pipe for future needs? Interconnections to Existing System How well is the system connected to the existing storm system, allowing for transfer of flows and load splitting? ---PAGE BREAK--- CONVEYANCE ALTERNATIVE ANALYSES Preliminary Engineering Report – August 2009 R. W. Beck 4-3 Traffic/Transit Disruptions Potential disruptions of commerce or traffic within the City were quantified by comparing various metrics that represent the movement of traffic and the location of business activities. The following considerations were used to compare potential for disruption along conveyance alignments: 1. Average Weekday Traffic (AWDT) – a measure of the traffic volume seen on that road on the average weekday. 2. Number of Driveways – an indication of the number of businesses along that particular street. 3. Number of Signalized Intersections – an indication of the number of side streets, businesses, and traffic volumes. 4. Lanes Available for Traffic During Construction – the number of available lanes for traffic assuming at least one lane will have to be shut down during construction. 5. Peak Volume, PM – Peak evening traffic volume using that street. 4.3 Conveyance Alignment Conveyance alternatives were developed and sized to convey as much of the Redmond Way and Bear Creek basins as possible toward a new treatment facility on the Sammamish River. In general, potential conveyance alignments were selected to be low enough to pick up the eastern Bear Creek Subbasin, have adequate slope and pipe cover, be able to intercept runoff from the adjacent laterals, and be within existing rights-of-way. Another important consideration in the selection of a conveyance alignment is the potential for conflict with existing utilities. Existing utilities, based on as-built and GIS records, are shown in Figure 4-11. This figure provides a close-up of the Redmond Way and Cleveland Street area for ease of use. In general, the highest concentration of utilities occurs along Cleveland Street. 4.3.1 Alignment Alternatives Considered During the initial review of the project terrain and existing rights-of-way, three main route corridors were reviewed, and a total of 12 alternatives involving variations of the three corridors were developed. Redmond Way Corridor Use of the Redmond Way Corridor would replace or supplement the capacity of the existing conveyance system currently serving the area. The pipeline route, shown in Figure 4-2, generally follows the existing stormwater pipeline system in Redmond 1 Note: Comcast has not provided utility mapping. ---PAGE BREAK--- Section 4 4-4 R. W. Beck Preliminary Engineering Report – August 2009 Way, but also reroutes flows from the Bear Creek Basin. These alternatives assume a new single pipeline along Redmond Way. If this route were chosen, a pipeline assessment could be completed to determine if the existing pipeline is in adequate condition to remain in use, allowing for a smaller, dual main. In addition, a north- south pipeline on 166th Avenue NE from NE 83rd Street to Redmond Way (see Figure 4-3) is needed with this alternative to convey additional runoff created when the dry wells are eliminated and the northeast portion of the basin is developed. Four alternatives were evaluated based on this alignment and are shown in Figure 4-2. Descriptions of each alternative are as follows. Alternative 1A: This alternative begins east of the intersection of Redmond Way and 170th Avenue NE at the entrance to the Bear Creek Village shopping center. Starting at this location enables flow from the Bear Creek Village parking lot and the area south of Avondale Way NE to be diverted from Bear Creek Basin toward the proposed treatment facility. The route proceeds west on Redmond Way to the stormwater treatment facility near the intersection of Redmond Way and 159th Avenue NE. Of the Redmond Way alternatives, this alternative conveys the largest amount of flow to the treatment facility. However, it requires that the existing Redmond Way stormwater system be completely replaced or a complete parallel system provided. Alternative 1B: Prior to having survey data, there was concern that the pipeline could not begin at the Bear Creek Village due to conflicting utilities and elevation constraints. Therefore, Alternative 1B begins at the intersection of Redmond Way and 170th Avenue NE. Flow is diverted from the Bear Creek Basin to the proposed treatment facility; however, in this alternative, runoff from the Bear Creek Village portion of the basin is not included. With the exception of the starting point, Alternatives 1A and 1B are identical. This alternative also requires that the existing stormwater system along Redmond Way be completely replaced or a complete parallel system provided. Alternative 1C: Alternative 1C assumes that the existing pipeline in Redmond Way is in adequate condition and is sized appropriately for the future flows. Therefore, this alternative connects the two basins by installing a pipe along Avondale Way from the intersection of Avondale Way and 170th Avenue NE to Redmond Way. Starting at this location allows flows to be conveyed from the Bear Creek Basin; however, it does not divert the runoff from the portion of the Bear Creek Basin south of Avondale, including the Bear Creek Village. This alternative uses as much of the existing Redmond Way stormwater system as possible. Alternative 1D: With Alternative 1D, the existing pipe in Redmond Way would only be replaced between Avondale Way and Leary Way. At Leary Way, the existing pipe increases in size to 24-inch. This alternative assumes that pipe would provide adequate capacity for the future development. This alternative does not pick up the flows from the area south of Avondale, including the Bear Creek Village, in the Bear Creek Basin. ---PAGE BREAK--- ---PAGE BREAK--- This page intentionally blank. ---PAGE BREAK--- ---PAGE BREAK--- This page intentionally blank. ---PAGE BREAK--- ---PAGE BREAK--- This page intentionally blank. ---PAGE BREAK--- CONVEYANCE ALTERNATIVE ANALYSES Preliminary Engineering Report – August 2009 R. W. Beck 4-11 BNSF/NE 76th Street Corridor These alternatives add a supplemental pipeline along the BNSF railroad or NE 76th Street and the new Bear Creek Parkway corridor along the south side of the BNSF right-of-way. Four alternative pipeline routes are shown on Figure 4-4. The pipeline size would be based on using the existing conveyance systems in Cleveland Street and Redmond Way to provide significant additional capacity. A north-south pipeline connection along 166th Avenue NE from NE 83rd Street to the new pipeline (see Figure 4-3 above) would be required for all four alternatives (Figure 4-4) to convey additional runoff created when the dry wells are eliminated and the northeast portion of the basin is developed. Descriptions of each alternative are as follows. Alternative 2A: The alignment begins at the Bear Creek Village shopping center on Redmond Way, proceeding west to 170th Avenue NE, then south to NE 76th Street across the railroad tracks. The pipeline then continues west along NE 76th to the stormwater treatment facility. With this starting location, flows from the Bear Creek Basin can be diverted from Bear Creek, including the runoff from Bear Creek Village and the area south of Avondale Way NE. This alignment avoids traffic issues related to construction along Redmond Way and Cleveland Street and diverts the most flow away from Bear Creek. Alternative 2B: Alternative 2B is essentially the same route as Alternative 2A, except that the pipeline is along the BNSF railway corridor instead of NE 76th Street. In this alternative, flows from the Bear Creek basin, including the runoff from Bear Creek Village and the area south of Avondale Way NE, are directed to the treatment facility. Confining this alignment to the railroad right-of-way avoids most existing utilities and traffic-related issues. Alternative 2C: Alternative 2C follows the same alignment as Alternative 2A from the Bear Creek Village to Leary Way. At Leary, the alignment turns south and intersects the Bear Creek Parkway Extension project. The Bear Creek Parkway project is extending Bear Creek Parkway to 159th Place NE. The pipeline would follow this roadway extension along 159th Place NE until it intersects Redmond Way. Alternative 2D: This alternative follows the 2C alignment to Leary Way. At Leary, this alignment proceeds south down Leary Way to the Sammamish River. This alternative would require two treatment sites but would avoid replacing the stormwater system along Redmond Way. Cleveland Street Corridor These alternatives replace or supplement the capacity of the existing conveyance system in Redmond Way by redirecting flow to Cleveland Street. As shown on Figure 4-5, the four alternatives evaluated assume a new pipeline on Cleveland Street. If this alternative were chosen, a pipeline assessment could be completed to determine if the existing stormwater system is in adequate condition to remain in use, which could allow for smaller, dual pipelines. A north-south pipeline on 166th Avenue NE from NE 83rd to Cleveland Street (see Figure 4-3 above) would be needed to redirect flows to Cleveland Street (Figure 4-5). Connections to the Bear Creek Basin would also be ---PAGE BREAK--- Section 4 4-12 R. W. Beck Preliminary Engineering Report – August 2009 constructed. The Cleveland Street corridor contains the highest concentration of utilities and high traffic impacts would be anticipated. Descriptions of each alternative are as follows. Alternative 3A: This alternative begins east of the intersection of Redmond Way and 170th Avenue NE at the entrance to the Bear Creek Village shopping center. Starting at this location enables flow from the Bear Creek Village parking lot as well as the area south of Avondale Way NE to be diverted from Bear Creek toward the proposed treatment facility. The route proceeds west on Redmond Way to Cleveland Street where a new or parallel pipe would convey flows from the Bear Creek Basin west to Redmond Way. After reaching Redmond Way, the pipeline continues west to the water quality facility. A portion of the existing system along Redmond Way may need to be upgraded depending on the connection point for flows from the northern basins. Alternative 3B: Similar to Alternative 1B, prior to having survey data, there was concern that the pipeline could not begin at the Bear Creek Village due to conflicting utilities and elevation constraints. Therefore, Alternative 3B begins at the intersection of Redmond Way and 170th Avenue NE. Flow is diverted from the Bear Creek basin to the proposed treatment facility; however, due to elevation constraints it is not feasible to divert the runoff from Bear Creek Village. The route proceeds west on Redmond Way to Cleveland Street. Depending on the condition of the existing pipes, either a new or a parallel pipe would convey flows. A portion of the existing system along Redmond Way may need to be upgraded depending on the connection point from the northern basins. After reaching Redmond Way, the alignment proceeds west and continues to the water quality facility. Alternative 3C: With this alternative, it was assumed that the existing stormwater pipelines in Cleveland Street were of adequate condition and size to accommodate the proposed improvements to the area. Therefore, this alignment begins at the intersection of Avondale Way and 170th Avenue NE and ends just beyond the intersection of Redmond Way and 168th Avenue NE. This alternative allows for flows from the Bear Creek basin to be diverted to the treatment facility; however, flows from Bear Creek Village and Avondale Way NE cannot be picked up using this alternative. This alternative uses as much of the existing Redmond Way and Cleveland Street stormwater system as possible. Alternative 3D: Alternative 3D begins at the intersection of Avondale Way and 170th Avenue NE, then continues south along Avondale Way to Cleveland Street and ends near the intersection of Cleveland Street and Leary Way NE. Starting at this location accommodates flows from the Bear Creek basin, with the exception of the area south of Avondale and Bear Creek Village. This alternative replaces (or parallels) the smaller diameter stormwater pipes along Cleveland Street until connecting to the existing 24-inch-diameter stormwater pipeline. ---PAGE BREAK--- ---PAGE BREAK--- This page intentionally blank. ---PAGE BREAK--- ---PAGE BREAK--- This page intentionally blank. ---PAGE BREAK--- CONVEYANCE ALTERNATIVE ANALYSES Preliminary Engineering Report – August 2009 R. W. Beck 4-17 4.3.2 Discussion of Conveyance Alternatives The 12 alternatives were reviewed by the design team and discussed with the City at the June workshop. The 12 alternatives were narrowed to three alternatives for further study. The three selected routes, including the 166th Avenue NE connection that is common to all three, are shown in Figures 4-2 through 4-5 and are summarized below. Of the four alternatives considered for the Redmond Way alignment, Alternative 1A (see Figure 4-2) was the preferred alignment due to its potential to divert the most flow from the Bear Creek Basin to the Redmond Way Basin. Alternative 1B was discarded when surveys confirmed that the elevations do allow for a pipe to the east to incorporate Bear Creek Village. Alternatives 1C and 1D were ruled out based on the existing pipe sizes not having sufficient capacity for the future flow conditions. For the BNSF/NE 76th Street Corridor (see Figure 4-4), a hybrid combination of Alternatives 2A and 2B was presented for consideration. Initially, Alternative 2A (NE 76th Street) was preferred due to uncertainty regarding the availability of the railroad right-of-way. However, the City feels that there is a high probability that the right-of- way will become available in time to support this project and as such would be the preferred alternative. Alternative 2B, the alignment along the railroad right-of-way, is preferred because it will have less impact on roadways, fewer utility conflicts, and takes advantage of land the City is planning to acquire for a trail. Alternative 2A will be considered as a backup should the railroad right-of-way not become available. Alternative 2C was not advanced as the Bear Creek Parkway project is too far into design and construction to accommodate the additional stormwater pipeline without significant changes. Alternative 2D was not studied further because it required two treatment facilities. The Cleveland Street Corridor is similar to the Redmond Way Corridor. Of the four alternatives considered, Alternative 3A (see Figure 4-5) is preferred because the pipeline can be sufficiently deep at the intersection of Redmond Way and Avondale Way to provide the option of collecting flows from Bear Creek Village. Alternatives 3B, 3C, and 3D were not advanced for similar reasons to Alternatives 1B, 1C, and 1D, respectively. 4.3.3 Preferred Conveyance Alternative The three selected conveyance alternatives were evaluated using the criteria discussed in Sections 2 and 4.2 and summarized in Table 4-1. Two key components to selecting the preferred conveyance alternative are community impacts and cost. Community Impacts Traffic impacts have been used as a quantitative method of determining impacts to the community. Redmond Way and Cleveland Street form a one-way couplet through downtown Redmond. This couplet is part of two different state routes, SR-202 and SR-908. Both of the state routes carry significant traffic volume during commute ---PAGE BREAK--- Section 4 4-18 R. W. Beck Preliminary Engineering Report – August 2009 times. As discussed in Section 4.2, five traffic-related criteria were reviewed for each alternative. Table 4-2 summarizes the data gathered for this review. Table 4-2 Traffic Evaluation Alignment Alternative Evaluation Measures NE 76th St Cleveland Street Redmond Way AWDT 4,110 18,240 17,850 Number of Driveways Affected 3 28 41 Number of Signalized Intersections Affected 1 6 7 Lanes Available for Traffic During Construction 1 1 2 Peak Volume (PM) 140 1,490 1,310 Ease of Construction (Costs) A side-by-side comparison of the planning-level costs for each of the conveyance alternatives is provided in Table 4-3 below. The least costly of the three alternatives is the BNSF/NE 76th Street corridor. This route utilizes the existing pipes in Redmond Way and Cleveland Street, and therefore has the smallest pipe size of the alternatives. This corridor has the least impact to traffic, and therefore lower costs for traffic mitigation and control throughout the project. The comparative costs for this corridor do not account for railroad use of the BNSF right-of-way. Selection of Alternative A more qualitative assessment of construction-related impacts to the downtown area was also generated using the criteria shown in Table 4-1. Each alternative is summarized in Table 4-3. Table 4-3 Conveyance Alternative Evaluation BNSF/76th Cleveland Redmond Basin Captured    Use of Existing System    Ease of Construction (cost)    Community Impact    Easements    O&M Considerations    Key:  Most preferred;  Acceptable;  Least preferred ---PAGE BREAK--- CONVEYANCE ALTERNATIVE ANALYSES Preliminary Engineering Report – August 2009 R. W. Beck 4-19 Based on the project criteria and input from the City, the BNSF railroad/NE 76th Street corridor is the recommended route. This alternative provides the following benefits when compared to the other alternatives:  Least disruptive to traffic flow in downtown core (NE 76th Street has only 4,100 average weekday trips).  Least disruptive to businesses (only three driveways and one signalized intersection are impacted).  Collects stormwater runoff from the largest drainage area (268 acres).  Least utility conflicts.  Can be easily connected to the Triangle and Bear Creek Parkway treatment sites. (See Section 4.3 for further discussion of these sites).  Utilizes the existing pipe systems in Cleveland Street and Redmond Way, thus requiring the smallest new pipeline size.  Least costly of the alternatives, based on pipe size, traffic impacts, and utility conflicts. (Note: the comparative costs do not account for railroad usage of the BNSF right-of-way.) There are a few challenges with this corridor as well, including the need to integrate the stormwater trunk design with a portion of the Bear Creek Parkway extension along 159th Place NE, which is now under construction. This corridor may also require several easements on the east end near 170th Avenue NE. Connection of the pipeline to the Nelson Brothers treatment site would also be more difficult than with the other stormwater pipeline alternatives. More significant challenges exist with the Redmond Way corridor. It is not the recommended conveyance alternative for the following reasons:  Significant disruption to traffic (17,900 average weekday trips on Redmond Way, which is 435 percent of the recommended corridor) and disruption to pedestrians throughout the downtown Redmond core.  Highly disruptive to businesses, with impacts to a significant number of driveways (41) and signalized intersections  One existing sewer pipe conflict cannot be avoided, which results in the need for a sanitary sewer to be constructed through the top half of the stormwater trunk.  Redmond Way is WSDOT right-of-way (SR-202 and SR-908), requiring considerable coordination.  Shortened work hours would be required to minimize impacts to the morning commute.  Collects runoff from a smaller drainage area (259 acres or –3 percent) than the recommended corridor alternative.  Cannot be easily connected to the Bear Creek Parkway treatment site. ---PAGE BREAK--- Section 4 4-20 R. W. Beck Preliminary Engineering Report – August 2009 The Cleveland Street Corridor also has significant challenges and is not the recommended conveyance alternative for the following reasons:  Significant disruption to traffic (18,200 average weekday trips, which is 440 percent of the recommended corridor) and disruption to pedestrians throughout the downtown Redmond core.  Cleveland Street has two lanes for traffic, with portions having parking along the side. The narrow working area would make it difficult to maintain traffic flow while installing the pipeline.  Highest number of existing utilities and conflicts.  Shortened work hours would be required to minimize impacts to the afternoon commute.  Highly disruptive to businesses due to impacts to a significant number of driveways (28) and signalized intersections  Cleveland Street is a WSDOT right-of-way (SR-202 and SR-908), requiring considerable coordination.  Collects runoff from a smaller drainage area (259 acres or –3 percent) than the recommended corridor alternative. ---PAGE BREAK--- Preliminary Engineering Report – August 2009 Section 5 WATER QUALITY TREATMENT ALTERNATIVE ANALYSES 5.1 Overview The objective of water quality treatment is to provide a regional stormwater quality treatment facility for the entire area tributary to the Redmond Way outfall. Water quality treatment alternatives considered different treatment methodologies as well as different treatment sites, as described below. 5.2 Evaluation Criteria The water quality treatment technology and site alternatives were evaluated using various differentiating criteria to aid in the selection of a preferred alternative(s). Some factors such as geotechnical or environmental impacts are generally considered the same regardless of the alternative, so they are not included in the comparisons. Table 5-1 provides a summary of the criteria used for comparing various conveyance alternatives. Table 5-1 Alternative Evaluation Criteria for Water Quality Treatment Criterion Description Footprint The physical footprint and easement area needed for the facility. The goal is to minimize the facility footprint. Higher Metals Treatment Goal is to provide Enhanced treatment, as defined in the Ecology Manual. The Washington State Department of Ecology (Ecology) does not specify a numerical removal criterion for Enhanced treatment; rather it defines Enhanced treatment as providing a higher level of treatment, specifically targeting metals copper and zinc). Enhanced treatment is normally required for new development draining to salmon-bearing waterways. Acceptable Head Loss The depth and distance to which water backs up in the conveyance pipe upstream of the treatment system. Minimal head loss is preferred. Pumping Goal is to avoid pumping. O&M Considerations The frequency and labor effort required for maintenance. Functions When Submerged Due to tailwater conditions at the system outfall to the Sammamish River, the system will often be submerged; ideally, the system will still be able to operate in a submerged condition. ---PAGE BREAK--- Section 5 5-2 R. W. Beck Preliminary Engineering Report – August 2009 5.3 Water Quality Treatment BMP The goal of the water quality treatment facility design is to provide treatment for the full water quality design flow rate for the Redmond Way outfall, considering the criteria stated above. However, a more modest treatment goal may be acceptable because this is a retrofit facility in advance of redevelopment. If the facility does not handle the full treatment flow at this time, it will be necessary to expand the facility in the future, so that the percentage of the treatment flow handled by the facility remains commensurate with the level of redevelopment. 5.3.1 Treatment BMPs Considered Treatment best management practices (BMPs) approved for use by Ecology were evaluated to determine their suitability for the Redmond Way regional facility. BMPs need to be capable of treating the water quality design flow, preferably to Enhanced treatment levels, within a footprint that minimizes disruption of the existing and proposed land uses in the downtown area. It was assumed that an off-line facility would be used, meaning that high flows exceeding the water quality design flow would be bypassed around the treatment facility. The water quality design flow for an off-line facility is 12.75 cubic feet per second (cfs) and the water quality design volume is 19.4 acre-feet, as determined using the basin HSPF and WWHM models (see Section 3.2.1). The treatment BMP must also function under a range of tailwater conditions at the outfall to the Sammamish River without causing street flooding upstream of the facility (see Section 3.4). The BMPs that were considered are described below. Wetpools Wetpools provide a permanent pool to capture and store the treatment design volume; storing water between storms allows for settling of particulate pollutants. Wetpools, however, do not provide effective treatment for metals and are not considered to be Enhanced treatment. The required storage volume as define by the Ecology regulations is 19.4 acre-feet. If this volume were placed along the gradient of the existing pipe, it would require a large storage pool, situated below the invert of the pipe; the pipe invert is approximately 13 feet below the ground surface and the treatment facility would be an additional 4 to 8 feet below the invert. Treatment Wetlands Treatment wetlands require an open surface water facility supporting wetland plants for pollutant removals. They typically require considerable space due to the nature of the facility as well as the depth of the associated conveyance systems. The design water quality volume is 19.4 acre-feet, which would require a 6.5-acre wetland. There is insufficient open space along the Sammamish River for this type of BMP. ---PAGE BREAK--- WATER QUALITY TREATMENT ALTERNATIVE ANALYSES Preliminary Engineering Report – August 2009 R. W. Beck 5-3 Sand Filters The 12.75 cfs design flow is too large for a sand filter. The filter area alone would be at least 7,000 square feet; an additional 2,100 square feet would be needed for a distribution manifold and pre-treatment swirl concentrators (for a total of 9,100 square feet). Pumping would likely be required. An underground sand filter of this size would also be difficult to maintain. Design Media Filtration Ecology has approved several filtration BMPs for Basic treatment designations (which are less than Enhanced treatment). Used in a treatment train, these BMPs may also qualify as Enhanced treatment. A commonly applied filter system is StormFilter, which uses canisters filled with filter media. However, these filters are not suitable for use in a persistently submerged condition, meaning that water would need to be pumped to allow the filters to function above the range of water levels expected in the Sammamish River. StormFilter produces a filter canister that operates at 11.3 gallons per minute. An estimated 510 canisters housed in a 3,000-square-foot vault would be required to treat the design flow rate of 12.75 cfs, plus 2,100 square feet for a distribution manifold and swirl concentrators (for a total of 5,100 square feet). Another filter option is EcoStorm Plus, by Royal Enterprises. EcoStorm Plus has been granted a Pilot Use Designation by Ecology. EcoStorm Plus treats stormwater by passing it through a porous concrete filter. The concrete is cast with a polymer additive designed to enhance adsorption of metals. Of the media filters currently available, the EcoStorm Plus system allows the highest treatment flow rate per filter surface area. EcoStorm Plus can also be operated in submerged condition, making it suitable for use adjacent to the Sammamish River where water levels in the river rise above the stormwater outfall for extended periods. Redmond has installed an EcoStorm Plus system at Luke McRedmond Park and is monitoring its performance. The complete system consists of a hydrodynamic separator providing pre-treatment, followed by EcoStorm Plus filters. Ecology’s Pilot Use Designation approves the EcoStorm Plus system (5-foot-diameter unit) for treatment at 360 gpm (0.8 cfs) at the water quality design flow rate calculated using a continuous model with a 15-minute time step. Eighteen units would be necessary to treat the 12.75-cfs design flow. With distribution and collection chambers, this system would have a footprint of approximately 4,500 square feet, including distribution manifold and swirl concentrators. Currently the test results at the Luke McRedmond site indicate that a treatment rate half of that approved by Ecology would make the system more reliable. A total of 36 units would be required at a treatment rate of 180 gpm rather than 360 gpm. The footprint required for 36 units is estimated to be 8,200 square feet. In its Pilot Use Designation Application, Royal Enterprises provided laboratory testing results demonstrating EcoStorm Plus removed more than 80 percent of total suspended solids (TSS). Royal Enterprises also provided to the authors of this report data from a European EcoStorm Plus installation; this data was not well documented, but ---PAGE BREAK--- Section 5 5-4 R. W. Beck Preliminary Engineering Report – August 2009 demonstrated greater than 80 percent removal of total copper and zinc. Testing is ongoing to verify these predicted removals. 5.3.2 Selection of Preferred Treatment BMP Treatment BMPs were evaluated considering the criteria in Table 5-1 and the site constraints. Table 5-2 provides a comparison of the various considerations. Note that treatment performance and suitability were the deciding factors, and cost was not a primary criterion. Table 5-2 Water Quality Treatment Alternative Evaluation EPlus StormFilter Wetpool Wetland Sand Filter Footprint      Higher Metals Treatment 1     Acceptable Head Loss      Pumping      O&M Considerations      Functions When Submerged      Key:  Most preferred;  Acceptable;  Least preferred 1 To be confirmed by testing of the McRedmond EcoStorm facility. The EcoStorm Plus system is the recommended treatment BMP for the Redmond Way water quality facility. The EcoStorm Plus system has the following advantages:  The system can operate in a submerged condition.  The system is designed for removal of metals, which, combined with sediment pre-treatment by hydrodynamic separators, would meet the intent of Enhanced Treatment. (Monitoring is in progress to verify metals removal performance.)  The system provides the smallest footprint among BMPs that target metals. Among the media filtration BMPs approved by Ecology Pilot, Conditional, or General Use Level Designation), EcoStorm Plus allows the highest treatment flow rate per filter surface area.  The system has acceptable head loss (nominally 2 to 8 inches). This recommendation is contingent upon test results demonstrating pollutant removal effectiveness expected from the ongoing Luke McRedmond Park monitoring. Results are expected to be made available by the end of 2009. ---PAGE BREAK--- WATER QUALITY TREATMENT ALTERNATIVE ANALYSES Preliminary Engineering Report – August 2009 R. W. Beck 5-5 If performance monitoring does not verify EcoStorm Plus performance, the next alternative currently approved by Ecology would be a media filtration system, which would require pumping. Another option could be to incorporate other BMPs upstream in the watershed to operate in conjunction with the EcoStorm Plus system. An example would be using non-infiltrating rain gardens for pollution-generating surfaces and/or increasing the frequency of street sweeping. This option could also include runoff reduction by infiltrating the clean runoff from the rooftops. These measures could help improve the overall performance of the regional treatment system by reducing the pollutant load delivered to the EcoStorm Plus facility. 5.4 Water Quality Treatment Site Treatment sites were evaluated considering their location in the basin and compatibility with urban land use. A facility site located close to the outfall would treat the largest amount of the basin. Due to the limited area available for this facility, an underground facility is considered preferable so as not to preclude other uses of the site. 5.4.1 Treatment Sites Considered Three site alternatives are proposed as shown on Figure 5-1 and discussed in the following subsections. Figure 5-1. Alternative Water Quality Treatment Sites ---PAGE BREAK--- Section 5 5-6 R. W. Beck Preliminary Engineering Report – August 2009 Triangle Site The Triangle site is located on Redmond Way in the parking lot of a private commercial office building. There is an existing oil-water separator on the site, which receives a portion of flows diverted from the Redmond Way storm drain. The parking lot in this site offers space for installation of an underground water quality facility. This site would require negligible additional pipe routing from the Redmond Way storm drain mainline. The site would function under gravity, but would require a treatment device with minimal head loss. The existing oil-water separator could be used to provide pre-treatment, which would extend the life of the cartridges. Ben Franklin Site The Ben Franklin site is located on an open (grass) parcel between the Sammamish River and the back of the Ben Franklin store at the Canyons shopping center. The site would require a pipe diversion from Redmond Way north to the site. There is an existing 24-inch-diameter pipe on the site that outfalls to the Sammamish River, but the pipe would need to be replaced at a lower elevation to allow positive drainage from any flows from Redmond Way. The treatment unit would need to be placed at a location that would accommodate future development of the site. Pre-treatment, if desired, would need to be added on to the unit. Bear Creek Parkway Site The Bear Creek Parkway site is owned by the City of Redmond. It was considered because the City owns the site and it provides enough space for the facility. However, it would not capture as much flow as the Triangle or Ben Franklin sites. Although the site is owned by the City, it has considerable public or commercial value, which offsets the cost of easements on the Triangle and Ben Franklin sites. 5.4.2 Selection of Preferred Treatment Site The project team determined that an EcoStorm Plus system located on the Triangle site would be the optimal facility to function within the design considerations described above. The elements of this preferred alternative are described below. The planning level costs for each of the treatment site alternatives are generally comparable. Greater easement costs would be required for the Triangle and Ben Franklin sites. The Bear Creek Parkway site would require an additional smaller facility the Triangle site) to capture flow from portions of the basin of the Bear Creek Parkway site, requiring capital and easement costs. ---PAGE BREAK--- WATER QUALITY TREATMENT ALTERNATIVE ANALYSES Preliminary Engineering Report – August 2009 R. W. Beck 5-7 Table 5-3 Treatment Site Alternative Evaluation Triangle Ben Franklin Bear Creek Parkway Easements    Low in Basin    Accommodates Existing or Proposed Land Use    Compatible with Proposed Conveyance Alignments    Avoid Localized Flooding    Maintenance Access    Key:  Most preferred;  Acceptable;  Least preferred The Triangle site is recommended because:  The presence of a stormwater treatment facility on this site is an established use.  It maximizes use of existing easement. The easement would require expansion but would be one contiguous easement.  It is low in the basin, capturing the maximum area in a single facility.  Any of the three stormwater trunk line alternatives from the basin could be routed to this location.  It makes use of the existing 30-inch-diameter outfall.  Parking impacts during maintenance can be mitigated by using the lot at Luke McRedmond Park. The Bear Creek Parkway site is on City-owned property, but was not selected because:  A smaller, second facility would still be needed at the Triangle site to provide treatment for 10 acres of the Bear Creek Parkway facility. Two sites would also need to be maintained.  Approximately 500 feet of additional pipe would be necessary to connect the Redmond Way stormwater trunk to this site (whether new mainline is placed in Redmond Way, or the existing Redmond Way connects to South Bypass alternatives).  The conveyance trunk from the facility to the outfall would have more utility conflicts. ---PAGE BREAK--- Section 5 5-8 R. W. Beck Preliminary Engineering Report – August 2009 The Ben Franklin site was not recommended because:  It would require a new easement or purchase of private property, whereas the City already has an easement for the Triangle site and owns the Bear Creek Parkway site.  With unknown plans for this site, maintenance access could be difficult and/or disruptive to other uses.  The use of this site may require new pipe under the railroad. It would probably be complicated and possibly costly to obtain an easement from the owners (and ownership is expected to change in the upcoming years).  This is high-value property that is planned for development. 5.5 Summary The elements of the preferred treatment facility alternative are as follows:  Route the new stormwater trunk to a diversion structure on the Triangle site.  Route the water quality design flow from the diversion structure to the treatment facility.  Install a treatment train consisting of 3 hydrodynamic separators followed by 36 EcoStorm Plus units. Each hydrodynamic separator would serve six EcoStorm Plus filters. (The recommendation for using EcoStorm Plus is pending the outcome of the monitoring that is currently being conducted.)  Outfall to the Sammamish River from the water quality treatment facility using the existing 30-inch-diameter pipe and outfall.  Route a 54-inch-diameter high-flow bypass through the parking lot on the north side of the treatment facility, creating a new outfall in the Sammamish River. ---PAGE BREAK--- Preliminary Engineering Report – August 2009 Section 6 OPERATION AND MAINTENANCE CONSIDERATIONS Operation and maintenance considerations were developed for the stormwater trunkline as well as the proposed water quality treatment facility. In general, the intent of the proposed regional treatment facility is to concentrate maintenance activities near the outfall rather than conduct maintenance activities distributed throughout the basin. Currently it is assumed that the City will still be obligated to maintain all of the storm drains (catch basins) throughout the tributary area as a condition of its NPDES permit. The Redmond Way stormwater trunk and regional treatment facility has been designed to focus treatment near the outfall to the greatest extent practicable and is considered to be in addition to, rather than in-lieu of maintenance distributed throughout the tributary area. A meeting was held with City of Redmond maintenance staff to discuss maintenance concerns or suggestions regarding the proposed facilities. The results of those discussions have been incorporated below. 6.1 Conveyance The entire conveyance trunkline has been designed to transport sediment toward the outfall. To the extent possible, pipe slopes have been selected to encourage self- cleansing velocities and sumps have been eliminated at structures along the pipeline to avoid trapping sediment at multiple locations. The overall pipe gradient, however, is relatively flat and low flow velocities are to be expected, especially for smaller size flows. Near the outfall, sections of the trunkline can be in a backwater condition for extended periods as a result of high water levels in the Sammamish River. Consequently, there is a potential for sediment deposition along portions to the proposed pipeline. One to two sedimentation vaults are proposed to control sediment deposition within the pipeline. These vaults would be designed to slow velocities, promote sedimentation, and provide a sump to collect the sediment that settles out. Potential locations include at the junction of the 166th Avenue NE and the NE 76th Street/BNSF right-of-way trunks and at a location just upstream from the treatment site. Potential vault sizes were evaluated by considering estimated solids (TSS) removal as a function of flow duration and typical sediment particle size distribution for urban runoff. The analysis assumes discrete-particle settling with removal related to the surface area of the vault. The cumulative annual removal considers the volume of flow expected to be passed at various flow rates for the storm trunk as designed. Figure 6-1 provides a summary as to the estimated annual TSS removal as a function of the vault surface area. Results suggest that a vault with a surface area of 200 square feet would be capable of removing about 15 percent of the annual TSS load. Tripling the area to about 600 square feet would provide an additional 11 percent removal. ---PAGE BREAK--- Section 6 6-2 R. W. Beck Preliminary Engineering Report – August 2009 Solids Removal Estimate for Sedimentation Vault Based on Floor Area 0% 5% 10% 15% 20% 25% 30% 35% 40% 0 200 400 [PHONE REDACTED] 1200 1400 1600 Floor Area (sq-ft) Figure 6-1. Estimated Annual Solids Removal The City of Redmond maintenance staff provided the following recommendations concerning the proposed facilities:  Make sure there is plenty of access to facilitate the operation of equipment and allow for visual inspection. Avoid the need for confined space entry.  It is important for equipment to have direct over-the-top access.  Each site should have adequate space available for a work area. It was suggested to have an area approximately 15 by 20 feet provided for parking or staging. Inserts in the pavement should be installed at key locations to allow for safety railing to be erected.  An operation and maintenance plan should be prepared, defining when maintenance should be conducted and the general procedure for a maintenance activity. 6.2 Water Quality Facility The water quality facility includes the flow splitter, the design media treatment units, and the outfall. Most of the maintenance activity will be centered on the design media filtration system. The other units will require periodic inspection and maintenance as needed. The flow splitter will require removal of floatables as well as the periodic removal of sediment that may be deposited. Annual TSS Removal ---PAGE BREAK--- OPERATION AND MAINTENANCE CONSIDERATIONS Preliminary Engineering Report – August 2009 R. W. Beck 6-3 The design media filtration system will require routine monitoring and periodic maintenance to make sure that it is operating as intended. EcoStorm Plus is the treatment facility that has been initially proposed. Experience to date at the Luke McRedmond Park test site, has shown that the treatment system can be prone to plugging and requires periodic backflushing to prevent the filters from becoming plugged. The manufacturer is conducting additional testing to confirm the system performance. The City may want to consider alternative treatment methods if the system being tested proves to be chronically subject to plugging and/or requires an inordinate amount of maintenance time The entire treatment system includes an EcoStorm hydrodynamic separator followed by individual EcoStorm Plus design media filtration systems. There are a total of 6 hydrodynamic separators and 36 filters. Six filters are connected to each hydrodynamic separator. Each operating unit consisting of the hydrodynamic separator and six associated filters can be taken off-line to allow for maintenance while the other units remain in operation. Sediment and floatables will be collected within the hydrodynamic separators and will require periodic cleaning using a vacuum (vactor) truck. Experience on the Luke McRedmond Park site has shown that it is important to provide access directly over the sump of the separator so the vacuum hose can have clear access. Each EcoStorm filter unit contains a sump and a fixed filter that also require periodic maintenance. The manufacturer’s recommended maintenance procedure is as follows:  Using a vacuum truck, remove standing water and any fine sediment from the top of the filter.  Remove remaining water and vacuum the sump area beneath the filter.  Gently backflush the filters by spraying water across the top surface of the filters. At the Luke McRedmond Park site, this has been accomplished using a fire hose hooked up to a hydrant. The manufacturer estimates that a minimum of 350 to 400 gallons of clean water is required to backflush each filter. The Redmond Way facility is being designed to allow the filters to be backflushed in a more automated manner. Backflushing using a drawdown method is proposed rather than requiring each individual filter to be washed manually using a water hose. Each operating unit consisting of six filters will be filled with water to a specified water level above the filter. Water then will be released (or vacuumed) from the bottom, forcing the standing water to flow downward through the filters. This approach is currently being developed by the vendor and so far, appears to be viable. Maintenance requires a significant amount of water. It is recommended that a hydrant be provided as a part of the project that will provide a suitable source of water. Disposal of the water will need to be accomplished either by using vacuum trucks or by possibly discharging into a sanitary sewer. For the Redmond Way site, it is recommended that an arrangement with King County Wastewater Treatment Division be made to allow the City to discharge into the nearby sanitary sewer. Currently the City has, on occasion, been able to discharge into the sanitary sewer when cleaning the existing coalescing plate oil-water separator that is on-site. Maintenance staff ---PAGE BREAK--- Section 6 6-4 R. W. Beck Preliminary Engineering Report – August 2009 recommend a formalized agreement with King County to ensure consistency of the practice. The frequency of inspection and cleaning is dependent on the solids loading. For the Redmond Way site, it is recommended that monitoring equipment be installed to allow head loss to be measured as a function of flow. Potential blockages in the filters will be indicated by more and more head being required to pass flows. Replacement of the entire filter will be required over time as fine sediment becomes lodged in the filter and cannot be removed, or the adsorption sites available for metals removal become used up. A replacement frequency of once every five years has been suggested by the manufacturer, but this, again, depends on the pollutant loading of the particular site. The annual solids removal for the site is estimated to be 40 to 45 cubic yards of material, provided that the facility attains at least 80 percent solids removal. By comparison, the existing oil-water separator removes an estimated 14 cubic yards of material based on the monitoring conducted after it was constructed (Entranco 1996). Some of the material may be accounted for in the various units of the treatment facility—some could be accounted for in the sumps of the sedimentation vaults proposed for the conveyance line. Additional considerations offered by City of Redmond maintenance staff are similar to those listed previously for conveyance and include the following comments directed toward the treatment system itself.  The hydrodynamic separators need to have access directly over the sump so staff can have clear access to the sump.  There should be access to the manifold system to make sure staff can get in to clean it out should it be plugged. It was suggested to consider using a 4-foot-wide concrete vault with a sump to distribute and collect the flows.  Make sure there is enough space available in the parking lot to accommodate equipment and staging.  Ladders into structures are OK but not a necessity. ---PAGE BREAK--- Preliminary Engineering Report – August 2009 Section 7 IMPLEMENTATION 7.1 Estimated Cost of Preferred Alternative A preliminary cost estimate was developed for the preferred alternative. It includes estimated construction costs but does not include costs associated with property acquisition or acquiring easements. The estimated construction cost is $14,836,000, which includes $10,163,000 for the stormwater trunk and $4,673,000 for the treatment facility. A detailed breakdown of the basis of the cost is included in Appendix A. The cost estimate includes a significant contingency (40 percent), considered appropriate for the current level of design. Uncertainties in the cost estimate are related to when the project actually goes to bid and the bidding/economic climate at that time. There could also be significant added costs not currently accounted for such as the potential to have to dispose of contaminated soils, challenges related to minimizing construction impacts to the downtown area, and/or the need to make special accommodations for locating the conveyance line within an active railroad corridor. 7.2 Implementation Schedule Implementation of the project is generally considered to involve at least two phases – one being the construction of the treatment facility, and the other being the construction of the stormwater trunkline. Each can be completed independently of the other. The conveyance portion (trunkline) of the project can be further divided into separate phases to build different sections of the pipe. An example is the 166th Avenue NE trunkline and/or sections of the NE 76th Street/BNSF right-of-way trunkline. Seasonal requirements affecting work include any work conducted within the ordinary high water mark (limited to the construction of the outfall) or construction in seasonally low groundwater periods to minimize the need for dewatering during construction. In general, the portions of the project that are potentially affected by seasonally high groundwater include the treatment site and the western portions of the pipeline alignment where the pipe is deeper. It is recommended that some parts of the conveyance pipeline be constructed first, allowing some additional time to confirm portions of the route selection that currently may be controlled by ownership such as the BNSF corridor. Construction of the treatment facility should be delayed until the performance of the proposed treatment system can be verified. The City would like to begin construction of portions of the project in 2010. About 10 months will be required for design, bid, and award before construction can begin. For ---PAGE BREAK--- Section 7 7-2 R. W. Beck Preliminary Engineering Report – August 2009 example, if a final decision is made on pipeline alignment, or portions of the alignment, by July 2009, construction could begin in May 2010. Construction of the Redmond Way trunkline and treatment facility will also need to be coordinated with other projects planned for the area. This includes roadway and sanitary sewer projects to be constructed within the vicinity of Redmond Way. ---PAGE BREAK--- Appendix A CONCEPTUAL CONSTRUCTION COST ESTIMATE ---PAGE BREAK--- CHECKED BY: R.NELSON BY: A. BAKER DATE: 1/9/2009 DESCRIPTION UNIT QUANTITY UNIT PRICE AMOUNT PREPARATION MOBILIZATION 10% LS 1 278,700 $ 278,700 $ DEMOLITION/CLEARING AND GRUBBING LS 1 40,000 $ 40,000 $ SAWCUTTING, 6" ASPHALT LF 400 6 $ 2,400 $ PAVEMENT REMOVAL AND DISPOSAL SY 1,300 26 $ 33,800 $ SIDEWALK AND CURB REMOVAL AND DISPOSAL SY 150 23 $ 3,500 $ SPCC PLAN LS 1 3,000 $ 3,000 $ TEMP CONSTRUCTION FENCING-CHAIN LINK LF 800 18 $ 14,400 $ TEMPORARY STORMWATER BYPASS LS 1 5,000 $ 5,000 $ STREAM ISOLATION CURTAIN EA 1 15,000 $ 15,000 $ TREATMENT SYSTEM CONCRETE DIVERSION STRUCTURE LS 1 100,000 $ 100,000 $ SWIRL CONCENTRATOR-10' DIAMETER EA 3 30,000 $ 90,000 $ ECOSTORM PLUS EA 18 38,000 $ 684,000 $ 48" EPOXY COATED STEEL PIPES LB 43,500 6 $ 261,000 $ VALVES, GATES AND MISC. LS 1 30,000 $ 30,000 $ MH/CB TYPE 2 60 IN. DIAM. EA 4 6,000 $ 24,000 $ EXCAVATION AND HAUL CY 10,000 30 $ 300,000 $ GRAVEL BORROW INCL HAUL TON 11,500 30 $ 345,000 $ SHORING SF 2,800 20 $ 56,000 $ DEWATERING LS 1 250,000 $ 250,000 $ REMOVE EXISTING SYSTEM LS 1 20,000 $ 20,000 $ FLOW AND LEVEL MONITORING AND TELEMETRY LS 1 75,000 $ 75,000 $ BYPASS PIPE AND OUTFALL EXCAVATION AND HAUL CY 1,300 30 $ 39,000 $ GRAVEL BORROW INCL HAUL TON 1,500 30 $ 45,000 $ SHORING/TRENCH BOX SF 1,800 20 $ 36,000 $ DEWATERING LS 1 35,000 $ 35,000 $ OUTFALL RESTORATION LS 1 5,000 $ 5,000 $ CORRUGATED POLYETHYLENE STORM SEWER PIPE 54 IN. DIAM. LF 300 215 $ 64,500 $ TESC PIPE AND TREATMENT AREA LS 1 40,000 $ 40,000 $ RESTORATION PARK AND RIVER BANK SY 300 100 $ 30,000 $ PRIVATE PROPERTY LS 1 80,000 $ 80,000 $ DOWNTOWN/REDMOND WAY STORMWATER TRUNK & WATER QUALITY TREATMENT FACILITY PRELIMINARY CONSTRUCTION COST ESTIMATE - TREATMENT FACILITY ---PAGE BREAK--- CHECKED BY: R.NELSON BY: A. BAKER DATE: 1/9/2009 DESCRIPTION UNIT QUANTITY UNIT PRICE AMOUNT DOWNTOWN/REDMOND WAY STORMWATER TRUNK & WATER QUALITY TREATMENT FACILITY PRELIMINARY CONSTRUCTION COST ESTIMATE - TREATMENT FACILITY OTHER ITEMS UTILITY CONFLICTS EA 4 15,000 $ 60,000 $ Subtotal 3,065,000 $ CONTINGENCY 40% 1,226,000 $ Construction Subtotal (Rounded) 4,291,000 $ STATE SALES TAX 8.9% 381,899 $ NOTES: 1. COSTS DO NOT INCLUDE DESIGN, PERMITTING, CONSTRUCTION ADMINISTRATION 2. COSTS DO NOT INCLUDE STORMWATER TRUNK. 3. COSTS ARE IN 2008 DOLLARS. 4. COSTS DO NOT INCLUDE LAND ACQUISITION OR EASEMENTS. Total Estimated Project Cost 4,673,000 $ ---PAGE BREAK--- BNSF RR CHECKED BY: R.NELSON BY: A. BAKER DATE: 1/9/2009 DESCRIPTION UNIT QUANTITY UNIT PRICE AMOUNT PREPARATION MOBILIZATION 10% LS 1 606,000 $ 606,000 $ DEMOLITION LS 1 40,000 $ 40,000 $ SAWCUTTING, 6" ASPHALT LF 3,000 6 $ 18,000 $ SAWCUTTING, 12" ASPHALT AND CONCRETE LF 100 9 $ 900 $ PAVEMENT REMOVAL AND DISPOSAL SY 2,700 26 $ 70,200 $ SIDEWALK AND CURB REMOVAL AND DISPOSAL SY 150 23 $ 3,500 $ PIPE REMOVAL AND DISPOSAL LF 500 19 $ 9,500 $ CB/MH REMOVAL AND DISPOSAL EA 5 700 $ 3,500 $ SPCC PLAN LS 1 3,000 $ 3,000 $ TEMP CONSTRUCTION FENCING-CHAIN LINK LF 1,000 18 $ 18,000 $ CONSTRUCTION SURVEYING LS 1 30,000 $ 30,000 $ STORM SEWER CATCH BASIN TYPE 1 EA 10 1,500 $ 15,000 $ MH/CB TYPE 2 54 IN. DIAM. EA 7 4,900 $ 34,300 $ MH/CB TYPE 2 60 IN. DIAM. EA 8 6,000 $ 48,000 $ MH/CB TYPE 2 72 IN. DIAM. EA 10 7,500 $ 75,000 $ MH/CB TYPE 2 84 IN. DIAM. EA 5 9,000 $ 45,000 $ MH/CB TYPE 2 96 IN. DIAM. EA 1 14,000 $ 14,000 $ EXTRA DEPTH VF 17 200 $ 3,500 $ CORRUGATED POLYETHYLENE STORM SEWER PIPE 36 IN. DIAM. LF 2,500 125 $ 312,500 $ CORRUGATED POLYETHYLENE STORM SEWER PIPE 42 IN. DIAM. LF 1,300 140 $ 182,000 $ CORRUGATED POLYETHYLENE STORM SEWER PIPE 48 IN. DIAM. LF 2,900 180 $ 522,000 $ CORRUGATED POLYETHYLENE STORM SEWER PIPE 54 IN. DIAM. LF 400 215 $ 86,000 $ TRENCH BOX SF 50,000 20 $ 1,000,000 $ JACK AND BORE, 36 IN DIAM LF 100 700 $ 70,000 $ JACK AND BORE, 42 IN DIAM LF 100 900 $ 90,000 $ JACK AND BORE, 48 IN DIAM LF 100 1,000 $ 100,000 $ JACKING PITS EA 6 40,000 $ 240,000 $ PLUGGING EXISTING PIPE EA 5 130 $ 650 $ ABANDON EXISTING MANHOLE/CB EA 5 500 $ 2,500 $ REROUTE DRAINAGE AT SAG AND TRIANGLE AREA LS 1 30,000 $ 30,000 $ DEWATERING LS 1 200,000 $ 200,000 $ EXCAVATION AND HAUL CY 37,000 30 $ 1,110,000 $ GRAVEL BORROW INCL HAUL TON 19,000 30 $ 570,000 $ SOIL REMEDIATION CY 7,000 60 $ 420,000 $ DOWNTOWN/REDMOND WAY STORMWATER TRUNK & WATER QUALITY TREATMENT FACILITY PRELIMINARY CONSTRUCTION COST ESTIMATE - STORMWATER TRUNK ---PAGE BREAK--- BNSF RR CHECKED BY: R.NELSON BY: A. BAKER DATE: 1/9/2009 DESCRIPTION UNIT QUANTITY UNIT PRICE AMOUNT DOWNTOWN/REDMOND WAY STORMWATER TRUNK & WATER QUALITY TREATMENT FACILITY PRELIMINARY CONSTRUCTION COST ESTIMATE - STORMWATER TRUNK PAVEMENT HOT-MIX ASPHALT TON 800 135 $ 108,000 $ COLD-MIX ASPHALT TON 800 130 $ 104,000 $ CRUSHED SURFACING TON 567 35 $ 20,000 $ CURB AND GUTTER LF 300 30 $ 9,000 $ CONCRETE SIDEWALK/DRIVEWAY SY 300 35 $ 10,500 $ PAVEMENT STRIPING LF 3,000 3 $ 9,000 $ TRAFFIC LOOPS AND SIGNALS INTERSECTION 4 2,000 $ 8,000 $ TRAFFIC PROJECT TEMPORARY TRAFFIC CONTROL HOUR 1,200 80 $ 96,000 $ TRAFFIC CONTROL SUPERVISOR HOUR 160 50 $ 8,000 $ CONSTRUCTION SIGNS AND DEVICES LS 1 20,000 $ 20,000 $ OTHER ITEMS UTILITY CONFLICTS EA 20 15,000 $ 300,000 $ Subtotal 6,666,000 $ CONTINGENCY 40% 2,666,000 $ Construction Subtotal (Rounded) 9,332,000 $ STATE SALES TAX 8.9% 831,000 $ NOTES: 1. COSTS DO NOT INCLUDE DESIGN, PERMITTING, CONSTRUCTION ADMINISTRATION 2. COSTS DO NOT INCLUDE TREATMENT SYSTEM. 3. COSTS ARE IN 2008 DOLLARS. 4. COSTS DO NOT INCLUDE LAND ACQUISITION OR EASEMENTS. 10,163,000 $ Total Estimated Project Cost ---PAGE BREAK--- Appendix D TECHNICAL STUDIES ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- Attachment C ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- AVONDALE WY NE 80th ST REDMOND WY 166th AVE NE Stormwater Capital Projects Downtown Regional Facilities (Original Plan -2006) Bear Creek Pkwy 85th St. WQF m Redmond Way WQF m McRedmond WQF m Leary STW m m Redmond Way Storm Trunk Safeway WQF m m m Legend Regional Facilities River/Creek City Limits Watersheds ROW · 0 775 1,550 387.5 Feet Sammamish River Bear Creek 550 490150 ---PAGE BREAK--- AVONDALE WY NE 80th ST REDMOND WY 166th AVE NE Stormwater Capital Projects Downtown Regional Facilities (Updated Plan -2010) Bear Creek Pkwy 85th St. WQF m Redmond Way WQF m McRedmond WQF 2006 m Leary STW 2008 m m Redmond Way Storm Trunk (2010) Safeway WQF m m m Legend Regional Facilities Operational River/Creek City Limits Watersheds ROW · 0 760 1,520 380 Feet Sammamish River Bear Creek 550 490150 ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- Attachment D ---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---