Document Redmond_doc_28272bface

PRELIMINARY STORM DRAINAGE REPORT FOR ROSEHILL COTTAGES CITY OF REDMOND IN KING COUNTY, WASHINGTON Project Manager: Prepared by: Approved by: Date: Revised: Core No.: David E. Cayton. P.E. Preston J. Longoni, E.I.T. Michael A. Moody, P.E. June 2017 13060T ---PAGE BREAK--- TABLE OF CONTENTS Core Design, Inc. Rosehill Cottages Page ii SECTION 1: PROJECT OVERVIEW 1 Figure 1-1: Vicinity Map 2 SECTION 2: CONDITIONS AND REQUIREMENTS SUMMARY 1 2.1 Minimum Requirements 1 2.1.1 Minimum Requirement Preparation of Stormwater Site 1 2.1.2 Minimum Requirement Construction Stormwater Pollution Prevention Plan 1 2.1.3 Minimum Requirement Source Control of Pollution 1 2.1.4 Minimum Requirement Preservation of Natural Drainage Systems and Outfalls 1 2.1.5 Minimum Requirements On-Site Stormwater Management 1 2.1.6 Minimum Requirement Runoff Treatment 1 2.1.7 Minimum Requirement Flow Control 1 2.1.8 Minimum Requirement Wetlands Protection 2 2.1.9 Minimum Requirement Operation and Maintenance 2 SECTION 3: OFFSITE ANALYSIS 5 SECTION 4: FLOW CONTROL AND WATER QUALITY DESIGN 7 4.1 Hydraulic Analysis 7 4.1.1 Project LID Feasibility 7 4.1.2 Pre-Developed Conditions 9 Table 4.1: Pre-Developed Conditions Summary (North) 9 Table 4.2: Pre-Developed Conditions Summary (South) 9 4.1.3 Developed Conditions 9 Table 4.3: Developed Conditions Summary (North Basin) 10 Table 4.4: Developed Conditions Summary (South Basin) 10 Figure 4-1: Existing Conditions Exhibit 11 Figure 4-2: Developed Conditions Exhibit 12 4.2 Detention Facility Design 13 4.3 Water Quality Facility Design 13 APPENDIX 17 Appendix A – MGS Flood Reports 18 North Basin 19 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages iii South Basin 26 Appendix B – Geotechnical Engineering Report 33 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 1 SECTION 1: PROJECT OVERVIEW The Rosehill Cottages Project is located on the east side of 132nd Avenue NE at the end of NE 112th Place in Redmond, Washington. See the Vicinity Map on the following page. The proposed site consists of one parcel (parcel number [PHONE REDACTED]) which is 10.85 acres. The property is bounded by single-family residences to the north, west, Native Growth Protection Area (NGPA) Tract to the south and Aerojet properties to the east. The property is accessed via 132nd Avenue NE. A joint north-south PSE (transmission line) and Olympic Petroleum Pipeline easement are located along the eastern property line, but are located outside of the proposed development. The project parcel is currently vacant land and is panhandle shaped. There is a significant amount of elevation change east of the panhandle sloping west to east, with the largest grade change (approximately 50 percent slope) on the east side of the site. The site has a west-east valley that nearly bisects the parcel midway. The runoff from the site generally flows eastward where it enters the Aerojet bypass ditch and eventually converges with the storm drainage along Willows Road NE. There are two flatter ridges that split around the west-east valley from the panhandle. Due to steep slopes north and south of these ridges, approximately 35 percent of the site is developable. These steep slope areas are covered in underbrush, ferns and are heavily vegetated with coniferous and deciduous trees. The property north and south at the east end of the panhandle receives some upstream runoff. In the developed condition, walls will be placed along these boundaries. The underdrain for these walls will discharge around the improvements to the site. The project proposal is for the construction of 28 detached cottage homes. Detached garages and open parking stalls are proposed to serve the cottage homes. The cottage homes are proposed to be built in three clusters across the site, with open space and walkways serving each cluster. Storm drainage will discharge to one of two storm facility systems forming two separate basins. The storm facility system for each basin, North Basin and South Basin, will consist of a StormFilter system for treatment prior to discharge to an infiltration vault. See Site Plan in Section 4 of this report. The detention/water quality facilities will be designed per the Washington State Department of Ecology’s 2012 Stormwater Management Manual for Western Washington, as amended in 2014 (2014 and the City of Redmond 2017 Technical Notebook Issue 7A (City Technical Notebook). The drainage analysis was modeled using MGS Flood software. ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 2 Figure 1-1: Vicinity Map ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 1 SECTION 2: CONDITIONS AND REQUIREMENTS SUMMARY The proposed project is classified as a “Large Project” per Chapter 3 of the City of Redmond Technical Notebook. Therefore, all ten minimum requirements will be addressed per Section 6.2 in the Technical Notebook. Section 2.5 in Volume I of the 2014 lists the nine Minimum Requirements for Development. Chapter 2 of the City of Redmond Technical Notebook lists any modifications to the DOE minimum requirements. The nine minimum requirements and how each requirement is addressed are listed below. 2.1 Minimum Requirements 2.1.1 Minimum Requirement Preparation of Stormwater Site Plans Preliminary Civil Plans under separate cover and a Preliminary Storm Drainage Report herein have been prepared for the subject project. 2.1.2 Minimum Requirement Construction Stormwater Pollution Prevention Plan A will be prepared and submitted during final design. 2.1.3 Minimum Requirement Source Control of Pollution This minimum requirement will be addressed during final design. 2.1.4 Minimum Requirement Preservation of Natural Drainage Systems and Outfalls Drainage from the developed site will be fully infiltrated. If emergency overflow of the infiltration vaults were to occur, the natural discharge locations will be mimicked by way of tight-lining the overflows to the bottom of the ravine that flows easterly off the site in the natural direction and location. 2.1.5 Minimum Requirements On-Site Stormwater Management The project will comply with the Low Impact Development Performance Standards, per Table 2.0 included at the end of this section. The stormwater discharges shall match developed discharge durations for the range of pre-developed discharge rates from 8% of the 2-year peak flow to 50% of the 2-year peak flow. Since the site is also required to meet minimum requirement #7 – flow control – the durations shall be matched from 8% of the 2-year flow through the 50-year. Since the site proposed to fully infiltration stormwater up through the 50-year storm at a minimum, the LID performance and standard flow control standards will be satisfied. All landscaped and open areas will have compost amended soils per BMP T5.13. 2.1.6 Minimum Requirement Runoff Treatment Design of the treatment facilities are described in Section 4 of this report. Placement of the treatment facilities are shown on the Preliminary Civil Plans. 2.1.7 Minimum Requirement Flow Control Design of the flow control facility is described in Section 4 of this report. Two separate infiltration vaults are proposed to effectively manage the on-site stormwater for flow control. Placement of the infiltration vaults are shown on the Preliminary Civil Plans. ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 2 2.1.8 Minimum Requirement Wetlands Protection There is an existing wetland and stream to the south of the site. Development will impact the buffers and the project will be required to provide mitigation. 2.1.9 Minimum Requirement Operation and Maintenance Operations and Maintenance Guidelines will be provided during final design. ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 3 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 4 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 5 SECTION 3: OFFSITE ANALYSIS Upstream Some offsite drainage from the west currently drains onto the site. This drainage will be intercepted by wall drains and discharged around the site improvements. Date of Field Inspection: May 21, 2013 Weather Conditions: Cloudy, periodic showers, lower 50° F Field Inspection performed by: Dean Furr, P.E. For the following discussion please refer to the Exhibit” at the back of this section, where all the point numbers are shown. Runoff from the site follows in a general eastern direction. The panhandle portion of the site contains the portion of paved NE 112th Place. Runoff flows to unimproved conveyances at the paved edge and flows eastward at a four percent slope. The runoff enters the larger site area and continues to flow into a gully. Runoff flows down the gully, approximately 18 percent slope, which flattens out and forms a wide grassy area. This flat area looks to be constructed during the installation of the gas main and/or the transmission lines. Stormwater turns into a sheet flow for approximately 110 feet to the eastern property line. Stormwater exits the eastern property line and the analysis begins at Point 1 on the Exhibit. Stormwater continues to flow in an easterly direction, downslope through a vegetated ravine (Point 2) where it enters into a well-defined ditch on the Aerojet Property (Point Stormwater flows through the grass-lined ditch (Point 4) where it converges with stormwater from the west (Point This stormwater comes from the wetland south of the site. Stormwater continues to flow south within the ditch where it enters 18-inch and 24-inch culverts (Point There is sediment deposited at the end of the culverts, but they remain operational. The ditch continues southward where it enters a 36-inch corrugated metal pipe culvert (Point Stormwater continues within the ditch flowing eastward where the slope becomes steep. The ditch becomes a ravine with near vertical walls (Point 8) and enters a 36-inch pipe (Point The stormwater continues eastward in the ditch (Point 10) where it enters a detention pond on the south side of the Willows Creek Corporate Center (Point 11). This concludes the one-quarter mile analysis. ---PAGE BREAK--- ---PAGE BREAK--- SE Redmond Grass Lawn Spiritbrook Viewpoint Open Space Viewpoint Idylwood Beach Cascade View Westside Bridle Crest Trail Site Redmond West Wetlands Luke McRedmond Landing Edge Skate Park ORSCC Anderson OFH Bear Creek Reservoir Jonathan Hartman Sixty Acres (King County) Marymoor (King County) Juel Farrel- McWhirter Conrad Olson Farm Bear and Evans Creek Greenway Arthur Johnson Meadow NE Redmond Sammamish Valley Willows Creek Scotts Pond Sunset Gardens Municipal Campus Perrigo Nike Perrigo Heights L a k e L a k e S a m m a m i s h S a m m a m i s h U V 520 U V 520 188th AVE NE NE 124th ST AVON DALE WY CLEVEL A ND S T NE 24th ST NE 40th ST 166th AVE NE 156th AVE NE 172nd AVE NE 160th AVE NE NE 116th ST NE 80th ST NE 80th ST NE 104th ST NE 20th ST 164th AVE NE 132nd AVE NE NE 79th ST NE 76th ST 1 6 2nd AVE NE 154th PL NE 154 t h AVE NE NE 111th ST NE 90th ST E LK S AMMA MISH PKW Y 152nd AVE NE 185th AVE NE 180th AVE NE NE 128th ST UNION HILL RD B E A R C REE K P K WY NE 60th ST 154th AVE NE NE 124th WY NE 36t h ST 178th PL NE 132nd AVE NE NE 116th ST O LD R ED M O ND RD W L K SAMMAM I SH P K WY RED-WOOD RD 148th AVE NE BEL-RED RD 171st AV E N E WILL O WS RD 180th AVE NE 140th AVE NE 161st AVE NE 1 6 0 t h A V E NE NE 100th ST AVONDALE RD NE 85th ST NE 83rd ST 172nd AVE NE REDMOND WY 148th AVE NE NE 75th ST NE 5 1st ST 150th AVE NE REDMOND WY AVONDA L E RD 50 100 400 450 350 150 250 300 200 350 250 300 150 200 150 100 300 450 50 400 200 50 50 50 50 250 150 100 150 50 100 100 100 200 350 100 250 300 300 300 350 200 350 300 250 150 100 300 100 450 50 250 350 300 250 300 150 250 400 350 200 50 50 150 50 300 100 400 150 250 150 300 200 50 100 50 50 350 200 150 200 300 200 250 150 400 250 450 50 300 300 50 300 150 300 400 50 50 250 300 200 350 250 100 50 100 50 300 100 Erosion Hazard Areas Critical Areas Map City of Redmond, Washington Ü 0 0.5 1 Miles Disclaimer: This map is created and maintained by GIS Services Group,Finance and Information Services, City of Redmond, Washington, for reference purposes only. The City makes no guarantee as to the accuracy of the features shown on this map. File Name:\\redmond.man\fs\GISUser\GIS\GISServicesProject\GISServices\RedmondGovWebsite\03GIS\ErosionHazardAreas_11x17.mxd Effective: 05/28/2005 Note: This map shall be used as a general guide. It represents approximate locations. Consult the Critical Areas Ordinance (CAO) for reporting requirements. In the event there is a conflict between the map and the criteria or standards of the CAO, the criteria shall prevail. Data Source: SCS Soil Survey Contour Erosion Hazard Area City Limit Water Park and Open Space SITE ---PAGE BREAK--- SE Redmond Grass Lawn Spiritbrook Viewpoint Open Space Viewpoint Idylwood Beach Cascade View Westside Bridle Crest Trail Site Redmond West Wetlands Luke McRedmond Landing Edge Skate Park ORSCC Anderson OFH Bear Creek Reservoir Jonathan Hartman Sixty Acres (King County) Marymoor (King County) Juel Farrel- McWhirter Conrad Olson Farm Bear and Evans Creek Greenway Arthur Johnson Meadow NE Redmond Sammamish Valley Willows Creek Scotts Pond Sunset Gardens Municipal Campus Perrigo Nike Perrigo Heights L a k e L a k e S a m m a m i s h S a m m a m i s h U V 520 U V 520 188th AVE NE NE 124th ST AVON DALE WY CLEVEL A ND S T NE 24th ST NE 40th ST 166th AVE NE 156th AVE NE 172nd AVE NE 160th AVE NE NE 116th ST NE 80th ST NE 80th ST NE 104th ST NE 20th ST 164th AVE NE 132nd AVE NE NE 79th ST NE 76th ST 1 6 2nd AVE NE 154th PL NE 154 t h AVE NE NE 111th ST NE 90th ST E LK S AMMA MISH PKW Y 152nd AVE NE 185th AVE NE 180th AVE NE NE 128th ST UNION HILL RD B E A R C REE K P K WY NE 60th ST 154th AVE NE NE 124th WY NE 36t h ST 178th PL NE 132nd AVE NE NE 116th ST O LD R ED M O ND RD W L K SAMMAM I SH P K WY RED-WOOD RD 148th AVE NE BEL-RED RD 171st AV E N E WILL O WS RD 180th AVE NE 140th AVE NE 161st AVE NE 1 6 0 t h A V E NE NE 100th ST AVONDALE RD NE 85th ST NE 83rd ST 172nd AVE NE REDMOND WY 148th AVE NE NE 75th ST NE 5 1st ST 150th AVE NE REDMOND WY AVONDA L E RD Fish and Wildlife Habitat Conservation Areas (Core Preservation Areas) Critical Areas Map City of Redmond, Washington Ü 0 0.5 1 Miles Disclaimer: This map is created and maintained by GIS Services Group,Finance and Information Services, City of Redmond, Washington, for reference purposes only. The City makes no guarantee as to the accuracy of the features shown on this map. File Name:\\redmond.man\fs\GISUser\GIS\GISServicesProject\GISServices\RedmondGovWebsite\03GIS\FishWildlifAreas_11x17.mxd City Limit Park and Open Space Water Effective: 05/28/2005 Class 1 Streams and Buffers Native Growth Protection Easements Open Space Easements Transfer Development Rights Easements Note: This map shall be used as a general guide. It represents approximate locations. Consult the Critical Areas Ordinance (CAO) for reporting requirements. In the event there is a conflict between the map and the criteria or standards of the CAO, the criteria shall prevail. Data Source: USGS Geologic Maps SITE ---PAGE BREAK--- SE Redmond Grass Lawn Spiritbrook Viewpoint Open Space Viewpoint Idylwood Beach Cascade View Westside Bridle Crest Trail Site Redmond West Wetlands Luke McRedmond Landing Edge Skate Park ORSCC Anderson OFH Bear Creek Reservoir Jonathan Hartman Sixty Acres (King County) Marymoor (King County) Juel Farrel- McWhirter Conrad Olson Farm Bear and Evans Creek Greenway Arthur Johnson Meadow NE Redmond Sammamish Valley Willows Creek Scotts Pond Sunset Gardens Municipal Campus Perrigo Nike Perrigo Heights L a k e L a k e S a m m a m i s h S a m m a m i s h U V 520 U V 520 188th AVE NE NE 124th ST AVON DALE WY CLEVEL A ND S T NE 24th ST NE 40th ST 166th AVE NE 156th AVE NE 172nd AVE NE 160th AVE NE NE 116th ST NE 80th ST NE 80th ST NE 104th ST NE 20th ST 164th AVE NE 132nd AVE NE NE 79th ST NE 76th ST 1 6 2nd AVE NE 154th PL NE 154 t h AVE NE NE 111th ST NE 90th ST E LK S AMMA MISH PKW Y 152nd AVE NE 185th AVE NE 180th AVE NE NE 128th ST UNION HILL RD B E A R C REE K P K WY NE 60th ST 154th AVE NE NE 124th WY NE 36t h ST 178th PL NE 132nd AVE NE NE 116th ST O LD R ED M O ND RD W L K SAMMAM I SH P K WY RED-WOOD RD 148th AVE NE BEL-RED RD 171st AV E N E WILL O WS RD 180th AVE NE 140th AVE NE 161st AVE NE 1 6 0 t h A V E NE NE 100th ST AVONDALE RD NE 85th ST NE 83rd ST 172nd AVE NE REDMOND WY 148th AVE NE NE 75th ST NE 5 1st ST 150th AVE NE REDMOND WY AVONDA L E RD Seismic Hazard Areas Critical Areas Map City of Redmond, Washington Ü 0 0.5 1 Miles Disclaimer: This map is created and maintained by GIS Services Group,Finance and Information Services, City of Redmond, Washington, for reference purposes only. The City makes no guarantee as to the accuracy of the features shown on this map. File Name:\\redmond.man\fs\GISUser\GIS\GISServicesProject\GISServices\RedmondGovWebsite\03GIS\SeismicHazardAreas_11x17.mxd Effective: 05/28/2005 Data Source: USGS Geologic Maps Note: This map shall be used as a general guide. It represents approximate locations. Consult the Critical Areas Ordinance (CAO) for reporting requirements. In the event there is a conflict between the map and the criteria or standards of the CAO, the criteria shall prevail. Seismic Hazard Area City Limit Park and Open Space Water SITE ---PAGE BREAK--- SITE ---PAGE BREAK---      ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! 450 090 460 030 260 170 400 4 240 320 5b 050 070 490140 580 560 250 550 060 640 610 490020 040 490080 470 500 010 630 130 490010 490070 490100 220 110 020 5c 230 660 340 490120 650 080 670 120 410 620 490090 280 490130 590 440 490150 540 490060 5a 270 100 510 300 150 570 370 210 310 330 490110 082 380 490190 600 490030 200 390 190 420 081 490170 071 530 072 490160 350 360 430 290 140 490180 160 180 460 490040 520 680 490045 490043 490050 490046 NA Redmond Watershed Map City of Redmond, Washington 11/18/2010 Ü 0 0.5 1 Miles Disclaimer: This map is created and maintained by GIS Services Group,Finance and Information Services, City of Redmond, Washington, for reference purposes only. The City makes no guarantee as to the accuracy of the features shown on this map. File Name:File Name:\\redmond.man\fs\GISUser\GIS\GISServicesProject\GISServices\RedmondGovWebsite\03GIS\Watersheds_11x17.mxd Watershed Park and Open Space Water Note: Redmond’s primary watersheds are subdivisions of the Sammamish watershed that drain to Lake Washington. Each watershed is defined by a group of streams, pipes, and topographic features that drain to a discrete location (Pour Point) where the water “pours” into Lake Sammamish or the Sammamish River. Some watersheds are further subdivided (i.e. watershed 490, the largest watershed in Redmond is divided into secondary watersheds with secondary pour points that all drain to Bear Creek). ! Pour Points  Denotes Infiltration City Limit SITE ---PAGE BREAK--- SE Redmond Grass Lawn Spiritbrook Viewpoint Open Space Viewpoint Idylwood Beach Cascade View Westside Bridle Crest Trail Site Redmond West Wetlands Luke McRedmond Landing Edge Skate Park ORSCC Anderson OFH Bear Creek Reservoir Jonathan Hartman Sixty Acres (King County) Marymoor (King County) Juel Farrel- McWhirter Conrad Olson Farm Bear and Evans Creek Greenway Arthur Johnson Meadow NE Redmond Sammamish Valley Willows Creek Scotts Pond Sunset Gardens Municipal Campus Perrigo Nike Perrigo Heights L a k e L a k e S a m m a m i s h S a m m a m i s h U V 520 U V 520 188th AVE NE NE 124th ST AVON DALE WY CLEVEL A ND S T NE 24th ST NE 40th ST 166th AVE NE 156th AVE NE 172nd AVE NE 160th AVE NE NE 116th ST NE 80th ST NE 80th ST NE 104th ST NE 20th ST 164th AVE NE 132nd AVE NE NE 79th ST NE 76th ST 1 6 2nd AVE NE 154th PL NE 154 t h AVE NE NE 111th ST NE 90th ST E LK S AMMA MISH PKW Y 152nd AVE NE 185th AVE NE 180th AVE NE NE 128th ST UNION HILL RD B E A R C REE K P K WY NE 60th ST 154th AVE NE NE 124th WY NE 36t h ST 178th PL NE 132nd AVE NE NE 116th ST O LD R ED M O ND RD W L K SAMMAM I SH P K WY RED-WOOD RD 148th AVE NE BEL-RED RD 171st AV E N E WILL O WS RD 180th AVE NE 140th AVE NE 161st AVE NE 1 6 0 t h A V E NE NE 100th ST AVONDALE RD NE 85th ST NE 83rd ST 172nd AVE NE REDMOND WY 148th AVE NE NE 75th ST NE 5 1st ST 150th AVE NE REDMOND WY AVONDA L E RD Wellhead Protection Zones City of Redmond, Washington 11/18/2010 Ü 0 0.5 1 Miles Disclaimer: This map is created and maintained by GIS Services Group,Finance and Information Services, City of Redmond, Washington, for reference purposes only. The City makes no guarantee as to the accuracy of the features shown on this map. File Name:\\redmond.man\fs\GISUser\GIS\GISServicesProject\GISServices\RedmondGovWebsite\03GIS\WellheadProtectionZone_11x17.mxd Wellhead Zone 2 Wellhead Zone 1 Wellhead Zone 4 City Limit Park and Open Space Water Wellhead Zone 3 SITE ---PAGE BREAK--- SE Redmond Grass Lawn Spiritbrook Viewpoint Open Space Viewpoint Idylwood Beach Cascade View Westside Bridle Crest Trail Site Redmond West Wetlands Luke McRedmond Landing Edge Skate Park ORSCC Anderson OFH Bear Creek Reservoir Jonathan Hartman Sixty Acres (King County) Marymoor (King County) Juel Farrel- McWhirter Conrad Olson Farm Bear and Evans Creek Greenway Arthur Johnson Meadow NE Redmond Sammamish Valley Willows Creek Scotts Pond Sunset Gardens Municipal Campus Perrigo Nike Perrigo Heights L a k e L a k e S a m m a m i s h S a m m a m i s h U V 520 U V 520 188th AVE NE NE 124th ST AVON DALE WY CLEVEL A ND S T NE 24th ST NE 40th ST 166th AVE NE 156th AVE NE 172nd AVE NE 160th AVE NE NE 116th ST NE 80th ST NE 80th ST NE 104th ST NE 20th ST 164th AVE NE 132nd AVE NE NE 79th ST NE 76th ST 1 6 2nd AVE NE 154th PL NE 154 t h AVE NE NE 111th ST NE 90th ST E LK S AMMA MISH PKW Y 152nd AVE NE 185th AVE NE 180th AVE NE NE 128th ST UNION HILL RD B E A R C REE K P K WY NE 60th ST 154th AVE NE NE 124th WY NE 36t h ST 178th PL NE 132nd AVE NE NE 116th ST O LD R ED M O ND RD W L K SAMMAM I SH P K WY RED-WOOD RD 148th AVE NE BEL-RED RD 171st AV E N E WILL O WS RD 180th AVE NE 140th AVE NE 161st AVE NE 1 6 0 t h A V E NE NE 100th ST AVONDALE RD NE 85th ST NE 83rd ST 172nd AVE NE REDMOND WY 148th AVE NE NE 75th ST NE 5 1st ST 150th AVE NE REDMOND WY AVONDA L E RD Wetlands Critical Areas Map City of Redmond, Washington Ü 0 0.5 1 Miles Disclaimer: This map is created and maintained by GIS Services Group,Finance and Information Services, City of Redmond, Washington, for reference purposes only. The City makes no guarantee as to the accuracy of the features shown on this map. File Name:\\redmond.man\fs\GISUser\GIS\GISServicesProject\GISServices\RedmondGovWebsite\03GIS\Wetlands_11x17.mxd Wetland Mixed Wetland/Upland City Limit Park and Open Space Water Effective: 05/28/2005 Data Source: USGS National Wetland Inventory Aerial Photo Interpretation SCS Soil Survey City of Redmond Note: This map shall be used as a general guide. It represents approximate locations. Consult the Critical Areas Ordinance (CAO) for reporting requirements. In the event there is a conflict between the map and the criteria or standards of the CAO, the criteria shall prevail. SITE ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 7 SECTION 4: FLOW CONTROL AND WATER QUALITY DESIGN 4.1 Hydraulic Analysis The drainage analysis was modeled using the MGS Flood software. The on-site soils are Alderwood gravelly sandy loam per the USDA NRCS Web Soils Survey. This soil type has a SCS Hydrologic Soil Group classification of the equivalent of “till”. Per the geotechnical report by Associated Earth Sciences, Inc., included in Appendix B, the design infiltration rate for the north vault is 2-inches per hour, and 3- inches per hour for the south vault. 4.1.1 Project LID Feasibility See the “Flow Chart for Determining LID MR #5 Requirements” on the following page. ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 8 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 9 4.1.2 Pre-Developed Conditions The subject property is 10.85 acres in total, and is currently covered with native vegetation. There are no existing structures on-site, and the only existing hard surface is an existing gravel access road. The site slopes heavily to the east. Due to steep slopes and their buffers, only 3.75 acres will be disturbed for the development. The remaining areas are therefore excluded from the stormwater calculations in both the pre-developed and developed conditions. In the pre-developed condition, the entire construction site will be modeled as “till-forest”. Refer to Tables 4.1 and 4.2 (below) for a summary of the pre- developed conditions, and Figure 4-1: Pre-Developed Conditions exhibit included at the end of this section. Table 4.1: Pre-Developed Conditions Summary (North) Surface Cover Type Area (acres) Till-Forest 1.00 Total 1.00 Table 4.2: Pre-Developed Conditions Summary (South) Surface Cover Type Area (acres) Till-Forest 2.75 Total 2.75 The areas in Tables 4.1 and 4.2 above were used as inputs to MGS Flood to model the pre-developed condition. The full MGS Flood report is included In Appendix A of this report. 4.1.3 Developed Conditions The proposed development includes the construction of 28 cottages, 5 one-story parking garages, and associated roadways, parking stalls, and utilities. Flow control and the LID Performance Standard will be achieved by on-site infiltration vaults. Treatment of runoff for basic water quality is proposed through two Contech Stormfilter facilities, one located upstream of each infiltration vault. Runoff from the roadways, roofs, sidewalks, and landscaped areas will be collected by catch basins inlets and conveyed to the Stormfilters and infiltration facilities via 12-inch pipe. Roof and footing drains will by tight-lined to the conveyance system. Tables 4.3 and 4.4 (below) summarize the developed basin areas that were used to compute the developed flow rates and inflows to the infiltration vaults. Also, refer to Figure 4-2: Developed Conditions exhibit. ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 10 Table 4.3: Developed Conditions Summary (North Basin) Surface Cover Type Area (acres) Till – Grass 0.43 Impervious 0.57 Total 1.00 Table 4.4: Developed Conditions Summary (South Basin) Surface Cover Type Area (acres) Till – Grass 1.11 Impervious 1.64 Total 2.75 ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 13 4.2 Detention Facility Design Per the DOE manual, the standard flow control requirement is such that the developed (mitigated) condition discharge durations match the existing condition durations from 50% of the 2-year to the 50- year storm events and that the developed 2-year and 10-year peak discharge rates do not exceed the existing 2-year and 10-year peak discharge rates, respectively. In addition, the LID performance standard requires that the pre-developed durations are not exceeded from 8% of the 2-year to 50% of the 2-year peak. Both infiltration vaults adequately infiltrate the 50-year storm, and therefore comply with each standard. The infiltration vaults are designed in accordance with the 2014 and are modeled using the MGS Flood software. The full MGS Flood reports for the North and South infiltration vault sizing are included in Appendix A. 4.3 Water Quality Facility Design Water quality treatment for the site is designed per the Basic Water Quality Treatment menu. Water quality treatment for both basins will be via StormFilter systems. For each basin, a StormFilter will be installed prior to infiltration. For preliminary purposes, conceptual stormfilter sizes have been assumed from a past size and cost estimate from Contech, which is included on the following page. The stormfilter for the North Basin is assumed to be a 96” Manhole with 12 ZPG media cartridges, and the stormfilter for the South Basin is assumed to be an 8’x14’ Stormfilter Vault with 21 ZPG media cartridges. ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 14 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 15 ---PAGE BREAK--- Core Design, Inc. Redmond Cottages Page 16 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 17 APPENDIX ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 18 Appendix A – MGS Flood Reports ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 19 North Basin MGS FLOOD PROJECT REPORT Program Version: 4.38 Program License Number: 200210008 Project Simulation Performed on: 05/01/2017 5:31 PM Report Generation Date: 05/01/2017 5:32 PM Input File Name: Redmond Cottages - North Infiltration Vault.fld Project Name: Redmond Cottages - North Vault Analysis Title: Comments: PRECIPITATION INPUT Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Climatic Region Number: 13 Full Period of Record Available used for Routing Precipitation Station : 96004005 Puget East 40 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961040 Puget East 40 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : USGS Default Default HSPF Parameters Used (Not Modified by User) WATERSHED DEFINITION Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 1.000 1.000 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 1.000 1.000 PREDEVELOPED Number of Subbasins: 1 Subbasin : Predev -------Area(Acres) Till Forest 1.000 Till Pasture 0.000 Till Grass 0.000 Outwash Forest 0.000 Outwash Pasture 0.000 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 20 Outwash Grass 0.000 Wetland 0.000 Green Roof 0.000 User 2 0.000 Impervious 0.000 Subbasin Total 1.000 POSTDEVELOPED Number of Subbasins: 1 Subbasin : North Basin -------Area(Acres) Till Forest 0.000 Till Pasture 0.000 Till Grass 0.430 Outwash Forest 0.000 Outwash Pasture 0.000 Outwash Grass 0.000 Wetland 0.000 Green Roof 0.000 User 2 0.000 Impervious 0.570 Subbasin Total 1.000 LINK DATA PREDEVELOPED Number of Links: 0 LINK DATA POSTDEVELOPED Number of Links: 2 Link Name: North Vault Link Type: Structure Link Name: New Copy Lnk2 Prismatic Pond Option Used Pond Floor Elevation (ft) : 280.00 Riser Crest Elevation (ft) : 286.00 Max Pond Elevation (ft) : 287.00 Storage Depth (ft) : 6.00 Pond Bottom Length (ft) : 49.0 Pond Bottom Width (ft) : 20.0 Pond Side Slopes (ft/ft) : L1= 0.00 L2= 0.00 W1= 0.00 W2= 0.00 Bottom Area (sq-ft) : 980. Area at Riser Crest El (sq-ft) : 980. ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 21 (acres) : 0.022 Volume at Riser Crest (cu-ft) : 5,880. (ac-ft) : 0.135 Area at Max Elevation (sq-ft) : 980. (acres) : 0.022 Vol at Max Elevation (cu-ft) : 6,958. (ac-ft) : 0.160 Constant Infiltration Option Used Infiltration Rate (in/hr): 2.00 Riser Geometry Riser Structure Type : Circular Riser Diameter (in) : 18.00 Common Length (ft) : 0.000 Riser Crest Elevation : 286.00 ft Hydraulic Structure Geometry Number of Devices: 0 Link Name: New Copy Lnk2 Link Type: Copy Link: None FREQUENCY AND DURATION PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 POSTDEVELOPED Number of Subbasins: 1 Number of Links: 2 Subbasin: North Basin Flood Frequency Data(cfs) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) Flood Peak (cfs) 2-Year 0.251 5-Year 0.324 10-Year 0.402 25-Year 0.540 50-Year 0.661 100-Year 0.816 200-Year 0.824 Link: North Vault Link Inflow Frequency Stats ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 22 Flood Frequency Data(cfs) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) Flood Peak (cfs) 2-Year 0.251 5-Year 0.324 10-Year 0.402 25-Year 0.540 50-Year 0.661 100-Year 0.816 200-Year 0.824 Link: North Vault Link Outflow 1 Frequency Stats Flood Frequency Data(cfs) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) Flood Peak (cfs) 2-Year 1.375E-05 5-Year 2.530E-05 10-Year 3.748E-05 25-Year 5.109E-05 50-Year 5.693E-05 100-Year 2.083E-02 200-Year 0.187 Link: North Vault Link WSEL Stats WSEL Frequency Data(ft) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) WSEL Peak (ft) 1.05-Year 280.531 1.11-Year 280.689 1.25-Year 280.881 2.00-Year 281.374 3.33-Year 281.974 5-Year 282.533 10-Year 283.751 25-Year 285.075 50-Year 285.694 100-Year 286.006 Link: New Copy Lnk2 Link Inflow Frequency Stats Flood Frequency Data(cfs) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) Flood Peak (cfs) 2-Year 1.375E-05 5-Year 2.530E-05 10-Year 3.748E-05 25-Year 5.109E-05 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 23 50-Year 5.693E-05 100-Year 2.083E-02 200-Year 0.187 ***********Groundwater Recharge Summary Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) Subbasin: Predev 172.429 Total: 172.429 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) Subbasin: North Basin 52.551 Link: North Vault 342.033 Link: New Copy Lnk2 0.000 Total: 394.583 Total Predevelopment Recharge is Less than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 1.091 ac-ft/year, Post Developed: 2.497 ac-ft/year Quality Facility Data PREDEVELOPED Number of Links: 0 POSTDEVELOPED Number of Links: 2 Link: North Vault Basic Wet Pond Volume (91% Exceedance): 3002. cu-ft Computed Large Wet Pond Volume, 1.5*Basic Volume: 4503. cu-ft Time to Infiltrate 91% Treatment Volume, (Hours): 18.52 Infiltration/Filtration Inflow Volume (ac-ft): 342.03 Inflow Volume Including PPT-Evap (ac-ft): 342.03 Total Runoff Infiltrated (ac-ft): 342.03, 100.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To System (ac-ft): 0.04 Secondary Outflow To System (ac-ft): 0.00 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 24 Percent Treated (Infiltrated+Filtered)/Total Volume: 100.00% Link: New Copy Lnk2 Infiltration/Filtration Inflow Volume (ac-ft): 0.04 Inflow Volume Including PPT-Evap (ac-ft): 0.04 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To System (ac-ft): 0.04 Secondary Outflow To System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ***********Compliance Point Results Scenario Predeveloped Compliance Subbasin: Predev Scenario Postdeveloped Compliance Link: New Copy Lnk2 Point of Compliance Flow Frequency Data Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) 2-Year 2.131E-02 2-Year 1.375E-05 5-Year 3.473E-02 5-Year 2.530E-05 10-Year 4.680E-02 10-Year 3.748E-05 25-Year 5.933E-02 25-Year 5.109E-05 50-Year 7.572E-02 50-Year 5.693E-05 100-Year 8.205E-02 100-Year 2.083E-02 200-Year 0.128 200-Year 0.187 Record too Short to Compute Peak Discharge for These Recurrence Intervals Flow Duration Performance Excursion at Predeveloped 50%Q2 (Must be Less Than -100.0% PASS Maximum Excursion from 50%Q2 to Q2 (Must be Less Than -99.9% PASS Maximum Excursion from Q2 to Q50 (Must be less than 10%): -40.6% PASS Percent Excursion from Q2 to Q50 (Must be less than 50%): 0.0% PASS MEETS ALL FLOW DURATION DESIGN CRITERIA: PASS LID Duration Performance Excursion at Predeveloped 8%Q2 (Must be Less Than -100.0% PASS Maximum Excursion from 8%Q2 to 50%Q2 (Must be Less Than -100.0% PASS MEETS ALL LID DURATION DESIGN CRITERIA: PASS ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 25 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 26 South Basin MGS FLOOD PROJECT REPORT Program Version: 4.38 Program License Number: 200210008 Project Simulation Performed on: 05/01/2017 5:36 PM Report Generation Date: 05/01/2017 5:38 PM Input File Name: Redmond Cottages - South Infiltration Vault.fld Project Name: Redmond Cottages - South Infiltration Vault Analysis Title: Comments: PRECIPITATION INPUT Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Climatic Region Number: 13 Full Period of Record Available used for Routing Precipitation Station : 96004005 Puget East 40 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961040 Puget East 40 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : USGS Default Default HSPF Parameters Used (Not Modified by User) WATERSHED DEFINITION Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 2.750 2.750 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 2.750 2.750 PREDEVELOPED Number of Subbasins: 1 Subbasin : Predev -------Area(Acres) Till Forest 2.750 Till Pasture 0.000 Till Grass 0.000 Outwash Forest 0.000 Outwash Pasture 0.000 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 27 Outwash Grass 0.000 Wetland 0.000 Green Roof 0.000 User 2 0.000 Impervious 0.000 Subbasin Total 2.750 POSTDEVELOPED Number of Subbasins: 1 Subbasin : South Basin -------Area(Acres) Till Forest 0.000 Till Pasture 0.000 Till Grass 1.110 Outwash Forest 0.000 Outwash Pasture 0.000 Outwash Grass 0.000 Wetland 0.000 Green Roof 0.000 User 2 0.000 Impervious 1.640 Subbasin Total 2.750 LINK DATA PREDEVELOPED Number of Links: 0 LINK DATA POSTDEVELOPED Number of Links: 2 Link Name: South Vault Link Type: Structure Link Name: New Copy Lnk2 Prismatic Pond Option Used Pond Floor Elevation (ft) : 249.00 Riser Crest Elevation (ft) : 259.00 Max Pond Elevation (ft) : 260.00 Storage Depth (ft) : 10.00 Pond Bottom Length (ft) : 68.0 Pond Bottom Width (ft) : 25.0 Pond Side Slopes (ft/ft) : L1= 0.00 L2= 0.00 W1= 0.00 W2= 0.00 Bottom Area (sq-ft) : 1700. Area at Riser Crest El (sq-ft) : 1,700. ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 28 (acres) : 0.039 Volume at Riser Crest (cu-ft) : 17,000. (ac-ft) : 0.390 Area at Max Elevation (sq-ft) : 1700. (acres) : 0.039 Vol at Max Elevation (cu-ft) : 19,040. (ac-ft) : 0.437 Constant Infiltration Option Used Infiltration Rate (in/hr): 3.00 Riser Geometry Riser Structure Type : Circular Riser Diameter (in) : 18.00 Common Length (ft) : 0.000 Riser Crest Elevation : 259.00 ft Hydraulic Structure Geometry Number of Devices: 0 Link Name: New Copy Lnk2 Link Type: Copy Link: None FREQUENCY AND DURATION PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 POSTDEVELOPED Number of Subbasins: 1 Number of Links: 2 Subbasin: South Basin Flood Frequency Data(cfs) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) Flood Peak (cfs) 2-Year 0.709 5-Year 0.908 10-Year 1.139 25-Year 1.526 50-Year 1.841 100-Year 2.285 200-Year 2.301 Link: South Vault Link Inflow Frequency Stats ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 29 Flood Frequency Data(cfs) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) Flood Peak (cfs) 2-Year 0.709 5-Year 0.908 10-Year 1.139 25-Year 1.526 50-Year 1.841 100-Year 2.285 200-Year 2.301 Link: South Vault Link Outflow 1 Frequency Stats Flood Frequency Data(cfs) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) Flood Peak (cfs) 2-Year 2.431E-05 5-Year 4.422E-05 10-Year 6.383E-05 25-Year 8.828E-05 50-Year 1.179E-02 100-Year 0.209 200-Year 0.584 Link: South Vault Link WSEL Stats WSEL Frequency Data(ft) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) WSEL Peak (ft) 1.05-Year 249.971 1.11-Year 250.316 1.25-Year 250.636 2.00-Year 251.434 3.33-Year 252.502 5-Year 253.419 10-Year 255.381 25-Year 257.817 50-Year 258.729 100-Year 259.054 Link: New Copy Lnk2 Link Inflow Frequency Stats Flood Frequency Data(cfs) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) Flood Peak (cfs) 2-Year 2.431E-05 5-Year 4.422E-05 10-Year 6.383E-05 25-Year 8.828E-05 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 30 50-Year 1.179E-02 100-Year 0.209 200-Year 0.584 ***********Groundwater Recharge Summary Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) Subbasin: Predev 474.180 Total: 474.180 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) Subbasin: South Basin 135.654 Link: South Vault 958.515 Link: New Copy Lnk2 0.000 Total: 1094.169 Total Predevelopment Recharge is Less than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 3.001 ac-ft/year, Post Developed: 6.925 ac-ft/year Quality Facility Data PREDEVELOPED Number of Links: 0 POSTDEVELOPED Number of Links: 2 Link: South Vault Basic Wet Pond Volume (91% Exceedance): 8462. cu-ft Computed Large Wet Pond Volume, 1.5*Basic Volume: 12693. cu-ft Time to Infiltrate 91% Treatment Volume, (Hours): 20.01 Infiltration/Filtration Inflow Volume (ac-ft): 958.52 Inflow Volume Including PPT-Evap (ac-ft): 958.52 Total Runoff Infiltrated (ac-ft): 958.52, 100.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To System (ac-ft): 0.15 Secondary Outflow To System (ac-ft): 0.00 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 31 Percent Treated (Infiltrated+Filtered)/Total Volume: 100.00% Link: New Copy Lnk2 Infiltration/Filtration Inflow Volume (ac-ft): 0.15 Inflow Volume Including PPT-Evap (ac-ft): 0.15 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To System (ac-ft): 0.15 Secondary Outflow To System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ***********Compliance Point Results Scenario Predeveloped Compliance Subbasin: Predev Scenario Postdeveloped Compliance Link: New Copy Lnk2 Point of Compliance Flow Frequency Data Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) 2-Year 5.860E-02 2-Year 2.431E-05 5-Year 9.551E-02 5-Year 4.422E-05 10-Year 0.129 10-Year 6.383E-05 25-Year 0.163 25-Year 8.828E-05 50-Year 0.208 50-Year 1.179E-02 100-Year 0.226 100-Year 0.209 200-Year 0.351 200-Year 0.584 Record too Short to Compute Peak Discharge for These Recurrence Intervals Flow Duration Performance Excursion at Predeveloped 50%Q2 (Must be Less Than -99.9% PASS Maximum Excursion from 50%Q2 to Q2 (Must be Less Than -99.7% PASS Maximum Excursion from Q2 to Q50 (Must be less than 10%): -0.9% PASS Percent Excursion from Q2 to Q50 (Must be less than 50%): 0.0% PASS MEETS ALL FLOW DURATION DESIGN CRITERIA: PASS LID Duration Performance Excursion at Predeveloped 8%Q2 (Must be Less Than -100.0% PASS Maximum Excursion from 8%Q2 to 50%Q2 (Must be Less Than -99.9% PASS MEETS ALL LID DURATION DESIGN CRITERIA: PASS ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 32 ---PAGE BREAK--- Core Design, Inc. Rosehill Cottages Page 33 Appendix B – Geotechnical Engineering Report ---PAGE BREAK--- Hydrogeologic and Supplemental Geotechnical Engineering Report ROSE HILL COTTAGES Redmond, Washington Prepared for Wilmoor Development Corporation Project No. KE110304B February 27, 2015 ---PAGE BREAK--- ---PAGE BREAK--- HYDROGEOLOGIC AND SUPPLEMENTAL GEOTECHNICAL ENGINEERING REPORT ROSE HILL COTTAGES Redmond, Washington Prepared for: Wilmoor Development Corporation 16981 Redmond Way Redmond, Washington 98052 Prepared by: Associated Earth Sciences, Inc. 911 5th Avenue Kirkland, Washington 98033 [PHONE REDACTED] Fax: [PHONE REDACTED] Project No. KE110304B February 27, 2015 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions I. PROJECT AND SITE CONDITIONS 1.0 INTRODUCTION This report presents the results of our hydrogeologic study and supplemental geotechnical study for the subject site. The location of the site is shown on the “Vicinity Map,” Figure 1. The approximate locations of the explorations completed to date for this project are presented on the “Site and Exploration Plan” Figure 2. The proposed development is presented on the “Site Development Plan,” Figure 3. Logs of the subsurface explorations, laboratory testing data, hydrogeologic analyses and slope stability analyses are included in Appendices A through D. The conclusions and recommendations contained in this report should be reviewed and modified, or verified, as the project moves forward. 1.1 Purpose and Scope The purpose of this study was to evaluate storm water infiltration feasibility, develop infiltration rates for vault design and analyze the impacts of storm water infiltration on slope stability. Associated Earth Sciences, Inc. (AESI) completed previous reports for the site titled “Subsurface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report” dated January 23, 2007 for the site and “Critical Areas Report” dated October 12, 2011 for an off-site sewer to the east associated with the planned development. Our current study included a review of geologic literature, previous explorations completed by AESI, additional deep subsurface explorations, infiltration testing, laboratory testing, ground water mounding analysis and slope stability analysis. Verification of geologic conditions and deeper than previously conducted explorations were required in order to determine the depth to the water table, thickness of unsaturated soils, and vertical extent of the infiltration receptor unit. 1.2 Authorization Written authorization to proceed with the geotechnical/hydrogeological aspects of this report was granted by Mr. Greg Wilson, in general accordance with our proposal letter dated July 16, 2014. This report has been prepared for the exclusive use of Wilmoor Development Corporation and their agents for specific application to this project. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering/hydrogeologic practices in effect in this area at the time our report was prepared. No other warranty, express or implied, is made. February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 1 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions 2.0 PROJECT AND SITE DESCRIPTION The property consists of an undeveloped, forested parcel (King County Parcel No. [PHONE REDACTED]) of approximately 11 acres located east of the intersection of NE 112th Place and 132nd Avenue NE in Redmond, Washington in the northwest quarter of Section 34, Township 26 North, Range 5 East, W.M. There are northern, central, and southern ravines that trend in an east-west direction across the property that contain slopes inclined at greater than 40 percent. Presently, the project area is predominantly comprised of undeveloped vegetated land. It is our understanding that the site development will include subdivision of the property into 24 residential lots, construction of single-family residential homes, construction of eight garage buildings, driveway, rockeries, retaining walls, and landscape areas. The development will essentially follow the relatively level portion of the site at the crest of the northern, central, and southern ravines. Infiltration vaults are planned on the northern and southern sides of the site. Site grading will involve cuts and fills to create building pads for planned residential buildings. Cut rockery walls up to 8 feet, reinforced fill rockeries up to 11 feet, and segmental block retaining walls up to 8 feet are planned. Excavations will be required for the proposed underground infiltration vaults up to 10 feet deep. 3.0 SUBSURFACE EXPLORATION AESI previously conducted subsurface exploration of the project site in December 2006 for a geologic hazard and geotechnical engineering study. The results of the study were presented in our “Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report” dated January 23, 2007. Our understanding of the project at the time was that the site would be developed for residential properties. Currently, we are assessing infiltration feasibility and slope stability in the project site in order to provide infiltration facility design recommendations as requested by Wilmoor Development. AESI observed subsurface exploration and monitoring well construction at the site September 29, 2014 through December 29, 2014. This work supplements previous relatively shallow exploration pits excavated at the site on December 19, 2006. Our current field study included drilling two deep exploration borings that were completed as monitoring wells (MW-1 and MW-2). These were completed in order to gain subsurface soil and ground water information for hydrogeologic and geotechnical engineering purposes. The exploration locations were selected within the vicinity of the northern and southern proposed vault systems and were estimated based on measurements from surface control points. AESI also observed excavation and construction of two pit drains (PD-1 and PD-2) as well as excavation of an exploration pit (EP-9). PD-1 and EP-9 are located in the vicinity of the proposed southern vaults on the eastern and westernmost end of the vault footprint, respectively. PD-2 is located in the vicinity of the February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 2 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions proposed northern vault. The approximate locations of MW-1, MW-2, PD-1, PD-2, and EP-9 are shown on the “Site and Exploration Plan” (Figure The various types of sediments, as well as the depths where characteristics of the sediments changed, are indicated on the exploration logs included in Appendix A. The depths indicated on the logs where conditions changed may represent gradational variations between sediment types in the field. The number, locations, and depths of the explorations were completed within site and budgetary constraints. Because of the nature of exploratory work below ground, extrapolation of subsurface conditions may sometimes be present due to the random nature of deposition and the alteration of topography by past grading and/or filling. The nature and extent of any variations between the field explorations may not become fully evident until construction. If variations are observed at that time, it may be necessary to re-evaluate specific recommendations in this report and make appropriate changes. 3.1 Exploratory Borings and Monitoring Wells AESI observed subsurface exploration and well installation at the site September 29 through October 1, 2014. This work supplements earlier explorations conducted in December 2006. Our current field study included advancing hollow-stem auger tools with a tracked-mounted drill rig (Volvo E95) provided by Boretec 1, Inc. (Boretec) under subcontract to AESI. Hollow-stem auger drilling produced disturbed but representative samples obtained using the Standard Penetration Test (SPT) procedure in accordance with American Society for Testing and Materials (ASTM): D 1586. This test and sampling method consists of driving a standard, 2-inch outside-diameter, split-barrel sampler a distance of 18 inches into the soil with a 140-pound hammer free-falling a distance of 30 inches. The number of blows for each 6-inch interval is recorded, and the number of blows required to drive the sampler the final 12 inches is known as the Standard Penetration Resistance or blow count. If a total of 50 is recorded within one 6-inch interval, the blow count is recorded as the number of blows for the corresponding number of inches of penetration. The resistance, or N-value, provides a measure of the relative density of granular soils or the relative consistency of cohesive soils; these values are plotted on the exploration boring logs included in Appendix A. Borings were continuously observed and logged by a representative from our firm. The samples were transported to AESI’s laboratory for further classification and laboratory testing, as necessary. On-site exploration pits previously completed by AESI are also attached to this report. The depths indicated on the logs where conditions changed may represent gradational variations between sediment types in the field. The exploration logs attached to this report are based on field logs, drilling action, and inspection of the samples secured. The borings were completed as monitoring wells (MW-1 and MW-2) to gain subsurface soil and ground water information. MW-1 was completed within the vicinity of the proposed northern vault while MW-2 was completed in the vicinity of the February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 3 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions proposed southern vault. The monitoring wells were completed with 2-inch-diameter, 10-foot-long schedule 40 polyvinyl chloride (PVC) well screen, 2-inch-diameter solid PVC casing, an 8-inch-diameter surface seal, and flush-mount well monuments. The exploration locations were estimated based on measurements from surface control points. The approximate locations of the exploration locations are shown on the “Site and Exploration Plan” (Figure 3.2 Exploration Pits Subsurface exploration completed for this phase of work included the advancement of three exploration pits, two of which were completed as pit drains PD-1 and PD-2 (Figure 2) on November 12 and December 29, 2014, respectively. Previous subsurface exploration by AESI at the site included eight exploration pits (EP-1 through EP-8) and a recent exploration pit designated EP-9. The exploration pits were excavated with a trackhoe under subcontract to AESI. The pits permitted direct, visual observation of subsurface conditions. Materials encountered in the exploration pits were studied and classified in the field by an engineering geologist from our firm. The exploration pits were backfilled immediately after examination and logging. 3.3 Infiltration Testing and Pit Drain Construction Pit drain testing was completed at the locations noted on Figure 2 as PD-1 and PD-2. The infiltration tests were conducted by introducing water into the pea gravel-filled pit drain (Figure Pit drains PD-1 and PD-2 were excavated bucket width (approximately 2.5 feet) and extended to 18 feet and 19.25 feet below ground surface (bgs), respectively. Two-inch-diameter Schedule-40 PVC pipe (for use as a piezometer) was installed into each pit. The piezometer extended to the bottom of the exploration pit and was machine-slotted on the bottom 6 feet of PD-1 and 5 feet of PD-2. PD-1 and PD-2 were backfilled with clean pea gravel to a depth of 2 feet and 4.25 feet bgs, respectively. A 2-inch-diameter elbowed PVC pipe with the bottom 4-feet machine-slotted, was installed into the upper few feet of the pea gravel. This pipe was used to introduce water into the constructed drain for infiltration testing. A separation filter fabric was placed over the top of the pea gravel backfill, then the remaining 2 and 4.25 feet (PD-1 and PD-2, respectively) was backfilled with native material. Infiltration testing is discussed in more detail later in this report. Materials encountered during the excavation of the two pit drains were studied and classified in the field by geologists from AESI. Selected samples were then transported to AESI’s laboratory for further visual classification. The types of sediments, as well as the depths where characteristics of the sediments changed, are indicated on the exploration logs presented in Appendix A. February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 4 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions 3.4 Stream and Slope Reconnaissance Stream and slope reconnaissance was completed in the three ravines (Labeled as 1, 2, and 3 on Figure 2) within or near the project area boundary. Geologists from AESI accessed the ravines via the pedestrian walkway/gasline road and walked upgradient along the valley bottom. The channel morphology and slope conditions were observed, noted, and mapped. The locations of our observations as well as a topographic profile along the creek bed for Transect 1 is presented in Figure 5. Locations were determined using a hip chain to record distance walked and a Light Detection and Ranging (LiDAR) map. Transect 1 (Figure 5) extended from Station 1 upslope to Station 17 and covered a distance of approximately 1,200 feet. The average gradient of the channel was about 11 percent with a total elevation change of about 140 feet. Channel widths varied from less than 1 foot to about 5 feet. Water was observed flowing into a culvert at Station 1. The stream width was about 16 inches and depth was approximately 18 inches. At Station 2 water was still present but no apparent flow was observed. The approximate elevation of the observed spring zone at Station 4 was 210 feet above mean sea level (amsl) and it is interpreted to represent base flow formed by discharge from the Vashon Advance Aquifer (see Section 5.1 for details). The channel was dry and incised approximately 100 feet upstream at Station 5 and was defined by vertical slopes approximately 6 feet high. The slopes consisted of fine to medium sand and stream width was about 18 to 24 inches. At Station 6 a knick-point approximately 4 feet high was encountered. The knick-point consisted of dense, unsorted, silty fine sand with trace gravel overlying oxidized orange-brown sand and was interpreted to represent advance outwash. A confluence of two tributaries was encountered at Station 15 and reconnaissance continued along the northern tributary. At Station 17 a 6-foot-high knick-point was encountered consisting of Vashon glacial till overlying advance outwash. The knick-point was heavily covered by debris such as downed small trees and broken fencing from nearby residential homes. The reconnaissance was completed at 132nd Avenue. Reconnaissance of Transects 2 and 3 provided no significant geologic unit observations due to a lack of subsurface exposures, defined channels, or spring zones. 4.0 SUBSURFACE CONDITIONS Subsurface conditions at the project site were inferred from AESI’s subsurface exploration accomplished for this study and previous study; our visual reconnaissance of the site; and review of selected geologic literature. As shown on the exploration logs, the explorations completed for this study generally encountered a layer of topsoil/forest duff overlying native glacial sediments interpreted as Vashon lodgement till and advance outwash which overly pre-Fraser fine-grained sediments in the areas explored. Fill was also encountered in EP-1 with February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 5 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions a thickness of approximately 4 feet. The following section presents more detailed subsurface information organized from the shallowest (youngest) to the deepest (oldest) sediment types. The on-site native sediments are mapped as Vashon age lodgement till and Vashon advance outwash on the U.S. Geological Survey (USGS) Miscellaneous Field Studies Map MF-1543, scale 1:24,000, titled Geologic Map of the Kirkland Quadrangle, Washington – 1983 by J.P. Minard. Quaternary alluvium sediments are also mapped in close proximity to the site. 4.1 Stratigraphy Topsoil/Forest Duff A surficial layer of grass and organic topsoil was encountered at the locations of the explorations completed for this study. Due to the high organic content and varied fines, these materials are not considered suitable for storm water infiltration. Fill Fill soils (those not naturally placed) ranging from sandy silt to silty sand with varying amounts of gravel and organic content were encountered in exploration EP-1. The depth of existing fill at this location was near ground surface (below the forest duff and topsoil) to 4 feet below the surface in EP-1. The fines content of fill can be highly variable and where containing relatively high fines would be considered moisture-sensitive. The existing fill should not be used for infiltration of site storm water. Vashon Lodgement Till (Qvt) Each of the exploration pits except EP-1 and EP-9 encountered native sediments consisting of medium dense grading to very dense silty sand containing some gravel near the surface (below the forest duff and topsoil) to the top of the underlying advance outwash deposit at a depth of approximately 9 feet below the surface in EP-2, approximately 12 feet in EP-5, approximately 5 feet in EP-6, EP-7, and EP-8, and approximately 2.5 feet in PD-2. The lodgement till was also encountered in EP-3 and EP-4 to the full 12- to 14-foot depths of the pits. Lodgement till was deposited at the base of an active continental glacier and was compacted by the weight of the overlying glacial ice. Lodgement till is not suitable for use as a storm water infiltration receptor due to its high density and high silt content. Vashon Advance Outwash (Qva) Exploration pits EP-2, EP-5, EP-6, EP-7, EP-8, EP-9, pit drains PD-1 and PD-2, and monitoring wells MW-1 and MW-2 encountered very dense sand with variable gravel and silt fractions February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 6 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions below the lodgement till interpreted to represent advance outwash. The advance outwash encountered in all of the exploration pits extended to the full 14-foot depths and the full 17-foot depth in EP-9. Advance outwash was also observed extending to the full 18-foot depth in PD-1 and from 2.5 feet to 19.25 feet bgs in PD-2. In MW-1 and MW-2 the outwash was encountered near the surface to depths of 102.5 feet and 67.5 feet bgs, respectively. Advance outwash was deposited by meltwater streams emanating from an advancing continental ice sheet, and was subsequently glacially overridden and compacted. Unsaturated advance outwash is suitable for use as a storm water infiltration receptor under most circumstances and with proper characterization of the receptor and proper infiltration system design. Olympia Non-Glacial Fine-Grain Deposits Olympia non-glacial fine-grained deposits were encountered in monitoring wells MW-1 and MW-2 beneath advance outwash deposits. The non-glacial material consisted of gray silt with varying amounts of fine sand. The sediments collected from MW-1 and MW-2 borings contained scattered and bedded organic fragments beginning at approximately 102.5 and 67.5 feet bgs. A color change from brownish gray to gray, increased percentage of silt, and the occurrence of organic fragments indicated a contact between Vashon advance outwash and Olympia non-glacial sediments at a depth of about 102.5 and 67.5 feet bgs. The organics were sent to Beta Analytic to perform radiocarbon age-dating. Testing results indicated the organics were between 39,100 and 40,600 years old, confirming the Olympic non- glacial age date. Review of Selected Available Geologic Data We reviewed selected available data related to site geology and hydrogeology. We reviewed J.P. Minard, 1983, Geologic Map of Kirkland Quadrangle, Washington: USGS, Miscellaneous Field Studies Map MF-1543, scale 1:24,000. This published map indicates that the site is expected to be underlain by advance outwash sediments and Vashon lodgement till. As represented on the schematic hydrogeologic Cross-Section A-A’ (Figure 6) Vashon advance outwash and Olympia non-glacial sediments are present along the slope outside of the project site. At an elevation of about 130 feet, older alluvium approximately 30 feet thick is present along the slope and is overlain in the valley by younger alluvium. 4.2 Laboratory Analysis We selected samples from MW-1, MW-2, PD-1, PD-2, and EP-9 for mechanical grain-size analysis testing on a dry weight basis in accordance with ASTM: D 422-63. Grain-size data is summarized in Table 1. The laboratory data sheets are included in Appendix B. In addition, two samples were selected from MW-1 for direct shear testing. February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 7 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions ASTM Gradation Testing The laboratory analysis indicated that the receptor sediments at the depth tested would primarily be classified as silty sand to sand with some fines. The fine content ranged from 2.9 to 17.4 percent fines (material passing the No. 200 sieve) in the samples tested. USDA Soil Textural Classification We applied the U.S. Department of Agriculture (USDA) Soil Textural Classification method to the normalized grain size distributions for our selected soil samples. The grain size distributions were normalized to the No. 10 sieve—i.e., the coarse sand and gravel fraction of the sample is discounted and the remainder is taken as 100 percent of the sample. Based on the USDA Textural Triangle, the site soils tested would be classified as sand, except for MW-1 at 60 feet and MW-2 at 30 feet which are classified as sand to loamy sand deposits. Table 1 Summary of Grain Size Analyses MW Nos. and Depth in Feet Sieve Results – ASTM Percent Passing Primary USCS Soil Classification No. 4 No. 40 No. 200 D10 (mm) MW-1 at 40’+42.5’ 100.0 52.9 8.4 0.093 Medium SAND MW-1 at 57.5’+60’ 100.0 99.6 15.9 0.042 Fine SAND MW-1 at 65’+70’+72.5’ 100.0 98.7 10.4 0.068 Fine SAND MW-2 at 20’ 100.0 97.7 10.3 0.068 Fine SAND MW-2 at 30’+32.5’ 100.0 98.9 17.4 0.031 Fine SAND MW-2 at 47.5’+50’ 99.4 29.5 7.8 0.110 Medium SAND PD-1 at 7’ 90.2 46.2 16.2 0.000 Medium SAND PD-1 at 17.5’ 100.0 21.4 2.9 0.263 Medium SAND PD-2 at 13.5’ 99.8 62.3 3.7 0.156 Fine SAND PD-2 at 19’ 100.0 83.5 6.1 0.031 Fine SAND EP-9 at 16.5’ 100.0 90.6 3.5 0.161 Fine SAND Pea Gravel Backfill 18.8 1.2 0.9 3.274 Fine GRAVEL MW – Monitoring Well ASTM – American Society for Testing and Materials USCS – Unified Soil Classification System Direct Shear Testing Two samples were selected from MW-1 for direct shear testing to determine angle of friction and cohesion values for use in slope stability analysis. Samples collected using the SPT method were remolded in our laboratory and subjected to a range of normal loads using our standard February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 8 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions direct shear apparatus in accordance with ASTM:D 3080 in order to develop soil strength relationships for sandy and silty soils observed within the advance outwash. Graphical plots of the direct shear results for the samples tested are presented in Appendix B. A summary of the results is shown in Table 2 below. Table 2 Summary of Direct Shear Testing MW Nos. and Sample Depth in Feet Friction Angle (degrees) Cohesion (psf) Soil Type MW-1 at 32.5’ 27 950 Sandy SILT MW-1 at 45’ 35 650 Fine SAND psf = pounds per square foot 5.0 GROUND WATER CONDITIONS Monitoring wells MW-1 and MW-2 were completed on the north and south side of the ravine that bisects the site. MW-1 is located near the proposed location of the northern vault at the end of the cleared access way and MW-2 is located approximately 350 feet east along a gravel road at the approximate location of the southern vaults. Ground water was encountered in MW-1 at the time of drilling on September 30, 2014 at approximately 95 feet bgs. The well was allowed to equilibrate overnight after well completion on September 30, and ground water was measured on October 1, 2014 in MW-1 at 93.4 feet bgs. Ground water was encountered in MW-2 at the time of drilling on October 1, 2014 at approximately 55 feet bgs. The well was measured at the end of well construction at 54.1 feet bgs. Ground water was measured again after well development at approximately 93.4 feet bgs in MW-1 and at 54.2 feet bgs in MW-2 on October 6, 2014. The ground surface elevation at the well locations has not been surveyed. The approximate land surface elevations based on the provided site plan are approximately 303 feet amsl at MW-1 and 262 feet amsl at MW-2. The estimated elevation of the ground water in MW-1 was about 210 feet amsl and about 207 feet amsl in MW-2 on October 6, 2014. 5.1 Deep Regional Ground Water (Vashon Advance Aquifer) A regional, unconfined aquifer system is formed in the basal portion of the Vashon advance outwash deposits that underlie the project area. The aquifer is informally termed the Vashon Advance Aquifer in this report. The aquifer is present beneath the entire project area. The base of the aquifer is underlain by older Olympia non-glacial sandy silt deposits encountered in February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 9 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions on-site explorations MW-1 and MW-2, as illustrated on the hydrogeologic cross-sections (Figures 5 through In the vicinity of the project, the Vashon Advance Aquifer receives recharge from dispersed, downward infiltration through lodgement till. As previously mentioned, the Vashon advance outwash was encountered in EP-2, EP-5, EP-6, EP-7, EP-8, EP-9, PD-1, PD-2, MW-1, and MW-2. The exploration pits were terminated within the advance outwash at approximately 14 feet. MW-1 and MW-2 encountered the top of the clean Vashon advance outwash at approximately 37.5 feet and near ground surface, and penetrated the underlying contact with pre-Fraser sediments at 102.5 feet and 67.5 feet. The Vashon Advance Aquifer was encountered about 94 feet bgs and was approximately 9 feet thick in MW-1. The Vashon Advance Aquifer was encountered about 54 feet bgs and was approximately 13.5 feet thick in MW-2. Based on ground water elevations estimated from MW-1 and MW-2, off-site well data, and spring elevations in the ravine south of the property, ground water is interpreted to flow east. The ground water was observed during site reconnaissance discharging at a spring zone near elevation 210 feet amsl at the base of the southern ravine (Station 4) on October 7, 2014. 5.2 Ground Water Level Monitoring After the wells were constructed, AESI was on-site on October 6, 2014 to develop the two wells. At this time the initial depths to ground water were recorded. For seasonal high water table monitoring, we installed pressure transducers connected to automatic data loggers in the wells. The data loggers will record hourly water levels, and will be left in place for a period of 6 months. Hand measurements of the water levels in the wells are collected once every other month in conjunction with downloading of water level data recorded by the data logger. The data is downloaded, entered into a spreadsheet, and compensated for barometric pressure effects, and calibrated with the manual water level meter measurements. Figure 7 is a hydrograph from September 30, 2014 to February 26, 2015. The data shown indicates MW-1 has increased from initial measurements by about 0.2 feet and MW-2 has increased by about 0.5 feet. 6.0 FIELD INFILTRATION TESTING METHODS AND RESULTS Two infiltration pit drain tests were completed in the pea gravel-filled pit drains, installed as described above. The two tests were performed on November 20, 2014 and December 30, 2014 (PD-1 and PD-2, respectively). Data loggers were installed in the pit drain piezometers and were used to record water levels at 5-second intervals. During the test, depth to water, flow rate, and total flow were also manually recorded at approximately 15-minute intervals. February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 10 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions Water was introduced at a constant rate to bring the water up to the proposed vault bottom elevation outlined in CORE Design, Inc.’s (CORE) previous design plan (10 feet bgs for the northern vault and 250.88 feet elevation for the southern vaults). Once the water reached the proposed vault bottom the flow rate was decreased in order to stabilize the water level. The flow rate remained relatively constant for the final approximately 3 and 6 hours (PD-1 and PD-2, respectively) into the inlet pipe of the pit drain via an electronic flow meter with instantaneous flow rate and total flow volume readouts. The meter was connected to a water truck to provide a relatively constant flow for the duration of the test. The water level (head) that developed within each pit drain was allowed to gradually rise over the course of the test at a constant flow rate. During the testing, the water level rose 12.5 feet and 13.5 feet within PD-1 and PD-2, respectively. These water levels corresponded to about 0.5 feet and 4.3 feet of water within the proposed vaults for PD-1 and PD-2, respectively. Water was introduced continuously into the pit for approximately 3.5 hours (PD-1) and 8 hours (PD-2). After water was turned off, the level of water was monitored in the pit drain piezometer for at least 1 hour as it dropped. The average flow rate of water introduced into PD-1 for the final 1.8 hours of the inflow phase of the test was around 14 gallons per minute (gpm). For the final 4.6 hours of the inflow phase of the test was around 6.5 gpm in PD-2. Results of inflow testing indicate an infiltration rate of approximately 3 and 2 inches per hour (in/hr) for PD-1 (South Vault vicinity) and PD-2 (North Vault vicinity), respectively. Hydraulic conductivity is the measure of the resistance to movement of water flowing through a porous media. 7.0 GROUND WATER MOUNDING ANALYSIS Ground water mounding analyses for the two proposed infiltration facilities were completed to simulate the maximum ground water mound height and compare it to the design high water elevation in the proposed infiltration vaults. Ground water mounding can occur when water is introduced into an infiltration facility at a higher rate than can be conveyed from the area beneath the facility. The introduced water can “mound” on the ground water table or on a less-permeable silty interbed within the receptor sands and gravels during a storm event. When the storm event is over and water is not being introduced into the system, the mound will normally dissipate. The mounding analysis is used to simulate the maximum ground water mound beneath the facility during a design storm series. Figures 8 and 9 illustrate the maximum mound height within the vaults and the maximum height at the slope face as a conservative estimate. The MODRET computer program was used to model potential ground water mounding beneath the infiltration facility under two design time series provided by CORE. The MODRET program February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 11 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions utilizes the Greene Ampt method for unsaturated conditions and the USGS MODFLOW model for saturated conditions. For each facility, CORE provided two storm water hydrographs, one from a period which includes the highest flow rate (peak flow) and one from a period of maximum volume, derived from the King County Runoff Time Series In CORE’s analysis, the period of the peak flow hydrograph is December 24, 2007 to January 24, 2008, with the peak flow occurring on January 9, 2008. The 30-day date range with the maximum volume was February 12, 2003 through March 13, 2003. CORE also provided vault elevation and volume parameters in letters dated February 4, 2015 (North Vault), and January 16, 2015 (South Vaults), which are included in Appendix C. The soil and ground water input parameters used in the MODRET evaluation were consistent with field/laboratory data and applicable published hydrogeologic literature. The model input parameters are included in the “Summary of Unsaturated and Saturated Input Parameters” (Appendix C) and an explanation of the basis for all parameters used is included in Table 3. February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 12 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions Table 3 Basis for MODRET Input Parameters CORE = CORE Design, Inc., the project civil engineer/hydrologist. AESI = Associated Earth Sciences, Inc. DHWL = design high water level. ft2 = square feet. ft3 = cubic feet. ft = feet. ft/day = feet per day. Kvs = Saturated vertical hydraulic conductivity. The effective aquifer base in the model was determined from monitoring wells installed on the site. Monitoring well MW-1 was completed near the footprint of the proposed North Vault, and encountered an interval of silty interbeds within the Vashon advance outwash unit between about 29.5 and 37.5 feet bgs (approximately 273.5 and 265.5 feet amsl). Monitoring well MW-2 was installed adjacent to the proposed footprint of South Vault 2, and encountered Olympia non-glacial fine-grained deposits at a depth of 67.5 feet, which is equivalent to an elevation of approximately 195 feet amsl. Model input values for effective aquifer base of Parameter North Vault South Vault 2 Basis Pond Bottom Area (ft2) 1,360.0 336.0 CORE. Pond Volume Between Bottom and DHWL (ft3) 8,174.0 3,242.4 CORE. Pond Length to Width Ratio 1.2 2.3 CORE. Elevation of Effective Aquifer Base 273.5 195.0 AESI/MODRET – subsurface data (see text). Elevation of Seasonal High Ground Water Table (ft) 274.5 211.0 AESI – South Vault - based on monitoring, North Vault, no water present on silt interbeds, assumed 1-foot (see text). Elevation of Starting Water Level (ft) 286.5 251.38 Facility bottom elevation (CORE). Elevation of Pond Bottom (ft) 286.5 251.38 CORE. Design High Water Elevation (ft) 292.51 261.03 CORE. Storage Coefficient of Soil for Unsaturated Analysis 0.20 0.20 AESI - Within range of published values for the soil types present. Unsaturated Vertical Hydraulic Conductivity (Kvu) (ft/day) 2.67 4.0 Kvs x 2/3. See text. Factor of Safety for Kvu 2 2 Standard value. Saturated Horizontal Hydraulic Conductivity (Khs) (ft/day) 12.0 18.0 3 x Kvs (see text). Storage Coefficient of Soil for Saturated Analysis 0.20 0.20 AESI - Within range of published values for the soil types present. Average Effective Storage Coefficient of Pond/Exfiltration Trench 1.00 1.00 CORE. Time Increment During Storm Event (hours) 24 24 Increments match hydrograph time steps. Time Increment After Storm Event (hours) 24 24 Increments match hydrograph time steps. Total Number of Increments After Storm Event 6 6 Program default. February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 13 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions 273.5 feet (North Vault) and 195 feet (South Vault) were used in the analyses. It should be noted that the aquifer base for the North Vault was set as the top of a silt interbed within the advance outwash encountered during our explorations. The MODRET model input value for seasonal high ground water table for the North Vault analysis was artificially set to 1 foot above the silt interbed zone, or 274.5 feet. The seasonal high ground water table in the South Vault analysis was derived from ground water level monitoring. Hydraulic conductivity values were selected based on the drain testing performed at each vault location (PD-1 at the South Vault and PD-2 at the North Vault). For the North Vault, an infiltration rate of 2 in/hr was derived. Two in/hr is equivalent to 4 feet per day (ft/day). This value is assumed to represent a saturated vertical hydraulic conductivity (Kvs). To derive the unsaturated vertical hydraulic conductivity (Kvu), Kvs is multiplied by 2/3 (Andreyev & Wiseman, 1989), resulting in a Kvu value of 2.67 ft/day. In accordance with the King County MODRET Submittal Guide (King County Land Use Inspection Section, 2007) the saturated horizontal hydraulic conductivity (Khs) is derived by multiplying Kvs by 3, for horizontally stratified soils, resulting in a Khs value of 12 ft/day. For the South Vault, an infiltration rate of 3 in/hr was derived. Three in/hr is equivalent to 6 ft/day. Applying the above conventions to this value, we derived a Kvu value of 4 ft/day, and a Khs value of 18 ft/day for the South Vault. For the South Vault, CORE has designed the system to include two vaults, as shown in their “South Vault Mounding Analysis Parameters,” included in Appendix C. South Vault 1 has a bottom area of 1,200 square feet, and South Vault 2 has a bottom footprint area of 336 square feet. The two vaults are designed with the same bottom and design high water elevations, and are tied together with a level pipe. As a conservative measure, the ground water mounding analysis was performed using only one vault (South Vault 2) using the full inflow hydrographs. The MODRET simulation indicates that the infiltration facilities will have the capacity to infiltrate all of the storm water runoff routed to the facility during the design storm series provided by CORE for these analyses. In the ground water mounding simulation for the North Vault, the maximum mound height reached a height of approximately 12.6 feet amsl under the peak flow hydrograph. This occurs directly beneath the vault footprint at 432 hours after the beginning of the simulation. Under the maximum volume hydrograph, the maximum mound height was 12 feet above the silt layer and remained below the base of the proposed vault of 286.5 feet. The design high water elevation in the North Vault is 292.51 feet. February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 14 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Project and Site Conditions In the mounding analysis for the South Vault, the ground water mounding simulations under both the peak flow and maximum volume hydrographs indicated that the simulated maximum ground water mound height of less than 5 feet remained below the proposed vault bottom of 261.03 feet. The summaries of results from the MODRET analyses are included in Appendix C. The MODRET program was also used to predict how the ground water mounds propagated to the faces of the steep slopes. The proposed North Vault location is approximately 125 feet from the slope face to the southeast, at the elevation of the inferred, water table (approximately 274 feet amsl). At this distance, the MODRET model predicted a maximum rise in water height of about 1 foot based on the inflow hydrographs provided by CORE. The proposed footprint of South Vault No. 2 is approximately 125 feet from the 210-foot elevation contour on the steep slope to the south of the vault. At this distance, the MODRET model predicted a rise in water table height of less than 1 foot. February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 15 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Geologic Hazards II. GEOLOGIC HAZARDS 8.0 SLOPE STABILITY ASSESSMENT Our geologic research, site reconnaissance and site explorations indicate that the subject site is underlain by glacially consolidated till and outwash sediments. No emergent seepage was observed during our reconnaissance of the on-site slopes. No evidence indicative of historical landslide activity on the slopes was observed, such as scarps, tension cracks, or unusual topography. We analyzed the static and seismic stability of the slopes adjacent to the proposed infiltration vaults using the computer software program Slope/W Version 5.20 and the results of our ground water mounding analysis which indicated a maximum ground water table rise of 1 foot adjacent to the slope face. Soil parameters used for our stability analyses are summarized in Table 4. These parameters were derived based on the soils encountered in our borings, established correlations, direct shear testing and previous experience in similar soils in the Puget Sound area. We developed cross sections of the slopes using a topographic survey of the site developed by CORE Design. The effects of seismic accelerations on the slope during a potential earthquake were also evaluated using a pseudostatic lateral acceleration value of 0.22g. Our stability analysis incorporating the ground water rise of 1 foot indicates the slopes adjacent to both northern and southern vaults have safety factors greater than 1.5 for the static loading case and greater than 1.1 for the seismic loading case. A summary of our stability analysis results is presented in Table 5 and details are included in Appendix D. Table 4 Summary of Soil Parameters for Stability Analysis Soil Unit Friction Angle (degrees) Cohesion (psf) Unit Weight (pcf) Advance Outwash (silty sand/sandy silt) 27 500 130 Advance Outwash (silty sand) 35 400 130 psf = pounds per square foot pcf = pounds per cubic foot Table 5 Summary of Slope Stability Results Location Minimum Static Factor of Safety Minimum Seismic Factor of Safety Slope south of Northern Infiltration Vault 1.9 1.2 Slope south of Southern Infiltration Vault 1.8 1.2 February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 16 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Hydrogeologic Design Conclusions and Recommendations III. HYDROGEOLOGIC DESIGN CONCLUSIONS AND RECOMMENDATIONS Infiltration of treated stormwater into the shallow Vashon advance outwash sands within the footprint of the proposed vaults is feasible and recommended. Based on our infiltration testing and analyses we recommend infiltration rates of 2 and 3 in/hr for the North and South Vaults, respectively. Use of these infiltration rates is predicated on the installation of pit drains or trenches being completed in the bottoms of the vaults per the recommendations in this section. 9.0 INFILTRATION TRENCH RECOMMENDATIONS This study has demonstrated that infiltration trenches can enhance infiltration facility performance by penetrating low-permeability interbeds, resulting in a higher degree of connectivity with more permeable receptor horizons. We recommend that trenches (pit drains) be included as part of the infiltration system design. We recommend that infiltration trenches be excavated from the base of the constructed infiltration vault(s), to depths of 20 feet below the base of the vaults in both the North Vault (recommended bottom of pit drain/trench = 266 feet amsl) and the South Vault (recommended bottom of pit drain/trench = 231 feet amsl). The base of the infiltration vault within the proposed infiltration footprint must be excavated into the advance outwash. We recommend that pits be excavated with a tracked excavator after the vault subgrade elevation has been reached. Typical trench width would be bucket width (3 to 5 feet). The of the trenches would vary by vault. In the North Vault, we recommend two parallel trenches be constructed, approximately 20 feet in length each. In South Vault 1, we recommend a single, 50-foot-long trench be constructed down the center of the vault. In South Vault 2, we recommend that a single, 20-foot-long trench be constructed. A minimum 2-inch inside-diameter PVC piezometer should be installed into each trench, which includes 5 feet of machine slotted 2-inch PVC well screen and an end cap. Each pit drain should be backfilled with washed gravel which meets the sieve gradation in Table 6 or similar, as approved by AESI. A separation sand media a minimum of 12 inches thick should be placed on top of the gravel backfill, and filter sand a minimum of 6 inches thick should be placed above the separation sand. The filter sand should extend across the entire infiltration vault subgrade. All materials must be staged on-site prior to excavating the pit drains. Management of the stockpiles and transferring the gravel must include provisions for keeping the gravel clean and free of fines. AESI must be present for the construction of all pit drains. Contaminated gravel will be rejected. February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 17 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Hydrogeologic Design Conclusions and Recommendations Table 6 Pit Drain Backfill Sieve Size Percent Passing Gravel Backfill Separation Sand Filter Sand ½ inch 100 - - 3/8 inch 80-100 100 - US #4 5-15 95-100 95-100 US #8 0-10 0-5 70-100 US #16 - - 40-90 US #30 - - 25-75 US #50 - - 2-25 US #100 0-0.6 0-0.6 <2 US #200 (Wet Sieve) 0-0.5 0-0.3 <1 US #270 (Wet Sieve) 0-0.3 - - We recommend that an infiltration trench testing program be completed, which would include testing each trench in order to verify performance. For each infiltration trench, testing would include discharging water through AESI’s digital flow meter at known rates and recording the water levels with a digital water level meter in the piezometer. The flow rate should be sufficiently high to raise the level in the trench to within a few feet of the top of the trench. Testing duration should be a minimum of 5 hours of flow, followed by falling head measurements. February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 18 ---PAGE BREAK--- Rose Hill Cottages Hydrogeologic and Supplemental Geotechnical Engineering Report Redmond, Washington Supplemental Geotechnical Design Conclusions and Recommendations IV. SUPPLEMENTAL GEOTECHNICAL DESIGN CONCLUSIONS AND RECOMMENDATIONS Since our 2007 geotechnical report was issued, development plans for the site have progressed. The conclusions and recommendations presented in our 2007 report are still considered valid for the project; however, specific elements of the current project such as cut rockeries, reinforced fill rockeries, and segmental block walls were not included in our original report and will be addressed during final project design. In addition, the City of Redmond has adopted the 2012 International Building Code (IBC) for seismic design. Our 2007 report was completed when the 2003 IBC was being used. 10.0 SEISMIC DESIGN It is our opinion that any earthquake damage to the proposed structures, when founded on suitable bearing strata in accordance with the recommendations contained within our 2007 report, will be caused by the intensity and acceleration associated with a specific seismic event. Structural design of the buildings should follow 2012 IBC standards using Site Class as defined in Table 20.3-1 of American Society of Civil Engineers (ASCE) 7 – Minimum Design Loads for Buildings and Other Structures. 11.0 SLOPE STABILITY Based on the currently proposed development and additional subsurface explorations completed, slope stability was analyzed to determine potential impacts of increased ground water levels due to the northern and southern infiltration vaults. Acceptable factors of safety were achieved for both the static and seismic stability cases with elevated ground water levels generated from our mounding analyses. In our opinion, the steep slope buffer of 15 feet recommended in our 2007 report is still considered acceptable. February 27, 2015 ASSOCIATED EARTH SCIENCES, INC. SS/pc – KE110304B3 – Projects\20110304\KE\WP Page 19 ---PAGE BREAK--- ---PAGE BREAK--- Kirkland Redmond UNINCORPORATED Copyright:© 2013 National Geographic Society, i-cubed REFERENCE: USGS, KING CO VICINITY MAP ROSE HILL COTTAGES REDMOND, WASHINGTON FIGURE 1 DATE 10/14 PROJ. NO. KE110304B 0 2000 1000 FEET NOTE: BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION. Document Path: H:\GIS_Projects\zYear2011\110304 Property\mxd\Berg_ProjectVicinity.mxd ± NE 124TH ST 132nd Ave NE NE 112th Pl NE 111th Ct SITE ¥ 405 ---PAGE BREAK--- %2 B B' C' C A A' 3 2 1 EP-9 NE 110th Pl NE 111th Pl 132nd Ave NE Willows Rd NE NE 114th St 133rd Ave NE 131st Ave NE NE 112th St NE 113th St NE 112th Pl NE 111th Ct NE 116th St NE 110th Ct NE 115th Ct Lake Wash Technical College AcRd 360 340 300 280 260 200 180 160 140 120 100 80 60 40 320 240 220 200 140 340 EP-1 EP-2 EP-3 EP-4 EP-5 EP-6 EP-7 EP-8 MW-1 MW-2 PD-1 PD-2 0 250 125 FEET FIGURE 2 DATE 2/15 PROJ. NO. KE110304B REFERENCE: PSLC, KING CO. NOTE: BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION. Document Path: H:\GIS_Projects\zYear2011\110304 Property\mxd\Berg_SiteExplorationPlan.mxd SITE AND EXPLORATION PLAN ROSE HILL COTTAGES REDMOND, WASHINGTON ± LEGEND EXPLORATION TYPE EXPLORATION PIT MONITORING WELL %2 PIT DRAIN SPRING ZONE CROSS SECTION RAVINE RECONNAISSANCE CONTOUR 20 FT CONTOUR 5 FT ---PAGE BREAK--- a s s o c i a t e d e a r t h s c i e n c e s i n c o r p o r a t e d FEET 40 80 0 N REFERENCE: CORE DESIGN FIGURE 3 DATE 2/15 PROJ. NO. KE110304B 110304 Property \ 110304 F3 Site Development Plan 2-15.cdr SITE DEVELOPMENT PLAN ROSE HILL COTTAGES REDMOND, WASHINGTON D’ E’ E D NOTE: SECTIONS D-D’ AND E-E’ USED IN SLOPE STABILITY MODELING. REFER TO APPENDIX D FOR DETAILS. ---PAGE BREAK--- ---PAGE BREAK--- a s s o c i a t e d e a r t h s c i e n c e s i n c o r p o r a t e d REFERENCE: SKETCH FIGURE 5 DATE 2/15 PROJ. NO. KE110304B 110304 Property \ 110304 F5 Unnamed Creek Basin - Stream Reconnaissance 2-19-2015 Detail 1.cdr UNNAMED CREEK BASIN - STREAM RECONNAISSANCE DETAIL 1 ROSE HILL COTTAGES REDMOND, WASHINGTON NOTE: CHANNEL GRADIENT ESTIMATED FROM LiDAR BASE TOPOGRAPHY ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- APPENDIX A EXPLORATION LOGS ---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--- APPENDIX B LABORATORY TESTING DATA ---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--- APPENDIX C GROUND WATER MOUNDING ANALYSIS DATA ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- APPENDIX D SLOPE STABILITY ANALYSIS RESULTS ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK---