Stormwater Site Plan. Yelm Skate Park. Prepared for: City of Yelm 105 Yelm Avenue West Yelm, WA

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1 Stormwater Site Plan Yelm Skate Park Prepared for: City of Yelm 105 Yelm Avenue West Yelm, WA July 27 nd 2015

2 STORMWATER SITE PLAN 07/27/2015 PROJECT: Yelm Skate Park st Street NE Yelm, WA APPLICANT: City of Yelm 105 Yelm Avenue West Yelm, WA PROPERTY OWNER: City of Yelm 105 Yelm Avenue West Yelm, WA ENGINEER: BCRA 2106 Pacific Avenue, Suite 300 Tacoma, WA PREPARED BY: Zachary M. Crum, P.E. zcrum@bcradesign.com REVIEWED BY: Andy Epstein, P.E. aepstein@bcradesign.com I hereby state that this report for the Yelm Skate Park project has been prepared by me or under my supervision and meets the standard of care and expertise which is usual and customary in this community for professional engineers.

3 TABLE OF CONTENTS Chapter 1 Project Overview...4 Chapter 2 Existing Condition Summary...6 Chapter 3 Offsite Analysis...7 Chapter 4 Permanent Stormwater Control Plan...7 Section 1 Existing Site Hydrology... 7 Section 2 Developed Site Hydrology... 8 Section 3 Performance Goals and Standards Section 4 Flow Control System Section 5 Water Quality System Section 6 Conveyance System Analysis and Design Chapter 5 Construction Stormwater Pollution Prevention Plan (SWPPP) Chapter 6 Special Reports and Studies Chapter 7 Other Permits Chapter 8 Operation and Maintenance Manual LIST OF FIGURES & TABLES Figure 1.1 Vicinity Map... Figure 1.2 Site Map... Figure 2.1 Firmette... Table Developed Basin Areas... Figure WWHM Mitigated On-site to StormTech Facility... Figure WWHM Mitigated Off-Site Pervious Sidewalks... Figure StormTech SC-740 Infiltration Facility... Figure Pervious Asphalt Sidewalk Infiltration... Figure Flow Chart for Determining Requirements for Redevelopment... Figure Upper Perimeter Swale Manning s Calculation... APPENDICES Appendix A Geotechnical Report Appendix B Drainage Basin Map Appendix C Drawings Appendix D StormTech SC-740 Cut Sheet BCRADESIGN.COM 2

4 CHAPTER 1 PROJECT OVERVIEW This project includes a new skate park with perimeter landscaping and pedestrian access from the Yelm-Tenino Trail in Yelm, WA. The skate park is proposed on the approximately 0.25 acre parcel, number , located in Section 19, Township 17, and Range 2E of the Mckenzies Addition to Yelm. The property is located to the south of Yelm City Hall and west of the intersection of 1 st Street South (Highway 507) and Washington Ave SE. An existing parking lot borders the site to the east and landscaped areas surround the northwest and western portions of the site. Refer to Vicinity and Site Maps in Figures 1.1 and 1.2 below. Figure 1.1: Vicinity Map PROJECT SITE BCRADESIGN.COM 3

5 Figure Site Map PROJECT SITE A brief description of the site and project can be found below: The project will demolish an existing 2,280 sf three-sided metal building on site and construct a concrete paved skate park with an upper area and a lower area connected with ramps, stairs and other skatepark features. The upper area is approximately 2.5 feet higher than the lower area and features a four foot deep bowl. The skate park is surrounded by perimeter fencing, landscaping. Pedestrian sidewalks access the park from both Highway 507 right of way (ROW) and the Yelm Tenino Trail. In addition to the existing metal building, the remainder of the site is covered by a gravel parking area that has overgrown with vegetation in some area and a small portion of asphalt pavement. The site was formerly used by Yelm Public Works Department as an equipment yard and has since been used to temporarily store concrete rubble and other materials as seen in Figure 1.2. BCRADESIGN.COM 4

6 In the existing condition, there is no stormwater conveyance system in place. Stormwater runoff currently sheet flows from a high point on the site to the north and south edges of the property and either infiltrates on-site or disperses through vegetated areas where it eventually infiltrates. In the developed condition, on-site stormwater runoff will sheet from the concrete skate park surface and landscaped areas into perimeter swales, which convey drainage to catch basins located in low points on the north end of the site. Runoff entering the upper bowl will be collected by a floor drain and conveyed directly to the catch basin on the north end of the site to the west of the sidewalk. The onsite catch basins will collect drainage from the perimeter swales and the bowl and discharge into a manhole that connects to an underground infiltration system. The system uses five StormTech SC-740 chambers to provide enough storage and bottom area to infiltrate 100 percent of all flows within the Western Washington Hydrology Model 2012 (WWHM) modeling data. Due to grading and site constraints adjacent to the upper area of the skate park, a perforated interceptor drain pipe will be installed at the bottom of the swale to assist in collecting and conveying flows entering the western perimeter swale. The swale has a minimum slope of 0.35 percent and the pipe is designed at 1.00%. The northern sidewalks and landscape restoration are considered to be off-site. Due to the flatness of the site these flows cannot easily be captured and conveyed to the infiltration system. Instead the sidewalks will be constructed of pervious asphalt with permeable layers of rock beneath to infiltrate all runoff contained within the modeling data within Western Washington Hydrology Model (WWHM). The WWHM modeling presented later in this report shows that this meets the standard flow control requirement. Refer to Appendix B and C for the Developed Condition Drainage Basin Map and Grading and Drainage Plan. CHAPTER 2 EXISTING CONDITION SUMMARY The total site area is acres, which includes off-site areas of approximately acres, which will be used for the sidewalk connections to the Yelm Tenino Trail to the north and the existing parking lot to the east. Existing ground cover is primarily impervious, but has been overgrown with vegetation due to the lack of storm drainage. BCRADESIGN.COM 5

7 There is no existing conveyance system within the project site to capture and convey stormwater runoff. It is assumed that stormwater either infiltrates on-site or sheet flows offsite where it infiltrates in the surrounding vegetation or is eventually captured by existing downstream conveyance systems. On-site topography is generally flat with moderate slopes ranging from 0-3% across the site. A higher portion of the site exists in the western corner of the site around elevation 355. The remainder of the site is around elevation 354. The site contains no hazardous or difficult site conditions. The project site is not within the High Ground Water Hazard Area and is outside of the 100 year flood plain, refer to the FIRMette in Figure 2 1 below. Figure 0.1: FIRMette Project Site A geotechnical report prepared, by Associated Earth Sciences, Inc., for this project dated May 15 th 2015, describes the on-site soils as feet of fill and feet of topsoil underlain by recessional outwash. Groundwater was encountered in the boring that was performed on-site BCRADESIGN.COM 6

8 at a depth of 24 ft below the existing ground surface. The groundwater was observed in April of 2015 and was assumed to be near the seasonal high and was not anticipated to have an adverse effect on the proposed infiltration system. The geotechnical engineer performed a boring and five test pits to determine a design infiltration rate for the on-site soils. Laboratory sieve date produced a recommended design infiltration rate of 20 inches per hour as obtained by the Massmann equation described in Volume III, Section 3.3.6, of the 2012 Washington State Department of Ecology Stormwater Management Manual for Western Washington. This rate is used in the modeling presented later in this report. A copy of the Geotechnical report, with a full description of the soils found on site, can be found in Appendix A of this report. CHAPTER 3 OFFSITE ANALYSIS The project proposes on-site infiltration within the StormTech SC-740 chambers, which infiltrate 100% of the storm events contained within the rainfall data in WWHM without overflow conveyance. Due to the flow control characteristics provided by onsite infiltration it was determined that a quantitative offsite downstream analysis was not necessary. Refer to models presented later in this report for an explanation of the proposed flow control system. CHAPTER 4 PERMANENT STORMWATER CONTROL PLAN SECTION 1 - EXISTING SITE HYDROLOGY The existing acre site relies primarily on infiltration and dispersion to manage stormwater runoff. There are no conveyance systems in place to collect and convey stormwater and therefore the site operates independently from any of the surrounding systems. This project is subject to both Minimum Requirement 6 and 7 of the 2012 Department of Ecology Stormwater Manual for Western Washington (SWMM). However, Minimum Requirement# 6: Runoff Treatment does not apply to the project because the skate park surface is not considered to be a pollution generating hard surface (PGHS). The Pre-Developed condition was not modeled in WWHM in order to show compliance with the Flow Control requirement. The infiltration facilities presented in the following section will BCRADESIGN.COM 7

9 reliably infiltrate all flows within the WWHM modeling data and therefore the standard flow control requirement is achieved. SECTION 2 DEVELOPED SITE HYDROLOGY In the developed condition, on-site stormwater is collected from the skate park s impervious and pervious surfaces in an upper and lower swale. The upper swale collects drainage from the upper deck and surrounding perimeter landscaping. Likewise, the lower swale collects drainage from the lower deck of the park and it s surrounding landscaping. Due to grading and site constraints, both swales were required to be installed at low slopes. The upper swale is proposed at a slope of 0.35% and the lower swale is proposed at 1%. The upper swale requires an interceptor drain to convey runoff from the upper deck via a six inch perforated pipe because of its low slope. Refer to conveyance calculations presented later in this report for sizing. Both swales and the interceptor drain convey stormwater to two catch basins in the northern portion of the site. These basins serve as junctions to the primary manhole connected to the infiltration system. The catch basin to the west of the StormTech junction manhole also collects drainage from the upper bowl. All collected on-site flows are directed to the StormTech infiltration facility where they will infiltrate into native subgrade. The system has been fit with a 24 inch pipe to allow for maintenance access for periodic inspection and cleaning to be performed by the City of Yelm. If this system fails to infiltrate due to sediment loading above the design level, it will back up out of the conveyance system and overtop the swale on the west side of the site. These overflows will enter the pervious asphalt sidewalk and infiltrate or overtop the sidewalk and infiltrate in the surrounding landscaping. Off-site flows will infiltrate through the pervious asphalt pavement section to the subgrade where they will also infiltrate into the native soils. The total site area used in the calculations is acres. This area includes both the on-site concrete impervious and pervious landscaping, and the offsite pervious asphalt sidewalks (modeled and shown as impervious). All surfaces in the developed condition are not subject to vehicle traffic or any other type of pollutant loading and are considered non-pollution generating surfaces. BCRADESIGN.COM 8

10 The on-site soils are classified as Hydrologic Soil Group A/B and the following Basin Area types were used in the modeling for impervious and pervious areas: A/B, Lawn, Flat for all landscaped areas ROADS/FLAT for the skate park surface SIDEWALKS/FLAT for all sidewalks A summary of the On-site and Offsite basins follows: Sub- Basin Pollution- Generating Impervious Area (ac) Table Developed Basin Areas Non-Pollution Generating Impervious Area (ac) Pollution- Generation Pervious Area (ac) Non-Pollution Generating Pervious Area (ac) Total Area (ac) On-Site Off-Site Refer to the Drainage Basin Map in Appendix B and Grading and Drainage Plan in Appendix C for a depiction of onsite and offsite impervious and pervious areas and proposed storm drainage layout. The developed site s basins were modeled in WWHM, as shown in the following figures. BCRADESIGN.COM 9

11 Figure 4.2.1: WWHM Mitigated On-site to StormTech Facility BCRADESIGN.COM 10

12 Figure 4.2.2: WWHM Mitigated Off-Site Pervious Sidewalks The On-Site basin was modeled with discharge to the five StormTech SC-740 chambers. These chambers were modeled by using a Gravel Trench/Bed element with a design infiltration rate of 20 in/hr as recommended by the geotechnical report. The bottom area of the chambers was inputted based upon the manufacturers cut sheet included in Appendix D. Each layer of the facility was given an estimated average porosity and an overflow riser was set at the top of the chamber to ensure that the stage of the facility did not rise above the top of the facility. Refer to Figure below for the modeling input and outcome. BCRADESIGN.COM 11

13 Figure 4.2.3: StormTech SC-740 Infiltration Facility As shown in Figure 4.2.3, 100 percent of the volume produced by the WWHM data was infiltrated through the bottom of the facility. The offsite basin was also modeled with a Gravel Trench/Bed element. The layers of the trench represent a two inch layer of AASHTO No. 57 rock and a four inch layer of WSDOT (2) Permeable Ballast, which make up the reservoir section beneath the pervious asphalt section and promote infiltration. The dimensions for the sidewalk represent the total area in a single rectangular area. An infiltration rate of 20 in/hr was also applied to the bottom of this BCRADESIGN.COM 12

14 facility as recommended by the geotechnical report. Refer to Figure below for the modeling input and outcome. Figure 4.2.4: Pervious Asphalt Sidewalk Infiltration As shown in Figure 4.2.3, 100 percent of the volume produced by the WWHM data was infiltrated through the bottom of the facility. BCRADESIGN.COM 13

15 SECTION 3 - PERFORMANCE GOALS AND STANDARDS Minimum Requirements #1-9 apply to the new and replaced impervious surfaces per Figure 2.3 in Volume 1 of the SWMM (Refer to Figure 3-1 below). Figure 4.3.1: Flow Chart for Determining Requirements for Redevelopment The following describes how each minimum requirement is fulfilled by this project; BCRADESIGN.COM 14

16 Minimum Requirement # 1 Preparation of Stormwater Site Plan: This report fulfills this requirement. Minimum Requirement # 2 Construction Stormwater Pollution Prevention Plan (SWPPP) A SWPPP has been prepared for this project and is submitted under a separate cover. Minimum Requirement # 3 Source Control of Pollution This project will rely on natural infiltration of stormwater on-site. None of the proposed on-site surfaces are considered to be pollution generating hard surfaces and there are no pollutants of concern anticipated from the on-site materials. Minimum Requirement # 4 Preservation of Natural Drainage Systems and Outfalls The project will maintain natural drainage systems and outfalls by relying on the on-site infiltration. There will be no new connections to existing storm drainage systems and stormwater will infiltrate and contribute to the local groundwater systems. Minimum Requirement # 5 On-Site Stormwater Management On-site stormwater management will be provided by capturing and conveying all runoff within the project site and the right of way to the onsite infiltration systems. Because the project will be infiltrating 100% of all stormwater runoff contained within the modeling, the flow control standard requirement is waived. Therefore the LID Performance Standard is not a requirement of this project. Minimum Requirement # 6 Runoff Treatment Water Quality systems will not be required for this project because the total of pollution generating hard surface (PGIS) is less than 5,000 sf. Minimum Requirement # 7 Flow Control The flow control standard requirement applies to this project because it creates, through a combination of effective hard surfaces and converted vegetation, an increase in the 10 yr flow frequency as estimated by WWHM. This was not modeled, but inferred from the fact that the site was previously somewhat vegetated and will be developed with predominantly impervious surface. The standard requirement is met using an underground infiltration system made of five StormTech SC-740 Chambers. This system BCRADESIGN.COM 15

17 is shown to infiltrate 100 percent of the runoff volume produced by WWHM and therefore meets the standard requirement. Minimum Requirement # 8 Wetlands Protection This project does not discharge directly or indirectly to any known wetlands, therefore this minimum requirement does not apply to the project. Minimum Requirement # 9 Operation and Maintenance An operation and maintenance (O&M) manual for all stormwater facilities proposed by this project will be submitted with a later submittal. SECTION 4 - FLOW CONTROL SYSTEM As described above, the flow control system will be comprised of an infiltration system made up of a row of five StormTech SC-740 Chambers (See Appendix D for manufacturer s cut sheet). The layout of the system can be seen in Appendix C. Stormwater runoff from the site will enter the chambers on the north side of the facility and disperse within the rock section beneath the chambers. The water will be filtered by geotextile fabrics wrapped around the chambers and the outside of the facility. The stormwater will then infiltrate through the native subgrade at a rate of 20 in/hr. This system achieves the standard flow control requirement by infiltrating the total volume produced by the storm data within WWHM. SECTION 5 - WATER QUALITY SYSTEM A water quality system is not proposed for the project. Minimum Requirement# 6: Runoff Treatment does not apply to the project because the skate park surface is not considered to be a pollution generating hard surface (PGHS). SECTION 6 - CONVEYANCE SYSTEM ANALYSIS AND DESIGN The on-site conveyance system is comprised two perimeter swales, a 6 perforated interceptor drain, 8 collection piping, a 6 area drain, and a 24 pipe connected to the StormTech facility. BCRADESIGN.COM 16

18 The worst case scenarios for the on-site conveyance are the 6 perforated interceptor drain and the lower perimeter swale. Conveyance calculations showing the designed conveyance capacities of these systems are presented below. Refer to Drainage Basin Map in Appendix B. Interceptor Drain Diameter 6 Slope = 1% N= (PVC) Length = 186 ft Basin Areas o Impervious = Acres o Pervious = Acres Using Manning s equation for circular pipe flow the interceptor drain can convey up to 0.61 cfs with a roughness coefficient of n=0.012 when flowing full at a one percent slope. This flow is greater than the 100 year produced by the site when calculated using the Rational Method. Refer to the calculation presented below: Rational Method 100 Year Storm Q=CiA C=0.9 (Impervious) C=.17 (pervious) A= Basin Area (Acres) Composite CA = (0.9*0.055) + (0.17*0.045) = Impervious Pervious i = Rainfall Intensity (in/hr) Where I is calculated with i=m/(tc)^n (WSDOT Hydraulics Manual) m= 8.17 (100 yr Olympia) n=0.480 (100 yr Olympia) Tc= 5 min (conservative) i= 3.77 in/hr for all basins 100 Year Flow Calculation Q=i*CA composite Q100 = 3.77 *0.057 = 0.21 cfs < Full Flow of % Therefore, the 6 interceptor drain has capacity as designed. BCRADESIGN.COM 17

19 Lower Perimeter Swale Lower Swale Manning s Top Width = 2.7 ft Bottom Width = 0 ft Depth = 6 Slope = 1.00% n= Refer to the v-channel calculation presented in Figure below. Figure 4.6.1: Upper Perimeter Swale Manning s Calculation Q100 Rational Method 100 Year Storm Q=CiA C=0.9 (Impervious) C=.17 (pervious) A= Basin Area (Acres) Composite CA = (0.9*0.1) + (0.17*0.032) = Impervious Pervious i = Rainfall Intensity (in/hr) Where I is calculated with i=m/(tc)^n (WSDOT Hydraulics Manual) m= 8.17 (100 yr Olympia) BCRADESIGN.COM 18

20 n=0.480 (100 yr Olympia) Tc= 5 min (conservative) i= 3.77 in/hr for all basins 100 Year Flow Calculation Q=i*CA composite Q100 = 3.77 *0.095 = cfs < Full Flow of the lower 1.0 % BCRADESIGN.COM 19

21 CHAPTER 5 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN (SWPPP) The SWPPP will be submitted under a separate cover. BCRADESIGN.COM 20

22 CHAPTER 6 SPECIAL REPORTS AND STUDIES There are no additional special reports or studies. BCRADESIGN.COM 21

23 CHAPTER 7 OTHER PERMITS No additional permits are required for this project. BCRADESIGN.COM 22

24 CHAPTER 8 OPERATION AND MAINTENANCE MANUAL BCRADESIGN.COM 24

25 Maintenance Plan Goal The City of Yelm will be responsible for the maintenance and operation of the on-site stormwater facilities. The objective of the following plan is to provide the owner a manual for maintaining the on-site stormwater conveyance system. The attached checklists will be used in maintaining the facilities. Introduction/System Overview The onsite stormwater management facilities include perimeter swales, an area drain, a StormTech infiltration system, catch basins, stormwater conveyance piping, and pervious asphalt pavement. The StormTech infiltration system is located beneath the skate park surface. The sites catch basins and stormwater conveyance elements are located in various places around the project site. The pervious asphalt pavement is located in the sidewalks serving the skate park from the Yelm Tenino Trail to the north and the existing parking lot to the east. A site plan with the locations of the stormwater facilities is provided and can be found on the next page.

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27 Refer to Appendix C for detailed drawings of all the on-site stormwater management facilities. The on-site storm system requires regular maintenance. The conveyance system must be inspected after large storm events. Leaves and debris shall be swept clean of the catch basin grates. Sumps of the catch basins must also be cleaned periodically. The City of Yelm will be the entity responsible for the maintenance of the onsite storm system. The address and contact information for The City of Yelm is: City of Yelm 105 Yelm Avenue West Yelm, WA The maintenance standards are used as inspection forms for the system and its associated components. Record the date each time an inspection is completed and note any problems and actions taken, records of inspection and maintenance must be kept for five (5) years. A sample maintenance log is provided at the end of this document. Keep completed forms with the Operations and Maintenance Manual onsite at all times. The City of Yelm shall keep the Operations and Maintenance Manual available for maintenance personnel. City staff may request to review the maintenance forms as a part of their inspection process. Some components or facilities do not need to be looked at every time an inspection is conducted. Use the suggested frequency at the left of each item as a guideline for activities to be completed with each inspection. A brief description of each stormwater facility and its function is provided below: The area drain is located in the upper bowl. The drain collects all stormwater that enters the bowl and conveys it to the catch basin to the north. The StormTech infiltration system is shown in Appendix C. The system is designed to infiltrate stormwater from all on-site areas collected from the skate park surface and perimeter landscaping. A catch basin s function is to collect, convey, and temporarily store stormwater sheet flow or stormwater conveyance. The catch basin is a concrete or plastic box or cylinder that will have a grate to allow stormwater to flow into the drain. Catch basins are installed at the flow line of the perimeter swales so that surface water is collected through the grate inlet. Grate inlets are called out as beehives or domes, which allow water to still enter the catch basin if debris builds up. Conveyance pipes are located underground and are connected to catch basins. Conveyance pipes use gravity to convey stormwater downstream.

28 The attached checklists indicate maintenance actions which must be performed to keep the system in proper operating condition. The facility-specific maintenance standards contained in this section are intended to be conditions for determining if maintenance actions are required as identified through inspection. They are not intended to be measures of the facility s required condition at all times between inspections. In other words, exceeding these conditions at any time between inspections and/or maintenance does not automatically constitute a violation of these standards. However, based upon inspection observations, the inspection and maintenance schedules shall be adjusted to minimize the length of time that a facility is in a condition that requires a maintenance action. An estimate for maintaining each stormwater drainage system has been provided below. These values are an estimate and are subject to change. The estimate shall not be considered the final cost of maintenance for each system and is estimated to be the cost of a single unit. 1. StormTech: a. The Isolator row of the StormTech facility must be cleaned using a JetVac process when sediment within the row reaches a 3in depth. Refer to the maintenance procedures attached to this manual. Variable cost for repairs, typical maintenance cost approximately $ Catch Basin: a. For each catch basin it is estimated to cost $ to vacuum, pressure wash, replace filter, and dispose of waste. Maintenance tasks and frequencies of each task for each facility are provided on the next page.

29 Maintenance Program Cover Sheet Inspection Period: Number of Sheets Attached: Date Inspected: Name of Inspector: Inspector s Signature:

30 Instructions for Use of Maintenance Checklists The following pages contain maintenance needs for most of the components that are part of the onsite drainage system, as well as for some components that may not be part of the onsite drainage system. Inform Thurston County if there are any components that are missing from these pages. Ignore requirements that do not apply to the onsite system. A checklist should be completed for all onsite system components on the following schedule: (1) Monthly from November through April. (2) Twice a year for catch basins, preferably once in late summer (September) and in early spring. (3) After any major storm (use 1-inch in 24 hours as a guideline). Use photocopies of the Operation and Maintenance Manual to check off any problems found with the onsite stormwater facilities every time an inspection takes place. Add comments on problems found and actions taken. Keep the checked sheets filed for future reference, as they will be used to write an annual report. Some items do not need to be looked at every time an inspection is done. Use the suggested frequency stated for each item as a guideline during inspection.

31 Detention Retention Water Quality Save Valuable Land and Protect Water Resources A division of Isolator Row O&M Manual StormTech Chamber System for Stormwater Management

32 1.0 The Isolator Row 1.1 INTRODUCTION An important component of any Stormwater Pollution Prevention Plan is inspection and maintenance. The StormTech Isolator Row is a patented technique to inexpensively enhance Total Suspended Solids (TSS) removal and provide easy access for inspection and maintenance. The Isolator Row is typically designed to capture the first flush and offers the versatility to be sized on a volume basis or flow rate basis. An upstream manhole not only provides access to the Isolator Row but typically includes a high flow weir such that storm water flowrates or volumes that exceed the capacity of the Isolator Row overtop the over flow weir and discharge through a manifold to the other chambers. The Isolator Row may also be part of a treatment train. By treating storm water prior to entry into the chamber system, the service life can be extended and pollutants such as hydrocarbons can be captured. Pre-treatment best management practices can be as simple as deep sump catch basins, oil-water separators or can be innovative storm water treatment devices. The design of the treatment train and selection of pretreatment devices by the design engineer is often driven by regulatory requirements. Whether pretreatment is used or not, the Isolator Row is recommended by StormTech as an effective means to minimize maintenance requirements and maintenance costs. Looking down the Isolator Row from the manhole opening, woven geotextile is shown between the chamber and stone base. 1.2 THE ISOLATOR ROW The Isolator Row is a row of StormTech chambers, either SC-310, SC-310-3, SC-740, DC-780, MC-3500 or MC models, that is surrounded with filter fabric and connected to a closely located manhole for easy access. The fabric-wrapped chambers pro vide for settling and filtration of sediment as storm water rises in the Isolator Row and ultimately passes through the filter fabric. The open bottom chambers and perforated sidewalls (SC-310, SC and SC-740 models) allow storm water to flow both vertically and horizon tally out of the chambers. Sediments are cap tured in the Isolator Row protecting the storage areas of the adjacent stone and chambers from sediment accumulation. Note: See the StormTech Design Manual for detailed information on designing inlets for a StormTech system, including the Isolator Row. StormTech Isolator Row with Overflow Spillway (not to scale) MANHOLE WITH OVERFLOW WEIR OPTIONAL PRE-TREATMENT STORMTECH ISOLATOR ROW Two different fabrics are used for the Isolator Row. A woven geotextile fabric is placed between the stone and the Isolator Row chambers. The tough geo textile provides a media for storm water filtration and provides a durable surface for maintenance operations. It is also designed to prevent scour of the underlying stone and remain intact during high pressure jetting. A non-woven fabric is placed over the chambers to provide a filter media for flows passing through the perforations in the sidewall of the chamber. The non-woven fabric is not required over the DC-780, MC-3500 or MC-4500 models as these chambers do not have perforated side walls. ECCENTRIC HEADER OPTIONAL ACCESS STORMTECH CHAMBERS 2 Call StormTech at or visit our website at for technical and product information.

33 2.0 Isolator Row Inspection/Maintenance 2.1 INSPECTION The frequency of Inspection and Maintenance varies by location. A routine inspection schedule needs to be established for each individual location based upon site specific variables. The type of land use (i.e. industrial, commercial, residential), anticipated pollutant load, percent imperviousness, climate, etc. all play a critical role in determining the actual frequency of inspection and maintenance practices. At a minimum, StormTech recommends annual inspections. Initially, the Isolator Row should be inspected every 6 months for the first year of operation. For sub sequent years, the inspection should be adjusted based upon previous observation of sediment deposition. The Isolator Row incorporates a combination of standard manhole(s) and strategically located inspection ports (as needed). The inspection ports allow for easy access to the system from the surface, eliminating the need to perform a confined space entry for inspection purposes. If upon visual inspection it is found that sediment has accumulated, a stadia rod should be inserted to determine the depth of sediment. When the average depth of sediment exceeds 3 inches throughout the length of the Isolator Row, clean-out should be performed. 2.2 MAINTENANCE The Isolator Row was designed to reduce the cost of periodic maintenance. By isolating sediments to just one row, costs are dramatically reduced by eliminating the need to clean out each row of the entire storage bed. If inspection indicates the potential need for maintenance, access is provided via a manhole(s) located on the end(s) of the row for cleanout. If entry into the manhole is required, please follow local and OSHA rules for a confined space entries. Examples of culvert cleaning nozzles appropriate for Isolator Row maintenance. (These are not StormTech products.) Maintenance is accomplished with the JetVac process. The JetVac process utilizes a high pressure water nozzle to propel itself down the Isolator Row while scouring and suspending sediments. As the nozzle is retrieved, the captured pollutants are flushed back into the manhole for vacuuming. Most sewer and pipe maintenance companies have vacuum/jetvac combination vehicles. Selection of an appropriate JetVac nozzle will improve maintenance efficiency. Fixed nozzles designed for culverts or large diameter pipe cleaning are preferable. Rear facing jets with an effective spread of at least 45 are best. Most JetVac reels have 400 feet of hose allowing maintenance of an Isolator Row up to 50 chambers long. The JetVac process shall only be performed on StormTech Isolator Rows that have AASHTO class 1 woven geotextile (as specified by StormTech) over their angular base stone. StormTech Isolator Row (not to scale) NOTE: NON-WOVEN FABRIC IS ONLY REQUIRED OVER THE INLET PIPE CONNECTION INTO THE END CAP FOR DC-780, MC-3500 AND MC-4500 CHAMBER MODELS AND IS NOT REQUIRED OVER THE ENTIRE ISOLATOR ROW. Call StormTech at or visit our website at for technical and product information. 3

34 3.0 Isolator Row Step By Step Maintenance Procedures Step 1) Inspect Isolator Row for sediment A) Inspection ports (if present) i. Remove lid from floor box frame ii. Remove cap from inspection riser iii. Using a flashlight and stadia rod, measure depth of sediment and record results on maintenance log. iv. If sediment is at, or above, 3 inch depth proceed to Step 2. If not proceed to step 3. B) All Isolator Rows i. Remove cover from manhole at upstream end of Isolator Row ii. StormTech Isolator Row (not to scale) 1) B) 1) A) 2 Using a flashlight, inspect down Isolator Row through outlet pipe 1. Mirrors on poles or cameras may be used to avoid a confined space entry 2. Follow OSHA regulations for confined space entry if entering manhole iii. If sediment is at or above the lower row of sidewall holes (approximately 3 inches) proceed to Step 2. If not proceed to Step 3. Step 2) Clean out Isolator Row using the JetVac process A) A fixed culvert cleaning nozzle with rear facing nozzle spread of 45 inches or more is preferable B) Apply multiple passes of JetVac until backflush water is clean C) Vacuum manhole sump as required Step 3) Replace all caps, lids and covers, record observations and actions Step 4) Inspect & clean catch basins and manholes upstream of the StormTech system 4 Sample Maintenance Log Stadia Rod Readings Fixed point Fixed point Date to chamber to top of bottom (1) sediment (2) Sediment Depth Observations/Actions Inspector (1) - (2) 3/15/ ft. none New installation. Fixed point is Cl frame at grade djm 9/24/ ft. Some grit felt sm 6/20/ ft. Mucky feel, debris visible in manhole and in rv Isolator row, maintenance due 7/7/ ft. 0 System jetted and vacuumed djm Detention Retention Water Quality A division of 70 Inwood Road, Suite 3 Rocky Hill Connecticut fax ADS Terms and Conditions of Sale are available on the ADS website, Advanced Drainage Systems, the ADS logo, and the green stripe are registered trademarks of Advanced Drainage Systems. Stormtech and the Isolator Row are registered trademarks of StormTech, Inc. Green Building Council Member logo is a registered trademark of the U.S. Green Building Council Advanced Drainage Systems, Inc. SO /13

35 No. 2 Infiltration Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Performed General Trash & Debris See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Poisonous/Noxious Vegetation Contaminants and Pollution See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Rodent Holes See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1) Storage Area Sediment Water ponding in infiltration pond after rainfall ceases and appropriate time allowed for infiltration. Treatment basins should infiltrate Water Quality Design Storm Volume within 48 hours, and empty within 24 hours after cessation of most rain events. (A percolation test pit or test of facility indicates facility is only working at 90% of its designed capabilities. Test every 2 to 5 years. If two inches or more sediment is present, remove). Sediment is removed and/or facility is cleaned so that infiltration system works according to design. Filter Bags (if applicable) Filled with Sediment and Debris Sediment and debris fill bag more than 1/2 full. Filter bag is replaced or system is redesigned. Rock Filters Sediment and Debris By visual inspection, little or no water flows through filter during heavy rain storms. Gravel in rock filter is replaced. Side Slopes of Pond Emergency Overflow Spillway and Berms over 4 feet in height. Erosion See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Tree Growth See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Piping See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Emergency Overflow Spillway Rock Missing See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Erosion See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Pre-settling Ponds and Vaults Facility or sump filled with Sediment and/or debris 6" or designed sediment trap depth of sediment. Sediment is removed. Volume V Runoff Treatment BMPs August

36 No. 5 Catch Basins Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is performed General Trash & Debris Trash or debris which is located immediately in front of the catch basin opening or is blocking inletting capacity of the basin by more than 10%. No Trash or debris located immediately in front of catch basin or on grate opening. Trash or debris (in the basin) that exceeds 60 percent of the sump depth as measured from the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of six inches clearance from the debris surface to the invert of the lowest pipe. No trash or debris in the catch basin. Trash or debris in any inlet or outlet pipe blocking more than 1/3 of its height. Inlet and outlet pipes free of trash or debris. Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane). No dead animals or vegetation present within the catch basin. Sediment Sediment (in the basin) that exceeds 60 percent of the sump depth as measured from the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of 6 inches clearance from the sediment surface to the invert of the lowest pipe. No sediment in the catch basin Structure Damage to Frame and/or Top Slab Fractures or Cracks in Basin Walls/ Bottom Settlement/ Misalignment Vegetation Contamination and Pollution Top slab has holes larger than 2 square inches or cracks wider than 1/4 inch (Intent is to make sure no material is running into basin). Frame not sitting flush on top slab, i.e., separation of more than 3/4 inch of the frame from the top slab. Frame not securely attached Maintenance person judges that structure is unsound. Grout fillet has separated or cracked wider than 1/2 inch and longer than 1 foot at the joint of any inlet/outlet pipe or any evidence of soil particles entering catch basin through cracks. If failure of basin has created a safety, function, or design problem. Vegetation growing across and blocking more than 10% of the basin opening. Vegetation growing in inlet/outlet pipe joints that is more than six inches tall and less than six inches apart. See "Detention Ponds" (No. 1). Top slab is free of holes and cracks. Frame is sitting flush on the riser rings or top slab and firmly attached. Basin replaced or repaired to design standards. Pipe is regrouted and secure at basin wall. Basin replaced or repaired to design standards. No vegetation blocking opening to basin. No vegetation or root growth present. No pollution present. Volume V Runoff Treatment BMPs August

37 No. 5 Catch Basins Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is performed Catch Basin Cover Cover Not in Place Cover is missing or only partially in place. Any open catch basin requires maintenance. Catch basin cover is closed Locking Mechanism Not Working Mechanism cannot be opened by one maintenance person with proper tools. Bolts into frame have less than 1/2 inch of thread. Mechanism opens with proper tools. Cover Difficult to Remove One maintenance person cannot remove lid after applying normal lifting pressure. (Intent is keep cover from sealing off access to maintenance.) Cover can be removed by one maintenance person. Ladder Ladder Rungs Unsafe Ladder is unsafe due to missing rungs, not securely attached to basin wall, misalignment, rust, cracks, or sharp edges. Ladder meets design standards and allows maintenance person safe access. Metal Grates (If Applicable) Grate opening Unsafe Grate with opening wider than 7/8 inch. Grate opening meets design standards. Trash and Debris Trash and debris that is blocking more than 20% of grate surface inletting capacity. Grate free of trash and debris. Damaged or Missing. Grate missing or broken member(s) of the grate. Grate is in place and meets design standards. No. 6 Debris Barriers (e.g., Trash Racks) Maintenance Components Defect Condition When Maintenance is Needed Results Expected When Maintenance is Performed General Trash and Debris Trash or debris that is plugging more than 20% of the openings in the barrier. Barrier cleared to design flow capacity. Metal Damaged/ Missing Bars. Bars are bent out of shape more than 3 inches. Bars in place with no bends more than 3/4 inch. Bars are missing or entire barrier missing. Bars in place according to design. Bars are loose and rust is causing 50% deterioration to any part of barrier. Barrier replaced or repaired to design standards. Inlet/Outlet Pipe Debris barrier missing or not attached to pipe Barrier firmly attached to pipe Volume V Runoff Treatment BMPs August

38 No. 7 Energy Dissipaters Maintenance Components External: Rock Pad Dispersion Trench Internal: Manhole/Chamber Defect Missing or Moved Rock Conditions When Maintenance is Needed Only one layer of rock exists above native soil in area five square feet or larger, or any exposure of native soil. Results Expected When Maintenance is Performed Rock pad replaced to design standards. Erosion Soil erosion in or adjacent to rock pad. Rock pad replaced to design standards. Pipe Plugged with Sediment Not Discharging Water Properly Perforations Plugged. Water Flows Out Top of Distributor Catch Basin. Receiving Area Over- Saturated Worn or Damaged Post, Baffles, Side of Chamber Other Defects Accumulated sediment that exceeds 20% of the design depth. Visual evidence of water discharging at concentrated points along trench (normal condition is a sheet flow of water along trench). Intent is to prevent erosion damage. Over 1/2 of perforations in pipe are plugged with debris and sediment. Maintenance person observes or receives credible report of water flowing out during any storm less than the design storm or its causing or appears likely to cause damage. Water in receiving area is causing or has potential of causing landslide problems. Structure dissipating flow deteriorates to 1/2 of original size or any concentrated worn spot exceeding one square foot which would make structure unsound. Pipe cleaned/flushed so that it matches design. Trench redesigned or rebuilt to standards. Perforated pipe cleaned or replaced. Facility rebuilt or redesigned to standards. No danger of landslides. Structure replaced to design standards. See Catch Basins (No. 5). See Catch Basins (No. 5). Volume V Runoff Treatment BMPs August

39 No. 18 Catchbasin Inserts Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is Performed General Sediment Accumulation When sediment forms a cap over the insert media of the insert and/or unit. No sediment cap on the insert media and its unit. Trash and Debris Accumulation Trash and debris accumulates on insert unit creating a blockage/restriction. Trash and debris removed from insert unit. Runoff freely flows into catch basin. Media Insert Not Removing Oil Effluent water from media insert has a visible sheen. Effluent water from media insert is free of oils and has no visible sheen. Media Insert Water Saturated Catch basin insert is saturated with water and no longer has the capacity to absorb. Remove and replace media insert Media Insert-Oil Saturated Media oil saturated due to petroleum spill that drains into catch basin. Remove and replace media insert. Media Insert Use Beyond Normal Product Life Media has been used beyond the typical average life of media insert product. Remove and replace media at regular intervals, depending on insert product. Volume V Runoff Treatment BMPs August

40 SAMPLE MAINTENACNCE ACTIVITY LOG Maintenance Program Cover Sheet Inspection Period: Number of Sheets Attached: Date Inspected: Name of Inspector: Inspector s Signature: Instructions for Use of Maintenance Checklists The following pages contain maintenance needs for most of the components that are part of the onsite drainage system, as well as for some components that may not be part of the onsite drainage system. Inform Thurston County if there are any components that are missing from these pages. Ignore requirements that do not apply to the onsite system. A checklist should be completed for all onsite system components on the following schedule: (1) Monthly from November through April. (2) Twice a year for catch basins, preferably once in late summer (September) and in early spring. (3) After any major storm (use 1-inch in 24 hours as a guideline). Use photocopies of the Operation and Maintenance Manual to check off any problems found with the onsite stormwater facilities every time an inspection takes place. Add comments on problems found and actions taken. Keep the checked sheets filed for future reference, as they will be used to write an annual report. Some items do not need to be looked at every time an inspection is done. Use the suggested frequency stated for each item as a guideline during inspection.

41 No. 5 Catch Basins Maintenance Component General Defect Conditions When Maintenance is Needed Results Expected When Maintenance is performed Trash & Debris Trash or debris which is located immediately in front of the catch basin opening or is blocking inletting capacity of the basin by more than 10%. Trash or debris (in the basin) that exceeds 60 percent of the sump depth as measured from the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of six inches clearance from the debris surface to the invert of the lowest pipe. Trash or debris in any inlet or outlet pipe blocking more than 1/3 of its height. Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane). Sediment Sediment (in the basin) that exceeds 60 percent of the sump depth as measured from the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of 6 inches clearance from the sediment surface to the invert of the lowest pipe. Structure Damage to Frame and/or Top Slab Fractures or Cracks in Basin Walls/ Bottom Top slab has holes larger than 2 square inches or cracks wider than 1/4 inch (Intent is to make sure no material is running into basin). Frame not sitting flush on top slab, i.e., separation of more than 3/4 inch of the frame from the top slab. Frame not securely attached Maintenance person judges that structure is unsound. Grout fillet has separated or cracked wider than 1/2 inch and longer than 1 foot at the joint of any inlet/outlet pipe or any evidence of soil particles entering catch basin through cracks. No Trash or debris located immediately in front of catch basin or on grate opening. No trash or debris in the catch basin. Inlet and outlet pipes free of trash or debris. No dead animals or vegetation present within the catch basin. No sediment in the catch basin Top slab is free of holes and cracks. Frame is sitting flush on the riser rings or top slab and firmly attached. Basin replaced or repaired to design standards. SAMPLE Settlement/ Misalignment Vegetation Contamination and Pollution If failure of basin has created a safety, function, or design problem. Vegetation growing across and blocking more than 10% of the basin opening. Vegetation growing in inlet/outlet pipe joints that is more than six inches tall and less than six inches apart. See "Detention Ponds" (No. 1). Pipe is regrouted and secure at basin wall. Basin replaced or repaired to design standards. No vegetation blocking opening to basin. No vegetation or root growth present. No pollution present. 10/15/15 REMOVED ALL TRASH AND DEBRIS FROM CATCH BASIN GRATE 10/15/15 VACUUMED OUT ALL SEDIMENT FROM CATCH BASIN SUMP 10/15/15 REMOVED ALL VEGETATION FROM CATCH BASIN GRATE AND INLET PIPE Volume V Runoff Treatment BMPs August

42 APPENDIX A GEOTECHNICAL REPORT BCRADESIGN.COM 24

43 a s s o e a r t h c i a t e d s c i e n c e s i n c o r p o r a t e d Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report YELM SKATE PARK Yelm, Washington Prepared For: BCRA Project No. KE140343A May 15, 2015 Associated Earth Sciences, Inc th Avenue Kirkland, WA P (425) F (425)

44 May 15, 2015 Project No. KE140343A BCRA 2106 Pacific Avenue, Suite 300 Tacoma, Washington Attention: Mr. Daren Crabill Subject: Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Yelm Skate Park 203 SE 1 st Street Yelm, Washington Dear Mr. Crabill: We are pleased to present the enclosed copies of the above-referenced report. This report summarizes the results of our subsurface exploration, geologic hazard, and geotechnical engineering studies, and offers recommendations for the preliminary design and development of the proposed project. Our recommendations are preliminary in that structure locations and construction details have not been finalized at the time of this report. We have enjoyed working with you on this study and are confident that the recommendations presented in this report will aid in the successful completion of your project. If you should have any questions or if we can be of additional help to you, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington G. Aaron McMichael, P.E. Associate Engineer GAM/pc KE140343A2 Projects\ \KE\WP Kirkland Office 911 Fifth Avenue Kirkland, WA P F Everett Office 2911 ½ Hewitt Avenue, Suite 2 Everett, WA P F Tacoma Office 1552 Commerce Street, Suite 102 Tacoma, WA P F

45 SUBSURFACE EXPLORATION, GEOLOGIC HAZARD, AND GEOTECHNICAL ENGINEERING REPORT Yelm Skate Park Yelm, Washington Prepared for: BCRA 2106 Pacific Avenue, Suite 300 Tacoma, Washington Prepared by: Associated Earth Sciences, Inc th Avenue Kirkland, Washington Fax: May 15, 2015 Project No. KE140343A

46 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Project and Site Conditions I. PROJECT AND SITE CONDITIONS 1.0 INTRODUCTION This report presents the results of our subsurface exploration, geologic hazard, and geotechnical engineering study for the subject project. Our recommendations are preliminary in that structure locations and construction details have not been finalized at the time of this report. The location of the subject site is shown on the Vicinity Map, Figure 1. The approximate locations of the explorations accomplished for this study are presented on the Site and Exploration Plan, Figure 2. In the event that any changes in the nature or design of the proposed layout is planned, the conclusions and recommendations contained in this report should be reviewed and modified, or verified, as appropriate 1.1 Purpose and Scope The purpose of this study was to provide subsurface data to be used in the design and development of the subject project. Our study included a review of available geologic literature, excavation of exploration pits, drilling one exploration boring, and performing geologic studies to assess the type, thickness, distribution, and physical properties of the subsurface sediments and shallow ground water conditions. Geotechnical engineering studies were also conducted to assess the type of suitable foundation, allowable foundation soil bearing pressures, anticipated settlements, retaining wall lateral pressures, floor support recommendations, drainage considerations, and storm water infiltration recommendations. This report summarizes our current fieldwork and offers preliminary development recommendations based on our present understanding of the project. 1.2 Authorization Authorization to proceed with this study was granted by BCRA. Our study was accomplished in general accordance with our scope of work letter dated June 12, This report has been prepared for the exclusive use of BCRA 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 and engineering geology practices in effect in this area at the time our report was prepared. No other warranty, express or implied, is made. 2.0 PROJECT AND SITE DESCRIPTION The subject site consists of an irregularly shaped parcel of approximately 0.25 acre located at 203 SE 1 st Street in Yelm, Washington. It is our understanding that the property was formerly May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 1

47 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Project and Site Conditions used as the Yelm public works equipment yard. A three-sided, covered storage structure spans the full depth of the site along the southwest property margin. A small storage shed extends off of this structure at its north end. The remainder of the property is vacant and surfaced with gravel and crushed rock. The topography of the site is relatively flat. It is our understanding that current plans include demolition of the existing structures and redevelopment of the property as a skate park. The skate park will include areas of pavement and concrete skate bowl. The base of the bowl is anticipated to be approximately 2 to 2.5 feet below the existing ground surface. Conceptually, the skate park will include some retaining walls, stairs, and other structures. It is anticipated that storm water will be infiltrated on-site with the base of the infiltration facility located approximately 6 feet below the existing ground surface. The conceptual locations of the skate bowl, storm water infiltration facility, and other structures are depicted on the Site and Exploration Plan, Figure SUBSURFACE EXPLORATION Our field study included drilling one exploration boring and excavating five exploration pits to evaluate subsurface conditions at the site. The various types of sediments, as well as the depths where characteristics of the sediments changed, are indicated on the exploration logs presented in Appendix A. The depths indicated on the logs where conditions changed may represent gradational variations between sediment types in the field. Our explorations were approximately located in the field relative to known site features shown on a conceptual site plan provided by BCRA. The locations of the explorations are shown on Figure 2. The conclusions and recommendations presented in this report are based, in part, on the explorations completed for this study. The number, locations, and depths of the explorations were completed within site and budgetary constraints. Because of the nature of exploratory work below ground, interpolation of subsurface conditions between field explorations is necessary. It should be noted that subsurface conditions differing from those depicted on the logs may be present at the site 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 Exploration Boring Exploration boring EB-1 was completed by advancing a 4¼-inch, inside-diameter, hollow-stem auger with a truck-mounted drill rig. During the drilling process, samples were generally obtained at 2.5- to 5.0-foot-depth intervals. The boring was continuously observed and logged May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 2

48 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Project and Site Conditions by an engineering geologist from our firm. The exploration log presented in Appendix A is based on the field log, drilling action, and inspection of the samples secured. Disturbed but representative samples were obtained by using the Standard Penetration Test (SPT) procedure in accordance with American Society for Testing and Materials (ASTM):D 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 ( N ) 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 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 attached boring logs. Due to the gravelly textural composition of the sediments encountered, sample recovery was generally poor and many of the recorded blow counts are likely overstated. 3.2 Exploration Pits Five exploration pits were excavated at the using a rubber-tired backhoe provided by the City of Yelm. 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. All exploration pits were backfilled immediately after examination and logging. Samples collected from the exploration pits and boring were classified in the field and representative portions placed in watertight containers. The samples were then transported to our laboratory for further visual classification and laboratory testing, as necessary. 4.0 SUBSURFACE CONDITIONS Subsurface conditions at the project site were inferred from the field explorations accomplished for this study, visual reconnaissance of the site, and review of applicable geologic literature. As shown on the field logs, sediments encountered in the exploration borings generally consisted of sandy gravel with minor quantities of silt. The following section presents more detailed subsurface information organized from the youngest to the oldest sediment types. May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 3

49 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Project and Site Conditions 4.1 Stratigraphy Fill Fill soils (those not naturally placed) were encountered at all of the exploration locations. Fill encountered in exploration pit EP-4, located in the southern portion of the site, generally consisted of loose to medium dense, very gravelly sand with minor quantities of silt and scattered debris (wire and plastic). At this location, the fill extended to a depth of approximately 5 feet. It is our understanding that an underground storage tank (UST) formerly located in this portion of the site was recently removed. The fill encountered in exploration pit EP-4 likely consists of backfill placed in the former UST excavation. Fill soil encountered in the other explorations advanced at the site generally consisted of medium dense, gray, 5 / 8 -inch minus crushed rock. The thickness of the crushed rock ranged from approximately 1 to 1.5 feet. The existing fill is not considered suitable for foundation support. Topsoil The crushed rock fill encountered in our explorations was underlain by medium dense, black, gravelly topsoil. The gravelly topsoil ranged in thickness from approximately 0.5 to 1.5 feet. Based on laboratory testing of the topsoil collected from exploration pit EP-5, the organic content of the topsoil is relatively low (approximately 4 percent). This is consistent with testing previously conducted by Associated Earth Sciences, Inc. (AESI) in the project area. In our opinion, the existing topsoil is suitable for foundation support, provided it is free of roots and other deleterious materials, and has been recompacted to a firm and unyielding condition. A copy of the testing results is included in Appendix B. Vashon Recessional Outwash Sediments encountered below the surficial fill and/or topsoil horizon generally consisted of medium dense, sandy to very sandy gravel with minor quantities of silt, abundant cobbles and scattered small boulders. We interpret these sediments to be representative of Vashon recessional outwash. The Vashon recessional outwash was deposited by meltwater streams that flowed off of the retreating glacial ice during the Vashon Stade of the Fraser Glaciation, approximately 12,000 to 15,000 years ago. The recessional outwash extended beyond the maximum depths explored of approximately 8 to 31.5 feet. May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 4

50 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Project and Site Conditions 4.2 Geologic Mapping Review of the regional geologic map of the area by Drost et al. (1998) indicates that the subject site is underlain by Vashon recessional outwash. Our interpretation of the sediments encountered in our explorations is in general agreement with the regional geologic map. 4.3 Hydrology Ground water seepage was encountered in exploration boring EB-1 below a depth of approximately 24 feet. It should be noted that the occurrence and level of ground water seepage at the site may vary in response to such factors as changes in season, precipitation, and site use. May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 5

51 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Geologic Hazards and Mitigations II. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on the geologic, slope, and shallow ground water conditions, as observed and discussed herein. 5.0 SEISMIC HAZARDS AND MITIGATION Earthquakes occur in the Puget Lowland with great regularity. The vast majority of these events are small, and are usually not felt by people. However, large earthquakes do occur, as evidenced by the 1949, 7.2-magnitude event; the 2001, 6.8-magnitude event; and the 1965, 6.5-magnitude event. The 1949 earthquake appears to have been the largest in this region during recorded history and was centered in the Olympia area. Evaluation of earthquake return rates indicates that an earthquake of the magnitude between 5.5 and 6.0 is likely within a given 20- to 40-year period. Generally, there are four types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture, 2) seismically induced landslides, 3) liquefaction, and 4) ground motion. The potential for each of these hazards to adversely impact the proposed project is discussed below. 5.1 Surficial Ground Rupture Generally, the largest earthquakes that have occurred in the Puget Sound area are sub-crustal events with epicenters ranging from 50 to 70 kilometers in depth. Earthquakes that are generated at such depths usually do not result in fault rupture at the ground surface. Based on current knowledge, the subject property is not located near known surface faults. Therefore, based on current information, the risk of damage to planned improvements as a result of surface rupture due to faulting is low, in our opinion. 5.2 Seismically Induced Landslides The risk of damage to the proposed project by landsliding under either static or seismic conditions is low due to the lack of steep slopes on or adjacent to the subject site. No mitigation of landslide hazards is warranted. 5.3 Liquefaction The encountered stratigraphy has a low potential for liquefaction due to the coarse, gravelly texture of the underlying sediments and the relatively large depth to the water table. No mitigation of liquefaction hazards is warranted. May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 6

52 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Geologic Hazards and Mitigations 5.4 Ground Motion It is our opinion that any earthquake damage to the proposed structure, when founded on suitable bearing strata in accordance with the recommendations contained herein, will be caused by the intensity and acceleration associated with the event and not any of the above-discussed impacts. Structural design of the proposed structures should follow 2012 International Building Code (IBC) standards using Site Class D as defined in Table of American Society of Civil Engineers (ASCE) 7 Minimum Design Loads for Buildings and Other Structures. 6.0 LAHAR HAZARDS The term lahar refers to a volcanic mudflow composed of sediments, water, and entrained debris. It is well-documented that, over many thousands of years, numerous lahars have originated on Mt. Rainier and flowed down the river channels emanating from the mountain. These lahars have occurred at sporadic intervals (possibly averaging one every few centuries) and in a wide range of sizes. Published hazard maps prepared by the Pierce County Department of Emergency Management indicate that the Nisqually River channel represents a likely path for a future large lahar. However, because the project is located approximately 2 miles west of this river channel, it lies outside of the mapped lahar hazard zone. 7.0 EROSION HAZARDS AND MITIGATION Due to the relatively level topography throughout the site vicinity, and the coarse texture of the underlying sediments, it is our opinion that the erosion hazard risk at the site is low. May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 7

53 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Preliminary Design Recommendations III. PRELIMINARY DESIGN RECOMMENDATIONS 8.0 INTRODUCTION Our exploration indicates that, from a geotechnical standpoint, the parcel is suitable for the proposed development provided the recommendations contained herein are properly followed. The foundation bearing stratum is relatively shallow, and conventional spread footing foundations may be utilized. 9.0 SITE PREPARATION 9.1 Clearing and Stripping Following demolition of the existing structures, any remaining foundation elements or existing utilities located below the proposed structures should be removed or relocated. The resulting depressions should be backfilled with structural fill as discussed under the Structural Fill section of this report. Any existing vegetation, pavement, and any other deleterious materials should be stripped from the proposed building and pavement areas. Areas where loose surficial soils exist due to grubbing operations should be considered as fill to the depth of disturbance and treated as subsequently recommended for structural fill placement. Any existing fill soils located below foundation areas should be stripped down to the underlying, medium dense natural outwash sediments or gravelly topsoil, provided it is free of roots or other deleterious materials. These sediments were generally encountered in our explorations at depths of approximately 1 to 1.5 feet. One exception was the location of exploration pit EP-4, located in the former UST excavation, where sediments suitable for foundation support were encountered at a depth of approximately 5 feet. The suitability of any gravelly topsoil left below foundation areas should be verified by AESI. We recommend that existing fill soils in the former UST excavation and in the exploration pits excavated for this study be removed and replaced with structural fill. The existing crushed rock surfacing that blankets the majority of the site may remain below pavement areas, provided that it is firm and unyielding, but should be removed where it is present below foundation areas. After stripping and grubbing operations have been completed, we recommend that the soil exposed in proposed pavement areas be recompacted to a firm and unyielding condition. The pavement subgrade should then be proof-rolled. We recommend that the proof-roll be observed by AESI. Any soft or yielding areas identified during proof-rolling should be overexcavated and backfilled with structural fill. May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 8

54 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Preliminary Design Recommendations 9.2 Temporary and Permanent Cut Slopes In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction based on the local conditions encountered at that time. For planning purposes, we anticipate that temporary, unsupported cut slopes within the existing fill and natural recessional outwash sediments can be made at a maximum slope of 1.5H:1V (Horizontal:Vertical). As is typical with earthwork operations, some sloughing and raveling may occur, and cut slopes may have to be adjusted in the field. In addition, WISHA/OSHA regulations should be followed at all times. Permanent cut slopes should not exceed an inclination of 2H:1V. 9.3 Site Disturbance The existing fill soils and natural sediments underlying the site consist of sand and gravel with minor quantities of silt. These materials are not considered moisture sensitive. The topsoil layer that underlies the surficial crushed rock fill layer does contain significant quantities of silt and is considered moderately moisture sensitive and subject to disturbance when wet. Where the topsoil is exposed during construction, the contractor must use care during wet weather site preparation and excavation operations so that the topsoil is not softened. If disturbance occurs, the softened soils should be removed and the area brought to grade with structural fill. If the topsoil horizon is exposed in access and staging areas consideration should be given to protect the subgrade in these areas with an appropriate section of crushed rock or asphalt treated base (ATB). If crushed rock is considered for the access and staging areas, it should be underlain by engineering stabilization fabric (such as Mirafi 500X or approved equivalent) to reduce the potential of fine-grained materials pumping up through the rock during wet weather and turning the area to mud. The fabric will also aid in supporting construction equipment, thus reducing the amount of crushed rock required. We recommend that at least 10 inches of rock be placed over the fabric. Crushed rock used for access and staging areas should be of at least 2-inch size STRUCTURAL FILL Placement of structural fill may be necessary to establish desired grades in some areas or to backfill utility trenches or around foundations. All references to structural fill in this report refer to subgrade preparation, fill type, and placement and compaction of materials as discussed in this section. If a percentage of compaction is specified under another section of this report, the value given in that section should be used. May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 9

55 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Preliminary Design Recommendations 10.1 Subgrade Compaction After overexcavation/stripping has been performed to the satisfaction of the geotechnical engineer/engineering geologist, the upper 12 inches of exposed ground should be recompacted to a firm and unyielding condition. After recompaction of the exposed ground is tested and approved, structural fill may be placed to attain desired grades Structural Fill Compaction Structural fill is defined as non-organic soil, acceptable to the geotechnical engineer, placed in maximum 8-inch loose lifts, with each lift being compacted to at least 95 percent of the modified Proctor maximum dry density using ASTM:D 1557 as the standard. Utility trench backfill should be placed and compacted in accordance with applicable municipal codes and standards. The top of the compacted fill should extend horizontally a minimum distance of 3 feet beyond footings or pavement edges before sloping down at an angle no steeper than 2H:1V. Fill slopes should either be overbuilt and trimmed back to final grade or surface-compacted to the specified density. The on-site recessional outwash sediments are suitable for use as structural fill, but contain some oversized materials. We recommend that cobbles larger than 8 inches and boulders be excluded from use in structural fill Moisture-Sensitive Fill Soils in which the amount of fine-grained material (smaller than No. 200 sieve) is greater than approximately 5 percent (measured on the minus No. 4 sieve size) should be considered moisture-sensitive. Use of moisture-sensitive soil in structural fills should be limited to favorable dry weather conditions. If fill is placed during wet weather or if proper compaction cannot be attained, a select import or on-site material consisting of a clean, free-draining gravel and/or sand should be used. Free-draining fill consists of non-organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction. The on-site recessional outwash generally contains only minor quantities of silt is not considered to be particularly moisture sensitive Structural Fill Testing The contractor should note that any proposed fill soils must be evaluated by AESI prior to their use in fills. This would require that we have a sample of the material at least 3 business days in advance to perform a Proctor test and determine its field compaction standard. A representative from our firm should inspect the stripped subgrade and be present during placement of structural fill to observe the work and perform a representative number of May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 10

56 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Preliminary Design Recommendations in-place density tests. In this way, the adequacy of the earthwork may be evaluated as filling progresses and any problem areas may be corrected at that time. It is important to understand that taking random compaction tests on a part-time basis will not assure uniformity or acceptable performance of a fill. As such, we are available to aid the owner in developing a suitable monitoring and testing frequency FOUNDATIONS 11.1 Allowable Soil Bearing Pressure Spread footings may be used for support of the proposed structures when founded either directly on the medium dense gravelly topsoil, the underlying recessional outwash, or on structural fill placed over these materials. Any gravelly topsoil remaining below foundation areas must be free of roots or any other deleterious materials, as verified at the time of construction by AESI. Structural fill placed below footing areas should extend horizontally beyond the footing edges a distance equal to or greater than the thickness of the fill. Sediments suitable for foundation support were generally encountered in our explorations below depths of approximately 1 to 1.5 feet. The exception was exploration pit EP-4, located in the former UST excavation where the fill extended to a depth of approximately 5 feet. We recommend that all fill soils located below foundation areas, including those within the former UST excavation and in the exploration pits excavated for this study, be overexcavated and replaced with structural fill. For footings founded either directly upon the medium dense recessional outwash, or on structural fill placed over these materials, we recommend that an allowable bearing pressure of 2,000 pounds per square foot (psf) be used for design purposes, including both dead and live loads. An increase in the allowable bearing pressure of one-third may be used for short-term wind or seismic loading 11.2 Footing Depths All footings should be buried a minimum of 18 inches into the surrounding soil for frost protection. All footings must penetrate to the prescribed bearing stratum, and no footings should be founded in or above loose, organic, or existing fill soils Footings Adjacent to Cuts The area bounded by lines extending downward at 1H:1V from any footing must not intersect another footing or intersect a filled area that has not been compacted to at least 95 percent of ASTM:D In addition, a 1.5H:1V line extending down from any footing must not daylight May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 11

57 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Preliminary Design Recommendations because sloughing or raveling may eventually undermine the footing. Thus, footings should not be placed near the edges of steps or cuts in the bearing soils Footing Settlement Anticipated settlement of footings founded as described above should be on the order of 1 inch or less. However, disturbed soil not removed from footing excavations prior to footing placement could result in increased settlements Footing Subgrade Bearing Verification All footing areas should be observed by AESI prior to placing concrete to verify that the exposed soils can support the design foundation bearing pressure and that construction conforms with the recommendations in this report. Foundation bearing verification may also be required by the City of Yelm Foundation Drainage Footing drains should be provided as discussed under the Drainage Considerations section of this report LATERAL WALL PRESSURES All backfill behind walls or around foundations should be placed following our recommendations for structural fill and as described in this section of the report. Horizontally backfilled walls, that are free to yield laterally at least 0.1 percent of their height, may be designed using an equivalent fluid equal to 35 pounds per cubic foot (pcf). Fully restrained, horizontally backfilled, rigid walls that cannot yield should be designed for an equivalent fluid of 55 pcf. Walls that retain sloping backfill at a maximum angle of 50 percent should be designed for 50 pcf for yielding conditions and 80 pcf for restrained conditions. If parking areas or driveways are adjacent to walls, a surcharge equivalent to 2 feet of retained soil should be added to the wall height in determining lateral design forces Wall Backfill The lateral pressures presented above are based on the conditions of a uniform backfill consisting of either the on-site recessional outwash sediments or imported sand and gravel compacted to 90 percent of ASTM:D A higher degree of compaction is not recommended, as this will increase the pressure acting on the walls. A lower compaction may result in unacceptable settlement behind the walls. Thus, the compaction level is critical and must be tested by our firm during placement. May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 12

58 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Preliminary Design Recommendations 12.2 Wall Drainage It is imperative that proper drainage be provided so that hydrostatic pressures do not develop against the walls. This would involve installation of a minimum 1-foot-wide blanket drain for the full wall height using imported, washed gravel against the walls Passive Resistance and Friction Factor Lateral loads can be resisted by friction between the foundation and the supporting medium dense natural sediments or supporting structural fill soils, or by passive earth pressure acting on the buried portions of the foundations. The foundations must be backfilled with compacted structural fill to achieve the passive resistance provided below. We recommend the following design parameters: Passive equivalent fluid = 300 pcf Coefficient of friction = 0.35 The above values are allowable Seismic Surcharge As required by the 2012 IBC, retaining wall design should include a seismic surcharge pressure in addition to the equivalent fluid pressures presented above. We recommend a seismic surcharge pressure of 9H and 11H psf where H is the wall height in feet for the active and at-rest loading conditions, respectively. The seismic surcharge should be modeled as a rectangular distribution with the resultant applied at the midpoint of the wall DRAINAGE CONSIDERATIONS All retaining and perimeter footing walls should be provided with a drain at the footing elevation. The drains should consist of rigid, perforated, polyvinyl chloride (PVC) pipe surrounded by washed gravel. The level of the perforations in the pipe should be set approximately 2 inches below the bottom of the footing, and the drains should be constructed with sufficient gradient to allow gravity flow to an approved point of discharge. All retaining walls should be lined with a minimum, 12-inch-thick, washed gravel blanket provided to within 1 foot of finish grade, and which ties into the footing drain. Surface runoff should not discharge into the footing drain system, but should be handled by a separate, rigid, tightline drain. May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 13

59 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Preliminary Design Recommendations 14.0 STORM WATER INFILTRATION It is our understanding that preliminary plans include on-site infiltration of storm water. The conceptual location of the infiltration facility is shown on Figure 2. We also understand that the base of the infiltration facility will be located approximately 6 feet below the existing ground surface. Recessional outwash encountered at and below this depth in the area of the proposed infiltration facility consisted of sandy gravel with minor quantities of silt. In our opinion, the recessional outwash is a suitable receptor soil for on-site infiltration. Ground water was encountered in exploration boring EB-1 at a depth of 24 feet below the existing ground surface. Exploration boring EB-1 was completed on April 27, 2015 which should be near the seasonal high elevation for the water table surface. It is our opinion that the depth to ground water is sufficient to support site infiltration Design Infiltration Rate In order to evaluate a suitable design infiltration rate for the proposed facility, laboratory sieve analyses were conducted on six samples of the recessional outwash. The locations and depths of the samples tested are summarized below in Table 1. Copies of the laboratory reports are included in Appendix B. Table 1 Summary of sieve sample collection locations and depths Sample Location Depth (feet) EP EP EP EP EP EP Based on the laboratory sieve data, we recommend a design infiltration rate for the proposed facility of 20 inches per hour. The recommended design infiltration rate assumes that the storm water will be infiltrated into the recessional outwash approximately where shown on Figure 2 at a depth of approximately 6 feet. We recommend that AESI conduct a geotechnical review the infiltration system plans once they become available to verify that they conform with our recommendations. We also recommend that AESI observe soil conditions in the infiltration facility at the time of construction to verify that they conform with those upon which the recommended infiltration rate is based. The recommended design infiltration rate was obtained using the Massmann equation as described in Volume III, Section of the 2012 Washington State Department of Ecology Stormwater Management Manual for Western Washington. May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 14

60 Yelm Skate Park Yelm, Washington Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Preliminary Design Recommendations 14.2 Cation Exchange Capacity and Organic Carbon Content Laboratory testing to evaluate the cation exchange capacity (CEC) and organic carbon content of the receptor soils was conducted on one sample of the recessional outwash collected from exploration pit EP-1 at a depth of approximately 6 to 7 feet. The purpose of the testing was to evaluate water quality treatment characteristics of the receptor soil. The results of the analyses are summarized below in Table 2. Copies of the laboratory reports are included in Appendix B. Table 2 Water Quality Treatment Parameters Sample ID CEC (meq/100g) Organic Carbon (percent) EP-1/6-7 ft CEC = cation exchange capacity Meq/100g = milliequivalents per 100 grams of soil 15.0 PROJECT DESIGN AND CONSTRUCTION MONITORING We are available to provide additional geotechnical consultation as the project design develops and possibly changes from that upon which this report is based. If significant changes in grading are made, we recommend that AESI perform a geotechnical review of the plans prior to final design completion. In this way, our earthwork and foundation recommendations may be properly interpreted and implemented in the design. We are also available to provide geotechnical engineering and monitoring services during construction. The integrity of the foundations depends on proper site preparation and construction procedures. In addition, engineering decisions may have to be made in the field in the event that variations in subsurface conditions become apparent. Construction monitoring services are not part of this current scope of work. If these services are desired, please let us know, and we will prepare a proposal. May 15, 2015 ASSOCIATED EARTH SCIENCES, INC. TJP/pc KE140343A2 Projects\ \KE\WP Page 15

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62 510 YELM! SITE Document Path: H:\GIS_Projects\aTemplates\aVM_Template\ProjectVicinity_Thurston.mxd 507 REFERENCE: USGS, THURSTON CO NOTE: BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION. Copyright: 2013 National Geographic Society, FEET i-cubed VICINTY MAP YELM SKATE PARK YELM, WASHINGTON ± FIGURE 1 DATE 5/15 PROJ. NO. KE140343A

63 EP-3 EP-2 EB-1 EP-1 APPROXIMATE LOCATION OF EXPLORATION BORING Yelm Skate Park \ F2 Site and Exploration Plan.cdr REFERENCE: BCRA 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 EP-4 EP-5 NOTE: BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION. SITE AND EXPLORATION PLAN YELM SKATE PARK YELM, WASHINGTON APPROXIMATE LOCATION OF EXPLORATION PIT TYP N NO SCALE FIGURE 2 DATE 4/15 PROJ. NO. KE140343A

64 APPENDIX A Exploration Logs

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85 APPENDIX B DRAINAGE BASIN MAP BCRADESIGN.COM 25

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87 APPENDIX C - DRAWINGS BCRADESIGN.COM 26

88 APPENDIX D STORMTECH SC740 CHAMBERS BCRADESIGN.COM 27

89 StormTech SC-740 Chamber Designed to meet the most stringent industry performance standards for superior structural integrity while providing designers with a cost-effective method to save valuable land and protect water resources. The StormTech system is designed primarily to be used under parking lots thus maximizing land usage for commercial and municipal applications. ACCEPTS 4" (100 SCH 40 PIPE FOR OPTIONAL INSPECTION PORT StormTech SC-740 Chamber (not to scale) Nominal Chamber Specifications Size (L x W x H) 85.4" x 51.0" x 30.0" (2170 x 1295 x 762 mm) Chamber Storage 45.9 ft 3 (1.30 m 3 ) Minimum Installed Storage* 74.9 ft 3 (2.12 m 3 ) Weight 74.0 lbs (33.6 kg) Shipping 30 chambers/pallet 60 end caps/pallet 12 pallets/truck 8" (203 mm) 30.0" (762 mm) 24" (610 mm) DIA. MAX SC-740 End Cap 51.0" (1295 mm) 90.7" (2300 mm) SC-740 Chamber 85.4" (2170 mm) INSTALLED Typical Cross Section Detail (not to scale) THE INSTALLED CHAMBER SYSTEM SHALL PROVIDE THE LOAD FACTORS SPECIFIED IN THE AASHTO LRFD BRIDGE DESIGN SPECIFICATIONS SECTION FOR EARTH AND LIVE LOADS, WITH CONSIDERATION FOR IMPACT AND MULTIPLE VEHICLE PRESENCES. 3/4-2" (19-50 mm) CLEAN, CRUSHED, ANGULAR STONE SC-740 CHAMBER ADS 601 GEOTEXTILE OR EQUAL CHAMBERS SHALL MEET ASTM F STANDARD SPECIFICATION FOR POLYETHYLENE (PE) CORRUGATED WALL STORMWATER COLLECTION CHAMBERS. GRANULAR WELL GRADED SOIL/AGGREGATE MIXTURES, <35% FINES. COMPACT IN 6" (150 mm) LIFTS TO 95% STANDARD PROCTOR DENSITY. SEE THE TABLE OF ACCEPTABLE FILL MATERIALS. PAVEMENT SC-740 END CAP FOR UNPAVED INSTALLATION WHERE RUTTING FROM VEHICLES MAY OCCUR, INCREASE COVER TO 24" (610 MM) 96" 18" (460 mm) (2440 mm) MIN. MAX. 6" (150 mm) MIN. 30" (762 mm) SC-740 DEPTH OF STONE TO BE DETERMINED BY DESIGN ENGINEER* 6" (150 mm) MIN. MADE IN THE U.S.A. DESIGN ENGINEER IS RESPONSIBLE FOR ENSURING THE REQUIRED BEARING CAPACITY OF SUBGRADE SOILS* 6" (150 mm) MIN. 51" (1295 mm) MIN. 12" MIN. (305 mm) TYP. THIS CROSS SECTION DETAILS THE REQUIREMENTS NECESSARY TO SATISFY THE LOAD FACTORS SPECIFIED IN THE AASHTO LRFD BRIDGE DESIGN SPECIFICATIONS SECTION FOR EARTH AND LIVE LOADS USING STORMTECH CHAMBERS