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9904 - Stormwater Site Plan Report - 11-19-2024Larson & Associates surveyors, engineers and planners 9027 Pacific Avenue, Suite 4 Tacoma, WA 98444 PF A--- D- 1 Ni STORMWATER SITE PLAN PROPONENT: C&E DEVELOPMENTS, LLC P.O. BOX 2983 YELM, WA. 98597 PH: (360) 400-0432 PREPARED BY: Larson & Associates surveyors, engineers and planners 9027 Pacific Avenue, Suite 4 Tacoma, WA 98444 (253) 474-3404 November 19, 2024 PROJECT ENGINEER'S CERTIFICATION.......................................................................................................... 1 STORMWATER SITE PLAN CHAPTER 1 - PROJECT OVERVIEW .......................................................................................................................... 2 CHAPTER 2 - EXISTING SITE CONDITIONS SUMMARY ............................................................................................. 2 CHAPTER 3 - OFF-SITE ANALYSIS .......................................................................................................................... 2 CHAPTER 4 - PERMANENT STORMWATER CONTROL PLAN .................................................................................. 3-5 SECTION 1 - PRE-DEVELOPED SITE HYDROLOGY ............................................................................................ 3 SECTION 2 - DEVELOPED SITE HYDROLOGY ................................................................................................... 3 SECTION 3 - PERFORMANCE STANDARDS AND GOALS ................................................................................. 3-4 SECTION 4 - FLOW CONTROL SYSTEM ..........................................................................................................4-5 SECTION 5 - WATER QUALITY SYSTEM ........................................................................................................... 5 SECTION 6 - CONVEYANCE SYSTEM ANALYSIS AND DESIGN .......................................................................... 5 CHAPTER 5 - CONSTRUCTION SWPPP .................................................................................................................... 5 CHAPTER 6 - SPECIAL REPORTS AND STUDIES ......................................................................................................... 6 CHAPTER 7 - OTHER PERMITS .................................................................................................................................. 6 CHAPTER 8 - OPERATION AND MAINTENANCE MANUAL ........................................................................................ 6 CHAPTER 9 - BOND QUANTITIES WORKSHEET ....................................................................................................... 6 STORMWATER CALCULATIONS ....................................................................................................................7-12 APPENDICES APPENDIX "A" .......................................................................................... OPERATION AND MAINTENANCE MANUAL APPENDIX "B" ......................................................................................................... MISCELLANEOUS INFORMATION 1 CHAPTER 1 – PROJECT OVERVIEW The “Rhoton Road Binding Site Plan” project is located in the SE1/4 of the NW1/4 of Section 19, Township 17 North, Range 2 East of the Willamette Meridian in the City of Yelm in Thurston County, Washington. The proposal consists of creating (7) building pads for uses such as warehousing, equipment storage, light manufacturing and potential hardware store. An internal paved access, parking stalls, sidewalk and associated utilities including onsite private storm drainage, public water main and sewer S.T.E.P. force main extensions. The property is approximately 3.28 acres in size located on parcel No's 22719240201 and 22719240203. All building roof runoff will be collected and infiltrated directly into the ground via corresponding infiltration trenches, since it is considered “clean” per Department of Ecology standards and no formal water quality treatment is required for these roof surfaces. Stormwater runoff from the access road, parking areas, sidewalk and curb will be collected via catch basins set along inverted “crown” pavement flowline and routed to their corresponding infiltration trench which will then infiltrate stormwater to the native soils below. Prior to conveyance to the infiltration trench, stormwater will be routed to and through an Oldcastle (or approved equal) perkfilter system providing basic treatment of stormwater. All other disturbed pervious areas will be amended to meet the BMPT5.13 per the DOE manual. Stormwater BMPS have been designed per the 2019 DOE Stormwater Management Manual. CCHHAAPPTTEERR 22 –– EEXXIISSTTIINNGG CCOONNDDIITTIIOONNSS SSUUMMMMAARRYY The site is located northwest of the intersection of Rhoton Rd NW and Northern Pacific Rd NW. Surrounding properties consist of single family residence to the west, industrial/commercial to the south and north, a church to the south and Roton Rd SE to the east. The project area is vacant with prairie grass and a few trees onsite. The site has an approximate high point elevation of 339 in the southwest. The site slopes from west to east with an approximate low point elevation of 332 in the east. Stormwater runoff presently sheet flows across the site from the west to east and is infiltrated through the “good” free draining soils located across the site. Per the N.R.C.S. soils map, on-site soils consist of Spanaway gravelly sandy loam, 0 to 3 percent slopes and Spanaway stony sandy loam, 3 to 15 percent slopes. These soils will be very conducive to infiltration of stormwater for proposed improvements onsite. A geotechnical report was completed by Quality Geo NW, PLLC dated 8/24/2023. They recommend that a design infiltration rate of 20 in/hr be utilized to size in-ground infiltration facilities. See the Geotechnical Report in Appendix B for additional information. CCHHAAPPTTEERR 33 –– OOFFFF--SSIITTEE AANNAALLYYSSIISS We do not expect any offsite stormwater to enter the site from the surrounding properties. Also, all stormwater created with this proposal will be infiltrated onsite without any anticipated offsite discharge of “design” storm events. 2 CCHHAAPPTTEERR 44 –– PPEERRMMAANNEENNTT SSTTOORRMMWWAATTEERR CCOONNTTRROOLL PPLLAANN SECTION 1 – PRE-DEVELOPED SITE HYDROLOGY As previously discussed, the site is located northwest of the intersection of Rhoton Rd NW and Northern Pacific Rd NW. The project area is vacant with prairie grass and a few trees onsite. The site has an approximate high point elevation of 339 in the southwest. The site slopes from west to east with an approximate low point elevation of 332 in the east. Stormwater runoff presently sheet flows across the site from the west to east and is infiltrated through the “good” free draining soils located across the site. SECTION 2 – DEVELOPED SITE HYDROLOGY All building roof runoff will be collected and infiltrated directly into the ground via corresponding infiltration trenches, since it is considered “clean” per Department of Ecology standards and no formal water quality treatment is required for these roof surfaces. Stormwater runoff from the access road, parking areas, sidewalk and curb will be collected via catch basins set along inverted “crown” pavement flowline and routed to their corresponding infiltration trench which will then infiltrate stormwater to the native soils below. Prior to conveyance to the infiltration trench, stormwater will be routed to and through an Oldcastle (or approved equal) perkfilter system providing basic treatment of stormwater. All other disturbed pervious areas will be amended to meet the BMPT5.13 per the DOE manual. Stormwater BMPS have been designed per the 2019 DOE Stormwater Management Manual. Developed Area Table Onsite Offsite Total Total 3.246 AC 0.035 AC 3.281 AC Pervious (Yard/Landscape) 1.287 AC 0.020 AC 1.307 AC Impervious 1.959 AC 0.015 AC 1.974 AC Building Roof 0.861 AC ------ 0.861 AC Road/Curb/Gutter 0.919 AC 0.015 AC 0.934 AC Sidewalk 0.179 AC ------ 0.179 AC SECTION 3 – PERFORMANCE STANDARDS AND GOALS Minimum requirements 1-9 apply to this project as written in the 2019 Department of Ecology Stormwater Management Manual for Western Washington as we are proposing more than 5,000 SF of replaced impervious surface. See below for additional information regarding the minimum requirements, which have been addressed. Discussion of Minimum Requirements 1-9: a. Minimum Requirement #1: Preparation of Stormwater Site Plan This report and the associated plan set fulfill this requirement. b. Minimum Requirement #2: Construction SWPPP The separate document titled “Construction SWPPP” fulfills this requirement. 3 c. Minimum Requirement #3: Source Control of Pollution Appendix “A” of the Construction SWPPP contains information on BMP’S to Consider for all Activities that will satisfy this requirement. d. Minimum Requirement #4: Preservation of Natural Drainage Systems and Outfalls This requirement is met since stormwater from all impervious surfaces will be collected on-site with release to its natural downstream direction of flow via infiltration. e. Minimum Requirement #5: On-Site Stormwater Management All stormwater created will be infiltrated onsite within properly sized infiltration trenches designed per the 2019 DOE Stormwater Management Manual. f. Minimum Requirement #6: Runoff Treatment Roof runoff will not be required to be treated as it is considered clean by Department of Ecology standards. PGIS runoff will be treated via two separate Oldcastle Perkfilter treatment systems prior to being infiltrated onsite. g. Minimum Requirement #7: Flow Control Flow control is being met through infiltration of all stormwater runoff from this proposal. See the infiltration trench calculations in the section titled “Stormwater Calculations”. h. Minimum Requirement #8: Wetlands Protection To the best of our knowledge, there are no wetlands located onsite. Per the Thurston County GIS, there is a wetland area located offsite to the southwest and we have reviewed Figure I-3.5 from the 2019 SWMMWW and plan to employ standard erosion control BMPs such as siltation fencing along the down gradient side of the site and installation of CB inlet protection within all proposed catchbasins onsite to ensure this very minimal development proposal does not have any negative impacts on any offsite areas. We would also like note to that the proposed impervious surface associated with this project proposal has been designed to fully infiltrate “design” storm events within proposed underground infiltration trench facilities as modeled with an approved continuous runoff model (MGS FLOOD). Further, any disturbed pervious surfaces onsite associated with this project will be properly soil amended following D.O.E. soil amendment BMP T5.13, as required. i. Minimum Requirement #9: Operation and Maintenance See Appendix “A” Operation and Maintenance Manual for required information. SECTION 4 – FLOW CONTROL SYSTEM As previously discussed, all runoff from proposed impervious and pervious runoff will be collected and infiltrated into one of the four (4) proposed infiltration trenches. Each of these infiltration trenches have been designed per the DOE 2019 stormwater manual, Volume V, Chapter 5 and have been sized utilizing MGSFlood Continuous Runoff Modeling Program. All other disturbed areas will be amended per DOE BMP T5.13. See the tables below for contributing areas to each of the four (4) infiltration trenches. 4 Contributing Areas to Infiltration Trench #1: Developed Area Table Onsite Offsite Total Total 1.411 AC 0.035 AC 1.446 AC Pervious (Yard/Landscape) 0.651 AC 0.020 AC 0.671 AC Impervious 0.760 AC 0.015 AC 0.775 AC Building Roof (Pads 1 & 2) 0.256 AC ------ 0.256 AC Road/Curb/Gutter 0.396 AC 0.015 AC 0.411 AC Sidewalk 0.108 AC ------ 0.108 AC Contributing Areas to Infiltration Trench #2: Developed Area Table Total Total 1.368 AC Pervious (Yard/Landscape) 0.636 AC Impervious 0.732 AC Building Roof (Pad 3) 0.138 AC Road/Curb/Gutter 0.523 AC Sidewalk 0.071 AC Contributing Areas to Infiltration Trench #3: Developed Area Table Total Total 0.314 AC Impervious 0.314 AC Building Roof (Pads 4 & 5) 0.314 AC Contributing Areas to Infiltration Trench #4: Developed Area Table Total Total 0.153 AC Impervious 0.153 AC Building Roof (Pads 6 & 7) 0.153 AC SECTION 5 – WATER QUALITY SYSTEM Roof runoff will not be required to be treated as it is considered “clean” by Department of Ecology standards. PGIS runoff associated with this proposal will be treated via two separate Oldcastle Perkfilter treatment systems. Each of these treatment devices have been sized utilizing the 15 min. offline water quality flow calculated utilizing the MGSFlood Continuous Runoff Modeling software. SECTION 6 – CONVEYANCE SYSTEM ANALYSIS AND DESIGN Our proposal includes a 6” – 12” storm pipe to convey all of the on-site stormwater. A sizing calculation has been provided in the section titled “Stormwater Calculations” which proves the pipe size is adequate. CCHHAAPPTTEERR 55 –– CCOONNSSTTRRUUCCTTIIOONN SSWWPPPPPP See the separate document titled “Construction SWPPP” for additional information. 5 CCHHAAPPTTEERR 66 –– SSPPEECCIIAALL RREEPPOORRTT AANNDD SSTTUUDDIIEESS A geotechnical report was completed by Quality Geo NW, PLLC dated 8/24/2023. They recommend that a design infiltration rate of 20 in/hr be utilized to size in-ground infiltration facilities. According to the report, no groundwater was encountered during test pit exploration. See the Geotechnical Report in Appendix B for additional information. CCHHAAPPTTEERR 77 –– OOTTHHEERR PPEERRMMIITTSS Other permits for this project are as follows (but not limited to): •Site Plan Review •Individual Building Permits CCHHAAPPTTEERR 88 –– OOPPEERRAATTIIOONN AANNDD MMAAIINNTTEENNAANNCCEE MMAANNUUAALL See Appendix “A” Operation and Maintenance Manual for required information. CCHHAAPPTTEERR 99 –– BBOONNDD QQUUAANNTTIITTIIEESS WWOORRKKSSHHEEEETT No bonds are required at this time therefore this chapter is not applicable. 6 STORMWATER CALCULATIONS 7 RHOTON ROAD BINDING SITE PLAN 8 SITE FLOW CONTROL / LID PERFORMANCE STANDARD ————————————————————————————————— MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.62 Program License Number: 200810005 Project Simulation Performed on: 11/12/2024 3:50 PM Report Generation Date: 11/12/2024 3:52 PM ————————————————————————————————— Input File Name: Site Flow Control.fld Project Name: C&E Commercial Analysis Title: Infiltration Trench Sizing Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Full Period of Record Available used for Routing Climatic Region Number: 16 Precipitation Station : 96004405 Puget East 44 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961044 Puget East 44 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : Ecology Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 3.281 3.281 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 3.281 3.281 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- A/B, Forest, Flat 3.281 ---------------------------------------------- 9 Subbasin Total 3.281 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 4 ---------- Subbasin : Contr. to Trench #4 ---------- -------Area (Acres) -------- ROOF TOPS/FLAT 0.153 ---------------------------------------------- Subbasin Total 0.153 ---------- Subbasin : Contr. to Trench #1 ---------- -------Area (Acres) -------- A/B, Pasture, Mod 0.671 ROADS/FLAT 0.411 ROOF TOPS/FLAT 0.256 SIDEWALKS/FLAT 0.108 ---------------------------------------------- Subbasin Total 1.446 ---------- Subbasin : Contr. to Trench #2 ---------- -------Area (Acres) -------- A/B, Pasture, Mod 0.636 ROADS/FLAT 0.523 ROOF TOPS/FLAT 0.138 SIDEWALKS/FLAT 0.071 ---------------------------------------------- Subbasin Total 1.368 ---------- Subbasin : Contr. to Trench #3 ---------- -------Area (Acres) -------- ROOF TOPS/FLAT 0.314 ---------------------------------------------- Subbasin Total 0.314 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 5 ------------------------------------------ Link Name: Trench #4 Link Type: Infiltration Trench 10 Downstream Link Name: New Copy Lnk2 Trench Type : Trench on Embankment Sideslope Trench Length (ft) : 25.00 Trench Width (ft) : 5.00 Trench Depth (ft) : 4.00 Trench Bottom Elev (ft) : 100.00 Trench Rockfill Porosity (%) : 30.00 Constant Infiltration Option Used Infiltration Rate (in/hr): 20.00 ------------------------------------------ Link Name: New Copy Lnk2 Link Type: Copy Downstream Link: None ------------------------------------------ Link Name: Trench #1 Link Type: Infiltration Trench Downstream Link Name: New Copy Lnk2 Trench Type : Trench on Embankment Sideslope Trench Length (ft) : 59.00 Trench Width (ft) : 9.00 Trench Depth (ft) : 4.00 Trench Bottom Elev (ft) : 100.00 Trench Rockfill Porosity (%) : 30.00 Constant Infiltration Option Used Infiltration Rate (in/hr): 20.00 ------------------------------------------ Link Name: Trench #2 Link Type: Infiltration Trench Downstream Link Name: New Copy Lnk2 Trench Type : Trench on Embankment Sideslope Trench Length (ft) : 64.00 Trench Width (ft) : 7.00 Trench Depth (ft) : 4.00 Trench Bottom Elev (ft) : 100.00 Trench Rockfill Porosity (%) : 30.00 Constant Infiltration Option Used Infiltration Rate (in/hr): 20.00 ------------------------------------------ Link Name: Trench #3 Link Type: Infiltration Trench Downstream Link Name: New Copy Lnk2 11 Trench Type : Trench on Embankment Sideslope Trench Length (ft) : 36.00 Trench Width (ft) : 5.00 Trench Depth (ft) : 4.00 Trench Bottom Elev (ft) : 100.00 Trench Rockfill Porosity (%) : 30.00 Constant Infiltration Option Used Infiltration Rate (in/hr): 20.00 **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 4 Number of Links: 5 ***********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: Subbasin 1 1026.429 _____________________________________ Total: 1026.429 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Contr. to Trench #4 0.000 Subbasin: Contr. to Trench #1 228.314 Subbasin: Contr. to Trench #2 216.405 Subbasin: Contr. to Trench #3 0.000 Link: Trench #4 Not Computed Link: New Copy Lnk2 0.000 Link: Trench #1 Not Computed Link: Trench #2 Not Computed Link: Trench #3 Not Computed _____________________________________ Total: 444.718 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 6.496 ac-ft/year, Post Developed: 2.815 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED 12 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 5 ********** Link: New Copy Lnk2 ********** 2-Year Discharge Rate : 0.000 cfs 15-Minute Timestep, Water Quality Treatment Design Discharge On-line Design Discharge Rate (91% Exceedance): 0.24 cfs Off-line Design Discharge Rate (91% Exceedance): 0.24 cfs Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 0.02 Inflow Volume Including PPT-Evap (ac-ft): 0.02 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To Downstream System (ac-ft): 0.02 Secondary Outflow To Downstream System (ac-ft): 0.00 Volume Lost to ET (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered+ET)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: Subbasin 1 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 2.544E-03 2-Year 0.000 5-Year 2.624E-03 5-Year 0.000 10-Year 2.643E-03 10-Year 0.000 25-Year 9.934E-03 25-Year 0.000 50-Year 1.242E-02 50-Year 0.000 100-Year 1.800E-02 100-Year 0.000 200-Year 2.704E-02 200-Year 0.565 500-Year 3.909E-02 500-Year 1.327 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals **** Flow Duration Performance **** Excursion at Predeveloped 50%Q2 (Must be Less Than or Equal to 0%): -99.9% PASS Maximum Excursion from 50%Q2 to Q2 (Must be Less Than or Equal to 0%): -98.7% PASS Maximum Excursion from Q2 to Q50 (Must be less than 10%): -66.7% PASS Percent Excursion from Q2 to Q50 (Must be less than 50%): 0.0% PASS 13 ------------------------------------------------------------------------------------------------- MEETS ALL FLOW DURATION DESIGN CRITERIA: PASS ------------------------------------------------------------------------------------------------- **** LID Duration Performance **** Excursion at Predeveloped 8%Q2 (Must be Less Than 0%): -100.0% PASS Maximum Excursion from 8%Q2 to 50%Q2 (Must be Less Than 0%): -99.9% PASS ------------------------------------------------------------------------------------------------- MEETS ALL LID DURATION DESIGN CRITERIA: PASS ------------------------------------------------------------------------------------------------- 14 INFILTRATION TRENCH #1 WATER QUALITY SIZING / PIPE SIZING ————————————————————————————————— MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.62 Program License Number: 200810005 Project Simulation Performed on: 11/07/2024 10:31 AM Report Generation Date: 11/07/2024 10:31 AM ————————————————————————————————— Input File Name: Infiltration Trench #1 Water Quality.fld Project Name: C&E Commercial Analysis Title: Infiltration Trench Sizing Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Full Period of Record Available used for Routing Climatic Region Number: 16 Precipitation Station : 96004405 Puget East 44 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961044 Puget East 44 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : Ecology Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 1.190 1.190 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 1.190 1.190 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- A/B, Forest, Flat 1.190 ---------------------------------------------- 15 Subbasin Total 1.190 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- A/B, Pasture, Mod 0.671 ROADS/FLAT 0.411 SIDEWALKS/FLAT 0.108 ---------------------------------------------- Subbasin Total 1.190 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: New Copy Lnk1 Link Type: Copy Downstream Link: None **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 1 ***********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: Subbasin 1 372.280 _____________________________________ Total: 372.280 16 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Subbasin 1 228.314 Link: New Copy Lnk1 0.000 _____________________________________ Total: 228.314 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 2.356 ac-ft/year, Post Developed: 1.445 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ********** Link: New Copy Lnk1 ********** 2-Year Discharge Rate : 0.213 cfs 15-Minute Timestep, Water Quality Treatment Design Discharge On-line Design Discharge Rate (91% Exceedance): 0.08 cfs Off-line Design Discharge Rate (91% Exceedance): 0.05 cfs  Used to Size Oldcastle Perkfilter Device Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 260.28 Inflow Volume Including PPT-Evap (ac-ft): 260.28 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To Downstream System (ac-ft): 260.28 Secondary Outflow To Downstream System (ac-ft): 0.00 Volume Lost to ET (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered+ET)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: Subbasin 1 Scenario Postdeveloped Compliance Link: New Copy Lnk1 *** 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) ---------------------------------------------------------------------------------------------------------------------- 17 2-Year 9.229E-04 2-Year 0.213 5-Year 9.518E-04 5-Year 0.275 10-Year 9.587E-04 10-Year 0.328 25-Year 3.603E-03 25-Year 0.405 50-Year 4.506E-03 50-Year 0.486 100-Year 6.529E-03 100-Year 0.605  Used to Size Storm Pipe 200-Year 9.806E-03 200-Year 0.645 500-Year 1.418E-02 500-Year 0.696 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals 18 INFILTRATION TRENCH #2 WATER QUALITY SIZING / PIPE SIZING ————————————————————————————————— MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.62 Program License Number: 200810005 Project Simulation Performed on: 11/12/2024 2:46 PM Report Generation Date: 11/12/2024 3:13 PM ————————————————————————————————— Input File Name: Infiltration Trench #2 water quality.fld Project Name: C&E Commercial Analysis Title: Infiltration Trench Sizing Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Full Period of Record Available used for Routing Climatic Region Number: 16 Precipitation Station : 96004405 Puget East 44 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961044 Puget East 44 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : Ecology Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 1.230 1.230 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 1.230 1.230 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- A/B, Forest, Flat 1.230 ---------------------------------------------- 19 Subbasin Total 1.230 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- A/B, Pasture, Mod 0.636 ROADS/FLAT 0.523 SIDEWALKS/FLAT 0.071 ---------------------------------------------- Subbasin Total 1.230 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: New Copy Lnk1 Link Type: Copy Downstream Link: None **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 1 ***********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: Subbasin 1 384.793 _____________________________________ Total: 384.793 20 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Subbasin 1 216.405 Link: New Copy Lnk1 0.000 _____________________________________ Total: 216.405 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 2.435 ac-ft/year, Post Developed: 1.370 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ********** Link: New Copy Lnk1 ********** 2-Year Discharge Rate : 0.244 cfs 15-Minute Timestep, Water Quality Treatment Design Discharge On-line Design Discharge Rate (91% Exceedance): 0.10 cfs Off-line Design Discharge Rate (91% Exceedance): 0.05 cfs  Used for Sizing Oldcastle Perkfilter Device Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 297.83 Inflow Volume Including PPT-Evap (ac-ft): 297.83 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To Downstream System (ac-ft): 297.83 Secondary Outflow To Downstream System (ac-ft): 0.00 Volume Lost to ET (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered+ET)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: Subbasin 1 Scenario Postdeveloped Compliance Link: New Copy Lnk1 *** 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) ---------------------------------------------------------------------------------------------------------------------- 21 2-Year 9.539E-04 2-Year 0.244 5-Year 9.838E-04 5-Year 0.315 10-Year 9.909E-04 10-Year 0.372 25-Year 3.724E-03 25-Year 0.464 50-Year 4.657E-03 50-Year 0.556 100-Year 6.748E-03 100-Year 0.692  Used to Size Storm Pipe 200-Year 1.014E-02 200-Year 0.738 500-Year 1.466E-02 500-Year 0.796 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals 22 23 APPENDIX “A” OPERATION & MAINTENANCE MANUAL A1 OPERATION & MAINTENANCE MANUAL Description of “Rhoton Road Binding Site Plan” Stormwater System. All building roof runoff will be collected and infiltrated directly into the ground via corresponding infiltration trenches, since it is considered “clean” per Department of Ecology standards and no formal water quality treatment is required for these roof surfaces. Stormwater runoff from the access road, parking areas, sidewalk and curb will be collected via catch basins set along inverted “crown” pavement flowline and routed to their corresponding infiltration trench which will then infiltrate stormwater to the native soils below. Prior to conveyance to the infiltration trench, stormwater will be routed to and through an Oldcastle (or approved equal) perkfilter system providing basic treatment of stormwater. All other disturbed pervious areas onsite will be amended per DOE BMP T5.13. RESPONSIBLE PARTY FOR THE MAINTENANCE OF THE PRIVATE STORM DRAINAGE SYSTEM UNTIL WHICH TIME THE HOME OWNER TAKES OVER RESPONSIBILITY: C&E DEVELOPMENTS, LLC P.O. BOX 2983 YELM, WA. 98597 PH: (360) 400-0432 ESTIMATED ANNUAL COST OF MAINTENANCE OF THE PRIVATE STORM DRAINAGE SYSTEM AS IDENTIFIED IN ATTACHMENT “A” IS $3500 PER YEAR. NOTE: THIS OPERATION AND MAINTENANCE MANUAL SHALL BE KEPT AT THE PROJECT SITE AT ALL TIMES AND SHALL BE MADE AVAILABLE TO THE CITY OF YELM FOR INSPECTION UPON REQUEST. A2 ATTACHMENT “A” A3 ATTACHMENT "A" MAINTENANCE PROGRAM 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 your drainage system, as well as for some components that you may not have. Let the City know if there are any components that are missing from these pages. Ignore the requirements that do not apply to your system. You should plan to complete a checklist for all system components on the following schedule: (1) Monthly from November through April (2) Once in late summer (preferable September) (3) After any major storm (use 1-inch in 24 hours as a guideline), items marked "S" only. Using photocopies of these pages, check off the problems you looked for each time you did an inspection. Add comments on problems found and actions taken. Keep these "checked" sheets in your files, as they will be used to write your annual report. Some items do not need to be looked at every time an inspection is done. Use the suggested frequency at the left of each item as a guideline for your inspection. A4 ATTACHMENT "A" (CONTINUED) Maintenance Checklist for Fencing/Shrubbery Screen/Other Landscaping Frequency Drainage System Feature  Problem Conditions to Check For Conditions That Should Exist M General Missing or broken parts/dead shrubbery Any defect in the fence or screen that permits easy entry to a facility. Fence is mended or shrubs replaced to form a solid barrier to entry. M,S Erosion Erosion has resulted in an opening under a fence that allows entry by people or pets. Replace soil under fence so that no opening exceeds 4 inches in height. M Unruly vegetation Shrubbery is growing out of control or is infested with weeds. Shrubbery is trimmed and weeded to provide appealing aesthetics. Do not use chemicals to control weeds. A Wire Fences Damaged parts Posts out of plumb more than 6 inches. Posts plumb to within 1-1/2 inches of plumb. A Top rails bent more than 6 inches. Top rail free of bends greater than 1 inch. A Any part of fence (including posts, top rails, and fabric) more than 1 foot out of design alignment. Fence is aligned and meets design standards. A Missing or loose tension wire. Tension wire in place and holding fabric. A Missing or loose barbed wire that is sagging more than 2-1/2 inches between posts. Barbed wire in place with less than 3/4-inch sag between posts. A Extension arm missing, broken, or bent out of shape more than 1-1/2 inches. Extension arm in place with no bends larger than 3/4 inch. A Deteriorated paint or protective coating Part or parts that have a rusting or scaling condition that has affected structural adequacy. Structurally adequate posts or parts with a uniform protective coating. M Openings in fabric Openings in fabric are such that an 8-inch diameter ball could fit through. No openings in fabric. If you are unsure whether a problem exists, please contact a Professional Engineer. Comments: Key: A=Annual (March or April preferred) M=Monthly (see schedule) S=After major storms (use 1-inch in 24 hours as a guideline) A5 ATTACHMENT "A" (CONTINUED) Maintenance Checklist for Conveyance Systems (Pipes, Ditches, and Swales) Frequency Drainage System Feature  Problem Conditions to Check For Conditions That Should Exist M,S Pipes Sediment & debris Accumulated sediment that exceeds 20% of the diameter of the pipe. Pipe cleaned of all sediment and debris. M Vegetation Vegetation that reduces free movement of water through pipes. All vegetation removed so water flows freely through pipes. A Damaged (rusted, bent, or crushed) Protective coating is damaged; rust is causing more than 50% deterioration to any part of pipe. Pipe repaired or replaced. M Any dent that significantly impedes flow (i.e., decreases the cross section area of pipe by more than 20%). Pipe repaired or replaced. M Pipe has major cracks or tears allowing groundwater leakage. Pipe repaired or replaced. M,S Open ditches Trash & debris Dumping of yard wastes such as grass clippings and branches into basin. Unsightly accumulation of nondegradable materials such as glass, plastic, metal, foam, and coated paper. Remove trash and debris and dispose as prescribed by the County. M Sediment buildup Accumulated sediment that exceeds 20% of the design depth. Ditch cleaned of all sediment and debris so that it matches design. A Vegetation Vegetation (e.g., weedy shrubs or saplings) that reduces free movements of water through ditches. Water flows freely through ditches. Grassy vegetation should be left alone. M Erosion damage to slopes See Ponds Checklist. See Ponds Checklist. A Rock lining out of place or missing (if applicable) Maintenance person can see native soil beneath the rock lining. Replace rocks to design standard. Varies Catch basins See Catch Basins Checklist. See Catch Basins Checklist. M,S Swales Trash & debris See above for Ditches. See above for Ditches. M Sediment buildup See above for Ditches. Vegetation may need to be replanted after cleaning. Vegetation not Grass cover is sparse and Aerate soils and reseed and A6 M growing or overgrown seedy or areas are overgrown with woody vegetation. mulch bare areas. Maintain grass height at a minimum of 6 inches for best stormwater treatment. Remove woody growth, recontour, and reseed as necessary. M,S Erosion damage to slopes See Ponds Checklist. See Ponds Checklist. M Conversion by homeowner to incompatible use Swale has been filed in or blocked by shed, woodpile, shrubbery, etc. If possible, speak with homeowner and request that swale area be restored. Contact the County to report problem if not rectified voluntarily. A Swale does not drain Water stands in swale or flow velocity is very slow. Stagnation occurs. A survey may be needed to check grades. Grades need to be in 1-5% range if possible. If grade is less than 1% underdrains may need to be installed. If you are unsure whether a problem exists, please contact a Professional Engineer. Comments: Key: A=Annual (March or April preferred) M=Monthly (see schedule) S=After major storms (use 1-inch in 24 hours as a guideline) A7 ATTACHMENT "A" (CONTINUED) Maintenance Checklist for Grounds (Landscaping) Frequency Drainage System Feature  Problem Conditions to Check For Conditions That Should Exist M General Weeds (nonpoisono us) Weeds growing in more than 20% of the landscaped area (trees and shrubs only). Weeds present in less than 5% of the landscaped area. M Insect hazard Any presence of poison ivy or other poisonous vegetation or insect nests. No poisonous vegetation or insect nests present in lanscaped area. M,S Trash or litter See Ponds Checklist. See Ponds Checklist. M,S Erosion of Ground Surface Noticeable rills are seen in landscaped areas. Causes of erosion are identified and steps taken to slow down/spread out the water. Eroded areas are filled, contoured, and seeded. A Trees and shrubs Damage Limbs or parts of trees or shrubs that are split or broken which affect more than 25% of the total foliage of the tree or shrub. Trim trees/shrubs to restore shape. Replace trees/shrubs with severe damage. M Trees or shrubs that have been blown down or knocked over. Replant tree, inspecting for injury to stem or roots. Replace if severely damaged. A Trees or shrubs which are not adequately supported or are leaning over, causing exposure of the roots. Place stakes and rubber-coated ties around young trees/shrubs for support. If you are unsure whether a problem exists, please contact a Professional Engineer. Comments: Key: A=Annual (March or April preferred) M=Monthly (see schedule) S=After major storms (use 1-inch in 24 hours as a guideline) A8 Maintenance Com- ponent Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Performed Liner (if Applic- able) Liner is visible and has more than three 1/4-inch holes in it. Liner repaired or replaced. Liner is fully covered.  Ponds Berms (Dikes)      Settlements    Any part of berm which has settled 4 inches lower than the design elevation  If settlement is apparent, measure berm to determine amount of settlement Settling can be an indication of more severe problems with the berm or outlet works. A  licensed engineer in the state of Washington should be consulted to determine the source of  the settlement. Dike is built back to the design elevation.   Piping   Discernable water flow through pond berm. Ongoing erosion with potential for erosion to con- tinue. (Recommend a Goethechnical engineer be called in to inspect and evaluate condition and  recommend repair of condition. Piping eliminated. Erosion potential resolved.  Emergency Overflow/  Spillway and Berms  over 4 feet in height     Tree Growth     Tree growth on emergency spillways creates blockage problems and may cause failure of the  berm due to uncontrolled overtopping. Tree growth on berms over 4 feet in height may lead to piping through the berm which could  lead to failure of the berm. Trees should be removed. If root system is small (base less than 4 inches) the root system may be left in  place. Otherwise the roots should be removed and the berm restored. A licensed engineer in the state of  Washington should be consulted for proper berm/spillway restoration.  Piping   Discernable water flow through pond berm. Ongoing erosion with potential for erosion to con- tinue. (Recommend a Geotechnical engineer be called in to inspect and evaluate condition and  recommend repair of condition. Piping eliminated. Erosion potential resolved.   Emergency Over- flow/Spillway   Emergency Over- flow/Spillway   Only one layer of rock exists above native soil in area five square feet or larger, or any expos- ure of native soil at the top of out flow path of spillway. (Rip-rap on inside slopes need not be replaced.) Rocks and pad depth are restored to design standards.   Erosion See "Side Slopes of Pond"   Table V-A.1: Maintenance Standards - Detention Ponds (continued) Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Per- formed General Trash & Debris See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Deten- tion Ponds  Poisonous/Noxious   Vegetation See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Deten- tion Ponds Contaminants and  Pol- lution See  Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Deten- tion Ponds Rodent Holes See Table V-A.1: Maintenance Standards - Detention Ponds See  Table V-A.1: Maintenance Standards - Deten- tion Ponds 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. Sediment is  removed and/or facility is cleaned so  that infiltration system works  according to design. Table V-A.2: Maintenance Standards - Infiltration 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1006A9 Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Per- formed (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).  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 Erosion See Table V-A.1: Maintenance Standards - Detention Ponds See  Table V-A.1: Maintenance Standards - Deten- tion Ponds Emergency Overflow  Spillway  and Berms over 4 feet in height. Tree Growth See  Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Deten- tion Ponds Piping See Table V-A.1: Maintenance Standards - Detention Ponds See  Table V-A.1: Maintenance Standards - Deten- tion Ponds Emergency Overflow  Spillway Rock Missing See  Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Deten- tion Ponds Erosion See  Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Deten- tion Ponds 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. Table V-A.2: Maintenance Standards - Infiltration (continued) Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is Per- formed Storage Area       Plugged Air Vents One-half of the  cross section of a vent is blocked at any point or the vent is damaged. Vents open and  functioning. Debris and  Sediment Accumulated  sediment depth exceeds 10% of the diameter of the storage area for 1/2 length  of storage vault or any point  depth exceeds 15% of diameter.  (Example: 72-inch  storage tank would require cleaning when sediment reaches depth of 7 inches  for more than 1/2 length of  tank.) All sediment and  debris removed from storage  area. Joints Between  Tank/Pipe Section Any openings or  voids allowing material to be transported into facility. (Will require  engineering analysis to determine structural stability). All joint between  tank/pipe sections are sealed. Tank Pipe Bent Out  of Shape Any part of  tank/pipe is bent out of shape more than 10% of its design shape. (Review  required by engineer to determine  structural stability).Tank/pipe repaired  or replaced to design. Vault Structure  Includes Cracks in Wall, Bottom,  Damage to Frame and/or Top Slab Cracks wider than  1/2-inch and any evidence of soil particles entering the structure through  the cracks, or main- tenance/inspection personnel determines that the vault is  not structurally sound. Cracks wider than  1/2-inch at the joint of any inlet/outlet pipe or any evidence of soil  particles entering the vault through the  walls. Vault replaced or  repaired to design spe- cifications and is structurally sound. No cracks more  than 1/4-inch wide at the joint of  the inlet/outlet pipe. Table V-A.3: Maintenance Standards - Closed Detention Systems (Tanks/Vaults) 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1007A10 Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is per- formed 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%. 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).   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. 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 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 Top slab is free  of holes and cracks. Frame is sitting  flush on the riser rings or top slab  and firmly attached. Fractures or  Cracks in  Basin Walls/ Bottom 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. Basin replaced or  repaired to design standards. Pipe is regrouted  and secure at basin wall. Settlement/  Mis- alignment If failure of  basin has created a safety, function, or design problem. Basin replaced or  repaired to design standards. Vegetation 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. No vegetation  blocking opening to basin. No vegetation or  root growth present. Contamination and  Pol- lution See Table V-A.1: Maintenance Standards - Detention Ponds No pollution  present. Catch Basin  Cover Cover Not in Place Cover is missing  or only partially in place. Any open catch basin requires maintenance.Cover/grate is in place, meets design standards,  and is secured 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 per- son. 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 main- tenance 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, meets the design standards, and  is installed and aligned with the flow path. Table V-A.5: Maintenance Standards - Catch Basins 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1009A11 Maintenance Component Defect Condition When Maintenance is Needed Results Expected When Maintenance is Performed Flow Spreader Flow spreader  uneven or clogged so that flows are not uniformly distributed across sand  fil- ter.Spreader leveled  and cleaned so that flows are spread evenly over sand filter. Damaged Pipes Any part of the  piping that is crushed or deformed more than 20% or any other failure to the   piping.Pipe repaired or  replaced. Table V-A.13: Maintenance Standards - Sand Filters (Above Ground/Open) (continued) Maintenance Component Defect Condition When Maintenance is Needed Results Expected When Maintenance is Performed Below  Ground   Vault. Sediment  Accumulation on Sand Media Section Sediment depth  exceeds 1/2-inch.No sediment  deposits on sand filter section that which would impede permeability of  the  filter section. Sediment  Accumulation in Pre-Settling Portion  of Vault Sediment  accumulation in vault bottom exceeds the depth of the sediment zone plus  6- inches.No sediment  deposits in first chamber of vault. Trash/Debris  Accumulation Trash and debris  accumulated in vault, or pipe inlet/outlet, floatables and non-floatables.   Trash and debris  removed from vault and inlet/outlet piping. Sediment in Drain  Pipes/Cleanouts When drain pipes,  cleanouts become full with sediment and/or debris.Sediment and  debris removed. Short Circuiting When seepage/flow  occurs along the vault walls and corners. Sand eroding near inflow area.Sand filter media  section re-laid and compacted along perimeter of vault to form a semi- seal. Erosion  protection added to dissipate force of incoming flow and curtail erosion. Damaged Pipes Inlet or outlet  piping damaged or broken and in need of repair.Pipe repaired  and/or replaced. Access Cover  Damaged/Not Working Cover cannot be opened,  corrosion/deformation of cover. Maintenance person  cannot remove cover using normal lifting pressure. Cover repaired to  proper working specifications or replaced. Ventilation Ventilation area  blocked or plugged Blocking material  removed or cleared from ventilation area. A specified % of the vault  surface  area must provide ventilation to the vault interior (see design  specifications).  Vault Structure  Damaged; Includes Cracks in  Walls, Bottom, Damage to Frame and/or Top  Slab. Cracks wider than 1/2-inch  or evidence of soil particles entering the structure through the  cracks, or  maintenance/inspection personnel determine that the vault is not structurally   sound. Cracks wider than  1/2-inch at the joint of any inlet/outlet pipe or evidence of soil particles   entering through the cracks. Vault replaced or  repairs made so that vault meets design specifications and is struc- turally  sound. Vault repaired so  that no cracks exist wider than 1/4-inch at the joint of the inlet/outlet   pipe. Baffles/Internal  walls Baffles or walls  corroding, cracking, warping and/or showing signs of failure as determined  by  maintenance/inspection person.Baffles repaired  or replaced to specifications. Access Ladder  Damaged Ladder is corroded  or deteriorated, not functioning properly, not securely attached to structure   wall, missing rungs, cracks, and misaligned. Ladder replaced or  repaired to specifications, and is safe to use as determined by  inspection  personnel. Table V-A.14: Maintenance Standards - Sand Filters (Below Ground/Enclosed) Maintenance Component Defect Condition When Maintenance is Needed Results Expected When Maintenance is Performed Below Ground Sediment  Accumulation on Media.Sediment depth  exceeds 0.25-inches.No sediment  deposits which would impede permeability of the  Table V-A.15: Maintenance Standards - Manufactured Media Filters 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1014A12 Maintenance Component Defect Condition When Maintenance is Needed Results Expected When Maintenance is Performed Vault compost media. Sediment  Accumulation in Vault Sediment depth  exceeds 6-inches in first chamber.No sediment  deposits in vault bottom of first chamber. Trash/Debris  Accumulation Trash and debris  accumulated on compost filter bed.Trash and debris removed  from the compost filter bed. Sediment in Drain  Pipes/Clean-Outs When drain pipes,  clean-outs, become full with sediment and/or debris.Sediment and  debris removed. Damaged Pipes Any part of the  pipes that are crushed or damaged due to corrosion and/or settlement.Pipe repaired  and/or replaced. Access Cover  Damaged/Not Working Cover cannot be  opened; one person cannot open the cover using normal lifting pressure,  cor- rosion/deformation of cover.Cover repaired to  proper working specifications or replaced. Vault Structure  Includes Cracks in Wall, Bottom,  Damage to Frame and/or Top Slab Cracks wider than  1/2-inch or evidence of soil particles entering the structure through the  cracks, or main- tenance/inspection personnel determine that the vault is not  structurally sound. Cracks wider than  1/2-inch at the joint of any inlet/outlet pipe or evidence of soil particles  entering through the  cracks. Vault replaced or  repairs made so that vault meets design spe- cifications and is structurally  sound. Vault repaired so  that no cracks exist wider than 1/4-inch at the  joint of the inlet/outlet  pipe. Baffles Baffles corroding,  cracking warping, and/or showing signs of failure as determined by  maintenance/inspection  person.Baffles repaired  or replaced to specifications. Access Ladder  Damaged Ladder is corroded  or deteriorated, not functioning properly, not securely attached to structure  wall, missing  rungs, cracks, and misaligned. Ladder replaced or  repaired and meets specifications, and is safe  to use as determined by  inspection personnel. Below Ground   Cartridge Type Media Drawdown of water  through the media takes longer than 1 hour, and/or overflow occurs  frequently.Media cartridges  replaced. Short Circuiting Flows do not  properly enter filter cartridges.Filter cartridges  replaced. Table V-A.15: Maintenance Standards - Manufactured Media Filters (continued) 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1015A13 ATTACHMENT “B” A14 INSTRUCTIONS FOR THE OWNER/S IN Rhoton Road Binding Site Plan POLLUTION SOURCE CONTROLS The attached material includes information on pollution source controls. Pollution source controls are actions taken by a person or person representing a business to reduce the amount of pollution reaching surface and ground waters. Pollution source controls also called “best management practices” (BMP’s) include: Altering the activity (e.g., substitute not-toxic products or recycle) Enclosing or covering the activity. Segregating the activity (e.g. diverting surface water runoff away from an area that is contaminated.) Pollution source controls are needed because of the contamination found in surface water runoff from commercial areas and the effect of this contamination on aquatic life and human health. Research on urban runoff in the Puget Sound area and elsewhere has found oil and grease, nutrients, organic substances, toxic metals, bacteria, viruses, and sediments at unacceptable levels. Effects of contaminate runoff include closure of shellfish harvesting areas and swimming areas, pollution of wells, mortality of young fish and other aquatic organisms, tumors on fish, and impairment of fish reproduction. The Rhoton Road Binding Site Plan project contains impervious surfaces that will collect contaminates from automobiles, garbage, and improperly disposed of chemicals. These materials are conveyed to the storm drainage systems and will enter into the ground water, if not treated properly. Attachment “B” contains a number of BMP’s for various uses within the development site. Each owner shall give a copy of the BMP’s suitable to this or her respective activity. If a certain activity is not contained in Attachment “B”, please contact Larson and Associates at 253-474- 3404 for a specific BMP activity type. A15 REQUIRED ACTIONS OF ALL OWNERS The following actions shall be taken by all owners to ensure that pollution generated on The Rhoton Road Binding Site Plan project is minimized. 1) Warning signs (e.g. “Dump no waste – drains to Stream”) shall be stenciled or embossed adjacent to all catch basin inlets. They shall be repainted once a year or more as necessary. 2) Paved roadways shall be swept twice a year. It is recommended that newer high-velocity vacuum sweeper be used. 3) The storm drainage system shall be maintained per Attachment “A” 4) No activities shall be conducted on the property that is likely to result in a short-term high concentration discharge of pollution to the storm system. Such activities shall include, but are not limited to car washes, vehicle maintenance, and cleaning of equipment and or vehicles, unless the project has been properly permitted for such uses and the BMP’s for such uses have been received by the owner. 5) Automobile fluids, chemicals etc. shall be disposed of legally and properly. 6) All garbage shall be contained in appropriate containers. A16 4.3 BMPs TO CONSIDER FOR ALL ACTIVITIES This is a summary of items that each business/homeowner should consider. As stated before, most of these are common sense, housekeeping types of solutions, but if each business/homeowner would take some action on each of these, the improvement in water quality would be substantial. 1. Avoid the activity or reduce its occurrence If you can, avoid the activity or do it less frequently. If there a substitute process or a different material you can use to get the job done? Can you do a larger run of a process at one time, thus reducing the number of times per week or month it needs to be repeated? For instance, raw materials could be delivered close to the time of use instead of being stockpiled and exposed to the weather. Perhaps you could avoid one solvent-washing step altogether. The Department of Ecology or the Thurston County Health Department can provide pollution prevention assistance. 2. Move the activity indoors Sometimes it is fairly easy to move an activity indoors out of the weather. The benefits of this are twofold; you prevent runoff contamination, and you provide for easier, more controlled cleanup if a spill occurs. An example would be unloading and storing barrels of chemicals inside a garage area instead of doing it outside. Please be aware that moving storage areas indoors may require installation of fire suppression equipment or other building modifications as required by the Uniform Building Code, the Uniform Fire Code, or local ordinances. 3. Use less material Don’t buy or use more material than you really need. This not only helps keep potential disposal, storage and pollution problems to a minimum, but will probably save you money, too. 4. Use the least toxic materials available Investigate the use of materials that are less toxic than what you use now. Perhaps a causic-type detergent or a solvent could be replaced with a more environmentally friendly product. Remember that even if you do switch to a biodegradable product, nothing but uncontaminated water is allowed to enter the storm drain system. 5. Create and maintain vegetated areas near activity locations Vegetation of various kinds can help filter pollutants out of stormwater, so it is advisable to route stormwater through vegetated areas located near your activity. For instance, many parking lots contain grassy islands, typically formed in a “hump”. By creating those islands as depressions instead of humps, they can be used to treat runoff from the parking lot or roof. Also, don’t forget the erosion control benefits of vegetation at your site. A17 6. Locate activities as far as possible from surface drainage paths Activities located as far as possible from known drainage paths, ditches, streams, and drains will be less likely to pollute, since it will take longer for material to reach the drainage feature. This gives you more time to react in the event of a spill, or if it is a “housekeeping” issue may protect the local waters long enough for you to clean up the area around the activity. Don’t forget that groundwater issues are always prominent, no matter where the activity is located so the actions taken on your site on a day-to-day basis are always important, even in dry weather. 7. Keep storm drain systems clean Pollutants can concentrate over time in storm drainage structures such as catch basins, ditches and storm drains. When a large storm event occurs, it can mobilize these pollutants and carry them to receiving waters. Develop and implement maintenance practices, inspections, and schedules for treatment devices (e.g., detention ponds, oil/water separators, vegetated swales, etc.). Requirements for cleaning catch basins will be discussed later in the specific BMP S.9. 8. Reduce, reuse and recycle as much as possible Always look for ways to recycle instead of just disposing. This can save money as well as keep both hazardous and non-hazardous materials out of the landfills. You can learn more about other businesses that have made process changes allowing recycling of chemicals by calling the DOE at 1-800-RECYCLE and requesting publication #9245 and 90-22. Another unique recycling opportunity for businesses is available through the “matchmaker”, helping one company’s waste become another company’s asset. For instance, waste peach pits from a cannery become potpourri ingredients to another’s business. Call IMEX at 206-625-623 to list your potentially usable solid or chemical waste in their publication. 9. Be an advocate for stormwater pollution prevention Help friends, partners and business associates find ways to reduce stormwater pollution in their activities. Most people want clean water, and do not pollute intentionally. Share your ideas and the BMPs in this manual to get them thinking about how their everyday activities affect water quality. 10. Report Violators Allowing anyone to pollute our waters is wrong. We all must do our part to protect water, fish, wildlife and our own health, by employing proper BMPs, and reporting those who are causing pollution. A18 STORMWATER MANAGEMENT MANUAL FOR THE PUGET SOUND BASIN II-5.10 BMPS FOR SMALL PARCELS A Small Parcel Stormwater Management Plan must be developed which satisfies the Small Parcel Minimum Requirements found in Volume II, Chapter II-2. These in turn may be satisfied by employing a suitable selection from the following list of BMPs. BMP ES.10 PLANNED CLEARING AND GRADING Plan and implementation proper clearing and grading of the site. It is most important only to clear the areas needed, thus keeping exposed areas to a minimum. Phase clearing so that only those areas that are actively being worked are uncovered. Note: Clearing limits should be flagged in the lot or area prior to initiating clearing. BMP ES.20 EXCAVATING BASEMENT SOIL Located excavated basement soil a reasonable distance behind the curb, such as in the backyard or side yard area. This will increase the distance eroded soil must travel to reach the storm sewer system. Soil piles should be covered until the soil is either used or removed. Piles should be situated so that sediment does not run into the street or adjoining yards. BMP ES.30 BACKFILLING Backfill basement walls as soon as possible and rough grade the lot. This will eliminate large soil mounds which are highly erodible and prepares the lot for temporary cover which will further reduce erosion potential. BMP ES.40 REMOVAL OF EXCESS SOIL Remove excess soil from the site as soon as possible after backfilling. This will eliminate any sediment loss from surplus fill. BMP ES.50 MANAGEMENT OF SOIL BANKS If a lot has a soil bank higher than the curb, a trench or berm should be installed moving the bank several feet behind the curb. This will reduce the occurrence of gully and hill erosion while providing a storage and settling area for stormwater. BMP ES.60 CONSTRUCTION ROAD ACCESS Apply gravel or crushed rock to the driveway area and restrict truck traffic to this one route. Driveway paving can be installed directly over the gravel. This measure will eliminate soil from adhering to tires and stops soil from washing into the street. This measure requires periodic inspection and maintenance including washing, top-dressing with additional stone, reworking and compaction. (For further details see BMP E2.10, Chapter II-5.7.1). A19 BMP ES.70 SOIL STABILIZATION Stabilized denuded areas of the site by mulching, seeding, planting, or sodding. For further details on standards and specifications, see BMPs No. E1.10, E1.15, E1.35, E1.40 in Chapter II-5. BMP ES.80 STREET CLEANING Provide for periodic street cleaning to remove any sediment that may have been tracked out. Sediment should be removed by shoveling or sweeping and carefully removed to a suitable disposal area where it will not be re-eroded. II-5.11 References (1) Goldman, Steven J., Erosion and Sediment Control Handbook, McGraw-Hill, 1986. (2) Horner, Richard R., Juno Guedry and Michael H. Kortenhof, Highway Construction Site Erosion and Pollution Control Manual, Washington State Department of Transportation with the United States Department of Transportation Federal Highway Administration, WA-RD 200.2, January, 1990. (3) Metro, Summary of Preliminary Data Analysis – BMP Survey of Single Family Residential Construction Sites, January, 1984. (4) Brandy, Nile C., The Nature and Properties of Soils, Eight Edition, MacMillan, 1974. A20 APPENDIX “B” MISCELLANOUS INFORMATION B1 B2 B3 B4 B5 B6 B7 Quality Geo NW, PLLC Serving All of Washington & Oregon | Geotechnical Investigations & Engineering Consultation Phone: 360-878-9705| Web: qualitygeonw.com | Mail: 4631 Whitman Ln SE, Ste D, Lacey, WA 98513 8/24/2023 C&E Developments, LLC c/o: Larson & Associates, Inc PO Box 2983 Attn: Steve Voorhies Yelm, WA 9027 Pacific Ave, Ste 4 Tacoma, WA Subject: C&E - Geotechnical Services Report TPN: 22719240203 & 22719240201, Rhoton Rd, Yelm, WA Project Number: QG23-138 Dear Client, At your request, Quality Geo NW, PLLC (QG) has completed a soils investigation of the above- referenced project. The investigation was performed in accordance with our proposal for professional services. We would be pleased to continue our role as your geotechnical consultant of record during the project planning and construction phases, as local inspection firms have not been found to be as familiar or reliably experienced with geotechnical design. This may include soil subgrade inspections, periodic review of special inspection reports, or supplemental recommendations if changes occur during construction. We will happily meet with you at your convenience to discuss these and other additional Time & Materials services. We thank you for the opportunity to be of service on this project and trust this report satisfies your project needs currently. QG wishes you the best while completing the project. Respectfully Submitted, Quality Geo NW, PLLC Luke Preston McCann, L.E.G. Ray Gean II Owner + Principal Staff Geologist/Project Manager B8 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 2 SOILS REPORT C&E GEOTECHNICAL CONSULTATION TPN: 22719240203 & 22719240201, RHOTON ROAD YELM, WA C&E Developments, LLC c/o: Larson & Associates, Inc PO Box 2983 Attn: Steve Voorhies Yelm, WA 9027 Pacific Ave, Ste 4 Tacoma, WA Prepared by: Approved by: Alexander Barnes, G.I.T. Luke Preston McCann, L.E.G. Staff Geologist, Laboratory Supervisor Principal Licensed Engineering Geologist Quality Geo NW, PLLC Geotechnical Investigation & Engineering Consultation Phone: 360-878-9750| Web: qualitygeonw.com Mail: 4631 Whitman Ln SE, Ste D, Lacey, WA 98513 8/24/2023 QG Project # QG23-138 Copyright © 2023 Quality Geo NW, PLLC All Rights Reserved 8/24/2023 B9 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 3 TABLE OF CONTENTS 1.0 INTRODUCTION ...............................................................................................................4 1.1 PROJECT DESCRIPTION ............................................................................................................................. 4 1.2 FIELD WORK ................................................................................................................................................ 4 2.0 EXISTING SITE CONDITIONS ........................................................................................5 2.1 AREA GEOLOGY .......................................................................................................................................... 5 2.2 SITE & SURFACE CONDITIONS ................................................................................................................ 5 2.3 SOIL LOG ....................................................................................................................................................... 5 2.4 SURFACE WATER AND GROUNDWATER CONDITIONS ..................................................................... 6 3.0 GEOTECHNICAL RECOMMENDATIONS .....................................................................7 3.1 SHALLOW FOUNDATION RECOMMENDATIONS ................................................................................. 7 3.1.1 BUILDING SLAB ON GRADE FLOOR ............................................................................................. 8 3.2 INFILTRATION RATE DETERMINATION ................................................................................................ 9 3.2.1 GRADATION ANALYSIS METHODS & RESULTS ......................................................................... 9 3.2.2 TREATMENT POTENTIAL .............................................................................................................. 11 3.2.3 DRAINAGE RECOMMENDATIONS ............................................................................................... 11 4.0 CONSTRUCTION RECOMMENDATIONS ...................................................................12 4.1 EARTHWORK ............................................................................................................................................. 12 4.1.1 GRADING & EXCAVATION ............................................................................................................ 12 4.1.2 SUBGRADE EVALUATION & PREPARATION ............................................................................ 12 4.1.3 SITE PREPARATION, EROSION CONTROLL, WET WEATHER............................................... 12 4.2 STRUCTURAL FILL MATERIALS AND COMPACTION ....................................................................... 13 4.2.1 MATERIALS ...................................................................................................................................... 13 4.2.2 FILL PLACEMENT AND COMPACTION ...................................................................................... 14 4.3 TEMPORARY EXCAVATIONS AND TRENCHES .................................................................................. 14 5.0 SPECIAL INSPECTION ...................................................................................................16 6.0 LIMITATIONS ..................................................................................................................17 Region & Vicinity Maps ................................................................................................................ 18 Exploration Map ............................................................................................................................. 19 Exploration Logs ............................................................................................................................ 20 Laboratory Results ......................................................................................................................... 25 B10 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 4 1.0 INTRODUCTION This report presents the findings and recommendations of Quality Geo NW’s (QG) soil investigation conducted in support of new site surface improvements. 1.1 PROJECT DESCRIPTION QG understands the project entails new construction within two presently undeveloped parcels. QG has been contracted to perform a soils investigation of the proposed site to provide foundation, stormwater, and earthwork recommendations. 1.2 FIELD WORK Site exploration activities were performed on 7/17/2023 and 8/15/2023. Exploration locations were marked in the field by a QG Staff Geologist with respect to the provided map and cleared for public and private conductible utilities. Our exploration locations were selected by a QG Staff Geologist prior to fieldwork to provide safest access to relevant soil conditions. The geologist directed the advancement of 4 excavated test pits (TP). The test pits were advanced within the vicinity of the anticipated development footprint areas, to maximum depths of 10.0 feet below present grade (BPG) in general accordance with the specified contract depth. During explorations, QG logged each soil horizon encountered and field classified them in accordance with the Unified Soil Classification System (USCS). Representative soil samples were collected from each unit, identified according to boring location and depth, placed in plastic bags to protect against moisture loss, and were transported to the soil laboratory for supplemental classification and other tests. B11 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 5 2.0 EXISTING SITE CONDITIONS 2.1 AREA GEOLOGY QG reviewed available map publications to assess known geologic conditions and hazards present at the site location. The Washington Geologic Information Portal (WGIP), maintained by the Department of Natural Resources Division of Geology and Earth Resources, provides 1:100,000- scale geologic mapping of the region. The geology of the site location and vicinity consists of continental glacial outwash and gravel (Qgog). The deposits on site are described as “Recessional and proglacial, stratified pebble, cobble, and boulder gravel deposited in meltwater streams and their deltas; locally contains ice-contact deposits.” The WGIP Map also offers layers of mapped geohazard conditions within the state. According to the regional-scale interactive map, there are no mapped recent deep seated landslide deposits to exist within the vicinity of the parcel. Available LiDAR imagery of the site did not reveal obvious or prominent landslide features within the site as well as within the vicinity. The United States Department of Agriculture portal (USDA) provides a soil mapping of the region. The soils in the vicinity are mapped as Spanaway gravelly sandy loam (110), these are formed by outwash plains and terrace deposits. The parent material for these soils is volcanic ash over gravelly outwash. The soils are described as gravelly sandy loam from 0 to 15 inches, very gravelly loam from 15 to 20 inches, and extremely gravelly sand from 20 to 60+ inches. Depth to restrictive feature is more than 80 inches. Capacity of most limiting layer to transmit water (ksat), is listed as high (1.98 to 5.95 in/hr). Depth to water table is more than 80 inches. 2.2 SITE & SURFACE CONDITIONS The project area is relatively flat, near the same elevation as the adjacent road. There are very few trees within the parcels, which mostly populate the perimeter of the properties. The remainder of the vegetation consists of grasses and low-lying shrubs, which have been mowed. There are no buildings on the site. The parcel to the north is owned by CalPortland, to the south is the Yelm Church of Christ and Yelm Boat & RV storage. The parcel to the west has residential structures and the east bounded by NW Rhoton Rd. 2.3 SOIL LOG Site soil conditions were generally consistent across the property and within both test pits. Representative lab samples were taken from TP-2. Soil conditions on site were as follows: B12 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 6 • 0’ to 0.5’ – Topsoil: An overriding 0.5-foot to 1-foot layer of topsoil was present over the site, high in organic content in the form of grass roots. This layer was brown, loose, and dry with cobbles. In TP-4 peat fill/soils were encountered as topsoil down to depths of 4-feet. • 0.5’ to 10.0’ – Well/Poorly Graded Gravel with Sand (GW/GP) Beneath the topsoil is a layer of brown, dry to moist cobbly soil with some organics present. An abundance of cobbles up to 2-feet in diameter was present in both test pits, consistently rounded at all depths. No groundwater was encountered in either of the test pits. TP-2 encountered refusal at 5 feet below grade due to the size of the boulders. In TP-4, a highly organic peaty fill was encountered from 0 to 4-foot depth before returning to GP soils. This soil contained a variety of organic material from decaying organic debris to live roots, had few cobbles, and was dark brown in color. Additionally, this soil is much less dense than the underlying gravel material. 2.4 SURFACE WATER AND GROUNDWATER CONDITIONS No active surface water features are present on site. In the near vicinity, Yelm Creek is ~550 feet west of the parcel. Based on well logs made publicly available by the WA Department of Ecology, the groundwater table is reported to exist at approximately 22 feet beneath the entire site. QG’s scope of work did not include determination or monitoring of seasonal groundwater elevation variations, formal documentation of wet season site conditions, or conclusive measurement of groundwater elevations at depths past the extent feasible for explorations at the time of the field explorations. B13 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 7 3.0 GEOTECHNICAL RECOMMENDATIONS 3.1 SHALLOW FOUNDATION RECOMMENDATIONS Assuming site preparation is completed as described below, we recommend the following: • Subgrade Preparation QG recommends excavating and clearing any loose or organic cover soils, peat soils, uncontrolled fill, including the overriding layer of topsoil where necessary, from areas of proposed pavement construction, down to firm bearing conditions and benching the final bottom of subgrade elevation flat. Excavations should be performed with a smooth blade bucket to limit disturbance of subgrade soils. Vibratory compaction methods are suitable for densification of the non-organic native soils. After excavations have been completed to the planned subgrade elevations, but before placing fill or structural elements, the exposed subgrade should be evaluated under the periodic guidance of a QG representative. Any areas that are identified as being soft or yielding during subgrade evaluation should be brought to the attention of the geotechnical engineer. Where over excavation is performed below a structure, the over excavation area should extend beyond the outside of the footing a distance equal to the depth of the over excavation below the footing. The over-excavated areas should be backfilled with properly compacted structural fill. The proposed buildings may utilize either stepped or continuous footings with slab-on-grade elements. For continuous footing elements, upon reaching bearing strata, we recommend benching foundation lines flat. Continuous perimeter and strip foundations may be stepped as needed to accommodate variations in final subgrade level. We also recommend maximum steps of 18 inches with spacing of at least 5 feet be constructed unless specified otherwise by the design engineer. Structural fill may then be placed as needed to reestablish final foundation grade. • Allowable Bearing Capacity: Up to 1,500 pounds per square foot (psf) for foundations placed on compacted native soil or approved structural fill, placed in accordance with the recommendations of Section 4.2. Bearing capacities, at or below 1,500 psf may eliminate the need for additional inspection requirements if approved by the county. The allowable bearing capacity may be increased by 1/3 for transient loading due to wind and seismic events. • Minimum Footing Depth: For a shallow perimeter and spread footing system, all exterior footings shall be embedded a minimum of 18 inches and all interior footings shall be embedded a minimum of 12 inches B14 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 8 below the lowest adjacent finished grade, but not less than the depth required by design. However, all footings must also penetrate to the prescribed bearing stratum cited above. Minimum depths are referenced per IBC requirements for frost protection; other design concerns may dictate greater values be applied. • Minimum Footing Width: Footings should be proportioned to meet the stated bearing capacity and/or the IBC 2018 (or current) minimum requirements. For a shallow perimeter and spread footing system, continuous strip footings should be a minimum of 16 inches wide and interior or isolated column footings should be a minimum of 24 inches wide. • Estimated Settlements: All concrete settles after placement. We estimate that the maximum settlements will be on the order of 0.5 inch, or less, with a differential settlement of ½ inch, or less, over 50 linear feet. Settlement is anticipated to occur soon after the load is applied during construction. 3.1.1 BUILDING SLAB ON GRADE FLOOR QG anticipates that slab-on-grade floors are planned for the interior of the proposed building. Based on typical construction practices, we assume finished slab grade will be similar to or marginally above present grade for the below recommendations. If floor grades are planned to be substantially raised or lowered from existing grade, QG should be contacted to provide revised or alternative recommendations. • Capillary Break: A capillary break will be helpful to maintain a dry slab floor and reduce the potential for floor damage resulting from shallow perched water inundation. To provide a capillary moisture break, a 6-inch thick, properly compacted granular mat consisting of open-graded, free- draining angular aggregate is recommended below floor slabs. To provide additional slab structural support, or to substitute for a structural fill base pad where specified, QG recommends the capillary break should consist of crushed rock all passing the 1-inch sieve and no more than 3 percent (by weight) passing the U.S. No. #4 sieve, compacted in accordance with Section 4.2.2 of this report. • Vapor Barrier: A vapor retarding membrane such as 10 mil polyethylene film should be placed beneath all floor slabs to prevent transmission of moisture where floor coverings may be affected. Care should be taken during construction not to puncture or damage the membrane. To protect the membrane, a layer of sand no more than 2 inches thick may be placed over the membrane if B15 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 9 desired. If excessive relict organic fill material is discovered at any location, additional sealant or more industrial gas barriers may be required to prevent off-gassing of decaying material from infiltrating the new structure. These measures shall be determined by the structural engineer to meet local code requirements as necessary. •Structural Design Considerations: QG assumes the design and specifications of slabs will be assessed by the project design engineer. We suggest a minimum unreinforced concrete structural section of 4.0 inches be considered to help protect against cracking and localized settlement, especially where larger equipment or localized loads are anticipated. It is generally recommended that any floor slabs and annular exterior concrete paving subject to vehicular loading be designed to incorporate reinforcing. Additionally, some level of reinforcing, such as a wire mesh may be desirable to prolong slab life due to the overwhelming presence of such poor underlying soils. It should be noted that QG does not express any guarantee or warranty for proposed slab sections. 3.2 INFILTRATION RATE DETERMINATION QG understands the design of on-site stormwater controls are pending the results of this study to confirm design parameters and interpreted depths to perched seasonal groundwater and restrictive soil features. 3.2.1 GRADATION ANALYSIS METHODS & RESULTS During test pit excavations for general site investigation, QG additionally collected representative samples of native soil deposits among potential infiltration strata and depths from TP-1 to characterize the local infiltration conditions. We understand the project will be subject to infiltration design based on the Washington Department of Ecology Stormwater Management Manual for Western Washington (DoE SMMWW). For initial site infiltration characterization within the scope of this study, laboratory gradation analyses were completed including sieve and hydrometer tests for stormwater design characterization and rate determination to supplement field observations. Results of laboratory testing in terms of rate calculation are summarized below. Laboratory results were interpreted to recommended design inputs in accordance with methods of the Stormwater Design Manual. Gradation results were applied to the Massmann (2003) equation (1) to calculate Ksat representing the initial saturated hydraulic conductivity. (1) log10(Ksat) = -1.57 + 1.90*D10 + 0.015*D60 - 0.013*D90 - 2.08*ff B16 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 10 Corrected Ksat values presented below are a product of the initial Ksat and correction factor CFT. For a generalized site-wide design situation, we have applied a site variability factor of CFv = 0.7 along with typical values of CFt = 0.4 (for the Grain Size Method) and CFm = 0.9 (assuming standard influent control). (2) CFT = CFv x CFt x CFm = 0.7 x 0.4 x 0.9 = 0.25 Results were cross-referenced with test pit logs to determine the validity and suitability of unique materials as an infiltration receptor. Additional reduction factors were applied for practical rate determination based on our professional judgement. Table 1. Results Of Massmann Analysis TP # Sample Depth (BPG) Unit Extent (ft) Soil Type D10 D60 D90 Fines (%) Ksat (in/hr) Corrected Ksat (in/hr) LT Design Infiltration Rate(in/hr) Cation Exchange Capacity (meq/100g) Organic Content % 2 2 ft 0.5ft to 10.0ft GW 0.559 28.17 44.54 4.8 487.85 60.98 20.0 5.4 2.5 2 6 ft 0.5ft to 10.0ft GP 0.408 20.52 42.26 4.4 211.15 26.39 20.0 6.2 1.4 Beneath topsoil, the lower gravelly soils were observed to generally exhibit minimal fines content and minimal oxidation patterns. In-ground infiltration structures are required to maintain a minimum 5-feet separation from restrictive soil & groundwater features. For in-ground infiltration galleries, we recommend a maximum design rate of up to 20.0 inches/hour be considered. Available well logs did not indicate the potential for shallow ground water. The required separation appears generally achievable across the site. At this time, QG does not recommend mounding analysis due to the generally suitable site conditions. Alternatives to in-ground infiltration include the use of rain gardens, bio-swales, or pervious pavement, which can be considered at the discretion of the designer and client depending on final development needs and constraints. for shallow infiltration features utilizing treatment media, we recommend a maximum design rate of up to 1.0 inch/hour be considered. This considers potential reductions from compaction during construction. QG recommends the facility designer review these results and stated assumptions per reference literature to ensure applicability with the proposed development, level of anticipated controls, and long- term maintenance plan. The designer may make reasonable adjustments to correction factors and the resulting design values based on these criteria to ensure design and operational intent is met. We recommend that we be contacted if substantial changes to rate determination are considered. B17 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 11 3.2.2 TREATMENT POTENTIAL Depending on stormwater and runoff sources, some stormwater features, such as rain gardens or pervious pavements may require treatment. Stormwater facilities utilizing native soils as treatment media typically require Cation Exchange Capacities (CEC) of greater than 5 milliequivalents per 100grams (meq/100g) and organic contents greater than 1% (this may vary depending on local code). Soils across the site do the minimum standards for treatment potential. 3.2.3 DRAINAGE RECOMMENDATIONS QG recommends proper drainage controls for stormwater runoff during and after site development to protect the site. The ground surface adjacent to structures should be sloped to drain away at a 5% minimum to prevent ponding of water adjacent to them. Foundations shall incorporate a wraparound footing drain composed of imported clean granular drain rock. There shall be a perforated drainpipe connected around the perimeter of the footing drain (within the rock) graded to gravity drain to an outfall pipe, to allow any accumulated water to be released to an approved drainage feature or location. The outfall point must be lower in elevation than the lowest point of possible water accumulation in the mat fill, so as to allow any captured water within the mat or crawlspace to completely drain away from the building footprint preventing standing water from accumulating. QG recommends all stormwater catchments (new or existing) be tightlined (piped) away from structures to an existing catch basin, stormwater system, established channel, or approved outfall to be released using appropriate energy-dissipating features at the outfall to minimize point erosion. Roof and footing drains should be tightlined separately or should be gathered in an appropriately sized catch basin structure and redistributed collectively. If storm drains are incorporated for impervious flatworks (driveways, sidewalks, etc.) collected waters should also be discharged according to the above recommendations. B18 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 12 4.0 CONSTRUCTION RECOMMENDATIONS 4.1 EARTHWORK 4.1.1 GRADING & EXCAVATION A grading plan was not available to QG at the time of this report. However, based on provided conceptual plans, this study assumes finished site grade will approximate current grade. Therefore, depths referred to in this report are considered roughly equivalent to final depths. Excavations can generally be performed with conventional earthmoving equipment such as bulldozers, scrapers, and excavators. 4.1.2 SUBGRADE EVALUATION & PREPARATION After excavations have been completed to the planned subgrade elevations, but before placing fill or structural elements, the exposed subgrade should be evaluated under the part-time observation and guidance of a QG representative. The special inspection firm should continuously evaluate all backfilling. Any areas that are identified as being soft or yielding during subgrade evaluation should be over excavated to a firm and unyielding condition or to the depth determined by the geotechnical engineer. Where over excavation is performed below a structure, the over excavation area should extend beyond the outside of the footing a distance equal to the depth of the over excavation below the footing. The over-excavated areas should be backfilled with properly compacted structural fill. 4.1.3 SITE PREPARATION, EROSION CONTROLL, WET WEATHER Any silty or organic rich native soils may be moisture-sensitive and become soft and difficult to traverse with construction equipment when wet. During wet weather, the contractor should take measures to protect any exposed soil subgrades, limit construction traffic during earthwork activities, and limit machine use only to areas undergoing active preparation. Once the geotechnical engineer has approved the subgrade, further measures should be implemented to prevent degradation or disturbance of the subgrade. These measures could include, but are not limited to, placing a layer of crushed rock or lean concrete on the exposed subgrade, or covering the exposed subgrade with a plastic tarp and keeping construction traffic off the subgrade. Once the subgrade has been approved, any disturbance because the subgrade was not protected should be repaired by the contractor at no cost to the owner. During wet weather, earthen berms or other methods should be used to prevent runoff from draining into excavations. All runoffs should be collected and disposed of properly. Measures may B19 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 13 also be required to reduce the moisture content of on-site soils in the event of wet weather. These measures can include, but are not limited to, air drying and soil amendment, etc. QG recommends earthwork activities take place during the summer dry season. 4.2 STRUCTURAL FILL MATERIALS AND COMPACTION 4.2.1 MATERIALS All material placed below structures or pavement areas should be considered structural fill. Excavated native soils may be considered suitable for reuse as structural fill on a case-by-case basis. Imported material can also be used as structural fill. Care should be taken by the earthwork contractor during grading to avoid contaminating stockpiled soils that are planned for reuse as structural fill with native organic materials. Frozen soil is not suitable for use as structural fill. Fill material may not be placed on frozen soil. Structural fill material shall be free of deleterious materials, have a maximum particle size of 4 inches, and be compactable to the required compaction level. Imported structural fill material should conform to the WSDOT manual Section 9-03.14(1) Gravel Borrow, or an approved alternative import material. Controlled-density fill (CDF) or lean mix concrete can be used as an alternative to structural fill materials, except in areas where free-draining materials are required or specified. Imported materials utilized for trench back fill shall conform to Section 9-03.19, Trench Backfill, of the most recent edition (at the time of construction) of the State of Washington Department of Transportation Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT Standard Specifications). Imported materials utilize as grade fill beneath roads shall conform to WSDOT Section 9-03.10, Gravel Base. Pipe bedding material should conform to the manufacturer’s recommendations and be worked around the pipe to provide uniform support. Cobbles exposed in the bottom of utility excavations should be covered with pipe bedding or removed to avoid inducing concentrated stresses on the pipe. Soils with fines content near or greater than 10% fines content may likely be moisture sensitive and become difficult to use during wet weather. Care should be taken by the earthwork contractor during grading to avoid contaminating stockpiled soils that are planned for reuse as structural fill with native organic materials. The contractor should submit samples of each of the required earthwork materials to the materials testing lab for evaluation and approval prior to delivery to the site. The samples should be B20 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 14 submitted at least 5 days prior to their delivery and sufficiently in advance of the work to allow the contractor to identify alternative sources if the material proves unsatisfactory. 4.2.2 FILL PLACEMENT AND COMPACTION For lateral and bearing support, structural fill placement below footings shall extend at minimum a distance past each edge of the base of the footing equal to the depth of structural fill placed below the footing [i.e. extending at least a 1H:1V past both the interior and the exterior of the concrete footing]. Prior to placement and compaction, structural fill should be moisture conditioned to within 3 percent of its optimum moisture content. Loose lifts of structural fill shall not exceed 12 inches in thickness. All structural fill shall be compacted to a firm and unyielding condition and to a minimum percent compaction based on its modified Proctor maximum dry density as determined per ASTM D1557. Structural fill placed beneath each of the following shall be compacted to the indicated percent compaction: • Foundation and Floor Slab Subgrades: 95 Percent • Pavement Subgrades & wall backfill (upper 2 feet): 95 Percent • Pavement Subgrades & wall backfill (below 2 feet): 90 Percent • Utility Trenches (upper 4 feet): 95 Percent • Utility Trenches (below 4 feet): 90 Percent A sufficient number of tests should be performed to verify compaction of each lift. The number of tests required will vary depending on the fill material, its moisture condition and the equipment being used. Initially, more frequent tests will be required while the contractor establishes the means and methods required to achieve proper compaction. Jetting or flooding is not a substitute for mechanical compaction and should not be allowed. 4.3 TEMPORARY EXCAVATIONS AND TRENCHES All excavations and trenches must comply with applicable local, state, and federal safety regulations. Construction site safety is the sole responsibility of the Contractor, who shall also be solely responsible for the means, methods, and sequencing of construction operations. We are providing soil type information solely as a service to our client for planning purposes. Under no circumstances should the information be interpreted to mean that QG is assuming responsibility for construction site safety or the Contractor’s activities; such responsibility is not being implied and should not be inferred. The contractor shall be responsible for the safety of personnel working in utility trenches. Given that steep excavations in native soils may be prone to caving, we recommend all utility trenches, but particularly those greater than 4 feet in depth, be supported in B21 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 15 accordance with state and federal safety regulations. Heavy construction equipment, building materials, excavated soil, and vehicular traffic should not be allowed near the top of any excavation. Temporary excavations and trenches should be protected from the elements by covering them with plastic sheeting or some other similar impermeable material. Sheeting sections should overlap by at least 12 inches and be tightly secured with sandbags, tires, staking, or other means to prevent wind from exposing the soils under the sheeting. B22 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 16 5.0 SPECIAL INSPECTION The recommendations made in this report assume that an adequate program of tests and observations will be made throughout construction to verify compliance with these recommendations. Testing and observations performed during construction should include, but not necessarily be limited to, the following: • Geotechnical plan review and engineering consultation as needed prior to construction phase, • Observations and testing during site preparation, earthwork, structural fill, and pavement section placement, • Consultation on temporary excavation cutslopes and shoring if needed, • Consultation as necessary during construction. QG recommends that we be retained for construction phase soils testing and periodic earthwork observation in accordance with the local code requirements. We also strongly recommend that QG be retained as the project Geotechnical Engineering Firm of Record (GER) during the construction of this project to perform periodic supplementary geotechnical observations and review the special inspectors reports during construction. Our knowledge of the project site and the design recommendations contained herein will be of great benefit in the event that difficulties arise and either modifications or additional geotechnical engineering recommendations are required or desired. We can also, in a timely fashion observe the actual soil conditions encountered during construction, evaluate the applicability of the recommendations presented in this report to the soil conditions encountered, and recommend appropriate changes in design or construction procedures if conditions differ from those described herein. We would be pleased to meet with you at your convenience to discuss the Time & Materials scope and cost for these services. B23 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 17 6.0 LIMITATIONS Upon acceptance and use of this report, and its interpretations and recommendations, the user shall agree to indemnify and hold harmless QG, including its owners, employees and subcontractors, from any adverse effects resulting from development and occupation of the subject site. Ultimately, it is the owner’s choice to develop and live in such an area of possible geohazards (which exist in perpetuity across the earth in one form or another), and therefore the future consequences, both anticipated and unknown, are solely the responsibility of the owner. By using this report for development of the subject property, the owner must accept and understand that it is not possible to fully anticipate all inherent risks of development. The recommendations provided above are intended to reduce (but may not eliminate) such risks. This report does not represent a construction specification or engineered plan and shall not be used or referenced as such. The information included in this report should be considered supplemental to the requirements contained in the project plans & specifications and should be read in conjunction with the above referenced information. The selected recommendations presented in this report are intended to inform only the specific corresponding subjects. All other requirements of the above-mentioned items remain valid, unless otherwise specified. Recommendations contained in this report are based on our understanding of the proposed development and construction activities, field observations and explorations, and laboratory test results. It is possible that soil and groundwater conditions could vary and differ between or beyond the points explored. If soil or groundwater conditions are encountered during construction that differ from those described herein, or if the scope of the proposed construction changes from that described in this report, QG should be notified immediately in order to review and provide supplemental recommendations. The findings of this study are limited by the level of scope applied. We have prepared this report in substantial accordance with the generally accepted geotechnical engineering practice as it exists in the subject region. No warranty, expressed or implied, is made. The recommendations provided in this report assume that an adequate program of tests and observations will be conducted by a WABO approved special inspection firm during the construction phase in order to evaluate compliance with our recommendations. This report may be used only by the Client and their design consultants and only for the purposes stated within a reasonable time from its issuance, but in no event later than 18 months from the date of the report. It is the Client's responsibility to ensure that the Designer, Contractor, Subcontractors, etc. are made aware of this report in its entirety. Note that if another firm assumes Geotechnical Engineer of Record responsibilities, they need to review this report and either concur with the findings, conclusions, and recommendations or provide alternate findings, conclusions and recommendation. Land or facility use, on- and off-site conditions, regulations, or other factors may change over time, and additional work may be required. Based on the intended use of the report, QG may recommend that additional work be performed and that an updated report be issued. Non-compliance with any of these requirements by the Client or anyone else will release QG from any liability resulting from the use of this report. The Client, the design consultants, and any unauthorized party, agree to defend, indemnify, and hold harmless QG from any claim or liability associated with such unauthorized use or non-compliance. We recommend that QG be given the opportunity to review the final project plans and specifications to evaluate if our recommendations have been properly interpreted. We assume no responsibility for misinterpretation of our recommendations. B24 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 18 Region & Vicinity Maps REGION VICINITY Quality Geo NW, PLLC Site Region C&E Geo Figure 1 Source: Google Imagery, 2023 Scale & Locations are approx. Not for Construction B25 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 19 Exploration Map Figure 2 Source: Thurston Co. GIS, 2023 Scale & Locations are approx. Not for Construction 30 0 SCALE (FEET) Quality Geo NW, PLLC Site Map C&E Geo Building Pad 4 Parcel Boundaries Building Pad 2 Building Pad 1 Building Pad 7 Building Pad 8 Bu i l d i n g P a d 5 Building Pad 6 TP-4 TP-2 TP-3 TP-1 B26 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 20 Exploration Logs B27 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 21 B28 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 22 B29 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 23 B30 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 24 B31 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 25 Laboratory Results B32 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 26 B33 C&E Geo - Soils Report Quality Geo NW, PLLC 8/24/2023 Project # QG23-138 27 B34