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BLD2021-00602 - 05 stormwater drainage report
Saez Consulting Engineers Inc. 748 Winslow Way E Bainbridge Island WA 98110 / 206-842-4188 www.saezconsult.com Quilcene School District #48 Bus Barn Relocation 294715 US Hwy 101 PO Box 40 · Quilcene, WA 98376 Storm Drainage Report For: Quilcene School District #48 c/o Frank Redmond Superintendent Jurisdiction: Jefferson County, Washington Solicitation: RFQ Progressive-Design-Build Services QSD Bus Barn Replacement Project dated April 21/28, 2021. By: Saez Consulting Engineers Inc. (SCE) September 14, 2021 Received by DCD 10/12/2021 QSD – Bus Barn Relocation Drainage Report 9/14/21 SCE Inc. Page 2 of 7 Table of Contents 1. Overview & Project Description 2. Existing and Downstream Conditions 3. Developed Conditions 4. Storm Water Management Requirements & BMP’s Appendix 1. SWMMWW2019 Figure I-3.2 Flow Chart 2. SWMMWW2019 Table I-3.2 The List Approach 3. Hydraulic Calculations and Detail (WWHM12) 4. Operation and Maintenance Guidelines Project References under separate cover 1. Civil plans & details 09-15-21 2. Site Topographical Survey Mapping 07-28-21 3. Site Geotechnical Report 07-31-21 4. Architectural/Structural plans & details 5. M.E.P. plans & details 6. Recorded Property Survey 01-04-1989 7. Septic Design Received by DCD 10/12/2021 QSD – Bus Barn Relocation Drainage Report 9/15/21 SCE Inc. Page 3 of 7 1. Overview & Project Description: The site is located on SEC 24, TWP 27, RNG 2W W.M. Lot area Bloc 3, Acres 4.64 ac approx. 202,118 sq. ft.) Latitude, Longitude: 47.82251, -122.87279 elevation 37 to 25 ft. Parcel no. 937-200-301 County file no. 644737 The existing parcel is currently partially developed with approximately 1.6 acres of gravel areas, 16 parking stalls, and one 1600 SF mobile building and a 370 SF loafing-shed for life stock. The redevelopment of this site will include the relocation of the existing bus barn on the north parcel (Block 2) with a new 4,880 SF structure, the addition of 6 school-bus parking areas, 20 vehicular parking stalls, and a 6 bus-drop off at the north side of E Rose St. totaling 29,344 SF of Pollutant Generating Impervious Surfaces (PGIS), and 1,908 SF non- PGIS. Vicinity Map Received by DCD 10/12/2021 QSD – Bus Barn Relocation Drainage Report 9/14/21 SCE Inc. Page 4 of 7 2. Existing and Downstream Conditions: The site is bound by the Old Railroad Grade Road to the west, E Rose Street to the north, Linger Longer Road to the south and McArdle to the east. The Big Quilcene River runs W-E approximately 1400 LF (0.3 miles) south of the site and approximately the same distance to marsh land and tide flats to the east draining into Quilcene Bay. The site grades are gradual from W to E at an average of 2-3% slope. The site soils are sand and gravel with high permeability and groundwater elevation fluctuating seasonally to as high as 7 feet from ground level. This area of the site is a groundwater recharge zone provided by Jefferson County in the preapplication meeting 07- 22-21. The site does not receive significant off-site runoff, if any, based on field observations topographical data and geotechnical information. 3. Developed Conditions: The re-development of this site proposes approximately 0.89 acres of impervious surfaces that include crush-rock surfacing driveway ingress and egress, parking, concrete sidewalks along E Rose St., the new bus barn structure, and an asphalt bus drop-off lane on the north side of E Rose St. The proposed stormwater mitigation for this site will consist of a runoff catchment system, a water quality (WQ) bioretention/infiltration cell “raingarden” (an LID feature, WDOE approved for Enhanced Treatment) preceding an infiltration gallery, all sized utilizing the Western Washington Hydraulic Model Version 12 edition (WWHM12) software as required by the Department of Ecology (WDOE) and as adopted by the Jefferson County code. Refer to Appendix 3 for the analysis, output, and dimensions. 4. Storm Water Management Requirements & BMP’s: In compliance with the Stormwater Management Manual for Western Washington 2019 edition (SWMM2019) Figure I3.2 Flow Chart for Determining Requirements for Redevelopment in Appendix 1, observance of all 9 minimum requirements (MR’s) below apply: Received by DCD 10/12/2021 QSD – Bus Barn Relocation Drainage Report 9/14/21 SCE Inc. Page 5 of 7 I-3.4.1 MR1: Preparation of Stormwater Site Plans Addressed by the QSD Bus Relocation Civil Plans/Drawings under separate cover. I-3.4.2 MR2: Construction Stormwater Pollution Addressed by: Civil Plans under separate cover drawings C2.0, C2.1 Civil Site Demo and temporary erosion and sedimentation control (TESC) and general notes. Due to the high permeability of the site soils (sand and gravels) it will be unlikely that silted run-off will be expected to leave the site during construction. However, multiple TESC measures are proposed to meet the intent of the construction stormwater pollution requirements to ensure compliance. I-3.4.3 MR3: Source Control of Pollution Addressed by: Civil Plans under separate cover drawings C2.0, C2.1 Civil Site Demo and TESC, and general notes. I-3.4.4 MR4: Preservation of Natural Drainage Systems The post-developed site natural drainage remains in the same drainage basin as the pre-developed site condition. No basin diversion is proposed with this project, and therefore, this requirement is met to its full extent. I-3.4.5 MR5: On-Site Stormwater Management The post-developed site does utilize on-site storm management as identified on Civil drawings C3.0 and 3.1 Site Grading and Drainage Plan and reference details which addresses all 9 Minimum Requirements per SWMM2019 Figure I3.2 Flow Chart and Table I-3.2 The List Approach for MR5 Compliance. List #2 for MR1-9 project requirements under section “Other Hard Surface”, there are 4 LID mitigating options. The appropriate option for this project is a bioretention/infiltration BMP, option 3. All other LID options 1, 2, and 4 are not as applicable based on the existing and proposed site conditions. Refer to Appendices 2 & 3. I-3.4.6 MR6: Runoff Treatment (WQ) The run-off enhanced treatment is met by utilizing a Bioretention/infiltration cell (rain garden) prior to discharging to the proposed flow-control infiltration gallery downstream as Received by DCD 10/12/2021 QSD – Bus Barn Relocation Drainage Report 9/14/21 SCE Inc. Page 6 of 7 identified in I-3.4.5 MR5 above and with supporting calculations and details in Appendix 3. I-3.4.7 MR7: Flow Control Flow control will be managed post WQ BMP’s as identified in MR5 & 6 above. The peak flows will be managed by a 70’x100’ infiltration trench as sized per the WWHM12 model with supporting calculations in Appendix 3. We suggest that instead of excavating the entire infiltration trench, as dimensioned in the civil plans, that the perforated distribution pipe is trenched and installed in the native soils acting as drain rock. Or have the native soil be cleaned of fines for the same purpose. Note that surface native soils per the Geotech report show up to 57 inches per hour permeable characteristics. I-3.4.8 MR8: Wetlands Protection There are no wetlands nor wetland buffers on-site within ¼ mile of the site and therefore, this requirement is not applicable, for the discharge of this post-developed mitigated storm discharge does not impact or affect a downstream wetland condition. Nonetheless, enhanced treatment is being provided by the biofiltration cell in which case the wetland protection would be complied to. It is unlikely that surface run-off will leave the site even at peak precipitation events. I-3.4.9 MR9: Operation and Maintenance (O&M) O&M guidelines for Bioretention are included in Appendix 4. Received by DCD 10/12/2021 QSD – Bus Barn Relocation Drainage Report 9/14/21 SCE Inc. Page 7 of 7 Appendices Received by DCD 10/12/2021 Appendix 1Received by DCD 10/12/2021 List #1 (For MR #1 - #5 Projects That Are Not Flow Control Exempt) List #2 (For MR #1 - #9 Projects That Are Not Flow Control Exempt) List #3 (For Flow Control Exempt Pro- jects) Surface Type: Lawn and Landscaped Areas BMP T5.13: Post-Construction Soil Quality and Depth BMP T5.13: Post-Construction Soil Quality and Depth BMP T5.13: Post-Construction Soil Quality and Depth Surface Type: Roofs 1. BMP T5.30: Full Dis- persion or BMP T5.10A: Downspout Full Infiltration 1. BMP T5.30: Full Dis- persion or BMP T5.10A: Downspout Full Infiltration 1. BMP T5.10A: Downspout Full Infiltration 2. BMP T5.14: Rain Gardens or BMP T7.30: Bioretention 2. BMP T7.30: Bioretention 2. BMP T5.10B: Downspout Dispersion Systems 3. BMP T5.10B: Downspout Dispersion Systems 3. BMP T5.10B: Downspout Dispersion Systems 3. BMP T5.10C: Perforated Stub-out Connections 4. BMP T5.10C: Perforated Stub-out Connections 4. BMP T5.10C: Perforated Stub-out Connections Surface Type: Other Hard Surfaces 1. BMP T5.30: Full Dis- persion 1. BMP T5.30: Full Dis- persion BMP T5.12: Sheet Flow Dis- persion or BMP T5.11: Concentrated Flow Dispersion 2. BMP T5.15: Permeable Pavements or BMP T5.14: Rain Gardens or BMP T7.30: Bioretention 2. BMP T5.15: Permeable Pavements 3. BMP T5.12: Sheet Flow Dispersion or BMP T5.11: Concentrated Flow Dispersion 3. BMP T7.30: Bioretention 4. BMP T5.12: Sheet Flow Dispersion or BMP T5.11: Concentrated Flow Dispersion Notes for using the List Approach: 1. Size BMP T5.14: Rain Gardens and BMP T7.30: Bioretention used in the List Approach to have a minimum horizontal projected surface area below the overflow which is at least 5% of the area drain- Table I-3.2: The List Approach for MR5 Compliance 2019 Stormwater Management Manual for Western Washington Volume I -Chapter 3 -Page 120 Appendix 2Received by DCD 10/12/2021 WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Bus Barn Relocation – Bioretention & Infiltration gallery Site Name: Quilcene School District Site Address: City: Quilcene Report Date: 9/9/2021 Gage: Quilcene Data Start: 1948/10/01 Data End: 2009/09/30 Precip Scale: 1.11 Version Date: 2019/09/13 Version: 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1: 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No Groundwater: No Pervious Land Use acre C, Forest, Flat .89 Pervious Total 0.89 Impervious Land Use acre Impervious Total 0 Basin Total 0.89 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No Groundwater: No Appendix 3Received by DCD 10/12/2021 Pervious Land Use acre Pervious Total 0 Impervious Land Use acre PARKING MOD 0.89 Impervious Total 0.89 Basin Total 0.89 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Surface retention 1 Surface retention 1 ___________________________________________________________________ Name: Bioretention 1 Bottom Length: 30.00 ft. Bottom Width: 30.00 ft. Material thickness of first layer: 1.5 Material type for first layer: SMMWW 12 in/hr. Material thickness of second layer: 0 Material type for second layer: Sand Material thickness of third layer: 0 Material type for third layer: GRAVEL Infiltration On Infiltration rate: 4.25 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 253.861 Total Volume Through Riser (ac-ft.): 24.668 Total Volume Through Facility (ac-ft.): 278.529 Percent Infiltrated: 91.14 Total Precip Applied to Facility: 9.804 Total Evap From Facility: 2.675 Underdrain used Underdrain Diameter (feet): 0 Orifice Diameter (in.): 0 Offset (in.): 0 Flow Through Underdrain (ac-ft.): 0 Total Outflow (ac-ft.): 278.529 Percent Through Underdrain: 0 Discharge Structure Riser Height: 1 ft. Riser Diameter: 6 in. Element Flows To: Outlet 1 Outlet 2 Gravel Trench Bed 1 ___________________________________________________________________ Bioretention 1 Hydraulic Table Appendix 3Received by DCD 10/12/2021 Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.0349 0.0000 0.0000 0.0000 0.0385 0.0345 0.0004 0.0000 0.0000 0.0769 0.0341 0.0007 0.0000 0.0000 0.1154 0.0337 0.0011 0.0000 0.0000 0.1538 0.0333 0.0015 0.0000 0.0002 0.1923 0.0329 0.0019 0.0000 0.0016 0.2308 0.0325 0.0023 0.0000 0.0024 0.2692 0.0321 0.0027 0.0000 0.0035 0.3077 0.0317 0.0031 0.0000 0.0049 0.3462 0.0313 0.0035 0.0000 0.0066 0.3846 0.0309 0.0039 0.0000 0.0085 0.4231 0.0305 0.0043 0.0000 0.0108 0.4615 0.0301 0.0048 0.0000 0.0133 0.5000 0.0298 0.0052 0.0000 0.0162 0.5385 0.0294 0.0057 0.0000 0.0195 0.5769 0.0290 0.0061 0.0000 0.0231 0.6154 0.0286 0.0066 0.0000 0.0271 0.6538 0.0282 0.0070 0.0000 0.0315 0.6923 0.0279 0.0075 0.0000 0.0363 0.7308 0.0275 0.0080 0.0000 0.0415 0.7692 0.0271 0.0084 0.0000 0.0472 0.8077 0.0268 0.0089 0.0000 0.0532 0.8462 0.0264 0.0094 0.0000 0.0597 0.8846 0.0261 0.0099 0.0000 0.0667 0.9231 0.0257 0.0104 0.0000 0.0741 0.9615 0.0254 0.0109 0.0000 0.0820 1.0000 0.0250 0.0115 0.0000 0.0885 1.0385 0.0247 0.0120 0.0000 0.0885 1.0769 0.0243 0.0125 0.0000 0.0885 1.1154 0.0240 0.0131 0.0000 0.0885 1.1538 0.0236 0.0136 0.0000 0.0885 1.1923 0.0233 0.0142 0.0000 0.0885 1.2308 0.0229 0.0147 0.0000 0.0885 1.2692 0.0226 0.0153 0.0000 0.0885 1.3077 0.0223 0.0159 0.0000 0.0885 1.3462 0.0220 0.0165 0.0000 0.0885 1.3846 0.0216 0.0170 0.0000 0.0885 1.4231 0.0213 0.0176 0.0000 0.0885 1.4615 0.0210 0.0182 0.0000 0.0885 1.5000 0.0207 0.0188 0.0000 0.0885 Surface retention 1 Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) To Amended(cfs) Wetted Surface 1.5000 0.0349 0.0188 0.0000 0.2500 0.0000 1.5385 0.0353 0.0202 0.0000 0.2500 0.0000 1.5769 0.0357 0.0216 0.0000 0.2628 0.0000 1.6154 0.0362 0.0230 0.0000 0.2692 0.0000 1.6538 0.0366 0.0243 0.0000 0.2756 0.0000 1.6923 0.0370 0.0258 0.0000 0.2821 0.0000 1.7308 0.0374 0.0272 0.0000 0.2885 0.0000 1.7692 0.0379 0.0286 0.0000 0.2949 0.0000 1.8077 0.0383 0.0301 0.0000 0.3013 0.0000 1.8462 0.0387 0.0316 0.0000 0.3077 0.0000 1.8846 0.0392 0.0331 0.0000 0.3141 0.0000 1.9231 0.0396 0.0346 0.0000 0.3205 0.0000 1.9615 0.0401 0.0361 0.0000 0.3269 0.0000 Appendix 3Received by DCD 10/12/2021 2.0000 0.0405 0.0377 0.0000 0.3333 0.0000 2.0385 0.0409 0.0393 0.0000 0.3397 0.0000 2.0769 0.0414 0.0408 0.0000 0.3462 0.0000 2.1154 0.0418 0.0424 0.0000 0.3526 0.0000 2.1538 0.0423 0.0441 0.0000 0.3590 0.0000 2.1923 0.0428 0.0457 0.0000 0.3654 0.0000 2.2308 0.0432 0.0473 0.0000 0.3718 0.0000 2.2692 0.0437 0.0490 0.0000 0.3782 0.0000 2.3077 0.0441 0.0507 0.0000 0.3846 0.0000 2.3462 0.0446 0.0524 0.0000 0.3910 0.0000 2.3846 0.0451 0.0541 0.0000 0.3974 0.0000 2.4231 0.0455 0.0559 0.0000 0.4038 0.0000 2.4615 0.0460 0.0576 0.0000 0.4103 0.0000 2.5000 0.0465 0.0594 0.0000 0.4167 0.0000 2.5385 0.0470 0.0612 0.0399 0.4167 0.0000 2.5769 0.0474 0.0630 0.1109 0.4167 0.0000 2.6154 0.0479 0.0649 0.1943 0.4167 0.0000 2.6538 0.0484 0.0667 0.2743 0.4167 0.0000 2.6923 0.0489 0.0686 0.3368 0.4167 0.0000 2.7308 0.0494 0.0705 0.3761 0.4167 0.0000 2.7692 0.0499 0.0724 0.4086 0.4167 0.0000 2.8077 0.0504 0.0743 0.4368 0.4167 0.0000 2.8462 0.0509 0.0763 0.4633 0.4167 0.0000 2.8846 0.0514 0.0782 0.4883 0.4167 0.0000 2.9231 0.0519 0.0802 0.5122 0.4167 0.0000 2.9615 0.0524 0.0822 0.5349 0.4167 0.0000 3.0000 0.0529 0.0842 0.5568 0.4167 0.0000 3.0385 0.0534 0.0863 0.5778 0.4167 0.0000 3.0769 0.0539 0.0884 0.5981 0.4167 0.0000 3.1154 0.0544 0.0904 0.6177 0.4167 0.0000 3.1538 0.0549 0.0925 0.6367 0.4167 0.0000 3.1923 0.0555 0.0947 0.6552 0.4167 0.0000 3.2308 0.0560 0.0968 0.6731 0.4167 0.0000 3.2692 0.0565 0.0990 0.6906 0.4167 0.0000 3.3077 0.0570 0.1012 0.7077 0.4167 0.0000 3.3462 0.0576 0.1034 0.7243 0.4167 0.0000 3.3846 0.0581 0.1056 0.7406 0.4167 0.0000 3.4231 0.0586 0.1078 0.7565 0.4167 0.0000 3.4615 0.0592 0.1101 0.7721 0.4167 0.0000 3.5000 0.0597 0.1124 0.7874 0.4167 0.0000 3.5000 0.0597 0.1124 0.8024 0.4167 0.0000 ___________________________________________________________________ Name : Surface retention 1 Element Flows To: Outlet 1 Outlet 2 Gravel Trench Bed 1 Bioretention 1 ___________________________________________________________________ Name : Gravel Trench Bed 1 Bottom Length: 100.00 ft. Bottom Width: 70.00 ft. Trench bottom slope 1: 0 To 1 Trench Left side slope 0: 0 To 1 Trench right side slope 2: 0 To 1 Appendix 3Received by DCD 10/12/2021 Material thickness of first layer: 4 Pour Space of material for first layer: 0.333 Material thickness of second layer: 0 Pour Space of material for second layer: 0 Material thickness of third layer: 0 Pour Space of material for third layer: 0 Infiltration On Infiltration rate: 4.25 Infiltration safety factor: 0.5 Total Volume Infiltrated (ac-ft.): 31.124 Total Volume Through Riser (ac-ft.): 0 Total Volume Through Facility (ac-ft.): 31.124 Percent Infiltrated: 100 Total Precip Applied to Facility: 6.495 Total Evap From Facility: 0.038 Discharge Structure Riser Height: 4 ft. Riser Diameter: 6 in. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Gravel Trench Bed Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.160 0.000 0.000 0.000 0.0556 0.160 0.003 0.000 0.344 0.1111 0.160 0.005 0.000 0.344 0.1667 0.160 0.008 0.000 0.344 0.2222 0.160 0.011 0.000 0.344 0.2778 0.160 0.014 0.000 0.344 0.3333 0.160 0.017 0.000 0.344 0.3889 0.160 0.020 0.000 0.344 0.4444 0.160 0.023 0.000 0.344 0.5000 0.160 0.026 0.000 0.344 0.5556 0.160 0.029 0.000 0.344 0.6111 0.160 0.032 0.000 0.344 0.6667 0.160 0.035 0.000 0.344 0.7222 0.160 0.038 0.000 0.344 0.7778 0.160 0.041 0.000 0.344 0.8333 0.160 0.044 0.000 0.344 0.8889 0.160 0.047 0.000 0.344 0.9444 0.160 0.050 0.000 0.344 1.0000 0.160 0.053 0.000 0.344 1.0556 0.160 0.056 0.000 0.344 1.1111 0.160 0.059 0.000 0.344 1.1667 0.160 0.062 0.000 0.344 1.2222 0.160 0.065 0.000 0.344 1.2778 0.160 0.068 0.000 0.344 1.3333 0.160 0.071 0.000 0.344 1.3889 0.160 0.074 0.000 0.344 1.4444 0.160 0.077 0.000 0.344 1.5000 0.160 0.080 0.000 0.344 1.5556 0.160 0.083 0.000 0.344 Appendix 3Received by DCD 10/12/2021 1.6111 0.160 0.086 0.000 0.344 1.6667 0.160 0.089 0.000 0.344 1.7222 0.160 0.092 0.000 0.344 1.7778 0.160 0.095 0.000 0.344 1.8333 0.160 0.098 0.000 0.344 1.8889 0.160 0.101 0.000 0.344 1.9444 0.160 0.104 0.000 0.344 2.0000 0.160 0.107 0.000 0.344 2.0556 0.160 0.110 0.000 0.344 2.1111 0.160 0.113 0.000 0.344 2.1667 0.160 0.115 0.000 0.344 2.2222 0.160 0.118 0.000 0.344 2.2778 0.160 0.121 0.000 0.344 2.3333 0.160 0.124 0.000 0.344 2.3889 0.160 0.127 0.000 0.344 2.4444 0.160 0.130 0.000 0.344 2.5000 0.160 0.133 0.000 0.344 2.5556 0.160 0.136 0.000 0.344 2.6111 0.160 0.139 0.000 0.344 2.6667 0.160 0.142 0.000 0.344 2.7222 0.160 0.145 0.000 0.344 2.7778 0.160 0.148 0.000 0.344 2.8333 0.160 0.151 0.000 0.344 2.8889 0.160 0.154 0.000 0.344 2.9444 0.160 0.157 0.000 0.344 3.0000 0.160 0.160 0.000 0.344 3.0556 0.160 0.163 0.000 0.344 3.1111 0.160 0.166 0.000 0.344 3.1667 0.160 0.169 0.000 0.344 3.2222 0.160 0.172 0.000 0.344 3.2778 0.160 0.175 0.000 0.344 3.3333 0.160 0.178 0.000 0.344 3.3889 0.160 0.181 0.000 0.344 3.4444 0.160 0.184 0.000 0.344 3.5000 0.160 0.187 0.000 0.344 3.5556 0.160 0.190 0.000 0.344 3.6111 0.160 0.193 0.000 0.344 3.6667 0.160 0.196 0.000 0.344 3.7222 0.160 0.199 0.000 0.344 3.7778 0.160 0.202 0.000 0.344 3.8333 0.160 0.205 0.000 0.344 3.8889 0.160 0.208 0.000 0.344 3.9444 0.160 0.211 0.000 0.344 4.0000 0.160 0.214 0.000 0.344 4.0556 0.160 0.223 0.068 0.344 4.1111 0.160 0.231 0.184 0.344 4.1667 0.160 0.240 0.297 0.344 4.2222 0.160 0.249 0.369 0.344 4.2778 0.160 0.258 0.415 0.344 4.3333 0.160 0.267 0.454 0.344 4.3889 0.160 0.276 0.491 0.344 4.4444 0.160 0.285 0.524 0.344 4.5000 0.160 0.294 0.556 0.344 4.5556 0.160 0.303 0.586 0.344 4.6111 0.160 0.312 0.615 0.344 4.6667 0.160 0.321 0.642 0.344 4.7222 0.160 0.330 0.669 0.344 Appendix 3Received by DCD 10/12/2021 4.7778 0.160 0.339 0.694 0.344 4.8333 0.160 0.348 0.718 0.344 4.8889 0.160 0.356 0.742 0.344 4.9444 0.160 0.365 0.765 0.344 5.0000 0.160 0.374 0.787 0.344 ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Land use Totals for POC #1 Total Pervious Area:0.89 Total Impervious Area:0 ___________________________________________________________________ Mitigated Land use Totals for POC #1 Total Pervious Area:0 Total Impervious Area:0.89 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.150684 5 year 0.256889 10 year 0.343545 25 year 0.472642 50 year 0.583734 100 year 0.708191 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0 5 year 0 10 year 0 25 year 0 50 year 0 100 year 0 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.370 0.000 1950 0.098 0.000 1951 0.211 0.000 1952 0.136 0.000 1953 0.114 0.000 1954 0.270 0.000 1955 0.335 0.000 1956 1.142 0.000 1957 0.230 0.000 1958 0.365 0.000 Appendix 3Received by DCD 10/12/2021 1959 0.238 0.000 1960 0.140 0.000 1961 0.419 0.000 1962 0.094 0.000 1963 0.150 0.000 1964 0.111 0.000 1965 0.053 0.000 1966 0.382 0.000 1967 0.193 0.000 1968 0.203 0.000 1969 0.149 0.000 1970 0.190 0.000 1971 0.237 0.000 1972 0.198 0.000 1973 0.115 0.000 1974 0.181 0.000 1975 0.165 0.000 1976 0.216 0.000 1977 0.106 0.000 1978 0.174 0.000 1979 0.126 0.000 1980 0.120 0.000 1981 0.077 0.000 1982 0.083 0.000 1983 0.174 0.000 1984 0.057 0.000 1985 0.046 0.000 1986 0.141 0.000 1987 0.159 0.000 1988 0.105 0.000 1989 0.054 0.000 1990 0.054 0.000 1991 0.115 0.000 1992 0.137 0.000 1993 0.066 0.000 1994 0.195 0.000 1995 0.147 0.000 1996 0.199 0.000 1997 0.141 0.000 1998 0.160 0.000 1999 0.241 0.000 2000 0.083 0.000 2001 0.041 0.000 2002 0.392 0.000 2003 0.336 0.000 2004 0.121 0.000 2005 0.216 0.000 2006 0.265 0.000 2007 0.199 0.000 2008 0.169 0.000 2009 0.078 0.000 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 1.1422 0.0000 Appendix 3Received by DCD 10/12/2021 2 0.4194 0.0000 3 0.3923 0.0000 4 0.3817 0.0000 5 0.3698 0.0000 6 0.3646 0.0000 7 0.3361 0.0000 8 0.3346 0.0000 9 0.2700 0.0000 10 0.2653 0.0000 11 0.2406 0.0000 12 0.2378 0.0000 13 0.2369 0.0000 14 0.2297 0.0000 15 0.2159 0.0000 16 0.2158 0.0000 17 0.2113 0.0000 18 0.2030 0.0000 19 0.1992 0.0000 20 0.1991 0.0000 21 0.1982 0.0000 22 0.1950 0.0000 23 0.1928 0.0000 24 0.1904 0.0000 25 0.1813 0.0000 26 0.1740 0.0000 27 0.1735 0.0000 28 0.1686 0.0000 29 0.1647 0.0000 30 0.1596 0.0000 31 0.1588 0.0000 32 0.1495 0.0000 33 0.1494 0.0000 34 0.1473 0.0000 35 0.1415 0.0000 36 0.1414 0.0000 37 0.1398 0.0000 38 0.1369 0.0000 39 0.1364 0.0000 40 0.1261 0.0000 41 0.1207 0.0000 42 0.1196 0.0000 43 0.1154 0.0000 44 0.1148 0.0000 45 0.1137 0.0000 46 0.1107 0.0000 47 0.1061 0.0000 48 0.1050 0.0000 49 0.0976 0.0000 50 0.0939 0.0000 51 0.0833 0.0000 52 0.0831 0.0000 53 0.0782 0.0000 54 0.0765 0.0000 55 0.0663 0.0000 56 0.0573 0.0000 57 0.0541 0.0000 58 0.0537 0.0000 Appendix 3Received by DCD 10/12/2021 59 0.0528 0.0000 60 0.0461 0.0000 61 0.0409 0.0000 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0753 4055 0 0 Pass 0.0805 2943 0 0 Pass 0.0856 2106 0 0 Pass 0.0907 1497 0 0 Pass 0.0959 1094 0 0 Pass 0.1010 835 0 0 Pass 0.1062 693 0 0 Pass 0.1113 579 0 0 Pass 0.1164 440 0 0 Pass 0.1216 332 0 0 Pass 0.1267 251 0 0 Pass 0.1318 196 0 0 Pass 0.1370 162 0 0 Pass 0.1421 121 0 0 Pass 0.1472 112 0 0 Pass 0.1524 95 0 0 Pass 0.1575 81 0 0 Pass 0.1626 74 0 0 Pass 0.1678 69 0 0 Pass 0.1729 64 0 0 Pass 0.1780 58 0 0 Pass 0.1832 54 0 0 Pass 0.1883 52 0 0 Pass 0.1935 45 0 0 Pass 0.1986 41 0 0 Pass 0.2037 35 0 0 Pass 0.2089 33 0 0 Pass 0.2140 31 0 0 Pass 0.2191 27 0 0 Pass 0.2243 25 0 0 Pass 0.2294 24 0 0 Pass 0.2345 23 0 0 Pass 0.2397 20 0 0 Pass 0.2448 19 0 0 Pass 0.2499 19 0 0 Pass 0.2551 17 0 0 Pass 0.2602 17 0 0 Pass 0.2653 17 0 0 Pass 0.2705 14 0 0 Pass 0.2756 12 0 0 Pass 0.2808 12 0 0 Pass 0.2859 12 0 0 Pass 0.2910 12 0 0 Pass 0.2962 12 0 0 Pass 0.3013 12 0 0 Pass Appendix 3Received by DCD 10/12/2021 0.3064 12 0 0 Pass 0.3116 10 0 0 Pass 0.3167 10 0 0 Pass 0.3218 10 0 0 Pass 0.3270 10 0 0 Pass 0.3321 10 0 0 Pass 0.3372 8 0 0 Pass 0.3424 8 0 0 Pass 0.3475 7 0 0 Pass 0.3526 7 0 0 Pass 0.3578 7 0 0 Pass 0.3629 7 0 0 Pass 0.3681 6 0 0 Pass 0.3732 5 0 0 Pass 0.3783 5 0 0 Pass 0.3835 4 0 0 Pass 0.3886 4 0 0 Pass 0.3937 3 0 0 Pass 0.3989 3 0 0 Pass 0.4040 3 0 0 Pass 0.4091 3 0 0 Pass 0.4143 3 0 0 Pass 0.4194 3 0 0 Pass 0.4245 2 0 0 Pass 0.4297 2 0 0 Pass 0.4348 2 0 0 Pass 0.4399 2 0 0 Pass 0.4451 2 0 0 Pass 0.4502 2 0 0 Pass 0.4554 2 0 0 Pass 0.4605 2 0 0 Pass 0.4656 2 0 0 Pass 0.4708 2 0 0 Pass 0.4759 2 0 0 Pass 0.4810 2 0 0 Pass 0.4862 2 0 0 Pass 0.4913 2 0 0 Pass 0.4964 2 0 0 Pass 0.5016 2 0 0 Pass 0.5067 2 0 0 Pass 0.5118 2 0 0 Pass 0.5170 2 0 0 Pass 0.5221 2 0 0 Pass 0.5272 2 0 0 Pass 0.5324 2 0 0 Pass 0.5375 2 0 0 Pass 0.5427 2 0 0 Pass 0.5478 2 0 0 Pass 0.5529 2 0 0 Pass 0.5581 1 0 0 Pass 0.5632 1 0 0 Pass 0.5683 1 0 0 Pass 0.5735 1 0 0 Pass 0.5786 1 0 0 Pass 0.5837 1 0 0 Pass _____________________________________________________ Appendix 3Received by DCD 10/12/2021 ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. ___________________________________________________________________ LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Gravel Trench Bed 1 POC N 28.32 N 100.00 retention 1 N 253.46 N 91.14 Total Volume Infiltrated 281.78 0.00 0.00 92.03 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Passed ___________________________________________________________________ Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2021; All Rights Reserved. Appendix 3Received by DCD 10/12/2021 Maintenance Com- ponent Recommended Frequency a Condition when Maintenance is Needed (Stand- ards)Action Needed (Procedures) Inspection Routine Main- tenance Facility Footprint Earthen side slopes and berms B, S Erosion (gullies/ rills) greater than 2 inches deep around inlets, outlet, and alongside slopes l Eliminate cause of erosion and stabilize damaged area (regrade, rock, vegetation, erosion control matting) l For deep channels or cuts (over 3 inches in ponding depth), temporary erosion control measures should be put in place until permanent repairs can be made. l Properly designed, constructed and established facilities with appropriate flow velocities should not have erosion prob- lems except perhaps in extreme events. If erosion problems persist, the following should be reassessed: (1) flow volumes from contributing areas and bioretention facility sizing; (2) flow velocities and gradients within the facility; and (3) flow dissipation and erosion protection strategies at the facility inlet. A Erosion of sides causes slope to become a hazard Take actions to eliminate the hazard and stabilize slopes A, S Settlement greater than 3 inches (relative to undis- turbed sections of berm)Restore to design height A, S Downstream face of berm wet, seeps or leaks evid- ent Plug any holes and compact berm (may require consultation with engineer, particularly for larger berms) A Any evidence of rodent holes or water piping in berm l Eradicate rodents (see "Pest control") l Fill holes and compact (may require consultation with engineer, particularly for larger berms) Concrete sidewalls A Cracks or failure of concrete sidewalls l Repair/ seal cracks l Replace if repair is insufficient Rockery sidewalls A Rockery side walls are insecure Stabilize rockery sidewalls (may require consultation with engineer, particularly for walls 4 feet or greater in height) Facility area All maintenance vis- its (at least bian- nually) Trash and debris present Clean out trash and debris Facility bottom area A, S Accumulated sediment to extent that infiltration rate is reduced (see "Ponded water") or surface storage capacity significantly impacted l Remove excess sediment l Replace any vegetation damaged or destroyed by sediment accumulation and removal l Mulch newly planted vegetation l Identify and control the sediment source (if feasible) l If accumulated sediment is recurrent, consider adding presettlement or installing berms to create a forebay at the inlet During/after fall leaf drop Accumulated leaves in facility Remove leaves if there is a risk to clogging outlet structure or water flow is impeded Low permeability check dams and weirs A, S Sediment, vegetation, or debris accumulated at or blocking (or having the potential to block) check dam, flow control weir or orifice Clear the blockage A, S Erosion and/or undercutting present Repair and take preventative measures to prevent future erosion and/or undercutting A Grade board or top of weir damaged or not level Restore to level position Table V-A.21: Maintenance Standards - Bioretention Facilities 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1019 Appendix 4Received by DCD 10/12/2021 Maintenance Com- ponent Recommended Frequency a Condition when Maintenance is Needed (Stand- ards)Action Needed (Procedures) Inspection Routine Main- tenance Ponded water B, S Excessive ponding water: Water overflows during storms smaller than the design event or ponded water remains in the basin 48 hours or longer after the end of a storm. Determine cause and resolve in the following order: 1. Confirm leaf or debris buildup in the bottom of the facility is not impeding infiltration. If necessary, remove leaf lit- ter/debris. 2. Ensure that underdrain (if present) is not clogged. If necessary, clear underdrain. 3. Check for other water inputs (e.g., groundwater, illicit connections). 4. Verify that the facility is sized appropriately for the contributing area. Confirm that the contributing area has not increased. If steps #1-4 do not solve the problem, the bioretention soil is likely clogged by sediment accumulation at the surface or has become overly compacted. Dig a small hole to observe soil profile and identify compaction depth or clogging front to help determine the soil depth to be removed or otherwise rehabilitated (e.g., tilled). Consultation with an engineer is recommended. Bioretention soil mix As needed Bioretention soil mix protection is needed when per- forming maintenance requiring entrance into the facil- ity footprint l Minimize all loading in the facility footprint (foot traffic and other loads) to the degree feasible in order to prevent com- paction of bioretention soils. l Never drive equipment or apply heavy loads in facility footprint. l Because the risk of compaction is higher during saturated soil conditions, any type of loading in the cell (including foot traffic) should be minimized during wet conditions. l Consider measures to distribute loading if heavy foot traffic is required or equipment must be placed in facility. As an example, boards may be placed across soil to distribute loads and minimize compaction. l If compaction occurs, soil must be loosened or otherwise rehabilitated to original design state. Inlets/Outlets/Pipes Splash block inlet A Water is not being directed properly to the facility and away from the inlet structure Reconfigure/ repair blocks to direct water to facility and away from structure Curb cut inlet/outlet M during the wet season and before severe storm is fore- casted Weekly during fall leaf drop Accumulated leaves at curb cuts Clear leaves (particularly important for key inlets and low points along long, linear facilities) Pipe inlet/outlet A Pipe is damaged Repair/ replace W Pipe is clogged Remove roots or debris A, S Sediment, debris, trash, or mulch reducing capacity of inlet/outlet l Clear the blockage l Identify the source of the blockage and take actions to prevent future blockages Weekly during fall leaf drop Accumulated leaves at inlets/outlets Clear leaves (particularly important for key inlets and low points along long, linear facilities) A Maintain access for inspections l Clear vegetation (transplant vegetation when possible) within 1 foot of inlets and outlets, maintain access pathways l Consultation with a landscape architect is recommended for removal, transplant, or substitution of plants Table V-A.21: Maintenance Standards - Bioretention Facilities (continued) 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1020 Appendix 4Received by DCD 10/12/2021 Maintenance Com- ponent Recommended Frequency a Condition when Maintenance is Needed (Stand- ards)Action Needed (Procedures) Inspection Routine Main- tenance Erosion control at inlet A Concentrated flows are causing erosion Maintain a cover of rock or cobbles or other erosion protection measure (e.g., matting) to protect the ground where con- centrated water enters the facility (e.g., a pipe, curb cut or swale) Trash rack S Trash or other debris present on trash rack Remove/dispose A Bar screen damaged or missing Repair/replace Overflow A, S Capacity reduced by sediment or debris Remove sediment or debris/dispose Underdrain pipe Clean pipe as needed Clean orifice at least biannually (may need more fre- quent cleaning dur- ing wet season) l Plant roots, sediment or debris reducing capa- city of underdrain l Prolonged surface ponding (see "Ponded water" l Jet clean or rotary cut debris/roots from underdrain(s) l If underdrains are equipped with a flow restrictor (e.g., orifice) to attenuate flows, the orifice must be cleaned regularly. Vegetation Facility bottom area and upland slope veget- ation Fall and Spring Vegetation survival rate falls below 75% within first two years of establishment (unless project O&M manual or record drawing stipulates more or less than 75% survival rate). l Determine cause of poor vegetation growth and correct condition l Replant as necessary to obtain 75% survival rate or greater. Refer to original planting plan, or approved jurisdictional species list for appropriate plant replacements (See Appendix 3 - Bioretention Plant List, in the LID Technical Guid- ance Manual for Puget Sound, (Hinman and Wulkan, 2012)). l Confirm that plant selection is appropriate for site growing conditions l Consultation with a landscape architect is recommended for removal, transplant, or substitution of plants Vegetation (general)As needed Presence of diseased plants and plant material l Remove any diseased plants or plant parts and dispose of in an approved location (e.g., commercial landfill) to avoid risk of spreading the disease to other plants l Disinfect gardening tools after pruning to prevent the spread of disease l See the Pacific Northwest Plant Disease Management Handbook (Pscheidt and Ocamb, 2016) for information on dis- ease recognition and for additional resources l Replant as necessary according to recommendations provided for "facility bottom area and upland slope vegetation". Trees and shrubs All pruning seasons (timing varies by species) Pruning as needed l Prune trees and shrubs in a manner appropriate for each species. Pruning should be performed by landscape pro- fessionals familiar with proper pruning techniques l All pruning of mature trees should be performed by or under the direct guidance of an ISA certified arborist A Large trees and shrubs interfere with operation of the facility or access for maintenance l Prune trees and shrubs using most current ANSI A300 standards and ISA BMPs. l Remove trees and shrubs, if necessary. Fall and Spring Standing dead vegetation is present l Remove standing dead vegetation l Replace dead vegetation within 30 days of reported dead and dying plants (as practical depending on weather/planting season) l If vegetation replacement is not feasible within 30 days, and absence of vegetation may result in erosion problems, temporary erosion control measures should be put in place immediately. l Determine cause of dead vegetation and address issue, if possible Table V-A.21: Maintenance Standards - Bioretention Facilities (continued) 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1021 Appendix 4 Received by DCD 10/12/2021 Maintenance Com- ponent Recommended Frequency a Condition when Maintenance is Needed (Stand- ards)Action Needed (Procedures) Inspection Routine Main- tenance l If specific plants have a high mortality rate, assess the cause and replace with appropriate species. Consultation with a landscape architect is recommended. Fall and Spring Planting beneath mature trees l When working around and below mature trees, follow the most current ANSI A300 standards and ISA BMPs to the extent practicable (e.g., take care to minimize any damage to tree roots and avoid compaction of soil). l Planting of small shrubs or groundcovers beneath mature trees may be desirable in some cases; such plantings should use mainly plants that come as bulbs, bare root or in 4-inch pots; plants should be in no larger than 1-gallon con- tainers. Fall and Spring Presence of or need for stakes and guys (tree growth, maturation, and support needs) l Verify location of facility liners and underdrain (if any) prior to stake installation in order to prevent liner puncture or pipe damage l Monitor tree support systems: Repair and adjust as needed to provide support and prevent damage to tree. l Remove tree supports (stakes, guys, etc.) after one growing season or maximum of 1 year. l Backfill stake holes after removal. Trees and shrubs adja- cent to vehicle travel areas (or areas where visibility needs to be maintained) A Vegetation causes some visibility (line of sight) or driver safety issues l Maintain appropriate height for sight clearance l When continued, regular pruning (more than one time/ growing season) is required to maintain visual sight lines for safety or clearance along a walk or drive, consider relocating the plant to a more appropriate location. l Remove or transplant if continual safety hazard l Consultation with a landscape architect is recommended for removal, transplant, or substitution of plants Flowering plants A Dead or spent flowers present Remove spent flowers (deadhead) Perennials Fall Spent plants Cut back dying or dead and fallen foliage and stems Emergent vegetation Spring Vegetation compromises conveyance Hand rake sedges and rushes with a small rake or fingers to remove dead foliage before new growth emerges in spring or earlier only if the foliage is blocking water flow (sedges and rushes do not respond well to pruning) Ornamental grasses (perennial) Winter and Spring Dead material from previous year's growing cycle or dead collapsed foliage l Leave dry foliage for winter interest l Hand rake with a small rake or fingers to remove dead foliage back to within several inches from the soil before new growth emerges in spring or earlier if the foliage collapses and is blocking water flow Ornamental grasses (evergreen) Fall and Spring Dead growth present in spring l Hand rake with a small rake or fingers to remove dead growth before new growth emerges in spring l Clean, rake, and comb grasses when they become too tall l Cut back to ground or thin every 2-3 years as needed Noxious weeds M (March - October, preceding seed dis- persal) Listed noxious vegetation is present (refer to current county noxious weed list) l By law, class A & B noxious weeds must be removed, bagged and disposed as garbage immediately l Reasonable attempts must be made to remove and dispose of class C noxious weeds l It is strongly encouraged that herbicides and pesticides not be used in order to protect water quality; use of herbicides and pesticides may be prohibited in some jurisdictions l Apply mulch after weed removal (see "Mulch") Weeds M (March - October, Weeds are present l Remove weeds with their roots manually with pincer-type weeding tools, flame weeders, or hot water weeders as Table V-A.21: Maintenance Standards - Bioretention Facilities (continued) 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1022 Appendix 4Received by DCD 10/12/2021 Maintenance Com- ponent Recommended Frequency a Condition when Maintenance is Needed (Stand- ards)Action Needed (Procedures) Inspection Routine Main- tenance preceding seed dis- persal) appropriate l Follow IPM protocols for weed management (see "Additional Maintenance Resources" section for more information on IPM protocols) Excessive vegetation Once in early to mid- May and once in early- to mid- September Low-lying vegetation growing beyond facility edge onto sidewalks, paths, or street edge poses ped- estrian safety hazard or may clog adjacent permeable pavement surfaces due to associated leaf litter, mulch, and soil l Edge or trim groundcovers and shrubs at facility edge l Avoid mechanical blade-type edger and do not use edger or trimmer within 2 feet of tree trunks l While some clippings can be left in the facility to replenish organic material in the soil, excessive leaf litter can cause surface soil clogging As needed Excessive vegetation density inhibits stormwater flow beyond design ponding or becomes a hazard for pedestrian and vehicular circulation and safety l Determine whether pruning or other routine maintenance is adequate to maintain proper plant density and aesthetics l Determine if planting type should be replaced to avoid ongoing maintenance issues (an aggressive grower under per- fect growing conditions should be transplanted to a location where it will not impact flow) l Remove plants that are weak, broken or not true to form; replace in-kind l Thin grass or plants impacting facility function without leaving visual holes or bare soil areas l Consultation with a landscape architect is recommended for removal, transplant, or substitution of plants As needed Vegetation blocking curb cuts, causing excessive sediment buildup and flow bypass Remove vegetation and sediment buildup Mulch Mulch Following weeding Bare spots (without mulch cover) are present or mulch depth less than 2 inches l Supplement mulch with hand tools to a depth of 2 to 3 inches l Replenish mulch per O&M manual. Often coarse compost is used in the bottom of the facility and arborist wood chips are used on side slopes and rim (above typical water levels) l Keep all mulch away from woody stems Watering Irrigation system (if any) Based on man- ufacturer's instruc- tions Irrigation system present Follow manufacturer's instructions for O&M A Sprinklers or drip irrigation not directed/located to properly water plants Redirect sprinklers or move drip irrigation to desired areas Summer watering (first year) Once every 1-2 weeks or as needed during prolonged dry periods Trees, shrubs and groundcovers in first year of estab- lishment period l 10 to 15 gallons per tree l 3 to 5 gallons per shrub l 2 gallons water per square foot for groundcover areas l Water deeply, but infrequently, so that the top 6 to 12 inches of the root zone is moist l Use soaker hoses or spot water with a shower type wand when irrigation system is not present o Pulse water to enhance soil absorption, when feasible Table V-A.21: Maintenance Standards - Bioretention Facilities (continued) 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1023 Appendix 4Received by DCD 10/12/2021 Maintenance Com- ponent Recommended Frequency a Condition when Maintenance is Needed (Stand- ards)Action Needed (Procedures) Inspection Routine Main- tenance o Pre-moisten soil to break surface tension of dry or hydrophobic soils/mulch, followed by several more passes. With this method , each pass increases soil absorption and allows more water to infiltrate prior to runoff l Add a tree bag or slow-release watering device (e.g., bucket with a perforated bottom) for watering newly installed trees when irrigation system is not present Summer watering (second and third years) Once every 2-4 weeks or as needed during prolonged dry periods Trees, shrubs and groundcovers in second or third year of establishment period l 10 to 15 gallons per tree l 3 to 5 gallons per shrub l 2 gallons water per square foot for groundcover areas l Water deeply, but infrequently, so that the top 6 to 12 inches of the root zone is moist l Use soaker hoses or spot water with a shower type wand when irrigation system is not present o Pulse water to enhance soil absorption, when feasible o Pre-moisten soil to break surface tension of dry or hydrophobic soils/mulch, followed by several more passes. With this method , each pass increases soil absorption and allows more water to infiltrate prior to runoff Summer watering (after establishment) As needed Established vegetation (after 3 years) l Plants are typically selected to be drought tolerant and not require regular watering after establishment; however, trees may take up to 5 years of watering to become fully established l Identify trigger mechanisms for drought-stress (e.g., leaf wilt, leaf senescence, etc.) of different species and water immediately after initial signs of stress appear l Water during drought conditions or more often if necessary to maintain plant cover Pest Control Mosquitoes B, S Standing water remains for more than 3 days after the end of a storm l Identify the cause of the standing water and take appropriate actions to address the problem (see "Ponded water") l To facilitate maintenance, manually remove standing water and direct to the storm drainage system (if runoff is from non pollution-generating surfaces) or sanitary sewer system (if runoff is from pollution-generating surfaces) after get- ting approval from sanitary sewer authority. l Use of pesticides or Bacillus thuringiensis israelensis (Bti) may be considered only as a temporary measure while addressing the standing water cause. If overflow to a surface water will occur within 2 weeks after pesticide use, apply for coverage under the Aquatic Mosquito Control NPDES General Permit. Nuisance animals As needed Nuisance animals causing erosion, damaging plants, or depositing large volumes of feces l Reduce site conditions that attract nuisance species where possible (e.g., plant shrubs and tall grasses to reduce open areas for geese, etc.) l Place predator decoys l Follow IPM protocols for specific nuisance animal issues (see "Additional Maintenance Resources" section for more information on IPM protocols) l Remove pet waste regularly l For public and right-of-way sites consider adding garbage cans with dog bags for picking up pet waste. Insect pests Every site visit associated with Signs of pests, such as wilting leaves, chewed leaves and bark, spotting or other indicators l Reduce hiding places for pests by removing diseased and dead plants l For infestations, follow IPM protocols (see "Additional Maintenance Resources" section for more information on IPM Table V-A.21: Maintenance Standards - Bioretention Facilities (continued) 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1024 Appendix 4Received by DCD 10/12/2021 Maintenance Com- ponent Recommended Frequency a Condition when Maintenance is Needed (Stand- ards)Action Needed (Procedures) Inspection Routine Main- tenance vegetation man- agement protocols) Note that the inspection and routine maintenance frequencies listed above are recommended by Ecology. They do not supersede or replace the municipal stormwater permit requirements for inspection frequency required of municipal stormwater per- mittees for "stormwater treatment and flow control BMPs/facilities". a Frequency: A = Annually; B = Biannually (twice per year); M = Monthly; W = At least one visit should occur during the wet season (for debris/clog related maintenance, this inspection/maintenance visit should occur in the early fall, after deciduous trees have lost their leaves); S = Perform inspections after major storm events (24-hour storm event with a 10-year or greater recurrence interval). IPM - Integrated Pest Management ISA - International Society of Arboriculture Table V-A.21: Maintenance Standards - Bioretention Facilities (continued) Component Recommended Frequency a Condition when Maintenance is Needed (Standards)Action Needed (Procedures) Inspection Routine Maintenance Surface/Wearing Course Permeable Pave- ments, all A, S Runoff from adjacent pervious areas deposits soil, mulch or sediment on paving l Clean deposited soil or other materials from permeable pavement or other adjacent surfacing l Check if surface elevation of planted area is too high, or slopes towards pavement, and can be regraded (prior to regrading, protect permeable pavement by covering with temporary plastic and secure covering in place) l Mulch and/or plant all exposed soils that may erode to pavement surface Porous asphalt or per- vious concrete A or B None (routine maintenance) Clean surface debris from pavement surface using one or a combination of the following methods: l Remove sediment, debris, trash, vegetation, and other debris deposited onto pavement (rakes and leaf blowers can be used for removing leaves) l Vacuum/sweep permeable paving installation using: o Walk-behind vacuum (sidewalks) o High efficiency regenerative air or vacuum sweeper (roadways, parking lots) o ShopVac or brush brooms (small areas) l Hand held pressure washer or power washer with rotating brushes Follow equipment manufacturer guidelines for when equipment is most effective for cleaning permeable pavement. Dry weather is more effective for some equipment. Ab Surface is clogged: Ponding on surface or water flows off the permeable pavement surface dur- ing a rain event (does not infiltrate) l Review the overall performance of the facility (note that small clogged areas may not reduce overall per- formance of facility) l Test the surface infiltration rate using ASTM C1701 as a corrective maintenance indicator. Perform one test per installation, up to 2,500 square feet. Perform an additional test for each additional 2,500 square feet up to 15,000 square feet total. Above 15,000 square feet, add one test for every 10,000 square feet. l If the results indicate an infiltration rate of 10 inches per hour or less, then perform corrective maintenance to restore permeability. To clean clogged pavement surfaces, use one or combination of the following methods: Table V-A.22: Maintenance Standards - Permeable Pavement 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1025 Appendix 4Received by DCD 10/12/2021