Laserfiche WebLink
2019 SWMMWW MINIMUM REOUIREMENTS SUMMARY <br />MR : MINIMUM REQUIREMENT <br />SSP : STORMWATER SITE PLAN <br />MR #1 PREPARATION OF STORMWATER SITE PLAN: <br />Stormwater site plan follows 2019 Stormwater Management Manual for Western <br />Washington. <br />MR #2 CONSTRUCTION OF STORMWATER POLLUTION PREVENTION <br />PLAN (SWPPP): A SWPPP is provided under Section IV. <br />MR #3 SOURCE CONTROL OF POLLUTION: No source control pollutants pertain to <br />the proposed project; therefore, no BMPs are required for the proposed project. <br />MR #4 PRESERVATION OF NATURAL DRAINAGE SYSTEMS AND <br />OUTFALLS: The roof drains will be connected to the existing drainage system along <br />Wetmore Ave to continue its natural drainage path. The runoff from other hard surfaces <br />will be infiltrated via permeable pavement. <br />MR #5 ONSITE STORMWATER MANAGEMENT: Per Minimum Requirement #5 <br />(Section I-3.4.5 of the SWMMWW), the following NPGIS BMPs shall be applied to <br />provide onsite stormwater management and must be considered in the following order per <br />List #2: Full Dispersion, Infiltration, Bioretention, Basic Dispersion, and then Perforated <br />Stub -Out Connections. Full Dispersion is infeasible because the required native vegetation <br />preservation could not be achieved for the LDMR zoned project. Full Infiltration is also not <br />feasible as the design infiltration rate is only 0.21 in/hr which is less than the recommended <br />0.3 in/hr. Also, Glacial Till was observed at 1.5-ft below ground surface. Please refer to the <br />Geotech Report attached under Section VI. Basic dispersion is not feasible due to the lack <br />of required vegetated flowpath. Perforated stub -out connections are infeasible because they <br />cannot be located under impervious surface. The roof drains will be directly connected to <br />the existing drainage system along Wetmore Ave. The following BMPs shall be applied to <br />the other hard surfaces: Full dispersion, Infiltration, Permeable Pavement, Bioretention, <br />and then Dispersion. Full Dispersion is infeasible because the required native vegetation <br />preservation could not be achieved for the LDMR zoned project. The driveways for both <br />lots will be permeable pavement. Post -Construction Soil Quality and Depth BMP T.5.13 is <br />proposed to provide onsite stormwater management for the pervious areas of the site. <br />MR #6 RUNOFF TREATMENT: Water quality requirements are exempt for the project <br />because the proposed PGIS is only 2,175 SF, which is less than the threshold of 5,000 SF. <br />MR #7 FLOW CONTROL: Flow control requirements are exempt because the new <br />effective impervious area is only 3,823 SF, which is less than the threshold of 5,000 SF. <br />Insight Engineering Co. — Stormwater Site Plan 05/31/2022 <br />- 5 - <br />