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17 <br /> <br />Stormwater Management <br /> <br />• Stormwater management design must incorporate filtration and infiltration elements. This <br />could include such features as rain gardens, swales, dry creeks, infiltration chambers, and <br />other ecologically based methods along with more traditional ponds and pipes. <br /> <br />• Stormwater management ponds, if used, should be designed to be a site amenity, including <br />appropriate landscape elements. <br /> <br />Per the revised Storm Water Management Report prepared by Anderson-Johnson Associates <br />dated March 11, 2019, May 8, 2020 July 13, 2020, rate control is being accomplished using a <br />combination of a dry pond and a storm water treatment pond. The dry pond is now located <br />where the original community gardens were proposed. The proposed rate is less than 80% of <br />the existing rate of runoff. <br /> <br />Water quality treatment is accomplished at the single stormwater treatment pond. True <br />infiltration was considered during the design phase, but several factors contributed to not <br />pursuing infiltration practices. First, shallow groundwater exists on site. According to the soil <br />borings, groundwater is in the 895 to 897 elevation range. A majority of the low points are <br />around elevation 905 with one parking lot having a low point of about 902.5. This would mean <br />the surface of an infiltration area would need to be at elevation 900 - 901 for effective drainage <br />to occur. Additionally, the site has been maximized and there is not adequate space for <br />effective infiltration practices. <br /> <br />Instead, a stormwater pond has been constructed. The stormwater pond, in addition to <br />providing rate control, has been sized to provide adequate dead storage below the normal water <br />level to meet water quality requirements. Finally, an irrigation pumping station will be <br />constructed at the stormwater pond to draw water from the pond to irrigate the surrounding <br />areas. <br /> <br />As detailed in the May 11, 2020 Council staff report and Resolution No. 22-44 approving PUD <br />Development Stage Plan Amendment #1 to the site plan and grading & drainage plan, the <br />clubhouse was omitted in order to enlarge to the stormwater pond to provide more capacity. <br /> <br />Pond Size Comparison <br /> <br /> Original Pond 3P Enlarged Pond 3P <br />Surface Area 0.56 acres 0.82 acres <br />Volume 2.810 acre ft 3.869 acre ft <br /> <br />RCWD issued an amended Conditional Approval Pending Receipt of Changes (CAPROC) on <br />March 13, 2020. The District Engineer finds the revised grading and stormwater management <br />plans compliant with RCWD rules. <br /> <br />The City’s stormwater management ordinance requires 4 ft of separation between low floor <br />freeboard and groundwater. In order to minimize the site being built up to meet this