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8. RUN-OFF TREATMENT (MR #6) <br /> This project is estimated to install a total of 3,995 sf of new PGHS including future <br /> driveway surfaces and any off-site road improvements. However, all of the on-site PGHS <br /> (driveways) will be infiltrated using permeable pavement and the project Geotech has <br /> confirmed that the on-site soils have the necessary cation exchange capacity to meet the <br /> treatment requirements. <br /> The cation exchange capacity (CEC) of at least 5 milliequivalents/100 grams is required <br /> for treatment, however as noted the greotech report states that the existing soil meets the <br /> CEC and organic content criteria. <br /> 9. FLOW CONTROL (MR #7) <br /> For this project the total area to be disturbed is 0.55 acres. This project is located at a <br /> high point there is no off-site runoff tributary to the on-site improvements. However, this <br /> project has two threshold discharge areas (Basin 'A' and Basin `B'). Approximately 800 sf <br /> (0.02 ac) of sidewalk will be added to Basin 'A' and approximately 13,795 sf (0.32 ac) of <br /> future roof, driveway and sidewalk will be added to Basin `B'. <br /> This project proposes to construct 14,595 sf (0.34 ac) of new impervious surfaces, <br /> including off-site,frontage improvements and on-site driveways, walks/patios, and roof, <br /> with the remainder being converted to lawn for the entire project site. <br /> All future roof surfaces will be infiltrated on-site via infiltration trenches and all driveway <br /> areas will be constructed of permeable "pavement. Therefore,' these surfaces -are <br /> considered' ineffective' impervious surfaces. The on-site ineffective areas total <br /> approximately 11,695 sf(0.27 ac). <br /> The only effective impervious surfaces proposed for this project is the new off-site frontage <br /> improvements required for the sidewalk and some pavement section. These off-site areas <br /> total approximately 2,900 sf(0.07 ac), which is below the thresholds for MR 6 and MR 7. <br /> Basin Summary Table <br /> Effective Ineffective Proposed Total Disturbed <br /> Impervious (ac) Impervious Pervious (ac) Area (ac) <br /> . .,(ac) <br /> Basin A 0.02 (sidewalk) 0 0 0.02 <br /> Basin B 0.05 (sidewalk) 0.27 0.21 0.53 <br /> Seaht7rst"SP 18-0727 <br /> September 2019 Page 12 <br />