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<br />RCWD Alternative Compliance Sequencing Report <br />City of St. Anthony Village PAGE 17 <br />WSB Project No. 1626-53 <br /> <br />Table 2: Equivalent Annual Total Phosphorus and Total Suspended Solids Removal <br />Subwatershed <br />Annual volume reduction <br />resulting from infiltration <br />system to meet RCWD <br />requirements (ft3) <br />Equivalent annual <br />total phosphorus <br />removal <br />(lbs/year) <br />Equivalent <br />annual total <br />suspended <br />solids removal <br />(tons/year) <br />Silver Lake ROW 1,362,648 30.1 5.90 <br />RC Ditch 3 ROW 2,036,987 45.6 8.94 <br />Mississippi River ROW 367,918 8.2 1.61 <br />Public Projects <br />(outside of ROW) <br />Central Parking Lot <br />(RCWD 01-103) 11,888 0.3 0.06 <br />St. Anthony Schools <br />(RCWD 09-004) 39,181 0.9 0.18 <br />TOTAL 3,818,622 85 16.65 <br /> <br />The pollutant-based standards indicated on Table 2 are calculated based on the <br />following: <br /> <br />Total Phosphorus <br />A TP concentration of 0.97 pounds per acre-foot (0.36 mg/L) of runoff was <br />used to convert runoff volume to TP load removal. This is consistent with <br />event mean concentrations established under the approved TMDL for Silver <br />Lake. <br /> <br />The RCWD Engineer has noted that this TP concentration is higher than <br />what is typically observed within this portion of the RCWD. To remain <br />consistent with the TMDL documents, however, the concentration has been <br />found acceptable for this analysis. It should be noted that most BMP <br />benefits in the report, including the benefits of volume reduction BMPs, are <br />measured as a percentage of retained load. Therefore the finite load is less <br />important than the percent of load that must be retained to meet the water <br />quality standard. By using the load concentration presented in the TMDL, <br />the extent that BMPs are able to meet TMDL goals can be better estimated. <br /> <br />Total Suspended Solids <br />A TSS concentration of 0.190 tons per acre-foot (140 mg/L) of runoff was <br />used to convert runoff volume to TSS load removal. This is based on data <br />presented in “Protecting Water Quality in Urban Areas”, which is founded <br />in part by the Nationwide Urban Runoff Program (NURP) Studies. <br /> <br />Although both TP and TSS removal equivalents are quantified, TP is the primary <br />pollutant considered for water quality improvements within the City of St. Anthony. <br />Silver Lake is impaired for nutrients and targeting TP will help ensure that TMDL