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,. ~~ . <br />..r <br />~- ' <br />6 ANNUAL STORMWATER POLLUTANT LOADS <br />6.1 Introduction <br />This section summarizes the methodology and results of annual pollutant load calculations for <br />the City of Eugene. Background information and permit requirements are provided in this <br />subsection. The general methodology, assumptions and model input are provided in Section 6.2. <br />Summaries of the annual pollutant load calculations for the City's MS4 permit area are provided <br />in Section 6.3. <br />6.1.1 Background <br />Stormwater pollutant loads are the mass of pollutants washed off land surfaces by stormwater <br />runoff. Many water quality impact assessments are based on pollutant concentrations including <br />dissolved oxygen levels, toxicity and aesthetics. For the original (1994) permit application, the <br />City provided an estimate of stormwater pollutant loads for specific pollutants of concern: <br />biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended: solids <br />(TSS), total dissolved solids, nitrate, total kjeldahl nitrogen (TKN), total phosphorus, ortho- <br />phosphate, cadmium, copper, lead and zinc. The original pollutant load calculations conducted <br />in 1994 were based on City of Eugene stormwater sampling data and were supplemented by <br />National Urban Runoff Program (NURP) data. <br />6.1.2 Permit Renewal Requirements <br />As part of this 2008 permit renewal application, the City is required to provide an"updated <br />estimate of total annual stormwater pollutant loads" for the original pollutants of concern and <br />other stormwater pollutants on the 303(d) list as directed by DEQ. DEQ has not requested any <br />changes to this list. Also, DEQ requested that permittees "provide an updated assessment <br />comparing pollutant loads permitted in 2004 with expected pollutant loads during the 2009 <br />permit cycle10." Since the City of Eugene was not a part of the reconsideration process in 2005, <br />an updated estimate of pollutant loads was not required. A discussion of the qualitative <br />comparison of the 1994 pollutant loads estimate and the updated 2008 pollutant loads estimate is <br />provided. <br />6.2 Methodology and Assumptions <br />The updated annual stormwater pollutant load estimates were determined using a spreadsheet <br />model that employs the EPA simple method, commonly used for estimating pollutant loads for <br />urban land uses. This subsection describes the information and assumptions were used to <br />generate input for the spreadsheet model. <br />to DEQ e-mail dated 6/3/08 to permittees entitled "LUCS and antidegradation." <br />10-81 <br />