2009-02-26_REPORT - C1980005 (7)

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listed on the standards table (Table 9) and are also the same as those used in the water quality reports. The frequency column on Table 10 indicates the number of exceedences out of the total number of samples (i.e., 1/2 indicates one exceedence out of two samples). Below is a summary of standards that were exceeded. Given in parenthesis is the source and use of each standard. Although the CDPHE does not indicate between livestock and irrigation uses in their surface water agricultural standards, they have done so in their similar ground water agricultural standards (see Table 5). For the sake of discussion, SCC chooses to use those ground water use standards classifications (livestock or irrigation) for surface water use evaluation. Parameter # of Sites / # of Excursions Cadmium (CDPHE irrigation) 1/1 Nickel (CDPHE irrigation) 1/1 Manganese (CDPHE irrigation) 11/17 This summary indicates that only three CDPHE surface water agricultural use standards were exceeded . The manganese standard was exceeded at eleven sites. However, as indicated in the recently revised CDPHE Regulation 31, the standard of 0.2 mg/1, applies to plants grown in acidic (<6.0 pH) soils. In alkaline soils, as are found in the Seneca II region, a more appropriate (EPA) standard would be 10 mg/1. The maximum manganese value observed this year at any NPDES outfall was 3.62 mg/l at NPDES 008. All stream sites had manganese values less than 0.60 mg/1, and all but one spoil springs were less than 5 mg/1. It should also be noted that the site on Grassy Creek (SSG1) that is upstream of Seneca II discharges also experienced exceedences of the 0.2 mg/l standard. Spoil Spring 6 exceeded the cadmium, nickel and manganese agricultural standards. However, a same day sample collected downstream at Spoil Spring 6A experienced none of these exceedances. 18