2016-10-17_REPORT - C1982057 - Laserfiche WebLink

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Iron excursions were likely the result of high suspended solids (TSS) and are generally observed during snowmelt runoff. This strict aquatic life standard (1.11 mg/1) was exceeded in over half of the pre -mining stream samples. The acute manganese standard (4.738 mg/1) was exceeded on October 8 at Site WSSPGI with a value of 5.27 mg/1. However, as indicated in the recently revised CDPHE Regulation 31, the standard applies to plants grown in acidic (<6.0 pH) soils. In alkaline soils, as are found in the Seneca II -W region, a more appropriate (EPA) standard would be 10 mg/l. Pre -mining manganese values often exceeded the standard. The drinking water standard for mercury is 2 ug/l. The aquatic life standard for mercury is 0.01 ug/l, which is set to protect the average human consumer of fish. SCC's lab uses a method with a detection limit of 0.2 ug/l. None of the samples collected this year were above the detection limit. During the last NPDES permit renewal, the CDPHE performed a reasonable potential analysis on SCC's outfalls. It determined that there was no reasonable potential for SCC's outfalls to exceed the mercury limit; therefore, mercury monitoring is no longer required for SCC's outfalls. The nitrite standard (0.05 mg/1) was exceeded on October 8 at Site WSSPGI with a value of 0.07 mg/l. Nitrites are unstable in aerated water (Hem, 1985), and will oxidize to nitrates. The sulfide data presented in Appendix E are the total of both the ionized (S-) and un -ionized (H2S) forms of hydrogen sulfide. The un- ionized form is the potentially toxic form, and is the basis on the CDPHE water quality standard. A procedure for calculating the un -ionized form may be found on the website: http://www.mullalyengineering.com.au/images/product/file/Problem of Hydr ogen Sulphide in Sewers.pdf page 5, Table 1. NPDES Effluent Criteria (Permit No. CO -0000221). No excursions of NPDES limits occurred this year. 24