2010-03-22_REPORT - C1994082 (2)

Home Browse Search

This strict aquatic life standard was exceeded in 38% of the premining stream samples. One sample from NPDESI2 exceeded the nitrite standard. Nitrites are unstable in aerated water (Hem, 1989), and will oxidize to nitrates. Three samples from NPDESI3 exceeded the chronic selenium standard, 4.6 ug/l. One of the same samples also exceeded the acute standard, 18.4 ug/1. Samples from Sage Creek did not exceed the standard. Seven samples from five sites experienced an exceedance of the sulfide standard (0.002 mg/l un-ionized) this year. Three of these excursions occurred in April, when suspended solids are relatively high. The analytical method available to SCC detects both dissolved sulfides and acid-soluble metallic sulfides present in suspended matter. It is suspected that a large portion of the sulfides detected is of the latter type, which would bias the un-ionized results high. Any dissolved sulfides present in surface water should eventually oxidize to sulfates. NPDES Effluent Criteria (Permit No. CO-0000221). One excursions of NPDES effluent criteria occurred this year. This excursion occurred at NPDESII during high volume snowme.lt runoff. Below is a summary of the excursions. More details may be found in the July 28, 2009 cover letter for the second quarter Discharge Monitoring Reports, of which the CDRMS was copied. A sample collected at NPDESII on April 23 had a total recoverable iron concentration of 1810 ug/1. The effluent limit is 1000 ug/l. However, in August 2008, the Colorado Water Quality Control Commission authorized a temporary modification for the total recoverable iron standard to be set at "existing quality" for Yampa Segment 13e, Sage Creek, to which this pond discharges to. Seneca is currently gathering information to provide to the Commission (by May 31, 2011) what "existing quality" is for this stream segment. This excursion was most likely caused by snowmelt runoff. 14