HYDRO24583 - Laserfiche WebLink

Home Browse Search

COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale - Page 26. Permit No. CO-0027154 VII. PUBLIC NOTICE COMMENTS (continued) The permittee submitted several pages of silver effluent monitoring data for outfalls 001, 005 and 007. The data were collected for the mining permit issued by the Colorado Division of Minerals and Geology (CDMG). The Water Quality Control Division reviewed the data and determined that the levels for outfalls 001, 005 and 007 were well below the applicable limitations. The data are summarized in the following table. Outfall Maximum Concentration No. of Samoles Period of Racord 001 0.2 ug/Z 24 10/80 - 6/91 005 70 ug/F* 350+/- 3/64 - 9/91 007 0.8 ug/Y 16 9/85 - 6/91 * The high data point occurred in April, 1984. Data from 1/85 through 6/91 show no values higher than 4.9 ug/Y. The majority are below the detection limit. These data show that the actual discharge concentrations for outfalls 001 and 007 are well below the effluent limitations of 0.003/0.079 mg/Y (or 3/79 ug/Y) (30-day average/daily maximum). On the basis of all summarized effluent data, silver limitations are being excluded from outfalls 001 and 007. Periodic monitoring will be required to determine whether the concentrations remain low. If levels rise, the permit may be reopened to add limitations and/or other appropriate conditions. Because outfall 005 effluent silver levels have exceeded the chronic limitation, silver effluent limitations will be imposed. The permittee would need to demonstrate that effluent concentrations in the future are well below these limitations for a minimum of two years before the Division could consider eliminating these limitations. TVS Hardness Value: Tha Division used a hardness value of 839 mg/Z to calculate the TVS standards for copper and silver. After the draft permit went to public notice, the Division was informed by EPA of guidance that recommended using upper and lower default values for hardness when actual values were outside the defaults. The upper default 1s 400 mg/Y. The Division communicated this guidance to the permittee. The permittee submitted several more data points.of hardness than were previously available. Although a new mean hardness has not been 'calculated, this data would raise the mean even higher than 839 mg/Y. The Division's Standards Unit reviewed the data along with available aquatic survey information and concluded that the receiving water would be protected with effluent limitations based on the 839 mg/Y hardness value. As pzeviously discussed, silver limitations are not necessary at this time. Copper limitations will remain unchanged for the time being. After at least ona year, if the permittee believes they have accumulated effluent data to support removal of copper limitations for one or more of these outfalls, they can request a permit amendment at that time.