Laserfiche WebLink
~` COLORADO DEPARTMENT O~EALTH, Water Quality Control ~ision <br />Permit Number CO-0032751 Page 7 . <br />DISCUSSION: (Continued) <br />B. Effluent Limitations for Cadmium (Cd). Conner (Cu). Lead (Pb). Mercury <br />(Hg). and Zinc (Zn): (Cont.) <br />(WQS) for Cd, Cu, Pb, and Zn are based on hardness-dependent calculations <br />indicated in Table III of the $asic Standards and Methodologies o <br />Surface Water (Reference 1). The Mercury WQS are also based upon certain <br />values specified in Table III. These metal limits are based on a mass <br />balance equation that involves the calculated WQS, the chronic stream low <br />flow (3E30) for chronic conditions (30 day average) or the acute stream <br />low flow (lE3) for acute toxicity (daily maximum) determinations, the <br />seasonal effluent flows (Q2) from both the Cross Mine and the Caribou <br />Mine, and the ambient upstream concentration (H1) for Coon Track Creek <br />(which is an assumed zero ambient concentration above the Carlbcu Mine). <br />Because of the close proximity of the two facility discharges within the <br />stream segment, it was necessary to calculate the total maximumm daily load <br />(TMDL) which the receiving stream can assimilate; the assimilative <br />capacity is detenalned through use of the mass balance equation. The <br />loading is then apportioned to each discharger based upon historic <br />discharge flow rates with both dischargers in this case required to meet <br />equal effluent limitations. Should the permittee in the future reach <br />agreement as to a different allocation of the TMDL, the permit may be so <br />amended at that time. The mass balance calculations for determining the <br />water quality standard-based limitations are included in Appendix C, and <br />the mean discharge concentrations for the Caribou Mine are in ,appendix D. <br />As of July 31, 1988, changes to the Basic Standards and Methodologies for <br />Surface Water became effective. As part of these changes, sin~:e the time <br />of public notice for this permit, standards for the metals limits of this <br />permit have now been based on a hardness-dependent equation rather than on <br />total or total recoverable metals. In addition, the Water Quality Control <br />Commission has determined that, in translating these new stand~irds into <br />permit requirements, that limitations are to be expressed as potentially <br />dissolved rather than the dissolved fraction. <br />C. Monitorine and Reporting Frecuency: <br />The monitoring frequency for the parameters is summarized in T:ible 2. <br />Monitoring for potentially dissolved cadmium, copper, lead, anti zinc has <br />been increased to weekly as a result of chronic non-compliance. Reports <br />shall continue to be submitted on a monthly basis. <br />The previous permit requirement for a six-time analysis for iron, <br />dissolved manganese, and sulfide as H2S (undissociated) was sut~mitted with <br />the monthly discharge monitoring reports for 14 months during ].985 and <br />1986. These samples indicated average concentrations of 0.15 mg/1 for <br />total iron (with most samples K0.1 mg/1), 0.10 mg/1 for manganese, and <br />0.15 mg/1 for sulfide (however, most samples were below the detection <br />level, K0.05 mg/1, for this parameter). Based upon an evaluation of the <br />data that was submitted for these three parameters, the Division has <br />determined that no further monitoring for these three parameters is <br />necessary. <br />