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<br />' 2.2.1.6 NPDES Discharges At present, BME has 15 NPDES outfalls. Only three ouffalls <br />(DP1, RP2/3 and SS-1) experienced a discharge during this monitoring period. The outfall <br />RP2/3 experienced one discharge due to a storm in October, 1997 and the Ouffall SS-1 <br />experienced two discharges due to storm evens in October, 1997 and June, 1998. The <br />' storms exceeded 10-year event. None of the outfalls at the sump dewatering holes are <br />discharging since the January 31, 1996 underground fire episode. The NPDES discharge <br />' quality parameters for the water year are summarized in Table 2.4 <br />2.2.1.7 Whole Effluent Toxicity Testing No WET testing was conducted during the 1997- <br />' 1998 water year since there was no discharge of the underground water from the sump <br />dewatering holes or from ouffall 004 (Pond PP2). A history of WET testing at Deserado Mine <br />follows below: <br />BME started the whole effluent toxicity (WET) testing program beginning in the fourth quarter <br />' of 1989. The mine water effluent was found to be toxic to the test species. Accelerated <br />testing was conducted but the toxicity to the species continued. <br />' In a meeting with Colorado Water Quality Control Division (WQCD) staff on January 31, 1992, <br />the BME staff reiterated the biomonitoring events, and various measures taken to identify the <br />' toxicants and to reduce the toxicity. BME took the following steps to identify potential <br />toxicants. <br />1 In the early stages of WET testing, the associated HZS in the effluent was <br />deemed to be a potential toxicant. However, a WET testing done by ENSR <br />' Consulting in June 1990 after removing HZS by aeration still showed toxicity. <br />This result indicated that some other factor(s) also contributed to the toxicity. <br />1 In September, 1990, ENSR Consulting was directed to conduct a "toxicity <br />characterization" study to identify the primary cause of the toxicity. This study <br />considered pH effects, volatile organic carbon, metals chelation, aeration, total <br />dissolved solids (TDS) and ammonia. The lab determined high TDS <br />t (chlorides) as the primary cause of the toxicity. However, a recent review <br />shows no correlation between LCD values and chloride or TDS levels. <br />' BME took the following measures to reduce toxicity of the effluent. <br />' On-site aeration structures were installed for HZS removal before discharging <br />the effluent. <br /> <br />19 <br />1 <br />