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<br />2.2.2.6 NPDES Discharges At present, BME has 15 NPDES ouffalls. Only three outfalls (DP1, <br />RP2J3 and RP4) experienced a discharge during this monitoring period. The ouffalls RP2/3 and <br />' PR4 experienced one discharge due to a storm event in September, 1997. This storm exceeded <br />10-year event. None of the ouffalls at the sump dewatering holes are discharging since the <br />January 31, 1996 underground fire episode. The NPDES discharge qualify parameters for the <br />' water year are summarized in Table 2-4. <br />' 2.2.2.7 Whole Effluent Toxicity Testing No WET testing was conducted during the 1996-1997 <br />water year since there was no discharge of the underground water from the sump dewatering <br />holes or from ouffall 004 (Pond PP2). A history of WET testing at Deserado Mine follows below: <br />' BME started the whole effluent toxicity (WET) testing program beginning in the fourth quarter of <br />1989. The mine water effluent was found to be toxic to the test species. Accelerated testing was <br />conducted but the toxicity to the species continued. <br />In a meeting with Colorado Water Quality Control Division (WQCD) staff on January 31, 1992, the <br />BME staff reiterated the biomonitoring events, and various measures taken to identity the toxicants <br />and to reduce the toxicity. BME took the following steps to identify potential toxicants. <br />• In the early stages of WET testing, the associated HZS in the effluent was deemed to be <br />' a potential toxicant. However, a WET testing done by ENSR Consulting in June 1990 after <br />removing H2S by aeration still showed toxicity. This result indicated that some other <br />factor(s) also contributed to the toxicity. <br />' • In September, 1990, ENSR Consulting was directed to conduct a "toxicity characterization° <br />' study to identify the primary cause of the toxicity. This study considered pH effects, vola- <br />tile organic carbon, metals chelation, aeration, total dissolved solids (TDS) and ammonia. <br />The lab determined high TDS (chlorides) as the primary cause of the toxicity. However, <br />' a recent review 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 the effluent. <br />' • A pilot test was conducted to identify a flocculent for removing high levels of oil and grease <br />' from the effluent. <br /> <br />' 14 <br /> <br />