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• Numerous samples from Johnson Gulch have been colleded at the S74 site. This site is downstream of <br />the settling reservoirs. A large fluduation in TDS has occurred in Johnson Gulch, while the TSS in this <br />gulch has not been observed as high as the concentrations in No Name. Significant total iron concentra- <br />tions, greater than the maximum allowable of 4 mg/I, have occurred in Johnson Gulch. Data from an <br />analysis of water from reservoirs 1 and 6 of Johnson Gulch are given in Table 4.8-9. <br />TSS levels observed from the operational monitoring (see Table 4.8-8) of the surtace water sites have <br />been high at some sites. For example, No Name site SS had a maximum value of 20,900 mg/I. <br />However, natural TSS concentrations in the Trapper drainages have been measured that are similar to <br />the maximum values observed in the No Name and other disturbed drainages. A TSS of 21,900 mgA <br />was measured on the East Pyeatt (S3) drainage during a large runoff event on April 1, 1987, prior to <br />mining in this drainage. A maximum TSS of 56,230 mg/I has been measured on Flume Gulch at the S1 <br />site on August 15, 1989 during high flow conditions. No mining has occurred in Flume Gulch. The high- <br />est TSS concentrations during runoff events are more difficult to obtain because they generally occur <br />during the rising stage or near the peak stage during a flood. This show that a very large TSS woukl be <br />required before it can be attributed to mining impads when based only on the TSS value. The sediment <br />control strudures have definitely decreased the TSS concentrations from Trapper Mine, based on a <br />comparison of monitoring results from the disturbed and undisturbed drainages. <br />The TDS values which have been otuerved during operational surtace water monitoring (see Table 4.8-8) <br />• have been similar to the pre-mine results (see Table 2.7-18). The maximum TDS observed at site S5, <br />(NPDES002) was 2230 mg/I prior to mining in this drainage. The maximum TDS value observed in <br />Flume Gulch (S7) is similar to the maximum pre-mining No Name value, while the maximum natural level <br />observed in East Pyeatt Gulch is higher at 3210 mg/l. Higher natural values of 4780 and 4510 mgll were <br />observed at the Lower Flume Gulch (S2) and S4 sites. <br />The higher TDS concentrations observed in Johnson Gulch are within the observed natural range in con- <br />centrations at Trapper Mine. The higher TDS values for NPDES 001 an: 2550, 2630, 2894, 2550, 2530 <br />and 2590 mgll for May 1984, November 1989, March 1992, July 1995, Odober 1995 and November <br />1998, respedively. Some increase in TDS concentration may be due to mining in Johnson Gulch <br />because the TDS from Johnson Gulch Spring probabty has been afteded by the backfill aquifer's higher <br />TDS. The backfill TDS is expeded to deGine in the future, which should allow the Johnson Gulch Spring <br />TDS to return to pre-mine levels. This may be difficult to see in data from NPDES 001 site because n is <br />presently difficuR to determine whether mining has afteded the observed TDS values at NPDES 001. <br />• <br />4.222 <br />2-76 <br />~//fi~9$ <br />