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• Numerous samples from Johnson Gulch have been collected at the S14 site. This site is downstream of <br />the settling reservoirs. A large fluctuation 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 mgA; 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 surface water sites have <br />been high at some sites. For example, No Name site S5 had a maximum value of 20,900 mgA. However, <br />natural TSS concentrations in the Trapper drainages have been measured that are similar to the <br />maximum values observed in the No Name and other disturbed drainages. A TSS of 21,900 mgA was <br />measured on the East Pyeatt (S3) drainage during a large runoff event on April 1, 1987, priorto mining in <br />this drainage. A maximum TSS of. 56,230 mgA has been measured on Flume Gulch at the S1 site on <br />August 15, 1989 during high flow conditions. No mining had occurred in Flume Gulch. The highest TSS <br />concentrations during runoff events are more difficult to obtain because they generally occur during the <br />rising stage or near the peak stage during a flood. This shows that a very large TSS would be required <br />before it can be attributed to mining impacts when based only on the TSS value. The sediment control <br />structures have definitely decreased the TSS concentrations from Trapper Mine, based on a comparison <br />of monitoring results from the disturbed and undisturbed drainages. <br />The TDS values which have been observed during operational surface 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 mgA prior to mining in this drainage. The maximum TDS value observed in Flume <br />Gulch (S1) 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 mgA. Higher natural values of 4780 and 4510 mgA 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 are 2550, 2630, 2894, 2550, 2530 <br />and 2590 mgA for May 1984, November 1989, March 1992, July 1995, October 1995 and November <br />1996, respectively. Some increase in TDS concentration may be due to mining in Johnson Gulch <br />because the TDS from Johnson Gulch Spring probably has been affected by the backfill aquifer's higher <br />TDS. The backfill TDS is expected to decline 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 it is <br />presently difficult to determine whether mining has affected the observed TDS values at NPDES 001. <br />4-222 <br />