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Numerous samples from Johnson Gulch have been ccllecled 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 mg/1, 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 significantly higher than pre-mine results. For example, the maximum pre-mine concentration at <br />No Name site S5 was 230 mg/I while a maximum value of 20,900 mg/l has been observed since the start <br />of mining. Natural TSS concentrations in the Trapper drainages have been measured that ere similar to <br />the maximum values observed in the No Name and other disturbed drainages. A TSS of 21,900 mg/I <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/l 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. Therefore, it is difficult to determine <br />whether 56,000 mg/I is the maximum natural level for TSS from the Trapper drainages. It does show <br />that a very large TSS would be required before it can be contributed to mining impacts when based only <br />on the TSS value. The sediment control structures have definitely decreased the TSS concentrations <br />from Trapper Mine, based on a comparison of monitoring results from the disturbed and undisturbed <br />drainages. <br />The TDS values which have been observed during operational surface water monitoring (see Table <br />4.8-8) have been similar to the pre-mine results (see Table 2.7-18). The maximum TDS observed at site <br />S5, (NPDES002) was 2230 mg/I prior to mining in this drainage. It is doubtful that the period of record <br />prior to mining is long enough in this drainage to have defined the full range of TDS concentrations. The <br />maximum TDS value observed in Flume Gulch (S1) is similar to the maximum pre-mining No Name <br />value, while the maximum natural level observed in East Pyeatt Gulch is higher at 3210 mg/I. Higher <br />natural values of 4780 and 4510 mgA were observed at the Lower Flume Gulch (S2) and S4 sites. <br />The higher TDS concentretions observed in Johnson Gulch are within the observed natural range in con- <br />centrations at Trapper Mine. The higher TDS value for NPDES 001 are 2550, 2630, 2894, 2550, 2530 <br />and 2590 mg/I for May 1984, November 1989, March 1992, July 1995, October 1995 and November <br />1998, 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 R is <br />presently difficult to determine whether mining has affected the observed TDS values at NPDES 001. <br />:~ <br />4-222 <br />T2-76 <br />x//9/98 <br />