2015-08-18_PERMIT FILE - C1982056A (4)

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Baseline water quality of Fish Creek upstream of the mine is typically a calcium sulfate - bicarbonate type with •relatively high concentrations of magnesium and moderate to low dissolved solids. The Trilinear Diagram Plot illustrates typical surface water chemistry for the Fish Creek Site 16 and Station 1001 included in Figures 6 -f and 6 -g, respectively. Station 1002 and 1003 located downstream show a shift to higher dissolved solids and higher concentrations of sulfate and sodium as illustrated by the Trilinear Diagram Plot for the Fish Creek Stations 1002 (26) and 1003 included in Figures 6 -h and 64, respectively. • • Water quality seasonal plots on Fish Creek included in Figures 6-j, 6 -k, and 6 -1 show no trends in the plotted water quality characteristics over the relevant monitoring period. The plots do illustrate the seasonal trends in TDS as well as the changes along the stream reach through Twentymile Park. Upstream of the mine, TDS levels vary from about 250 mg/l during the high snowmelt runoff months of March, April, and May to concentrations about 500 mg/l during low flow periods for the months of July, August, and September. Downstream near the mouth of Fish Creek, TDS levels vary from about 200 mg/1 to concentrations in excess of 1000 mg/l. No obvious seasonal trend appears at the downstream station, although TDS concentrations appear to decrease during the summer months. The seasonal plots in Figure 6 -m of Fish Creek water quality at Station 1002/26 show that stream standards for iron, copper, and TDS are often exceeded. Period of record water quality data for Fish Creek surface sites (16, 16A, 307, 302, SW -13, 1002, SW -14, SW -15, 305 62 and 1003) are provided in Table 10, Surface Water Data. Baseline water quality characteristics on Trout Creek are characterized by data from Station 69 located on Trout Creek above the confluence with Fish Creek (Map 13, Twentymile Park Hydrology). Baseline water chemistry on Foidel Creek is a calcium - bicarbonate type with relatively high concentrations of magnesium and sulfate (Figure 6 -o). The seasonal plots in Figure 6 -n do not reveal pronounced seasonal patterns for TDS. Highest concentrations appear during the spring and late summer. Iron, manganese, sulfate and TSS all show a similar pattern of high concentrations in March through June with substantial decreases in concentrations during the remainder of the year. The iron, manganese and TSS pattern is typical of the pattern observed on other streams such as Fish Creek and Foidel Creek. The sulfate pattern is atypical. It is possible that this pattern for sulfate occurs as a result of baseflow contributions to Trout Creek from a ground water aquifer that is predominantly a calcium - bicarbonate type. The seasonal plots in Figure 6 -n of Trout Creek water quality show that stream standards or irrigation standards for sulfate, suspended solids, and iron are often exceeded during spring runoff. Total manganese and copper appear to be well below the stream standards. Further baseline water quality characterization of streams in the general area was facilitated by use of a digital - computer modeling analysis of water quantity and quality conditions in streams of the Trout Creek Basin and in a reach of the Yampa River upstream and downstream from the confluence of Trout Creek (Exhibit 32, quantity and Quality Modeling Analyses of Surface -Water Resources of the Trout Creek Basin). In this modeling analysis, ambient (i.e., baseline) streamflow and selected water - quality characteristics were depicted using historical data available over an 8 -year period of record (1976 through 1983 water years) at approximately 24 monitoring sites located throughout the study area. Much of the available monitoring data is referenced herein. In order to achieve a better balance of streamflows and associated chemical solute loads in the Trout Creek Basin, estimated flows and water - quality characteristics are introduced at 6 additional locations in the stream system that have not been monitored to account for observed conditions at actual monitoring sites (Exhibit 32, Quantity and Quality Modeling Analyses of Surface -Water Resources of the Trout Creek Basin). Water quality constituents of interest considered in the modeling analysis included: specific conductance, dissolved solids, total suspended solids, and suspended sediment as indicator variables; calcium, magnesium, sodium, and potassium as major cations; bicarbonate, sulfate, and chloride as major anions; dissolved solids as sum -of- constituents as a check on directly analyzed dissolved - solids concentrations, and total iron and total manganese PR 03 -06 2.04 -35 concentrations as indicator trace metals. 05/07/03