2018-04-02_REVISION - C1982056 - Laserfiche WebLink

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Response: - In order to address this comment, it is important to understand the purpose, intent, and limitations of the referenced water quality projections presented in Exhibit 32. Exhibit 32 is a report prepared by In-situ Inc. in 1985, which utilized modeling to characterize ambient conditions and project future water quality in area drainages, based on limited baseline flow and water quality data, regression analysis, and specific assumptions and methods, as stated in the report. The report reflects modeling (projected) results for four, 8 -year periods extending from 1985 through 2017, and uses eight years of pre -mining data (1976 — 1985) as a check to calibrate the model predictions. For Lower Middle, Fish, and Trout creeks, Exhibit 32 acknowledges specific considerations relating to the accuracy and use of modeling results for EC, TDS, and sulfate (Exhibit 32, pgs 31 - 33). A key consideration in any water quality analysis for this area is that ambient levels of the indicator parameters are relatively high due to natural geologic factors, and for the sub -watersheds noted (Lower Middle, Fish, and Trout creeks) runoff contributions from previous surface mining operations in the area are an important factor (not specifically addressed in the water quality modeling effort and report). In the "Summary and Conclusions" section (Exhibit 32, pgs 39 — 43) of the report, however, it is noteworthy that the report states; "Those anticipated dissolved -solids loads are barely discernible relative to average ambient conditions in Trout Creek (about 70 tons/day) or the Yampa River (about 250 tons/day)." For reference, the following summarizes the results of the referenced modeling effort (Exhibit 32, Table 10), and includes average values from TC's ongoing hydrologic monitoring program for the period 2009 — 2015 (all monitoring data through the present is presented in TC's Annual Hydrology Reports). Drainage/Parameter Modeling Results Calibration Ambient Predicted (Baseline) Predicted Values (8 -Yr Intervals) Av. Values 2009-2015 Monitorin Lower Middle Creek EC 760 771 1,048 1,220/950/948/934 1,700 TDS 888 898 864 1,056/812/810/797 1,120 Sulfate 406 388 372 570/377/375/366 645 Lower Fish Creek EC 491 491 460 456/488/457/409 870 TDS 441 441 430 443/471/444/402 645 Sulfate 172 172 150 176/196/177/148 277 Lower Trout Creek EC 381 381 ND 367/359/348/322 640 TDS 396 397 ND 345/338/328/314 429 Sulfate 159 159 ND 144/139/133/123 217 Yampa River EC 265 265 240 241/240/238/236 ND TDS 156 156 169 166/166/164/162 ND Sulfate 34 34 38 39/38/37/36 ND Notes: Lower Middle Creek is subject to water quality influences from previous surface mining operations (Eckman Park Mines Mine No. 1, and Mine No. 3), irrigation and grazing, and recent residential development Lower Fish Creek is subject to water quality influences from previous surface mining operations (Mine No. 2, the Seneca Mine, and the Mine No. 3 Tipple), and irrigation and grazing Lower Trout Creek is subject to water quality influences from all of the above, plus the Edna Mine ND — No baseline data was available for Lower Trout Creek, and TC does not monitor the Yampa River In evaluating the values presented in the table above, the monitoring values should be compared with applicable water quality standards for the relevant water uses, which are limited to livestock use (TDS of 7,000 mg/1) and