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STATE iii iiiiiiiiiiiu iii 999 OF COLORADO DIVISION OF MINERALS AND GEOLOGY Deponnx•m of Natural Resources 1111 Sherman 51., Ruom 215 Denver, Colurado 8U2U3 DIVISION O F Rhone: amt ahh-;st„ MINERAL S FAX: (303) 8328105 & August 30, 1999 G E O L O G Y RECLAMATION MINING•SAFETY Mr. Michael Altavilla Seneca Coal Company eat o.,-ens P.O. Drawer 670 cOtef~°r Hayden, CO 81639 Greh E l4'alcher Erecnnre DveUOr Michael B. Lnny RE: Seneca II-W, Permit No. C-82-057 D.~~~o„D~re~~n~ 1998 Annual Hydrology Report Review Dear Mr. Altavilla: The Division has reviewed Seneca Coal Company's (BCC's) 1998 Annual Hydrology Report (AHR) for the Seneca II-W Mine. The frequency of data collection is in compliance with the approved monitoring plan contained in the Seneca II-W permit document. SCC did a good job at collecting and reporting the required monitoring data. The Division had several comments on the 1997 AHR in our review letter dated October 15, 1998. SCC addressed these comments and incorporated the Division's recommendations into the 1998 AHR. The Division has the following comments concerning the 1998 AHR. 1. SCC has compiled a list of ground water standards for agricultural uses (Table 5) and a list of surface water standards for agricultural uses (Table 9). As suggested by the Division, these lists have been composed mostly of Colorado Department of Public Health and Environment (CDPHE) ground water standards as of April 1996 and CDPHE surface water standards as of August 1997, respectively. Please note that the standards have been recently updated. The last effective update for both the ground water standards and surface water standards was March, 1999. 2. The Division notes that the AHR record indicates apparent exceedances of the CDPHE Basic Standards for Ground Water. As reported in the 1998 AHR and previous AHRs, isolated exceedances of ground water standards have occurred for certain metal constituents, chloride, fluoride total dissolved solids (TDB), and sulfate. TDS increases in groundwater resulting from mining activities are presented in detail in the Probable Hydrologic Consequences (PHC) discussion in the permit document. In addition, trend analysis is provided for TDS at each ground water well location in [he AHR. Has SCC identified the potential source for the apparent elevated levels of certain metals, chloride, fluoride, and for sulfate presented in Table 6 of the 1998 AHR? Are concentrations for these parameters significant]y higher than corresponding baseline levels, and does the overall trend indicate increasing or decreasing concentrations for these constituents?