2013-04-18_PERMIT FILE - C2009087A

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RULE 2 - PERMITS Geochemical processes (carbonate dissolution and cation exchange of calcium and magnesium for • sodium) occurring as the groundwater flows through the rocks results in groundwater containing higher proportions of sodium in downgradient areas. Seasonal variations are not evident. The exception to the typical overburden and Wadge Coal water quality type is the groundwater from well SW17 in the north - central part of the permit area. Samples from that well are mixed - cation sulfate type water with much higher TDS concentration and lower pH, similar to groundwater from the spoils units. Oxidation of sulfur minerals present in the coal and overburden and dissolution of sulfate minerals such as gypsum in oxidizing environments results in groundwater with higher sulfate concentrations and more sulfate as a proportion of total anions. These processes predominate in the spoils, and flow of groundwater from the adjacent Seneca spoils into the adjacent Wadge Coal may have influenced the water quality in SW17. Groundwater quality in the underburden is more variable than in the coal and overburden. Underburden groundwater exhibits a wide range of TDS concentrations (490 to 2,560 mg/L). Generally the water is sodium bicarbonate type, but two wells in the southern part of the permit area exhibit different water types. Well CWU13 yields sodium bicarbonate chloride type water with up to 1,490 mg/L TDS, and Well CWU14 yields sodium sulfate type water with a significant amount of chloride and up to 2,560 mg/L TDS. Seasonal variations are not evident. The outlier relative to groundwater quality in all three bedrock units is the YOV28- YW28 -YWU28 site just southwest of the permit area and adjacent to and down -dip of mined areas at the Yoast mine. Groundwater from the overburden, Wadge Coal, and underburden units is calcium magnesium • bicarbonate sulfate water with moderate TDS concentrations (840 to 1,520 mg/L) and slightly acidic pH, characteristics not resembled by any other groundwaters in the area. The groundwater in this area may be influenced by the mining activity updip from the wells. These wells are also farther upgradient along the groundwater flow path, and so could be expected to exhibit groundwater quality different from wells farther downgradient. Groundwater in the alluvium of Little Grassy Creek is mixed - cation sulfate type with high TDS concentrations (1830 to 5470 mg/L) and slightly basic pH. At wells SGAL71 and SLGAL32, TDS concentrations are generally higher in the spring (May) samples than in the fall (October/November) samples and fluctuate 700 to 800 mg/L seasonally. A slight reversal of this seasonal variation of TDS is seen in SGAL70, in the Grassy Creek drainage. Over the historical period of record for SGAL71 (see Exhibit 2.04.7 -E1, Hydrologic Information), the TDS increased from a range of 1,600 to 2,000 mg/L during earlier part of the period of record (1988 to 1998) to a range of about 3,400 to 4,200 mg/L more recently (2005 to 2009). During that time, the relative proportions of sulfate increased and sodium decreased. The TDS in SGAL70 has experienced mild fluctuations in the same time period (1130 to 3030 mg/L) with no multi -year trend evident. The changes suggest that groundwater from the adjacent Seneca spoils has affected the alluvial groundwater quality in the Little Grassy Creek drainage, but not down gradient in the Grassy Creek drainage. Spoil well SSP27 in the northern part of the permit area yields magnesium sulfate type groundwater with high TDS concentration (3,800 to 4,800 mg/L) and slightly basic pH, very similar to the groundwater in the Little Grassy Creek alluvium but with slightly more magnesium. Seasonally, the • TDS is higher in the spring (May) samples than the fall (September- October) samples, with seasonal fluctuations of up to 800 mg/L. Over the historical period of record for SSP27 (see Exhibit 2.04.7 -E1, Hydrologic Information), the TDS has increased since about 1985 from about 2,500 mg/L to about PSCM Permit App. 2.04 -59 Revision 12/17/09