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~z/~ /~3 WFC SUBMITTAL 3 EXPECTED REGIONAL HYDROLOGIC IMPACTS OF MINING (APACHE, CIRUELA AND SANTISTEVAN CANYONS) Undermining Apache, Santistevan and Ciruela Canyons should not result in mateial damage to surface and/or alluvial aquifer systems present. This conclusion is supported by calculations attached) which demonstrate that even at conservatively assumed high surface flow conditons, the low transmissivities of the 400 to 800 feet of overburden will allow insignificant amounts of surface water to reach the mine workings. It is WFC's contention that no significant alluvial aquifers are present in these canyons. Rather, isolated areas of subsurface water occur in colluvial fill material. This is evidenced by the limited areal extent of hydrophytic vegetation and from drilling experience by WFC in similar side canyons near Segundo, Colorado. Additionally, based on subsidence data collected over longwall and room and pillar mining areas at the Allen Mine, subsidence should not materially increase this transmissivity, as the overburden subsides as a unit with very little horizontal strain or surface expression. Partial subsidence data results indicate a maximum vertical displacement of about 3 feet over a 6 foot high longwall panel and maximum horizontal displacement of less than 1 foot ~WOOdWdrd-Clyde report 9-9-83). Approximately 3 miles of the western part of Apache Canyon have been undermined with total extraction over the past 30 years. There is no surface indication of subsidence evident: power poles have remained vertical, no cracks are present in the road or side hills, trees remain vertical, and side hills have apparently remained stable. Both the Allen and Maxwell Mines underly the same strata. These strata do not contain significant aquifers due to their discontinuous and lenticular nature. The only water-bearing strata of any consequence are some of the coal seams themselves, such as the Maxwell seam. On the basis that no overlying aquifers exist, it appears evident that undermining will not materially affect groundwater regimes. The attached tables and exhibits summarize results of inflow studies performed recently in the Allen and Maxwell Mines. Water inflows in the Allen Mine have averaged approximately 123 gpm for the third quarter 1983. Of that amount, approximately 88 gpm is being generated from mined out gob areas totalling approximately 2800 acres. The northerly half of-that acreage is under the Purgatoire River and the southerly half is under Apache Canyon. It is impossible to determine how much of this 88 gpm.is from surface sources and how much is from groundwater sources; however, it appears evident that this small drainage rate from a large undermined area should not reflect material impact on water available to overlying isolated alluvial aquifers or the overall hydrologic regime of the area. Inflows in the Maxwell Mine have averaged about 30 gpm for the third quarter 1983. Approximately 16 gpm is from the air shafts and a drill hole and the remainder is from seepage originating in the coal seam aquifer. There is no evidence that any of this inflow is from surface sources. The 16 gpm from the shafts and drill hole is likely from overlying coal seams and/or other localized water-bearing strata.