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• July 1993 -37- 923-2515 7.0 MATERIAL DAMAGE ASSESSMENT There are no flood irrigated agricultural fields in alluvial material along Grassy Creek, Unnamed Draw, Annand Draw, and Scotchmans Gulch. A small portion of an agricultural field, located neaz the confluence of Annand Draw and Scotchmans Gulch, is the only subirrigated field in the study area in crop production. A material damage assessment of the 12 acre subirrigation portion of this field, which is not an AVF, follows. The entire field and the 12 acre portion is alternately planted to wheat and bazley and cropped two out of three yeazs (Hockett 1993). According to the ASCS data (Daughenbaugh 1992) this large field of which includes the 12 acres of subirrigation produces 26 bushels per acre of wheat and 32 bushels per acre of barley. There are no data specific to the 12 acre portion of the larger • field. However, Hockett (1993), the owner, estimates the productivity to be 10-15% less than the portion of the field at higher elevations due to the high water table and alkaline conditions. Adjusted productivity values for the 12 acre portion of the field are 22.1 to 23.4 bushels per acre of wheat and 27.2 to 28.8 bushels per acre of bazley. Future mine outflows may increase the total dissolved solids ('TDS) of the ground water causing a decrease in agricultural productivity. The background conductivity is 4.07 mmhos/cm from site WRD-1, immediately down drainage from the grain field. The projected TDS of the ground water is 3500 mg/1 (Smith 1993), which converts to 4.8965 mmhos/cm or a 27% increase in TDS. The predicted TDS value is a measurement of the alluvial water from the Spoil Spring and Spoil Well site of the nearby Seneca mine. Because of the proximity of the Seneca Mine, similar topography, geology, and climate, the TDS value is believed to be a good estimate of the change in alluvial water expected from the Yoast mine. ~J Golder Associates