2010-05-07_GENERAL DOCUMENTS - C2009087

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Camiletti ranch is attributed to the Fish Creek AVF, located in sections 10 and 15, TSN, R86W. The Division affirms its previous AVF determinations for the Grassy Creek and Little Grassy Creek AVFs that were made in the 1981 findings document of the Seneca Il Mine (C-1980- 005). Those previous determinations are provided below. The confluence of Grassy Creek and Little Grassy Creek, the narrow strip along Little grassy Creek and land adjacent to Fish Creek were determined by the Division to be Alluvial Valley Floors based on the geomorphology, shallow ground water levels, soils, vegetation, land use and infra-red photos as demonstrated by the following discussion. Exhibit 7-16 of the application delineates the areas that are characterized by alluvial fill material. There are no terraces associated with any of the areas. The confluence of Grassy Creek and Little Grassy Creek is approximately 45 acres with alluvial material averaging 40 feet deep. The strip along Little Grassy Creek is very narrow and comprises approximately 40 acres in total with alluvial material up to 51 feet deep. Grassy Creek and its tributary, Little Crassy Creek, cover 3.07 square miles or 72% of the permit area. The drainage from the mine area accounts for 12.5% of the overall Grassy Creek Basin. Two unnamed tributaries of the Fish Creek drainage basin are located in the southern permit area. About 1.22 square miles or 1.5% of the total Fish Creek Basin will be affected by Seneca II. The quality and quantity of the two drainage basins is influenced strongly by spring runoff creating seasonal fluctuations as is characteristic of streams in the upper Colorado River Basin. The average flow in Grassy Creek, measured at SW-S-2 (Exhibit 7-2) is 1,827 gpm with a recorded high of 12,280 gpm during spring runoff and a low of 28 gpm during low flow. During spring alkalinity is lowest and during summer and winter alkalinity is somewhat higher. Acidity is the mirror image of alkalinity. The concentrations of total iron varies with suspended solids which increase during high runoff periods. Manganese exhibits the same seasonal fluctuations as iron and total suspended solids. pH has shown no apparent variations. Groundwater levels measured in alluvial wells GW-S6--A, GW-531, GW- S33(Exhibit 7-2) demonstrate subirrigation availability. The water quality analysis indicates a slight to highly mineralized Ca-Mg-SO4 or Ca-Mg- 504- HCO3 type water with near normal pH and high sulfate concentrations. The amount of trace metals was low with the exception of high manganese levels in all wells. The application states that the high salinity of the groundwater makes it unsuitable for irrigation. The Division disagrees with this conclusion since a comparison of water quality data collected during the growing season (Table7-25) to a more recent flood irrigation water quality classification (USDI, 1968) shows a classification having a low salinity hazard. Peabody Sage Creek Mine 36 May 7, 2010