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Nine wells are used to monitor alluvial water quality in the drainages. Two wells aze located along Cow Camp Creek, one along Bond Creek, two along Grassy Creek and four along Little Grassy Creek. All of these wells exhibit seasonal variations. The Grassy Creek alluvial system is down gradient of mining and the wells were constructed after mining in the Grassy Creek drainage. Progressing downstream, the little Grassy Creek alluvial aquifer becomes increasingly affected by spoils water discharge. Spoils The resaturation of portions of the backfilled pits has been expressed as spoil aquifers. Water percolates through the replaced spoil material and flows down-gradient until it reaches the lower-most highwall where the infiltration rate into bedrock is much lower than flow through the spoil. When the elevation head of the spoil aquifer exceeds the ground surface elevation, the spoil water discharges in the form of springs at the topographically lowest point along the reclaimed highwall. Nine spoil springs have been identified, eight of which are monitored by Seneca Coal Company. in addition, Seneca Coal Company has historically monitored thirteen spoil wells as part of the approved monitoring plan. Water from the spoils exhibit elevated concentrations of sulfate, manganese, and magnesium. TDS concentrations in water from spoil wells have generally risen during the period of monitoring but seem to level out at about 4000 mg/1. Several exceptions are S25-S, which has reached concentrations as high as 5700 mg/1, S26-S which reached levels as high as 4300 mg/1 but has dropped off to around 3500 mg/l, and S27-S which has climbed gradually to about 3300 mg/I TDS. Spoil springs show the same range of concentrations as the wells. In 1977, the Water Resources Division of the United States Geological Survey (USGS) began a lysimeter study at the Seneca II Mine to determine spoil aquifer dischazge quality, and how that quality changes over time. Stipulation No. 23 in the original permit required the applicant to submit the USGS report to the Division upon its completion. In 1994, the USGS published Water-Resources Investigations Report 92-4187 titled, Hydrolosv and Geochemistry of a Surface Coal Mine in Northwestern Colorado. The report describes the sources of hydrologic recharge to and from reclaimed spoil, the relative contributions of recharge to the reclaimed spoil aquifer from identified source waters, and the water movement and geochemical reactions that control water quality in reclaimed spoil. 23