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_17_ The Upland Terrace deposits which unconformabiy overly the Pierre shale and the Coalmont Formation have sufficient permeability to store and transmit water, Ground water in this aquifer is under unconfined water table conditions. Recharge to this aquifer is primarily through infiltration during snowmelt and during sporadic precipitation events. Ground water within these deposits flows down along the contact between the permeable terrace deposits and the bedrock. Springs and seeps develop where this contact has been exposed by headword eroding streams. One such spring has been identified in an area adjacent to the Wyoming Fuel mine on a small tributary of the North Fork of Bolton Draw. This spring feeds a small pond used for stock and wildlife watering. No wells are located within the Upland Terrace Deposits. The alluvium of the Canadian River is coarse-grained and supports agriculture through both subirrigation and flood irrigation. Recharge to this aquifer is primarily from the river and the numerous irrigation ditches which traverse the wide flood plain. The tributaries and the alluvium of the tributaries which flow through the three mines contribute very little to recharge of the Canadian River alluvium. This is due to the low contribution of surface flow (Williams Draw flowed for only 60 days in 1980) and the low permeability of the tributary's alluvium. The alluvium of Mann Draw is a poor aquifer consisting of fine-grained sand, silt and clay. The alluvium in the area of the Bourg Mine is thin (0 to 20 feet thick) and is restricted to narrow bands paralleling the stream course. The alluvium of Sudduth, Williams and Bush Draws contain water table aquifers which are highly variable in their aquifer charactistics. This is due to the lenticular and discontinuous nature of the more permeable sands and gravels. The ground water in these aquifers has high salinity and total dissolved solids concentrations. The poor water quality is the result of teaching of the marine Pierre Shale in the headwaters of these streams. Bolton Draw contains alluvium and recent streamlaid deposits. This alluvium is fine-grained and contains only 5.4 acres of subirrigated vegetation. This subirrigated area is a perched aquifer which is isolated from a deeper water table aquifer downstream. Recharge takes place during brief periods of runoff. Wyoming Fuel has installed an alluvial monitoring hole, well #2, in the Bolton Draw alluvium. Ground water quality samples taken from this well are high in total dissolved solids (TDS) and are of a sodium sulfate type. No water supply wells are completed in the Bolton Draw alluvium. The high TDS, 7220 mg/1, and high sulfate, 2390 to 4030 mg/1, severly restrict the beneficial use of the Bolton Draw alluvial ground water for irrigation or stock watering. Following mining at the Bourg Mine, a new aquifer will be created within the spoils. The spoil aquifer will be recharged by water from faults encountered during mining, and through infiltration and deep percolation of surface water, Both of these sources are closely Linked to snowmelt and to a lesser degree infrequent precipitation events. Wyoming Fuel has conducted an infiltration study in and near reclained areas of their Pit 1. At site 1, the reclaimed spoil area yielded an infiltration rate of 2 inches per hour, and at site 2, an undisturbed sandy loam adjacent to the reclaimed area yielded an infiltration rate of 14 inches per hour. The lower infiltration rate over the spoils was attributed to a mixing of topsoil types, Coalmont and Fluetsch. The initial infiltration rates in the reclaimed areas are expected to be lower than the pre-mining conditions.