The present report is the result of a 2-year investigation of the hydrology of Piceance Creek basin conducted by the U.S. Geological Survey in cooperation with the Colorado Department of Natural Resources. This project was one of four concurrent projects contracted in 1972 by the State of Colorado to investigate the possible effects of oil-shale development on the environment of the Piceance basin. Thome Ecological Institute was contracted to make an environmental inventory and impact study; Colorado State University was contracted to study revegetation and rehabilitation of disturbed land; and the Oil Shale Regional Planning Commission was contracted to study regional development and land-use planning. The combined results of these studies should provide the base data necessary to monitor and evaluate the environmental effects of future oil-shale development. To coordinate the activities of the four concurrent oil-shale studies, the Oil Shale Coordinating Committee was established. Within this framework, a Water Resources Steering Committee was formed to monitor the conduct and progress of the hydrologic investigations.

The present report is the result of a 2-year investigation of the hydrology of Piceance Creek basin conducted by the U.S. Geological Survey in cooperation with the Colorado Department of Natural Resources. This project was one of four concurrent projects contracted in 1972 by the State of Colorado to investigate the possible effects of oil-shale development on the environment of the Piceance basin. Thome Ecological Institute was contracted to make an environmental inventory and impact study; Colorado State University was contracted to study revegetation and rehabilitation of disturbed land; and the Oil Shale Regional Planning Commission was contracted to study regional development and land-use planning. The combined results of these studies should provide the base data necessary to monitor and evaluate the environmental effects of future oil-shale development. To coordinate the activities of the four concurrent oil-shale studies, the Oil Shale Coordinating Committee was established. Within this framework, a Water Resources Steering Committee was formed to monitor the conduct and progress of the hydrologic investigations.

The water supply for the Pueblo Army Depot, 15 miles east of Pueblo, Colo., is obtained from wells that tap an aquifer in terrace alluvium. Withdrawals have resulted in a water-level decline of 27 feet, which adversely affects the discharge rate ot individual wells. Furthermore, excessive pumpage has resulted in progressive deterioration o f water quality. Over a 20-year period, hardness has increased from 70 milligrams per i er to 135 milligrams per liter and dissolved-solids content has increased from 250 milligrams per liter to 370 milligrams per 1i ter.Two new supply wells were drilled in the southern part of the Depot and were tested to determine aquifer properties and probable production rate. The hydraulic conductivity determined from these tests ranged from about 350 to nearly 600 gallons per day per square foot. The transmissivity for the full thi c kness of the aquifer is in ~he range of 7,500 to 12,000 gallons per day per foot.The two new s upply wel ls can be pumped at a combined rat e of about 140 gallons pe r minute. If pumpage in the existing well field is reduced by the same amount, some re co ve ry of water levels in the field will occur and th e trend in wat e r quality deterioration may slow or e ven reverse.

Twenty-four test holes were drilled in the Piceance basin, northwestern Colorado, to obtain geohydrologic data from the Uinta and Green River Formations of Eocene age. The test holes were drilled by the air-rotary method and completed in stratigraphic intervals above and below the Mahogany zone in the Parachute Creek Member of the Green River Formation. The interval from land surface to the top of the Mahogany zone, which includes the Uinta Formation, was designated as the upper aquifer, and the interval from the base of the Mahogany zone to the base of the permeable section of the Green River Formation was designated as the lower aquifer. Depths of test holes ranged from 640 to 2,800 feet. The maximum quantity of water discharged during the air drilling of individual test holes ranged from 14 to 880 gallons per minute. The specific conductance of water discharged during drilling ranged from 100 to 50,000 micromhos per centimeter at 25 degrees Celsius.Aquifer tests made during drilling indicate transmissivity at four sites ranged from 100 to 1,600 feet squared per day and the storage coefficient at two sites ranged from 1x10~4 to 1.6x10'^. Depths to the static water level ranged from 30 to 695 feet.Water levels were measured in each test well, and potentiometric maps constructed from these measurements are comparable in configuration and altitude to those previously drawn from composite-head data.Water samples taken during drilling indicate that, except for water from the Uinta Formation, the water in Piceance basin is generally not suited for domestic water supply due to the presence of excessive amounts of certain trace constituents, notably fluoride. The average concentration of dissolved solids, based on data from the test holes, was 909 milligrams per liter for the Uinta Formation, 828 milligrams per liter for the upper part of the Parachute Creek Member of the Green River Formation, and 3,^60 milligrams per liter for the lower part of the Parachute Creek Member.

Approximately 1,400 feet of continuous core was taken.between 800-2,214 feet in depth from USBM/AEC Colorado core hole No. 2* The drill site is located in the .Picean.ce Creek basin, Rio Blanco County, Colorado* From ground surface the drill hole penetrated 1,120 feet of the Evacuation Creek Member and 10094 feet of oil shale in the Parachute Creek Member of the Green River Formation* Oil shale yielding more than 20 gallons.per ton occurs between 1,260-2,214 feet in depth* A gas explosion near the bottom of the hole resulted in abandonment of the exploratory hole which was still in oil shale* The top of the nahcolite zone is at 1,693 feet. Below this depth the core contains common to abundant amounts of sodium bicarbonate salt intermixed with oil shale 0 .The core is divided into seven structural zones that reflect changes in joint intensity, core loss and broken core due to natural causes* The zone of poor core recovery is in the interval between ls 300-1,450 feet. Results of preliminary geophysical log analyses indicate that oil yields determined by Fischer assay compare favorably with yields determined by geophysical log analyses. There is strong evidence that analyses of complete core data from Colorado core holes No. 1 and No.. 2 reveal a reliable relationship between geophysical log response and oil yield. The quality of the logs is poor in the rich shale section and the possibility of repeating the logging program should be considered* Observations during drilling, coring, and hydrologic testing of USBM/AEC Colorado core hole No. 2 reveal that the Parachute Creek Member of the Green River Formation is the principal aquifer and the water in the Parachute Creek Member is under artesian pressure. The upper part of the aquifer has a higher hydrostatic head than, and is hydro logically separated from,, the lower part of the aquifer. The transmissionity of the aquifer is about 3500 gpd per foot* The maximum water yield of the core hole during testing was about 500 gpnu Chemical analyses of water samples indicate that the content of dissolved solids is low, the principal ions being sodium and bicarbonate. Although the hole was originally cored' to a depth of 2,214 feet, the present depth is about 2,100 feet. This report presents a preliminary evaluation of dore examination, geophysical log interpretation and Ipiydrological' tests from the USBM/AEC Colorado core hole No. 2. The cooperation of the U.S. Bureau of (fines is gratefully acknowledged. The reader is referred to Carroll and others (1967) for comparison of USBM/AEC Colorado core hole No. 1 with USBM/AEC Colorado core hole No. 2.