Geohydrologic data from twenty-four test holes drilled in the Piceance Basin, Rio Blanco County, Colorado, 1975-76

Abstract

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.

Chemistry and age of groundwater in bedrock aquifers of the Piceance and Yellow Creek watersheds, Rio Blanco County, Colorado, 2010-12

“…3). These intervals are sometimes collectively referred to as the saline zone (Robson and Saulnier, 1981;Welder and Saulnier, 1978). Nahcolite and probably halite also once occurred at shallower depths, but they have been mostly leached out (Johnson and Brownfield, 2013).…”

“…The 14 wells were selected to broadly encompass the area in which gas development is expected to continue and expand in the foreseeable future (Bureau of Land Management, 2013). Detailed information on construction of the USGS wells in the 1970s is in Welder and Saulnier (1978). Wells 13A and 13B, constructed in the 1970s, were modified by the USGS in 2010 to reduce the length of the open interval in the wells (Appendix figs.…”

“…Most of the selected wells are open to aquifers either above or below the Mahogany zone, but wells 9B and 15B appear to be open to parts of the Mahogany zone in addition to water-bearing zones below the Mahogany zone on the basis of isopach maps for the area (Johnson and others, 2010). Additional USGS wells installed in the 1970s were considered for use in this study (Welder and Saulnier, 1978), but they were not selected either because they could not be located in the field or because borehole geophysical logs collected from the wells during the reconnaissance phase of this project showed that they were not suitable for sampling. Garden Gulch Member (part)…”

“…Several studies have examined the geochemistry of groundwater in the watersheds (for example, Welder and Saulnier, 1978;Robson and Saulnier, 1981;Slawson and others, 1982;Kimball, 1984;Day and others, 2010), mostly in relation to oil shale, but published studies of the geochemistry of shallow groundwater as it may relate to natural-gas reservoirs are scarce. Some monitoring of groundwater quality is being done by energy companies but little of that information is publically available (U.S. Geological Survey, 2012a).…”

Hydrogeochemistry and simulated solute transport, Piceance Basin, northwestern Colorado

“…Because of the small permeability of this zone (Dale and Weeks, 1978), the minerals can be dissolved only when fractures, wells, or adjacent dissolution have exposed the minerals to water. Welder and Saulnier (1978) and Dale and Weeks (1978) report that water' from the leached zone in the central part of the basin, where the saline zone is thickest, has a specific conductance that ranges from 1,100 to 1,600 ymho/cm (micromhos per centimeter at 25°C). These relatively small values of specific conductance indicate that only limited dissolution is occurring at the top of the present saline zone.…”