Geology topics

Research about El Paso, Texas

Source-linked reports with geographic coverage including El Paso, Texas.

8 recordsLinked to original sources

USGS2012

Digital outcrop model of stratigraphy and breccias of the southern Franklin Mountains, El Paso, Texas

This chapter reviews and synthesizes the lithostratigraphy, biostratigraphy, chronostratigraphy, and breccia types of the southwestern part of the great American carbonate bank in the southern Franklin Mountains (SFM), El Paso, Texas. Primary stratigraphic units of focus are the Lower Ordovician El Paso and Upper Ordovician Montoya Groups. These groups preserve breccias formed by collapse of a paleocave system. Precambrian and Silurian units are discussed in the context of breccia clast composition and relative timing of breccia emplacement. Specific attention is paid to the juxtaposition of the top-Sauk second-order supersequence unconformity between the El Paso and Montoya Groups and its relationship to breccias above and below it. The unconformity represents a 10-m.y. exposure event that separates Upper and Lower Ordovician carbonates. The top-Sauk exposure has been previously documented as a significant karst horizon across much of North America. The breccias of the SFM were previously described as the result of collapsed paleocaves that formed during subaerial exposure related to the Sauk-Tippecanoe unconformity. A new approach in this work uses traditional field mapping combined with high-resolution ( 1-m [ 3.3-ft] point spacing) airborne light detection and ranging (LIDAR) data over 24 km 2 (9 mi 2 ) to map breccia and relevant stratal surfaces. Airborne LIDAR data were used to create a digital outcrop model of the SFM from which a detailed (1:2000 scale) geologic map was created. The geologic map includes formation, fault, and breccia contacts. The digital outcrop model was used to interpret three-dimensional spatial relationships of breccia bodies with respect to the current understanding of the tectonic and stratigraphic evolution of the SFM. The data presented here are used to discuss potential stratigraphic, temporal, and tectonic controls on the formation of caves within the study area that eventually collapsed to form the breccias currently exposed in outcrop.

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USGS1999

Geologic and hydrologic data for the municipal solid waste landfill facility, U.S. Army Air Defense Artillery Center and Fort Bliss, El Paso County, Texas

Geologic and hydrologic data for the Municipal Solid Waste Landfill Facility on the U.S. Army Air Defense Artillery Center and Fort Bliss in El Paso County, Texas, were collected by the U.S. Geological Survey in cooperation with the U.S. Department of the Army. The 106.03-acre landfill has been in operation since January 1974. The landfill contains household refuse, Post solid wastes, bulky items, grass and tree trimmings from family housing, refuse from litter cans, construction debris, classified waste (dry), dead animals, asbestos, and empty oil cans. The depth of the filled areas is about 30 feet and the cover, consisting of locally derived material, is 2 to 3 feet thick. Geologic and hydrologic data were collected at or adjacent to the landfill during (1) drilling of 10 30- to 31-foot boreholes that were completed with gas-monitoring probes, (2) drilling of a 59-foot borehole, (3) drilling of a 355-foot borehole that was completed as a ground-water monitoring well, and (4) in situ measurements made on the landfill cover. After completion, the gas- monitoring probes were monitored on a quarterly basis (1 year total) for gases generated by the landfill. Water samples were collected from the ground-water monitoring well for chemical analysis. Data collection is divided into two elements: geologic data and hydrologic data. Geologic data include lithologic descriptions of cores and cuttings, geophysical logs, soil- gas and ambient-air analyses, and chemical analyses of soil. Hydrologic data include physical properties, total organic carbon, and pH of soil and sediment samples; soil-water chloride and soil-moisture analyses; physical properties of the landfill cover; measurements of depth to ground water; and ground-water chemical analyses. Interpretation of data is not included in this report.

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USGS1996

Hydrogeology and ground-water quality of the chromic acid pit site, U.S. Army Air Defense Artillery Center and Fort Bliss, El Paso, Texas

The Chromic Acid Pit site is an inactive waste disposal site that is regulated by the Resource Conservation and Recovery Act of 1976. The 2.2-cubic-yard cement-lined pit was operated from 1980 to 1983 by a contractor to the U.S. Army Air Defense Artillery Center and Fort Bliss. The pit, located on the Fort Bliss military reservation, in El Paso, Texas, was used for disposal and evaporation of chromic acid waste generated from chrome plating operations. The site was certified closed in 1989 and the Texas Natural Resources Conservation Commission issued Permit Number HW-50296 (U.S. Environmental Protection Agency Permit Number TX4213720101), which approved and implemented post-closure care for the Chromic Acid Pit site. In accordance with an approved post-closure plan, the U.S. Geological Survey is cooperating with the U.S. Army in evaluating hydrogeologic conditions and ground- water quality at the site. One upgradient and two downgradient ground-water monitoring wells were installed adjacent to the chromic acid pit by a private contractor. Quarterly ground-water sampling of these wells by the U.S. Geological Survey began in December 1993. The Chromic Acid Pit site is situated in the Hueco Bolson intermontane valley. The Hueco Bolson is a primary source of ground water in the El Paso area. City of El Paso and U.S. Army water-supply wells are located on all sides of the study area and are completed 600 to more than 1,200 feet below land surface. The ground-water level in the area of the Chromic Acid Pit site has declined about 25 feet from 1982 to 1993. Depth to water at the Chromic Acid Pit site in September 1994 was about 284 feet below land surface; ground-water flow is to the southeast. Ground-water samples collected from monitoring wells at the Chromic Acid Pit site contained dissolved-solids concentrations of 442 to 564 milligrams per liter. Nitrate as nitrogen concentrations ranged from 2.1 to 2.7 milligrams per liter; nitrite plus nitrate as nitrogen concentrations ranged from 2.3 to 3.0 milligrams per liter. Nitrate concentrations are abnormally high in the Old Mesa well field located about 5,000 feet southwest of the Chromic Acid Pit site. Volatile and semivolatile organic compounds in water samples were analyzed for the first sampling round; no confirmed volatile or semivolatile organic compounds were detected above the laboratory reporting limits. Total chromium concentrations ranged from 0.0099 to 0.092 milligram per liter; dissolved chromium concentrations ranged from 0.0068 to 0.0094 milligram per liter. Overall, water-quality characteristics in water from the chromic acid pit ground-water monitoring wells are similar to those in the surrounding area. Detected chemical concentrations in water from the chromic acid pit monitoring wells during the four sampling periods were below U.S. Environmental Protection Agency-established maximum contaminant levels for public drinking water supplies. Statistical analyses were performed on 39 of the chemical constituents analyzed for in ground water from the chromic acid pit monitoring wells. Concentrations of chloride and fluoride were significantly less in water from the downgradient wells than in water from the upgradient well, whereas concentrations of nitrate as nitrogen, nitrite plus nitrate as nitrogen, and dissolved solids were significantly greater in water from the downgradient wells than in water from the upgradient well. Concentrations of nitrate as nitrogen were significantly different in water from the two downgradient wells. Differences detected through statistical analysis of chemical constituents of water in the chromic acid pit monitoring wells did not appear to indicate a release of hazardous chemicals from the chromic acid pit. There was no indication of ground-water contamination in either downgradient well.

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USGS1996

Ground-water quality, water year 1995, and statistical analysis of ground-water-quality data, water years 1994-95, at the chromic acid pit site, U.S. Army Air Defense Artillery Center and Fort Bliss, El Paso, Texas

The Chromic Acid Pit site is an inactive waste disposal site that is regulated by the Resource Conservation and Recovery Act of 1976. The 2.2-cubic-yard cement-lined pit was operated from 1980 to 1983 by a contractor to the U.S. Army Air Defense Artillery Center and Fort Bliss. The pit, located on the Fort Bliss military reservation in El Paso, Texas, was used for disposal and evaporation of chromic acid waste generated from chrome plating operations. The site was closed in 1989, and the Texas Natural Resources Conservation Commission issued permit number HW-50296 (U.S. Environmental Protection Agency number TX4213720101), which approved and implemented post-closure care for the Chromic Acid Pit site. In accordance with an approved post-closure plan, the U.S. Geological Survey is cooperating with the U.S. Army in monitoring and evaluating ground-water quality at the site. One upgradient ground-water monitoring well (MW1) and two downgradient ground-water monitoring wells (MW2 and MW3), installed adjacent to the chromic acid pit, are monitored on a quarterly basis. Ground-water sampling of these wells by the U.S. Geological Survey began in December 1993. The ground-water level, measured in a production well located approximately 1,700 feet southeast of the Chromic Acid Pit site, has declined about 29.43 feet from 1982 to 1995. Depth to water at the Chromic Acid Pit site in September 1995 was 284.2 to 286.5 feet below land surface; ground-water flow at the water table is assumed to be toward the southeast. Ground-water samples collected from monitoring wells at the Chromic Acid Pit site during water year 1995 contained dissolved- solids concentrations of 481 to 516 milligrams per liter. Total chromium concentrations detected above the laboratory reporting limit ranged from 0.0061 to 0.030 milligram per liter; dissolved chromium concentrations ranged from 0.0040 to 0.010 milligram per liter. Nitrate as nitrogen concentrations ranged from 2.1 to 2.8 milligrams per liter; nitrite plus nitrate as nitrogen concentrations ranged from 2.4 to 3.2 milligrams per liter. Water samples from wells MW1 and MW2 were analyzed for volatile organic compounds for the first quarter; no confirmed volatile organic compounds were detected above laboratory reporting limits. Detected chemical concentrations in water from the chromic acid pit monitoring wells during the four sampling periods were below U.S. Environmental Protection Agency-established maximum contaminant levels for public drinking-water supplies. Overall, water-quality characteristics of water from the chromic acid pit ground-water monitoring wells are similar to those of other wells in the surrounding area. Statistical analyses were performed on 56 of the chemical constituents analyzed for in ground water from the chromic acid pit monitoring wells. Concentrations of chloride, fluoride, sulfate, and potassium were significantly less in water from one or both downgradient wells than in water from the upgradient well. Concentrations of nitrate as nitrogen, nitrite plus nitrate as nitrogen, and dissolved solids were significantly greater in water from the downgradient wells than in water from the upgradient well. Concentrations of nitrate as nitrogen, chloride, and potassium were significantly different in water from the two downgradient wells. Statistical analysis of chemical constituents in water from the chromic acid pit monitoring wells did not appear to indicate a release of hazardous chemicals from the chromic acid pit. There was no indication of ground-water contamination in either downgradient well.

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USGS1994

Hydrogeologic and water-quality data from wells near the Hueco Bolson Recharge Project area, El Paso, Texas, 1990 and 1991

Tertiary-treated wastewater currently (1991) is being injected into the Hueco bolson aquifer at a site in northeastern El Paso, Texas, to supplement the quantity of available freshwater. Hydrologic data were compiled and water-quality and bacterial data were collected from existing wells near the Hueco Bolson Recharge Project (HBRP) in August and September 1990 and 1991. Borehole tracer tests indicated upward ground-water flow in nearly all tested intervals of several observation wells. The cumulative volume of injected water was less than the volume produced from wells adjacent to the HBRP area. Water levels in three production wells, located more than 1.5 miles from the injection wells, declined at rates comparable to those observed before injection operations. Water levels in wells located within 0.75 mile of the injection-well pipeline declined at a slower rate after HBRP injection operations had begun. Between 1985 and 1991, water levels in observation wells located within 700 feet of an injection well either did not appreciably decline, or declined at smaller rates than water levels in more distant production wells. Trihalomethane compounds were detected in water from 8 of the 16 observation and production wells sampled in 1990 and in 10 of the 17 wells sampled in 1991. Concentrations of trihalomethane compounds in these samples ranged from 0.05 to 1.9 |lg/L (micrograms per liter) in 1990 and from 0.05 to 1.4 |ig/L in 1991. Concentrations of trihalomethane compounds in samples of injected water from two wells were 27.8 and 34.6 |J,g/L respectively, in 1991. Dibromomethane and dichloromethane were detected in water from injection wells and from observation wells within about 700 feet of the injection wells. Aerobic bacteria were determined to be the only bacteria type present in ground water except for samples from two wells, which also contained denitrifying bacteria. The populations of aerobic bacteria determined in ground water ranged from 80 to more than 160,000 most probable number of organisms per milliliter of sample.

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USGS1994

Hydrogeology and selected water-quality aspects of the Hueco Bolson Aquifer at the Hueco Bolson Recharge Project area, El Paso, Texas

Samples of ground water and tertiary-treated water were evaluated to determine the distribution of injected water and trihalomethane compounds in the Hueco bolson aquifer near El Paso, Texas. Chloride and nitrate concentrations and oxygen-18/oxygen-16 (δ 18 O) values were used with end-member mixing analysis to estimate the fractional contributions of injected water, irrigation-affected water, saline ground water, and freshwater to ground-water chemistry. Several laterally continuous sand and gravel layers are the principal water-yielding lithologies in the aquifer. The potentiometric surface sloped toward the south and southwest during January 1990. Average linear ground-water velocities were as large as 1.4 feet per day near the zone of largest hydraulic conductivity and were substantially smaller farther south and east. Ground-water samples from as far as 2,900 feet from an injection well contained injectedwater tracers and trihalomethane compounds. Ground-water samples with injected-water tracers and no trihalomethane compounds may indicate infiltration from septic systems or oxidation ponds. Apparent breakthrough velocities of injected water in the aquifer ranged from 0.13 to 1.3 feet per day. Irrigation-affected water and saline water also were identified in water from several wells. Ground-water transport of bromoform and dibromochloromethane is attenuated relative to injected water, chloroform, and dichlorobromomethane. Microbial transformation of bromoform and dibromochloromethane probably was responsible for their disappearance from ground water. Chloroform and dichlorobromomethane concentrations were affected principally by advective and dispersive transport of injected water.

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USGS1985

A preliminary assessment of land-surface subsidence in the El Paso area, Texas

The northeast and southeast parts of the El Paso area are underlain by Hueco bolson deposits as much as 9,000 feet thick. The deposits consist of lenses of gravel, sand, silt, and clay. In the Rio Grande Valley, about 400 to 450 feet of these deposits have been eroded and replaced with as much as 200 feet of alluvium. Ground water in the shallow alluvial aquifer in the Rio Grande Valley and in the Hueco bolson aquifer outside the valley is under water-table conditions, whereas ground water in the bolson aquifer in the valley is under leaky artesian conditions. Maximum water-level declines in the Hueco bolson aquifer are 110 feet east of the Franklin Mountains and 150 feet in the downtown El Paso area. For the shallow aquifer, the maximum declines have been 125 feet in the downtown area. Compressable materials in the freshwater zone of the aquifer range from 50 to 450 feet. Recharge from the Rio Grande to the shallow alluvial aquifer has increased from an estimated 15,000 acre-feet during 1968 to 30,000 acre-feet during 1983, an increase of about 1,000 acre-feet per year. Leakage from the Rio Grande is expected to continually increase in the near future because of a continued decline in ground-water levels. The amount of leakages from the canals is much less than from the river. Releveling of bench marks along lines to the northeast and the southeast of the Rio Grande, and along its channel commonly show land subsidence of about 0.2 foot. The maximum measured subsidence is 0.41 foot along the river in the Chamizal zone. No subsidence was detected at the Riverside Diversion Dam. A comparison of subsidence, water-level declines, and clay thickness along the three survey lines shows the expected correlation of greater subsidence with thicker accumulated clay material for a given decline in water levels. The preconsolidation stress was expected to range from 85 to 115 feet of water-level decline on the basis of subsidence studies in Arizona and California. A study of specific-unit compaction along the three survey lines shows that the values usually range between 1.0 to 2.5 x 10-5 feet per feet squared. These values are comparable to the ones computed in the Tulare-Wasco, California, and Houston-Galveston, Texas, areas following the exceedance of the local preconsolidation stress. Because of this comparability, the specific-unit compaction for future periods in the El Paso area probably will not increase dramatically when the preconsolidation stress is exceeded, if it has not already been exceeded. In addition to regional subsidence, local subsidence is indicated by observable surface fractures but has not been verified by precise leveling. These local areas coincide with areas that historically were swamps along the Rio Grande.

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USGS1969

The use of Schlumberger and equatorial soundings in groundwater investigations near El Paso, Texas

Electrical soundings using the symmetric AMNB Schlumberger and the bipole-dipole equatorial arrays were made along two profiles near El Paso, Texas, in support of a groundwater exploration program which included seismic refraction and gravity surveys. Electrode spacings (AB/2 or R) reaching 12,000 ft allowed exploration to depths of about 7000 ft. Geoelectrical information on the subsurface materials was augmented by sounding with the bilateral equatorial configuration and by transforming Schlumberger curves into dipole-polar sounding curves with formulas developed by Al'pin and by Tsekov. The bilateral equatorial sounding curves were found useful for detecting the direction of dip of highly resistive bedrocks whereas transformed sounding curves were used to evaluate the average longitudinal resistivity, and hence the depth, to the "electric basement." A few of the Schlumberger sounding curves were either clearly or subtly distorted by nonhorizontal geologic structures. The interpretation of these sounding curves illustrates the requirement for careful analysis in processing electrical prospecting data obtained over complex geologic conditions. The interpretation of a combined Schlumberger-equatorial sounding curve, which did not agree with the preliminary interpretation of seismic refraction data, was confirmed to be correct by data from a test well drilled to a depth of 4363 ft. The application of electrical sounding data in the El Paso area furnished valuable information on the depth to fresh-water-saltwater interfaces and on the depth to highly resistive impervious bedrocks.

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