Search USGS⌕ Search

Geology topics

Randell J. Laczniak

Publications and source records attributed to Randell J. Laczniak.

26 records · Page 2Linked to original sources
USGS2003

Estimated ground-water withdrawals from the Death Valley regional flow system, Nevada and California, 1913-98

Ground-water withdrawals from 1913 through 1998 from the Death Valley regional flow system have been compiled to support a regional, three-dimensional, transient ground-water flow model. Withdrawal locations and depths of production intervals were estimated and associated errors were reported for 9,300 wells. Withdrawals were grouped into three categories: mining, public-supply, and commercial water use; domestic water use; and irrigation water use. In this report, groupings were based on the method used to estimate pumpage. Cumulative ground-water withdrawals from 1913 through 1998 totaled 3 million acre-feet, most of which was used to irrigate alfalfa. Annual withdrawal for irrigation ranged from 80 to almost 100 percent of the total pumpage. About 75,000 acre-feet was withdrawn for irrigation in 1998. Annual irrigation withdrawals generally were estimated as the product of irrigated acreage and application rate. About 320 fields totaling 11,000 acres were identified in six hydrographic areas. Annual application rates for high water-use crops ranged from 5 feet in Penoyer Valley to 9 feet in Pahrump Valley. The uncertainty in the estimates of ground-water withdrawals was attributed primarily to the uncertainty of application rate estimates. Annual ground-water withdrawal was estimated at about 90,000 acre-feet in 1998 with an assigned uncertainty bounded by 60,000 to 130,000 acre-feet.

California, Nevada↗
USGS2001

Ground-water discharge determined from estimates of evapotranspiration, Death Valley regional flow system, Nevada and California

The Death Valley regional flow system (DVRFS) is one of the larger ground-water flow systems in the southwestern United States and includes much of southern Nevada and the Death Valley region of eastern California. Centrally located within the ground-water flow system is the Nevada Test Site (NTS). The NTS, a large tract covering about 1,375 square miles, historically has been used for testing nuclear devices and currently is being studied as a potential repository for the long-term storage of high-level nuclear waste generated in the United States. The U.S. Department of Energy, as mandated by Federal and State regulators, is evaluating the risk associated with contaminants that have been or may be introduced into the subsurface as a consequence of any past or future activities at the NTS. Because subsurface contaminants can be transported away from the NTS by ground water, components of the ground-water budget are of great interest. One such component is regional ground-water discharge. Most of the ground water leaving the DVRFS is limited to local areas where geologic and hydrologic conditions force ground water upward toward the surface to discharge at springs and seeps. Available estimates of ground-water discharge are based primarily on early work done as part of regional reconnaissance studies. These early efforts covered large, geologically complex areas and often applied substantially different techniques to estimate ground-water discharge. This report describes the results of a study that provides more consistent, accurate, and scientifically defensible measures of regional ground-water losses from each of the major discharge areas of the DVRFS. Estimates of ground-water discharge presented in this report are based on a rigorous quantification of local evapotranspiration (ET). The study identifies areas of ongoing ground-water ET, delineates different ET areas based on similarities in vegetation and soil-moisture conditions, and determines an ET rate for each delineated area. Each area, referred to as an ET unit, generally consists of one or more assemblages of local phreatophytes or a unique moist soil environment. Ten ET units are identified throughout the DVRFS based on differences in spectral-reflectance characteristics. Spectral differences are determined from satellite imagery acquired June 21, 1989, and June 13, 1992. The units identified include areas of open playa, moist bare soils, sparse to dense vegetation, and open water. ET rates estimated for each ET unit range from a few tenths of a foot per year for open playa to nearly 9 feet per year for open water. Mean annual ET estimates are computed for each discharge area by summing estimates of annual ET from each ET unit within a discharge area. The estimate of annual ET from each ET unit is computed as the product of an ET unit's acreage and estimated ET rate. Estimates of mean annual ET range from 450 acre-feet in the Franklin Well area to 30,000 acre-feet in Sarcobatus Flat. Ground-water discharge is estimated as annual ET minus that part of ET attributed to local precipitation. Mean annual ground-water discharge estimates range from 350 acre-feet in the Franklin Well area to 18,000 acre-feet in Ash Meadows. Generally, these estimates are greater for the northern discharge areas (Sarcobatus Flat and Oasis Valley) and less for the southern discharge areas (Franklin Lake, Shoshone area, and Tecopa/ California Valley area) than those previously reported.

California, Nevada↗
USGS1999

Gravity and magnetic study of the Pahute Mesa and Oasis Valley region, Nye County, Nevada

Regional gravity and aeromagnetic maps reveal the existence of deep basins underlying much of the southwestern Nevada volcanic field, approximately 150 km northwest of Las Vegas. These maps also indicate the presence of prominent features (geophysical lineaments) within and beneath the basin fill. Detailed gravity surveys were conducted in order to characterize the nature of the basin boundaries, delineate additional subsurface features, and evaluate their possible influence on the movement of ground-water. Geophysical modeling of gravity and aeromagnetic data indicates that many of the features may be related to processes of caldera formation. Collapse of the various calderas within the volcanic field resulted in dense basement rocks occurring at greater depths within caldera boundaries. Modeling indicates that collapse occurred along faults that are arcuate and steeply dipping. There are indications that the basement in the western Pahute Mesa - Oasis Valley region consists predominantly of granitic and/or fine-grained siliceous sedimentary rocks that may be less permeable to groundwater flow than the predominantly fractured carbonate rock basement to the east and southeast of the study area. The northeast-trending Thirsty Canyon lineament, expressed on gravity and basin thickness maps, separates dense volcanic rocks on the northwest from less dense intracaldera accumulations in the Silent Canyon and Timber Mountain caldera complexes. The source of the lineament is an approximately 2-km wide ring fracture system with step-like differential displacements, perhaps localized on a pre-existing northeast-trending Basin and Range fault. Due to vertical offsets, the Thirsty Canyon fault zone probably juxtaposes rock types of different permeability and, thus, it may act as a barrier to ground-water flow and deflect flow from Pahute Mesa along its flanks toward Oasis Valley. Within the Thirsty Canyon fault zone, highly fractured rocks may serve also as a conduit, depending upon the degree of alteration and its effect on porosity and permeability. In the Oasis Valley region, other structures that may influence ground-water flow include the western and southern boundaries of the Oasis Valley basin, where the basement abruptly shallows.

Nevada↗
USGS1999

Digital Geologic Map of the Nevada Test Site and Vicinity, Nye, Lincoln, and Clark Counties, Nevada, and Inyo County, California

This digital geologic map of the Nevada Test Site (NTS) and vicinity, as well as its accompanying digital geophysical maps, are compiled at 1:100,000 scale. The map compilation presents new polygon (geologic map unit contacts), line (fault, fold axis, metamorphic isograd, dike, and caldera wall) and point (structural attitude) vector data for the NTS and vicinity, Nye, Lincoln, and Clark Counties, Nevada, and Inyo County, California. The map area covers two 30 x 60-minute quadrangles-the Pahute Mesa quadrangle to the north and the Beatty quadrangle to the south-plus a strip of 7.5-minute quadrangles on the east side-72 quadrangles in all. In addition to the NTS, the map area includes the rest of the southwest Nevada volcanic field, part of the Walker Lane, most of the Amargosa Desert, part of the Funeral and Grapevine Mountains, some of Death Valley, and the northern Spring Mountains. This geologic map improves on previous geologic mapping of the same area (Wahl and others, 1997) by providing new and updated Quaternary and bedrock geology, new geophysical interpretations of faults beneath the basins, and improved GIS coverages. Concurrent publications to this one include a new isostatic gravity map (Ponce and others, 1999) and a new aeromagnetic map (Ponce, 1999).

Open-File Report↗
USGS1990

Conceptualization and analysis of ground-water flow system in the Coastal Plain of Virginia and adjacent parts of Maryland and North Carolina

This report presents the results of a study of the ground-water flow system in the Coastal Plain of Virginia and adjacent parts of Maryland and North Carolina. The ground-water flow system consists of water-table aquifer and an underlying sequence of confined aquifers and intervening confining units composed of unconsolidated sand and clay .Water levels have declined steadily, and cones of depression have expanded and coalesced around major ground-water withdrawal centers. A digital flow model was developed to enhance knowledge of the behavior of the ground-water flow system in response to its development. Transmissivity and vertical leakance maps were developed for each aquifer and confining unit. The model was calibrated to simulate ground-water flow within the system under both prepumping and pumping conditions. Simulated prepumping potentiometric-surface maps indicate that regional movement of ground water was from the Fall Line toward coastal areas and that local movement of ground water was from interfluves toward major river valleys. Maps of simulated prepumping flow across confining units show that most recharge occurred in narrow bands approximately parallel to the Fall Line and under interfluves and that discharge was toward major river valleys and coastal water. Simulated prepumping rates of recharge into the confined aquifer system from the water-table aquifer varied up to 3 .2 inches per year (in/yr), and rates of discharge out of the confined system varied up to 2.8 in/yr. Ten pumping periods covering 90 years (yr) of withdrawal simulated the history of ground-water development. Simulated potentiometric-surface maps for 1980 show lowered water levels and the development of coalescing cones of depression around the cities of Franklin, Suffolk, and Williamsburg and the town of West Point, all in Virginia. The largest simulated decline in water level, about 210 feet (ft) ,was near Franklin. Water budgets indicate that over the period of simulation (1891-1980) (1) pumpage from the model area increased by about 105 million gallons per day (Mgal/d), (2) lateral boundary outflow increased by about 5 Mgal/d, (3) ground-water flow to streams and coastal water decreased by about 107.5 Mgal/d, (4) lateral boundary inflow increased by about0.7 Mgal/d, and (5) water released from aquifer storage increased by about 1 .6 Mgal/d. The difference between total inflow and total outflow is the numerical truncation error of the digital simulation. Analysis of water budgets for individual confined aquifers shows that the major source of water supplied to wells was vertical leakage induced through confining units by pumping. Simulated rates of recharge into the confined aquifer system at the end of the final pumping period (1980) varied up to 3.8in/yr,and simulated rates of discharge out of the confined system varied up to 2.2in/yr. Results of simulations show an increase of about 110Mgal/d into the confined system from the unconfined system over the period of simulation. This increase in flow into the confined system affected local discharge of ground water to streams and regional discharge to coastal water. Withdrawal of groundwater from the confined aquifers also induced brackish water from Chesapeake Bay into the confined system. Results of sensitivity analyses indicate that simulated water levels are more sensitive to decreases in aquifer transmissivity and confining unit vertical hydraulic conductivity than to increases in these properties. Lowering the storage coefficient of an aquifer had minimal effect on simulated water levels, whereas increasing the storage coefficient had a much more significant effect. The effect of confining unit storage is shown to be insignificant if it is assumed that the water released from confining unit storage is attributable to the compressibility of water only.

Maryland, North Carolina, Virginia↗