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Charles E. Heywood

Publications and source records attributed to Charles E. Heywood.

18 recordsLinked to original sources
USGS2024

Simulation of groundwater flow and brine discharge to the Dolores River in the Paradox Valley, Montrose County, Colorado

Salinity, or total dissolved solids (TDS), of the Colorado River affects agricultural, municipal, and industrial water users and is an important concern in the Western United States. In the Paradox Valley of southwestern Colorado, natural discharge of sodium-chloride brine to the Dolores River from the underlying core of a salt-valley anticline accounts for about 6 percent of the salinity load to the Colorado River. Formation of the Paradox Valley began during the Miocene, and subsequent erosion exposed the Pennsylvania Paradox Formation in the core of the anticline where a cap rock, collapse features, breccia, and sodium-chloride saturated brine developed at the top of the exposed salt diapir. The discharge of brine to the Dolores River is affected by these dissolution features, along with seasonal hydrologic conditions and density-dependent flow between older dense brine and the younger fresh groundwater in the overlying alluvial aquifer. To reduce TDS concentrations in the Dolores River through the Paradox Valley, the Bureau of Reclamation has pumped brine from a series of shallow wells adjacent to the river since July 1996. The pumped brine is collected and piped to a deep disposal well where it is injected into the Mississippian Leadville Limestone at a depth of about 4,570-meters below land surface. The pumping and injection operation is collectively known as the Paradox Valley Unit (PVU), and by 2015, the PVU had substantially reduced TDS concentrations in the Dolores River by about 70 percent. Since 2019, injection-pressure limits and related seismic activity have constrained deep-well injection and thus brine pumping at the PVU. In cooperation with the Bureau of Reclamation, the U.S. Geological Survey developed a MODFLOW-6 three-dimensional, variable-density groundwater flow and TDS transport model of the Paradox Valley to evaluate the effects of PVU pumping operations on brine discharge to the Dolores River and to guide additional research. The finite-difference model grid consists of 76 rows and 48 columns oriented from northwest to southeast in alignment with valley topography and groundwater-flow directions in the near-surface freshwater alluvial aquifer. A 7-layer hydrogeologic framework was developed from existing datasets to represent the alluvial aquifer, cap rock, collapse breccia, and groundwater flow and TDS transport from the underlying Paradox Formation salt to the Dolores River. The model represents a 33-year transient calibration period from 1987 through 2020 that includes pre-PVU conditions from 1987 through June 1996 and post-PVU conditions from July 1996 through 2020. A 1,000-year simulation of groundwater flow and coupled TDS transport computed the initial conditions for the subsequent 33-year transient simulation. Observations of precipitation, streamflow, evaporation, agricultural land use, and PVU brine pumping rates were used to specify appropriate boundary conditions to the model representing time-varying recharge, tributary streamflow, groundwater underflow, evapotranspiration (ET), and PVU pumping. Values for average monthly streamflow and TDS concentration at the upstream streamgage, the Dolores River at Bedrock (USGS streamgage 09169500), were specified as model input where the Dolores River enters Paradox Valley. Observed pumping from the PVU, water levels and TDS concentrations in groundwater, and streamflow and estimated TDS concentrations at the downstream streamgage, the Dolores River near Bedrock (USGS streamgage 09171100), were calibration targets that constrained the manual calibration of model parameters representing aquifer hydraulic conductivity, storage, streambed conductance, recharge, and (ET). Two primary model-calibration targets were the match between observed and simulated TDS mass flux from PVU pumping wells and the match between estimated and simulated TDS mass flux to the Dolores River. The simulated TDS mass withdrawn by pumping wells is calculated by the model as the product of the assigned pumping rate and simulated groundwater TDS concentrations. Because actual pumping rates were assigned as simulated values, the total simulated PVU pumping for the 33-year calibration is within 0.5 percent of the observed values. However, simulated concentrations and thus mass flux of TDS withdrawn by the PVU pumping wells were consistently about 26 percent less than observed values for all the simulated time periods (33-year simulation, pre-PVU, and post-PVU). The representation of brine inflow was explored through additional modeling to evaluate the effect of the simulated brine source on groundwater TDS concentrations. Results indicated that a saturated-salt constant-flux brine source best replicated the magnitude and transient pattern observed for TDS mass flux from PVU pumping wells. The simulated TDS mass flux to the Dolores River is compared to estimates based on observed streamflow and specific conductance (SC) data for the downstream streamgage. The calibrated model provided a close fit of simulated to measured streamflow at the downstream streamgage, and the calibrated model fit to estimated TDS concentrations at the downstream streamgage was reasonable. The greatest differences between simulated and estimated values occurred during drought periods from June 2000 to March 2003, May 2012 to June 2013, and October 2013 to October 2014, when simulated TDS concentrations in the river were greater than estimated concentrations. In general, simulated TDS mass flux to the river for the pre-PVU period is in good agreement with estimated values (2-percent difference), but the model overestimated TDS mass flux to the river by about 41 percent during the post-PVU period. The model uncertainty with respect to TDS mass flux to the river indicates other processes or model parameters not well represented by the model are affecting the system, especially during drought. During model calibration, the most sensitive parameters were identified as vertical hydraulic conductivity of the alluvial aquifer, conductance of the Dolores River streambed, ET extinction depth and rate, and recharge rate. Five 5-year scenarios of conditions for 2021–25 were simulated to assist evaluation of alternative strategies to manage the discharge of brine into the Dolores River. The first scenario simulates no PVU pumping and serves as a base case for comparison to the other scenarios. Two scenarios simulate the effects of varying withdrawal timing at an annual rate about one-third less than during 2010 through 2018. During high-flow spring snowmelt runoff periods when brine discharge is naturally minimized, PVU pumping does not substantially affect salinity in the Dolores River, and comparison of these two scenarios indicates that scheduling brine withdrawals during times of low river stage is nearly as effective at reducing TDS mass flux to the river as pumping brine year-round. Cessation of pumping during periods of high river stage may be advantageous for system maintenance, brine injection, and seismic-risk reduction. The fourth scenario tested the effect of reducing irrigation-return flow on brine discharge and predicted a slight reduction of TDS mass flux to the Dolores River, but not as great a reduction as that of using the PVU to remove brine. The fifth scenario simulated 5 years of drought conditions without PVU pumping and indicates brine discharge during drought about 15 percent greater than during average hydrologic conditions. Results from scenario 5 are consistent with the calibrated model results and indicate that aquifer properties and ET processes and parameters may be affecting simulation results during drought. The Paradox Valley groundwater model provides a reasonable overall match to observed conditions in the Dolores River. The model is useful for evaluating relative differences between brine management scenarios to inform PVU operational decisions and to identify gaps in data and process understanding. Representation of the brine source, hydraulic-conductivity parameters, and recharge and ET processes were identified as potential areas for additional field and modeling research. Additional research in the Paradox Valley might include field-data collection that provides additional information on the hydrogeologic framework, groundwater levels, groundwater TDS concentrations, stream characteristics, and aquifer properties. Additional modeling efforts could benefit from applying advanced tools for model development, calibration, and visualization including parameter-estimation and sensitivity analysis. Statistical evaluation of known model uncertainties such as hydraulic conductivity, streambed conductance, representations of the brine source, recharge, and ET could improve the match between simulated and estimated TDS mass flux from PVU pumping wells and to the Dolores River further informing model predictions and system understanding for the Paradox Valley.

Colorado↗
USGS2019

Simulation of groundwater flow and chloride transport in the “1,500-foot” sand, “2,400-foot” sand, and “2,800-foot” sand of the Baton Rouge area, Louisiana

Groundwater withdrawals since the 1940s have lowered water levels, altered groundwater-flow directions, and caused saltwater to intrude within some freshwater-containing sands of the fluvial-deltaic Southern Hills regional aquifer system beneath Baton Rouge, Louisiana. New interpretations of stratigraphic correlations amongst geophysical well logs were utilized to revise a hydrogeologic framework that delineates the depth and thickness variations of aquifers and confining units in the Southern Hills regional aquifer system. A groundwater-flow and chloride-transport model incorporating the revised framework was constructed to assess the effects of groundwater withdrawals on the rate and pathways of saltwater migration in the “1,500-foot” sand, “2,400-foot” sand, and the “2,800-foot” sand. Groundwater withdrawals reported since 1940 were compiled to specify annual average withdrawal rates through 2016 for 722 wells. Regional groundwater flow throughout the Southern Hills regional aquifer system was first simulated with MODFLOW, and flow-model parameters were calibrated to 8,810 water levels observed through 2016 by using the parameter-estimation code PEST++. Saltwater transport was subsequently simulated for the “1,500-foot” sand, “2,400-foot” sand, and the “2,800-foot” sand by using the variable-density code, SEAWAT. Chloride-concentration measurements were used as a proxy for saltwater to formulate the concentration initial conditions and calibrate the transport-model parameters. Three groundwater-management scenarios were simulated to evaluate the effects of different groundwater withdrawals on future groundwater levels and saltwater concentrations in the “1,500-foot” sand, “2,400-foot” sand, and “2,800-foot” sand. All three scenarios simulated the period from 2017 through 2112 (96 years), and the water levels and concentrations simulated for 2047 and 2112 were compared among the scenarios. The first scenario simulated a continuation of groundwater withdrawals at 2016 rates and represents the “status quo” of groundwater withdrawals. The second scenario simulated the effects of discontinuing 10,620 gallons per minute (gal/min) of withdrawals from the “2,800-foot” sand, and the third scenario simulated reallocating 2,000 gal/min of withdrawals from the “1,500-foot” sand to the “2,800-foot” sand. Continuation of the “status quo” withdrawals results in lower water levels by 2047 around groundwater-withdrawal locations in the “1,500-foot” sand, “2,400-foot” sand, and “2,800-foot” sand. By 2112, water levels recover to higher levels as flow in the aquifer approaches equilibrium. Saltwater within the “1,500-foot” sand would continue migrating toward public-supply wells located 2.4 miles (mi) north of the Baton Rouge Fault, but a “scavenger well” that removes relatively concentrated water from the base of the “1,500-foot” sand attenuates chloride concentrations at the public-supply wells. Saltwater within the “2,400-foot” sand would continue to encroach on a well with large withdrawals and farther east within an area about 1 mi north of the Baton Rouge Fault. Saltwater within the “2,800-foot” sand would migrate northward toward withdrawal wells located about 3 mi north of the industrial district. Cessation of 10,620 gal/min of industrial withdrawals from the “2,800-foot” sand about 12 mi northwest of the industrial district (scenario 2) would cause a substantial water-level recovery in the “2,800-foot” sand in the area of discontinued withdrawals. Groundwater levels 3 mi north of the industrial district would be 25–30 feet higher in 2047 than predicted for the “status quo” withdrawals. Saltwater encroachment toward wells north of the industrial district would be slowed because of the decreased hydraulic gradient. Reallocating 2,000 gal/min of withdrawals from the “1,500-foot” sand to the “2,800-foot” sand 12 mi northwest of the industrial district (scenario 3) would have a negligible effect on water levels and chloride concentrations in the “1,500-foot” sand 15 mi to the south-southeast where saltwater is encroaching toward wells in the “1,500-foot” sand. Within the “2,800-foot” sand, the area of saltwater encroachment is only 3 mi from increased withdrawals in the “2,800-foot” sand, and water levels would be about 5 feet lower in 2047 than for the “status quo” scenario. A larger hydraulic gradient would cause slightly faster saltwater transport and higher chloride concentrations within this area of the “2,800-foot” sand.

Louisiana↗
USGS2016

Simulation of groundwater storage changes in the eastern Pasco Basin, Washington

The Miocene Columbia River Basalt Group and younger sedimentary deposits of lacustrine, fluvial, eolian, and cataclysmic-flood origins compose the aquifer system of the Pasco Basin in eastern Washington. Irrigation return flow and canal leakage from the Columbia Basin Project have caused groundwater levels to rise substantially in some areas, contributing to landslides along the Columbia River. Water resource managers are considering extraction of additional stored groundwater to supply increasing demand and possibly mitigate problems caused by the increased water levels. To help address these concerns, the transient groundwater model of the Pasco Basin documented in this report was developed to quantify the changes in groundwater flow and storage. The MODFLOW model uses a 1-kilometer finite-difference grid and is constrained by logs and water levels from 846 wells in the study area. Eight model layers represent five sedimentary hydrogeologic units and underlying basalt formations. Head‑dependent flux boundaries represent the Columbia and Snake Rivers to the west and south, respectively, underflow to and (or) from adjacent areas to the northeast, and discharge to agricultural drains, springs, and groundwater withdrawal wells. Specified flux boundaries represent recharge from infiltrated precipitation and anthropogenic sources, including irrigation return flow and leakage from water-distribution canals. The model was calibrated with the parameter ‑ estimation code PEST++ to groundwater levels measured from 1907 through 2013 and measured discharge to springs and estimated discharge to agricultural drains. Increased recharge since pre-development resulted in a 6.8 million acre-feet increase in storage in the 508-14 administrative area of the Pasco Basin. Four groundwater-management scenarios simulate the 7-year drawdown resulting from withdrawals in different locations. Withdrawals of 2 million gallons per day (Mgal/d) from a hypothetical well field in the upper Ringold Formation along the Columbia River could generate 30–70 feet of drawdown, which may reduce landslide susceptibility along the White Bluffs. Drawdowns resulting from a 1 Mgal/d withdrawal from wells screened in either Pasco gravels, upper Ringold Formation, or both Ringold Formation and underlying basalt are simulated in the other three scenarios, and differ because of the contrasting hydraulic conductivities within the screened intervals.

Washington↗
USGS2015

Simulation of groundwater flow and chloride transport in the “1,200-foot” sand with scenarios to mitigate saltwater migration in the “2,000-foot” sand in the Baton Rouge area, Louisiana

Groundwater withdrawals have caused saltwater to encroach into freshwater-bearing aquifers beneath Baton Rouge, Louisiana. The 10 aquifers beneath the Baton Rouge area, which includes East and West Baton Rouge Parishes, Pointe Coupee Parish, and East and West Feliciana Parishes, provided about 184.3 million gallons per day (Mgal/d) for public supply and industrial use in 2012. Groundwater withdrawals from the “1,200-foot” sand in East Baton Rouge Parish have caused water-level drawdown as large as 177 feet (ft) north of the Baton Rouge Fault and limited saltwater encroachment from south of the fault. The recently developed groundwater model for simulating transport in the “2,000-foot” sand was rediscretized to also enable transport simulation within the “1,200-foot” sand and was updated with groundwater withdrawal data through 2012. The model was recalibrated to water-level observation data through 2012 with the parameter-estimation code PEST and calibrated to observed chloride concentrations at observation wells within the “1,200-foot” sand and “2,000-foot” sand. The model is designed to evaluate strategies to control saltwater migration, including changes in the distribution of groundwater withdrawals and installation of scavenger wells to intercept saltwater before it reaches existing production wells. Seven hypothetical scenarios predict the effects of different groundwater withdrawal options on groundwater levels and the transport of chloride within the “1,200-foot” sand and the “2,000-foot” sand during 2015–2112. The predicted water levels and concentrations for all scenarios are depicted in maps for the years 2047 and 2112. The first scenario is a base case for comparison to the six other scenarios and simulates continuation of 2012 reported groundwater withdrawals through 2112 (100 years). The second scenario that simulates increased withdrawals from industrial wells in the “1,200-foot” sand predicts that water levels will be 12–25 ft lower by 2047 and that there will be a negligible difference in chloride concentrations within the “1,200-foot” sand. The five other scenarios simulate the effects of various withdrawal schemes on water levels and chloride concentrations within the “2,000-foot” sand. Amongst these five other scenarios, three of the scenarios simulate only various withdrawal reductions, whereas the two others also incorporate withdrawals from a scavenger well that is designed to extract salty water from the base of the “2,000-foot” sand. Two alternative pumping rates (2.5 Mgal/d and 1.25 Mgal/d) are simulated in each of the scavenger-well scenarios. For the “2,000-foot” sand scenarios, comparison of the predicted effects of the scenarios is facilitated by graphs of predicted chloride concentrations through time at selected observation wells, plots of salt mass in the aquifer through time, and a summary of the predicted plume area and average concentration. In all scenarios, water levels essentially equilibrate by 2047, after 30 years of simulated constant withdrawal rates. Although predicted water-level recovery within the “2,000-foot” sand is greatest for the scenario with the greatest reduction in groundwater withdrawal from that aquifer, the scavenger-well scenarios are most effective in mitigating the future extent and concentration of the chloride plume. The simulated scavenger-well withdrawal rate has more influence on the plume area and concentration than do differences among the scenarios in industrial and public-supply withdrawal rates.

Louisiana, Mississippi↗
USGS2014

Simulation of the effects of seasonally varying pumping on intraborehole flow and the vulnerability of public-supply wells to contamination

Public-supply wells with long screens in alluvial aquifers can produce waters of differing quality from different depths. Seasonal changes in quality are linked to seasonal changes in pumping rates that influence the distribution of flow into the well screens under pumping conditions and the magnitude and direction of intraborehole flow within the wells under ambient conditions. Groundwater flow and transport simulations with MODFLOW and MT3DMS were developed to quantify the effects of changes in average seasonal pumping rates on intraborehole flow and water quality at two long-screened, public-supply wells, in Albuquerque, New Mexico and Modesto, California, where widespread pumping has altered groundwater flow patterns. Simulation results indicate that both wells produce water requiring additional treatment to maintain potable quality in winter when groundwater withdrawals are reduced because less water is derived from parts of the aquifer that contain water requiring less treatment. Simulation results indicate that the water quality at both wells could be improved by increasing average winter-pumping rates to induce more lateral flow from parts of the aquifer that contain better quality water. Arsenic-bearing water produced by the Albuquerque well could be reduced from 55% to 45% by doubling average winter-pumping rate, while nitrate- and uranium-bearing water produced by the Modesto well could be reduced from 95% to 65% by nearly tripling the average winter-pumping rate. Higher average winter-pumping rates would also reduce the volume of intraborehole flow within both wells and prevent the exchange of poor quality water between shallow and deep parts of both aquifers.

California;New Mexico↗
USGS2014

Simulated and measured water levels and estimated water-level changes in the Albuquerque area, central New Mexico, 1950-2012

The City of Albuquerque, the major population center in New Mexico, underwent a more than fivefold population increase between 1950 and 2010. Before 2009, groundwater was the primary source of the City of Albuquerque’s municipal water supply, but since that time, the city has diverted water through the San Juan-Chama Drinking Water Project to augment municipal water supplies. Consequently, there is interest in understanding how groundwater levels changed in response to groundwater pumping, surface-water diversions, and conservation measures. To give a more detailed history of water-level changes from 1950 through 2012, the U.S. Geological Survey, in cooperation with the Albuquerque Bernalillo County Water Utility Authority, created maps showing water-level contours and changes by contouring water-table elevations and production-zone hydraulic heads that were simulated with a recently updated regional-scale transient groundwater-flow model at 10-year intervals from 1950 to 2000 and again for 2008. Both the water-table elevations and production-zone hydraulic heads declined over time with the largest change occurring between 1970 and 1980, which was a period of rapid population growth and groundwater use. Declines in the water-table elevations and production-zone hydraulic heads are focused around major pumping centers and are largest in the production zone. Hydrographs from nine production-zone piezometers in the modeled area indicated varying responses to the increased use of surface-water diversions during 2009–12, with responses related to the locations of the wells within the study area and their proximity to pumping centers and the Rio Grande.

New Mexico↗
USGS2014

Simulation of groundwater flow in the "1,500-foot" sand and "2,000-foot" sand, with scenarios to mitigate saltwater migration in the "2,000-foot" sand of the Baton Rouge area, Louisiana

Groundwater withdrawals have caused saltwater to encroach into freshwater-bearing aquifers beneath Baton Rouge, Louisiana. Groundwater investigations in the 1960s identified a freshwater-saltwater interface located at the Baton Rouge Fault, across which abrupt changes in water levels occur. Aquifers south of the fault generally contain saltwater, and aquifers north of the fault contain freshwater, though limited saltwater encroachment has been detected within 7 of the 10 aquifers north of the fault. The 10 aquifers beneath the Baton Rouge area, which includes East and West Baton Rouge Parishes, Pointe Coupee Parish, and East and West Feliciana Parishes, provided about 167 million gallons per day (Mgal/d) for public supply and industrial use in 2010. Groundwater withdrawals from the “2,000-foot” sand in East Baton Rouge Parish have caused water-level drawdown as great as 356 feet (ft) and induced saltwater movement northward across the fault. Saltwater encroachment threatens industrial wells that are located about 3 miles north of the fault. Constant and variable-density groundwater models were developed with the MODFLOW and SEAWAT groundwater modeling codes to evaluate strategies to control saltwater migration, including changes in the distribution of groundwater withdrawals and installation of “scavenger” wells to intercept saltwater before it reaches existing production wells. Six hypothetical scenarios simulated the effects of different groundwater withdrawal options on groundwater levels within the “1,500-foot” sand and the “2,000-foot” sand and the transport of saltwater within the “2,000-foot” sand during 2008–47. Scenario 1 is considered a base case for comparison to the other five scenarios and simulates continuation of 2007 reported groundwater withdrawals. Scenario 2 simulates discontinuation of withdrawals from seven selected industrial wells located in the northwest corner of East Baton Rouge Parish and predicts that water levels within the “1,500-foot” sand will be about 10 to 12 ft higher with this withdrawal reduction than under scenario 1. Scenario 3 simulates the effects of a scavenger well on water levels and chloride concentrations within the “2,000-foot” sand. The scavenger well, which withdraws water from the base of the “2,000-foot” sand at a rate of 2.0 Mgal/d, is simulated at two possible locations. In comparison to the concentrations simulated in scenario 1, operation of the scavenger well at the locations specified in scenario 3 reduces the chloride concentrations at all existing chloride-observation well locations. Scenario 4 simulates a 3.6 Mgal/d reduction in total groundwater withdrawals from selected wells screened in the “2,000-foot” sand that are located in the Baton Rouge industrial district. Under scenario 4, chloride concentrations decrease in the leading portion of the plume south of the industrial district but increase in areas farther east. Scenario 5 simulates the effects of total cessation of withdrawals from the “2,000-foot” sand in the industrial district, which causes a change in the groundwater-flow direction toward municipal supply wells and increased chloride concentrations in the area where municipal supply wells are located. Scenario 6 simulates the combined effect of withdrawal reductions from the “2,000-foot” sand and operation of a scavenger well and was most effective at decreasing the size of the plume area and median and mean chloride concentrations within the “2000-foot” sand in the Baton Rouge area.

Louisiana↗
USGS2013

Simulation of groundwater flow in the "1,500-foot" sand and "2,000-foot" sand and movement of saltwater in the "2,000-foot" sand of the Baton Rouge area, Louisiana

Groundwater withdrawals have caused saltwater to encroach into freshwater-bearing aquifers beneath Baton Rouge, Louisiana. Groundwater investigations in the 1960s identified a freshwater-saltwater interface located at the Baton Rouge Fault, across which abrupt changes in water levels occur. Aquifers south of the fault generally contain saltwater, and aquifers north of the fault contain freshwater, though limited saltwater encroachment has been detected within 7 of the 10 aquifers north of the fault. The 10 aquifers beneath the Baton Rouge area, which includes East and West Baton Rouge Parishes, Pointe Coupee Parish, and East and West Feliciana Parishes, provided about 167 million gallons per day (Mgal/day) for public supply and industrial use in 2010. Groundwater withdrawals from an aquifer that is 2,000-feet (ft) deep in East Baton Rouge Parish (the “2,000-foot” sand of the Baton Rouge area) have caused water-level drawdown up to 356 ft and induced saltwater movement northward across the fault. Groundwater withdrawals from the “2,000-foot” sand averaged 23.9 Mgal/d during 2010. Saltwater encroachment threatens wells that are located about 3 miles north of the fault, where industrial withdrawals account for about 66 percent of the water withdrawn from the “2,000-foot” sand in East Baton Rouge Parish. Constant and variable-density groundwater models were developed with the MODFLOW and SEAWAT groundwater modeling codes to evaluate strategies to control saltwater migration, including changes in the distribution of groundwater withdrawals and installation of “scavenger” wells to intercept saltwater before it reaches existing production wells. Five hypothetical scenarios simulated the effects of different groundwater withdrawal options on groundwater levels within the “1,500-foot” sand and the “2,000-foot” sand and the transport of saltwater within the “2,000-foot” sand. Scenario 1 is considered a base case for comparison to the other four scenarios and simulates continuation of 2007 reported groundwater withdrawals. Scenario 2 simulates discontinuation of withdrawals from seven selected industrial wells located in the northwest corner of East Baton Rouge Parish, and water levels within the “1,500-foot” sand were predicted to be about 15 to 20 ft higher under this withdrawal scenario than under scenario 1. Scenario 3 simulates the effects of a scavenger well, which withdraws water from the base of the “2,000-foot” sand at a rate of 2 Mgal/d, at two possible locations on water levels and concentrations within the “2,000-foot” sand. In comparison to the concentrations simulated in scenario 1, operation of the scavenger well in the locations specified in scenario 3 reduces the chloride concentrations at all existing chloride-observation well locations. Scenario 4 simulates a 3.6 Mgal/d reduction in total groundwater withdrawals from selected wells screened in the “2,000-foot” sand that are located in the Baton Rouge industrial district. For scenario 4, the median and mean plume concentrations are slightly lower than scenario 1. Scenario 5 simulates the effect of total cessation of groundwater withdrawals from the “2,000-foot” sand in the industrial district. The simulated chloride-concentration distribution in scenario 5 reflects the change in groundwater flow direction. Although some saltwater would continue to cross the Baton Rouge Fault and encroach toward municipal supply wells, further encroachment toward the industrial district would be abated.

Louisiana;Mississippi↗
USGS2013

Simulations of groundwater flow, transport, and age in Albuquerque, New Mexico, for a study of transport of anthropogenic and natural contaminants (TANC) to public-supply wells

Vulnerability to contamination from manmade and natural sources can be characterized by the groundwater-age distribution measured in a supply well and the associated implications for the source depths of the withdrawn water. Coupled groundwater flow and transport models were developed to simulate the transport of the geochemical age-tracers carbon-14, tritium, and three chlorofluorocarbon species to public-supply wells in Albuquerque, New Mexico. A separate, regional-scale simulation of transport of carbon-14 that used the flow-field computed by a previously documented regional groundwater flow model was calibrated and used to specify the initial concentrations of carbon-14 in the local-scale transport model. Observations of the concentrations of each of the five chemical species, in addition to water-level observations and measurements of intra-borehole flow within a public-supply well, were used to calibrate parameters of the local-scale groundwater flow and transport models. The calibrated groundwater flow model simulates the mixing of “young” groundwater, which entered the groundwater flow system after 1950 as recharge at the water table, with older resident groundwater that is more likely associated with natural contaminants. Complexity of the aquifer system in the zone of transport between the water table and public-supply well screens was simulated with a geostatistically generated stratigraphic realization based upon observed lithologic transitions at borehole control locations. Because effective porosity was simulated as spatially uniform, the simulated age tracers are more efficiently transported through the portions of the simulated aquifer with relatively higher simulated hydraulic conductivity. Non-pumping groundwater wells with long screens that connect aquifer intervals having different hydraulic heads can provide alternate pathways for contaminant transport that are faster than the advective transport through the aquifer material. Simulation of flow and transport through these wells requires time discretization that adequately represents periods of pumping and non-pumping. The effects of intra-borehole flow are not fully represented in the simulation because it employs seasonal stress periods, which are longer than periods of pumping and non-pumping. Further simulations utilizing daily pumpage data and model stress periods may help quantify the relative effects of intra-borehole versus advective aquifer flow on the transport of contaminants near the public-supply wells. The fraction of young water withdrawn from the studied supply well varies with simulated pumping rates due to changes in the relative contributions to flow from different aquifer intervals. The advective transport of dissolved solutes from a known contaminant source to the public-supply wells was simulated by using particle-tracking. Because of the transient groundwater flow field, scenarios with alternative contaminant release times result in different simulated-particle fates, most of which are withdrawn from the aquifer at wells that are between the source and the studied supply well. The relatively small effective porosity required to simulate advective transport from the simulated contaminant source to the studied supply well is representative of a preferential pathway and not the predominant aquifer effective porosity that was estimated by the calibration of the model to observed chemical-tracer concentrations.

New Mexico↗
USGS2012

Assessing the vulnerability of public-supply wells to contamination: Rio Grande aquifer system in Albuquerque, New Mexico

This fact sheet highlights findings from the vulnerability study of a public-supply well in Albuquerque, New Mexico (hereafter referred to as “the study well”). The study well produces about 3,000 gallons of water per minute from the Rio Grande aquifer system. Water samples were collected at the study well, at two other nearby public-supply wells, and at monitoring wells installed in or near the simulated zone of contribution to the study well. Untreated water samples from the study well contained arsenic at concentrations exceeding the Maximum Contaminant Level (MCL) of 10 micrograms per liter (µg/L) established by the U.S. Environmental Protection Agency for drinking water. Volatile organic compounds (VOCs) and nitrate also were detected, although at concentrations at least an order of magnitude less than established drinking-water standards, where such standards exist. Overall, study findings point to four primary influences on the movement and (or) fate of contaminants and the vulnerability of the public-supply well in Albuquerque: (1) groundwater age (how long ago water entered, or recharged, the aquifer), (2) groundwater development (introduction of manmade recharge and discharge sources), (3) natural geochemical conditions of the aquifer, and (4) seasonal pumping stresses. Concentrations of the isotope carbon-14 indicate that groundwater from most sampled wells in the local study area is predominantly water that entered, or recharged, the aquifer more than 6,000 years ago. However, the additional presence of the age tracer tritium in several groundwater samples at concentrations above 0.3 tritium units indicates that young (post-1950) recharge is reaching the aquifer across broad areas beneath Albuquerque. This young recharge is mixing with the thousands-of-years-old water, is migrating to depths as great as 245 feet below the water table, and is traveling to some (but not all) of the public-supply wells sampled. Most groundwater samples containing a fraction of young water also contain manmade VOCs, including chloroform (a byproduct of drinking-water chlorination), which indicates that the source of young recharge is, at least in part, infiltration of chlorinated municipal-supply water from leaking waterlines and sewerlines or from turf watering. Other likely manmade, urban recharge sources are seepage from constructed ponds and unlined portions of a stormwater diversion channel. A regional-scale computer-model simulation of groundwater flow and transport to the public-supply well shows that manmade sources of recharge and discharge that were added after about 1930 have greatly altered directions of groundwater flow near Albuquerque and have caused water levels to decline by as much as 120 feet. Local-scale simulations show that seasonal changes in the pumping schedule of the study well affect the age and quality of water produced by the well. Increased pumping during the summer causes significant volumes of water to flow downward from the shallow to the intermediate zones of the aquifer, causing a higher fraction of young water to be produced by the well in the summer than in the winter months and a corresponding increase in VOC detections in the summer relative to the winter. During the winter when the study-well pump is idle for several hours each day, old, high-arsenic water from the deep zone of the aquifer travels up the wellbore and exits into the intermediate zone of the aquifer. When the pump is activated in the winter (for a relatively short time each day), some of the leaked, high-arsenic water is recaptured by the well. This results in a higher arsenic concentration (commonly more than 12 µg/L) in water produced in the winter than in the summer, and a smaller fraction of young water being produced by the well in the winter than in the summer (6 percent in the winter, compared to 11 percent in the summer). Knowledge of the vertical flow direction (both natural and pumping-enhanced) in the vicinity of a long-screened well, coupled with understanding of variations in contaminant concentrations with depth in the aquifer, can help water managers predict the positive or negative effect that wellbore flow will have on water quality and can lead to development of strategies to mitigate contamination (such as changes in pumping schedules or development of devices to inhibit wellbore flow when the pump is off).

New Mexico↗
USGS2009

Simulation of Groundwater Flow in the Coastal Plain Aquifer System of Virginia

The groundwater model documented in this report simulates the transient evolution of water levels in the aquifers and confining units of the Virginia Coastal Plain and adjacent portions of Maryland and North Carolina since 1890. Groundwater withdrawals have lowered water levels in Virginia Coastal Plain aquifers and have resulted in drawdown in the Potomac aquifer exceeding 200 feet in some areas. The discovery of the Chesapeake Bay impact crater and a revised conceptualization of the Potomac aquifer are two major changes to the hydrogeologic framework that have been incorporated into the groundwater model. The spatial scale of the model was selected on the basis of the primary function of the model of assessing the regional water-level responses of the confined aquifers beneath the Coastal Plain. The local horizontal groundwater flow through the surficial aquifer is not intended to be accurately simulated. Representation of recharge, evapotranspiration, and interaction with surface-water features, such as major rivers, lakes, the Chesapeake Bay, and the Atlantic Ocean, enable simulation of shallow flow-system details that influence locations of recharge to and discharge from the deeper confined flow system. The increased density of groundwater associated with the transition from fresh to salty groundwater near the Atlantic Ocean affects regional groundwater flow and was simulated with the Variable Density Flow Process of SEAWAT (a U.S. Geological Survey program for simulation of three-dimensional variable-density groundwater flow and transport). The groundwater density distribution was generated by a separate 108,000-year simulation of Pleistocene freshwater flushing around the Chesapeake Bay impact crater during transient sea-level changes. Specified-flux boundaries simulate increasing groundwater underflow out of the model domain into Maryland and minor underflow from the Piedmont Province into the model domain. Reported withdrawals accounted for approximately 75 percent of the total groundwater withdrawn from Coastal Plain aquifers during the year 2000. Unreported self-supplied withdrawals were simulated in the groundwater model by specifying their probable locations, magnitudes, and aquifer assignments on the basis of a separate study of domestic-well characteristics in Virginia. The groundwater flow model was calibrated to 7,183 historic water-level observations from 497 observation wells with the parameter-estimation codes UCODE-2005 and PEST. Most water-level observations were from the Potomac aquifer system, which permitted a more complex spatial distribution of simulated hydraulic conductivity within the Potomac aquifer than was possible for other aquifers. Zone, function, and pilot-point approaches were used to distribute assigned hydraulic properties within the aquifer system. The good fit (root mean square error = 3.6 feet) of simulated to observed water levels and reasonableness of the estimated parameter values indicate the model is a good representation of the physical groundwater flow system. The magnitudes and temporal and spatial distributions of residuals indicate no appreciable model bias. The model is intended to be useful for predicting changes in regional groundwater levels in the confined aquifer system in response to future pumping. Because the transient release of water stored in low-permeability confining units is simulated, drawdowns resulting from simulated pumping stresses may change substantially through time before reaching steady state. Consequently, transient simulations of water levels at different future times will be more accurate than a steady-state simulation for evaluating probable future aquifer-system responses to proposed pumping.

Scientific Investigations Report↗
USGS2003

Simulated ground-water flow in the Hueco Bolson, an alluvial-basin aquifer system near El Paso, Texas

The neighboring cities of El Paso, Texas, and Ciudad Juarez, Chihuahua, Mexico, have historically relied on ground-water withdrawals from the Hueco Bolson, an alluvial-aquifer system, to supply water to their growing populations. By 1996, ground-water drawdown exceeded 60 meters in some areas under Ciudad Juarez and El Paso. A simulation of steady-state and transient ground-water flow in the Hueco Bolson in westernmost Texas, south-central New Mexico, and northern Chihuahua, Mexico, was developed using MODFLOW-96. The model is needed by El Paso Water Utilities to evaluate strategies for obtaining the most beneficial use of the Hueco Bolson aquifer system. The transient simulation represents a period of 100 years beginning in 1903 and ending in 2002. The period 1903 through 1968 was represented with 66 annual stress periods, and the period 1969 through 2002 was represented with 408 monthly stress periods. The ground-water flow model was calibrated using MODFLOWP and UCODE. Parameter values representing aquifer properties and boundary conditions were adjusted through nonlinear regression in a transient-state simulation with 96 annual time steps to produce a model that approximated (1) 4,352 water levels measured in 292 wells from 1912 to 1995, (2) three seepage-loss rates from a reach of the Rio Grande during periods from 1979 to 1981, (3) three seepage-loss rates from a reach of the Franklin Canal during periods from 1990 to 1992, and (4) 24 seepage rates into irrigation drains from 1961 to 1983. Once a calibrated model was obtained with MODFLOWP and UCODE, the optimal parameter set was used to create an equivalent MODFLOW-96 simulation with monthly temporal discretization to improve computations of seepage from the Rio Grande and to define the flow field for a chloride-transport simulation. Model boundary conditions were modified at appropriate times during the simulation to represent changes in well pumpage, drainage of agricultural fields, and channel modifications of the Rio Grande. The model input was generated from geographic information system databases, which facilitated rapid model construction and enabled testing of several conceptualizations of hydrogeologic facies boundaries. Specific yield of unconfined layers and hydraulic conductance of Quaternary faults in the fluvial facies were the most sensitive model parameters, suggesting that ground-water flow is impeded across the fault planes.

Water-Resources Investigations Report↗
USGS2003

Chemistry and age of ground water in the southwestern Hueco Bolson, New Mexico and Texas

This report, prepared in cooperation with El Paso Water Utilities, presents the results of an investigation to determine the chemistry and age of ground water on the southwestern side of the Hueco Bolson. The radioactive isotope carbon-14 was used to estimate the length of time that water from wells has been isolated from the atmosphere, which is the modern carbon-14 reservoir. Nine wells on the southwestern side of the Hueco Bolson were sampled for analysis of common constituents, nutrients, total organic carbon, trace elements, stable isotopes, and radioactive isotopes. Dissolved-solids concentrations in water from the wells sampled ranged from 269 to 2,630 milligrams per liter. Sodium concentrations generally increased linearly with chloride concentrations, possibly indicating mixing of dilute recharge water with sodium chloride brine. Concentrations of nutrients and trace elements generally were small. The deuterium and oxygen-18 composition in all samples except those from wells adjacent to the Rio Grande indicates that infiltration of precipitation is the main source of water to these wells and that evaporation has not affected the isotopic composition of the water. The source of water from wells adjacent to the Rio Grande is probably not the same source as the water from wells adjacent to the Franklin Mountains. The calculated apparent carbon-14 ages ranged from 12,100 to 25,500 years.

Water-Resources Investigations Report↗
USGS2003

Summary of extensometric measurements in El Paso, Texas

Two counter-weighted-pipe borehole extensometers were installed on the left bank of the Rio Grande between El Paso, Texas, and Ciudad Juarez, Chihuahua, Mexico, in 1992. A shallow extensometer measures vertical compaction in the 6- to 100-meter aquifer-system depth interval. A deep extensometer measures vertical compaction in the 6- to 305-meter aquifer-system depth interval. Both extensometers are referenced to the same surface datum, which allows time-series differencing to determine vertical compaction in the depth interval between 100 and 305 meters. From April 2, 1993, through June 13, 2002, 1.6 centimeters of compaction occurred in the 6-to 305-m depth interval. Until February 1999, most aquifer-system compaction occurred in the deeper aquifer-system interval between 100 and 305 meters, from which ground water was extracted. After that time, compaction in the shallow interval from 6 to 100 meters was predominant and attained a maximum of 7.6 millimeters by June 13, 2002. Minor residual compaction is expected to continue; continued maintenance of the El Paso extensometers would document this process.

Water-Resources Investigations Report↗
USGS2002

Estimation of alluvial-fill thickness in the Mimbres ground-water basin, New Mexico, from interpretation of isostatic residual gravity anomalies

The geologic structure of the Mimbres ground-water basin in southwest New Mexico is characterized by north- and northwest-trending structural subbasins. Sedimentation of Miocene and Pliocene age has filled and obscured the boundaries of these subbasins and formed potentially productive aquifers of varied thickness. The location and depth of the subbasins can be estimated from analysis of isostatic residual gravity anomalies. Density contrasts of various basement lithologies generate complex regional gravity trends, which are convolved with the gravity signal from the Miocene and Pliocene alluvial fill. An iterative scheme was used to separate these regional gravity trends from the alluvial-fill gravity signal, which was inverted with estimated depth-density relations to compute the thickness of the alluvial fill at 1-kilometer spacing. The thickness estimates were constrained by exploratory drill-hole information, interpreted seismic-refraction profiles, and location of bedrock lithology from surficial geologic mapping. The resulting map of alluvial-fill thickness suggests large areas of thin alluvium that separate deep structural subbasins.

Water-Resources Investigations Report↗
USGS2002

Ground displacements caused by aquifer-system water-level variations observed using interferometric synthetic aperture radar near Albuquerque, New Mexico

Six synthetic aperture radar (SAR) images were processed to form five unwrapped interferometric (InSAR) images of the greater metropolitan area in the Albuquerque Basin. Most interference patterns in the images were caused by range displacements resulting from changes in land-surface elevation. Loci of land- surface elevation changes correlate with changes in aquifer-system water levels and largely result from the elastic response of the aquifer-system skeletal material to changes in pore-fluid pressure. The magnitude of the observed land-surface subsidence and rebound suggests that aquifer-system deformation resulting from ground-water withdrawals in the Albuquerque area has probably remained in the elastic (recoverable) range from July 1993 through September 1999. Evidence of inelastic (permanent) land subsidence in the Rio Rancho area exists, but its relation to compaction of the aquifer system is inconclusive because of insufficient water-level data. Patterns of elastic deformation in both Albuquerque and Rio Rancho suggest that intrabasin faults impede ground- water-pressure diffusion at seasonal time scales and that these faults are probably important in controlling patterns of regional ground-water flow.

Water-Resources Investigations Report↗
USGS2001

Analytical results of a long-term aquifer test conducted near the Rio Grande, Albuquerque, New Mexico, with a section on piezometric-extensometric test results

The City of Albuquerque, New Mexico, is interested in gaining a better understanding, both quantitative and qualitative, of the aquifer system in and around Albuquerque. Currently (2000), the City of Albuquerque and surrounding municipalities are completely dependent on ground-water reserves for their municipal water supply. This report presents the results of a long-term aquifer test conducted near the Rio Grande in Albuquerque. The long-term aquifer test was conducted during the winter of 1994-95. The City of Albuquerque Griegos 1 water production well was pumped continuously for 54 days at an average pumping rate of 2,331 gallons per minute. During the 54-day pumping and a 30-day recovery period, water levels were recorded in a monitoring network that consisted of 3 production wells and 19 piezometers located at nine sites. These wells and piezometers were screened in river alluvium and (or) the upper and middle parts of the Santa Fe Group aquifer system. In addition to the measurement of water levels, aquifer-system compaction was monitored during the aquifer test by an extensometer. Well-bore video and flowmeter surveys were conducted in the Griegos 1 water production well at the end of the recovery period to identify the location of primary water- producing zones along the screened interval. Analytical results from the aquifer test presented in this report are based on the methods used to analyze a leaky confined aquifer system and were performed using the computer software package AQTESOLV. Estimated transmissivities for the Griegos 1 and 4 water production wells ranged from 10,570 to 24,810 feet squared per day; the storage coefficient for the Griegos 4 well was 0.0025. A transmissivity of 13,540 feet squared per day and a storage coefficient of 0.0011 were estimated from the data collected from a piezometer completed in the production interval of the Griegos 1 well.

New Mexico↗