Remediating Contaminant Plumes in Groundwater with Shallow Excavations Containing Coarse Reactive Media.

A groundwater flow and mass transport model tested the capability of shallow excavations filled with coarse, reactive media to remediate a hypothetical unconfined aquifer with a maximum saturated thickness of 5 m. Modeled as contaminant sinks, the rectangular excavations were 10 m downgradient of an initial contaminant plume originating from a source at the top of the aquifer. The initial plume was approximately 259 m long, 23 m wide, and 5 m thick, with a downgradient tip located approximately 100 m upgradient of the site boundary.

Nitrate Concentration Patterns Over Space and Time in a Regionally Sloping Sedimentary Aquifer, Texas, USA.

Nitrate concentrations in a regionally sloping sedimentary aquifer were compiled every 4 years from 1999 to 2015. Sampled wells ranged from 14.6 m deep in the outcrop zone to 1031.

A reconnaissance analysis of groundwater quality in the Eagle Ford shale region reveals two distinct bromide/chloride populations.

The extraction of oil and natural gas from unconventional shale formations has prompted a series of investigations to examine the quality of the groundwater in the overlying aquifers. Here we present a reconnaissance analysis of groundwater quality in the Eagle Ford region of southern Texas. These data reveal two distinct sample populations that are differentiable by bromide/chloride ratios.

Exceedance Frequency Analysis of Contaminants in Streams Under Dry-Weather Conditions in Denton, Texas.

Percentages of dry-weather stream samples exceeding water quality criteria for ten parameters were compiled for mixed land use watersheds in north-central Texas. Most problematic were total suspended solids (TSS), total dissolved solids (TDS), ammonia, nitrate, phosphorus and copper. Nutrients had much higher exceedance frequency at a sampling station impacted by wastewater discharge.

A Comprehensive Analysis of Groundwater Quality in The Barnett Shale Region.

The exploration of unconventional shale energy reserves and the extensive use of hydraulic fracturing during well stimulation have raised concerns about the potential effects of unconventional oil and gas extraction (UOG) on the environment. Most accounts of groundwater contamination have focused primarily on the compositional analysis of dissolved gases to address whether UOG activities have had deleterious effects on overlying aquifers. Here, we present an analysis of 550 groundwater samples collected from private and public supply water wells drawing from aquifers overlying the Barnett shale formation of Texas.

Comparison of permeable reactive barrier, funnel and gate, nonpumped wells, and low-capacity wells for groundwater remediation.

This modeling study compared the performance of a no-action and four active groundwater remediation alternatives: a permeable reactive barrier, a funnel and gate, nonpumped wells with filter media, and a low-capacity extraction and injection well. The simulated aquifer had an average seepage velocity of 0.04 m d(-1), and the initial contaminant plume was 58 m long and 13 m wide.

Shallow, non-pumped wells: a low-energy alternative for cleaning polluted groundwater.

This modeling study evaluated the capability of non-pumped wells with filter media for preventing contaminant plumes from migrating offsite. Linear configurations of non-pumped wells were compared to permeable reactive barriers in simulated shallow homogeneous and heterogeneous aquifers. While permeable reactive barriers enabled faster contaminant removal and shorter distances of contaminant travel, non-pumped wells also prevented offsite contaminant migration.

Relative efficiency of multi-transect, non-pumped, reactive well networks for removing contaminated groundwater.

Alternative networks of non-pumped wells filled with reactive media were evaluated for groundwater remediation capability. Wells were screened across the saturated zone of a simulated, unconfined aquifer with a heterogeneous hydraulic conductivity. A numerical mass transport model generated an initial contaminant plume and then simulated its movement through different networks of non-pumped wells.

Effect of aquifer heterogeneity on non-pumped, reactive well networks for removing pollutants in groundwater.

This purpose of this study was to evaluate the impact of heterogeneity in aquifer hydraulic conductivity on configurations of non-pumped wells filled with reactive media for removing contaminant plumes in groundwater. Among one homogeneous and three heterogeneous simulated aquifers, 2-16 wells were necessary to contain a plume, with no clear relationship between degree of heterogeneity and number of wells. Generally, heterogeneous aquifers with initial plumes having broad rather than narrow downgradient margins required more wells and showed greater tendency for plumes to move around wells.

Assessment of multi-gate interceptors equipped with baffles in contaminated aquifers.

Funnel-and-gate structures with three gates, two funnels (collinear with gates), and two perpendicular flow-directing vanes (baffles) were assessed for capturing contaminated groundwater in a hypothetical unconfined aquifer. Simulated structures, anchored into an underlying aquiclude, were 35 m wide. One 5-m wide gate occupied the center, and two 3-m wide gates occupied the ends, of each structure.

Funnel-and-gate remediation systems augmented with passive filter wells.

The objective of this study was to evaluate the ability of funnel-and-gate structures augmented with passive wells containing filter cartridges to capture contaminated groundwater in hypothetical, homogeneous and heterogeneous, unconfined aquifers. Perpendicular to groundwater flow, linear structures were 15 m wide, 1 m thick, and keyed into the base of the aquifer. Gates occupied 4 m of the total width of each simulated structure; one gate was 5 m from a contaminant plume's leading tip, while others occupied cross-gradient margins of the plume.

Viability of longitudinal trenches for capturing contaminated groundwater.

Using a groundwater flow and mass transport model, this study compared the capability of trenches with permeable backfill for capturing hypothetical contaminant plumes in homogeneous and heterogeneous unconfined aquifers. Longitudinal (parallel to groundwater flow), as well as conventional transverse (perpendicular to groundwater flow) trench configurations were considered. Alternate trench configurations intercepted the leading tip of an initial contaminant plume and had identical length, equal to the cross-gradient width of the plume.

Elevated fluoride and selenium in west Texas groundwater.

Fluoride and selenium concentrations, along with total dissolved solids and depth of intake, were compiled, mapped, and analyzed for 634 water wells in the High Plains Aquifer, northwest Texas. Approximately 19% of fluoride observations exceeded the maximum contaminant level (MCL) for drinking water. Additionally, 4% of selenium observations exceeded the MCL for drinking water, and 19% exceeded the recommended limit for irrigation water.

Evaluation of reactive well networks for remediating heterogeneous aquifers.

Alternative configurations of non-pumped wells filled with reactive media were evaluated for removing hypothetical contaminant plumes. All wells were screened across the saturated zone of a simulated unconfined aquifer. Three heterogeneous hydraulic conductivity distributions (cases) were considered.

Distribution of arsenic concentrations in groundwater of the Seymour Aquifer, Texas, USA.

The purpose of this study was to investigate arsenic concentrations in the Seymour Aquifer. Discontinuous alluvium of the aquifer occupies a broad, semi-arid region of northern Texas, USA. Throughout the formation's outcrop, permeable deposits and unconfined conditions may facilitate downward travel of contaminants applied to the land surface.

Mass transport in groundwater near hanging-wall interceptors.

This study investigated mass transport near trenches designed to capture contaminated groundwater. Numerical models simulated migration of contaminant plumes toward trenches oriented perpendicular to regional groundwater flow, partially penetrating a hypothetical unconfined aquifer. Plumes originated at the top of the simulated groundwater flow system.

Evaluation of ecological and in vitro effects of boron on prostate cancer risk (United States).

Objective: To determine: (1) the correlation of prostate cancer incidence and mortality with groundwater boron and selenium concentrations; and (2) the impact of boron on prostate cancer cell proliferation during co-treatment with alternative chemo-preventative agents, along with boron pre-treatment effects on cell sensitivity to ionizing radiation.

Methods: For regression analysis, data on prostate cancer incidence and mortality were obtained from the Texas Cancer Registry, while groundwater boron and selenium concentrations were derived from the Texas Water Development Board. Cultured DU-145 prostate cancer cells were used to assess the impact of boric acid on cell proliferation when applied in combination with selenomethionine and genistein, or preceding radiation exposure.

Heuristic for constructing minimum-well groundwater monitoring configurations at waste storage facilities.

A graphical heuristic was designed and evaluated for locating detection wells in aquifers beneath landfills. The heuristic identifies locations of a minimum number of wells on a compliance boundary to detect potential contaminant releases from a landfill. It maximizes gaps between wells while ensuring no potential releases pass between them.

Effect of setback distance on ability of gravel trenches to intercept contaminated groundwater.

Computer simulations tested the ability of gravel interceptor trenches to capture a plume of contaminated groundwater. The plume had a maximum length and width of 87 and 19 m, respectively. In alternate simulations, one-meter wide trenches were located 5, 10, 20, and 50 m downgradient of the plume.

Augmenting groundwater monitoring networks near landfills with slurry cutoff walls.

This study investigated the use of slurry cutoff walls in conjunction with monitoring wells to detect contaminant releases from a solid waste landfill. The 50 m wide by 75 m long landfill was oriented oblique to regional groundwater flow in a shallow sand aquifer. Computer models calculated flow fields and the detection capability of six monitoring networks, four including a 1 m wide by 50 m long cutoff wall at various positions along the landfill's downgradient boundaries and upgradient of the landfill.

Boron and selenium contamination in south Texas groundwater.

Boron and selenium concentrations from 112 water wells in an irrigated agricultural region of south Texas were compiled, mapped, and statistically analyzed. Wells in the study area produce water from the Gulf Coast Aquifer System, comprising coastward sloping beds of clay, silt, sand, and gravel. Nearly 84 percent of boron observations exceeded the 600 ug/L advisory level for drinking water, 70% exceeded the 1250 ug/L level for sensitive crops, and 24% exceeded the 3750 ug/L level for tolerant crops.

Performance comparison of interceptor trench configurations for extracting contaminated groundwater.

Computer simulations tested the capability of five alternative interceptor trench configurations to capture an enclave (plume) of contaminated groundwater. The configurations included a single linear segment and angled segments, at 90 degrees and 135 degrees, with a common endpoint. Alternative angled configurations both faced and opposed the contaminant plume.

Oil production and groundwater quality in the Edwards-Trinity Plateau Aquifer, Texas.

Chloride concentrations and chloride/bromide ratios from 198 water wells in the Edwards-Trinity Plateau Aquifer were compiled, mapped, and evaluated within the context of regional geology and land use. The study area occupies eight counties in west-central Texas, within which oil production and agriculture are predominant land uses. Samples from 49 wells had chloride concentrations above the 250 mg/l secondary drinking water standard, 22 samples had greater than 500 mg/l chloride, and 9 samples exceeded 1000 mg/l chloride.

Viability of interceptor trenches for monitoring groundwater quality near landfills.

Computer models were used to quantify the detection capability of four alternative groundwater monitoring systems in a shallow aquifer near a 50-m by 75-m landfill oriented oblique to groundwater flow. The monitoring systems included a network of five wells, and 1-m, 3-m, and 5-m wide gravel interceptor trenches. Each trench was 42-m long.