Secondary Maximum Contaminant Level Research Articles

Sustainability of Regional Groundwater Quality in Response to Managed Aquifer Recharge

AbstractGrowing demands on water supply worldwide have resulted in aquifer overdraft in many regions, especially in alluvial basins under intensive irrigation. This further leads to serious deterioration of groundwater quality. Managed aquifer recharge (MAR) has been shown to mitigate groundwater overdraft, but whether MAR can actually stabilize or reverse the ongoing declines in regional groundwater quality caused by non‐point sources has not been demonstrated. This study was intended to address the question by investigating impacts of different MAR strategies on regional groundwater quality. A geostatistical model was first used to characterize a heterogeneous alluvial aquifer system in a portion of the Tulare Lake Basin. Three‐dimensional numerical models were then employed to simulate groundwater flow and mass transport. Next, MAR strategies were applied in locations with different geological conditions or joint with different irrigation activities, and their performances were evaluated. Results demonstrate the potential of significant, long‐term benefits for regional groundwater quality by applying strategic, high‐intensity recharge operations on geologically favorable subregions. Siting MAR above the incised valley fill (IVF) deposit, a near‐surface paleochannel containing unusually coarse, high‐conductivity hydrofacies, leads to more extensive improvement in the groundwater quality in terms of salinity due to significant vertical flow and lateral outward flow from the IVF. Overall, decades would be required to alleviate groundwater quality concerns in the studied 189 km2 region. The simulations indicate that the deep concentrations remain below the secondary maximum contaminant level as the solute mass migrates downward with the prominent contribution from the attenuation via dispersion and matrix diffusion.

Drinking water disparities and aluminum concentrations: Assessing socio-spatial dimensions across an urban landscape

The United States Environmental Protection Agency does not enforce a maximum contaminant level of Aluminum (Al) in treated drinking water and trace amounts are commonly found in household tap water. Al is known to impact the aesthetics of tap water, and research shows that exposure may have adverse impacts on human health. Socioeconomic status (SES) may play a role in Al exposure since some water treatment plants utilize “Alum” as an affordable treatment method, even though higher Al concentrations can result in finished drinking water. The objective of this study is to identify socio-spatial variations in concentrations of Al in household tap water across a highly diverse urban landscape. A total of 96 households in eastern Palm Beach County, Florida were randomly selected and tap water samples were collected from an unfiltered faucet and tested for Al. Al was above method detection limit in 56% of the samples analyzed, and 6% of the samples were above Florida’s secondary maximum contaminant level (concentrations ranged from 0.009 mg/L - 0.429 mg/L). Significant spatial clusters of higher Al concentrations in areas of lower SES were identified using local spatial autocorrelation (Getis-Ord Gi*). Maximum Likelihood of Spatial Lag and Spatial Weighted Least Squares HET regression models confirm a significant association between higher Al concentrations in tap water and lower SES. The findings of this study may be useful to water officials who aim to reduce levels of Al in tap water by prioritizing communities that experience the greatest socioeconomic deprivation.

Effects of return flows on stream water quality and availability in the Upper Colorado, Delaware, and Illinois River Basins

Understanding effects of human water use and subsequent return flows on the availability and suitability of water for downstream uses is critical to efficient and effective watershed management. We compared spatially detailed estimates of stream chemistry within three watersheds in diverse settings to available standards to isolate effects of wastewater and irrigation return flows on the suitability of downstream waters for maintaining healthy aquatic ecosystems and for selected human uses. Mean-annual flow-weighted total and source-specific concentrations of nitrogen and phosphorus in individual stream reaches within the Upper Colorado, Delaware, and Illinois River Basins and of total dissolved solids within stream reaches of the Upper Colorado River Basin were estimated from previously calibrated regional watershed models. Estimated concentrations of both nitrogen and phosphorus in most stream reaches in all three watersheds (at least 78%, by length) exceed recommended standards for the protection of aquatic ecosystems, although concentrations in relatively few streams exceed such standards due to contributions from wastewater return flows, alone. Consequently, efforts to reduce wastewater nutrient effluent may provide important local downstream benefits but would likely have minimal impact on regional ecological conditions. Similarly, estimated mean-annual flow-weighted total dissolved solids concentrations in the Upper Colorado River Basin exceed standards for agricultural water use and (or) the secondary maximum contaminant level (SMCL) for drinking water in 52% of streams (by length), but rarely due to effects of irrigation return flows, alone. Dissolved solids in most tributaries of the Upper Colorado River are attributable primarily to natural sources.

Evaluation of Extensive Secondary Maximum Contaminant Level Exceedances Following Remediation by In Situ Chemical Oxidation

AbstractIn situ chemical oxidation (ISCO) with activated persulfate is commonly used for the remediation of petroleum impacted soil and groundwater because of its proven efficiency and the perception that reaction end products are completely innocuous. While the reaction products are less hazardous compared to the contaminants being treated, they may inadvertently prolong site closure in areas that have adopted the U.S. Environmental Protection Agency (EPA) Secondary Maximum Contaminant Levels (SMCLs) as enforceable standards. This study examines the occurrence and persistence of iron, manganese, sulfate, sodium, and total dissolved solids (TDS) in groundwater following persulfate ISCO. The concentrations of these chemicals were observed remaining above their respective regulatory criteria almost 3 years following the chemical application. Background concentrations and mobilization due to the petroleum contamination and ISCO application are also evaluated. Baseline sampling revealed substantially higher iron and manganese concentrations inside the plume area compared to the upgradient and downgradient wells suggesting mobilization due to redox reactions occurring inside of the plume. Iron was not a component in the applied chemical formula, yet the iron concentration spiked by 366% in the key monitoring well during the first post‐remediation monitoring event. Ionic interactions between the ISCO amendment and native soils are believed to be responsible for displacing significant quantities of iron from the soil. Sulfate, sodium, and TDS exceedances are primarily associated with decomposition products of the ISCO amendments. The iron, manganese, sulfate, sodium, and TDS concentrations are trending downward over time, but still exceed regulatory criteria or pre‐ISCO concentrations.

Analysis of the novel NCWELL database highlights two decades of co-occurrence of toxic metals in North Carolina private well water: Public health and environmental justice implications

Private well users are particularly vulnerable to metal exposure as they are not protected by the Safe Drinking Water Act. In North Carolina (NC), approximately 2.4 million individuals rely on private well water. In the present study, we constructed the NCWELL database: a comprehensive database of 117,960 geocoded well water tests over twenty-years in NC inclusive of 28 metals/metalloids. The NCWELL database was analyzed to identify areas of concern for single and co-occurring toxic metal contamination of private wells in NC. County-level population-at-risk rankings were calculated by combining toxic metal levels and the proportion of residents relying on well water. Additionally, k-means analysis was used to identify counties with critical co-occurrence of toxic metals. In the NCWELL database, inorganic arsenic (iAs) and lead (Pb) were detected above the EPA standards of 10 and 15 ppb in over 2500 and over 3000 tests, respectively. Shockingly, iAs was observed at levels up to 806 ppb and Pb at levels up to 105,440 ppb. Manganese (Mn) was detected above the EPA lifetime Health Advisory Limit in 4.9% and above the secondary Maximum Contaminant Level in 24.3% of all well water tests in NC, with a maximum concentration of 46,300 ppb reported. Mixtures-based analysis identified four distinct clusters of counties, one demonstrating high iAs and Mn and another with high Pb. Over the twenty-year period, metal levels remained high, indicative of sustained contamination in areas of concern. This study provides a novel database for researchers and concerned citizens in NC, demonstrates a methodology for identifying priority geographic regions for single and multiple contaminants, and has environmental justice implications in NC where metal exposure via private well water remains a serious public health concern.

Effect of Fertilizer on Water Quality of Creeks over Time

Many people use fertilizer for commercial use, but are unaware of its harmful impacts. The main two ingredients in fertilizer are phosphorus and nitrogen, which are present in fertilizers through compounds such as ammonium phosphate and nitrate. Excess nitrates are dangerous as high nitrate levels in drinking water can cause infants to develop illnesses. In this experiment, we studied the effects of fertilizer on the water quality of Saratoga Creek over time. For 4 days, we measured the total dissolved solids (TDS), pH, and nitrate levels of eight creekwater samples after three fertilizer treatments of 0.5 tsp, 1 tsp, and 1.5 tsp were added. Results showed that fertilizer had a significant effect on all 3 indicators, with TDS levels substantially exceeding the 500 ppm level suggested in the “U.S. Secondary Maximum Contaminant Levels” (SMCLs) and nitrate concentrations surpassing the 10 ppm standard in drinking water set by the EPA. TDS concentrations for the 3 fertilizer treatments at 4 days exceeded the standard by around 6, 12, and 20 times respectively, while pH levels dropped below the acceptable range of 6.5-8.5. Nitrate levels spiked at two days, then gradually returned to their original levels. Although TDS does not pose as great a health risk, high nitrate levels in water can have damaging effects on people’s health if consumed, and low pH levels can contaminate the habitats of aquatic species. Therefore, we suggest that people limit their fertilizer use to protect the environment and their peers.

Using Boosted Regression Tree Models to Predict Salinity in Mississippi Embayment Aquifers, Central United States

AbstractHigh salinity limits groundwater use in parts of the Mississippi embayment. Machine learning was used to create spatially continuous and three‐dimensional predictions of salinity across drinking‐water aquifers in the embayment. Boosted regression tree (BRT) models, a type of machine learning, were used to predict specific conductance (SC) and chloride (Cl), and total dissolved solids (TDS) was calculated from a correlation with SC. Explanatory variables for BRT models included well location and construction, surficial variables (e.g., soils and land use), and variables extracted from a groundwater‐flow model, including simulated groundwater ages. BRT model fits (r2) were 0.74 (SC and Cl) and 0.62 (TDS). BRT models provided spatially continuous salinity predictions across surficial and deeper aquifers where discrete water‐quality samples were missing. Uncertainty was smaller where salinity was lower, and models tended to underpredict in areas of highest salinity. Despite this, BRT models were able to capture areas of documented high salinity that exceed the TDS secondary maximum contaminant level for drinking water of 500 mg/L. Variables that served as surrogates for position along groundwater flowpaths were the most important predictors, indicating that much of the control on dissolved solids is related to rock‐water interaction as residence time increases. BRT models additionally support hypotheses of both surficial and deep sources of salinity.

Fluoride occurrence in United States groundwater

Data from 38,105 wells were used to characterize fluoride (F) occurrence in untreated United States (U.S.) groundwater. For domestic wells (n = 11,032), water from which is generally not purposely fluoridated or monitored for quality, 10.9% of the samples have F concentrations >0.7 mg/L (U.S. Public Health Service recommended optimal F concentration in drinking water for preventing tooth decay) (87% are <0.7 mg/L); 2.6% have F > 2 mg/L (EPA Secondary Maximum Contaminant Level, SMCL); and 0.6% have F > 4 mg/L (EPA MCL). The data indicate the biggest concern with F in domestic wells at the national scale could be one of under consumption of F with respect to the oral-health benchmark (0.7 mg/L). Elevated F concentrations relative to the SMCL and MCL are regionally important, particularly in the western U.S. Statistical comparisons of potentially important controlling factors in four F-concentration categories (<0.1–0.7 mg/L; >0.7–2 mg/L; >2–4 mg/L; >4 mg/L) at the national scale indicate the highest F-concentration category is associated with groundwater that has significantly greater pH values, TDS and alkalinity concentrations, and well depths, and lower Ca/Na ratios and mean annual precipitation, than the lowest F-concentration category. The relative importance of the controlling factors appears to be regionally variable. Three case studies illustrate the spatial variability in controlling factors using groundwater-age (groundwater residence time), water-isotope (evaporative concentration), and water-temperature (geothermal processes) data. Populations potentially served by domestic wells with F concentrations <0.7, >0.7, >2, and >4 mg/L are estimated to be ~28,200,000, ~3,110,000; ~522,000; and ~172,000 people, respectively, in 40 principal aquifers with at least 25 F analyses per aquifer.

The relation of geogenic contaminants to groundwater age, aquifer hydrologic position, water type, and redox conditions in Atlantic and Gulf Coastal Plain aquifers, eastern and south-central USA

Groundwater age distributions developed from carbon-14 (14C), tritium (3H), and helium-4 (4He) concentrations, along with aquifer hydrologic position, water type, and redox conditions, were compared to geogenic contaminants of concern (GCOC) from 252 public-supply wells in six Atlantic and Gulf Coastal Plain unconsolidated-sediment aquifers. Concentrations of one or more GCOCs in 168 (67%) wells exceeded MCLs (maximum contaminant levels), SMCLs (secondary MCLs), or HBSLs (health-based screening levels). Human-health benchmark thresholds (MCLs or HBSLs) were exceeded in 31 (12%) wells, and included 0.8% for fluoride (F), 2.4% for arsenic (As), 4% for lead-210 (210Pb), and 6.7% for polonium-210 (210Po). Values of pH increase with age and were outside the SMCL in 31% of wells (23% < 6.5 and 7.5% > 8.5, SMCL). Among GCOCs with concentrations that increased significantly with groundwater age, the frequency of sentry threshold exceedances (i.e., one-half of MCL, SMCL, or HBSL) included 40% for dissolved solids (DS), 12% for chloride (Cl), 3.6% for F, 4.4% for As, and 9.5% for 210Po. Iron (Fe) concentrations did not correlate with groundwater age, but exceeded sentry thresholds in 29% of wells. Groundwater age, water types, redox, pH, and GCOCs varied because of unique hydrogeologic features of the aquifers (recharge locations and geometry). As expected, primarily confined aquifers had young, oxic, low to near-neutral pH water near the outcrop (recharge area), and older, reduced, high pH water deeper and farther along flow paths. However, unique aquifer hydrogeologic conditions, such as multiple-recharge zones produced anomalous patterns of young and old groundwater at varying depths and locations along flow paths. Evidence for this variability is seen in disequilibrium patterns in the progression of the chemical evolution of groundwater with hydrologic position. When hydrogeologic differences are considered, groundwater age combined with hydrologic-position data, can provide a strong basis for inferring potential occurrence of GCOCs.

Pilot Plant Performance Comparing Carbon-Based and Membrane-Based Potable Reuse Schemes

Two pilot-scale advanced water treatment plants using tertiary-treated biological nutrient removal wastewater effluent were operated simultaneously to demonstrate and compare treatment performances and process operations. Final effluent from both the plants was compared for its suitability to recharge a potable water supply aquifer. The two treatment approaches included a carbon-based treatment process (flocculation/sedimentation, ozone-biofiltration, granular activated carbon (GAC) adsorption, ultraviolet (UV) disinfection; 20,000 L/day) and a membrane-based treatment process (ultrafiltration, reverse osmosis, UV-hydrogen peroxide advanced oxidation; 160,000 L/day). Both processes were found to be reliable in producing water that met all United States Safe Drinking Water Act's primary maximum contaminant levels (MCLs). The carbon-based process often exceeded the secondary MCL for total dissolved solids due to background salinity in the source water. Results showed that both systems performed comparably with respect to removal of pathogens, fecal indicators, and contaminants of emerging concern. Total organic carbon (TOC) was removed to below 0.5 mg/L by the membrane-based process. For the carbon-based process, GAC media exhaustion over the course of the pilot operation resulted in an increase in finished water TOC from <0.5 to ∼4 mg/L. Disinfection byproducts, including trihalomethanes and haloacetic acids were not measured above their respective MCL after 8 h of free chlorine contact in a simulated distribution system test. N-nitrosodimethylamine was removed below 10 ng/L by the GAC with 20 min of empty bed contact time after 20,000 bed volumes.

Pilot testing of direct and indirect potable water reuse using multi-stage ozone-biofiltration without reverse osmosis

Pilot testing of direct potable reuse (DPR) using multi-stage ozone and biological filtration as an alternative treatment train without reverse osmosis (RO) was investigated. This study examined four blending ratios of advanced treated reclaimed water from the F. Wayne Hill Water Resources Center (FWH WRC) in Gwinnett County, Georgia, combined with the existing drinking water treatment plant raw water supply, Lake Lanier, for potable water production. Baseline testing with 100 percent (%) Lake Lanier water was initially conducted; followed by testing blends of 15, 25, 50, and 100% reclaimed water from FWH WRC. Finished water quality from the DPR pilot was compared to drinking water standards, and emerging microbial and chemical contaminants were also evaluated. Results were benchmarked against a parallel indirect potable reuse (IPR) pilot receiving 100% of the raw water from Lake Lanier. Finished water quality from the DPR pilot at the 15% blend complied with the United States primary and secondary maximum contaminant levels (MCLs and SMCLs, respectively). However, exceedances of one or more MCLs or SMCLs were observed at higher blends. Importantly, reclaimed water from FWH WRC was of equal or better quality for all microbiological targets tested compared to Lake Lanier, indicating that a DPR scenario could lower acute risks from microbial pathogens compared to current practices. Finished water from the DPR pilot had no detections of microorganisms, even at the 100% FWH WRC effluent blend. Microbiological targets tested included heterotrophic plate counts, total and fecal coliforms, Escherichia coli, somatic and male-specific coliphage, Clostridium perfringens, Enterococci, Legionella, Cryptosporidium, and Giardia.There were water quality challenges, primarily associated with nitrate originating from incomplete denitrification and bromate formation from ozonation at the FWH WRC. These challenges highlight the importance of upstream process monitoring and control at the advanced wastewater treatment facility if DPR is considered.This research demonstrated that ozone with biological filtration could achieve potable water quality criteria, without the use of RO, in cases where nitrate is below the MCL of 10 mg nitrogen per liter and total dissolved solids are below the SMCL of 500 mg per liter.

Interpretation of storage and retrieval major-ion chemistry, with emphasis on significant sulfate and sodium concentrations in the White River watershed, northwestern Nebraska, United States

The White River watershed encompasses four major tributaries within a basin area of 130 km2 (1595 mi2) in extreme northwestern Nebraska. An examination of the historical (1968–1975) aqueous geochemistry data (major cations and anions and total dissolved solids [TDS]) supplied by the Nebraska Department of Environmental Quality revealed that the TDS is relatively low (130–1200 mg/L), excluding Big Cottonwood Creek (BCC), with a basin-wide median of 340 mg/L. The median TDS for the BCC is 1880 mg/L (brackish); the median values for Na and SO4 are 385 and 897 mg/L, respectively. Mineralization in the river increases steadily downstream. The scatter plots of meq/L concentrations for selected anions and cations reveal the impact of silicate mineral (e.g., feldspar) weathering on the aqueous geochemistry throughout the watershed. These ubiquitous feldspar minerals most likely originated along the eastern slope of the Front Range during the Late Cretaceous and Tertiary (Laramide orogeny). Twenty-nine samples for three White River stations and the BCC exceed the US Environmental Protection Agency secondary maximum contaminant levels for TDS and/or SO4 in drinking water supplies at 500 and 250 mg/L, respectively. Uncontaminated streams that drain marine shales (typically containing S-bearing minerals) nationwide typically show an excess of Na and a deficiency of Ca and Mg. This is due in part to cation exchange of Ca in solution for Na on clay minerals. Consequently, the weathering of shale terrains commonly produces an Na-SO4 brackish surface-water runoff as is the case with BCC, which drains the Pierre Shale hills.

Bromide and Other Halide Ion Removal From Drinking Waters Using Silver‐Amended Coagulation

High bromide ion concentrations are of concern because of formation of brominated disinfection byproducts in drinking water, which may be more toxic than their chlorinated analogs. Jar tests dosed with alum and silver were performed on several water samples with chloride‐to‐bromide (Cl:Br) ratios ranging from 15 to 866 mg Cl/mg Br. In lower‐chloride waters (15 mg Cl/mg Br), silver‐amended coagulation (SAC) removed 20–90% of the initial bromide. In higher‐chloride water (525 mg Cl/mg Br), a silver dose of 15 mol Ag/mol Br achieved 40% bromide removal. Iodide and chloride removal also occurred during silver addition. SAC did not influence total organic carbon or turbidity removal, and residual silver was below the secondary maximum contaminant level but was successful in decreasing trihalomethane (THM) formation from 44 to 28 μg/L by shifting away from brominated THM species. SAC may only be applicable and cost‐effective in a narrow range of waters with lower Cl:Br ratios, and other technologies should be developed for waters with &gt;300 mg Cl/mg Br.

Karst hydrogeological observations in Tra Linh and Quang Uyen districts, Cao Bang province, Vietnam

The Tra Linh and Quang Uyen Districts are located in Cao Bang Province, Northeastern Vietnam, where abundant rainfall combined with considerable soluble limestones of Devonian, Carboniferous, and Permian ages support a spectacular tower karst landscape. This paper is a comprehensive study based on geologic, tectonic, and hydrogeological observations in the Tra Linh and Quang Uyen Districts, Cao Bang Province, Vietnam, enhanced with water-quality samples collected from 31 sites. Each location was sampled once, in March 2012 or February 2014, except Hang Ban Lang (HQ-31) and Hang Ban Nua (HQ-32) springs, which were sampled twice to determine variability in water quality. The water samples were analyzed for physical proprieties and chemical and isotopic composition. To better understand the impact of the lithologic factor to the development of the karst landscape in the study area, two rock samples were collected and analyzed during the 2014 trip. Four additional rock samples were collected for comparison from areas located in similar humid subtropical climate as the study area; three from Thailand and one from Alabama, USA. The data and analyses presented herein are performed for the first time in the study area. Results showed that groundwater quality met US drinking-water standards, with only manganese exceeded secondary maximum contaminant levels (MCLs) in seven samples. Specific conductance values for the water samples ranged from 153.2 to 421.6 µS/cm. The pH values ranged from 6.51 to 8.29, total hardness (as CaCO3) was between 85 and 326 mg/L, the total alkalinity as CaCO3 varied from 68 to 207 mg/L, and carbon dioxide varied between 32.4 and 123.4 mg/L. The water chemistry is dominated by calcium. The highest concentrations of calcite were recorded in the rock samples collected in Vietnam. The water samples collected in the Cao Bang Province are depleted in both 18O and deuterium with a d-excess value above ~ 10‰ and have a median value of 13.16‰. Some samples exhibited lesser (three samples with values under 10; a sinking stream, a karst window, and a lake) or higher deuterium excess values due to local variations in humidity, temperature, and wind speed. The data set reported here only represents a local and time-limited snapshot of the water isotopic compositions. Further studies are required to confirm our preliminary results from Cao Bang Province.

The Effect of Leaky Well Permeability Distribution on Probabilistic Risk Maps in Geologic Carbon Storage

A probabilistic methodology to generate “risk maps” for determining the spatial extent and associated probability of groundwater leakage risk at Geologic Carbon Storage (GCS) sites was recently developed and is tested for well permeability distribution sensitivity here. Although the risk map methodology is general and may be used to assess leakage of either CO2 or brine, the degree to which risk may occur via plugged and abandoned (P&A) brine leakage is arguably the most uncertain. This uncertainty stems from the possibility of a high number of undocumented wells at a given injection site which, even when properly plugged, may yield a number of different leakage pathways. Furthermore, determining the spatial extent and probability of brine leakage through P&A wells is not straightforward. The aforementioned risk maps are probabilistic and are based on the premise that two of the greatest sources of uncertainty in brine leakage through P&A wells are the location of the unknown well with respect to the injection well and the permeability of the leaky well (which can span over several orders of magnitude). The methodology utilizes either analytical solutions or numerical simulations in conjunction with probability theory to generate spatial distributions of risk. Risk is defined with either no-impact levels (i.e. zero brine concentration above background in the drinking water aquifer) or other user defined thresholds such as the secondary maximum contaminant level (SMCL) for total dissolved solids, a non-health related standard related to water hardness, color, and taste. These probabilistic maps can be used to provide risk-based descriptions of the injection area to inform site selection prior to injection and monitoring during or after injection has ceased, similar to the United States Environmental Protection Agency's definition of the area of review (AoR). However, unlike the AoR definition, we differentiate risks according to a tiered approach, where CO2 leakage risk and brine leakage risk through P&A wells and open wellbores are assessed separately given that not only do the risks differ considerably, the spatial extents of each hazard do as well. A strength of this methodology is its demonstrated efficiency, which unlike computationally expensive Monte Carlo techniques that could require several thousands of simulations, requires only on the order of tens of simulations. Here, we assess the sensitivity of risk maps of a hypothetical, yet realistic GCS leakage scenario. In this sensitivity analysis, risk maps are generated with varying leaky well permeability distributions including differences in distribution modality and distribution variance. This work is motivated by the unknown quality to which many wells are sealed and/or the degree to which they degrade over time, in addition to the sheer unknown quantity of which P&A wells may be present at a single Geologic Carbon Storage site. Quantitative probabilities of exceeding contamination thresholds in the USDW are used for discussion, a practical metric for decision-makers and stakeholders. Results show that the modality of the leaky P&A distribution plays an important role in the risk profile and that larger variances in leaky P&A well permeability distribution may result in an overall lower profile of risk, depending on the upper-threshold of the distribution.

Solute distribution in the Ogallala Aquifer, Texas: lithium, fluoride, nitrate, chloride and bromide

Spatial patterns of lithium, fluoride, nitrate, chloride and bromide in the Ogallala Aquifer of northwestern Texas were mapped and evaluated. Solute concentrations and depths were compiled for 705 water wells sampled between 2008 and 2014. Lithium concentrations were high relative to typical groundwater; median and maximum concentrations were 66.8 and 2,790 ug/L, respectively. Almost half of the fluoride observations equaled or exceeded the secondary maximum contaminant level (MCL) of 2 mg/L. Many nitrate observations exceeded the MCL of 44.3 mg/L, and several chloride observations exceeded the secondary MCL of 250 mg/L, with a maximum concentration nearly ten times that level. Most bromide observations were less than 0.15 mg/L; however, some observations exceeded 10 mg/L. Several wells had high chloride/bromide ratios and high chloride concentrations. Generally, concentrations of all solutes were higher in the southern part of the aquifer, where wells are relatively shallow. Solute concentrations documented in this study are likely influenced by water–rock interaction within the aquifer, as well as mixing with groundwater in underlying bedrock containing evaporite minerals. Agricultural practices and possibly oilfield activity also affect water quality in the Ogallala Aquifer.

Sources of high-chloride water and managed aquifer recharge in an alluvial aquifer in California, USA

As a result of pumping in excess of recharge, water levels in alluvial aquifers within the Eastern San Joaquin Groundwater Subbasin, 130 km east of San Francisco (California, USA), declined below sea level in the early 1950s and have remained so to the present. Chloride concentrations in some wells increased during that time and exceeded the US Environmental Protection Agency’s secondary maximum contaminant level of 250 mg/L, resulting in removal of some wells from service. Sources of high-chloride water include irrigation return in 16 % of sampled wells and water from delta sediments and deeper groundwater in 50 % of sampled wells. Chloride concentrations resulting from irrigation return commonly did not exceed 100 mg/L, although nitrate concentrations were as high as 25 mg/L as nitrogen. Chloride concentrations ranged from less than 100–2,050 mg/L in wells affected by water from delta sediments and deeper groundwater. Sequential electromagnetic logs show movement of high-chloride water from delta sediments to pumping wells through permeable interconnected aquifer layers. δD and δ18O data show most groundwater originated as recharge along the front of the Sierra Nevada, but tritium and carbon-14 data suggest recharge rates in this area are low and have decreased over recent geologic time. Managed aquifer recharge at two sites show differences in water-level responses to recharge and in the physical movement of recharged water with depth related to subsurface geology. Well-bore flow logs also show rapid movement of water from recharge sites through permeable interconnected aquifer layers to pumping wells.

Pre-drilling water-quality data of groundwater prior to shale gas drilling in the Appalachian Basin: Analysis of the Chesapeake Energy Corporation dataset

Unconventional natural gas production in the Marcellus and Utica formations of the Northeastern United States raises concerns about potential impacts to shallow groundwater. We examined and interpreted 13,040 analyses from pre-drilling groundwater samples from domestic water wells in northeastern (NE) Pennsylvania and 8004 samples from water wells in the “Western Area” which includes southwest Pennsylvania, eastern Ohio, and north-central West Virginia. These samples were acquired on behalf of Chesapeake Energy Corporation as part of its local pre-drilling water supply monitoring program. We evaluated concentrations of major ions and metals relative to federal drinking-water-quality standards upon which regulatory decisions are often based. Chesapeake’s dataset, the most comprehensive for these areas, shows that exceedance of at least one water-quality standard occurs in 63% of water well samples in NE Pennsylvania and 87% in the Western Area. In NE Pennsylvania, 10% of the samples exceeded one or more of the United States Environmental Protection Agency’s (USEPA) primary maximum contaminant levels (MCLs) for drinking-water supplies, 46.1% of the samples exceeded one or more of USEPA secondary maximum contaminant levels (SMCLs), and another 7% exceeded one or more of USEPA health advisory or regional screening levels for tap water.In the Western Area 8% of samples exceeded one or more MCLs, 65% exceeded one or more SMCLs, and 15% exceeded one or more health advisory or regional screening levels for tap water. Chesapeake’s dataset, orders of magnitude larger than any in previously published literature, shows that water-quality exceedances relate to factors such: as where the sample occurs within the groundwater flow system, the natural groundwater chemical type (hydrochemical facies), the geologic unit producing the water, and/or the topographic position (valley versus upland). Our comparison of these results to historical groundwater data from NE Pennsylvania, which pre-dates most unconventional shale gas development, shows that the recent pre-drilling geochemical data is similar to historical data. We see no broad changes in variability of chemical quality in this large dataset to suggest any unusual salinization caused by possible release of produced waters from oil and gas operations, even after thousands of gas wells have been drilled among tens of thousands of domestic wells within the two areas studied. Our evaluation also agrees with early researchers such as Piper (1933) and Lohman (1939, 1937) who found that the saline waters in both areas underlie fresher groundwater. The saline water is naturally-occurring connate brine or salt water which has not been flushed by circulating meteoric water; rather than vertical migration of salt water from deep strata such as the Marcellus shale as suggested by Warner et al. (2012). Elevated metals concentrations, particularly iron and manganese, partly relate to sample turbidity; dissolved metals would provide a more accurate measurement of metals in shallow groundwater than does the total metals analysis typically required by regulations.

Critical review and rethinking of USEPA secondary standards for maintaining organoleptic quality of drinking water.

Consumers assess their tap water primarily by its taste, odor, and appearance. Starting in 1979, USEPA promulgated Secondary Maximum Contaminant Levels (SMCLs) as guidance for contaminants with organoleptic effects and also to maintain consumers’ confidence in tap water. This review assesses the basis for the 15 SMCLs (aluminum, chloride, color, copper, corrosivity, fluoride, foaming agents, iron, manganese, odor, pH, silver, sulfate, total dissolved solids, zinc) and summarizes advances in scientific knowledge since their promulgation. SMCLs for aluminum, color, pH, silver, sulfate, total dissolved solids, and zinc are appropriate at current values and remain consistent with sensory science literature. Recent advances in sensory and health sciences indicate that SMCLs for chloride, copper, fluoride, iron, and manganese are too high to minimize organoleptic effects. The SMCLs for corrosivity and foaming agents may be outdated. The SMCL for odor requires rethinking as the test does not correlate with consumer complaints. Since current stresses on source and treated waters include chemical spills, algal blooms, and increased salinization, organoleptic episodes that negatively impact consumer confidence and perception of tap water still occur and may increase. Thus, adherence to SMCLs can help maintain production of palatable water along with consumers’ confidence in their water providers.

Association between arsenic, cadmium, manganese, and lead levels in private wells and birth defects prevalence in North Carolina: a semi-ecologic study.

BackgroundToxic metals including arsenic, cadmium, manganese, and lead are known human developmental toxicants that are able to cross the placental barrier from mother to fetus. In this population-based study, we assess the association between metal concentrations in private well water and birth defect prevalence in North Carolina.MethodsA semi-ecologic study was conducted including 20,151 infants born between 2003 and 2008 with selected birth defects (cases) identified by the North Carolina Birth Defects Monitoring Program, and 668,381 non-malformed infants (controls). Maternal residences at delivery and over 10,000 well locations measured for metals by the North Carolina Division of Public Health were geocoded. The average level of each metal was calculated among wells sampled within North Carolina census tracts. Individual exposure was assigned as the average metal level of the census tract that contained the geocoded maternal residence. Prevalence ratios (PR) with 95% confidence intervals (CI) were calculated to estimate the association between the prevalence of birth defects in the highest category (≥90th percentile) of average census tract metal levels and compared to the lowest category (≤50th percentile).ResultsStatewide, private well metal levels exceeded the EPA Maximum Contaminant Level (MCL) or secondary MCL for arsenic, cadmium, manganese, and lead in 2.4, 0.1, 20.5, and 3.1 percent of wells tested. Elevated manganese levels were statistically significantly associated with a higher prevalence of conotruncal heart defects (PR: 1.6 95% CI: 1.1-2.5).ConclusionsThese findings suggest an ecologic association between higher manganese concentrations in drinking water and the prevalence of conotruncal heart defects.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2458-14-955) contains supplementary material, which is available to authorized users.