Selective pressure on microbial communities in a drinking water aquifer - Geochemical parameters vs. micropollutants

Groundwater quality is crucial for drinking water production, but groundwater resources are increasingly threatened by contamination with pesticides. As pesticides often occur at micropollutant concentrations, they are unattractive carbon sources for microorganisms and typically remain recalcitrant. Exploring microbial communities in aquifers used for drinking water production is an essential first step towards understanding the fate of micropollutants in groundwater. In this study, we investigated the interaction between groundwater geochemistry, pesticide presence, and microbial communities in an aquifer used for drinking water production. Two groundwater monitoring wells in The Netherlands were sampled in 2014, 2015, and 2016. In both wells, water was sampled from five discrete depths ranging from 13 to 54 m and was analyzed for geochemical parameters, pesticide concentrations and microbial community composition using 16S rRNA gene sequencing and qPCR. Groundwater geochemistry was stable throughout the study period and pesticides were heterogeneously distributed at low concentrations (μg L^-1 range). Microbial community composition was also stable throughout the sampling period. Integration of a unique dataset of chemical and microbial data showed that geochemical parameters and to a lesser extent pesticides exerted selective pressure on microbial communities. Microbial communities in both wells showed similar composition in the deeper aquifer, where pumping results in horizontal flow. This study provides insight into groundwater parameters that shape microbial community composition. This information can contribute to the future implementation of remediation technologies to guarantee safe drinking water production.

Quantifying Regional Methane Emissions in the New Mexico Permian Basin with a Comprehensive Aerial Survey

Limiting emissions of climate-warming methane from oil and gas (O&G) is a major opportunity for short-term climate benefits. We deploy a basin-wide airborne survey of O&G extraction and transportation activities in the New Mexico Permian Basin, spanning 35 923 km², 26 292 active wells, and over 15 000 km of natural gas pipelines using an independently validated hyperspectral methane point source detection and quantification system. The airborne survey repeatedly visited over 90% of the active wells in the survey region throughout October 2018 to January 2020, totaling approximately 98 000 well site visits. We estimate total O&G methane emissions in this area at 194 (+72/-68, 95% CI) metric tonnes per hour (t/h), or 9.4% (+3.5%/-3.3%) of gross gas production. 50% of observed emissions come from large emission sources with persistence-averaged emission rates over 308 kg/h. The fact that a large sample size is required to characterize the heavy tail of the distribution emphasizes the importance of capturing low-probability, high-consequence events through basin-wide surveys when estimating regional O&G methane emissions.

Private Well Testing in Peri-Urban African-American Communities Lacking Access to Regulated Municipal Drinking Water: A Mental Models Approach to Risk Communication

Majority African-American neighborhoods on the edges of North Carolina municipalities are less likely than white peri-urban neighborhoods to be served by a community system regulated under the Safe Drinking Water Act. These households rely on unregulated private wells, which are at much higher risk of contamination than neighboring community water supplies. Yet, risk awareness of consuming well water is low, and no prior research has tested risk communication interventions for these communities. We present a randomized-controlled trial of an oversized postcard to promote water testing among this audience. The postcard design followed the mental models approach to risk communication. To our knowledge, this is the first U.S. randomized-controlled trial of a mailed communication to promote water testing in any audience and one of few trials of the mental models approach. We evaluated the postcard's effects on self-reported water testing with and without a free water test offer (vs. no-intervention control) via a survey mailed one month after the interventions. The combined communication and free test doubled the odds of self-reported water testing, compared to the control group (p = 0.046). It increased the odds of testing by 65%, compared to the free test alone. Recall of receiving a postcard about water testing increased the odds of self-reported testing twelve-fold (p < 0.001). Although these results suggest that targeted risk information delivered by mail can promote water testing when paired with a free test, the mechanism remains unclear. Additional research on beliefs influencing perceptions about well water may yield interventions that are even more effective.

Potential effects on groundwater quality associated with infiltrating stormwater through dry wells for aquifer recharge

Dry wells (gravity-fed infiltration wells) have frequently been used to recharge aquifers with stormwater, especially in urban areas, as well as manage flood risk and reduce surface water body contamination from stormwater pollutants. However, only limited assessment of their potential adverse impacts on groundwater quality exists. Dry well recharge can bypass significant portions of the filtering-capacity of the vadose zone. Stormwater and groundwater monitoring data and analysis of transport of a wide range of historic and current-use stormwater chemicals of concern is lacking. To address these gaps, two dry wells were constructed with vegetated and structural pretreatment features to assess the likelihood of stormwater contaminants reaching the aquifer. We monitored, assessed, and compared the presence of contaminants in stormwater to water quality in the vadose zone and shallow groundwater after it passed through the dry well. The dry wells were installed at a suburban residential and at a suburban commercial site. The selected sites were overlying a regional, unconsolidated, and highly heterogeneous alluvial aquifer system. Stormwater, vadose zone, and groundwater samples were collected during five storms and analyzed for over 200 contaminants of concern. Relatively few contaminants were detected in stormwater, generally at low concentrations. Prior to stormwater entering the dry well, 50-65% of contaminants were removed by vegetated pretreatment. In groundwater, metals such as aluminum and iron were detected at similar concentrations in both upgradient and downgradient wells, suggesting the source of these metals was not dry well effluent. Naturally occurring metals such as chromium and arsenic were not detected in stormwater but were found at elevated concentrations in groundwater. A modeling assessment suggests that the travel time of metals and hydrophobic organic contaminants to the water table at these sites ranges from years to centuries, whereas water soluble pesticides would likely reach the water table within days to months. The modeling assessment also showed that more vulnerable sites with higher fraction of alluvial sands would have much shorter contaminant travel times. However, none of the contaminants assessed reached concentrations that pose a risk to human health across the scenarios considered. No evidence was found, either through direct measurements or vadose zone modeling, that contaminants present in suburban stormwater degraded or would degrade groundwater quality at the studied sites and site conditions. Future work is needed to address emerging contaminants of concern.

Hydrological components of groundwater recharge in leaky aquifers adjacent to semipervious streambank: analytical study

Groundwater resources can be artificially augmented by managed aquifer recharge especially in arid and semi-arid areas. Unlike most of the existing results which focus only on impervious aquifer base and assume perfect hydraulic connection between aquifer and adjacent stream, the present study addresses the recharge process in a more realistic case of leaky aquifer interacting with semipervious streambank. The mathematical model relies on 2D linearized Boussinesq equation with Robin boundary condition accounting for hydraulic resistance owing to semiperviousness of the streambed. The method of Green's function offers an integral representation of hydraulic head in semi-infinite aquifer domain in response to time-varying recharge from a rectangular basin. Hydrological components of groundwater recharge are derived taking into account volumetric rates of leakage, mound storage, and outflow to adjacent stream. Hypothetical test cases illustrate how sum of these components exactly counterbalances the volumetric rate of recharge received by the aquifer at each instant of time, and this is in full conformity with the expected mass balance at aquifer scale. The most influential parameters affecting the model outputs are identified through sensitivity analysis. Furthermore, interaction of pumping wells with groundwater mound is examined. Performance of the present results is assessed against numerical counterparts from finite element method, and extremely good agreement is found for temporal mound peaks.

Assessing cumulative water impacts from shale oil and gas production: Permian Basin case study

Quantifying impacts of unconventional oil and gas production on water resources and aquatic habitats is critical for developing management approaches for mitigation. The study objective was to evaluate impacts of oil and gas production on groundwater and surface water and assess approaches to reduce these impacts using the Permian Basin as a case study. Water demand for hydraulic fracturing (HF) was compared to water supplies. We also examined contamination from surface spills. Results show that water demand for HF peaked in 2019, representing ~35% of water use in non-mining sectors. Most HF water was sourced from aquifers with ~1,100 wells drilled in the Ogallala aquifer in 2019. The State monitoring network did not show regional groundwater depletion but was not sufficiently dense to address local impacts. Groundwater depletion is more critical in the western Delaware Basin within the Permian Basin because groundwater is connected to large flowing springs (e.g. San Solomon Springs) and to the Pecos River which has total dissolved solids ranging from ~3000 to 14,000 mg/L. Most produced water (70-80%) is disposed in shallow geologic units that could result in overpressuring and potential groundwater contamination from leakage through ~70,000 abandoned oil wells, including orphaned wells. While there is little evidence of leakage from abandoned wells, the state monitoring system was not designed to assess leakage from these wells. Oil spill counts totaled ~11,000 in the Permian (2009-2018). Approaches to mitigating adverse impacts on water management include reuse of PW for HF; however, there is an excess of PW in the Delaware Basin. Treatment and reuse in other sectors outside of oil and gas are also possibilities. Data gaps include reporting of water sources for HF, PW quality data required for assessing treatment and reuse, subsurface disposal capacity for accommodating PW, and spills from PW in Texas.

Development and application of a contaminant transport model for groundwater remediation and reservoir protection: a case study from India

The upper Kodaganar basin, located in Dindigul district of Tamil Nadu, India, is composed of hard rock terrain. Groundwater is the major source of domestic and irrigation needs and it is being contaminated by tannery wastewater that is discharged into the nearby Sengulam Lake. The main aim of this work was to develop a contaminant transport model using the total dissolved solids (TDS) concentration of groundwater measured in the basin. The model was developed to predict the fate of contaminant in the aquifer. The TDS concentrations in the wells ranged from 249 to 20,120 mg/L, wherein extremely high values were observed in some of the severely contaminated wells. Three scenarios were proposed to predict the fate of the contaminant and to mitigate the effect of contaminant on groundwater receptors for the year 2020: scenario I: developed with the existing discharge conditions; scenario II: developed with discharge as per the standards; scenario III: developed with zero discharge. The results of this study showed that scenario III reduced the contaminated area from 12 km² to 6 km². The reduction in area for different concentration contours, namely 2000 mg/L, 5000 mg/L, 10,000 mg/L, and 15,000 mg/L, was 2 km², 0.5 km², 0.2 km², and 0.1 km², respectively, and the groundwater remediation was expected to take 2050 years. Hence, there is an urgent need for the application of clean and resource efficient technologies in process industries, and the implementation of suitable wastewater treatment technologies to prevent ground water pollution in the region.

Geochemistry and Provenance of Springs in a Baja California Sur Mountain Catchment

Fractured rock aquifers cover much of Earth's surface and are important mountain sites for groundwater recharge but are poorly understood. To investigate groundwater systematics of a fractured-dominated aquifer in Baja California Sur, Mexico, we examined the spatial patterns of aquifer recharge and connectivity using the geochemistry of springs. We evaluate a range of geochemical data within the context of two endmember hypotheses describing spatial recharge patterns and fracture connectivity. Hypothesis 1 is that the aquifer system is segmented, and springs are fed by local recharge. Hypothesis 2 is that the aquifer system is well connected, with dominant recharge occurring in the higher elevations. The study site is a small <15 km² catchment. Thirty-four distinct springs and two wells were identified in the study area, and 24 of these sites were sampled for geochemical analyses along an elevation gradient and canyon transect. These analyses included major ion composition, trace element and strontium isotopes, δ¹⁸ O and δ² H isotopes, radiocarbon, and tritium. δ¹⁸ O and δ² H isotopes suggest that the precipitation feeding the groundwater system has at least two distinct sources. Carbon isotopes showed a change along the canyon transect, suggesting that shorter flowpaths feed springs in the top of the transect, and longer flowpaths discharge near the bottom. Geochemical interpretations support a combination of the two proposed hypotheses. Understanding of the connectivity and provenance of these springs is significant as they are the primary source of water for the communities that inhabit this region and may be impacted by changes in recharge and use.

Free-Phase Gas Detection in Groundwater Wells via Water Pressure and Continuous Field Parameters

Detection of free-phase gas (FPG) in groundwater wells is critical for accurate assessment of dissolved gas concentrations and the occurrence of FPG in the subsurface, with consequent implications for understanding groundwater contamination and greenhouse gas emissions. However, identifying FPG is challenging during routine groundwater monitoring and there is poor agreement on the best approach to detect the occurrence of FPG in groundwater. In this study, laboratory experiments in a water column were designed to mimic nonflowing and flowing conditions in a groundwater well to evaluate how the presence of FPG affects water pressure and commonly used continuous field parameters. The laboratory results were extrapolated to interpret field data at an abandoned exploration well with episodic release of free-gas CO₂ . The FPG effect on water pressure varied between flowing and nonflowing wells, and depending on whether the FPG was above or below the sensor. Electrical conductivity values were decreased and/or behaved erratically when FPG was present in the water column. Findings from this study have shown that the combined measurement of water pressure, electrical conductivity, and total dissolved gas pressure can provide information about the occurrence of FPG in groundwater wells. Measurement of these parameters at different depths can also provide information about relative depths and amounts of FPG within the well water column. This approach can be used for long-term monitoring of groundwater gases, managing gas-locking in production wells with gassy groundwater, and measuring fugitive greenhouse gas emissions from groundwater wells.

Commingled Fluids in Abandoned Boreholes: Proximity Analysis of a Hidden Liability

The interactions between old abandoned wellbores of suspect well integrity with hydraulic fracturing (HF), enhanced oil recovery (EOR), or salt water disposal (SWD) operations can result in upward leakage of deep aqueous liquids into overlying aquifers. This potential for upward fluid migration is largely unquantified as monitoring abandoned wells is rarely done, and leakage may go unnoticed especially when in deeper aquifers. This study performs a proximity analysis between old abandoned wells and HF, EOR, and SWD wells, and identifies commingled old abandoned wellbores, which are those wells where groundwater may flow from one aquifer to one or more other aquifers, to identify the locations with the greatest potential for upward aqueous fluid migration at three study sites in the Western Canadian Sedimentary Basin. Our analysis indicates that at all three study sites there are several locations where HF, EOR, or SWD operations are located in close proximity to a given old abandoned well. Much of this overlap occurs in formations above typically produced hydrocarbon reservoirs but below exploited potable aquifers, otherwise known as the intermediate zone, which is often connected between abandonment plugs in old abandoned wells. Information on the intermediate zone is often lacking, and this study suggests that unanticipated alterations to groundwater flow systems within the intermediate zone may be occurring. Results indicate the need for more field-based research on the intermediate zone.

Abnormal groundwater levels and microbial communities in the Pohang Enhanced Geothermal System site wells pre- and post-Mw 5.5 earthquake in Korea

In this study, two geothermal wells (PX-1 and PX-2) exhibiting abnormal groundwater levels and microbial communities were examined at the Enhanced Geothermal System site before and after the Pohang earthquake (November 2017). Furthermore, the EXP-1 well level, water temperature, microbial communities and their association with earthquakes, as well as the possibility of future earthquakes were explored. The primary objectives of this research were to: (1) perform correlation and cluster analyses of hydrophysical parameters for earthquakes using next-generation sequencing; (2) analyze pre-, co-, and post-seismic changes in groundwater levels, temperatures, and microbial communities; and (3) further assess the analyzed results of the post-earthquake changes in the groundwater levels and temperatures to interpret their implications. Although the pre-earthquake water levels in the three wells were unknown, their depth-to-water levels post-earthquake ranged from 50.33-98.20 m, 570.91-735.00 m, and 47.70-56.04 m for wells PX-1 (depth 4362 m), PX-2 (4348 m), and EXP-1 (180 m), respectively. In particular, the water levels of PX-2 were abnormally low compared with the surrounding area. Moreover, the geothermal wells demonstrated unstable microbial communities prior to the earthquake. However, while the microbial communities of PX-1 recovered relatively quickly post-earthquake, those of PX-2 failed to stabilize even within two years after the earthquake. Thus, it was inferred here that the PX-2 well is more closely related to seismic activity, the effects of which can still be seen. Accordingly, it is important that PX-2 is continuously monitored until June 2024, the minimum period predicted for the water levels to reach stability.

Multi-objective optimal model for sustainable management of groundwater resources in an arid and semiarid area using a coupled optimization-simulation modeling

Excessive exploitation of groundwater resources can increase the concentration of pollutants in addition to the progressive drawdown of groundwater table. In this research, to achieve aquifer quantitative and qualitative (QQ) sustainable development, an optimal scenario for withdrawing from operation wells is proposed. At the first step, the aquifer QQ simulation was carried out with the GMS model. The developed code in MATLAB2018b in the second step provides the link between the simulation and the NSGA-II optimization tools. In the third step, a multi-objective coupled optimization-simulation model based on GMS and NSGA-II developed. Finally, optimal scenario was chosen based on applying the multiple criteria decision-making (MCDM) and Berda Aggregation Method (BAM). The results show that reducing the current withdrawal rate to 51.55% can establish the QQ stability of the aquifer. This decrease in groundwater abstraction has led to a 4.6 m increase in groundwater level (GWL) over 3 years (average 19 cm per month). The spatial and temporal distribution of nitrate concentration after applying the optimal discharge of wells shows the nitrate concentration in central and eastern parts of the aquifer has greatly reduced. Developed sustainable management model can be used to provide a real operation planning of wells to improvement of the QQ status of groundwater in each unconfined aquifer.

Staged energy and water quality optimization for large water distribution systems

Simultaneous optimization of energy and water quality in real-time large-sized water distribution systems is a daunting task for water suppliers. The complexity of energy optimization increases with a large number of pipes, scheduling of several pumps, and adjustments of tanks' water levels. Most of the simultaneous energy and water quality optimization approaches evaluate small (or hypothetical) networks or compromise water quality. In the proposed staged approach, Stage 1 uses a risk-based approach to optimally locate the chlorine boosters in a large distribution system based on residual chlorine failures and the associated consequences in different land uses of the service area. Integrating EPANET and CPLEX software, Stage 2 uses mixed integer goal programming for optimizing the day-ahead pump scheduling. The objective function minimizes the pumping energy cost as well as the undesirable deviations from goal constraints, such as expected water demand. Stage 3 evaluates the combined hydraulics and water quality performances at the network level. The implementation of the proposed approach on a real-time large-sized network of Al-Khobar City in Saudi Arabia, with 44 groundwater wells, 12 reservoirs, 2 storage tanks, 191 mains, 141 junctions, and 17 pumps, illustrated the practicality of the framework. Simulating the network with an optimal pumping schedule and chlorine boosters' locations shows a 40% improvement in water quality performance, desired hydraulics performance with optimal pump scheduling, and an average 20% energy cost reduction compared to the normal (unoptimized) base case scenario.

The variable presence of Leptospira in the environment; an epidemiological explanation based on serial analysis of water samples

Human leptospirosis involves the classic epidemiological triad (agent, host and environment); hence the investigations should include the knowledge on Leptospira within the animals and the environment. The objectives of this study are to explore the abundance of Leptospira in different climate zones of Sri Lanka and to describe the presence of Leptospira in the same water source at serial time points. First, water and soil samples were collected from different parts of Sri Lanka (Component-1); second, water sampling continued only in the dry zone (Component-2). Finally, serial water sampling from ten open wells was performed at five different time points (Component-3). Quantitative PCR of water and metagenomic sequencing of soil were performed to detect Leptospira. Three replicates for each sample were used for PCR testing, and positive result of two or more replicates was defined as 'strongly positive,' and one positive replicate was defined as positive. In the water and soil sample analysis in the whole country (Component-1), two out of 12 water sites were positive, and both were situated in the wet zone. Very small quantities of the genus Leptospira were detected by 16 amplicon analysis of soil in all 11 sites. In the dry zone water sample analysis (Component-2), only samples from 6 out of 26 sites were positive, of which one site was strongly positive. In the serial sample analysis (Component-3), Six, five, four, five, and six wells were positive in serial measurements. All wells were positive for at least one time point, while only one well was positive for all five time points. Proximity to the tank and greater distances from the main road were associated with strong positive results for Leptospira (P<0.05). The presence of Leptospira was not consistent, indicating the variable abundance of Leptospira in the natural environment. This intermittent nature of positivity could be explained by the repetitive contamination by animal urine.

Optimization of well field management to mitigate groundwater contamination using a simulation model and evolutionary algorithm

Groundwater represents the most important available freshwater reserves and is of critical importance to global water and food security. Old environmental burdens that have led to the spread of contaminants in groundwater limit its use, thus interventions to mitigate contamination must often be carried out to ensure a safe drinking water supply. This study presents the optimization of well field management designs to reduce the desethylatrazine (DEA) concentration in the deep wells of the Brest Water Works (Central Slovenia). It investigates artificial recharge by injection wells using water from the nearby river and elaborates five well field management scenarios prioritizing different objectives. A multi-objective simulation-optimization framework was developed. A transient groundwater flow and solute transport model was applied to simulate the effects of the proposed recharge and pumping regimes. The shuffled complex evolution method was used to identify optimal values of well field management variables (location of injection well(s), minimum required injection rate, maximum pumping rate from production well) in the proposed scenarios. Model simulations showed that optimized well field management designs can significantly reduce DEA concentration in production wells (below 0.05 μg/L), assure compliance with water quality standards with (26%) reduced injection rate, and, with the implementation of two injection wells, achieve lower DEA concentration and higher pumping rate (up to 27 L/s). The optimization solutions depend on the defined well field management priorities and reveal a trade-off between the objectives (reduction of DEA concentration, increase of pumping rate, and reduction of injection rate). The impact of management variables on mitigation efficiency is not uniform and largely depends on the location of the injection well(s), which increases the complexity of mitigation design. The study has shown that the presented approach can be efficiently used for finding optimal mitigation designs and supporting water managers with information for planning mitigation measures.

Groundwater in Southern Vietnam: Understanding geochemical processes to better preserve the critical water resource

A thorough understanding of groundwater geochemical characteristics and dominant hydro(bio)geochemical processes in the aquifers is valuable for sustainable groundwater protection. With this respect, this study provides a comprehensive assessment of hydrogeochemical characteristics of groundwater in sedimentary aquifers of the Southern region of Vietnam. The dataset comprised 291 water samples collected in rainy and dry seasons from 155 wells, and their chemical compositions of dissolved ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃^-, Cl^-, SO₄^2-, NO₃^-, NH₄⁺, Fe, total dissolved solids) and pH. We calculated the groundwater quality index to determine the suitability of groundwater for drinking purposes. Accordingly, about 47% of groundwater samples range from poor to unsuitable quality for drinking purposes, in which total dissolved solid (TDS) and high iron concentrations are primary factors. We also examined hydrogeochemical characteristics by multivariate statistical analyses (Hierarchical Cluster Analysis and Principal Component Analysis). The results demonstrated four groups of water: fresh groundwater (TDS < 1 g/L) in the highland (Group 1), lowland fresh-to-saline groundwater (2a), lowland saline groundwater (2b), and lowland saline/acidic groundwater (2c). Although the highland area is currently not impacted by salinization, the contamination by nitrate and chloride associated with a dense urban population and agricultural practices is deteriorating its fresh groundwater resources. On the other hand, the lowland area of Southern Vietnam is highly vulnerable to seawater intrusion (groups 2b and 2c). Only 34% out of 191 samples collected in the lowland area of southern Vietnam remained fresh. In this light, this study depicted the specific geographical location for various groundwater groups in Southern Vietnam. This finding is significant to assist water scientists and decision-makers in implementing targetted groundwater management measures as prevention and protection strategies should be tailored to groundwater geochemical characteristics and the dominant hydro(bio)geochemical processes.

Machine learning predictions of nitrate in groundwater used for drinking supply in the conterminous United States

Groundwater is an important source of drinking water supplies in the conterminous United State (CONUS), and presence of high nitrate concentrations may limit usability of groundwater in some areas because of the potential negative health effects. Prediction of locations of high nitrate groundwater is needed to focus mitigation and relief efforts. A three-dimensional extreme gradient boosting (XGB) machine learning model was developed to predict the distribution of nitrate. Nitrate was predicted at a 1 km resolution for two drinking water zones, each of variable depth, one for domestic supply and one for public supply. The model used measured nitrate concentrations from 12,082 wells and included predictor variables representing well characteristics, hydrologic conditions, soil type, geology, land use, climate, and nitrogen inputs. Predictor variables derived from empirical or numerical process-based models were also included to integrate information on controlling processes and conditions. The model provided accurate estimates at national and regional scales: the training (R² of 0.83) and hold-out (R² of 0.49) data fits compared favorably to previous studies. Predicted nitrate concentrations were less than 1 mg/L across most of the CONUS. Nationally, well depth, soil and climate characteristics, and the absence of developed land use were among the most influential explanatory factors. Only 1% of the area in either water supply zone had predicted nitrate concentrations greater than 10 mg/L; however, about 1.4 M people depend on groundwater for their drinking supplies in those areas. Predicted high concentrations of nitrate were most prevalent in the central CONUS. In areas of predicted high nitrate concentration, applied manure, farm fertilizer, and agricultural land use were influential predictor variables. This work represents the first application of XGB to a three-dimensional national-scale groundwater quality model and provides a significant milestone in the efforts to document nitrate in groundwater across the CONUS.

User experience of point-of-use water treatment for private wells in North Carolina: Implications for outreach and well stewardship

Private well users are potentially exposed to a range of chemical contaminants through their drinking water. Point-of-use (POU) water treatment represents one potential solution to reduce harmful exposures through well water, but well users frequently do not adopt household treatment even if they learn their water is contaminated. This study elucidates the experiences, perceptions, and beliefs of 17 households on private wells in North Carolina that participated in a pilot-scale POU water treatment intervention to better understand the drivers and barriers of POU treatment adoption among well users. The intervention consisted of an under-sink activated carbon block POU filter designed to remove lead and two long-chain perfluoroalkyl acids. Filter effluents and influents were tested monthly for eight months. Questionnaires administered before and after the intervention showed a significant decrease in participants' perceived vulnerability to well water contamination, with 77% feeling vulnerable to poor well water quality before, compared to 23% after the filter was installed. However, the POU filters did not fully eliminate feelings of water insecurity (for example, concerns about exposure to contaminants when bathing remained). Lack of knowledge and skills associated with installing and maintaining POU treatment were important barriers to adoption for some well users. Perceptions of POU treatment were also significantly correlated with the intent to implement other well stewardship behaviors such as well water testing. The results highlight the need for strengthened outreach and support programs that provide technical assistance, education, and financial support for households relying on private wells.

Populations using public-supply groundwater in the conterminous U.S. 2010; Identifying the wells, hydrogeologic regions, and hydrogeologic mapping units

Most Americans receive their drinking water from publicly supplied sources, a large portion of it from groundwater. Mapping these populations consistently and at a high resolution is important for understanding where the resource is used and needs to be protected. The results show that 269 million people are supplied by public supply, 107 million are supplied by groundwater and 162 million are supplied by surface water. The population using public supply drinking water was mapped in two ways: the census enhanced method (CEM) evenly distributes the population across populated census blocks, and the urban land-use enhanced method (ULUEM) distributes the population only to certain urban land use designations. In addition, a two-dimensional polygon dataset was created for the conterminous U.S. that identifies 177 unique Hydrogeologic Mapping Units (HMUs) with similar hydrogeologic characteristics. The HMUs do not overlap, but they can delineate areas where stacked hydrogeologic regions (HRs) contribute drinking water from below the surface. HRs are waterbearing geologic regions identified as either a principal aquifers (PA) or secondary hydrogeologic regions (SHR). Within each HMU, the wells were used to determine the proportion of each HR that is providing groundwater to the HMU. In 63% of the HMUs, a single HR is providing water to the public supply wells located within it, while the rest of the HMUs show that the wells are tapping up to a maximum of four stacked HRs. In total, groundwater from 108 HRs provide drinking water for public supply, six of which provide more than 50% of the groundwater used for public supply drinking water. The aquifer serving the largest number of equivalent people (>17 million) is the glacial aquifer. The HR providing the greatest number of people per km² is the Biscayne aquifer in Florida at nearly 453 people per km².

Uranium isotopes in groundwater in Ho Chi Minh City and related issues: Health risks, environmental effects, and mitigation methods

Groundwater is regularly used for many purposes, such as drinking and agricultural irrigation systems. Still, it contains high levels of radionuclides (e.g., ²³⁸U, ²³²Th, and ²²⁶Ra) that are potentially hazardous to humans and the environment. In this study, activity concentrations of uranium isotopes were analyzed in 15 groundwater samples taken from 15 bored wells in Thu Duc district, Ho Chi Minh City, Vietnam. Environmental effects of the irrigation system with groundwater on agricultural soil in the study area were assessed by models. It was found that the activity concentrations of ²³⁸U and ²³⁴U in groundwater samples were in the ranges of (13.5-268.7) mBq l^-1 and (20.2-438.3) mBq l^-1, respectively. The ratio ²³⁴U/²³⁸U values were ranged from 1.12 to 2, with an average value of 1.44. Based on the model prediction, 25 years irrigation with the groundwater can inject 94.8 Bq both uranium isotopes in 1 kg topsoil. For investigated groundwater samples, the proposed removal method using K₂FeO₄ removed 74.28% and 81.04% for ²³⁴U and ²³⁸U, respectively.

Pharmaceuticals and personal care products in aquatic environments and their removal by algae-based systems

The consumption of pharmaceuticals and personal care products (PPCPs) has been widely increasing, yet up to 90-95% of PPCPs consumed by human are excreted unmetabolized. Moreover, the most of PPCPs cannot be fully removed by wastewater treatment plants (WWTPs), which release PPCPs to natural water bodies, affecting aquatic ecosystems and potentially humans. This study sought to review the occurrence of PPCPs in natural water bodies globally, and assess the effects of important factors on the fluxes of pollutants into receiving waterways. The highest ibuprofen concentration (3738 ng/L) in tap water was reported in Nigeria, and the highest naproxen concentration (37,700 ng/L) was reported in groundwater wells in Penn State, USA. Moreover, the PPCPs have affected aquatic organisms such as fish. For instance, up to 24.4 × 10³ ng/g of atenolol was detected in P. lineatus. Amongst different technologies to eliminate PPCPs, algae-based systems are environmentally friendly and effective because of the photosynthetic ability of algae to absorb CO₂ and their flexibility to grow in different wastewater. Up to 99% of triclosan and less than 10% of trimethoprim were removed by Nannochloris sp., green algae. Moreover, variable concentrations of PPCPs might adversely affect the growth and production of algae. The exposure of algae to high concentrations of PPCPs can reduce the content of chlorophyll and protein due to producing reactive oxygen species (ROS), and affecting expression of some genes in chlorophyll (rbcL, psbA, psaB and psbc).

A multi-isotopic evaluation of groundwater in a rapidly developing area and implications for water management in hyper-arid regions

Management of water resources in hyper-arid areas faces vital challenges in a global climate change context. Consequently, understanding the effects on groundwater sources can help mitigating the problem of water scarcity and the negative impact of human intervention on the environment. A case study area in the hyper-arid climate of the United Arab Emirates, was tackled here with the focus on applying stable isotopes as tools for evaluating groundwater sources and quality assessment. The results of major ions indicate variable increase in groundwater salinity moving away from Al Hajar Mountains recharge areas to the discharge areas (Arabian Gulf coast). The data of stable isotopes (δ¹⁸O_H2O, δ²H_H2O, δ¹⁸O_NO3, δ¹⁵N_NO3, δ¹⁸O_SO4, δ³⁴S_SO4, δ¹¹B) suggest impact of paleo-groundwater in the abstractions of the wells nearest to the coast. Nitrate isotopes indicate farming activities sources that can be masked due to the contribution from the nitrate-poor paleo-groundwater. Nitrate reduction processes are expected near to the recharge front. Sulphate and boron isotopes further suggest that influence of ancient evaporite dissolution in salinization. Management efforts should be focused on the diffuse sources of quality mitigations that can be vital in fingerprinting local and regional (transboundary) effects.

Spatial and temporal dynamics and potential pathogenicity of fecal coliforms in coastal shallow groundwater wells

Access to water through shallow groundwater wells is a common practice in coastal settlements. This, coupled with a lack of planning for wastewater disposal promotes fecal contamination of groundwater and poses a threat to human health. Here, the spatial and temporal dynamics of groundwater fecal contamination was evaluated during summer and winter (2013 and 2014) in a coastal protected area having a high touristic relevance (Cabo Polonio, Uruguay). Fecal coliforms (FC) abundance in groundwater was significantly higher during summer, related to an influx of ~ 1000 tourists per day. A significant spatial autocorrelation was found in 2014, when the abundance of FC in a well was influenced by its three nearest wells (Moran and Geary tests). The applied statistical models (mixed models) indicated that total phosphorus and organic matter were the variables significantly explaining FC abundance. The risk for human health was estimated using groundwater-extracted DNA and qPCR of genes encoding for E. coli virulence factors (stx1, stx2, and eae). Potential Shiga toxin-producing enteropathogenic and enterohemorrhagic pathotypes were detected, even at FC abundances ≤ 1 CFU (100 mL^-1). Moreover, we found that contaminated groundwater reached the beach, being the presence of FC in sand detected even in winter and showing its highest frequency nearby groundwater wells consistently having high FC abundance (hot spots). Altogether, the results show that fecal contamination of shallow groundwater in Cabo Polonio involves a risk for human health that intensifies during summer (associated to a significant increase of tourists). This contamination also impacts the beach, where FC can remain through the whole year.

Inequities in Drinking Water Quality Among Domestic Well Communities and Community Water Systems, California, 2011‒2019

Objectives. To evaluate universal access to clean drinking water by characterizing relationships between community sociodemographics and water contaminants in California domestic well areas (DWAs) and community water systems (CWSs). Methods. We integrated domestic well locations, CWS service boundaries, residential parcels, building footprints, and 2013-2017 American Community Survey data to estimate sociodemographic characteristics for DWAs and CWSs statewide. We derived mean drinking and groundwater contaminant concentrations of arsenic, nitrate, and hexavalent chromium (Cr[VI]) between 2011 and 2019 and used multivariate models to estimate relationships between sociodemographic variables and contaminant concentrations. Results. We estimated that more than 1.3 million Californians (3.4%) use domestic wells and more than 370 000 Californians rely on drinking water with average contaminant concentrations at or above regulatory standards for 1 or more of the contaminants considered. Higher proportions of people of color were associated with greater drinking water contamination. Conclusions. Poor water quality disproportionately impacts communities of color in California, with the highest estimated arsenic, nitrate, and Cr(VI) concentrations in areas of domestic well use. Domestic well communities must be included in efforts to achieve California's Human Right to Water. (Am J Public Health. 2022;112(1):88-97. https://doi.org/10.2105/AJPH.2021.306561).

Water leak control for the oil-producing wells using Downhole Water Sink Technology

Casing or tubing leaks cause unwanted water production from oil-producing wells. Many chemical and mechanic water control technologies can be used to solve this problem, including squeezing chemical shutoff fluids into the targeted zone or using plugs, cement, packers, patches to block the leakage. Although those methods are field-proven to be effective, the mechanical solutions may require well logs to detect the water entry point in the well. Chemical methods may present environment risks. In this study, an alternative method, Downhole Water Sink, is proposed to solve the problem of unwanted water production from a casing or tubing leak. The effectiveness of this method to control water production in a well with casing or tubing leaks is tested using the Hele-Shaw experimental model. The results show that this method can control unwanted water production via dynamic control of the pressure drawdown in the reservoir. From a technical standpoint, the advantage of this technology is that it eliminates the need to run logs to locate the water entry point and does not require chemical injection into the formation. From an environmental standpoint, this technology has the circular economy elements. Because the produced water in this technology contains little or no oil, it can be reused for reinjection into the reservoir for water flooding or pressure maintenance purposes. Therefore, a production-reinjection process to recycle the produced water is established to reduce the pollution caused by discharging the wastewater into the environment.