Drinking Water Wells Research Articles

Association between private drinking water wells and the incidence of Campylobacteriosis in Maryland: An ecological analysis using Foodborne Diseases Active Surveillance Network (FoodNet) data (2007–2016)

Campylobacter is a leading cause of bacterial foodborne illness in the United States. Campylobacter infections have most often been associated with food-related risk factors, such as the consumption of poultry and raw milk. Socioeconomic, agricultural and environmental factors, including drinking water source, can also influence the risk of campylobacteriosis. Approximately 19% of Maryland residents rely on private wells as their sole source of water. Given that the federal Safe Drinking Water Act does not regulate the water quality of private wells, these could be important non-foodborne transmission pathways for Campylobacter. To address this issue, data on the number of culture-confirmed cases of Campylobacter infection in Maryland between 2007 and 2016 were obtained from the Foodborne Diseases Active Surveillance Network. Cases were linked by zip code with data from the Maryland well permits registry, the 2010 U.S. Census, the 2016 American Community Survey, and the USDA Agricultural Census. Campylobacteriosis incidence rates and well prevalence were calculated by zip code. Negative binomial regression models were then constructed to evaluate the association between the prevalence of private wells, presence/absence of animal feeding operations and the incidence of campylobacteriosis across the physiographic provinces in Maryland. From 2007 to 2016, a total of 5746 cases of campylobacteriosis were reported in Maryland, and annual incidence rates ranged from 6.65 to 11.59 per 100,000 people. In our statewide analysis, a significant positive association was observed between well prevalence and increased campylobacteriosis incidence at the zip code level (Incidence Rate Ratio (IRR) = 1.35, 95% Confidence Interval (CI) = 1.11, 1.63). A significant positive association was also observed between well prevalence and increased campylobacteriosis incidence in the Appalachian and Coastal provinces of Maryland (IRR = 2.94, 95% CI = 1.11, 7.76 and IRR = 1.70, 95% CI = 1.25, 2.31, respectively). The presence of broiler chicken operations, increasing median age and percentage of residents living in poverty were also significantly associated with campylobacteriosis incidence at the zip code level in some physiographic provinces in Maryland. To our knowledge, these are the first US data to demonstrate an association between prevalence of private wells and campylobacteriosis incidence at the zip code level.

Micro- and nano-scale mineralogical characterization of Fe(II)-oxidizing bacterial stalks.

Neutrophilic, microaerobic Fe(II)-oxidizing bacteria (FeOB) from marine and freshwater environments are known to generate twisted ribbon-like organo-mineral stalks. These structures, which are extracellularly precipitated, are susceptible to chemical influences in the environment once synthesized. In this paper, we characterize the minerals associated with freshwater FeOB stalks in order to evaluate key organo-mineral mechanisms involved in biomineral formation. Micro-Raman spectroscopy and Field Emission Scanning Electron Microscopy revealed that FeOB isolated from drinking water wells in Sweden produced stalks with ferrihydrite, lepidocrocite and goethite as main mineral components. Based on our observations made by micro-Raman Spectroscopy, field emission scanning electron microscopy and scanning transmission electron microscope combined with electron energy-loss spectroscopy, we propose a model that describes the crystal-growth mechanism, the Fe-oxidation state, and the mineralogical state of the stalks, as well as the biogenic contribution to these features. Our study suggests that the main crystal-growth mechanism in stalks includes nanoparticle aggregation and dissolution/re-precipitation reactions, which are dominant near the organic exopolymeric material produced by the microorganism and in the peripheral region of the stalk, respectively.

On the conceptual complexity of non-point source management: impact of spatial variability

Abstract. Non-point source (NPS) pollution has degraded groundwater quality of unconsolidated sedimentary basins over many decades. Properly conceptualizing NPS pollution from the well scale to the regional scale leads to complex and expensive numerical models: key controlling factors of NPS pollution – recharge rate, leakage of pollutants, and soil and aquifer hydraulic properties – are spatially and, for recharge and pollutant leakage, temporally variable. This leads to high uncertainty in predicting well pollution. On the other hand, concentration levels of some key NPS contaminants (salinity, nitrate) vary within a limited range (< 2 orders of magnitude), and significant mixing occurs across the aquifer profile along the most critical compliance surface: drinking water wells with their extended vertical screen length. Given these two unique NPS contamination conditions, we here investigate the degree to which NPS travel time to wells and the NPS source area associated with an individual well can be appropriately captured, for practical applications, when spatiotemporally variable recharge, contaminant leakage rates, or hydraulic conductivity are represented through a sub-regionally homogenized parametrization. We employ a Monte Carlo-based stochastic framework to assess the impact of model homogenization on key management metrics for NPS contamination. Results indicate that travel time distributions are relatively insensitive to the spatial variability of recharge and contaminant loading, while capture zone and contaminant time series exhibit some sensitivity to source variability. In contrast, homogenization of aquifer heterogeneity significantly affects the uncertainty assessment of travel times and capture zone delineation. Surprisingly, the statistics of relevant NPS well concentrations (fast and intermediate travel times) are fairly well reproduced by a series of equivalent homogeneous aquifers, highlighting the dominant role of NPS solute mixing along well screens.

Isolation distance between municipal solid waste landfills and drinking water wells for bacteria attenuation and safe drinking

Groundwater pollution and human health risks caused by leachate leakage have become a worldwide environmental problem, and the harm and influence of bacteria in leachate have received increased attention. Setting the isolation distance between landfill sites and groundwater isolation targets is particularly important. Firstly, the intensity model of pollutant leakage source and solute transport model were established for the isolation of pathogenic Escherichia coli. Then, the migration, removal and reduction of bacteria in the aerated zone and ground were simulated. Finally, the isolation distance was calculated based on the acceptable water quality limits, and the influence of hydrogeological arameters was analyzed based on the parameter uncertainty. The results of this study suggest that the isolation distances vary widely ranging from 106 m–5.46 km in sand aquifers, 292 m–13.5 km in gravel aquifers and 2.4–58.7 km in coarse gravel aquifers. The gradient change of groundwater from 0.001 to 0.05 resulted in the isolation distance at the highest gradient position being 2–30 times greater than that at the lowest gradient position. There was a difference in the influence of the thickness of the vadose zone. For example, under the same conditions, with the increase of the thickness of the aeration zone, the isolation distance will be reduced by 1.5–5 times, or under the same thickness of the aeration zone, the isolation distance will be significantly shortened. Accordingly, this needs to be determined based on specific safety isolation requirements. In conclusion, this research has important guiding significance for the environmental safety assessment technology of municipal solid waste landfill.

3D inversion of MT data from northern Mexico for geothermal exploration using TEM data as constraints

San Felipe's area has geothermal surface manifestations such as hot springs and high temperature in drinking water wells. As a first stage of the geothermal exploration program, a regional geophysical survey has been carried out where 17 MT (Magnetotelluric) and TEM (Transient Electromagnetic) soundings were recorded along 4 different profiles. Both techniques were applied in the same spots and the TEM data are used to correct for static shift in MT data. Transient responses were measured from 1 to 70 ms, using a 50 x 50m2 single-loop configuration. MT signals were recorded with Metronix systems in the period range from 0.001 to 100 s. A robust processing scheme is applied to the MT time series and estimated Transfer Functions are appraised. The dimensionality analysis of MT data suggests a 1D and 3D subsurface structure. Thereby, a three-dimensional inversion of MT data is later carried out. The information obtained from the inversion modeling of TEM data is incorporated into the 3D MT inversion scheme. Thus, unconstrained and constrained inverse models are achieved and appraised. The preferred 3D inversion model is correlated to geological information of the survey area and a conductive structure is interpreted as a sedimentary basin at its shallow part and as a fault zone with geothermal fluids at depths >1.5 km.

History and Sources of Co-Occurring Pesticides in an Abstraction Well Unraveled by Age Distributions of Depth-Specific Groundwater Samples.

When groundwater-based drinking water supply becomes contaminated, the timing and source of contamination are obvious questions. However, contaminants often have diffuse sources and different contaminants may have different sources even in a single groundwater well, making these questions complicated to answer. Age dating of groundwater has been used to reconstruct contaminant travel times to wells; however, critics have highlighted that groundwater flow is often complex with mixing of groundwater of different ages. In drinking water wells, where water is typically abstracted from a large depth interval, such mixing is even more problematic. We present a way to overcome some of the obstacles in identifying the source and age of contaminants in drinking water wells by combining depth-specific sampling with age tracer modeling, particle tracking simulations, geological characterization, and contaminant properties. This multitool approach was applied to a drinking water well, where bentazon and dichlorprop contamination was found to have different pollutant sources and release histories, even though both pesticides can be associated with the same land use. Bentazon was derived from recent application to a golf course, while dichlorprop was derived from agricultural use more than 30 years ago. The advantages, limitations, and pitfalls of the proposed course of action are then further discussed.

Assessing the impacts of groundwater abstractions on flow regime and stream biota: Combining SWAT-MODFLOW with flow-biota empirical models

Assessing the impacts of groundwater abstractions on stream ecosystems is crucial for developing water planning and regulations in lowland areas that are highly dependent on groundwater, such as Denmark. To assess the effects of groundwater abstractions on flow regime and stream biota in a lowland groundwater-dominant catchment, we combined the SWAT-MODFLOW model with flow-biota empirical models including indices for three key biological taxonomic identities (fish, macroinvertebrates, and macrophytes). We assessed the effects of the current level of abstractions and also ran a scenario for assessing the effect of extreme groundwater abstractions (pumping rates of the drinking water wells were increased by 20 times in one subbasin of the catchment). Three subbasin outlets representing stream segments of different sizes were used for this evaluation. Current groundwater abstraction level had only minor impacts on the flow regime and stream biotic indices at the three subbasin outlets. The extreme abstractions, however, led to significant impacts on the small stream but had comparatively minor effects on the larger streams. The fish index responded most negatively to the groundwater abstractions, followed by the macrophyte index, decreasing, respectively, by 23.5% and 11.2% in the small stream in the extreme groundwater abstraction scenario. No apparent impact was found on macroinvertebrates in any of the three subbasin outlets. We conclude that this novel approach of a combined modelling system is a useful tool to quantitatively assess the effects of groundwater abstractions on stream biota and thereby support water planning and regulations related to groundwater abstractions. We highlight the need for developing improved biotic models that target specifically small headwater streams, which are often most affected by water abstraction.

Modeling the persistence of viruses in untreated groundwater.

Several factors can affect virus behavior and persistence in water sources. Historically linear models have been used to describe persistence over time; however, these models do not consider all of the factors that can affect inactivation kinetics or the observed patterns of decay. Meanwhile, applying the appropriate persistence model is critical for ensuring that decision makers are minimizing human health risk in the event of contamination and exposure to contaminated groundwater. Therefore, to address uncertainty in predictions of decay or virus concentrations over time, this study fit seventeen different linear and nonlinear mathematical models to persistence data from a previously conducted sampling study on drinking water wells throughout the United States. The models were fit using Maximum Likelihood Estimation and the best fitting models were determined by the Bayesian Information Criterion. The purpose of the study was to identify the best model for estimating decay of viruses in groundwater and to determine if model uncertainty contributes to erroneous predictions of viral contamination when only conventional models are considered. For the datasets analyzed in this study, the Juneja and Marks models and the exponential damped model were more representative of the persistence of viruses in groundwater than the traditionally used linear models. The results from this study were then evaluated with classification trees in order to identify more relevant modeling methodology for future research. The classification trees aid in narrowing the scope of appropriate persistence models based on characteristics of the experimental conditions and water sampled.

Identification of the components of a complex groundwater flow system subjected to intensive exploitation

The Mexico City region, like many other densely populated regions in the world, has problems in guaranteeing the supply of drinking water to its inhabitants. Its groundwater flow system is subject to intensive exploitation. To ensure proper water management, it is important to understand the behavior of groundwater flow system components under conditions of intensive exploitation. In this study, we analyzed 169 samples from drinking water supply wells, according to their chemistry. The principal components of the flow system were inferred using exploratory statistical analysis and analysis of the mixture of the end-members of the hydrochemical dataset. Four components were identified: (1) waters of recent infiltration and local circulation, (2) waters with evidence of intermediate chemical evolution, (3) waters that are chemically more evolved and of large flow trajectories, (4) waters that are chemically more evolved and of deep circulation. A relationship between the components, the structural geology, and the recharge zones was established. The mixing proportion of the four components in each water sample extracted from drinking water wells was identified. It was observed that the faults and the design of screened section of the well tubes influenced the mixtures captured by the wells. The impact generated by the intensive exploitation with respect to the distribution of the components within the flow system was evaluated.

Occurrence and distribution of hexavalent chromium in groundwater from North Carolina, USA

Hexavalent chromium (Cr(VI)) is a groundwater contaminant that is potentially harmful to human health. Understanding the occurrence of Cr(VI) in groundwater resources is critical for evaluating its risks to human health. Here we report a large dataset (n = 1362) of Cr(VI) and total chromium (CrT) concentrations in public, private, and monitoring wells from different aquifers across North Carolina. These water quality data come from new and previous measurements conducted at Duke University, as well as data reported by the U.S. Environmental Protection Agency, the N.C. Department of Environmental Quality, and the U.S. Geological Survey. The data confirm that Cr(VI) is the predominant species of dissolved Cr and that groundwater from aquifers in the Piedmont region contain significantly higher concentrations than groundwater from the coastal plain. Though there is only one exceedance of the U.S. EPA Maximum Contaminant Level (100 µg/L for CrT) in the dataset, over half of all wells measured for Cr(VI) (470 out of 865) in the dataset exceeded the N.C. Health Advisory Level of 0.07 µg/L. Using information from this dataset, we explore three different approaches to predicting Cr(VI) in groundwater: (1) CrT concentrations as a proxy for Cr(VI); (2) Exceedance probabilities of health goals for groundwater from aquifers located in specific geologic areas; and (3) Censored linear regression using commonly measured field parameters (pH, electrical conductivity, dissolved oxygen) with relationships to Cr(VI) as regressors. Combining these approaches, we have identified several areas in the Piedmont region where Cr(VI) in drinking water wells is expected to be higher than the advisory level, which coincide with large population groundwater reliant populations. While this study focuses on N.C., the wide-spread occurrence of Cr(VI) in groundwater at concentrations above health guidelines in aquifers of the Piedmont region could pose high human health risks to large populations in the eastern U.S.

Sources and behavior of trace elements in groundwater in the South Eastern Desert, Egypt.

Due to water scarcity, the groundwater will represent an essential source of water in many communities worldwide. This study was carried out to investigate the main hydrogeochemical characteristic of trace elements composition, their sources, and its vulnerability in groundwater to the human population. Fifteen groundwater samples were collected from boreholes and hand dug wells from the South Eastern Desert, Egypt, and analyzed for Al, As, B, Fe, Mn, Cd, Co, Cr, Cu, Hg, Ni, Pb, Rb, Sb, Sr, Th, U, V, and Zn using inductively coupled plasma mass spectrometry. Multivariate analyses were applied to identify the distribution and potential source of trace elements. The groundwater is tapped from the Miocene and the fractured basement rock aquifers. The mean concentrations of trace elements exceed the guideline values of all organizations, except in some wells for Zn, Cu, and Co. Cationic trace elements declined in the order of Mn > Fe > Zn > Al > V > Ni > Rb > Sr > U > Cu > Cr > Co > Cd > Pb > Th > Sb > Hg. Oxyanions As (mean 15.48 mg/L) and B (mean 1.24 mg/L) showed very high concentrations and higher than the average WHO concentrations in water suggesting potential adverse toxicity to all aquatic organisms. Five factor analyses indicated that different geochemical contributions are involved in the chemical characteristics of groundwater in the study area. Water-rock interaction and dissolution processes in bed rocks from different coastal Miocene deposits, meta-volcanics, basic-ultrabasic rocks, granitic and meta-sediments, seawater intrusion, residential wastes, and mining activities, in addition to the pH/Eh conditions, adsorption, and surface complexation during the chemical weathering are the main factors influence the trace elements distribution in groundwater. Results from this study for the six different groundwater aquifers are a unique insight into the sources and mobility of the observed trace elements in the groundwater and can be used in the assessment of contamination for drinking water wells. The association of trace elements from different aquifers might be useful in tracers studies of water-rock interaction. Due to the enrichment of trace elements in nearshore and crystalline groundwater aquifers in the study area and in similar areas worldwide, treatment technologies, and sustainable water management processes should be applied to prevent severe risks to the communities.

Groundwater microbial diversity and antibiotic resistance linked to human population density in Yucatan Peninsula, Mexico.

Microbial community composition in selected karst groundwater sites in the Yucatan Peninsula, Mexico, was assessed to determine the environmental variables influencing groundwater microbial diversity. The karst aquifer system is a groundwater-dependent ecosystem and is the world's second largest underwater karst cave system. The area's geology allows precipitation to infiltrate into the groundwater system and prevents accumulation of surface water; as such, groundwater is the only source of fresh water on the peninsula. The sampling locations consisted of three karst sinkholes that extend through the freshwater zone into the saline water, and an abandoned drinking water well of an ocean-side resort, during the dry and rainy seasons. The analysis showed that highly diverse microbial communities are present in the Yucatan groundwater, sustained by permanently warm temperatures and high nutrient input from human activity. Proximity to densely populated areas, such as tourist resorts, is the most important factor influencing both the diversity and presence of fecal bacteria and the antibiotic resistance profile.

Wastewater impacts on groundwater at a fractured sedimentary bedrock site in Ontario, Canada: implications for First Nations’ source-water protection

The impacts of wastewater on Indigenous drinking water sources is an issue of concern across Canada. This study investigated the wastewater impacts on groundwater resources at a First Nations reserve located on a vulnerable fractured sedimentary bedrock aquifer in southern Ontario. The objectives were to examine the spatiotemporal variability of a variety of tracers of wastewater and their movement to groundwater. The tracers included nitrate, E. coli, total coliforms, and the artificial sweeteners sucralose, acesulfame, and cyclamate. Isotopes in the groundwater were also examined, including tritium and the isotopes of oxygen and nitrogen in dissolved inorganic nitrate. Three multilevel monitoring systems (seven-channel continuous multi-channel tubing) were retrofitted in unused drinking-water wells on the reserve and monitored from December 2015 to November 2016. Results indicate that groundwater at various depths has been impacted by the septic systems on the reserve. The fractures intersected by the three retrofitted wells contain a mix of newly recharged and older water, and contaminant peaks do not always correspond with ports aligned with higher hydraulic conductivity, showing variable travel times for the constituents. The selection of wastewater management systems that are appropriate for the particular hydrogeological setting on the reserves is critical to providing safe, clean drinking water to Indigenous communities. In particular, special consideration should be made for communities situated on fractured sedimentary bedrock aquifers with thin overburden.

Occurrence of organic compounds in groundwater of Saudi Arabia.

The presence of organic compounds in drinking water is well recognized in many developing countries; however, the occurrence of organic contaminants in the groundwater of Saudi Arabia, which is the main source of drinking water in the country, is not well documented. A national comprehensive study was carried out to assess the occurrence of organic compounds in groundwater wells used for drinking water purpose, in different regions of Saudi Arabia. A total of 993 well water samples were collected from all 13 administrative regions of the kingdom. Samples were analyzed for a total of 131 organic compounds using the standard methods. The results indicated that total organic carbon values were in the range of 0.01 to 84.13 mg/L with an average weighted value of 12.61 mg/L. Organic compounds were detected in only 9 regions, with 19.84% of the samples containing organic compounds. Only 96 wells (9.67%) showed contents of organic compounds above the safe limits. Pesticides were not detected in any of the well water samples. Overall, organic compounds were found in only 197 out of 993 wells (19.84%) in the whole country. Most of the wells containing organic compounds were located in residential, industrial, and agriculture areas. Riyadh region and Eastern Province were found to have the most affected wells as compared to other regions. Several regions did not show any organic compounds in the well waters.It can be said that the problem of groundwater contamination with organic compounds in Saudi Arabia is not acute and is manageable at present. It is, however, recommended that a regular monitoring of drinking water wells of all regions should be carried out by the competent authorities for organic compounds to know any contamination if and when it happens. Preventing such contaminants from reaching drinking water sources and protecting drinking water well heads from such contaminants remains a priority.

Identification of the Hydrogeochemical Processes and Assessment of Groundwater Quality, Using Multivariate Statistical Approaches and Water Quality Index in a Wastewater Irrigated Region

Groundwater quality and availability are essential for human consumption and social and economic activities in arid and semiarid regions. Many developing countries use wastewater for irrigation, which has in most cases led to groundwater pollution. The Mezquital Valley, a semiarid region in central Mexico, is the largest agricultural irrigation region in the world, and it has relied on wastewater from Mexico City for over 100 years. Limited research has been conducted on the impact of irrigation practices on groundwater quality on the Mezquital Valley. In this study, 31 drinking water wells were sampled. Groundwater quality was determined using the water quality index (WQI) for drinking purposes. The hydrogeochemical process and the spatial variability of groundwater quality were analyzed using principal component analysis (PCA) and K-means clustering multivariate geostatistical tools. This study highlights the value of combining various approaches, such as multivariate geostatistical methods and WQI, for the identification of hydrogeochemical processes in the evolution of groundwater in a wastewater irrigated region. The PCA results revealed that salinization and pollution (wastewater irrigation and fertilizers) followed by geogenic sources (dissolution of carbonates) have a significant effect on groundwater quality. Groundwater quality evolution was grouped into cluster 1 and cluster 2, which were classified as unsuitable (low quality) and suitable (acceptable quality) for drinking purposes, respectively. Cluster 1 is located in wastewater irrigated zones, urban areas, and the surroundings of the Tula River. Cluster 2 locations are found in recharge zones, rural settlements, and seasonal agricultural fields. The results of this study strongly suggest that water management strategies that include a groundwater monitoring plan, as well as research-based wastewater irrigation regulations, in the Mezquital Valley are warranted.

Ample Arsenite Bio-Oxidation Activity in Bangladesh Drinking Water Wells: A Bonanza for Bioremediation?

Millions of people worldwide are at risk of arsenic poisoning from their drinking water. In Bangladesh the problem extends to rural drinking water wells, where non-biological solutions are not feasible. In serial enrichment cultures of water from various Bangladesh drinking water wells, we found transfer-persistent arsenite oxidation activity under four conditions (aerobic/anaerobic; heterotrophic/autotrophic). This suggests that biological decontamination may help ameliorate the problem. The enriched microbial communities were phylogenetically at least as diverse as the unenriched communities: they contained a bonanza of 16S rRNA gene sequences. These related to Hydrogenophaga, Acinetobacter, Dechloromonas, Comamonas, and Rhizobium/Agrobacterium species. In addition, the enriched microbiomes contained genes highly similar to the arsenite oxidase (aioA) gene of chemolithoautotrophic (e.g., Paracoccus sp. SY) and heterotrophic arsenite-oxidizing strains. The enriched cultures also contained aioA phylotypes not detected in the previous survey of uncultivated samples from the same wells. Anaerobic enrichments disclosed a wider diversity of arsenite oxidizing aioA phylotypes than did aerobic enrichments. The cultivatable chemolithoautotrophic and heterotrophic arsenite oxidizers are of great interest for future in or ex-situ arsenic bioremediation technologies for the detoxification of drinking water by oxidizing arsenite to arsenate that should then precipitates with iron oxides. The microbial activities required for such a technology seem present, amplifiable, diverse and hence robust.

Occurrence and Sources of Radium in Groundwater Associated with Oil Fields in the Southern San Joaquin Valley, California.

Geochemical data from 40 water wells were used to examine the occurrence and sources of radium (Ra) in groundwater associated with three oil fields in California (Fruitvale, Lost Hills, South Belridge). 226Ra+228Ra activities (range = 0.010-0.51 Bq/L) exceeded the 0.185 Bq/L drinking-water standard in 18% of the wells (not drinking-water wells). Radium activities were correlated with TDS concentrations (p < 0.001, ρ = 0.90, range = 145-15,900 mg/L), Mn + Fe concentrations (p < 0.001, ρ = 0.82, range = <0.005-18.5 mg/L), and pH (p < 0.001, ρ = -0.67, range = 6.2-9.2), indicating Ra in groundwater was influenced by salinity, redox, and pH. Ra-rich groundwater was mixed with up to 45% oil-field water at some locations, primarily infiltrating through unlined disposal ponds, based on Cl, Li, noble-gas, and other data. Yet 228Ra/226Ra ratios in pond-impacted groundwater (median = 3.1) differed from those in oil-field water (median = 0.51). PHREEQC mixing calculations and spatial geochemical variations suggest that the Ra in the oil-field water was removed by coprecipitation with secondary barite and adsorption on Mn-Fe precipitates in the near-pond environment. The saline, organic-rich oil-field water subsequently mobilized Ra from downgradient aquifer sediments via Ra-desorption and Mn/Fe-reduction processes. This study demonstrates that infiltration of oil-field water may leach Ra into groundwater by changing salinity and redox conditions in the subsurface rather than by mixing with a high-Ra source.

Mobility and sorption assessment of selected pesticides in alluvial aquifer.

The objective of the paper was to use transport model of selected pesticides (carbendazim, acetamiprid and imidacloprid) in determination of linear sorption coefficients in alluvial aquifer. For constructing transport model, results of a field experiment at the location of Kovin-Dubovac drainage system in Serbia were used in order to set hydraulic parameters (hydraulic conductivity, aquifer layer thickness of the observed area, effective porosity etc.). The field experiment consisted of a tracer test during which concentrations of non-reactive tracer (Cl-) and selected pesticides (carbendazim, acetamiprid and imidacloprid) were monitored. For better characterization of hydraulic parameters, a pumping test was conducted at the observed well and results were used in designing transport model. Simulation model was constructed with Lizza groundwater flow software and W.O.D.A. (Well Outline and Design Aid) solver. Obtained linear sorption coefficients in the sand and gravel water-bearing layer were 0.14mLg-1 for carbendazim and 0.11mLg-1 for acetamiprid and imidacloprid. Results from this study are a unique insight into mobility of observed pesticides in the alluvial groundwater in natural conditions and can be used in contamination assessment for drinking water wells.

Exploring private water wells for fecal sources and evidence of pathogen presence in the context of current testing practices for potability in Ontario

Abstract Private water wells provide drinking water for an estimated 4.1 million households in Canada yet remain understudied in the context of microbial water quality or human health impacts. As there exists little systematic surveillance for enteric infections or outbreaks related to well water sources, consumers may be at risk of waterborne infectious diseases. A standard protocol in Ontario requires 200 mL of water, collected, and submitted by well owners, half of which is used to analyze for Escherichia coli and total coliforms (TCs). The aim of this study was to determine the efficacy of testing small water volumes and to survey for other contaminants in addition to bacterial indicators to inform pathogen prevalence and fecal source in drinking water wells. Samples were assessed for E. coli and TCs, by culture, and genetic markers of Bacteroides spp., Campylobacter spp., Salmonella spp., and Shiga toxin-producing E. coli, using qPCR. The source of fecal contamination varied by the geographic region and may be explained by septic tank density and underlying geology, among other factors. A small number of samples (1.9%) showed the evidence of contamination with enteric pathogens. Lastly, E. coli measured by qPCR, as opposed to culture, correlated more strongly to Bacteroides markers.

Estimated burden of disease from arsenic in drinking water supplied by domestic wells in the United States.

Well water around the world can be contaminated with arsenic, a naturally occurring geological element that has been associated with myriad adverse health effects. Persons obtaining their drinking water from private wells are often responsible for well testing and water treatment. High levels of arsenic have been reported in well water-supplied areas of the United States. We quantified - in cases and dollars - the potential burden of disease associated with the ingestion of arsenic through private well drinking water supplies in the United States. To estimate cancer and cardiovascular disease burden, we developed a Monte Carlo model integrating three input streams: (1) regional concentrations of arsenic in drinking water wells across the United States; (2) dose-response relationships in the form of cancer slope factors and hazard ratios; and (3) economic cost estimates developed for morbidity endpoints using 'cost-of-illness' methods and for mortality using 'value per statistical life' estimates. Exposure to arsenic in drinking water from U.S. domestic wells is modeled to contribute 500 annual premature deaths from ischemic heart disease and 1,000 annual cancer cases (half of them fatal), monetized at $10.9 billion (2017 USD) annually. These considerable public health burden estimates can be compared with the burdens of other priority public health issues to assist in decision-making.