Madeline B. Gotkowitz

Source and transport of human enteric viruses in deep municipal water supply wells.

Until recently, few water utilities or researchers were aware of possible virus presence in deep aquifers and wells. During 2008 and 2009 we collected a time series of virus samples from six deep municipal water-supply wells. The wells range in depth from approximately 220 to 300 m and draw water from a sandstone aquifer. Three of these wells draw water from beneath a regional aquitard, and three draw water from both above and below the aquitard. We also sampled a local lake and untreated sewage as potential virus sources. Viruses were detected up to 61% of the time in each well sampled, and many groundwater samples were positive for virus infectivity. Lake samples contained viruses over 75% of the time. Virus concentrations and serotypes observed varied markedly with time in all samples. Sewage samples were all extremely high in virus concentration. Virus serotypes detected in sewage and groundwater were temporally correlated, suggesting very rapid virus transport, on the order of weeks, from the source(s) to wells. Adenovirus and enterovirus levels in the wells were associated with precipitation events. The most likely source of the viruses in the wells was leakage of untreated sewage from sanitary sewer pipes.

Effects of Climate and Sewer Condition on Virus Transport to Groundwater.

Pathogen contamination from leaky sanitary sewers poses a threat to groundwater quality in urban areas, yet the spatial and temporal dimensions of this contamination are not well understood. In this study, 16 monitoring wells and six municipal wells were repeatedly sampled for human enteric viruses. Viruses were detected infrequently, in 17 of 455 samples, compared to previous sampling at these wells. Thirteen of the 22 wells sampled were virus-positive at least once. While the highest virus concentrations occurred in shallower wells, shallow and deep wells were virus-positive at similar rates. Virus presence in groundwater was temporally coincident, with 16 of 17 virus-positive samples collected in a six-month period. Detections were associated with precipitation and occurred infrequently during a prolonged drought. The study purposely included sites with sewers of differing age and material. The rates of virus detections in groundwater were similar at all study sites during this study. However, a relationship between sewer age and virus detections emerged when compared to data from an earlier study, conducted during high precipitation conditions. Taken together, these data indicate that sewer condition and climate affect urban groundwater contamination by human enteric viruses.

Using Groundwater Models to Evaluate Strategies for Drinking-Water Protection in Rural Subdivisions

Problem: Groundwater contamination is a concern in rural residential subdivisions where numerous septic systems and private wells are sited in close proximity. Although most state codes regulate the construction and location of private wells, these regulations do not usually account for site-specific conditions that may impact drinking-water quality. Purpose: Groundwater models provide a technical basis for delineating groundwater flow to domestic wells. Despite their widespread use in the hydrologic sciences, planners and developers rarely have access to such models. We aimed to assess existing regulations for domestic wells and septic systems and illustrate how groundwater models can be used to evaluate strategies for additional drinking-water protection in unsewered residential subdivisions. Methods: We developed groundwater flow models for two subdivisions in southern Wisconsin, analyzed the results, and disseminated them to local officials, developers, and residents. Results and conclusions: Models of both subdivisions indicate that deeper individual wells or a single community well within a protected source area would improve the likelihood of obtaining high-quality drinking water. In response, several homeowners in one subdivision chose to pay for deeper wells and well casings or individual home water-treatment systems. The developer of the second site incorporated an unenforceable recommendation for deeper well casings into subdivision covenants, but none of the wells drilled so far have followed the recommendation. Implementing and enforcing well construction or setback criteria based on model results may require changing Wisconsin state codes to explicitly define what can and cannot be regulated at the local level. Takeaway for practice: Hydrogeologists can use standard groundwater modeling methods and information about local hydrologic conditions to inform planners as they develop guidelines to improve drinking-water quality. Partnerships between local hydrogeologists and planners are essential because differences in hydrogeologic setting, groundwater quality concerns, and regulatory structure will cause model results and proposed guidelines to vary on a case-by-case basis. Research support: Funding for this research was provided by the EPA Science to Achieve Results (STAR) graduate fellowship program, the University of Wisconsin Groundwater Resources Advisory Council (administered by the Wisconsin Water Resources Institute), and the Wisconsin Department of Natural Resources.

Arsenic geochemistry and hydrostratigraphy in midwestern U.S. glacial deposits.

Arsenic concentrations exceeding the U.S. EPAs 10 μg/L standard are common in glacial aquifers in the midwestern United States. Previous studies have indicated that arsenic occurs naturally in these aquifers in association with metal-(hydr)oxides and is released to groundwater under reducing conditions generated by microbial oxidation of organic matter. Despite this delineation of the arsenic source and mechanism of arsenic mobilization, identification of arsenic-impacted aquifers is hindered by the heterogeneous and discontinuous nature of glacial sediments. In much of the Midwest, the hydrostratigraphy of glacial deposits is not sufficiently characterized to predict where elevated arsenic concentrations are likely to occur. This case study from southeast Wisconsin presents a detailed characterization of local stratigraphy, hydrostratigraphy, and geochemistry of the Pleistocene glacial deposits and underlying Silurian dolomite. Analyses of a single core, water chemistry data, and well construction reports enabled identification of two aquifers separated by an organic-rich aquitard. The upper, unconfined aquifer provides potable water, whereas arsenic generally exceeds 10 μg/L in the deeper aquifer. Although coring and detailed hydrostratigraphic characterization are often considered impractical, our results demonstrate that a single core improved interpretation of the complex lithology and hydrostratigraphy. This detailed characterization of hydrostratigraphy facilitated development of well construction guidelines and lays the ground work for further studies of the complex interactions among aquifer sediments, hydrogeology, water chemistry, and microbiology that lead to elevated arsenic in groundwater.