Drinking Water Maximum Contaminant Level Research Articles

Benefit‐cost estimation for alternative drinking water maximum contaminant levels

A simulation model for estimating compliance behavior and resulting costs at U.S. Community Water Suppliers is developed and applied to the evaluation of a more stringent maximum contaminant level (MCL) for arsenic. Probability distributions of source water arsenic concentrations are simulated using a statistical model conditioned on system location (state) and source water type (surface water or groundwater). This model is fit to two recent national surveys of source waters, then applied with the model explanatory variables for the population of U.S. Community Water Suppliers. Existing treatment types and arsenic removal efficiencies are also simulated. Utilities with finished water arsenic concentrations above the proposed MCL are assumed to select the least cost option compatible with their existing treatment from among 21 available compliance strategies and processes for meeting the standard. Estimated costs and arsenic exposure reductions at individual suppliers are aggregated to estimate the national compliance cost, arsenic exposure reduction, and resulting bladder cancer risk reduction. Uncertainties in the estimates are characterized based on uncertainties in the occurrence model parameters, existing treatment types, treatment removal efficiencies, costs, and the bladder cancer dose‐response function for arsenic.

Groundwater Quality Beneath Irrigated Vegetable Fields in a North‐Central U.S. Sand Plain

AbstractThe dramatic expansion of irrigated agriculture since about 1970 in the north‐central USA has been accompanied by NO3 and pesticide pollution of groundwater. The expansion has been concentrated in areas with sandy soils and shallow water tables, such as the Wisconsin central sand plain. In some parts of this sand plain, most wells contain detectable pesticide residues and NO3‐N concentrations that exceed the 10 mg L−1 U.S. drinking water maximum contaminant level (MCL). To evaluate the effects on groundwater quality of this agricultural system, we monitored solutes 23 times during a 2‐yr period in the upper 3 m of the aquifer beneath and immediately upgradient of four irrigated vegetable fields. Groundwater beneath fields had significantly greater concentrations of most solutes and lower pH than upgradient groundwater. Especially pronounced were Ca, Cl, K, Mg, and NO3 differences, with concentrations 5 to 26 times greater under fields. Nitrate N concentrations averaged 21 mg L−1 under fields, compared with 1 mg L−1 upgradient. Pesticide residues were ubiquitous beneath fields, and generally persisted for many months after application. Pesticide concentrations often exceeded Wisconsin preventive‐action limits (PALs), but seldom exceeded federal MCLs. Even when agricultural management approximated best management practice (BMP) recommendations, the NO3 concentration beneath these fields approached double the MCL, indicating a need for new approaches to control agricultural groundwater pollution.

Chloroform: An EPA Test Case

In March 1998, the U.S. Environmental Protection Agency (EPA) published a proposal to raise the drinking water maximum contaminant level goal (MCLG) for chloroform, a suspected human carcinogen, from zero to 300 parts per billion. The proposal marked a departure from the agency's traditional reliance on linear dose-response models in performing risk assessment, and reflected the new thinking contained in the 1996 draft update to the agency's cancer risk assessment guidelines. The updated guidelines emphasize mechanisms of action and descriptions of the conditions under which carcinogenic hazards are likely to be expressed.

Electrosorption and Reduction of Pertechnetate by Anodically Polarized Magnetite

The radionuclide technetium is a common surface and groundwater contaminant at many nuclear fuels processing facilities. This research investigated a new method for removing pertechnetate from contaminated waters based on the low aqueous solubility of reduced technetium species. The removal method involved electrostatic adsorption of pertechnetate at an anodically polarized magnetite electrode, followed by reduction of the adsorbed Tc(VII). This method was capable of reducing technetium associated β activity below the 900 pCi/L drinking water maximum contaminant level set by the US EPA for manmade β activity. Upon termination of the applied polarization, the reduced technetium species remained adhered to the magnetite electrode under anaerobic conditions. Under aerobic conditions, the technetium was slowly released back into solution, indicating that the reduced technetium is afforded a degree of cathodic protection due to preferential oxidation of the magnetite. The advantages of this electrosorption/red...

Spatial and Temporal Variations in Nitrate Contamination of a Rural Aquifer, California

AbstractThe quality of ground water in the Sierra Pelona watershed, California is examined as an example of a small rural groundwater basin in a mountainous area of arid climate. Water quality in this region has been seriously impacted by nitrate (NO3) contamination with 42% of wells sampled exceeding the EPA public drinking water maximum contaminant level (MCL) of 10 mg/L as NO3‐N at some point during 1992–1993. High NO3‐N concentrations reported from this region suggest degradation of water quality due to anthropogenic activity. Dissolved ion concentrations, particularly NO3, chloride and calcium varied radically in 55% of well waters sampled prior to, following, and months after an unusually wet winter. Our extensive well sampling program, chemical results and delineation of spatial and temporal NO3‐N variation allow us to constrain possible contamination sources and transport mechanisms active in the Sierra Pelona basin. The spatial distribution and temporal variability of NO3 indicate three patterns of contamination: (i) isolated wells impacted by numerous, localized NO3 sources which erratically affect a single well without significantly contaminating neighboring ones; (ii) a tight cluster of wells, unusually low in other ions but consistently high in NO3; (iii) moderate and generally consistent NO3 concentrations, found over a large, diffuse region of the Sierra Pelona alluvial aquifer. An understanding of the differing NO3 source(s) and contamination mode(s) that contribute to these observed contaminant patterns is critical to development and success of any strategy for contaminant mitigation and/or remediation.

Oxyanion Concentrations in Eastern Sierra Nevada Rivers – 2. Arsenic and Phosphate

Water samples were collected from the Truckee River-Pyramid Lake system, the Walker River-Walker Lake system, and the Carson River, all located in eastern California and western Nevada, U.S.A., at three different times (i.e., summer 1991, spring 1992, and autumn 1992) over a two year period. The concentrations of As, Na, Cl, ΣPO4, and pH were measured in these river samples and the associated terminal lakes. Arsenic values ranged from below 13 nmol/kg near Truckee, California to 160 nmol/kg at Nixon, Nevada in the Truckee River, from 40 nmol/kg in the headwaters of both West and East Walker Rivers to 270 nmol/kg below Weber Reservoir on the main branch of the Walker River, and from <27 nmol/kg to 234 nmol/kg for the lower Carson River system. Arsenic concentrations in Steamboat Creek (0.91 μmol/kg–1.80 μmol/kg) in the Truckee River catchment are above the U.S. EPA drinking water maximum contaminant level of 0.67 μmol/kg, as are the As concentrations in both Pyramid Lake (1.33 μmol/kg–1.57 μmol/kg ) and Walker Lake (13.7 μmol/kg–18.7 μmol/kg). Sources of As for all three rivers include weathering of As-rich rocks and/or regolith and input of high-As geothermal spring waters, both processes primarily, although not exclusively, adding As to the headwater regions of these rivers. Steamboat Hot Springs (29 μmol/kg ≤ As ≤ 54.5 μmol/kg), for example, is identified as a source of As to the Truckee River via Steamboat Creek. The high As concentrations in Pyramid and Walker Lakes are likely due to (1) desorption of arsenate from aquatic particulate matter in these high pH waters (9.0 ≤ pH ≤ 9.5), (2) limited biologic uptake of arsenate, and (3) evaporative concentration of the lake waters. Evaluation of molar ΣPO4}/As ratios of river waters and geothermal spring waters (e.g., Steamboat Hot Springs), indicates that phosphate is substantially enriched in Steamboat Creek as well as the mid to lower reaches of the Walker and Carson Rivers. These regions of each river are dominated by agricultural interests and, additionally, in the case of Steamboat Creek, residential areas and golf courses. Our data strongly imply that phosphate-rich agricultural return flow has likely added P to these streams and, consequently, increased their respective P:As ratios.

Field evaluation of perox-pure™ chemical oxidation technology

This paper presents the field evaluation results for an advanced chemical oxidation technology developed by Peroxidation Systems, Inc., of Tucson, Arizona. The technology, known as the perox-pure™ technology, was evaluated under the U.S. Environmental Protection Agency Superfund Innovative Technology Evaluation program at Lawrence Livermore National Laboratory (LLNL), Site 300 in Tracy, California, in September 1992. The perox-pure™ technology uses ultraviolet radiation and hydrogen peroxide to oxidize dissolved organic compounds in water. At the LLNL site, this technology was evaluated in treating groundwater contaminated with volatile organic compounds (VOC) including trichloroethene (TCE); tetrachloroethene (PCE); 1,1,1-trichloroethane (TCA); 1,1-dichloroethane (DCA); and chloroform. The perox-pure™ system generally produced an effluent that contained TCE, PCE, and DCA at levels below detection limits, and TCA and chloroform at levels slightly above detection limits. The system achieved maximum removal efficiencies of greater than 99.9, 98.7, and 95.8 percent for TCE, PCE, and DCA, respectively. The system also achieved removal efficiencies of up to 92.9 and 93.6 percent for TCA and chloroform, respectively. The treatment system effluent met California drinking water action levels and federal drinking water maximum contaminant levels for all VOCs at the 95 percent confidence level. Cost analysis indicated that the groundwater remediation cost for a 50-gallon per minute perox-pure™ system would range from $7 to $11 per 1,000 gallons, depending on contaminated groundwater characteristics. Of this total cost, the perox-pure™ system direct treatment cost would range from $3 to $5 per 1,000 gallons.

Arsenic and fluoride in the upper madison river system: Firehole and gibbon rivers and their tributaries, yellowstone national park, wyoming, and southeast montana

Chemical analyses of 21 water samples from the Firehole and Gibbon Rivers, which combine to form the Madison River, gave arsenic and fluoride values above the Environmental Protection Agency Interim Primary Drinking Water maximum contaminant levels (0.05 mg/l arsenic and 2.0 mg/l fluoride). On 18 October, 1975, during a period of moderate flow (16,600 l/s), the Madison River at West Yellowstone contained 0.23 mg/l arsenic and 6.2 mg/l fluoride. Below Hebgen Lake the Madison River during periods of high flow (56,000 liter/s at West Yellowstone and 708,000 liter/s below Hebgen Lake) would contain 0.05 mg/l arsenic at both stations and 1.5 and 4.0 mg/l fluoride at West Yellowstone and below Hebgen Lake, respectively. The strong correlations of arsenic and fluoride with other chemical constituents of the river water at the sampling sites demonstrate the conservative nature of each element after it reaches the Madison River system. Calculations indicate that water from three sampling sites is above saturation with respect to fluorite.