Agency Maximum Contaminant Level Research Articles

Effect of geochemical conditions on radium mobility in discrete intervals within the Midwestern Cambrian-Ordovician aquifer system

Radium (Ra) commonly occurs in groundwater obtained from the Midwestern Cambrian-Ordovician aquifer system (C-O-AS) at activities approaching and exceeding the United States Environmental Protection Agency's Maximum Contaminant Level (MCL) of 5 pCi/L for combined 226Ra and 228Ra. The occurrence of Ra(II) in groundwater is dependent on a number of factors, including the prevalence of parent radionuclides within hydrogeological strata, as well as aquifer geochemical conditions. Interbedded aquifer and aquitard sequences within the Midwestern C-O-AS are stratified with respect to Ra(II) activity and geochemical conditions, and thus the formations that serve as Ra(II) sources to groundwater remain poorly constrained. This study analyzes aqueous samples collected from short-screened wells at various depths within the Midwestern C-O-AS near Madison, WI, USA, to determine geochemical parameters including dissolved oxygen; pH; major and minor ions; and metals, including 226Ra, 228Ra, and parent isotopes 238U and 232Th. Additionally, the elemental composition of aquifer solids is determined as a function of depth. Within solid phases, 238U and 232Th occur in both fine-grained facies and as coatings on sandstone minerals. Most groundwater samples contain dissolved combined Ra(II) lower than 2.5 pCi/L; however, one well completed in the unconfined and one well completed in the confined portion of the groundwater system exceed 3.5 pCi/L. In the confined system, anoxic conditions are associated with elevated Ra(II) concentrations, while in the upper, oxic aquifer, elevated total dissolved solids are positively related to Ra(II). These results demonstrate that multiple factors impact Ra(II) sources and mobility in the regionally unconfined portion of the Midwestern C-O-AS.

Distribution of 222Rn in groundwater and estimation of resulting radiation dose to different age groups: A case study from Bangalore City

ABSTRACTIngesting waters holding high levels of natural occurring radioactive element like Radon would contribute to increase in the effective dose received by people followed by an increased prevalence of cancer. The current study is an attempt to describe the extent of contribution of 222Rn to natural background radiation and the resultant effective dose to public of different age groups. In order to do so, 65 groundwater samples from selected parts of Bangalore city were collected and analyzed for radon activity using RAD7 radon monitor coupled with RAD H2O accessories. The radon activity was in the range of 3.05–696 Bq/L (mean: 91.39 Bq/L) and 92.31% of the groundwater samples recorded elevated radon concentration above the United States environmental protection agency (USEPA's) Maximum Contaminant Level (MCL) value of 300 pCi/L, corresponding to 11.1 Bq/L. The mean annual effective dose contribution of people falling under different age groups (viz., infants, children, teens: males and females, adults: males and females, pregnant and lactating women) due to ingestion of water-borne 222Rn ranged from 0.082 to 0.444 mSv/y and was found to be higher in all the age groups of males compared to respective female age groups, but well within the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and World Health Organization (WHO) proposed limit of 1 mSv/y.

Elevated levels of diesel range organic compounds in groundwater near Marcellus gas operations are derived from surface activities

Hundreds of organic chemicals are used during natural gas extraction via high-volume hydraulic fracturing (HVHF). However, it is unclear whether these chemicals, injected into deep shale horizons, reach shallow groundwater aquifers and affect local water quality, either from those deep HVHF injection sites or from the surface or shallow subsurface. Here, we report detectable levels of organic compounds in shallow groundwater samples from private residential wells overlying the Marcellus Shale in northeastern Pennsylvania. Analyses of purgeable and extractable organic compounds from 64 groundwater samples revealed trace levels of volatile organic compounds, well below the Environmental Protection Agency's maximum contaminant levels, and low levels of both gasoline range (0-8 ppb) and diesel range organic compounds (DRO; 0-157 ppb). A compound-specific analysis revealed the presence of bis(2-ethylhexyl) phthalate, which is a disclosed HVHF additive, that was notably absent in a representative geogenic water sample and field blanks. Pairing these analyses with (i) inorganic chemical fingerprinting of deep saline groundwater, (ii) characteristic noble gas isotopes, and (iii) spatial relationships between active shale gas extraction wells and wells with disclosed environmental health and safety violations, we differentiate between a chemical signature associated with naturally occurring saline groundwater and one associated with alternative anthropogenic routes from the surface (e.g., accidental spills or leaks). The data support a transport mechanism of DRO to groundwater via accidental release of fracturing fluid chemicals derived from the surface rather than subsurface flow of these fluids from the underlying shale formation.

Estimation of radon concentration in groundwater of coastal area in Baleshwar district of Odisha, India

The present study was carried out to determine the distribution of radon (222Rn) activity concentration measured using Durridge RAD-7 in the groundwater samples in the coastal area of Baleshwar district, Odisha, India. The 222Rn activities in 10 groundwater samples of coastal area of Baleshwar were measured and the values of 222Rn ranged between 1.6 ± 0.21 and 17.0 ± 1.69 kBq m−3 with an average value of 8.98 ± 0.85 kBq m−3, and seven samples were well within the Environmental Protection Agency's maximum contaminant level of 11.1 kBq m−3 while three samples were more than the maximum contaminant level of 11.1 kBq m−3. The effective dose per m3 and annual effective dose values were varying with respect to the increase in radon concentration and were significantly lower than the United Nations Scientific Committee on the Effects of Atomic Radiation and WHO recommended limit for members of the public of 1 mSv y−1.

Environmental Implications of Cured-in-Place Pipe Rehabilitation Technology

Cured-in-place pipe (CIPP) technology is commonly used for pipe rehabilitation, and transportation agencies are increasingly using it to repair damaged pipe culverts. In typical CIPP applications, a lining tube saturated with a styrene-based thermosetting resin is installed into the damaged pipe. Subsequent curing with a heat source results in a pipe within a pipe. In this study, seven styrene-based, steam-cured CIPP installations in surface water and storm water conveyances in Virginia were identified and observed over the course of 1 year. Although the sites were not directly linked to sources of drinking water, styrene levels at five sites were higher than the Environmental Protection Agency's maximum contaminant level for drinking water of 0.1 mg/L. These concentrations were detected at these sites for a minimum of 5 days to 71 days after installation. Certain measurements were also found to exceed the concentration required to kill 50% of several freshwater aquatic indicator species. The findings suggest that the elevated styrene levels could have resulted from one or a combination of the following: ( a) installation practices that did not capture condensate containing styrene, ( b) uncured resin that escaped from the liner during installation, ( c) insufficient curing of the resin, and ( d) some degree of permeability in the lining material. In response to the preliminary findings of this study, the Virginia Department of Transportation suspended the use of styrene CIPP for conveying surface or storm water while the department further evaluated CIPP repair and subsequently developed new requirements for these installations.

Arsenic in groundwaters in the Northern Appalachian Mountain belt: A review of patterns and processes

Naturally occurring arsenic in the bedrock of the Northern Appalachian Mountain belt was first recognized in the late 19th century. The knowledge of the behavior of arsenic in groundwater in this region has lagged behind nearly a century, with the popular press reporting on local studies in the early 1980s, and most peer-reviewed research articles on regional patterns conducted and written in the late 1990s and early 2000s. Research reports have shown that within this high arsenic region, between 6% and 22% of households using private drinking water wells contain arsenic in excess of 10 µg/L, the United States Environmental Protection Agency's maximum contaminant level. In nearly all reports, arsenic in drinking water was derived from naturally occurring geologic sources, typically arsenopyrite, substituted sulfides such as arsenian pyrite, and nanoscale minerals such as westerveldite. In most studies, arsenic concentrations in groundwater were controlled by pH dependent adsorption to mineral surfaces, most commonly iron oxide minerals. In some cases, reductive dissolution of iron minerals has been shown to increase arsenic concentrations in groundwater, more commonly associated with anthropogenic activities such as landfills. Evidence of nitrate reduction promoting the presence of arsenic(V) and iron(III) minerals in anoxic environments has been shown to occur in surface waters, and in this manuscript we show this process perhaps applies to groundwater. The geologic explanation for the high arsenic region in the Northern Appalachian Mountain belt is most likely the crustal recycling of arsenic as an incompatible element during tectonic activity. Accretion of multiple terranes, in particular Avalonia and the Central Maine Terrane of New England appear to be connected to the presence of high concentrations of arsenic. Continued tectonic activity and recycling of these older terranes may also be responsible for the high arsenic observed in the Triassic rift basins, e.g. the Newark Basin. There are only two well-known cases of anthropogenic contamination of the environment in the northern Appalachian Mountain belt, both of which are industrial sites with surface contamination at that infiltrated the local groundwater.

Effects of time and point-of-use devices on arsenic levels in Southeastern Michigan drinking water, USA

Health effects associated with chronic, low-level exposures to arsenic in drinking water (<100 μg/L) remain unclear, in part due to uncertainties in assessing exposure. Drinking water concentrations have been used to assess past exposure to arsenic in epidemiological studies, under the assumption that a single measurement can be used to estimate historical exposure. This study aims to better understand (1) temporal variability in arsenic concentrations in drinking water and (2) the impact of point-of-use (POU) treatment devices on arsenic exposure measurements, and on reliability of the exposure measurement for population-level studies. Multiple drinking water samples were collected at two points in time (an average of fourteen months apart) for 261 individuals enrolled in a case-control study of arsenic exposure and bladder cancer in Michigan. Sources of drinking water included private wells (n=221), public water supplies (n=33), and bottled water (n=7); mean arsenic concentration was highest in private wells (7.28 μg/L) and lowest in bottled water samples (0.28 μg/L). Arsenic concentrations in primary drinking water samples were highly correlated (r=0.88, p<0.0001, n=196), with 3% of the water sources exceeding the United States Environmental Protection Agency's Maximum Contaminant Level (MCL) in one sample but not in the other sample. Measurement reproducibility did not vary by type of POU device (e.g., softener, filter, reverse osmosis system). Arsenic concentrations did differ, however, between samples treated with POU devices and untreated samples taken on the same day. Substantial differences in arsenic concentrations were consistently observed for reverse osmosis systems; other POU devices had variable effects on arsenic concentrations. These results indicate that while a single residential arsenic measurement may be used to represent exposure in this region, researchers must obtain information on changes in water source and POU treatment devices to better characterize population exposures over time.

Domestic well water quality within tribal lands of eastern Nebraska

Recent surveys of Native Americans suggest that individuals living on reservations may be at greater environmental/health risk than the population at large due to water-quality problems. Despite these surveys, no comprehensive study of environmental conditions within Native American lands as a whole has been undertaken. This study compares water-quality data from two reservations in eastern Nebraska, the Omaha and the Santee Sioux Reservations, with existing regional, state, and national datasets to determine if differences exist between reservation and non-reservation groundwater quality. An area of concern within both reservations is the high percentage of domestic wells containing coliform bacteria and exceeding the US Environmental Protection Agency (US EPA) maximum contaminant level (MCL) for nitrate-nitrogen (NO3-N). It appears that the presence of these contaminants may be linked to factors such as well construction, maintenance, and land use patterns in the immediate vicinity of the wells rather than agricultural non-point source pollution.

Heterogeneities in ground-water geochemistry in a sand aquifer beneath an irrigated field

The contamination of shallow aquifers by elevated nitrate concentrations is a common problem in many rural regions of the world. Aquifers under irrigated land are especially susceptible to this type of contamination. An intensive three-dimensional investigation of water chemistry was undertaken in a shallow unconfined sand aquifer in an area of intensive irrigation in Mason County, Illinois, in order to investigate processes affecting water quality. Results reveal considerable heterogeneity in the aqueous chemistry in three spatial dimensions and temporally. Recharge is rapid in this system and the water chemistry of the recharge water is variable both spatially and temporally, being especially influenced by agricultural practices. Nitrate concentrations are elevated in a zone between about 6 and 10 m beneath the surface, although in certain areas and at certain times this zone was not found. The maximum nitrate concentrations in this zone were slightly greater than 20 mg l −1 as N, well above the US Environmental Protection Agency's maximum contaminant level (MCL) of 10 mg l −1. Nitrate was generally absent both above and below this depth in the aquifer. Water relatively depleted in nitrate recharges the aquifer from the surface at the site, producing a zone of dilute water near the water table. Beneath the plume, denitrification reactions are responsible for removing nitrate from solution, probably mainly coupled to oxidation of sulfide minerals; tritium data suggest that vertical movement of solutes is rapid and thus there has been enough time to transport surface-applied fertilizer to depths in excess of 30 m in the aquifer. This rapid vertical movement is almost certainly enhanced by intensive irrigation in the county. A number of aqueous species and chemical parameters (Ca, Mg, Sr, Fe, Si, dissolved inorganic carbon (DIC), dissolved oxygen, total dissolved solids, and pH) are correlated with nitrate concentrations, primarily because, like nitrate, they are either a significant fraction of fertilizers or are redox-sensitive. Drinking water quality is generally not degraded by fertilizer applications in this area, because almost all drinking-water wells are screened well below the zone of elevated nitrate concentrations.

Occurrence of Selected Herbicides and Herbicide Degradation Products in Iowa's Ground Water, 1995

AbstractHerbicide compounds were prevalent in ground water across Iowa, being detected in 70% of the 106 municipal wells sampled during the summer of 1995. Herbicide degradation products were three of the four most frequently detected compounds for this study. The degradation product alachlor ethanesulfonic acid was the most frequently detected compound (65.1%), followed by atrazine (40.6%), and the degradation products deethylatrazine (34.9%), and cyanazine amide (19.8%). The corn herbicide acetochlor, first registered for widespread use in the United States in March 1994, was detected in a single water sample. No reported herbicide compound concentrations for this study exceeded currem U.S. Environmental Protection Agency's maximum contaminant levels or health advisory levels for drinking water, although the herbicide degradation products examined have yet to have such levels established.The occurrence of herbicide compounds had a significant, inverse relation to well depth and a significant, positive relation to dissolved‐oxygen concentration. It is felt that both well depth and dissolved oxygen are acting as rough surrogates to ground‐water age, with younger ground water being more likely to contain herbicide compounds. The occurrence of herbicide compounds was substantially different among the major aquifer types across Iowa, being detected in 82.5% of the alluvial, 81.8% of the bedrock/ karst region, 40.0% of the glacial‐drift, and 25.0% of the bedrock/nonkarst region aquifers. The observed distribution was partially attributed to variations in general ground‐water age among these aquifer types. A significant, inverse relation was determined between total herbicide compound concentrations in ground water and the average soil slope within a 2‐km radius of sampled wells. Steeper soil slopes may increase the likelihood of surface runoff occurring rather than ground‐water infiltration–decreasing the transport of herbicide compounds to ground water. As expected, a significant positive relation was determined between intensity of herbicide use and herbicide concentrations in ground water.