Groundwater-quality data from the National Water-Quality Assessment Project, January through December 2014 and select quality-control data from May 2012 through December 2014

Self Cite

This is the first assessment of groundwater from public-supply wells across the United States to analyze for >100 pesticide degradates and to provide human-health context for degradates without benchmarks. Samples from 1204 wells in aquifers representing 70% of the volume pumped for drinking supply were analyzed for 109 pesticides (active ingredients) and 116 degradates. Among the 41% of wells where pesticide compounds were detected, nearly two-thirds contained compound mixtures and three-quarters contained degradates. Atrazine, hexazinone, prometon, tebuthiuron, four atrazine degradates, and one metolachlor degradate were each detected in >5% of wells. Detection frequencies were largest for aquifers with more shallow, unconfined wells producing modern-age groundwater. To screen for potential human-health concerns, benchmark quotients (BQs) were calculated by dividing concentrations by the human-health benchmark, when available. For degradates without benchmarks, estimated values (estimated benchmark quotients (BQE)) were first calculated by assuming equimolar toxicity to the most toxic parent; final analysis excluded degradates with likely overestimated toxicity. Six pesticide compounds and 1.6% of wells had concentrations approaching levels of potential concern (individual or summed BQ or BQE values >0.1), and none exceeded these levels (values >1). Therefore, although pesticide compounds occurred frequently, concentrations were low, even accounting for mixtures and degradates without benchmarks.

Section: Methodsmentioning

confidence: 99%

Pesticides and Pesticide Degradates in Groundwater Used for Public Supply across the United States: Occurrence and Human-Health Context

Bexfield

Belitz

Lindsey

et al. 2020

Self Cite

“…The study design allows for comparison among regional aquifers (i.e., PAs), as well as broad lithologic groups, confinement status, and general aqueous geochemical properties, but is limited in describing local geological variability. Equal-area grids, with one randomly sampled well per grid cell, were used to obtain spatially representative unbiased assessments of the quality of source waters in each PA. , The 19 PAs represent seven primary lithology groups: felsic crystalline rocks, basalts and volcanic rocks, carbonate rocks, sandstones, semiconsolidated coastal sands, and sands and gravels of either glacial or nonglacial (fluvial/alluvial) origin. ,,, Collected samples represent water produced from long well screens or open boreholes that represent broad-scale conditions but preclude determination of specific yield from locally variable geology intercepted by the well (PA acronyms, primary lithology, number of samples, and frequency of occurrence for 222 Rn, 210 Pb, and 210 Po relative to respective concentration thresholds are listed in Table SI-1). In the North Atlantic (NACP) and Southeastern Coastal Plain (SECP) PAs, specific regionally stacked aquifers that are separated by confining units were selected for monitoring, based on their importance as sources of public-drinking-water supplies; , thus, 23 networks were sampled in 19 PAs (Table SI-1).…”

Section: Methodsmentioning

confidence: 99%

“…Data Access. The data sets containing the radionuclide data and ancillary water-quality data are compiled by Arnold et al (2016, 2017, 2018, and 2020), − and are available through the ScienceBase catalog of the USGS for download at , , , and , respectively.…”

mentioning

confidence: 99%

Occurrence and Geochemistry of Lead-210 and Polonium-210 Radionuclides in Public-Drinking-Water Supplies from Principal Aquifers of the United States

Szabó

Stackelberg

Cravotta

2020

Self Cite

On the basis of lifetime cancer risks, lead-210 (210Pb) and polonium-210 (210Po) ≥ 1.0 and 0.7 pCi/L (picocuries per liter), respectively, in drinking-water supplies may pose human-health concerns. 210Pb and 210Po were detected at concentrations greater than these thresholds at 3.7 and 1.5%, respectively, of filtered untreated groundwater samples from 1263 public-supply wells in 19 principal aquifers across the United States. Nationally, 72% of samples with radon-222 (222Rn) concentrations > 4000 pCi/L had 210Pb ≥ 1.0 pCi/L. 210Pb is mobilized by alpha recoil associated with the decay of 222Rn and short-lived progeny. 210Pb concentrations ≥ 1.0 pCi/L occurred most frequently where acidic groundwaters inhibited 210Pb readsorption (felsic-crystalline rocks) and where reducing alkaline conditions favored dissolution of iron–manganese- (Fe–Mn-) oxyhydroxides (which adsorb 210Pb) and formation of lead–carbonate complexes (enhancing lead (Pb) mobility). 210Po concentrations ≥ 0.7 pCi/L occurred almost exclusively in confined Coastal Plain aquifers where old (low percent-modern carbon-14) groundwaters were reducing, with high pH (>7.5) and high sodium/chloride (Na/Cl) ratios resulting from cation exchange. In high-pH environments, aqueous polonium (Po) is poorly sorbed, occurring as dihydrogen polonate (H2PoO3(aq)) or, under strongly reducing conditions, as a hydrogen-polonide anion (HPo–). Fe–Mn- and sulfate-reduction and cation-exchange processes may mobilize polonium from mineral surfaces. Po2+ occurrence in low-to-neutral-pH waters is attenuated by adsorption.

“…Data tables and detailed descriptions of the procedures used to collect and analyze groundwater samples are provided elsewhere. , Brief descriptions of these procedures are provided below. In the Columbia Plateau (CP) study area, groundwater-quality samples were collected in 2014 from twenty-three shallow monitoring wells screened in the overburden beneath cropland and twenty-seven domestic or public supply wells typically screened in basalt aquifers (Figure S1).…”

Section: Methods and Datamentioning

confidence: 99%

Using Age Tracers and Decadal Sampling to Discern Trends in Nitrate, Arsenic, and Uranium in Groundwater Beneath Irrigated Cropland

Tesoriero

Burow

Frans

et al. 2019

Self Cite

Repeat sampling and age tracers were used to examine trends in nitrate, arsenic, and uranium concentrations in groundwater beneath irrigated cropland. Much higher nitrate concentrations in shallow modern groundwater were observed at both the Columbia Plateau and High Plains sites (median values of 10.2 and 15.4 mg/L as N, respectively) than in groundwater that recharged prior to the onset of intensive irrigation (median values of <1 and <4 mg/L as N, respectively). Repeat sampling of these well networks indicates that high nitrate concentrations in modern, shallow groundwater have been sustained for decades, posing a future risk to older, deeper groundwater used for drinking water. In fact, nitrate concentrations in older modern water (30−60 years since recharge) at the High Plains site have increased in the past decade. Groundwater irrigated areas in the Columbia Plateau tend to have higher nitrate concentrations in groundwater than continued...