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If groundwater is contaminated, will water from the well be contaminated?

Eberts SM - Ground Water (2014)

View Article: PubMed Central - PubMed

Affiliation: U.S. Geological Survey, 6480 Doubletree Ave., Columbus, OH 43229. smeberts@usgs.gov.

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In a recent study of public-supply-well water quality in the United States, nearly two-thirds ofall samples from 932 public wells tapping 30 regionally extensive aquifers contained detectableamounts of drinking-water contaminants that originated entirely or primarily from manmade sources.Twenty-two percent of the samples contained at least one contaminant (manmade or naturallyoccurring) at concentrations greater than drinking-water standards or other human health benchmarks... For example, groundwater age can serve as a measure of intrinsicsusceptibility, but it might not be feasible to estimate groundwater age for the large number ofwells that would be necessary for assessing public-supply-well vulnerability across a regionallyextensive aquifer... In contrast, the percentage of well-drained soils—which does not accountfor as many underlying processes as groundwater age—might be a suitable measure of intrinsicsusceptibility for an aquifer-wide assessment of public wells... Given this definition of water quality and the widespread detection of low levels of contaminantsin water from public-supply wells, the following is a relevant question for wellfield operators,water-resources managers, drinking-water regulators, and scientists who constantly need to stretchlimited resources, “If groundwater is contaminated, will water from the well becontaminated?” The answer is, “it depends. ” That is, it depends on theproportions of (and contaminant concentrations in) the different waters in the aquifer that enterand mix in the well... For example,, simulate water-quality responses to hypotheticalnonpoint-source contamination at several public-supply wells that produce different combinations ofyoung and old (pre-1950s) groundwater... They show that wells with large fractions of young waterwould respond faster to land use change designed to reduce chemical fluxes to the water table,whereas wells with small fractions of young water would benefit from greater in-well dilution ofmanmade contaminants by old, unaffected water (Figure 2). demonstrate how point-sourcecontaminant releases of varying magnitude can affect supply wells operating at different extractionrates, and state, “We do not advocate reliance on in-well blending to maintain water supplystandards but …... Distinguishing situations in which lowconcentrations in public wells represent the tip-of-the-iceberg (in terms of water quality) fromthose that represent the maximum or near maximum concentration for the produced water (given thecontaminant source) is critical for sustaining high-quality groundwater sources of drinking water.In other words, if one simply wants to know whether a manmade contaminant might reach a well, it maybe sufficient to analyze the water from the well for extremely low concentrations of the contaminantto confirm a connection between the well and a local (often unknown) source of contamination... The paper by Chapelle et al. in this issue describes numerical mass balance modeling thatexplores the relation between aquifer geochemical conditions and water quality at public-supplywells... Finally, the paper by Böhlke et al. in this issue introduces an interactiveeducational webtool that allows one to explore the effects of aquifer-well interactions on the agemixture of water from a well, along with the influence of this age mixture on contaminant trends inthe well water... The complexity of the water mixture in samples from such wells canrequire more elaborate interpretation than what is required for samples from monitoring wellsbecause of the relatively large aquifer volume and associated conditions sampled by public wells;however, public-supply-well samples can be interpreted in ways that lead to valuable observationsand conclusions... Knowing what water-quality variables tomeasure, what spatial and temporal scales on which to measure them and how to interpret theresulting data can help resource managers explain and forecast the quality of water from theirwells... Developing an understanding of the vulnerability factor (or factors) that most influencetypical wells in different “type settings” is a logical next step, followed by anextrapolation of this understanding to less studied wells and areas.

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Location of selected wells having low concentrations of manmade and naturally occurringdrinking-water contaminants, typifying different aquifer-well combinations. Woodbury, Connecticut:volatile organic compounds (VOCs), nitrate, pesticides, uranium, and radon; unconsolidated sediment(sand); mostly oxic conditions; short well screen (10s of feet); and young water in well. NearTampa, Florida: VOCs, nitrate, pesticides, arsenic, uranium, and radon; carbonate rocks; oxic andanoxic conditions; open hole; and mix of very young and generally young water in well. York,Nebraska: VOCs, uranium, and arsenic; layered unconsolidated sediment (sand); anoxic conditions inconfined aquifer; well screen beneath clay confining unit; and mix of young and old water inwell.
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fig01: Location of selected wells having low concentrations of manmade and naturally occurringdrinking-water contaminants, typifying different aquifer-well combinations. Woodbury, Connecticut:volatile organic compounds (VOCs), nitrate, pesticides, uranium, and radon; unconsolidated sediment(sand); mostly oxic conditions; short well screen (10s of feet); and young water in well. NearTampa, Florida: VOCs, nitrate, pesticides, arsenic, uranium, and radon; carbonate rocks; oxic andanoxic conditions; open hole; and mix of very young and generally young water in well. York,Nebraska: VOCs, uranium, and arsenic; layered unconsolidated sediment (sand); anoxic conditions inconfined aquifer; well screen beneath clay confining unit; and mix of young and old water inwell.

Mentions: Site-specific assessments are best for identifying the most beneficial protection mechanisms foran individual well, which can differ even for wells with similar contaminant detections. Forexample, source water protection in Woodbury, Connecticut (Figure1), depends on the entire community, because the groundwater throughout the local sandaquifer is oxic and very young (generally <15 years). Preferential flow along karst featuresin a semi-confined carbonate-rock aquifer used for public supply near Tampa, Florida, causesdifferent public-supply wells to be more or less hydraulically connected to an overlying, morevulnerable sand aquifer. Consequently, the degree of protection for public wells in this area couldbe tied to the similarity between the water chemistry at the wells and the water chemistry in thesand aquifer. In York, Nebraska, preventing down-wellbore flow in multi-aquifer irrigation andsupply wells that are located upgradient of confined-aquifer public-supply wells would best preventshallow contaminated groundwater from reaching the water-supply aquifer in the first place (Eberts et al. 2013).


If groundwater is contaminated, will water from the well be contaminated?

Eberts SM - Ground Water (2014)

Location of selected wells having low concentrations of manmade and naturally occurringdrinking-water contaminants, typifying different aquifer-well combinations. Woodbury, Connecticut:volatile organic compounds (VOCs), nitrate, pesticides, uranium, and radon; unconsolidated sediment(sand); mostly oxic conditions; short well screen (10s of feet); and young water in well. NearTampa, Florida: VOCs, nitrate, pesticides, arsenic, uranium, and radon; carbonate rocks; oxic andanoxic conditions; open hole; and mix of very young and generally young water in well. York,Nebraska: VOCs, uranium, and arsenic; layered unconsolidated sediment (sand); anoxic conditions inconfined aquifer; well screen beneath clay confining unit; and mix of young and old water inwell.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4265273&req=5

fig01: Location of selected wells having low concentrations of manmade and naturally occurringdrinking-water contaminants, typifying different aquifer-well combinations. Woodbury, Connecticut:volatile organic compounds (VOCs), nitrate, pesticides, uranium, and radon; unconsolidated sediment(sand); mostly oxic conditions; short well screen (10s of feet); and young water in well. NearTampa, Florida: VOCs, nitrate, pesticides, arsenic, uranium, and radon; carbonate rocks; oxic andanoxic conditions; open hole; and mix of very young and generally young water in well. York,Nebraska: VOCs, uranium, and arsenic; layered unconsolidated sediment (sand); anoxic conditions inconfined aquifer; well screen beneath clay confining unit; and mix of young and old water inwell.
Mentions: Site-specific assessments are best for identifying the most beneficial protection mechanisms foran individual well, which can differ even for wells with similar contaminant detections. Forexample, source water protection in Woodbury, Connecticut (Figure1), depends on the entire community, because the groundwater throughout the local sandaquifer is oxic and very young (generally <15 years). Preferential flow along karst featuresin a semi-confined carbonate-rock aquifer used for public supply near Tampa, Florida, causesdifferent public-supply wells to be more or less hydraulically connected to an overlying, morevulnerable sand aquifer. Consequently, the degree of protection for public wells in this area couldbe tied to the similarity between the water chemistry at the wells and the water chemistry in thesand aquifer. In York, Nebraska, preventing down-wellbore flow in multi-aquifer irrigation andsupply wells that are located upgradient of confined-aquifer public-supply wells would best preventshallow contaminated groundwater from reaching the water-supply aquifer in the first place (Eberts et al. 2013).

View Article: PubMed Central - PubMed

Affiliation: U.S. Geological Survey, 6480 Doubletree Ave., Columbus, OH 43229. smeberts@usgs.gov.

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

In a recent study of public-supply-well water quality in the United States, nearly two-thirds ofall samples from 932 public wells tapping 30 regionally extensive aquifers contained detectableamounts of drinking-water contaminants that originated entirely or primarily from manmade sources.Twenty-two percent of the samples contained at least one contaminant (manmade or naturallyoccurring) at concentrations greater than drinking-water standards or other human health benchmarks... For example, groundwater age can serve as a measure of intrinsicsusceptibility, but it might not be feasible to estimate groundwater age for the large number ofwells that would be necessary for assessing public-supply-well vulnerability across a regionallyextensive aquifer... In contrast, the percentage of well-drained soils—which does not accountfor as many underlying processes as groundwater age—might be a suitable measure of intrinsicsusceptibility for an aquifer-wide assessment of public wells... Given this definition of water quality and the widespread detection of low levels of contaminantsin water from public-supply wells, the following is a relevant question for wellfield operators,water-resources managers, drinking-water regulators, and scientists who constantly need to stretchlimited resources, “If groundwater is contaminated, will water from the well becontaminated?” The answer is, “it depends. ” That is, it depends on theproportions of (and contaminant concentrations in) the different waters in the aquifer that enterand mix in the well... For example,, simulate water-quality responses to hypotheticalnonpoint-source contamination at several public-supply wells that produce different combinations ofyoung and old (pre-1950s) groundwater... They show that wells with large fractions of young waterwould respond faster to land use change designed to reduce chemical fluxes to the water table,whereas wells with small fractions of young water would benefit from greater in-well dilution ofmanmade contaminants by old, unaffected water (Figure 2). demonstrate how point-sourcecontaminant releases of varying magnitude can affect supply wells operating at different extractionrates, and state, “We do not advocate reliance on in-well blending to maintain water supplystandards but …... Distinguishing situations in which lowconcentrations in public wells represent the tip-of-the-iceberg (in terms of water quality) fromthose that represent the maximum or near maximum concentration for the produced water (given thecontaminant source) is critical for sustaining high-quality groundwater sources of drinking water.In other words, if one simply wants to know whether a manmade contaminant might reach a well, it maybe sufficient to analyze the water from the well for extremely low concentrations of the contaminantto confirm a connection between the well and a local (often unknown) source of contamination... The paper by Chapelle et al. in this issue describes numerical mass balance modeling thatexplores the relation between aquifer geochemical conditions and water quality at public-supplywells... Finally, the paper by Böhlke et al. in this issue introduces an interactiveeducational webtool that allows one to explore the effects of aquifer-well interactions on the agemixture of water from a well, along with the influence of this age mixture on contaminant trends inthe well water... The complexity of the water mixture in samples from such wells canrequire more elaborate interpretation than what is required for samples from monitoring wellsbecause of the relatively large aquifer volume and associated conditions sampled by public wells;however, public-supply-well samples can be interpreted in ways that lead to valuable observationsand conclusions... Knowing what water-quality variables tomeasure, what spatial and temporal scales on which to measure them and how to interpret theresulting data can help resource managers explain and forecast the quality of water from theirwells... Developing an understanding of the vulnerability factor (or factors) that most influencetypical wells in different “type settings” is a logical next step, followed by anextrapolation of this understanding to less studied wells and areas.

Show MeSH