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Effects of seasonal operation on the quality of water produced by public-supply wells.

Bexfield LM, Jurgens BC - Ground Water (2014)

Bottom Line: Seasonal variability in groundwater pumping is common in many places, but resulting effects of seasonal pumping stress on the quality of water produced by public-supply wells are not thoroughly understood.Seasonal variability in contaminant concentrations in Modesto is influenced primarily by effects of summer pumping on vertical hydraulic gradients that drive migration of shallow groundwater through the aquifer to supply wells.Results suggest that even in aquifers dominated by old groundwater, changes to seasonal pumping patterns and/or to depth of well completion can help reduce vulnerability to selected contaminants of either natural or anthropogenic origin.

View Article: PubMed Central - PubMed

Affiliation: U.S. Geological Survey, Placer Hall, 6000 J St., Sacramento, CA 95819.

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When the Modesto study well (MSW) is idle for long periods during the winter, flow through the wellbore results in movement of young groundwater with high specific conductance and elevated uranium and nitrate concentrations from shallower parts of the aquifer to greater depths, as illustrated by continuous water-level and specific-conductance data from the deep completion of a monitoring-well nest less than 30 m away (modified from Jurgens et al. 2008). When the MSW is pumped during the winter, it discharges larger amounts of contaminated groundwater than would otherwise be present if deep storage of formerly shallow groundwater did not occur.
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fig06: When the Modesto study well (MSW) is idle for long periods during the winter, flow through the wellbore results in movement of young groundwater with high specific conductance and elevated uranium and nitrate concentrations from shallower parts of the aquifer to greater depths, as illustrated by continuous water-level and specific-conductance data from the deep completion of a monitoring-well nest less than 30 m away (modified from Jurgens et al. 2008). When the MSW is pumped during the winter, it discharges larger amounts of contaminated groundwater than would otherwise be present if deep storage of formerly shallow groundwater did not occur.

Mentions: Continuous hydraulic-head and specific-conductance data from the monitoring-well nest located within 30 m of the MSW (Figure 6) show that seasonal changes in the quality of water from the MSW are as a result of wellbore flow that occurs during prolonged periods of nonoperation. The steep vertical hydraulic gradient across the screened interval of the MSW causes shallow groundwater to enter the well or annular space and move downward through the wellbore when the well is not pumping; this flow exits the wellbore near the bottom of the well and enters the deep part of the aquifer (Jurgens et al. 2008). Movement of shallow groundwater into the deep part of the aquifer is reflected by the rise in hydraulic head and specific conductance in the deep monitoring well when the MSW has been idle for long periods (Figure 6). The head and conductance data begin to fall during the summer, when long periods of pumping cause the stored shallow groundwater to be evacuated from the deep part of the aquifer.


Effects of seasonal operation on the quality of water produced by public-supply wells.

Bexfield LM, Jurgens BC - Ground Water (2014)

When the Modesto study well (MSW) is idle for long periods during the winter, flow through the wellbore results in movement of young groundwater with high specific conductance and elevated uranium and nitrate concentrations from shallower parts of the aquifer to greater depths, as illustrated by continuous water-level and specific-conductance data from the deep completion of a monitoring-well nest less than 30 m away (modified from Jurgens et al. 2008). When the MSW is pumped during the winter, it discharges larger amounts of contaminated groundwater than would otherwise be present if deep storage of formerly shallow groundwater did not occur.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4265191&req=5

fig06: When the Modesto study well (MSW) is idle for long periods during the winter, flow through the wellbore results in movement of young groundwater with high specific conductance and elevated uranium and nitrate concentrations from shallower parts of the aquifer to greater depths, as illustrated by continuous water-level and specific-conductance data from the deep completion of a monitoring-well nest less than 30 m away (modified from Jurgens et al. 2008). When the MSW is pumped during the winter, it discharges larger amounts of contaminated groundwater than would otherwise be present if deep storage of formerly shallow groundwater did not occur.
Mentions: Continuous hydraulic-head and specific-conductance data from the monitoring-well nest located within 30 m of the MSW (Figure 6) show that seasonal changes in the quality of water from the MSW are as a result of wellbore flow that occurs during prolonged periods of nonoperation. The steep vertical hydraulic gradient across the screened interval of the MSW causes shallow groundwater to enter the well or annular space and move downward through the wellbore when the well is not pumping; this flow exits the wellbore near the bottom of the well and enters the deep part of the aquifer (Jurgens et al. 2008). Movement of shallow groundwater into the deep part of the aquifer is reflected by the rise in hydraulic head and specific conductance in the deep monitoring well when the MSW has been idle for long periods (Figure 6). The head and conductance data begin to fall during the summer, when long periods of pumping cause the stored shallow groundwater to be evacuated from the deep part of the aquifer.

Bottom Line: Seasonal variability in groundwater pumping is common in many places, but resulting effects of seasonal pumping stress on the quality of water produced by public-supply wells are not thoroughly understood.Seasonal variability in contaminant concentrations in Modesto is influenced primarily by effects of summer pumping on vertical hydraulic gradients that drive migration of shallow groundwater through the aquifer to supply wells.Results suggest that even in aquifers dominated by old groundwater, changes to seasonal pumping patterns and/or to depth of well completion can help reduce vulnerability to selected contaminants of either natural or anthropogenic origin.

View Article: PubMed Central - PubMed

Affiliation: U.S. Geological Survey, Placer Hall, 6000 J St., Sacramento, CA 95819.

Show MeSH