Scientific Investigations Report 2007–5133
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Areas contributing recharge and sources of water to a production well field in the Village of Harrisville and to a production well field in the Town of Richmond were delineated on the basis of calibrated, steady-state ground-water-flow models representing average hydrologic conditions. The study sites represent contrasting glacial valley-fill settings. The area contributing recharge to a well is defined as the surface area where water recharges the ground water and then flows toward and discharges to the well.
In Harrisville, the production well field is composed of three wells in a narrow, approximately 0.5-mile-wide, valley-fill setting on opposite sides of Batty Brook, a small intermittent stream that drains 0.64 square mile at its confluence with the Clear River. Glacial stratified deposits are generally less areally extensive than previously published. The production wells are screened in a thin (30 feet) but transmissive aquifer. Paired measurements of ground-water and surface-water levels indicated that the direction of flow between the brook and the aquifer was generally downward during pumping conditions. Long-term mean annual streamflow from two streams upgradient of the well field totaled 0.72 cubic feet per second.
The simulated area contributing recharge for the 2005 average well-field withdrawal rate of 224 gallons per minute extended upgradient to ground-water divides in upland areas and encompassed 0.17 square mile. The well field derived 62 percent of pumped water from intercepted ground water and 38 percent from infiltrated stream water from the Batty Brook watershed. For the maximum simulated well-field withdrawal of 600 gallons per minute, the area contributing recharge expanded to 0.44 square mile to intercept additional ground water and infiltration of stream water; the percentage of water derived from surface water, however, was the same as for the average pumping rate. Because of the small size of Batty Brook watershed, most of the precipitation recharge in the watershed was withdrawn by the well field at the maximum rate either by intercepted ground water or indirectly by infiltrated stream water. Because the production wells are screened in a thin and transmissive aquifer in a small watershed, simulated ground-water traveltimes from recharge locations to the discharging wells were relatively short: 93 percent of the traveltimes were 10 years or less.
In Richmond, the production well field is composed of two wells adjacent to and east of the Wood River in a moderately broad, approximately 1.2-mile-wide, valley-fill setting. The wells are screened in a transmissive aquifer with saturated thickness greater than 60 feet. Streamflow measurements in Baker Brook, a tributary to the Wood River 0.4 mile north of the well-field site, indicated that natural net loss of streamflow between the upland-valley contact and a downstream site was 0.12 cubic feet per second under average hydrologic conditions.
Simulated areas contributing recharge for the maximum well-field pumping rate of 675 gallons per minute and for one-half the maximum rate extended northeastward from the well field to ground-water divides in upland areas. The area contributing recharge also included a remote, isolated area on the opposite side of the Wood River from the well field. The model simulation indicated that the well field did not derive any of its water from the Wood River because of the large watershed and associated quantity of ground water available for capture by the well field.
The area contributing recharge for one-half the maximum rate was 0.31 square mile and the primary source of water to the well field was direct precipitation recharge. Fifteen percent of the water withdrawn from the production wells, however, was obtained from Baker Brook, indicating the importance of even small, distant tributary streams to the contributing area to a well. The area contributing recharge on the opposite side of the Wood River is a small upland till area. For the maximum pumping rate, the 0.66-square-mile area contributing recharge extended farther up and down the valley to intercept additional ground water and infiltration from Baker Brook; the percentage of pumped water derived from Baker Brook (10 percent), however, was less than for the lower pumping rate. The area contributing recharge across the Wood River included upland till and stratified deposits near the upland-valley contact. Because the Richmond well field is in a larger watershed with saturated sediments thicker than at the Harrisville site, the overall ground-water traveltimes are greater: only 54 percent of the traveltimes are 10 years or less.
Hydrologic factors that most affected the simulated areas contributing recharge to production wells in the two contrasting valley-fill settings were recharge rates, the locations of upgradient ground-water divides, aquifer transmissivity, and, depending on the setting, the hydraulic connection between surface water and the aquifer. A well in the vicinity of a surface-water source may not always induce flow from that source, even if surface and ground waters are well connected, because the amount of water that a well draws from surface water also depends on the pumping rate and the quantity of ground water that the well can intercept. The area contributing recharge to a well also may include areas on the opposite side of a river from the well, despite the fact that the river is a major source of water in close proximity to the well. Under pumping conditions, precipitation recharge originating on the opposite side of a river may pass beneath the river and discharge to the well, although there may be little or no induced infiltration of river water. Areas contributing recharge can also extend into upland areas to ground-water divides and can also include isolated areas remote from a well.
Abstract
Introduction
Purpose and Scope
Description of Study Sites and Previous Investigations
Numerical Modeling
Hydraulic Properties
Recharge Rates
Harrisville Study Site
Geology
Hydrology
Ground-Water-Flow Model
Model Design
Simulation of Ground-Water Flow
Areas Contributing Recharge to Production Wells
Sensitivity and Uncertainty Analysis
Richmond Study Site
Geology
Hydrology
Ground-Water-Flow Model
Model Design
Simulation of Ground-Water Flow
Areas Contributing Recharge to Production Wells
Sensitivity and Uncertainty Analysis
Summary and Conclusions
Acknowledgments
References Cited
1–4. Maps showing—
1. Study sites in Rhode Island and selected U.S. Geological Survey long-term network streamflow-gaging stations and observation wells, and National Oceanic and Atmospheric Administration climatological stations
2. Production wells, section lines, selected borings and observation wells, model extent, and surficial geology, Harrisville study site, Rhode Island
3. Data-collection network near production wells and water levels on June 24, 2004, Harrisville study site, Rhode Island
4. Bedrock-surface contours, Harrisville study site, Rhode Island
5. Geologic cross sections showing Harrisville study site, Rhode Island
6–7. Graphs showing—
6. Water levels measured in observation well BUW187, 1997–2006, Harrisville study site, Rhode Island
7. Paired surface-water altitudes and ground-water altitudes at selected streambed piezometers, 2004–2006, Harrisville study site, Rhode Island
8. Map showing model-boundary types, recharge rates, simulated water-table contours for nonpumping, steady-state conditions, and spatial distribution of residuals (measured-simulated), Harrisville study site, Rhode Island
9. Graphs showing (A) relation between simulated and measured ground-water levels and (B) residual (measured minus simulated) ground-water levels as a function of measured ground-water levels, Harrisville study site, Rhode Island10–16. Maps showing—
10. Simulated area contributing recharge to the Harrisville well field at its average pumping rate of 224 gallons per minute, Harrisville study site, Rhode Island
11. Simulated area contributing recharge to the Harrisville well field at its maximum pumping rate of 600 gallons per minute, Harrisville study site, Rhode Island
12. Simulated traveltimes to the Harrisville well field at its maximum pumping rate of 600 gallons per minute, Harrisville study site, Rhode Island
13. Sensitivity analysis of the effects of multiplying the vertical hydraulic conductivity of streambed sediments at the well-field site by 0.5 and by 2, Harrisville study site, Rhode Island
14. Sensitivity analysis of the effects of multiplying the hydraulic conductivity of stratified deposits by 0.75 and by 1.25, Harrisville study site, Rhode Island 15. Sensitivity analysis of the effects of multiplying recharge rates by 0.75 and by 1.25, Harrisville study site, Rhode Island
16. Production wells, section lines, selected borings and observation wells, model extent, surficial geology, and bedrock-surface contours, Richmond study site, Rhode Island
17. Geologic cross sections showing Richmond study site, Rhode Island
18. Map showing model-boundary types, recharge rates, simulated water-table contours for nonpumping, steady-state conditions, and spatial distribution of residuals (measured-simulated), Richmond study site, Rhode Island
19. Graphs showing (A) relation between simulated and measured ground-water levels and (B) residual (measured minus simulated) ground-water levels as a function of measured ground-water levels, Richmond study site, Rhode Island
20–24. Maps showing—20. Simulated area contributing recharge to the Richmond well field at 337.5 gallons per minute, which is half of its maximum pumping rate of 675 gallons per minute, Richmond study site, Rhode Island
21. Simulated area contributing recharge to the Richmond well field at its maximum pumping rate of 675 gallons per minute, Richmond study site, Rhode Island
22. Simulated traveltimes to the Richmond well field at its maximum pumping rate of 675 gallons per minute, Richmond study site, Rhode Island
23. Sensitivity analysis of the effects of multiplying the hydraulic conductivity of stratified deposits by 0.75 and by 1.25, Richmond study site, Rhode Island 24. Sensitivity analysis of the effects of multiplying recharge rates by 0.75 and by 1.25, Richmond study site, Rhode Island
1. Characteristics of the production wells for the Harrisville and Richmond study sites, Rhode Island
2. Streamflow and drainage-area characteristics of the Branch and Nipmuc River streamflow-gaging stations, Harrisville study site, Rhode Island
3. Summary of the long-term mean annual streamflow analysis for the temporary streamflow-gaging stations upstream of the well-field site, Harrisville study site, Rhode Island
4. Summary of simulated values for hydraulic properties and recharge rates in the ground-water-flow model for the Harrisville study site, Rhode Island
5. Simulated steady-state average annual hydrologic budget for nonpumping conditions, Harrisville study site, Rhode Island
6. Sizes of areas contributing recharge to the Harrisville production well field (Central Street) and the percentages of water withdrawn from different sources, Harrisville study site, Rhode Island
7. Streamflow and drainage-area characteristics of selected streamflow-gaging stations in and near the Richmond study site, Rhode Island
8. Summary of the long-term mean annual ground-water discharge analysis for partial-record sites, Richmond study site, Rhode Island
9. Summary of simulated values for hydraulic properties and recharge rates in the ground-water-flow model for the Richmond study site, Rhode Island
10. Simulated steady-state average annual hydrologic budget for nonpumping conditions, Richmond study site, Rhode Island
11. Sizes of areas contributing recharge to the Richmond production well field and the percentages of water withdrawn from different sources, Richmond study site, Rhode Island
Friesz, P.J., and Stone, J.R., 2007, Simulation of ground-water flow and areas contributing recharge to production wells in contrasting glacial valley-fill settings, Rhode Island: U.S. Geological Survey Scientific Investigations Report 2007–5133, 50 p.
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