Prepared in cooperation with the Rhode Island Department of Health Delineation and Prediction Uncertainty of Areas Contributing Recharge to Selected Well Fields in Wetland and Coastal Settings, Southern Rhode Island Scientific Investigations Report 2010–5060 U.S. Department of the Interior U.S. Geological Survey This page has been left blank intentionally. Delineation and Prediction Uncertainty of Areas Contributing Recharge to Selected Well Fields in Wetland and Coastal Settings, Southern Rhode Island By Paul J. Friesz Prepared in cooperation with the Rhode Island Department of Health Scientific Investigations Report 2010–5060 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2010 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Friesz, P.J., 2010, Delineation and prediction uncertainty of areas contributing recharge to selected well fields in wet- land and coastal settings, southern Rhode Island: U.S. Geological Survey Scientific Investigations Report 2010–5060, 69 p. (Also available online at http://pubs.usgs.gov/sir/2010/5060.) iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................2 Purpose and Scope ..............................................................................................................................4 Overview of Study Site Settings and Previous Investigations ......................................................4 Numerical Modeling ......................................................................................................................................5 Hydraulic Properties.............................................................................................................................5 Recharge Rates .....................................................................................................................................6 South Kingstown Study Site .........................................................................................................................7 Geology ...................................................................................................................................................9 Hydrology .............................................................................................................................................11 Simulation of Groundwater Flow and Areas Contributing Recharge .........................................14 Model Extent and Spatial Discretization ................................................................................14 Boundary Conditions and Model Parameters .......................................................................19 Observations ...............................................................................................................................22 Estimation of Parameters .........................................................................................................23 Simulated Water-Table Contours and Water Budget ..........................................................27 Deterministic Areas Contributing Recharge .........................................................................27 Probabilistic Areas Contributing Recharge ...........................................................................30 Charlestown Study Site...............................................................................................................................39 Geology .................................................................................................................................................39 Hydrology .............................................................................................................................................39 Simulation of Groundwater Flow and Areas Contributing Recharge .........................................42 Model Extent and Spatial Discretization ................................................................................42 Boundary Conditions and Model Parameters .......................................................................43 Observations ...............................................................................................................................43 Estimation of Parameters .........................................................................................................46 Simulated Water-Table Contours and Water Budget ..........................................................50 Deterministic Areas Contributing Recharge .........................................................................50 Probabilistic Areas Contributing Recharge ...........................................................................54 Summary and Conclusions .........................................................................................................................60 Acknowledgments .......................................................................................................................................62 References Cited..........................................................................................................................................62 Appendix 1. Water depth, and thickness of peat and organic-rich sediment (location of profiles shown on figures 3 and 20), South Kingstown and Charlestown study sites, southern Rhode Island ...................................................................................................66 Appendix 2. A, Stage of Worden Pond and B, stage of Tucker Pond and water levels in a pond-bottom piezometer, 2006–2008 (location of measurement sites shown on figure 3), South Kingstown study site, southern Rhode Island ...........................................68 Appendix 3. Streamflow measurements made at partial-record sites (location of partial-record sites shown on figures 3 and 20), South Kingstown and Charlestown study sites, southern Rhode Island ..................................................................69 iv Figures 1. Map showing study site well fields in South Kingstown and Charlestown, Rhode Island, and selected water-supply districts, U.S. Geological Survey (USGS) long-term network streamgages and observation wells, and a National Oceanic and Atmospheric Administration (NOAA) climatological station .........................................3 2. Map showing production wells, section line, selected borings, model extent, bedrock-surface contours, and surficial geology, South Kingstown study site, southern Rhode Island. Bedrock-surface contours from Masterson and others (2007) ..................................................................................................................................8 3. Map showing data-collection network near production wells, South Kingstown study site, southern Rhode Island ............................................................................................10 4. Diagram showing geologic cross section, South Kingstown study site, southern Rhode Island ................................................................................................................................12 5. Graph showing streamflow for the Beaver River streamgage (01117468) near Usquepaug, Rhode Island, during 1999–2008 (streamgage location shown on figure 1) ...................................................................................................................................14 6. Graphs showing water levels measured in observation well CHW18 during 1951–60, 1988–92, and 1999–2008, Charlestown, Rhode Island (well location shown in figure 1) ....................................................................................................................................15 7. Graph showing stage of wetland and water levels in piezometers screened in peat, and in sand and gravel near A, west well field and B, east well field, 2007–2008, South Kingstown study site, southern Rhode Island ........................................16 8. Graph showing plot of drawdown with time compared to a Theis type curve and a leaky-aquifer type curve for a piezometer screened beneath the wetland near the east well field, March14–April 3, 2008, South Kingstown study site, southern Rhode Island ................................................................................................................................18 9. Map showing model-boundary types and observations, South Kingstown study site, southern Rhode Island ......................................................................................................20