Use of a Numerical Model to Simulate the Hydrologic System and Transport of Contaminants Near Joint Base Cape Cod, Western Cape Cod, Massachusetts

• DOI: 10.3133/sir20185139
• Publication Date: 2019-04-18T17:04:30Z
• Authors: Donald A. Walter; Timothy D. McCobb; Michael N. Fienen
• Keywords: Bedrock; Groundwater model

First posted April 18, 2019 For additional information, contact: Director, New England Water Science Center U.S. Geological Survey331 Commerce Way, Suite 2Pembroke, NH 03275 Historical training and operational activities at Joint Base Cape Cod (JBCC) on western Cod, Massachusetts, have resulted in the release of contaminants into an underlying glacial aquifer that is sole source water to surrounding communities. Remedial systems been installed contain remove contamination from aquifer. Groundwater withdrawals for public supply are expected increase as region continues urbanize. Increases water-supply wastewater return flow likely will affect hydrologic system around JBCC could transport any may remain following remediation JBCC. The Survey, cooperation with Air Force Civil Engineer Center, developed a numerical, steady-state regional model Sagamore lens evaluated potential effects future (2030) groundwater levels, streamflows, hydraulic gradients, advective near JBCC.The consists generally sandy sediments underlain by impermeable bedrock bounded laterally freshwater/saltwater interface. Data altitude surface, position interface, lithology aquifer, spatial distribution recharge, boundaries were incorporated three-dimensional, finite-difference model.Some inputs numerical model—aquifer properties, leakances, recharge—are represented parameters facilitate estimation optimal parameter values inverse calibration. A hybrid parameterization scheme, both zones piecewise constancy pilot points, used represent conductivity; other adjustable include boundary leakance, porosity. subsurface contamination, ages compiled, evaluated, develop observations long-term average gradients advective-transport patterns. These conditions combined parameterized calibration estimate best fit observations.Current (2010) simulated calibrated characterize determine increased patterns radially outward water-table divide northern part JBCC; diverges toward all points compass. Most contaminant occur shallow parts On average, about one-half flux occurs shallowest 20 percent saturated thickness; even more predominant streams lakes. Projected increases decrease levels maximum 1.2 feet drawdowns exceeding 1 foot limited areas largest withdrawals, such JBCC, Long Pond Falmouth, eastern Barnstable. Streamflow decreases 6 percent; drawdowns. Changes hydraulic-gradient directions table exceed degree 13 divides where gradient magnitudes small large withdrawals. Predictions randomly selected locations similar current results indicate projected but small.Several assumptions inherent model, including weights calibration, representation local-scale heterogeneity, simulation predictions; these alternative models calibrations. Eight calibrations performed which different, reasonable, used. preferred had overall observations.Fine-grained silty many silt lenses can locally gradients. set silts different correlation distances conductivities indicated explicitly representing implicit heterogeneity be sufficient scale regional-scale coastal boundary, two seabeds their associated interface positions test importance assumed coastal-boundary condition. predictions streamflow—streamflows smaller (silty) seabed leakances. However, transport, particularly between models, indicating leakance does not simulations inland