Ground Water Flow Simulation of a Glacial Aquifer and its Implication for the Management of University of Water Supply System during Drought Periods

Nadim, F., and Bagtzoglou, A.C. Department of Civil & Environmental Engineering, The University of Connecticut Starn, J.J. U.S. Geological Survey

Abstract Approximately one quarter of the University of Connecticut campus’ and the town of Storrs’ water demand is supplied from four wells along the valley of the . The Fenton River well field was installed in 1947 and has yielded 0.5 to 1.0 million gallons per day since then. The Fenton River valley is filled with sand and gravel in a glacial stratified aquifer to a maximum depth of about 60 feet. Aquifers in glacial stratified deposits are generally the highest yielding aquifers in Connecticut. The stratified glacial deposits receive recharge directly from precipitation on the deposits and indirectly from precipitation on upland areas. The pumping wells developed in the Fenton River valley also can induce infiltration through the riverbed. Previous studies at the University of Connecticut well field have shown that streambed infiltration can contribute about 33% of the pumped water from the Fenton River well field under normal pumping conditions. In this article, simulations of the effect of pumping wells on streambed infiltration during drought periods are discussed. The role of bedrock contribution to recharge of the aquifer was studied with the aid of bedrock monitoring wells and existing geological information of the study area. The goal of this study is to design a management scenario that takes into account all existing aquifer recharge sources and assists the University in sustaining the town and University water supply while minimizing the impacts on streamflow and fish habitat.

Introduction The University of Connecticut (UConn) water supply is obtained from four wells located along the valley of the Fenton River and four wells located along the valley of the (about 2 miles east and west of the university campus, respectively). The Fenton River wells (Table 1) were installed beginning in 1926 and have produced up to 0.5 to 1.0 million gallons per day (MGD) (1.31 cubic feet per second, cfs) since that time (Rahn, 1971; LBG 2002). The Connecticut Department of Environmental Protection (CTDEP) has registered the four Fenton River wells for a maximum withdrawal rate of 0.8443 MGD (LBG, 2002). The amount of water withdrawn from the Fenton River wells from 1994 through 2002 varies (Table 2). From 1989 to 1997, water demand decreased due to a reduction in student residential population. However, in February of 1999, the UConn Board of Trustees accepted a plan to increase total student enrollment by approximately 3,000 at the Storrs campus by 2003. This brought the total enrollment to approximately 18,000. In addition to an increase in University population, non-university population also increased during the period of 1998 – 1999. The UConn domestic water-supply system provides potable water for approximately 10,000 resident students, 7,000 nonresident students, and 4,000 faculty and staff at the Storrs Campus. In addition, private homes, apartments, and some local businesses totaling approximately 2,000 people also are served by this system. It should be noted that during 1996 and 1997, all University water-piping systems were repaired for leaks, and this could have had significant impact on the reduction of water consumption.

Table 1. Characteristics of the Fenton River pumping wells Well A (Dug Well) Installed 1926 28’ deep 24” O. D. Casing Screen Length (NA) Well B (Gravel Packed) Installed 1949 70’ deep 12” O. D. Casing Screen Length 21.5’ Well B (Gravel Packed) Installed 1949 63’ deep 12” O. D. Casing Screen Length 21.5’ Well B (Gravel Packed) Installed 1959 59’ deep 12” O. D. Casing Screen Length 15’

863 Table 2. Amount of water withdrawn during the period 1994 to 2002. Year The Fenton Well Field (MG/Yr.) The Willimantic Well Field (MG/Yr.) 1994 75 441 1995 84 427 1996 85 383 1997 63 360 1998 63 351 1999 56 NA 2000 83 NA 2001 39 NA 2002 82 NA NA = data not available

Hydrogeology of the Fenton River area The Fenton River is located in the Watershed, which is part of the Thames River Basin (Rahn, 1970). The average annual precipitation at the National Oceanic and Atmospheric Administration (NOAA) gauge located in Storrs, Connecticut was 47.34 inches for the period of 1961 – 1997 (LBG, 2002). The Fenton River watershed covers an area of approximately 34.36 square miles. In the Thames River Basin, runoff is estimated to average about half of the precipitation rate (22.5 – 24 inches/yr. or 1.64 –1.74 cfs/mi2). Therefore, the annual direct discharge from the Fenton River to the can be estimated at 56.35 cfs (36.41 MGD) (Hoag et al., 2002). In August of 1966 (August 30 to September 3, 1966) the Fenton River had completely dried up in the area of the well field. The streamflow had disappeared adjacent to Well B and reappeared about 0.5 miles downstream (Rahn, 1971). The Fenton River valley is filled with glacial stratified deposits (GSD) to a depth of about 60 feet (Rahn, 1971). Aquifers in GSD are considered the best aquifers in Connecticut. The average transmissivity of these aquifers is about 9,500 ft2/d (Randall et al., 1988), and properly constructed wells can yield several hundred to over 1,000 gpm (Rahn, 1971). The uplands surrounding the valley are covered by glacial till, a non-sorted, non-stratified material that ranges from less than 15 feet thick (thin till) to tens of feet thick (thick till). Glacial till has an average transmissivity of about 40 ft2/d (Randall and others, 1988), and properly constructed wells can yield 3 to 5 gpm (Rahn, 1971). Bedrock wells in the Fenton River area are completed in Paleozoic gneiss and can yield enough water for domestic or small industrial usage. Recharge to the Fenton River aquifer is largely from precipitation (minus the effects of evapotranspiration and surface runoff). Ground water generally moves laterally from recharge areas on the hill slopes and the GSD into the Fenton River. Additional recharge to the pumping wells is from infiltration induced from the Fenton River. Rahn (1971) studied the UConn well field and showed that streambed infiltration contributed up to 33% of the pumped water from the Fenton River well field under normal pumping conditions. Leggett Brashears and Graham (2002) indicated that the rate of water withdrawal from the aquifer was approximately equal to the rate of ground-water inflow to the Fenton River. Therefore, the wells could significantly impact the River flows during drought periods (LBG, 2002).

Pumping Scenarios Rahn (1971) defined three scenarios related to pumping in GSD. He stated that before pumping, ground water was recharging the stream flow. When pumping started, ground water would recharge the stream and also flow from the stream toward the pumping wells. After a long period of pumping when steady state conditions prevailed, he stated that the ground-water table would detach itself from the riverbed and vertical seepage of water from the streambed would recharge the aquifer with a time lag.

Model Description In this study, the effect of pumping wells on streambed infiltration during drought periods is being simulated with the aid of a computer model. A graphical user interface (GUI) to MODFLOW by the United States Geological Survey (USGS) is used to create model input files. The GUI is developed in a numerical environment program called Argus-ONE (ArgusOne, Version 4.2). The GIS layers pertaining to the Fenton River watershed were linked to MODFLOW-2000 (Harbaugh et al., 2000), which is being used to simulate ground-water flow during steady state and transient conditions. The finite-difference grid in MODFLOW-2000 is assumed to be rectangular horizontally, but the grid can be distorted vertically. Time increments in MODFLOW are grouped into periods of constant stress (stress periods) and shorter intervals within the stress periods (time steps). The time-dependent input data can be changed at every stress period.

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Work in Progress The simulation of a drought period in the Fenton River pumping well field is conducted for 30, 60, 120, and 180 days of continuous pumping for each one of the four wells A, B, C, and D in turn (approximately 500 gpm for each well). To simulate drought conditions, four different recharge values of 0, 2, 4, and 6 inches per year are applied. The contribution of water stored in the upland sections of the model domain (till, thick till and fractured bedrock) to the pumping wells will be assessed with simulation of drought conditions, and the amount of induced streambed infiltration will be determined. With recent refinement of ground water resource evaluation, it may now be possible to precisely quantify the amount of streambed infiltration towards the pumping well and predict the stream flow and ground water behavior during drought periods.

865 References Argus One Numerical Environment – A GIS Modeling System, 2001, Argus Interware, Inc. Jericho, NY, USA. Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, M.G., 2000, MODFLOW-2000, the U.S. Geological Survey modular ground- water model -- User guide to modularization concepts and the Ground-Water Flow Process: U.S.G.S. Open-File Report 00-92, 121 p. Hoag, G. E., Ogden, F., Neumann, R., Perkins, C., Starn, J., Warner, G., 2002. Long-Term Impact Analysis of the University of Connecticut’s Fenton River Water Supply Wells on the Habitat of the Fenton River, Proposal submitted to the University of Connecticut. Leggete, Brashears & Graham (LBG), Inc., 2002. Level A Mapping for Fenton River Field University of Connecticut, Final Report prepared for the University of Connecticut, LBG Trumbull, Connecticut. Rahn, P., The Hydrogeology of an Induced Streambed Infiltration Area, Ground Water, 1971, 21-32. Randall, A.D., Francis, R.M., Frimpter, M.H., and Emery, J.M., 1988, Region 19, Northeastern Appalachians, Chapter 22, in The Geology of North America, Volume O-2, Hydrogeology, Back, W., Rosenshein, J.S., and Seaber, P.R. eds.: Geological Society of America, Boulder, Colorado, pp 177-187. Rahn, P., Surficial Geology of the Spring Hill Quadrangle, [Hartford] State Geological and Natural History Survey of Connecticut, 1970.

Biographical Sketches

Farhad Nadim Farhad Nadim is a researcher at the Environmental Research Institute and a Ph.D. student at the University of Connecticut majoring in Environmental Engineering. Farhad Nadim holds Master of Science Degrees in Environmental Engineering from the University of Connecticut (1996) and the University of New Haven (1991). His Ph.D. research is focused on numerical simulation of the aquifer systems feeding the University of Connecticut pumping fields in the Fenton River Watershed. He has also conducted extensive bench-scale and pilot-scale research studies for remediation of soils contaminated with light and heavy petroleum products, coal tar and chlorinated solvents. He can be reached at Environmental Research Institute, the University of Connecticut, U-5210 Storrs, CT 06269-5210, Tel: (860) 486-4015, Fax: (860) 486-5488, email: [email protected].

Amvrossios C. Bagtzoglou Amvrossios C. Bagtzoglou is an associate professor at the Department of Civil and Environmental Engineering at the University of Connecticut. He received his Ph.D. degree in Water Resources and Environmental Engineering from the University of California (1990). He specializes in numerical modeling of environmental processes. Professor Bagtzoglou has published numerous papers in archival journals, book chapters, conference proceedings, and technical reports. He was/is Associate Editor for the journals Groundwater (1994-97), Water Resources Research (1999-2004), Environmental Forensics (2002-), and the Journal of the Water Resources Research Association (2003-). On top of his editorial duties, Professor Bagtzoglou reviews papers regularly for 18 technical journals. He is a member of several national and international professional organizations, the AGU Hydrology Section Groundwater Technical Committee, the ASCE Groundwater Hydrology Committee, Subject Matter Expert of Pacific Northwest National Laboratory (US DOE), the IAEG Commission, and the Study Science and Technical Advisory Committee. He can be reached at the Department of Civil and Environmental Engineering, 261 Glenbrook Road, Unit 2037, University of Connecticut, Storrs, CT 06269-2037, Tel: (860) 486-4017, Fax: (860) 486-2298, e-mail: [email protected] Jeffrey Starn Jeffrey Starn received a BS in Geology from Allegheny College and a Master of Science degree in Environmental Studies from Ohio University. He has been a hydrologist for 22 years, starting with the Peace Corps in Sierra Leone, West Africa in 1982. He has worked for the U.S. EPA in Atlanta, Georgia and for the USGS in Louisville, Kentucky. He is currently the head of the hydrologic studies section with the USGS in East Hartford, Connecticut, where his work focuses on flow in fractured rock aquifers, watershed simulation, and solute transport. He can be reached at U.S. Geological Survey 101 Pitkin Street East Hartford, CT 06108, Tel: (860) 291-6746, e-mail: [email protected]

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