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Scientific Investigations Report 2010–5142

Prepared in cooperation with the Town of Newtown, Connecticut

Hydrogeology and Numerical Simulation of the Unconsolidated Glacial Aquifer in the Pootatuck River Basin, Newtown, Connecticut

By Carl S. Carlson, Remo A. Mondazzi, David M. Bjerklie, and Craig J. Brown

ABSTRACT

A study of the groundwater and stream-aquifer interaction in the Pootatuck River Basin, Newtown, Connecticut, was conducted to analyze the effect of production wells on the groundwater levels and streamflow in the Pootatuck River as part of a cooperative program between the U.S. Geological Survey and Newtown, Connecticut. This study will help address concerns about the increasing competition for water for human uses and protection of aquatic habitat. The groundwater-flow model developed in the study was designed for use as a tool to assist planners in assessing the effects of potential future development, which will change the amount and distribution of recharge available to the groundwater system.

Several different techniques were used to investigate the interconnection between the stream and the aquifer. Temperature, groundwater levels, stream stage, and stable-isotope data collected during aquifer tests at the principal production wells in the Pootatuck River Basin, as well as groundwater-flow simulations of the system, indicate that more than half of the water pumped from the wells comes from the Pootatuck River. This finding potentially has a large effect on approaches for protecting the water quality of the pumped water. Increases in the amount of impervious surface from future development will reduce and redistribute recharge to the groundwater system. The simulation of future development scenarios showed a decrease in the simulated base flow in the main stem of the Pootatuck River and in all of the 26 simulated subbasins, with some of the subbasins showing a decrease of more than 20 percent when new development had 85 percent impervious area.

The groundwater-flow model and particle tracking were used to determine areas that contribute recharge to the five production wells available for use in the Pootatuck River Basin. These areas included narrow portions of the aquifer that extended beyond the immediate upgradient areas, probably because of deeper groundwater-flow paths.

First posted July 2010

For additional information contact:
Director,
U.S. Geological Survey
Connecticut Water Science Center
101 Pitkin Street East Hartford, CT 06108
http://ct.usgs.gov/

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Suggested citation:

Carlson, C.S., Mondazzi, R.A., Bjerklie, D.M., and Brown, C.J., 2010, Hydrogeology and numerical simulation of the unconsolidated glacial aquifer in the Pootatuck River Basin, Newtown, Connecticut: U.S. Geological Survey Scientific Investigations Report 2010–5142, 84 p., available at http://pubs.usgs.gov/sir/2010/5142/.



Contents

Abstract

Introduction

Purpose and Scope

Location and Description

Previous Investigations

Hydrogeology of the Pootatuck River Valley

Physiography and Geology

Description of Hydrologic Units

Data Collection and Analysis

Methods of Data Collection

Streamflow

Observation Wells and Streambed Piezometers

Groundwater-Level Monitoring

Temperature Monitoring

Aquifer Test

Water-Quality and Stable-Isotope Analysis

Fairfield Hills Well Field

Site Description

Pumping Information

Aquifer Tests at Fairfield Hills Well Field

Groundwater-Level Monitoring

Surface-Water Monitoring

Temperature Monitoring

Water-Quality and Isotope Analysis

Analysis of Aquifer Tests at Fairfield Hills Well Field

United Water Well Field

Site Description

Pumping Information

Induced Infiltration Test at United Water Well Field

Groundwater and Surface-Water-Level Monitoring

Temperature Monitoring

Historical Aquifer Tests

Analysis of Historical Aquifer Test at United Water Well Field

Development of the Groundwater-Flow Models

Development of a Conceptual Model of the Pootatuck River Basin

Development of Numerical Models

Model Discretization and Boundaries

Model Calibration

Well-Field-Scale Models

Fairfield Hills Well-Field-Scale Model

Simulation of Aquifer Test

Model Calibration and Hydraulic Properties

Steady-State Model

United Water Well-Field-Scale Model

Simulation of Reverse Aquifer Test

Model Calibration and Hydraulic Properties

Limitations of Well-Field-Scale Models

Basin-Scale Model

Layer Distribution

Hydrologic Boundaries

Hydrologic Stresses

Recharge

Pumping

Hydraulic Properties

Basin-Scale, Steady-State Model Calibration

Water-Level Data

Streamflow Data

Model Limitations

Sensitivity Analysis of Groundwater-Flow Models

Streambed Conductance

Hydraulic Conductivity

Recharge

Delineation of Areas Contributing Recharge to Production Wells

Simulated Groundwater Levels and Drawdown

Delineation of Groundwater-Recharge Areas

Sensitivity Analysis of Groundwater Recharge Areas

Streambed Conductance

Hydraulic Conductivity

Recharge

Simulation of the Interaction between Groundwater and Surface Water

Sensitivity Analysis of Simulated Groundwater Levels

Sensitivity Analysis of Stream Base Flow in the Pootatuck Rive

Simulated Water Budgets

Simulated Effect of Future Recharge Conditions

Base Flows in the Main Stem Pootatuck River—Future Scenarios

Water Budgets in Subbasins of Pootatuck River—Future Scenarios

Summary

Acknowledgments

References Cited

Appendix. Spatially-Distributed Recharge



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