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Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

By Stephen P. Garabedian and Janet Radway Stone

Water-Resources Investigations Report 03-4320

ABSTRACT

Areas contributing water to the Dry Brook public-supply well in South Hadley, Massachusetts, were delineated with a numerical ground-water-flow model that is based on geologic and hydrologic information for the confined sand and gravel aquifer pumped by the supply well. The study area is along the Connecticut River in central Massachusetts, about 12 miles north of Springfield, Massachusetts. Geologic units in the study area consist of Mesozoic-aged sedimentary and igneous bedrock, late-Pleistocene glaciolacustrine sediments, and recent alluvial deposits of the Connecticut River flood plain. Dry Brook Hill, immediately south of the supply well, is a large subaqueous lacustrine fan and delta formed during the last glacial retreat by sediment deposition into glacial Lake Hitchcock from a meltwater tunnel that was likely near where the Connecticut River cuts through the Holyoke Range. The sediments that compose the aquifer grade from very coarse sand and gravel along the northern flank of the hill, to medium sands in the body of the hill, and to finer-grained sediments along the southern flank of the hill. The interbedded and overlapping fine-grained lacustrine sediments associated with Dry Brook Hill include varved silt and clay deposits. These fine-grained sediments form a confining bed above the coarse-grained aquifer at the supply well and partially extend under the Connecticut River adjacent to the supply well.

Ground-water flow in the aquifer supplying water to Dry Brook well was simulated with the U.S. Geological Survey ground-water-flow modeling code MODFLOW. The Dry Brook aquifer model was calibrated to drawdown data collected from 8 observation wells during an aquifer test conducted by pumping the supply well for 10 days at a rate of 122.2 cubic feet per minute (ft3/min; 914 gallons per minute) and to water levels collected from observation wells across the study area. Generally, the largest hydraulic conductivity values used in the model were in the sand and gravel aquifer near the Dry Brook well, which is consistent with the geologic information. Results of aquifer-test simulation indicated that spatially variable aquifer hydraulic properties and boundary conditions affected heads and ground-water flow near the well. A comparison and analysis of water-level fluctuations in study area wells to fluctuations in the Connecticut River indicated a hydraulic connection of the aquifer with the river, which is also consistent with geologic information. Simulated ground-water levels indicated that most ground water in the study area flowed toward and discharged to the Connecticut River and the Dry Brook well. Small amounts of ground water also discharged to smaller streams (Dry Brook and Bachelor Brook) in the study area.

Areas contributing water to the well were delineated with the MODPATH particle-tracking routine. Results of the contributing-area analysis indicated that the greatest sources of water to the well were recharge in the Dry Brook Hill area and infiltration of Connecticut River water in an area beyond the extent of the confining bed where the aquifer is in hydraulic connection with the river. The amount of water entering the Dry Brook well from recharge dominated at a lower pumping rate (40.0 ft3/min); about 90 percent of the pumped water originated from recharge and boundary flow, and infiltration from the Connecticut River supplied the remaining 10 percent. At a high pumping rate (122.2 ft3/min), however, about half of the water pumped from the Dry Brook well originated from recharge and boundary flow (49 percent), and half originated from infiltration of water from the Connecticut River (51 percent).

Results of a sensitivity analysis of the extent of areas contributing water to the Dry Brook well when pumped at 122.2 ft3/min indicated that the size of these areas did not substantially change when aquifer properties were varied. In contrast, however, the size of these areas changed most when the recharge rate was modified. When the recharge rate was decreased by 25 percent, the extent of the area increased by about 200 feet farther to the south and east across Dry Brook Hill. When recharge was increased by 25 percent, the extent of the area decreased by about 200 feet on the south and east sides of Dry Brook Hill. The flow contribution from the Connecticut River increased to 60 percent of the total pumpage when the recharge was decreased by 25 percent, as compared to 43 percent of the total pumpage when recharge was increased by 25 percent. These results indicated Dry Brook Hill is important to the protection of the water quality in the Dry Brook well because this area contributes water under a number of simulated conditions, and is potentially vulnerable to contamination because of its permeable sandy soils and aquifer materials.

On the basis of this study, the important components needed in future studies to properly delineate areas contributing water to public-supply wells developed in confined aquifers include geologic information on the vertical and lateral extent of the confining beds and aquifer materials, and a conceptual model of ground-water flow in the aquifer based on hydrogeologic data that takes into consideration the movement of ground water from recharge to discharge areas. Other components include hydrologic data quantifying aquifer gains and losses of water from streams and ponds, and accurate estimates of recharge rates, which appear to be an important determinant of the extent of the areas contributing water to supply wells across Massachusetts, including those in confined ground-water-flow systems.

CONTENTS

Abstract

Introduction

Purpose and Scope

Description of Study Area

Acknowledgments

Physiography and Geology

Bedrock Geology

Surficial Geology.

Glacial Till

Glacial Stratified Deposits

Coarse-Grained Deposits

Fine-Grained Deposits

Hydrology

Streamflow

Ground-Water Levels and Flow

Ground-Water Recharge and Discharge

Aquifer Responses to Pumping

Simulation of Ground-Water Flow

Model Design and Boundary Conditions

Hydraulic Properties and Recharge Rates

Pumping Stresses

Model Calibration

Delineation of Areas Contributing Water to Dry Brook Well

Sensitivity and Uncertainty Analysis

Transient Analysis and Contributing Watersheds

Suggestions for Future Study

Summary and Conclusions

References Cited

FIGURES

1–2.Maps showing:

1.Location of the Dry Brook study area, Hadley, Holyoke, and South Hadley, Massachusetts

2. Wells used in the study of the Dry Brook area, Hadley, Holyoke, and South Hadley

3. Surficial materials map and locations of cross sections shown in figure 4, Dry Brook study area, Hadley, Holyoke, and South Hadley

4. Geologic cross sections, Dry Brook study area, Holyoke and South Hadley

5.Map showing the altitude of the bedrock surface in the Dry Brook study area, Hadley, Holyoke, and South Hadley

6.Photographs showing examples of glacial deposits in the Dry Brook study area, Hadley, Holyoke, and South Hadley: A, gravel and sand beds in an ice-marginal delta; B, flat-lying gravel topset beds overlying dipping sandy foreset beds in the Pearl City delta, South Hadley; C, glacial Lake Hitchcock varved silt (darker layers) and clay (lighter layers), and (D) typical red till in the Hartford Basin

7–8.Maps showing:

7.Locations of streamflow measurements for Elmer and Dry Brooks, Dry Brook study area, Hadley, Holyoke, and South Hadley

8.Ground-water levels measured in the Dry Brook study area on November 16, 2000, Hadley, Holyoke, and South Hadley

9–10.Graphs showing:

9.Ground-water levels measured in well GKW-68 in Granby

10.Ground-water levels measured in well SUW-81 compared to the stage of the Connecticut River at Montague

11.Map showing observation-well network for a 10-day aquifer test of Dry Brook well (September 24, 1998–October 5, 1998), South Hadley

12–14.Graphs showing:

12.Drawdowns in observation wells during the Dry Brook well 10-day aquifer test (September 24, 1998–October 5, 1998), South Hadley

13.Drawdowns in observation wells during the Dry Brook well 10-day aquifer test (September 24, 1998–October 5, 1998) using relative time scale, South Hadley

14.Connecticut River stage compared to water levels measured in observation wells SUW-84 and SUW- 51 during the Dry Brook well 10-day aquifer test, South Hadley

15.Map showing the lateral extent of and boundary conditions for the MODFLOW model grid in the Dry Brook study area, Hadley, Holyoke, and South Hadley

16.Geologic cross sections showing the vertical distribution of MODFLOW model layers in the Dry Brook study area, Holyoke and South Hadley

17.Map and graphs showing model-calibration results comparing observed and simulated drawdown at observation wells during the Dry Brook well 10-day aquifer test, South Hadley

18.Graph showing observed and simulated drawdowns at the end of the Dry Brook well 10-day aquifer test in relation to radial distance from the well, South Hadley

19–23.Maps showing:

19.Steady-state simulated water-level contours for layers 3 and 4 at a pumping rate of 40.0 cubic feet per minute in the Dry Brook study area, Hadley, Holyoke, and South Hadley

20.Extent of the simulated area contributing water to the Dry Brook well at pumping rates of A, 40.0; and B, 122.2 cubic feet per minute, Hadley, Holyoke, and South Hadley

21.Sensitivity to various parameters of the simulated area contributing water to the Dry Brook well at a pumping rate of 122.2 cubic feet per minute for A, cases B and C; and B, cases D–H, Hadley, Holyoke, and South Hadley

22.Simulated ground-water-level contours for layers 3 and 4 at a pumping rate of 122.2 cubic feet per minute after a transient, 180-day period of no recharge and associated zone of ground-water flow towards the Dry Brook well, Hadley, Holyoke, and South Hadley

23.Zone of contribution and associated watershed areas contributing water to the Dry Brook well at a pumping rate of 122.2 cubic feet per minute, Hadley, Holyoke, and South Hadley.

TABLES

1.Records of selected wells and test borings in the Dry Brook study area, Hadley, Holyoke, and South Hadley, Massachusetts

2.Streamflow measurements for Elmer and Dry Brooks, South Hadley, September 8, 2000

3.Manual ground-water-level measurements in Dry Brook study area, South Hadley

4.Aquifer properties and recharge rates for the Dry Brook study area, Hadley, Holyoke, and South Hadley

5.Comparison of observed to simulated drawdowns at the end of the 10-day Dry Brook well aquifer test (September 25, 1998–October 5, 1998), South Hadley

6.Comparison of observed to steady-state simulated ground-water levels under an average pumping rate of 40.0 cubic feet per minute, Dry Brook study area, South Hadley

7.Comparison of steady-state model-simulated water budgets under average and the Massachusetts Department of Environmental Protection’s approved-yield pumping rates, and various model-parameter test simulations for the Dry Brook study area, Hadley, Holyoke, and South Hadley



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The citation for this report, in USGS format, is as follows:

Garabedian, S.P., Stone, J.R., 2004, Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts: U.S. Geological Survey Water-Resources Investigations Report 03-4320, 56 p.


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