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Estimated Water Use and Availability in the Pawcatuck Basin, Southern Rhode Island and Southeastern Connecticut, 1995-99

By Emily C. Wild and Mark T. Nimiroski

Scientific Investigations Report 2004-5020

ABSTRACT

In 1988, the Pawcatuck Basin (302.4 square miles) in southern Rhode Island (245.3 square miles) and southeastern Connecticut (57.12 square miles) was defined as a sole-source aquifer for 14 towns in southern Rhode Island and 4 towns in southeastern Connecticut. To determine water use and availability, the six subbasins in the Pawcatuck Basin were delineated on the basis of the surface- and ground-water system drainage areas. From 1995 through 1999, five major water suppliers in the basin withdrew an average of 6.768 million gallons per day from the aquifers. The estimated water withdrawals from minor water suppliers during the study period were 0.099 million gallons per day. Self-supplied domestic, industrial, commercial, and agricultural withdrawals from the basin averaged 4.386 million gallons per day. Water use in the basin averaged 7.401 million gallons per day. The average return flow in the basin was 7.855 million gallons per day, which included effluent from permitted facilities and self-disposed water users.

The PART program, a computerized hydrograph-separation application, was used for five selected index stream-gaging stations to determine water availability on the basis of the 75th, 50th, and 25th percentiles of the total base flow, the base flow minus the 7-day, 10-year flow criteria, and the base flow minus the Aquatic Base Flow criteria at the index stations. The differences in the surface- and ground-water system drainage areas in the summer were applied to the water availability calculated at the index stations and subbasins.

The base-flow contributions from sand and gravel deposits at the index stations were computed for June, July, August, and September, and applied to the percentage of surficial deposits at each index station. The base-flow contributions were converted to a per unit area at the station for the till, and for the sand and gravel deposits, and applied to the subbasins. The statistics used to estimate the gross yield of base flow, as well as subtracting out the two low-flow criteria, resulted in various water-availability values at each index station, which were present in the subbasin after applying the per unit area rates from the index station. The results from the Chipuxet and Arcadia stream-gaging stations were lowest in September at the 75th and 25th percentiles, and August flows were lowest for the summer at the 50th percentile. For the other three index stations, September flows were the lowest for the summer.

Because water withdrawals and use are greater during the summer than other times of the year, water availability in June, July, August, and September was assessed and compared to water withdrawals in the basin and subbasins. The ratios were calculated by using the water-availability flow scenarios at the 75th, 50th, and 25th percentiles for the subbasins, which are based on total water available from base-flow contributions from till deposits and sand and gravel deposits in the subbasins. For the study period, the withdrawals in August were higher than the other summer months. The ratios were close to one in August for the estimated gross yield and 7-day, 10-year flow criterion, and were close to one in September for the estimated Aquatic Base Flow criterion water-availability scenarios in the Pawcatuck Basin. The closer the ratio is to one, the closer the withdrawals are to the estimated water available, and the net water available decreases.

To determine the effects of streamflow depletion from continuous water withdrawals, the program STRMDEPL was used to simulate public wells and well fields at a constant pumping rate based on the 1999 summer average for each withdrawal, over a period of 180 days. The streamflow depletion was 86, 95, 93, 96, and 98 percent at 30 days for Kingston wells 1 and 2, Westerly well fields 1 and 2, and well 3, respectively. A long-term hydrologic budget was calculated for the Pawcatuck Basin to identify and assess the basin and subbasin inflow and outflows. The water withdrawals and return flows used in the budget were from 1995 through 1999. For the hydrologic budget, it was assumed that inflow equals outflow, which resulted in 723.1 million gallons per day in the basin. The estimated inflows from precipitation and water return flow were 99 and 1 percent in the basin, respectively. The estimated outflows from evapotranspiration, streamflow, and water withdrawals were 43, 56, and 1 percent, respectively.

A long-term hydrologic budget was calculated for the Pawcatuck Basin to identify and assess the basin and subbasin inflow and outflows. The water withdrawals and return flows used in the budget were from 1995 through 1999. For the hydrologic budget, it was assumed that inflow equals outflow, which resulted in 723.1 million gallons per day in the basin. The estimated inflows from precipitation and water return flow were 99 and 1 percent in the basin, respectively. The estimated outflows from evapotranspiration, streamflow, and water withdrawals were 43, 56, and 1 percent, respectively.

CONTENTS

Abstract

Introduction

Purpose and Scope

Previous Investigations

Acknowledgments

The Pawcatuck Basin

Pawcatuck Subbasins

Minor Civil Divisions

Water Use

New England Water-Use Data System

Public Water Supply and Interbasin Transfers

Domestic Water Use

Public-Supply Use

Self-Supplied Use

Commercial and Industrial Water Use

Public-Supply Use

Self-Supplied Use

Agricultural Water Use

Return Flow and Interbasin Transfers

Site-Specific Return Flow

Aggregate Return Flow

Interbasin Transfers

Water Availability

Summer Water Availability by Subbasin

Streamflow Depletion

Water Budget

Summary

References Cited

Glossary

FIGURES

1, 2.Diagram showing:

1.The modified hydrologic cycle

2.The components of water use

3-5.Maps showing:

3.The Pawcatuck Basin and subbasins, southern Rhode Island and southeastern Connecticut

4.Aquifers and selected withdrawal wells for the subbasins in the Pawcatuck Basin, 1995–99

5.Stream-gaging stations and wastewater-treatment facilities associated with the Pawcatuck Basin, 1995–99

6–13. Diagrams showing:

6.Public-supply withdrawals, and self-supplied domestic, commercial, industrial, and agricultural withdrawals for the subbasins in the Pawcatuck Basin, 1995–99

7.Public-supply and self-supplied domestic, commercial, industrial, and agricultural water use for the subbasins in the Pawcatuck Basin, 1995–99

8.Wastewater-treatment facilities, Rhode Island Pollutant Discharge Elimination System, and self-disposed domestic, commercial, and industrial water return flow for the subbasins in the Pawcatuck Basin, 1995–99

9.Kingston Water District withdrawals, distribution, and estimated water uses in the Pawcatuck Basin and basin exports, 1995–99

10.United Water of Rhode Island withdrawals, treatment, distributions, non-account water use in the Pawcatuck Basin and basin exports, 1995–99

11.University of Rhode Island withdrawals, water uses, and estimated exported return flow in the Pawcatuck Basin, 1995–99

12.Richmond Water Supply withdrawals, estimated distributions, and estimated water uses in the Pawcatuck Basin, 1995–99

13.Westerly Water Department withdrawals, distributions, and estimated water uses in the Pawcatuck Basin and basin exports, 1995–99

14–16. Diagrams showing:

14.Estimated water availability for June, July, August, and September from sand and gravel deposits for the subbasins in the Pawcatuck Basin based on the A, 50th percentile; B, 50th percentile minus the 7-day, 10-year flow criteria; and C, 50th percentile minus the Aquatic Base Flow criteria .

15.Estimated water availability for June, July, August, and September from till deposits for the subbasins in the Pawcatuck Basin based on the A, 50th percentile; B, 50th percentile minus the 7-day, 10-year flow criteria; and C, 50th percentile minus the Aquatic Base Flow criteria

16.Estimated water availability for June, July, August, and September for the subbasins in the Pawcatuck Basin based on the A, 50th percentile; B, 50th percentile minus the 7-day, 10-year flow criteria; and C, 50th percentile minus the Aquatic Base Flow criteria

17.Map showing the water-withdrawal to water-availability ratio in A, July; B, August; and C, September for the subbasins in the Pawcatuck Basin at the 50th percentile minus the 7-day, 10-year flow criteria

18, 19.Graphs showing:

18.Decimal percentage of streamflow depletion simulation during 180 days of continuous pumping for Kingston Water District wells 1 and 2, Pawcatuck Basin

19.Decimal percentage of streamflow depletion simulation during 180 days of continuous pumping for Westerly Water Department wellfields 1 and 2, and well 3, Pawcatuck Basin

TABLES

1.Total town populations by subbasins for 1990, estimated populations 1995–99, and estimated public and self supply and disposal populations in the Pawcatuck Basin, southern Rhode Island and southeastern Connecticut

2.Summary of climatological data pertinent to the Pawcatuck Basin

3.Town land area and land-use area by category in the subbasins of the Pawcatuck Basin

4. Land-use area and percent land-use area by water-supply district for the subbasins in the Pawcatuck Basin study area and areas outside of the Pawcatuck Basin

5.Surface-water and ground-water drainage areas, the percentage of sand and gravel deposits and till deposits, and the ground-water reservoirs for the subbasins in the Pawcatuck Basin

6.Defined subbasins in the Pawcatuck Basin study area in Rhode Island compared to the 10-digit and 12-digit hydrologic units from the Natural Resources Conservation Service, Watershed Boundary Dataset in Rhode Island

7.Summary of total land area, land area in the Pawcatuck Basin, total 1990 populations, total estimated 1995–99 populations, estimated 1995-99 populations in the Pawcatuck Basin, and land-use area by category in the Pawcatuck Basin

8.Water suppliers by subbasins in the Pawcatuck Basin

9. Minor suppliers by subbasins in the Pawcatuck Basin

10.Ground-water and surface-water withdrawals by town and subbasin in the Pawcatuck Basin, 1995–99

11.Estimated water use by town and subbasin in the Pawcatuck Basin, 1995–99

12.Consumptive water use by town and subbasin in the Pawcatuck Basin, 1995–99

13.Estimated water use per 2-digit Standard Industrial Classification code by town in the Pawcatuck Basin, 1995–99

14.Estimated public- and self-disposed domestic, commercial, and industrial, and metered return flow by subbasin in the Pawcatuck Basin, 1995–99

15.Return flows by subbasin for the Rhode Island Pollutant Discharge Elimination System sites in the Pawcatuck Basin, 1995–99

16.Return flow from wastewater-treatment facilities within and outside of the Pawcatuck Basin, 1995–99

17.Summary of estimated water withdrawals, imports, exports, use, non-account water use, consumptive use, and return flow in the Pawcatuck Basin, 1995–99

18.U.S. Geological Survey stream-gaging stations and minimum streamflows in the Pawcatuck Basin

19.Summer water availability for selected stream-gaging stations in the Pawcatuck Basin

20.Estimated gross yield, gross yield minus the 7-day, 10-year flow, and gross yield minus the Aquatic Base Flow of water availability for June, July, August, and September in the Pawcatuck Basin

21.Estimated gross yield of water availability for June, July, August, and September in the Pawcatuck Basin

22.Average water withdrawals for June, July, August, and September in the subbasins in the Pawcatuck Basin, 1995–99

23.Summary of water withdrawals to availability ratios for June, July, August, and September in the Pawcatuck Basin

24.Monthly water withdrawals and withdrawal to availability ratios for the Chipuxet stream-gaging station in the Pawcatuck Basin

25.Average distance, transmissivity, diffusivity, pumping rate, streamflow-depletion rates, and and streamflow of rivers from the Kingston and Westerly public- supply wells and well fields used in Jenkins analysis in the Pawcatuck Basin

26.Average pumping rate and streamflow depletion from selected Kingston and Westerly public-supply wells used in Jenkins analysis during June, July, August, and September of 1999 in the Pawcatuck Basin

27.Average streamflow at the Chipuxet River and Pawcatuck River stream-gaging stations during June, July, August, and September of 1999 in the Pawcatuck Basin

28.Pumping rate for 180 days and percent streamflow depletion divided by pumping rate from selected public-supply withdrawal wells for the Kingston Water District and Westerly Water Department used in Jenkins analysis in 1999 in the Pawcatuck Basin

29.Average water budget by subbasin for the Pawcatuck Basin


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

Wild, E.C., and Nimiroski, M.T., 2004, Estimated water use and availability in the Pawcatuck Basin, southern Rhode Island and southeastern Connecticut, 1995–99: U.S. Geological Survey Scientific Investigations Report 2004-5020, 80 p.


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