CONTRIBUTING RECHARGE AREAS TO 

WATER-SUPPLY WELLS AT WRIGHTPATTERSON AIR FORCE BASE, OHIO

by Rodney A. Sheets

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 94-4231

Prepared in cooperation with 

WRIGHT-PATTERSON AIR FORCE BASE

Columbus, Ohio 

1994
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBIT, Secretary

U.S. GEOLOGICAL SURVEY 

GORDON P. EATON, Director

For additional information Copies of this report may

write to: be purchased from:

District Chief U.S. Geological Survey

Water Resources Division Earth Science Information Center

U.S. Geological Survey Open-File Reports Section

975 West Third Avenue Box 25286, MS 517

Columbus, OH 43212-3192 Denver Federal Center

	Denver, CO 80225
CONTENTS

Abstract.................................................................................................................................................................^^ 1

Introduction........................................................................................................................................................................... 2

Purpose and scope....................................................................................................................................................... 2

Previous mvestigations..........................................................^ 2

Methods of investigation....................................................................................................................................................... 5

Numerical modeling.................................................................................................................................................... 5

Particle tracking........................................................................................................................................................... 5

Use of a geographic information system..................................................................................................................... 5

Hydrologic setting of the Wright-Patterson Air Force Base area.......................................................................................... 5

Surface-water flow....................................................................................................................................................... 5

Ground-water flow....................................................................................................................................................... 6

Contributing recharge areas to water-supply wells............................................................................................................... 6

Simulation of ground-water flow................................................................................................................................. 6

Input parameters...................................................................^^ 10

Calibration targets.............................................................................................................................................. 11

Sensitivity analyses............................................................................................................................................ 11

Limitations of flow model................................................................................................................................. 13

Delineation by particle tracking .................................................................................................................................. 13

Uncertainty analyses.......................................................................................................................................... 23

Limitations of tracking procedure..................................................................................................................... 29

Summary and conclusions.................................................................................................._^ 32

References cited..................................................................................................................................................................... 35

FIGURES

1-3. Maps showing:

1. Location of Wright-Patterson Air Force Base and administrative areas............................................................ 3

2. Location of well fields in the study area............................................................................................................ 4

3. Ground-water levels and generalized flow directions in the upland bedrock

and valley-train deposits................................................................................................................................... 7

4. Contributing recharge area to a single discharging well in a simplified hypothetical

ground-water-flow system......................................................................................................................................... 8

5. Map showing model grid in relation to modeled area................................................................................................ 9

6. Generalized sectional view of the ground-water-flow model, Wright-Patterson Air Force Base, Ohio.................... 10

7-10. Graphs showing:

7. Sensitivity of simulated heads to changes in horizontal hydraulic conductivity, riverbed conductance, 

and vertical hydraulic conductance in model of ground-water-flow system, 

Wright-Patterson Air Force Base, Ohio, and vicinity....................................................................................... 12

8. Sensitivity of simulated flows to Mad River South and Hebble Creek to changes in hydrogeologic

parameters in the model of the ground-water-flow system, Wright-Patterson Air Force Base, Ohio.............. 14

9. Sensitivity of simulated flows from Hills 1 and 2 to changes in hydrogeologic parameters

in the model of the ground-water-flow system, Wright-Patterson Air Force Base, Ohio................................. 15

10. Sensitivity of simulated flows under Huffman Dam to changes in hydrogeologic parameters

in the model of the ground-water-flow system, Wright-Patterson Air Force Base, Ohio................................. 16

11. Map showing 1-, 5-, and 10-year ^contributing recharge areas to the Skeel Road and East Well Fields.................... 17

Contents III
12-14. Maps showing contributing recharge areas to Skeel Road and Area B Well Fields:

12. Under normal pumping conditions.................................................................................................................... 19

13. Under intermediate pumping conditions........................................................................................................... 20

14. Under maximum capacity pumping conditions................................................................................................. 21

15. Graphs showing change in contributing recharge areas in relation to pumping rates at

Skeel Road and Area B Well Fields, Wright-Patterson Air Force Base, Ohio.......................................................... 22

16-18. Maps showing contributing recharge areas to the East Well Field:

16. Under October-December 1987 pumping conditions........................................................................................ 24

17. Under intermediate pumping conditions........................................................................................................... 25

18. Under maximum capacity pumping conditions................................................................................................. 26

19-20. Graphs showing variations of the contributing recharge areas of Skeel Road Well Field, 

Wright-Patterson Air Force Base, Ohio, in relation to changes:

19. In horizontal hydraulic conductivity of the upland bedrock and the buried-valley aquifer,

under normal pumping conditions.................................................................................................................... 27

20. Of porosity of the upland bedrock and the buried-valley aquifer,

under normal pumping conditions.................................................................................................................... 28

21-23. Graphs showing variations of the contributing recharge areas of Area B Well Field, 

Wright-Patterson Air Force Base, Ohio, in relation to changes:

21. Of horizontal hydraulic conductivity of the upland bedrock and buried-valley aquifer,

under normal pumping conditions.................................................................................................................... 30

22. Of porosity of the upland bedrock and buried-valley aquifer, under normal pumping conditions................... 31

23. Of riverbed conductance, under normal pumping conditions........................................................................... 32

24. Contributing recharge areas to the Skeel Road and Area B Well Fields,

under current (1994) pumping conditions, including pumping of wells at Huffman Dam....................................... 33

TABLES

 

1. Pumping rates and contributing recharge areas to well fields at Wright-Patterson Air Force Base, Ohio............. 18

CONVERSION FACTORS

_______Multiply_______________By_____________To obtain____

Length 

inch (in.) 25.4 millimeter

foot (ft) 0.3048 meter 

mile (mi) 1.609 kilometer

Area

square foot (ft2) 0.09290 square meter 

square mile (mi ) 2.590 square kilometer

Volume 

gallon (gal) 3.785 liter

Flow 

million gallons per day (Mgal/d) 0.04381 cubic meters per second

foot per day (ft/d) 0.3048 meter per day 

foot squared per day (ft2/d) 0.09290 meter square per day

Temperature is given in degrees Celsius (°C), which can be converted to degrees

Fahrenheit (°F) by use of the following equation:

F=1.8(°C) + 32

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 

1929) a geodetic datum derived from a general adjustment of the first-order level nets of both the United 

States and Canada, formerly called Sea Level Datum of 1929.

IV Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
Contributing Recharge Areas of Water-Supply Wells at 

Wright-Patterson Air Force Base, Ohio

By Rodney A. Sheets

Abstract

Wright-Patterson Air Force Base, in southwestern Ohio, has operated three well fields 

Area B, Skeel Road, and the East Well Fields to 

supply potable water for consumption and use for 

base activities. To protect these well fields from 

contamination and to comply with the Ohio Wellhead Protection Plan, the Base is developing a 

wellhead-protection program for the well fields.

A three-dimensional, steady-state groundwater-flow model was developed in 1993 to simulate heads in (1) the buried-valley aquifer system 

that is tapped by the two active well fields, and in 

(2) an upland bedrock aquifer that may supply 

water to the wells. An advective particle-tracking 

algorithm that requires estimated porosities and 

simulated heads was used to estimate groundwater-flow pathlines and traveltimes to the active 

well fields. Contributing recharge areas (CRA's) 

areas on the water table that contribute water to a 

well or well field were generated for 1-, 5-, and 

10-year traveltimes.

Results from the simulation and subsequent 

particle tracking indicate that the CRA's for the 

Skeel Road Well Field are oval and extend northward, toward the Mad River, as pumping at the 

well field increases. The sizes of the 1-, 5-, and 10- 

year CRA's of Skeel Road Well Field, under maximum pumping conditions, are approximately 0.5, 

1.5, and 3.2 square miles, respectively. The CRA's 

for the Area B Well Field extend to the north, up 

the Mad River Valley; as pumping increases at the 

well field, the CRA's extend up the Mad River Valley under Huffman Dam. The sizes of the 1-, 5-, 

and 10-year CRA's of Area B Well Field, under 

maximum pumping conditions, are approximately

0.1, 0.5, and 0.9 square miles, respectively..The 

CRA's for the East Well Field are affected by 

nearby streams under average pumping conditions. The sizes of the 1-, 5-, and 10-year CRA's of 

the East Well Field, under maximum pumping 

conditions, are approximately 0.2, 1.2, and 

2.4 square miles, respectively. However, as pumping increases at the East Well Field, the groundwater-flow model develops numerical instabilities 

which limit the usefulness of the CRA's.

Sensitivity analyses show that variation of 

horizontal hydraulic conductivity and porosity in 

the upland bedrock does not affect the CRA's of 

the Skeel Road Well Field but does have a slight 

affect on the CRA's of the Area B Well Field. 

Uncertainties in horizontal hydraulic conductivity 

and porosity of the valley-train deposits have the 

largest effect on the size and shape of the CRA's of 

the Skeel Road Well Field. The position and size 

of the CRA's of Area B are probably also controlled by induced infiltration from the nearby 

Mad River and by pumping at the Rohrer's Island 

Well Field. However, uncertainty in riverbed conductance, which affects induced infiltration, does 

not significantly affect the size and shape of these 

CRA's.

Pumping centers not included in the groundwater-flow model do not appreciably affect the 

CRA's of the Area B and Skeel Road Well Fields 

under normal pumping. The pumping centers, 

located near Huffman Dam, will probably limit the 

northern extent of the CRA's of Area B Well Field 

under greater than normal pumping conditions. 

The CRA's of the East Well Field will propagate 

farther to the northeast and southwest as a result of 

the increased pumping-related stress to the aquifer 

system.

Abstract
INTRODUCTION

Officially recognized as a Department of 

Defense facility in 1948, Wright-Patterson Air Force 

Base (hereafter referred to as "WPAFB" or "the 

Base") is one of the most important U.S. Air Force 

installations in the world. Environmental effects of 

day-to-day operations and waste disposal were rarely 

considered in the past and these activities at the Base 

have had an adverse effect on the water quality on the 

Base (Weston, Incorporated, 1983).

Located in Greene, Clark, and Montgomery 

Counties in southwestern Ohio, the Base encompasses 

approximately 8,500 acres and is divided into two 

administrative areas Areas A and C, and Area B 

(fig. 1). The Base overlies the Mad River buried-valley 

aquifer, which consists of highly permeable glacialdrift deposits. This aquifer is heavily used for water 

supplies, including supplies for the cities of Dayton 

and Fairbom, for the Base, and for industrial users. 

Several studies began in the 1980's to identify and 

control subsurface migration of environmental contamination on and off the Base. One of these studies 

by the U.S. Geological Survey (USGS) examined the 

ground-water-flow system of the area by use of a 

numerical ground-water-flow model and other techniques (Dumouchelle and others, 1993). The model 

was developed to help Base officials and researchers 

better understand regional ground-water flow.

The Base currently (1994) operates two watersupply well fields on Base property Skeel Road Well 

Field and Area B Well Field (fig. 2). Skeel Road Well 

Field also includes a well used for the Base Commissary. Pumping at the East Well Field (fig. 2) was suspended in 1987 because of water-quality concerns 

(L. Rodgers, Wright-Patterson Air Force Base, oral 

commun., 1993). All wells in the three well fields are 

completed in the buried-valley aquifer.

The Ohio Environmental Protection Agency 

(OEPA), through its Wellhead Protection (WHP) Program, has recommended that all water-supply facilities 

that rely on ground water develop a WHP strategy that 

includes establishing protection areas around wells 

(Ohio Environmental Protection Agency, 1992). No 

specific enabling legislation exists for the WHP Program, but under the Federal Safe Drinking Water Act 

Amendments of 1986, the State is required to fully

implement the Program. Several WHP area delineation methods based on ground-water traveltime are 

acceptable under the WHP Program, including 

calculated-fixed-radius, analytical, semi-analytical, 

and numerical. An inventory of hazardous-material 

storage and handling areas including landfills and 

buildings, can be used in combination with the delineation methods described here to develop a WHP program. Owing in part to OEPA recommendations, the 

Base has begun a WHP program to help protect all 

three well fields from contamination. The USGS, in 

cooperation with the WPAFB, has simulated groundwater flow and used particle-tracking to delineate contributing recharge areas to water-supply wells on the 

Base.

Purpose and Scope

The purpose of this report is to describe the 

delineation of contributing recharge areas (GRA's) of 

water-supply well fields at Wright-Patterson Air Force 

Base. The CRA's are based on simulated ground-water 

flow from a previously calibrated numerical groundwater-flow model of the area. A particle-tracking 

scheme that uses hydraulic heads and flow-distribution 

output from the model is used to calculate groundwater-flow traveltimes. The areal extent of the CRA's 

is described relative to pumping conditions and variations in model parameters. Limitations of the flow 

model, particle tracking, and the CRA's also are discussed.

Previous Investigations

Studies of the water resources of the WPAFB 

area began in the 1940's. Several site-specific studies 

have focussed on the geology and hydrology of the 

known waste disposal or storage sites on the Base 

(Roy F. Weston, Incorporated, 1983, 1989; Dames & 

Moore, 1986a, 1986b; IT Corporation, 1990). 

Dumouchelle and others (1993) describe the studies 

important to the development of a regional groundwater-flow model and also outline the results of previous studies by the USGS, including regional groundwater-level and bedrock-configuration maps. 

Dumouchelle and others (1993) also summarize several studies pertaining to the hydrology of the areas 

surrounding WPAFB.

2 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
84°07'3Cr 84°00'

39°52'30" -

39°45' tBase map digitized from U.S. Geological Survey 

Bellbrook. 1965. photorevised 1987; Dayton North, 

1965. photorevised 1981; Dayton South. 1966. 

photorevised 1981; Donnelsville. 1965, 

photorevised 1973. photoinspected 1983; 

Fairtoom. 1965. photorevised 1988: New Carlisle. 

1955. photorevised 1968 and 1973. 

photoinspected 1984: Tipp City. 1965. 

photorevised 1982: Xenia. 1965. photorevised 

1987: Yellow Springs. 1968. photorevised 1975. 

Polyconic projection

4 MILES

I I I I I 

0123 4 KILOMETERS

OHIO 

Study Area

EXPLANATION

WRIGHT-PATTERSON AIR FORCE BASE 

MODELED-AREA BOUNDARY

others -Patterson Air Force Base ^ administrative areas. (From Dumouchelle and

Introduction
84°07' 30" 84°05' 84°02P 30"

39° 50'

39°4T 30"

Base map digitized from U.S. Geological Survey 

Dayton North, 1965, photorevised, 1981; Falrbom, 

1965, photorevised, 1988. Polyconlc projection

5,000 10,000 FEET

WJ] Field 

name

ArenB

Eas

Steel Roid

US Geological Survey 

identifier

Ml-UI

MT-122

MT123

GR166

GR 149

GR ISO

GR152

GR153

GR 154

OR 155

GR-156

GR 157

GR 158

OR- 1 61

GR-162

OR- 163

OR164

Wright-Pntereon 

Air Foice BMC 

identifier

B-l (1)

B-2A (2A)

B-4 (4)

B5 (5J

B \ (A)

B-B (B)

EC (C)

B-E (E)

B F (F)

AC-4 (4)

AC-8 (8)

AC-9 (9)

AC6 (6)

AC-7 (7)

AC 3 (3)

AC-1 (1)

AC-2 (2)

I

1,000 2,000 METERS

EXPLANATION

ROHRERS ISLAND WELL FIELD

XX WRIGHT-PATTERSON AIR FORCE 

BASE BOUNDARY

GR ISO

if WELL LOCATION AND IDENTIFIER

Figure 2. Location of well fields in the study area.

4 Contributing Recharge Areas of Water-Suppiy Welis at Wright-Panerson Air Force Base, Ohio
METHODS OF INVESTIGATION Use of a Geographic Information System

The computer codes used to simulate groundwater flow and levels and to generate ground-waterflow paths and traveltimes are described within this 

section. A geographic information system was used to 

calculate and display the CRA's. The theory and 

implementation of the ground-water-flow model and 

particle-tracking program are further described in separate documentation, as referenced.

Numerical Modeling

The USGS modular, finite-difference computer 

code, MODFLOW (McDonald and Harbaugh, 1988), 

was used to simulate three-dimensional, steady-state 

ground-water flow of an approximately 100-mi2 area 

including the Base (fig. 1; Dumouchelle and others, 

1993). MODFLOW iteratively solves the groundwater-flow equation in three dimensions by way of a 

block-centered, finite-difference approach. In MODFLOW, layers can be simulated as confined orunconfined or as a combination of confined and unconfined. 

MODFLOW can be used to simulate external stresses 

to the ground-water system, such as areal recharge, 

evapotranspiration, stream gains and losses, and 

pumped wells.

Particle Tracking

A particle-tracking program, MODPATH (Pollock, 1989), was used to calculate ground-water-flow 

paths and advective traveltimes from the hydraulic 

heads and flow distribution computed by MODFLOW. 

Advective particle tracking is based on the assumption 

that transport is by advection only; chemical and biological attenuation, solid-phase partitioning, dispersion, and diffusion are not considered. Traveltime and 

positional information are computed by use of a semianalytical particle-tracking scheme based on the 

assumption that the directional ground-water velocity 

components within a model cell vary linearly. The 

velocity components are based on the intercell flow 

rates computed by MODFLOW Hypothetical particles 

of water can be tracked up or down the hydraulic gradient (backward or forward) within the computed flow 

field. Backward tracking can be used to track particles 

to their recharge locations; forward tracking enables 

the user to track particles to their discharge locations.

A geographic information system (GIS) consisting of mapping software integrated with a relationaldata-base management system was used to aid in 

delineating the CRA's. In this study, ARC/INFO1 was 

the GIS used to store and manipulate ground-water 

traveltimes and pathlines and to calculate and display 

the CRA's.

HYDROLOGIC SETTING OF THE WRIGHTPATTERSON AIR FORCE BASE AREA

Topography in the study area ranges from 

moderately hilly in the uplands to generally flat near 

major rivers or streams. The major river valleys are 

typically broad flood plains of perennial rivers. The 

valleys are underlain almost everywhere by productive 

valley-train or alluvial aquifers. Elevations in the 

uplands range from 800 to 1,000 ft, and the 

topography is controlled by the underlying limestone 

and shale bedrock. Intermittent streams are common 

on the uplands. Detailed descriptions of geology can 

be found in Walton and Scudder (1960) and Norris and 

Spieker(1966).

The Mad River, which flows generally northeast 

to southwest across the study area (fig. 1), has the 

highest sustained dry-weather flow (relative to drainage area) in Ohio (Cross and Feulner, 1964). The Mad 

River also flows across a buried-valley system that 

contains one of Ohio's most productive aquifers one 

of five in the State designated as a Sole Source Aquifer 

(U.S. Environmental Protection Agency, 1993).

Surface-Water Flow

The Mad River and its tributaries drain almost 

the entire area (fig. 1). Most of the streams in the 

uplands are intermittent, whereas those in the valleys 

are perennial. A gain/loss study by the USGS on the 

Mad River and its major tributaries in July 1991 

(Shindel and others, 1991) indicates that the Mad 

River receives recharge from ground water along most 

of the reaches north of Huffman Dam, a flood-control 

structure that does not restrict normal flow (fig. 1).

!Use of trade or company names is for identification 

purposes only and does not constitute endorsement by the 

U.S. Geological Survey.

Hydrologic Setting of the Wright-Patterson Air Force Base 5
South of Huffman Dam, flow in the Mad River is 

diverted to recharge lagoons for the city of Dayton's 

Rohrer's Island Well Field. Pumping from this well 

field also induces recharge from the lagoons to the 

aquifer. Ground-water levels in the area are indicative 

of these gains and losses.

Ground-Water Flow

The buried-valley aquifer underlying the Mad 

River consists of valley-train and alluvial deposits that 

primarily are poorly sorted sands and gravels interspersed with till units. Horizontal hydraulic conductivities range from 134 to 334 ft/d for the sands and 

gravels (Dumouchelle and others, 1993). Horizontal 

hydraulic conductivities of the till, based on permeameter and aquifer tests, range from 0.004 to 

0.067 ft/d (Dumouchelle and others, 1993). The valley 

walls and bottom are bounded by interbedded Ordovician shales and limestones. These Ordovician rocks 

are virtually impermeable; horizontal hydraulic conductivities range from 10"5 to 10"7 ft/d based on laboratory analysis of cores, and from 0.0016 to 12 ft/d 

based on aquifer tests (Casey, 1992; Dumouchelle and 

others, 1993). The latter method results in larger estimates of hydraulic conductivity because flow to a well 

is dominated by fracture systems. The bedrockcontrolled uplands (fig. 3) bounding the valleys are 

underlain by a Silurian limestone aquifer that is capable of producing sufficient amounts of water for 

domestic supplies. Horizontal hydraulic conductivities 

are reported to range from 10'2 to 5 x 102 ft/d (Casey, 

1992). Overlying this limestone aquifer is a generally 

thin layer of clay-rich, fine-grained tills that have low 

permeability. Hydraulic properties of these tills are 

likely similar to those of the tills within the sands and 

gravels of the buried-valley aquifer.

Ground water generally flows toward the Mad 

River except in areas where pumping of wells affects 

the natural gradient. A ground-water-level map (fig. 3) 

shows generalized flow directions in the upland bedrock and in the valley-train deposits (Schalk, 1992). 

Ground-water levels generally mimic topography; 

and, as expected, flow gradients are steepest in the 

uplands.

CONTRIBUTING RECHARGE AREAS TO 

WATER-SUPPLY WELLS

The area contributing recharge to a discharging 

well is the surface area that defines the location of the 

water entering the ground-water system at the water 

table that flows to the well and is eventually discharged from the well (Reilly and Pollock, 1993). Particles of water that reach the water table by infiltration 

of precipitation (recharge) and travel to a pumped well 

are in the CRA for that well. Figure 4 shows the relation between the contributing recharge area and the 

zone of contribution, which is the volumetric portion 

of the aquifer from which water is diverted to a 

pumped well (Morrissey, 1989). Most water recharging the aquifers at WPAFB consists of areal recharge 

(Dumouchelle and others, 1993) and as a result, the 

definition by Reilly and Pollock (1993) is appropriate.

CRA's can be delineated by tracking hypothetical particles of water from their recharge locations on 

the water table to their eventual discharge locations by 

use of a ground-water-flow model and a particle-tracking code. For this investigation, hydraulic heads and 

intercell flows output by a ground-water-flow model of 

the area (Dumouchelle and others, 1993) were input 

into the computer program MODPATH (Pollock, 

1989). Ground-water-flow paths and advective traveltimes were calculated by MODPATH, which computes 

the average linear velocity component of flow for each 

active cell in the model. MODPATH also computes the 

principal component of the velocity vector for each 

cell to determine particle paths and traveltimes.

Simulation of Ground-Water Flow

A ground-water-flow model calibrated to 

steady-state ground-water-flow conditions of 

September-October 1987 was developed by 

Dumouchelle and others (1993) for the area including 

the Base. The purpose of the model was, in part, to 

determine and evaluate sources and sinks of regional 

ground-water flow. These sources and sinks included 

the Mad River and its tributaries because surfacewater/ground-water relations need to be understood in 

this type of hydrogeologic setting.

The model grid used for the flow model is 

shown in figure 5; grid cell dimensions were 500, 750 

or 1,000 ft on a side; the smallest cell dimensions are 

in the area around Huffman Dam. The model consists

6 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
84°00'

39°52'30H 

Base map digitized from U.S. Geological Survey 

Bellt>rook. 1965. photorevised 1987; Dayton North. 

1965. photorevised 1981: Dayton South. 1966. 

photorevised 1981: Donnelsvilte. 1965. 

photorevised 1973. photoiospected 1983: 

Fairborn. 1965. photorevised 1988: New Carlisle. 

1955. photorevised 1968 and 1973. 

photoinspected 1984: Tipp City. 1965. 

photorevised 1982: Xenia. 1965. photorevised 

1987; Yellow Springs. 1968. photorevised 1975. 

Polyconic projection

4 MILES

J

I I I I 

0123 4 KILOMETERS

EXPLANATION

UPLAND BEDROCK

WRIGHT-PATTERSON AIR FORCE BASE

 840 GROUND-WATER-LEVEL CONTOUR Shows 

altitude of composite ground-water surface 

in the uppermost aquifer. Contour interval 

20 feet. Datum is sea level

 MODELED-AREA BOUNDARY

 LOCAL GROUND-WATER DIVIDE

-^ LOCAL DIRECTION OF GROUND-WATER FLOW

Figure 3. Ground-water levels and generalized flow directions in the upland bedrock and valley-train 

deposits. (From Dumouchelle and others, 1993, fig. 11.)

Contributing Recharge Areas to Water-Supply Wells 7
Areal recharge

Contributing 

recharge 

area ___

^ Discharging 

r well

Land surface

- . 

Water taBRT

Zone of contribution

Bounding 

flow lines

CROSS-SECTIONAL VIEW NOT TO SCALE

Contributing

recharge

area

ounding flow line

Discharging well

Bounding flow line

MAP VIEW NOT TO SCALE

Figure 4. Contributing recharge area to a single discharging well in a simplified hypothetical ground-waterflow system. (Modified from Reilly and Pollock, 1993, fig. 1.)

8 Contributing Recharge Areas of Water-Supply Wells at Wrlght-Patterson Air Force Base, Ohio
EXPLANATION 

WRIGHT-PATTERSON AIR FORCE BASE

 . MAD RIVER

 MODELED-AREA BOUNDARY 

(ACTIVE CELLS LIE WITHIN)

Figure 5

. Model grid in relation to modeled area. (From Dumouchelle and others, 1993, fig. 19.)

Contributing Recharge Areas to Water-Supply Wells 9
Buried-valley aquifer 

___________^

Figure 6. Generalized sectional view of the ground-water-flow model, Wright-Patterson Air Force Base, Ohio. 

(From Dumouchelle and others, 1993, fig. 21.)

of three layers, as can be seen in the sectional view of 

the model shown in figure 6. Layer 1, the uppermost 

layer, ranges in thickness from 20 to 200 ft and simulates flow in the uppermost part of the buried-valley 

aquifer and the entire permeable thickness of upland 

bedrock aquifer. The base of the uppermost part of the 

buried-valley aquifer is characterized by the presence 

of discontinuous deposits of poorly permeable clays 

and silts. Layer 2 of the model simulates the central 

part of the buried-valley aquifer, in which most of the 

water-supply wells are completed. Layer 3 of the 

model simulates Hie part of buried-valley aquifer that 

is bounded by the bottom of layer 2 and the Ordovician bedrock at the bottom of the valley. The boundary 

between layers 2 and 3 generally corresponds to a discontinuous till unit. Lateral boundaries to groundwater flow were based on ground-water divides, surface-water bodies, and calculated flux through valley 

cross-sections. A complete description of the groundwater-flow model can be found in Dumouchelle and

others (1993). Because the model and its results are 

used to delineate the CRA's described in this report, a 

brief discussion of the input parameters and sensitivity 

analyses is given here.

Input Parameters

Layer 1 of the model was simulated as an 

unconfined aquifer. Horizontal hydraulic conductivities (Klh) in the areas containing upland bedrock in 

the model generally ranged from 0.2 to 1 ft/d. In the 

uppermost buried-valley aquifer, Klh values of 5 to 

210 ft/d were assigned on the basis of aquifer-test data 

and calibration of the model. A transitional zone of 

intermediate Kih was used along the valley walls 

because of the presence of clay-rich sediments draping 

the valley walls; in addition, use of an intermediate 

Klh allows for a smooth transition between upland and 

valley hydraulic conductivities.

10 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
Layers 2 and 3, present only in the bedrock valleys, were modeled as confined aquifers. Transmissivities (T2 and T3) ranged from 4 to 76,600 ft2/d and also 

were based on aquifer-test data and refined with model 

calibration. Transmissivities in the central parts of the 

valleys were higher than on the flanks of the valleys. 

Vertical leakance between layers one and two (Vj) and 

between layers 2 and 3 (¥2) was used to simulate the 

discontinuous till units.

Areal recharge to the ground-water-flow system 

from precipitation was distributed to the uppermost 

active nodes in the model. Recharge rates ranged from 

1 to 6 in/yr in the uplands and from 6 to 15 in/yr in the 

valleys and were based on previous studies, surficial 

geology, and recession-curve analysis.

Pumping rates for the period of calibration were 

obtained for all pumping centers producing greater 

than approximately 10 gal/min. Primarily, these centers are in industrial areas, in or near municipalities, 

and on the Base. The city of Dayton's Rohrer's Island 

Well Field (fig. 2) was the largest pumping center 

included in the model; withdrawals were approximately 50 Mgal/d. For the steady-state calibration of 

(he model, Skeel Road and East Well Fields were 

pumping at 1.9 and 1.1 Mgal/d, respectively. Area B 

wells were not active for the time period used for the 

calibration.

Perennial streams in the area were modeled as 

such, and streambed conductances (Kriv ) were based 

on seepage-meter measurements for the Mad River 

and Hebble Creek. Intermittent streams, present primarily in the uplands, were modeled as drains.

Calibration Targets

Ground-water levels at 330 wells, measured in 

late 1987, were compared with simulated heads during 

Ihe steady-state calibration process. Measured gains to 

and losses from streams in the area were also compared to simulated gains and losses. Vertical hydraulic 

gradients between shallow, intermediate, and deep 

well clusters completed in the valley fill also were 

used during calibration to refine the vertical groundwater-flow component. Previous estimates of groundwater flow from the upland bedrock to the valley-train 

were also used qualitatively during calibration.

Sensitivity Analyses

Systematic changes in aquifer parameters input 

to the ground-water-flow model were made by

Dumouchelle and others (1993) to ascertain the sensitivity of the model to these parameters. Because the 

uncertainty of the size and shape of the CRA's is 

related to the sensitivity of the model to input parameters, a discussion of model sensitivity to input parameters affecting CRA's is necessary here. The sensitivity 

analysis presented here and in Dumouchelle and others (1993) is supplemented by an uncertainty analysis 

of the CRA's, described later in this report.

The input parameters that were varied during 

the sensitivity analysis were horizontal hydraulic conductivity of layer 1 (Klh), vertical leakance between 

layers 1 and 2 (Vj), vertical leakance between layers 2 

and 3 (¥2), transmissivity of layer 2 (T2), transmissivity of layer 3 (T3), areal recharge to the aquifers 

(RCH), and riverbed conductance (Kriv). The 

responses of hydraulic heads in the uplands and buried 

valleys, Mad River and tributary discharges, and flows 

from the upland bedrock and under Huffman Dam 

were examined during sensitivity analyses in relation 

to input-parameter variation. These outputs from the 

model may affect the size and shape of the CRA's for 

the Skeel Road and Area B Well Fields.

Simulated hydraulic heads were most sensitive 

to changes in Kj h in the uplands and in the valley-train 

deposits. Multiplying K^ of the uplands by 0.1 

resulted in an 800-percent increase in the root-meansquare error of head residuals. Multiplying Klh of the 

valley-train deposits by 0.1 caused a 500-percent 

increase in the root-mean-square error of head residuals. Head residuals also are affected significantly by 

decreases to Kriv and Vj These relations are shown in 

figure 7. The changes in Kj h also affected the intercell 

flows calculated by the model. The intercell flows 

were somewhat sensitive to positive changes in upland 

Klh, negative changes in Vj, and any changes to areal 

recharge of the valley-train deposits.

Dumouchelle and others (1993) described specific stream reaches and valley segments along which 

discharges and fluxes were analyzed: Hebble Creek, 

Mad River North and South, Trout Creek, Hills 1 and 

2, and Huffman Dam (fig. 2). A discussion of model 

sensitivity to simulated discharges in Mad River South 

and Hebble Creek is necessary here because the Mad 

River is adjacent to the Area B wells, and Hebble 

Creek is adjacent to the Skeel Road and East Well 

Fields. Surface-water inputs from Mad River South 

and Hebble Creek to these well fields could affect their 

CRA's.

Contributing Recharge Areas to Water-Supply Wells 11
800

600

400 -

200

ALL WELLS

WELLS IN VALLEY-TRAIN DEPOSITS"

WELLS IN UPLANDS

MULTIPLICATION FACTOR FOR HORIZONTAL HYDRAULIC 

CONDUCTIVITY OF UPLANDS, LAYER 1

3,000

2,000

1,000

-1,000

I I I I I I I I I

N\A

-50 -40 -30 -20-10 0 10 20 30 40 50 

PERCENT CHANGE IN RIVERBED CONDUCTANCE

0.1 10

MULTIPLICATION FACTOR FOR HORIZONTAL HYDRAULIC 

CONDUCTIVITY OF VALLEY TRAIN, LAYER 1

2,000

1,500

1,000

500

0.1 10

MULTIPLICATION FACTOR FOR VERTICAL HYDRAULIC 

CONDUCTANCE, LAYERS 1 AND 2

Figure 7. Sensitivity of simulated heads to changes in horizontal hydraulic conductivity, riverbed conductance, 

and vertical hydraulic conductance in model of ground-water-flow system, Wright-Patterson Air Force Base, 

Ohio, and vicinity. (Modified from Dumouchelle and others, 1993, fig. 34.)

12 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
Hebble Creek flows through an underground 

pipe and a concrete channel in the reach adjacent to 

Skeel Road Well Field, thereby preventing significant 

surface-water influence on well production. Results of 

sensitivity analyses of various hydraulic parameters 

and the effects of changes in these parameters to discharges in Mad River South and Hebble Creek are 

shown in figure 8. The most significant effects are seen 

when the vertical conductance between layers 1 and 2 

is decreased, simulating a less permeable confining 

unit between these layers. The sensitivity analyses also 

show that variations in areal recharge also will significantly affect the simulated discharges to Hebble 

Creek.

The effects of flow from Hills 1 and 2 also are 

important because of the proximity of these hills to the 

East and Skeel Road Well Fields, respectively. The 

results of sensitivity analyses of the selected discharges and fluxes are shown in figure 9. Variations in 

areal recharge to the upland areas and in the horizontal 

hydraulic conductivity of the upland areas have the 

most significant effect on flows from Hills 1 and 2. 

Changes in ground-water flows under Huffman Dam 

are important to the CRA's of the Area B Well Field. 

Changes in T2 have almost a one-to-one relation to 

changes in flow under Huffman Dam (fig. 10). Variations in Vj also significantly affect flows under Huffman Dam (fig. 10).

Limitations of Flow Model

A ground-water-flow model is a numerical representation of a ground-water-flow system and, as 

such, has limitations. These limitations can be a result 

of the code used to solve the ground-water-flow equation, the hydrologic data available for inclusion in 

defining boundary conditions or calibration, or the 

scale at which the model is used. Numerical approximations and convergence criteria used in the code for 

solving the ground-water-flow equations may affect 

how well the model reflects the ground-water-flow 

system. Uncertainty in physical measurements used to 

calibrate the model, such as streamflow measurements 

or well pumpage, can lead to uncertainty in how well 

the model is calibrated. The model by Dumouchelle 

and others (1993) was developed to examine regional 

ground-water flow; more localized flow was not examined in their analyses. These and other limitations of 

the ground-water-flow model have direct bearing on 

the simulations of the contributing recharge areas and 

are examined later with the limitations of the particletracking analyses. The limitations of the groundwater-flow model are discussed in detail in 

Dumouchelle and others (1993).

Delineation by Particle Tracking

Hydraulic heads and intercell flows output from 

the previously described model (Dumouchelle and 

others, 1993) were input to the computer program 

MODPATH to determine CRA's as a function of 

pumping rate and porosity. Four hypothetical particles 

of water were placed on the water table in each grid 

cell and tracked to their eventual discharge points; the 

trajectories of particles that discharged to wells in 

Base well fields were saved with the traveltime information. The particle paths, as well as traveltimes, were 

input into ARC/INFO, and initial particle locations 

with traveltimes from 0 to 1, 1 to 5, and 5 to 10 years 

(1-, 5-, and 10- years) were grouped to create 1-, 5- 

and 10-year CRA's for normal, intermediate, and maximum pumping rates.

The CRA's to the Skeel Road and East Well 

Fields, under October-December 1987 steady-state 

conditions are shown in figure 11. Records of pumping 

rates were averaged for October-December 1987 and 

are approximately 1.9 and 1.1 Mgal/d for Skeel Road 

and East Well Fields, respectively. Because of waterquality concerns (Linda Rogers, Wright-Patterson Air 

Force Base, oral comm., 1993), the East Well Field has 

been unused since late in 1987.

The description of the CRA's that follows concentrates on the Skeel Road and Area B Well Fields. 

However, because the East Well Field may be used in 

the future for water supply, the East Well Field is 

accounted for in describing variations in CRA's in 

response to pumping.

Normal, intermediate, and maximum-capacity 

pumping rates were input into the ground-water-flow 

model by Dumouchelle and others (1993) in a series of 

predictive simulations. Normal pumping rates were 

determined from average pumping at each well field 

over a period of time, and the maximum pumping 

capacity of each well was defined with reference to 

well and aquifer-test information. Maximum-capacity 

data were compiled to compute a worst-case scenario 

of the CRA's. The average of normal and maximum 

pumping (intermediate) was also used in the analysis 

to refine the range of pumping conditions. Porosities, 

which are required by the particle-tracking code, were 

estimated from specific yields derived from aquifer

Contributing Recharge Areas to Water-Supply Wells 13
20

10

a:

UJ

I -20

O -30

........ K1h , VALLEY-TRAIN DEPOSITS

: v, ^-'

UJ 

O 

DC 

UJ

0.1 1 10 

MULTIPLICATION FACTOR FOR HYDRAULIC 

CONDUCTIVITY, LAYER 1 (K1h), OR VERTICAL 

CONDUCTANCE BETWEEN LAYERS 1 AND 2 (Vj)

20

15

10

-5

RCH, VALLEY-TRAIN DEPOSITS

- KH

-50 -40 -30 -20 -10 0 10 20 30 40 50

PERCENT CHANGE IN RECHARGE (RCH) OR 

RIVERBED CONDUCTANCE (Krb)

UJ 

UJ

cc 

o

UJ

CD 

CD 

UJ

X

300

200 -

100 -

o -

-100

Ki h , VALLEY-TRAIN DEPOSITS

0.1 1 10

MULTIPLICATION FACTOR FOR HYDRAULIC

CONDUCTIVITY, LAYER 1 (K1h), OR VERTICAL

CONDUCTANCE BETWEEN LAYERS 1 AND 2 (V^

300

200

100

-100

-200

i I i I I I I i l 

 RCH. VALLEY-TRAIN DEPOSITS 

....... Krb

 T2

-50 -40 -30 -20 -10 0 10 20 30 40 50

PERCENT CHANGE IN RECHARGE (RCH), RIVERBED 

CONDUCTANCE (Krb), OR TRANSMISSIVITY OF LAYER 2 (T2)

Figure 8. Sensitivity of simulated flows to Mad River South and Hebble Creek to changes in hydrogeologic 

parameters in the model of the ground-water-flow system, Wright-Patterson Air Force Base, Ohio. (Modified from Dumouchelle and others, 1993, figs. 37-38.)

14 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
40

30

20

10

I 

O

LL -10

O

hz

LU 

O

a: LU 

a.

K1h> UPLANDS

K1h , VALLEY-TRAIN DEPOSITS

0.1 1 10

MULTIPLICATION FACTOR FOR HYDRAULIC

CONDUCTIVITY, LAYER 1 (K1h ), OR VERTICAL

CONDUCTANCE BETWEEN LAYERS 1 AND 2 (V^

60

40

20

-20

-40

-60

RCH, UPLANDS 

Krb

-50 -40 -30 -20 -10 0 10 20 30 40 50

PERCENT CHANGE IN RECHARGE (RCH) OR 

RIVERBED CONDUCTANCE (Krb)

300

200

100

-100

K1h> UPLANDS

K1h, VALLEY-TRAIN DEPOSITS

0.1 1 10

LU 

O

< 30 

O

MULTIPLICATION FACTOR FOR HYDRAULIC

CONDUCTIVITY, LAYER 1 (K1h), OR VERTICAL

CONDUCTANCE BETWEEN LAYERS 1 AND 2 (V^

20

10

-10

-20

-30

-50 -40 -30 -20 -10 0 10 20 30 40 50

PERCENT CHANGE IN RECHARGE (RCH) OR 

RIVERBED CONDUCTANCE (Krb)

Figure 9. Sensitivity of simulated flows from Hills 1 and 2 to changes in hydrogeologic parameters in the 

model of the ground-water-flow system, Wright-Patterson Air Force Base, Ohio. (Modified from 

Dumouchelle and others, 1993, fig. 36.)

Contributing Recharge Areas to Water-Supply Wells 15
150

100

50

o

< -50

-100

0.1

K 1h, VALLEY-TRAIN DEPOSITS

1 10

MULTIPLICATION FACTOR FOR HYDRAULIC

CONDUCTIVITY, LAYER 1 (K1h), OR VERTICAL

CONDUCTANCE BETWEEN LAYERS 1 AND 2 (V^

X 60 

O

tI 40 

oc

LLI 

Q.

20

-20

-40

-60

-50 -40 -30 -20 -10 0 10 20 30 40 50

PERCENT CHANGE IN RIVERBED CONDUCTANCE (KJ 

OR TRANSMISSIVITY OF LAYER 2 (T2)

Figure 10. Sensitivity of simulated flows under Huffman Dam to changes in hydrogeologic parameters in 

the model of the ground-water-flow system, Wright-Patterson Air Force Base, Ohio. (Modified from 

Dumouchelle and others, 1993, figs. 37-38.)

16 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
84°07r 30" 84°05' 84°02' 30'

39°50' :.

39°4T 30"

Base map digitized from U.S. Geological Survey 

Dayton North, 1965, photorevised, 1981; Fairbom. 

1965, photorevised, 1988. Polyconic projection

5.000 10,000 FEET

1,000 2,000 METERS

EXPLANATION

P7 10-YEAR CONTRIBUTING RECHARGE AREA 

m 5-YEAR CONTRIBUTING RECHARGE AREA 

m 1-YEAR CONTRIBUTING RECHARGE AREA

,'\ BOUNDARY OF UPLAND BEDROCK

WRIGHT-PATTERSON AIR FORCE 

BASE BOUNDARY

WELL LOCATION

Figure 11. One-, 5-, and 10-year contributing recharge areas to the Skeel Road and East Well Fields (Pumping 

rates for the well fields are based on October-December 1987 conditions).

Contributing Recharge Areas to Water-Supply Wells 17
test data in the area (Johnson, 1967). The assigned 

porosities are 0.20,0.25, and 0.15 for layers 1,2, and 3 

of the ground-water-flow model, respectively. The 

sensitivity of variations in porosity is examined later 

in this report.

The previously described ground-water-flow 

model (Dumouchelle and others, 1993) was modified 

to incorporate pumping at the Area B Well Field. 

Increased pumping in this area caused a numerical 

instability in the model (resulting in dry model cells) 

near the boundary of the upland bedrock and valleytrain deposits. This instability was resolved with a 

minor lowering of the bottom of layer 1 and slightly 

increasing recharge rates along this boundary. Hydraulic heads and intercell flows predicted by the modified 

model were compared with those of the original 

model, and differences in model results are small. For 

example, the overall water budget shows differences 

of less than 0.1 percent, and the root-mean-squared 

error of head residuals in the modified model differs 

by less than 1 percent from that of the original model. 

The modified model was used for all CRA analyses.

The yearly average pumping rate for October 

1986 through November 1987, was 1.9 Mgal/d for 

Skeel Road Well Field; this rate is assumed, for simulation purposes, to be the normal pumping rate for 

these wells. The maximum capacity of the wells that 

make up the Skeel Road Well Field is approximately 

6.3 Mgal/d. Pumping data from July 1989 to March 

1990 for the Area B Well Field indicate an assumed 

normal pumping rate of approximately 1.7 Mgal/d. 

Maximum capacity of the wells in the Area B Well 

Field is approximately 4.6 Mgal/d. For all simulations 

including Area B and Skeel Road Well Fields, the East 

Well Field is not pumping.

The traveltime-delineated CRA's for the Skeel 

Road and Area B Well Fields, under normal, intermediate, and maximum pumping, are shown in figures 12 

through 14. The pumping rates used for these simulations and the resulting size of the CRA's for the Base 

well fields are given in table 1. Figure 15 illustrates the 

nearly linear relation between the size of the CRA's 

and pumping rates.

Table 1 . Pumping rates and contributing recharge areas to 

well fields at Wright-Patterson Air Force Base, Ohio

[Mgal/d, million gallons per day; mi2, square miles; Normal pumping for 

Skeel Road and East Well Fields based on October-December 1987 averages; normal pumping for Area B Well Field based on July 1989-March 

1990 averages. Maximum pumping is maximum capacity of the well field, 

based on well-test data. Intermediate pumping is midway between normal 

and maximum.

Pumping Contributing recharge areas

Condition

Rate (mP)

(Mgal/d) 1-year 5-year 10-year

Skeel Road Well Field

Normal 

Intermediate 

Maximum

1.9 0.33 0.89 

4.1 .44 1.15 

6.3 .51 1.45

1.78 

2.46 

3.24

Area B Well Field

Normal 

Intermediate 

Maximum

1.7 0.038 0.201 

3.2 .047 .357 

4.6 .065 .502

0.343 

.549 

.863

East Well Field

Normal 

Intermediate 

Maximum

1.1 0.056 0.428 

3.7 .283 .968 

6.2 .241 1.218

0.694 

1.492 

2.449

The CRA's for the Skeel Road Well Field are 

generally oval, extending to the north and east (up the 

Mad River valley) for the northernmost wells and to 

the south and east for the southern wells in the well 

field (fig. 12). As pumping rates increase, the CRA's 

for the northernmost wells extend further upvalley and 

toward a losing reach of Mad River. The Skeel Road 

CRA's are not affected appreciably by surface-water 

sources. Hebble Creek in the reach near the wells is in 

a concrete channel, and this reach was not simulated in 

the model. The shape of the CRA's for the wells is 

generally typical of wells placed in a homogeneous, 

isotropic unconfined aquifer in a uniform regional 

velocity field. Wells further to the south are more 

affected by ground-water flow entering the Mad River 

valley from the upland area to the east and from a tributary buried valley oriented approximately northwestsoutheast (fig. 3).

The smaller size of the CRA's for the Area B 

Well Field is primarily the result of high rates of 

induced infiltration from the Mad River, the effects of 

the nearby well field at Rohrer's Island, and the bedrock hill in the northeast part of Area B (fig. 3). As 

stated before, the pumping rate at the Rohrer's Island 

Well Field is approximately 50 Mgal/d. Pumping at 

Rohrer's Island Well Field and the upland area to the 

south and east of Area B Well Field restricts the CRA's 

to the Mad River Valley and the tributary valley. As 

pumping rates increase at the Area B Well Field, the 

CRA increases in size to the northeast, up the Mad

18 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
84°02'30"

39° 50'

39°4T 30"

Base map digitized from U.S. Geological Survey 

Dayton North, 1965, photorevised, 1981; Fairbom, 

1965, photorevised, 1988. Polyconic projection

5,000 10,000 FEET

1,000 2,000 METERS

EXPLANATION

r 10-YEAR CONTRIBUTING RECHARGE AREA

H 5-YEAR CONTRIBUTING RECHARGE AREA

 1-YEAR CONTRIBUTING RECHARGE AREA

,'\ BOUNDARY OF UPLAND BEDROCK

^ WRIGHT-PATTERSON AIR FORCE 

BASE BOUNDARY

if WELL LOCATION

Figure 12. Contributing recharge areas to Skeel Road and Area B Well Fields under normal pumping conditions (1.9 and 1.7 million gallons per day, respectively).

Contributing Recharge Areas to Water-Supply Wells 19
°or 30' 84°05'

39° 50'

39°4r 30"

84°02' 30'

Base map digitized from U.S. Geological Survey 

Dayton North, 1965. photorevised, 1981; Fairbom, 

1965, photorevised, 1988. Polyconic projection

5,000 10,000 FEET

1,000 2,000 METERS

EXPLANATION

F 10-YEAR CONTRIBUTING RECHARGE AREA

m 5-YEAR CONTRIBUTING RECHARGE AREA

m 1-YEAR CONTRIBUTING RECHARGE AREA

,'\ BOUNDARY OF UPLAND BEDROCK

*^ WRIGHT-PATTERSON AIR FORCE 

BASE BOUNDARY

if WELL LOCATION

Figure 13. Contributing recharge areas to Skeel Road and Area B Well Fields under intermediate pumping 

conditions (4.1 and 3.2 million gallons per day, respectively).

20 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
84°07' 30" 84°05' 84°02' 30"

39° 50'

39°47 30"

Base map digitized from U.S. Geological Survey 

Dayton North, 1965, photorevteed, 1981; Fairbom, 

1965, photorevised, 1988. Polyconic projection

5,000 

I

10,000 FEET

I I I . .

I ' ' ' ' I 

1,000 2,000 METERS

EXPLANATION

F 10-YEAR CONTRIBUTING RECHARGE AREA

H 5-YEAR CONTRIBUTING RECHARGE AREA

* 1-YEAR CONTRIBUTING RECHARGE AREA

,'\ BOUNDARY OF UPLAND BEDROCK

*^ WRIGHT-PATTERSON AIR FORCE 

BASE BOUNDARY

* WELL LOCATION

Figure 14. Contributing recharge areas to Skeel Road and Area B Well Fields under maximum capacity 

pumping conditions (6.3 and 4.6 million gallons per day, respectively).

Contributing Recharge Areas to Water-Supply Wells 21
y

3.5

3.0

2.5

2.0

1.5

1.0

0.5

u

Z 0

1.0

0.8

0.6

0.4

0.2

SKEEL ROAD WELL FIELD

PUMPING RATE, 

IN MILLION GALLONS PER DAY

AREA B WELL FIELD

EXPLANATION

10-YEAR CONTRIBUTING 

RECHARGE AREA

5-YEAR CONTRIBUTING 

RECHARGE AREA

- 1-YEAR CONTRIBUTING 

RECHARGE AREA

PUMPING RATE, 

IN MILLION GALLONS PER DAY

Figure 15. Change in contributing recharge areas in relation to pumping rates at Skeel Road and Area B 

Well Fields, Wright-Patterson Air Force Base, Ohio (Pumping rates range from normal pumping (OctoberDecember 1987 averages) to maximum capacity pumping for each well field).

22 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
River Valley. The CRA's for Area B include the Huffman Dam area and, under maximum pumping conditions, part of the East Well Field (which is not 

pumping in these simulations). The CRA's for Area B 

also become larger, with increased pumping, to the 

south along the tributary valley to the Mad River 

valley.

CRA's for the East Well Field, under normal 

(1.1 Mgal/d), intermediate (3.7 Mgal/d), and maximum (6.2 Mgal/d) pumping conditions (table 1) are 

shown in figures 16 through 18. In these simulations, 

Skeel Road Well Field is pumping at normal rates, and 

Area B Well Field is not pumping. The circular CRA's 

Irend south and east at normal pumping rales (fig. 16); 

at intermediate and maximum pumping rates, the 

CRA's shift to the north and northeast (figs. 17 and 

18). These simulations show that ground-water flow in 

Mad River Valley and in the tributary valley to the 

southeast of Areas A and C are the main areas contributing recharge to the wells in the East Well Field. 

Under normal, and to a lesser extent, intermediate 

pumping conditions, some ground water flows to 

Hebble Creek, which is not in a concrete channel near 

the East Well Field and to an unnamed tributary near 

the East Well Field; this ground water is not captured 

by the wells.

Under intermediate and maximum pumping, a 

few cells in the simulated upper model layer go dry. In 

I he actual hydrologic system, pumping at high rates in 

the vicinity of the East Well Field have, in fact, caused 

the upper several feet of the aquifer to be dewatered. 

In 1993, pumping at Huffman Dam and to the west of 

the East Well Field is suspected to have caused two 

small lakes to the west of the East Well Field to almost 

go dry; water levels in wells adjacent to the lakes were 

10 to 15 ft below 1987 levels. The East Well Field is 

near the edge of the buried-valley aquifer, and the 

valley-train deposits are considerably thinner to the 

west of the well field. Near the East Well Field and 

along a northeast-southwest trend, few nodes contribute recharge to the wells (figs. 17 and 18). When the 

cells go dry in the model, particles of water in the cells 

to the southwest of the well field have to travel around 

the dry cells to reach the discharge points at the wells; 

the resulting traveltimes exceed ten years, and the 

positions of the particles are not part of the CRA's. The 

traveltimes and particle paths in the area immediately 

to the southwest of the well field are therefore unreliable because of the dry cells.

Uncertainty Analyses

Areas contributing recharge to pumped wells 

can vary in response to a number of factors. The variation of these areas (hence, the uncertainty in the accuracy of these areas) for Skeel Road and Area B Well 

Fields, based upon changes in hydraulic parameters of 

the aquifer, is given in this section.

The effect of pumping at one well field on the 

CRA of the other well field was determined. For this 

analysis, pumping rates were held constant at the Area 

B Well Field while pumping at Skeel Road Well Field 

was cycled through normal, intermediate, and maximum rates. Rates at Skeel Road Well Field were then 

held constant as pumping at Area B Well Field was 

cycled through various pumping rates. Pumping at 

Skeel Road Well Field does not affect the size or shape 

of the CRA's of Area B Well Field; likewise, pumping 

at Area B Well Field does not affect the size or shape 

of the CRA's of Skeel Road Well Field.

The input parameters to the model and the 

particle-tracking program were systematically 

changed to examine the effects of uncertainties in 

hydrogeologic parameters on the areal extent of the 

CRA's. These input parameters included hydraulic 

conductivity or transmissivity, effective porosity, areal 

recharge, and riverbed conductance. Examination of 

the sensitivity analyses of the model by Dumouchelle 

and others (1993) and initial CRA analyses indicated 

that flows in the buried-valley aquifer and flows from 

the upland bedrock were most likely to affect the 

CRA's of Skeel Road Well Field (figs. 7 through 9). 

Similar analyses of the Area B Well Field indicated 

that rates of infiltration from the Mad River, flows 

from Hills 1 and 2, and ground-water flow under Huffman Dam would most likely affect the CRA's of Area 

B Well Field (figs. 7 through 9).

Changes in hydraulic conductivity and transmissivities (Klh, T2^ ^3) of the glacial-drift aquifer significantly affect the size and shape of the 1- and 5-year 

CRA's for the Skeel Road Well Field. The relations 

between the CRA's and horizontal hydraulic conductivities of the buried-valley aquifer and in the upland 

bedrock are shown in figure 19. Porosity variations in 

the buried-valley aquifer also have a great effect on the 

CRA's; increases in porosity decrease the CRA's (fig. 

20). Changes in horizontal hydraulic conductivity and 

porosity in the upland bedrock have no effect on the 

CRA's of Skeel Road Well Field (see also figs. 19 and 

20).

Contributing Recharge Areas to Water-Supply Wells 23
84°0r 30" 84°05f 84°02' 30'

39° 50'

39°47 30"

Base map digitized from U.S. Geological Survey 

Dayton North, 1965, photorevlsed, 1981; Falrbom, 

1965, photorevised, 1988. Polyconic projection

5.000

I .

10,000 FEET

J

I ' ' 

1,000 2,000 METERS

EXPLANATION

R 10-YEAR CONTRIBUTING RECHARGE AREA

 5-YEAR CONTRIBUTING RECHARGE AREA

 1-YEAR CONTRIBUTING RECHARGE AREA

/\ BOUNDARY OF UPLAND BEDROCK

s~* WRIGHT-PATTERSON AIR FORCE 

BASE BOUNDARY

 WELL LOCATION

Figure 16. Contributing recharge areas to the East Well Field under October-December 1987 pumping conditions (1.1 million gallons per day).

24 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
84°or so- 84°05' 84°02' 30"

39° 50' 5

39°47" 30"

Base map digitized from U.S. Geological Survey 

Dayton North, 1965, photorevised, 1981; Fairbom, 

1965. photorevised, 1988. Polyconlc projection

5,000

"ITIr~|IITTI

1,000 2,000 METERS

10.000 FEET 

I

EXPLANATION

F 10-YEAR CONTRIBUTING RECHARGE AREA 

H 5-YEAR CONTRIBUTING RECHARGE AREA 

H 1-YEAR CONTRIBUTING RECHARGE AREA

,'\ BOUNDARY OF UPLAND BEDROCK

WRIGHT-PATTERSON AIR FORCE 

BASE BOUNDARY

WELL LOCATION

Figure 17. Contributing recharge areas to the East Well Field under intermediate pumping conditions 

(3.7 million gallons per day).

Contributing Recharge Areas to Water-Supply Wells 25
84°07 30" 84°05' 84°02' 30"

39°50' ;:

39°47 30"

Base map digitized from U.S. Geological Survey 

Dayton North, 1965, photorevised, 1981; Fairbom, 

1965, photorevised, 1988. Polyconic projection

5,000 10,000 FEET

I ' ' ' ' I

1,000 2,000 METERS

EXPLANATION

P 10-YEAR CONTRIBUTING RECHARGE AREA

8 5-YEAR CONTRIBUTING RECHARGE AREA

 1-YEAR CONTRIBUTING RECHARGE AREA

,'\ BOUNDARY OF UPLAND BEDROCK

XX WRIGHT-PATTERSON AIR FORCE 

BASE BOUNDARY

* WELL LOCATION

Figure 18. Contributing recharge areas to the East Well Field under maximum capacity pumping conditions 

(6.2 million gallons per day).

26 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
3.5

3.0

2.5

2.0

1.5

1.0

0.5

UPLAND BEDROCK

0.1

3.5

£ 3.0

2.5

2.0

1.5

1.0

0.5

0.1

10

MULTIPLICATION FACTOR FOR HORIZONTAL HYDRAULIC CONDUCTIVITY, 

IN FEET PER DAY

BURIED-VALLEY AQUIFER

EXPLANATION

10-YEAR CONTRIBUTING 

RECHARGE AREA

5-YEAR CONTRIBUTING 

RECHARGE AREA

 1-YEAR CONTRIBUTING 

RECHARGE AREA

10

MULTIPLICATION FACTOR FOR HORIZONTAL HYDRAULIC CONDUCTIVITY, 

IN FEET PER DAY

Figure 19. Variations of the contributing recharge areas of Skeel Road Well Field, Wright-Patterson Air Force 

Base, Ohio, in relation to changes in horizontal hydraulic conductivity of the upland bedrock and buried-valley 

aquifer under normal pumping conditions.

Contributing Recharge Areas to Water-Supply Wells 27
2.5

2.0

1.5

1.0

0.5

2.5

2.0

1.5

1.0

D.5

UPLAND BEDROCK

-50 -40 -30 -20 -10 0 10 20 

PERCENT CHANGE IN POROSITY

30 40 50

BURIED-VALLEY AQUIFER

EXPLANATION

10-YEAR CONTRIBUTING 

RECHARGE AREA

5-YEAR CONTRIBUTING 

RECHARGE AREA

. 1-YEAR CONTRIBUTING 

RECHARGE AREA

-50 -40 -30 -20 -10 0 10 20 

PERCENT CHANGE IN POROSITY

30 40 50

Figure 20. Variations of the contributing recharge areas of Skeel Road Well Field, Wright-Patterson Air 

Force Base, Ohio, in relation to changes of porosity of the upland bedrock and buried-valley aquifer under 

normal pumping conditions.

28 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
The Area B wells are completed in the valleytrain deposits near the Mad River and near upland bedrock. To examine the effects on the size of the CRA's 

on flow from the upland bedrock and flow under Huffman Dam, horizontal hydraulic conductivities and 

porosities for the upper model layer (Klh) were varied, 

under normal pumping. Changes in Kjh have little 

affect on the size of the 1- or 5-year CRA's, except at 

much higher horizontal hydraulic conductivities (fig. 

21). As shown in figure 22, porosity changes in the 

buried-valley aquifer and upland bedrock also have little affect on the size of the CRA's. Horizontal hydraulic conductivity and porosity variations in the bedrock 

have a slight effect on the size of the CRA's because of 

the proximity of upland bedrock to the wells. Riverbed 

hydraulic conductance (Kriv) was also varied to examine the effect on the CRA's of Area B Well Field 

because of the proximity of the Mad River and the 

probable effect of induced infiltration, as shown on 

figures 12 through 14. However, the results of these 

variations, shown in figure 23, indicate that variations 

in Kriv do not affect the size of the CRA's. As the 

CRA's expand, more water from the Mad River is 

available to the wells. Hydrologic boundaries near the 

Area B Well Field upland bedrock, the well field at 

Rohrer's Island, and the Mad River cause the CRA's 

to expand up the Mad River Valley. This result is 

expected, because simulated flows from Mad River 

South (fig. 7) and flow through Huffman Dam (fig. 9) 

also are not sensitive to changes in Kriv. Pumping variations at Rohrer's Island were not examined in these 

analyses because the well field has maintained constant pumping rates over many years.

Limitations of Tracking Procedure

As stated previously in this report, the model on 

which the CRA's are based has limitations that may 

affect the CRA's. The particle-tracking code also has 

limitations, which are outlined here. Mercer and Faust 

(1986) summarize the limitations and sources of error 

in modeling, and Pollock (1989) discusses the limitations of the particle tracking procedure at length. The 

most significant limiting factor in particle tracking, 

and therefore in the contributing recharge analyses 

presented herein, is the numerical model on which the 

analyses are based. The numerical model from which 

the heads and flows are generated and used in particle 

tracking is a numerical representation of the natural 

flow system. Numerical approximations, convergence 

tolerances, and scale limitations can all affect how

well the model mimics the actual flow system. Grid 

structure, boundary definitions, and calibration data 

also can affect the accuracy of the model and therefore 

the particle tracking and delineation of a CRA. Errors 

from numerical approximations are assumed to be 

minimized by trial-and-error adjustment during calibration, but a discussion of the scale limitations is 

required here. The model developed previously was 

designed to investigate regional ground-water flow 

and more local flow, such as flow to smaller streams, 

may not be well represented by the model. However, 

the analyses presented in this report indicate that local 

flow, at the scale of CRA's, is well represented (for 

example, fig. 11). A complete discussion of the limitations of the model is given in Dumouchelle and others 

(1993).

The particle-tracking scheme used by MODPATH is valid only for computing and interpolating 

advective velocities from intercell flows such as those 

output by MODFLOW Accordingly, the CRA's are 

based on advective particle movement and traveltimes no diffusion or dispersion is incorporated into 

the movement of particles that make up the CRA's.

The analyses presented herein are based on a 

model of steady-state conditions changes in pumping or other stresses in the system over time may affect 

the particle pathlines and traveltimes incorporated into 

the CRA's. Since construction of the model, several 

factors have altered the ground-water-flow system. 

The most significant factor is the addition of pumped 

wells to the area. Wells currently (1994) producing 

approximately 3 Mgal/d have been placed on the 

downstream side of Huffman Dam, and a well 

(extraction well) producing approximately 0.9 Mgal/d 

has been placed about 1 mi northeast of Huffman Dam 

(fig. 24). The effect of these pumping centers on the 

size of the Skeel Road and Area B Well Fields was 

examined by use of a predictive simulation (fig. 24).

Current (1994) pumping at the Huffman Dam 

wells and the extraction well do not appreciably affect 

the size or the shape of either the CRA's of the Area B 

or Skeel Road Well Fields under normal pumping conditions. Results of the particle-tracking analyses indicate that additional wells will alter the ground-waterflow system in the vicinity of Huffman Dam and will 

affect the CRA's for the East Well Field. The CRA's 

for Area B, under intermediate and maximum pumping (fig. 14 and 15, respectively) would not extend into 

Areas A and C. Further expansion of the CRA's to the 

south of the Area B wells is likely under these

Contributing Recharge Areas to Water-Supply Wells 29
0.5

0.4

0.3

0.2

0.1

Ul 

DC

§

^ 0

UPLAND BEDROCK

| °'5

oc

(3

E 0.4 

Ko 

o

0.3

0.2

0.1

0.1 1

MULTIPLICATION FACTOR

FOR HORIZONTAL HYDRAULIC CONDUCTIVITY,

IN FEET PER DAY

10

BURIED-VALLEY AQUIFER

EXPLANATION

10-YEAR CONTRIBUTING 

RECHARGE AREA

5-YEAR CONTRIBUTING 

RECHARGE AREA

1-YEAR CONTRIBUTING 

RECHARGE AREA

0.1 1

MULTIPLICATION FACTOR

FOR HORIZONTAL HYDRAULIC CONDUCTIVITY,

IN FEET PER DAY

10

Figure 21. Variations of the contributing recharge areas of Area B Well Field, Wright-Patterson Air Force 

Base, Ohio, in relation to changes of horizontal hydraulic conductivity of the upland bedrock and buriedvalley aquifer under normal pumping conditions.

30 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
0.5

0.4

0.3

0.2

0.5

0.4

0.3

0.2

0.1

UPLAND BEDROCK

-50 -40 -30 -20 -10 0 10 20 

PERCENT CHANGE IN POROSITY

30 40 50

BURIED-VALLEY AQUIFER

EXPLANATION

10-YEAR CONTRIBUTING 

RECHARGE AREA

5-YEAR CONTRIBUTING 

RECHARGE AREA

. 1-YEAR CONTRIBUTING 

RECHARGE AREA

-50 -40 -30 -20 -10 0 10 20 

PERCENT CHANGE IN POROSITY

30 40 50

Figure 22.Variations of the contributing recharge areas of Area B Well Field, Wright-Patterson Air Force Base, 

Ohio, in relation to changes of porosity of the upland bedrock and buried-valley aquifer under normal pumping 

conditions.

Contributing Recharge Areas to Water-Supply Wells 31
<

UJ 

OL

UJ 

(5 (0

0.5

0.4

0.3

P£ 0.2

0.1

EXPLANATION

10-YEAR CONTRIBUTING 

RECHARGE AREA

5-YEAR CONTRIBUTING 

RECHARGE AREA

. 1-YEAR CONTRIBUTING 

RECHARGE AREA

-50 -40 -30 -20 -10 10 20 30 40 50

RIVERBED CONDUCTANCE, 

IN FEET PER DAY

Figure 23.Variations of the contributing recharge areas of Area B Well Field, Wright-Patterson Air Force Base, 

Ohio, in relation to changes of riverbed conductance under normal pumping conditions.

conditions. The CRA's for the East Well Field would 

shift more to the south and probably would extend further to the northeast and southeast, owing to the additional stress to the northwest. The decreased water 

levels in the area of Huffman Dam from the additional 

pumping would possibly decrease the total yield 

expected from the East Well Field.

SUMMARY AND CONCLUSIONS

The contributing recharge areas (CRA's) of the 

Skeel Road, East, and Area B Well Fields on WrightPatterson Air Force Base were delineated by use of a 

particle-tracking code that uses hydraulic head and 

flow data generated by a previously developed numerical ground-water-flow model. Hypothetical particles 

of water are simulated in the flow field and tracked, in 

relation to time, to discharge locations. The particles 

of water that were initially on the water table 

(recharge) and discharged to a water-supply well in

one of the well fields on the Base are considered to be 

in the CRA for that well field. A geographic information system was used to help delineate 1-, 5-, and 

10-year CRA's for each of the well fields on the Base.

Three possible pumping scenarios at the three 

well fields were examined; increased pumping at each 

of the well fields resulted in the largest CRA's, with a 

nearly linear relation between pumping rate and area. 

The input parameters to the model and the particletracking program were systematically changed to 

examine the effects of uncertainties in hydrogeologic 

parameters, such as hydraulic conductivity and 

recharge, on the areal extent of the CRA's for the 

Skeel Road and Area B Well Fields. This type of analysis was not completed for East Well Field because it 

has not been used since 1987, owing to water-quality 

concerns.

Results from the simulation and subsequent 

particle tracking analyses indicate that the CRA's of 

the Skeel Road Well Field are generally oval and 

extend northward up the Mad River Valley. With

32 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
84007 30" 84°05' 84°02' 30"

39°50' ; -

39°47 30"

Base map digitized from U.S. Geological Survey 

Dayton North, 1965, photorevteed, 1981; Falrbom, 

1965, photorevised, 1988. Polyconlc projection

5,000 I

I I I I I I I T

10,000 FEET 

I

1,000 2,000 METERS

EXPLANATION

10-YEAR CONTRIBUTING RECHARGE AREA 

5-YEAR CONTRIBUTING RECHARGE AREA 

1-YEAR CONTRIBUTING RECHARGE AREA

BOUNDARY OF UPLAND BEDROCK

WRIGHT-PATTERSON AIR FORCE 

BASE BOUNDARY

WELL LOCATION

Figure 24. Contributing recharge areas to the Skeel Road and Area B Well Fields under current (1994) 

pumping conditions, including pumping of wells at Huffman Dam.

Contributing Recharge Areas to Water-Supply Wells 33
increased pumping, the CRA's extend northward 

toward the Mad River. The sizes of the 1-, 5-, and 

10-year CRA's of the Skeel Road Well Field, under 

maximum pumping conditions, are approximately 

0.5,1.5, and 3.2 mi2, respectively. Uncertainties in the 

values of horizontal hydraulic conductivity and porosity of the valley-train deposits have the largest effect 

on the size of the CRA's. No effect is seen on the size 

or shape of the CRA's of Skeel Road when horizontal 

hydraulic conductivity of the upland bedrock and 

riverbed conductance are varied.

The CRA's of the Area B Well Field extend 

north, up the Mad River Valley and south, up a 

tributary buried valley of the Mad River Valley. As 

pumping increases, the CRA's extend further up the 

Mad River Valley, into Areas A and C. The sizes of the 

1-, 5-, and 10-year CRA's of Area B Well Field, under 

maximum pumping conditions, are approximately 0.1, 

0.5, and 0.9 mi2, respectively. The CRA's are smaller 

than the CRA's of Skeel Road Well Field because of 

lower pumping rates and more induced infiltration 

from surface-water sources. The CRA's of Area B 

Well Field are not significantly affected by any of the 

hydrogeologic parameters tested, although the sensitivity analyses of the model indicate that the upland 

bedrock should affect the CRA's. Variation in riverbed 

conductance does not affect the size of the CRA's of 

the Area B Well Field, although the wells are in close 

proximity to the Mad River, and induced infiltration 

controls the size of the CRA's. Pumping at the nearby

Rohrer's Island Well Field, flow from the nearby 

upland area, and the close proximity of the Mad River 

to the pumping center controls the shape and size of 

the CRA's of Area B Well Field.

At normal pumping rates, the CRA's of the East 

Well Field are generally circular but are affected by 

ground-water discharge to nearby streams. The 1-, 5-, 

and 10-year CRA's of the East Well Field, under maximum pumping conditions are approximately 0.2,1.2, 

and 2.4 mi2, respectively; at greater than normal 

pumping rates, however, limitations in the model 

decrease the usefulness of the CRA analysis for this 

well field.

The ground-water-flow system of the Base has 

undergone significant changes since the completion of 

the ground-water-flow model. Increased withdrawals 

of ground water in the vicinity of Huffman Dam were 

input to the model to simulate current (1994) pumping 

conditions. The additional pumping does not seem to 

affect the CRA's for Area B and Skeel Road Well 

Fields under normal pumping conditions. Under maximum pumping conditions at the Area B Well Field, its 

CRA's would likely propagate further southward, 

instead of extending into Areas A and C. The CRA's of 

the Skeel Road Well Field would not be appreciably 

affected by the pumping at Huffman Dam. The CRA's 

of the East Well Field would probably shift more to the 

northeast and southeast, owing to the additional pumping stress imposed on the ground-water-flow system.

34 Contributing Recharge Areas of Water-Supply Wells at Wright-Patterson Air Force Base, Ohio
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unit of the carbonate aquifer system in the Midwestern 

Basins and Arches Region of Indiana, Ohio, Michigan, 

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92-489, 2 sheets, scale 1:1,000,000.

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 1986b, Installation Restoration Program 

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J.T., 1993, Hydrogeology, simulated ground-water 

flow, and ground-water quality, Wright-Patterson Air 

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Morrissey, D.J., 1989, Estimation of the recharge area contributing water to a pumped well in a glacial-drift, 

river-valley aquifer: U.S. Geological Survey WaterSupply Paper 2338,41 p.

Norris, S.E., and Spieker, A.M., 1966, Ground-water 

resources of the Dayton area, Ohio: U.S. Geological 

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Pollock, D.W, 1989, Documentation of computer programs 

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areas contributing recharge to wells in shallow aquifers, U.S. Geological Survey Water-Supply Paper 

2412,21 p.

Schalk, C.W., 1992, Ground-water levels and flow in the 

vicinity of Wright-Patterson Air Force Base, Ohio, 

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Water-Resources Investigations Report 92-4022, 

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L.E., 1991, Water resources data, Ohio, water year 

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Summary and Conclusions 35