Water from the coastal plain aquifers in the Washington, D.C., metropolitan area /

WATER FROM THE COASTAL 

PLAIN AQUIFERS IN THE 

WASHINGTON, D.C., 

METRO PO LIT AN AREA 

GEOLOGICAL SURVEY CIRCULAR 697 

Water From the Coastal 

Plain Aquifiers in the 

Washington, D.C., 

Metropolitan Area 

By S. S. Papadopulos, R. R. Bennett, F. K. Mack, and 

P. C. Trescott 

GEOLOGICAL SURVEY CIRCULAR 697 

J914 
United States Department of the Interior 

ROGERS C. B. MORTON, Secretory 

Geological Survey 

V. E. McKelvey, Director 

Free on application to the U.S. Geological Survey, National Center, Reston, Va. 22092 
CONTENTS 

Page 

)Lbstract ---------------------------------------------------------------- 1 

Introduction ------------------------------------------------------------ 1 Hydrogeologic setting _________________________________________ ---------- 2 

)Lnalysis ---------------------------------------------------------------- 4 

Water-supply potential _______ --____ --_____ -------------------- __ - _-- 6 

Emergency vvater supply --------------------------------------------- 7 

Summary and conclusions ------------------------------------------------ 7 

References -------------------------------------------------------------- 11 

ILLUSTRATIONS 

FIGURES 1-6. Map shovving1. Location of the study area ----------------------------

2. Transmissivity of the Magothy aquifer -----------------

3. Transmissivity of the Patapsco aquifer ----------------

4. Transmissivity of the Patuxent aquifer ----------------

5. Model area and locations of boundaries and 

of hypothetical vvell field ----------------------------

6. Dravvdovvn at the end of the third 100-day 

pumping cycle ------------------------------------- 7. Plan and section of idealized vvell configuration at a test site __ 

Page 

2 

3 

4 

5 

6 

8 

10 

III 

Water from the Coastal Plain Aquifers in the 

Washington, D.C., Metropolitan Area 

By S. S. Papadopulos, R. R. Bennett, F. K. Mack, and P. C. Trescott 

ABSTRACT charging the aquifers to increase yields; 

A brief study of the Atlantic Coastal Plain aquifers 

in the vicinity of the Washington, D.C., metropolitan 

area was made, using available data, to estimate the 

water-supply potential of these aquifers and to determine the possibility of developing an emergency water 

supply during droughts. Assuming that the data available are representative, the study indicates that the 

water-supply potential of these aquifers, within an 

assumed 30-mil.e radius of Washington, D.C., is about 

170 million gallons per day. That is, these aquifers, 

which are now furnishing an estimated 60 million gallons per day, could be developed to supply an additional 

110 million gallons per day on a continuous basis. This 

quantity might be even larger if a significant amount 

of water is derived from leakage through finer grained 

confining beds, but further studies would be necessary 

to determine the amount of leakage and the long-term 

effects of large-scale continuous use. Furthermore, 

under intermittent pumping conditions, an assumed 

emergency supply of 100 million gallons per day could 

probably be developed from well fields within a 30-mile 

radius of Washington. An exploration and testing program would be necessary to assess the reliability of 

these preliminary estimates. 

INTRODUCTION 

On September 20, 1972, at the request of the 

Washington Area Interstate Water Resources 

Program Task Force, a meeting was held between representatives of the Task Force, the 

U.S. Geological Survey, the Virginia State 

Water Control Board, Division of Water Resources, and the Maryland Water Resources 

Administration. At this meeting, the Task 

Force requested information on the following: 

1. Development possibilities of ground water 

in and around the Washington metropolitan area, within the Potomac and 

Patuxent River basins; 

2. Possibilities and problems of artificially re1 

and 

3. Possibilities for the use of aquifers as reservoirs to augment streamflow during lowflow periods. 

To investigate these possibilities, a work 

force was formed consisting of J. T. Callahan 

(chairman), R. R. Bennett, F. K. Mack, S. S. 

Papadopulos, P. C. Trescott and R. L. Wait, all 

of the U.S. Geological Survey, E. W. Ramsey 

of the Virginia State Water Control Board, 

Division of Water Resources, and Arnold 

Schiffman of the Maryland Water Resources 

Administration. 

As members of this work force, the authors 

made a quick reconnaissance analysis by digital simulation of the Coastal Plain aquifers, on 

the basis of available geologic and hydrologic 

data. The study was confined to the first item 

of the Task Force request. Specifically, the objectives of the analysis were: 

1. To estimate the water-supply potential of 

these aquifers in the Washington metropolitan area; and 

2. To determine the possibility of developing 

an assumed emergency water supply of 

100 mgd (million gallons per day) during 

droughts. 

The results of the study were included in an 

administrative letter submitted to the Washington Area Interstate Water Resources Program Task Force on November 9, 1972, with 

appropriate references to the preliminary nature of the results due to the potential inaccuracies in such an analysis. 

The Task Force later requested the U.S. Geological Survey, by letter of April 9, 1973, to 

formulate a testing program that would be 

needed to assess the reliability of the digital 
simulation results, and this program was formulated and submitted to the Task Force by 

letter of June 4, 1973. 

The purpose of this circular is to present the 

data used and the assumptions made in the 

simulation of the aquifers and the results of 

the analysis and to describe a drilling and testing program that could be implemented to 

assess the reliability of these preliminary 

results. 

The Task Force was charged with the objective of preparing an implementable action program to (1) alleviate immediate or short-term 

problems of providing sufficient water supply 

of good quality to meet demands and to (2) 

provide for the reduction of pollutants entering 

the Potomac River to reduce its polluted condition. To the extent that the U.S. Geological 

Survey is requested to assess the water-resources aspects of other alternatives, the basic 

data and their evaluation will be published in 

subsequent circulars. 

HYDROGEOLOGIC SETTING 

The middle Atlantic Coastal Plain is the 

region that lies southeast of a line extending 

from Richmond, Va., northeast through the 

Washington metropolitan area and Baltimore, 

Md. (See fig. 1.) The hydrogeology of various 

parts of the Coastal Plain in the vicinity of the 

Washington metropolitan area has been discussed in many reports (Brookhart and Bennion, 1949; Bennett and Meyer, 1952; Meyer, 

1,952; Otton, 1955; Johnston and others, 1962; 

Mack, 1962, 1966, 1974; Johnston, 1964; Otton 

10 15 20 STATUTE MILES 

L-L..L_L.I.__.l _ _____.__ ---' - _L_J 

5 0 5 10 15 20 25 30 KILOMETERS ~__L___J __j____j___j 

FIGURE 1.-Location of study area. 

2 
and others, 1964; Back, 1966; Crooks and 

others, 1967; Slaughter and Otton, 1968; 

Weigle and others, 1970; Cederstrom and others, 1971; Hansen, 1972; Brown and others, 

1972; Cushing and others, 1973). 

In brief, the Coastal Plain is underlain by a 

wedge-shaped mass of sediments ranging in 

thickness from near zero at the inland edge of 

the Coastal Plain to more than 2,000 feet about 

30 miles southeast of Washington. Extensive 

layers of sand and gravelly sand within this 

wedge-shaped mass, which is composed largely of silt and clay, form the primary Coastal 

Plain aquifers-known as the Magothy, the 

Patapsco, and the Patuxent, in order of increasing depth of occurrence below land surface. These aquifers crop out in ill-defined 

bands several miles wide parallel to the edge 

COASTAL __ ..f..L~-- or-------

,....-

c;:f:>X- ,.....,..... ~r 

/ 

-2-

Transmissivity, in 

. 1000 ft 2 /d 

of the Coastal Plain and dip to the southeast 

toward the coast beneath younger sediments. 

With the exception of these outerop areas, 

water in the aquifers occurs under confined 

(artesian) conditions. The aquifers receive 

recharge from precipitation at places within 

the outcrop areas and probably from leakage 

through the confining beds in some areas. 

Transmissivity 1 maps for the Magothy, Patapsco, and Patuxent aquifers, prepared on the 

basis of available aquifer test data (Bennett 

and Meyer, 1952; Otton, 1955; Mack, 1962, 

1966, 197 4; Otton and others, 1964; Slaughter 

and Otton, 1968), are shown in figures 2-4. 

The combined transmissivity of the aquifers 

t Transmissivity is the rate at which water is transmitted 

through a unit width of the aquifer under a unit hydraulic 

gradient. 

10 15 20 STATUTE MILES 

FIGURE 2.-Transmissivity of the Magothy aquifer. 

3 
-2-

Transmissivity, in 

1000 ft2/d 

Control point 

10 15 20 STATUTE MILES 

25 30 KILOMETERS 

FIGURE 3.-Transmissivity of the Patapsco aquifer. 

ranges from 1,000 ft2/d (feet squared per day) 

in the south to 25,000 ft2 /d northeast of Washington, where the aquifers are thicker and 

more permeable. 

Present pumpage from these aquifers in the 

vicinity of the Washington metropolitan area 

is estimated to be 30 mgd for public, industrial, 

and institutional water supplies in Charles, 

Prince Georges, and Anne Arundel Counties in 

Maryland. In addition, many small domestic 

systems use ground water. On the basis of estimates of population not served by public water 

supplies, pumpage by domestic systems may be 

as much as 30 mgd, bringing the total estimate 

of pumpage to 60 mgd. About 34 mgd of this 

estimated total is pumped in Anne Arundel 

County, mainly in an area of high transmissivity north of Annapolis. 

4 

The chemical quality of water from the 

Coastal Plain aquifers, in various locations 

near the Washington metropolitan area, has 

been discussed by Otton (1955), Mack (1962, 

1966, 1974), and Slaughter and Otton (1968). 

In general, the quality differs from place to 

place and from aquifer to aquifer at the same 

site. Although untreated ground water in some 

areas is satisfactory for use in public watersupply systems, water in other areas may require conventional treatment to correct for 

acidity, high iron content, or excessive 

hardness. 

ANALYSIS 

The customary technique used to analyze the 

water-supply potential of an aquifer system in 

a way that permits study of the reaction of the 
-<-

Transmissivity, in 

1000 ft 2/d' 

-~· 

20 STATUTE MILES 

_/ 

/ 

/ 

_/ 

FIGURE 4.-Transmissivity of the Patuxent aquifer. 

system to various assumed conditions of development is to create a digital computer model 

of the system. Such a model incorporates all 

that is known about the geologic setting, the 

physical boundaries, and the hydrologic characteristics of the aquifer or aquifers. When a 

model is completed, the conditions under which 

the aquifer system will be operated must be 

defined or assumed in order to use the mode'i 

to predict how water levels or the water yield 

will be affected under these assumed conditions. 

To attain the objectives of this study, the 

Coastal Plain aquifers were simulated by a 

mathematical digital computer model that was 

first developed and later revised by U.S. Geological Survey scientists (Pinder, 1970; Trescott, 1973) . To estimate the effects of largescale ground-water development, an area much 

5 

larger than the Washington metropolitan area 

-an area of about 7,000 square miles, roughly 

70 miles wide and 100 miles long in a northeast-southwest direction-had to be· modeled. 

In setting up the model of each aquifer, the 

transmissivity distribution shown in figures 2-

4 and a uniform storage coefficient 2 of 0.0002 

were used. Outcrop areas along the inland edge 

of the Coastal Plain were treated as recharge 

boundaries along which water levels remain 

constant and are not affected by the development of the aquifers. The other boundaries of 

the model area were treated as being impermeable (no flow across the boundary in either direction). The model area and the approximate 

2 The storage coefficient is the volume of water an aquifer 

releases from or takes into storage per unit surface area of the 

aquifer per unit change in the water level of the aquifer. 
location of the boundaries are shown in figure 

5. In the absence of reliable data on the hydraulic properties of extensive saturated silt 

and clay layers that overlie and are interbedded within the aquifers, it was assumed that no 

water leaked through or from these layers and 

that the outcrop areas were the only source of 

recharge to the aquifers. In all probability some 

water does leak from associated fine-grained 

materials, and therefore the computations of 

water availability and water-level effects are 

conservative; that is, the computed water 

yields are probably lower than actual yields, 

and the computed water-level declines are 

probably greater than actual declines. 

WATER-SUPPLY POTENTIAL 

For the purpose of this analysis, the watersupply potential of an artesian aquifer in an 

area of interest was defined as the maximum 

quantity of water that can be withdrawn continuously from the aquifer, within the area of 

interest, without dewatering the aquifer; that 

is, without lowering water levels below the 

top of the aquifer. In estimating the watersupply potential, as defined above, of the Coastal Plain aquifers in the Washington metropolitan area, the area of interest was assumed to 

lie within a 30-mile radius of Washington, 

D.C. Each of the three aquifers was modeled 

separately by imposing a gradient equal to the 

----------

Patuxent 

III/IIIII. Potopsco 

Mogothy 

10 15 20 STATUTE MILES 

FIGURE 5.-Model area and locations of boundaries and of hypothetical well field. 

6 
dip of the aquifer between the recharge boundary along its outcrop area and a semicircle at 

the assumed 30-mile radius from Washington. 

(See fig. 5.) That is, the water levels along the 

semicircle were assumed to be lowered to the 

top of each aquifer while water levels were 

assumed to be unaffected along its recharge 

boundary. The steady flow computed for these 

conditions was taken as the potential of the 

aquifer. Thus, the water-supply potential of 

the Coastal Plain aquifers was computed to be 

about 40 mgd from the Magothy, 50 mgd from 

the Patapsco, and 80 mgd from the Patuxenta total of 170 mgd from all three aquifers. Considering the estimated present pumpage of 60 

mgd, the additional quantity of water that 

could be developed from these aquifers, on a 

continuous basis, is 110 mgd. 

EMERGENCY WATER SUPPLY 

The assumed 100 mgd for an emergency 

water supply is slightly less than the additional 

110 mgd of water that could be developed from 

the Coastal Plain aquifers. Furthermore, 

pumpage for an emergency supply would not 

be continuous. Therefore, in terms of water 

availability, it is possible to develop the assumed emergency supply. The analysis in this 

case was made to determine the effects of such 

a development on the regional water levels. 

The first step in the analysis was to choose 

an example of an area, within the assumed 30-

mile radius of Washington, where the emergency supply could be developed with a relatively high yield well field. Several computer 

solutions of the model were made, each with a 

different assumed location for a well field. On 

the basis of these solutions, an area that lies 

on a northeast-southwest line east of Washington, as shown in figure 5, was selected for the 

hypothetical location of such a well field. The 

combined transmissivity of the aquifers at this 

location is relatively high, and their depth allows for large drawdowns and, consequently, 

high well yields. There are probably other areas 

having a similar potential, and additional data 

and analysis could indicate that locations other 

than the one here selected are preferable. 

The second step of the analysis was to assume a pumping schedule according to which 

7 

the assumed 100-mgd emergency supply would 

be developed from the hypothetical well field. 

It was assumed that pumpage during 100 consecutive days, recurring in each of 3 consecutive years of drought, might be necessary. Such 

assumed conditions represent an extreme 

drought. Thus, the computation sequence comprised a 100-day pumping cycle followed by a 

265-day recovery, a second pumping cycle of 

100 days followed by a 265-day recovery, and a 

third 100-day pumping cycle, after which the 

sequence terminated. 

Initial computer solutions of the model indicated that the Magothy aquifer contributed 46 

percent of the well-field yield, the Patapsco 41 

percent, and the Patuxent 13 percent. The low 

contribution of the Patuxent aquifer to the 

yield of the well field and its depth and thickness at the location of the hypothetical well 

field-about 1,400 feet below land surface and 

about 400 feet thick-led to the assumption 

that it would be preferable to develop the 

emergency supply from the upper two aquifers, 

the Magothy and the Patapsco. Thus, well 

depths are considerably reduced in exchange 

for a relatively small increase in the drawdown 

of the water levels. 

On the basis of all these assumptions, the 

model was operated using the combined transmissivity of the Magothy and the Patapsco, a 

storage coefficient of 0.0002, and a pumpage of 

100 mgd from the wen· field according to the 

pumping schedule given above, and the effects 

of the pumpage on the regional water levels 

were computed. The areal extent and magnitude of the dra wdown around the hypothetical 

well field, at the end of the third 100-day pumping cycle, is shown in figure 6. 

SUMMARY AND CONCLUSIONS 

The results of the preliminary simulation 

study suggest that developing a large water 

supply from the Coastal Plain aquifers in the 

Washington metropolitan area is physically 

possible. In the study, no consideration was 

given to legal, political, and economic constraints or to other nonhydrologic factors. 

According to the model, the water-supply 

potential of these aquifers-the quantity of 
10 15 20 STATUTE MILES L-.l-.J_~-------'-------"-- _L __ ~' 

5 0 5 10 15 20 25 30 KILOMETERS LL..u...ll___l ____J _ _j___J_______J._____J 

FIGURE 6.-Drawdown at the end of the third 100-day pumping cycle. 

water that can be continuously withdrawn 

from these aquifers within an assumed 30-mile 

radius of Washington-is about 170 mgd. Present pumpage in the area is estimated to be 60 

mgd; therefore an additional 110 mgd could be 

developed from these aquifers. No allowance 

was made in the model for recharge by leakage 

from or through confining beds. The data available do not permit a reliable estimate of the 

leakage that can be induced by pumping; however, the water-supply potential of the aquifers 

might be much larger if recharge from leakage 

occurs. Additional studies would be necessary 

to determine the impact of such large-scale 

continuous withdrawals from the aquifers on 

water levels and streamflow. Studies would 

8 

also be necessary to evaluate potential hazards 

of land subsidence and salt-water encroachm·ent. 

Under an assumption of intermittent pumping for an em·ergency supply of 100 mgd, the 

model indicates that the supply can be developed through a properly designed and positioned well field. For such short-term pumpage 

(100 days, as assumed), most of the pumped 

water will be derived from storage within the 

Magothy and Patapsco aquifers. The forecasted 

drawdown distribution around the hypothetical well field, shown in figure 6, indicates that 

development of the assumed emergency supply would lower the regional potentiometric 

surface of the aquifers for a considerable dis-
tance from the well field. As a consequence of 

pumping, water levels would be lowered in 

many wells ; thus pumping costs would be increased or yields would be decreased for many 

other users of ground water in the area. The 

effects of development would gradually diminish, as water levels recovered, and would disappear if the time between droughts is sufficient to allow full recovery of water levels. 

The provisional estimates gained from this 

preliminary study indicate that the Coastal 

Plain aquifers, extending eastward from Washington, D.C., represent a large water-resource 

potential that may bear importantly on the 

future growth of the metropolitan area. However, if large-scale development of the water 

resources is ever contemplated, the nature, degree, and extent of all consequent effects of 

obtaining water from the Coastal :plain aquifers should be accurately evaluated. 

Further field investigations for obtaining 

additional data for more reliable estimates of 

the potential of the Coastal Plain aquifers and 

of the effects of large-scale development of 

these aquifers would improve the reliability of 

the results. A testing program to obtain additional data on the properties of the aquifers 

and on the properties of· the finer grained confining beds could consist of a set of drilling and 

testing procedures implemented at several sites 

where data are needed. An outline for procedures that could be followed at each typical 

test site is presented below: 

1. Drill a probe hole through the Coastal Plain 

sediments to bedrock, obtain formation 

samples, and run geophY'sical logs. 

2. On the basis of the above, identify the principal water-bearing zones. 

3. Drill a test well, the well to be constructed 

so that each principal water-bearing zone 

can be pumped individually or in combination with one or more adjacent zones. 

4. Convert the probe hole to an observation 

well in the deepest zone and drill additional observation wells. Two observation wells, ideally, would be completed in 

9 

each principal zone at distances of aPproximately 200 feet and 2,000 feet from 

the test well, respectively. 

5. Make aquifer tests. Each principal zone 

could be tested individually by isolating 

it in the test well. A final test could be 

made with the test well open to all zones. 

The tests, ideally, would have a minimum 

duration of (1) 7 days pumping and 7 

days recovery for the uppermost zone and 

the final test and (2) 3 day.s pumping and 

3 days recovery for all other zones. 

An idealized well configuration for a test 

site is shown in figure 7. Although the number 

and depth of productive zones may differ from 

site to site, it was assumed that four productive zones at depths of 500, 800, 1,000 and 1,500 

feet below land surface would typify the principal test sites. At some sites the data obtained 

from the probe hole may possibly indicate that 

further testing is not warranted. 

A testing program similar to the one outlined 

above would provide data for a more reliable 

model to estimate ground-water availability 

and to s·elect optimum well-field locations for 

emergency water supplies. It would also provide data necessary for proper well and wellfield design and information on the quality of 

ground water in different areas and formations. 

However, the data currently available plus 

new data obtained by the drilling and testing 

program would ,still answer only some of the 

questions related to the water-supply source 

and would not provide all the answers to all the 

cause-effect questions that may be raised. 

A unique advantage of a ground-water 

source is that it may be developed incrementally as need and economics dictate. Although the 

drilling and testing program would add significantly to the data base, the experience to be 

gained from observing the response of the 

regional hydrologic system to a subsequent 

incremental development as a source of supply 

will provide the most reliable basis for evaluating the long-term impact of large-scale continuous use. 
LJJ 

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Cluster of 

observation Test 

wells well 

PLAN VIEW 

SECTION VIEW 

Land surface 

Cluster of 

observation 

wells 

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2000--·~----------~-----------------------------

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FIGURE 7.-Plan and section of idealized well configuration at a test site. 

10 
REFERENCES 

Back, William, 1966, Hydrochemical facies and groundwater flow patterns in northern part of Atlantic 

Coastal Plain: U.S. Geol. Survey Prof. Paper 498-

A, 41 p. 

Bennett, R. R., and Meyer, R. R., 1952, Geology and 

ground-water resources of the Baltimore area: 

Maryland Dept. Geology, Mines and Water Resources Bull. 4, 573 p. 

Brookhart, J. W., and Bennion, V. R., 1949, The water 

resources of Anne Arundel County: Maryland 

Dept. Geology, Mines and Water Resources Bull. 

5, 149 p. 

Brown, P. M., Miller, J. A., and Swain, F. M., 1972, 

Structural and stratigraphic framework, and spatial distribution of permeability of the Atlantic 

Coastal Plain, North Carolina to New York: U.S. 

Geol. Survey Prof. Paper 796, 79 p. 

Cederstrom, D. J., Baker, J. A., and Tarver, G. R., 

1971, North Atlantic Regional Water Resources 

Study, Appendix D-Geology and Groundwater: 

U.S. Geol. Survey open-file report, 240 p. 

Crooks, J. W., O'Bryan, Deric, and others, 1967, Water 

Resources of the Patuxent River basin, Maryland: 

U.S. Geol. Survey Hydrol. lnv. Atlas HA-244. 

Cushing, E. M., Kantrowitz, I. H., and Taylor, K. R., 

1973, Water resources of the Delmarva Peninsula: 

U.S. Geol. Survey Prof. Paper 822,58 p. 

Hansen, H. J., III, 19·72, A user's guide for the artesian 

aquifers of the Maryland Coastal Plain, Parts 1 

and 2: Maryland Geological Survey. 

Johnston, P.M., 1964, Geology and ground-water resources of Washington, D.C., and vicinity: U.S. 

Geol. Survey Water-Supply Paper 1776, 97 p. 

Johnston, P. M., Pollock, S. J., and Weist, W. G., Jr., 

1962, Ground-water resources of the Potomac 

11 

River Basin, Appendix G.: Potomac River basin 

report, U.S. Army Corps of Engineers Dist., Baltimore, Md. 

Mack, F. K., 1962, Ground-water supplies for industrial 

and urban development in Anne Arundel County: 

Maryland Dept. Geology, Mines and Water Resources Bull. 26, 90 p. 

--- 1966, Ground water in Prince Georges County: 

Maryland Geol. Survey Bull. 29, 101 p. 

--- 1974, An evaluation of the Magothy aquifer in 

the Annapolis area, Maryland: Maryland Geol. 

Survey Rept. of Inv. (In press.) 

Meyer, Gerald, 1952, Ground-water resources, in Geology and ground-water resources of Prince 

Georges County: Maryland Dept. Geol., Mines and 

Water Resources Bull. 10, p. 82-254. 

Otton, E. G., 1955, Ground-water resources of the 

Southern Maryland coastal plain: Maryland Dept. 

Geology, Mines and Water Resources Bull. 15, 

347 p. 

Otton, E. G., Martin, R. 0. R., and Durum, W. H., 1964, 

Water resources of the Baltimore area, Maryland, 

U.S. Geol. Survey Water-Supply Paper 1499--F, 

105 p. 

Pinder, G. F., 1970, An iterative digital model for 

aquifer evaluation: U.S. Geol. Survey ope·n-file 

Rept., 44 p. 

Slaughter, T. H., and Otton, E. G., 1968, Availability 

of ground water in Charles County: Maryland 

Geol. Survey Bull. 30, 100 p. 

Trescott, P. C., 1973, Iterative digital model for aquifer 

·evaluations: U.S. Geol. Survey open-file Rept., 63 

p. 

Weigle, J. M., Webb, W. E., and Gardner, R. A., 1970, 

Water resources of southern Maryland: U.S. 

Geol. Survey Hydrol. Inv. Atlas HA-365. 

'I< U.s. GOVERNMENT PRINTING OFFICE: 1974-543-583/11.0