Cover. Photograph shows a yellowish-tan bluff of weathered Aquia Formation along the Severn River, visible from the Route 50 bridge 

north of Annapolis, Maryland (Photograph by Daniel J. Soeder, August 2006).
Effects of Withdrawals on Ground-Water 

Levels in Southern Maryland and the 

Adjacent Eastern Shore, 1980–2005

By Daniel J. Soeder, Jeff P. Raffensperger, and Mark R. Nardi

Prepared in cooperation with the

Maryland Geological Survey and the

Maryland Power Plant Research Program

Scientific Investigations Report 2007–5249

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Soeder, D.J., Raffensperger, J.P., and Nardi, M.R., 2007, Effects of withdrawals on ground-water levels in 

Southern Maryland and the adjacent Eastern Shore, 1980–2005: U.S. Geological Survey Scientific Investigations 

Report 2007–5249, 82 p.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................1

Description of Study Area ...................................................................................................................2

Background............................................................................................................................................3

Methods of Analysis......................................................................................................................................5

Ground-Water Levels ...........................................................................................................................5

Water-Use Data.....................................................................................................................................6

Hydrologic Data Analyses...................................................................................................................6

Hydrogeologic Framework..................................................................................................................7

Hydrogeology..................................................................................................................................................7

Potomac Group......................................................................................................................................7

Patuxent Aquifer and Arundel Clay Confining Bed ................................................................7

Lower Patapsco Aquifer and Confining Bed...........................................................................9

Upper Patapsco Aquifer and Confining Bed .........................................................................10

Magothy and Monmouth Aquifers and Matawan Confining Bed...............................................10

Pamunkey Group.................................................................................................................................11

Brightseat Confining Bed .........................................................................................................11

Aquia Aquifer, Marlboro Clay, and Lower Nanjemoy Confining Beds ..............................11

Piney Point-Nanjemoy Aquifer................................................................................................12

Chesapeake Group .............................................................................................................................12

Water Use and Water Levels in Confined Aquifers ...............................................................................13

Patuxent Aquifer.................................................................................................................................15

Patapsco Aquifer................................................................................................................................18

Lower Patapsco Aquifer...........................................................................................................18

Upper Patapsco Aquifer...........................................................................................................25

Magothy Aquifer.................................................................................................................................32

Aquia Aquifer.......................................................................................................................................39

Piney Point-Nanjemoy Aquifer.........................................................................................................46

Relations Between Withdrawals and Water-Level Drawdowns.........................................................49

Effects of Withdrawal on Multiple Aquifers...................................................................................49

Linear Decline of Potentiometric Surfaces ....................................................................................54

Modeling Experiment ................................................................................................................55

Modeling Results .......................................................................................................................57

Summary and Conclusions.........................................................................................................................60

Acknowledgments.......................................................................................................................................61

References Cited..........................................................................................................................................61

Appendix 1. Bibliography of U.S. Geological Survey Southern Maryland Potentiometric 

Surface Maps: 1980, 1985, 1990, 1995, and 2000.......................................................................66

Appendix 2. Access to U.S. Geological Survey Water Data................................................................70

Appendix 3. Southern Maryland Ground-Water-Level Data Used in This Report ...........................71
iv

Figures

1. Map showing location of study area in the Atlantic Coastal Plain of Maryland ...............2

2. Graph showing sources of water supply in 2004 for the Southern Maryland counties 

in the study area ...........................................................................................................................2

3. Schematic diagram showing the Atlantic Coastal Plain aquifer system ............................3

4. Hydrograph showing water levels in the Piney Point-Nanjemoy aquifer for 

Well DO Db 17 located on Taylors Island, Maryland...............................................................4

5. Graph showing total annual ground-water withdrawals reported in the 

U.S. Geological Survey AWUDS database for the six major aquifers in the 

Southern Maryland study area from 1980 to 2004.................................................................13

6. Histogram showing Southern Maryland population estimates by county from 

1990 to 2005..................................................................................................................................14

7. Graph showing population growth rates for counties in the study area from 

1990 to 2005..................................................................................................................................14

8–10. Histograms showing—

8. Population growth in smaller counties in the study area from 1990 to 2005............15

9. Ground-water use by county in the study area, shown as a function of major 

use category for 2004........................................................................................................16

10. Trends in ground-water withdrawals from the Patuxent aquifer at four major 

pumping centers in Anne Arundel and Prince George’s Counties from 

1980 to 2004.........................................................................................................................16

11. Map showing potentiometric surface and water use, Patuxent aquifer, 2005.................17

12. Histogram showing ground-water withdrawals from the lower Patapsco aquifer 

at five major pumping centers in Anne Arundel and Charles Counties from 

1980 to 2004..................................................................................................................................19

13–17. Maps showing—

13. Potentiometric surface and water use, lower Patapsco aquifer, 1985.....................20

14. Potentiometric surface and water use, lower Patapsco aquifer, 1995.....................21

15. Potentiometric surface and water use, lower Patapsco aquifer, 2005.....................22

16. Potentiometric difference, lower Patapsco aquifer, 1985 to 1995.............................23

17. Potentiometric difference, lower Patapsco aquifer, 1995 to 2005.............................24

18. Histogram showing trends in ground-water withdrawals from the upper Patapsco 

aquifer at six major pumping centers in Southern Maryland from 1980 to 2004..............26

19–23. Maps showing—

19. Potentiometric surface and water use, upper Patapsco aquifer, 1985 ....................27

20. Potentiometric surface and water use, upper Patapsco aquifer, 1995 ....................28

21. Potentiometric surface and water use, upper Patapsco aquifer, 2005 ....................29

22. Potentiometric difference, upper Patapsco aquifer, 1985 to 1995.............................30

23. Potentiometric difference, upper Patapsco aquifer, 1995 to 2005.............................31

24. Histogram showing trends in ground-water withdrawals from the Magothy aquifer 

at five major pumping centers in Southern Maryland from 1980 to 2004 ..........................33

25–29. Maps showing—

25. Potentiometric surface and water use, Magothy aquifer, 1985.................................34

26. Potentiometric surface and water use, Magothy aquifer, 1995.................................35

27. Potentiometric surface and water use, Magothy aquifer, 2005.................................36

28. Potentiometric difference, Magothy aquifer, 1985 to 1995 .........................................37

29. Potentiometric difference, Magothy aquifer, 1995 to 2005 .........................................38
v

30. Histogram showing trends in ground-water withdrawals from the Aquia aquifer 

at five major pumping centers in Southern Maryland from 1980 to 2004 ..........................40

31–35. Maps showing—

31. Potentiometric surface and water use, Aquia aquifer, 1985 ......................................41

32. Potentiometric surface and water use, Aquia aquifer, 1995 ......................................42

33. Potentiometric surface and water use, Aquia aquifer, 2005 ......................................43

34. Potentiometric difference, Aquia aquifer, 1985 to 1995...............................................44

35. Potentiometric difference, Aquia aquifer, 1995 to 2005...............................................45

36. Histogram showing trends in ground-water withdrawals from the Piney PointNanjemoy aquifer at five major pumping centers in Southern Maryland from 

1980 to 2004..................................................................................................................................47

37. Map showing potentiometric surface and water use, Piney Point-Nanjemoy 

aquifer, 2005.................................................................................................................................48

38. Histogram showing annual total ground-water withdrawals from the lower 

Patapsco aquifer in Charles County, Maryland, since 1980 ................................................49

39. Hydrographs showing Patuxent and lower Patapsco aquifer observation wells in 

Charles County, Maryland, responding to ground-water withdrawals from the 

lower Patapsco aquifer .............................................................................................................50

40. Histogram showing total ground-water withdrawals reported for St. Mary’s 

County from the Aquia and Piney Point-Nanjemoy aquifers from 1980 to 2004 ...............51

41–45. Hydrographs showing—

41. Ground-water-level responses in the Piney Point-Nanjemoy aquifer in 

Well CA Fe 22, and the drop in the potentiometric surface of the underlying 

Aquia aquifer in southern Calvert County, Maryland...................................................52

42. Ground-water-level responses in the Piney Point-Nanjemoy aquifer in 

Well SM Eg 27, and the drop in the potentiometric surface of the underlying 

Aquia aquifer in southern St. Mary’s County, Maryland .............................................52

43. Ground-water-level responses in the Piney Point-Nanjemoy aquifer in 

Well SM Fg 45, and the drop in the potentiometric surface of the underlying 

Aquia aquifer in southern St. Mary’s County, Maryland .............................................53

44. Ground-water-level responses in the Piney Point-Nanjemoy aquifer in 

Well SM Df 66, and the drop in the potentiometric surface of the underlying 

Aquia aquifer in southern St. Mary’s County, Maryland .............................................53

45. Nearly linear declines in the potentiometric surfaces over 30 years in four 

representative wells from Calvert and St. Mary’s Counties, Maryland....................54

46. Schematic diagram showing the modified hypothetical (A) aquifer, and 

(B) aquifer-aquitard....................................................................................................................56

47–48. Graphs showing—

47. Withdrawal rates used for generation of drawdown scenarios ...............................56

48. Time-drawdown patterns calculated for a single pumping well in a perfectly 

confined, unbounded aquifer under three different withdrawal rate patterns.......57

49. Diagram showing drawdown in the potentiometric surface for the scenario with 

multiple wells under a constant withdrawal rate at time t = 22.8 years............................58

50–51. Graphs showing—

50. Time-drawdown patterns calculated for multiple pumping wells in a perfectly 

confined, unbounded aquifer under three different withdrawal rate patterns.......58

51. Time-drawdown patterns calculated for multiple pumping wells in a leaky, 

unbounded aquifer under three different withdrawal rate patterns.........................58
vi

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

cubic foot (ft3) 7.4805 gallons (gal)

Flow rate

gallons/minute (gal/min) 1,440 gallons/day (gal/d)

inches/year (in/yr) 2.54 centimeter/year (cm/yr)

foot squared per minute 1,440 square foot per day

foot squared per day 0.0929 square meter per day

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) by the 

following equation: °C = (°F – 32) / 1.8

Water Year as used in this report begins on October 1 and runs through the following 

September 30.

Vertical and Horizontal Datums: Vertical elevations and altitudes are referenced to the National 

Geodetic Vertical Datum of 1929 (NGVD29), a geodetic surface derived from a reference geoid 

and first-order level nets of the United States and Canada. The more recent North American 

Vertical Datum of 1988 (NAVD88) was not used, because all of the land surface and water-level 

elevations taken from the U.S. Geological Survey database for this report are referenced to 

NGVD29, and are internally consistent. Horizontal coordinate data for well locations presented 

as decimal latitude and longitude are referenced to the North American Datum of 1983 (NAD83).

52. Diagram showing drawdown in the potentiometric surfaces for the scenarios 

with multiple wells under a constant withdrawal rate at time t = 22.8 years and 

with (A) no-flow, and (B) constant-head boundaries imposed at one edge of the 

modeled region (eastern side)..................................................................................................59

53. Graphs showing time-drawdown patterns calculated for multiple pumping wells in 

an aquifer under three different withdrawal rate patterns and with (A) no-flow, and 

(B) constant-head boundaries imposed at the eastern end of the modeled region .......60

Table

1. Generalized stratigraphy and hydrogeology of Southern Maryland and adjacent 

Eastern Shore................................................................................................................................8

Conversion Factors and Datums
vii

ACRONYMS AND ABBREVIATIONS

AWUDS Aggregated Water Use Data System (USGS database)

ft feet

ft2/day square feet per day (transmissivity)

gal/d gallons per day (water production)

gal/min gallons per minute (water production)

GIS Geographic Information System

GWSI Ground Water Site Inventory (USGS database)

in/yr inches per year (recharge)

K hydraulic conductivity; in this report, horizontal hydraulic conductivity 

 of an aquifer

K-T Cretaceous-Tertiary (geological time boundary)

MD DNR Maryland Department of Natural Resources

MDE Maryland Department of the Environment

Mgal/d million gallons per day (water production)

MGS Maryland Geological Survey

mi miles

NASPR Naval Air Station, Patuxent River

NWIS National Water Information System (USGS database)

PPRP Power Plant Research Program

Q flow; in this report, the rate of ground-water discharge from a pumped well

RASA Regional Aquifer-System Analysis (USGS Program)

SWUDS Site-Specific Water Use Data System (USGS database)

T aquifer transmissivity, expressed in feet squared per minute or day

USGS U.S. Geological Survey (Department of the Interior)

WSSC Washington Suburban Sanitary Commission

Abstract

Ground water is the primary source of water supply in 

most areas of Maryland’s Atlantic Coastal Plain, including 

Southern Maryland. The counties in this area are experiencing 

some of the most rapid growth and development in the State, 

resulting in an increased demand for ground-water production. 

The cooperative, basic water-data program of the U.S. 

Geological Survey and the Maryland Geological Survey has 

collected long-term observations of ground-water levels in 

Southern Maryland and parts of the Eastern Shore for many 

decades. Additional water-level observations were made by 

both agencies beginning in the 1970s, under the Power Plant 

Research Program of the Maryland Department of Natural 

Resources. These long-term water levels commonly show 

significant declines over several decades, which are attributed 

to ground-water withdrawals. Ground-water-level trends since 

1980 in major Coastal Plain aquifers such as the Piney PointNanjemoy, Aquia, Magothy, upper Patapsco, lower Patapsco, 

and Patuxent were compared to water use and withdrawal data. 

Potentiometric surface maps show that most of the declines 

in ground-water levels can be directly related to effects from 

major pumping centers. There is also evidence that deep drawdowns in some pumped aquifers may be causing declines in 

adjacent, unpumped aquifers.

Water-level hydrographs of many wells in Southern 

Maryland show linear declines in levels year after year, 

instead of the gradual leveling-off that would be expected as 

the aquifers equilibrate with pumping. A continual increase 

in the volumes of water being withdrawn from the aquifers is 

one explanation for why they are not reaching equilibrium. 

Although reported ground-water production in Southern 

Maryland has increased somewhat over the past several 

decades, the reported increases are often not large enough 

to account for the observed water-level declines. Numerical 

modeling simulations indicate that a steady, annual increase 

in the number of small wells could account for the observed 

aquifer behavior. Such wells, being pumped at rates below 

the minimum legal reporting threshold of 10,000 gallons 

per day, might be the source of the additional withdrawals. 

More detailed water-use data, especially from domestic 

wells, central-pivot irrigation wells, and other small users 

not currently reporting withdrawals to the State, may help to 

determine the cause of the aquifer declines. 

Introduction

Ground-water-level data have been collected from wells 

in Southern Maryland and the adjacent Eastern Shore for 

many years by the U.S. Geological Survey (USGS) and the 

Maryland Geological Survey (MGS) in cooperation with other 

Maryland State agencies and local governments. Over a period 

of several decades, many of the measured ground-water levels 

show large declines, which are related to the withdrawal or 

pumping of water from the aquifers.

Purpose and Scope

This report documents and describes drawdowns in the 

major aquifers of Southern Maryland and the adjacent Eastern 

Shore in the context of ground-water withdrawals. The intent 

is to provide an empirical analysis of ground-water declines 

over the past 25 years related to withdrawals. This report 

updates a similar study by Achmad and Hansen (2001), and 

provides a comparison of water-level declines over the past 

decade (1995–2005) with those from the previous decade 

(1985–1995). The report also suggests some future studies that 

may provide management tools for the Southern Maryland 

ground-water resource. These include investigations of the 

potential for leakage through confining layers, and the possible role of unreported increases in domestic pumpage as a 

contributing factor in water-level declines. 

Effects of Withdrawals on Ground-Water Levels in 

Southern Maryland and the Adjacent Eastern Shore, 

1980–2005

By Daniel J. Soeder, Jeff P. Raffensperger, and Mark R. Nardi 1

1

 U.S. Geological Survey, MD-DE-DC Water Science Center, 

5522 Research Park Drive, Baltimore, MD 21228
2 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Description of Study Area

The study area for this report includes Anne Arundel, 

Prince George’s, Calvert, Charles and St. Mary’s Counties in 

Southern Maryland, and parts of Kent, Queen Anne’s, Talbot, 

and Dorchester Counties on Maryland’s Eastern Shore. The 

location of the study area and its approximate boundary are 

shown in figure 1.

Ground water is the primary source of water supply in 

most of the study area. The two most populous counties in 

the study area, Anne Arundel County, south of Baltimore, and 

Prince George’s County, east of Washington, D.C., used the 

most water (fig. 2). The majority of the water supply in Prince 

George’s County is from surface water supplied by the Washington Suburban Sanitary Commission (WSSC). The generally 

flat, low-relief topography of the Atlantic Coastal Plain Physiographic Province throughout the remainder of the study area 

results in broad, shallow stream valleys, making surface-water 

reservoirs impractical in many areas for large-volume water 

supplies. The region is underlain by thick sand and gravel 

sediments, however, which provide an abundant ground-water 

resource. These unconsolidated sediments consist mainly of 

Cretaceous-to-Quaternary-age materials that overlie consolidated rock of suspected Jurassic, Triassic, Early Paleozoic and 

(or) Precambrian age (Hansen and Edwards, 1986). 

The consolidated rocks of the Piedmont dip to the south 

and east from the “Fall Line” (fig. 1). This is the physiographic break between the Piedmont uplands and the lowlands 

of the Atlantic Coastal Plain, and is often marked by waterfalls 

on streams that cross it. The rocks of the Piedmont descend 

beneath unconsolidated materials that form the sediments of 

the Atlantic Coastal Plain. The sediments thicken to the south 

and east, forming a wedge-shaped body of material consisting 

of generally fluvial and deltaic sediments overlain by coastal 

and marine sediments. The sediment wedge thins to a featheredge at the Fall Line, and reaches a thickness of more than 

7,500 ft (feet) at the Atlantic coast (Wilson and Fleck, 1990). 

A schematic cross section of the Atlantic Coastal Plain aquifer 

system aligned approximately with section A-A′ in figure 1 is 

shown in figure 3.

The wedge of unconsolidated sediment consists of layers 

of sands and gravels, separated by layers of silts and clays. 

The coarse-grained sand and gravel beds are aquifers, which 

readily produce ground water. The finer-grained silt and clay 

layers are confining units, which act as barriers to water flow. 

Recharge areas for the aquifers are updip, where they outcrop or subcrop near the surface. Total dissolved solids in the 

ground water tend to increase in a downdip direction within 

the aquifers. Deeper ground water generally contains too much 

salt and other minerals to be drinkable. 

The USGS and MGS have been measuring ground-water 

levels in Maryland wells on a regular basis since the 1940s 

(Curtin and Dine, 1995). The Maryland Department of Natural 

Resources (MD DNR), through the Power Plant Research 

Program (PPRP), supported the measurement of ground-water 

Figure 1. Location of study area in the Atlantic Coastal Plain of 

Maryland [Refer to figure 3 for line of section A-A’] (Modified from 

Shedlock and others, 2006).

Figure 2. Sources of water supply in 2004 for the Southern 

Maryland counties in the study area (From U.S. Geological 

Survey AWUDS database).
Introduction 3

levels and construction of a series of potentiometric surface 

maps using 1975 data that were published beginning in 1978 

(Achmad and Hansen, 2001). Previously published potentiometric surface difference maps show ground-water levels 

declining over time at many locations in the Coastal Plain. The 

cause of this decline is ground-water withdrawal or pumpage 

from the major aquifer units. Water-use data show that the 

withdrawal rates have been generally increasing over time, 

resulting in linear or sometimes accelerating decline rates of 

the potentiometric surfaces of the major aquifers. 

Background

Water-level data have been collected from Southern 

Maryland wells on a regular basis since the inception of the 

Maryland Observation-Well Network in 1943 (Smigaj and 

Davis, 1987). Water-use data in Maryland have been collected 

since at least 1900 (Wheeler and Wilde, 1989). This section 

does not provide a complete review of the literature of groundwater observations in Southern Maryland, but it presents a historical overview of the data that are available, and illustrates 

the long-standing concerns over water resources and water use 

in Southern Maryland. 

The history of the collection of water-level data from 

Southern Maryland wells has been summarized by Achmad 

and Hansen (2001). Potentiometric surface maps and waterlevel difference maps for the Aquia and Magothy aquifers 

have been published occasionally since 1975, and annually 

since 1984 (S.E. Curtin, U.S. Geological Survey, oral commun., 2007). Maps for the upper Patapsco and lower Patapsco 

aquifers were published annually beginning in 1990. Sporadic 

publication of these maps dates as far back as 1978. The most 

recent set of potentiometric surface and difference maps for 

the PPRP were published in 2004, presenting data collected 

in 2003 (see for example, Curtin and others, 2005). In the 

past, each map from each aquifer was published as a separate 

report. This report attempts to incorporate all of them into a 

single volume, updating the maps with the 2005 ground-waterlevel data, and including water-use data from the same areas. 

A bibliography of these past reports is included as appendix 1 

for the years covered by this report (1980, 1985, 1990, 1995, 

and 2000) to facilitate comparisons. 

Water-level data collected from 1946 to 1994 at 458 

wells in Southern Maryland were summarized by Curtin and 

Dine (1995). Many of their hydrographs showed a decline in 

ground-water levels over time, and quite a few of these graphs 

showed a more rapid decline in water levels after the late 

1980s. The rate of decline varies between aquifers and wells, 

but the general trend for confined aquifer wells is a steady 

decline in water levels through the mid-1980s, accelerating in 

the late 1980s. Some of the hydrographs showed that groundwater levels remained steady, however, and a few even show 

levels rising during this same time period. These data indicate 

that there are complex relations between ground-water levels 

and withdrawals in Southern Maryland. 

Information on water resources in Southern Maryland 

was assembled by Weigle and others (1970) from Prince 

George’s County to the mouth of the Potomac River, as part 

of the National USGS Hydrologic Investigations Atlas, which 

consists of a map of ground-water flow and the potentiometric surface for the Piney Point and Aquia aquifers, a map of 

ground-water yields from these units, and a sheet with some 

information on water quality and streamflow. 

A report by Williams (1979) presents the results of some 

early computer modeling simulations of ground-water declines 

in the Piney Point aquifer. Drawdowns as great as 180 ft 

were predicted for the Cambridge area in Dorchester County 

by 1990 if withdrawals at Cambridge were increased to the 

maximum ground-water appropriation limit. Although the 

Piney Point aquifer has indeed undergone drawdown since 

the 1970s, it is less than that modeled by Williams (1979). 

Well DO Db 17, located on Taylors Island and screened in 

the Piney Point-Nanjemoy aquifer, is in close proximity to 

a simulated 40-ft-drawdown contour modeled by Williams 

(1979) under the maximum withdrawal scenario of Cambridge 

pumping. The hydrograph in figure 4 shows that the actual 

drawdown in this well since 1979 was only about 8 ft, with 

some recovery in the last 3 years. 

Otton (1955) was one of the first authors to describe the 

relation between ground-water-level declines in Southern 

Maryland and increases in ground-water withdrawal. A later 

report by Mack and others (1983) correlated withdrawals at 

the Chalk Point Power Plant and in the Waldorf area with a 

regional decline in the potentiometric surface of the Magothy 

aquifer, and with the formation of large cones of depression 

in these areas. Their report estimated that the regional potentiometric surface in the Magothy aquifer was 30 ft above sea 

Figure 3. The Atlantic Coastal Plain aquifer system [Line of 

section shown in figure 1] (From Shedlock and others, 2006).
4 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

level at Chalk Point, and 50 ft above sea level at Waldorf prior 

to ground-water withdrawal. This surface had declined to more 

than 10 ft below sea level at Chalk Point and over 40 ft below 

sea level near Waldorf by 1975, and was more than 20 ft below 

sea level at Chalk Point and about 70 ft below sea level at 

Waldorf by 1981 (Mack and others, 1983). 

A number of basic ground-water-resource assessments for 

the confined aquifers in Southern Maryland have been done 

on a county-by-county basis. Data from more than 1,200 wells 

in Anne Arundel County were compiled by Lucas (1976), and 

a similar compilation of 604 wells in Calvert County and 904 

in St. Mary’s County was assembled by Drummond (1984). 

Ground-water-flow models of some aquifers were developed 

to assess the municipal water-supply potential from the major 

units, and also to investigate the production of high-quality 

water at various simulated pumping rates. Mack and Achmad 

(1986) evaluated the water-supply potential of the Potomac 

Group aquifers in Anne Arundel County, for example. In a 

later report, Fleck and Andreasen (1996) assessed groundwater flow and quality by modeling the Aquia, Magothy and 

upper Patapsco aquifers in east-central Anne Arundel County. 

Anne Arundel County also had simulations and assessments 

performed on the Patapsco aquifer near Glen Burnie (Achmad, 

1991), on the Magothy aquifer near Annapolis (Mack, 1974), 

and on the Aquia and Magothy aquifers in the southern part of 

the County (Andreasen, 2002). Similar assessments were done 

in Calvert and St. Mary’s Counties on the Aquia and Piney 

Point-Nanjemoy aquifers (Achmad and Hansen, 1997), and on 

a number of aquifers near Waldorf in Charles County (Wilson 

and Fleck, 1990). 

An improved understanding of the Coastal Plain geologic 

framework has been developed over the past few decades by 

various authors as part of these local ground-water assessments, or through independent geological investigations. The 

proceedings of a 1988 USGS workshop on the geology of 

Atlantic Coastal Plain sediments were assembled by Gohn 

(1992). The geology of the Coastal Plain sediments can be 

complex, especially in the Cretaceous-age fluvial deposits of 

the Potomac Group, where time-equivalent stratigraphy and 

lithology often do not match. Hydrogeologic investigations 

of the Potomac Group sediments have often been localized, 

as reported by Hiortdahl (1997) for example, in northwestern 

Charles County. The fluvial channel sands, overbank deposits, 

and lag gravels of the Potomac Group are difficult to correlate 

over even short distances. 

Aquifer boundaries generally coincide with formation 

boundaries, but this is not always the case. Facies changes and 

changes in thickness of the units can significantly alter hydrologic properties laterally within a formation, thereby affecting ground-water productivity. A report by Hansen (1974) on 

the Aquia Formation describes an example of facies changes 

within a single geological formation deposited contemporaneously in a nearshore lagoon, an offshore sand bar, and farther 

offshore on a shelf. The coarse, sand bar deposits form the 

main productive aquifer, whereas the finer-grained lagoonal 

and shelf sediments form either a poor aquifer or a confining 

unit. Such lateral variations in lithology are not uncommon in 

Coastal Plain sediments, and must be taken into account when 

assessing regional aquifer productivity. The geologic framework of the Southern Maryland Coastal Plain is described in 

more detail elsewhere in the report. 

The USGS, under the Regional Aquifer-System Analysis (RASA) Program, analyzed the geologic, hydrologic, 

and geochemical properties of aquifer systems on a regional 

scale to better understand, predict, and manage ground-water 

resources. The aquifers underlying the northern Atlantic 

Coastal Plain from North Carolina to New York were one of 

the regional systems studied (Trapp and Meisler, 1992). The 

Cretaceous and younger sediments throughout this broad 

region were subdivided into 11 regional aquifers separated 

by 9 confining units (Trapp, 1992). A sub-regional study of 

the Coastal Plain in Maryland, Delaware, and the District of 

Columbia included 11 aquifers and 10 confining beds (Vroblesky and Fleck, 1991). These were then correlated to the 

hydrogeologic units used in other sub-regional RASA studies 

in Virginia and New Jersey. This hydrogeologic framework 

was used to provide a basis for the construction of a subregional, digital, multilayer, ground-water-flow model of the 

local aquifer system in Maryland, Delaware, and the District 

of Columbia, which was fitted into the regional flow model 

developed for the entire area from North Carolina to New York 

(Vroblesky and Fleck, 1991; Trapp, 1992). 

Concerns about the sustainability of ground-water supplies in Southern Maryland have been expressed at the local 

government level since the late 1990s. St. Mary’s County 

established a Water Policy Task Force in 2000 to investigate 

the adequacy of future supplies from the Aquia and Piney 

Point-Nanjemoy aquifers. The task force concluded that the 

County would need to develop additional supplies from the 

deeper Potomac Group aquifers to make up for the projected 

shortfall (St. Mary’s County, written commun., 2000). In 

response to these findings, a project was initiated with MGS 

by the commissioners of Calvert, Charles, and St. Mary’s 

Figure 4. Water levels in the Piney Point-Nanjemoy aquifer for 

Well DO Db 17 located on Taylors Island, Maryland.
Methods of Analysis 5

Counties to assess the water-supply potential of aquifers 

in Southern Maryland. A report on the study prepared by 

MGS (Drummond, 2005) concluded that the projected water 

demands into 2030 could be met by developing new sources 

of supply in deeper aquifers, and by careful management of 

production from the aquifers that have already been utilized.

An advisory committee to the Governor of Maryland, 

formed in response to a statewide drought in 2002, produced 

a report on managing water resources in the State (Wolman, 2004). The committee found that the population of 

Maryland had increased by 35 percent from 1970 to 2000, 

and is expected to grow an additional 20 percent by the year 

2030, which could increase the demands on water resources, 

especially ground water. As a result of the committee’s report, 

a comprehensive assessment of ground water in the Atlantic 

Coastal Plain in Maryland was undertaken by the Maryland 

Department of the Environment (MDE), MGS, and the USGS 

(Shedlock and others, 2006). The information presented in this 

report will be used in that assessment.

Methods of Analysis

The data used in this report were reviewed, approved, 

and published ground-water-level measurements collected by 

either the USGS or MGS. The data were retrieved from the 

Ground Water Site Inventory (GWSI) database, which is part 

of National Water Information System (NWIS), managed by 

the USGS. The wells selected for data retrieval were those 

used by Curtin and others (2005) to construct the previously 

published potentiometric surface maps for the PPRP. Wateruse data were retrieved from the Site-Specific Water Use Data 

System (SWUDS) or the Aggregated Water Use Data System 

(AWUDS), both of which are maintained by the USGS. 

Ground-Water Levels

Ground-water-level measurements were retrieved 

from GWSI from 1980 through 2005 for over 400 wells 

and placed in a spreadsheet. Some of the wells had monthly 

measurements, others had twice-yearly measurements, and 

others had a combination of one or the other, which varied by 

water year. Instructions on methods for performing similar 

data retrievals using the USGS public water data website are 

included in appendix 2. 

The ground-water-level data were selected to populate a 

second spreadsheet in 5-year increments from 1980 through 

2005 for the four major Coastal Plain aquifers: Aquia, Magothy, upper Patapsco, and lower Patapsco, sorted by aquifer 

and year. When possible, ground-water-level measurements 

taken near the end of each water year (the September or October monthly measurement) were used to represent the annual, 

lowest ground-water level. Many wells do not have groundwater levels extending back to 1980, and some wells do not 

have records that extend all the way to 2005. 

Ground-water-level data also were retrieved from the 

Piney Point-Nanjemoy and Patuxent aquifers. Fewer wells are 

screened in these two aquifers than those screened in the other 

four aquifers in the study area. As such, less ground-waterlevel data were available for the Piney Point-Nanjemoy and 

Patuxent aquifers, and data were gathered from Water Year 

2005 only, so that 2005 potentiometric surface maps could be 

created. All of the ground-water level data evaluated for this 

study are included as appendix 3. 

Geographic Information System (GIS) software was used 

to create the initial potentiometric surface maps, and also to 

create potentiometric difference maps to evaluate changes 

in water levels. Potentiometric surface maps for the years 

1985, 1995, and 2005 were constructed for the Aquia, Magothy, upper Patapsco, and lower Patapsco aquifers to graphically show the areas of greatest stress (cones of depression), 

changes in these units over time, and directions of groundwater flow. The surfaces are drawn relative to sea level, as 

defined by the National Geodetic Vertical Datum of 1929, a 

geodetic surface derived from a reference geoid and first-order 

level nets of the United States and Canada. The maps include 

the locations of major ground-water withdrawal sites to show 

the relation between pumping centers and aquifer drawdowns. 

Potentiometric surface difference maps were constructed 

for the Aquia, Magothy, upper, and lower Patapsco aquifers in 

Southern Maryland to show the changes in the potentiometric 

surface over a fixed time interval. Water-level difference maps 

were constructed for 1985 through 1995, and also for 1995 

through 2005. Comparisons of the differences in the potentiometric surfaces of the major aquifers during these two time 

periods show the changes in ground-water withdrawals across 

two different decades. 

The contours were initially generated using GIS software 

with a kriging algorithm, but difficulties ensued because of the 

inability of the algorithm to deal with drawdowns in separate 

pumping centers. Instead of making separate “bulls eyes,” the 

algorithm tried to connect similar levels together throughout 

the map area. It was hoped that automated contouring could 

be combined with GIS to rapidly produce the Coastal Plain 

potentiometric surface maps, but it became apparent that manual oversight and technical judgment are necessary for generating reliable maps. Surfer2

 contouring software was used 

in a second attempt, but this too, required significant manual 

oversight. The advantage of Surfer over the GIS contouring 

software is that it was easier to make adjustments and corrections to the lines. The experience with automated contouring 

software to produce potentiometric surface and difference 

maps indicated that it can be useful, if properly reviewed and 

adjusted. The initial, draft maps can be produced more rapidly 

with the software than drawing by hand, and once the lines 

are corrected, the electronic maps can be uploaded into commercial drawing or drafting software and turned into a final 

product fairly quickly. 

2

 Surfer is a product of RockWare, Inc., 2221 East Street, #101, Golden, CO 

80401 (http://www.rockware.com).
6 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Water-Use Data

Water-use data for Southern Maryland were analyzed to 

assess the volumes of water pumped from various aquifers at 

different well field locations. The expectation was that analysis 

of these data over time would provide an indication of the total 

volume of water removed from the aquifer, and would relate to 

the drawdowns observed on the potentiometric surface maps. 

Water-use data for Maryland are compiled annually by the 

USGS in cooperation with MDE. 

MDE administers the water-appropriation permit program 

for public water supply, industrial, commercial, irrigation, 

and power plant water uses, but not for livestock and most 

domestic water use. Water users who withdraw more than 

10,000 gal/d (gallons per day) are required to submit monthly 

withdrawal reports twice a year to MDE. The water-use 

data are stored in a database maintained by MDE. Domestic 

withdrawals from private wells are estimated by the USGS at 

80 gal/d per capita (a national average), and then combined 

with population estimates for the number of people per 

household to derive a withdrawal value for individual wells. 

Quality assurance of the water-use data in the USGS 

database involves checking data from the current year with the 

previous year’s water-use data, and comparing it to the permitted amount. The data are entered into the USGS SWUDS database, which stores water-use data for specific wells, or well 

fields. Water use data are aggregated by county and aquifer in 

the USGS AWUDS database. 

During 2000, about 245 Mgal/d (million gallons per 

day) of the freshwater used in Maryland was from the Coastal 

Plain, representing 27 percent of the state total (Wheeler, 

2003). Of that amount, about 66 Mgal/d was from surfacewater sources, and 179 Mgal/d (73 percent) was from groundwater sources. Ground-water withdrawals in the Coastal Plain 

have increased about 32 percent since 1980, with withdrawals 

by public-water suppliers increasing nearly 34 percent and 

irrigation withdrawals increasing over 100 percent. Public 

supply and self-supplied domestic water withdrawals make 

up 86 percent of the current freshwater withdrawals in 

Southern Maryland. 

Total annual water withdrawals were estimated by taking 

the daily average in Mgal/d for pumping from each reporting 

site in any given year, and multiplying by 365 to get the yearly 

total in Mgal/yr (millions of gallons per year). The annual 

totals for all sites reporting for an aquifer were then summed 

to arrive at the total withdrawal from that aquifer for the given 

year. Different aquifers were compared during the same year 

to determine the contribution of each to the total ground-water 

supply, and year-to-year comparisons of withdrawals from a 

single aquifer showed trends in water use and growth.

Hydrologic Data Analyses

Hydrographs for selected wells were constructed to 

graphically display the trends of water levels over time, along 

with the rates of decline. Analyses of the Southern Maryland 

aquifers using hydrographs, potentiometric surface maps, 

difference maps, and water-use data were used to assess the 

effects of withdrawals on water levels.

An important factor in assessing ground-water-level 

trends is the evaluation of the effects of withdrawals from 

adjacent aquifers. Some aquifers may be hydraulically 

connected through leaky confining beds, so that pumping from 

one aquifer causes water levels to decline in adjacent aquifers. 

An example of such a semi-confined aquifer is the upper 

Patapsco in east-central Anne Arundel County, Maryland, 

which has a hydraulic connection to the overlying Magothy 

aquifer (Achmad and Hansen, 2001). Water levels were 

compared to pumping centers on potentiometric surface maps 

to correlate areas of reduced levels to areas of high water use 

in adjacent aquifers.

The potentiometric surface maps for each of the major 

aquifers include the locations of large pumping centers 

reported in the water-use data (10,000 gal/d or greater). 

These maps reveal certain large aquifer drawdowns as cones 

of depression in the potentiometric surface, which usually 

coincide with major pumping centers. An aquifer showing 

a noticeable degree of drawdown at a location with little or 

no pumpage raised the possibility that the aquifer might be 

responding to pumpage from underlying or overlying units. It 

is also possible that the aquifer was responding to unreported 

water use, or to local pumping effects. 

Eight hydrographs were constructed to investigate the 

effects of withdrawals from adjacent aquifers on aquifers that 

were unpumped, or moderately pumped. This was done for 

the Patuxent and lower Patapsco aquifers in Charles County, 

and for the Aquia and Piney Point-Nanjemoy aquifers in 

St. Mary’s County. Water levels in adjacent aquifers were 

estimated from the potentiometric surface contour maps in 

cases where an observation well in the pumped aquifer was 

not close to an observation well in the unpumped aquifer. 

These empirical correlations were then used to investigate the 

effects that high rates of pumping might have on water levels 

in the adjacent aquifers. 

Water withdrawn from a well is obtained from elastic 

storage within the aquifer. Initially, water will be removed 

from storage in the immediate vicinity of the well, reducing 

the hydraulic head and inducing flow toward the well. These 

reductions in hydraulic head, or drawdown, will propagate 

outward, forming a cone of depression in the potentiometric 

surface of the aquifer. At an observation well within the cone 

of depression, the rate of drawdown will be at a maximum 

initially; the rate of drawdown will decrease with time, so 

that the drawdown will eventually be approximately logarithmic in time.

Many of the hydrographs of Southern Maryland observation wells do not follow the expected logarithmic curve 

mathematically defined by Theis (1935) for a pumped aquifer, 

but drop continually in a straight line. The most likely cause 

is a constant increase in the amount of water being withdrawn 

from the aquifer. This is not fully supported by the available 
Hydrogeology 7

water-use data, however. In some cases, trends in the volume 

of withdrawals reported to MDE do not appear to be large 

enough to account for the observed drops in aquifer water 

levels. This was investigated through the use of some standard hydrologic modeling in an attempt to develop possible 

explanations. One answer may be that increased amounts of 

water are being pumped from the aquifer by large numbers of 

domestic wells, which individually produce too little water to 

be within the minimum legal reporting threshold for the wateruse data.

Hydrogeologic Framework

The hydrogeologic framework was assembled from existing Coastal Plain geologic data obtained from a wide variety 

of sources, including geologic maps and reports produced 

at the Regional, State, and County levels. Many of the geologic formation names and initial publications of type-section 

descriptions in the Coastal Plain of the Mid-Atlantic region 

originated from N.H. Darton, W.B. Clark, and other early 

geologists in the 19th Century. These efforts have been documented by Wilmarth (1957). The geologic descriptions have 

been updated by Nancy Stamm of the USGS in the National 

Geologic Map Database, available on the web at http://ngmdb.

usgs.gov/. Information on the hydrologic properties of the 

various Coastal Plain units also was taken from a variety of 

sources. Because the properties of many of these formations 

change with location, and the depositional environments, 

formation boundaries, and ages have been re-interpreted by 

different authors, multiple references were cited to accurately 

describe the geology and hydrogeology in the study area. 

Hydrogeology

In the Atlantic Coastal Plain, the primary geologic 

formations of interest containing the confined aquifers are 

Cretaceous and Tertiary in age. A generalized cross section 

constructed for the sediments in the Coastal Plain of Maryland 

is shown in figure 3, and was adapted from Shedlock and 

others (2006). An important aspect of the geologic framework 

is that the Coastal Plain sediments dip and thicken toward the 

east and southeast, forming a wedge-shaped body that thins to 

a feather edge against the consolidated rocks of the Piedmont, 

and thickens toward the Atlantic Ocean. Other large-scale 

features of the geology include (1) a number of stratigraphic 

units at the thicker, eastern side of the sediment wedge are 

not present in the thinner, western part, and (2) sediments at 

the surface become increasingly younger toward the east. 

This eastward-thickening wedge of sediment exerts major 

controls on the location and depth of aquifers in the Maryland 

Coastal Plain. 

The consolidated basement rocks of suspected Jurassic, 

Triassic, Paleozoic, and (or) Precambrian age form the base of 

the Coastal Plain aquifer system (Hansen and Edwards, 1986). 

Overlying the basement rocks are terrestrial sediments that 

were eroded from the ancestral Appalachian and Piedmont 

highland areas and deposited during the Cretaceous Period. 

These deposits consist of the fluvial-deltaic sediments of the 

Lower Cretaceous Potomac Group (Patuxent Formation, Arundel Clay, and Patapsco Formation), and the fluvio-marine and 

marine sediments of the Upper Cretaceous Magothy, Matawan 

and Severn Formations. The remainder of the sedimentary 

sequence in Southern Maryland consists of Tertiary coastal 

and marine deposits, overlain by Quaternary fluvial and 

marine sediments. A generalized geologic framework for the 

Coastal Plain of Southern Maryland is shown in table 1.

Potomac Group

The Potomac Formation was first described by McGee in 

1886, and named for exposures along the Potomac River near 

Washington, D.C. (Wilmarth, 1957). It was recognized as the 

basal sedimentary unit of the Coastal Plain in that it usually 

rests on gneiss or other consolidated rocks of the Piedmont. 

The Potomac Formation was raised to the rank of group by 

Clark and Bibbins (1897), who subdivided it into three formations: the basal Patuxent Formation, overlain by the Arundel 

Clay (also referred to as the Arundel Formation by some 

authors), which is overlain in turn by the Patapsco Formation. 

Hansen (1984) added an additional basal subsurface formation 

to the Potomac Group underlying the eastern Delmarva Peninsula that he named the “Waste Gate,” which was described as a 

brine aquifer isolated from the freshwater-flow system (Trapp, 

1992). A number of authors have attempted to refine the 

stratigraphic boundaries and correlations within the Potomac 

Group, including Groot (1955), Brenner (1963), and Jordan 

(1968, 1983). The time-stratigraphic equivalence of various 

sedimentary bodies within the Potomac Group has often been 

determined by palynological studies of spores and pollen, due 

to discontinuities and facies changes within contemporaneous 

depositional units (Hiortdahl, 1997). As an example, Mack and 

Achmad (1986) reported that sand lenses 25 ft thick at certain 

locations in the Potomac have been found to be much thicker, 

thinner, or absent at lateral distances of only 25 to 100 ft. 

The Potomac Group contains three major aquifers in 

Southern Maryland. These are the Patuxent aquifer, at the base 

of the group and within the Patuxent Formation, and two aquifers within the Patapsco Formation (upper and lower Patapsco 

aquifers). The Arundel Clay, lying between the Patuxent and 

Patapsco Formations, forms a confining unit. The Patapsco 

Formation contains clay confining units that separate the upper 

and lower Patapsco aquifers. These aquifers are described in 

greater detail in the following sections.

Patuxent Aquifer and Arundel Clay Confining Bed

The Patuxent aquifer consists of multiple sand layers in 

the Patuxent Formation of varying thickness and lateral extent. 

The Patuxent Formation was described by Clark (1897) as 
8 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Table 1. Generalized stratigraphy and hydrogeology of Southern Maryland and adjacent Eastern Shore.

[From Achmad and Hansen, 2001; Trapp, 1992; and modified after D.C. Andreasen, Maryland Geological Survey, oral commun., 2006; 

and H.J. Hansen, Maryland Geological Survey, written commun., 2007; RASA, Regional Aquifer-System Analysis Program (U.S. Geological Survey)]
Hydrogeology 9

a cross-bedded, arkosic sand with layers of relatively pure 

sand, although some of the arenaceous beds contain clay 

lumps and sandy clays. Clark stated that the sediments show 

evidence of shallow-water deposition. The lithology of the 

Patuxent Formation was described by Glaser (1969) as a 

medium-grained to coarse-grained sand or pebbly sand and 

gravel, interbedded with relatively thin, pale-gray clays. The 

formation is composed of generally finer-grained sands in 

the upper part, where it is overlain and confined by the lowpermeability Arundel Clay. The general lack of silt and clay 

in the lower part of the Patuxent Formation indicates that the 

sands were deposited in a relatively high-energy, fluvial, and 

deltaic environment (Glaser, 1969). 

The Patuxent aquifer is capable of yielding large quantities of water to wells. Well fields in Anne Arundel and Prince 

George’s Counties have produced yields as high as 2 Mgal/d, 

and yields of 0.5 to 1 Mgal/d are not uncommon (Mack and 

Achmad, 1986). Within the study area, the Patuxent aquifer is 

pumped only in Anne Arundel, Prince George’s and Charles 

Counties. The aquifer is relatively thin to the north, and 

pinches out in the northwestern part of Anne Arundel County 

(Mack and Achmad, 1986). The recharge area for the Patuxent 

aquifer is a relatively narrow outcrop band located between the 

western limit of the overlying Arundel Clay and the pinch-out 

of the Patuxent against the consolidated rocks of the Piedmont 

a few miles farther west (Mack and Achmad, 1986). This 

outcrop band runs parallel to the Fall Line through the northeastern part of the Washington, D.C., western Prince George’s 

County, the eastern edges of Montgomery and Howard Counties, and into northwestern Anne Arundel County (Achmad 

and Hansen, 2001).

Overlying the Patuxent aquifer is the Arundel Clay, 

which forms an effective confining bed in most areas, separating the Patuxent aquifer from the overlying lower Patapsco 

aquifer. Clark (1897) described the Arundel Clay from stream 

valley outcrops as a series of large and small lenses of carbonaceous, iron-bearing clay, up to 125 ft in thickness. Achmad 

and Hansen (2001) reported that the Arundel Clay can be 

300 to 400 ft thick in Southern Maryland. Hiortdahl (1997) 

described the Arundel Clay in Charles County as a dark gray 

to maroon, tough, massive clay containing abundant lignite 

and siderite concretions. He noted that the clay is very dense, 

and was more difficult to penetrate with a drill rig than the 

overlying and underlying sands. The Arundel Clay was probably deposited in a low-energy river flood plain and swamp 

environment (Glaser, 1976). The association of massive clays, 

lignitic logs, rooted stumps, occasional dinosaur bones, and 

the complete absence of marine fossils indicate that the clay 

was deposited in shallow, backswamp basins maintained by 

ponded drainage and slow sediment influx (Glaser, 1969). 

The contact between the top of the Arundel Clay and the overlying Patapsco Formation was described as unconformable 

(Brenner, 1963).

Lower Patapsco Aquifer and Confining Bed

The lower Patapsco aquifer consists of multiple sand 

layers and lenses within the lower part of the Patapsco 

Formation. The Patapsco Formation was described by 

Clark (1897) as colored and variegated clays, which grade 

into lighter-colored sandy clays with interstratified sandy 

bands of coarser materials. In Charles County, Hiortdahl 

(1997) described the lithology of the Patapsco Formation 

as consisting of layers of fine- to medium-grained sand to 

silt, separated by thick clay layers. The descriptions indicate 

that the Patapsco Formation is generally finer-grained than 

the underlying Patuxent sands, which was confirmed by 

Hiortdahl (1997) on the basis of continuous drill core from 

Well CH Bb 22 at Indian Head. He also stated that beds of 

lignitic plant remains were common in some of the Patapsco 

Formation deposits in this core, further indicating a lowerenergy depositional environment. Nevertheless, Patapsco 

sediments are often very similar to the Patuxent sediments, 

and differentiation of the two units based solely on lithologic 

properties can be difficult (Glaser, 1969). The outcrop and 

recharge area for the Patapsco Formation runs northeast from 

the eastern side of Washington, D.C. to the southeastern side 

of Baltimore City, through western Prince George’s and Anne 

Arundel Counties (Achmad and Hansen, 2001).

Hiortdahl (1997) noted a number of sequences of 

upward-fining sediments in a Patapsco Formation core from 

Charles County. These graded sequences typically began with 

a coarse sand or gravel/pebble zone at the base that grades 

upward into medium- and fine-grained sand, overlain by silt, 

and eventually grading into silty, hard gray clay containing lignite and carbonaceous plant remains. Glaser (1969) interpreted 

the lithologic character of the Patapsco Formation as typical 

of deposition on a low deltaic plain by sluggish, low-gradient, 

and perhaps meandering rivers. The graded bedding noted by 

Hiortdahl (1997) appears to support this interpretation: as a 

stream meanders across a flood plain, different flow regimes 

control the sedimentation at different times in any particular 

location, resulting in uniform, gradual changes in grain size. A 

series of fluvial deposits graded in this manner are known as 

“fluvial cyclothems” (Allen, 1970).

Despite the finer-grained nature of the sediments, Mack 

and Achmad (1986) reported that the lower Patapsco aquifer 

is capable of yielding 0.5 to 2 Mgal/d from individual wells 

in most locations where it has been tested in Anne Arundel County. They noted that one well owned by the City of 

Annapolis yielded about 1.5 Mgal/d. 

The confining layer separating the lower and upper 

Patapsco aquifers was described by Mack and Achmad (1986) 

as unnamed massive beds of clay with low vertical hydraulic 

conductivity, although some layers within the confining 

bed are more permeable. They reported a thickness of over 

200 ft at Annapolis. Hiortdahl (1997) did not describe the 

confining layer as a distinct, single unit in Charles County, 

but mentioned three relatively continuous sand layers, 

separated by clay beds or lenses, which appear to be aquifers 
10 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

in the Patapsco Formation at Indian Head. The confining 

layer separating the lower and upper Patapsco aquifers was 

informally named the Patapsco confining bed by Achmad and 

Hansen (2001), who described it as multi-colored, massive, 

clayey beds of low hydraulic conductivity, although they also 

noted that at some locations, it may be more sandy and less 

effective as a confining unit. The representative thickness of 

the confining bed was given by Achmad and Hansen (2001) 

as 250 ft in Anne Arundel County, 170 ft in Charles County, 

and 300 ft in St. Mary’s County. This report refers to the 

confining layer as the “lower Patapsco confining bed” (table 1) 

to differentiate it from the confining unit overlying the upper 

Patapsco aquifer. 

Upper Patapsco Aquifer and Confining Bed

The upper Patapsco aquifer consists of multiple sand 

layers and lenses within the upper part of the Patapsco Formation. The upper Patapsco aquifer was described by Mack and 

Achmad (1986) as “one of the best water-bearing formations 

in Anne Arundel County,” although they noted that it is much 

more limited in aerial extent than the deeper lower Patapsco 

and Patuxent aquifers. The upper Patapsco consists of the 

same type of fluvial, interbedded, fine- to medium-grained 

sand, silt, and clay layers as the lower Patapsco.

Overlying the upper Patapsco aquifer is the fine-grained, 

clayey, upper Patapsco confining bed (table 1). The thickness 

and vertical hydraulic conductivity of this confining layer 

are quite variable according to Mack and Achmad (1986). 

They reported thicknesses ranging from 50 to 100 ft in Anne 

Arundel County. Achmad and Hansen (2001) described the 

confining unit as a gray, red, and orange clay, and noted that it 

thins to the northwest toward the outcrop area of the Patapsco 

Formation. Gaps in the upper Patapsco confining bed in eastcentral Anne Arundel County result in a direct hydraulic connection between the upper Patapsco aquifer and the overlying 

Magothy aquifer (Mack and Andreasen, 1991). 

Magothy and Monmouth Aquifers and 

Matawan Confining Bed

The Magothy aquifer consists of sandy beds of the 

Magothy Formation, and in some areas may include sands of 

the Patapsco Formation (Mack, 1977). The Magothy Formation was first described and named by N.H. Darton in 1893 

(Wilmarth, 1957). According to Hansen (1972), the lithology 

consists of unconsolidated light gray to white, fine to medium 

quartz sand and fine gravel, containing pyrite and lignite, with 

glauconite in the upper part. The lower parts of the Magothy 

Formation are characterized by massive beds of uniform, 

coarse-grained sands (Andreasen, 2002). The Magothy thins to 

the south and west, disappearing entirely before reaching the 

vicinity of the Potomac River (Achmad and Hansen, 2001). It 

is absent in southern Charles County, and in all but the most 

northern part of St. Mary’s County. The outcrop and recharge 

area occurs in a narrow band through the northern end of 

Prince George’s County and across north-central Anne Arundel County (Achmad and Hansen, 2001). On the New Jersey 

Coastal Plain, the Raritan Formation is present between the 

Magothy and the Potomac, but the Raritan is not recognized as 

a separate unit in Southern Maryland. The Magothy Formation 

has been interpreted in New Jersey as a transitional delta-front 

or prograding delta deposit (Sugarman, 1992), implying that a 

reduction in grain size occurs from the depocenter toward the 

fringes of the sediment body. In Maryland, it changes facies 

from coarse sand and gravel at the southwestern end of the 

outcrop belt to interbedded silt, clay, and sand to the northeast 

(Trapp, 1992), leading to the interpretation that it is a coarse 

fluvial deposit in updip locations, grading into a finer, estuarine-lagoonal-tidal-shoreface deposit downdip (Glaser, 1969). 

The Magothy Formation is part of a transgressive sequence 

from Lower Cretaceous fluvial-dominated deposits to Tertiary 

marine-dominated strata (Hansen, 1972). 

The Magothy aquifer has been described by Andreasen (2002) in central and southern Anne Arundel County as 

consisting of lower and upper sand units separated by 20 to 

50 ft of clay. Mack (1974) also depicted an upper and lower 

unit separated by 10 to 20 ft of clay, and noted that the coarse 

sand layers interbedded with clay result in hydraulic conductivites that are much higher in the horizontal direction than the 

vertical. Achmad and Hansen (2001) identified the Magothy 

aquifer as a single unit throughout Southern Maryland. 

The confining beds overlying the Magothy aquifer are 

made up of several geologic units that may, in places, also 

function as aquifers (Achmad and Hansen, 2001). These beds 

consist of the predominantly marine sediments of the Matawan 

and Monmouth (or equivalent Severn) Formations. In Anne 

Arundel County, the Matawan Formation consists of dark gray 

and black silty clay, and acts as a confining unit on top of the 

Magothy aquifer (Andreasen, 2002). Achmad and Hansen 

(2001) described the Matawan and Monmouth Formations in 

Southern Maryland as fine-grained, dark gray, micaceous, silty 

or clayey sand and clay, and treated them collectively, along 

with the overlying Brightseat Formation, as a confining unit. 

The Severn Formation is stratigraphically equivalent to 

the upper part of the Monmouth Group in New Jersey (Hansen 

and Drummond, 1994). The Severn Formation was initially 

named by N.H. Darton in 1891 as a unit distinctly separable 

from the New Jersey Cretaceous “green sand” series, but the 

name was discarded by the USGS in 1938 (Wilmarth, 1957). It 

has since been reinstated, and the Severn Formation is located 

above the Matawan Formation at the type locality in Anne 

Arundel County (Andreasen, 2002). The Severn Formation on 

the upper Eastern Shore of Maryland, the underlying Mount 

Laurel Sand in Delaware and New Jersey, and the Wenonah 

Formation in New Jersey form a regional coastal Atlantic 

aquifer named the “Peedee-Severn” in the RASA reports 

(Trapp, 1992). The geologic relations in this part of the stratigraphic section are somewhat confusing, because different 

names were used at different times to describe the same units. 
Hydrogeology 11

For simplicity, the Monmouth aquifer is shown in table 1 as 

the water-bearing sand within the stratigraphically equivalent 

Severn and Monmouth Formations. It should be noted that 

the Monmouth is a minor aquifer in Southern Maryland, and 

is often combined with the Aquia aquifer in Anne Arundel 

County. It becomes thinner and more clayey to the south, 

where it functions as a confining bed (D.C. Andreasen, Maryland Geological Survey, written commun., 2007).

Pamunkey Group

The Tertiary-age Pamunkey Formation was initially 

named by N.H. Darton in 1891, who described it as a 

homogenous sheet of fine-grained materials (Wilmarth, 

1957). Clark and Martin (1901) elevated the Pamunkey from a 

formation to a group, and divided it into the Aquia Formation 

in the lower part, and the Nanjemoy Formation in the upper. 

Like other Coastal Plain sedimentary units, the stratigraphy 

has evolved through re-interpretation over the years. The 

currently accepted formations that make up the Pamunkey 

Group include (from bottom to top) the Brightseat, Aquia, 

Marlboro Clay, Nanjemoy, and Piney Point in Maryland, 

with the Chickahominy overlying the Piney Point in Virginia 

(Rader and Evans, 1993). The group is dated from early 

Paleocene to late Eocene in age. Individual units are discussed 

in detail below. 

Brightseat Confining Bed

The Brightseat is the basal formation of the Pamunkey 

Group, and was named by Bennett and Collins (1952) to 

describe a dark gray, micaceous sandy clay unit with a thickness of 4 to 8 ft, exposed in a creek in Prince George’s County, 

Maryland. In the subsurface of eastern Maryland, the Brightseat Formation ranges from 50 to 75 ft thick. The CretaceousTertiary (K-T) boundary occurs between the top of the Severn 

Formation and the base of the overlying Brightseat Formation; 

however, in Southern Maryland, the contact between these two 

formations is described as unconformable (Bennett and Collins, 1952), so the iridium-rich clay layer identified by Alvarez 

and others (1980) at the actual K-T boundary is absent. There 

has been some debate about whether the Brightseat should be 

considered a member of the overlying Aquia Formation, or 

left to stand as a formation on its own. Although the Brightseat is thin, it is relatively widespread, and may be important 

as a confining unit (Achmad and Hansen, 2001). It is considered a “poorly confined” confining unit in Anne Arundel 

County by Andreasen (2002), allowing a hydraulic connection 

between the Aquia and Severn Formations. He includes both 

the Brightseat and Severn, along with the Aquia Formation, as 

component parts of the “Aquia aquifer.” 

Aquia Aquifer, Marlboro Clay, and 

Lower Nanjemoy Confining Beds

The Aquia Formation was named by Clark and Martin 

(1901) during a revision of Eocene stratigraphy in Maryland, 

upgrading it from a “stage” in the Pamunkey Group described 

by Clark a few years earlier. The lithology consists of fine- to 

medium-grained, glauconitic quartz sand (Nogan, 1964). It is 

frequently referred to as a “greensand” because of the abundant glauconite content. The color can vary from dark greenish gray in unweathered zones to bright yellowish-tan where 

weathered. The lower boundary of the Aquia Formation with 

the underlying Brightseat is often marked by a bed of mollusc 

shells, and the Brightseat is composed of a finer glauconitic 

quartz sand, with grains approximately half the diameter of 

the Aquia sands (Nogan, 1964). This basal part of the Pamunkey Group represents a regressive depositional sequence into 

a shoaling sea. The finer-grained Brightseat was deposited 

in fairly deep continental shelf waters, the coarser Aquia in 

higher-energy, shallow water near shore, and the Marlboro 

Clay above the Aquia was deposited in a shallow, brackish, 

low-energy environment, possibly a lagoon (Nogan, 1964). 

The outcrop and recharge area for the Aquia Formation extends in an irregular band from the Potomac River in 

western Charles County, through Prince George’s County and 

into eastern Anne Arundel County, where it forms prominent, 

yellowish-tan bluffs along some of the tributary streams into 

Chesapeake Bay (Hansen, 1974). Bluffs composed of weathered Aquia sand are visible along the Severn River north of 

Annapolis from the bridge on highway U.S. 50 (a photograph 

of one of these bluffs is shown on the cover of this report). 

Outcrops continue on the Eastern Shore along the Chester 

River and northward to the Sassafras River (Hansen, 1974). 

The Aquia Formation has been eroded away under the 

Chesapeake Bay from just south of the Bay Bridge northward 

to the outcrop boundary (Chapelle and Drummond, 1983). A 

paleochannel of the ancestral Susquehanna River downcut several hundred feet below current sea level during a Pleistocene 

glacial lowstand, and eroded completely through the Aquia 

Formation in this area. 

An investigation of sedimentary facies in the Aquia 

Formation by Hansen (1974) provides some insight into how 

depositional environments can affect the performance of a single geological unit as an aquifer. The Aquia has three distinct 

facies identified in the Coastal Plain of Maryland. The first is 

a coarse, sandy-textured facies running parallel to the outcrop 

belt, which is interpreted to have been an offshore sand bank 

or barrier island. The second is a fine, glauconitic, sand-siltclay facies that occurs in the southern parts of the Western 

Shore, and is interpreted to have been deposited in a lower 

energy, inner-shelf or lagoonal environment landward of the 

sand bank. The third is a thin, very muddy facies underlying 

the Eastern Shore and known only from drill cores (it does not 

outcrop); this is interpreted to be outer shelf sediments deposited in deeper water, seaward of the sand bank. The coarse, 

sand-bank facies form an excellent aquifer, but the finer, 
12 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

inner-shelf facies is generally a poor aquifer. The thin, muddy, 

outer-shelf facies of the Aquia Formation under the Eastern 

Shore is not considered to be an aquifer (Hansen, 1974). 

The Aquia is an important aquifer in Southern Maryland. 

The greatest reported well yields in the Aquia aquifer are as 

high as 500 gal/min (gallons per minute) in eastern St. Mary’s 

and southern Calvert counties (Weigle and others, 1970). 

Water from the Aquia aquifer is often described as being 

“hard” because of the relatively high calcium bicarbonate 

content (Andreasen, 2002). The source of the dissolved minerals appears to be layers of weathered marine invertebrate shell 

material that are common throughout the formation. 

The confining unit overlying the Aquia Formation consists of the Marlboro Clay and the lower part of the Nanjemoy 

Formation (Achmad and Hansen, 2001). The Marlboro Clay 

was named by Clark and Martin (1901) for exposures of a 

red clay bed at the base of the Nanjemoy Formation in Prince 

George’s County. It was originally considered to be part of 

the Nanjemoy, but was discovered to be uniform and widespread, extending into Virginia, and it was raised to the rank of 

formation by Glaser (1971). It was described by Achmad and 

Hansen (2001) as a red, plastic clay interbedded with gray silt, 

up to 30 ft thick. The basal contact of the clay with the top of 

the underlying Aquia Formation is thought to be an unconformity (Glaser, 1971).

The lower part of the overlying Nanjemoy Formation, 

which forms some of the confining unit above the Aquia, was 

described by Achmad and Hansen (2001) as a glauconitic, 

very fine muddy sand to sandy clay, ranging in thickness from 

45 ft to 170 ft. 

Piney Point-Nanjemoy Aquifer

The Nanjemoy Formation was named by Clark and 

Martin (1901) as the upper formation in the Pamunkey Group. 

The Nanjemoy was described by McCartan (1989) as a dark 

green to olive, glauconitic quartz sand and dark silty clay, up 

to 230 ft thick, and early Eocene in age. It crops out in valleys 

in the western part of Charles County. It was deposited in a 

shallow shelf environment, and the upper and lower contacts 

are highly burrowed (McCartan, 1989). 

The overlying Piney Point Formation consists of a 

wedge-shaped body of sand and interspersed shell beds in 

conformable contact with the Nanjemoy Formation below and 

the Calvert Formation above. The lithology is described as an 

olive gray and green, poorly sorted, medium to coarse glauconitic quartz sand, with scattered pebbles and moldic limestone 

layers (Rader and Evans, 1993). The Piney Point is truncated 

and buried by the overlying beds of the Calvert Formation 

(Achmad and Hansen, 2001), and it was originally thought 

that this unit was not exposed anywhere at the surface, but 

was only known through drill cores (Otton, 1955). In fact, the 

“type section” is located in a well drilled in 1950 at the tip of 

the Piney Point Peninsula, in St. Mary’s County, Maryland. 

Ward (1985) later discovered that a Piney Point lithologic 

section more than 28 ft thick could be pieced together from 

a number of small exposures along the Pamunkey River in 

Virginia, where he established a reference section and informally subdivided the unit into three beds. According to Otton 

(1955), the Piney Point attains a maximum thickness of about 

60 ft in southern Calvert County, and Achmad and Hansen 

(2001) reported a thickness of up to 130 ft at Point Lookout 

in the southern tip of St. Mary’s County. It is considered to 

be middle Eocene in age based on fossil contents, including the presence of a large oyster, Cubitostrea sellaformis, 

a middle Eocene marker (Rader and Evans, 1993). Like the 

Aquia Formation, the Piney Point Formation has been eroded 

away under the Chesapeake Bay north of Calvert Cliffs by a 

paleochannel of the ancestral Susquehanna River (Achmad 

and Hansen, 1997).

From oldest to youngest, the Piney Point-Nanjemoy 

aquifer consists of the following stratigraphic units: (1) the 

upper part of the lower Eocene Nanjemoy Formation, (2) the 

middle Eocene Piney Point Formation, (3) unnamed beds that 

are possibly early Oligocene in age and may correlate with the 

Old Church Formation described by Ward (1985), and (4) the 

basal strata of the lower to middle Miocene Calvert Formation (Hansen, 1995). As the Piney Point-Nanjemoy aquifer has 

very limited surface outcrops, most of the recharge is thought 

to occur through poorly confined layers. Well yields as high as 

500 gal/min have been reported for the Piney Point-Nanjemoy 

in Calvert and St. Mary’s Counties (Weigle and others, 1970).

Chesapeake Group

The confining unit overlying the Piney Point-Nanjemoy 

aquifer is the basal part of the Chesapeake Group. The Chesapeake Formation was named by Darton (1891) for Mioceneage marine deposits which outcrop near the Chesapeake Bay 

in both Maryland and Virginia. It was raised to the status of a 

group in 1894 by Dall, and applied to all Miocene strata from 

Florida to Delaware, although the component formations differ 

from place to place (Wilmarth, 1957). Current usage does not 

generally extend the Chesapeake Group any farther south than 

the North Carolina Coastal Plain, and there has been considerable debate on how to divide the group into formations and 

correlate it elsewhere. In Southern Maryland, the Chesapeake 

Group consists of the Calvert Formation at the base, overlain 

by the Choptank and St. Mary’s Formations (Achmad and 

Hansen, 2001). The Yorktown Formation is a fourth member 

that occurs above the St. Mary’s Formation in eastern Virginia 

(Stephenson and MacNeil, 1954). 

The Chesapeake Group consists of fine to coarse quartz 

sand, shelly and diatomaceous, with intervals of silt and clay, 

deposited mainly in shallow middle and inner continental shelf 

waters (Rader and Evans, 1993). In Southern Maryland, it 

ranges in thickness from 50 ft in Charles County to 215 ft in 

central Calvert County (Achmad and Hansen, 2001). Aquifers 

in the Chesapeake Group, principally the Cheswold, Federalsburg, and Frederica, are important water sources for Maryland 

and Delaware on the central and eastern Delmarva Peninsula. 
Water Use and Water Levels in Confined Aquifers 13

In Southern Maryland, the Chesapeake Group consists mostly 

of confining units (D.C. Andreasen, Maryland Geological 

Survey, written commun., 2007).

Water Use and Water Levels in 

Confined Aquifers

Total ground-water use in Southern Maryland and the 

counties on the adjacent Eastern Shore has increased from 

about 42 Mgal/d in the early 1980s to nearly 65 Mgal/d in 

2005. The contribution of water supplied from the various 

major aquifers has also shifted over time, as shown in 

figure 5. This figure shows all reported withdrawals by users 

with permits for 10,000 gal/d or more, and domestic use estimated by population density. 

The Patuxent, Magothy, and Piney Point-Nanjemoy aquifers are currently used less than they were in the 1980s, but 

withdrawals have increased from the Aquia, upper Patapsco, 

and lower Patapsco aquifers. The upper Patapsco and Piney 

Point-Nanjemoy aquifers are relatively minor contributors in 

terms of the overall water supply. 

Population growth in Maryland has been steady from 

the 1960s onward (Wheeler, 2003). Census data for the counties in the study area show details of these trends in figures 6 

and 7 from 1990 through 2005 (U.S. Census Bureau, 2006). 

Population increased in Southern Maryland and the Eastern 

Shore counties of Dorchester, Talbot, and Queen Anne’s over 

the past 15 years, although at disproportionate rates (fig. 6). 

Calvert County experienced the highest rate of growth, 

with more than a 50-percent increase in population between 

1990 and 2005 (fig. 7). The number of people in Charles 

County increased by about 30 percent over the same period, 

while St. Mary’s County had about 25 percent growth. The 

high growth rates in these semi-rural counties east of Washington, D.C., which depend on ground water for domestic and 

municipal supplies, have probably affected aquifer drawdown 

in these locations. The reported municipal pumpages in these 

counties do not always appear to be increasing at the same 

rate as the populations. Much of the water may be withdrawn 

by domestic wells, which are not accurately captured in the 

SWUDS water-use database because domestic withdrawals are 

estimated, not reported.

The number of people in the large, urban counties (population over 250,000) in the study area increased by 18 percent 

in Anne Arundel County, and by 15 percent in Prince George’s 

County. These two counties were already quite populous, 

however, and reporting a percentage masks growth in total 

numbers from 1990 to 2005 that were higher than any of the 

other counties in the study area: 123,418 people in Prince 

George’s County, and 83,639 in Anne Arundel County (U.S. 

Census Bureau, 2006). 

The other counties experienced population increases 

of less than 40,000 people, and Queen Anne’s, Talbot, and 

Dorchester Counties increased less than 20,000. Dorchester 

County, with the smallest population in the study area, also 

had the smallest population increase in both percentage 

(4 percent between 1990 and 2005) and in absolute numbers, 

adding less than 1,200 people. Population increases in the 

Figure 5. Total annual groundwater withdrawals reported in the 

U.S. Geological Survey AWUDS 

database for the six major aquifers 

in the Southern Maryland study 

area from 1980 to 2004.
14 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 6. Southern Maryland population estimates by county from 1990 to 2005 (Source: U.S. Census Bureau, 2006).

Figure 7. Population growth rates 

for counties in the study area from 

1990 to 2005 (Source: U.S. Census 

Bureau, 2006).
Water Use and Water Levels in Confined Aquifers 15

smaller counties of the study area (less than 250,000 people) 

from 1990 to 2005 are shown in figure 8. 

The distribution of ground-water use on a county-bycounty basis for the study area is shown in figure 9, broken 

down by major category. Rural counties like Dorchester use a 

much larger percentage of ground water for farming activities, 

specifically irrigating crops and watering livestock. More 

densely populated, urban counties like Anne Arundel tend 

to use more water for public supply, and counties dominated 

by scattered rural populations with generally non-farming 

occupations, such as Calvert, use ground water primarily for 

domestic supply. Prince George’s County has an even larger 

urban population than Anne Arundel, but uses more surface 

water for public supply (fig. 2). The use of ground water 

in thermoelectric power plants is a fairly small percentage 

of the total ground water withdrawn (shown in fig. 9 for 

Calvert and Charles Counties). Ground-water withdrawals 

and potentiometric surface declines in Southern Maryland 

are discussed in each of the following sections for the major 

aquifers, starting with the oldest units in the geologic column 

and working upward.

Patuxent Aquifer

Ground-water withdrawals from the Patuxent aquifer are 

most common just to the east of the outcrop in Prince George’s 

and Anne Arundel Counties (Mack and Achmad, 1986). 

Major pumping centers in Anne Arundel County are near 

Dorsey Road in the northern part of the county, and at Crofton 

Meadows, and Fort Meade. In Prince George’s County, the 

major pumpage occurs at the Town of Bowie. The history of 

withdrawals from the major pumping centers are shown for the 

period 1980 through 2004 in figure 10, and the sites are shown 

in figure 11. 

Pumpage from the Patuxent aquifer in northern Anne 

Arundel County reached rates as high as 4.5 Mgal/d in 1983, 

but this was reduced to around 3 Mgal/d in successive years, 

and remained constant at approximately that level. Withdrawals from the two main Patuxent aquifer pumpage centers 

at Fort Meade are shown as a combined value in figure 10. 

Withdrawal rates have ranged from about 0.5 Mgal/d in the 

early 1980s to more than 4 Mgal/d in 1990, before dropping 

back to less than 1.5 Mgal/d throughout the remainder of 

the 1990s (after falling below 1 Mgal/d in the early 1990s). 

Rates increased again from 2003–04 to above 2 Mgal/d. The 

higher-use periods appear to coincide with periods of greater 

military activity at Fort Meade, such as the Persian Gulf War 

in 1990–91, and the Iraq War in 2003–04.

The Patuxent water supply for the Town of Bowie 

was initially established in the 1960s, and withdrawal rates 

typically ranged from about 1 to 1.4 Mgal/d (D.C. Andreasen, 

Maryland Geological Survey, written commun., 2007). After 

1992, Patuxent withdrawals at Bowie gradually declined 

below 1 Mgal/d, presumably as additional water supplies came 

Figure 8. Population growth 

in smaller counties in the study 

area from 1990 to 2005 (Source: 

U.S. Census Bureau, 2006).
16 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 9. Ground-water use by county in the study area, shown as a function of major use category for 2004 

(From U.S. Geological Survey AWUDS database).

Figure 10. Trends in ground-water withdrawals from the Patuxent aquifer at four major pumping centers in Anne Arundel and 

Prince George’s Counties from 1980 to 2004.
Water Use and Water Levels in Confined Aquifers 17

Figure 11. Potentiometric surface and water use, Patuxent aquifer, 2005.
18 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

online. Withdrawals from the Patuxent aquifer at Crofton 

Meadows, however, have peaked twice, once in the early 

1990s at more than 3 Mgal/d, and then declining to below 

1 Mgal/d before exceeding 3 Mgal/d levels again about 

10 years later. Water-supply pumpage at Crofton Meadows 

is distributed between the Patuxent aquifer and the lower 

Patapsco aquifer. The year-to-year changes in withdrawal rates 

from the Patuxent that are visible in figure 10 are probably 

related more to operational issues than to water-supply issues 

(D.C. Andreasen, Maryland Geological Survey, written 

commun., 2007). It should also be noted that in addition to the 

well field at Crofton Meadows, Anne Arundel County also had 

a municipal supply field in the Patuxent aquifer at Crofton, 

which was abandoned in 1992. 

Patuxent aquifer withdrawals in Charles County are significantly less than those in Anne Arundel or Prince George’s 

Counties. The maximum withdrawal in the water-use records 

was 0.16 Mgal/d from a well at South Hampton in 2001.

The potentiometric surface map of the Patuxent aquifer in the study area is shown in figure 11. The outcrop (and 

recharge) area shown on this and all subsequent maps in this 

report follow the boundaries defined by Vroblesky and Fleck 

(1991) in their Coastal Plain RASA report. 

A large cone of depression is visible in northern Anne 

Arundel County, corresponding to the pumping center on 

Dorsey Road. Cones of depression are also centered on 

ground-water withdrawal locations at Fort Meade and Crofton 

Meadows. A mound-like feature is shown on the potentiometric surface of the Patuxent aquifer east of Fort Meade at Kings 

Heights. This is a real feature in the data, and may be caused 

by an isolated sand unit within the Patuxent aquifer system 

(D.C. Andreasen, Maryland Geological Survey, written commun., 2007). 

Another broad cone of depression in Charles County 

centered on Bryons Road between the towns of Indian Head 

and LaPlata resulted from increased utilization of the Patuxent aquifer in northwestern Charles County, as water demands 

increased with population growth.

All of the 2005 potentiometric surface maps constructed 

for this report show ground-water withdrawals for 2004, the 

most recent year for which reviewed and approved data were 

available. It is not unreasonable to expect that ground-water 

drawdowns observed in 2005 were caused by 2004 pumpages. 

The 2004 water-use data have been checked as closely as possible against the 2005 water-use data that were available when 

this report was being prepared, and no significant differences 

were noted.

Patapsco Aquifer

Ground-water withdrawals from the Patapsco Formation 

are reported separately for the lower Patapsco and upper Patapsco aquifers. These are described in separate sections below.

Lower Patapsco Aquifer

As shown in figure 12, the largest volume of water 

pumped from the lower Patapsco aquifer at a single location 

occurred in the Anne Arundel County well field at Severndale. 

Withdrawal rates were approximately 2 to 3.5 Mgal/d during 

the 1980s, increasing to more than 6 Mgal/d in the mid-1990s. 

Pumping at the Town of Arnold, near the City of Annapolis 

on the Broadneck Peninsula, began in the early 1990s, and has 

been maintained at a rate of about 2 Mgal/d through the present. The annual water report to consumers from Anne Arundel 

County (2006) indicates that the populous Broadneck Peninsula is mainly supplied with water from the Severndale and 

Arnold pumping centers. 

Other areas of drawdown in the lower Patapsco aquifer in 

Southern Maryland are in Charles County, at Waldorf, LaPlata, 

Indian Head, and at the Morgantown Powerplant. Pumpinginduced drawdowns increased over time, and are shown in the 

series of lower Patapsco potentiometric surface maps for 1985, 

1995, and 2005 (figs. 13–15). A cone of depression approximately 35 ft below sea level had developed in the vicinity of 

Severndale by 1985, which increased to about 62 ft below sea 

level in 1995, and developed to a depth of over 90 ft below 

sea level by 2005. Drawdowns to a depth of about 55 ft below 

sea level are also shown on the 1995 potentiometric surface at 

Arnold after pumping began in 1992. In 2005, the largest cone 

of depression in the lower Patapsco aquifer in Southern Maryland was located in an area of northern and western Charles 

County, with drawdowns nearly 200 ft below sea level at 

Waldorf and LaPlata (fig. 15). A number of production wells 

withdrawing between 0.1 and 1 Mgal/d are located in the Waldorf area, at LaPlata, and in the Indian Head-Bryons Road area 

to the west. Ground water in the lower Patapsco near Indian 

Head has been pumped at a rate of about 1 Mgal/d since 1980 

(fig. 12). Ground-water withdrawals in Charles County and in 

Southern Prince George’s County have resulted in declines in 

ground-water levels in the lower Patapsco aquifer. 

A number of observation wells screened in the underlying Patuxent aquifer, which is lightly pumped, also showed 

declines (Andreasen, 1999). The possibility of pumpage from 

one aquifer affecting water levels in adjacent aquifers is discussed in more detail in a later section of this report.

A map of the difference in the potentiometric surface of 

the lower Patapsco aquifer is shown in figure 16 for the period 

1985 to 1995, and a similar map is shown in figure 17 for the 

period 1995 to 2005. The differences in the potentiometric 

surface from 1985 to 1995 are most pronounced in central 

Anne Arundel County and Charles County, and were presumably caused by ground-water withdrawals at Severndale and in 

the vicinity of Waldorf. The 1995–2005 difference map shows 

some recovery of the potentiometric surface at Arnold, but 

continued declines at Severndale and in Charles County. 
Water Use and Water Levels in Confined Aquifers 19

Figure 12. Ground-water withdrawals from the lower Patapsco aquifer at five major pumping centers in Anne Arundel and 

Charles Counties from 1980 to 2004 (From U.S. Geological Survey AWUDS database).
20 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 13. Potentiometric surface and water use, lower Patapsco aquifer, 1985.
Water Use and Water Levels in Confined Aquifers 21

Figure 14. Potentiometric surface and water use, lower Patapsco aquifer, 1995.
22 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 15. Potentiometric surface and water use, lower Patapsco aquifer, 2005.
Water Use and Water Levels in Confined Aquifers 23

Figure 16. Potentiometric difference, lower Patapsco aquifer, 1985 to 1995.
24 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 17. Potentiometric difference, lower Patapsco aquifer, 1995 to 2005.
Water Use and Water Levels in Confined Aquifers 25

2007). The potentiometric surface map (fig. 21) shows local 

declines as great as -120 ft in the upper Patapsco aquifer by 

2005. Wilson and Fleck (1990) reported that transmissivities 

of the upper Patapsco aquifer and its equivalents in Charles 

County are higher to the north and east of the Waldorf area. 

The reduced transmissivity of the upper Patapsco aquifer in 

southwestern Charles County may be responsible for the large 

cones of depression under relatively low pumping rates as 

shown in the potentiometric surface maps of this area.

It is also possible that drawdowns in the upper Patapsco 

aquifer in the Waldorf-LaPlata area might be a response to 

the significant withdrawals of ground water from the lower 

Patapsco aquifer at this location. As noted earlier, Achmad and 

Hansen (2001) reported that the confining bed between the 

lower and upper Patapsco aquifers was sandy and less effective at some locations. The upper Patapsco at Waldorf-LaPlata 

might be affected by pumpage from the lower Patapsco.

The upper Patapsco aquifer is not pumped in Calvert 

County and is used only to a limited extent in St. Mary’s 

County. An assessment of the projected water demands to the 

year 2030 in these counties led Drummond (2005) to conclude 

that new sources of supply would have to be developed, and 

drilling into deeper aquifers like the upper Patapsco was a 

solution suggested for obtaining additional ground water. Total 

reported withdrawals from the upper Patapsco aquifer in 

St. Mary’s County were less than 0.1 Mgal/d until the late 

1990s, but had increased to 0.47 Mgal/d by 2004.

A map of the difference in the potentiometric surface of 

the lower Patapsco aquifer is shown in figure 22 for the period 

1985 to 1995, and a similar map is shown in figure 23 for the 

period 1995 to 2005. The 1985–95 map shows the effects of 

drawdown in the vicinity of Annapolis, and near the Chalk 

Point Power Plant, which is a relatively minor user, at about 

0.3 to 0.4 Mgal/d. The 1995–2005 map shows some recovery 

at Annapolis and Chalk Point, but continued declines in western Charles County, and new declines in St. Mary’s County. 

Upper Patapsco Aquifer

Ground-water withdrawals from the upper Patapsco 

aquifer tend to be lower in total volume than those from the 

lower Patapsco aquifer. The main user of ground water from 

the upper Patapsco aquifer is the City of Annapolis, as shown 

in figure 18. Water from the upper Patapsco aquifer is supplied 

by a well field within the City of Annapolis (AA1932G101), 

and a second nearby at Broad Creek (AA1968G006) on 

the west side of town. The combined withdrawals from 

these two well fields are shown as “Annapolis” in figure 18. 

The municipal area also is supplied by a well field located 

northeast of the city near the Town of Arnold. As shown in 

figure 18, these pumping localities have withdrawn the largest 

amounts of ground water from the upper Patapsco aquifer over 

the past 25 years. 

A number of ground-water withdrawals from the upper 

Patapsco aquifer did not begin until the early 1990s, for example, near the Eastern Shore towns of Easton and Cambridge 

(fig. 18). Water supplies at Severndale from the lower Patapsco aquifer were supplemented by ground-water withdrawals 

from the upper Patapsco aquifer beginning in the 1990s. The 

trend appears to be toward greater use of this aquifer.

The only major ground-water withdrawals from the upper 

Patapsco aquifer in Southern Maryland are reported for the 

Chalk Point Power Plant in southern Prince George’s County. 

The water-use data since 1980 show Chalk Point steadily withdrawing less than 0.5 Mgal/d from the upper Patapsco aquifer. 

Potentiometric surface maps of the upper Patapsco 

aquifer for 1985, 1995, and 2005 are shown in figures 19, 20, 

and 21. An unexpected feature of these maps is the cone of 

depression centered on the Waldorf-LaPlata area in Charles 

County. None of the individual wells or well fields in this 

part of Charles County are reported as withdrawing water at 

rates higher than 100,000 gal/d, and there are many smaller 

users (S.E. Curtin, U.S. Geological Survey, oral commun., 
26 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 18. Trends in ground-water withdrawals from the upper Patapsco aquifer at six major pumping centers in 

Southern Maryland from 1980 to 2004. (Annapolis and Arnold are both in the Annapolis metropolitan area.)
Water Use and Water Levels in Confined Aquifers 27

Figure 19. Potentiometric surface and water use, upper Patapsco aquifer, 1985.
28 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 20. Potentiometric surface and water use, upper Patapsco aquifer, 1995.
Water Use and Water Levels in Confined Aquifers 29

Figure 21. Potentiometric surface and water use, upper Patapsco aquifer, 2005.
30 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 22. Potentiometric difference, upper Patapsco aquifer, 1985 to 1995.
Water Use and Water Levels in Confined Aquifers 31

Figure 23. Potentiometric difference, upper Patapsco aquifer, 1995 to 2005.
32 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Magothy Aquifer

As shown in figure 24, rates of ground-water withdrawal 

from the Magothy aquifer were relatively high at the City of 

Annapolis in the early 1980s, exceeding 4 Mgal/d in some 

years. During this time, the Town of Bowie and production 

wells in the Waldorf area also were withdrawing 2 to 3 Mgal/d 

from the aquifer. The Town of Bowie severely reduced and 

maintained withdrawals from the Magothy aquifer at less than 

0.3 Mgal/d since 1988. Production at the City of Annapolis 

and near Waldorf has continued to steadily withdraw 1.5 to 

nearly 3 Mgal/d. The values shown in figure 24 for these 

two locations represent the sum totals of multiple production 

wells reported for each area. The Chalk Point Power Plant 

has withdrawn slightly more to slightly less than 0.5 Mgal/d 

since 1980. Production at Easton from the Magothy aquifer 

has dropped by about half since 1990, compared to withdrawal 

rates in the 1980s. 

Potentiometric surface maps and ground-water withdrawal centers for the Magothy aquifer are shown for 1985, 

1995, and 2005 in figures 25–27. Sustained, high rates of 

pumpage at the City of Annapolis in Anne Arundel County, 

in the range of 1–2 Mgal/d for the last decade, resulted in the 

development of a relatively shallow cone of depression in the 

potentiometric surface of the Magothy aquifer. A group of 

wells in the Waldorf area pumping less than 0.1 Mgal/d have 

created a broad and deep cone of depression in the potentiometric surface, however. A similar cone of depression in the 

potentiometric surface of the Magothy aquifer at the Chalk 

Point Power Plant resulted from pumpage of about 0.5 Mgal/d 

from 1980 to 2004. 

Yields from the Magothy aquifer vary at different locations, probably because of variations in hydraulic conductivity 

due to facies changes within the formation. This also occurs 

in the upper Patapsco aquifer as described previously. The 

Magothy Formation was noted in the hydrogeologic framework section of this report as thinning to the south and west in 

Southern Maryland, with the subsurface boundary located only 

about 8 mi (miles) southwest of Chalk Point. The finer-grained 

sands in this area (Hansen, 1972) may be responsible for the 

reduced hydraulic conductivity of the aquifer and result in a 

greater drawdown. 

A map of the difference in the potentiometric surface of 

the Magothy aquifer is shown in figure 28 for the period 1985 

to 1995, and a similar map is shown in figure 29 for the period 

1995 to 2005. The earlier map shows a broad area of decline 

to the southwest, toward the Town of Bowie and the Waldorf 

area. Waldorf has continued to withdraw ground water from 

the Magothy aquifer at 2 to 3 Mgal/d since 1980, pumping 

from a number of small production wells. This steady withdrawal has maintained a broad and deep cone of depression in 

northern Charles County that continues to develop. 

Reductions in ground-water withdrawals from the 

Magothy aquifer by the Town of Bowie, shown in figure 24 

as decreasing from about 2.5 Mgal/d in the early 1980s to 

less than 0.2 Mgal/d beginning in 1988, have resulted in the 

recovery of water levels. This can be seen on the potentiometric surface difference maps (figs. 28 and 29) as a positive 

recovery of the potentiometric surface in central and northern 

Prince George’s County. 
Water Use and Water Levels in Confined Aquifers 33

Figure 24. Trends in ground-water withdrawals from the Magothy aquifer at five major pumping centers in 

Southern Maryland from 1980 to 2004 (Withdrawal data for Annapolis and Waldorf are aggregated from multiple wells) 

(Source: U.S. Geological Survey AWUDS database).
34 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 25. Potentiometric surface and water use, Magothy aquifer, 1985.
Water Use and Water Levels in Confined Aquifers 35

Figure 26. Potentiometric surface and water use, Magothy aquifer, 1995.
36 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 27. Potentiometric surface and water use, Magothy aquifer, 2005.
Water Use and Water Levels in Confined Aquifers 37

Figure 28. Potentiometric difference, Magothy aquifer, 1985 to 1995.
38 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 29. Potentiometric difference, Magothy aquifer, 1995 to 2005.
Water Use and Water Levels in Confined Aquifers 39

Arundel County, and at multiple locations on the Eastern 

Shore have produced little individual disturbance in the 

potentiometric surface compared to the cone of depression in 

the Solomons Island/NASPR area. The collective volume of 

ground-water withdrawn from this aquifer by these smaller 

users has probably been significant, however (D.C. Andreasen, 

Maryland Geological Survey, written commun., 2007). 

Different sedimentary facies of the Aquia Formation 

affect yields from the Aquia aquifer. The Aquia Formation 

contains coarse, sandy-textured, high-transmissivity, beachface or offshore bar sands extending along and parallel to the 

outcrop belt (Hansen, 1974), which make an excellent aquifer. 

Toward the southern parts of the study area, the coarse sand 

grades into a finer-grained lagoonal facies, which is often considered a marginal to poor aquifer. On the Eastern Shore, the 

Aquia Formation is composed of a thin, muddy, offshore shelf 

facies, which is not a productive aquifer (Hansen, 1974). This 

transition between the sandy offshore bar and muddy shelf 

facies is shown in figures 31–33 as a dashed boundary running 

northeastward through Dorchester and Talbot Counties. 

The large withdrawals at Solomons Island, NASPR, and 

the Town of Lexington Park are responsible for the deep cones 

of depression in southern Calvert and St. Mary’s Counties; 

however, the drawdowns may also be partly due to the lower 

transmissivity of the finer-grained Aquia Formation lagoonal 

facies in this area. The more transmissive parts of the Aquia 

aquifer, in northern Calvert and southern Anne Arundel Counties, show less drawdown. 

Maps of the difference in the potentiometric surface of 

the Aquia aquifer for the period 1985 to 1995, and 1995 to 

2005, respectively, are shown in figures 34 and 35. Declines 

of more than 60 ft occurred near NASPR from 1985 to 1995, 

decreasing to about 20 ft by 2005.

Aquia Aquifer

Significant rates of ground-water withdrawal from the 

Aquia aquifer in Southern Maryland began in 1942, when 

the U.S. Navy constructed Naval Air Station, Patuxent River 

(NASPR) and Webster Outlying Field on the Point Lookout 

Peninsula in the southernmost part of St. Mary’s County 

(Klohe and Feehley, 2001). The Naval Air Station and the 

Town of Lexington Park outside its front gate have withdrawn 

water from the Aquia aquifer at a steady rate of about 

2 Mgal/d since 1980, as shown in figure 30. No other Aquia 

well field in the study area has withdrawn water from this 

aquifer at this magnitude or duration. The second largest well 

field, at Solomons Island, has steadily climbed to a rate of 

1 Mgal/d, and is only a few miles from NASPR, just across 

the Patuxent River to the north. Potentiometric surface maps 

and ground-water withdrawal centers for the Aquia aquifer are 

shown for 1985, 1995, and 2005 in figures 31–33. Groundwater withdrawals from the Aquia aquifer at NASPR and 

Solomons Island have resulted in regional drawdown of the 

potentiometric surface.

Ground-water withdrawals at NASPR and the Town of 

Lexington Park have created a large cone of depression in the 

potentiometric surface of the Aquia aquifer, which reached a 

depth of more than 150 ft below sea level in 2005. Groundwater withdrawal from the Aquia aquifer at the Calvert Cliffs 

Power Plant, which increased slightly in the mid-1990s to near 

0.5 Mgal/d, is visible on the potentiometric surface maps as a 

slight “indentation” in the northern curve of the contour lines 

around NASPR and Solomons Island. The effect of pumpage wells near the Town of Chesapeake Beach, located in 

northern Calvert County, is also visible on some of the maps, 

most noticeably in 2005 (fig. 33). Many other small users of 

the Aquia aquifer in northern Calvert County, southern Anne 
40 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 30. Trends in ground-water withdrawals from the Aquia aquifer at five major pumping centers in Southern 

Maryland from 1980 to 2004.
Water Use and Water Levels in Confined Aquifers 41

Figure 31. Potentiometric surface and water use, Aquia aquifer, 1985.
42 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 32. Potentiometric surface and water use, Aquia aquifer, 1995.
Water Use and Water Levels in Confined Aquifers 43

Figure 33. Potentiometric surface and water use, Aquia aquifer, 2005.
44 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 34. Potentiometric difference, Aquia aquifer, 1985 to 1995.
Water Use and Water Levels in Confined Aquifers 45

Figure 35. Potentiometric difference, Aquia aquifer, 1995 to 2005.
46 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Piney Point-Nanjemoy Aquifer

The largest user of water from the Piney Point-Nanjemoy 

aquifer is the City of Cambridge on the Eastern Shore. With 

the exception of the year 1981, when withdrawals averaged 

1.3 Mgal/d, the City of Cambridge consistently pumped 2.5 

to 3 Mgal/d from the Piney Point-Nanjemoy between 1980 

and 1990 (fig. 36). Withdrawals after 1990 were cut back to 

less than 1.5 Mgal/d, and from the late 1990s through 2004, 

pumpage was about 1 Mgal/d. This was probably the result 

of some shifting of withdrawals to the deeper upper Patapsco 

aquifer in 1992 (fig. 18). Several other small towns in western 

Dorchester and Talbot Counties obtain municipal water supplies from the Piney Point-Nanjemoy aquifer, although these 

withdrawals are generally 0.1 Mgal/d or less. The Piney PointNanjemoy aquifer also is an important municipal water source 

for the Town of Dover, Delaware (Leahy, 1976). 

Withdrawals from the Piney Point-Nanjemoy aquifer on 

the Western Shore of Chesapeake Bay are relatively minor, 

even for the highest levels of production at Solomons Island 

and NASPR. The Naval Air Station and adjacent Town of 

Lexington Park, which have steadily withdrawn 2.5 to 

3 Mgal/d from the Aquia aquifer since 1980, pumped only 

a few hundred thousand gallons per day from the overlying 

Piney Point-Nanjemoy aquifer over the same period. Pumpage 

at Solomons Island also has been modest, peaking at less 

than 0.5 Mgal/d in the mid-1990s. Because this aquifer is 

at relatively shallow depths on the Western Shore, there are 

a significant number of small domestic users (Achmad and 

Hansen, 1997; table 3), as well as commercial users in Calvert 

and St. Mary’s Counties (Curtin and Dine, 1995). 

A map of the potentiometric surface of the Piney PointNanjemoy aquifer in 2005 is shown in figure 37. A 1994 

potentiometric surface map of the aquifer (Achmad and Hansen, 1997) showed a major drawdown centered at Cambridge. 

Due to the lack of more recent water-level data east of Taylors 

Island, it is unclear if the same cone of depression was present 

in 2005. The City of Cambridge reduced pumpage from the 

Piney Point-Nanjemoy aquifer beginning in 1991, however, so 

drawdowns in 2005 were probably less than those shown by 

Achmad and Hansen (1997) a decade earlier. The hydrograph 

for Well DO Db 17 on Taylors Island (fig. 4) shows a steep 

decline from 1993 to 2003, followed by a recovery between 

2003 and 2005. 

The Piney Point-Nanjemoy aquifer is shallow enough 

that a ground-water divide is formed by the Chesapeake Bay 

and underlying paleochannels created during a lowstand of sea 

level by the ancestral Susquehanna River. The paleochannels 

were back-filled with silt as sea levels rose, which prevents 

pressure changes in the aquifer from transmitting across 

Chesapeake Bay (Achmad and Hansen, 1997; fig. 5). South of 

Calvert Cliffs, where the Piney Point Formation is deeper, it 

is separated from the paleochannels by clay confining beds. It 

is unlikely that drawdown from pumpage of the Piney PointNanjemoy aquifer at Cambridge is responsible for the cones of 

depression at St. Leonard in Calvert County, or near NASPR 

in St. Mary’s County. 

The cone of depression in the Piney Point-Nanjemoy 

aquifer near NASPR is consistent with the large head decline 

in the underlying Aquia aquifer. This may indicate downward 

leakage, which is discussed in more detail in the section on 

“Effects of Withdrawal on Multiple Aquifers” elsewhere in 

this report. 
Water Use and Water Levels in Confined Aquifers 47

Figure 36. Trends in ground-water withdrawals from the Piney Point-Nanjemoy aquifer at five major pumping centers in 

Southern Maryland from 1980 to 2004 (Source: U.S. Geological Survey AWUDS database).
48 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 37. Potentiometric surface and water use, Piney Point-Nanjemoy aquifer, 2005.
Relations Between Withdrawals and Water-Level Drawdowns 49

Relations Between Withdrawals and 

Water-Level Drawdowns

A direct cause-and-effect relation often occurs between 

withdrawals from confined aquifers, and observed drawdowns 

of water levels. Although this relation can often be verified 

by correlating withdrawals with water-level changes, the task 

becomes more problematic in complex hydrogeologic settings, 

and with greater amounts of withdrawal. 

The Coastal Plain sediments in Southern Maryland form 

a stacked stratigraphic sequence. The major aquifers are 

generally separated by continuous, low-permeability confining units; in some places, however, the confining beds may be 

more permeable (“leaky”), thinner, or absent altogether. As 

previously described in the hydrogeologic framework section, the sedimentary units tend to vary laterally, changing in 

thickness, grain size, clay content, and physical properties as a 

function of the ancient depositional or erosional environments. 

Mack and Achmad (1986) illustrated the discontinuous nature 

of confining units in their investigation of Potomac Group 

aquifers (Patuxent, lower Patapsco, and upper Patapsco), 

reporting poorly confined aquifers or confining beds that thin 

laterally over short distances. Confining units commonly form 

less than perfect seals on the aquifers, and leakage between 

adjacent aquifers may occur as water is withdrawn. 

Effects of Withdrawal on Multiple Aquifers

One of the issues in water use and aquifer resource 

assessment concerns the degree of hydraulic connection 

between aquifers, and whether major drawdowns caused 

by pumping in one aquifer can affect pressure heads in 

“unpumped” aquifers above or below the pumped unit. There 

appears to be some evidence supporting this possibility at two 

locations—the Patuxent aquifer in Charles County, and the 

Piney Point-Nanjemoy aquifer in St. Mary’s County.

Withdrawals from the lower Patapsco aquifer in Charles 

County and southern Prince George’s County increased in the 

mid-1980s, rising to just over 5 Mgal/d by 1988, and reaching 

6 Mgal/d in 1990 (Andreasen, 1999; fig. 18). The total annual 

rates of all the lower Patapsco ground-water withdrawals 

reported for Charles County since 1980 are shown in 

figure 38. A steady increase in withdrawals occurred through 

the 1980s, leveling to a sustained higher rate in the 1990s. 

Ground-water withdrawals from the lower Patapsco 

aquifer in Charles County and southern Prince George’s 

County of about 3 Mgal/d took place during the early to 

mid-1980s, resulting in a water-level drop of about 20 ft in 

the lower Patapsco aquifer at Well CH Ce 37 near La Plata, 

and a lesser drop of 2 to 3 ft in the lower Patapsco aquifer at 

Well CH Da 20 at Douglas Point on the south bend of the 

Figure 38. Annual total groundwater withdrawals from the lower 

Patapsco aquifer in Charles 

County, Maryland, since 1980 

(Source: U.S. Geological Survey 

AWUDS database).
50 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Potomac River, some 20 mi from La Plata (Andreasen, 1999). 

The Patuxent aquifer at Douglas Point, monitored in 

Well CH Da 18, showed a response identical to the lower 

Patapsco above it during this period, but to a somewhat lesser 

degree. Andreasen (1999) also reported that ground-water 

levels in the Patuxent aquifer may be affected locally by 

withdrawals from the overlying lower Patapsco aquifer near 

the Indian Head area of Charles County.

Ground-water levels in the lower Patapsco aquifer 

in LaPlata Observation Well CH Ce 37 responded to this 

withdrawal by dropping from about -20 ft in 1981 to 

-40 ft in 1987, and then falling further with the increase in 

pumpage rates to a level of -120 ft by 1995, as shown on 

the hydrograph in figure 39. Ground-water levels in lower 

Patapsco Observation Well CH Da 20, near Douglas Point, 

also responded to this pumpage to a lesser degree. Groundwater levels in the underlying Patuxent aquifer in Well CH 

Be 57 near Waldorf declined by about 11 ft between 1986 

and 1995, even though there is no reported Patuxent pumpage 

in the area. Ground-water levels in Well CH Da 18 in the 

Patuxent aquifer at Douglas Point also showed a response 

to this increased lower Patapsco pumpage, with the decline 

curve of the hydrograph becoming steeper after crossing 

an inflection point at about 1986. Well CH Be 57, which is 

closer to the pumping center, shows a slightly steeper rate of 

decline than Well CH Da 18, some distance south near the 

Potomac River. Andreasen (1999) concluded that pumpage 

from the lower Patapsco aquifer may affect water levels in the 

underlying Patuxent aquifer in localized areas within Charles 

County, where the intervening Arundel Clay confining bed is 

relatively thin or contains sandy sections. This interconnection 

is probably limited, however, given the general continuity, 

thickness (100–300 ft), and low permeability of the Arundel 

Clay throughout most of Charles County. It was also noted 

earlier that declines in the upper Patapsco aquifer in the 

vicinity of Waldorf-LaPlata (figs. 19–21) might also be 

partially caused by withdrawals from the lower Patapsco.

The potentiometric surface map of the Piney PointNanjemoy aquifer in 2005 shows a moderate cone of 

depression near NASPR (fig. 37). The total, annual groundwater withdrawals from the Piney Point-Nanjemoy and Aquia 

aquifers reported for St. Mary’s County from 1980–2004 are 

shown in figure 40. Withdrawals from the Aquia aquifer in this 

county increased from 1.5 Mgal/d in 1981, to over 4.5 Mgal/d 

in 2002. Ground-water withdrawals from the Piney PointFigure 39. Patuxent and lower Patapsco aquifer observation wells in Charles County, Maryland, responding to groundwater withdrawals from the lower Patapsco aquifer (Source: U.S. Geological Survey GWSI database).
Relations Between Withdrawals and Water-Level Drawdowns 51

Nanjemoy aquifer, in comparison, remained below 1 Mgal/d 

during this same period, and were mostly below 0.5 Mgal/d. 

Yields from Piney Point-Nanjemoy aquifer wells of over 

500 gal/min were recorded in the vicinity of NASPR (Weigle 

and others, 1970), indicating that for the entire county, the 

aquifer should be capable of a sustained withdrawal on the 

order of 0.5 Mgal/d without suffering significant drawdown.

The Aquia aquifer, on the other hand, has been pumped 

at relatively high rates for many years in St. Mary’s County, as 

shown in figure 40. The aquifer response to this ground-water 

withdrawal has been a steep decline in ground-water levels in 

observation wells near NASPR, in some cases nearly 100 ft 

over the past 30 years. Even Aquia aquifer observation wells 

located a moderate distance from the pumping centers at the 

NASPR and Lexington Park show fairly steep, steady declines 

of tens of feet in ground-water levels. It is possible that these 

deep drawdowns in the Aquia aquifer might be responsible 

for water-level declines in the overlying Piney PointNanjemoy aquifer. 

In order to investigate this possibility, hydrographs were 

constructed from water-level data in the USGS GWSI database 

for four Piney Point-Nanjemoy observation wells located in 

southern Calvert County and St. Mary’s County within the 

Aquia aquifer cone of depression at NASPR and Lexington 

Park. Although these Piney Point-Nanjemoy observation 

wells do not penetrate to the depth of the Aquia aquifer and 

no direct ground-water-level data are available, elevations of 

the ground-water surface in the Aquia aquifer were estimated 

from the Aquia potentiometric surface maps in this report 

(figs. 31–33). The hydrographs for the observation wells are 

shown in figures 41–44, and the well locations are shown 

on the Piney Point-Nanjemoy potentiometric surface map in 

figure 37. 

The Well CA Fe 22 hydrograph (fig. 41) shows a definite 

drop in the water level in the Piney Point-Nanjemoy aquifer, 

which could be related to the decline in the potentiometric 

surface of the underlying Aquia aquifer. There is no reported 

pumpage from the Piney Point-Nanjemoy aquifer in the southernmost part of Calvert County near this well, and aquifer levels may be responding to pumpage from the underlying Aquia 

aquifer. The SM Eg 27 (fig. 42) and SM Fg 45 (fig. 43) wells 

show drawdown effects similar to the CA Fe 22 well. The SM 

Df 66 well (fig. 44) shows a drawdown response until about 

1987, when it began recovering for unknown reasons. 

Figure 40. Total ground-water withdrawals reported for St. Mary’s County from the Aquia and Piney Point-Nanjemoy aquifers 

from 1980 to 2004 (Source: U.S. Geological Survey AWUDS database).
52 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 41. Ground-water-level responses in the Piney Point-Nanjemoy aquifer in 

Well CA Fe 22, and the drop in the potentiometric surface of the underlying Aquia aquifer in 

southern Calvert County, Maryland.

Figure 42. Ground-water-level responses in the Piney Point-Nanjemoy aquifer in 

Well SM Eg 27, and the drop in the potentiometric surface of the underlying Aquia aquifer in 

southern St. Mary’s County, Maryland.
Relations Between Withdrawals and Water-Level Drawdowns 53

Figure 43. Ground-water-level responses in the Piney Point-Nanjemoy aquifer in 

Well SM Fg 45, and the drop in the potentiometric surface of the underlying Aquia aquifer in 

southern St. Mary’s County, Maryland.

Figure 44. Ground-water-level responses in the Piney Point-Nanjemoy aquifer in 

Well SM Df 66, and the drop in the potentiometric surface of the underlying Aquia aquifer in 

southern St. Mary’s County, Maryland.
54 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

These hydrographs indicate a possible connection 

between the two aquifers, which could be an important 

consideration for future assessments of ground-water 

withdrawals in Southern Maryland. Current water resource 

planning often assumes that untapped aquifers are available 

as a reserve water supply for the future (Drummond, 2005). 

Drawdowns in adjacent aquifers could mean that these other 

ground-water resources might not be as readily available as 

expected, however. More definitive information on hydraulic 

connections between these aquifers is needed to better 

understand this issue. 

Linear Decline of Potentiometric Surfaces

The effect of withdrawal rate on drawdown in a hypothetical aquifer was analyzed to determine possible withdrawal 

rate scenarios that would lead to linear declines in hydraulic 

head over time, such as those commonly observed in wells in 

southern Maryland. Time-drawdown response in a perfectly 

confined aquifer under a constant pumping rate usually follows a nearly logarithmic curve mathematically defined by 

Theis (1935), with the rate of change of drawdown decreasing 

through time. 

Water withdrawn from a well is obtained from elastic 

storage within the aquifer. Initially, water will be removed 

from storage in the immediate vicinity of the well, reducing 

the hydraulic head and inducing flow toward the well. These 

reductions in hydraulic head, or drawdown, will propagate 

outward, forming a cone of depression in the potentiometric 

surface of the aquifer. At an observation well within the cone 

of depression, the rate of drawdown will be at a maximum 

initially; the rate of drawdown will decrease with time, so that 

the drawdown will eventually be approximately logarithmic 

in time.

Some examples of linear declines are shown in figure 45 

for a number of ground-water-level measurements in Southern 

Maryland wells taken from the USGS GWSI database. 

Well SM Dd 50 appears to follow the pattern predicted by 

Theis (1935), with the rate of decline decreasing significantly, 

and flattening out beginning in 1998. By comparison, the 

rate of ground-water decline in Well CA Gd 6 has actually 

increased since the mid-1980s, with the decline curve steepening. Linear declines are visible in the other two wells, where 

the hydrographs show little sign of flattening out. Well SM Ff 

36 has been nearly straight-edge linear since the late 1980s.

Figure 45. Nearly linear declines in the potentiometric surfaces over 30 years in four representative wells from Calvert 

and St. Mary’s Counties, Maryland.
Relations Between Withdrawals and Water-Level Drawdowns 55

Only a few physical phenomena can cause an aquifer 

to behave in this manner. One possibility is a steady increase 

in withdrawal from production wells to supply ever greater 

amounts of water to growing populations. Constant increases 

in pumping prevent the cone of depression in the aquifer from 

reaching stability, and water levels fall steadily. This scenario 

is partly supported by the reported water-use data in the study 

area, which generally show a gradual but continuous increase 

in ground-water withdrawals over the past 30 years to 

service growing populations (fig. 5). In Charles, Calvert and 

St. Mary’s Counties, however, there are not many big municipal suppliers, and production has changed very little for years 

in some cases, as shown in figure 38. 

Another possible explanation for the linear drawdowns in 

Southern Maryland is an increase in the number of domestic 

supply wells completed in the confined aquifers. Domestic 

withdrawal data are not reported directly to the State for wateruse compilation, unless the permit holder exceeds a threshold 

of 10,000 gal/d, which is much more water than most 

homeowners use. Domestic water use is estimated instead 

on the basis of rural population, and assumes a per capita 

withdrawal of 80 gal/d. An ongoing proliferation of domestic 

wells in rapidly developing areas could have a significant 

impact on aquifer drawdowns, while at the same time being 

undercounted due to the lag time inherent in population 

estimates (U.S. Census Bureau, 2006).

Simple numerical modeling runs provide some constraints for these scenarios. The modeling was done to see if 

the scenarios were plausible, and to investigate possible effects 

on ground-water levels from an annual increase in the number 

of small domestic wells pumping from a specific aquifer. A 

simulated aquifer of representative thickness, lateral dimensions, hydraulic properties, and boundaries was modeled under 

a variety of withdrawal patterns, ranging from constant, steady 

pumpage to withdrawals exponentially increasing through 

time. The calculated reactions of the simulated aquifer under 

these various conditions were compared to the actual groundwater-level data to see which pattern of withdrawal showed the 

closest match to the real aquifer. 

Modeling Experiment

A series of mathematical solutions to the equations for 

unsteady flow to a well were constructed to examine the effect 

of different patterns of withdrawal on the rate and shape of a 

ground-water decline curve in an observation well in a hypothetical aquifer. The goal of this exercise was to determine 

possible withdrawal rate scenarios that might lead to linear 

declines in hydraulic heads through time, similar to those 

observed in actual wells in the study area. The experiment also 

attempted to assess the sensitivity of time-drawdown response 

to natural factors such as aquifer leakage and boundaries. 

The aquifer was assumed to be homogeneous and isotropic, with all wells fully penetrating, allowing for the use of 

analytical solutions to the governing equation for a perfectly 

confined aquifer:

∂

∂

+

∂

∂ = ∂∂

2

2

h 1

r r

h

r

S

T

h

t

,

(1)

where

h is the hydraulic head in feet, 

r is radial distance in feet from the 

pumping well, 

S is the dimensionless aquifer storativity, 

T is the aquifer transmissivity in square feet 

per minute, 

and

t is time in minutes.

An analytical solution to this equation was provided by Theis 

(1935). For the case of a simple leaky aquifer, with no storage 

in the overlying aquitard, the governing equation may be 

written: 

∂

∂

+

∂

∂ − = ∂∂

2

2 2

h 1

r r

h

r

h

B

S

T

h

t

,

(2)

where

B is a function of the transmissivity of the 

aquifer and the hydraulic conductivity 

and thickness of the aquitard (B2 = Tba/Ka, 

where ba is the aquitard thickness, and Ka

is the aquitard hydraulic conductivity).

Analytical solutions to this form of the equation were provided 

by Hantush (1956) and Hantush and Jacob (1955).

The analytical solutions to these governing equations 

were coded in MATLAB modeling software, based on the 

work of Fleming and others (2002). Multiple wells, variable 

withdrawal rates, and for some cases, an imposed constanthead or no-flow boundary condition were handled through the 

principle of superposition of solutions and the use of image 

wells (Freeze and Cherry, 1979). 

The hypothetical aquifer modeled for this exercise was 

of constant thickness (100 ft) and transmissivity was set at 

1,000 ft2/day (square feet per day). The values used for these 

properties are based on reported ranges for the confined 

aquifers of southern Maryland (Fleck and Vroblesky, 1996). 

For the scenarios involving a leaky aquifer, the aquitard 

thickness and transmissivity also were constant (100 ft 

and 0.001 ft2/day, respectively). Hydraulic heads were 

calculated on a 20-mi by 20-mi gridded area equivalent to 

400 mi2 (square miles). Additionally, hydraulic heads were 

calculated as a function of time for approximately 22.8 years 

(12,000,000 minutes) at an observation well in the center of 

the hypothetical aquifer at coordinate position 0,0 as shown 

for the conceptual design in figure 46. Additional scenarios 

invoked a constant-head or no-flow boundary on the eastern 

side of the aquifer.
56 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

In addition to the natural factors of boundaries and 

aquifer leakage, scenarios were constructed under a variety of 

withdrawal rate patterns:

1. Constant withdrawal rate through time,

2. Linearly increasing withdrawal rate through time, and

3. An exponentially increasing withdrawal rate through time.

The withdrawal rates were determined in such a manner 

that the total volume of water withdrawn was the same in all 

cases. Finally, scenarios were constructed for the case of a 

single pumping well 5 mi west of the observation well, and 

for the case of 1,000 wells randomly distributed throughout 

the modeled region. The withdrawal rate patterns used in the 

modeling are shown in figure 47, and equate to an average 

pumping rate for each of the 1,000 wells of approximately 

215 gal/d. 

For the case of a single pumping well in a perfectly confined aquifer without boundaries, drawdown at the observation 

well depends strongly on the pattern of withdrawal, as shown 

graphically in figure 48. For the cases of non-constant withdrawal rates, drawdown is not asymptotic, but resembles the 

inverse of the withdrawal rates shown in figure 47. 

Time-drawdown response in the case of linearly increasing withdrawal rates is very nearly linear, and in the case of an 

exponentially increasing withdrawal rate, the rate of decline in 

hydraulic head increases with time. This finding has important 

implications for ground-water resource management, as well 

as for understanding historical well hydrographs. Although 

it is not unexpected that a transient stress (such as a variable 

withdrawal rate) would result in a transient response, it is 

worth emphasizing that ground-water levels in confined aquifers will continue to decline unless withdrawal rates are either 

reduced or held constant. This leads to the supposition that the 

nearly linear time-drawdown pattern observed for many wells 

in Southern Maryland (fig. 45) could be the result of a nearly 

linear increase in the rate of ground-water withdrawn 

(fig. 5) to supply growing populations (fig. 7). More precise 

data on human populations and water-supply options, as well 

as a more rigorous handling of the statistics, may be helpful in 

the future to clarify the relations and processes involved.

The case described above relies on numerous simplifying 

assumptions—a single pumping well in a homogeneous, isotropic, perfectly confined aquifer of infinite extent. Additional 

scenarios were calculated under somewhat more realistic 

assumptions, such as using multiple wells with variable pumping times, incorporating a leaky aquitard, and imposing boundary conditions on one side of the aquifer (fig. 46). Figure 46. The modified hypothetical (A) aquifer, and (B) aquiferaquitard.

Figure 47. Withdrawal rates used for generation of drawdown 

scenarios.
Relations Between Withdrawals and Water-Level Drawdowns 57

The multiple-well scenarios were run several different 

ways. In all scenarios, 1,000 wells were distributed randomly 

throughout the modeled region. For the case of a constant 

withdrawal rate, all “pumps” were activated at time zero, and 

withdrawal proceeded at a constant rate for the duration of the 

run (22.8 years). In cases where the ground-water withdrawal 

rate has gradually increased, new wells were added to the 

aquifer sequentially through time until the total of 1,000 was 

reached. To provide a linearly increasing total withdrawal rate, 

each well was pumped at a constant rate from its “completion” 

date to the end of the model run. For an exponentially increasing total withdrawal rate, the pumping rates were increased 

slightly for each successive well added to the scenario. 

Modeling Results

Adding multiple wells creates a general decline in the 

potentiometric surface (fig. 49), with the largest drawdown 

near the center, due to overlapping (superposition) of each 

well’s individual cone of depression. The calculated timedrawdown response at the “observation well” shown in 

figure 50 is similar to the case of a single pumping well. In 

the constant withdrawal scenario, multiple pumping wells, 

all “completed” at time zero and with the same pumping rate, 

produce a time-drawdown response that resembles a Theis 

curve. For the case of a linearly increasing withdrawal rate, 

the time-drawdown pattern is nearly linear. Lastly, an exponentially increasing withdrawal rate produces a pattern of 

increasing rate of decline in hydraulic head with time at the 

observation well. 

As a well is pumped, water is removed from storage 

and the hydraulic head (and, therefore, fluid pressure) are 

reduced; the decrease in hydraulic head expands laterally to 

create a cone of depression in the potentiometric surface. Also, 

vertical hydraulic gradients are created within the area of the 

cone of depression between the aquifer and the overlying (and 

underlying) aquitard(s), creating the possibility of leakage 

across the confining unit(s). This leakage can be substantial, 

and obviously depends in part on the transmissivity of the 

aquitard. Leakage has been shown to be important in the 

confined aquifers in southern Maryland (Fleck and Vroblesky, 

1996). Time-drawdown response near pumping wells in leaky 

aquifers resembles the Theis curve; however, because leakage provides an additional source of water, the drawdown will 

reach equilibrium more quickly as the leakage balances the 

rate of pumping. Drawdown of leaky aquifers will generally 

be less than if the aquifer was perfectly confined.

For the case of multiple wells in a leaky aquifer, the 

time-drawdown response calculated for the observation 

well under the three different withdrawal rate patterns is 

shown in figure 51. As expected, the drawdown is less than 

for the perfectly confined case under all three withdrawal 

rate scenarios. A constant withdrawal rate produces a timedrawdown response very typical of leaky aquifers, equilibrating at approximately 3 ft of drawdown after 10–15 years of 

pumping. Linearly and exponentially increasing withdrawal 

rates produce linear and increasing-with-time time-drawdown 

responses, respectively.

Aquifers are never truly unbounded, and it is very likely 

that an aquifer experiencing withdrawals on the spatial and 

temporal scale used for this exercise would display timedrawdown response indicating the presence of one or more 

boundaries. A no-flow boundary may be present where the 

aquifer pinches out or is truncated by a less permeable unit. 

A constant-head boundary may be present where an aquifer 

is in direct contact with a surface-water body. More complex 

boundary conditions are also likely, and the relative distance 

between the region of interest and the boundary should be considered in any analysis.

For this exercise, both no-flow and constant-head boundaries were imposed at the eastern end of the model domain, to 

determine their possible effects on time-drawdown response in 

the aquifer. Conceptually, a no-flow boundary reduces the part 

of the aquifer available to supply water to the well; as a result, 

more water must be withdrawn from the aquifer between the 

pumping well and the boundary, and drawdown will generally be greater. Conversely, a constant-head boundary may be 

thought of as an unlimited source of water; drawdown will 

generally be less (and in fact, will be zero at the boundary 

itself). In either case, the cone of depression around a pumped 

well will not be radially symmetric. Characteristics for the two 

different boundary conditions are shown in figure 52.

The calculated time-drawdown response at the 

observation well under the three withdrawal rate patterns is 

shown in figure 53. The general observations made in regard 

to the scenarios discussed earlier apply to these cases as well. 

Figure 48. Time-drawdown patterns calculated for a single 

pumping well in a perfectly confined, unbounded aquifer 

under three different withdrawal rate patterns.
58 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Figure 49. Drawdown in the potentiometric surface for the scenario with multiple wells under a constant withdrawal 

rate at time t = 22.8 years.

Figure 50. Time-drawdown patterns calculated for multiple 

pumping wells in a perfectly confined, unbounded aquifer 

under three different withdrawal rate patterns.

Figure 51. Time-drawdown patterns calculated for multiple 

pumping wells in a leaky, unbounded aquifer under three 

different withdrawal rate patterns.
Relations Between Withdrawals and Water-Level Drawdowns 59

Figure 52. Drawdown in the potentiometric surfaces for the scenarios with multiple wells under a constant withdrawal 

rate at time t = 22.8 years and with (A) no-flow, and (B) constant-head boundaries imposed at one edge of the modeled 

region (eastern side).
60 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

A constant withdrawal rate produces Theis-curve response 

in the case of a no-flow boundary, and an asymptotic timedrawdown response in the case of a constant-head boundary. 

Under either boundary condition scenario, linearly increasing 

withdrawal leads to a nearly linear time-drawdown response, 

and an exponential increase in withdrawal leads to a timedrawdown response in which the rate of change of drawdown 

increases with time. This analysis also provides a possible 

explanation for some nonlinear well hydrographs.

In summary, linear declines in the hydraulic head of a 

well, as observed in many of the regularly measured aquifer 

observation wells in the confined aquifers of Southern Maryland, are probably the result of linearly increasing rates of 

withdrawal. This conclusion holds for single or multiple wells, 

under leaky or perfectly confined aquifer conditions, and 

regardless of the presence or absence of no-flow or constanthead boundaries. 

The exact mechanism of this withdrawal is unclear, but 

is probably due to increased pumpage from large supply 

wells, which is supported at least in part by the water-use data, 

and (or) by increased numbers of domestic wells, which are 

mostly estimated and not actually counted. Most likely, it is a 

combination of both factors. Obtaining more precise numbers 

on the rates of withdrawal from confined aquifers by both public and domestic wells is critically important for better management of the aquifer resource. Large numbers of domestic 

wells withdrawing from the same aquifer may be responsible 

for greater aquifer drawdowns than expected in areas of Southern Maryland with significant suburban residential development, such as Charles, Calvert and St. Mary’s Counties.

Summary and Conclusions

The major findings of this report and conclusions from 

the investigation are summarized as follows:

Ground water has been and will continue to be an important source of supply in Southern Maryland and throughout the 

Atlantic Coastal Plain. Reported withdrawals in the Southern 

Maryland and Eastern Shore study area have increased from 

about 42 to nearly 65 million gallons per day from the early 

1980s through 2005. This represents an increase of more than 

50 percent, which can be projected to continue as populations 

grow. Additional sources of water will be needed to meet 

future demands. 

The hydrogeologic framework of the Coastal Plain sediments is complex. Interpretations of the geology have evolved 

over time through different authors, and have often been 

made only sporadically for specific, small study areas. The 

Cretaceous-age, stratigraphically lower aquifers in the study 

area, consisting of the Patuxent, lower Patapsco, and upper 

Patapsco aquifers within the Potomac Group, are composed 

of complex sequences of fluvial and deltaic sands, silts, and 

clays, with hydrologic properties that may differ greatly across 

short expanses. These units are generally difficult to correlate 

over any distance, and prediction of the aquifer properties at 

any particular location is problematic. The stratigraphically 

higher aquifers, including the Magothy, Tertiary-age Aquia, 

and Piney Point-Nanjemoy aquifers, are coastal marine, continental shelf, and estuarine deposits with aquifer properties that 

tend to change in a more uniform, predictable manner.

The sensitivity of an aquifer to drawdown is related 

both to withdrawal rates and to the aquifer’s hydraulic and 

hydrologic properties. Many, if not most, of the confined 

aquifers in the Coastal Plain have hydrologic properties that 

vary with lithologic facies, depth, or other geological factors. 

Hydraulic conductivity, in particular, appears to be a function 

Figure 53. Time-drawdown patterns calculated for multiple 

pumping wells in an aquifer under three different withdrawal 

rate patterns and with (A) no-flow, and (B) constant-head 

boundaries imposed at the eastern end of the modeled region.
References Cited 61

of lithologic facies. Withdrawal of water from an aquifer with 

relatively high transmissivity results in less drawdown near the 

pumping well than does a similar withdrawal from an aquifer 

with relatively low transmissivity. An improved understanding of the relation between aquifer properties and geological 

factors may lead to better predictability and management of 

ground-water resources in Southern Maryland and the adjacent 

Eastern Shore.

Although there are exceptions, as a general rule, water 

levels in the confined aquifers of the Southern Maryland 

study area have been decreasing since about 1980. The rates 

of decline vary by location, but result in cones of depression in the potentiometric surfaces for some aquifers in some 

locations. These cones of depression are usually centered on 

large pumping centers within an aquifer; however, evidence 

indicates that deep declines caused by ground-water withdrawals can affect adjacent aquifers. 

Water withdrawals by domestic well users appear to be 

a significant factor in overall aquifer water-level drawdowns 

in Southern Maryland. The linear drop in some observation 

well hydrographs is best explained by annual increases in the 

total amount of water withdrawn from the aquifer. Modeling 

experiments indicated that linear declines in the hydraulic 

head of a well, such as those observed in many observation 

wells in the confined aquifers of Southern Maryland, are probably the result of linearly increasing rates of withdrawal. This 

conclusion holds for single or multiple wells, under leaky or 

perfectly confined aquifer conditions, and regardless of the 

presence or absence of no-flow or constant-head boundaries. 

Reported withdrawals, however, generally have not increased 

at a rate sufficient to explain the declines. The most plausible 

explanation for the behavior of the aquifer is that additional 

withdrawals are from unreported, domestic-use wells. Obtaining more accurate data on the numbers and rates of pumping 

from domestic wells could provide a better understanding of 

aquifer response. 

Acknowledgments

The authors would like to express thanks to our USGS 

and MGS colleagues for their help and contributions. David 

Bolton, David Drummond, and especially David Andreasen of 

MGS helped clarify the geologic framework, aquifer-naming 

conventions, and ground-water withdrawal locations in this 

report. Harry Hansen, retired from MGS, kindly reviewed 

the section on Coastal Plain geology and stratigraphy. 

Potentiometric surface maps of the study area from previous 

years were provided by Stephen Curtin of the USGS, who also 

supplied helpful advice and suggestions. Wendy McPherson 

of the USGS extracted the MDE water-use data from the 

SWUDS database, and provided a written description of how 

it is gathered and processed. Nancy Stamm of the USGS 

provided helpful comments on the use of the geologic names 

database. Cheryl Klohe and Douglas Yeskis of the USGS 

supplied additional background materials, and Johnesha 

Inham, a USGS intern, helped to sort and organize the waterlevel data from hundreds of wells. Timothy Auer of the USGS 

superbly rendered all of the figures, graphs, and maps into 

USGS format, Valerie Gaine provided a careful edit, and 

Andrew LaMotte provided GIS support. 

Finally, the authors thank Stephen Curtin and David 

Andreasen for thorough and thoughtful technical reviews of 

the manuscript, and Chester Zenone for providing useful comments and clarifications in the final review. Their suggestions 

greatly improved the report. 

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Appendixes 1–3
66 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Appendix 1. Bibliography of U.S. Geological Survey Southern Maryland 

Potentiometric Surface Maps: 1980, 1985, 1990, 1995, and 2000

Information on historical maps is provided for comparison with the maps included in this report. Citation format 

is that of the USGS Library, and includes library call number and accessibility options.

1980

Aquia

U.S. Geological Survey Open-File Report 81–416 (1981): Map showing the potentiometric surface of the 

Aquia aquifer, May 19–23, 1980.

Authors: Chapelle, Frank; Drummond, Dave; Curley, Tracey

USGS Library Call Number: M(200) R29o no.81-416

Access: Library (paper copy) only.

Magothy

U.S. Geological Survey Open-File Report 81–633 (1981): Map showing the potentiometric surface of the 

Magothy aquifer in Southern Maryland, August 1980.

Authors: Mack, F.K.; Wheeler, J.C.; Curtin, S.E.

USGS Library Call Number: (200) R29o no.81-633

Access: Library (paper copy) only.

(Note: Patapsco maps not published before 1990; Aquia and Magothy maps only.)

1985

Aquia

U.S. Geological Survey Water-Resources Investigations Report 87–4029 (1987): The potentiometric 

surface of the Aquia aquifer in Southern Maryland, September 1985.

Authors: Mack, F.K.; Wheeler, J.C.; Curtin, S.E.; Andreasen, D.C.

USGS Library Call Number: (200) WRi no.87-4029

Access: Library (paper copy) only.

Magothy

U.S. Geological Survey Water-Resources Investigations Report 87–4025 (1987): The potentiometric 

surface of the Magothy aquifer in Southern Maryland, September 1985.

Authors: Mack, F.K.; Wheeler, J.C.; Curtin, S.E.; Andreasen, D.C.

USGS Library Call Number: (200) WRi no.87-4025

Access: Electronic image available.

(Note: Patapsco maps not published before 1990; Aquia and Magothy maps only.)
Appendix 1 67

1990

Aquia

U.S. Geological Survey Open-File Report 92–459 (1992): Potentiometric surface of the Aquia aquifer in 

Southern Maryland, September 1990.

Authors: Mack, F.K.; Curtin, S.E.; Andreasen, D.C.; Wheeler, J.C.

USGS Library Call Number: M(200) R29o no.92-459 

Access: Electronic image available.

Magothy

U.S. Geological Survey Open-File Report 92–460 (1992): Potentiometric surface of the Magothy aquifer 

in Southern Maryland, September 1990.

Authors: Mack, F.K.; Curtin, S.E.; Andreasen, D.C.; Wheeler, J.C.

USGS Library Call Number: M(200) R29o no.92-460

Access: Electronic image available.

Upper Patapsco

U.S. Geological Survey Open-File Report 92–461 (1992): Potentiometric surface of the upper Patapsco 

aquifer in Southern Maryland, September 1990.

Authors: Mack, F.K.; Curtin, S.E.; Andreasen, D.C.; Wheeler, J.C.

USGS Library Call Number: M(200) R29o no.92-461

Access: Electronic image available.

Lower Patapsco

U.S. Geological Survey Open-File Report 92–462 (1992): Potentiometric surface of the lower Patapsco 

aquifer in Southern Maryland, September 1990.

Authors: Mack, F.K.; Curtin, S.E.; Andreasen, D.C.; Wheeler, J.C.

USGS Library Call Number: M(200) R29o no.92-462

Access: Electronic image available.
68 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

1995

Aquia

U.S. Geological Survey Open-File Report 96–620 (1997): Potentiometric surface of the Aquia aquifer in 

Southern Maryland, September 1995.

Authors: Curtin, S.E.; Andreasen, D.C.; Mack, F.K.

USGS Library Call Number: (200) R29o no.96-620

Access: Electronic image available.

Magothy

U.S. Geological Survey Open-File Report 96–621 (1996): Potentiometric surface of the Magothy aquifer 

in Southern Maryland, September 1995.

Authors: Curtin, S.E.; Andreasen, D.C.; Mack, F.K.

USGS Library Call Number: (200) R29o no.96-621

Access: Electronic image available.

Upper Patapsco

U.S. Geological Survey Open-File Report 96–622 (1996): Potentiometric surface of the upper Patapsco 

aquifer in Southern Maryland, September 1995.

Authors: Curtin, S.E.; Andreasen, D.C.; Mack, F.K.

USGS Library Call Number: (200) R29o no.96-622

Access: Electronic image available.

Lower Patapsco

U.S. Geological Survey Open-File Report 96–623 (1996): Potentiometric surface of the lower Patapsco 

aquifer in Southern Maryland, September 1995.

Authors: Curtin, S.E.; Andreasen, D.C.; Mack, F.K.

USGS Library Call Number: (200) R29o no.96-623

Access: Electronic image available.
Appendix 1 69

2000

Aquia

U.S. Geological Survey Open-File Report 02–244 (2002): Potentiometric surface of the Aquia aquifer in 

Southern Maryland, September 2000.

Authors: Curtin, S.E.; Andreasen, D.C.; Wheeler, J.C.

USGS Library Call Number: M(200) R29o no.2002-244

Access: Electronic image available.

Magothy

U.S. Geological Survey Open-File Report 02–245 (2002): Potentiometric surface of the Magothy aquifer 

in Southern Maryland, September 2000.

Authors: Curtin, S.E.; Andreasen, D.C.; Wheeler, J.C.

USGS Library Call Number: M(200) R29o no.2002-245

Access: Electronic image available.

Upper Patapsco

U.S. Geological Survey Open-File Report 02–246 (2002): Potentiometric surface of the upper Patapsco 

aquifer in Southern Maryland, September 2000.

Authors: Curtin, S.E.; Andreasen, D.C.; Wheeler, J.C.

USGS Library Call Number: M(200) R29o no.2002-246

Access: Electronic image available.

Lower Patapsco

U.S. Geological Survey Open-File Report 02–247 (2002): Potentiometric surface of the lower Patapsco 

aquifer in Southern Maryland, September 2000.

Authors: Curtin, S.E.; Andreasen, D.C.; Wheeler, J.C.

USGS Library Call Number: M(200) R29o no.2002-247

Access: Electronic image available.
70 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Appendix 2. Access to U.S. Geological Survey Water Data

Water data from the U.S. Geological Survey can be accessed online via the National Water Information System 

(NWIS), by following the step-by-step instructions below.

1. Start by visiting the USGS water data page at http://waterdata.usgs.gov/nwis.

2. In the box at the upper right, select the data category of interest (for example, ground water).

3. In the adjacent box, select the geographic area of interest (for example, Maryland). This will bring up the 

local data and site-selection page.

4. To access real-time ground-water data, select the “real time data” button. Please be aware that locations 

providing real-time ground-water data are limited. Select “field water-level measurements” to access the 

standard, manual, periodic ground-water-level measurements for individual wells. 

5. This will bring up a site-selection criteria menu page. Multiple sites can be selected by number, name, aquifer, or other attributes on this menu. Select the search criteria, click the submit button, and enter the values 

for the selection criteria on the next menu. Selecting by latitude/longitude box, county, or aquifer code 

will likely return a large number of sites, many of which may be project wells with only one measurement. 

Select the “number of measurements” box and increase the value to 10 or 12 to eliminate single-measurement wells. 

6. If the USGS site ID number is known, check only the box marked “site number” on the site-selection criteria menu page and click submit. Enter the FULL number of the site ID in the box on the next menu page—

including all the zeros, and click the submit button.

7. Click the desired sites on the site list. The individual web page will come up, showing the data graphically 

in a hydrograph. If tabular data (numbers) are desired instead, select “Table of Data” under the box marked 

“output format” on the data page. The time span of the retrieval can also be changed by using the “reselect 

period” button and specifying different starting and ending dates. Ground-water-level data can be retrieved 

up to and including the most recent measurement entered into the database. All data for the current water 

year are considered provisional, however, and may be subjected to review and changes until published in the 

annual data report. These instructions were successfully executed in 2007 by D. Soeder.
Appendix 3 71

Appendix 3. Southern Maryland ground-water-level data used in this report.—Continued

[All depth and elevation measurements are in feet. Land and water elevations are measured from the National Geodetic Vertical Datum of 1929 

(NGVD29). Digital latitude and longitude measured with respect to North American Datum 1983 (NAD83); --, no data]

Well name USGS ID

Location NAD83 Land 

elevation

Water levels in feet relative to NGVD29

Latitude Longitude 2005 2000 1995 1990 1985 1980

Aquia aquifer

AA Cf 122 390149076261702 39.03038890 -76.43773750 20.0 1.40 2.60 2.10 3.10 2.40 2.90

AA Cg 25 390127076240301 39.02427797 -76.40051418 17.3 0.94 1.59 1.33 1.05 0.40 --

AA De 102 385512076331602 38.92011310 -76.55412800 49.6 9.66 9.17 7.93 9.81 8.99 10.59

AA De 137 385930076342102 38.99177795 -76.57218569 133.6 -- -- 33.79 32.94 36.18 --

AA De 173 385628076323101 38.94122380 -76.54162799 34.0 -- 2.04 1.17 -- -- --

AA Df 98 385550076292101 38.93066879 -76.48884808 11.3 1.90 1.92 1.32 1.72 -- --

AA Df 103 385623076274401 38.93983528 -76.46190312 26.5 -- 24.09 21.64 23.03 -- --

AA Ed 45 385406076383901 38.90177960 -76.64385339 110.0 40.35 39.90 39.40 41.89 43.05 45.12

AA Ed 49 385249076382101 38.88039125 -76.63885290 60.0 20.86 21.74 20.61 24.35 25.25 29.83

AA Ee 67 385124076322001 38.85678145 -76.53857026 11.2 -8.55 -6.29 -7.56 -3.46 -2.81 0.08

AA Ef 17 385318076294501 38.88844763 -76.49551374 20.2 -- 4.10 1.17 1.90 -0.40 2.79

AA Fd 43 384646076352401 38.77956066 -76.58968223 150.0 -- -19.38 -18.71 -9.19 -2.73 3.36

AA Fd 46 384727076382501 38.79094883 -76.63996286 140.3 -17.81 -11.46 -11.19 -4.14 -0.60 9.20

AA Fe 46 384840076312801 38.81122714 -76.52412398 8.5 -23.17 -18.67 -20.89 -12.27 -7.72 -3.97

AA Fe 48 384508076334101 38.75233936 -76.56106899 85.0 -33.26 -27.10 -24.56 -14.40 -7.12 2.22

AA Fe 60 384917076305802 38.82150473 -76.51579051 8.5 -19.08 -14.68 -- -- -- --

AA Fe 92 384644076331201 38.77900546 -76.55301359 9.0 -33.92 -26.53 -- -- -- --

CA Ba 11 384357076401601 38.73261660 -76.67079721 115.3 -40.40 -27.47 -26.49 -14.93 -8.15 -4.61

CA Ba 13 384231076412501 38.70872819 -76.68996469 56.0 -37.41 -27.63 -23.60 -13.25 -4.80 8.59

CA Bb 27 384333076394701 38.72595018 -76.66274113 137.9 -44.30 -32.28 -30.48 -18.03 -9.59 0.94

CA Bb 33 384222076380101 38.70622871 -76.63329482 110.6 -47.64 -35.45 -- -19.47 -7.45 3.68

CA Bc 25 384114076320301 38.68734102 -76.53384467 17.8 -17.85 -26.74 -37.28 -- -- --

CA Bc 32 384238076340301 38.71067358 -76.56718005 129.3 -- -- -35.71 -21.58 -12.68 -2.68

CA Bc 44 384243076320201 38.71206271 -76.53356707 7.6 -45.32 -40.20 -36.07 -- -- --

CA Ca 12 383737076401601 38.62706385 -76.67079606 53.9 -43.36 -34.23 -27.00 -17.54 -9.21 3.27

CA Cb 26 383837076381001 38.64373027 -76.63579433 115.3 -51.34 -38.97 -30.69 -18.46 -8.96 4.33

CA Cb 32 383632076392701 38.60900883 -76.65718402 95.2 -57.35 -45.30 -36.01 -23.60 -14.52 -0.38

CA Cb 37 383501076362001 38.58373188 -76.60523653 23.8 -- -- -36.54 -24.52 -14.48 -2.88

CA Cc 18 383940076314801 38.66123049 -76.52967756 111.3 -48.61 -39.48 -31.95 -21.67 -14.39 -6.39

CA Cc 39 383934076320202 38.65956383 -76.53356665 93.7 -- -39.86 -32.64 -22.23 -14.77 -6.29

CA Cc 57 383605076344601 38.60150933 -76.57912418 138.6 -55.83 -45.20 -34.52 -22.72 -13.69 -4.97

CA Cc 58 383924076341201 38.65678589 -76.56967972 122.5 -49.35 -38.75 -30.80 -19.40 -10.65 2.10

CA Db 40 383053076382101 38.51484463 -76.63884873 23.4 -66.88 -56.12 -44.26 -28.45 -25.91 -7.42

CA Db 47 383239076354201 38.54428840 -76.59468004 140.4 -68.07 -56.48 -44.20 -31.20 -20.97 -12.40

CA Dc 29 383025076304701 38.50706708 -76.51273101 123.1 -63.93 -56.98 -43.33 -27.49 -18.81 -8.59
72 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Appendix 3. Southern Maryland ground-water-level data used in this report.—Continued

[All depth and elevation measurements are in feet. Land and water elevations are measured from the National Geodetic Vertical Datum of 1929 

(NGVD29). Digital latitude and longitude measured with respect to North American Datum 1983 (NAD83); --, no data]

Well name USGS ID

Location NAD83 Land 

elevation

Water levels in feet relative to NGVD29

Latitude Longitude 2005 2000 1995 1990 1985 1980

Aquia aquifer—Continued

CA Ed 42 382528076280701 38.43123443 -76.46300729 121.7 -90.69 -82.19 -69.77 -39.10 -34.84 --

CA Ed 52 382549076260101 38.43040093 -76.43328409 10.0 -99.59 -98.26 -86.27 -- -- --

CA Fd 54 382407076260301 38.40206788 -76.43383978 129.4 -106.72 -95.86 -80.51 -47.45 -35.45 -24.33

CA Fd 68 382128076271301 38.35790179 -76.45328509 90.4 -- -- -106.94 -71.13 -41.39 --

CA Fd 69 382015076271501 38.33762422 -76.45384076 21.0 -- -141.11 -113.06 -84.16 -48.30 --

CA Fd 70 382155076254502 38.36540155 -76.42883974 108.5 -142.42 -122.90 -101.05 -68.82 -39.50 --

CA Fe 19 382316076243201 38.38790120 -76.40856118 113.4 -- -100.05 -83.51 -53.88 -41.68 -25.38

CA Fe 20 382325076245601 38.39040122 -76.41522807 114.5 -- -102.61 -84.09 -50.92 -34.99 -25.33

CA Fe 30 382134076233301 38.35956803 -76.39217179 118.8 -120.17 -- -89.75 -61.67 -- --

CA Gd 6 381952076270901 38.33123539 -76.45217406 12.7 -151.91 -132.37 -111.62 -85.44 -49.91 -42.93

CH Bg 11 383536076473601 38.59345318 -76.79302354 196.8 -40.86 -33.11 -23.49 -10.92 -3.03 21.63

CH Ce 41 382225076591002 38.54039844 -76.98580733 194.2 -25.12 -20.88 -16.75 -- -- --

CH Cg 20 383251076480001 38.54762118 -76.79968993 181.6 -54.75 -43.49 -33.37 -20.50 -12.50 -2.28

CH Cg 21 383009076481201 38.50262250 -76.80302290 184.2 -64.50 -50.16 -40.00 -17.28 -13.76 5.72

CH Ch 15 383043076404501 38.51206691 -76.67885078 9.8 -63.70 -53.90 -42.69 -28.29 -17.75 -3.68

CH Df 17 382800076530301 38.46678988 -76.88385908 161.0 -61.80 -45.63 -36.67 -21.07 -9.73 10.65

CH Ff 59 381639076523201 38.27762869 -76.87524772 8.0 -39.99 -31.88 -23.36 -15.86 -8.75 -1.39

DO Db18 382807076175801 38.46873317 -76.29911305 1.5 -- -55.54 -44.12 -29.23 -- --

DO Db19 382847076190901 38.47984429 -76.31883590 1.5 -66.26 -57.01 -45.64 -31.43 -- --

KE Cd 44 391432076015501 39.24233150 -76.03161140 50.0 13.82 8.75 10.41 7.25 2.79 3.94

KE Dc 91 390626076083302 39.10733302 -76.14217115 4.6 0.98 0.65 -0.02 -- -- --

PG Hf 35 383228076410601 38.54123278 -76.68468474 11.2 -61.84 -50.46 -39.28 -25.04 -- --

PG Hf 42 383348076411303 38.56345439 -76.68662954 27.8 -59.21 -47.65 -36.89 -23.42 -- --

QA Bc 17 391203076024303 39.20094315 -76.04494493 25.0 11.60 14.95 13.00 14.90 14.82 --

QA Db32 390201076182703 39.03372248 -76.30717813 18.0 1.17 1.77 1.13 0.92 1.08 --

QA Db35 390119076191001 39.02205595 -76.31912290 7.5 1.55 2.09 1.10 0.88 1.51 --

QA Db37 390023076174302 39.00650065 -76.29495549 7.1 -1.25 -0.27 -1.32 -1.88 -1.19 --

QA De27 390251076034401 39.04761175 -76.06188876 10.2 -18.24 -8.85 -- -- -- --

QA Ea78 385718076211502 38.95511290 -76.35384487 11.8 -1.54 -0.76 -1.23 -1.79 -0.41 --

QA Ea80 385757076200102 38.96594599 -76.33328901 8.5 -3.03 -1.82 -2.56 -2.77 -1.95 --

QA Eb 113 385748076172001 38.96344615 -76.28856540 11.3 -8.83 -7.46 -8.03 -6.66 -5.76 --

QA Eb 155 385843076155302 38.97872357 -76.26439846 3.9 -7.64 -6.07 -7.08 -5.80 -4.37 --

QA Eb 156 385852076195201 38.98122338 -76.33078935 12.0 -2.74 -1.48 -2.08 -2.14 -1.20 --

QA Fc 7 385429076120201 38.90816973 -76.20022712 10.0 -25.84 -19.61 -23.18 -17.79 -14.84 -10.54

SM Bb 15 382838076470101 38.4773455 -76.78330006 165.40 -69.66 -54.69 -42.79 -27.33 -13.46 1.96
Appendix 3 73

Appendix 3. Southern Maryland ground-water-level data used in this report.—Continued

[All depth and elevation measurements are in feet. Land and water elevations are measured from the National Geodetic Vertical Datum of 1929 

(NGVD29). Digital latitude and longitude measured with respect to North American Datum 1983 (NAD83); --, no data]

Well name USGS ID

Location NAD83 Land 

elevation

Water levels in feet relative to NGVD29

Latitude Longitude 2005 2000 1995 1990 1985 1980

Aquia aquifer—Continued

SM Ca 6 382248076500101 38.38012583 -76.83330201 143.85 -55.77 -44.10 -33.98 -22.28 -10.87 3.10

SM Cc 8 382235076435801 38.37651487 -76.73246535 128.85 -63.00 -50.25 -39.03 -23.96 -12.88 --

SM Cc 22 382055076404601 38.34873729 -76.67912944 133 -64.29 -51.87 -38.68 -26.49 -15.89 -4.40

SM Ce 38 382222076304602 38.3395691 -76.51245419 15.92 -127.25 -111.00 -85.78 -81.17 -56.12 -28.18

SM Dc 42 381648076421801 38.28012808 -76.70468677 13.5 -67.40 -55.33 -45.97 -34.00 -23.95 --

SM Dc 59 381807076442801 38.30207246 -76.74079961 40.89 -58.03 -46.37 -36.81 -25.95 -16.21 -13.41

SM Dd 01 381745076381201 38.29596013 -76.63634979 93.28 -91.50 -71.22 -63.34 -47.47 -30.01 -21.72

SM Dd 44 381557076395701 38.26596116 -76.66551817 31 -64.45 -67.42 -55.18 -45.90 -31.73 -16.40

SM Dd 47 381537076384601 38.26040542 -76.64579495 10 -79.83 -65.38 -56.18 -44.49 -33.49 -20.27

SM Dd 49 381616076364702 38.27123805 -76.6127376 118.94 -90.71 -71.95 -62.59 -46.52 -34.98 -27.70

SM Dd 50 381807076380001 38.30207108 -76.63301624 99.4 -82.91 -75.91 -62.86 -47.49 -37.06 -30.06

SM Df 01 381552076265001 38.26484714 -76.44689638 93.35 -140.69 -144.75 -113.04 -106.94 -71.65 --

SM Df 10 381715076261601 38.28679129 -76.438007 46 -146.02 -137.75 -115.4 -- -51.15 --

SM Df 42 381537076272401 38.26040281 -76.45634121 86.5 -165.14 -149.14 -125.87 -106.81 -71.56 -43.50

SM Df 61 381604076271701 38.26818049 -76.4532855 108.86 -153.99 -181.19 -124.41 -95.10 -70.93 --

SM Df 71 381527076283101 38.25762522 -76.47495307 69.15 -147.70 -134.08 -114.73 -94.29 -62.31 -59.15

SM Df 80 381532076250101 38.25901362 -76.41661743 42 -137.90 -122.35 -99.67 -81.87 -54.30 -53.10

SM Df 86 381548076272103 38.26345833 -76.45550783 112.09 -164.40 -149.35 -125.71 -106.25 -81.62 -67.43

SM Df 95 381617076263201 38.27151369 -76.44134058 80 -149.8 -137.46 -118 -- -- --

SM Df 96 381724076253901 38.29012451 -76.42717329 9 -146 -135.17 -109.53 -- -- --

SM Df 98 381634076270501 38.27623594 -76.4510632 80.46 -145.15 -147.95 -183.19 -- -- --

SM Dg 5 381805076225701 38.30067962 -76.38244934 21.4 -73.15 -117.75 -84.59 -67.67 -44.80 -42.05

SM Dg 10 381555076244801 38.26540242 -76.41300616 22 -142.25 -127.32 -104.09 -77.12 -57.54 -44.21

SM Dg 14 381813076232501 38.30317966 -76.39050519 19 -135.65 -121.75 -95.46 -- -- --

SM Dg 16 381624076235601 38.27234668 -76.39856113 11.15 -138.82 -125.3 -106.85 -- -- --

SM Dg 18 381607076241401 38.26956896 -76.402728 18 -134.35 -119.56 -103.5 -- -- --

SM Dg 19 381747076223901 38.29623517 -76.376338 10 -129.55 -116.35 -100.39 -- -- --

SM Fe 31 380834076303402 38.14290512 -76.50912114 8 -79.14 -73.05 -62.02 -44.79 -29.74 -26.46

SM Ff 64 380821076255501 38.13929316 -76.43161793 10 -87.2 -86.02 -76.64 -- -- --

TA Cc 50 384707076133202 38.78567286 -76.22661425 8 -39.2 -31.82 -33.05 -- -- --

Magothy aquifer

AA Cc 95 390247076403501 39.04649876 -76.67607829 131.09 88.99 84.23 85.48 87.91 86.71 92.32

AA Cc 117 390103076402603 39.01761031 -76.67357794 134.14 50.48 48.67 48.88 51.78 53.24 56.34

AA Cd 12 390124076361202 39.02344392 -76.60302027 98.82 14.07 15.72 13.01 14.09 14.77 13.08

AA Cd 48 390001076364301 39.00038866 -76.61163149 102.8 10.69 12.82 10.66 15.96 16.70 22.66

AA Cd 78 390238076373301 39.04399906 -76.62552112 128.82 43.66 39.55 40.05 43.04 44.75 50.02
74 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Appendix 3. Southern Maryland ground-water-level data used in this report.—Continued

[All depth and elevation measurements are in feet. Land and water elevations are measured from the National Geodetic Vertical Datum of 1929 

(NGVD29). Digital latitude and longitude measured with respect to North American Datum 1983 (NAD83); --, no data]

Well name USGS ID

Location NAD83 Land 

elevation

Water levels in feet relative to NGVD29

Latitude Longitude 2005 2000 1995 1990 1985 1980

Magothy aquifer—Continued

AA Cd 85 390032076383001 39.00899949 -76.64135466 46.55 -- 30.85 29.62 32.70 33.29 35.90

AA Cd 87 390224076383501 39.04011014 -76.64274385 75.27 58.35 53.90 53.87 57.17 57.66 63.78

AA Ce 69 390115076303003 39.02094444 -76.50801734 18.9 -17.36 -4.87 -12.37 -5.40 -10.00 -2.55

AA Ce 103 390214076342201 39.03733276 -76.57246385 59.2 2.10 2.69 1.54 1.20 2.33 --

AA Ce 105 390310076340701 39.05288811 -76.56829713 41 -- -1.33 -2.54 -1.53 -1.57 -0.10

AA Ce 110 390231076320601 39.04205510 -76.53468490 75.58 -- -- -1.04 0.25 -1.42 0.93

AA Ce 114 390130076311501 39.02511098 -76.52051774 84.23 -15.45 -7.13 -11.99 -6.44 -9.07 -2.81

AA Ce 128 390404076300703 39.06788823 -76.50162836 7.13 -6.90 -1.09 -3.23 -0.41 -- --

AA Ce 130 390148076325202 39.03011077 -76.54746303 2.68 -8.22 -5.73 -8.65 -4.32 -- --

AA Ce 133 390410076302401 39.06955484 -76.50635074 15.14 -3.26 -0.02 -1.66 0.06 -- --

AA Ce 138 390049076322702 39.01372216 -76.54051831 69 -14.07 -9.29 -14.69 -- -- --

AA Cf 39 390142076254901 39.02844452 -76.42995950 23.34 -- -- -13.45 -10.66 -9.31 -0.50

AA Cf 99 390150076283002 39.03066661 -76.47468304 93.7 -28.19 -9.16 -17.19 -11.03 -11.65 -6.59

AA Cf 104 390242076274501 39.04511088 -76.46218270 26.77 -23.70 -9.92 -16.68 -9.68 -12.10 -5.49

AA Cf 129 390149076261704 39.03038892 -76.43773751 18 -- -11.12 -15.92 -10.36 -11.28 --

AA Cf 130 390108076253501 39.01900022 -76.42607048 20.69 -- -9.96 -13.38 -8.46 -8.43 --

AA Cf 141 390326076295003 39.05733284 -76.49690597 61.5 -- -- -7.29 -3.34 -- --

AA Cf 152 390121076253301 39.02250000 -76.42583333 22 -22.80 -14.18 -- -- -- --

AA Cg 8 390125076240502 39.02372242 -76.40106975 17.8 -- -8.92 -- -6.38 -4.14 -1.36

AA Dc 13 385800076410301 38.96677791 -76.68385556 123.45 -- -- 23.07 27.01 25.23 38.32

AA Dc 15 385928076414601 38.99122176 -76.69580059 109.99 32.79 33.09 32.85 34.06 34.57 35.98

AA Dc 16 385637076400801 38.94372296 -76.66857704 92.19 -- -- 16.61 22.66 25.81 28.15

AA Dc 20 385637076400802 38.94372296 -76.66857704 92.19 15.16 19.01 -- -- -- --

AA Dd 24 385722076385701 38.95622280 -76.64885427 162.46 -- -- 13.02 19.35 20.94 25.31

AA Dd 37 385807076351901 38.96872286 -76.58829686 132.93 -6.04 -2.46 -5.73 3.42 3.30 8.33

AA Dd 40 385511076373101 38.91983489 -76.62496401 135.79 0.9 5.51 2.59 10.71 16.75 21.97

AA Dd 42 385808076373502 38.96900041 -76.62607589 105.48 6.67 10.37 10.30 14.92 16.15 20.16

AA De 1 385915076340401 38.98761141 -76.56718545 13.72 -21.81 -13.37 -30.35 -16.92 -27.84 -25.48

AA De 75 385758076342702 38.96622300 -76.57385189 67.17 -- -1.83 -6.42 0.93 0.87 4.14

AA De 101 385512076331601 38.92011312 -76.55412796 49.42 -- -4.68 -5.85 1.73 2.73 8.96

AA De 103 385512076331603 38.92011312 -76.55412796 49.67 -9.87 -4.90 -6.09 1.47 2.42 8.56

AA De 107 385720076302804 38.95566809 -76.50746049 41.17 -- -8.83 -12.58 -4.16 1.22 1.70

AA De 113 385929076324901 38.99150031 -76.54662935 89.89 -- -- -- -- -7.85 -4.61

AA De 124 385528076334601 38.92455741 -76.56246171 27.84 -7.73 -- -- 5.52 3.89 10.05

AA De 125 385526076334801 38.92400186 -76.56301727 31.74 -- -4.73 -6.35 1.63 2.44 8.52
Appendix 3 75

Appendix 3. Southern Maryland ground-water-level data used in this report.—Continued

[All depth and elevation measurements are in feet. Land and water elevations are measured from the National Geodetic Vertical Datum of 1929 

(NGVD29). Digital latitude and longitude measured with respect to North American Datum 1983 (NAD83); --, no data]

Well name USGS ID

Location NAD83 Land 

elevation

Water levels in feet relative to NGVD29

Latitude Longitude 2005 2000 1995 1990 1985 1980

Magothy aquifer—Continued

AA De 135 385932076344401 38.99233346 -76.57857479 48.8 -- -- -10.99 -1.38 -2.54 --

AA Df 20 385916076270702 38.98788963 -76.45162640 21.87 -17.12 -11.43 -13.71 -8.25 -9.40 -3.27

AA Df 64 385909076281704 38.98594520 -76.47107136 30.93 -- -12.46 -19.46 -10.81 -14.05 -6.54

AA Df 79 385905076293601 38.98483408 -76.49301641 5.17 -16.77 -10.62 -16.14 -7.29 -11.06 -4.30

AA Df 82 385953076280201 38.99816712 -76.46690492 87.77 -20.42 -10.54 -17.97 -9.46 -12.60 -5.11

AA Df 84 385518076282701 38.92178016 -76.47384740 7.32 -22.51 -15.84 -17.33 -- -1.94 4.96

AA Df 87 385934076274301 38.99288949 -76.46162684 19.86 -18.17 -9.81 -15.93 -7.86 -10.16 -0.42

AA Df 102 385726076284201 38.95733480 -76.47801519 22.12 -- -10.57 -12.80 -5.26 -- --

AA Ec 6 385122076405801 38.85622480 -76.68246566 55.07 -3.46 1.84 -0.32 6.76 12.32 15.76

AA Ed 39 385210076371002 38.86955831 -76.61912966 176.47 -3.33 0.86 0.42 7.74 10.06 --

AA Ed 65 385406076383902 38.90177962 -76.64385339 110 3.03 6.70 -- -- -- --

AA Ee 65 385306076301501 38.88511434 -76.50384727 27.19 -11.20 -7.66 -6.30 0.21 2.06 8.24

AA Fc 34 384833076415601 38.80928124 -76.69857717 51 -2.34 1.99 -- -- -- --

AA Fe 47 384843076312601 38.81206046 -76.52356842 6.36 -11.02 -7.83 -5.21 1.00 4.61 9.72

AA Fe 51 384917076305801 38.82150473 -76.51579051 8.5 -12.96 -9.28 -- -- -- --

AA Fe 56 384731076325501 38.79206074 -76.54829142 9 -- -10.88 -- -- -- --

AA Fe 93 384644076331202 38.77900546 -76.55301359 9 -14.65 -10.19 -- -- -- --

CA Ba 8 384401076404902 38.73372759 -76.67996440 59.16 -19.51 -12.37 -10.01 -2.93 -0.83 -8.75

CA Bb 10 384028076354201 38.67456310 -76.59468126 186.9 -32.57 -25.65 -19.60 -11.34 -7.56 -1.80

CA Bb 23 384458076375501 38.74956097 -76.63162850 146.86 -19.69 -13.08 -12.01 -4.63 0.91 6.74

CA Bb 25 384109076391101 38.68595130 -76.65274014 119.78 -26.02 -20.76 -16.80 -11.87 -3.52 5.98

CA Cc 56 383934076320001 38.65956383 -76.53301106 96.11 -33.83 -27.31 -20.02 -12.19 -5.02 2.53

CA Dc 35 383050076305501 38.51401138 -76.51495340 91.6 -35.50 -28.33 -20.67 -12.59 -6.24 0.47

CH Be 17 383502076565101 38.58400842 -76.94719515 204.23 -66.88 -60.86 -57.32 -- -41.92 --

CH Be 40 383553076562001 38.59817470 -76.93858384 209 -- -66.21 -60.69 -43.67 -45.05 --

CH Be 43 383819076555501 38.63872909 -76.93163942 216.79 -70.42 -60.09 -52.81 -46.85 -40.03 -32.34

CH Be 48 383649076554701 38.61372983 -76.92941698 207 -- -66.90 -62.63 -46.24 -49.78 --

CH Be 61 383855076562703 38.64872876 -76.94052864 220 -- -- -49.34 -- -- --

CH Bf 98 383739076543001 38.62761839 -76.90830529 216.39 -65.19 -56.83 -63.42 -44.86 -47.06 -29.06

CH Bf 101 383853076532601 38.64817341 -76.89024933 216.45 -- -50.47 -50.27 -33.52 -39.69 -25.57

CH Bf 124 383750076540801 38.63067388 -76.90191623 207.78 -76.11 -- -62.86 -45.96 -45.76 -31.37

CH Bf 132 383643076505201 38.61206353 -76.84746992 200 -54.92 -45.83 -46.04 -26.66 -33.36 -16.20

CH Bf 133 383640076545901 38.61122996 -76.91608320 223.5 -80.28 -68.91 -62.76 -46.44 -54.62 -31.98

CH Bf 134 383728076531701 38.62456301 -76.88774907 202.09 -88.95 -63.61 -57.70 -35.39 -48.52 -46.76

CH Bf 135 383814076500301 38.63734061 -76.83385862 207.82 -47.65 -36.94 -30.99 -9.60 -13.01 -15.86
76 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Appendix 3. Southern Maryland ground-water-level data used in this report.—Continued

[All depth and elevation measurements are in feet. Land and water elevations are measured from the National Geodetic Vertical Datum of 1929 

(NGVD29). Digital latitude and longitude measured with respect to North American Datum 1983 (NAD83); --, no data]

Well name USGS ID

Location NAD83 Land 

elevation

Water levels in feet relative to NGVD29

Latitude Longitude 2005 2000 1995 1990 1985 1980

Magothy aquifer—Continued

CH Bf 143 383918076522201 38.65511772 -76.87247107 206.59 -59.73 -51.06 -45.51 -26.64 -47.60 -18.43

CH Bf 145 383558076524501 38.59956378 -76.87885971 203 -- -58.70 -62.61 -38.25 -46.60 --

CH Bf 160 383913076510202 38.65372896 -76.85024816 202.2 -- -49.83 -45.91 -- -- --

CH Bg 10 383702076475001 38.61734135 -76.79691282 196.18 -- -37.07 -32.91 -23.02 -21.60 -4.26

CH Cf 29 383219076503502 38.53873238 -76.84274687 178.02 -59.09 -49.46 -41.66 -29.83 -27.64 -12.42

CH Cf 31 383301076531101 38.55039854 -76.88608178 165 -63.12 -50.76 -45.61 -30.54 -30.10 --

DO Ce 15 383408076042402 38.56900759 -76.07299564 6 -8.71 -5.76 -6.55 -9.86 -7.77 -7.94

KE Cb 97 391124076101001 39.19010967 -76.16911738 65.84 6.28 7.66 7.63 -- -- --

PG Cf 33 385806076435303 38.96844427 -76.73107937 115.4 46.62 50.45 48.84 52.38 51.31 --

PG Cf 79 385831076432102 38.97538862 -76.72219021 145 -- 42.88 42.07 -- -- --

PG De 21 385130076465501 38.85844637 -76.78163628 95.76 33.64 35.83 35.34 40.69 42.03 47.94

PG De 32 385323076471801 38.88983461 -76.78802541 131.85 50.82 52.77 51.97 55.78 57.10 61.34

PG Df 34 385037076430901 38.84372478 -76.71885614 84.78 5.65 8.83 8.45 16.67 20.11 --

PG Df 36 385029076430201 38.84150262 -76.71691159 64.98 -- 8.53 7.29 15.58 18.88 --

PG Ed 50 384715076522001 38.78761419 -76.87191639 240.88 16.49 21.82 2.75 25.87 -- --

PG Ef 34 384623076424001 38.77317080 -76.71079980 39.18 -7.11 -2.76 -0.15 6.77 9.08 16.84

PG Ef 40 384847076440401 38.81316975 -76.73413453 79.85 1.55 5.53 -- 14.07 16.50 23.40

PG Fd 32 384148076510901 38.69678323 -76.85219305 230.94 -25.52 -21.56 -17.57 -6.34 -7.89 7.51

PG Fd 39 384410076502501 38.73622655 -76.83997085 233.42 -8.58 -5.11 -4.24 2.67 7.26 17.91

PG Fd 41 384131076533301 38.69206100 -76.89219417 196.92 -28.95 -22.36 -15.96 -8.88 -10.32 3.78

PG Fe 30 384453076482101 38.74817077 -76.80552559 237.59 -7.74 -1.87 1.25 7.28 4.79 19.64

PG Ge 15 383940076461301 38.66122904 -76.76996804 210.51 -29.89 -25.06 -20.06 -10.44 -9.14 5.03

PG Gf 35 383832076414701 38.64234108 -76.69607538 34.96 -31.06 -25.01 -18.65 -10.73 -5.43 5.56

PG Hf 33 383250076405302 38.54734373 -76.68107351 10.36 -- -- -64.77 -54.27 -63.46 -189.43

PG Hf 36 383248076405302 38.54678819 -76.68107350 11.69 -- -69.92 -69.77 -58.72 -73.53 -74.46

PG Hf 41 383348076411302 38.56345439 -76.68662954 28.3 -49.90 -43.74 -41.88 -32.80 -- --

QA Ea 27 385718076205501 38.95400183 -76.34801133 18.27 -14.43 -11.00 -8.89 -3.48 -- 3.77

Upper Patapsco aquifer

AA Ad 108 391032076385906 39.17566368 -76.64941189 78.31 71.39 71.75 70.13 71.70 69.63 --

AA Bd 99 390604076354501 39.10122060 -76.59552052 137 53.39 46.68 49.49 53.15 52.30 58.73

AA Bd 159 390737076374402 39.12705338 -76.62857740 75.48 38.15 36.50 33.10 36.55 37.82 --

AA Be 102 390559076312602 39.09983209 -76.52357362 36.36 9.96 8.21 7.74 9.62 7.61 10.87

AA Bf 3 390945076285601 39.16260912 -76.48190574 20.38 6.07 6.77 5.76 7.00 4.98 4.91

AA Cc 43 390422076414501 39.07288717 -76.69552364 180 121.55 118.25 119.04 120.52 126.88 126.45

AA Cc 116 390103076402602 39.01761031 -76.67357794 134.35 7.61 15.92 26.41 25.85 42.39 45.35

AA Cc 127 390122076434601 39.02288773 -76.72913525 135 -- 56.11 59.92 -- -- --

AA Cc 131 390126076413404 39.02399901 -76.69246747 102 34.74 38.55 39.93 -- -- --

AA Ce 70 390115076303002 39.02094444 -76.50801734 18.2 -25.09 -6.85 -15.51 -8.03 -13.88 -2.80
Appendix 3 77

Appendix 3. Southern Maryland ground-water-level data used in this report.—Continued

[All depth and elevation measurements are in feet. Land and water elevations are measured from the National Geodetic Vertical Datum of 1929 

(NGVD29). Digital latitude and longitude measured with respect to North American Datum 1983 (NAD83); --, no data]

Well name USGS ID

Location NAD83 Land 

elevation

Water levels in feet relative to NGVD29

Latitude Longitude 2005 2000 1995 1990 1985 1980

Upper Patapsco aquifer—Continued

AA Ce 120 390303076344301 39.05094364 -76.57829744 161.8 7.70 7.69 6.58 9.52 9.62 11.87

AA Ce 137 390043076345402 39.01205531 -76.58135287 57.5 0.17 1.67 4.85 -- -- --

AA Cf 119 390203076292801 39.03427764 -76.49079463 131.03 -- -19.40 -36.18 -26.43 -- --

AA Cf 120 390203076292301 39.03427764 -76.48940570 125.98 -- -- -- -36.38 -- -21.02

AA Cf 121 390149076261701 39.03038892 -76.43773751 20 -23.48 -13.77 -19.83 -15.20 -17.11 -6.23

AA Cf 128 390149076261703 39.03038892 -76.43773751 14 -- -- -18.10 -11.90 -13.79 -6.03

AA Cf 134 390121076270501 39.02261122 -76.45107122 24 -24.43 -12.13 -18.74 -13.54 -13.95 --

AA Cg 24 390123076241603 39.02316687 -76.40412540 12.68 -15.35 -9.59 -11.08 -6.36 -6.32 -0.97

AA De 95 385853076333001 38.98150050 -76.55801837 73.2 -20.65 -23.77 -35.22 -14.46 -11.04 -8.30

AA De 128 385530076334701 38.92511295 -76.56273951 28.31 -9.02 -4.11 -5.45 2.32 4.54 11.45

AA De 199 385753076310801 38.96483446 -76.51857223 35 -17.79 -12.61 -18.05 -9.00 -- --

AA De 205 385628076323102 38.94122380 -76.54162799 33.46 -11.87 -6.57 -8.61 -2.54 -- --

AA Df 19 385921076270701 38.98955626 -76.45079309 15.84 -20.10 -11.79 -17.30 -8.50 -10.99 -3.22

AA Df 65 385913076281401 38.98705629 -76.45079309 15.84 -- -49.71 -63.01 -- -50.80 --

AA Df 89 385934076274302 38.99288949 -76.46162684 20.58 -19.39 -11.77 -12.85 -8.69 -14.72 -2.93

AA Df 99 385905076293604 38.98483408 -76.49301641 5.17 -23.17 -25.46 -27.28 -21.26 -- --

AA Df 100 385905076293603 38.98483408 -76.49301641 5.17 -16.61 -10.04 -16.12 -7.35 -- --

AA Ec 12 385125076404801 38.65956383 -76.68000000 55 0.22 4.00 -- -- -- --

CA Cc 55 383934076320201 38.65956383 -76.53356665 95.98 -17.80 -13.25 -8.62 -2.67 2.14 8.64

CH Be 60 383706076575604 38.61845178 -76.96525147 212.8 -51.61 -40.34 -31.30 -22.13 -- --

CH Bf 151 383508076540703 38.58567521 -76.90163812 192.8 -69.62 -56.57 -57.13 -39.23 -38.50 --

CH Bf 157 383637076545803 38.61122996 -76.91608320 225 -76.01 -61.11 -59.40 -44.70 -- --

CH Bf 158 383732076531902 38.62484077 -76.88830465 193 -52.76 -47.15 -40.51 -29.98 -- --

CH Cd 31 383222077004401 38.53956505 -77.01191924 130 -88.31 -70.02 -64.71 -- -- --

CH Cd 43 383328077010201 38.55789784 -77.01691945 68 -142.07 -127.83 -113.28 -- -- --

CH Ce 16 383217076590201 38.53817629 -76.98358503 188 -- -95.75 -86.16 -- -- --

CH Ce 30 383149076583801 38.53039876 -76.97691810 190 -92.00 -88.58 -91.42 -- -- --

CH Ce 50 383420076592501 38.57234193 -76.98997428 205 -69.55 -58.44 -54.45 -50.85 -43.85 -18.85

CH Cg 24 383254076481401 38.54845447 -76.80357896 171.04 -52.77 -- -- -- -- --

CH Da 21 382659077152401 38.44984513 -77.25636926 88 -15.20 -12.24 -9.86 -5.71 -2.24 -0.75

CH Dd 33 382607077002601 38.41929093 -76.99969605 99.8 -33.79 -26.20 -18.42 -9.68 -3.70 0.89

CH Dd 38 382925077010101 38.49039984 -77.01664135 60 -- -61.45 -52.32 -- -- --

CH Fe 5 381803076550801 38.30096131 -76.91858214 12 -55.09 -36.79 -36.90 -- -- --

DO Ce 88 383401076032001 38.56706296 -76.05521730 4.42 -- -8.99 -11.25 -12.17 -11.25 --

KE Cb 36 391400076101401 39.23344244 -76.17022876 40 -2.41 -0.45 0.56 2.57 4.16 --
78 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Appendix 3. Southern Maryland ground-water-level data used in this report.—Continued

[All depth and elevation measurements are in feet. Land and water elevations are measured from the National Geodetic Vertical Datum of 1929 

(NGVD29). Digital latitude and longitude measured with respect to North American Datum 1983 (NAD83); --, no data]

Well name USGS ID

Location NAD83 Land 

elevation

Water levels in feet relative to NGVD29

Latitude Longitude 2005 2000 1995 1990 1985 1980

Upper Patapsco aquifer—Continued

KE Cb 103 391124076101005 39.19010967 -76.16911738 65.6 -5.61 -3.34 -2.22 -- -- --

KE Db 40 390837076140401 39.14372123 -76.23412034 15 -5.68 -4.70 -2.53 0.79 -- 3.39

PG Cf 25 385529076443101 38.92483401 -76.74163517 106.29 -- -- 37.48 -- 46.39 50.47

PG De 33 385323076471802 38.88983461 -76.78802541 103.68 54.24 56.02 55.12 58.80 59.92 63.90

PG Ec 31 384616076570401 38.77122535 -76.95080738 256.04 -6.15 3.22 6.02 -- 25.37 27.10

PG Fb 36 384423077004501 38.73983694 -76.95080738 78 -24.4 -16.83 -13.3 -4.15 5.81 7.6

PG Hf 38 383248076405303 38.54678819 -76.68107350 11.6 -41.18 -34.57 -45.04 -36.98 -10.73 -9.9

PG Hf 40 383348076411301 38.56345439 -76.68662954 27.98 -41.26 -36.40 -31.49 -23.55 -- --

PG Hf 44 383250076405304 38.54734373 -76.68107351 10.48 -53.49 -35.41 -32.01 -23.54 -2.22 -3.83

QA Be 16 391203076024302 39.20094315 -76.04494493 25 -15.26 -8.94 -8.93 3.75 -- --

QA Eb 111 385751076171601 38.96427946 -76.28745430 14.03 -14.85 -11.47 -8.82 -2.57 -2.26 4.91

SM Df 84 381548076272102 38.26345833 -76.45550783 108.39 -47.79 -37.22 -26.48 -18.02 -10.22 --

SM Df 100 381721076264801 38.28916667 -76.44666667 21 -46.29 -36.79 -- -- -- --

SM Ff 36 380724076251901 38.12318216 -76.42189528 5.5 -36.14 -28.58 -20.47 -14.10 -- --

TA Cd 57 384709076050301 38.78594908 -76.08383090 12 -- -47.73 -34.25 -- -- --

Lower Patapsco aquifer

AA Ad 102 391032076385904 39.17566368 -76.08383090 12 4.15 3.08 5.51 2.22 -2.36 --

AA Ad 109 391006076380101 39.16844164 -76.63330012 35.78 39.44 39.61 38.00 38.01 27.38 --

AA Bc 176 390736076421602 39.12677523 -76.7041356 188.5 48.91 54.45 50.31 56.19 60.5 69.68

AA Bc 215 390700076412601 39.11677544 -76.69024614 124 37.53 43.25 38.48 44.02 -- --

AA Bd 37 390848076363601 39.14677541 -76.60968798 38.2 11.40 10.21 6.84 16.22 13.98 -21.38

AA Bd 56 390950076384001 39.16399721 -76.64413382 61.6 54.16 53.66 51.10 49.46 40.64 -59.44

AA Bd 101 390855076373402 39.14871975 -76.62579969 55 33.31 31.07 25.05 26.66 23.93 -24.53

AA Bd 105 390810076380702 39.13621988 -76.63496659 90 -- 51.94 46.83 -- 49.45 11.20

AA Bd 108 390917076381401 39.15483071 -76.63691125 70 -- -- 36.09 36.71 32.53 -76.19

AA Bd 109 390845076385801 39.14594189 -76.64913385 190 -- 63.07 61.20 59.10 59.07 -11.59

AA Bd 152 390821076365401 39.13927550 -76.61468811 53.29 26.55 24.04 20.65 23.85 23.01 --

AA Bd 155 390938076383701 39.16066393 -76.64330042 57.5 48.92 48.38 46.06 39.83 33.73 --

AA Bd 156 390922076371001 39.15621967 -76.61913284 68.99 23.02 25.19 19.06 20.53 17.04 --

AA Bd 157 390922076371001 39.15621967 -76.62857740 75.75 38.75 36.62 33.36 36.39 36.05 --

AA Bd 158 390744076390001 39.12899769 -76.64968928 108.25 60.41 56.96 53.50 56.13 55.08 --

AA Bd 160 390908076394402 39.15233062 -76.66191214 88 76.33 74.50 71.28 73.14 70.50 --

AA Bf 99 390654076283601 39.11510983 -76.47634993 40 -10.05 -- -- -- -- --

AA Cc 40 390423076432001 39.07316481 -76.72191340 136.92 88.35 87.11 86.39 88.17 88.01 89.59

AA Cc 82 390422076414505 39.07288717 -76.69552364 178.39 56.78 57.79 54.22 59.47 63.76 48.48

AA Cc 89 390010076415703 39.00288817 -76.69885633 52.77 13.15 14.54 11.87 24.00 41.55 42.38
Appendix 3 79

Appendix 3. Southern Maryland ground-water-level data used in this report.—Continued

[All depth and elevation measurements are in feet. Land and water elevations are measured from the National Geodetic Vertical Datum of 1929 

(NGVD29). Digital latitude and longitude measured with respect to North American Datum 1983 (NAD83); --, no data]

Well name USGS ID

Location NAD83 Land 

elevation

Water levels in feet relative to NGVD29

Latitude Longitude 2005 2000 1995 1990 1985 1980

Lower Patapsco aquifer—Continued

AA Cc 115 390103076402601 39.01761031 -76.67357794 134.38 -12.18 -11.17 -17.67 9.55 41.27 44.09

AA Cc 137 390126076402901 39.02399910 -76.67441136 115.34 14.21 21.03 22.66 -- -- --

Aa Cd 128 390327076363701 39.05761005 -76.60996516 110 18.12 -- -- -- -- --

AA Ce 94 390450076343503 39.08066544 -76.57607530 90 -91.46 -76.77 -62.20 -42.15 -35.32 -104.34

AA Ce 124 390303076344303 39.05094364 -76.57829744 160 -13.29 -11.81 -13.07 0.87 -5.00 9.06

Aa Ce 136 390043076345401 39.01205531 -76.58135287 60 -15.52 -12.07 -2.38 -- -- --

AA Cf 137 390205076292702 39.03483319 -76.49051685 124.3 -11.78 -50.60 -56.10 -- -- --

AA Cg 23 390123076241602 39.02316687 -76.40412540 12.57 -13.02 -20.34 -14.24 -2.30 3.04 7.06

AA De 177 385852076333201 38.98122272 -76.55857393 93.85 -- -- -20.73 -4.03 -- --

AA De 206 385833076332801 38.97594508 -76.55746267 81.74 -49.61 -18.51 -18.50 -- -- --

BA Gf 168 391257076282501 39.21594170 -76.47329448 10 -- -- -1.70 -0.55 -0.19 -0.89

BA Gf 178 391226076253401 39.20733088 -76.42579307 6 -- -- -0.22 1.28 1.98 1.43

Ca Fd 85 382236076255401 38.37679040 -76.43133979 105.98 -18.91 -- -- -- -- --

CH Bb 17 383524077111802 38.59011884 -77.18803553 52 -- -57.49 -64.32 -62.45 -- --

CH Bc 5 383524077094401 38.59011888 -77.16192368 38.2 -- -- -- -81.73 -69.77 --

CH Bc 24 383633077083001 38.60928501 -77.14136773 72 -121.70 -108.65 -112.75 -88.04 -- --

CH Bc 67 383606077092101 38.60178521 -77.15553473 30 -73.81 -79.32 -83.10 -- -- --

CH Bc 76 383754077051201 38.63178443 -77.08636630 171 -138.17 -116.28 -112.25 -- -- --

CH Bc 81 383709077061002 38.61928477 -77.10247779 156.46 -130.95 -111.55 -- -81.54 -- --

CH Bd 22 383740077043501 38.62789568 -77.07608819 175 -118.95 -108.44 -118.52 -- -- --

CH Bd 29 383805077045201 38.63483991 -77.08081060 170 -138.58 -115.95 -111.30 -- -- --

Ch Bd 35 383825077042601 38.64789509 -77.07358825 170 -- -112.32 -104.17 -- -- --

CH Bd 49 383617077015702 38.60484088 -77.03219788 183 -142.20 -114.52 -103.55 -- -- --

CH Bd 50 383734077044901 38.62622905 -77.07997718 180 -133.35 -110.18 -107.90 -- -- --

CH Bd 51 383715077014901 38.62095152 -77.02997567 185 -- -122.91 -98.25 -- -- --

CH Be 58 383706076575602 38.61845178 -78.96525150 212.5 -182.15 -152.91 -150.17 -- -24.10 --

CH Be 64 383553076562002 38.59817470 -76.93858384 209 -198.01 -147.21 -160.65 -- -- --

CH Bf 146 383508076540701 38.58567521 -76.90163812 192.8 -135.24 -130.87 -126.39 -94.53 -36.50 --

CH Bf 150 383901076524301 38.65039561 -76.87830454 215 -- -89.63 -86.21 -- -13.00 --

CH Cb 7 383422077114601 38.57289712 -77.19581333 36 -30.24 -36.31 -45.86 -49.42 -44.32 -37.62

CH Cb 11 383313077125401 38.55428654 -77.21470251 10 -49.18 -50.34 -46.80 -39.30 -- --

CH Cb 28 383315077131401 38.55484207 -77.22025822 5 -44.99 -43.99 -44.82 -43.10 -- --

CH Cb 38 383328077114201 38.55789757 -77.19470201 4 -60.26 -- -73.18 -73.25 -- --

CH Cb 42 383328077111702 38.55789758 -77.18775738 5 -81.08 -90.37 -91.56 -- -- --

CH Cc 31 383455077074401 38.58206362 -77.12858934 35 -99.65 -93.36 -- -- -- --
80 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Appendix 3. Southern Maryland ground-water-level data used in this report.—Continued

[All depth and elevation measurements are in feet. Land and water elevations are measured from the National Geodetic Vertical Datum of 1929 

(NGVD29). Digital latitude and longitude measured with respect to North American Datum 1983 (NAD83); --, no data]

Well name USGS ID

Location NAD83 Land 

elevation

Water levels in feet relative to NGVD29

Latitude Longitude 2005 2000 1995 1990 1985 1980

Lower Patapsco aquifer—Continued

CH Cd 42 383256077015301 38.54900919 -77.03108645 185 -110.56 -87.36 -76.75 -- -- --

CH Ce 35 383111076584801 38.51984351 -76.97969592 165 -123.31 -106.86 -98.82 -- -- --

CH Ce 37 383236076563901 38.54345407 -76.94386147 184.95 -126.25 -114.59 -121.42 -67.64 -32.36 -12.83

CH Ce 51 383111076570701 38.51984362 -76.95163939 150 -- -97.44 -94.68 -- -- --

CH Ce 53 383420076592504 38.57234193 -76.98997428 205 -100.55 -85.05 -73.70 -- -- --

CH Ce 56 383251076583901 38.54762048 -76.97719596 196.48 -180.41 -120.51 -- -- -- --

CH Da 20 382654077152701 38.44845629 -77.25720260 90 -14.80 -11.45 -9.22 -4.89 -1.26 0.31

CH Ee 70 382154076574801 38.36568153 -76.96386135 22.83 -104.62 -90.68 -95.96 -88.58 -82.15 -87.39

CH Ee 78 382240076582801 38.37790336 -76.97413948 75 -82.19 -79.90 -70.61 -66.83 -55.18 --

CH Ff 60 381806076545401 38.30179462 -76.91469316 12 -53.30 -38.40 -41.00 -- -- --

PG Be 14 390226076481001 39.04066508 -76.80247095 155 111.55 110.40 -- 111.83 111.64 113.91

PG Be 15 390253076482801 39.04816496 -76.80747117 145 -- 103.27 111.55 104.66 102.85 105.45

PG Cf 32 385806076435302 38.96844427 -76.73107937 115.4 15.17 16.72 12.64 37.71 -- 47.64

PG Cf 44 385944076433801 38.99566594 -76.72691267 44.34 -- 37.01 31.47 43.52 50.43 58.37

PG Cf 76 385757076440402 38.96594431 -76.73413502 127.61 12.86 14.72 13.10 39.89 43.11 48.80

PG Cf 78 385831076432101 38.97538862 -76.72219021 145 -- 21.56 17.56 -- -- --

PG Ed 34 384933076530001 38.82594675 -76.88302793 270 -1.74 4.16 10.92 20.19 32.13 35.04

PG Fc 17 384230076555501 38.70844926 -76.93163985 58.6 -- -35.12 -25.74 -7.80 4.60 8.76

PG Gd 5 383957076520601 38.66595075 -76.86802658 216.43 -- -76.33 -68.92 -- -- --

PG Hf 32 383250076405303 38.54734373 -76.68107351 10.48 -39.61 -32.22 -24.10 -12.14 1.78 7.55

QA Be 15 391203076024301 39.20094315 -76.04494493 25 -2.56 0.42 2.18 5.35 7.07 --

QA Eb 112 385751076171602 38.96427946 -76.28745430 13.92 -18.21 -16.97 -5.08 0.74 4.71 7.60

SM Bc 39 382605076430201 38.43484663 -76.71690860 161.54 -34.17 -- -- -- -- --

SM Dd 72 381626076393401 38.27391667 -76.65966667 109.99 -25.81 -- -- -- -- --
Appendix 3 81

Appendix 3. Southern Maryland ground-water-level data used in this report.—Continued

[All depth and elevation measurements are in feet. Land and water elevations are measured from the National Geodetic Vertical Datum 

of 1929 (NGVD29). Digital latitude and longitude measured with respect to North American Datum 1983 (NAD83); --, no data]

Well name USGS ID

Location NAD83 Land 

elevation

Water levels in feet relative to NGVD29

Latitude Longitude 2005 2004 2003

Piney Point-Nanjemoy aquifer

CA Db 86 383152076361701 38.53123315 -76.60440265 162.00 31.03 -- --

CA Ed 32 382527076280801 38.42429009 -76.46856306 100.00 -58.46 -- --

CA Ed 49 382733076290101 38.45928980 -76.48328557 100.00 -39.18 -- --

CA Fd 51 382408076260401 38.40234566 -76.43411756 129.40 -2.29 -- --

CA Fe 22 382318076242401 38.38845673 -76.40633888 113.90 -22.33 -- --

DO Bg 59 383708075503801 38.61900455 -75.84354571 25.00 -23.01 -- --

DO Cd 1 383151076080801 38.53095325 -76.13521954 4.00 -- -44 --

DO Ce 5 383340076041601 38.56122989 -76.07077331 18.00 -- -54.9 --

DO Db 17 382800076180701 38.46678876 -76.30161313 12.70 -8.7 -- --

QA Df 62 390039075560201 39.01094609 -75.93354928 16.23 -- -- 23.77

SM Bb 22 382838076470102 38.47734550 -76.78330006 165.20 143.12 -- --

SM Dd 46 381616076364701 38.27123805 -76.61273761 118.84 -9.77 -- --

SM Dd 62 381616076364703 38.27123805 -76.61273761 115.00 -14.37 -- --

SM Dd 63 381615076364701 38.27096027 -76.61273761 119.72 -10.66 -- --

SM Df 14 381719076264801 38.28901355 -76.44634070 17.71 -- -17.02 --

SM Df 66 381841076284401 38.31151356 -76.47856402 15.00 -24.45 -- --

SM Dg 20 381718076234001 38.28901316 -76.39467205 12.00 -23.02 -- --

SM Dg 21 381810076244601 38.30290205 -76.41189489 3.00 -21.21 -- --

SM Dg 22 381731076242401 38.29206877 -76.40633916 12.00 -27.59 -- --

SM Dg 24 381728076234601 38.29111111 -76.39611111 20.00 -- -13.94 --

SM Ef 89 381418076293601 38.23833333 -76.49333333 45.00 -36.33 -- --

SM Eg 27 381213076222801 38.20373615 -76.37411566 10.00 -23.53 -- --

SM Fe 30 380834076303401 38.14290512 -76.50912114 9.00 -18.01 -- --

SM Fg 45 380711076222201 38.11984827 -76.37244872 65.00 -27.87 -- --

TA Bf 73 385242075593101 38.87761384 -75.99299482 42.00 22.26 -- --

TA Cc 35 384923076100601 38.82317143 -76.16800162 5.00 -3.01 -- --

TA Cc 36 384514076103701 38.75400634 -76.17661163 7.00 -- -5.94 --

Patuxent aquifer

AA Ac 11 391101076404001 39.18371898 -76.67746857 132.28 4.62 -- --

AA Ad 29 391015076373501 39.17094164 -76.62607765 75.1 -38.1 -- --

AA Ad 90 391032076385902 39.17566368 -76.64941189 127.78 -49.93 -- --

AA Bb 67 390538076453001 39.09399768 -76.75802591 121.79 11.21 -- --

AA Bc 163 390524076442501 39.09010891 -76.73996976 164.85 -29.74 -- --
82 Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 1980–2005

Appendix 3. Southern Maryland ground-water-level data used in this report.—Continued

[All depth and elevation measurements are in feet. Land and water elevations are measured from the National Geodetic Vertical Datum 

of 1929 (NGVD29). Digital latitude and longitude measured with respect to North American Datum 1983 (NAD83); --, no data]

Well name USGS ID

Location NAD83 Land 

elevation

Water levels in feet relative to NGVD29

Latitude Longitude 2005 2004 2003

Patuxent aquifer—Continued

AA Bc 235 390513076434401 39.08705346 -76.72858045 131.28 -1.28 -- --

AA Bc 240 390752076441001 39.13121945 -76.73580346 233.75 26.25 -- --

AA Bd 57 390952076384102 39.16455276 -76.64441161 235.23 -165.23 -- --

AA Bd 179 390946076391601 39.16277778 -76.65444444 205.13 -118.13 -- --

AA Bd 182 390839076385703 39.14433333 -76.64933333 198.35 -18.35 -- --

AA Cb 1 390303076463201 39.05094274 -76.77524807 92.35 36.75 -- --

AA Cc 80 390422076414503 39.07288717 -76.69552364 133.26 45.11 -- --

AA Cc 81 390422076414504 39.07288717 -76.69552364 130.23 48.15 -- --

AA Cc 102 390004076420001 39.00122153 -76.69968967 64.72 -10.76 -- --

AA Cc 113 390256076413101 39.04899865 -76.69163437 156.03 -4.14 -- --

AA Cc 119 390437076432302 39.07705364 -76.72274680 135.92 3.08 -- --

AA Cc 121 390456076432501 39.08233134 -76.72330244 139.57 -20.57 -- --

AA Cc 124 390419076432301 39.07205371 -76.72274674 128.9 1.1 -- --

AA Cc 135 390126076403001 39.02399910 -76.67468914 141.17 -26.36 -- --

AA Ce 117 390450076343402 39.08066544 -76.57579752 90.05 -4.05 -- --

AA Cg 22 390123076241601 39.02316687 -76.40412540 20.29 -7.68 -- --

AA De 203 385854076333202 38.98177826 -76.55857394 100.96 -6.57 -- --

CH Bc 75 383645077062401 38.61261830 -77.10636674 156.13 -31.54 -- --

CH Bc 77 383644077055501 38.61234054 -77.09831095 128.52 -31.88 -- --

CH Bc 78 383809077053401 38.63595096 -77.09247762 50.96 -30.83 -- --

CH Bc 80 383645077062402 38.61261830 -77.10636674 145.20 -- -22.07 --

CH Bd 52 383553077032401 38.59817437 -77.05636520 78.30 -30.8 -- --

CH Be 57 383706076575601 38.61845178 -76.96525147 222.78 -10.52 -- --

CH Cc 34 383441077063901 38.57817487 -77.11053325 76.12 -34.3 -- --

CH Ce 57 383250076584001 38.54734271 -76.97747375 203.22 -9.75 -- --

CH Da 18 382654077152501 38.44845629 -77.25664704 96.40 -6.5 -- --

PG Bc 16 390151076561501 39.03094285 -76.93719695 22.83 167.17 -- --

PG Be 23 390213076471301 39.03705404 -76.78663712 88.23 31.77 -- --

PG Cf 66 385745076445201 38.96261097 -76.74746879 151.22 -1.15 -- --

PG Cf 81 385745076445202 38.96261097 -76.74746879 138 -20.65 -- --

PG Fd 62 384309076511401 38.71928256 -76.85358218 230.3 -1.7 -- --

QA Eb 110 385751076171603 38.96427946 -76.28745430 11.17 2.81 -- --

Note: The Patuxent and Piney Point-Nanjemoy potentiometric surface maps were generated for 2005 only. Water-level data from 2005 were used when 

available; some data from 2004 and occasionally from 2003 were used when necessary.
Prepared by Publishing Service Centers 3 and 1.

Edited by Valerie M. Gaine.

Graphics by Timothy W. Auer.

Layout by Ann Marie Squillacci.

For additional information, contact:

Director, MD-DE-DC Water Science Center

U.S. Geological Survey

8987 Yellow Brick Road

Baltimore, MD 21237

or visit our Web site at:

http://md.water.usgs.gov