U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2012–5011

Prepared in cooperation with the

Naval Air Station Patuxent River

Groundwater Quality and Occurrence and Distribution 

of Selected Constituents in the Aquia and Upper 

Patapsco Aquifers, Naval Air Station Patuxent River, 

St. Mary’s County, Maryland, July 2008
Cover.  Aerial photograph of Naval Air Station Patuxent River taken by the National Aeronautics and Space Administration (NASA)

International Space Station Program, April 28, 2007.
Groundwater Quality and Occurrence 

and Distribution of Selected Constituents 

in the Aquia and Upper Patapsco Aquifers, 

Naval Air Station Patuxent River, 

St. Mary’s County, Maryland, July 2008

By Cheryl A. Dieter, Kimberly W. Campo, and Anna C. Baker

Scientific Investigations Report 2012–5011

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the 

Naval Air Station Patuxent River 
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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Suggested citation:

Dieter, C.A., Campo, K.W., and Baker, A.C., 2012, Groundwater quality and occurrence and distribution of selected 

constituents in the Aquia and Upper Patapsco aquifers, Naval Air Station Patuxent River, St. Mary’s County, Maryland, 

July 2008: U.S. Geological Survey Scientific Investigations Report 2012–5011, 16 p.

ISBN 978-1-4113-3356-7
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................2

Description of Study Area and Well Numbering System...............................................................2

Previous Investigations........................................................................................................................2

Sample Collection, Analysis, and Quality Control ....................................................................................4

Sample Collection and Analysis.........................................................................................................4

Quality Control.......................................................................................................................................6

Groundwater Quality and Occurrence and Distribution of Selected Constituents ............................7

Groundwater-Quality Characterization of the Aquia and Upper Patapsco 

Aquifers.....................................................................................................................................7

Comparison of Groundwater Quality in the Aquia and Upper Patapsco 

Aquifers, 1943–2008...............................................................................................................11

Arsenic and Tungsten ........................................................................................................................11

Saltwater Intrusion.............................................................................................................................14

Summary and Conclusions.........................................................................................................................15

Acknowledgments.......................................................................................................................................15

References Cited..........................................................................................................................................15
iv

Figures

1–2. Maps showing—

1. Location of Naval Air Station Patuxent River, St. Mary’s County, 

Maryland ...............................................................................................................................3

2. Selected well locations at Naval Air Station Patuxent River and 

Webster Outlying Field, St. Mary’s County, Maryland ...................................................5

3. Graphs showing comparisons of major ions in water samples collected 

from the Aquia and Upper Patapsco aquifers at the Naval Air Station 

Patuxent River (NASPR) and Webster Outlying Field (WOLF) locations 

in 1999–2001 and 2008 ................................................................................................................12

4. Piper diagram showing comparison of the average chemical composition 

of seawater to the chemical composition of groundwater from selected 

wells at Naval Air Station Patuxent River and Webster Outlying Field, 

St. Mary’s County, Maryland.....................................................................................................13

Tables

1. Hydrologic and corresponding geologic units at Naval Air Station Patuxent 

River and Webster Outlying Field, St. Mary’s County, Maryland ..........................................4

2. Records for selected wells at Naval Air Station Patuxent River and Webster 

Outlying Field, St. Mary’s County, Maryland.............................................................................6

3. Water-quality parameters with concentrations reported as estimated (E), 

justification for data qualifier, and long-term method detection levels 

(LT-MDLs) and laboratory reporting levels (LRLs) that bracket the 

estimated concentrations where applicable ...........................................................................7

4. Water quality and chemical composition of water samples collected from 

wells screened in the Aquia and Upper Patapsco aquifers, Naval Air Station 

Patuxent River and Webster Outlying Field, St. Mary’s County, Maryland, 

July 2008.........................................................................................................................................8

5. Comparison of average seawater and average connate water to groundwater 

samples collected in 2008 from the Aquia aquifer at Naval Air Station 

Patuxent River, and Webster Outlying Field, St. Mary’s County, Maryland.......................14
v

Conversion Factors and Datums

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

Area

acre 0.004047 square kilometer (km2

)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

 °F=(1.8×°C)+32

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25°C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).

Groundwater Quality and Occurrence and Distribution of 

Selected Constituents in the Aquia and Upper Patapsco 

Aquifers, Naval Air Station Patuxent River, St. Mary’s 

County, Maryland, July 2008

By Cheryl A. Dieter, Kimberly W. Campo, and Anna C. Baker

Abstract

The Naval Air Station Patuxent River in southern 

Maryland has continued to expand in the first decade of the 

21st century, contributing to rapid population growth in the 

surrounding area. The increase in population has caused State 

and County water managers and others to be concerned about 

the impact of population growth on the quantity and quality 

of groundwater supplies. The U.S. Geological Survey has 

been investigating the groundwater resources of the air station 

since 1998. As part of that ongoing investigation, groundwater was sampled in 2008 in six wells in the Aquia aquifer 

and two wells in the Upper Patapsco aquifer in the vicinity of 

Naval Air Station Patuxent River and Webster Outlying Field. 

Groundwater samples were analyzed for basic chemistry (field 

parameters, major ions, and nutrients) as well as several waterquality issues of concern including the occurrence of arsenic 

and tungsten, and saltwater intrusion.

The results of the 2008 groundwater-quality sampling 

indicate that the overall quality of groundwater in the Aquia 

aquifer has not changed since 1943; data are too limited to 

determine if groundwater quality has changed in the Upper 

Patapsco aquifer. At one well in the Aquia aquifer, the arsenic 

concentration exceeded the U.S. Environmental Protection 

Agency standard for drinking water. Arsenic was not detected 

in samples from the Upper Patapsco aquifer. Tungsten 

concentrations were detected at low concentrations near the 

laboratory reporting level in all eight samples. There was no 

evidence of saltwater intrusion in any of the wells.

Introduction

Development near the Naval Air Station Patuxent River 

(NAS Patuxent River) has resulted in rapid population growth 

in southern Maryland. This rapid population growth is a concern to State and County water managers, private citizens, and 

air station officials because of its impact on water supplies, as 

water withdrawals from groundwater have increased to meet 

increasing water demands. Increases in groundwater pumpage 

can lead to saltwater intrusion into freshwater aquifers from 

saline groundwater or from brackish water or seawater in 

coastal settings such as at NAS Patuxent River. Since 1998, 

the U.S. Geological Survey (USGS), in cooperation with 

the NAS Patuxent River, has been investigating the water 

resources of the Piney Point-Nanjemoy, Aquia, and more 

recently, the Upper Patapsco aquifers in the vicinity of the air 

station and Webster Outlying Field (WOLF) to understand 

the effects of water-use practices at NAS Patuxent River and 

WOLF on the water resources of the surrounding area.

In addition to saltwater intrusion, the NAS Patuxent 

River groundwater-quality assessment was designed to evaluate the occurrence and distribution of arsenic and tungsten. 

Arsenic is an element that occurs naturally in the environment 

and is present in the Aquia aquifer (Drummond and Bolton, 

2010). Arsenic also is a known human carcinogen (Agency 

for Toxic Substances and Disease Registry, 2007). The U.S. 

Environmental Protection Agency (USEPA) regulates arsenic concentrations in public drinking water and has set an 

enforceable Maximum Contaminant Level (MCL) of 10 μg/L 
2 Groundwater Quality and Occurrence of Selected Constituents, NAS Patuxent River, St. Mary’s County, Maryland, July 2008

(micrograms per liter) to protect public health and safety (U.S. 

Environmental Protection Agency, 2011). Tungsten is a metal 

that was used in “green” ammunitions by the military as an 

alternative to lead or depleted uranium. Tungsten has been 

detected in the soil and groundwater at firing ranges at other 

military facilities that have used tungsten ammunitions (U.S. 

Environmental Protection Agency, 2009). There is no Federal 

drinking-water standard established for tungsten; however, 

there is growing concern about the potential health effects 

of exposure to tungsten (Agency for Toxic Substances and 

Disease Registry, 2005). Tungsten ammunitions were not used 

at NAS Patuxent River; however, water resource managers 

wanted samples analyzed for tungsten as a preemptive measure for possible future requirements for military facilities to 

test for tungsten in groundwater. 

Purpose and Scope

The purpose of this report is to describe the occurrence 

and distribution of selected constituents in samples collected 

from eight wells screened in the Aquia and Upper Patapsco 

aquifers in July 2008 at NAS Patuxent River and WOLF. The 

report describes the general water chemistry of the aquifers, 

compares chemistry in samples collected in 1999–2001 and 

2008, describes the occurrence of arsenic and tungsten, and 

documents the status of saltwater intrusion. 

Description of Study Area and Well Numbering 

System

NAS Patuxent River is in St. Mary’s County in southern 

Maryland, near the convergence of the Patuxent River and 

Chesapeake Bay. WOLF is south of NAS Patuxent River, on 

the St. Mary’s River near St. Inigoes, Maryland (fig.1). NAS 

Patuxent River and WOLF encompass approximately 8,850 

acres (U.S. Navy, 2010). In 2010, NAS Patuxent River was 

the largest employer in St. Mary’s County, with a workforce of 

approximately 17,000 personnel (U.S. Navy, 2010).

The Aquia aquifer (table 1) is a deep, confined aquifer 

consisting of greenish-black quartz sand, glauconite, and 

lenses of clay and shell beds of the Aquia Formation (Chapelle 

and Drummond, 1983). The elevation of the top of the Aquia 

aquifer is approximately -450 ft (feet) relative to the North 

American Vertical Datum of 1988 (NAVD 88) beneath NAS 

Patuxent River and WOLF (Klohe and Feehley, 2001), and the 

thickness of the aquifer decreases from about 100 to 145 ft at 

NAS Patuxent River to about 50 ft at WOLF (Klohe and Kay, 

2007).

The Upper Patapsco aquifer is a deep, confined aquifer 

which underlies the Aquia aquifer and consists of sand units 

interbedded with silt and clay units and is part of the Patapsco 

Formation of the Potomac Group (Klohe and Kay, 2007). The 

elevation of the top of the Upper Patapsco aquifer is approximately -660 ft NAVD 88 at well SM Df 100 (fig. 2) at NAS 

Patuxent River and approximately -625 ft NAVD 88 at WOLF, 

and the thickness of the aquifer is approximately 200 to 240 ft 

at NAS Patuxent River and WOLF. 

The locations of wells discussed in this report are shown 

in figure 2. Well-construction data are presented in table 2. 

In this report, wells are listed by their USGS identification 

number. For example, well SM Dg 14 is a well located in St. 

Mary’s County, indicated by the first two letters “SM;” in the 

5-minute quadrangle (LaMotte, 2010) “Dg,” indicated by the 

second two letters; and is the 14th well mapped in the quadrangle, indicated by the last two numbers “14.” The 5-minute 

quadrangles are designated by upper-case letters from north to 

south (A through F in St. Mary’s County), and lower-case letters from west to east (a through h in St. Mary’s County).

Previous Investigations

The water quality of the confined aquifers of southern 

Maryland, which includes St. Mary’s and Calvert Counties, 

has been discussed in reports by both the USGS and the 

Maryland Geological Survey (MGS). One of the earliest 

reports describing water quality at NAS Patuxent River was 

a report by Bennett (1944) that provided water chemistry for 

four wells at the air station. The next report addressing water 

quality was by Chapelle and Drummond (1983). That report 

described the chemical evolution of groundwater in the Aquia 

and Piney Point-Nanjemoy aquifers in southern Maryland, 

including the NAS Patuxent River and WOLF areas. The 

groundwater type, or major ion chemistry, was found to 

change along the direction of flow. For example, the Aquia 

aquifer is generally calcium- and magnesium-bicarbonate type 

water with a pH of 6.5 to 7.5 near the outcrop/subcrop area, 

and changes downgradient to a sodium-bicarbonate type water 

with a relatively high pH, ranging from 7.5 to 8.5 (Chapelle 

and Drummond, 1983).

More recently, Klohe and Feehley (2001) described 

groundwater quality in the Piney Point-Nanjemoy and Aquia 

aquifers at NAS Patuxent River and WOLF. They found 

that groundwater in the Piney Point-Nanjemoy aquifer is of 

the calcium-magnesium-sodium-bicarbonate type, whereas 

groundwater in the Aquia aquifer is of the sodium-bicarbonate 

type. Klohe and Feehley (2001) compared historical data from 

groundwater samples collected from the Aquia aquifer in the 

1940s through the early 1960s (Chapelle and Drummond, 

1983) to samples collected in 1999, and found that the concentrations of major constituents had not changed appreciably in 

either the Piney Point-Nanjemoy aquifer or the Aquia aquifer. 

Klohe and Feehley (2001) also found no evidence of saltwater 

intrusion in either the Piney Point-Nanjemoy or the Aquia 

aquifer at NAS Patuxent River. At WOLF, the levels of some 

constituents in the Aquia aquifer were still within the range of 

values expected for freshwater, but were slightly higher than 

levels in the Aquia aquifer at NAS Patuxent River, which may 

indicate the very early stages of saltwater intrusion at WOLF 

(Klohe and Feehley, 2001). 
Introduction 3

Figure 1. Location of Naval Air Station Patuxent River, St. Mary’s County, Maryland (modified from Klohe and Kay, 

2007, fig. 1).
4 Groundwater Quality and Occurrence of Selected Constituents, NAS Patuxent River, St. Mary’s County, Maryland, July 2008

Table 1. Hydrologic and corresponding geologic units at Naval Air Station Patuxent River and Webster Outlying Field, St. Mary’s 

County, Maryland (modified from Klohe and Kay, 2007).

System Series Geologic unit Hydrologic unit

Quaternary Holocene to Pleistocene Surficial units 

(undifferentiated) Surficial aquifer

Tertiary

Pliocene

Miocene Chesapeake Group 

(undivided)

Upper confining unit

Piney Point-Nanjemoy aquifer Oligocene (?) unnamed Oligocene (?) Miocene (?) beds

Eocene

Piney Point Formation

Nanjemoy Formation

Middle confining unit

Paleocene

Marlboro Clay

Aquia Formation Aquia aquifer

Brightseat Formation Lower confining unit

Cretaceous Lower Cretaceous Patapsco Formation 

of the Potomac Group

Upper Patapsco aquifer

Confining unit

Undifferentiated aquifers and confining units

Klohe and Kay (2007) described water quality for two 

wells screened in the Upper Patapsco aquifer. On the basis 

of samples collected from the two wells, they found that the 

groundwater in the Upper Patapsco aquifer is sodium-bicarbonate type. Groundwater sampled as part of their study met 

all Federal drinking-water standards (for constituents that were 

analyzed for which Federal drinking-water standards have 

been established). 

Sample Collection, Analysis, and 

Quality Control

In July 2008, the USGS collected groundwater-quality 

samples from eight wells at NAS Patuxent River and WOLF. 

Field parameters, including temperature, pH, dissolved oxygen, alkalinity, and specific conductance, were measured at the 

wells at the time of sample collection. Samples were processed 

in the field and shipped to the analyzing laboratory.

Sample Collection and Analysis

Groundwater samples were collected by USGS personnel 

from five wells screened in the Aquia aquifer and one well 

screened in the Upper Patapsco aquifer at NAS Patuxent River 

(fig. 2). Samples also were collected from one well screened in 

the Aquia aquifer and one well screened in the Upper Patapsco 

aquifer at WOLF (fig. 2). All of the wells sampled were 

production wells that supply water for various uses at the air 

station and all had some type of chlorine treatment. All samples were collected from spigots before treatment or storage. 

Water-quality samples were collected and processed according 

to USGS protocols (U.S. Geological Survey, variously dated) 

and shipped to the USGS National Water Quality Laboratory 

(NWQL) in Denver, Colorado for analysis of major ions, 

selected minor ions, nutrients, arsenic, and tungsten. Data 

from these sampling events are reported in accordance with 

NWQL reporting protocols. 

The NWQL has established reporting conventions for 

low concentration water-quality data that are based upon two 

brackets for constituent concentration: the long-term method 

detection level (LT-MDL) and the laboratory reporting level 

(LRL). These markers were designed to reduce the occurrence 

of false positive and false negative detection errors to less 

than or equal to 1 percent. Concentrations reported as less 

than (<) a given value can be assumed to be less than the LRL 

for that constituent (Oblinger Childress and others, 1999). 

Concentrations are typically coded as estimated (E) because 

either the constituent measured has a concentration which is 

below the LRL but above the LT-MDL or the constituent concentration is measured outside the calibration range (Oblinger 

Childress and others, 1999). In the case of carbonate and 

bicarbonate, if there is discrepancy between the measured and 

theoretical endpoints for carbonate as determined via alkalinity titration, both carbonate and bicarbonate concentrations 

must be reported as estimated (U.S. Geological Survey, 2007). 

Constituents reported as estimated and an explanation for each 

case is given in table 3, and corresponding LRL and LT-MDL 

values are given where applicable. 
Sample Collection, Analysis, and Quality Control 5

Figure 2. Selected well locations at Naval Air Station Patuxent 

River and Webster Outlying Field, St. Mary’s County, Maryland 

(modified from Klohe and Kay, 2007).
6 Groundwater Quality and Occurrence of Selected Constituents, NAS Patuxent River, St. Mary’s County, Maryland, July 2008

Table 2. Records for selected wells at Naval Air Station Patuxent River and Webster Outlying Field, St. Mary’s County, Maryland.

[USGS, U.S. Geological Survey; NAVD 88, North American Vertical Datum of 1988]

USGS 

well 

number

Altitude 

of land 

surface 

(feet 

above 

NAVD 88)

Aquifer

Depth of 

well 

(feet 

below 

land 

surface)

Well 

diameter 

upperlower 

(inches)

Screen 

position 

(feet below 

land 

surface)

Date of 

construction

State of 

Maryland 

well permit 

number

Driller

SM Df 98 80 Aquia 575 8–6 525–575 12/15/1996 SM-94-0410 A.C. Schultes of Maryland

SM Df 99 44 Aquia 600 16–8 490–600 11/8/1994 SM-92-0642 Vans Construction Co.

SM Df 100 20 Upper 

Patapsco 910 10–8

706–716, 

744–754, 

835–860, 

882–892, 

900–905

8/4/2000 SM-94-3113 A.C. Schultes of Maryland

SM Dg 14 18 Aquia 542 8–6 490–540 4/22/1994 SM-92-0370 A.C. Schultes of Maryland

SM Dg 15 20 Aquia 500 8–5 450–500 12/17/1993 SM-92-0570 Patuxent Pump and Well Co.

SM Dg 19 9 Aquia 532 12–8 480–510 6/23/1988 SM-81-3345 Syndor Pump and Well Co.

SM Ff 35 4 Aquia 537 8–4 487–537 8/8/1975 SM-73-1496 A.C. Schultes of Maryland

SM Ff 65 9 Upper 

Patapsco 884 10–8

635–640, 

648–658, 

689–-694, 

782–792, 

846–856, 

864–874

8/10/2001 SM-94-3700 A.C. Schultes of Maryland

Quality Control

Quality-control samples were collected in addition to the 

environmental samples to estimate the magnitude of the bias 

and variability that results from sample collection, processing, 

and laboratory analysis. A field blank was collected at well 

SM Ff 65 using inorganic blank water certified by the USGS 

laboratory to test for potential sources of contamination of 

environmental samples during collection, shipping, or laboratory analysis. Replicate samples were collected at wells SM 

Df 98 and SM Df 100 to measure the variability in the waterquality data.

Quality-control results are presented along with environmental sample results in table 4. Field-blank data were 

reported as less than the LRL for all laboratory-measured 

constituents except calcium. Calcium had an estimated concentration of 0.03 mg/L (milligrams per liter), below the LRL 

of 0.04 mg/L, and was not a contamination concern because 

all environmental concentrations exceeded the reporting level 

by two orders of magnitude. The percent relative standard 

deviation (percent RSD) was calculated from the replicate data 

using the following equation:

( )

( )

2

1 2 / 2

Percent RSD 100

1 2 / 2

x x

x x

  − =    +   

where

x1 = the concentration of the environmental 

groundwater sample, and

x2 = the concentration of the replicate sample.

The percent RSD was less than 4 percent for all laboratory-measured constituents except iodide (percent RSD = 

7.4) and barium (percent RSD = 12.9) for well SM Df 98, and 

calcium (percent RSD = 12.9) and iron (percent RSD = 6.1) 

for well SM Df 100. For some of these constituents, the precision of reporting and the low concentration of the parameter 

resulted in a large calculated variability despite small differences in constituent concentration between environmental and 

replicate samples. Calculating percent RSDs near the reporting level where reporting intervals, the smallest increment by 

which reported values change, represent a significant proportion of the reported concentration can result in misleadingly 

high percent RSDs. 

The median of the percent RSDs for all laboratory-measured constituents was 0.6 percent, indicating that variability 

in the water-quality data are minimal, with the exception of 

data for iodide, barium, calcium, and iron. The percent RSD 

was less than 1.0 percent when field-measured values and 

laboratory-measured values for pH and specific conductance 

were compared.

(1)
Groundwater Quality and Occurrence and Distribution of Selected Constituents 7

Table 3. Water-quality parameters with concentrations reported as estimated (E), justification for data qualifier, and long-term 

method detection levels (LT-MDLs) and laboratory reporting levels (LRLs) that bracket the estimated concentrations where applicable.

[mg/L, milligrams per liter; μg/L, micrograms per liter; N/A, not applicable]

Constituents with 

values reported as 

“E”, estimated

LT-MDL 20081 LRL 20081 Reason for reporting value as estimated

Arsenic 0.03 μg/L 0.06 μg/L Concentration falls between LT-MDL and LRL.2

Bicarbonate (field) N/A N/A Alkalinity titration endpoint for carbonate does not match theoretical.3

Bromide 0.01 mg/L 0.02 mg/L Concentration falls between LT-MDL and LRL.

Calcium 0.02 mg/L 0.04 mg/L Concentration falls between LT-MDL and LRL.

Carbonate (field) N/A N/A Alkalinity titration endpoint for carbonate does not match theoretical.

Iron 4 μg/L 8 μg/L Concentration falls between LT-MDL and LRL.

Manganese 0.2 μg/L 0.4 μg/L Concentration falls between LT-MDL and LRL.

Nitrate + nitrite 0.02 mg/L 0.04 mg/L Concentration falls between LT-MDL and LRL.

Total Nitrogen 0.03 mg/L 0.06 mg/L Concentration falls between LT-MDL and LRL.

Tungsten 0.03 μg/L 0.06 μg/L Concentration falls between LT-MDL and LRL.

1

 Long-term method detection levels (LT-MDLs) and laboratory reporting levels (LRLs) 2008 from U.S. Geological Survey (2011).

2

 Reasoning for laboratory measurements being reported as estimated (E) from Oblinger Childress and others (1999).

3

 Reasoning for field measurements of carbonate and bicarbonate being reported as estimated (E) from U.S. Geological Survey (2007).

Groundwater Quality and Occurrence 

and Distribution of Selected 

Constituents

Groundwater samples were collected from wells screened 

in the Aquia and Upper Patapsco aquifers to describe the 

general water chemistry of these aquifers. The data were 

compared with data presented in previous USGS and MGS 

investigations (Bennett, 1944; Chapelle and Drummond, 1983; 

Klohe and Feehley, 2001; Klohe and Kay, 2007) to determine 

if water quality had changed over time in the aquifers. Sample 

data also were used to describe the occurrence and distribution 

of arsenic and tungsten, and the status of saltwater intrusion at 

NAS Patuxent River and WOLF. Results of the 2008 groundwater-sample analyses are provided in table 4.

Groundwater-Quality Characterization of the 

Aquia and Upper Patapsco Aquifers

Of the six wells in the Aquia aquifer from which groundwater samples were collected, the principal cations and anions 

in groundwater were sodium and bicarbonate, respectively 

(table 4). For the five Aquia aquifer wells at NAS Patuxent 

River, the pH ranged from 8.7 to 8.9, specific conductance 

ranged from 310 to 332 μS/cm (microsiemens per centimeter 

at 25 degrees Celsius), and alkalinity ranged from 150 to 164 

mg/L (as calcium carbonate). Total nitrogen concentrations 

were low, ranging from 0.14 to 0.19 mg/L, and only well SM 

Df 98 had a detectable concentration of nitrate plus nitrite with 

an estimated value of 0.23 mg/L (as N). The median concentrations of major cations and anions were 2.95 mg/L of calcium, 1.32 mg/L of magnesium, 6.99 mg/L of potassium, 70.8 

mg/L of sodium, 1.70 mg/L of chloride, 0.54 mg/L of fluoride, 

11.2 mg/L of silica, and 5.70 mg/L of sulfate. 

At WOLF, the water sampled from well SM Ff 35 

(screened in the Aquia aquifer) had a different chemistry than 

the chemistry in samples from the NAS Patuxent River wells. 

At well SM Ff 35, the Aquia aquifer pH was 8.6, specific 

conductance was 580 μS/cm, and alkalinity was 304 mg/L (as 

calcium carbonate). The total nitrogen concentration was 0.17 

mg/L, and the nitrite concentration was 0.003 mg/L (as N). 

The major cation and anion concentrations were 2.77 mg/L of 

calcium, 1.46 mg/L of magnesium, 7.67 mg/L of potassium, 

125 mg/L of sodium, 4.08 mg/L of chloride, 1.22 mg/L of 

fluoride, 11.1 mg/L of silica, and 12.6 mg/L of sulfate. The differences in water chemistry in the Aquia aquifer between NAS 

Patuxent River and WOLF may be due to chemical reactions 

between the groundwater and the aquifer matrix as the water 

moves downgradient from NAS Patuxent River toward WOLF 

(Chapelle and Drummond, 1983).
8 Groundwater Quality and Occurrence of Selected Constituents, NAS Patuxent River, St. Mary’s County, Maryland, July 2008 Table 4. Water quality and chemical composition of water samples collected from wells screened in the Aquia and Upper Patapsco aquifers, Naval Air Station Patuxent River and Webster Outlying Field, St. Mary’s County, Maryland, July 2008. [USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms per liter; E, estimated; <, less than; --, no data available; NASPR, Naval Air Station Patuxent River; WOLF, Webster Outlying Field; CaCO3, calcium carbonate; SiO2, silicon dioxide] USGS well number Aquifer (location) Date Dis- solved oxygen (mg/L) pH, water, unfiltered, field (standard units) pH, water, un- filtered, labora- tory (standard units) Specific conductance, water, unfiltered, laboratory (μS/cm at 25 degrees Celsius) Specific conductance, water, unfiltered, field (μS/cm at 25 degrees Celsius) Temperature, water (degrees Celsius) Calcium, water, filtered (mg/L) Mag- nesium, water, filtered (mg/L) Potassium, water, filtered (mg/L) Sodium, water, filtered (mg/L) SM Df 98 Aquia (NASPR) 7/15/2008 5.4 8.9 8.9 312 313 18.8 2.79 1.23 6.99 69.0 SM Df 98A Aquia (NASPR) 7/15/2008 -- -- 8.9 314 -- -- 2.77 1.20 6.99 68.3 SM Df 99 Aquia (NASPR) 7/15/2008 3.7 8.8 8.9 314 315 18.5 2.53 1.01 6.79 70.8 SM Dg 14 Aquia (NASPR) 7/16/2008 6.5 8.7 8.8 310 312 19.1 3.21 1.32 6.69 61.8 SM Dg 15 Aquia (NASPR) 7/15/2008 1.4 8.7 8.8 332 332 18.9 2.95 1.37 7.39 73.9 SM Dg 19 Aquia (NASPR) 7/15/2008 -- 8.7 8.8 329 328 19.6 3.22 1.38 7.09 71.3 SM Ff 35 Aquia (WOLF) 7/16/2008 7.1 8.6 8.7 577 580 20.2 2.77 1.46 7.67 125 SM Df 100 Upper Patapsco (NASPR) 7/15/2008 2.0 8.4 8.5 264 266 21.7 0.36 0.212 2.46 63.9 SM Df 100A Upper Patapsco (NASPR) 7/15/2008 -- -- 8.5 264 -- -- 0.30 0.201 2.37 64.2 SM Ff 65 Upper Patapsco (WOLF) 7/16/2008 6.2 8.6 8.7 525 531 21.8 0.71 0.389 3.83 118 SM Ff 65B Upper Patapsco (WOLF) 7/16/2008 -- -- 8.3 <8 -- -- E.03 <.020 <.02 <.12
Groundwater Quality and Occurrence and Distribution of Selected Constituents 9

Table 4. Water quality and chemical composition of water samples collected from wells screened in the Aquia and Upper Patapsco aquifers, Naval Air Station Patuxent River and Webster Outlying Field, St. Mary’s County, Maryland, July 2008.—Continued[USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms per liter; E, estimated; <, less than; --, no data available; NASPR, Naval Air Station Patuxent River; WOLF, Webster Outlying Field; CaCO , calcium carbonate; SiO , silicon dioxide] 3 2

Alkalin- Bicarbon- Carbon- ity, water, ate, ate, water, Total Nitrate filtered, Silica, Nitrite, water, Bromide, filtered, Chloride, Fluoride, Iodide, Sulfate, dissolved + nitrite, USGS inflec- water, water, Aquifer filtered, water, inflection water, water, water, water, solids, water, well Date tion point filtered filtered (location) inflection filtered point filtered filtered filtered filtered water, filtered number titration, (mg/L as (mg/L point titra- (mg/L) titration, (mg/L) (mg/L) (mg/L) (mg/L) filtered (mg/L as field SiO ) as N) 2 tion, field field (mg/L) N) (mg/L as (mg/L) (mg/L) CaCO )3

SM Df 98 Aquia 7/15/2008 152 177 E.02 4.0 1.86 0.54 0.009 11.8 5.99 191 E.023 <.002

(NASPR)

SM Df 98A Aquia 7/15/2008 -- -- E.01 -- 1.86 0.54 0.010 11.7 5.92 189 E.020 <.002

(NASPR)

SM Df 99 Aquia 7/15/2008 156 E182 E.02 E3.8 1.74 0.56 0.009 11.2 5.70 192 <.04 <.002

(NASPR)

SM Dg 14 Aquia 7/16/2008 150 179 E.01 2.2 1.70 0.53 0.008 10.4 5.36 180 <.04 <.002

(NASPR)

SM Dg 15 Aquia 7/15/2008 164 E193 E.02 E3.1 1.68 0.55 0.008 10.8 6.07 198 <.04 <.002

(NASPR)

SM Dg 19 Aquia 7/15/2008 164 E194 E.01 E2.9 1.60 0.53 0.006 11.2 5.56 208 <.04 <.002

(NASPR)

SM Ff 35 Aquia 7/16/2008 304 E364 E.02 E3.4 4.08 1.22 0.003 11.1 12.6 351 <.04 0.003

(WOLF)

SM Df 100 Upper 7/15/2008 126 152 <.02 1.0 3.25 0.44 <.002 11.5 5.27 166 <.04 <.002

Patapsco 

(NASPR)

SM Df 100A Upper 7/15/2008 -- -- <.02 -- 3.25 0.43 <.002 11.6 5.32 165 E.02 <.002

Patapsco 

(NASPR)

SM Ff 65 Upper 7/16/2008 261 311 E.01 3.6 1.48 0.82 0.004 10.6 12.6 319 <.04 <.002

Patapsco 

(WOLF)

SM Ff 65B Upper 7/16/2008 -- -- <.02 -- <.12 <.12 <.002 <.02 <.18 <10 <.04 <.002

Patapsco 

(WOLF)
10 Groundwater Quality and Occurrence of Selected Constituents, NAS Patuxent River, St. Mary’s County, Maryland, July 2008 Table 4. Water quality and chemical composition of water samples collected from wells screened in the Aquia and Upper Patapsco aquifers, Naval Air Station Patuxent River and Webster Outlying Field, St. Mary’s County, Maryland, July 2008.—Continued [USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms per liter; E, estimated; <, less than; --, no data available; NASPR, Naval Air Station Patuxent River; WOLF, Webster Outlying Field; CaCO , calcium carbonate; SiO , silicon dioxide] 3 2 Total nitrogen, Arsenic, USGS Barium, water, Boron, water, Iron, water, Manganese, Strontium, Tungsten, Aquifer water, unfiltered water, well Date filtered filtered filtered water, filtered water, filtered water, filtered (location) by analysis filtered number (μg/L) (μg/L) (μg/L) (μg/L) (μg/L) (μg/L) (mg/L) (μg/L) SM Df 98 Aquia 7/15/2008 0.17 6.2 0.6 169 E6 E.2 27.5 0.06 (NASPR) SM Df 98A Aquia 7/15/2008 0.17 6.2 0.5 168 <8 E.2 27.6 E.06 (NASPR) SM Df 99 Aquia 7/15/2008 0.18 5.8 0.7 175 9 E.2 28.0 0.08 (NASPR) SM Dg 14 Aquia 7/16/2008 0.14 9.0 0.6 177 9 0.6 40.9 0.08 (NASPR) SM Dg 15 Aquia 7/15/2008 0.17 7.4 0.6 178 <8 E.3 28.7 E.03 (NASPR) SM Dg 19 Aquia 7/15/2008 0.19 11.2 0.6 186 <8 0.4 36.2 E.04 (NASPR) SM Ff 35 Aquia 7/16/2008 0.17 1.8 2.6 301 9 0.7 41.5 E.05 (WOLF) SM Df 100 Upper 7/15/2008 E.05 <.06 6.2 151 36 9.0 6.3 E.05 Patapsco (NASPR) SM Df 100A Upper 7/15/2008 E.04 <.06 6.2 157 33 8.9 6.3 E.05 Patapsco (NASPR) SM Ff 65 Upper 7/16/2008 0.13 E.06 10.9 294 12 8.5 16.1 0.07 Patapsco (WOLF) SM Ff 65B Upper 7/16/2008 <.06 <.06 <.4 <6 <8 <.4 <.8 <.06 Patapsco (WOLF) A Replicate.

B Blank.
Groundwater Quality and Occurrence and Distribution of Selected Constituents 11

Water samples were collected from well SM Df 100, 

screened in the Upper Patapsco aquifer at NAS Patuxent 

River, and well SM Ff 65, screened in the Upper Patapsco 

aquifer at WOLF. As was the case with the Aquia aquifer 

samples, the principal cations and anions in the Upper 

Patapsco aquifer samples were sodium and bicarbonate, 

respectively. The water sample from the Upper Patapsco 

aquifer at WOLF typically had major ion concentrations that 

were approximately two times greater than the water sample 

from the Upper Patapsco aquifer at NAS Patuxent River (table 

4). For example, the concentration of calcium was 0.36 mg/L 

at NAS Patuxent River and 0.71 mg/L at WOLF, the concentration of fluoride was 0.44 mg/L at NAS Patuxent River and 

0.82 mg/L at WOLF, and the concentration of sodium was 

63.9 mg/L at NAS Patuxent River and 118 mg/L at WOLF. 

The ratios of these constituents however, are similar at NAS 

Patuxent River and WOLF. For example, the ratio of calcium 

to fluoride is 0.82 at NAS Patuxent River, and 0.87 at WOLF. 

Characterization of the water quality of the Upper Patapsco 

aquifer is limited due to the small dataset.

Comparison of Groundwater Quality in the Aquia 

and Upper Patapsco Aquifers, 1943–2008

Data from six Aquia aquifer wells and two Upper 

Patapsco aquifer wells sampled in 1999–2001 and resampled 

in 2008 were compared by bar chart and Piper diagram 

analysis to determine whether changes in water quality had 

occurred. Results from sampling of the Aquia aquifer were 

also compared with historical data presented in Klohe and 

Feehley (2001). 

Specific conductance and concentrations of major ions 

in selected water samples collected from the Aquia and Upper 

Patapsco aquifers at NAS Patuxent River and WOLF locations 

in 1999–2001 and 2008 are shown in figure 3 (A-H). The 

data show little variation in water chemistry in both aquifers 

between 1999–2001 and 2008, with the exception of chloride. 

Chloride concentrations were higher in 2008 in wells SM Ff 

35 and SM Df 100, however, a trend cannot be determined 

because there are only two data points for each well. 

Major ions in the samples collected in 1999–2001 and 

2008 were plotted on a Piper diagram for comparison among 

the water-quality datasets (fig. 4). Piper diagrams show the 

relative concentrations of major cations and anions as percentages of the total ionic concentration of the water (Piper, 1944). 

Waters with similar chemistry will plot in the same area on the 

diagram. The data from 1999–2001 and the data from 2008 

for the Aquia aquifer all plot in the same location in the Piper 

diagram with the exception of one sample (from well SM Df 

61, collected in 1999 only), indicating the water chemistry in 

the Aquia aquifer has not changed since 1999–2001 (fig. 4). 

The chemistry of the water at well SM Df 61 is similar to that 

of the Piney Point-Nanjemoy aquifer, possibly because (1) 

the well is screened in both aquifers, or (2) improper or faulty 

construction is allowing water from the Piney Point-Nanjemoy 

aquifer to leak into the well (Klohe and Feehley, 2001). 

Though the data collected from the Upper Patapsco aquifer are 

too limited to draw conclusive assumptions about the historical continuity of groundwater quality, results from 1999–2001 

and 2008 plot in the same location on the Piper diagram, 

indicating that water quality has been consistent with respect 

to these parameters. 

Historical data from groundwater samples collected 

from the Aquia aquifer in the 1940s through the early 1960s 

(Chapelle and Drummond, 1983) were presented in Klohe and 

Feehley (2001). During this period from the 1940s through 

2001, the water chemistry in groundwater samples from the 

Aquia aquifer has remained constant, thus it can be concluded 

that the water chemistry in the Aquia aquifer at NAS Patuxent 

River has not changed since the 1940s. This would be 

expected because deep confined aquifers such as the Aquia 

and Upper Patapsco aquifers are less susceptible to landsurface influences. Analysis of the Upper Patapsco aquifer 

was not included in the 2001 study, and thus no comparison of 

recent sampling with historical data is made here. 

Arsenic and Tungsten

Groundwater samples were collected and analyzed for 

arsenic to verify the presence and concentration of arsenic in 

the water-supply wells, and to serve as a baseline for comparison with arsenic concentrations in samples collected in future 

studies.

Arsenic concentrations in groundwater sampled from the 

six wells in the Aquia aquifer ranged from 1.8 μg/L to 11.2 

μg/L (table 4). The two wells located near the confluence of 

the Patuxent River and Chesapeake Bay at NAS Patuxent 

River (SM Dg 14 and SM Dg 19) had the highest arsenic 

concentrations—9 μg/L and 11.2 μg/L, respectively. The 

arsenic concentration at well SM Dg 19 was greater than the 

arsenic MCL of 10 μg/L. Arsenic concentrations in the two 

wells sampled in the Upper Patapsco aquifer were less than the 

MCL, and were less than or equal to the LRL (table 4).

Groundwater samples were collected and analyzed for 

tungsten to determine its occurrence in the water-supply wells 

at the air station. The LRL for tungsten was 0.06 μg/L for the 

period when the samples were collected and analyzed. Of the 

six wells where groundwater was sampled from the Aquia 

aquifer, tungsten concentrations in three wells were estimated. 

The tungsten concentrations in the Aquia aquifer samples 

ranged from E0.03 μg/L to 0.08 μg/L. The tungsten concentrations in the Upper Patapsco aquifer samples were E0.05 μg/L 

(SM Df 100, NAS Patuxent River) and 0.07 μg/L (SM Ff 65, 

WOLF) (table 4).
12 Groundwater Quality and Occurrence of Selected Constituents, NAS Patuxent River, St. Mary’s County, Maryland, July 2008

Figure 3. Comparisons of major ions in water samples collected from the Aquia and Upper Patapsco aquifers at the Naval 

Air Station Patuxent River (NASPR) and Webster Outlying Field (WOLF) locations in 1999–2001 and 2008.
Groundwater Quality and Occurrence and Distribution of Selected Constituents 13

Figure 4. Comparison of the average chemical composition of seawater to the chemical composition of groundwater 

from selected wells at Naval Air Station Patuxent River and Webster Outlying Field, St. Mary’s County, Maryland.
14 Groundwater Quality and Occurrence of Selected Constituents, NAS Patuxent River, St. Mary’s County, Maryland, July 2008

Saltwater Intrusion

Freshwater aquifers in coastal areas are vulnerable to 

contamination by saltwater intrusion, which is the movement 

of saline water into freshwater aquifers. Pumping from 

groundwater wells is most often the cause of saltwater intrusion in coastal areas (Barlow, 2003), leading to the eventual 

abandonment of water-supply wells when concentrations of 

Federally regulated saltwater-related contaminants exceed 

drinking-water standards. Seawater from the ocean and estuaries is a major source of saltwater in coastal aquifers; however, 

entrapped fossil seawater, or connate water, can be another 

source of contamination. The possibility of saltwater intrusion 

into the aquifers at the air station is a concern because of their 

proximity to saline Patuxent River, Chesapeake Bay, and 

other estuaries. Increased demands for water supply for the air 

station and adjacent communities have the potential to induce 

saltwater intrusion into the freshwater aquifers. Six wells 

screened in the Aquia aquifer and two wells screened in the 

Upper Patapsco aquifer were sampled to detect the possible 

presence of saltwater.

A Piper diagram was used to compare water chemistry 

in the Aquia and Upper Patapsco aquifers to the average 

water chemistry of seawater. Data from the six Aquia aquifer 

wells sampled in 2008 plot in the same area on the diagram, 

showing that groundwater from these wells has similar water 

chemistry; however, the chemistry is different from average 

seawater chemistry (fig. 4). Data from the two Upper Patapsco 

aquifer wells sampled in 2008 plot in the same area of the 

Piper diagram as the Aquia aquifer samples, and also had different water chemistry than seawater.

Saltwater intrusion can be indicated by high total dissolved solids (TDS), high concentrations of chloride and 

sulfate, calcium to magnesium (Ca:Mg) ratios equal to 1.0, 

sodium to chloride (Na:Cl) ratios equal to 2, and chloride to 

bromide (Cl:Br) ratios equal to 287.5 (Klohe and Feehley, 

2001). Saltwater is any water with TDS concentrations greater 

than 1,000 mg/L, but seawater TDS concentrations average 

approximately 35,000 mg/L (Barlow, 2003). The median TDS 

for the six samples collected from the Aquia aquifer was 195 

mg/L, with a maximum TDS of 351 mg/L at well SM Ff 35 

located at WOLF (table 4). The two Upper Patapsco aquifer 

samples had TDS concentrations of 166 mg/L (well SM Df 

100, NAS Patuxent River) and 319 mg/L (well SM Ff 65, 

WOLF) (table 4). In seawater, chloride concentrations are 

about 19,000 mg/L and sulfate concentrations are about 2,700 

mg/L (Hem, 1992). Chloride concentrations were less than 5 

mg/L and sulfate concentrations were less than 15 mg/L in the 

six Aquia aquifer wells and the two Upper Patapsco aquifer 

wells (tables 4 and 5). All indicators of saltwater intrusion 

were therefore well below seawater concentrations, indicating 

that saltwater intrusion has not occurred at NAS Patuxent 

River or WOLF.

Table 5. Comparison of average seawater and average connate water to groundwater samples collected in 2008 from the Aquia 

aquifer at Naval Air Station Patuxent River, and Webster Outlying Field, St. Mary’s County, Maryland.

[TDS, total dissolved solids; Ca, calcium; Mg, magnesium; Na, sodium; Cl, chloride; Br, bromide; mg/L, milligrams per liter; μg/L, micrograms per liter; 

all ratios are reported in mg/L to mg/L; NASPR, Naval Air Station Patuxent River; WOLF, Webster Outlying Field]

Average seawater Average connate water

Aquia aquifer at 

NASPR 

(5 samples )

Aquia aquifer at 

WOLF 

(1 sample)

TDS 35,000 mg/L (Barlow, 2003) 180–208 mg/L 351 mg/L

Sulfate 2,700 mg/L (Hem,1992; Drever, 1988) 5.36–6.07 mg/L 12.6 mg/L

Chloride 19,000 mg/L (Hem, 1992) 1.6–1.86 mg/L 4.08 mg/L

Ca:Mg 1 (Piper and others, 1953) 2.2–2.5 1.9

Na:Cl 2 (Piper and others, 1953) 0.5 (Faure, 1991) 36.4–44.6 30.6

Cl:Br 287.5 (Stumm and Morgan, 1995) 84–186 204

Barium 24–142 mg/L (Piper and others, 1953) 0.6–0.7 μg/L 2.6 μg/L

Iodide 30–80 mg/L (Piper and others, 1953) 0.006–0.009 mg/L 0.003 mg/L
References Cited 15

Summary and Conclusions

The Aquia and Upper Patapsco aquifers are water-supply 

sources for Naval Air Station Patuxent River (NAS Patuxent 

River) and Webster Outlying Field (WOLF) and the surrounding communities in southern Maryland, and there is 

concern about the effect of increasing water demands on the 

water quality in these aquifers. This report presents groundwater-quality data collected by the U.S. Geological Survey in 

July 2008 from eight wells screened in the Aquia and Upper 

Patapsco aquifers at NAS Patuxent River and WOLF.

Results of the groundwater sample analysis indicate 

that the principal cations and anions in groundwater samples 

collected from six wells screened in the Aquia aquifer were 

sodium and bicarbonate, respectively. The results also indicate 

that the principal cations and anions in groundwater samples 

collected from two wells screened in the Upper Patapsco aquifer were sodium and bicarbonate, respectively. Comparison of 

data from samples collected from 1943 to 1962, and samples 

collected in 1999 and 2008, indicates that water quality in the 

Aquia aquifer has not changed. Water-quality changes in the 

Upper Patapsco aquifer cannot be determined because of a 

limited dataset. 

Arsenic, a naturally occurring element in the environment, was detected in all wells in the Aquia aquifer at concentrations ranging from 1.8 μg/L (micrograms per liter) to 11.2 

μg/L. One well screened in the Aquia aquifer at NAS Patuxent 

River had an arsenic concentration greater than the U.S. 

Environmental Protection Agency’s Maximum Contaminant 

Level of 10 μg/L. Arsenic concentrations in the Upper 

Patapsco aquifer were equal to or less than the laboratory 

reporting level and were well below the U.S. Environmental 

Protection Agency Maximum Contaminant Level. Tungsten 

was detected in all eight samples, but at low concentrations 

(estimated 0.03 to 0.08 μg/L). The average chemistry of seawater was compared to the chemistry of the eight samples collected from the Aquia aquifer or the Upper Patapsco aquifer, 

but no evidence of saltwater intrusion was observed.

Acknowledgments

The authors thank Michael Oliver and Denis Gonda at 

NAS Patuxent River for assisting with the study and providing 

logistical support to collect the samples. The authors also 

thank USGS personnel for the preparation, collection, and 

processing of the analytical samples, especially Noelle Stroik 

and Joseph Sullivan, and the many reviewers of this report for 

their helpful comments, especially Brandon Fleming, Jeffrey 

Chanat, Douglas Chambers, and Jennifer Stanton.

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Prepared by USGS West Trenton Publishing Service Center.

Edited by Valerie M. Gaine.

Graphics and layout by Timothy W. Auer.

For additional information, contact:

Director, MD-DE-DC Water Science Center

U.S. Geological Survey

5522 Research Park Drive

Baltimore, MD 21228

or visit our Web site at:

http://md.water.usgs.gov
Dieter, C.A., and others—Groundwater Quality and Occurrence and Distribution of Selected Constituents, NAS Patuxent River, St. Mary’s County, Maryland, July 2008—Scientific Investigations Report 2012–5011

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