United States

Environmental Protection

Agency

Hydrogeologic Framework,

Ground-Water Geochemistry,

and Assessment of Nitrogen

Yield from Base Flow in Two

Agricultural Watersheds,

Kent County, Maryland
EPA/600/R-02/008

January 2002

Hydrogeologic Framework, Ground-Water

Geochemistry, and Assessment of Nitrogen

Yield from Base Flow in Two Agricultural

Watersheds, Kent County, Maryland

by

L. Joseph Bachman

U.S. Geological Survey

Baltimore, MD 21237

David E. Krantz

U.S. Geological Survey

Dover, DE 19901

Johnkarl Böhlke

U.S. Geological Survey

U.S. Department of the Interior

Reston, VA 20192

IAG #DW14937941

Project Officer

Mohamed M. Hantush

Subsurface Protection and Remediation Division

National Risk Management Research Laboratory

Ada, OK 74820

National Risk Management Research Laboratory

Office of Research and Development

U.S. Environmental Protection Agency

Cincinnati, OH 45268
ii

Notice

The information in this document has been funded by the U.S. Environmental Protection Agency (EPA)

under the auspices of the Ecosystem Restoration Research Program of the Office of Research and

Development’s National Risk Management Research Laboratory through an Interagency Agreement with the

Department of Interior’s U.S. Geological Survey under Agreement No. DW14937941. It has been subjected

to the Agency’s peer and administrative review, and has been approved for publication as an EPA document.

Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

All research projects making conclusions or recommendations based on environmental data and funded by

the Environmental Protection Agency are required to participate in the Agency Quality Assurance Program.

This project was conducted under an approved Quality Assurance Project Plan. The procedures specified in

this plan were used without exception. Information on the plan and documentation of the quality assurance

activities and results are available from the Principal Investigator.
iii

Foreword

The U.S. Environmental Protection Agency is charged by Congress with protecting the Nation’s land, air,

and water resources. Under a mandate of national environmental laws, the Agency strives to formulate and

implement actions leading to a compatible balance between human activities and the ability of natural

systems to support and nurture life. To meet this mandate, EPA’s research program is providing data and

technical support for solving environmental problems today and building a science knowledge base

necessary to manage our ecological resources wisely, understand how pollutants affect our health, and

prevent or reduce environmental risks in the future.

The National Risk Management Research Laboratory (NRMRL) is the Agency’s center for investigation of

technological and management approaches for preventing and reducing risks from pollution that threatens

human health and the environment. The focus of the Laboratory’s research program is on methods and their

cost-effectiveness for prevention and control of pollution to air, land, water, and subsurface resources;

protection of water quality in public water systems; remediation of contaminated sites, sediments and ground

water; prevention and control of indoor air pollution; and restoration of ecosystems. NRMRL collaborates

with both public and private sector partners to foster technologies that reduce the cost of compliance and to

anticipate emerging problems. NRMRL’s research provides solutions to environmental problems by:

developing and promoting technologies that protect and improve the environment; advancing scientific and

engineering information to support regulatory and policy decisions; and providing the technical support and

information transfer to ensure implementation of environmental regulations and strategies at the national,

state, and community levels.

Nutrient inputs from human activities have resulted in the “cultural eutrophication” of lakes and coastal

waters. This publication documents a study of the role of the shallow subsurface stratigraphy in determining

the potential for nutrient impacts from nitrogen species on water quality in streams as a result of groundwater discharges to the streams. The study focused on two adjacent watersheds in Kent County, Maryland,

that had similar topography, land use and soils. Although the watersheds were similar in landscape features

and land use, it was found that the hydrostratigraphy of the aquifer underlying the watershed had a dominant

role in producing the observed differences in nitrogen yields from the two watersheds. The study illustrates

the importance of understanding hydrogeology for management of nitrogen yields from watersheds to

coastal waters.

This publication has been produced as part of the Laboratory’s strategic long-term research plan. It is

published and made available by EPA’s Office of Research and Development to assist the user community

and to link researchers with their clients.

Stephen G. Schmelling, Acting Director

Subsurface Protection and Remediation Division

National Risk Management Research Laboratory
iv
v

Abstract Abstract

Hydrostratigraphic and geochemical data collected in two adjacent watersheds on the Delmarva Peninsula, in Kent County,

Maryland, indicate that shallow subsurface stratigraphy is an important factor that affects the concentrations of nitrogen in

ground water discharging as stream base flow. The flux of nitrogen from shallow aquifers can contribute substantially to the

eutrophication of streams and estuaries, degrading water quality and aquatic habitats. The information presented in this report

includes a hydrostratigraphic framework for the Locust Grove study area, analyses and interpretation of ground-water

chemistry, and an analysis of nutrient yields from stream base flow. An understanding of the processes by which ground-water

nitrogen discharges to streams is important for optimal management of nutrients in watersheds in which ground-water

discharge is an appreciable percentage of total streamflow. The U.S. Geological Survey, in cooperation with the U.S.

Environmental Protection Agency (USEPA), collected and analyzed hydrostratigraphic and geochemical data in support of

ground-water flow modeling by the USEPA.

The adjacent watersheds of Morgan Creek and Chesterville Branch have similar topography and land use; however, reported

nitrogen concentrations are generally 6 to 10 milligrams per liter in Chesterville Branch but only 2 to 4 milligrams per liter in

Morgan Creek. Ground water in the surficial aquifer in the recharge areas of both streams has high concentrations of nitrate

(greater than 10 milligrams per liter as N) and dissolved oxygen. One component of the ground water discharging to Morgan

Creek typically is anoxic and contains virtually no dissolved nitrate; most of the ground water discharging to Chesterville

Branch is oxygenated and contains moderately high concentrations of nitrate.

The surficial aquifer in the study area is composed of the deeply weathered sands and gravels of the Pensauken Formation (the

Columbia aquifer) and the underlying glauconitic sands of the upper Aquia Formation (the Aquia aquifer). The lower 6 to 9

meters of the Aquia Formation is a low-permeability silt-clay with abundant glauconite. The Aquia confining layer underlies

the Columbia-Aquia surficial aquifer throughout the study area. The sediment redox transition, identified in cores, that occurs

in the upper 0.5 to 1 meter of the Aquia confining layer is thought to be a site for subsurface denitrification of ground water.

The first confined aquifer is composed of the glauconitic sands in the upper 9 to 11 meters of the Hornerstown Formation. The

Hornerstown aquifer is underlain by 10 to 15 meters of glauconitic silt-clay at the base of the Hornerstown Formation (the

Hornerstown confining layer), and 5 meters of low-permeability clay in the underlying Severn Formation.

The Aquia and Hornerstown Formations dip and thicken to the southeast, and the Aquia confining layer subcrops shallowly

(within 5 meters of the land surface) in a band that strikes southwest to northeast across the northern edge of the study area. The

surficial aquifer is very thin (generally less than 5 meters) north of Morgan Creek, and the alluvial valley of Morgan Creek has

incised into the top of the Aquia confining layer. In contrast, the Aquia confining layer lies 22 meters below Chesterville

Branch, and the surficial aquifer approaches 30 meters in thickness (away from the creek).

Chemically reduced iron sulfides and glauconite in the Aquia confining layer are likely substrates for denitrification of nitrate

in ground water. Evidence from the dissolved concentrations of nitrate, sulfate, iron, argon, and nitrogen gas, and stable

nitrogen isotopes support the interpretation that ground water flowing near the top of the Aquia confining layer, or through the

confined Hornerstown aquifer, has undergone denitrification. This process appears to have the greatest effect on ground-water

chemistry north of Morgan Creek, where the surficial aquifer is thin and a greater percentage of the ground water contacts the

Aquia confining layer.

The base-flow discharges of total nitrogen from the two watersheds are of similar magnitude, although Chesterville Branch has

somewhat higher loads (29,000 kilograms of nitrogen per year) than Morgan Creek (20,000 kilograms of nitrogen per year),

although Morgan Creek has a larger drainage area and a greater discharge of water. The base-flow yield of nitrogen (load per

unit area) in Chesterville Branch (median of 0.058 grams per second per square kilometer at the outlet) is more than twice that

of Morgan Creek (median of 0.022 grams per second per square kilometer at the outlet), reflecting the higher concentration of

nitrate in ground water discharging to Chesterville Branch. Total nitrogen concentrations tend to decrease downstream in

Chesterville Branch and increase downstream in Morgan Creek. The downstream trend in Chesterville Branch may be affected

by instream nitrogen uptake and denitrification, and an increasing proportion of older, denitrified ground water in downstream

discharge. The downstream trends in Morgan Creek may be affected by inflow from tributaries, downstream changes in the

source of discharge water, and downstream changes in the riparian zone, which could affect the processes and degree of

denitrification.
vi

Although these two watersheds appear to have landscape features (such as topography, land use, and soils) that would produce

similar nitrogen discharges, a more detailed examination of landscape features indicates that Chesterville Branch has soils that

are slightly better drained, tributary stream outlets at higher altitudes, and a slightly higher percentage of agricultural land. All

of these factors have been related to higher nitrogen yields. Nonetheless, most of the data support the interpretation that

hydrostratigraphy has the greatest effect in producing the difference in nitrogen yields between the two watersheds.
vii

Contents Contents

Foreword ........................................................................................................................................................ iii

Abstract ........................................................................................................................................................... v

Figures .......................................................................................................................................................... viii

Tables .............................................................................................................................................................. x

SI Conversion Factors .................................................................................................................................... xi

Acknowledgments......................................................................................................................................... xii

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

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

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

Data-Collection Methods ................................................................................................................................ 9

Compilation of Existing Data .................................................................................................................. 9

Corehole Drilling ..................................................................................................................................... 9

Well Network and Water-Level Measurement...................................................................................... 10

Well Sampling ....................................................................................................................................... 11

Base-Flow Sampling .............................................................................................................................. 11

Chemical Analysis of Water Samples ................................................................................................... 13

Data Analysis ......................................................................................................................................... 13

Hydrogeologic Framework ........................................................................................................................... 15

Lithostratigraphic Units ......................................................................................................................... 16

Holocene Alluvial Sediments ......................................................................................................... 16

Pensauken Formation, Upper Miocene (?) / Lower Pliocene (?) .................................................. 17

Old Church (?) Formation, Upper Oligocene, and Calvert Formation,

Lower to Middle Miocene .............................................................................................................. 17

Aquia Formation, Upper Paleocene ............................................................................................... 17

Hornerstown Formation, Lower Paleocene .................................................................................... 18

Composite Hydrostratigraphic Sequence .............................................................................................. 18

Surficial Aquifer (Columbia and Aquia Aquifers) ........................................................................ 18

Aquia Confining Layer ................................................................................................................... 18

Hornerstown Aquifer and Hornerstown Confining Layer ............................................................. 19

Geometry of the Hydrostratigraphic Units ............................................................................................ 19

Ground-Water Flow Paths and Traveltimes .......................................................................................... 23

Ground-Water Geochemistry ........................................................................................................................ 27

Dissolved Nitrate and Denitrification .................................................................................................... 28

Nutrient Yields from Stream Base Flow ...................................................................................................... 31

Sampling at Fixed Sites ......................................................................................................................... 31

Base-Flow Synoptic Surveys ................................................................................................................. 32

Relation Between Nutrients and Landscape Factors ............................................................................. 43

Summary and Conclusions ........................................................................................................................... 49

References Cited ........................................................................................................................................... 51

Appendices

Appendix A. ........................................................................................................................................... 55

Appendix B. ........................................................................................................................................... 58

Appendix C. ........................................................................................................................................... 60

Appendix D. ........................................................................................................................................... 64

Appendix E. ........................................................................................................................................... 67

Appendix F. ........................................................................................................................................... 77
viii

Figures

1a. Index map showing the location of Chesapeake Bay, Delmarva Peninsula,

and the Locust Grove study area in Kent County, Maryland ......................................................................................... 3

1b. Index map showing the location of the Locust Grove study area in Kent County, Maryland ...................................... 4

2. Map of the Locust Grove study area, Kent County, Maryland, showing the location of stream-gaging

stations, surface-water sampling sites, wells, coreholes, and transects of the hydrostratigraphic sections ................... 5

3. Map showing land use in 1994 for the Morgan Creek and Chesterville Branch watersheds,

Kent County, Maryland ................................................................................................................................................... 6

4. Diagram showing the relative distribution of the age of discharging ground water in stream

headwaters and downstream .......................................................................................................................................... 14

5. Composite hydrostratigraphic sequence of the Locust Grove study area, Kent County, Maryland ............................ 15

6. Hydrostratigraphic section A-A’ along Route 213 at the northern boundary of the Locust Grove

study area, Kent County, Maryland .............................................................................................................................. 20

7. Hydrostratigraphic section B-B’ along Blacks Station Road and VanSants Corner Road running

diagonally through the middle of the Locust Grove study area, Kent County, Maryland ........................................... 20

8. Hydrostratigraphic section C-C” along Route 298, the western boundary of the Locust Grove

study area, Kent County, Maryland .............................................................................................................................. 21

9. Hydrostratigraphic section D-D’, the primary transect along Locust Grove Road from Locust Grove

to Chesterville, in the Locust Grove study area, Kent County, Maryland ................................................................... 21

10. Hydrostratigraphic section E-E’, the eastern boundary of the Locust Grove study area through Angelica

Nurseries, Kent County, Maryland ............................................................................................................................... 22

11. Map showing the extent of the subcropping Aquia confining layer and redox zone in the Locust Grove

study area, Kent County, Maryland, with subbasins for surface-water sampling sites ................................................ 23

12. Map showing the configuration of the water table and generalized ground-water flow, Locust Grove

study area, Kent County, Maryland, May 1998 ............................................................................................................ 24

13a Hydrogeologic section D-D’ (along Locust Grove Road) showing ground-water flow paths in the

shallow aquifer system, May 1998, Locust Grove study area, Kent County, Maryland ............................................. 25

13b. Hydrogeologic section C-C’ (along Route 298) showing ground-water flow paths in the shallow

aquifer system, May 1998, Locust Grove study area, Kent County, Maryland ........................................................... 26

14. Piper diagram showing chemistry of water from ground-water samples collected in July 1998 at the

Locust Grove study area, Kent County, Maryland ....................................................................................................... 27
ix

15. Plot showing the distribution of dissolved argon and nitrogen gas with relation to the solubility in air

and enrichment of nitrogen by denitrification, Locust Grove study area, Kent County, Maryland ............................ 28

16. Time-series plots of total dissolved nitrogen concentrations at the two fixed stream-sampling sites

(station numbers 01493112 and 01493500) in the Locust Grove study area, Kent County, Maryland ...................... 31

17. Map showing the areal distribution of total dissolved nitrogen concentrations in stream base flow for

the Locust Grove study area, Kent County, Maryland, April 1998 synoptic survey ................................................... 33

18. Plots of observed downstream trends of stream discharge, specific discharge, total dissolved nitrogen

concentration, instantaneous nitrogen load, and instantaneous nitrogen yield from base-flow synoptic

surveys in April and September 1998, Locust Grove study area, Kent County, Maryland ......................................... 34

19. Diagram showing expected downstream trends of nitrogen and related geochemical constituents from

a downstream increase in the discharge of old ground water ....................................................................................... 35

20. Plots of observed downstream trends of sulfate, magnesium, bicarbonate, and silica concentrations

from base-flow synoptic surveys in April and September 1998, Locust Grove study area, Kent County,

Maryland ........................................................................................................................................................................ 36

21. Diagram showing relations among discharge and concentrations of dissolved constituents in tributaries

and downstream sites under non-reactive mixing ......................................................................................................... 36

22. Map showing location of surface-water sampling stations and stream reaches on Morgan Creek and

Chesterville Branch in the Locust Grove study area, Kent County, Maryland ............................................................ 37

23. Scatterplot matrix showing relations among stream-outlet altitude, percentage of type C (moderately

poorly drained) soils, and percentage of agriculture in the Morgan Creek and Chesterville Branch basins,

Locust Grove study area, Kent County, Maryland ....................................................................................................... 46

24. Diagram showing relations among basin index, dissolved nitrogen concentration, and location

within the stream network, Locust Grove study area, Kent County, Maryland ........................................................... 47

25. Correlation between regional and local basin index scores for sites in the Locust Grove study area,

Kent County, Maryland ................................................................................................................................................. 47
x

Tables

1. Physical Characteristics of the Two Watersheds in the Locust Grove Study Area,

Kent County, Maryland ................................................................................................................................................... 7

2. Summary Information for the Coreholes Drilled in the Locust Grove Study Area, Kent County, Maryland ............. 10

3. Chlorofluorocarbon (CFC) Recharge Dates and Ground-water Ages from Wells in the Locust Grove

Study Area, Kent County, Maryland, sampled in 1998 ................................................................................................ 12

4. Summary of Base-flow Nitrogen Loads from the Locust Grove Study Area, Kent County, Maryland...................... 32

5A-D. Estimated Concentrations of Dissolved Constituents in Ground-water Discharge Calculated from Measured

Streamflow and Concentrations of Constituents at Upstream, Downstream, and Tributary Sampling Sites,

Locust Grove Study Area, Kent County, Maryland ..................................................................................................... 39

6. Correlation Coefficients for Landscape Variables Used in the Analysis of the Morgan Creek and

Chesterville Branch Watersheds, Locust Grove Study Area, Kent County, Maryland ................................................ 45

7. Results of Principal-components Analysis of Landscape Variables for the Morgan Creek and

Chesterville Branch Watersheds, Locust Grove Study Area, Kent County, Maryland ................................................ 46
xi

SI Conversion Factors SI Conversion Factors

Multiply By To obtain

inch (in) 2.54 centimeter (cm)

mile (mi) 1.609 kilometer (km)

square mile (mi2

) 2.590 square kilometer (km2)

cubic feet (ft3

) 28.32 liters

pounds (lb) 0.4536 kilograms

Temperature given in degrees Celsius (°C) can be converted to degrees Fahrenheit (°F) by use of the following equation:

°F = 1.8 (°C) + 32

Measurements in the interpretive sections of this report are given in metric units (modified SI system) to conform with U.S.

Government policy and generally accepted scientific practice. However, many of the field measurements were made using

U.S. Customary (“foot-pound”) units, and are so reported in the appendices. The conversion tables above will aid the reader

in converting from one system of measurement to the other.

In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 – a geodetic datum derived from a general

adjustment of the first-order level nets of the United States and Canada, formerly called the Sea Level Datum of 1929.

Chemical concentration is given in milligrams per liter (mg/L), which expresses the dissolved concentration of a constituent as

weight (milligrams) of solute per unit volume (liter) of water. For concentrations less than 7,000 mg/L, the numerical value is

the same as for concentrations in parts per million. Concentrations of nitrogen compounds, such as nitrate (NO3

—), are given

in units of milligrams per liter as nitrogen (N).

Stable isotopic composition of nitrogen compounds, such as nitrate, are reported in standard delta notation (δ15N), which relates

the ratio of 15N to 14N in the sample to the ratio in a reference standard; values are reported in units of per mil (l, or parts per

thousand).
xii

Acknowledgments

Mohamed Hantush of the U.S. EPA National Risk Management Research Laboratory (NRMRL) in Ada,

Oklahoma, wasthe U.S. EPA Project Officer and principal investigator for the overall project.  Stephen Kraemer

of NRMRL-Ada (now at the USEPA National Exposure Research Laboratory in Athens, Georgia) initiated the

research project through the EPA Ecosystems Restoration Program and served asthe USEPA Project Officer in

1997 prior to his move to the Athens laboratory. Jerome Cruz of ManTech Environmental Research Services

Corporation in Ada, Oklahoma, provided database and modeling support.   Thanks are offered to David

Hudson, Deborah Bringman, Anthony Tallman, Joseph Beman, and Lisa Donohoe of the USGS in Dover,

Delaware, and Elizabeth Marchand,James Dine, and Amy Derosier of the USGS in Baltimore, Maryland, who

collected and organized the field data.  Sarah Kelley (USGS in Baltimore) provided GIS support, and Tim Auer

(USGS in Baltimore) produced the final graphics for the report.  Roger Starsoneck of the USGS in Baltimore,

Maryland, located drilling sites, assisted with drilling operations, supervised the surveying activities to

determine well altitudes, and created and maintained data records for the wells.  Coreholes were drilled by

drillersfrom the Geologic Division of the USGS, and monitoring wells were installed by drillersfrom the New

Hampshire District of the USGS Water Resources Division.  Niel Plummer and Eurybiades Busenberg of the

USGS National Research Program in Reston, Virginia, analyzed chlorofluorocarbon age-dating tracers, dissolved nitrogen and argon, and major ionsforsome supplementalsamples.  Chemical analyses ofsurface-water

and ground-watersamples were performed in the USGS National Water Quality Laboratory (NWQL) in Denver,

Colorado.

Thanks are offered to the landowners who gave permission to enter their property to access a number of the

stream-sampling sites, and to the Maryland State Highway Administration and Kent County Government for

permission to drill coreholes and install monitoring wells on highway rights-of-way.  The management of

Angelica Nurseries was especially cooperative in allowing access to their land, providing information about

their production wells, and granting permission to install wells on their property and to collect water levels,

samples, and geophysical logs from their monitoring wells.
1

Introduction

Eutrophication of lakes and coastal waters has long been recognized as a major environmental problem in many parts of the world.

Increased inputs of mineral nutrients to lakes and coastal waters has led to increased biomass and organic carbon, which degrade the

aquatic environment. Although some eutrophication is due to natural causes, in the context of environmental management this term

usually represents the effects of “cultural eutrophication,” caused by inputs of nutrients from human activities (Richardson and

Jørgensen, 1996).

Eutrophication may be controlled by the availability of mineral nutrients, such as nitrogen, phosphorus, or silica, or it may be

affected by the availability of organic matter. For many years, research on the problem was focused on the input of nutrients from

surface-water discharge, especially nutrients associated with suspended sediment. This focus on runoff is reasonable for water

bodies where primary production is controlled by the availability of phosphorus (“phosphorus limited”), because phosphorus is

insoluble in oxidized environments, adsorbs strongly to sediment particles, and is transported with suspended sediment in surfacewater discharge. In many other ecosystems, however, primary productivity generally is nitrogen limited (Fisher and Butt, 1994;

Borum, 1996). The discharge of nitrogen compounds dissolved in ground water is likely to play a major role in the nutrient

dynamics of coastal waters in temperate regions because of the following factors: (1) nitrogen, in the form of nitrate, is much more

soluble than phosphorus in oxygenated environments; (2) nitrogen concentrations elevated above background levels have been

documented in shallow aquifers in many coastal areas (Bachman, 1984a; 1984b; Hamilton and others, 1993; Mueller and others,

1995; and Mueller and Helsel, 1996); and (3) ground-water discharge comprises an appreciable percentage of total streamflow in

many temperate areas. These factors have implications for environmental management, because the beneficial effects of nutrient

control may not be apparent immediately after the control practices have been implemented. Ground-water traveltimes are much

longer than surface-water traveltimes, on the order of years or decades rather than days or weeks, respectively. Consequently, the

effects of reducing the recharge of nutrients to an aquifer may be delayed for many years after the implementation of nutrientcontrol practices (Focazio and others, 1998).

The management of nutrient inputs to control eutrophication is relatively advanced in the Chesapeake Bay watershed. The

Chesapeake Bay is the Nation’s largest and most productive estuary, but the presence of toxic dinoflagellates and anoxic zones in

its deeper waters stress the estuarine ecosystem. Both of these stresses have been linked to nutrient enrichment (Fisher and Butt,

1994; Lewitus and others, 1995). Stream base-flow surveys indicate that ground-water nitrogen accounts for approximately 40 to

50 percent of the total nitrogen discharge to the bay from nontidal rivers and streams (Bachman and Phillips, 1996; Bachman and

others, 1998). Other investigations have provided estimates of ground-water flow rates from shallow aquifers (Simmons and

others, 1990; McFarland, 1995), descriptions of the relation between ground-water traveltimes and nitrogen concentrations (Dunkle

and others, 1993; Böhlke and Denver, 1995; and Speiran, 1996), and the relation between landscape features and water quality

(Bachman and Phillips, 1996; Phillips and Bachman, 1996).

Many aspects of the relation between the details of ground-water flow and geochemical processes that influence nitrogen discharge

from shallow aquifers have not been resolved. The results presented in this report further document the processes associated with

the flux of nitrogen to Chesapeake Bay by ground-water discharge. In particular, it has been suggested that geochemical reactions,

such as denitrification, may have the capacity to substantially reduce nitrogen loads in a watershed (Böhlke and Denver, 1995).

Denitrification is a process by which bacteria obtain energy by the chemical reduction of nitrate and the oxidation of organic matter

or other reduced compounds in the absence of oxygen. If carried to completion, denitrification transforms dissolved nitrate to

nitrogen gas. When denitrification occurs in a ground-water system, the nitrogen gas remains dissolved in the ground water until

it can escape to the atmosphere when the ground water discharges to a surface-water body.

The objectives of this project were to extend the results of the previous investigation by Böhlke and Denver (1995) that documented

the occurrence of denitrification in deep parts of the surficial aquifer, to relate the occurrence of denitrification to shallow

subsurface geologic formations, and to assess the effect of the discharge of denitrified water on the chemical composition of stream

base flow. This project focused on the relation between the hydrogeologic framework and nitrogen discharge from a shallow

Coastal Plain aquifer system.

This report contains a summary of the results of activities conducted by the U.S. Geological Survey (USGS) from 1997 through

2000 in support of a collaborative research effort between the USGS and the National Risk Management Research Laboratory
2

(NRMRL) of the U.S. Environmental Protection Agency (USEPA). The research project, “Geohydrologic Foundations for

Ecosystem Restoration,” is an examination of the movement and fate of nutrients, particularly nitrogen, in the subsurface at the

Locust Grove research site in the Chester River watershed on the Delmarva Peninsula (Figures 1a and 1b). Field data-collection

efforts by the USGS were based on an extensive network of stream-gaging stations, wells, surface-water-sampling sites, and

coreholes (Figure 2).

USEPA activities, as described by Hantush and Cruz (1999), included geological modeling, development of analytical and

numerical models of ground-water flow and nitrate transport, assessment of the watershed capacity for nitrogen reduction, and

management of a site database, which has been shared among project collaborators and is available for other investigators. The

major objective of the USGS activities were: (1) to describe the geometry of the shallow subsurface sediments and provide

stratigraphic interpretations for hydrogeologic models; (2) to describe the configuration of the water table and ground-water flow

paths in the surficial aquifer and the uppermost confined aquifer; (3) to provide evidence of hydrogeochemical processes that affect

nitrogen discharge to streams from ground water; and (4) to provide information needed to estimate the volume of ground-water

discharge and ground-water nitrogen loads.

Description of the Study Area

The Locust Grove study area is located in central Kent County, Maryland, (Figure 1), between the tidal Chester and Sassafras

Rivers, about 30 km south of Elkton, Maryland, and about 15 km northeast of Chestertown, Maryland. The study area consists of

the Morgan Creek and Chesterville Branch watersheds (Figure 2) above their respective stream-gaging stations. Although

topographic maps show no impoundments in these two streams, field technicians observed a small pond in the main channel of

Chesterville Branch downstream of site 01493110, and other field technicians have reported beaver dams and other obstructions to

streamflow on sections of both Chesterville Branch and Morgan Creek.

The gaging station at Morgan Creek near Kennedyville (site 01493500) is part of the USGS basic-data network for Maryland, and

discharge has been measured continuously at this site since 1951. The gaging station at Chesterville Branch near Crumpton

(site 01493112) was established in 1996, and is maintained as part of an ongoing USGS project to estimate river input of nutrients

to Chesapeake Bay. The combined area of both drainage basins is about 47 km2. Morgan Creek is a larger watershed (31 km2) than

Chesterville Branch (16 km2) (Figure 3; Table 1).

The soils in the two watersheds are generally well drained, with over half the land area in both watersheds classified as soil

hydrologic classes of “well-drained” (class A) and “moderately well-drained” (class B) (Maryland Department of State Planning,

1973). However, the Morgan Creek watershed does have a somewhat higher percentage of areas with “moderately poorly drained”

(class C) and “poorly drained” (class D) soils (Table 1).

Because of the fertile, well-drained soils, agriculture is the dominant land use in the study area, accounting for about 90 percent of

the watershed area (Figure 3; Table 1); Most of the cropland is in a rotation of corn, soybeans, and small grains. A significant part

of the Chesterville Branch watershed is under cultivation for nursery stock. Fields near the headwaters of Morgan Creek and along

some tributaries west and northwest of Morgan Creek near Kennedyville, Maryland (Figure 3), are used as pasture for dairy

operations. A few confined animal-feeding operations and poultry houses are scattered throughout the study area, but there are

fewer in this area than farther south on the Delmarva Peninsula. The primary area classified as urban is the village of Kennedyville,

located along the northwest edge of the Morgan Creek watershed (Figure 3). Some other areas shown as urban by the remotesensing land-cover classification system of Bara (1994) are commercial establishments or farm buildings. Woodlands and wetlands

are located almost exclusively in the riparian areas along Morgan Creek and Chesterville Branch.

The hydrologic setting of the study area has the potential to discharge large volumes of ground water to the streams. The study area

is located in the Atlantic Coastal Plain Physiographic Province, and is underlain by unconsolidated clastic sediments that can store

and transmit large volumes of ground water. The climate is humid temperate, with an excess of precipitation over evapotranspiration. The average rainfall is about 110 centimeters (42 inches) per year, and the average temperature is 13°C or 55°F (Vokes and

Edwards, 1974). Although rainfall is distributed relatively evenly throughout the year, evapotranspiration is substantially lower in

the winter because of the lower temperatures and dormant vegetation.

Previous Investigations Previous Investigations

The geologic framework of Kent County, Maryland, was first mapped by Clark (1915). The stratigraphic nomenclature underwent

various revisions over the years, culminating in work by Owens and Denny (1979), Owens and Minard (1979), and Hansen (1992).

Regional descriptions of the configuration of aquifers and confining layers in central Kent County are provided by Overbeck and

Slaughter (1958), Cushing and others (1973), Bachman (1984b), and Drummond (1998). Local-scale work at the Locust Grove site

began in 1988 as part of the Delmarva pilot project of the USGS National Water-Quality Assessment (NAWQA) program

(Shedlock and others, 1999). A general description of the hydrogeologic and water-quality conditions in the area was presented by

Hamilton and others (1993). Dunkle and others (1993) and Reilly and others (1994) applied age-dating tracers to describe groundwater flow in parts of the Chesterville Branch watershed. Böhlke and Denver (1995) used the estimated recharge dates and a variety

of geochemical data to describe the history of nitrogen recharge to the surficial aquifer, and discuss possible mechanisms for the

transport and fate of nitrogen in the Chesterville Branch and Morgan Creek watersheds.
3

DELAWARE

BAY

A

T

L

A

N

T

I

C

O

C

E

A

N

0

0 10

10

20

20

30 KILOMETERS

30 MILES

EXPLANATION

POTOMAC

RIVER

C

H

E

S

A

P

E

A

K

E

B

A

Y

DELMARVA PENINSULA

LOCUST GROVE STUDY AREA

DELAWARE RIVER

R.

RIVER

Patuxent River

Patapsco River

Severn

River

Bush

SUSQUEHANNA

Gunpowder R.

Middle R.

EASTERN BAY

Nanjemoy Cr.

Prettyboy Res

Loch Raven Res

Liberty

Lake

Pocomoke

River

CHINCOTEAGUE BAY

Manokin

R.

Choptank River

Nanticoke

River

L. Choptank R.

Fishing

Bay

Wicomico R. Nassawango

Creek

Choptank

River

Leipsic River

St. Jones R.

Murderkill River

Marshyho ep Creek

Broad Creek

Tuckahoe

Creek

Unicorn Br.

Elk

River

River

C & D

Christina River

Smyrna River

Sassafras

CANAL

Chester

River

Monocacy

River

WesternRun

Triadelphia

Res

Patuxent

River

Gunpowder Falls

Morgan Run

Gillis

Falls

Deer Creek

Tinkers Cr.

Piscataway Cr. Mattawoman Cr.

Zekiah

Swamp Run

Occoquan Cr.

Accotink

Cr.

Rehoboth Bay

Indian River Bay

Kent

Island

NEW

TALBOT

Prince

Frederick

Accomac

Eastville

Cambridge

Salisbury

Princess

Anne Snow Hill

Dover

Georgetown

Centreville

Denton

Easton

WILMINGTON

Elkton

Chestertown

Locust

Grove

Bel Air

Towson

Westminster

Ellicott City

Rockville

ANNAPOLIS

Upper

Marlboro

La Plata

Leonardtown

A C

C

O

M

A C

K

NORTHAMPTON

SOMERSET

DORCHESTER

WICOMICO

WORCESTER

CAROLINE SUSSEX

KENT

QUEEN

ANNES

CASTLE

KENT

CECIL HARFORD

BALTIMORE

CARROLL

FREDERICK

BALTIMORE

CITY

HOWARD

MONTGOMERY

PRINCE

GEORGES

CALVERT

ANNE ARUNDEL

CHARLES

S T. M A R Y S

PENNSYLVANIA

MARYLAND

NEW JERSEY

DELAWARE

MARYLAND

MARYLAND

VIRGINIA

VIRGINIA

MARYLAND

WASHINGTON,

D.C.

PA

D.C. WVA

VA

Chesapeake Bay

FALL LINE

NJ

MD

Locust Grove

Study Area

DE

ATLANTIC

OCEAN

80O

40O

75O

Location of Locust Grove study area

FALL

GENERALIZED

LINE

GENERALIZED

FALL

LINE

COASTAL PLAIN

PIEDMONT

38O

37O

39O

75O76O77O

Figure 1a. Figure 1a. Location of Chesapeake Bay, Delmarva Peninsula, and the Locust Grove study area in Kent County, Maryland.
4

Figure 1b. Figure 1b. Location of the Locust Grove study area in Kent County, Maryland.

SASSAFRAS

NATURAL

RESOURCES

MANAGEMENT

AREA

CHESTER

RIVER

Morgan

Chesterville

Branch

Creek

Turner Cr.

Freeman Cr.

Woodland Cr.

Lloyd Cr.

SASSAFRAS RIVER

Urieville

Community

Lake

CECIL

KEN

COUNTY T COUNTY

KENT COUNTY

QUEEN ANNES

COUNTY

291

20

291

290

213

292

298

298

298

448

444

447

444

566

292

213

297

561

290

Morgnec

Augustine

Herman

Still Pond

Road

Hwy.

Morgnec

Wallis Road

Road

Road

Cherry Lane

River Road

Chesterville

Bolton

Kentmore

Park

Road

Grove

Duck

Road

Puddle

Kennedyville Road

Browntown

Turner

Creek

Rd.

Road

Road

Blacks Station Rd.

Road

Road

Locust VanSants Corner Rd.

213

BETTERTON

COLEMAN

STILL POND

HEPBRON

LYNCH

KENNEDYVILLE

ROBINSON

CORNER

HASSENGERS

CORNER

MORGNEC

HOPEWELL CRUMPTON

CLEVERS

CORNER

CHESTERVILLE

GALENA

LAMBSON

LOCUST

GROVE

HARMONY

CORNER

CHESTERTOWN

75O75 55'00" O76 57'30" O76 00'00" O76 02'30" O05'00"

0

0

1

1 2

2

3 KILOMETERS

3 MILES

39

39

39

39

39

O

O

O

O

O

22'30"

20'00"

12'30"

15'00"

17'30"

75O52'30"

BOUNDARY OF LOCUST GROVE STUDY AREA
5

Figure 2. Figure 2. The Locust Grove study area, Kent County, Maryland, showing the locations of stream-gaging stations, surfacewater sampling sites, wells, coreholes, and transects of the hydrostratigraphic sections.
6

Figure 3. Figure 3. Land use in 1994 for the Morgan Creek and Chesterville Branch watersheds, Kent County, Maryland.
7

Table 1. Table 1. Physical Characteristics of the Two Watersheds in the Locust Grove Study Area, Kent County, Maryland

  		









     

 	    

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[Values are for the watershed areas above gaging station 01493112 on Chesterville Branch and station 01493500 on Morgan Creek; locations

of gaging stations shown in Figure 2. Compiled from data of Maryland Department of State Planning (1973). More complete data for these

watersheds and selected subwatersheds are presented in Appendix F. km, kilometers; km2, square kilometers.]
8
9

Data-Collection Methods Data-Collection Methods

Much of the geochemical interpretation presented in this report is based on numerous chemical analyses of water samples from the

Delmarva NAWQA and related projects; these data have been reported previously by Hamilton and others (1993) and Böhlke and

Denver (1995). New and refined hydrostratigraphic interpretations are based on drillers’ and gamma logs from 23 wells originally

described in previous studies, 10 private monitoring wells, and 33 new wells and 4 new coreholes drilled for this project. A

corehole is a drilled hole from which a sediment core has been recovered; a borehole is a more generic term for a drilled hole that

may include a well (a drilled hole with casing) or a rotary-drilled hole that was used only to collect cuttings and/or a geophysical

log. Monthly water-level measurements were made on all of the 63 wells in the network during the project. Additional groundwater samples were collected from 11 of the newly drilled wells for chemical analyses. Seventy-nine base-flow samples were

collected from 14 stream-sampling sites.

Compilation of Existing Data

Five categories of data were compiled from published and unpublished sources, and from data collected as part of this project.

These categories include: (1) geologic or geophysical logs from drill holes in the area, which provide information on the

hydrogeologic framework of the area; (2) measurements of ground-water levels and stream discharge, which provide information

on flow directions and flow quantities; (3) chemical analyses of water samples from wells, which provide information on the

geochemical processes controlling ground-water quality; (4) chemical analyses of stream base flow, which provide information

about surface- and ground-water geochemistry and nutrient yields from base flow; and (5) digital geographic data used for relating

base-flow nitrogen loads to landscape features. All existing data compiled for this project have been previously published (except

for some of the digital geographic data), although some original field records of published data also were examined. The data

include material originally reported by Overbeck and Slaughter (1958), Hansen (1992), Hamilton and others (1993), Tompkins and

others (1994), and Böhlke and Denver (1995).

The digital geographic data were compiled, stored, and analyzed using the ARC/INFO and ArcView geographic information

systems (GIS). Basin boundaries for all surface-water sampling sites were hand-digitized from paper copies of the USGS Betterton

and Galena 7 1⁄2-minute topographic quadrangle maps, produced at a scale of 1:24,000. Land use was derived from the MultiResolution Land Characteristics (MRLC) data set, which is based on land cover at 30-m resolution compiled in the early 1990s

(Bara, 1994). Soil characteristics were compiled from U.S. Department of Agriculture sources by Dr. Margaret Mayers-Norton,

formerly of the University of Maryland Horn Point Environmental Laboratory.

Corehole Drilling

Four coreholes drilled at the beginning of the project in October and November 1997, provide ground truth for interpreting

geophysical logs from other boreholes in the area, and details of the lithology relevant to ground-water-flow modeling and groundwater geochemistry. The four coreholes varied in depth from 25.9 to 39.6 m below land surface (Table 2), and all penetrated the

confining layer at the base of the surficial aquifer. Coreholes KE Be 185 (Locust Grove) and KE Be 186 (Chesterville Branch

North) align with the existing corehole KE Bf 180 (Hansen, 1992) along a transect that runs north-northwest to south-southeast, and

is very close to the regional dip of the subsurface formations (Figure 2). Coreholes KE Be 183 (Morgan Creek North) and

KE Be 184 (Morgan Creek South) are located on the upland approximately 0.3 km north and south, respectively, of Morgan Creek.

These two coreholes provide control along strike and away from the primary hydrostratigraphic transect along Maryland Road 444,

and detailed stratigraphy for the wells near Morgan Creek valley (Figure 2).

The four coreholes were drilled with a truck-mounted drill rig using mud-rotary methods and a 9-cm (centimeter)-diameter core

barrel with a hollow cutting head. A wire-line retrieval system was used to recover a 3-m (10-foot) inner core barrel that protects

a nominal 5-cm (2-inch)-diameter core. The core was removed from the inner core barrel in 0.6-m (2-foot) lengths, washed with

a fine spray of water to remove the drilling mud from the exterior, and placed in a partitioned storage box. The on-site geologist

measured, labeled, photographed, and described each section of the core while it was fresh. The hand-written notes from the

drilling operation and core descriptions, and the photographs of the cores are on file in the USGS Water Resources Division

Maryland-Delaware-D.C. District Office, in Baltimore, Maryland.

After each corehole was drilled to the maximum depth and the last section of core retrieved, the hole was filled with drilling mud

and the outer core barrel was removed. Natural-gamma and spontaneous-potential and electrical-resistivity logs were run in the

mudded hole. These logs are archived in the Maryland-Delaware-D.C. District geophysical-log repository in Baltimore, Maryland.
10

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Well Network and Water-Level Measurement Well Network and Water-Level Measurement

A network of 66 wells was used for the project. This network includes 23 existing wells from previous USGS NAWQA projects,

33 new wells installed in April 1998, and 10 private monitoring wells on the property of Angelica Nurseries (Figure 2). Information

on the characteristics of the existing wells is summarized in Appendix A, and information on the characteristics of the newly drilled

wells is summarized in Appendix B. During the course of the project, water levels in all of these wells were measured monthly,

from May 1998 through October 1999. A subset of the new wells was sampled for chemical analyses as described below.

The new wells installed for this project supplemented the existing wells in order to:

(1) Improve the spatial distribution of wells to better represent the water table and ground-water flow system across the

entire study area.

(2) Sample more points immediately below the water table (within 3 m of the seasonal water-table low) to document the

spatial distribution of nitrate-input concentrations and ground-water recharge rates.

(3) Sample ground water from the confined aquifer (Hornerstown Formation), which was not sampled previously, to

characterize its geochemistry.

(4) Sample discrete horizons near the base of the surficial aquifer above, at, and below the transition zone between

reduced and oxidized sediments that has been postulated as a source of electron donors for denitrification of ground

water (Böhlke and Denver, 1995).

The new wells were installed using hollow-stem auger methods according to the recommended procedures for the USGS NAWQA

Program (Koterba and others, 1996). The only deviation from these procedures was that the casing was not steam-cleaned prior to

installation, because the wells were not used to sample pesticides or volatile organic compounds. Only freshwater was used to flush

the hole. No bentonite drilling mud was circulated during drilling, which can fill pore spaces in the aquifer materials adjacent to the

well.

Wells were placed singly or in clusters of two or more to allow sampling of shallow and deep parts of the surficial aquifer. The hole

for the deeper well in a cluster was drilled first, then a gamma log was run through the auger flights before the well casing was put

in place to obtain lithostratigraphic information, and optimize the placement of the screen on the shallow well(s), and to avoid clay

lenses. In most cases, split-spoon samples were taken 0.5 m above and below the proposed depth for the screen. Because the upper

part of the surficial aquifer generally is very permeable throughout the study area, some of the shallow wells that are 9 m (30 ft)

deep or less were installed directly without running a gamma log first. Any wells that were not logged during installation had

gamma logs run the following week.

All wells were constructed with 5-cm-diameter PVC casing with internal threads. Screens have approximately 0.25-mm slots; most

screens installed were 0.45 or 0.6 m in length. In some cases, 0.3-m screens were installed to sample ground water from a very

narrow interval; for example, near the sediment redox transition at the base of the surficial aquifer associated with the first confining

layer.

The annular space between the casing and the walls of the 15-cm hole drilled with the auger was backfilled using materials dug from

the hole. The upper part of each hole was sealed with at least 0.6 m of bentonite at 1.5 m below land surface. Because most of the

wells were placed along the right-of-way of State or County roads, or along the edges of fields or service roads on private property,

all casings were cut off below land surface and a metal well cover was mounted flush with the land surface to avoid damage to the

wells by mowers and other equipment, and to avoid damage to the mowers and equipment from the wells.

All wells were surveyed for elevation of the measuring point of the well casing and the adjacent land surface using a Zeiss optical

surveying instrument. Survey transects were referenced to USGS benchmarks, or to a previously surveyed well if no benchmark

[Corehole sites are shown in Figure 2. m, meters; °, degrees; ’, minutes; ”, seconds.]

Table 2. Table 2. Summary Information for the Coreholes Drilled in the Locust Grove Study Area, Kent County, Maryland
11

was near. Survey transects were closed by backsighting to temporary benchmarks; all elevations are accurate to 0.3 cm and are

reported relative to sea level.

Latitude and longitude positions for all new USGS wells and private wells used during the project were measured with a Trimble

Pathfinder differential global positioning system (GPS) receiver. Coordinates of discrete reference locations were measured

repeatedly on different days; reproducibility was 0.1 second or better (approximately 3 m). All new wells were marked with the

well identification number on the cap and with an attached aluminum permit tag.

The new wells were developed by purging either manually with a bailer or with a downhole pump until the water was clear of

suspended solids. Some wells with high-turbidity water were revisited over a 2-week period for additional purging.

Two multiport ground-water samplers were installed to obtain water samples near the sediment redox transition at closely spaced

vertical intervals. The locations of these samplers are shown in Figure 2. They were installed at sites in which clusters of wells with

single, short (1- to 1.5-ft) screened intervals were completed at depths bracketing the redox transition zone. Split-spoon sediment

samples were collected during the installation of both multiport ground-water samplers to confirm the depth of the sediment redox

transition and to position the ports accordingly.

The multiport ground-water samplers were constructed with 5-cm-diameter schedule-80 PVC threaded casing. Each sampling port

is constructed of 1-cm-diameter Teflon tubing, which runs down the inside of the casing. The downhole end of each tube exits the

casing through a hole (port) drilled through the side of the casing. The end of the tube is cut diagonally, covered with a fine nylon

mesh, and secured to the casing with nylon pull-ties. Ports are spaced 30 cm (1 ft) apart on alternating sides in the lower 3 m (10 ft)

of the casing in both wells. In sampler KE Be 209, ports in an additional 3-m section from the bottom of the well are spaced 0.9 m

(3 ft) apart.

To finish the well, the annular space between the casing of the multiport well and the wall of the augered hole was filled with the

native material drilled from the hole. The top of each tube was covered with a tight-fitting removable cap, and the bundle of tubing

was coiled inside a plastic bag and secured in an alcove beneath the flush-mounted well cover. The tubes were color-coded and cut

to different lengths to identify the sampling depth.

The static water level in observation wells was measured by an electrical water-level depth sensor from a marked measurement

point on the well casing, and recorded to the nearest 0.01 ft. This follows the procedure described in the National Handbook of

Recommended Methods for Water-Data Acquisition (U.S. Geological Survey, 1977) and by Hardy and others (1989). Depth below

land surface and altitude relative to sea level are reported in feet (the units of the field measurement) and meters. All wells in the

network were measured monthly from May 1998 through October 1999; existing wells from the previous NAWQA project also

were measured in October 1997 and March 1998. The water-level measurements are listed in Appendix C.

Well Sampling

Water samples for chemical analysis were collected from 11 wells during July 1998, and from the multiport sampler KE Be 190

(Figure 2) in March 2000. Three wells were selected to examine the confined Hornerstown aquifer, two wells were selected to

obtain data from a previously unsampled recharge area in the surficial aquifer south of Morgan Creek, and the rest of the wells and

the multiport samplers were selected to obtain samples from the redox-transition zone. No ground-water samples were collected

below the redox transition from multiport sampler KE Be 209 because no water could be pumped from the low-permeability

sediments of the Aquia confining layer. Results of the chemical analyses are in Appendix D.

Water samples for analyses of major ions, nutrients, dissolved gases, and stable isotopes were collected from wells with a positivedisplacement, battery-operated submersible pump with a Teflon discharge tube. Samples for analyses of major ions, nutrients, and

dissolved gases were collected from the multiport sampler using a peristaltic pump and a silicone discharge tube.

Water samples were collected for the chlorofluorocarbon (CFC) age-dating tracers (Busenberg and Plummer, 1992) with a

peristaltic pump and a copper discharge tube. The date of ground-water recharge (and thereby the age of the water) was calculated

by relating historical atmospheric concentrations of CFC-11, CFC-12, and CFC-113 to concentrations measured in the ground

water. The ages were estimated by modeling expected recharge concentrations of the three CFC compounds based on Henry’s Law

(Busenberg and Plummer, 1992). Three replicate samples from each well were analyzed, and the reported ground-water age

represents the average of the three replicates (Table 3). Because age estimates from the different CFC compounds varied, the final

ground-water age reported in Appendix D is the average of the ages determined by each individual CFC compound.

Base-Flow Sampling

The seasonal and spatial variability of nitrogen discharge from stream base flow in the Morgan Creek and Chesterville Branch

watersheds were measured in three synoptic surveys from a network of 14 sites (Figure 2). Of these sites, eight are at outlets of firstorder drainage basins; the other six sites are on the mainstems of Morgan Creek and Chesterville Branch. The two sites farthest

downstream (sites 01493500 and 01493112) are located close to the transition between nontidal and tidal conditions. The baseflow sampling network was designed to describe the areal distribution of base-flow nitrogen and how nitrogen discharge varies

downstream within the watersheds. Samples collected at the two outlets were used to estimate the total discharge of nitrogen from
12

[“CFC Recharge Dates” are the calculated years in which each sampled parcel of ground water recharged the water table, based on historical

atmospheric CFC concentrations; “Modern” indicates a CFC concentration similar to that expected for water in equilibrium with 1998-99

atmospheric concentration; “Contaminated” indicates a CFC concentration higher than that expected from equilibrium with current or historical

atmospheric concentrations; n/d = not determined; ~, approximately; <, less than; >, greater than.]

Table 3. Table 3. Chlorofluorocarbon (CFC) Recharge Dates and Ground-water Ages from Wells Sampled in 1998

 CFC Recharge Dates CFC Recharge Ages Average

Well Sampling Average Average Average 

Recharge 

Age (years) 

And Date

Number Date CFC-11 CFC-12 CFC-113 CFC-11 CFC-12 CFC-113 

 

KE Be 50 07/24/98 1989.5 Modern 1990.5 9.6 7.1 9.1 8.6

 1989.5 Contaminated Modern 1990

 1988.0 1991.5 1988.5 

KE Be 158 07/21/98 1985.5 1986.5 1988.0 12.2 8.7 9.6 10.2

 1987.0 1991.5 1990.0 1988.5

 1986.5 1991.5 1993.0/1995.0 

KE Be 189 07/21/98 1949.0 1954.0 <1955 ~50 45.9 >43 >45 

 Hornerstown 1948.5 1951.5 <1955 <1953

 aquifer <1945 1952.5 <1955 

KE Be 192 07/21/98 Modern 1997.0 Contaminated n/d 1.9 n/d 1.9

 1993.5/1995.5 1996.0 Modern 1996.5

 Modern 1997.0 Modern 

KE Be 193 07/24/98 Contaminated Contaminated Contaminated n/d n/d n/d n/d 

 Contaminated Modern Contaminated 

 Contaminated Contaminated Contaminated 

KE Be 194 07/20/98 1985.5 1987.5 1986.5 13.1 10.9 11.6 11.8

 1985.5 1988.0 1991.5/1998.0 1987

 1985.5 1987.5 1987.5 

KE Be 195 07/20/98 1977.5 1976.5 1978.0 21.1 22.4 19.4 20.9

 deep in Aquia 1977.5 1976.0 1980.5 1978

 aquifer 1977.5 1976.0 1979.0 

KE Be 199 07/22/98 1978.0 1976.5 1976.5 21.1 21.9 22.2 21.7

 deep in Aquia 1978.0 1978.0 1976.5 1977

 aquifer 1976.5 1975.5 1976.0 

KE Be 200 07/22/98 1954.5 1955.0 1965.5 44.2 42.2 40.0 42.1

 Hornerstown 1955.0 1964.5 <1955 1956

 aquifer 1953.5 1949.5 <1955 

KE Be 206 07/22/98 1982.0 1982.0 1981.5 16.9 16.4 17.9 17.1

 1981.5 1982.0 1980.5 1981.5

 1981.5 1982.5 1980.0 

KE Be 207 07/23/98 1978.0 1978.0 1980.5 20.9 20.6 19.6 20.3

 deep in Aquia 1977.5 1978.0 1979.5 1978.5

 aquifer 1977.5 1978.0 1977.0 

KE Be 207 12/10/98 1977.0 1978.0 1979.5 21.8 21.1 19.3 20.7

 deep in Aquia 1977.5 1978.0 1980.0 1978

 aquifer 1977.0 1977.5 1979.5 

KE Be 208 07/23/98 1967.0 1967.0 1967.5 31.6 31.4 31.6 31.5

 deep in Aquia 1967.0 1967.0 1967.0 1967

 aquifer 1967.0 1967.5 1966.5 

KE Be 208 12/10/98 1968.0 1968.5 1968.0 30.9 30.4 31.9 31.1

 deep in Aquia 1968.0 1968.5 1966.0 1967.5

 aquifer 1968.0 1968.5 1967.0 

KE Be 210 07/22/98 1954.5 1959.5 <1955 48.8 46.1 >43 46

 Hornerstown 1949.0 1949.0 <1955 <1952

 aquifer <1945 1949.0 <1955 

KE Be 211 12/11/98 <1945 <1940 <1955 >50 >55 >44 >50

 Hornerstown <1945 <1940 <1955 <1950

 aquifer 

KE Be 212 07/23/98 1986.5 1991.5 1991.0 11.9 6.4 8.6 8.9

 1987.0 1992.5 1989.0 1989.5

 1986.5 1992.5 Modern 

KE Be 216 07/24/98 1987.0 1993.0 1990.0 11.4 5.7 8.9 8.7

 1987.5 1994.0 1988.5 1989.5

 1987.0 1991.5 1990.5 
13

the two watersheds during the study period. Samples were analyzed for nitrite-plus-nitrate nitrogen and ammonia-plus-organic

(Kjeldahl) nitrogen. These two analytes were added to obtain the total dissolved nitrogen concentration. The instantaneous

nitrogen load was calculated by multiplying the measured stream discharge (in units of volume per time) by the total dissolved

nitrogen concentration (in units of mass per volume) and adjusting the units to obtain values in gm sec-1 (units of mass per time).

Instantaneous yields were calculated by dividing the load by the drainage area to obtain units of gm sec-1 km-2.

Stream base-flow samples were collected from the entire network during synoptic surveys in April 1998, September 1998, and

February 2000. Samples were collected during both winter base flow and summer base flow to evaluate the effect of seasonal

differences in base-flow discharge and biological activity in the stream. Bachman and Phillips (1996) noted that base-flow

discharge of water in the central upland of the Delmarva Peninsula was approximately an order of magnitude lower in summer than

in winter, when evapotranspiration is minimal. They also noted that over the entire Delmarva Peninsula, base-flow nitrogen loads

and yields tended to be higher in winter. Base-flow samples also were collected monthly at the two downstream gaging stations

from April 1998 through March 1999. These monthly samples were supplemented by additional base-flow samples collected at

Chesterville Branch (site 01493112) before and after this period for other USGS projects. All base-flow samples were accompanied

by stream-discharge measurements made by use of standard USGS methods (U.S. Geological Survey, 1977). Results of the

chemical analyses of the base-flow samples are listed in Appendix E.

Chemical Analysis of Water Samples Chemical Analysis of Water Samples

Chemical analyses were made on samples filtered through a membrane filter with a 0.45-μm pore diameter to provide an

approximation of the “dissolved” concentration of solutes. In addition, unfiltered base-flow samples were analyzed for nitrogen

species and phosphate to determine the “total” (suspended and dissolved) concentrations of these constituents. Water samples

collected for CFC age-dating tracers and other dissolved gases were not filtered.

Many physical and chemical properties are unstable, and, therefore, were measured in the field. These include pH, temperature,

specific conductance, dissolved oxygen (measured on unfiltered samples), and carbonate alkalinity (measured on filtered samples).

The analysis methods follow those recommended by Wilde and Radtke (1998).

Samples for the analysis of major ions, silica, iron, nutrients, and total organic carbon were sent to the USGS NWQL in Arvada,

Colorado. Samples for stable isotopes, dissolved gases, and chlorofluorocarbon age-dating tracers, and a subset of samples for

major ions and nutrients were analyzed at the laboratories of the USGS National Research Program in Reston, Virginia.

Cations and silica were analyzed by plasma emission spectroscopy, sulfate and chloride by ion chromatography, and nitrogen

species and phosphate by various standard colorimetric methods (Fishman and Friedman, 1985). Quality-assurance methods used

at NWQL are described by Pritt and Raese (1995). In addition, field replicates were collected and analyzed. From these replicates,

variation (using the standard deviation of replicates as described by Taylor, 1988) of dissolved nitrogen concentrations due to

sampling and analytical methods is estimated to be 0.09 mg/L; variation of calcium, magnesium, and silica concentrations are less

than the precision of the analysis as described by Fishman and Friedman (1985).

Data Analysis Data Analysis

Processes affecting ground-water and surface-water geochemistry were evaluated by examining the relations between selected

constituents and their location in the watershed or along a ground-water flow path. Previous studies indicated that, in general, the

surficial aquifer has multiple ground-water flow paths with traveltimes (from recharge to discharge) that range from a year to

decades (Dunkle and others, 1993; Böhlke and Denver, 1995). The older ground water (from flow paths with long traveltimes)

tends to have lower nitrate concentrations than younger ground water (from flow paths with short traveltimes). The relative

proportion of old and young ground water discharging to a stream upstream of a sampling point will affect the concentration of

solutes in base flow at that sampling point. In a detailed investigation, Modica and others (1998) evaluated the flow systems,

ground-water traveltimes, and nitrate concentrations in a similar watershed in the Coastal Plain of New Jersey. Their model

simulation showed that ground-water discharge in the headwaters of a stream is dominated by relatively young water, whereas

farther downstream, ground-water discharge contains an appreciable component of older water mixed with the young water

(Figure 4). In order to evaluate this process in the Locust Grove study area, concentrations of nitrogen and other constituents that

are geochemical markers for old and young ground water were examined at seven sites along the mainstems of Morgan Creek and

Chesterville Branch. Observed trends in concentrations were compared to trends expected from various mixtures of old and young

ground water.

Although samples were analyzed for both nitrogen and phosphorus, this report focuses on the nitrogen data. Because phosphorus

adsorbs to soil particles under oxic conditions, it is likely that little phosphorus enters the oxygenated environment of the surficial

aquifer with recharging ground water. Further, the near-surface sediments in this area are not rich in phosphate, and even if there

were chemically reducing environments in the surficial aquifer, there is little potential for the mobilization of phosphorus. There is

some question as to whether the ground-water sampling methods used in this project actually measure dissolved phosphorus in the

aquifer, or colloidal particulate phosphorus that was stirred up by the sampling pumps and passed through the 0.45-μm filters used

to separate the “dissolved” from “particulate” fractions (M. T. Koterba, U.S. Geological Survey, oral commun., 1999).
14

Figure 4. Figure 4. Relative distribution of the age of discharging ground water in stream headwaters and downstream (adapted from

Modica and others, 1998).
15

Hydrogeologic Framework

The study area is located in the updip region of the Delmarva Peninsula, approximately 30 km from the Fall Line (Figure 1a). A

broad band of lower Tertiary and upper Cretaceous marine sedimentary sequences crops out or subcrops shallowly between the

Sassafras and Chester Rivers (Owens, 1967; Drummond, 1998). These Cretaceous and lower Tertiary units dip and thicken to the

southeast with the regional dip of crystalline rocks beneath the Coastal Plain.

Formations exposed above sea level in the area near Locust Grove (Figure 5) include the upper Cretaceous Mt. Laurel and Severn

Formations of the Monmouth Group, the lower Paleocene Hornerstown Formation, and the upper Paleocene Aquia Formation

(Minard, 1974; Hansen, 1992; Drummond, 1998). In the southeast corner of Kent County, including the southeast part of the study

area, younger marine sediments of the upper Oligocene Old Church (?) Formation and the Miocene Calvert Formation may overlie

the Aquia Formation (Hansen, 1992; Drummond, 1998). However, the Oligocene and Miocene sediments generally are very thin

(less than 1-2 m thick) north of the Chester River, and probably are not important as hydrostratigraphic units.

Figure 5. Figure 5. Composite hydrostratigraphic sequence of the Locust Grove study area, Kent County, Maryland.

80

70

60

50

40

30

20

10

0

DEPTH BELOW LAND SURFACE, IN METERS

0 20 40 60 80 100

GAMMA, IN COUNTS PER SECOND

i

HORNERSTOWN

CONFINING

LAYER

SEVERN

CONFINING

LAYER

MONMOUTH

AQUIFER

HORNERSTOWN

AQUIFER

AQUIA

CONFINING LAYER

AQUIA

AQUIFER

COLUMBIA

AQUIFER

Well KE Be 186 Well KE-94-0146

k

m

l

j

g

h

f

d

e

a

c

e

g f

d

a

b

c

e peak gamma response in

Aquia confining layer

j-k sandy bed in upper Severn

Formation

k top of Severn confining layer

m base of Severn confining

layer, top of Monmouth

aquifer

l peak gamma response in

Severn confining layer

i peak gamma response in

Hornerstown confining layer

j base of Hornerstown

confining layer

g top of sand of the

Hornerstown aquifer

h base of Hornerstown aquifer,

top of Hornerstown confining

layer

f base of Aquia confining layer,

top of Hornerstown Formation

d top of tight Aquia confining

layer

a land surface

b base of Pens uken Formation,

top of Aquia Formation

a

c base of Aquia aquifer, top of

Aquia confining layer

UPPER

MIOCENE (?)

LOWER

PLIOCENE (?)

PENSAUKEN

FORMATION

AQUIA

FORMATION

HORNERSTOWN

FORMATION

SEVERN

FORMATION

MT. LAUREL

FORMATION

UPPER

PALEOCENE

LOWER

PALEOCENE UPPER CRETACEOUS

COLUMBIA

AQUIFER

AQUIA

AQUIFER

HORNERSTOWN

AQUIFER

HORNERSTOWN

CONFINING

LAYER

AQUIA

CONFINING

LAYER

SEVERN

CONFINING LAYER

MONMOUTH

AQUIFER

SURFICIAL AQUIFER

HYDROSTRATIGRAPHIC

UNITS

LITHOSTRATIGRAPHIC

UNITS

HORIZONS

ON GAMMA LOG

NATURAL GAMMA RAY LOG

b
16

The upland in central and eastern Kent County above an altitude of approximately 15 m (50 ft) is capped by a gravelly coarse sand.

This unit has been mapped as the Pensauken Formation on the northern and central Delmarva Peninsula by correlation with similar

deposits along the flanks of the Delaware River valley in New Jersey (Owens and Denny, 1979; Owens and Minard, 1979). The age

of the Pensauken Formation has been estimated as latest Miocene to early Pliocene based on its stratigraphic position relative to

other dated units in New Jersey. Lithologically similar deposits that cover two-thirds of Delaware have been mapped as the

Columbia Formation (Jordan, 1962; 1964). Age estimates for the Columbia Formation are early to middle Pleistocene based on

pollen assemblages (Groot and Jordan, 1999). It is not clear whether the sediments mapped as the Pensauken Formation in

Maryland and the Columbia Formation in Delaware were deposited during the same period, or whether they represent two or more

depositional episodes with similar sediment provenance and depositional environment.

Middle to upper Quaternary deposits in Kent County include Pleistocene estuarine-terrace deposits and Holocene alluvial

sediments. Pleistocene terraces are restricted to the margins of the Sassafras and Chester Rivers, the mouths of the larger tributary

creeks, and the Chesapeake Bay shoreline in western Kent County. The highest terraces are at altitudes of approximately 15 m

above sea level. Although the lower reaches of Morgan Creek and Chesterville Branch cut across the Pleistocene terraces along the

Chester River, no Pleistocene estuarine deposits are within the immediate study area. However, the incised valleys of Morgan

Creek and Chesterville Branch are filled with Holocene alluvial sediments derived from the erosion of the adjacent upland.

Most of the upland in the study area away from the stream valleys is covered with a surficial deposit of loess (wind-blown silt) that

may be 0.3 to 1 m thick. Previous studies of soils in the northern Delmarva Peninsula have attributed the source of the loess to

estuarine silts that were deposited in the Delaware River estuary and subsequently exposed during late Quaternary lowstands of sea

level to be eroded and transported by winds (Carey and others, 1976).

Lithostratigraphic Units Lithostratigraphic Units

Four primary lithostratigraphic units compose the upper 30 m of the sedimentary column in the Locust Grove study area. These

units are:

(1) the Holocene alluvial sediments that fill the incised valleys of Morgan Creek and Chesterville Branch;

(2) the coarse fluvial sands and gravels of the Pensauken Formation that cap the upland;

(3) the Aquia Formation, which immediately underlies the Pensauken Formation throughout most of the study area; and

(4) the Hornerstown Formation, which underlies the Aquia Formation.

In this report, the Severn confining layer (Figure 5) is considered as the base of the active hydrogeologic system that interacts with

the streams in the study area, and, therefore, descriptions of underlying stratigraphic units are omitted.

Developing the hydrostratigraphic framework for the Locust Grove study area was an iterative process of interpreting cores and

geophysical logs, correlating lithostratigraphic units across the study area, and defining hydrostratigraphic units. The first step was

the description and interpretation of the lithology of the four new cores drilled for the project (Table 2). These cores were not

studied in the same detail as core KE Bf 180 (Hansen, 1992), and inference of physical properties and other characteristics is based

on correlation with core KE Bf 180. The new cores were described in sufficient detail to identify changes in grain size that relate

to permeability, and mineral composition and degree of weathering that relate to redox chemistry. The lithologic changes were

matched with excursions in the geophysical logs (natural gamma, electrical resistivity, and spontaneous potential) from the

coreholes. These features in the logs were used to define a set of specific horizons in the geophysical logs with consistent and

characteristic responses that could then be used to correlate lithostratigraphic horizons among the geophysical logs from all wells

in the study area.

An initial stratigraphic framework was developed by correlating the geophysical logs of the deepest wells and coreholes to

determine the general geometry and distribution of units. This correlation also was used to assemble a composite stratigraphic

sequence and define hydrostratigraphic units for the study area (Figure 5). Specific surfaces, such as the top of the clay-rich section

in the lower Aquia Formation, were mapped throughout the study area. This preliminary framework was refined subsequently by

checking the consistency of picks in cases where the interpretation of the geophysical log was uncertain, and by inferring the depths

to specific horizons in shallow wells.

Holocene Alluvial Sediments Holocene Alluvial Sediments

The valleys of Morgan Creek and Chesterville Branch are filled with 4 to 6 m of alluvium in the axis of the valleys, although this

thickness is inferred from relatively few holes. These sediments are dominantly coarse sands with gravels that were eroded from the

upland, and overlain by silty overbank deposits. The sands in the lower part of the alluvium may have interbedded lenses of silt,

poorly sorted silty sand, and peats; some beds also contain trace amounts of glauconite reworked from the Aquia Formation. The

silt overbank deposits that form the modern floodplain typically are 0.5 to 1 m thick and contain organic material accumulated from

the riparian forest. Bedding within the alluvial sediments represents transport and deposition during episodic storm events. The

alluvial valley of Chesterville Branch at Road 444 is 50 to 70 m wide; the valley of Morgan Creek at Road 298 is 80 to 100 m wide.
17

Pensauken Formation, Upper Miocene (?) / Lower Pliocene (?) Pensauken Formation, Upper Miocene (?) / Lower Pliocene (?)

The Pensauken Formation in Kent County is a thick sequence of medium to coarse sands and gravels, with common cobbles and

less common boulders. Sandy beds typically are poorly sorted and may have interbedded lenses of silt or clay. In exposures, this

unit contains cross-bedded sets in cut-and-fill channels 2 to 5 m deep. The sand grains generally are subrounded to subangular, and

are predominantly quartz with some feldspar. The fine-sand fraction may contain abundant heavy minerals; Hansen (1992)

reported the mineralogy of the heavy mineral sands. X-ray diffraction analyses of samples from core KE Bf 180 showed kaolinite,

illite, and smectite in the clay fraction (Hansen, 1992). Pebbles are rounded and dominantly vein quartz, quartzite, and chert, with

uncommon lithic clasts. The sediments of the Pensauken Formation typically are deeply weathered; the dominant colors are

yellowish-oranges, light to very light browns (tan), and light grays. Much of the feldspar and labile heavy mineral suite has been

leached and hydrated to form clays.

The sediments of the Pensauken Formation were deposited by a very large braided-river system that covered most of the central

Delmarva Peninsula (Owens and Denny, 1979). Fluvial erosion during the deposition of the Pensauken Formation truncated the

older Tertiary and Cretaceous sediments to create a regional angular unconformity. The base of the Pensauken Formation

underlying the Locust Grove study area generally is between 12 and 15 m asl, but is very irregular because of channelization and

scouring. The unit typically is 6 to 15 m thick, but Minard (1974) reported a maximum observed thickness of 44 m (145 ft) in a

paleochannel. Determining the base of the Pensauken Formation in the Locust Grove study area from geophysical logs without

lithologic control was difficult because the gamma response of the lower part of the Pensauken is very similar to that of the sand

facies in the upper Aquia Formation.

Old Church (?) Formation, Upper Oligocene, and Calvert Formation, Lower to Middle Miocene

Hansen (1992) reported 1.5 m (5 ft) of a glauconitic fine to medium sand with a late Oligocene foraminiferal assemblage in core KE

Bf 180. This unit was tentatively assigned to the Old Church Formation. Drummond (1998) showed the updip limit of the Calvert

Formation just to the north of the Chester River; the Calvert may extend into the southeast corner of the Locust Grove study area,

although it was not identified in core KE Bf 180. The Calvert Formation typically is a compacted marine silt with low permeability,

and is a regional confining or semi-confining layer south of the Chester River. Neither Old Church nor Calvert sediments were

confirmed in cores or geophysical logs collected for this project. However, a thin bed of silty fine sand similar to the description

of the Old Church (?) Formation was observed when augering the hole for well KE Be 216, which is approximately 700 m

northwest (updip) from corehole KE Bf 180.

Aquia Formation, Upper Paleocene

The upper Paleocene Aquia Formation underlies the Pensauken Formation throughout the study area except where the Pensauken

has been removed by erosion. The Aquia Formation is a coarsening-upward marine sequence with two distinct facies. The lower

section of the Aquia is a fine to medium sand with abundant (30 to 50 percent) glauconite grains and a sticky silt-clay matrix. When

seen in fresh cores, the sediments of this facies are dark greenish-gray to dusky blue-green, and show no evidence of leaching or

oxidation except at the upper and lower boundaries. Hansen (1992) and Minard (1974) give detailed descriptions of the lithology

of this facies, including the characteristics of the glauconite grains. Mollusk and brachiopod shells are preserved in this section of

the Aquia in coreholes KE Bf 180 (Hansen, 1992) and KE Be 186. The upper section of the Aquia Formation is a medium quartz

sand with a minor component of coarse sand grains and 5 to 15 percent glauconite. This section is weathered throughout its vertical

extent, and there is little silt-clay matrix between the sand grains. The sediments of the upper Aquia are light olive to light olivebrown with dark reddish-brown to dark gray flecks of glauconite, giving a “salt and pepper” appearance. Individual glauconite

grains in the upper section commonly have oxidized rinds or are worn and polished.

The transition between the upper sandy facies and the lower facies with the silt-clay matrix, referred to as the “redox transition

zone,” occurs in a 0.5 to 1 m interval at the base of the sandy facies. This textural change coincides with a transition from leached

and oxidized sediments above to relatively unaltered sediments with reduced mineral phases below. Iron oxides were observed

near this boundary in the cores. Joints and fractures that extend below this textural and sediment-redox transition have brown or

reddish-brown oxidized zones 1 to 5 mm wide, indicating localized flow of oxygenated ground water into this layer. A second

sediment-redox transition was observed at the base of the Aquia silt-clay facies, with oxidation proceeding upward from the

underlying sandy facies of the Hornerstown Formation. This lower redox transition was most prominent in corehole KE Be 183,

but was observed in all four cores collected in this project.

The updip limit of the Aquia Formation appears to be in a zone trending west-southwest to east-northeast immediately north of

Route 213 (Figure 2) at the northern boundary of the study area, but its exact location is poorly delineated by the available data. The

updip limit of the Aquia aquifer shown in a subcrop map for Kent County published by Drummond (1998) includes the

Hornerstown Formation as part of the Aquia aquifer, and does not specifically represent the areal extent of the Aquia Formation.

The silt-clay facies at the base of the Aquia Formation is within 14 m of the land surface in the three northernmost wells

(KE Be 187, KE Be 197, and KE Ae 29), and corehole KE Be 185 (Locust Grove) (Figure 2). The base of the Aquia Formation

drops from 10 m asl in corehole KE Be 185 (Locust Grove) at the northern boundary of the study area, to 21 m below sea level in

KE Bf 180 at the southern boundary. The Aquia thickens from 5 m to 28 m in the 6 km between the two coreholes. The
18

stratigraphic boundary between the upper and lower facies of the Aquia Formation appears clearly in gamma logs (Figure 5) and

was used as a marker horizon for correlation throughout the study area. Where the entire sequence of the Aquia Formation is

preserved downdip, the upper and lower facies are 19 and 9 m thick, respectively.

Hornerstown Formation, Lower Paleocene

The lower Paleocene Hornerstown Formation is lithologically very similar to the overlying upper Paleocene Aquia Formation. The

Hornerstown Formation also is a coarsening-upward sequence of marine glauconitic sands. In the study area, only corehole KE Bf

180 and wells KE-94-0146 and KE Be 171 penetrate the entire thickness of the Hornerstown Formation. The coreholes and the

deeper wells drilled for this project were completed in the upper section of the Hornerstown Formation. The lower 15 to 16 m of

the Hornerstown Formation has a substantial clay content based on the gamma logs; a prominent gamma excursion in the lower 2 m

of the unit probably is a relatively low-permeability clay bed. A larger gamma excursion in the underlying Severn Formation

indicates a clay bed that is a regional confining layer and an excellent marker horizon (Figure 5). The upper 10 to 13 m of the

Hornerstown Formation is predominantly sand. However, the uppermost 2 to 4 m of the Hornerstown, immediately below the siltclay-rich facies of the Aquia Formation, commonly has a substantial clay content, although not as much as in the lower section of

the Hornerstown.

The contacts between the Aquia and Hornerstown Formations in the four cores collected in this project were not as distinct as the

one described in core KE Bf 180 (Hansen, 1992). In this project, the base of the Aquia Formation was interpreted consistently as

the transition between the bottom of the silt-clay-rich facies of the Aquia and the top of the sandy facies of the Hornerstown; this

boundary can be identified readily in most of the geophysical logs. The actual stratigraphic unconformity between the two

formations could be verified only by detailed biostratigraphy across this interval.

Composite Hydrostratigraphic Sequence

Hydrostratigraphic units in the Locust Grove study area were defined from the permeabilities inferred from the sediment textures

in the cores and the character of the geophysical logs. Five hydrostratigraphic units were identified in the surficial and first confined

aquifer systems: the Columbia aquifer and the Aquia aquifer, which together make up the surficial aquifer, the Aquia confining

layer, the Hornerstown aquifer, and the Hornerstown confining layer. A very low-permeability clay bed in the Severn Formation

lies immediately below the Hornerstown confining layer throughout most of the study area to form a regional confining layer.

Surficial Aquifer (Columbia and Aquia Aquifers) Surficial Aquifer (Columbia and Aquia Aquifers)

By regional usage for the Delmarva Peninsula, the term “Columbia aquifer” includes the Pensauken Formation in Maryland and the

Columbia Formation in Delaware (Bachman 1984b). Drummond (1998) also included the Pleistocene terrace deposits in his

definition of the Columbia aquifer in Kent County, Maryland. Because no Pleistocene terrace deposits occur within the study area,

the Columbia aquifer as used in this project is restricted to the sands and gravels of the Pensauken Formation. In the Locust Grove

study area, the Columbia aquifer is less than 2.5 m thick updip in well KE Be 187, and greater than 10 m thick downdip. The base

of the Columbia aquifer cannot be readily identified in geophysical logs without lithologic control.

The upper sandy facies of the Aquia Formation is designated the “Aquia aquifer.” In previous usage by other investigators, the

Aquia aquifer in Kent County, Maryland, includes the glauconitic sands of the Aquia and Hornerstown Formations (Overbeck and

Slaughter, 1958; Otton and Mandle, 1984; Hansen, 1992; Drummond, 1998). However, the cores obtained as part of this project

indicate that the silt-clay layer at the base of the Aquia Formation is very impermeable (see “Aquia confining layer,” below), and

there is much less hydraulic connection between the Aquia and Hornerstown Formations than between the Aquia and overlying

Pensauken Formation. Thus, the “surficial aquifer” is defined here as the combined Pensauken Formation and upper sandy facies

of the Aquia Formation, and referred to as the Columbia-Aquia aquifer. As the sandy facies of the Aquia Formation pinches out

updip, toward the north of the study area, the surficial aquifer is composed solely of the Pensauken Formation, or Columbia aquifer.

Aquia Confining Layer Aquia Confining Layer

The silt-clay at the base of the Aquia Formation was recognized in previous studies, but was considered permeable or at least semipermeable, and therefore the Aquia and Hornerstown Formations were interpreted as hydraulically connected. The silt-clay facies

at the base of the Aquia Formation typically is from 6 to 9 m thick and can be identified in geophysical logs throughout the study

area. A very low-permeability clay-rich bed from 2 to 3 m thick occurs in the lower third of the unit and is associated with a peak

in the gamma logs. Fresh core material from this clay-rich bed, although plastic, was nearly dry in appearance. Geochemical and

age-dating evidence, discussed in the Ground-Water Geochemistry section, show substantial differences in the properties of ground

water above and below the silt-clay layer at the base of the Aquia Formation. These lines of evidence suggest that the lower Aquia

Formation is an effective confining layer. The possible exceptions to this are in areas of enhanced vertical hydraulic gradients, such

as discharge areas beneath streams and near production wells pumping from the sands in the upper part of the Hornerstown

Formation.
19

Hornerstown Aquifer and Hornerstown Confining Layer Hornerstown Aquifer and Hornerstown Confining Layer

The Hornerstown Formation, similar to the Aquia Formation, has an upper sandy facies and a lower silt-clay-rich facies that are

designated the “Hornerstown aquifer” and the “Hornerstown confining layer,” respectively (Figure 5). The thickness and clay

content inferred from gamma logs of these two Hornerstown units are more variable than those of the Aquia Formation in the

Locust Grove study area and across Kent County (see the hydrogeologic sections of Drummond, 1998). In the study area, the

Hornerstown aquifer is from 9 to 11 m thick, and the Hornerstown confining layer is from 10 to 15 m thick. The Hornerstown

confining layer is underlain by the Severn Formation, which includes at its base approximately 5 m of low-permeability clay; the

two units together form a regional confining layer that separates the Aquia/Hornerstown aquifer system from the Monmouth

aquifer. The subcrop area of the Hornerstown aquifer is to the north and northwest of Route 213 (Figure 1b). Part of this area is

deeply incised by tributaries extending south from the Sassafras River. The most likely recharge area for the Hornerstown aquifer

is the upland plain north of Kennedyville, Maryland, and northwest of the intersection of Routes 213 and 298.

Geometry of the Hydrostratigraphic Units Geometry of the Hydrostratigraphic Units

The five hydrostratigraphic sections presented in Figures 6 through 10 show the geometry of the primary hydrostratigraphic units,

coreholes, and wells in the Locust Grove study area. These sections were prepared by correlating lithostratigraphic and

hydrostratigraphic units away from the five coreholes using the geophysical logs from the deeper wells at each site. Sections A-A’

(Figure 6) and B-B’ (Figure 7) run mostly southwest to northeast, close to the regional strike of the Cretaceous and Tertiary units.

Sections C-C” (Figure 8), D-D’ (Figure 9), and E-E’ (Figure 10) run mostly north to south, close to the regional dip. Section D-D’

was the primary transect for the previous NAWQA project (Hamilton and others, 1993) and ground-water dating and flow-path

modeling studies (Dunkle and others, 1993; Reilly and others, 1994).

Hydrostratigraphic section A-A’ (Figure 6) runs west-southwest to east-northeast along Route 213 at the northern boundary of the

study area. This transect runs along the southern edge of the subcrop zone of the Aquia confining layer (Aquia CL). The surficial

aquifer is very thin, less than 3 m thick in places, because the sandy facies of the Aquia Formation (the Aquia aquifer, or Aquia AQ)

was removed by erosion prior to or during the deposition of the Pensauken Formation. The sands of the Pensauken Formation (the

Columbia aquifer) also thin across a subsurface high that probably was created because the silt-clay facies in the lower Aquia

Formation (the Aquia CL) is more resistant to erosion than the sands in the upper Aquia Formation. The updip limit of the

subcropping Aquia CL and the Hornerstown aquifer (Hornerstown AQ) are not known precisely because of a lack of boreholes for

control.

Section A-A’ straddles the surface-water drainage divide between the tributaries of the Sassafras River to the north and Morgan

Creek to the south. The saturated zone in the surficial aquifer overlying the Aquia CL is very thin. Wells KE Be 187 and KE Be

197 are screened at the base of the surficial aquifer. For well KE Be 187, the maximum thickness of the saturated zone was 1.5 m

in May 1998 and the minimum was 0.1 m in May 1999; for well KE Be 197, the maximum was 0.8 m in May 1998, and the well

was dry from November 1998 through August 1999, during a prolonged drought. It is inferred that ground water drains quickly off

the subsurface high of the subcropping Aquia CL through the coarse sands and gravels of the Pensauken Formation.

Hydrostratigraphic section B-B’ (Figure 7) runs diagonally across the study area, including part of the high ground along Blacks

Station Road that is the drainage divide between Morgan Creek and Chesterville Branch. The transect is oblique to the regional

strike, so it has a dip component. Only one well on the transect (KE Be 210) penetrates the Aquia CL; consequently,

hydrostratigraphic units could not be identified for most of this section.

Hydrostratigraphic section C-C” (Figure 8) runs north-south on the western border of the study area along Road 298 and crosses

Morgan Creek. The transect extends from the northern drainage divide for Morgan Creek (at well KE Be 187) to just south of the

southern drainage divide (at the well KE Be 195 cluster). Two coreholes, KE Be 183 (Morgan Creek North) and KE Be 184

(Morgan Creek South), provide lithologic control for the updip part of the section. The Aquia CL subcrops shallowly at the north

(updip) end of the section, beneath wells KE Be 187 and 188. These two wells are screened in the surficial (Columbia) aquifer at

the top of the confining layer. The holes for these two wells were not drilled through the Aquia CL, so the thickness of the confining

layer at these sites is not known. The most complete hydrostratigraphic sequence for the updip part of the section is provided by the

gamma log of the Nau Farm well. This sequence is projected along strike approximately 1.2 km due southwest onto section C-C”.

The surficial aquifer thins appreciably north of Morgan Creek as the top of the Aquia CL rises in altitude. The Pensauken

Formation typically is from 7 to 10 m thick south of Morgan Creek and the Aquia AQ thickens appreciably downdip, although the

actual geometry cannot be represented because of a lack of deep holes south of the KE Be 184 corehole. In Morgan Creek valley,

both the Pensauken Formation and the sandy facies of the Aquia Formation (the Aquia AQ) have been removed by stream incision.

The alluvial sediments filling the incised valley are 3.5 to 4 m thick in the center of the valley and sit directly on the Aquia CL. The

upper 2 or 3 meters of the Aquia CL also may have been eroded in the deepest part of the valley.

One notable feature of the C-C” section is the abrupt offset of the base of the Aquia CL between well KE Be 189 in Morgan Creek

valley and corehole KE Be 183 approximately 350 m to the north. This offset might be related to a fault, although this is a tentative

interpretation. Supporting evidence for a fault is based on the correlation of the base of the Aquia CL and the gamma log peak in

the Aquia CL in three deep holes (coreholes KE Be 183 and 184, and well KE Be 189) near Morgan Creek valley. The updip part
20

Figure 6. Figure 6. Hydrostratigraphic section A-A’ along Route 213 at the northern boundary of the Locust Grove study area, Kent

County, Maryland.

EXPLANATION

HYDROSTRATIGRAPHIC CONTACT (Queried where uncertain)

CONFINING LAYER

AQUIFER

WELL, WITH SCREENED INTERVAL

TD TOTAL DEPTH OF WELL, IN METERS (m) AND FEET (ft)

? ?

HYDROSTRATIGRAPHIC SECTION A-A'

(along Route 213)

0

Vertical scale greatly

exaggerated

1

DISTANCE, IN KILOMETERS

234

30

METERS

(West) (East)

METERS

30

20 TD 4.6 m

(15 ft) TD 6.4 m

(21 ft)

TD 29.0 m

(95 ft)

TD 29.0 m

(95 ft)

TD 16.8 m

(55 ft)

20

10 10

-10 -10

-20 -20

Sea Level Sea Level

A A' KE Be 187 (Intersects C-C') KE Be 197 Corehole KE Be 185 KE Be 200 Cluster (intersects D-D') KE Be Ae 29 Nau Farm Well (projected)

Land surface

?

?

AQUIA CONFINING LAYER

COLUMBIA AQUIFER

(PENSAUKEN FORMATION)

HORNERSTOWN CONFINING LAYER

HORNERSTOWN AQUIFER

Figure 7. Figure 7. Hydrostratigraphic section B-B’ along Blacks Station Road and VanSants Corner Road through the middle of the

Locust Grove study area, Kent County, Maryland.

EXPLANATION

HYDROSTRATIGRAPHIC CONTACT

(Dashed and queried where uncertain)

CONFINING LAYER

AQUIFER

WELL, WITH SCREENED INTERVAL

TOTAL DEPTH OF WELL,

IN METERS (m) AND FEET (ft)

TD

? ?

HYDROSTRATIGRAPHIC SECTION B-B'

(along Blacks Station Road and VanSants Corner Road)

0 1

DISTANCE, IN KILOMETERS

23456

30

(Southwest) (Northeast)

METERS METERS

30

20 20

10 10

-10 -10

-20 -20

Sea Level Sea Level

B B'

Vertical scale greatly

exaggerated

Land

surface

TD 9.1 m

(30 ft)

TD 9.1 m

(30 ft)

TD 9.1 m

(30 ft)

TD 9.1 m

(30 ft)

TD 15.2 m

(50 ft)

TD 26.5 m

(87 ft)

TD 10.7 m

(35 ft)

TD 16.8 m

(55 ft)

TD 18.2 m

(60 ft)

KE Be 196

KE Be 195 Cluster

(Drainage divide)

KE Be 201

KE Be 60

KE Be 202

KE Be 165 Cluster

KE Be 210 Cluster

(Intersects D-D

KE Be 57 Cluster

KE Be 51

')

KE Be 164 Cluster

(Intersects D-D')

Morgnec Road

Morgan Creek

Tributary

(PENSAUKEN FORMATION)

COLUMBIA

AQUIFER

AQUIA AQUIFER

AQUIA CONFINING LAYER

HORNERSTOWN

AQUIFER

?

?

?

?

(Intersects B-B')

TD 15.2 m (50 ft)
21

Figure 8. Figure 8. Hydrostratigraphic section C-C” along Harmony Woods Road (State Highway 298), the western boundary of the

Locust Grove study area, Kent County, Maryland.

Figure 9. Figure 9. Hydrostratigraphic section D-D’, the primary transect along Locust Grove Road from Locust Grove to Chesterville,

in the Locust Grove study area, Kent County, Maryland.

EXPLANATION

HYDROSTRATIGRAPHIC CONTACT

(Dashed and queried where uncertain)

CONFINING LAYER

AQUIFER

WELL, WITH SCREENED INTERVAL

TOTAL DEPTH OF WELL,

IN METERS (m) AND FEET (ft)

TD

? ?

HYDROSTRATIGRAPHIC SECTION C-C''

(along Route 298)

0 1

DISTANCE, IN KILOMETERS

23456

30

(North) (South)

METERS

Morgnec Road

METERS

30

20 20

10 10

-10 -10

-20 -20

Sea Level Sea Level

C C' C''

Vertical scale greatly

exaggerated

Land

KE Be 187

surface

(Intersects A-A')

KE Be 188

Nau Farm Well

(projected)

Corehole KE Be 183

KE Be 189

KE Be 193 Cluster

Corehole KE BE 184

KE Be 195 Cluster

(Drainage divide)

KE Be 196

(Intersects B-B')

KE Be 157 and KE Be 190

Morgan

Creek

Tributary

?

Morgan Creek

?

?

?

TD 4.6 m

(15 ft)

TD 4.6 m

(15 ft)

TD 29.0 m

(95 ft)

TD 27.9 m

(91.5 ft)

TD 18.2 m

(60 ft)

TD 9.1 m

(30 ft)

TOP OF

TD 25.9 m (85 ft)

TD 16.3 m (53.5 ft)

TD 7.6 m (25 ft)

HORNERSTOWN

CONFINING LAYER

AQUIA

CONFINING

LAYER

(PENSAUKEN FORMATION)

PENSAUKEN FORMATION

COLUMBIA

AQUIFER

HORNERST

AQUIA AQUIFER

OWN

AQUIFER

EXPLANATION

HYDROSTRATIGRAPHIC CONTACT

(Dashed and queried where uncertain)

CONFINING LAYER

AQUIFER

WELL, WITH SCREENED INTERVAL

TOTAL DEPTH OF WELL,

IN METERS (m) AND FEET (ft)

TD

? ?

HYDROSTRATIGRAPHIC SECTION D-D'

(along Locust Grove Road)

0 1

DISTANCE, IN KILOMETERS

23456

30

(North) (South)

METERS METERS

30

20 20

10 10

-10 -10

-20

-30 -30

-20

Sea Level Sea Level

D D'

Vertical scale greatly

exaggerated

Land surface

? ?

Corehole KE Be 185

KE Be 200 Cluster

(Intersects A-A')

Corehole KE Be 186

KE Be 61 Cluster

(Drainage divide)

KE Be 162 Cluster

KE Be 212

KE Be 63 Cluster

KE Be 211 and 159 Cluster

KE-94-0146 Cluster (projected)

Route 213

KE Be 210 Cluster

KE Be 165 Cluster

KE Be 164 Cluster

(Intersects B-B')

KE Be 171

(Intersects E-E

Morgnec Road

')

TD 29.0 m

(95 ft)

TD 26.5 m

(87 ft)

TD 15.2 m

(50 ft)

TD 15.2 m (50 ft)

TD 22.9 m (75 ft)

TD 39.6 m

(130 ft)

TD 84.4 m

(277 ft)

TD 18.2 m

(60 ft)

TD 21.3 m

(70 ft)

TD 32.6 m

(107 ft)

TD 137.2 m

(450 ft)

COLUMBIA AQUIFER

(PENSAUKEN FORMATION)

OLD CHURCH

FORMATION (?) AQUIA CONFINING

LAYER

AQUIA

AQUIFER

HORNERSTOW

HORNERST

N

OWN CONFINING LAYER

AQUIFER

Morgan Creek

Chesterville Branch
22

of section C-C” (Figure 8) shows a reversal of the regional dip to the southeast between corehole KE Be 184 (south) and well

KE Be 189 in Morgan Creek valley, and a steep rise between KE Be 189 and corehole KE Be 183 (north). The gamma peak in the

Aquia CL and the bottom of the Aquia CL drop in altitude by 2.0 and 0.8 m, respectively, from KE Be 184 to 189, and then rise by

6.75 and 8.0 m between KE Be 189 and KE Be 183. The regional dip estimated from section D-D’, which is roughly parallel to

section C-C”, is from 5.3 to 5.5 m/km (meters per kilometer). The steep dip between corehole KE Be 183 and well KE Be 189 is

between 20 and 23 m/km; even when using the more conservative correlation between coreholes KE Be 183 (north) and 184

(south), the dip is between 7.0 and 10.5 m/km. If this interpretation is correct, the downdropped side of the fault lies directly below

Morgan Creek, and the upthrown side is immediately to the north of the creek. The displacement across the possible fault is on the

order of 5 m. With only one transect crossing the potential fault, it is not possible to estimate the strike of the fault, although the

southwest-northeast trend of Morgan Creek may be a geomorphic expression.

If a fault is present beneath Morgan Creek, it may have a large effect on ground-water flow from the Hornerstown aquifer. The

entire confining layer in this area is 9-10 m thick, and the lowest-permeability part of the confining layer is 2-3 m thick. A 5-m

offset caused by a fault could breach the low-permeability part of the confining layer to create a lateral conduit that would allow

discharge of Hornerstown water directly to Morgan Creek.

Hydrostratigraphic section D-D’ (Figure 9) is the primary transect running north-south through the study area from Locust Grove

to Chesterville, Maryland. This transect is very close to the regional dip, contains two coreholes (KE Be 185 and 186), and five

deep wells that penetrate the Aquia CL and part or all of the Hornerstown Formation. All of the hydrostratigraphic units of the

surficial and first confined aquifer systems are shown in this section. The updip pinchout of the Aquia AQ is apparent, although the

Pensauken Formation (Columbia aquifer) is not as thin in the Locust Grove corehole (KE Be 185) as at the site of well KE Be 187

(Figure 9). Downdip, the Old Church (?) Formation overlies the Aquia AQ; farther downdip, south of the Chester River, the silty

Calvert Formation overlies the Aquia and it becomes a confined aquifer. The base of the Pensauken Formation drops 5 m in altitude

from the updip to the downdip end of the section.

Hydrostratigraphic section E-E’ (Figure 10) runs sub-parallel to section D-D’ and intersects D-D’ at the southern end. Section EE’ runs through Angelica Nurseries and is the eastern boundary of the study area. Because of the regional southwest-to-northeast

strike, the Aquia AQ is thicker in section E-E’ than in D-D’. Five deep holes provide excellent control for the position of the

Aquia CL. The transect crosses the three-way drainage divide between Morgan Creek, Chesterville Branch, and Woodland Creek

(to the northeast) near the site of wells KE Be 154 and KE Be 213. The Pensauken Formation thins considerably to the south

because of the headward erosion of the Chesterville Branch drainage.

Figure 10. Figure 10. Hydrostratigraphic section E-E’, the eastern boundary of the Locust Grove study area through Angelica Nurseries,

Kent County, Maryland.

EXPLANATION

HYDROSTRATIGRAPHIC CONTACT

(Dashed and queried where uncertain)

CONFINING LAYER

AQUIFER

WELL, WITH SCREENED INTERVAL

TOTAL DEPTH OF WELL,

IN METERS (m) AND FEET (ft)

TD

? ?

HYDROSTRATIGRAPHIC SECTION E-E'

(along Bolton Road and through Angelica Nurseries)

0 1

DISTANCE, IN KILOMETERS

23456

30

(North) (South)

METERS METERS

30

20 20

10 10

-10 -10

-20

-30 -30

-20

Sea Level Sea Level

E E'

Vertical scale greatly

exaggerated

Land surface

KE Be 51

KE Be 57

KE Be 154

KE Be 185 Cluster

KE Bf 186 and Block 3-54

KE Be 216 and KE-88-0696

Corehole KE Bf 180

KE Be 171

(Intersects E-E')

Morgnec Road

VanSants Corner Road

Nursery View Well

KE Be 215

(Drainage divide)

TD 10.7 m

(35 ft) TD 16.8 m

(55 ft)

TD 28.7 m

(94 ft)

TD 42.7 m

(140 ft)

TD 48.2 m

(158 ft)

TD 33.5 m

(110 ft)

TD 146.3 m

(480 ft) TD 137.2 m

(450 ft)

TD 18.1 m

(59.5 ft)

TD 17.5 m

(57.5 ft)

?

?

?

?

?

OLD CHURCH

FORMATION (?)

(PENSAUKEN

FORMATION) COLUMBIA AQUIFER

AQUIA AQUIFER

AQUIA CONFINING

HORNERSTOWN

HORNERST

CONFINING

OWN

LAYER

AQUIFER

LAYER
23

The extent of the shallow subcropping of the Aquia CL (Figure 11) was mapped using the coreholes and geophysical logs from this

project, and the more regional map presented by Drummond (1998). The subcropping zone was developed from the hydrostratigraphic

sections (Figures 6-10), and projected or inferred where core control is lacking. The trend of the subcropping zone roughly parallels

Morgan Creek to the north of the creek, and underlies the northern drainage divide for the Morgan Creek watershed. The tributaries

north of Morgan Creek all drain basins where the sedimentary redox zone at the top of the Aquia CL is within 10 or 15 m of the land

surface.

Ground-Water Flow Paths and Traveltimes Ground-Water Flow Paths and Traveltimes

The water-level measurements of wells screened in the Columbia-Aquia surficial aquifer indicate that ground-water flow patterns

are similar to those reported by Hamilton and others (1993). Ground-water levels from May 1998 (Appendix C), when the water

table was at its maximum height during the project, were used to create a water-table map (Figure 12) and to represent flow paths

in vertical sections (Figures 13a and 13b). The basic flow patterns were similar throughout the 1997-99 period of record, including

a period of extreme drought during the summer of 1999.

In general, water is recharged in the uplands, flows through the surficial aquifer, and discharges to the perennial streams (Figures

12 and 13). There is some evidence, particularly on the northern boundary of the Chesterville Branch watershed (Figure 12), that

ground-water divides do not coincide with surface-water divides; however, the relatively poor resolution of topographic mapping

in the study area makes precise delineation of surface-water divides difficult. A water-table high in the northeastern part of the

Morgan Creek watershed is inferred from data presented by Hamilton and others (1993). However, the wells that showed this

mound subsequently were destroyed, and were not available for this investigation.

The recharge areas and flow patterns of ground water in the Hornerstown aquifer are difficult to interpret from the limited number

of available wells. Downdip flow is indicated from well KE Be 210 to KE Be 211 (at Chesterville Branch) (Figure 13), but there

is also the possibility of flow to the north (updip) from a divide south of well KE Be 200 toward the Sassafras River watershed. It

is unclear whether most of the recharge to the Hornerstown aquifer comes from the outcrop/subcrop zone north of the study area,

or whether an appreciable proportion of the recharge is through the Aquia confining layer.

Ground-water traveltimes, as determined from CFC ages (Appendix D; E. Busenberg, U.S. Geological Survey, written commun.,

1998) are similar to those reported in earlier work (Dunkle and others, 1993; Reilly and others, 1994; Böhlke and Denver, 1995),

Figure 11. Figure 11. The extent of the subcropping Aquia confining layer and redox zone in the Locust Grove study area, Kent County,

Maryland, with subbasins for surface-water sampling sites.
24

and generally confirm the relation between traveltimes and parts of the ground-water flow system. The youngest ground water is

less than 10 years old and is found in shallow wells in recharge areas (for example, wells KE Be 192 and 194; Appendix D). Ground

water collected deeper in the surficial aquifer, such as from well KE Be 195, is on the order of 20 to 30 years old. Ground water

from the Hornerstown aquifer in the study area had not been sampled for geochemistry or age dating prior to this project.

Hornerstown water is consistently greater than 40 years old in all four wells sampled (Table 3), with progressively older CFC ages

downdip, from 42 years in well KE Be 200 to greater than 50 years in well KE Be 210. In addition, local trends in the

concentrations of 4He (helium-4) indicate that the downdip Hornerstown water may be 75 years old or older (E. Busenberg, U.S.

Geological Survey, written commun., 2000).

The ground water in the surficial aquifer that discharges to Morgan Creek follows flow paths very different from ground water that

discharges to Chesterville Branch because of the aquifer geometry. This geometry also results in generally longer ground-water

traveltimes for the Chesterville Branch watershed. Ground water discharging to Chesterville Branch behaves as if in a simple,

moderately deep, unconfined aquifer with an impermeable horizontal base. The details of flow may be slightly different from the

idealized conceptualization because of the southward dip (approximately 5 m/km) of the base of the Aquia aquifer. In general, the

flow paths that contact the reducing sediments at the base of the aquifer represent a relatively small fraction of the total discharge

to Chesterville Branch. Discharge to Morgan Creek is more complex. The Columbia-Aquia surficial aquifer is relatively thick only

southeast of Morgan Creek. The incised valley of Morgan Creek has cut down to, and probably into, the reduced sediments of the

Aquia confining layer (Figure 13b). Much of the ground water moving to Morgan Creek probably flows updip and contacts the

reducing sediments. This process was evaluated by Hantush and Cruz (1999) using numerical simulations based on the data

presented here. They found that the data were consistent with the concept that a large percentage of discharge to Morgan Creek

flows through the reducing layer at the base of the aquifer.

In addition to ground-water discharge from the lower part of the Aquia aquifer, Morgan Creek also may receive considerable

discharge from the Hornerstown aquifer. If a fault is present beneath Morgan Creek, it may allow appreciable ground-water flow

from the Hornerstown aquifer through a breached Aquia confining layer. The entire confining layer in this area is 9 to 10 m thick

and the lowest-permeability part of the confining layer is 2 to 3 m thick. A 5-m offset caused by a fault could breach the lowpermeability part of the confining layer to create a lateral conduit that would allow discharge of Hornerstown water directly to

Morgan Creek. However, further study is needed to verify the presence of the fault, and to document ground-water flow through

the confining layer.

Figure 12. Figure 12. Configuration of the water table and generalized ground-water flow, Locust Grove study area, Kent County,

Maryland, May 1998.

EXPLANATION

WATER-TABLE CONTOUR, IN METERS ABOVE SEA LEVEL

(Dashed where approximately located. Contour interval 2 meters.)

WELL USED FOR WATER-LEVEL MEASUREMENTS

(Number is altitude of water table, in meters above

sea level.)

GENERALIZED GROUND-WATER-FLOW DIRECTION

14

18.47

SURFACE-WATER DRAINAGE DIVIDE (BASIN BOUNDARY)

Morgan

Chesterville

Branch

Creek

Urieville

Community

Lake

291

290

213

213

292

298

298

448

444

566

290

Morgnec Road

Augustine

Herman Hwy.

Morgnec

Road

Cherry Lane

River Road

Grove

Duck

Road

Puddle

Kennedyville

Browntown Road

Road

Road

Chesterville

Road

Locust

Wallis Road

Bolton Road

447

HEPBRON KENNEDYVILLE

ROBINSON

CORNER

MORGNEC

CLEVERS

CORNER

CHESTERVILLE

LAMBSON

LOCUST

GROVE

HARMONY CORNER

18

18

16 18

14

14

14 12 12 14

12

12

16

16

16

16

19.41

19.51

11.68 11.34

13.52

16.52

18.58

17.25

18.57

18.47

18.12

18.26

16.11

17.76

18.76 17.62

18.12

16.75

15.38

14.45 17.29

15.59

12.37 13.44

14.40

13.20

16.44

17.94

17.65

75O75 55'00" O76 57'30" O00'00"

0

0

1

1 2 KILOMETERS

2 MILES

39O20'00"

39O

15'00"

39O

17'30"
25

Figure 13a. Figure 13a. Hydrogeologic section D-D’ (along Locust Grove Road) showing ground-water flow paths in the shallow aquifer

system, May 1998, Locust Grove study area, Kent County, Maryland.
26

Figure 13b. Figure 13b. Hydrogeologic section C-C’ (along Harmony Woods Road, State Highway 298) showing ground-water flow paths

in the shallow aquifer system, May 1998, Locust Grove study area, Kent County, Maryland.

HYDROGEOLOGIC SECTION C-C'

(updip part of section, along Route 298)

KE Be 187

(Intersects A-A')

KE Be 188

Nau Farm Well

(projected along strike)

Corehole KE Be 183

Alluvial fill in Morgan Creek valley

KE Be 189

KE Be 193 Cluster

Corehole KE Be 184

KE Be 157 and KE Be 190

Morgan Creek

?

?

?

?

?

?

AQUIA CONFINING LAYER

HORNERSTOWN

AQUIFER SURFICIAL AQUIFER

HORNERSTOWN

CONFINING LAYER

Tight part of Aquia Confining Layer

Land surface

19.41

18.51

11.34

12.20

13.52

13.58

13.54

11.68

Possible

Fault

0 1

DISTANCE, IN KILOMETERS

2

30

(North) (South)

METERS METERS

30

20 20

10 10

-10 -10

Sea

Level

Sea

Level

C C'

Vertical scale greatly

exaggerated

13.53

EXPLANATION

HYDROSTRATIGRAPHIC CONTACT

(Dashed and queried where uncertain)

AQUIFER

CONFINING LAYER

LOW PERM ABILITY ZONE OF

CONFINING LAYER

E

GENERALIZED GROUND-WATER FLOW

PATH (Dashed where inferred)

HIGH WATER TABLE, MAY 1998

LOW WATER TABLE, AUGUST 1999

WELL, WITH SCREENED INTERVAL

(Number is head representing the screened

interval, in meters above sea level.)

18.57

? ?
27

Ground-Water Geochemistr Geochemistry

The ground-water geochemistry of the study area has been described in some detail by Hamilton and others (1993) and Böhlke and

Denver (1995). The shallow aquifers contain three major water types: “young” (post-1970 recharge) agricultural ground water;

“old” (pre-1970 recharge) agricultural ground water; and “old” calcareous water. The “agricultural” ground water has concentrations of dissolved nitrate that are considerably elevated above natural background levels; “old” agricultural water has nitrate

concentrations of 2-3 mg/L as N and “young” agricultural water has nitrate concentrations greater than 3 mg/L as N. Nitrate

concentrations in young water can exceed 20 mg/L as N. Nitrate concentrations in the “calcareous” waters are near or below the

analytical detection limit (0.05 mg/L). Böhlke and Denver (1995) also reported that the relative concentrations of magnesium

generally covary with nitrate concentrations in ground water. This covariance results from the application of dolomitic limestone

(calcium-magnesium carbonate) as a soil amendment, which is apparently applied in proportion to the amount of nitrogen fertilizer

used.

Agricultural waters have dissolved oxygen concentrations exceeding 5 mg/L, whereas the “calcareous” waters have dissolved

oxygen concentrations close to zero mg/L. Low, but measurable, concentrations of dissolved oxygen were reported in a number of

wells sampled in the study area. These low concentrations were interpreted by Böhlke and Denver (1995) as representing mixtures

of oxygenated agricultural water and anoxic calcareous water. For the hydrogeochemical interpretations, these mixtures were

classified with the anoxic waters as “suboxic” (Böhlke and Denver, 1995).

Young agricultural waters were a calcium-magnesium nitrate-chloride type (Figure 14), reflecting the application of nitrogen and

potash (KCl) fertilizers and of dolomitic limestone for pH adjustment of soil (Hamilton and others, 1993). The older agricultural

Figure 14. Figure 14. Chemistry of water from ground-water samples collected in July 1998 at the Locust Grove study area, Kent County,

Maryland.

100

80

60

40

20

0

0

20

40

60

80

100

100

80

60

40

20

0

0

20

40

60

80

100

100

80

60

40

20

0 0

20

40

60

80

100

100

80

60

40

20

0

80

60

40

20

0

100

20

40

60

80

20

40

60

80

SODIUM + POTASSIUM

SULFATE + CHLORIDE + NITRATE

CALCIUM + SODIUM + POTASSIUM

CHLORIDE + NITRATE

CALCIUM SULFATE

MAGNESIUM

BICARBONATE

PERCENTAGE OF TOTAL MILLIEQUIVALENTS PER LITER

EXPLANATION

WELL SCREENED IN THE SURFICIAL AQUIFER

WELL SCREENED IN THE HORNERSTOWN AQUIFER
28

water was relatively enriched in sodium (Figure 14), probably because of water-rock interactions (Böhlke and Denver, 1995). The

calcareous water was found previously in discharge areas at various depths above the confining layer. The water is of a reduced

(suboxic) calcium-bicarbonate type (Figure 14), with bicarbonate concentrations roughly an order of magnitude higher than those

in the oxic agricultural waters because of calcium carbonate dissolution.

Ground-water sampling conducted during this project generally confirmed the conclusions of Böhlke and Denver (1995), including

the relations between recharge dates and nitrate concentrations (Appendix D). In addition, samples were collected from four new

wells in the Hornerstown aquifer, and a series of samples were collected from a multiport well near the bottom of the Aquia

Formation in the sediment redox transition. Ground water sampled from the multiport well had relatively low pH values, with

relatively low concentrations of dissolved oxygen, and relatively high concentrations of nitrate and sulfate (Appendix D).

Dissolved-gas analyses indicate that the multiport samples did not have substantial amounts of excess nitrogen gas from

denitrification (Figure 15). Thus, the multiport samples appear to represent a water type with agricultural contaminants and is partly

reduced, but has not been denitrified and has not encountered calcium carbonate. Waters from the confined Hornerstown aquifer

were an anoxic, calcium-bicarbonate type similar to the old calcareous waters identified previously above the confining layer in

discharge areas in stream valleys. The Hornerstown waters were relatively old (some more than 50 years old) and had relatively

high silica and sulfate concentrations and minor amounts of excess nitrogen gas, as did the discharging waters.

Dissolved Nitrate and Denitrification

In general, the highest concentrations of dissolved nitrate were found in the recharge areas of the surficial aquifer, whereas waters

with low concentrations of nitrate were found in discharge areas and commonly exhibited evidence of denitrification (Böhlke and

Denver, 1995). Stream base flow, which is composed primarily of ground-water discharge, had nitrate concentrations in Morgan

Creek (2.3 - 4.1 mg/L as N) that were appreciably lower than concentrations in Chesterville Branch (4.0 - 8.4 mg/L as N). Morgan

Creek appears to receive a greater proportion of denitrified ground water than Chesterville Branch.

All water samples from the Hornerstown aquifer contained excess dissolved nitrogen gas above saturated equilibrium, as

normalized to argon concentrations (Figure 15). The presence of excess nitrogen indicates that the water that recharged the

Hornerstown aquifer contained measurable dissolved nitrate, probably on the order of 1-2 mg/L as N, which had been denitrified

and transformed to dissolved nitrogen gas. Isotopic analyses of the nitrogen gas indicate that the Hornerstown waters may have had

nitrate with nitrogen isotope d15N values between 2 and 5 ‰ (per mil, or parts per thousand), similar to the values obtained by

Böhlke and Denver (1995) for ground water discharging in the stream valleys. The amount of excess nitrogen was slightly less in

the southernmost and deepest Hornerstown well (KE Be 211, farthest downgradient) than in the three shallower, upgradient

Hornerstown wells (KE Be 189, 200, and 210). All of the Hornerstown samples had low concentrations of CFCs and tritium,

Figure 15. Figure 15. Distribution of dissolved argon and dissolved nitrogen gas with relation to solubility in air and enrichment of

nitrogen by denitrification, Locust Grove study area, Kent County, Maryland.

22

20

18

16

14

12

10

400 450 500 550 600 650 700 750 800 850

CONCENTRATION OF DISSOLVED ARGON,

IN MICROMOLES PER LITER

CONCENTRATION OF DISSOLVED NITROGEN GAS,

IN MICROMOLES PER LITER

JULY 1998 SAMPLES

DECEMBER 1998 SAMPLES

KE Be 200

KE Be 200

KE Be 189

KE Be 159

KE Be 210

KE Be 210

EQUILIBRIUM,

AIR-SATURATED WATER,

0-30 CO

Addition of N gas

from denitrification

of nitrate

2
29

indicating that they were recharged before the mid-1900s. According to E. Busenberg (U.S. Geological Survey, written commun.,

2000), the ground water in well KE Be 211 had a higher concentration of radiogenic helium than the other samples, indicating that

well KE Be 211 probably contained the oldest ground water sampled, with an apparent age of about 75 years (although the

uncertainty of this age estimate is not well known). These data indicate that the ground water in the Hornerstown aquifer was

recharged within the last 100 years, and that the recharge area probably is in the northern part of the study area. Although the

recharge areas are not the same for all samples represented, the overall pattern of increasing nitrate concentrations over the last

75 years, with the most rapid increase between about 1960 and 1980, appears to be a general trend for the region.

Böhlke and Denver (1995) suggested three possible sources of electron acceptors for denitrification of ground water in the study

area:

• Oxidation of glauconite;

• Oxidation of iron-sulfide minerals; and/or

• Oxidation of organic matter.

The cores collected for this project show that the sediments in the upper sandy section of the Aquia Formation are extensively

oxidized, but there is an abrupt transition to sediments with predominately reduced mineral phases at the top of the Aquia confining

layer. Silica concentrations on the order of 20 mg/L in suboxic Aquia waters and 30 mg/L in Hornerstown waters are elevated

relative to concentrations of 10 mg/L that are typical of oxic Columbia-Aquia waters. The higher silica concentrations in the deeper

units are consistent with longer residence times and the dissolution of glauconite to release silica. Sulfate concentrations of oxic

Columbia-Aquia waters generally are below reporting levels (0.10 mg/L), whereas concentrations in suboxic Aquia and

Hornerstown waters generally range from 5 to 20 mg/L. Sulfate is a common product of the dissolution and oxidation of ironsulfide minerals, such as pyrite or marcasite. The data presented here provide no new insights into the relative importance of

organic matter oxidation. From mass-balance modeling and carbon stable-isotope data, Böhlke and Denver (1995) inferred that the

oxidation of organic matter was not the major mechanism for denitrification of the discharging ground water.

The samples collected from the multiport well (KE Be 190) and the nearby wells that are screened above and within the Aquia redox

transition zone provided inconclusive evidence on the relative importance of glauconite or iron-sulfide oxidation. Concentrations

of dissolved oxygen decreased in the ports located within the redox transition zone, but none were lower than 2 mg/L, indicating

oxic conditions or mixtures of oxic and anoxic water; this result also was true of the data from the cluster of individual wells. These

samples also contained nitrate concentrations of 5 to 6 mg/L as N from the sampling ports of well KE Be 190 and concentrations

of 11 to 12 mg/L as N in the well cluster. Sulfate concentrations from the ports of well KE Be 190 ranged from 15 to 23 mg/L,

similar to those of old anoxic water. The geochemical data for ground water from the lower Aquia aquifer could indicate that

sulfate was produced by iron-sulfide oxidation coupled with reduction of dissolved oxygen, which would not consume nitrate

(because the thermodynamic sequence of electron-accepting processes generally consumes dissolved oxygen before nitrate). If

iron-sulfide oxidation were driven mainly by dissolved oxygen, then the lower nitrate concentrations could represent older, pre1970 recharge, when nitrate concentrations were lower than in waters currently recharging at the water table.

Oxidation of pyrite by reduction of dissolved oxygen can be represented by:

4FeS2

 + 15O2 + 10H2O « 8SO4

-2 + 4FeOOH + 16H+ (1)

This reaction requires about 1.9 moles of oxygen to yield 1 mole of sulfate. In contrast, oxidation of pyrite by denitrification can

be represented by:

2FeS2 + 6NO3

-

 + 2H2O « 4SO4

-2 + 2FeOOH + 3N2

 + 2H+ (2)

In equation 2, 1.5 moles of nitrate are required to yield an additional mole of sulfate. Water recharging the surficial aquifer contains

on the order of 10 mg/L (~0.3 mmol/L, or millimoles per liter) dissolved oxygen, but variable concentrations of nitrate, ranging

from 2 mg/L (0.15 mmol/L) as N to over 10 mg/L (0.71 mmol/L) as N. In a ground-water chemical system not limited by the supply

of iron sulfide, consumption of dissolved oxygen should result in a sulfate concentration of 15 mg/L (0.16 mmol/L). Denitrification

of ground water with a nitrate concentration of 2 mg/L as N would result in an additional 9.6 mg/L (0.1 mmol/L) of sulfate.

Denitrification of ground water with a nitrate concentration of 10 mg/L as N would result in an additional sulfate concentration of

45 mg/L (0.47 mmol/L). Thus, sulfate concentrations above 15 mg/L could be interpreted as evidence that denitrification has

occurred, or that the ground water contained some sulfate when recharged. The latter appears to be the case for the multiport

samples, which did not contain excess nitrogen gas.

In summary, these results indicate that the samples collected from the multiport well did not contain denitrified ground water,

although several ports were deep enough to be within what appeared to be reduced glauconitic sediments in nearby cores. If the

samples from these sites did indeed represent ground water from within the reduced zone at the top of the confining layer, then these

observations could indicate that denitrification did not have a large effect on ground-water chemistry in the Aquia aquifer flow

system. It is possible that suboxic ground waters carrying nitrate moved along the redox boundary toward discharge sites without

losing measurable amounts of nitrate. Alternatively, reduced ground waters may be present but could not be sampled because the

construction of the multiport wells and piezometers permitted overlying oxic water to enter the screens (by downward flow in the
30

annular space around the well casing). This flow might have occurred because hydraulic conductivities within and below the

sediment redox transition at the top of the Aquia confining unit are much lower than that of the overlying sand of the Aquia aquifer.

Whether or not the persistence of nitrate in the multiport samples is an artifact of the well design, these results do not provide strong

support for appreciable denitrification above the confining layer.

Many of the chemical and chronological characteristics of the Hornerstown waters appear to match those of ground waters

discharging beneath the streams. Ground water from the four new wells screened in the Hornerstown confined aquifer was reduced,

alkaline, and nitrate-free. Ground water from all four contained minor amounts of excess nitrogen gas with an isotopic composition

(d15N [of excess N2

] = 2-5 ‰; J. Böhlke, U.S. Geological Survey, written commun., 2000) slightly different from that of

atmospheric nitrogen, which indicates that the Hornerstown waters were recharged with minor amounts of nitrate that was

denitrified subsequently. Böhlke and Denver (1995) identified tritium-poor ground water discharging to both streams, and

Hornerstown waters all appear to be older than mid-1900s. The isotopic composition of the Hornerstown N2 gas is consistent with

denitrification of nitrate similar to that of older ground water above the confining layer (data presented by Böhlke and Denver

[1995] in their figures 12 and 13); further, the apparent initial nitrate concentrations of the Hornerstown ground waters are

consistent with those of the discharging ground waters. The high alkalinities, moderate sulfate concentrations, and other chemical

characteristics of the Hornerstown waters match those of ground waters discharging at stream-sampling sites KE Be 172, 173, and

178. Water of this type has not yet been identified within the surficial aquifer, except near discharge zones (for example, well KE

Be 159 in the Chesterville Branch valley) with upward flow from deep in the surficial aquifer. These observations could be readily

explained if the Hornerstown ground-water flow system were connected with the overlying Columbia-Aquia aquifer, as suggested

by Böhlke and Denver (1995), but they are difficult to explain if the two flow systems are separated completely.

The similarity of nitrate concentrations, dissolved nitrogen and argon gases, ground-water age-dating estimates, and other chemical

signatures such as alkalinity and silica concentrations between discharging ground water in Morgan Creek as reported by Böhlke

and Denver (1995) and the Hornerstown ground water reported here, could indicate that discharge from the Hornerstown aquifer

may influence much of the chemical composition of ground-water discharge to Morgan Creek.
31

Nutrient Nutrient Yields fr ields from Stream Base Flow

The chemistry of stream base flow relates closely to the chemistry of ground water discharging to the stream. The spatial patterns

of base-flow chemistry within each watershed provide insight into the chemical environment of the surficial aquifer, allowing for

instream processes. The current project included three synoptic surveys of stream base flow at 14 sites in the Morgan Creek and

Chesterville Branch watersheds. These synoptic surveys sampled conditions during periods of low water table (September 1998)

and high water table (April 1998 and February 2000). The synoptic surveys were supplemented by monthly base-flow samples at

the Morgan Creek and Chesterville Branch gaging stations to provide a record of seasonal variability. These data were evaluated

to relate the loads and yields of nutrients from the two watersheds to landscape factors and geologic setting.

Sampling at Fixed Sites Sampling at Fixed Sites

Time-series plots of samples collected from the fixed sites (Figure 16) show seasonal variations in dissolved nitrogen concentrations. Concentrations tend to be lowest during the summer months. Low stream discharge in the summer is common in this area

because evapotranspiration removes water that would otherwise recharge the aquifer. The lower nitrogen concentrations are likely

due to uptake by stream phytoplankton, macrophytes, and submerged aquatic vegetation during the warmer growing season. The

data also show that Morgan Creek has lower nitrogen concentrations than Chesterville Branch in the upstream parts of the

watershed, as previously reported by Böhlke and Denver (1995).

Figure 16. Figure 16. Time-series plots of total dissolved nitrogen concentrations at the two fixed stream-sampling sites (station numbers

01493112 and 01493500) in the Locust Grove study area, Kent County, Maryland.

10

9

8

7

6

5

4

3

2

1

0

Jan Feb Mar

1998 1999 2000

Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar

CONCENTRATION OF TOTAL DISSOLVED NITROGEN,

IN MICROMOLES PER LITER

STATION 01493112 (Chesterville Branch near Crumpton, Maryland)

STATION 10493500 (Morgan Creek near Kennedyville, Maryland)
32

Although there is some overlap in the range of values, the nitrogen loads (mass per year) from Chesterville Branch generally are

higher than those from Morgan Creek (Table 4). Nitrogen yields (load per unit watershed area) are higher from Chesterville Branch

than from Morgan Creek. Chesterville Branch yields of 0.04-0.08 gm sec-1 km-2 are higher than those reported by Bachman and

Phillips (1996) for well-drained landscapes on the Delmarva Peninsula, which ranged from 0.02 to 0.04 gm sec-1 km-2. Morgan

Creek yields (0.01-0.03 gm sec-1 km-2) overlapped those of Chesterville Branch, and were slightly higher than yields reported for

poorly drained landscapes on the Delmarva Peninsula (0.007-0.02 gm sec-1 km-2) (Bachman and Phillips, 1996). Both of these

watersheds were considered to be in the well-drained landscape in the analysis by Bachman and Phillips (1996); the results

presented here further underscore the extent of variation in nitrogen yields within a given landscape class reported in that study.

Base-Flow Synoptic Surveys Base-Flow Synoptic Surveys

The data from the base-flow synoptic surveys also confirm observations by Böhlke and Denver (1995) that total nitrogen

concentrations in Morgan Creek generally are lower than those in Chesterville Branch (Figure 17). The synoptic surveys revealed

some fundamental differences in the patterns of occurrence of nitrogen and related chemical constituents between the two

watersheds. In particular, total nitrogen concentrations tended to decrease downstream in Chesterville Branch, whereas they

increased downstream in Morgan Creek (Figure 18). In both watersheds, stream discharge (of water) and nitrogen loads increase

monotonically downstream. The increasing trend of stream discharge indicates that both streams are gaining flow from groundwater discharge. Although loads in the two streams appear similar in the upstream reaches, they are consistently higher in

Chesterville Branch than in Morgan Creek at the downstream gage (Figure 18), even though Morgan Creek has consistently higher

discharge than Chesterville Branch for any given season (Figure 18).

The higher stream discharge in Morgan Creek may be due to the larger watershed area of Morgan Creek (31 km2

) as compared to

Chesterville Branch (16 km2

). The specific discharge (discharge per unit area of the watershed) for any given season is greater in

Chesterville Branch than in Morgan Creek (Figure 18). This pattern also occurs in the downstream trends of nitrogen yields

(Figure 18). Yields in Morgan Creek increase downstream, similar to nitrogen concentrations (Figure 18), whereas Chesterville

Branch displays a more variable trend similar to that of specific discharge. The higher yields in Chesterville Branch also appear to

be related to the nitrogen concentrations.

Böhlke and Denver (1995) presented evidence that the lower concentrations of nitrate in Morgan Creek were due to denitrification

in the discharge areas where the Aquia confining layer is shallow. However, it also is possible that the lower concentrations could

be due to the mixing of higher proportions of older ground water with low nitrate concentrations in base flow. These two

Table 4. Table 4. Summary of Base-flow Nitrogen Loads from the Locust Grove Study Area, Kent County, Maryland

[Estimates are based on monthly samples collected from April 1998 to March 1999 and one sample collected in February 2000. gm N sec-1,

grams of nitrogen per second; gm N sec-1km-2, grams of nitrogen per second per square kilometer; kg N year-1, kilograms of nitrogen per year.]

		 



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' 23 2

$
	 23 2#3

! 2 2

3$
	  2

5'  

+' 	!

  , 
 

'6 & $	  

$
	 22# 22

! 22 22 +' "	!

  , 
   

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	 223 22

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33

Figure 17. Figure 17. Areal distribution of total dissolved nitrogen concentrations in stream base flow for the Locust Grove study area,

Kent County, Maryland, April 1998 synoptic survey.

Morgan

Chesterville

Branch

Creek

Urieville

Community

Lake

291

290

213

213

292

298

298

448

444

566

290

Morgnec Road

Augustine

Herman Hwy.

Morgnec

Road

Cherry Lane

River Road

Grove

Duck

Road

Puddle

Kennedyville

Browntown

Road

Road

Road

Chesterville

Road

Locust

Wallis Road

Bolton Rd.

447

Blacks

Station

Road

VanSants

Corner Road

2.11

2.92

3.25

5.91

8.22

4.18

3.87

3.92

4.75

11.13

10.65

7.84

5.76

7.59

75O

75 55'00" O76 57'30" O00'00"

0

0

1

1 2 KILOMETERS

2 MILES

39O20'00"

39O

15'00"

39O

17'30"

EXPLANATION

SUBBASIN CONTRIBUTING TO EACH

STREAM-BASE-FLOW SITE

TOTAL DISS LVED NITROGEN CONCENTRATION,

in milligrams per liter as nitrogen

O

GREATER THAN 8.3

5.9 - 8.3

3.25 - 5.8

LESS THAN 3.25
34

Figure 18. Figure 18. Observed downstream trends of stream discharge, specific discharge, total dissolved nitrogen concentration,

instantaneous nitrogen load, and instantaneous nitrogen yield from base-flow synoptic surveys in April and

September 1998, Locust Grove study area, Kent County, Maryland.

0.30 12

10

8

6

4

2

0

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

0.25

0.20

0.15

0.10

0.05

0.00

0.015

0.010

0.005

0.000

876543210

DISCHARGE,

IN CUBIC METERS PER SECOND

SPECIFIC DISCHARGE,

IN CUBIC METERS PER SECOND

PER SQUARE KILOMETER

INSTANTANEOUS NITROGEN LOAD,

IN GRAMS PER SECOND

DISTANCE UPSTREAM OF GAGE,

IN KILOMETERS

DISTANCE UPSTREAM OF GAGE,

IN KILOMETERS

DISTANCE UPSTREAM OF GAGE,

IN KILOMETERS

DISTANCE UPSTREAM OF GAGE,

IN KILOMETERS

CONCENTRATION OF TOTAL

DISSOLVED NITROGEN,

IN MILLIGRAMS PER LITER

876543210

876543210 876543210

0.15

0.10

0.05

0.00

INSTANTANEOUS NITROGEN YIELD,

IN GRAMS PER SECOND

PER SQUARE KILOMETER

DISTANCE UPSTREAM OF GAGE,

IN KILOMETERS

876543210

EXPLANATION

BASE-FLOW SYNOPTIC SURVEYS

MORGAN CREEK, APRIL 1998

MORGAN CREEK, SEPTEMBER 1998

CHESTERVILLE BRANCH, APRIL 1998

CHESTERVILLE BRANCH, SEPTEMBER 1998

Flow direction

Flow direction

Flow direction

Flow direction

Flow direction
35

hypotheses can be evaluated from the distribution of selected geochemical constituents in base flow from the two basins. As

described above, ground water recharged before 1970 has lower nitrate concentrations than water recharged more recently. In

addition, old agricultural and old calcareous waters have had more contact time with the aquifer materials, and may be more

chemically evolved with higher concentrations of dissolved bicarbonate and silica than the young agricultural water. Further, the

work of Modica and others (1998) suggests that the proportion of older ground water discharging to a stream increases downstream

(Figure 4). In addition to lowering nitrogen concentrations, a larger proportion of older ground water in discharge to base flow also

would have the cumulative effect of an increasing downstream trend of bicarbonate and silica, and a decreasing trend of magnesium

(Figure 19).

The observed trends of bicarbonate, silica, and magnesium in Morgan Creek and Chesterville Branch were compared to the trends

expected from a systematically increasing proportion of discharge from old ground water (Figure 20). The observed data are

consistent with the expected trend for magnesium in all cases, and for bicarbonate in Chesterville Branch. However, bicarbonate

shows a decreasing trend in Morgan Creek (especially for the April 1998 samples), and both watersheds have decreasing

downstream trends in silica concentrations. Decreasing silica concentrations would be expected in Chesterville Branch, because

discharge of high-silica water from the Hornerstown aquifer is less likely than in the upstream reaches of Morgan Creek. The top

of the Hornerstown Formation dips to the south, and Chesterville Branch has not incised a stream channel through the Aquia

confining layer. This may not be the case in Morgan Creek, however, where the channel appears to follow the outcrop zone of the

Aquia confining layer (Figure 11), and there is some evidence of ground-water discharge from the Hornerstown aquifer (Böhlke

and Denver, 1995).

Iron-sulfide oxidation to produce sulfate is one possible redox process associated with denitrification. If denitrification were related

to iron-sulfide oxidation, then denitrified water would have sulfate concentrations elevated above background. However, the trends

of sulfate concentration shown in Figure 20 indicate that downstream water, which is hypothesized to have a greater proportion of

denitrified ground-water discharge, has lower concentrations of sulfate than upstream water.

The concentrations of dissolved constituents in base flow are not merely the aggregation of the concentrations of ground-water

discharge to the mainstem channel of the stream. Concentrations in base flow also are affected by the loads of constituents entering

from tributaries and processes occurring in the stream channel or alluvial sediments that may be sinks and sources for the dissolved

substances. Although a thorough discussion of riparian and instream processes is beyond the scope of this report, an analysis of the

effects of the mixing of water from tributaries provides some evidence that processes other than ground-water discharge are

affecting base-flow concentrations.

In a typical stream, the flow from two tributaries mixes in a downstream channel (Figure 21). Without the physical or geochemical

removal of a constituent, the downstream load, C3

Q3, is equal to the sum of the loads of the two upstream tributaries (C1Q1 and C2Q2)

plus the load derived from ground-water discharge CGWQGW:

C1

Q1 + C2Q2 + CGWQGW = C3Q3 (3)

where C is concentration (mass per volume), Q is discharge (volume per time), and GW refers to ground water.

Figure 19. Figure 19. Expected downstream trends of nitrogen and related geochemical constituents from a downstream increase in the

discharge of old ground water. NITROGEN

Headwaters

Flow direction Flow direction

Flow direction Flow direction

Headwaters Headwaters Gage Gage

Gage Gage Headwaters

SILICA

BICARBONATE MAGNESIUM
36

Figure 20. Figure 20. Observed downstream trends of sulfate, magnesium, bicarbonate, and silica concentrations from base-flow synoptic

surveys in April and September 1998, Locust Grove study area, Kent County, Maryland.

EXPLANATION

BASE-FLOW SYNOPTIC SURVEYS

MORGAN CREEK, APRIL 1998

MORGAN CREEK, SEPTEMBER 1998

CHESTERVILLE BRANCH, APRIL 1998

CHESTERVILLE BRANCH, SEPTEMBER 1998

0.3 0.6

0.5

0.4

0.3

0.24

0.20

0.16

0.12

0.08

0.2

0.1

0.0

1.0

0.8

0.6

0.4

0.2

0.0

876543210

CONCENTRATION OF SULFATE,

IN MILLIEQUIVALENTS PER LITER

CONCENTRATION OF BICARBONATE,

IN MILLIEQUIVALENTS PER LITER

CONCENTRATION OF SILICA,

IN MILLIMOLES PER LITER

DISTANCE UPSTREAM OF GAGE,

IN KILOMETERS

DISTANCE UPSTREAM OF GAGE,

IN KILOMETERS

DISTANCE UPSTREAM OF GAGE,

IN KILOMETERS

DISTANCE UPSTREAM OF GAGE,

IN KILOMETERS

CONCENTRATION OF MAGNESIUM,

IN MILLIEQUIVALENTS PER LITER

876543210

876543210 876543210

Flow direction

Flow direction

Flow direction

Flow direction

Figure 21. Figure 21. Relations among discharge and concentrations of dissolved constituents in tributaries and downstream sites under

non-reactive mixing.

EXPLANATION

SITE 1

SITE 3

SITE 2

Tributary 1

Tributary 2

C Q + C Q + C Q = C Q 11 22 GW GW 3 3

C

Q

C

Q Discharge of ground water between

sites 1 and 2 and site 3

Concentration of constituent in

ground water GW

GW

Discharge (volume per time)

Concentration (mass per volume)

C Q C Q

C Q

1 2

3

1 2

3
37

An estimate of ground-water inflow can be made by subtracting the upstream discharges (Q1 and Q2) from the downstream

discharge (Q3

):

QGW = Q3 – (Q1 + Q2) (4)

The expected average concentration of ground-water discharge between the tributaries and the downstream site can be estimated by

dividing equation (3) by the estimate of ground-water inflow and rearranging the terms:

CGW = C3

(Q3/QGW) – C1(Q1/QGW) – C2(Q2/QGW) (5)

A negative value of CGW for cases in which Q3

 is greater than the sum Q1+Q2 (for example, an effluent stream system with C3

considerably less than C1 or C2) is evidence of a physical or geochemical sink for the constituent. In such cases, the concentration

of ground-water inflow cannot be estimated. In other cases, further evidence is needed to determine whether instream or alluvialchannel processes are acting as a geochemical source or sink for the constituent.

An estimate of the downstream concentration C’3 can be made on the basis of any hypothesized average concentration of groundwater discharge, and this estimate can be compared to the actual measured downstream concentration. Rearranging equation 5

results in:

C’3

 = C1(Q1/Q3) + C2(Q2/Q3) + CGW(QGW/Q3) (6)

If the estimated value for C’3 is close to the measured value, it is likely that ground-water discharge with non-reactive mixing

accounts for most of the observed concentrations of dissolved constituents in base flow.

In the study area, these relations can be calculated at four reaches that have sites with upstream measurements, downstream

measurements, and measurements at tributaries:

Upstream Downstream Tributary

 site site site(s) site(s)

 Chesterville Branch

Reach C1: Reach C1: 01493110 01493111 01493109

Reach C2: Reach C2: 01493111 01493112 0149311110

 Morgan Creek: Morgan Creek:

Reach M1: Reach M1: 01493495 01493497 01493496

Reach M2: Reach M2: 01493497 01493499 01493498,

0149349810,

0149349820

The locations of these sites and the stream reaches C1, C2, M1, and M2 are shown in Figure 22.

Figure 22. Figure 22. Location of surface-water sampling stations and stream reaches on Morgan Creek and Chesterville Branch in the

Locust Grove study area, Kent County, Maryland.
38

Estimates from equations (5) and (6) of ground-water discharge, concentrations of selected constituents in ground water, and the

downstream concentration in the reach under the bounding condition of ground-water concentrations equal to zero are presented in

Tables 5a through 5d. A comparison of the estimated and observed constituents shows that they only are partially consistent with

the hypothesis of increased downstream contribution of older ground water. However, a number of interesting trends are evident

that could justify further evaluation of the data and additional study of the processes of ground-water discharge to streams in the

study area.

The most striking observation in Table 5a is that the decrease in nitrate (from greater than 10 mg/L down to 7.84 mg/L) observed

in Chesterville Branch reach C1 cannot be accounted for by inflow of lower-nitrate ground water. Even where the ground-water

discharge is nitrogen-free (the case in which CGW in equation 6 equals 0), the estimated downstream total-nitrogen concentration is

8.9 mg/L, higher than what is observed. Reach C1 of Chesterville Branch has a manmade pond that is approximately 10,000 m2

(about 2.5 acres). It is possible that this pond provides a geochemical environment that facilitates denitrification; alternatively, the

dissolved nitrogen may be taken up by plants.

The data in Table 5b provide evidence that inflow of low-nitrogen ground water contributes to the downstream decrease of nitrogen

concentrations in Chesterville Branch. In reach C2, the observed decline in total nitrogen concentrations (from 7.8 to 7.6 mg/L) can

be explained by the dilution of ground-water inflow with an average concentration of 8.1 mg/L (which can be obtained from a

mixture of old and young ground water) and by inflow from the tributary (site 0149311110) with a lower nitrate concentration

(5.8 mg/L). Bicarbonate concentrations in both reaches increase to a degree that can be explained by the input of high (greater than

0.5 meq/L) bicarbonate water typical of old calcareous ground water.

In Morgan Creek, the higher total nitrogen concentrations in the tributaries may explain in part why concentrations increase

downstream. In reach M1 (Figure 22), the average ground-water nitrogen concentration was calculated as 2.8 mg/L (Table 5c), this

mixture would have a considerable proportion of old calcareous water mixed with the young, high-nitrogen water. Discharge of

nitrogen-free ground water would result in a downstream concentration of 2.2 mg/L, below the observed value of 3.25 mg/L. In

addition, one tributary (site 01493496) with a higher nitrogen concentration (4.75 mg/L) may contribute to the observed

downstream increase in nitrogen concentration; this tributary watershed is underlain by a thicker sequence of the Columbia-Aquia

surficial aquifer rather than the shallow Aquia confining layer. Estimated ground-water bicarbonate inputs are consistent with a

source of old calcareous water, but estimated silica concentrations appear to be lower than those observed in ground water.

Estimated sulfate concentrations appear to be more typical of those observed in the Aquia redox transition zone than in the

Hornerstown aquifer.

In Morgan Creek reach M2 (Figure 22), the calculated ground-water nitrogen input is 6.3 mg/L (Table 5d); apparently the discharge

of the high-nitrogen tributaries (sites 01493498, 0149349810, and 0149349820) is not sufficient to account for the observed

increase in nitrogen concentration (from 3.3 to 3.9 mg/L) in this reach. The bicarbonate decrease observed in this reach may

indicate that the ground water being discharged is young, low-bicarbonate, high-nitrate water; however, the calculated groundwater concentration is negative, indicating that riparian or instream processes may be removing bicarbonate. Silica displays a

pattern similar to bicarbonate. The calculated sulfate concentration is not consistent with the calculated nitrogen concentration,

because it is more typical of Hornerstown water than water from the surficial aquifer.

The patterns observed in the base-flow synoptic surveys can be related to the hydrogeologic framework of the two watersheds.

Chesterville Branch reaches C1 and C2 are underlain by the thick Columbia-Aquia surficial aquifer. It is likely that only a small

percentage of the ground water discharging to Chesterville Branch flowed through the redox zone at the base of the Aquia aquifer

or from the Hornerstown aquifer. This watershed functions in a manner similar to those described by Modica and others (1998),

with a greater proportion of older ground water contributing to flow in the downstream reach. In addition, impoundments, both

natural (such as beaver dams) and artificial, may be sinks for nitrogen.

Morgan Creek reach M1 is underlain by a thin cover of the Columbia-Aquia aquifer, which makes it more likely that a greater

proportion of ground-water discharge flowed through the Aquia redox zone and was denitrified. At the downstream end, the stream

channel overlies the subcrop of the Aquia redox zone. The Aquia confining layer may be breached locally, either by faulting or

stream incision, and water from the Hornerstown aquifer may discharge through the alluvial fill. Alternatively, the tributary in

reach M1 is underlain by a thicker section of the Columbia-Aquia surficial aquifer, and higher-nitrate ground water may discharge

as base flow.

In Morgan Creek reach M2, the streambed and alluvial channel are underlain along the entire length of the reach by the Aquia

confining layer and the sedimentary redox zone. Nitrogen concentrations increase downstream, which could be explained by an

increased discharge of relatively high-nitrogen (~6 mg/L) ground water. These observations indicate that either the incised valley

in this reach does not penetrate the Aquia confining layer, or the alluvial fill is more fine-grained and Hornerstown water cannot

easily discharge to the stream. In addition, riparian and instream processes may be acting as sinks for bicarbonate and silica, or

sources for sulfate and other constituents.
39

[See Figure 22 for location of Reach C1; m3/s, cubic meters per second; mg/L, milligrams per liter; μmol/L, micromoles per liter; meq/L; milliequivalents per liter; –, no data available.]

Station number

Position ofsamplingsite

Discharge(m3/s)

Nitrogen,total(mg/Las N)

Silica,dissolved(μmol/L asSiO2 )

Bicarbonate,dissolved(meq/L asHCO3 )

Magnesium,dissolved(meq/Las Mg)

Sulfate, dissolved(meq/L as SO4 )

CHESTERVILLE BRANCH REACH C1

OBSERVED 

01493109 Tributary 0.01 11.13 0.14 0.25 0.91 0.35 01493110 Upstream 0.05 10.65 0.16 0.28 0.54 0.20 01493111 Downstream 0.07 7.84 0.15 0.43 0.42 0.12 

ESTIMATED FOR STREAM REACH 

Total streamflow (measured) 0.07 Ground-water discharge (14 percent of total streamflow) – 0.01 – – – – – Concentration in ground water – – A -6.35 0.14 1.18 A -0.45 A -0.42 

B Downstream concentration with Cgw = 0 – – 8.90 0.13 0.23 0.50 0.19 A A negative value for estimated concentration implies uptake or consumption of the constituent in the stream reach. B Estimated downstream concentration assuming that the dissolved concentration of the constituent in ground water is zero (Cgw = 0). 

Table 5A-5D. Table 5A-5D. Estimated Concentrations of Dissolved Constituents in Ground Water Discharge Calculated from Measured Stream Flow and Concentrations of

 Constituents at Upstream, Downstream, and Tributary Sampling Sites

Table 5A. Table 5A. Estimated Concentrations of Dissolved Constituents in Ground-water Discharge Calculated from Measured Streamflow and Concentrations of

Constituents at Upstream, Downstream, and Tributary Sampling Sites on the Chesterville Branch, Reach C1 in the Locust Grove Study Area, KentCounty, Maryland
40

Station number

Position ofsamplingsite

Discharge(m3/s)

Nitrogen,total(mg/Las N)

Silica,

dissolved(μmol/L asSiO2 )

Bicarbonate,dissolved(meq/L asHCO3 )

Magnesium,dissolved(meq/L asMg)

Sulfate,dissolved(meq/L as SO4 )

CHESTERVILLE BRANCH REACH C2

OBSERVED 

01493111 Upstream 0.07 7.84 0.15 0.43 0.42 0.11 0149311110 Tributary 0.04 5.76 0.13 0.34 0.39 0.08 01493112 Downstream 0.21 7.59 0.13 0.44 0.42 0.11 

ESTIMATED FOR STREAM REACH 

Total streamflow (measured) 0.21 Ground-water discharge (48 percent of total streamflow) – 0.10 – – – – – Concentration in ground water – – 8.18 0.12 A -0.48 0.43 0.13 

B Downstream concentration with Cgw = 0 – – 3.56 0.07 0.21 0.21 0.05 A A negative value for estimated concentration implies uptake or consumption of the constituent in the stream reach. B Estimated downstream concentration assuming that the dissolved concentration of the constituent in ground water is zero (Cgw = 0). 

Table 5B. Table 5B. Estimated Concentrations of Dissolved Constituents in Ground-water Discharge Calculated from Measured Streamflow and Concentrations of

Constituents at Upstream, Downstream, and Tributary Sampling Sites on Chesterville Branch, Reach C2 in the Locust Grove Study Area, KentCounty, Maryland

[See Figure 22 for location of Reach C2; m3/s, cubic meters per second; mg/L, milligrams per liter; μmol/L, micromoles per liter; meq/L; milliequivalents per liter; –, no data available.]
41

Station number

Position ofsamplingsite

Discharge(m3/s)

Nitrogen,total(mg/Las N)

Silica,dissolved(μmol/L asSiO2 )

Bicarbonate,dissolved(meq/L asHCO3 )

Magnesium,dissolved(meq/L as Mg)

Sulfate,dissolved(meq/L as SO4 )

MORGAN CREEK REACH M1

OBSERVED 

01493495 Upstream 0.07 292 0.11 0.64 0.48 0.17 01493496 Tributary 0.03 4.75 0.05 0.86 0.48 0.16 01493497 Downstream 0.16 3.25 0.10 0.78 0.44 0.13 

ESTIMATED FOR STREAM REACH 

Total streamflow (measured) 0.16 Ground-water discharge (38 percent of total streamflow) – 0.06 – – – – – Concentration in ground water – – 2.83 0.13 0.89 0.39 0.07 

B Downstream concentration with Cgw = 0 – 2.16 0.05 0.44 0.29 0.10 B Estimated downstream concentration assuming that the dissolved concentration of the constituent in ground water is zero (Cgw = 0). 

Table 5C. Table 5C. Estimated Concentrations of Dissolved Constituents in Ground-water Discharge Calculated from Measured Streamflow and Concentrations of

Constituents at Upstream, Downstream, and Tributary Sampling Sites on Morgan Creek, Reach M1 in the Locust Grove Study Area, Kent County,Maryland

[See Figure 22 for location of Reach M1; m3/s, cubic meters per second; mg/L, milligrams per liter; μmol/L, micromoles per liter; meq/L; milliequivalents per liter; –, no data available.]
42

Table 5D. Table 5D. Estimated Concentrations of Dissolved Constituents in Ground-water Discharge Calculated from Measured Streamflow and Concentrations of

Constituents at Upstream, Downstream, and Tributary Sampling Sites on Morgan Creek, Reach M2 in the Locust Grove Study Area, Kent County,Maryland

[See Figure 22 for location of Reach M2; m3/s, cubic meters per second; mg/L, milligrams per liter; μmol/L, micromoles per liter; meq/L; milliequivalents per liter; –, no data available.]

Station number

Position ofsamplingsite 

Discharge(m3/s)

Nitrogen,

total(mg/Las N)

Silica,dissolved(μmol/L as

SiO2 )

Bicarbonate,dissolved(meq/L asHCO3 )

Magnesium,dissolved(meq/L as Mg)

Sulfate,dissolved(meq/L as SO4 )

MORGAN CREEK REACH M2

OBSERVED 

01493497 Upstream 0.16 3.25 0.10 0.78 0.44 0.13 01493498 Tributary 0.02 4.18 0.17 0.74 0.39 0.17 0149349810 Tributary <0.01 5.91 0.09 0.96 0.56 0.21 0149349820 Upstream <0.01 8.22 0.15 0.48 0.71 0.23 01493499 Downstream 0.21 3.87 0.10 0.60 0.44 0.14 

ESTIMATED FOR STREAM REACH 

Total streamflow (measured) 0.21 Ground-water discharge (14 percent of total streamflow) – 0.03 – – – Concentration in ground water – – 6.34 0.00 A -0.49 0.38 0.15 

B Downstream concentration with Cgw = 0 – – 2.95 0.01 0.67 0.38 0.12 A A negative value for estimated concentration implies uptake or consumption of the constituent in the stream reach. B Estimated downstream concentration assuming that the dissolved concentration of the constituent in ground water is zero, (Cgw = 0). 
43

The relative importance of ground-water discharge to these two streams compared to the effects of riparian and instream processes

is not well understood. Additional investigations, including coring the alluvial fill, sampling ground water in the riparian zone, and

conducting more intensive biological and hydrochemical sampling in the streams, are needed to improve the understanding of baseflow nitrogen discharge in this area.

Relation Between Nutrients and Landscape Factors Relation Between Nutrients and Landscape Factors

Bachman (1984b), Hamilton and others (1993), Bachman and Phillips (1996), and Phillips and Bachman (1996) described the

variability in the landscape features on the Delmarva Peninsula and how this variability was related to the quality of ground water

and base flow. Hamilton and others (1993) developed the “hydrogeomorphic region” approach, whereby landscapes were defined

on the basis of the overall occurrence of certain mappable features, most notably the degree of stream incision, the drainage

characteristics of the soil, and the presence of shallow confining layers within the surficial aquifers. These features appear to be

related to the arrangement of ground-water flow paths and the presence of geochemical processes that can affect the chemical

composition of ground water (Bachman and Katz, 1986; Hamilton and others, 1993; and Bachman, 1994). Hydrogeomorphic

regions are independent of stream basins; thus the discharge from a basin could be a combination of several hydrogeomorphic

regions. Phillips and Bachman (1996) and Bachman and Phillips (1996) developed a “basin index” to characterize landscapes

within a drainage basin. The index is essentially the principal-components score using three basin characteristics (stream slope,

percentage of poorly drained soils, and forest cover in the basin) that appear to be related to the hydrogeomorphic regions.

The Locust Grove study area is in the well-drained upland hydrogeomorphic region defined by Hamilton and others (1993). This

area is characterized by a relatively thick (15-30 m) surficial aquifer, deeply incised stream valleys, and well-drained soils. Groundwater flow paths may extend from drainage divides to discharge in streams and penetrate to the base of the surficial aquifer. The

land use in the study area is mostly agricultural, and there is little interspersion of agricultural and wooded areas. The uplands are

farmed, and the woodlands and wetlands are restricted almost exclusively to the riparian areas (forest land use in Figure 3). The

well-drained upland was reported to have ground water with high concentrations of nitrogen (Hamilton and others, 1993).

Although the study area is entirely within the well-drained upland, the dissolved nitrogen concentrations vary considerably between

Chesterville Branch and Morgan Creek (Böhlke and Denver, 1995). A local-scale landscape analysis was conducted to aid

modelers in locating subregions within the study area that have similar hydrologic conditions. The analysis was based on the “basin

index” approach of Phillips and Bachman (1996), and tested by relating the basin index to constituent concentrations of water

samples collected during the base-flow synoptic surveys.

The original basin index was developed from landscape data for basins located throughout the Delmarva Peninsula. The welldrained upland in the Locust Grove study area represents one end-member of the landscapes used to classify the Delmarva

Peninsula; consequently, alternative classification variables were examined to determine whether they could provide better

correlation with water quality at the local scale. The following basin characteristics were examined:

(1) Topography

(1a) Stream slope and the variables used to calculate stream slope;

(1b) Stream-reach length;

(1c) Altitude of stream at the basin outlet; and

(1d) Stream-reach relief (difference in altitude between stream outlet and highest altitude of stream reach).

(2) Soil type

(2a) Percentage of well-drained (type A) soils in basin;

(2b) Percentage of moderately well-drained (type B) soils in basin;

(2c) Percentage of moderately poorly drained (type C) soils in basin; and

(2d) Percentage of poorly drained (type D) soils in basin.

(3) Land use

(3a) Percentage of agricultural land in basin;

(3b) Percentage of land in Animal Feeding Operations in basin;

(3c) Percentage of nursery operations in basin;

(3d) Percentage of urban land in basin; and

(3e) Percentage of forests and wetlands in basin.

Fourteen basins in the Chesterville Branch and Morgan Creek watersheds were delineated and used for the local-scale landscape

analysis (Figures 3 and 11). Nine of the basins are first-order, headwater watersheds; the others were included to examine
44

systematic changes in landscape and nutrient concentrations within a watershed. Basin characteristics for the sites sampled in the

base-flow synoptic surveys are listed in Appendix F.

The correlation pattern among the basin characteristics is shown in Table 6. In contrast to the findings of Phillips and Bachman

(1996), stream slope, the percentage of type D soils, and the percentage of forested land show no statistically significant correlation.

This result is not entirely unexpected, because the Locust Grove area represents one extreme of the landscapes in the Delmarva

Peninsula, and even the best correlations reported by Phillips and Bachman (1996) accounted for less than 40 percent of the total

variation. Despite this lack of correlation, the coefficients in Table 6 show some correlation among basin characteristics related to

topography, soil type, and land use. It appears that the strongest correlations are among the outlet altitude, percentage of type C

soils, and percentage of the basin in agriculture (Figure 23). Principal-components analysis was used on these three variables to

generate a principal-components score, which is essentially a new, synthetic variable that is based on the shared variance among the

original variables (Phillips and Bachman, 1996). The analysis was done on the rank-scores of the basin characteristics, which

results in a non-parametric test that requires no assumptions about the frequency distributions of the variables (Conover, 1980).

The analysis (Table 7) indicates that 77 percent of the variation was accounted for by the first eigenvalue of the correlation matrix

(the first principal component). All three variables are heavily loaded on the first component, and the communalities (the percent

of total variance of each variable accounted for by the first component) range from 71 to 86 percent. The resulting principalcomponents score is called the “local basin index” in this report to distinguish it from the “regional basin index” of Phillips and

Bachman (1996). The local basin index is computed from the altitude of the basin outlet, the percentage of type C soils, and

agricultural land use; the regional basin index is computed from the stream slope, the percentage of type D soils, and forested land

use.

The areal distribution of the local basin index (Figure 24) displays a systematic decrease from the headwaters of each basin to the

gaging station. This result is not unexpected because the outlet altitude also systematically decreases from the headwaters to the

gaging stations (which have the lowest outlet altitudes), and the other variables are correlated with the outlet altitude. This trend is

true for both the first-order headwater basins as well as the nested mainstem basins. The pattern is found in both Morgan Creek and

Chesterville Branch; however, the values of the basin index in the downstream basins of Morgan Creek are much more negative

than those in the downstream part of Chesterville Branch.

Although the variables of the regional basin index do not show significant correlations at the local scale, there are some indirect

relations (Table 6). The altitude of the basin outlet is significantly correlated with the length of the stream reach which, in turn, is

correlated with stream slope and the percent forested land in the basin. The outlet altitude also is significantly correlated with the

percentage of type D soils in the basin. The percentages of type D soils and forested land have a significant inverse correlation with

percentage of agricultural land within a basin.

The relations among basin index, nitrogen concentration, and location of sites within the stream network (Figure 24) show patterns

that could indicate that denitrification at the top of the Aquia confining layer is an important mechanism to explain the differences

between nitrogen concentrations in Morgan Creek and Chesterville Branch. This relation for the April 1998 synoptic data is shown

in Figure 24. The September 1998 synoptic data show a similar pattern, although the nitrogen concentrations generally are lower.

Most of the first-order basins, and many of the nested mainstem basins, show a rough correlation of increasing nitrogen with

increasing value of the local basin index. The nested mainstem basins display downstream patterns (increasing concentrations for

Morgan Creek and decreasing concentrations for Chesterville Branch) similar to the actual downstream plots of concentrations by

distance from the gage (Figures 17 and 24). The three samples that depart significantly from the correlation (sites 01493491,

01493495, and 01493496) are from the headwaters of Morgan Creek, in the area where the Aquia confining layer subcrops

shallowly, and allows a larger percentage of flow paths in the surficial aquifer to flow through the redox transition zone. The

nitrogen concentration at site 01493496 also may be explained in that the tributary sampled there was dammed into a small farm

pond until shortly before sampling, when the dam was breached. Base flow from site 01493496 could represent a certain amount

of ground-water discharge that has passed through former pond-bottom sediments that may still be under reducing conditions.
45

	
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Table 6. Table 6. Correlation Coefficients for Landscape Variables Used in the Analysis of the Morgan Creek and Chesterville Branch Watersheds, Locust Grove

Study Area, Kent County, Maryland

[Bold numbers are significant at á = 0.05; 16 pairs of variables; AFO = animal feeding operation; %, percent; soil types: A, well-drained; B, moderately well-drained; C, moderately

poorly drained; D, poorly drained]
46

Figure 23. Figure 23. Relations among stream-outlet altitude, percentage of type C (moderately poorly drained) soils, and percentage of

agriculture in the Morgan Creek and Chesterville Branch basins, Locust Grove study area, Kent County, Maryland.

25

20

Spearman rank correlation

coefficient = -0.54

p = 0.03

15

10

5

0

0 10 20 30 40 50 60

PERCENTAGE OF TYPE C SOILS IN BASIN

ALTITUDE OF BASIN OUTLET,

IN FEET ABOVE SEA LEVEL

Spearman rank correlation

coefficient = -0.69

p = 0.00 13

100

98

96

94

92

90

88

86 0 5 10 15 20 25

PERCENTAGE OF AGRICULTURAL

LAND IN BASIN

PERCENTAGE OF BASIN WITH

TYPE C SOILS

Spearman rank correlation

coefficient = 0.73

p = 0.0013

100

98

96

94

92

90

88

86 0 10 20 30 40 50 60

PERCENTAGE OF AGRICULTURAL

LAND IN BASIN

ALTITUDE OF BASIN OUTLET,

IN FEET ABOVE SEA LEVEL

Table 7. Table 7. Results of Principal-components Analysis of Landscape Variables for the Morgan Creek and Chesterville Branch

Watersheds, Locust Grove Study Area, Kent County, Maryland

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47

Figure 24. Figure 24. Relations among basin index, dissolved nitrogen concentration, and location within the stream network, Locust

Grove study area, Kent County, Maryland.

Figure 25. Figure 25. Correlation between regional and local basin index scores for sites in the Locust Grove study area, Kent County,

Maryland.

TOTAL DISSOLVED NITROGEN, IN MILLIGRAMS PER LITER

LOCAL-SCALE BASIN INDEX

EXPLANATION

12

10

8

6

4

2

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

1

1

1

1

1

1

1

1

Chesterville Branch

Morgan Creek SITE

3491

SITE

3495

SITE

3496

Upstream

Upstream

Downstream

Downstream

SITE ON FIRST-ORDER TRIBUTARY OF CHESTERVILLE BRANCH

SITE ON FIRST-ORDER TRIBUTARY OF MORGAN CREEK

SITE IN NESTED MAINSTEM BASIN

PATH OF STREAMFLOW ALONG MAINSTEM OF CREEK

PATH OF STREAMFLOW FROM TRIBUTARY INTO MAINSTEM

1

1

Spearman rank correlation

coefficient = -0.70

p = 0.0001

2

1

0

-1

-2

-2.6 -2.4 -2.2 -2.0 -1.8

LOCAL BASIN INDEX

REGIONAL BASIN INDEX
48
49

Summary and Conclusions Summary and Conclusions

This report presents the results of data collection and analysis by the U.S. Geological Survey in support of ground-water flow

modeling by the U.S. Environmental Protection Agency for the Locust Grove study area, Kent County, Maryland. This effort has

provided evidence that subsurface hydrostratigraphic units substantially affect the transport and fate of dissolved nitrogen through

the surficial aquifer to discharge as stream base flow. The highly permeable surficial aquifer in the study area is underlain by a lowpermeability confining layer, which dips to the south. Continuous cores and geophysical logs indicate that the confining layer

approaches the surface near the riparian zone of Morgan Creek, but is deeper than 20 to 30 meters below the surface near

Chesterville Branch. The Chesterville Branch watershed is completely underlain by a thick, permeable surficial aquifer that yields

considerable base flow, whereas much of the Morgan Creek watershed is underlain shallowly by low-permeability sediments.

In addition to affecting ground-water flow paths and discharge to streams, the confining layer also has a geochemical environment

that may be conducive to denitrification of dissolved nitrate in the ground water. Reduced-iron minerals are abundant in the

confining layer but generally have been removed by weathering from the overlying aquifer. Chemical analyses indicate that ground

water in the surficial aquifer evolves from a high-nitrate water dominated by calcium to a low-nitrate, bicarbonate water with more

sodium. The concentrations of dissolved nitrogen and argon gases; dissolved oxygen, iron, and sulfate; and nitrogen and carbon

isotopes as tracers, all provide evidence that the low-nitrogen water discharging to the streams originally contained considerable

amounts of nitrate that was subsequently denitrified. Ground water that discharges to Morgan Creek is more likely to interact with

the sedimentary redox zone at the top of the Aquia confining layer, and appears to have a higher proportion of denitrified water than

ground water that discharges to Chesterville Branch. The geochemical data also confirm that denitrification was not active in

ground waters in the surficial aquifer above the sediment redox transition. Nitrate in the ground water has remained stable for at

least 40 to 50 years where it flowed through the deeply weathered sediments and oxic conditions of the Columbia-Aquia surficial

aquifer.

Base-flow nitrogen yields are about twice as high from Chesterville Branch (median of 0.058 grams per second per square

kilometer) than from Morgan Creek (0.022 grams per second per square kilometer), although annual loads are only 45 percent

higher in Chesterville Branch (median of 29,000 kilograms per year) than in Morgan Creek (20,000 kilograms per year). Although

the two watersheds were identified as having similar hydrologic landscape characteristics in previous studies, a more detailed

analysis indicates that the Morgan Creek basin contains soils that are somewhat more poorly drained. Soil drainage, altitude of the

watershed or sub-watershed outlet, and the percentage of agricultural land use are related to each other and to total dissolved

nitrogen concentrations in stream base flow.

The base-flow synoptic data show that nitrate concentrations tend to increase downstream in Morgan Creek and decrease

downstream in Chesterville Branch. The downstream increase of nitrate concentrations in Morgan Creek may be due to flow from

tributaries in which ground-water discharge is less likely to be denitrified, or from a downstream decrease in denitrification of

discharging ground water. The downstream decrease of nitrate concentrations in Chesterville Branch may be due to a downstream

increase of instream denitrification and uptake by biota, or by an increase in the relative proportion of older ground-water

discharge; this older ground water may have relatively low nitrate concentrations either because of lower historic inputs of nitrogen

or because of denitrification. There also is some evidence that the shallow Aquia confining layer may be breached, possibly by a

fault, under the riparian zone of Morgan Creek near site 01493495, and low-nitrate water from the underlying confined

Hornerstown aquifer may be contributing to base flow.

Further study would help to better define the processes affecting ground-water discharge to streams. In particular, an extended

hydrostratigraphic framework and ground-water geochemistry from wells in downstream sections of the watersheds, below sites

01493495 and 01493110, would contribute to an improved understanding of the lower reaches of the two streams. More detailed

data on the shallow subsurface geology of the riparian zone would help determine whether Hornerstown water is discharging to

Morgan Creek, and provide further evidence to evaluate the role of organic-carbon oxidation as a mechanism for denitrification in

both watersheds. Additional wells in the Hornerstown aquifer, particularly to the north of the study area, would provide data on the

source of ground-water recharge and the geochemical evolution of water in the Hornerstown aquifer. Finally, additional chemical

and biological sampling of streamwater would be helpful in characterizing instream processes that may be sources and sinks for

nitrogen and other dissolved constituents.
50
51

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Modica, E., Buxton, H.T., and Plummer, L. N., 1998, Evaluating the source and residence times of groundwater seepage to streams,

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74 p.

Mueller, D.K., and Helsel, D.R., 1996, Nutrients in the Nation’s waters: Too much of a good thing?: U.S. Geological Survey

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53

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Office of Water Data Coordination, 872 p.

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Geological Survey Techniques of Water-Resources Investigations, Book 9, Chapter A6, [variously paged].
54
55

Appendix Appendix A
56

Aquifer codes: 112PCPC – Pensauken Formation 125AQUI – Aquia Formation 125 HRRS – Hornerstown Formation 211MMMT – Monmouth Formation 

Types of logs: D- Drillers G- Geologist J – Gamma E - Electric 

Method of determining altitude:

L – Level (surveyed) M – from topographic map 

 	
 




  	 



	 




 










	











	 



		

	 	



	 	





		

	 




		

	 	



	 	





		

	 




 

	


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!



KE Be 46 391832075560801 391832 755608 64 55 40 50 9 24 14 125AQUI D 55 M 10

KE Be 50 391851075561801 391851 755618 70.17 35 20 22 35.17 50.17 48.17 112PCPC D, J 31.5 L 0.01KE Be 51 391851075554401 391851 755544 70.01 35 24 27 35.01 46.01 43.01 112PCPC D, J 31 L 0.01KE Be 52 391810075555801 391810 755558 74.72 50 33 36 24.72 41.72 38.72 112PCPC D, J 46.5 L 0.01KE Be 53 391810075555802 391810 755558 74.61 25 20 22 49.61 54.61 52.61 112PCPC D 25 L 0.01KE Be 59 391832075560803 391832 755608 71.36 30 23.5 26.5 41.36 47.86 44.86 125AQUI D 30 L 0.01KE Be 60 391811075564901 391811 755649 78.12 30 24.5 26.5 48.12 53.62 51.62 125AQUI D 30 L 0.01KE Be 61 391810075555803 391803 755552 74.58 60 47.5 50.5 14.58 27.08 24.08 125AQUI D, J 46.5 L 0.01KE Be 62 391742075554801 391742 755548 60.7 30 22.5 25.5 30.7 38.2 35.2 125AQUI D 30 L 0.01KE Be 63 391721075554501 391721 755545 45.09 40 36.5 39.5 5.09 8.59 5.59 125AQUI D 40 L 0.01KE Be 64 391721075554502 391721 755545 45.11 20 13 16 25.11 32.11 29.11 125AQUI D 20 L 0.01KE Be 65 391608075594301 391608 755943 49 25 19 22 24 30 27 125AQUI D 25 M 1KE Be 156 391819075580901 391819 755809 38 20 11 14 18 27 24 125AQUI D, U 20 M 10KE Be 157 391818075560901 391818 755802 43 25 15 18 18 28 25 125AQUI D, U 25 M 10KE Be 158 391814075575501 391814 755755 65 40 31 34 25 34 31 125AQUI D, U 40 M 10KE Be 159 391720075554601 391720 755546 45.27 70 65.5 68.5 -24.73 -20.23 -23.23 125AQUI D, U 70 M 10KE Be 160 391720075554602 391720 755546 45.23 45 35 38 0.23 10.23 7.23 125AQUI D 45 M 10KE Be 161 391720075554603 391720 755546 45.18 25 16 19 20.18 29.18 26.18 125AQUI D 25 M 10

Appendix A. Appendix A. Wells from Previous Projects that Were Used for Water-level Measurements, Chemical Sampling of Ground Water, and the Hydrogeologic

Framework for the Locust Grove Study Area, Kent County, Maryland

[ddmmss are the digits for degrees, minutes, and seconds; –, information not available.]
57

 	
 




  	 



	 




 










	











	 



		

	 	



	 	





		

	 




		

	 	



	 	





		

	 




 

	


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!



KE Be 162 391742075554802 391742 755548 61.02 70 64 67 -8.98 -2.98 -5.98 125AQUI D 70 M 2

KE Be 163 391742075554803 391742 755548 60.84 45 40 43 15.84 20.84 17.84 125AQUI D 45 M 2KE Be 164 391832075560804 391832 755608 71.4 50 45 48 21.4 26.4 23.4 125AQUI D 50 M 1KE Be 165 391838075560901 391838 755609 65.65 50 45 48 15.65 20.65 17.65 125AQUI D 50 M 5KE Be 166 391838075560902 391838 755609 65.81 35 25 28 30.81 40.81 37.81 125AQUI D 35 M 5KE Be 167 391838075560903 391838 755609 65.92 25 15 18 40.92 50.92 47.92 125AQUI D 25 M 5KE Be 169 – 391719 755547 38.71 5.5 2.5 5.5 33.21 36.21 33.21 112PCPC – – L 1KE Be 170 391720075554701 391720 755547 40.3 6.9 3.9 6.9 33.4 36.4 33.4 112PCPC – – L 1KE Be 205 – 391732 755558 65.40 35.4 36.9 35.9 30.0 28.5 29.5 125AQUI – – – –KE Bf 186 – 391748 755442 62.15 32.2 33.7 32.2 30.0 28.5 30.0 125AQUI – – – –KE Be 216 – 391727 755509 63.55 33.6 35.1 33.6 30.0 28.5 30.0 125AQUI – – – –Block 3-54 – 391748 755442 62 158 115 150 -96 -53 -88 125HRRS G,E 158 M 1Block 6-12 – 391803 755532 62 84 60 80 -22 2 -18 125AQUI G,E 84 M 5KE-88-0695 – 391727 755535 45 75 55 75 -30 -10 -30 125AQUI G,E 75 M 5KE-88-0696 – 391727 755509 63.55 110 80 110 -46.45 -16.45 -46.45 125AQUI G,E 110 L 0.01KE-94-0144 – 391732 755558 66.02 87 50 80 -20.98 16.02 -13.98 125AQUI – – L 0.01KE-94-0145 – 391732 755558 66.01 150 110 150 -83.99 -43.99 -83.99 125HRRS G,E 149 L 0.01KE-94-0146 – 391732 755558 65.94 277 205 275 -211.1 -139.1 -209.1 211MNMT G,E 275 L 0.01

Appendix A. Appendix A. Wells from Previous Projects that Were Used for Water-level Measurements, Chemical Sampling of Ground Water, and the Hydrogeologic

Framework — continued
58

Appendix B
59

Aquifer codes: CLMB – Pensauken Fm; AQUI – Aquia Fm; CLVR - Calvert Fm; HRRS – Hornerstown Fm; “multiport” well has numerous very narrow screened intervals.

Maryland 

permit 

number 

Local well 

number 

Date 

installed 

Latitude 

ddmmss 

Longitude 

ddmmss 

Aquifer 

code 

Altitude of 

land 

surface 

(feet MSL)

Well depth 

(feet) 

Depth to 

top of 

screen 

(feet) 

Depth to 

bottom of 

screen 

(feet) 

Depth 

logged 

(gamma, 

feet) 

Altitude of 

bottom of 

well 

(feet MSL)

Altitude of 

top of 

screen 

(feet MSL)

Altitude of 

bottom of 

screen 

(feet MSL)

KE-94-0246 KE Be 187 04/21/98 391914 755842 CLMB 77.50 15.0 13.5 14.5 14.5 62.5 64.0 63.0KE-94-0247 KE Be 188 04/21/98 391904 755832 AQUI 64.13 15.0 13.5 14.5 14.5 49.1 50.6 49.6KE-94-0248 KE Be 189 04/19/98 391820 755802 HRRS 38.85 53.5 50.5 53.0 53.0 -14.7 -11.7 -14.2KE-94-0250 KE Be 190 04/15/98 391818 755758 AQUI 49.49 21.0 multiport multiport – 28.5 multiport multiport 

KE-94-0180 KE Be 191 04/15/98 391813 755752 AQUI 66.60 29.5 27.8 29.5 – 37.1 38.8 37.1

KE-94-0251 KE Be 192 04/15/98 391813 755752 AQUI 66.76 38.5 36.8 38.5 – 28.3 30.0 28.3KE-94-0252 KE Be 193 04/15/98 391813 755752 AQUI 66.81 42.0 40.5 41.5 – 24.8 26.3 25.3KE-94-0254 KE Be 194 04/16/98 391717 755710 CLMB 81.02 31.0 29.2 31.0 – 50.0 51.8 50.0KE-94-0253 KE Be 195 04/16/98 391717 755710 AQUI 81.02 60.0 57.0 59.8 59.0 21.0 24.0 21.2KE-94-0280 KE Be 196 04/16/98 391652 755707 CLVR 65.81 30.0 28.2 30.0 29.5 35.8 37.6 35.8KE-94-0255 KE Be 197 04/21/98 391925 755752 CLMB 76.79 21.0 19.5 20.5 20.2 55.8 57.3 56.3KE-94-0257 KE Be 198 04/14/98 391941 755701 CLMB 76.22 25.5 24.0 25.0 – 50.7 52.2 51.2KE-94-0256 KE Be 199 04/14/98 391941 755701 AQUI 76.28 31.0 29.5 30.5 – 45.3 46.8 45.8KE-94-0178 KE Be 200 04/14/98 391941 755701 HRRS 76.25 63.0 60.0 62.5 63.3 13.3 16.3 13.8KE-94-0258 KE Be 201 04/23/98 391758 755659 CLMB 69.85 30.0 28.5 29.5 29.5 39.9 41.4 40.4KE-94-0259 KE Be 202 04/23/98 391830 755626 CLMB 66.12 30.0 28.5 29.5 29.5 36.1 37.6 36.6KE-94-0260 KE Be 203 04/22/98 391713 755621 AQUI 60.99 30.0 29.0 30.0 28.0 31.0 32.0 31.0KE-94-0261 KE Be 204 04/23/98 391740 755615 AQUI 70.07 30.0 28.5 29.5 29.5 40.1 41.6 40.6KE-94-0262 KE Be 205 04/23/98 391732 755558 AQUI 65.40 30.0 28.5 29.5 – 35.4 36.9 35.9KE-94-0268 KE Be 206 04/18/98 391851 755617 AQUI 70.68 36.0 34.3 36.0 – 34.7 36.4 34.7KE-94-0267 KE Be 207 04/18/98 391849 755616 AQUI 70.03 43.5 42.0 43.0 – 26.5 28.0 27.0KE-94-0266 KE Be 208 04/18/98 391849 755616 AQUI 69.91 48.5 47.0 48.0 46.6 21.4 22.9 21.9KE-94-0265 KE Be 209 04/21/98 391849 755616 AQUI 69.57 44.2 multiport multiport – 25.4 multiport multiport 

KE-94-0264 KE Be 210 04/17/98 391851 755617 HRRS 70.47 87.0 84.0 87.0 97.0 -16.5 -13.5 -16.5

KE-94-0279 KE Be 211 04/22/98 391715 755542 HRRS 44.34 107.0 104.0 106.5 103.2 -62.7 -59.7 -62.2

KE-94-0269 KE Be 212 04/23/98 391659 755524 AQUI 61.05 30.0 28.5 29.5 29.0 31.1 32.6 31.6KE-94-0281 KE Be 213 04/20/98 391845 755511 AQUI 78.43 30.0 27.0 30.0 – 48.4 51.4 48.4KE-94-0271 KE Be 214 04/19/98 391832 755527 CLMB 79.32 29.5 28.0 29.0 – 49.8 51.3 50.3KE-94-0270 KE Be 215 04/19/98 391832 755527 AQUI 79.32 59.5 58.0 59.0 58.5 19.8 21.3 20.3KE-94-0272 KE Bf 184 04/20/98 391819 755458 CLMB 76.85 29.5 27.5 29.0 – 47.4 49.4 47.9KE-94-0273 KE Bf 185 04/20/98 391819 755458 AQUI 76.85 57.5 55.5 57.0 56.5 19.4 21.4 19.9KE-94-0275 KE Bf 186 04/20/98 391748 755442 AQUI 62.15 30.0 28.5 30.0 – 32.2 33.7 32.2KE-94-0277 KE Be 216 04/20/98 391727 755509 AQUI 63.55 30.0 28.5 30.0 – 33.6 35.1 33.6

Appendix B. Appendix B. Wells Installed in April 1998 that Were Used for Water-level Measurements, Chemical Sampling of Ground Water, and the Hydrogeologic

Framework for the Locust Grove Study Area, Kent County, Maryland

[ddmmss, digits of degrees, minutes, and seconds; MSL, mean sea level; –, not collected; n/a, not applicable.]
60

Appendix C
61

Date of measurement 

 10/08/97 03/12/98 05/06/98 06/23/98 07/30/98 09/03/98 10/30/98 11/30/98 12/22/98 01/27/99 03/05/99 04/08/99 05/13/99 07/16/99 08/25/99 09/23/99 09/30/99 10/22/99

Well numberKE Bf 154 – 32.02 32.26 31.89 21.26 30.19 6.70 29.19 28.64 29.46 29.59 30.20 29.54 28.68 12.90 29.43 29.72 29.74KE Bf 155 – 32.64 32.84 31.45 21.71 30.78 11.11 29.74 29.21 30.02 30.13 30.79 30.11 29.24 13.24 30.00 30.26 30.31KE-88-0696 – 46.70 47.28 46.69 45.87 45.10 44.37 44.03 43.90 43.99 44.34 44.98 44.79 43.56 42.73 43.65 44.06 44.53KE Be 216 – – 47.26 46.69 45.86 45.09 44.37 44.01 43.91 43.98 44.34 44.97 44.77 43.55 42.75 43.65 44.05 44.52KE Bf 186 – – 52.87 51.97 43.66 48.67 48.52 46.60 48.07 48.41 48.83 49.62 38.04 46.05 44.85 46.72 47.33 48.16Block 3-54 – 51.39 51.69 50.79 40.40 47.53 47.39 45.11 46.89 47.27 47.66 48.45 3.10 44.98 43.80 45.63 46.25 46.92KE Bf 184 – – 57.81 57.39 56.43 55.47 54.09 53.63 53.68 53.57 53.68 54.02 52.82 51.92 50.21 51.67 52.31 52.80KE Bf 185 – – 57.83 57.41 56.42 55.45 54.04 53.68 53.66 53.60 53.71 54.06 52.82 51.91 50.27 51.77 52.34 52.79KE Be 154 – 56.60 58.27 57.32 49.53 55.91 51.54 55.08 54.81 54.41 53.99 53.99 49.74 44.44 43.79 51.94 52.19 52.58KE Be 213 – – 58.29 57.19 54.34 55.84 50.57 55.06 54.83 54.53 54.02 54.00 51.50 50.07 49.96 51.98 52.17 52.59KE Be 214 – – 59.91 59.69 59.06 58.25 56.96 56.21 55.94 55.64 55.61 55.87 55.59 54.39 53.54 53.65 54.00 54.45KE Be 215 – – 59.92 59.68 59.04 58.24 56.93 56.19 55.97 55.63 55.60 55.87 55.60 54.38 53.53 53.67 54.02 54.43Block 6-12 – 51.78 52.36 51.84 50.85 50.10 49.06 48.15 48.37 48.58 48.98 49.45 48.98 47.65 46.57 48.14 48.41 48.51KE-88-0695 – 43.00 42.56 42.39 38.18 41.60 40.15 41.58 41.70 41.98 41.99 42.20 41.43 36.15 40.68 41.92 42.00 42.09KE Be 212 – – 43.32 42.27 41.11 40.16 39.52 39.29 38.25 39.46 39.79 40.55 40.50 38.81 37.68 38.87 39.40 40.25KE Be 211 – – 44.11 44.11 43.11 42.82 42.50 42.31 42.23 42.38 42.51 43.01 42.75 42.01 41.55 42.42 42.65 42.76KE Be 159 40.25 41.09 40.70 40.48 40.41 40.45 40.37 40.41 40.21 40.28 40.39 40.26 40.60 40.00 39.89 40.59 40.82 40.62KE Be 160 40.23 41.03 40.82 40.62 40.34 40.43 40.12 40.17 40.17 40.18 40.29 40.38 40.61 40.03 39.90 40.63 40.80 40.77KE Be 161 40.08 40.74 40.60 40.44 40.17 40.74 39.98 40.00 40.01 40.11 40.17 40.15 40.50 39.84 39.82 40.47 40.71 40.66KE Be 63 40.73 41.62 41.35 41.31 40.93 40.94 40.71 40.75 40.71 40.84 40.85 40.83 40.97 40.53 40.35 41.12 41.23 41.61

Appendix C. Appendix C. Water Levels in Observation Wells in the Locust Grove Study Area, Kent County, Maryland

 [Altitude in feet above mean sea level; –, not measured.]
62

Date of measurement 

 10/08/97 03/12/98 05/06/98 06/23/98 07/30/98 09/03/98 10/30/98 11/30/98 12/22/98 01/27/99 03/05/99 04/08/99 05/13/99 07/16/99 08/25/99 09/23/99 09/30/99 10/22/99

Well number:KE Be 64 40.74 41.66 41.36 41.22 40.90 41.03 40.70 40.71 40.38 40.97 40.99 40.94 41.03 40.42 40.37 41.13 41.25 41.65KE-94-0144 – 50.13 50.45 49.92 49.28 48.55 34.91 47.61 45.84 47.38 47.43 40.43 37.85 39.32 45.92 46.57 46.89 47.11KE-94-0145 – 49.90 50.20 49.69 49.04 48.40 35.38 47.44 45.76 47.33 47.29 37.27 35.84 38.39 45.82 46.51 46.78 46.99KE-94-0146 – 49.60 50.14 50.16 49.15 48.50 58.14 47.54 44.96 47.46 47.26 n/d 60.94 n/d 45.98 46.53 46.81 47.44KE Be 205 – – 50.24 49.70 49.06 48.15 46.59 47.47 45.01 47.27 47.25 46.84 46.64 45.55 45.71 46.36 46.76 46.85KE Be 203 – – 47.40 46.87 45.10 45.42 44.93 44.73 44.41 44.20 44.13 44.34 44.06 43.50 42.72 43.61 n/d 43.67KE Be 204 – – 54.96 54.67 54.01 53.18 52.00 51.67 51.07 50.69 50.38 50.57 50.66 50.05 49.56 49.50 49.65 49.88KE Be 62 51.56 53.78 53.89 53.34 52.55 52.01 51.26 50.81 50.74 50.95 50.91 51.30 50.86 49.85 48.66 49.99 50.23 50.40KE Be 162 51.52 53.75 53.93 53.32 52.52 52.02 51.28 50.81 50.75 50.94 50.92 51.28 50.86 49.85 48.84 49.97 50.23 50.60KE Be 163 51.59 53.82 53.94 53.35 52.55 52.03 51.29 50.83 50.77 50.94 50.93 51.31 50.87 49.89 48.87 50.00 50.25 50.54KE Be 61 55.18 57.87 59.16 58.55 57.95 57.16 55.80 55.13 54.88 54.49 54.68 55.04 55.01 53.88 53.12 53.41 53.81 54.47KE Be 53 55.01 58.12 59.46 58.87 58.25 57.44 56.15 55.42 55.17 54.88 54.95 55.35 55.33 54.24 Dry Dry 54.16 54.73KE Be 52 56.73 58.13 59.45 58.84 58.22 57.42 56.11 55.40 55.17 54.89 54.95 55.34 55.30 54.16 53.41 53.68 54.09 54.20KE Be 59 59.39 61.64 61.48 61.52 60.52 59.84 58.75 58.13 57.79 57.70 57.61 58.16 57.80 56.96 56.25 57.37 57.65 57.46KE Be 164 59.12 61.58 61.40 61.47 60.55 59.78 58.70 58.06 57.70 57.65 57.53 58.12 57.71 56.88 56.13 57.29 57.55 57.39KE Be 165 59.00 61.54 60.92 61.03 59.99 59.62 58.59 58.09 57.75 57.95 57.64 57.70 57.63 56.94 56.20 57.86 57.64 57.50KE Be 166 59.03 61.58 60.94 61.06 60.04 59.61 58.59 58.10 57.75 58.09 57.70 58.20 57.67 56.94 56.21 57.87 57.67 57.53KE Be 167 59.06 61.74 60.94 61.09 60.05 59.64 58.60 58.10 57.76 58.05 57.70 58.12 57.68 56.97 56.20 57.88 57.69 57.55KE Be 51 57.88 58.18 59.44 59.38 58.89 58.19 56.96 56.26 55.81 55.33 54.79 55.06 54.86 54.41 53.96 54.56 54.65 54.42KE Be 207 – – 60.84 60.96 59.87 59.29 58.63 58.21 57.78 57.78 57.64 58.41 57.73 56.90 56.09 57.00 57.28 57.20

Appendix C. Appendix C. Water Levels in Observation Wells in the Locust Grove Study Area, Kent County, Maryland — continued
63

Date of measurement 

 10/08/97 03/12/98 05/06/98 06/23/98 07/30/98 09/03/98 10/30/98 11/30/98 12/22/98 01/27/99 03/05/99 04/08/99 05/13/99 07/16/99 08/25/99 09/23/99 09/30/99 10/22/99

Well number:KE Be 208 – – 60.80 60.95 59.82 59.29 58.45 57.96 57.71 57.84 57.64 58.38 57.68 56.86 56.07 57.09 57.16 57.15KE Be 50 58.53 62.86 60.60 60.72 59.62 59.04 58.19 57.72 57.50 57.48 57.38 58.21 57.46 56.60 55.80 56.82 56.92 56.92KE Be 210 – – 60.69 61.02 59.85 59.26 58.71 58.30 57.68 57.79 57.68 58.33 57.36 56.51 55.98 56.90 56.98 57.01KE Be 206 – – 60.94 61.03 59.92 59.32 58.45 57.97 57.72 57.76 57.74 58.42 57.65 56.77 56.00 56.89 57.03 57.07KE Be 198 – – 57.91 58.01 57.67 57.20 56.37 55.72 55.31 54.89 54.01 54.09 53.82 53.42 53.07 52.86 52.97 53.08KE Be 199 – – 57.93 58.04 57.69 57.23 56.46 56.30 55.34 55.24 54.80 54.86 53.79 53.44 53.16 52.88 52.83 52.89KE Be 200 – – 57.93 58.04 57.72 58.25 54.41 55.95 55.39 54.84 54.10 54.12 53.88 53.46 53.11 53.00 52.96 52.97KE Be 197 – – 58.85 58.70 58.28 57.61 56.36 Dry Dry Dry Dry Dry Dry Dry Dry 56.37 56.50 56.34KE Be 187 – – 63.67 66.61 64.96 67.24 63.10 65.03 64.84 67.23 67.40 66.15 62.79 63.25 63.63 67.82 66.04 66.54KE Be 188 – – 60.72 61.12 59.98 59.75 58.28 57.68 57.11 57.51 56.50 56.57 55.82 55.13 54.57 56.31 56.11 56.05KE Be 189 – – 38.32 38.22 37.84 37.87 38.13 37.68 37.61 37.58 37.53 37.88 37.41 37.25 37.15 37.76 37.56 37.57KE Be 156 – 37.39 37.20 37.01 36.77 36.92 36.75 36.80 36.60 36.67 36.62 36.68 36.45 35.85 36.23 36.78 36.55 36.61KE Be 157 39.41 39.92 40.03 39.78 39.47 39.39 39.04 38.92 38.94 38.99 38.80 38.99 38.79 38.58 38.37 39.09 38.90 38.79KE Be 158 – 43.76 44.55 44.14 43.87 43.51 42.97 42.72 42.51 42.40 42.44 42.48 42.46 42.18 42.02 42.21 42.18 42.16KE Be 191 – – 44.36 43.97 43.69 43.36 42.80 42.54 42.36 42.21 42.14 42.33 42.29 42.04 41.85 42.01 42.01 42.00KE Be 192 – – 44.38 44.00 43.70 42.94 42.83 42.56 42.38 42.23 42.19 42.35 42.32 42.04 41.87 42.02 41.95 41.96KE Be 193 – – 44.42 44.04 43.74 43.41 42.85 42.64 42.40 42.26 42.22 42.41 42.36 42.09 41.90 41.96 42.01 42.02KE Be 201 – – 54.20 54.08 53.49 52.50 51.53 50.84 50.23 49.92 49.43 50.03 49.97 49.48 49.07 49.00 49.14 49.17KE Be 60 59.23 59.22 60.97 60.51 60.17 60.37 58.07 57.35 57.58 56.27 55.87 56.28 56.67 56.10 56.77 – – –KE Be 202 – – 56.59 56.60 55.61 55.03 54.19 53.60 53.13 53.08 53.03 53.44 53.23 52.68 52.06 53.21 53.56 53.47KE Be 195 – – 56.74 56.42 56.11 55.53 54.71 54.25 53.89 53.33 52.97 52.70 52.73 52.30 51.73 51.75 51.75 51.90KE Be 194 – – 56.74 56.45 56.11 55.54 54.73 54.24 53.90 53.41 52.87 52.70 52.75 52.30 51.74 51.54 51.68 51.95KE Be 196 – – 51.14 50.94 50.64 50.28 49.58 49.13 48.80 48.38 47.93 47.73 47.40 47.08 46.87 46.82 46.72 46.53

Appendix C. Appendix C. Water Levels in Observation Wells in the Locust Grove Study Area, Kent County, Maryland — continued
64

Appendix D
65

Appendix D. Appendix D. Chemical Analyses of Ground-water Samples Collected from Observation Wells in the Locust Grove Study Area, Kent County, Maryland

 [ –, no sample collected; <, less than.]

Station ID number Local well number Date sample collected Time sample collected Altitude of land surface, feet above sea level Static water level, feet below land surface Depth of well, feet below land surface Water temperature, in degrees Celsius Specific conductance, in microsiemens per centimeter at 25 degrees Celsius Dissolved oxygen, in milligrams per liter pH, in standard units 

 391717075571001 KE Be 194 07/20/98 1150 81 24.2 31 20.5 346 6.8 4.5  391717075571002 KE Be 195 07/20/98 1530 81 24.0 60 19.2 200 7.3 6.6  391820075580201 KE Be 189 07/21/98 1100 38.8 0.8 53 14.5 172 0 7  391813075575202 KE Be 192 07/21/98 1330 66.8 22.65 38.5 14.6 167 8.5 5  391941075570102 KE Be 199 07/22/98 1100 76.3 18.11 31 17.6 152 6.9 5.3  391941075570103 KE Be 200 07/22/98 0920 76.3 17.85 63 15.1 153 0 6.3  391851075561702 KE Be 206 07/22/98 1500 70.7 10.17 36 14.4 153 7.5 5.4  391851075561701 KE Be 210 07/22/98 1400 70.5 10.2 87 16.1 283 0.1 7.1  391659075552401 KE Be 212 07/23/98 1300 61 19.4 30 16.1 426 8.3 5  391849075561601 KE Be 207 07/23/98 1030 70 9.65 43 14.3 152 9 5.6  391849075561602 KE Be 208 07/23/98 0900 69.9 9.43 48 13.9 89 9.5 5.9 

Multiport sampler: Port depth:  391818075575801 KE Be 190-3 03/06/00 – 49.49 – 12.8 – 411 6.0 4.71 

 KE Be 190-4 03/06/00 – 49.49 – 13.8 – 506 5.4 4.81  KE Be 190-5 03/06/00 – 49.49 – 14.8 – 426 4.3 4.60  KE Be 190-6 03/06/00 – 49.49 – 15.8 – 270 2.7 4.77  KE Be 190-7 03/06/00 – 49.49 – 16.8 – 179 2.0 4.83  KE Be 190-8 03/06/00 – 49.49 – 17.8 – 202 2.5 4.98  KE Be 190-9 03/06/00 – 49.49 – 18.8 – 150 3.7 5.00 

Local well number Date sample collected Calcium, in milligrams per liter Magnesium, in milligrams per liter Sodium, in milligrams per liter Potassium, in milligrams per liter Silica, in milligrams per liter as Si Iron, in micrograms per liter Manganese, in micrograms per liter 

 KE Be 194 07/20/98 20 17 7.4 2.7 13 130 77  KE Be 195 07/20/98 15 4 19 1.9 11 <10 <4  KE Be 189 07/21/98 25 2.1 3 2.4 24 4100 14  KE Be 192 07/21/98 9.6 6.9 2.8 4.3 7.7 <10 181  KE Be 199 07/22/98 8.6 4.1 9.1 2.3 20 36 11  KE Be 200 07/22/98 8.1 2.7 3.7 3.4 28 16000 91  KE Be 206 07/22/98 11 3.4 8.2 1.9 17 <10 39  KE Be 210 07/22/98 43 2.6 3.5 4.4 38 1900 151  KE Be 212 07/23/98 – – – – – – – KE Be 207 07/23/98 – – – – – – – KE Be 208 07/23/98 – – – – – – –
66

Appendix D. Appendix D. Chemical Analyses of Ground-water Samples Collected from Observation Wells — continued

Local well 

number 

Date 

sample 

collected 

Alkalinity, in 

milligrams per 

liter as 

calcium 

carbonate 

Bicarbonate, 

in milligrams 

per liter 

Sulfate, in 

milligrams 

per liter 

Chloride, 

in 

milligrams 

per liter 

Fluoride, in 

milligrams 

per liter 

Ammonia plus 

organic 

nitrogen, 

in milligrams 

per liter as N 

Nitrite plus 

nitrate 

nitrogen, 

in milligrams 

per liter as N 

Orthophosphate, 

in milligrams 

per liter as P 

Groundwater age, 

in years 

Nitrogen-15 

 of nitrate, 

in į15N 

per mil 

Nitrogen gas, 

dissolved, 

milligrams per 

liter 

Argon gas, 

dissolved, 

milligrams per 

liter 

KE Be 194 07/20/98 10 12 0.12 84 <0.10 <0.10 3.58 0.011 11.8 3.7 14.45 0.56 KE Be 195 07/20/98 41 50 2.9 11 <0.10 <0.10 8.86 0.012 20.9 3.5 14.95 0.55 

KE Be 189 07/21/98 69 84 3.2 3.7 0.47 <0.10 0.055 <0.01 >40 – 22.01 0.08 KE Be 192 07/21/98 2 2 0.49 15 <010 <0.10 11.8 <0.01 1.9 3.4 16.23 0.62 KE Be 199 07/22/98 3 3 0.12 17 <0.10 <0.10 9.8 0.023 21.7 3.7 16.02 0.59 KE Be 200 07/22/98 34 41 18 7.3 0.28 <0.10 0.025 0.34 39.8 – 20.77 0.66 KE Be 206 07/22/98 7 8 <0.10 12 <0.10 <0.10 11.9 0.025 17.1 2.2 19.68 0.70 KE Be 210 07/22/98 156 190 18 2.1 0.61 <0.10 0.073 0.216 >40 – 21.28 0.69 KE Be 212 07/23/98 2 2 – – – <0.10 43 0.01 8.9 2.6 19.29 0.69 KE Be 207 07/23/98 8 10 – – – <0.10 9.04 0.202 20.3 3.6 18.96 0.68 KE Be 208 07/23/98 6 7 – – – <0.10 5.18 1.04 31.5 3.1 19.78 0.70 Multiport sampler: 

Nitrate, 1

in milligrams 

per liter as N

KE Be 190-3 03/06/00 1.3 15 92 – – 4.97 – – – – – KE Be 190-4 03/06/00 1.5 17 119 – – 5.15 – – – – – KE Be 190-5 03/06/00 0.6 22 86 – – 5.31 – – – – – KE Be 190-6 03/06/00 0.5 23 48 – – 6.16 – – – – – KE Be 190-7 03/06/00 1.0 21 18 – – 6.21 – – – – – KE Be 190-8 03/06/00 2.5 19 14 – – 5.89 – – – – – KE Be 190-9 03/06/00 3.0 18 12 – – 5.71 – – – – – 

1 Analysis from 3/6/2000 samples from multiport was for nitrate-nitrogen only. 
67

Appendix E
68

Appendix E. Appendix E. Chemical Analyses of Base-flow Samples from the Locust Grove Study Area, Kent County, Maryland

Station ID 

 [ –, sample not collected; <, less than. ]

number Station name Sample date 

Sample 

time 

(Eastern 

Standard 

Time) 

Discharge, 

in cubic meters 

per second 

Discharge, 

in cubic feet 

per second 

Temperature, 

in degrees Celsius 

Specific 

conductance, 

 in microsiemens 

per centimeter at 

25 degrees Celsius 

Dissolved oxygen, 

in milligrams 

per liter 

pH, 

in standard units 

Alkalinity, 

in milligrams 

per liter as 

calcium carbonate 

 01493109 COW C NR CHESTERVILLE, MD 04/14/1998 0915 0.009 0.33 12.8 238 9.6 6.6 12  01493109 COW C NR CHESTERVILLE, MD 09/21/1998 1030 0.003 0.12 19.4 219 6.6 5.6 14  01493109 COW C NR CHESTERVILLE, MD 03/02/2000 1030 0.008 0.28 9.5 181 11.9 6.2 16  01493110 CHESTERVILLE B NR CHESTERVILLE, MD 04/14/1998 1030 0.045 1.6 11.9 183 9.4 6.3 14  01493110 CHESTERVILLE B NR CHESTERVILLE, MD 09/21/1998 0915 0.018 0.63 18.8 213 7.2 6.2 22  01493110 CHESTERVILLE B NR CHESTERVILLE, MD 10/13/1999 0900 0.015 0.53 14 187 7.5 5.8 20  01493110 CHESTERVILLE B NR CHESTERVILLE, MD 02/24/2000 1200 0.022 0.78 9.2 187 11.0 6.5 17  01493111 CHESTERVILLE B AT CHESTERVILLE, MD 04/14/1998 1145 0.065 2.3 16.6 168 2.4 6.0 22  01493111 CHESTERVILLE B AT CHESTERVILLE, MD 09/21/1998 1200 0.059 2.1 20.5 162 6.3 6.2 32  0149311110 CHESTERVILLE B TR NR CHESTERVILLE, MD 04/14/1998 1315 0.042 1.5 18.6 141 6.2 6.5 20  0149311110 CHESTERVILLE B TR NR CHESTERVILLE, MD 09/21/1998 1315 0.008 0.3 21.2 150 8.2 6.2 25  01493112 CHESTERVILLE B NR CRUMPTON, MD 04/14/1998 1430 0.193 6.8 16.5 165 9.9 6.5 22  01493112 CHESTERVILLE B NR CRUMPTON, MD 04/30/1998 0945 0.221 7.8 14.5 164 7.8 6.8 25  01493112 CHESTERVILLE B NR CRUMPTON, MD 05/28/1998 0900 0.218 7.7 17.3 169 8.3 6.4 25  01493112 CHESTERVILLE B NR CRUMPTON, MD 06/29/1998 0900 0.193 6.8 20.3 166 6.8 6.5 27  01493112 CHESTERVILLE B NR CRUMPTON, MD 07/07/1998 1000 0.178 6.3 20 163 7.3 6.8 25  01493112 CHESTERVILLE B NR CRUMPTON, MD 07/28/1998 1200 0.142 5 23.5 171 7.2 5.6 –  01493112 CHESTERVILLE B NR CRUMPTON, MD 07/29/1998 0830 0.139 4.9 21.3 166 7.0 6.2 30  01493112 CHESTERVILLE B NR CRUMPTON, MD 08/27/1998 1100 0.142 5 22.4 172 7.8 6.2 –  01493112 CHESTERVILLE B NR CRUMPTON, MD 09/15/1998 0800 0.113 4 20 161 7.5 6.2 30  01493112 CHESTERVILLE B NR CRUMPTON, MD 09/21/1998 1445 0.142 5 20.7 164 7.8 6.5 31  01493112 CHESTERVILLE B NR CRUMPTON, MD 10/08/1998 0830 0.133 4.7 16.5 171 7.6 6.8 28  01493112 CHESTERVILLE B NR CRUMPTON, MD 10/19/1998 1200 0.122 4.3 – – 10.6 5.3 –  01493112 CHESTERVILLE B NR CRUMPTON, MD 11/05/1998 0900 0.116 4.1 8 171 9.4 7.1 24  01493112 CHESTERVILLE B NR CRUMPTON, MD 11/18/1998 1400 0.122 4.3 9 178 10.0 5.1 –  01493112 CHESTERVILLE B NR CRUMPTON, MD 12/01/1998 1100 0.091 3.2 11.5 173 8.7 6.9 – 
69

Appendix E. Appendix E. Chemical Analyses of Base-flow Samples — continued

Station ID 

number Station name Sample date 

Sample 

time 

(Eastern 

Standard 

Time) 

Discharge, 

in cubic meters 

per second 

Discharge, 

in cubic feet 

per second 

Temperature, 

in degrees Celsius 

Specific 

conductance, 

 in microsiemens 

per centimeter at 

25 degrees Celsius 

Dissolved oxygen, 

in milligrams 

per liter 

pH, 

in standard units 

Alkalinity, 

in milligrams 

per liter as 

calcium carbonate 

01493112 CHESTERVILLE B NR CRUMPTON, MD 12/21/1998 1130 0.272 9.6 9.5 121 5 5.7 – 01493112 CHESTERVILLE B NR CRUMPTON, MD 02/08/1999 1330 0.153 5.4 6.8 174 10.8 6.5 24 01493112 CHESTERVILLE B NR CRUMPTON, MD 02/24/1999 1130 0.122 4.3 4 179 – 7.1 – 01493112 CHESTERVILLE B NR CRUMPTON, MD 02/26/1999 1145 0.133 4.7 6 – 11.2 6.5 23 01493112 CHESTERVILLE B NR CRUMPTON, MD 03/10/1999 1200 0.139 4.9 4 179 12.3 6.5 18 01493112 CHESTERVILLE B NR CRUMPTON, MD 04/06/1999 1000 0.133 4.7 13 170 8.5 6.4 28 01493112 CHESTERVILLE B NR CRUMPTON, MD 04/21/1999 1000 0.130 4.6 10 124 10.2 6.8 27 01493112 CHESTERVILLE B NR CRUMPTON, MD 05/05/1999 1100 0.139 4.9 15 172 9.6 5.9 30 01493112 CHESTERVILLE B NR CRUMPTON, MD 05/17/1999 1030 0.130 4.6 16 172 9.7 5.9 – 01493112 CHESTERVILLE B NR CRUMPTON, MD 06/08/1999 1000 0.102 3.6 22.5 165 7 6.1 36 01493112 CHESTERVILLE B NR CRUMPTON, MD 06/20/1999 1700 0.193 6.8 – 165 – – – 01493112 CHESTERVILLE B NR CRUMPTON, MD 07/06/1999 1000 0.105 3.7 21 157 4.2 6.6 33 01493112 CHESTERVILLE B NR CRUMPTON, MD 07/21/1999 915 0.074 2.6 24 167 6.8 5.7 36 01493112 CHESTERVILLE B NR CRUMPTON, MD 08/03/1999 1000 0.071 2.5 21.7 174 7.3 7.2 35 01493112 CHESTERVILLE B NR CRUMPTON, MD 09/16/1999 1000 23.307 823 19 40 – 6 – 01493112 CHESTERVILLE B NR CRUMPTON, MD 10/01/1999 1030 0.159 5.6 16.6 153 7 6.4 28 01493112 CHESTERVILLE B NR CRUMPTON, MD 10/13/1999 1230 0.122 4.3 15.3 155 9.1 6.4 30 01493112 CHESTERVILLE B NR CRUMPTON, MD 11/10/1999 1200 0.125 4.4 10.7 163 8.7 6.2 32 01493112 CHESTERVILLE B NR CRUMPTON, MD 12/08/1999 1200 0.122 4.3 7.5 173 – 8 32 01493112 CHESTERVILLE B NR CRUMPTON, MD 01/04/2000 1010 0.156 5.5 11.6 153 9.2 7.3 27 01493112 CHESTERVILLE B NR CRUMPTON, MD 02/17/2000 1230 0.178 6.3 5.2 143 11.3 6.3 26 01493491 MORGAN C TR NR GALENA, MD 04/15/1998 1500 0.003 0.11 24.1 169 9.9 6.3 32 01493491 MORGAN C TR NR GALENA, MD 02/23/2000 1445 0.001 0.03 10.1 234 11.5 7.3 30 01493495 MORGAN C NR LOCUST GROVE, MD 04/14/1998 1130 0.065 2.3 13.6 168 7.9 5.1 32 01493495 MORGAN C NR LOCUST GROVE, MD 09/21/1998 1630 0.019 0.67 24.5 176 6.6 6.5 46 
70

Appendix E. Appendix E. Chemical Analyses of Base-flow Samples — continued

Station ID 

number Station name Sample date 

Sample 

time 

(Eastern 

Standard 

Time) 

Discharge, 

in cubic meters 

per second 

Discharge, 

in cubic feet 

per second 

Temperature, 

in degrees Celsius 

Specific 

conductance, 

 in microsiemens 

per centimeter at 

25 degrees Celsius 

Dissolved oxygen, 

in milligrams 

per liter 

pH, 

in standard units 

Alkalinity, 

in milligrams 

 per liter as 

calcium carbonate 

 01493495 MORGAN C NR LOCUST GROVE, MD 02/22/2000 1300 0.042 1.5 7.2 202 10.5 7.1 25  01493496 MORGAN C TR NR KENNEDYVILLE, MD 04/14/1998 1000 0.031 1.1 17 215 10.2 5.3 43  01493496 MORGAN C TR NR KENNEDYVILLE, MD 09/21/1998 1630 0.012 0.43 24 261 1 6.1 85  01493496 MORGAN C TR NR KENNEDYVILLE, MD 02/22/2000 1430 0.031 1.1 15.2 211 12.7 7.2 35  01493497 MORGAN C AT KENNEDYVILLE, MD 04/15/1998 1000 0.156 5.5 15.6 173 8.5 6.3 39  01493497 MORGAN C AT KENNEDYVILLE, MD 09/21/1998 1340 0.068 2.4 23.5 177 5.5 6.1 50  01493497 MORGAN C AT KENNEDYVILLE, MD 02/23/2000 1030 0.136 4.8 5 184 10.3 6.7 35  01493498 MORGAN C TR AT KENNEDYVILLE, MD 04/15/1998 1100 0.019 0.66 15.3 171 8.3 5.5 37  01493498 MORGAN C TR AT KENNEDYVILLE, MD 09/21/1998 1730 0.023 0.82 23.5 195 3.6 6.1 67  0149349810 MORGAN C TR NR MORGNEC, MD 04/14/1998 1300 0.003 0.09 21 240 7.3 5.5 48  0149349810 MORGAN C TR NR MORGNEC, MD 09/21/1998 1245 0.000 0.01 22 215 1.7 5.5 32  0149349810 MORGAN C TR NR MORGNEC, MD 02/23/2000 1330 0.003 0.11 12 187 2.3 6.6 24  0149349820 MORGAN C TR NR LYNCH, MD 04/15/1998 1330 0.003 0.12 18.7 252 8.6 5.8 24  0149349820 MORGAN C TR NR LYNCH, MD 02/25/2000 1330 0.003 0.09 11.8 279 12.8 7.1 29  01493499 MORGAN C NR WORTON, MD 04/14/1998 1630 0.210 7.4 18.6 173 10.1 6.3 30  01493499 MORGAN C NR WORTON, MD 09/21/1998 1045 0.125 4.4 21 184 6.5 5.8 48  01493499 MORGAN C NR WORTON, MD 02/25/2000 1100 0.181 6.4 9.3 178 9.6 7.1 32  01493500 MORGAN C NR KENNEDYVILLE, MD 04/14/1998 1500 0.280 9.9 17.4 170 11.4 6.7 30  01493500 MORGAN C NR KENNEDYVILLE, MD 05/20/1998 1030 0.227 8.0 21 176 5.2 5.9 –  01493500 MORGAN C NR KENNEDYVILLE, MD 06/24/1998 1030 0.246 8.7 24.2 179 4.9 5.4 –  01493500 MORGAN C NR KENNEDYVILLE, MD 07/28/1998 1100 0.167 5.9 23 179 6.4 5.4 –  01493500 MORGAN C NR KENNEDYVILLE, MD 08/27/1998 1000 0.136 4.8 24 184 7.2 6.5 –  01493500 MORGAN C NR KENNEDYVILLE, MD 09/21/1998 930 0.136 4.8 20.5 184 8.3 5.5 46  01493500 MORGAN C NR KENNEDYVILLE, MD 10/19/1998 1030 0.187 6.6 15.7 173 7.5 5.4 –  01493500 MORGAN C NR KENNEDYVILLE, MD 11/18/1998 1100 0.144 5.1 7.5 187 8.6 5.4 –  01493500 MORGAN C NR KENNEDYVILLE, MD 12/21/1998 1000 0.156 5.5 7 184 8.9 5.4 – 01493500 MORGAN C NR KENNEDYVILLE, MD 02/24/1999 1000 0.187 6.6 0.5 209 – 6.5 – 01493500 MORGAN C NR KENNEDYVILLE, MD 02/22/2000 1000 0.340 12 3.4 226 11.2 7.1 30 
71

Appendix E. Appendix E. Chemical Analyses of Base-flow Samples — continued

Station ID 

number Station name Sample date 

Calcium, 

dissolved, in 

milligrams 

per liter 

Magnesium, dissolved, in 

milligrams 

per liter 

Sodium, 

dissolved, in 

milligrams 

per liter 

Potassium, 

dissolved, in 

milligrams 

per liter 

Silica, 

dissolved, in 

milligrams 

per liter as Si 

Iron, 

dissolved, in 

micrograms 

per liter 

Manganese, 

dissolved, in 

milligrams 

per liter 

01493109 COW C NR CHESTERVILLE, MD 04/14/1998 15 11 5.7 3.7 8.3 21 189 01493109 COW C NR CHESTERVILLE, MD 09/21/1998 15 7.9 6.3 6.7 9.8 11 61 01493109 COW C NR CHESTERVILLE, MD 03/02/2000 14 6.8 5 3.2 8.8 13 50 01493110 CHESTERVILLE B NR CHESTERVILLE, MD 04/14/1998 15 6.5 4.2 2.9 9.4 14 61 01493110 CHESTERVILLE B NR CHESTERVILLE, MD 09/21/1998 18 6.4 4.4 8.8 12 19 26 01493110 CHESTERVILLE B NR CHESTERVILLE, MD 10/13/1999 17 6.8 4.5 4.2 11 18 74 01493110 CHESTERVILLE B NR CHESTERVILLE, MD 02/24/2000 16 6.6 4.7 3 9.5 10 37 01493111 CHESTERVILLE B AT CHESTERVILLE, MD 04/14/1998 15 5.1 4.6 2.8 9 52 147 01493111 CHESTERVILLE B AT CHESTERVILLE, MD 09/21/1998 15 5 4.9 3.8 6.2 23 113 0149311110 CHESTERVILLE B TR NR CHESTERVILLE, MD 04/14/1998 11 4.7 5.3 3.3 7.6 260 264 0149311110 CHESTERVILLE B TR NR CHESTERVILLE, MD 09/21/1998 13 4.5 5.5 3.8 11 27 211 01493112 CHESTERVILLE B NR CRUMPTON, MD 04/14/1998 15 5.1 5 3 7.8 110 148 01493112 CHESTERVILLE B NR CRUMPTON, MD 04/30/1998 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 05/28/1998 15 4.9 5.3 3.5 7.3 78 172 01493112 CHESTERVILLE B NR CRUMPTON, MD 06/29/1998 15 4.7 4.9 4.8 9.5 90 187 01493112 CHESTERVILLE B NR CRUMPTON, MD 07/07/1998 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 07/28/1998 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 07/29/1998 16 4.7 5.4 3.8 8.8 50 116 01493112 CHESTERVILLE B NR CRUMPTON, MD 08/27/1998 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 09/15/1998 15 4.3 4.9 4.1 9 250 110 01493112 CHESTERVILLE B NR CRUMPTON, MD 09/21/1998 15 4.6 5.4 3.7 8.4 30 93 01493112 CHESTERVILLE B NR CRUMPTON, MD 10/08/1998 15 4.6 5.1 3.7 9 52 100 01493112 CHESTERVILLE B NR CRUMPTON, MD 10/19/1998 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 11/05/1998 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 11/18/1998 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 12/01/1998 16 4.4 5.6 3.6 9.8 92 150 01493112 CHESTERVILLE B NR CRUMPTON, MD 12/21/1998 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 02/08/1999 15 4.4 5.4 3.3 10 110 237 
72

Appendix E. Appendix E. Chemical Analyses of Base-flow Samples — continued

Station ID 

number Station name Sample date 

Calcium, 

dissolved, in 

milligrams 

per liter 

Magnesium, dissolved, in 

milligrams 

per liter 

Sodium, 

dissolved, in 

milligrams 

per liter 

Potassium, 

dissolved, in 

milligrams 

per liter 

Silica, 

dissolved, in 

milligrams 

per liter as Si 

Iron, 

dissolved, in 

micrograms 

per liter 

Manganese, 

dissolved, in 

milligrams 

per liter 

01493112 CHESTERVILLE B NR CRUMPTON, MD 02/24/1999 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 02/26/1999 16 4.5 5.3 3.6 9.9 80 230 01493112 CHESTERVILLE B NR CRUMPTON, MD 03/10/1999 15 4.5 5.2 3.2 9.3 110 186 01493112 CHESTERVILLE B NR CRUMPTON, MD 04/06/1999 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 04/21/1999 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 05/05/1999 14 4.4 5.3 3 6.2 82 120 01493112 CHESTERVILLE B NR CRUMPTON, MD 05/17/1999 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 06/08/1999 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 06/20/1999 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 07/06/1999 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 07/21/1999 – – – – – – –01493112 CHESTERVILLE B NR CRUMPTON, MD 08/03/1999 17 4.3 5.5 3 8.1 18 78 01493112 CHESTERVILLE B NR CRUMPTON, MD 09/16/1999 – – – – 1.5 – –01493112 CHESTERVILLE B NR CRUMPTON, MD 10/01/1999 13 4.2 4.7 5.1 8.6 77 89 01493112 CHESTERVILLE B NR CRUMPTON, MD 10/13/1999 14 4.6 5.1 4.5 6.8 44 89 01493112 CHESTERVILLE B NR CRUMPTON, MD 11/10/1999 – – – – 8.6 – –01493112 CHESTERVILLE B NR CRUMPTON, MD 12/08/1999 – – – – 10 – –01493112 CHESTERVILLE B NR CRUMPTON, MD 01/04/2000 17 4.7 5.1 3.2 10 95 132 01493112 CHESTERVILLE B NR CRUMPTON, MD 02/17/2000 13 4.2 5.9 3.3 8 78 157 01493491 MORGAN C TR NR GALENA, MD 04/15/1998 11 6.2 8.2 6.3 4.8 720 157 01493491 MORGAN C TR NR GALENA, MD 02/23/2000 10.1 8.2 20 9.3 9.3 480 233 01493495 MORGAN C NR LOCUST GROVE, MD 04/14/1998 14 5.8 5.6 4.3 6.4 340 176 01493495 MORGAN C NR LOCUST GROVE, MD 09/21/1998 16 5.5 6.4 4.1 14 37 262 01493495 MORGAN C NR LOCUST GROVE, MD 02/22/2000 10 4.2 11 5.1 7.7 200 184 01493496 MORGAN C TR NR KENNEDYVILLE, MD 04/14/1998 19 5.8 7.3 4.4 2.9 450 280 01493496 MORGAN C TR NR KENNEDYVILLE, MD 09/21/1998 23 6.7 7.1 8.4 12 1600 1570 01493496 MORGAN C TR NR KENNEDYVILLE, MD 02/22/2000 9 3.2 13 8.5 4.5 25 122 01493497 MORGAN C AT KENNEDYVILLE, MD 04/15/1998 15 5.4 6.6 3.8 6.2 500 341 
73

Appendix E. Appendix E. Chemical Analyses of Base-flow Samples — continued

Station ID 

number 

Station Name Sample date 

Calcium, 

dissolved, in 

milligrams 

per liter 

Magnesium, dissolved, in 

milligrams 

per liter 

Sodium, 

dissolved, in 

milligrams 

per liter 

Potassium, 

dissolved, in 

milligrams 

per liter 

Silica, 

dissolved, in 

milligrams 

per liter as Si 

Iron, 

dissolved, in 

micrograms 

per liter 

Manganese, 

dissolved, in 

milligrams 

per liter 

01493497 MORGAN C AT KENNEDYVILLE, MD 09/21/1998 15 4.8 6.8 5.3 13 190 145 01493497 MORGAN C AT KENNEDYVILLE, MD 02/23/2000 11 4.1 11 5.7 7.7 220 332 01493498 MORGAN C TR AT KENNEDYVILLE, MD 04/15/1998 18 4.7 4.8 2.7 10 260 289 01493498 MORGAN C TR AT KENNEDYVILLE, MD 09/21/1998 21 4.6 5.2 3.9 14 120 414 0149349810 MORGAN C TR NR MORGNEC, MD 04/14/1998 22 6.8 7.4 5.8 5.3 700 579 0149349810 MORGAN C TR NR MORGNEC, MD 09/21/1998 14 5.7 8.6 4.6 11 55 380 0149349810 MORGAN C TR NR MORGNEC, MD 02/23/2000 11 4.4 9.8 9.7 3.2 62 152 0149349820 MORGAN C TR NR LYNCH, MD 04/15/1998 17 8.6 11 5.1 9.2 120 383 0149349820 MORGAN C TR NR LYNCH, MD 02/25/2000 18 8.5 12 5.6 10 250 426 01493499 MORGAN C NR WORTON, MD 04/14/1998 14 5.3 6.6 3.8 5.7 330 157 01493499 MORGAN C NR WORTON, MD 09/21/1998 15 5.3 6.8 4.9 13 62 140 01493499 MORGAN C NR WORTON, MD 02/25/2000 13 5.1 8.9 5.4 8.4 190 164 01493500 MORGAN C NR KENNEDYVILLE, MD 04/14/1998 14 5.3 6.3 3.6 6.1 250 184 01493500 MORGAN C NR KENNEDYVILLE, MD 05/20/1998 – – – – – – –01493500 MORGAN C NR KENNEDYVILLE, MD 06/24/1998 – – – – – – –01493500 MORGAN C NR KENNEDYVILLE, MD 07/28/1998 – – – – – – –01493500 MORGAN C NR KENNEDYVILLE, MD 08/27/1998 – – – – – – –01493500 MORGAN C NR KENNEDYVILLE, MD 09/21/1998 15 5.2 7.1 4.7 13 89 149 01493500 MORGAN C NR KENNEDYVILLE, MD 10/19/1998 – – – – – – –01493500 MORGAN C NR KENNEDYVILLE, MD 11/18/1998 – – – – – – –01493500 MORGAN C NR KENNEDYVILLE, MD 12/21/1998 – – – – – – –01493500 MORGAN C NR KENNEDYVILLE, MD 02/24/1999 – – – – – – –01493500 MORGAN C NR KENNEDYVILLE, MD 02/22/2000 11 4.4 12 5.8 7.5 150 183 
74

Appendix E. Appendix E. Chemical Analyses of Base-flow Samples — continued

Station ID 

number Station name Sample date 

Bicarbonate, 

dissolved, in 

milligrams 

per liter 

Sulfate, 

dissolved, in 

milligrams 

per liter 

Chloride, 

dissolved, in 

milligrams 

per liter 

Ammonia 

plus organic 

nitrogen, in 

milligrams 

per liter 

Nitrite plus 

nitrate 

nitrogen, in 

milligrams 

per liter 

Total 

nitrogen, 

dissolved, in 

milligrams 

per liter 

Total 

Phosphorus, 

in 

milligrams 

per liter 

Orthophosphate, in 

milligrams 

per liter as P 

01493109 COW C NR CHESTERVILLE, MD 04/14/1998 15 17 23 0.23 10.9 11.13 0.031 0.019 01493109 COW C NR CHESTERVILLE, MD 09/21/1998 17 11 18 0.43 12.3 12.73 0.093 0.027 01493109 COW C NR CHESTERVILLE, MD 03/02/2000 20 8.9 13 0.10 9.64 9.74 0.019 <.010 01493110 CHESTERVILLE B NR CHESTERVILLE, MD 04/14/1998 17 9.3 11 <.10 10.6 10.6 0.015 0.014 01493110 CHESTERVILLE B NR CHESTERVILLE, MD 09/21/1998 27 9.1 15 0.44 11.2 11.64 0.431 0.111 01493110 CHESTERVILLE B NR CHESTERVILLE, MD 10/13/1999 24 11 12 0.19 9.58 9.77 0.03 <.010 01493110 CHESTERVILLE B NR CHESTERVILLE, MD 02/24/2000 21 9.6 12 0.10 10.4 10.4 0.01 <.010 01493111 CHESTERVILLE B AT CHESTERVILLE, MD 04/14/1998 27 5.4 12 0.2 7.64 7.84 0.039 0.022 01493111 CHESTERVILLE B AT CHESTERVILLE, MD 09/21/1998 39 4.5 12 0.37 5.05 5.42 0.045 0.016 0149311110 CHESTERVILLE B TR NR CHESTERVILLE, MD 04/14/1998 24 3.9 11 0.34 5.42 5.76 0.091 0.023 0149311110 CHESTERVILLE B TR NR CHESTERVILLE, MD 09/21/1998 30 1.8 11 0.31 6.3 6.61 0.108 0.017 01493112 CHESTERVILLE B NR CRUMPTON, MD 04/14/1998 27 5.4 12 0.22 7.37 7.59 0.064 0.018 01493112 CHESTERVILLE B NR CRUMPTON, MD 04/30/1998 30 – – 0.23 6.26 6.49 0.024 <.010 

01493112 CHESTERVILLE B NR CRUMPTON, MD 05/28/1998 30 4.3 13 0.28 7.14 7.42 0.069 <.010 01493112 CHESTERVILLE B NR CRUMPTON, MD 06/29/1998 33 5 12 0.21 5.51 5.72 0.13 <.010 01493112 CHESTERVILLE B NR CRUMPTON, MD 07/07/1998 30 – – 0.19 6.58 6.77 0.044 0.011 01493112 CHESTERVILLE B NR CRUMPTON, MD 07/28/1998 – – – 0.43 5.76 6.19 – 0.013 

01493112 CHESTERVILLE B NR CRUMPTON, MD 07/29/1998 37 3.4 12 0.23 5.84 6.07 0.011 0.01 01493112 CHESTERVILLE B NR CRUMPTON, MD 08/27/1998 0 – – 0.36 5.52 5.88 0.028 <.010 

01493112 CHESTERVILLE B NR CRUMPTON, MD 09/15/1998 37 3.1 12 – – – – –

01493112 CHESTERVILLE B NR CRUMPTON, MD 09/21/1998 38 3.1 12 0.18 6.3 6.48 0.044 0.014 01493112 CHESTERVILLE B NR CRUMPTON, MD 10/08/1998 34 3.3 13 0.21 7.18 7.39 <.050 <.010 01493112 CHESTERVILLE B NR CRUMPTON, MD 10/19/1998 – – – 0.22 6.94 7.16 <.050 <.010 

01493112 CHESTERVILLE B NR CRUMPTON, MD 11/05/1998 29 – – 0.16 7.43 7.59 <.050 <.010 01493112 CHESTERVILLE B NR CRUMPTON, MD 11/18/1998 – – – 0.28 7.17 7.45 0.037 0.01 01493112 CHESTERVILLE B NR CRUMPTON, MD 12/01/1998 – 2.8 13 0.19 6.92 7.11 <.050 <.010 

01493112 CHESTERVILLE B NR CRUMPTON, MD 12/21/1998 – – – 0.2 8.36 8.56 0.032 0.016 

01493112 CHESTERVILLE B NR CRUMPTON, MD 02/08/1999 29 4.6 12 0.32 7.53 7.85 0.044 <.010 
75

Appendix E. Appendix E. Chemical Analyses of Base-flow Samples — continued

Station ID 

number Station name Sample date 

Bicarbonate, 

dissolved, in 

milligrams 

per liter 

Sulfate, 

dissolved, in 

milligrams 

per liter 

Chloride, 

dissolved, in 

milligrams 

per liter 

Ammonia 

plus organic 

nitrogen, in 

milligrams 

per liter 

Nitrite plus 

nitrate 

nitrogen, in 

milligrams 

per liter 

Total 

nitrogen, 

dissolved, in 

milligrams 

per liter 

Total 

Phosphorus, 

in 

milligrams 

per liter 

Orthophosphate, in 

milligrams 

per liter as P 

01493112 CHESTERVILLE B NR CRUMPTON, MD 02/24/1999 – – – 0.55 8.07 8.62 0.132 <.010 01493112 CHESTERVILLE B NR CRUMPTON, MD 02/26/1999 28 4.6 13 0.51 7.97 8.48 0.105 0.003 01493112 CHESTERVILLE B NR CRUMPTON, MD 03/10/1999 22 4.2 17 0.31 8.26 8.57 0.048 0.02 01493112 CHESTERVILLE B NR CRUMPTON, MD 04/06/1999 34 – – <.10 – – 0.042 0.044 

01493112 CHESTERVILLE B NR CRUMPTON, MD 04/21/1999 33 – – 0.28 5.8 6.08 0.041 <.010 

01493112 CHESTERVILLE B NR CRUMPTON, MD 05/05/1999 37 3.7 13 0.24 6.41 6.65 0.038 0.003 01493112 CHESTERVILLE B NR CRUMPTON, MD 05/17/1999 – – – 0.22 6.78 7 0.039 0.003 01493112 CHESTERVILLE B NR CRUMPTON, MD 06/08/1999 44 – – 0.32 5.17 5.49 0.079 0.005 01493112 CHESTERVILLE B NR CRUMPTON, MD 06/20/1999 – – – 0.32 4.58 4.9 0.06 0.002 01493112 CHESTERVILLE B NR CRUMPTON, MD 07/06/1999 40 – – 0.35 4.56 4.91 0.075 0.011 01493112 CHESTERVILLE B NR CRUMPTON, MD 07/21/1999 44 – – 0.42 3.29 3.71 0.044 0.014 01493112 CHESTERVILLE B NR CRUMPTON, MD 08/03/1999 43 2.8 12 0.15 4.9 5.05 0.03 0.011 01493112 CHESTERVILLE B NR CRUMPTON, MD 09/16/1999 – 0.49 0.609 1.099 1.13 0.094 01493112 CHESTERVILLE B NR CRUMPTON, MD 10/01/1999 34 4.8 13 0.28 4.01 4.29 0.06 0.027 01493112 CHESTERVILLE B NR CRUMPTON, MD 10/13/1999 37 5.6 13 0.23 4.87 5.1 0.033 <.010 01493112 CHESTERVILLE B NR CRUMPTON, MD 11/10/1999 39 – – 0.19 5.49 5.68 0.019 0.001 01493112 CHESTERVILLE B NR CRUMPTON, MD 12/08/1999 39 – – 0.18 5.47 5.65 0.034 0.001 01493112 CHESTERVILLE B NR CRUMPTON, MD 01/04/2000 33 4 13 0.17 7.04 7.21 0.024 0.001 01493112 CHESTERVILLE B NR CRUMPTON, MD 02/17/2000 32 5.7 13 0.26 5.37 5.63 0.065 <.010 01493491 MORGAN C TR NR GALENA, MD 04/15/1998 39 12 15 1.1 1.01 2.11 0.343 0.072 01493491 MORGAN C TR NR GALENA, MD 02/23/2000 37 11 31 1.2 1.45 2.65 0.204 0.034 01493495 MORGAN C NR LOCUST GROVE, MD 04/14/1998 39 8.3 13 0.44 2.48 2.92 0.115 0.021 01493495 MORGAN C NR LOCUST GROVE, MD 09/21/1998 56 3.6 14 0.49 2.35 2.84 0.088 0.018 01493495 MORGAN C NR LOCUST GROVE, MD 02/22/2000 30 6.7 24 0.59 2.49 3.08 0.169 0.011 01493496 MORGAN C TR NR KENNEDYVILLE, MD 04/14/1998 52 7.6 18 1.7 3.05 4.75 0.174 0.026 01493496 MORGAN C TR NR KENNEDYVILLE, MD 09/21/1998 104 2.3 19 1.1 0.098 1.198 0.512 0.015 01493496 MORGAN C TR NR KENNEDYVILLE, MD 02/22/2000 43 5.7 26 2.8 1.16 3.96 0.463 0.027 01493497 MORGAN C AT KENNEDYVILLE, MD 04/15/1998 48 6.3 14 0.67 2.58 3.25 0.139 0.023 
76

Appendix E. Appendix E. Chemical Analyses of Base-flow Samples — continued

Station ID 

number Station name Sample date 

Bicarbonate, 

dissolved, in 

milligrams 

per liter 

Sulfate, 

dissolved, in 

milligrams 

per liter 

Chloride, 

dissolved, in 

milligrams 

per liter 

Ammonia 

plus organic 

nitrogen, in 

milligrams 

per liter 

Nitrite plus 

nitrate 

nitrogen, in 

milligrams 

per liter 

Total 

nitrogen, 

dissolved, in 

milligrams 

per liter 

Total 

Phosphorus, 

in 

milligrams 

per liter 

Orthophosphate, in 

milligrams 

per liter as P 

01493497 MORGAN C AT KENNEDYVILLE, MD 09/21/1998 61 2.6 15 0.88 1.63 2.51 0.25 0.022 01493497 MORGAN C AT KENNEDYVILLE, MD 02/23/2000 43 6.1 22 1.4 2.36 3.76 0.267 0.016 01493498 MORGAN C TR AT KENNEDYVILLE, MD 04/15/1998 45 8.1 10 0.54 3.64 4.18 0.131 0.015 01493498 MORGAN C TR AT KENNEDYVILLE, MD 09/21/1998 82 3.3 11 0.48 0.263 0.743 0.201 0.016 0149349810 MORGAN C TR NR MORGNEC, MD 04/14/1998 59 10 20 1.5 4.41 5.91 0.211 0.036 0149349810 MORGAN C TR NR MORGNEC, MD 09/21/1998 39 1.1 21 1.7 8.32 10.02 0.066 0.016 0149349810 MORGAN C TR NR MORGNEC, MD 02/23/2000 29 8.5 22 0.89 4.07 4.96 0.515 <.010 0149349820 MORGAN C TR NR LYNCH, MD 04/15/1998 29 11 34 1.8 6.42 8.22 0.146 0.018 0149349820 MORGAN C TR NR LYNCH, MD 02/25/2000 35 16 37 0.48 5.04 5.52 0.078 <.010 01493499 MORGAN C NR WORTON, MD 04/14/1998 37 6.7 16 0.38 3.49 3.87 0.125 0.019 01493499 MORGAN C NR WORTON, MD 09/21/1998 59 3 17 0.4 2.33 2.73 0.091 0.028 01493499 MORGAN C NR WORTON, MD 02/25/2000 39 7.5 21 0.57 3.36 3.93 0.1 0.011 01493500 MORGAN C NR KENNEDYVILLE, MD 04/14/1998 37 6.7 15 0.41 3.51 3.92 0.104 0.019 01493500 MORGAN C NR KENNEDYVILLE, MD 05/20/1998 – – – 0.59 3.54 4.13 0.015 <.010 

01493500 MORGAN C NR KENNEDYVILLE, MD 06/24/1998 – – – 0.73 3.54 4.27 0.136 0.026 01493500 MORGAN C NR KENNEDYVILLE, MD 07/28/1998 – – – 0.43 2.61 3.04 – 0.019 

01493500 MORGAN C NR KENNEDYVILLE, MD 08/27/1998 – – – 0.42 2.26 2.68 0.111 0.011 

01493500 MORGAN C NR KENNEDYVILLE, MD 09/21/1998 56 3.1 16 0.39 2.69 3.08 0.094 0.019 01493500 MORGAN C NR KENNEDYVILLE, MD 10/19/1998 – – – 0.26 2.66 2.92 0.057 0.017 01493500 MORGAN C NR KENNEDYVILLE, MD 11/18/1998 – – – 0.36 2.62 2.98 0.057 0.011 01493500 MORGAN C NR KENNEDYVILLE, MD 12/21/1998 – – – 0.42 3.53 3.95 0.055 0.015 01493500 MORGAN C NR KENNEDYVILLE, MD 02/24/1999 – – – 1.2 4.07 5.27 0.138 0.013 

01493500 MORGAN C NR KENNEDYVILLE, MD 02/22/2000 37 7.8 25 0.66 2.76 3.42 0.151 0.012 
77

Appendix F
78

Site ID 

number Station name 

Drainage 

area 

(square 

miles) 

Regional 

basin 

index 

Local 

basin 

index 

Stream 

length 

(miles) 

Minimum 

altitude of 

stream 

(feet above 

sea level) 

Stream 

slope 

 

 01493 491 MORGAN CREEK TR NR GALENA MD 0.45 -2.53 1.75 0.35 55.00 14.41

 01493 495 MORGAN C NR LOCUST GROVE MD 3.18 -2.08 0.03 1.94 35.00 12.89

 01493 496 MORGAN C TR NR KENNEDYVILLE MD 1.33 -2.14 0.39 1.03 40.00 14.59

 01493 497 MORGAN C AT KENNEDYVILLE MD 6.16 -1.87 -0.81 3.10 25.00 11.31

 01493 498 MORGAN C TR AT KENNEDYVILLE MD 0.99 -1.76 -1.19 0.95 20.00 36.73

 01493 49810 MORGAN C TR NR MORGNEC MD 0.32 -2.35 -0.18 0.51 45.00 19.46

 01493 49820 MORGAN C TR NR LYNCH MD 0.54 -2.40 -0.22 1.04 20.00 38.65

 01493 499 MORGAN C NR WORTON MD 10.62 -2.13 -1.40 3.75 10.00 12.00

 01493 500 MORGAN C NR KENNEDYVILLE MD 11.99 -1.76 -1.57 5.38 2.00 10.77

 01493 109 COW C NR CHESTERVILLE MD 0.35 -2.59 1.28 0.53 40.00 38.02

 01493 110 CHESTERVILLE B NR CHESTERVILLE MD 1.29 -2.31 0.92 1.06 40.00 14.11

 01493 111 CHESTERVILLE B AT CHESTERVILLE MD 4.74 -2.06 0.07 2.19 25.00 13.71

 01493 11110 CHESTERVILLE B TR NR CHESTERVILLE MD 0.93 -2.06 -0.30 0.73 30.00 41.15

 01493 112 CHESTERVILLE B NR CRUMPTON MD 6.12 -1.98 -0.76 3.64 5.00 13.73

Appendix F. Appendix F. Basin Characteristics of Sites from the Base-flow Synoptic Surveys Used in the Landscape Analysis for the

Locust Grove Study Area, Kent County, Maryland

[Stations 01493 500 and 01493 112, in bold, are gaging stations; the regional and local basin indexes are explained in the Nutrient Yields from

Base Flow section of the report.]

Site ID 

number Station name 

Percentage of type A (welldrained) soils in watershed 

Percentage of type B 

(moderately well-drained) 

soils in watershed 

Percentage of type C 

(moderately poorly drained)

soils in watershed 

Percentage of type D (poorly

drained) soils in watershed 

Percentage of agricultural 

land in watershed 

Percentage of confined 

animal feeding operations 

 in watershed 

Percentage of nursery 

in watershed 

Percentage of urban land in 

watershed 

Percent of forest 

in watershed 

 

 01493 491 MORGAN CREEK TR NR GALENA MD 11.43 86.45 0.18 0.00 100.00 0.00 0.00 0.00 0.00

 01493 495 MORGAN C NR LOCUST GROVE MD 13.52 74.11 6.31 0.86 94.27 0.00 4.49 0.00 5.41

 01493 496 MORGAN C TR NR KENNEDYVILLE MD 6.45 72.86 12.76 3.28 97.66 0.00 0.00 1.74 2.34

 01493 497 MORGAN C AT KENNEDYVILLE MD 12.78 65.69 12.10 2.93 92.23 0.00 2.24 0.77 6.85

 01493 498 MORGAN C TR AT KENNEDYVILLE MD 19.18 49.86 17.39 5.77 92.49 0.00 0.00 0.00 7.51

 01493 49810 MORGAN C TR NR MORGNEC MD 13.81 41.77 24.32 3.14 94.32 0.00 0.00 0.00 0.00

 01493 49820 MORGAN C TR NR LYNCH MD 42.27 42.74 11.81 0.00 96.22 0.00 0.00 1.31 2.46

 01493 499 MORGAN C NR WORTON MD 25.53 56.38 15.63 1.56 90.60 12.51 0.00 0.00 3.81

 01493 500 MORGAN C NR KENNEDYVILLE MD 14.67 58.77 15.42 3.51 87.74 0.45 1.19 1.32 8.21

 01493 109 COW C NR CHESTERVILLE MD 33.88 59.50 3.55 0.00 100.00 0.00 0.00 0.00 0.00

 01493 110 CHESTERVILLE B NR CHESTERVILLE MD 42.66 48.59 3.98 0.09 97.32 0.00 29.95 0.00 2.68

 01493 111 CHESTERVILLE B AT CHESTERVILLE MD 32.40 51.18 4.93 1.46 94.56 0.00 26.49 0.00 5.10

 01493 11110 CHESTERVILLE B TR NR CHESTERVILLE MD 36.17 49.78 6.53 0.42 92.60 0.00 18.20 0.00 7.74

 01493 112 CHESTERVILLE B NR CRUMPTON MD 32.36 48.64 7.93 1.40 93.07 0.72 21.17 0.00 6.70
79
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