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Chesapeake Bay
Groundwater Toxics
Loading Workshop
Proceedings
Basin wide Toxics Reduction Strategy Reevaluation Report
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Chesapeake Bay Program
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Chesapeake Bay Groundwater
Toxics Loading Workshop
Proceedings
Sponsored by the
Chesapeake Bay Program Toxics Subcommittee
April 15-16,1992
...L..-A 13107
Produced for the Chesapeake Bay Program
under Interagency Agreement No. DW64943642-01
Printed by the U.S. Environmental Protection Agency for the Chesapeake Bay Program
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PROCEEDINGS OF THE
CHESAPEAKE BAY PROGRAM
TOXICS SUBCOMMITTEE
SPONSORED
CHESAPEAKE BAY GROUNDWATER TOXICS
LOADING WORKSHOP
U. S. EPA Chesapeake Bay Program Office
Chesapeake Bay Information and Conference Center
Annapolis, Maryland
April 15 -16, 1992
1. BACKGROUND/OBJECTIVE
The Basinwide Toxics Reduction Strategy committed the Chesapeake Bay signatories to
develop a Toxic Loading Inventory of toxic substance loadings from point and nonpoint sources.
Point source loads include inputs from industrial, municipal and federal facilities. Nonpoint-source
loads include inputs from atmospheric, shipping, urban, agriculture and groundwater sources. With
the exception of groundwater, toxic substance loading and release estimates were developed for these
sources using available data.
The Chesapeake Bay Groundwater Toxics Loading Workshop was held April 15 - 16, 1992
at the U.S. Environmental Protection Agency (EPA) Chesapeake Bay Program Office in Annapolis,
Maryland. The workshop was held to assess the significance of toxic substances transported by
groundwater to the Chesapeake Bay and its tidal tributaries and to develop a strategy for quantifying
these loads. The workshop was also one in a series of critical issue forums directed at developing
a technical consensus on the nature, extent and magnitude of Chesapeake Bay Toxics problems, as
part of the reevaluation of the Basinwide Toxics Reduction Strategy. The workshop, sponsored by
the Chesapeake Bay Program's Toxics Subcommittee, was attended by representatives from state and
federal agencies, academic institutions, and interested individuals conducting groundwater studies or
involved in groundwater protection programs.
The workshop participants reviewed and discussed available information on results from
groundwater studies and developed a strategy to provide a first order estimate of the magnitude of
groundwater loads of toxic substances to Chesapeake Bay and its tidal tributaries. The participants
also recommended that groundwater loads of nutrients should be assessed concurrently with the toxic
substance loads.
A major accomplishment of the workshop was a summary of the current state of knowledge
regarding the significance of groundwater as a transport mechanism for toxic substances and nutrients
to Chesapeake Bay. The primary conclusions of the workshop were:
1. Groundwater itself is not a source of toxic substances, rather, it stores and transports
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toxic substances and nutrients that have infiltrated to the groundwater from point and
nonpoint sources.
2. Groundwater delivers more than one-half of the freshwater that enters Chesapeake
Bay. This large volume of freshwater is transported to the Bay as base flow and as
direct discharge or upwelling. Base flow represents groundwater discharge to non-
tidal streams and tributaries, while upwelling represents groundwater discharged
directly to the Bay mainstem and/or to the Bay's tidal tributaries.
3. The majority of the groundwater flow to the Bay is transported from shallow aquifers
that are most sensitive to anthropogenic impacts.
4. Detectable concentrations of toxic substances and nutrients have been observed in
shallow aquifers.
5. Surface runoff may be a larger transporter of agricultural herbicides to streams and
tributaries than groundwater inflows.
6. The potential for toxic substances to be transported by groundwater and subsequently
discharged to the Bay and its tidal tributaries may be greatest at the local scale, close
to the source.
7. The potential for nutrient loads to be transported in groundwater and subsequently
discharged to the Bay and its tidal tributaries may be significant at both the local and
regional scales.
2. STRATEGY TO QUANTIFY GROUNDWATER POLLUTANT LOADS TO THE
CHESAPEAKE BAY
As part of the strategy, the workshop participants targeted the Chesapeake Bay Toxics of
Concern, the secondary list of Toxics of Concern, and nutrients. It was felt that these constituents
have the highest potential to adversely impact Bay water quality. This section summarizes the
primary elements of a strategy recommended by the workshop participants for quantifying loadings
transported to the Chesapeake Bay by groundwater. The actions the workshop participants believed
were necessary to implement this strategy are as follows:
1. Utilize results from the fall line monitoring program to estimate groundwater
discharge and toxic substance and nutrient loads to non-tidal streams and tributaries
above the fall line. This approach segments the Bay watershed into areas above the
fall line and below the fall line. The areas above the fall line are underlain by
consolidated rock aquifers, while the areas below the fall line are underlain by
unconsolidated sediment aquifers. Nutrient loads could be estimated at all major
tributary fall line stations, while loads of toxic substances could be estimated at the
Susquehanna, James and Potomac River fall line stations where monitoring for both
toxic substances and nutrients is currently in place.
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a. Estimate groundwater base flow above the fall line and integrate with fall line
station concentration data to estimate loads for the major tributaries.
b. Because of the large volume of groundwater, potentially high loads of toxics
and nutrients can be estimated from relatively low concentrations.
Consequently, ultra-clean field sampling and low-level analytical detection
limits must be employed to ensure high quality data. The calculation
procedures used to estimate loadings from these data must be consistent and
utilize appropriate measures of statistical uncertainty.
2. Classify "hydrogeomorphic regions" for shallow aquifers below the fall line in the
unconsolidated sediments of the Coastal Plain physiographic province. These areas
have a distinctive combination of hydrogeologic and geochemical characteristics, such
as shallow geology, geomorphology, soil type, organic content of shallow sediments,
and hydrology. These attributes impart a characteristic groundwater flow and water
quality pattern that increases the potential for similar groundwater loadings.
3. Review literature and ongoing studies within each "hydrogeomorphic region" to
compile data and better define physical and geochemical characteristics,
concentrations of chemical constituents, and information gaps.
a. Physical Characteristics
Define hydrology (surface and groundwater interaction).
Evaluate methods to estimate volume of shallow groundwater flow
based on available data and perform calculations using best available
methods.
Identify recharge areas and discharge areas.
Develop map of Chesapeake Bay groundwater watersheds (similar to
surface watersheds).
Identify soils with high potential for leaching using:
• VIRGIS
• EMAP land use characterization
• recharge area maps.
b. Chemical Constituents
Measure or estimate concentrations of toxic substances and nutrients.
Define transport chemistry for similar pollutants (soluble and
insoluble, etc.).
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Explore development of toxic substance and nutrient concentration
characteristics for each land use in the recharge areas.
c. Information Gaps
Identify information gaps and areas requiring additional refinement.
Develop proposals that expand existing or planned studies to address
identified gaps.
Coordinate efforts between Chesapeake Bay Program Subcommittees
(Toxics Subcommittee, Nonpoint Source Subcommittee, Modeling
Subcommittee, etc.) and agencies with related expert knowledge.
4. Work within existing projects and through the Chesapeake Bay Program
Subcommittees to address information gaps.
Add sampling stations to existing monitoring programs to get base flow and
concentration data.
Target sampling station locations based on areas of greatest anthropogenic
impacts.
Explore correlations between herbicide application, groundwater
concentrations, and edge of field export.
Extrapolate findings to similar hydrogeomorphic regions.
5. Estimate groundwater chemical constituent loads for below the fall line areas within
the hydrogeomorphic classification system where the data exist.
6. Extrapolate the estimates to similar hydrogeomorphic areas below the fall line where
information is not available.
7. Target major Superfund and RCRA sites the Bay tidal waters.
Access federal and state electronic and paper files (RCRIS and CERCLIS) to
estimate potential toxic substance loads to groundwater at the local scale.
Attempt to provide cumulative loading estimates from hazardous waste sites.
8. Evaluate other potential sources of loadings of toxic substances to the Bay.
Identify and evaluate pesticide mixing and loading facilities as potential
sources of pesticides to groundwater and surface water.
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Investigate effect of groundwater flushing of toxic substances from bottom
sediments previously contaminated by other sources.
9. Establish lines of communication to coordinate the development of groundwater
loading estimates and management efforts.
a. Groundwater load estimates
Strive for consistent methods between states.
b. Management efforts
Recognize that groundwater movement transcends political boundaries
and that a cooperative regional approach is required for its protection.
Target leadership at state level.
Evaluate the effectiveness of best management practices to protect
groundwater and surface water.
c. Bay Program coordination
Establish responsibility to coordinate Chesapeake Bay Program efforts
to protect groundwater between Bay Program committees and
subcommittees.
2. TECHNICAL STATEMENTS SUPPORTING THE WORKSHOP CONCLUSIONS AND
LOAD ESTIMATION STRATEGY
The following background information, summarized from several of the workshop
presentations, is provided to facilitate understanding of the proposed strategy to quantify loadings
of toxic substances transported by groundwater.
Aquifers
There are two general types of aquifers within the Chesapeake Bay watershed: shallow, near
surface aquifers and deep, confined aquifers. Most of the groundwater discharge delivered to the
Chesapeake Bay tidal and non-tidal system is from shallow aquifers, not the deeper confined
aquifers. The flow of groundwater between the shallow aquifers and the underlying deeper aquifers
is constrained by less permeable sediments (confining units). Groundwater flow models have
indicated prepumped recharge and discharge rates for the confined aquifers in the Coastal Plain are
less than 1 inch per year, while recharge rates to the water table aquifer are commonly 10 inches per
year (Hamilton and Larson 1988; Laczniak and Meng 1988; Harsh and Laczniak 1990).
The shallow aquifers are located in either the consolidated crystalline and sedimentary rocks
found above the fall line or in the unconsolidated sediments of the Coastal Plain Province found
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below the fall line (McGreevy and Wheeler 1984). They discharge groundwater as base flow to
nontidal tributaries that subsequently flow as surface water to the Bay's mainstem tributaries or
mainstem, or upwell groundwater directly to the mainstem estuary or tidal tributaries.
Quantity of Groundwater Entering the Chesapeake Bay
The mean annual streamflow entering the Chesapeake Pay is approximately 18.9 million
gallons (at a rate of 80,000 cubic feet per second (cfs)) (Phillips, personal communication). More
than one-half of this fresh water is delivered by groundwater discharged through shallow aquifers
as base flow to tidal and nontidal tributaries or upwelled as direct discharge to the Bay. Sinnott and
Gushing (1978) estimate that approximately 55 percent of the stream flow below the fall line and 40
percent of the stream flow above the fall line is groundwater discharging as base flow (Table 1).
Other estimates of base flow as a total percentage of stream flow in the Chesapeake Bay watershed
range from 39 to 61 percent. Base flow accounts for an average of 52 percent of stream flow in the
Potomac River basin above the fall line (Trainer and Watkins 1975). In the area below the fall line,
57 percent of stream flow on the Delmarva Peninsula was attributed to base flow (Gushing et al.
1973). However, Bachman et al. (1992) estimated a higher base flow contribution of 63 to 88
percent on the Delmarva Peninsula.
Simmons (1989) estimated groundwater upwelled directly to the Bay to be about equal to the
discharge of the James River to tidal waters (2x10* cubic meters per day). Direct groundwater
discharge is a mixture of freshwater and seawater. Adjusting Simmon's estimate to account only for
freshwater contributions the amount of direct fresh groundwater discharge could be 1-2 orders of
magnitude less than that reported for submarine groundwater discharge (Reay and Simmons 1992).
Other researchers (Libelo et al. 1991; Zimmerman 1991) have reported that direct upwelling from
aquifers underlying tidal areas of tributaries may account for up to 25 percent of the fresh water
put to these surface-water bodies.
Table 1. Percent Estimates of Groundwater Discharge to the Chesapeake Bay
Base Flow to Tributaries Base Flow to Tributaries Direct Discharge to
Above the Fall Line JBelow the Fall Line Tidal Waters
40%' 55%' 25 %5
52 %2 57 %3 15 %6
63-88 %4
1. Sinnot and Gushing, 1978.
2. Trainer and Watkins, 197S.
3. Gushing et«l., 1973.
4. Bachman etal., 1992.
5. Libelo, etal., 1991.
6. Simmons, 1989.
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Quality of Ground water Entering the Bay
Nutrient Concentrations
Nitrogen is the predominant nutrient of concern because it is water-soluble and more likely
to be leached to groundwater than phosphorus. In the Coastal Plain aquifers below the fall line, most
of the nitrogen occurs in the shallow unconfined systems (Staver and Brinsfield 1991). The USGS
National Water Quality Assessment also reported that water from more than 70 percent of wells in
the shallow water table aquifer of the Delmarva Peninsula had detectable concentrations of nitrate
and about 15 percent contained concentrations that exceeded 10 milligrams per liter (mg/L), the
maximum contaminant level for drinking water established by the U.S. EPA (Hamilton and Shedlock
1992). In contrast, median concentrations of nitrate in uncontaminated groundwater are less than
1 mg/1 (Speiran, personal communication). The highest concentrations were observed in shallow
groundwater aquifers of the Coastal Plain draining areas of agricultural land use.
Other studies report similar nitrogen concentrations in the groundwater. For example, studies
conducted below the fall line in the Coastal Plain on the eastern shore of Maryland and Virginia
reported nitrogen concentrations in the shallow aquifer as high as 38 mg/L (Bachman 1984;
Brinsfield and Staver 1989; Reay and Simmons 1992; Speiran, personal communication). The
Nomini Creek Watershed project in Virginia reported that the mean nitrogen concentration was
almost 5 mg/L, based on 119 samples collected at the site (Mostaghimi et al. 1989).
Studies in fractured flow systems west of the fall line indicate that monthly base flow nitrate
concentrations ranged from 1.7 to 14 mg/L. These studies include the Conestoga River headwaters
in Lancaster County, Pennsylvania; the Bush Run Creek site in the lower Susquehanna River basin;
and the Owl Run basin in Virginia.
Toxic Substances Concentrations
Excluding local contamination data at hazardous waste sites, there are very limited data on
toxic substance concentrations in groundwater within the Bay watershed; the available data are
primarily for pesticides. Atrazine and alachlor are the two most common pesticides detected. On
the Delmarva Peninsula, concentrations of pesticides were generally low; 94 percent of the water
samples with detectable concentrations were less than the U.S. EPA maximum contaminant and
health advisory levels for drinking water (Hamilton and Shedlock 1992). Similar results were found
at the Nomini Creek Watershed; over 21 pesticides were detected in the ground water, but only
atrazine, disulfoton, and paraquat occasionally exceeded the respective drinking water standards
(Mostaghimi et al. 1989).
In the ground water underlying the Owl Creek site in Virginia, which is above the fall line,
no pesticides have been detected (Mostaghimi et al. 1989). However, Hippe and co-workers (1992)
detected triazine herbicides in 42 of 50 wells sampled in the Cumberland Valley of Pennsylvania,
which is above the fall line.
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Estimates of Groundwater Loads
Nitrogen
Libelo and co-workers (1991) estimated that groundwater nitrogen contributions to the
Chesapeake Bay may represent 30 percent of the total load, based on initial estimates of groundwater
nitrogen loads to the James River (14.52 million pounds of nitrogen per year). Bachman and co-
workers (1992) estimated that the groundwater nitrogen load may be as high as 40 percent of the
total nitrogen load in areas of intense agricultural activity such as the Delmarva Peninsula.
Toxic Substances
No estimates of groundwater transported loadings of toxic substances were available at the
time the workshop was held.
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REFERENCES CITED
Bachman, L.J. 1984. Nitrate in the Columbia Aquifer, Central Delmarva Peninsula, Maryland.
U.S. Geological Survey Water Resources Investigation Report 84-822.
Bachman, L.J., P. J. Phillips, and L. D. Zynjunk. 1992. The Significance of Hydrologic
Landscapes in Estimating Nitrogen Loads in Base Flow to Estuarine Tributaries of the Chesapeake
Bay: American Geophysical Union, Spring 1992 Meeting.
Brinsfield, R. B. and K. W. Staver. 1989. Cover Crops: A Paragon for Nitrogen Management. In:
Proceedings Ground Water Issues and Solutions in the Potomac River Basin/Chesapeake Bay Region.
March 14-16, Washington, D.C. pp. 271-285.
Gushing, E.M., I. H. Kantrowity, and K. R. Taylor. 1973. Water Resources of the Delmarva
Peninsula: U.S. Geological Survey Professional Paper 822.
Hamilton, P.A. and J.D. Larson. 1988. Hydrology and Analysis of the Ground-Water Flow System
in the Coastal Plain of Southeastern Virginia: U.S. Geological Survey Water - Resources
Investigations Report 87-4240.
Hamilton, P. A. and R. J. Shedlock. 1992. Are Fertilizers and Pesticides in the Ground Water? A
Core Study of the Delmarva Peninsula, Delaware, Maryland, and Virginia. U. S. Geological Survey
Circular 1080.
Harsh, J.F. and R.J. Laczniak. 1990. Conceptualization and Analysis of Ground-Water Flow
System in the Coastal Plain of Virginia and Adjacent Parts of Maryland and North Carolina: U.S.
Geological Survey Water-Supply Paper 1404-F.
Hippe, D. J. Personal Communication. U.S. Geological Survey. February 1, 1993.
Laczniak, R.J. and A. A. Meng, III. 1988. Ground-Water Resources of the York-James Peninsula
of Virginia: U.S. Geological Survey Water-Resources Investigations Report 88-4059.
Libelo, L., W.G. Maclntyre, and G.H. Johnson. 1991. Groundwater Nutrient Discharge to the
Chesapeake Bay: Effects of Near-Shore Land Use Practices. In: Mihursky, J.A. and A. Chaney, eds.
New Perspectives in the Chesapeake System: A Research and Management Partnership. Proceedings
of a conference, December 4-6 1990, Baltimore, MD. Chesapeake Research Consortium Publication
No. 137.
McGreevy, L. J. and J. C. Wheeler. 1984. Maryland and the District of Columbia: Ground Water
Resources. U. S. Geological Survey Water Supply Paper 2275.
Mostaghimi, S., P.W. McClellan, U.S. Tim, T.A. Dillaha, R.K. Byler, V.O. Shanholtz and J.M.
Flagg. 1989. Impact of Agricultural Activities on Ground-Water Quality in Virginia. In: Proceedings
from Groundwater Issues and Solutions in the Potomac River Basin/Chesapeake Bay Region. March
14-16, 1989, Washington, DC. pp. 421-435.
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Phillips, S. Personal Communication. U.S. Geological Survey. May 21, 1993.
Reay, W. G., and G. M. Simmons. 1992. Groundwater Discharge in Coastal Systems: Implications
for Chesapeake Bay. In: Perspectives on Chesapeake Bay, 1992: Advances in Estuarine Sciences.
Chesapeake Research Consortium Publication No. 143.
Simmons, G. M. 1989. The Chesapeake Bay's Hidden Tributary: Submarine Ground-Water
Discharge. In Proceedings from Ground Water Issues and Solutions in the Potomac
River/Chesapeake Bay Region, Washington, DC.
Sinnott, A. and E. M. Gushing. 1978. Summary Appraisals of the Nation's Ground-Water
Resources - Mid-Atlantic Region. U.S. Geological Survey Professional Paper 813-T.
Speiran, G. Personal Communication. U.S. Geological Survey. January 14, 1993.
Staver, K.W. and R.B. Brinsfield. 1991. Groundwater Discharge Patterns in Maryland Coastal Plain
Agricultural Systems. In: Mihursky, J.A. and A. Chaney, eds. New Perspectives in the Chesapeake
System: A Research and Management Partnership. Proceedings of a Conference, December 4-6,
1990, Baltimore, MD. Chesapeake Research Consortium Publication No. 137.
Trainer, F.W. and F. A. Watkins. 1975. Geohydrologic Reconnaissance of the Upper Potomac
River Basin. U.S. Geological Survey Water Supply Paper 2035.
Zimmerman, C. 1991. Submarine Groundwater Discharge to the Patuxent River and Chesapeake
Bay, In: Mihursky, J. A. and A. Chaney, eds. New Perspectives in the Chesapeake System: A
Research and Management Partnership. Proceedings of a Conference, december 4-6, 1990,
Baltimore, MD. Chesapeake Research Consortium Publication No. 137
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NAME
David Andreasen
Joseph Bachman
Paula Ballaron
Jerusalem Bekele
Donna Belval
John Bergquist
Russell Brinsfield
Sumner Crosby
David Drummond
Rob Esworthy
Brenda Feit
Mike Flagg
Kendra Gassel
Cindy Greene
Dan Hippe
Larry Huffman
Norbert Jaworski
Charles Job
Anita Key
Suzanne Lussier
Joseph Macknis
J.V. O'Connor
Scott Phillips
Lynn Poorman
William Reay
Stuart Reese
Lorie Roeser
Bruce Rundell
Natalie Valette-Silver
John Simmons
Gary Speiran
Fred Suffian
Alan Taylor
Horacio Tablada
Charles Takita
Chris Victoria
Bill Ward
Roster of Participants
Chesapeake Bay Groundwater Toxics
Loading Workshop
April 15-16, 1992
AFFILIATION
Maryland Geological Survey
U.S.Geological Survey - Towson
Susquehanna River Basin Commission
District of Columbia Dept. of Consumer and Regulatory Affairs
U. S. Geological Survey - Richmond, VA
Maryland Department of Agriculture
Univ. Of Maryland/Wye Research and Education Center
U. S. Environmental Protection Agency, Region III
Maryland Geological Survey
U.S. Environmental Protection Agency, Office of Policy, Planning and
Evaluation
U. S. Geological Survey - Towson, MD
Virginia Department of Soil and Water Conservation
ICF, Inc.
U. S. Environmental Protection Agency, Region III
U. S. Geological Survey - Towson, MD
ICF, Inc.
U. S. Environmental Protection Agency, Office of Research and
Development
U. S. Environmental Protection Agency
District of Columbia Dept. of Consumer and Regulatory Affairs
U. S. Environmental Protection Agency, Region III
U. S. Environmental Protection Agency, Chesapeake Bay Program Office
University of the District of Columbia
U. S. Geological Survey - Towson, MD
Maryland Department of the Environment
Virginia Polytechnical Institute and State University
Pennsylvania Department of Environmental Regulation
U. S. Environmental Protection Agency, Chesapeake Bay Program Office
U. S. Environmental Protection Agency, Region III
National Oceanographic and Atmospheric Administration
U. S. Environmental Protection Agency
U. S. Geological Survey - Richmond, VA
U. S. Environmental Protection Agency, Region III
University of Maryland
Maryland Department of the Environment
Susquehanna River Basin Commission
U. S. Fish and Wildlife Service, Chesapeake Bay Estuary Program
ICF, Inc.
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