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CHAPTER 4

SOURCE WATER QUALITY
MANAGEMENT
GROUNDWATER
Stuart A. Smith, CGWP
Consulting Hydrogeologist, Smith-Comeskey Ground Water
Science, Ada, Ohio

GROUNDWATER SOURCE QUALITY:
RELATIONSHIP WITH SURFACE WATER
AND REGULATION
The topic of groundwater source quality is a complicated one, with numerous influences, both natural and human in origin. Aside from frequently being more accessible (drilling a well near a facility is often more convenient than piping in surface
water from a remote location), groundwater is typically chosen because its natural
level of quality requires less treatment to ensure safe, potable consumption by
humans. Although many groundwaters benefit from aesthetic treatment, and sometimes from treatment to remove constituents such as metals and arsenic that pose
long-term health risks, in general groundwater sources compare favorably against
surface water due to the reduced treatment needed. In the dangerous modern world,
groundwater sources are far less vulnerable to terrorist attack than surface water
reservoirs, just as they were recognized as being less vulnerable to nuclear fallout
during the political atmosphere of the 1950s and 1960s.
Arguably, surface water and groundwater form a water resource continuum in
any hydrologic setting (e.g., Winter et al., 1998), and from a groundwater-biased
view, surface water bodies are often simply points where the water table rises above
the surface. Thus impacts on one part of this continuum can affect the other over
time. However, the hydraulic connections between these two resources can be
obscure (at least superficially), and surface water and groundwater management
strategies in the United States (regulatory issues are discussed in Chapter 1) tend to
follow different paths.
Surface water management assumes that the source is impaired and unsafe for
consumption without elaborate treatment (a point not always conceded where

source surface waters are of high quality, such as in Portland, Oregon, and New York

4.1


4.2

CHAPTER FOUR

City). By contrast, because the advantages of groundwater include a perceived
reduced vulnerability and need for treatment, groundwater protection strategies,
such as those in the United States, have traditionally focused on protection of that
quality. This approach (and a procedural defeat for artificial separation of groundwater and surface water) is belatedly being reflected in the U.S. regulatory sphere in
the change to source water assessment and protection instead of “wellhead protection” and “surface water rules” as separate emphases.
However, experience of the last several decades has shown that groundwater
sources are not uniquely immune to contamination, and that once contaminated by
chemical or radiological agents, they are almost always difficult to clean up.
Recently, attention has refocused on the risk of pathogen transport to wells. A common conclusion of all groundwater contamination research is that prevention is far
more effective than remediation or treatment in assuring the quality of groundwater
supply sources. Prevention takes the form of management.
The intent of this chapter section is to introduce the reader to influences on
groundwater quality, management options, and tools to improve understanding of
the groundwater resource and thus improve its management and protection as it
relates to water supply.

GENERAL OVERVIEW OF GROUNDWATER
SOURCES AND IMPACTS ON THEIR QUALITY
The key to understanding and managing groundwater quality in water supply planning is to understand that both aquifer hydrologic characteristics and the causes and
effects of groundwater contamination are complex and highly site-specific. Groundwater quality management is most effective when it can respond to the specifics of
individual aquifers, wellfields, and even individual wells.

For example, in both porous media (sand/sand-and-gravel/sandstone) and
fractured-rock aquifers, hydraulic conductivity and its derivative values can vary
by orders of magnitude over short distances (meters to kilometers). Flow velocities can also vary by similar dimensions over meter differences horizontally and
vertically. Pressure changes near a well may cause flow characteristics to vary significantly in a distance of one meter away from the well.
Changes in each of the just-mentioned hydrologic characteristics can affect
groundwater quality by changing local constituent concentrations. Likewise, localized differences in formation geochemistry (e.g., organic content, iron, and other
mineral transformations) affect water quality. A third factor is the influence of the
aquifer microflora in a specific fracture or aquifer zone tapped by wells. Work in the
last 20 years has revealed the extent and complexity of the microbial ecosystems that
inhabit aquifers (e.g., Chapelle, 1993; Amy and Haldeman, 1997).
The extent of human impact also depends on (1) how potential contaminants are
handled; (2) the physical-chemical characteristics of such materials if they are released
to the ground; and (3) the hydrologic characteristics of the location where a release
occurs. If the soil has a low hydraulic conductivity, contamination may be very limited,
even if application (e.g., oil spills or herbicides) is relatively intense. On the other hand,
if conductivity is high and there is a direct contact with an aquifer, a small release may
have a large impact. A further human impact is the presence of abandoned wells or
other underground workings that provide conduits through low-conductivity soils.
All of these factors are site-specific, but they can be understood and managed if
identified. Thus, effective water supply management of source groundwater (and


SOURCE WATER QUALITY MANAGEMENT

4.3

avoiding unnecessary treatment) depends on adequate local knowledge of the
groundwater system being utilized.

Types of Aquifer Settings in North America

and Their Quality Management Issues
North America has vast and widely distributed groundwater resources that occur in
many types of aquifers (see Figure 4.1). In addition to this hydrogeologic variety,
North America offers extreme variability in climate and degree of human development. From the standpoint of groundwater development, these range from areas of
abundant groundwater and very low population density in western Canada to high
population densities in urban centers in the dry southwestern United States and
northern and central Mexico, where groundwater overdrafts are an important water
management problem.
Large areas of the central and western United States (like large regions of the
world) and Mexico struggle to effectively and equitably manage groundwater
resources that could very easily become depleted by overuse. Prominent examples
include the decades-long efforts to manage the Edwards aquifer in Texas, and the
Ogallala aquifer, which spans the central United States east of the Front Range of
the Rockies. In the long term, questions must be asked, such as how sustainable is the
high-water-use, technological civilization in the desert U.S.West (established during a
200-year historically wet period)? What kind of population density is sustainable on

FIGURE 4.1 (a) Groundwater regions of the United States. (Source: Van der Leeden, Troise, and
Todd. 1990. Originally from R. C. Heath. “Classification of ground-water regions of the United
States.” Ground Water, 20(4), 1982. Reprinted with the permission of the National Ground Water
Association.)


FIGURE 4.1 (Continued) (b) Occurrence of aquifers in the United States.
[Abbreviations: (1) Aquifers: P, principal aquifer in region; I, important aquifer in region; M, minor aquifer in region; U, unimportant as an aquifer in region.
(2) Rock terms: S, sand; Ss, sandstone; G, gravel; C, conglomerate; Sh, shale; Ls, limestone; Fm, formation; Gp, group.]
(1)
Geologic
Age and
Rock Type

(2)
Western
Mountain
Ranges

(3)
Arid
Basins

(4)
Columbia
Lava
Plateau

(5)

(6)
High
Plains

(7)
Unglaciated
Central
Region

(8)
Glaciated
Central
Region

Colorado
Plateau

(9)
Unglaciated
Appalachian
Region

(10)
Glaciated
Appalachian
Region

(11)
Atlantic and
Gulf Coastal
Plain

(12)
Special
Comments

Cenozoic
Quaternary
Alluvium
and related
deposits
(primarily—
recent and

Pleistocene
sediments
and may
include
some of
Pliocene
age)

S and G deposits in valleys and
along
stream
courses.
Highly productive but
not greatly
developed—P to
M.

S and G deposits in valleys and
along
stream
courses.
Highly
developed
with local
depletion.
Storage
large but
perennial
recharge
limited—P.

S and G deposits along
streams,
interbedded
with
basalt—I to
M.

U

S and G
along water
courses.
Sand dune
deposits—P
(in part).

S and G
along water
courses and
in terrace
deposits—I
(limited).

S and G
along water
courses—M.

S and G along water
courses and in terrace

deposits. Not developed.

S and G
along water
courses and
in terrace
and littoral
deposits,
especially in
the Mississippi and
tributary
valleys. Not
highly
developed
in East and
South.
Some depletion in Gulf
Coast—I.

Glacial
drift, especially outwash
(Pleistocene)

S and G deposits in
northern
part of
region—I.

S and G deposits especially in
northern

part of
region and
in some valleys—I.

S and G
outwash,
especially in
Spo-kane
area—I.

U

S and G
outwash,
much of it
reworked
(see
above)—I.

S and G
outwash
especially
along northern boundary of
region—I.

S and G
outwash,
terrace
deposits and
lenses in till

throughout
region—P
(in part).

S and G
outwash in
northern
part. Not
highly
developed—M.

S and G
outwash in
Mississippi
Valley (see
above)—I.

S and G
outwash,
terrace
deposits
and lenses
in till.
Locally
highly

The most
widespread
and important
aquifers in

the United
States. Well
over onehalf of all
groundwater
pumped in
United
States is
withdrawn
from these
aquifers.
Many are
easily available for
artificial
recharge
and induced
infiltration.
Subject to
saltwater

4.4


FIGURE 4.1 (Continued) (b) Occurrence of aquifers in the United States.
[Abbreviations: (1) Aquifers: P, principal aquifer in region; I, important aquifer in region; M, minor aquifer in region; U, unimportant as an aquifer in region.
(2) Rock terms: S, sand; Ss, sandstone; G, gravel; C, conglomerate; Sh, shale; Ls, limestone; Fm, formation; Gp, group.]
(1)
Geologic
Age and
Rock Type

(2)
Western
Mountain
Ranges

(3)
Arid
Basins

(4)
Columbia
Lava
Plateau

(5)

(6)

Colorado
Plateau

High
Plains

(7)
Unglaciated
Central
Region

(8)

Glaciated
Central
Region

(9)
Unglaciated
Appalachian
Region

(10)
Glaciated
Appalachian
Region

(11)
Atlantic and
Gulf Coastal
Plain

developed—I.

(12)
Special
Comments
contamination in
coastal
areas.

Other Pleistocene sediments

Alluvial Fm and other
basin deposits in the southern part—M to P (see Alluvium above).

U

U

Alluviated
plains and
valley fills—
M to I.

U

U

U

U

Coquina,
limestone,
sand, and
marl Fms in
Florida—M.

Tertiary
Sediments,
Pliocene

S and G in
valley fill
and terrace
deposits.
Not highly
developed—M.

Some S and
G in valley
fill—M.

U

U

Ogalalla
Fm in High
Plains.
Extensive S
and G with
huge storage
but little
recharge
locally.
Much depletion—P (in
part).

U

U

Absent

Absent

Dewitt Ss
in Texas. Citronelle and
LaFayette
Fms in Gulf
States—I.

Miocene

Ellensburg
Fm in Washington—I;
elsewhere—
U.

U

Ellensburg
FM in Washington—I;
elsewhere—
U.

U

Arikaree
Fm—M.

Arikaree
Fm—M.

Flaxville
and other
terrace
deposits. S
and G in
northwestern part—
M.

Absent

Absent

New Jersey,
Maryland,
Delaware,
Virginia—
Cohansey
and Calvert
Fms—I.

4.5

Delaware
to North
Carolina—
St. Marys
and Calvert

Fms—I.

Aquifers in
coastal
areas subject to saltwater
encroachment and
contamination.

Continued


FIGURE 4.1 (Continued) (b) Occurrence of aquifers in the United States.
[Abbreviations: (1) Aquifers: P, principal aquifer in region; I, important aquifer in region; M, minor aquifer in region; U, unimportant as an aquifer in region.
(2) Rock terms: S, sand; Ss, sandstone; G, gravel; C, conglomerate; Sh, shale; Ls, limestone; Fm, formation; Gp, group.]
(1)
Geologic
Age and
Rock Type

(2)
Western
Mountain
Ranges

(3)
Arid
Basins

(4)
Columbia

Lava
Plateau

(5)

(6)

Colorado
Plateau

High
Plains

(7)
Unglaciated
Central
Region

(8)
Glaciated
Central
Region

(9)
Unglaciated
Appalachian
Region

(10)
Glaciated

Appalachian
Region

(11)
Atlantic and
Gulf Coastal
Plain

(12)
Special
Comments

Georgia
and
Florida—
Tampa Ls,
Alluvium
Bluff Gp,
and Tamiami Fm—I.
Eastern
Texas—
Oakville
and Catahoula Ss—I.
Oligocene

U

U

U

U

Brule clay,
locally—I;
elsewhere—
U.

U

U

Absent

Absent

Suwannee
Fm, Byram
Ls, and
Vicksburg
Gp—I.

Eocene

Knight and
Almy Fm in
southwest
Wyoming—
M.

U

U

Knight and
Almy Fm in
southwest
Wyoming,
Chuska
Ss, and
Tohatchi Sh
in northwest
Arizona and
northeast
New Mexico—M.

U

Claibourne
and Wilcox
Gp in southern Illinois
(?), Kentucky, and
Missouri—
M; elsewhere—U.

Absent

Absent

Absent

New Jersey,
Maryland,
Delaware,
Virginia—
Pamunkey
Gp—I.
North Carolina to
Florida—
Ocala Ls
and Castle
Hayne

Includes
the principal formations (Ocala
Ls, especially) of
the great
Floridan
aquifer.
Subject to
saltwater
contamina-

4.6


FIGURE 4.1 (Continued) (b) Occurrence of aquifers in the United States.
[Abbreviations: (1) Aquifers: P, principal aquifer in region; I, important aquifer in region; M, minor aquifer in region; U, unimportant as an aquifer in region.
(2) Rock terms: S, sand; Ss, sandstone; G, gravel; C, conglomerate; Sh, shale; Ls, limestone; Fm, formation; Gp, group.]
(1)

Geologic
Age and
Rock Type

(2)
Western
Mountain
Ranges

(3)
Arid
Basins

(4)
Columbia
Lava
Plateau

(5)

(6)

Colorado
Plateau

High
Plains

(7)
Unglaciated

Central
Region

(8)
Glaciated
Central
Region

(9)
Unglaciated
Appalachian
Region

(10)
Glaciated
Appalachian
Region

(11)
Atlantic and
Gulf Coastal
Plain

Special
Comments

Marl—P (in
part).
Florida—
Avon Park

Ls., South
Carolina to
Mexican
border,
Claibourne
Gp, Wilcox
Gp—I.

tion in
coastal
areas but
source of
largest
groundwater
supply in
southeastern United
States.

Clayton Fm
in Georgia—I.
Paleocene

U

U

U

U

Ft. Union
Gp—M.

Ft. Union
Gp—M.

Ft. Union
Gp—M.

Absent

Absent

Volcanic
rocks, primarily
basalt

U

Local
flows—M.

Many interbedded
basalt flows
from Eocene to Pliocene—P.

Local
flows—M.

Absent

Absent

Absent

Absent

Absent

Source: Reprinted with permission from F. Van der Leeden, F. L. Troise, and D. K. Todd. The Water Encyclopedia.
Boca Raton, FL: Lewis Publishers, 1990. Copyright CRC Press, Boca Raton, Florida.

Absent

(12)

4.7


4.8

CHAPTER FOUR

FIGURE 4.1 (Continued ) (c) Groundwater potential in Canada. (Source: Van der Leeden,
Troise, and Todd, 1990. Adapted from P. H. Pearse et al., 1985. Currents of Change: Final Report—
Inquiry on Federal Water Policy. Ottawa, Canada. Reproduced with the permission of Environment
Canada, 1999.)

Florida’s abundant aquifers without water quality degradation? Do our current
groundwater “sustainable yield” concepts bear scrutiny (Sophocleous, 1997)?

Groundwater management issues involve but extend beyond human water supply and also intersect with surface water quality and quantity issues. In the case of
both the Edwards and the Ogallala aquifers, and the surficial aquifers of Florida,
management has to consider the water needs of agricultural and human water supply, but equally so, the maintenance of wildlife habitats. The Edwards feeds prominent springs (supporting rare aquatic species), as well as culturally and ecologically
important streams. The Everglades in Florida represent a water system incorporating both “surface” and “ground” water.The Ogallala involves formations too deep to
be directly involved in surface water maintenance; however in the same region surficial aquifers along the North and South Platte, the Missouri, and other rivers in the
western Mississippi watershed are critical to maintaining wildlife habitat. As with
wetlands management strategies all over the United States, the Ogallala and High
Plains management equation involves finding the optimal distribution of water withdrawal among groundwater and surface water resources. In all of these cases, quality is a factor. Where groundwater is overused, water quality and the quality of
aquatic ecosystems are also commonly degraded.
What are the consequences? The technology to drill and pump wells essentially
made settled rural and town life possible in the Great Plains of the United States and
south-central Canada, as well as in very similar locations in Australia, where no useful surface water was available nearby. In many communities, stations, and farms in
these areas, wells can be drilled to groundwater, often hundreds of meters deep. If
groundwater sources become depleted or contaminated, many farms or communities


SOURCE WATER QUALITY MANAGEMENT

4.9

in North Dakota or Queensland, for example, could not be maintained economically.
With the years-long drought in Queensland, inhabitants recently were actually facing
the possibility of abandoning their towns due to dwindling groundwater reserves.
Agriculture, especially in production of food for human consumption, has become
highly dependent on irrigation. The food economy of the United States is highly
dependent on the production of fresh vegetables from California, Florida, and Mexico,
mostly sustained by irrigation. Israel, as a modern society established in a near-desert,
is totally dependent upon irrigated agriculture. If large-scale, groundwater-dependent
irrigation were to become impractical, major changes would be necessary in food
production and distribution worldwide. In the case of the United States, water for

irrigation reserved by prior appropriation can only be available for human water
supply if these rights are purchased or abandoned. “Water farming” or purchasing
prior agricultural water rights to groundwater reserves for urban water supply is an
issue with many economic, cultural, and emotional aspects. If water farming reserves
groundwater formerly allocated to agriculture for direct human use, how are fresh
produce, cotton, or animal feed crops produced? Would all of this be shifted back to
the wetter (but colder) eastern United States, raising costs and requiring increased
expenditures of hydrocarbons for greenhouse heating?
Even within a relatively small and water-rich part of North America, great variety
in water availability and quality can occur, illustrating the need for flexible and sitespecific management. The situation in western Ohio and eastern Indiana (e.g., Lloyd
and Lyke, 1995) is only one of many such examples. The region is underlain by an
extensive carbonate-rock aquifer that is largely underutilized due to low population
density, and relatively protected due to glacial clay till coverage. However, local overdrafting and contamination of this aquifer can and does occur. By contrast, carbonate
rock in southern Ohio and Indiana (laid down under different depositional conditions) provides poor yields to wells. Within this area of unproductive rock, Dayton
and Columbus, Ohio, and many smaller communities are underlain by large and productive glacial-outwash aquifers. These aquifers are at once both productive and vulnerable (sometimes being the only flat places to build factories, drill oil wells, etc.).
As in southern Ohio, in much of New England, municipal groundwater supplies
can only be developed in relatively vulnerable (and highly developed) glacio-fluvial
aquifers, although adequate household yields are possible from rock wells. However,
population densities and intensity of land use is high. Overuse and vulnerability to
contamination make management of these aquifers a critical environmental imperative for the region that is only now being addressed seriously.

PATTERNS OF PRIVATE AND PUBLIC
GROUNDWATER SOURCE USES:
QUALITY MANAGEMENT ISSUES
North America has a relatively high density of private groundwater supply use, particularly in the eastern United States (see Figure 4.2). Private wells have long been
the principal mode of water supply for widely spaced rural homesteads and many
small villages. This contrasts with France, for example, where public water service to
rural properties is the rule.
Local variability in the quality and availability of groundwater influences pressure to develop or extend public water supply distribution systems in rural settings.
Constructing individual water supply wells is always more cost-effective where

groundwater is abundant and of suitable quality. Where natural groundwater quality


4.10

CHAPTER FOUR

FIGURE 4.2 Density of housing units using on-site domestic water supply systems in the United
States (by county). (Source: U.S. Environmental Protection Agency, Office of Water Supply, Office
of Solid Waste Management Programs, 1977. The Report to Congress: Waste Disposal Practices and
Their Effects on Ground Water. Reprinted in Van der Leeden, Troise, and Todd, 1990.)

is exceptionally poor or where supplies are insufficient, the more costly option of
piping treated water from a centralized source is a solution to provide suitable
water. In the United States, the development of systems to provide public water to
rural residents has been promoted and funded by the federal government. Many
areas have mixed individual private well and public piped water supply options.

Rural Groundwater Quality Management
Managing rural water quality is a significant challenge due to its site-specific nature
and the typically inadequate financial and human resources available to address
problems.
Microbial Health Risks. The most commonly detected problem of rural private
wells is the occurrence of total-coliform (TC) bacteria positives. Statistically meaningful studies over the years have shown that a significant number of wells sampled
are positive for total coliform bacteria. The most recent data available from largescale studies (results from Midwest studies by the Centers for Disease Control and
Prevention) show 41 percent TC positive and 11 percent fecal coliform positive
(CDC, 1998) in the population of wells sampled. Such contamination is mostly due
to well-construction deficiencies and deterioration (Exner et al., 1985; Smith, 1997;
NGWA, 1998). It is rare that a large volume of an aquifer is contaminated by sewage
waste, although such incidents have occurred (Ground Water Geology Section,

1961). A relatively new concern in the United States is the microbial impact of concentrated animal farm operations (CAFO) through faults in animal waste manage-


SOURCE WATER QUALITY MANAGEMENT

4.11

ment. So far, this has been addressed as a surface water concern, but the potential
exists for new phenomena such as the spread to nearby wells of antibiotic-resistant
Salmonella sp. from chicken manure deposited on shallow bedrock.
Correlations made in CDC (1998) suggest that positive TC results increase with
increasing well age, poor well condition and maintenance, shallow depth, and certain
well types (e.g., dug), supporting the value of well construction standards and well
maintenance (Smith, 1997). However, recent research in relatively undisturbed
aquifers (e.g., Jones et al., 1989) raises the question of whether bacteria that are
capable of positive growth in coliform media are native to aquifers, and not indicators of contamination from the outside.
Pesticides and Nitrates. Another problem is pesticide and nitrate infiltration from
surface contamination, discussed in greater detail later in this chapter. This is a typically rural to suburban groundwater quality concern, since these chemicals are used
in agricultural and horticultural activities. Pesticides and nitrates represent the main
sources of chemical aquifer contamination in agricultural zones (Dupuy, 1997). The
matter of pesticide and nitrate contamination is also a good illustration of the interactions among (and need to understand) use and application methods, hydrogeology, climatic factors, and site-specific circumstances in prevention and prevention in
management. In contrast to the limited understanding of the microbial impacts of
industrial-scale agriculture, nitrate impact management for facilities such as CAFO
is relatively well understood. However, experience in the Netherlands, where rises in
groundwater nitrate levels are attributed to manure spreading, provides a sobering
example of the possibilities.
Public Water Supply Wells. Incidents of contamination are not unique to private
wells. However, public wells are more likely to be isolated from contamination
sources and better constructed. As is the case for coliform contamination, older,
deteriorated, and poorly constructed wells (public or private) were more likely to be

contaminated (EPA, 1990; USGS, 1997).
Nitrate and pesticide occurrence in wells is most likely where there is a high density of wells and on-site waste disposal systems (which are themselves often forgotten or neglected by their users). Situations can be particularly acute when combined
with a vulnerable aquifer setting such as a shallow limestone. Numerous abandoned
but unsealed or poorly sealed wells (Gass et al., 1977; Banks, 1984; Smith, 1994) may
serve as conduits for contamination to move to the subsurface.
Natural Environmental Impacts on Groundwater Quality
Groundwater quality reflects the physical, chemical, and biological actions interacting with the water itself. As part of the hydrologic cycle, the water falls as precipitation and is influenced by soil and organisms at or near the surface. As groundwater
in the saturated zone, it is affected by the nature of the formations (including their
microbial ecologies) in which the water has been stored. The influence of the aquifer
formation depends on how long the water has been held in the aquifer, and how
rapidly stored water is recharged by fresh water from the surface.
Aquifer Formation Composition and Storage Effects
Groundwater movement is relatively slow, even in the most dynamic flow systems.
Water moves in close contact with the minerals that make up the particles or fracture channels of the aquifer formation.


4.12

CHAPTER FOUR

These minerals reflect the depositional environment of the formation. For example, limestone, laid down as carbonate-rich sediments, fossils, and fossil debris, consists of calcium carbonate with impurities. Dolomite rock is chemically altered
limestone containing a high fraction of magnesium. Carbonate rock aquifers typically
provide an alkaline, high total dissolved solids (TDS) water that also has high calcium
and/or magnesium hardness, but as illustrated in Figure 4.3, quality can vary greatly
among carbonate aquifers with somewhat varying histories (e.g., Cummings, 1989).
Sandstone (cemented quartz sands) and volcanic rock, by contrast, may be acidic
(unless cemented by carbonates). The water may be relatively soft, especially with
sodium minerals in the rock matrix, or low in TDS (but not always).
The chemical influences of glacial and alluvial sands and gravels tend to reflect
the composition of the source rock of the formation material.

All natural aquifer formations have impurities that provide additional complexity to the water. Most aquifers contain iron, and many contain manganese and other
minor metal constituents as well. Certain igneous and metamorphic rocks, and the
shales, sandstones, and unconsolidated deposits derived from them, may have high
heavy metal or radionuclide contents.
A tragic example is that of the arsenic-rich alluvial and deltaic formations of
Bangladesh and the West Bengal state of India which were tapped for tubewells to
replace poor-quality shallow groundwater and surface water sources (e.g., Bhattacharya et al., 1997; Mushtaq et al., 1997). These sediments were derived from Asrich continental source rocks. Formations laid down near geo-historical continental
margins (which may be different from continental margins now) may contain significant amounts of evaporites, such as rock salt or gypsum, that contribute chlorides or
sulfates.
Elevated radon and other radionuclides (e.g., radium) levels in groundwater
closely match the geographical distribution of rock types rich in radioactive minerals (e.g., New England, the Canadian Shield region of the United States and Canada,
shale areas of Ohio and the east, and sediments derived from them). See Figure 4.4.
Sediments derived from metamorphic source rocks may contain elevated solidphase radionuclides, for example the Kirkwood-Cohansey aquifer of New Jersey
(USGS, 1998a). Phosphate deposits in Florida with high radioactive-isotope content
may be added to this group.
Deep formations well isolated from surface hydrologic recharge usually contain
briny fluids (usually geochemically distinct from shallower groundwater), which
may migrate to freshwater aquifers along density gradients if there are pathways
such as faults or boreholes open between the formations. Table 4.1 is a generalized
summary of water qualities that may be expected from wells developed in various
aquifers.
Table 4.2 shows variation in mean analytical values for selected parameters
among aquifers in one area (Michigan), illustrating how difficult generalizations
about water quality and source geochemistry can be.

Aquifer Biogeochemistry
Lithology (rock type and composition) sets the broad tone for natural groundwater
quality, but the effects of microbial ecology in aquifers, typically driving redox reactions, provide additional complexity at the local scale. Many oxidation-reduction
(redox) transformations of common metals can occur without the mediation of
microorganisms, but are not likely to occur at ambient groundwater temperatures

and measured bulk redox potentials. An example is the oxidation MnII to MnIV,


FIGURE 4.3 Chemical characteristics of water from bedrock (Silurian, Ordovician, Cambrian, and Precambrian ages). (Source: Cummings, 1989.)

4.13


4.14

CHAPTER FOUR

FIGURE 4.4 Distribution of radon in groundwater mapped by county, based on available data
and aquifer type. (Source: J. Michel. 1987. In Environmental Radon (pp. 81–130). Ed. by C. R. Cothern and J. E. Smith. New York: Plenum Press.)

which occurs at approximately Eh +600 to 700 at pH and temperature ranges
encountered in potable groundwater (Hem 1985). Figure 4.5 illustrates the Eh-pH
ranges of stability for Mn species (gray areas are MnIV solids). Such a high redox
potential is unlikely in groundwater, and in fact, MnIV is encountered in groundwater with much lower measured bulk Eh. Reductions of Fe, Mn, As, and a variety of
other metals have been demonstrated to be microbially controlled. Both the oxidation and reduction of sulfur species largely involve bacteria except at extreme temperatures and pressures. Research on these activities to-date was summarized in
Chapelle (1993) and Amy and Haldeman (1997) and continues actively.
The presence of organic carbon is an important factor influencing the activities of
microorganisms. Both coal and hydrocarbons, which are extensively distributed in
formations throughout the United States and around the world, are ready sources of
organic carbon for bacteria. Acidic coal mine waters provide the preferred environment for iron-oxidizing bacteria, which, ironically, are chemolithotrophs and do not
commonly utilize organic C.
Hydrocarbons, common in carbonate and other reduced sediments such as
shales, provide the type of organic carbon compounds and the reductive conditions
that promote sulfate reduction (and hydrogen sulfide formation) or methanogenesis by microorganisms. Jones et al. (1989) summarizes the occurrence and ecology of
sulfate-reducing bacteria and methanogens in aquifers. Where ready sources of sulfate (e.g., gypsum) as well as short-chain hydrocarbons (e.g., acetate) are available,

H2S production can be intense. This is well illustrated in carbonate aquifers across
the U.S. Great Lakes region.
Relatively high microbiological activity in aquifers can contribute significant
amounts of carbon dioxide, producing gaseous waters and lower pH, thereby shifting
the carbonate balance toward bicarbonate. This condition can in turn contribute to
greater dissolution of Ca and Mg from rock and very high hardness. Figure 4.6 is a


TABLE 4.1 Representative Water Quality of Aquifer Types*
Carbonate
hardness
occurrence

Total dissolved
solids

Dominate
dissolved mineral
characteristics

Metal and
radionuclide
characteristics

Basalt

Very low
<250 mg/L†

Very low <120 mg/L

Na, Cl, Si far from saturation

May have high and exotic metal
and radionuclide concentrations

Carbonate

High >500

Very high >500

Ca, Mg carbonates (near saturation),
major sulfate admixture, may be
closely associated with evaporite
deposits

High Fe, “dirtier” formations may
have radionuclides at levels
greater than U.S. MCLs

Igneous and
metamorphic
rocks

Low <250

Low to moderate <120–500

Mixed, depending on rock mineral

origin

May have high and exotic metal
and radionuclide concentrations

Surficial
sands/gravels

Very low to
moderate
<250–500

Moderate 120–240. Glacial-fluvial
deposits may be have high
carbonate hardness.

Mixed, depending on rock mineral
origin. Glacial-fluvial deposits
may be more carbonate
dominated.

Low Fe except where concentrated
by biological action (e.g.,
Kirkwood-Cohansey aquifer,
Pine Barrens, NJ), typically low
metal contents in pumped
groundwater.

Sandstone

Low to moderate

Moderate

Mixed, depending on rock mineral
origin. Sandstones with carbonate cementation are closer to
carbonate saturation. In the U.S.
east, often intermixed with coal
deposits.

Low to high depending on
cementation material and sand
origin, and degree of water flushing over time. May have
radionuclides above U.S. MCLs
depending on sand origin (sands
are major sources of uranium
deposits).

Shale

Moderate

Moderate

* These summaries are highly generalized and may likely be different regionally or locally. Water quality should be
investigated at the wellfield or aquifer scale.
†
Numbers from Lehr et al. (1980) and considered general and representative.

Often high radon and other radio

nuclides and metals (typically
poorly flushed).

4.15


4.16

CHAPTER FOUR

TABLE 4.2 Selected Median Values of Physical-Chemical Parameters from Michigan Aquifers

Source
Glacial sand (Pleistocene)
Glacial gravel (Pleistocene)
Engadine dolomite
Paleozoic dolomite
Sylvania sandstone
Freda sandstone
Portage Lake volcanics

Ca hardness
(total) in mg/L

Fe (dissolved)
in µg/L

Boron (total)
in µg/L

Chloride
(dissolved) (mg/L)

8
27
515
250
600
101
29

50
270
1290
160
1800
16
47

<20
40
80
80
110
640
700

1.5
1.8
1.2

1.3
47
11
5.3

Source: Cummings (1989), Appendix A.

summary of the carbon system influencing aquifer conditions. Table 4.3 is a summary
of physical-chemical activities often influenced by microorganisms in the subsurface.
When wells are installed in formations, redox gradients form due to both abiotic
and biotic effects on metal species (Cullimore, 1993). These gradients can be very
sharp. Iron can oxidize readily at the appropriate redox potential along these gradients, and microorganisms associated with iron precipitation are often found preferentially at Eh-pH environmental conditions as found in Figure 4.7 (Smith and Tuovinen,
1985). Manganese, where present and in solution as Mn(II), also oxidizes catalytically
to Mn(IV) due to the activity of bacteria (Hatva et al., 1985; Vuorinen et al., 1988), a
mechanism also involved in at least some Fe(II)-Fe(III) oxidation (Hatva et al., 1985).
Hydrogen sulfide is also oxidized by various S-oxidizers to So and then to sulfate. The
resulting oxidized products (solid S and sulfate salts) usually cause clogging in well
intake screens, pumps, and piping, and discoloration and odors in the water.

Human Impacts
In addition to understanding and taking into consideration factors in natural
groundwater quality, management of groundwater source quality is also concerned
about human impacts. Within the overall scope of management, regulation is largely
focused on human impacts. Adverse human impacts include providing routes for
potential pathogens or chemicals to reach groundwater, and aquifer depletion.
Other human activities can prevent or mitigate such adverse effects, and these are
the agents of appropriate stewardship of the groundwater resource.

Health-Related Microbiological Occurrence in Groundwater
Groundwater is a preferred source of water supply due to natural removal of undesirable microorganisms and viruses, especially where minimal treatment is the highest priority (e.g., small systems and private wells).

Although bacteria are not uncommon in groundwater, attenuation by various
means reduces total coliform and fecal indicator bacteria, commonly to undetectable levels. A persistent coliform bacteria presence in groundwater samples usually indicates short-circuited flow from a surface source [although some research
(Jones et al., 1989) shows doubt about that assumption]. Pathogenic bacteria or protozoa are not known to be native to or commonly occur in groundwater except
where direct and close sources of innoculant are present.


SOURCE WATER QUALITY MANAGEMENT

4.17

FIGURE 4.5 Fields of stability of manganese solids and equilibrium
dissolved manganese activity as a function of Eh and pH at 25°C and 1
atmosphere pressure. Activity of sulfur species 96 mg/L as SO42−, and carbon dioxide species 61 mg/L as HCO3. (Source: Hem, 1985, p. 87.)

While viruses have been detected in groundwater, little has been known about
their occurrence in aquifers. At the present time, intensive field research is limited,
and conclusions that can be drawn from it are preliminary. A study sampling from
460 wells across the United States managed by the American Water Works Service
Company (LeChevallier, 1997) showed that viral occurrence may be expected in
many groundwater sources. Culturable viruses (cultured on tissue cells) were
detected in samples from 7 percent of the sites (LeChevallier, 1997), illustrating how
differences in methods affect detection statistics. Methods and their varying results
are discussed in Abbaszadegan et al. (1998).


4.18

CHAPTER FOUR

FIGURE 4.6 Carbon cycling in local flow systems. (Source: F. H. Chapelle.

1993. Ground-Water Microbiology and Geochemistry. Copyright © 1993 John
Wiley & Sons. Reprinted by permission of John Wiley & Sons, Inc.)

Conclusions about viral numbers and role in human disease have been difficult to
make, although viruses have been linked to enteric disease outbreaks from groundwater sources (e.g., Craun and Calderon, 1997). However, such outbreaks have to be
obvious to be noticed.Assessment of the occurrence of viruses at less-than-outbreak
levels has been hampered by limits in collection and analysis methods.
TABLE 4.3 Representative Microbially Influenced Chemical and Redox Activities in Aquifers

Calcite dissolution
Fe reduction
SO42− reduction
Methanogenesis

Reaction activity*

Microbiological influence†

CaCO3 + H2CO3 → Ca2+ + 2 HCO3
Fe3+ + e = Fe2+
SO42− + 10H+ + e = H2S + 4H2O
CO2 + 6H+ + e = CH4 + H2O

Respiration: DOC removed and CO2 added.
Dissimilatory use of ions such as Fe3+ or
SO42− as final electron acceptors.
Dissimilatory reduction by archaebacteria.

Sources: * Freeze and Cherry (1979).
†

Chapelle (1993).


SOURCE WATER QUALITY MANAGEMENT

4.19

FIGURE 4.7 Eh-pH diagram for major iron species in
relation to the occurrence of iron bacteria in the environment. (Source: S. A. Smith and O. H. Touvinen. “Environmental analysis of iron-precipitating bacteria in ground
water and wells.” Ground Water Monitoring Review, 5(4),
1985: 45–52.)

Transport and fate of microflora and viruses depends on a complex interaction of
soil characteristics, hydrology, climate, water quality, and features of the organisms or
viruses themselves. Gerba and Bitton (1984) provide a conceptual review of transport
and attenuation of bacteria and viruses in soil and groundwater. Tables 4.4 and 4.5
summarize factors affecting enteric bacteria survival and viral movement in soils.
Groundwater has characteristics that may tend to favor the transport of viable
viruses: absence of strong oxidants, cool temperatures, and frequently alkaline pH.
However, reported transport distances have been on the meter scale. Yates (1997)
reported viruses detected 402 m downgradient from a landfill on Long Island, New
York, and three m below land-applied sludge (both potentially intense sources of
viral inoculum). Bales et al. (1995) showed movement upwards of 14 m for bacteriophage PDF-1 in 24 days in a glacial sand. Attenuation factors clearly are at work at
least in granular aquifers (Bales et al., 1995). Schijven and Rietveld (1997) report
≥2.6 to 2.7 log removal of enteroviruses and ≥4.7 to 4.8 log removal of reoviruses
over 30 m bank filtration distances in the Netherlands.
While these studies provide evidence for mechanisms that provide impediment
to viral transport, the degree of removal inactivation have been difficult to model
(Schijven and Rietveld, 1997; Yates, 1997) and can be reversible (Bales et al., 1995).
All of these factors have relevance to water supply in determining what is necessary in risk assessment, and how to site and protect water supply wells. The Groundwater (Disinfection) Rule (GWDR), currently under development by the U.S. EPA

4.20

CHAPTER FOUR

TABLE 4.4 Factors Affecting Survival of Enteric Bacteria in Soil
Factor

Comments

Moisture content

Greater survival time in moist soils and during times of
high rainfall

Moisture-holding capacity

Survival time is less in sandy soils with lower waterholding capacity

Temperature

Longer survival at low temperatures; longer survival in
winter than in summer

pH

Shorter survival time in acid soils (pH 3–5) than in
alkaline soils

Sunlight

Shorter survival time at soil surface

Organic matter

Increased survival and possible regrowth when sufficient
amounts of organic matter are present

Antagonism from soil microflora

Increased survival time in sterile soil

Source: C. P. Gerba and G. Bitton. “Microbial pollutants: Their survival and transport pattern to groundwater.” Pp. 65–88 in Groundwater Pollution Microbiology. C. P. Gerba and G. Bitton, eds. New York: WileyInterscience, 1984. Copyright © 1984 John Wiley & Sons. Reprinted by permission of John Wiley & Sons, Inc.

(Macler, 1996; Macler and Pontius, 1997) and intended for promulgation early in the
first decade of the twenty-first Century, will focus on minimizing risk of viral disease
in groundwater-source public water systems. The mentioned research on viral occurrence, transport, and fate is intended to support the GWDR development effort,
which is a regulatory process being developed on emerging and uncertain science.
TABLE 4.5 Factors That May Influence Virus Movement to Groundwater
Factor

Comments

Soil type

Fine-textured soils retain viruses more effectively than light-textured
soils. Iron oxides increase the adsorptive capacity of soils. Muck soils
are generally poor adsorbents.

pH

Generally, adsorption increases when pH decreases. However, the
reported trends are not clear-cut due to complicating factors.

Cations

Adsorption increases in the presence of cations (cations help reduce
repulsive forces on both virus and soil particles). Rainwater may
desorb viruses from soil to its low conductivity.

Soluble organics

Generally compete with viruses for adsorption sites. No significant
competition at concentrations found wastewater effluents. Humic
and fulvic acid reduce virus adsorption to soils.

Virus type

Adsorption to soils varies with virus type and strain. Viruses may have
different isoelectric points.

Flow rate

The higher the flow rate, the lower virus adsorption soils.

Saturated versus
unsaturated flow

Virus movement is less under unsaturated flow conditions.

Source: C. P. Gerba and G. Bitton.“Microbial pollutants:Their survival and transport pattern to groundwater.” Pp. 65–88 in Groundwater Pollution Microbiology. C. P. Gerba and G. Bitton, eds. New York: WileyInterscience, 1984. Copyright © 1984 John Wiley & Sons. Reprinted by permission of John Wiley & Sons, Inc.


SOURCE WATER QUALITY MANAGEMENT

4.21

Point-Source Chemical Contamination
Point-source contamination of groundwater is that resulting from defined sources of
small areal extent such as single locations or properties. Eliminating it has been a
major focus of public health regulation for many years in North America and elsewhere in the world. Leaking septic tanks or privies are point sources identified as
public health risks generations ago. More recently, point sources of chemical contaminants such as underground storage tanks or waste pits have been the focus of
environmental regulation.
Point sources are frequently identifiable as sources of contamination by field
checking and testing. They are typically closely regulated by government agencies.
Examples include municipal or hazardous waste landfills, underground storage tanks,
or deep injection wells. They are readily eliminated as groundwater risks by such mitigating actions as repair, replacement, or sealing. Effectiveness of the “repair” can
often be judged quickly by the result of greatly reduced or eliminated contamination.
However, reduction or elimination of contamination after a point source is removed
may also take many years. Point sources can also be addressed in public health regulation because it is often possible to assign blame for allowing the problem to occur.
Nonpoint Chemical Contamination
Surface-water nonpoint contamination is a well-known problem that is extensively
discussed in the literature and elsewhere in this text. Nonpoint-source contaminants
such as nitrate or pesticides also reach groundwater from regional use at the surface.
An example might be elevated nitrate levels in shallow wells in an area of sandy soils
where there is extensive use of fertilizers and septic tanks. This is a worldwide problem in areas of vulnerable soil situations.
In many regions, nitrate concentration levels in groundwater can reach and
exceed water quality criteria (e.g., U.S. drinking water, 10 mg NO3/L, E.U. ambient,
50 mg NO3/L). The increasing use of mineral fertilizers in some regions and the

intensive exploitation of the aquifers for crop irrigation have led to groundwater
contamination by nitrates (e.g., Dupuy et al., 1997; USGS, 1997). The dynamics
(long-term persistence) and extensiveness (regional contamination) of this contamination, as well as uncertainty about behavior in aquifers, make it a sensitive environmental issue.
The USGS (1997), summarizing current USGS study results, reports that over
300 studies of pesticide occurrences in groundwater and soils have been carried out
during the past 30 years. Further data are being compiled in the National Water
Quality Assessment Program (NAWQA). Provisional summary data and interpretation (subject to revision) are available from the USGS on the World Wide Web (e.g.,
USGS, 1998b), a mechanism that permits rapid, but fluid publication of such information. USGS studies have shown that:
1. Pesticides from every major chemical class have been detected in groundwater.
2. Pesticides are commonly present in low concentrations in groundwater beneath
agricultural areas, but seldom exceed water quality standards.
Occurrence of pesticides in groundwater follows a pattern resembling that of coliform bacteria occurrence (Figure 4.8).
The USGS currently has come to a several conclusions on pesticide and nitrate
contamination occurrences associated with cropland (USGS, 1997):


4.22

CHAPTER FOUR

Detection more likely

•
•
•
•
•
•
•
•

High pesticide use
High recharge
High soil permeability
Unconsolidated or karst
No confirming layer(s)
Dug or driven wells

• Low pesticide use
• Low recharge
• Low soil permeability
• Bedrock
• Thick confirming layer(s)
• Drilled wells
• Deep wells
• Wells with proper seals

Shallow wells
Wells with leaky seals
Detection less likely

FIGURE 4.8 USGS arrow from //water.wr.usgs.gov/pnsp/
images/gw7.gif.

1. Factors most strongly associated with increased likelihood of pesticide occurrence in wells are high pesticide use, high recharge by either precipitation or irrigation, and shallow, inadequately sealed, or older wells (consistent with results
reported by EPA 1990) (Figures 4.9 and 4.10).
2. They are more likely to occur where groundwater is particularly vulnerable, such
as shallow, unprotected sands, or highly solutioned (karstic) or fractured rock.
3. Pesticide contamination is generally more likely in shallow groundwater than in
deep groundwater, and where well screens are located close to the water table,

but such relations are not always clear-cut.
4. Frequencies of pesticide detection are almost always low in low-use areas, but
vary widely in areas of high use.
5. Pesticide levels in groundwater show pronounced seasonal variability in agricultural areas [consistent with Dupuy (1997)], with maximum values often following
spring applications. Temporal variations in pesticide concentrations decrease
with increasing depth and are generally larger in unconsolidated deposits than in
bedrock.
As with pesticides, the risk of groundwater contamination by nitrate is not the same
everywhere (Nolan and Ruddy, 1996). Figure 4.11 shows four groups in order of
increasing risk related to soil characteristics:
1.
2.
3.
4.

Poorly drained soils with low nitrogen input (white area on the map)
Well-drained soils with low nitrogen input (light gray area)
Poorly drained soils with high nitrogen input (medium gray area)
Well-drained soils with high nitrogen input (dark grayish area)

Well-drained soils can easily transmit water and nitrate to groundwater. In contrast,
the other three groups have a lower risk of nitrate contamination because of poorly
drained soils and/or low nitrogen input. Poorly drained soils transmit water and
chemicals at a slower rate than well-drained soils (Nolan and Ruddy, 1996). Drains
and ditches commonly are used to remove excess water from poorly drained agricul-


4.23

PROPORTION OF SAMPLED WELLS IN COUNTY WITH

ATRAZINE DETECTIONS, IN PERCENT

SOURCE WATER QUALITY MANAGEMENT

100
90
80
70
60
50
40
30
20
10
0
1,000

10,000

100,000

1,000,000

COUNTYWIDE ATRAZINE USE,
IN POUNDS OF ACTIVE INGREDIENT PER YEAR

FIGURE 4.9 Proportion of sampled wells with atrazine detections in
relation to countywide use. Wells were sampled as part of the National
Alachlor Well-Water Survey. (Source: U.S. Geological Survey, Pesticides
in Ground Water, USGS Fact Sheet FS-244-95, />pnsp/gw/gw5.html.)

EXPLANATION
Insufficient data

1 - 10% of sampled
wells

None detected

> 10% of sampled
wells

FIGURE 4.10 Frequency of triazine herbicide detection in counties with ten
or more wells sampled during the Cooperative Private Well Testing Program.
(Source: U.S. Geological Survey, Pesticides in Ground Water, USGS Fact Sheet
FS-244-95, />

4.24

CHAPTER FOUR

FIGURE 4.11 Areas in the United States most vulnerable to nitrate contamination of groundwater (shown in grayish blue on the map) generally have well-drained soils and high-nitrogen input
from fertilizer, manure, and atmospheric deposition. High-risk areas occur primarily in the western,
midwestern, and southeastern portions of the nation. (Source: U.S. Geological Survey Fact Sheet
FS-092-96, />
tural fields, diverting nitrate to nearby streams (and thus making it a surface water
problem).
The effects of application of fertilizers is illustrated by studies from the United
Kingdom. The British Geological Survey (BGS) has been studying the problem of
nitrates in groundwater for over 15 years.As is the case elsewhere in Europe, the concentrations of nitrate in groundwater in the principal British aquifers are generally

rising, and some groundwater sources already exceed the EC Drinking Water Directive limit of 50 mg/L NO3 (11.3 mg/L NO3-N).The BGS suggests that many others are
likely to exceed this limit if current agricultural practices continue unchanged.
Investigations at four grassland sites on the chalk of southern England between
1987 and 1989 (Figure 4.12) demonstrated that the majority of pore water nitrate
concentrations under most of the grazed grassland sites investigated exceed the EC
limit and that leaching from grazed grassland receiving more than about 100 kg
N/ha/yr is likely to give rise to nitrate concentrations above the EC limit in groundwater recharge. Typical nitrate concentrations in the unsaturated zone beneath
grazed grassland sites (Figure 4.13) are in the range of 10 to 100 mg/L NO3-N, with
marked peaks as high as 250 mg/L NO3-N. This compares with values of less than
5 mg/L NO3-N measured under lower-productivity grassland, and is also higher than
levels observed under intensively cultivated land. Nitrate losses expressed as a percentage equivalent of the nitrogen input to the land range from 15 up to 45 percent,
showing a broad correlation between the implied leaching loss and the quantity of
nitrogen applied (BGS, 1997).
There is historically less information available on pesticide occurrence beneath
nonagricultural land, such as residential areas and golf courses, despite chemical application rates that often exceed those for most crops. However, studies of golf courses on


SOURCE WATER QUALITY MANAGEMENT

4.25

FIGURE 4.12 Outcrop of chalk aquifer in SE England and location of grassland investigation sites. (Source: BD/IPR/20-7, British Geological Survey. © NERC.All rights reserved.
/>
Cape Cod, Massachusetts, and in Florida (Cohen, 1996; Cohen et al., 1990; Swancar,
1996) shed some illumination. Swancar (1996) found pesticides in groundwater at
seven of nine golf courses, with 45 percent at trace concentrations and 92 percent
below MCLs or health advisory levels (HALs). In the Florida study, there was one
trace diazinon detection, although this insecticide was banned for golf courses in the
1980s. This raises the question of the poorly known contribution of lawn application, a
possible source of the diazinon occurrence in the Florida study (Cohen, 1996).

The nature of land use controls also has to be considered carefully. For example,
protection zones around public supply wells are often used as a setback to reduce or
prevent contamination of groundwater. Nitrate concentrations can be reduced by
establishing zones in which agriculture would be restricted, perhaps by replacement
of arable farming with grassland or woodland, with appropriate compensation to
farmers. The BGS studies indicate that, where grassland is to be a land use option in
plans to reduce nitrate concentrations in groundwater supply sources, restrictions on
fertilizer applications to the grassland may be required.
The discharge of groundwater contaminants to surface water is another aspect of
the relationship between groundwater and surface water. For example, sources of elevated TDS, salt, metals, or industrial chemicals may have their source in groundwater
that contains or is contaminated with these constituents. The potential for close interaction of ground and surface waters is illustrated by detections of pesticides in sam-