United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Ada, OK 74820
Research and Development
EPA/600/SR-97/023
July 1997
of
to
Mark E. Jensen, Mike Lowe, and Michael Wireman
Methods commonly used to delineate
protection zones for water-supply wells
are often not directly applicable for
springs. This investigation focuses on
characterization of the hydrogeologic
setting using hydrogeologic mapping
methods to identify geologic and
hydrologic features that control ground-
water flow to springs to aid in delineating
protection zones. Thesetechniqueswere
applied at two public-supply springs
selected to represent diverse geologic
settings. One spring discharges from a
fractured carbonate system and one from
a clastic-rock aquifer. Results of this
investigation allowed development of the
conceptual model for site hydrology and
identification of potential constraints on
ground-water flow and protective zones
at each site. The report discusses
results from these case studies and a
general methodology for applying these
techniques to delineation of protection
zones around springs. The
hydrogeologic conceptual model
resulting from the use of these tools
provides the framework for identifying
significant data gaps and implementing
studies to obtain any additional
information required for reliable and
practicable protection zone delineation.
This Project Summary was developed
by EPA's National Risk Management
Research Laboratory's Subsurface
Protection and Remediation Division,
Ada, OK, to announce key findings of the
research projectthat is fully documented
in a separate report of the same title (see
Project Report ordering information at
back).
Introduction
In the United States, over 3400 public
water-supply systems obtain part or all of
their drinking water from springs. These
systems provide water for more than seven
million people. One of the six critical
elements of a wellhead protection program
is delineation of a scientifically valid
protection zone around public water-supply
wells and springs. Hydrogeologic mapping
may be used at many sites to identify
geologic and hydrologic controls on ground-
water flow to springs and to locate flow
boundaries. Protection zones may be
specified based on flow boundaries at sites
where the zone of contribution to the spring
is practicable to protect.
Hydrogeologic mapping, as applied in
this project, refers predominantly to geologic,
hydrologic, geochemical, and geophysical
techniques for characterizing subsurface
features using the surface expression and
geophysical or geochemical signatures of
such features. These techniques include:
« fracture-trace analysis,
« analysis of land surface topography,
« geologic mapping,
« potentiometric surface mapping,
• geophysical surveys,
• tracer studies,
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• stable and radioactive isotope studies,
and
• geochemical characterization.
Objective Methodology
The objective of this cooperative research
project was to investigate the use of
hydrogeologic mapping to determine the
zones of contribution to two springs and
application of this information to delineation
of potential protection zones at the field
sites. Hydrogeologic mapping was chosen
as the primary focus forthis project because
of its applicability as an initial
characterization step in many settings that
include strongly anisotropic aquifers, such
as fractured bedrock. Additional
considerations included the relatively low
cost and low technological requirements of
many of these tools.
The methodology applied in this study
integrated information from multiple
hydrogeologic mapping methods. An initial
conceptual model for each site was
developed through review of site-specific
literature, principally, documents obtained
from state and federal agencies and local
universities. Based on this model, potential
ground-water flow controls were identified.
Applicable hydrogeologic mapping methods
were chosen to test assumptions of the
conceptual model and delineate geologic
and hydrologic controls. Results from these
studies were used to locate potential ground-
water flow boundaries defining the zones of
contribution to the springs and evaluate the
effects of potential controls. The results
were then evaluated for use in delineating
potential protection zones. Monitoring wells
were installed at each site to provide litholog-
ic/stratigraphic information and allow limited
hydraulic testing. Results of these
subsurface investigations were compared
with information inferred from the
hydrogeologic mapping.
The objective of this report is to evaluate
the utility and limitations of the hydrogeologic
mapping studies performed at these sites
for delineating the zones of contribution and
protection zones around the springs. A
general methodologyforapplying such basic
characterization techniques is also
discussed. The report is designed to aid
investigators involved in planning
characterization studies leading to the
establishment of protection zones around
springs.
Results and Discussion
Two study sites were chosen to represent
different geologic settings for springs:
fractured carbonate aquifers and clastic-
rock aquifers. Hydrogeologic mapping
methods applied at these sites included
geologic mapping (stratigraphic and structur-
al), topographic analysis, fracture-trace
analysis, geochemical characterization,
isotope studies, and catchment area
estimation. Geologic mapping, fracture trace
analysis, and topographic analysis were
applied in an attempt to infer the extent of
aquifers, identify lithologic units that may
act as flow boundaries or pathways, map
joint patterns or karst features that may act
as flow paths, identify faults that may act as
flow barriers or flow paths, and identify
potential recharge areas. Analyses of
ground-water chemistry and tritium activity
were used to inferaquiferlithology, potential
seasonal fluctuations in ground-water flow
paths, and relative ground-water residence
times. Estimates of the required catchment
area were calculated from spring discharge
measurements and potential recharge
estimates for comparison with other
estimates of the zone of contribution.
Carbonate Aquifer
Olsens Spring, located in Mantua Valley
in the Wasatch Range of northern Utah,
discharges about 1,700 l/min (1.0 ft3/s) from
jointed Cambrian dolomite. West Hallings
Spring, which discharges about 6,400 l/min
(3.8 fP/s) from a faulted limestone, is located
approximately 275 m (900 ft) southwest of
Olsens Spring within the same surface
drainage basin. These springs are a source
of potable water for Brigham City, which has
a population of about 17,000. The area
surrounding the springs is mostly hilly and
mountainous, underlain by a Paleozoic-age
stratigraphic section of interbedded
limestone, dolomite, shale, and quartzite
that has been tilted, faulted, and fractured
by thrust faulting and normal faulting. This
study focused on Olsens Spring. However,
West Hallings Spring and other springs in
Mantua Valley were considered during these
investigations, as appropriate.
Geologic mapping was conducted
throughout the surface drainage basin
surrounding West Hallings Spring and
Olsens Spring following analysis of fracture
traces and lineaments visible in aerial photo-
graphs. No faults were mapped in the
immediate area of Olsens Spring. However,
West Hallings Spring did appear to be
located on afault. Ground-waterflowtothis
spring may be influenced by this feature.
Extensive north to northeast trending joints
were observed in outcrops throughout the
area indicating that ground-water flow may
be predominantly controlled by secondary
porosity, transmissivity may be relatively
high, and that the area surrounding the
spring may be vulnerable to contamination
from surface sources. No karst features
were observed during the geologic mapping.
Based on these results, no geologic units
sufficiently competent to behave as
boundaries to ground-water flow could be
identified.
Monthly analyses of physical/chemical
parameters (i.e., temperature, pH, specific
conductance, and turbidity) in water from
Olsens Spring revealed no significant
fluctuations and very low turbidity during a
one year period. This indicates ground-
water residence time was sufficient to mask
any variations due to seasonal variation in
recharge. Quarterly analyses of major ions
were used to determine hydrochemical
facies, mineral saturation indices, and
calcium/magnesium molar ratios. No
significant shifts in hydrochemical facies
that could be related to temporal fluctuations
in ground-water flow paths were observed.
Calcium/magnesium molar ratios were
stable and indicated ground-water flow
through formations composed largely of
dolomite. Calcite saturation indices were
generally positive, indicating sufficient
residence time for saturation to occur. A
potential temporal trend in the calcite
saturation index suggested a possible
seasonal variation in saturation that may be
related to decreases in residence time
associated with increased recharge.
Analyses of tritium activity indicated the
average ground-water age was less than
approximately 40 years and, potentially,
less than 20 years.
Estimates of the catchment area required
to support the combined discharge from
Olsens Spring and West Hallings Spring
ranged from 10 km2 (4 mi2) to 54 km2 (21 mi2).
The upper limit of this range is significantly
largerthan the area of the surface drainage
basin (approximately 17 km2 [6.5 mi2]),
indicating that the zone of contribution to
these springs may be greater than the
drainage basin. However, there is significant
uncertainty in estimation of the catchment
area.
In order to obtain direct information
concerning subsurface conditions and initial
estimates of hydraulic parameters, two
monitoring wells were installed topographi-
cally upgradient of Olsens Spring. Short-
term, single-well pumping tests were
conducted to obtain preliminary estimates
of transmissivity nearthe wells. Transmiss-
ivity estimated from these tests ranged from
270 m2/d (2900 ft2/d)to 550 m2/d (5900 ft2/d),
supporting the conceptual model of a
relatively transmissive aquifer near the
springs. Results of a tracer study also
indicated that ground-water velocity near
the springs was relatively high.
These data appear to support the
hydrogeologic conceptual model of a system
that may be dominated by flow through
interconnected fractures. However,
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additional studies would be required to better
define potential conduit flow components.
The evidence forthis model includes highly
fractured bedrock units, stable field
parameters, relatively stable water
chemistry, very low turbidity, and relatively
young ground water. As indicated by
hydrogeologic mapping and in situ studies,
transmissivity and ground-water velocity
near the springs appear to be relatively
high. Significant anisotropy may exist due
to the dominant north to northeast trending
fractures.
Although potential controls on ground-
water flow were identified, definite flow
boundaries were not located using
hydrogeologic mapping techniques. The
minimum zone of contribution to Olsens
Spring and West Mailings Spring was
estimated to be the surface drainage basin.
The shallow flow system within the basin
may potentially be bounded by ground-water
flow divides coincident with the topographic
divides. However, the zone of contribution
for these springs may be larger than the
surrounding surface drainage basin. These
data suggest that possible protection zones
around these springs should encompass
the entire surface drainage basin and may
extend beyond the basin boundaries.
Additional studies, potentially including
installation of a piezometric network and
extensive aquifertesting, would be required
to better define the zone of contribution and
more reliable protection zones around these
springs.
Clastic-Rock Aquifer
Sheep Spring is located in southwestern
Utah and discharges 7.5 l/min (2 gal/min)
from interbedded siltstone, sandstone, and
shale. This spring is part of the Santa Clara
city water system, which serves about 1520
people, and is representative of many low-
flowrate springs used for drinking water in
this area. Inflow to the collection tunnel
appears to discharge from a sandstone
layer approximately 0.5 m (1.5 ft) thick and
from joints in units below this layer. The
sandstone layer consists of very fine- to
fine-grained silty sandstone and interbed-
ded siltstone. Ground water discharges
both from joints and pore spaces in the
sandstone matrix. This layer appears to be
transmitting much of the ground water to
Sheep Spring. Minor seeps, other small
springs, and vegetation are localized near
outcrops of this unit.
Based on topography and review of
previous regional studies, the zone of
contribution extends north of Sheep Spring.
Thetopographicdrainage divide, which may
coincide with a ground-water flow divide
forming a hydrologic boundary to flow, is
approximately 24 km (15 mi) north of the
spring. An analysis of fracture traces from
aerial photographs was conducted prior to
detailed geologic mapping of an area of
about 4.5 km2 (1.75 mi2) within the potential
zone of contribution to Sheep Spring.
Although significant, individual fracture
traces were not observed near the spring;
aerial photographs indicated a pervasive
north-trending fracture system exists in this
area. The bedrock is highlyjointed at Sheep
Spring and throughout the zone of contribu-
tion. The joints strike approximately north
and dip steeply to the east and west. These
data indicate that ground water may be
vulnerable to surface contamination sources
with fractures serving as pathways for rapid
transport to the aquifer. The system may
also be highly anisotropic due to the
predominant north-trending joint orientation.
A seasonal variation in water tempera-
ture of approximately 4.5° C (8.1° F), which
appears to be related to air temperature,
was observed during monthly analysis of
physical/chemical parameters in waterfrom
Sheep Spring. Other physical/chemical field
parameters, including discharge rate, did
not vary significantly. Water from the spring
is a calcium-sulfate type ground water
without significant seasonal variation to
indicate fluctuations in ground-water flow
paths. Average ground-water residence
time based on analysis of tritium activity
probably was greater than 40 years.
Constant discharge rate, relatively constant
physical and geochemical parameters, and
the relatively low tritium activity are
indications that ground water discharging at
Sheep Spring may have a relatively long
residence time.
Three monitoring wells were installed
about 26 m (85 ft) north of the Sheep Spring
collection tunnel. Two of the wells were
cored through the sandstone layer identified
during the surface mapping to provide strati-
graphic control and obtain a sample for
porosity measurements. Hydraulic
conductivity of the formation estimated from
rising head slug tests ranged from about
0.04 m/d (0.1 ft/d) to 0.2 m/d (0.6 ft/d). A
study conducted by previous investigators
estimated a hydraulic conductivity of 0.3 m/d
(1 ft/d) based on aquifer characteristics of
the same formation and the specific capacity
of a well located approximately 4 km (2.5 mi)
from Sheep Spring. Results from this study
and the previous work indicated hydraulic
conductivity in this formation may be relative-
ly low. However, more extensive testing
would be required to better define hydraulic
parameters and potential anisotropy at the
site.
The hydrogeologic conceptual model
developed from these studies is one of a
spring discharging from a fractured clastic-
rock aquifer of low hydraulic conductivity
with ground water moving through both
primary and secondary porosity. The system
may be highly anisotropic with preferential
flow along the north-trending joints. Sheep
Spring appears to be a local discharge point
with a potentially large zone of contribution
for ground water with a moderate to long
residence time.
This information was evaluated for use in
delineation of potential protection zones
around the spring. Ground-water flow
boundaries near the spring could not be
inferred from these studies. Hydrogeologic
mapping indicated that the distance to the
hydraulically upgradient limit of the potential
zone of contribution was approximately
24 km (15 mi) based on analysis of land
surface topography. However, a relatively
low ground-water seepage velocity may limit
the zone of contribution within specified
time periods to a much smaller area.
Protection zones that cover the entire zone
of contribution may be too large to be
effectively managed by the water supplier.
Other approaches (e.g., ground-watertime-
of~travel estimates) may be useful in refining
the size of the protection zones. For
example, using the limited hydraulic data
that are available, ground water discharging
at the spring may have traveled less than
approximately 660 m (2200 ft) within a
15-yeartime frame. Additional studies would
be required to delineate reliable protection
zones based on such techniques.
Conclusions
Recommendations
Hydrogeologic mapping provided
information on aquifer characteristics
including aquifer lithology, vulnerability to
surface sources of contamination,
boundaries on average ground-water
residence times, transmissivity, potential
recharge area, and potential geologic/
hydrologic controls on ground-water flow.
Specific findings and recommendations from
these studies are:
1. Hydrogeologic mapping techniques are
relatively low cost characterization
tools. These methods commonly will
provide information essential for
conceptual model development,
planning subsurface investigations, and
defining protection zones based on
ground-water flow boundaries. It is
recommended that the utility of such
techniques be evaluated early in all
spring protection zone delineation
projects.
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2. Development of a conceptual model
for site hydrogeology is an essential
element in the delineation process. The
model serves as the focus for
characterization efforts, allowing
important assumptions and potential
ground-water flow controls to be
identified and studied.
3. Applicable hydrogeologic mapping
techniques depend on site conditions
and the information gaps that are
identified. Availabletechniques include
geologic, hydrologic, geophysical, and
geochemical characterization tools.
Mapping of the ground-water flow
system using potentiometric information
is an extremely powerful tool that should
be used whenever data are obtainable.
4. Ground-water flow boundaries that may
serve as boundaries of practicable
protection zones around springs may
not be definable using only
hydrogeologic mapping techniques.
Incorporation of additional delineation
tools, such as ground-water time-of-
travel estimation, and performance of
detailed subsurface investigations may
be required to define more reliable and
manageable protection zones at some
sites.
Mark E. Jensen is with the Utah Department of Environmental Quality, Salt Lake City, UT
84114-4830; Mike Lowe is with the Utah Geological Survey, Salt Lake City, UT 84109-1491;
and Michael Wireman is with the U.S. EPA, Denver, CO 80202-2405.
Steven D, Acree is the EPA Project Officer (see below).
The complete report, entitled "Investigation of Hydrogeologic Mapping to Delineate Protection
Zones Around Springs Report of Two Case Studies," ( Order No. XXXX-X; Cost: $X.OO,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4850
The EPA Project Officer can be contacted at:
U.S. Environmental Protection Agency
National Risk Management Research Laboratory
Subsurface Protection and Remediation Division
P.O. Box 1198
Ada, OK 74820
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