United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Las Vegas, NV 89193-3478
Research and Development
EPA/600/SR-93/107 September 1993
w EPA Project Summary
Case Studies in Wellhead
Protection Area
Delineation and Monitoring
Beth A. Moore
Groundwater monitoring is one of
many management options for Well-
head Protection Program implementa-
tion. Groundwater parameters are
monitored (1) to assess source-control
measures, (2) to monitor compliance
with drinking water standards at sites
other than the wellhead, and (3) to pro-
vide advance warning of contaminants
in ground water. Cooperative research
was conducted with five municipalities
to develop long-term monitoring pro-
grams for their existing wellhead pro-
tection areas. The product of this
research is a technical assistance docu-
ment which contains a methodology
for planning and implementing a well-
head protection monitoring program.
The methodology emphasizes source
assessment, correct wellhead protec-
tion area delineation, and hydrogeo-
logic characterization. Five case studies
are included in the document to exem-
plify the monitoring methodology for
different hydrogeologic and contami-
nant source settings.
The five case study research sites
include Stevens Point, Wl; Littleton, IMA;
Sioux Falls, SD; Dover, NH; and Spring-
field, MO. Three of these municipalities
obtain their drinking water from uncon-
fined aquifers; two aquifers receive sig-
nificant recharge from a nearby pond
and river. Two other case study sites
are situated in fractured-bedrock and
karst limestone aquifers. The document
emphasizes a multi-disciplinary ap-
proach for hydrogeologic characteriza-
tion, wellhead protection area
delineation, and flowpath assessment.
Hydrogeologic characterization tech-
niques include: well installation, water
quality sampling and assessment, geo-
logic and structural-control mapping,
aquifer testing, dye tracing, borehole
geophysics, analytical solutions, and
groundwater flow modeling. Long-term
monitoring programs for wellhead pro-
tection include monitoring objectives,
existing and new monitoring sites, guid-
ance for monitoring site construction
and installation, sampling protocol, op-
timal monitoring parameters and fre-
quencies, and quality assurance and
quality control considerations.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems Laboratory, Las Vegas, NV, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The increasing contaminant threat to
public water supply wells has created a
new political and technical awareness of
groundwater protection programs. Recog-
nizing the need for conjunctive manage-
ment of contaminant sources and public
water supplies to prevent, or minimize,
groundwater quality degradation, Congress
amended the Safe Drinking Water Act in
1986 to include Section 1428. This sec-
tion mandated the development of the
Wellhead Protection Program (WHPP),
which established a legal framework to
protect public water supply wells, wellfields,
and springs from contamination. An im-
portant technical element of WHPP imple-
mentation is wellhead protection area
Printed on Recycled Paper
-------
Landfill
Monitoring well
WHPA
Water well
Water table
Ground-water
contamination plume
Figure 1. Conceptual wellhead protection area and monitoring scenario.
delineation. A wellhead protection area
(WHPA) is defined as the surface and
subsurface area surrounding a well,
wellfield, or spring, through which con-
taminants may pass and reach the ground
water contributing to the supply source
(Figure 1). Criteria and methods for WHPA
delineation are given in several U.S. Envi-
ronmental Protection Agency (EPA) guid-
ance documents.
Groundwater monitoring may enhance
source characterization, WHPA delinea-
tion, and new water supply evaluation.
This technical assistance document pro-
vides information to local, state, and tribal
governments and the EPA Regions in their
implementation of WHPPs. The primary
goals of this document are to present a
monitoring methodology for WHPAs and
to exemplify this methodology in five
unique case study settings.
Wellhead Protection Area
Monitoring
In 1989, U.S. EPA's Environmental
Monitoring Systems Laboratory (EMSL) at
Las Vegas, NV, engaged in cooperative
research with five carefully selected mu-
nicipalities to develop proposed, long-term
monitoring programs for their existing
WHPAs. The product of the cooperative
research contains two types of informa-
tion:
(1) A recommended methodology for
planning and implementing a well-
head protection monitoring pro-
gram which emphasizes source
assessment, correct WHPA de-
lineation, and hydrogeologic char-
acterization.
(2) Five case" study narratives used
to exemplify the monitoring meth-
odology for different hydrogeo-
logic and contaminant source
settings (Table 1).
The monitoring methodology is intended
to serve as a guide for WHPP imp-
lementors in establishing technically de-
fensible, reliable, and effective groundwa-
ter monitoring programs for wellhead pro-
tection. This methodology emphasizes
saturated zone monitoring. The first four
case study narratives are presented in the
document in order of increasing hydro-
geologic complexity (aquifer heterogene-
ity). The exception to this organization is
the Springfield, MO, case study, which is
presented in abbreviated form in an ap-
pendix.
Basic hydrogeology concepts and equa-
tions are reviewed including: groundwa-
ter systems and flow, conceptual hydro-
geologic models and flow nets, and accu-
rate delineation and monitoring in differ-
ent hydrogeologic settings. The spectrum
of unconfined to confined aquifer condi-
tions is discussed in relation to porous,
granular aquifers; fractured-bedrock aqui-
fers; and karst aquifers.
Physical and chemical parameter moni-
toring apply to wellhead protection. Three
types of groundwater monitoring are use-
ful in managing WHPAs: ambient trend,
source assessment, and early-warning
detection monitoring. Ambient trend moni-
toring detects the temporal and spatial
trends in physical and chemical quality of
the groundwater system. Source assess-
ment monitoring evaluates the existing or
potential impacts on the physical or chemi-
cal groundwater system from a proposed,
active, or abandoned contaminant source.
Early-warning detection monitoring is con-
ducted upgradient from the wellhead,
based on known travel times, to trigger a
contingency response to prevent public
exposure to contaminants. These types of
monitoring are incorporated to measure or
detect contaminants in aquifers, and
should not be mistaken as preventative or
remedial measures.
-------
Table 1. Characteristics of the Case Study Research Sites.
Municipality
Hydrogeologic setting
Characterization tasks
Stevens Point, Wl
Littleton, MA
Sioux Falls, SD
Dover, NH
Springfield, MO
Unconfined aquifer
Unconfined aquifer, rehcarge from
Spectacle Pond
Undonfined aquifer; recharge from the
Big Sioux River
Fractured-bedrock aquifer, discrete
flow system
Mature karst (porous limestone)
aquifer, conduit flow system
Flowsystem modeledwith FLOWPATH (2-dimensional, steady
state); point and nonpoint sources assessed
Flow system modeled with FLOWPATH (2-dimensional,
steady state); MODFLOW (3-dimensional, steady state);
and FLOWCAD (2-dimensional, transient); Industrial and
commercial point sources assessed
Flow system modeled with FLOWPATH (2-dimensional,
steady state); Big Sioux River assessed as a line source;
point and nonpoint sources present
Flow system characterized with lineament analysis,
structural control mapping, aquifer testing, dye tracing, and
borehole geophysics; a few commercial, point sources,
and natural sources
Flow system determined by watershed boundaries, dye
tracing, and flow analysis; point and nonpoint sources
assessed
Source assessment is a critical first step
in designing an effective monitoring pro-
gram. Target monitoring parameters for
early-warning detection and source as-
sessment are selected from a compre-
hensive list of known and suspected con-
taminants associated with land-use activi-
ties and practices. Optimal monitoring sites
may be determined, reflecting prioritization
of sources. An inventory of common
sources of contamination within and in
proximity to WHPAs is included.
The monitoring methodology is divided
into three phases:
• Phase I: WHPP Elements and
Scoping Tasks
• Phase II: Research Monitoring Pro-
gram
• Phase III: Wellhead Protection Moni-
toring Program
Phase I WHPP elements and scoping
tasks include: designating roles and a
management framework, preliminary
WHPA delineation, and source assess-
ment. To support the research monitoring
task, an initial information base of ancil-
lary and monitoring data should be com-
piled and reviewed to determine data limi-
tations and gaps. The strategy is to maxi-
mize information content; to define moni-
toring objectives; and to conduct field stud-
ies with the least, but still adequate num-
ber of monitoring points. Existing monitor-
ing sites identified in this phase can be
incorporated in the long-term monitoring
network. Phase I generally requires a 3-
to 6-month period for completion.
Phase II is aptly named the Research
Monitoring Program, or the phase of ac-
quiring information pertaining to how the
subsurface system operates and of for-
mulating interpretations. Research moni-
toring is conducted to improve, or verify,
elements of the hydrogeologic conceptual
model. A technically defensible concep-
tual flow model ensures a more protective
and reliable monitoring program. Research
monitoring for wellhead protection includes
baseline water quality characterization,
aquifer testing and characterization, re-
fined or verified WHPA delineation, and
groundwater flowpath determination to re-
late sources to the water supply well or
spring. The product of research monitor-
ing is a proposed long-term monitoring
program that may be partly implemented
in Phase II. Phase II may require 1 to 1.5
years for completion, depending on the
complexity of the site hydrogeology and
the quality of the initial information base.
The by-product of Phases I and II is a
proposed wellhead protection monitoring
program, Phase III. Generally, the pro-
gram is submitted as a plan to be imple-
mented in stages, as labor and financial
resources become available. The plan
should include an organization chart, a
source assessment map and list, and a
map depicting the WHPA and protective
zones, as well as a description of the
delineation criteria and method(s). Gen-
eral and specific objectives for ambient
trend, source assessment, and early-warn-
ing detection monitoring should be de-
tailed. Each objective should justify the
selection of monitoring sites, parameters,
and frequencies.
The locations of existing and recom-
mended monitoring sites in the proposed
network should be shown on a map. A
formal identification system with a mini-
mum set of data elements should be used
to label each site. The integrity of the
design and construction of each existing
site should be considered prior to inclu-
sion in the monitoring network to ensure
data quality. New sites that require instal-
lation should be described in detail, con-
cerning completion depth, open or
screened interval, schematic design, and
construction materials, as well as the meth-
ods of installation, development, and test-
ing. Physical and chemical parameters to
be monitored at select frequencies should
be listed and technically justified. Monitor-
ing site information should be stored in an
automated data base for convenient and
safe storage, update, and retrieval. Each
monitoring program should formulate a
minimum set of quality assurance and con-
trol objectives to match the objectives of
the wellhead protection monitoring pro-
gram.
A 15-step approach for the design of a
wellhead protection monitoring program is
depicted as a flowchart in Figure 2. The
monitoring program should be reviewed
and improved in an iterative process over
the life span of the WHPP. The organiza-
tion of the case studies research follows
the logical outline of Phases I, II, and III.
-------
Stevens Point, Wl: Case Study
The city of Stevens Point is located in
central Wisconsin and has a population of
approximately 23,000. The source of the
city water supply is from the Airport and
Iverson wellfields. These wellfields pump
an average of 5 million gallons of water
per day from a shallow, unconfined aqui-
fer. The aquifer is composed of coarse,
unconsolidated sediments deposited by
meltwater during the Wisconsin glaciation.
The preliminary wellhead protection zones
for the combined wellfields were based on
estimates of the zone of influence, the 5-
year time-of-travel (TOT) zone (analyti-
cally determined), and the recharge area.
In the review process, the validity of the
5-year TOT calculation was questioned,
and the WHPA was never promulgated.
An extensive, historical source assess-
ment was conducted within the B Zone of
the preliminary WHPA using aerial photo-
graphic interpretation techniques combined
with conventional methods such as sur-
veys of directories, local and state records,
visual inspections, and monitoring data.
Point and nonpoint sources were identi-
fied, ranked, and prioritized for manage-
ment and regulation. Existing contaminant
sources were given highest priority. Po-
tential sources were then prioritized based
on source type, quantity, hazard, and lo-
cation.
A network of 55 monitoring sites (single
monitoring wells, well nests, and a multi-
level well) were used to measure water
levels, to sample ground water, and to
conduct aquifer tests in the unconfined
aquifer. Of the total network, three single
wells and four well nests represent new
monitoring points installed for this research.
Aquifer parameter results from slug, con-
stant-discharge, and recovery tests indi-
cate a range of hydraulic conductivity val-
ues for three distinct geologic settings:
820 to 1,700 ft per day (ft/d) for the buried
valley, 220 to 240 ft/d for outwash plains,
and 2 to 3 ft/d for bedrock highs.
Hydrochemical data indicate that nitro-
gen concentrations, a key indicator of con-
tamination, have increased over time.
Currently, nitrogen concentrations in the
monitoring network range from less than
0.2 to 26.0 mg/L Other indicators of
groundwater degradation include iron and
manganese from organic-rich soils located
along the Plover River, chloride in proxim-
ity to roads where de-icing occurs, and
previous volatile organic compound con-
tamination at the Airport and several un-
derground storage tanks.
A two-dimensional, groundwater flow
model (FLOWPATH) was used to delin-
eate the 5- and 10-year TOT zones for
the Airport and Iverson wellfields. In corn-
Monitoring
program design
Conduct source assessment
within WHPA
Determine sampling frequencies
for monitoring parameters
Compile & organize existing
information base
Assess need for new
monitoring sites
Identify deficiencies of
information base
Establish new
monitoring sites
Determine data & processing
needs for system characterization
Implement monitoring
program
Establish monitoring
objectives
Review & interpret
monitoring results
Determine monitoring
objectives
Incorporate interpretations in
characterization assessments
Identify existing monitoring
sites based on objectives
Update monitoring objectives,
network design, & program
f Iterate monitoring N
V process J
Figure 2. Flowchart of the 15-step monitoring methodology for wellhead protection areas
parison, the previous, analytically derived
B Zone is larger; however, the 5-year TOT
zone from FLOWPATH extends farther to
the east due to the effects of pumping at
the Iverson wellfield and the presence of
bedrock highs.
A long-term groundwater monitoring net-
work is proposed for the Airport and
Iverson wellfields consisting of 34 existing
and proposed wells. Nine new well loca-
tions are proposed to fill data gaps in the
existing network, primarily along the
boundaries of the 5- and 10-year TOT
zones. Wells in the long-term monitoring
network should be sampled twice a year
in April and September for indicator pa-
rameters. Water levels should be recorded
each time a well is sampled. Compliance
monitoring networks are recommended for
point sources of highest priority.
The wellhead protection contingency
plan consists of three components: (1)
reaction to the early-warning detection sys-
tem based on preventive action and state
drinking water limits, (2) spill response,
and (3) new water-supply development
and implementation.
Littleton, MA: Case Study
The town of Littleton is located approxi-
mately 35 miles northwest of Boston in
northeastern Massachusetts. The daily
water demand for the town's population of
7,300 is from 800,000 to 1,500,000 gal-
lons per day from four production wells.
Techniques for refined delineation and
long-term monitoring of the WHPA sur-
rounding Production Well Number 5 (PW-
5) are discussed. Production Well Num-
ber 5 is completed at a depth of 167 ft
4
-------
within saturated, stratified valley-fill depos-
its. The aquifer is unconfined and receives
significant surface-water recharge (20 to
25%) from nearby Spectacle Pond and
Bennetts Brook.
Land-use activities within the .WHPA
cover a range of commercial, industrial,
and to a lesser degree, agricultural opera-
tions. Collectively, these land-use activi-
ties pose potential contamination threats
to the aquifer, including heavy metals, vola-
tile organic compounds, pesticides, and
nutrients. Baseline monitoring results indi-
cate that groundwater quality within the
capture zone of PW-5 is currently unaf-
fected by source operations. Sodium is
the only exception. Slightly elevated lev-
els of sodium in surface water and the
shallow aquifer are attributed to roadway
de-icing. Manganese and iron concentra-
tions are elevated throughout the recharge
area of PW-5, primarily because of their
occurrence in wetland sediments and gla-
cial deposits. The levels of these param-
eters have increased at PW-5 for several
years and may warrant treatment in the
future.
The PW-5 WHPA consists of three pro-
tection zones delineated using a combi-
nation of numerical groundwater flow mod-
els (FLOWPATH, FLOWCAD, and
MODFLOW) and hydrogeologic mapping.
Zone I is the 400-foot sanitary protective
radius mandated by the State of Massa-
chusetts. Zone II is the most critical man-
agement area and was delineated con-
servatively as the union of three numeri-
cal capture zone solutions. These numeri-
cal solutions incorporate two- and three-
dimensional flow, as well as steady-state
and transient flow conditions. Local and
regional groundwater flow simulations are
based on the results of short- and long-
term aquifer testing.
Zone II generally represents the steady-
state capture zone for PW-5 that corre-
sponds approximately to the 400-day
travel-time contour. Flowpath simulations
indicate that Zone II extends to the bot-
tom of the aquifer and is constrained by
bedrock and glacial till. Within Zone II,
three existing wells and two new wells are
proposed for inclusion in the monitoring
network for early-warning detection and
source assessment purposes. These wells
lie along either the 150-day or the 300-
day travel-time contours. Screened inter-
vals for the new monitoring wells were
chosen based on results from MODPATH
computer flow simulations. Monitoring pa-
rameter groups for these wells include
general water quality, site-specific, and
physical parameters. Recommended moni-
toring frequencies for these parameter
groups vary from quarterly to annually,
depending on the travel-time distance from
the monitoring well to PW-5 and the moni-
toring well depth.
Zone III is defined as the upgradient
area of the aquifer that contributes to Zone
II and extends to the watershed bound-
ary. Zone III is monitored at two surface-
water locations, one at the inflow and one
at the outflow of Spectacle Pond. In addi-
tion, Zone III is monitored biannually at
existing compliance networks around
waste management and industrial sites.
Monitoring parameters for the compliance
wells include general water quality, site-
specific, and physical parameter groups.
The Littleton WHPP incorporates con-
tingency planning. Catastrophic releases
initiate a spill-response plan that involves
many departments and agencies. In the
event of contamination of PW-5 or an-
' other production well, Littleton has sited
a new production well. The proposed well
site is approved by the State, and protec-
tion Zones I, II, and III are delineated. The
adjacent town of Boxborough shares the
recharge area to the proposed well.
Boxborough has adopted complementary
strategies with Littleton to ensure its water
quality protection.
Sioux Falls, SD: Case Study
The city of Sioux Falls is located in the
southeast corner of South Dakota. The
Big Sioux aquifer is the primary source of
water for about 125,000 persons in the
Sioux Falls metropolitan area. One of the
municipal wells in the Big Sioux aquifer,
the airport wellfield, is underlain by surficial,
glacial outwash deposits. The Big Sioux
River is located directly west of the airport
wellfield and flows south over and through
the outwash, draining approximately 4,000
square miles of upstream land.
The city's wells pump most of their wa-
ter directly from the aquifer and a small
quantity from the Big Sioux River. How-
ever, the river is hydraulically connected
to the aquifer, and recharge from the river
in the airport wellfield area is significant.
In 1988, approximately 79% of the re-
charge to the airport wellfield aquifer was
induced from the river due to wells pump-
ing. Induced flow from the river to the
aquifer is demonstrated by decreased flow
in the river during low recharge periods.
This research was conducted to evalu-
ate (1) the hydraulic connection between
the Big Sioux River and the adjacent aqui-
fer, and (2) the potential impact of the
river on aquifer water quality. In the
broader perspective, additional goals in-
cluded refined delineation of the wellfield
protection area and design of a long-term
water quality monitoring program.
Drilling logs indicate that the thickness
of the aquifer in the wellfield area ranges
from 20 to 50 ft. Aquifer testing results
yield an average hydraulic conductivity
value of 800 ft/d and a transmissivity value
of approximately 21,000 ft2/d for the aqui-
fer.
Many potential point sources of con-
tamination exist in the study area. These
include: industrial and commercial areas,
the South Dakota Air National Guard facil-
ity, a petroleum pipeline, the Sioux Falls
Regional Airport, and a decommissioned
municipal landfill. The threat of contami-
nation from these sources is underscored
by the recent history of contaminant re-
leases in the area.
To estimate groundwater travel times in
the study area, aquifer testing, dye trac-
ing, and groundwater modeling were em-
ployed. During aquifer testing, two dye
injections were made. The first dye was
injected in a well approximately 40 ft north
of the pumping well. Detectable dye con-
centrations first arrived at the pumped well
after about 12 hours. The second dye
was injected in a well near the edge of the
river, approximately 140 ft north of the
pumping well. Detectable dye concentra-
tions from the second injection site first
arrived at the pumped well in 7 to 9 days.
Aquifer testing and dye-tracing results in-
dicate that a contaminant could travel from
the river to the wellfield in less than 9
days.
A two-dimensional, steady-state model
(FLOWPATH) was used to generate time-
related capture zones for the municipal
wells and to simulate contaminant travel
times. One-, two-, and five-year capture
zones were calculated for each of the
municipal wells in the airport wellfield.
Modeling of simulated spill sites from sev-
eral of the potential point-source contami-
nation areas indicates that contaminants
entering the aquifer at areas to the north
and south of the well field could reach the
municipal wells in 1 to 2 years.
The City of Sioux Falls and Minnehaha
County have delineated wellhead protec-
tion areas by using the hydrogeologic-
mapping method. Wellhead protection or-
dinances are designed to impose guide-
lines and restrictions on new land uses, or
proposed changes in existing use, in or-
der to protect the aquifer water quality.
A wellhead protection monitoring pro-
gram at the airport wellfield is proposed to
document ambient water quality conditions
and to serve as an early-warning detec-
tion system. Line-source monitoring is pro-
posed to monitor the Big Sioux aquifer
and the diversion canal for contaminants
that could potentially enter the aquifer.
Point-source and nonpoint-source moni-
-------
toring are proposed to monitor water qual-
ity between the airport wellfield and po-
tential sources. The categories of param-
eters for monitoring are general water qual-
ity, volatile organic compounds, trace met-
als, pesticides, and nutrients. Sampling
frequencies for each of the categories were
selected as a function of the type of source
to be monitored.
Contingency planning is warranted to
establish emergency responses to con-
taminant releases at the surface of the
aquifer and in the river. Alternative water
supply development must also be contin-
ued as part of the contingency planning
effort.
Dover, NH: Case Study
Dover is a city of 26,000 people located
in the seacoast region of New Hampshire.
To meet the increasing water supply de-
mands of the future, the city embarked on
a water exploration effort in a fractured-
bedrock aquifer at the Blackwater Brook
site. A test well was installed to a depth of
400 ft in the bedrock aquifer as part of the
groundwater exploration program. A well-
head protection area and groundwater
monitoring strategy were established for
the test well. This study describes how
the conceptual hydrogeologic model for
the site was developed and refined.
The bedrock aquifer consists primarily
of quartz monzonite and metasedimentary
rocks that interfinger along a fractured,
faulted contact zone trending north 60 de-
grees east (N60°E). A N5-10°W trending
lineament and fracture zone intersects the
N60°E zone at the site. The bedrock aqui-
fer Is directly overlain by Pleistocene-age
sands and gravels. These sediments are
overlain by low-permeability marine clay
and lodgement till. It is estimated that
20% of the water produced from the bed-
rock aquifer is derived from overburden
sediments in the watershed area.
Four overburden and bedrock well pairs
constitute the present monitoring network
for the test well. Two well pairs lie along
the N60°E faulted contact zone, and two
well pairs lie along the perpendicular
N30°W trend. The test well and four of
five bedrock wells airlift in excess of 150
gal/min. Few contaminant threats exist
near the site. Baseline sampling indicates
that minor, elevated levels of iron, manga-
nese, and radon pose the only water qual-
ity problems at present.
Test drilling and borehole surveys (cali-
per, video camera, acoustic televiewer,
thermal-pulse flowmeter, and hydro-
physical logging) indicate that fracturing
and groundwater flow are highly discrete.
Flow occurs at isolated, definable depths
rather than uniformly along the length of
the borehole. Hydrophysical logging indi-
cates that the borehole water is distinctly
layered with respect to the fluid electrical
conductivity parameter. Most borehole
water is produced by moderately to steeply
dipping fractures and fracture zones that
intersect the wells.
Aquifer testing and dye-trace results in-
dicate that the N30°W and N60°E direc-
tions have higher aquifer transmissivities
relative to the surrounding bedrock matrix.
Drawdown contours are elongate about
the N30°W well alignment, suggesting pre-
ferred flow in this direction. Dye-trace re-
sults indicate more rapid travel of injected
dye along the N30°W direction than the
N60°E direction. Dye traveled 152 ft in
130 minutes (the time of first arrival of the
dye) from injection in a bedrock monitor-
ing well along the N30°W trend to the test
well, which was pumped at 200 gal/min.
This represents a velocity of 1,680 ft/d.
Dye injected in a bedrock monitoring well
located 596 ft from the test well arrived
there in 148Siours, indicating a velocity of
96 ft/d along the N60°E direction.
Flowmeter and acoustic televiewer sur-
veys indicate that a moderately
west-dipping fracture zone provides inter-
connection between the test well and bed-
rock well R2 along the N30°W trend. Lack-
ing discrete flow information beyond the
test well and well R2, statistical fracture
descriptions become good approximations
of flowpaths at increasing distances from
the site. Therefore, prominent fracture
peaks along the N5-10°W and N60°E
trends represent the most probable flow
directions within the bedrock fracture sys-
tem at Blackwater Brook. The N60°E trend
is substantiated by the existence of the
faulted, fractured contact zone along this
strike. Evidence to suggest preferred flow
along the N5-10°W direction is structural
and hydrogeologic. Structural control is
inferred by strong expression of the linea-
ment on several platforms of photography
and in outcrop fracture trends. Enhanced
transmissivity along the N30°W direction
is attributed to the proximity and similar
orientation of the N5-10°W fracture zone.
A quadratic equation is derived from
accepted hydrogeologic relationships
(Darcy's Law and the Thiem equation). In
this equation, groundwater travel time (de-
termined using the time of first arrival of
dye at the test well) is directly proportional
to the square root of distance from the
test well. Constants of proportionality for
the quadratic relationship are calculated
for the N30°W and the N60°E directions
based on dye-trace velocities. Distances
for the 200-day and 1,000-day TOT thresh-
olds are then calculated for the two frac-
ture zone directions: N5-10°W and N60°E.
Three wellhead protection zones are
delineated within the recharge area for
the test well using a variety of criteria and
methods. Zone I is the state-mandated
400-foot sanitary radius. Zone IIA con-
sists of two 1,000-foot-wide "arms" along
the N5-10°W and N60°E directions, ex-
tending to the 200-day TOT distances.
Zone IIB is the area within a smooth curve
connecting the outer boundaries of Zone
IIA, producing an oval shape. Zone III is
the upgradient area contributing to the
1,000-day TOT distance modified by hy-
drogeologic features. Recommended regu-
lation of the wellhead protection zones
varies from complete control and restric-
tion of activities in Zone I to public educa-
tion in Zone III.
A major component of wellhead protec-
tion program management is long-term
groundwater monitoring. Under present
conditions, monitoring of the test well and
existing monitoring wells will focus on a
moderate effort to assess ambient water
quality and physical parameters. After the
production well is developed, the monitor-
ing frequency and list of monitoring pa-
rameters increases. Proposed frequencies,
parameters, and new sites for monitoring
derive from technical and management
goals. Action levels are proposed to trig-
ger contingency responses.
-&U.S. GOVERNMENT PRINTING OFFICE: 1993 - 7504711/80082
-------
-------
Bath A. Moore iswith Lockheed Environmental Systems & Technologies Company,
Las Vegas, NV 89119.
Steven P. Gardner Is the EPA Project Officer (see below).
The complete report, entitled "Case Studies in Wellhead Protection Area Delineation
and Monitoring," (Order No. PB93-213510AS; Cost: $61.00, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Las Vegas, NV 89193-3478
United States
Environmental Protection
Agency
Centerfor Environmental Researchlnformation
Cincinnati, OH 45268
Official Business
Penalty for Private Use $300
BULK RATE
POSTAGES FEES PAID
EPA
PERMIT NO. G-35
EPA/600/SR-93/107
------- |