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OTHER EFFORTS IN PROGRESS
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REGIONAL ASSISTANCE FOR STATE PROGRAM DEVELOPMENT
NATIONAL WELLHEAD CONFERENCE
(NEW ORLEANS, LOUISIANA - DECEMBER 1988)
OVERVIEW OF W.H.P. MANAGEMENT STRATEGIES
OVERVIEW OF CONTAMINATION SOURCES; FOCUS ON LIGHT
INDUSTRY
RISK ASSESSMENT AND MANAGEMENT IN W.H.P.
APPROACHES FOR FINANCING W.H.P. IMPLEMENTATION
CONTINGENCY PLANS; T.A.D. AND PILOT PROJECTS
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1. INTRODUCTION
1.1 BACKGROUND
The Amendments to the Safe Drinking Water Act (SDWA), passed
in June 1986, established the first nationwide program to
protect ground-water resources used for public water supplies
from a wide range of potential threats. The SDWA seeks to
accomplish this goal through the establishment of State
Wellhead Protection (WHP) Programs which "protect wellhead
areas within their jurisdiction from contaminants which may
have any adverse effect on the health of persons."
One of the major WHP elements is the determination of zones
within which contaminant source assessment and management
will be addressed. These zones, called Wellhead Protection
Areas (WHPAs), are defined in the SDWA as "the surface and
subsurface area surrounding a water well or wellfield,
supplying a public water system, through which contaminants
are reasonably likely to move toward and reach such water
well or wellfield." Hence, the law establishes the concept
of protecting a portion of the recharge areas to these points
of public drinking-water withdrawal. States are given
flexibility in determining appropriate approaches to WHPA
delineation, and the Environmental Protection Agency (EPA),
Office of Ground Water Protection (OGWP) has prepared
technical guidelines to assist on the hydrogeologic aspects
of this task in the publication of "Guidelines for Delinea-
tion of Wellhead Protection Areas", June 1987. Additional
guidance is available with respect to funding and implementa-
tion of a WHPA in the following OGWP's guidelines:
"Guidelines for Applicants for State Wellhead Protection
Program Assistance Funds Under the Safe Drinking Water
Act" (EPA, 1987b)
"Surface Geophysical Techniques for Aquifer and Wellhead
Protection Delineation" (EPA, 1987c)
"Model Assessment for Delineating Wellhead Protection
Areas" (EPA, 1988d)
This manual was prepared to accompany the Wellhead Protection
Area Delineation Training Course presented by the OGWP at
regional centers during the period August to November 1988.
It is the intent of this course to provide participants with
an introduction to the criteria and methods used in delineat-
ing WHPAs as well as the background in ground-water flow
fundamentals required to apply those methods correctly. The
1-1
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lecture material is supplemented with simple problem
exercises that demonstrate the mechanics of the various
methods and case studies that summarize actual WHPA delinea-
tion projects.
The tutorial sections of the manual are written in a style
that falls between the terse outline or "bullet" format used
in presentation slides and the in-depth explanations found in
most textbooks. The idea is to convey, in one- or two-
sentence paragraphs, the important concepts, points, and
issues concerning a topic. The readers can move quickly
through a topic identifying those points with which they are
familiar, as well as those which are new and may require
further investigation. A list of references is provided at
the end of the manual (Appendix A) to direct the readers to
available research materials.
Copies of the slides used in each lecture are included at the
end of each section to allow participants to easily follow
each lecture. These figures also serve to illustrate topics
discussed in the body of the text and are referenced by slide
number in the section to which they pertain.
Additional copies of this training document are available by
contacting:
Office of Ground-Water Protection
U.S. Environmental Protection Agency
Washington, DC 20460
1.2 TRAINING COURSE OBJECTIVES
Wellhead Protection Area (WHPA) delineation is based on an
analysis of criteria, such as radial distance, drawdown
caused by pumpage, ground-water travel time, flow boundaries,
or assimilative capacity in the zone surrounding the well.
The criteria and thresholds define the general technical
basis of the WHPA, and delineation methods are subsequently
used to translate or apply these criteria to develop
on-the-ground or on-the-map WHPA boundaries.
The Wellhead Protection Area Delineation Training Course was
designed for those involved in delineating WHPAs or in
reviewing proposed delineations. The course presents the
fundamentals of ground-water flow, well hydraulics, and
contaminant transport to provide the necessary technical
background for the delineation process. It also covers
1-2
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aspects of the WHP program pertaining to wellhead nomencla-
ture, delineation criteria and delineation methods. Hands-on
exercise have been developed to lead participants through the
mechanics of applying each method. To foster an appreciation
for some of the complexities that can be encountered in "real
world" situations, case studies are presented for a variety
of different hydrogeologic settings. Case studies are also
used as a basis for comparing the delineation areas produced
by several different methods at a single site.
The WHPA Delineation Training Course was designed to
meet the following objectives:
Introduce the criteria and methods recommended in EPA
guidelines for delineating WHPAs,
Develop a practical understanding through instruc-
tion, examples, case studies, and hands-on exercises
of the methods used to translate delineation criteria
to on-the-map WHPAS,
Introduce and evaluate various analytical and
numerical tools available to implement delineation
methods
1-3
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2. Fundamentals
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PRESENTATION SLIDES
FUNDAMENTALS OF GROUND-WATER FLOW
Slide 2.01
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BERNOULLI'S RELATIONSHIP
where: h = hydraulic head
Z = elevation head
P — pressure head
'•!•'"
•'
I Oi •
surement -"T^
•
V
- .
•:' t '
: P
h
Z
I
-
I
i
Ground surface
Datum (usually sea level):
z = 0
Slide 2.02
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WELL
/
X
/
X
/
/
SCREEN ZONE
LINE OF
EQUAL HEAD
Water levels in wells controlled by hydraulic head
at the screen zone (after Fetter, 1980).
Slide 2.03
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WATER TABLE
~ Q.I
DIRECTION OF FLOW
Slide 2.04
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Sand and Gravel
PORE SPACES
Consolidated Rock
FRACTURE
FAULT
Carbonate Rock
SOLUTION
CHANNEL
Volcanic Rock
SHRINKAGE
CRACKS
CHANNEL
Rock texture in major aquifer types (Walton, 1970).
Slide 2.05
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WATER
IN (Q)
FLOW
AREA
(A)
HYDRAULIC
GRADIENT (I)
n
HYDRAULIC CONDUCTIVITY
OF SAND (K)
LENGTH
WATER
OUT (Q)
OL
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05
Q = KIA
Pore
Water
Velocity
Ki
porosity
-------
A
SURFACE WATER
B
GROUND WATER
A.
B.
Flow paths of molecules of water in turbulent flow.
Flow paths of molecules of water in lanunar flow.
(Fetter, 1980)
Slide 2.07
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100
Flow Velocity Ranges
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Flow Velocities (cm/sec
0.1
001
Conduit Flow Karst
Diffuse Flow Karst
Sandstone (fractured and jointed)
Volcanic Basalts (fractured and jointed)
Fractured Metamorphic
Gravels and Conglomerates
Alluvial Sand and Gravel
Unconsolidated Sands
Consolidated Sandstones
Saprolite
Glacial Till
0.001
00001 0.00001
10"6
LEGEND:
Measured data point reported in literature
Velocity ranges reported in literature
— — — — Extrapolated velocity range interpreted from literature
SOURCE After Everett. 1987
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TRANSMISSIVITY
T = K b
b = aquifer thickness
3H5et&J2oDiiruog3J§gb
• r — discharge that occurs through
unit width and aquifer height b
under a hydraulic gradient of 1
K — discharge that occurs
through unit cross section
1 ft square under a
hydraulic gradient of 1
(Source: Driscoll, 1986)
Slide 2.09
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Ground-water Flow System (Stream
Valley) Under Natural Conditions
..G round-water
Divide
L
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REGIONAL
DISCHARGE
AREA
LOCAL
RECHARGE
AREA LOCAL
DISCHARGE
AREA
REGIONAL
RECHARGE
AREA
REGl
Ground-water flow pattern in a homogeneous isotropic
aquifer with moderate relief.
Slide 2.11
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ro
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02S
o.i s
WSCHARGE TO
REGIONAL STREAM
AND WETLANDS
DISCHARGE TO
GAINING STREAMS
0.1 S 0.2 S "0.3 S 0.4 S 0.5 S 0.6 S 0.7 S 0.8 S 0.9 S S
CO
0.2 S
0.1 S
REGIONAL STREAM
AND WETLANDS
0 0.1 S 0.2S " 0.3S 0.4S 0.5S 0.6S 0.7S 0.8S 0.9S S
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MONITORING WELLS
POTENTIOMETRIC
SURFACE
WELL
SCREEN
Relationships within the hydrologic system.
Slide 2.13
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Confined Aquifer with Upward Leakage
Abandoned or Inadequately
Cased or Cemented Wells '
Water Production Well
Potentiometric
Surface
-_— Confining
i-: unit ,
;-£3 lAciuitard_l
•• Confined
o- Aquifer
«••.•••. .-r.-V' -•••.•?•:' .'
.••"..*•' V^T^^T""*.*-• »*0'f'*-
^-^<:;2±
' * '
Direction of Ground-water Flow
Slide 2.14
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Confined Aquifer with Downward Leakage
Abandoned or Inadequately
Cased or Cemented Well
Water Production Well
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% Uncorif inediS Wate
1 Aquifer tj Tabl
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v?)vS;;S^«:::f:Sy?S:^ Poten
SSP£8&££ Surf a
_- Confmmq i_-
-I Unit
— - J Aqtiitard I_ r;-:
•• Aquifer _ _^'
Direction of Ground-water Flow
Slide 2.15
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PRESENTATION SLIDES
FUNDAMENTALS OF CONTAMINANT TRANSPORT
Slide 2.16
-------
DIRECT INTRODUCTION OF CONTAMINANTS IN THE
IMMEDIATE WELL AREA
MICROBIAL CONTAMINANTS
CHEMICAL CONTAMINANTS
Slide 2.17
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OPERATIONS WITH POTENTIAL THREAT
TO GROUND WATER
GAS STATIONS/SERVICE STATIONS, TRUCK TERMINALS
OIL PIPELINES
SNOW DUMPS, RAILROAD YARDS, GRAVEYARDS,
STORMWATER IMPOUNDMENT SITES
INDUSTRIAL MANUFACTURERS: CHEMICALS, PESTICIDES/
HERBICIDES, PAPER, LEATHER PRODUCTS, TEXTILES,
RUBBER, PLASTIC/FIBERGLASS, SILICONE/GLASS,
ELECTRICAL EQUIPMENT, PHARMACEUTICALS
SINGLE-FAMILY SEPTIC SYSTEMS
AGRICULTURAL PESTICIDE/HERBICIDE/FERTILIZER USE
Slide 2.18
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UNSATURATED AND SATURATED ZONES
WATER
TABLE
GROUND SURFACE
SOIL MOISTURE
PORE SPACES PARTIALLY
FILLED WITH WATER
CAPILLARY RISE
FROM WATER TABLE
GROUND WATER
(after Edward E. Johnson, Inc., 1966)
Slide 2.19
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CONTAMINANT TRANSPORT IN
FLOWING GROUND WATER
CONTAMINANT
SAND GRAINS
DIRECTION OF
GRetJND-WATER FLOW
A-T /
»
(Freeze and Cherry, 1979)
Slide 2.20
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ADVECTION
Advection = transport by flowing ground water
Contaminant moves at rate of ground-water flow;
sharp concentration front; no spreading
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0
Plug Flow
Distance
Slide 2.21
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DISPERSION
DISPERSION = spreading of contaminant plume
Dispersion due to mixing and diffusion spreads
contaminants as they are advected;
sharp concentration front is smeared
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Ground-Water Flow
Distance
/
Plug Flow
/
Dispersed
Front
*c« r>
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Slide 2.22
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Hydrodynamic Dispersion j
Hvdrodvnamic Dispersion
Qf -two Processes:
Mechanical Dispersion and Molecular Diffusion
= DIJ * Dd
D i - Mechanical Dispersion (mixing)
D, = a v
, ,,
a ij - Dispersivity
V |j - Pore Water Velocity
- Molecular Diffusion
Dd = DoT
• '
Do - Free Water Diffusivity
T -Tortuosity (IW«- <
port at
( *rJ**
1<,**J
to
Slide 2.23
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Plume Formation for Continuous
and Instantaneous Point Sources
Uniform flow
Continuous
point source
of Tracer
(a)
Uniform flow
Instantaneous
point source
(b)
(Freeze and Cherry, 1979)
Slide 2.24
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Scale-Dependence of Hydrodynamic Dispersion
AVERAGE FLOW
(from Skibitzkie and Robinson, 1963)
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Q_
5
Q
Z)
O
SAND,GRAVEL,
SANDSTONE
LIMESTONE, BASALT,
GRANITE a SCHIST
I 10 IOO IOOO
DISTANCE (m)
Slide 2.25
(from Lallemand-Barres and Peaudecerf, 1978)
-------
PETROLEUM PRODUCT REACHING GROUND WATER
RECHARGE
OIL PHASE
(Oil body)
VAPOR
ZONE
UNSATURATED ZONE
WATER TABLE
.CAPILLARY
FRINGE
SATURATED ZONE
O)
(after Schwl lie, 1975)
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EFFECTS OF DENSITY ON MIGRATION OF CONTAMINANTS
ro
ro
SOURCE OF PRODUCT
( Greater density than water
SOURCE OF PRODUCT
( Lesser dentity than water )
DIRECTION OF
GROUND-WATER FLOW
FLOW OF DISSOLVED PRODUCT
CONFINING BED
-------
PREDICTING CONTAMINANT MIGRATION
ACCURATELY PREDICTING TRANSPORT OF DISSOLVED
CONTAMINANTS IS DIFFICULT:
Discontinuous discharges may produce "slugs" of
contaminated water, causing wide spatial and
temporal variations in water quality
Geochemical reactions between the contaminants and
geologic materials can also cause wide fluctuations
in concentration
Computer modeling of contaminant transport processes
is not as reliable as ground-water flow modeling due
to greater complexities and uncertainties involved
THE PROBLEM BECOMES EVEN MORE DIFFICULT FOR
CASES INVOLVING:
Non-Aqueous Phase Fluids
Density-Dependent Flow
Degrading or Highly-Reactive Constituents
Transport in Fractured-Rock Aquifers
Slide 2.28
-------
PRESENTATION SLIDES
FUNDAMENTALS OF WELL HYDRAULICS
Slide 2.29
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SOURCE
PUMPING
WELL
LOW PERMEABILITY FORMATION
Pumpage reversing gradients under a river
SURFACE
Slide 2.30
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CONE OF DEPRESSION
Land surface
Cone of
depression
v
Unconfined
Limits of cone
Of depression
Land surface
Flow lines
aquifer
Confining bed
Pottnt lomttric turfoc*
'" Q """""""
Drawdown
\
Confining bed
X/VXXX XX
Confined aquifer
Cone of
depression
I r t i i >>>>>>>)/;
Confining bed
s//s
cL
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(Source: Heath, 1983)
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Terminology for Wellhead Protection
Area Delineation (Hypothetical
Pumping Well in Porous Media)
GROUNDWATER
DIVIDE
(B) PLAN VIEW
LEGEND:
V Water table
» Ground-water Flow Direction
• Pumping Well
ZOI Zone of Influence
zoc Zone of Contribution
PREPUMPING
WATER LEVEL
CONE OF
DEPRESSION
A VERTICAL PROFILE
-" DRAWDOWN
CONTOURS
NOT TO SCALE
Slide 2.32
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DARCY'S LAW IN RADIAL DIMENSIONS
where:
substituting:
Q = K I A
A = 2-rrrb (area of cylinder)
I = dh
dr
Q = 2TtrbK dh
dr
Slide 2.33
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EQUILIBRIUM FLOW TO A WELL
IN A CONFINED AQUIFER
Land surface
Original piezometric surface
\
Cone of depression
Confined aquifer
^mm/MMMMMmm^^^
where: h1 = hydraulic head at point nearest the well
= hydraulic head at point further from well
= discharge
= hydraulic conductivity
= aquifer thickness
= distance from well to point of h1
= distance from well to point of h2
M
h2
Q
K
b
Slide 2.34
-------
EQUILIBRIUM FLOW EQUATION
dh= Q dr
2*bK r
/*ha A
I dh = Q /dr
x 1 i_ Ix • " "~
h 2;rbK y r
In _r2
r,
where: h1 = hydraulic head at point nearest the well
h2 = hydraulic head at point further from well
= discharge
K = hydraulic conductivity
b = aquifer thickness
r, = distance from well to point of h1
r2 = distance from well to point of h2 ^
v"
Slide 2.35
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THIEM EQUATION
CONFINED
528 Q (log r,/r,)
bK
UNCONFINED
= 1055 Q (log r,/ri)
K
Slide 2.36
-------
DISTANCE DRAWDOWN RELATIONSHIP
Drawdown In feet
O o 00 OJ •*" tO O
/
r
s
s
\
/
X
ll
h
Con
. - IV —
r2
X
h
- i
Illl ,
eof
s*^
-'3-
1
dep
X
x
re
/*•
s
slonv
r»j^
^ i
h,
' ^
X
->
x^
x
x
x
s
™
i \
h3
, ,
10 100
Distance In feet from discharging well
1000
(Source: Heath, 1983)
Slide 2.37
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NON-EQUILIBRIUM FLOW EQUATION
i — - —
(THEIS EQUATION)
s = 114.6Q W(u)
T
u= 1.87 i*S
Tt TKt
r ;*
s = DRAWDOWN (feet)
Q= PUMPING RATE (gpm)
T= TRANSMISSIVITY (g
S = STORAGE COEFFICIENT
r = DISTANCE FROM PUMPED WELL TO
OBSERVATION WELL (ft)
= TIME (days)
W(u)= WELL FUNCTION (APPENDIX C)
Slide 2.38
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0
£0
c
1 10
^
2
0
20
0
g
c
o 10
1
2
0
20
U- Radius = ->-
(A) | 18,000 ft (5,490m)
~iivi3!:tss^' x ' K ' FTT'-" ••'^iii&i-*—
^^Hwi/Y •+£^^
^ ^^ Transmissivity = 10,000 gpd/ft (124 m'/day)
> (/
.
i
s = 22 ft (6.7m) >-»
k — Radius = 40,000 ft (12,200 m) >•
(B) |
s = 2.5 ft (0.8m) >-V
Transmissivity = 100,000 gpd/ft (1,240 m'/day)
-
*» f°
^,«,»<*
fAJ** /
«**'**'W!
^ -*^
lAc. /
or^
L. ^r*^
jV
Effect of different coefficients of transmissivity on the shape, depth, and extent of the cone
of depression. Pumping rate and other factors are constant. (Source: Driscoll 1986)
CO
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RECHARGE BOUNDARY - PLAN VIEW
Recharge boundary
Resultant
cone or
depression
Recharge
cone
(Source: Heath, 1983)
Slide 2.40
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IMPERMEABLE BOUNDARY - PLAN VIEW
1 I /
Equipotentiol line
/\
X
\
_ _/_. _L I .<_ ' «
•^6'J ' '
' . Image ^V ^VSL /
-I«l« /^t^7^' /
V »' \
« >\ / ^,
/ il
El 1 V' Nx 7
^ T "\ / x
e; v x
(Source: Heath, 1983)
Slide 2.41
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Well Interference
well
A
well
B
Cone of
depression with
well A pumping
Static Potentiometnc surface
-~ Cone of
depression if well B were
pumping and well A were idle
Confined aquifer
Cone of
depression with both
well A and B pumping
(Source: Heath, 1983)
Slide 2.42
-------
PRESENTATION SLIDES
FUNDAMENTAL CONCEPTS EXERCISE
Slide 2.43
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FUNDAMENTAL CONCEPTS EXERCISE
WATER-SUPPLY WELL SCREENED IN SHALLOW CONFINED
AQUIFER
TRANSMISSIVITY = 1 0,000 GALLONS PER DAY PER FOOT
• STORAGE COEFFICIENT =.0001
PUMPING RATE = 200 GALLONS PER MINUTE
••
Slide 2.44
-------
EXERCISES :
USING THE THEIS EQUATION, ESTIMATE DRAWDOWN
OBSERVED AT 100 FEET AND 1000 FEET AFTER 100
DAYS OF PUMPING
NOTE:
CALCULATE u AND DETERMINE W(u) USING THE
WELL FUNCTION TABLE IN APPENDIX C
) PLOT THESE DRAWDOWN POINTS (DRAWDOWN ON
VERTICAL, ARITHMETIC SCALE) VS. DISTANCE TO
PUMPING WELL ON SEMILOG GRAPH PAPER
WHAT IS THE RADIUS OF THE ZONE OF INFLUENCE ?
4) AT WHAT RADIUS IS A 1 FOOT DRAWDOWN OBSERVED ?
Slide 2.45
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2. REVIEW OF FUNDAMENTAL CONCEPTS
2.1 GROUND-WATER FLOW
Bernoulli, in 1738, developed the fundamental relationship
for describing ground-water energy levels (Slide 2.2).
h = Z + P
where:
h = hydraulic head
Z = elevation head
P = pressure head
Ground water moves from a position of high hydraulic head to
a position of low hydraulic head. For example, in a water-
table aquifer, ground water will generally move from an area
of high water-table elevations to an adjoining area of low
water-table elevation (Slide 2.3).
The direction of ground-water flow can be determined from a
contour map of water levels (equipotential lines). Flow will
generally be perpendicular to the equipotential lines in the
direction of decreasing hydraulic heads (Slide 2.4)..
Ground-water flow occurs in the voids or pore spaces within
earth materials (Slide 2.5). Porosity is commonly cataloged
into primary and secondary. Primary porosity refers to the
intergranular spaces while secondary porosity refers to
larger non-capillary voids such as fractures or solution
channels.
Ground-water flow in porous, granular media is primarily
laminar. The term laminar means that molecules of water
follow each other along the same flow paths, instead of
crossing over to intersect and mix with other flow paths
(Slide 2.7).
Laminar flow can be described by a relationship known as
Darcy's law (given below).
Q = K I A
Where Q = discharge (L3/T)
K = hydraulic conductivity (L/T)
I = hydraulic gradient, and
A = cross-sectional area of flow (L2)
2-1
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Darcy's law can not be applied accurately where flow becomes
turbulent as may be the case in settings dominated by flow in
secondary porosity such as conduit karst and fractured
bedrock geology.
Hydraulic conductivity (K) is a property specific to the
earth material K can vary several orders of magnitude within
a single geologic unit and is expressed in units such as
ft/day, cm/sec, or gpd/ft2.
Transmissivity, a term hydrogeologists commonly use to
describe the hydraulic capacity of an aquifer is the product
of K and the aquifer thickness (Slide 2.9).
Ground-water velocity through pore spaces (pore water
velocity), V, is described by the equation:
V = KI
n
Where n = porosity of the medium.
Because all pores may not be interconnected (i.e., some
porosity may not contribute to flow), velocity calculations
should be based on the "effective" porosity. Effective
porosity in aquifers is often equated with that porosity
drainable under gravity (i.e., specific yield).
The velocity of ground-water flow in aquifers generally
ranges from a few inches to a few feet-per-day, and is
determined by the hydraulic conductivity, porosity, and
hydraulic gradient.
Natural Ground-Water Flow Systems
A ground-water flow system consists of the entirety of a
ground-water body extending from its recharge area to its
discharge area. Boundaries of flow systems are those such as
impermeable geologic boundaries, flow divides and flow lines
that separate parallel flow systems (Slide 2.10).
The mass balance for a ground-water flow system estimates the
mass of water entering the flow system through recharge,
leaving the system through discharge, and being added to or
depleted from storage within the flow system. Calculations
should show that these terms are in balance (i.e., sum to
zero).
2-2
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Flow systems have geometries that reflect the scale of
spatial variations in topography, hydrology, and earth
materials (Slide 2.11). Where these variations are minor,
large regional flow systems develop. Where variations are
large, the result are many, small local flow systems (Slide
2.12).
Unconfined flow systems have an upper water surface (water
table) that rises and falls freely. The water table may drop
tens of feet during periods of extreme drought.
Recharge to a water-table aquifer occurs wherever rainfall or
surface water infiltrates downward through the soil to the
water table.
Recharge to an unconfined flow system, as a rule, is more
rapid and of a higher magnitude compared to that of a
confined aquifer.
Confined aquifers occur beneath lower permeability "confining
units." The water level in a well screened into the top of a
confined aquifer will rise above the bottom of the confining
unit to a level referred to as the potentiometric surface
(Slide 2.13).
Recharge to a confined aquifer is generally reduced compared
to a non-confined aquifer. Water levels in a confined
aquifer generally change less radically throughout the year
than do those of an unconfined aquifer.
Confinement is a "sliding scale" between totally unconfined
(water-table) settings where aquifers are in direct hydro-
logic connection with activities on the land surface, and
well-confined settings where there is a little or no
hydrologic interconnection (under current climatic and
hydrogeologic conditions) between deeper aquifers tapped by
public-supply wells and surficial aquifers or surface
sources of pollution.
Ground-water will flow across the confining unit depending
upon the hydraulic head relationships. If the hydraulic head
in the confined aquifer is greater than the hydraulic head in
the overlying aquifer, flow will be upward across the
confining unit (Slide 2.14). This case presents a low
potential for contamination of the lower aquifer in the event
that the upper aquifer becomes contaminated.
2-3
-------
Downward leakage across the confining unit will occur if the
head relationships described above are reversed (Slide 2.15).
However, the presence of the confining unit and its lower
permeability will act to increase travel time and may also
result in reduced contaminant concentration levels if
contaminants should migrate across the confining unit.
The protection provided under confined conditions can be
related to depth from land surface. Shallow confining
conditions within 100 feet of the land surface, are generally
considered less protective than deeper confining conditions.
They may have approximately the same vulnerability to
contamination as an unconfined aquifer.
Deep confining conditions, 300 feet or more below land
surface, generally exhibit truer isolation from the surface
and, therefore, provide a relatively large margin of safety.
Such aquifers are typically consolidated except for in
coastal plain and alluvial materials. Deeper confining
units will generally have lower permeabilities.
The protective properties of a confining unit can be bypassed
on account of artificial pathways such as improperly
constructed wells or other man-made apertures.
Pumping of a confined unit can change the hydraulic head
relationships across the confining unit in the vicinity of
the well in such a way as to reverse flow directions or
increase the rate of flow across the confining unit.
An assessment of the degree of confinement may be a viable
component of a WHPA program. Part of the assessment may
include reviews of the geologic and hydrologic relationships
among aquifers, and whether or how much of the water supplied
by confined wells in the State is from recent surface
recharge in the immediate vicinity of the well, how much from
changes in aquifer storage, how much from distant areas
(representing water that recharged the aquifer hundreds to
thousands of years in the past), etc.
2.2 CONTAMINANT TRANSPORT
Contaminant Threats
The delineation of WHPAs will be designed to protect wells
from three general categories of threats:
Direct introduction of contaminants in the immediate
well area
Microbial contaminants
2-4
-------
Chemical contaminants
A basic aspect of the WHP Program is protection of the area
immediately contiguous to the well (e.g., pumps, pipes,
casing) from the direct introduction of contaminants near the
land surface. These contaminants may originate from
accidental spills, road runoff, leakage of chemicals or other
incidents and are carried across the land surface to the
well. These threats are avoided by "delineating" or
maintaining some immediate zone around the well where access
and surface runoff is controlled.
A second basic aspect of WHP is protection from microbial
contamination, especially bacteria and viruses that may
remain in water delivered to consumers even after treatment.
A third basic aspect is of particular importance: the broader
range of threats posed by various chemical contaminants.
Many of these chemicals are very persistent in the subsur-
face, and can theoretically traval long distances before
being adsorbed by subsurface media, transformed to less
harmful chemicals, diluted to non-harmful concentrations or
other rendered less threatening.
WHPA programs are intended to identify sources of these
threats. A list of source operations is provided in the
Grants Guidelines (EPA 1987b), Exhibit 6.
Radiological contaminants may constitute a threat in areas
with more waste piles, low-level radioactive waste-disposal
sites, and other sources. Naturally occuring radiological
threats, such as radon, are generally not considered an
anthropogenic source.
Vadose Zone Movement
Contaminants originating above the saturated zone generally
move vertically downward through the vadose zone to the water
table (Slide 2.19).
Contaminants moving through the vadose zone may be attenuated
by sorption onto soil particles, oxidation/precipitation,
microbial activity, or uptake by plants.
Attenuation process in the vadose zone are much more
effective than in the saturated zone. Unfortunately, these
processes are difficult to characterize and model. It is
difficult to account for them in transport calculations.
2-5
-------
Saturated Zone Movement
Contaminant movement in the saturated zone is dependent in
part upon the solubility, density, miscibility, and reactive-
ness of the constituent.
Dissolved chemicals in the saturated zone will flow with the
ground water. The distribution of a dissolved chemical in
the ground-water system in space and time (i.e. the shape,
extent, and rate of movement of the plume) is governed by the
processes of advection and hydrodynamic dispersion (Slide
2.20).
Advection refers to the movement of a dissolved chemical by
the bulk mass of flowing ground water (Slide 2.21).
Hydrodynamic dispersion is a combination of plume spreading
due to molecular diffusion along chemical gradients, and to
mechanical mixing of the plume with surrounding waters as it
moves through the pore spaces (Slide 2.22).
Dispersion is the principal factor causing dilution of the
contaminants within the plume.
In most aquifers, the component of dispersion due to
mechanical mixing is several orders of magnitude greater
than the molecular diffusion effect.
The shape and size of the plume depends on a number of
factors including the local geologic framework, local and
regional ground-water flow, the type and concentration of
contaminants, and variations in the rates of introduction of
contaminants from the source (Slide 2.24).
Layering or intermixed zones of contrasting particle size
distributions (i.e., sand stringers in a silt matrix) can
accentrate dispersion (Slide 2.25).
Where ground-water flow is through fractured rock or solution
cavities, predicting the migration of contaminants is orders
of magnitude more complex than in the case of sand aquifers.
In opposition to advection and dispersion, several processes
may inhibit the migration of contaminants including reduced
solubility, adsorption, and degradation (e.g. microbial
degradation, radioactive decay).
Varying levels of plume attenuation may take place depending
on the complex interaction of a suite of factors including
the physical and chemical properties of the geologic medium,
the chemical properties of the contaminants, background
2-6
-------
chemistry of the natural ground water, flow rate, avail-
ability of oxygen, and microbial activity.
Density and miscibility of the contaminated fluids are also
important factors controlling the formation and migration of
a plume.
Slightly miscible fluids may flow in separate phases creating
a coherent plume that mixes very little with the surrounding
ground water as it migrates (Slide 2.26).
Less dense fluids may float on the surface of the water
table/capillary fringe and may move in a slightly different
direction from the general ground-water flow direction.
Higher density fluids tend to sink through the saturated zone
eventually reaching the bottom of the aquifer where they may
move in directions radically different from the overall
ground-water flow direction (Slide 2.27).
Undissolved phases may give off vapors which migrate through
the unsaturated zone in patterns which are unrelated to the
ground-water flow system.
There can be numerous distinct plumes of contamination moving
away from a site.
Lenses of sand and clay can cause other variations in plume
migration due to stratification of the contaminants.
Pumping from wells can modify ground-water flow patterns
and, consequently, alter the movement of a contamination
plume. Contaminants within the ZOC will migrate toward the
well.
Predicting Contaminant Migration
Accurately predicting the transport of dissolved contaminants
is difficult; computer modeling of contaminant transport is
not as reliable as ground-water flow modeling. The problem
becomes more difficult where non-aqueous phase fluids,
density-dependent flow, transport of chemically reactive
constituents, or transport in fractured rock aquifers are
involved.
Discontinuous discharges may result in "slugs" of con-
taminated water, causing wide spatial and temporal fluctua-
tions in well-water quality.
2-7
-------
Detailed monitoring of sites more than five years old has
revealed fluctuations in the concentrations of some con-
stituents while other constituents remained relatively
constant. This phenomenon is caused by the solution and
dissolution of certain chemicals as the plume of contamina-
tion interacts with geologic materials in its path.
In addition to the parameters required to model the flow
system, transport modeling requires the hydraulic heads
predicted by the flow modeling, estimates of the parameters
that comprise hydrodynaraic dispersion, effective porosity
distribution, background water chemistry, transport proper-
ties of constituents (solubility, retardation and decay
factors) , strength and temporal fluctuations in waste
source, and estimates of concentration initial and boundary
conditions.
2.3 WELL HYDRAULICS AND AQUIFER RESPONSE TO PUMPING
The action of pumping water from a well causes a reduction in
hydraulic head, commonly referred to as drawdown, in the
aquifer media surrounding the well. Drawdown decreases away
from the well to a point of no influence. The distance to
this point is referred to as the radius of influence.
Plotted in plan view, this radius is called the zone of
influence (ZOI) (Slide 2.31).
In three dimensions, drawdown occurs as an inverted cone and
for this reason is referred to as the cone of depression.
The dimensions of the cone of depression are related to the
pumping rate, duration of pumping, regional hydraulic
gradient and aquifer hydraulic properties.
The area or volume of an aquifer that contributes water to a
pumping well is called the zone of contribution (ZOC).
Except under idealized conditions, the ZOC overlaps the ZOI
but is not totally coincidental. Ideal conditions where the
ZOC and ZOI are nearly identical involve highly productive
water-table aquifers with nearly flat water tables (i.e.,
extremely low hydraulic gradients) under unpumped conditions.
Flow to a well can best be explained for an idealized
confined aquifer with a single pumping well. Idealized means
an infinite, horizontal aquifer of uniform thickness and
possessing homogenous and isotropic hydraulic properties.
2-8
-------
Darcy's law can be modified to account for radial flow as
follows:
Q = K I A
where: A = 27rrb (area of cylinder)
I = dh
dr
substituting:
Q = 2?rrbK dh
dr
Differences in hydraulic head between two points on the cone
of depression in a confined aquifer at equilibrium conditions
(Slide 2.3) are explained as follows:
dh = 0
2:rbK
dh
- hi -
27rbK
In
where: h^ =_hydraulic head at point nearest the well
h2 = hydraulic head at point further from well
Q = discharge
K = hydraulic conductivity
b = aquifer thickness
ri = distance from well to point of h^
r2 = distance from well to point of h2
Referred to as the Thiem equation, this equation can be used
when all dynamic conditions have reached equilibrium (i.e., Q
is constant, ZOI has stabilized, and water enters the well
uniformly from all directions). All flow is assumed to be
horizontal, and the well is assumed to fully penetrate the
aquifer.
2-9
-------
For standard english units in log base 10, the Theim equation
for confined conditions is:
h2 - hi = 528 0 flog r2/rH
bK
For unconfined conditions (standard english units log base
10) the Thiem equation is:
(h22 - hx2) = 1055 0 flog r2/rll
K
The unconfined equation looks different (hydraulic heads are
squared) because of the need to account for dewatering of the
aquifer near the well as a result of drawdown. The aquifer
thickness, b, varies with distance to the pumping well. The
result is a decrease in aquifer transmissivity as the flowing
water approaches the well. Thus a greater hydraulic head
loss is needed to pump an unconfined aquifer at the same Q
compared to a confined aquifer.
The Thiem equation, shows that hydraulic head varies linearly
with the logarithm of distance to the well (radius). Plotted
on semilog paper, drawdown vs. distance occurs as a straight
line. The distance-drawdown relationship for equilibrium
conditions can be useful for determining WHPAs as will be
explained later.
Under non equilibrium (often referred to as transient)
conditions in an idealized, confined aquifer, the Theis
equation, provided below, is employed to explain drawdowns in
an observation well. As the well is pumped over time,
drawdown in an observation well increases in a logarithmic
relation as shown in the Theis curve.
s = 114.60 W(u)
T
where s = drawdown (h0 - h, ft)
Q = pumping rate (gal/min)
T = transmissivity (gal/day-ft)
W(u) = Theis well function
and u = 1.87r2S
Tt
2-10
-------
where S = storage coefficient (unitless)
r = distance from pumping well to observation well (ft)
t = time (days)
234
W(u) = -0.5772 - loge u + u - u +u - u_
2-2! 3-31 4-4!
W(u) can be read from a table after determining u (see
Appendix C.).
Aquifer tests to determine hydraulic parameters involves
matching a log x log plot of drawdown vs. time to the Theis
type curve. A different type curve is used in nonideal con-
ditions, such as unconfined conditions or where leakage
occurs across confining layers. Corrections are needed to
account for partial well penetration, aquifer boundaries, and
recharge boundaries.
Leakage across a confining layer will result in a smaller ZOI
and ZOC than would be calculated based solely on the pumped
aquifer hydraulic properties (Slides 2.40 and 2.41).
Recharge at a boundary near the well or the presence of an
impermeable (i.e., no flow boundary) will cause an asymmetric
ZOI and ZOC that would be calculated based solely on the
pumped aquifer hydraulic properties or will result in an
asymmetric ZOI and ZOC on the pumped aquifer hydraulic
properties (Slides 2.40 and 2.41).
2.4 FUNDAMENTAL CONCEPTS EXERCISE
A water supply well is screened in a shallow confined aquifer
with a transmissivity of 10,000 gpd/ft2 and storage co-
efficient of 1.0 X 10~4. If the well is pumped at 200 gpm,
how much drawdown would be observed after 100 days of pumping
at distances of 100 feet and 1000 feet? This exercise will
require first a calculation of u, then a tabular estimation
of W(u) in order to determine drawdown, s. Values of W(u) can
be found in Appendix C. After making these calculations,
plot these two drawdown points vs distance to the pumping
well on semilog graph paper (note drawdown should be on
vertical arithmetic scale and distance to pumping well on the
log scale). What is the radius of the zone of influence? At
what distance (radius) is a 1 foot drawdown achieved?
2-11
-------
2.4 FUNDAMENTAL CONCEPTS EXERCISE ANSWER
1) Calculate drawdown
a) Calculate u:
u = 1.87 r s
Tt
for r = 100 feet:
u = 1.87 flOQl fO.OOOl)
10,000 (100)
u = 1.9 X 10~6
W(u) = 12.6 (from table)
b) Calculate drawdown, s:
S = 114.6 Q [W(U)]
T
for r = 100 ft
S = 114.6 (2001 (12.61
10,000
for r = 1000 feet:
2
u = 1.8? fioooi to.oooii
10,000 (100)
u = 1.9 X 10 ~4
W(u) =8.0 (from table)
for r = 1000 ft
28.88 ft
S = 114.6 (200)
10,000
S = 18.33 ft
c) Distance-drawdown plot attached
d) ZOI = 52,000 ft in radius
e) drawdown of 1 ft is at 42,000 ft
2-12
-------
3. Elements
-------
PRESENTATION SLIDES
WELLHEAD TERMINOLOGY
Slide 3.01
-------
WHPA DELINE. M: GUIDELINES (CRITERIA AND METHODS)
BASIC DEFINITIONS
—.
*
CO
o
ro
CRITERIA
CRITERIA
THRESHOLDS
METHODS
Fundamental factors affecting likelihood
of contaminants reaching well
associated
with criteria
Technical
thresholds to be mapped and WHPAs
therefore delineated
-------
Terminology for Wellhead Protection
Area Delineation (Hypothetical
Pumping Well in Porous Media)
GROUNDWATER
DIVIDE
CONE OF
DEPRESSION
PREPUMPING
WATER LEVEL
(A) VERTICAL PROFILE
(B) PLAN VIEW
LEGEND:
V Water table
• Ground-water Flow Direction
• Pumping Well
ZOI Zone of Influence
ZOC Zone of Contribution
NOT TO SCALE
Slide 3.03
-------
Terminology for Wellhead Protection
Area Delineation (Hypothetical
Contaminant Transport in Porous Media)
-ZOT (10 YR)-
ZOC
GROUND-WATER
DIVIDE
LAND SURFACE
LEGEND: (B) PLAN VIEW
S Water Table
I *••'•-' I 10 Year Zone of Transport
•*—— Direction of Ground-water Flow
PREPUMPING
WATER LEVEL
CONE OF
DEPRESSION
VERTICAL PROFII
ZOC Zone of Contribution
ZOI . Zone of Influence
ZOT Zone of Transport
Slide 3.04
NOT TO SCALE
-------
Terminology for Wellhead Protection Area Delineation
(Hypothetical Ground-water Basin in Mature Karst)
VERTICAL PROFILE
rr \ r
zoc
WATER SUPPLY
SPRING
A1
PLAN VIEW
NOTE: The "ZOC" shown was delineated with purpose of
including all principal areas contributing to the cave
based on inferred surface and subsurface drainage
areas.
LEGEND:
O Sinkhole
• Water Supply Spring
—^-»- Surface Stream
—— Conduit System
V. Water Table
I I Limestone
SOURCE: Modified from Quinlan and Ewers. 1985
Slide 3.05
NOT TO SCALE
-------
Terminology for Wellhead Protection Area
Delineation (Hypothetical Ground-water
Basin in Fractured Rock)
Ground-
water
Divide
y * . /
Fractured Rocks
I
X
VERTICAL PROFILE
Stream
A'
\
PLAN VIEW
SOURCE: Modified from Otton. 1981
LEGEND:
Water Table
Fractures
— — Ground-water Divide
Slide 3.06
NOT TO SCALE
-------
Terminology for Wellhead Protection Area Delination
Hypothetical Confined Aquifer in Porous Media
ZOI
h-
Abandoned or Inadequately)
Cased or Cemented Well j
-Area of Net Downward Leakage
Water Production Well
Potentiometric
;•; Unconfined ;:•;
K Aquifer £
I-i Confining -~-
-I Unit . -
-__|Aquitardl -;
LEGEND
Direction of Water Flow
Contaminant Flow
ZOI Zone of Influence
-3Z Water Table
NOTE: ZOI is larger than area of downward leakage
Slide 3.07
-------
PRESENTATION SLIDES
WELLHEAD DELINEATION CRITERIA
(OVERVIEW)
Slide 3.08
-------
WHPA DELINEATION PROCESS
SELECT APPROPRIATE CRITERION
AND THRESHOLD £*>«»»T'
TO PROTECT WELLHEAD AREA
SELECT APPROPRIATE METHOD
TO IMPLEMENT CRITERION
Slide 3.09
-------
DELINEATION CRITERIA
DISTANCE
DRAWDOWN
TIME OF TRAVEL
FLOW BOUNDARIES
ASSIMILATIVE CAPACITY
Slide 3.10
-------
WHPA DELINu JN: GUIDELINES (CRITERIA)
DISTANCE: COMMENTS
w
ex
0
Simplest, quickest and cheapest way to
provide protection
Often used as "First Step", or for
microbial protection
Accuracy depends on hydrogeologic setting
Protectiveness depends on threshold
-------
WHPA DELINEATION: GUIDELINES (CRITERIA)
DRAWDOWN: COMMENTS
OL
-------
Aquifer with
\A/nfpr
ancj High
Rainfall Conditions, Where Boundaries of
ZOI and ZOC Approximately Coincide
(Conceptual)
LAND SURFACE
PREPUMPING
WATER LEVEL
BEDROCK SURFACE
CONE OF
DEPRESSION
(A) VERTICAL PROFILE
DRAWDOWN
CONTOURS
NOTE:
For the case of small hydraulic
gradient, the ZOI— ZOC
LEGEND:
* Direction of Ground-water Flow
(B) PLAN VIEW
^g—Water Table
WHPA
Slide 3.13
NOT TO SCALE
-------
WHPA DEL. .ATION: GUIDELINES (CRITERIA)
CO
ff
T1ME-OF-TRAVEL: COMMENTS
• Considers physical processes and flow velocities
• Velocities withjp^pniiif^ffi VBfy enormously
• Accuracy depends on method used
• Protectiveness depends on threshold
-------
Terminology for Wellhead Protection
Area Delineation (Hypothetical
Contaminant Transport in Porous Media)
-zoTjio YR)-
zoc
K1 GROUND-WATER
DIVIDE
LAND SURFACE
PREPUMPING
WATER LEVEL
CONE OF
DEPRESSION
VERTICAL PROFII
A1
LEGEND:
-------
WHPA DELINEATION: GUIDELINES (CRITERIA)
FLOW BOUNDARIES: COMMENTS
QL
(D
CO
o>
Key criterion for certain aquifer types
• Ideal for fifTlf^ flnu'fRrf?
Less suited for large or deep/confined aquifers
except near boundaries
-------
Flow Boundaries Criteria
(Conceptual)
River Discharging to Ground-water
(a)
(b)
PUMPING WELL -
Low-permeability rock
NOTE:
(a) The ground-water divide induced by the river is an example
of the type of surface feature that may be used as a physical
boundary criterion [Figure (a) modified from Driscoll (1986) ]
(b) The boundary between the "single valley system" and "the
regional system" is an example of the type of subsurface
feature that may be used as a physical boundary criterion
[Figure (b) modified from Fetter (1980) ].
V Water Table
—— Direction of Ground-water Flow
Slide 3.17
NOT TO SCALE
-------
WHPA DELINEATION: GUIDELINES (CRITERIA)
ASSIMILATIVE CAPACITY: COMMENTS
• Technically sophisticated
• Conceptual tie to management strategies
• Requires complex and expensive modeling
• No current examples for WHPAs with
multiple sources
co A/'*. . j»
ff
-------
Assimilative Capacity Criteria (Conceptual)
(a)
NOTE:
Continuous contamination
from a point-source plume
(b)
OL
CD
CO
BOUNDARY OF WHPA
3
Target Concentration
LEGEND:
5. Water Table
NOTE:
Ca>C,>C2
Where
Ca * Acceptable concentration at well
C) • Concfiiiration of Soutce 1 at well
Cj » Concentration of Source 2 at well
-------
WHPA DELINEATION: GUIDELINES (CRITERIA)
=
CL
-------
Relationship Between WHPA Delineation Criteria and Physical Processes
51
-------
Consideration Factors That May Affect
Criteria Selection
POLICY ISSUES
ATTENUATION
CONTAMINANT
XSITE-SPECIFIC
COSIDERATIONS
OTECTALL
OR PART OF
ZOC
(Hydrogeologic Setting,
Technical Capabilities,
Sources of Contamination,
Other Technical
Considerations)
Slide 3.22
-------
WHPA GOALS
REACTION TIME
ATTENUATION OF CONTAMINANTS
PROTECT ALL OR PART OF ZOC
Slide 3.23
-------
TECHNICAL SELECTION FACTORS
EASE OF APPLICATION
EASE OF QUANTIFICATION
VARIABILITY UNDER ACTUAL CONDITIONS
EASE OF FIELD VERIFICATION
ABILITY TO REFLECT STANDARDS
SUITABILITY FOR LOCAL HYDROGEOLOGY
ABILITY TO INCORPORATE PHYSICAL PROCESSES
Slide 3.24
-------
POLICY SELECTION FACTORS
EASE OF UNDERSTANDING
ECONOMY OF CRITERIA DEVELOPMENT
DEFENSIBILITY
PHASING
RELEVANCE TO PROTECTION GOAL
Slide 3.25
-------
PRESENTATION SLIDES
WELLHEAD DELINEATION METHODS
(OVERVIEW)
Slide 3.26
-------
WHPA DELINEATION PROCESS
SELECT APPROPRIATE CRITERION
AND THRESHOLD
TO PROTECT WELLHEAD AREA
I
SELECT APPROPRIATE METHOD
TO IMPLEMENT CRITERION
Slide 3.27
-------
WHPA DELINEATION METHODS
v^
x 1) ARBITRARY FIXED RADIUS
A.
2) CALCULATED FIXED RADIUS
£
3) SIMPLIFIED VARIABLE SHAPES
4) ANALYTICAL METHODS
5) HYDROGEOLOGIC MAPPING
6) NUMERICAL FLOW / TRANSPORT MODELS
Slide 3.28
-------
Interrelationships of WHPA Methods
QUANTITATIVE
ANALYTICAL. NUMERICAL
MODEL
ARBITRARY
FIXED
RADIUS
CALCULATED
FIXED
RADIUS
CALCULATED AREA
EXTENDED TO
BOUNDARY
HYDROGEOLOGIC
MAPPING
ARBITRARY
FIXED RADIUS
WITH EXTENSION TO
BOUNDARIES
(PHYSICAL OR HYDROLOGIC)
PHYSICAL
FEATURES
Slide 3.29
-------
METHODS DISCUSSION
EACH RELEVANT IN SOME SETTINGS
FIXED RADIUS QUICK AND MAY BE PROTECTIVE
IMPROVEMENTS AT MODEST COST WITH:
- CALCULATED'FIXED RADIUS
- SIMPLIFIED VARIABLE SHAPES
- ANALYTICAL MODELING METHODS
NUMERICAL MODELS - ACCURATE; COSTLY
COMPARATIVE ANALYSES ENCOURAGED
Slide 3.30
-------
METHODS VtrtSUS CRITERIA
^S. CRITERIA
METHOD ^X.
ARBITRARY FIXED
RADIUS
CALCULATED FIXED
RADIUS
SIMPLIFIED
VARIABLE SHAPES
ANALYTICAL
MODELS
NUMERICAL FLOW/
TRANSPORT MODELS
HYDROGEOLOGIC
MAPPING
DISTANCE
(L/M/H)
H
N/A
N/A
N/A
N/A
H
DRAWDOWN
(L/M/H)
N/A
H
N/A
H
H
N/A
TOT
(L/M/H)
N/A
H
M
H
H
N/A
PHYSICAL
BOUNDARIES
(L/M/H)
N/A
N/A
N/A
N/A
'N/A
H
ASSIMILA-
TIVE
CAPACITY
(L/M/H)
N/A
N/A
N/A
M
M
N/A
CO
L-LOW
M-MEDIUM
H-HIGH
N/A-NOT APPLICABLE
CO
CO
-------
to
a
a>
CO
CO
ro
TECHNICAL CONSIDERATIONS
INFLUENCING METHOD SELECTION
EASE OF APPLICATION
EXTENT OF USE
SIMPLICITY OF DATA REQUIREMENTS
SUITABILITY FOR HYDROGEOLOGIC SETTING
ACCURACY
-------
CO
5!
CD
CO
CO
CO
POLICY CONSIDERATIONS
INFLUENCING METHOD SELECTION
EASE OF UNDERSTANDING
ECONOMY OF METHOD APPLICATION
DEFENSIBILITY
RELEVANCE TO PROTECTION GOAL
-------
5
CD
w
DATA REQUIREMENTS FOR WHPA METHODS |
Data requirements
Application
Method KTQnl H S a R
Arbitrary Fixed Radius
Calculated Fixed Radius XX X
Simplified Variable Shapes X X
Analytical Methods X X X X X X
Hydrogeologlc Mapping
Numerical Models XXXX X X X X
PARAMETERS SYMBOL
Hydraulic Conductivity K
Transmlsslvlty T
Pumping Rate Q
Porosity n
Hydraulic Gradient 1
Saturated Thickness H
Storage Coefficient (Specific Yield) S
Dlsperslvlty <*
Recharge R
Hydrologlc Aquifer
Boundaries Geometries
X X
DIMENSIONS
Lrr
2
L rr
L3/T
dimenslonless
dimenslonless
L
dimenslonless
L
Lrr
-------
Costs of Delineation Associated with Various WHPA Methods
ift
11
p
u
;
Method
Arbitrary Fixed Radius
Calculated Fixed Radius
Simplified Variable Shapes
Analytical Methods
Hydrogeologlc Mapping
Numerical Modeling
Manhours
Required per Well
1-5
1-10
1-10
2-20
4-40
10-200+
Level of
Expertise*
1
2
2
3
3
4
Cost
per Well
$10-50
$13-125
$13-125
$30 - 300
$60 - 600
$175-3500+
Potential
Overhead Costs
L
L
L-M
M
M-H
H
* Hourly wages per level of expertise assumed to be:
(based on NWWA, 1985)
CO
OL
CD
W
CO
Ol
1. Non-Technical
2. Junior Hydrogeologlst/Geologlst
3. Mid-Level Hydrogeologlst/Modeler
4. Senior Hydrogeol
oglst/Modeler
$10.00
$12.50
$15.00
$17.50
-------
PRESENTATION SLIDES
ADEQUACY OF DELINEATION
Slide 3.36
-------
WHPA DELINEATION: ADEQUACY
ADEQUACY OF WELLHEAD
PROTECTION AREA DELINEATION
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WHPA DELINEATION: ADEQUACY
CONTENTS OF STATE SUBMITTAL
• Institutional process
• Delineation criteria and criteria
thresholds
• Delineation methods
• Phasing
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WHPA DELINEATION: GUIDANCE (INTRODUCTION)
ADDITIONAL BACKGROUND
Threats for WHPA delineation
- Direct introduction of contaminants
- Microbial contaminants
- Chemical contaminants^
Confined aquifers
• Require WHPA
• Assess threats to confinement
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WHPA DELINEATION: ADEQUACY
INSTITUTIONAL PROCESS
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Essential for "Adequacy"
Description - Develop and implement
technical elements
Roles - Operations and research groups
Approach - Legal incorporation
Coordination - Other hydrogeological efforts
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WHPA DELINEATION: ADEQUACY
CRITERIA
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Precedes method selection
Appropriateness depends on goal,
hydrogeology, policy
Key for chemical threats
Many adequate criteria
May combine criteria
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WHPA DELINEATION: ADEQUACY
CRITERIA THRESHOLDS
•. TOT < 5 to 1 0 yrs -- problem?
•' 4»*«x
**
•|>«4tt'it Jp- fat04»*«x en** *»«,**) +e
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«i *«^«. *i*tt ** V Ai?^'*' i-**/.*^ C»»^.e7*9fOo.±<9p /V ^»£C»'~
• Drawdown, boundaries are case-specific
• Relevant to confined aquifers
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WHPA DELINEATION: ADEQUACY
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METHODS
• Each relevant in some settings
• Fixed radius quick and may be protective
•
V1* • Improvements at modest cost with calculated
fixed, variable shapes, analytical
• Numerical models - accurate; costly
• May combine methods
• Comparative analyses encouraged
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WHPA DELINEATION: ADEQUACY
PHASING
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• Delineate ^5 "lany WHPAs as possible
• Constraints to 1989 deadline (**** a*
possible
- Criteria and methods /^** «>*
- Test cases fak*eu n *****
Phase by well yield, vulnerability, contaminant
e/> sources
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WHPA DELINEATION: ADEQUACY
WORK PLANS
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3. ELEMENTS OF WHPA DELINEATION
3.1 WELLHEAD TERMINOLOGY
The following WHPA terminology is defined in the WHPA
Delineation Guidelines (EPA, 1987a).
WHPA Criteria are conceptual standards that form the basis
for WHPA delineation and include distances, drawdown, time of
travel, assimilative capacity and flow boundaries.
WHPA Criteria thresholds are the numeric value selected for
each WHPA criteria used in a delineation (e.g., a distance
threshold of 1,000 feet).
Delineation Method is a technique used to translate the
select critria and criteria thresholds to actual, mappable
delineation boundaries.
Zone of Influence (ZOI) is the area surrounding a pumping
well within which the water table or potentiometric surfaces
have been changed due to ground-water withdrawal (Slide 3.3).
Zone of Contribution (ZOC) is the area surrounding a pumping
well that encompasses all areas or features that supply
ground-water recharge to the well (Slide 3.3).
Zone of Transport (ZOT) is the area surrounding a pumping
wells, bounded by an isochrone and/or isoconcentration
contour through which a contaminant may travel and reach the
well (Slide 3.4).
Mature karst ground-water basins are characerterized by
sinkholes, cave streams, and underground drainage. Flow is
generally confined to a complex network of solution channel
and cavernous conduits that is extemely difficult to infer
from the surface.
An approach to delineate WHPAs in mature karst settings might
be based on the boundaries of the ZOC as inferred from
divides and drainage boundaries.
Fractured bedrock aquifers limit flow to wells according to
the distribution and degree of interconnection that exists
between fractures and with variations in rainfall recharge.
Accurately determining the recharge area to a well in a
fracture setting is difficult (Slide 3.5).
3-1
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An assumption that the topographic divides or drainage
boundaries of a fractured bedrock aquifer represent the ZOC
may be the basis for WHPA delineations (Slide 3.6).
A confining layer may provide some protection for a water
source. Where the dominant flow through the confining layer
is toward the water-supply aquifer this should be examined as
an area of concern for WHPA delineation (Slide 3.7).
Another approach to confining conditions might focus in a
portion of the contributing area based upon some TOT
threshold within the aquifer.
3.2 WELLHEAD PROTECTION AREA DELINEATION CRITERIA
Delineation criteria can be catalogued into five types:
distance
drawdown
time of travel
flow boundaries
assimilative capacity
The choice of a criterion will involve consideration of both
technical and nontechnical factors. Considerations for
criteria selection are presented in the Wellhead Delineation
Guidelines. A list of examples for the delineation criteria
are also found in the Wellhead Delineation Guidelines (EPA,
1987a).
Distance Criterion
The distance criterion concept involves delineating a WHPA
using a radius or horizontal dimension measured from the
water supply well. The distance criterion may or may not
have a technical basis. For example, individual domestic
supply wells are often required to have a 100 ft to 200 ft
setback to on-site septic systems based on empirical evidence
concerning ground-water pollution control.
A distance-based WHPA could provide insufficient or ineffec-
tive protection in some cases. This criterion, however, is
easy to implement since a uniform distance would be required
from any well.
Examples include Edgartown, Massachusetts and the State of
Nebraska, where fixed circles of 2,500 feet and 1,000 feet
are used respectively.
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Drawdown Criterion
A drawdown criterion concerns the extent to which well
pumping lowers the water table of an unconfined aquifer, or
the potentioroetric surface of a confined aquifer. Such a
criterion is related to the cone of depression or zone of
influence (ZOI).
The drawdown approach is used to delineate the boundaries of
the ZOI or a major portion of a ZOI. This approach works
well in highly productive water-table aquifers with horizon-
tal water tables (Slide 3.13).
Examples of drawdown criteria thresholds include Dade County,
Florida where a 0.25 feet drawdown criterion threshold was
used and in Palm Beach County, Florida, where 1.0 feet of
drawdown was used.
The steep hydraulic gradients that result in the vicinity of
a pumping well can act to accelerate contaminant migration
toward the well. For this reason, the development of
drawdown criterion should consider the relationship between
pumping rates and contaminant migration.
Time of Travel Criterion
The time of travel (TOT) delineation criterion establishes a
maximum time for a ground-water contaminant to reach a well.
This approach incorporates a more comprehensive evaluation of
the physical processes of contaminant transport than the
previously discussed criteria (Slide 3.15).
Most time of travel methods have been developed based on the
physical process of advective transport and have not
considered the movement of specific contaminants. Generally
speaking, contaminants move at velocities slower than the
effective transport of water molecules.
At lower velocities, physical processes such as hydrodynamic
dispersion should be considered because of their potential to
cause a contaminant to reach a well sooner than would be
predicted using advective, Darcian TOT calculations.
Detailed discussions concerning dispersion and contaminant
transport are found in Anderson (1984), Bear (1979) and Fried
(1975).
Ground-water flow velocities under natural settings vary
considerably and are related to the types of aquifer media
(i.e., porosity and hydraulic conductivity). The highest
flow rates can be found in karst and fractured rock flow
3-3
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settings. In such settings the time of travel approach may
not be appropriate.
A maximum velocity or maximum travel time for contaminants to
reach a well is considered a conservative approach in that
the numerous factors operating along the contaminant flow
path to reduce, disperse or dilute the maximum concentration
provide for an additional level of safety.
Dade County Florida, as an example, employs two TOT criteria
thresholds. A 100 day TOT Zone is delineated for control of
entering viruses and a 210 day TOT is delineated to represent
the longest drought on record.
Flow Boundaries
Physical or hydraulic boundaries of an aquifer or ground-
water flow system can be used effectively to delineate the
bounds of the maximum potential zone of contribution (ZOC).
The physical limits of an aquifer, and a fixed regional
ground-water divide are examples of flow boundaries (Slide
3.17).
Flow boundary criteria may be very appropriate for flow
settings such as conduit karst and fractured bedrock
aquifers.
Flow divides, particularly those associated with gaining
streams may not always be shown to be appropriate flow
boundaries for purposes of WHPA delineation. For this
reason, a thorough technical evaluation may be necessary.
A flow boundary criterion can be especially useful for small
aquifers where travel times from the boundaries may be very
brief, or where the zone of influence is rapidly affected by
proximity to the physical limits of the aquifer.
Physical boundaries to aquifers have been employed as
criterion to delimit WHPAs in Vermont, Massachusetts and
Florida.
Assimilative Capacity
The assimilative capacity criterion for WHPA delineation may
apply a range of processes that attenuate contaminant
concentrations within a ground-water flow system. However,
no known examples of this approach to delineate WHPA has
been uncovered.
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The concept is to allow such processes to work providing that
contaminant levels reach acceptable levels before they reach
a well. Contaminant concentrations that exceed standards at
some distance away from the well, may attenuate as they
migrate to acceptable levels at the well screen (Slide 3.19).
The existence and magnitude of attenuation processes are
directly linked to the contaminants and aguifer properties.
They are not easily modelled or quantitatively determined.
Site specific data for specific contaminants would be needed
in order to use this approach.
Specific standards for the various contaminants may also have
to be developed if such standards do not exist.
Criteria Selection Considerations
Three major considerations for selecting WHPA delineation
criteria involve the overall protection goal, technical
considerations, and policy considerations. Detailed
discussion of these considerations is provided in WHPA
Delineation Guidelines.
Three general goals for ground-water protection in the
vicinity of wellheads involve the following:
reaction time — to provide a remedial action zone to
protect wells from unexpected contaminant releases,
attenuation of contaminants — attenuate the
concentrations of specific contaminants to desired
levels at the time they reach the wellhead, and
. protect all or part of ZOC — provide a well field
management zone in all or a major portion of the
existing or potential recharge area of the well.
Generally the criteria can be matched up to the specific
criteria goals as follows:
the remedial action zone goal is consistent with a
TOT criterion,
the zone for attenuation goal implies an assimilative
capacity criterion or possibly a TOT criterion, and
the wellfield management area goal is consistent
with a distance-drawdown or flow boundaries criteria.
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Six technical factors have been identified for evaluating the
appropriateness of each wellhead delineation criterion. A
table with matrix cells designed for assisting in such an
evaluation is provided in the WHPA Delineation Guidelines.
The technical merits of a criterion depend on the degree to
which the criterion incorporates those processes affecting
ground-water flow and contaminant transport, and the suit-
ability of the criterion for the local hydrogeologic
condition. A criterion such as drawdown, which considers
only the physical processes may have less technical merit
than a time of travel criterion which encompasses a more
complete range of processes explaining contaminant transport.
Technical factors are as follows:
ease of application. How easily can a technical user
apply the criteria. The more technically demanding
criteria require more advanced and specialized user
abilities. Does the implementing agency have such
abilities on staff?
ease of quantification. The suitability of a
criterion for use in guidelines of regulations may be
directly influenced by the ease to which a numerical
value can be placed or derived. The distance and
time of travel criterion are easily expressed in
numerical form. Others are not.
variability under actual conditions. Which hydraulic
conditions are expected to change (e.g., increased
pumping rates)? The criterion selected would most
likely need to allow for such variations. For
example, the time of travel criterion allows the user
to modify the size of the WHPA to reflect an
anticipated increase in pumping rates.
ease of field verification. The most appropriate
criterion would be one that could be calculated in
the office and accurately verified in the field. For
example, in a porous media aquifer, it is much more
difficult to verify calculated travel times than it
is drawdowns.
ability to reflect ground-water quality standards.
Where a protective goal to attenuate concentrations
of constituents is established, the delineation
criterion would be expected to be related to the
ability of the ground-water flow system to achieve
the water-quality standard given the expected
3-6
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contaminant levels. If little is known concerning
the behavior/attenuation of specific contaminants,
then a less quantitative delineation criterion would
be more appropriate.
suitability for a given hydroqeoloaic setting. As
discussed previously, selected criterion are more
appropriate in some hydrogeologic settings than
others.
ability to incorporate physical processes. Selection
of a criterion should include consideration of
whether the physical processes controlling con-
taminant transport are incorporated with the selected
criterion.
Policy Considerations
Five policy considerations for choosing a WHPA Criterion have
been identified. A table with a decision matrix is provided
in the WHPA Delineations Guidelines as an aid for making the
policy evaluation. Policy considerations are as follows:
ease of understanding. The ease with which the
general public can understand the criterion may be a
significant measure of its utility.
economy of criteria development. The cost of
developing the various criteria can vary substantial-
ly. Generally criteria that are more complex will
require a more highly trained staff for implementa-
tion.
defensibility. WHPA delineation criteria that are
clearly defined and defensible against potential
challenges in litigation will be most acceptable to
enforcement and permitting authorities. The more
technically defensible criteria will be favored.
usefulness for implementing phasing. Where a state
prefers to initiate their WHPA program in phases, the
first or interim stage might favor a less costly,
more easily implemented criterion. More sophisti-
cated criteria would be applied in later phases as
appropriate.
relevance to protection goal. The degree to which a
criterion allows for the attainment of the protective
goal or goals will be a decisive factor in the
selection process.
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3.3 WELLHEAD PROTECTION AREA DELINEATION METHODS
Once an appropriate Wellhead Protection Area (WHPA) delinea-
tion criterion and threshold have been decided upon (see
previous section), a method must be selected to implement the
criterion. In some cases, multiple protection zones may be
defined around a water-supply well or wellfield using
different thresholds for the same criterion. This would
require the use of a single method for repeated calculations.
In cases where multiple zones are delineated using different
criteria, several methods may be applied to the same site.
Six methods have been identified in the WHPA Delineation
guidance document (EPA 1987a) as having been used to
delineate protection areas. These methods, listed in order
of increasing cost and sophistication, are:
Arbitrary Fixed Radius Method - involves determination
of simple circular protection areas; size often based on
expert judgment.
Calculated Fixed Radius Method - similar to arbitrary
fixed radius method, but some properties of the
hydrogeologic system and well pumping rate incorporated
in determination of size of circle.
Simplified Variable Shapes Method - incorporate more
hydrogeologic information in the initial development
stages but, once developed, it is as easy to apply as
the fixed radius method.
Analytical Modeling Methods - involve the solution of
simplified ground-water flow and transport equations
using calculators or computers, and are based on a
simplified representation of the aquifer system.
Hydrogeologic Mapping Methods - use geologic and
geophysical techniques to determine flow system
properties and to identify flow boundaries.
Numerical Modeling Methods - similar to analytical
modeling methods but more powerful and flexible; often
incorporate data collected using hydrogeologic mapping
methods.
The methods are discussed in Chapter 4 of the Delineation
Guidelines (EPA, 1987a). Also the remainder of this training
manual is devoted to descriptions of the methods, discussions
of their advantages and disadvantages, case studies il-
lustrating their use in WHPA delineation studies, and
3-8
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exercises designed to familiarize the reader with the
practical aspects of applying the various models.
Method Selection Considerations
Selection of a WHPA delineation method is somewhat con-
strained once the desired delineation criterion has been
selected in that the method must be suitable to map the
criterion. Choice of method is tied less to the protection
goal than to accuracy of the delineation desired and the
financial resources available for delineation. Several
technical and policy considerations that may influence method
selection are discussed fully in the Delineation Guidelines
(EPA, 1987a) and summarized below.
Technical Considerations;
Extent of Use. How commonly is the method used?
Simplicity of Data. What data are required for the applica-
tion of method. Is the data site-specific or regional? Are
the financial resources to fund the necessary data collection
available? Is the data available through previous work or
reports and, if so, does the data need to be updated?
Suitability for a Given Hydrogeologic Setting. An important
consideration is whether or not the analytical method is
suitable for the hydrogeologic setting of interest. It is
necessary to evaluate the ability of an analytical model to
incorporate, or be adopted to incorporate, the hydrogeologic
characteristics of a site such as variable aquifer para-
meters, boundary conditions, and the effects of hydraulic
sources and sinks.
Accuracy. Perhaps the most important consideration. To what
degree do the results accurately compare to actual field
conditions?
Policy Considerations:
Ease of Understanding. Can the principles underlying the
method be understood by nontechnical personnel?
Economy of Application. Higher relative costs can inhibit
the use of one method over another. Costs that may con-
tribute to implementation expense include those for data
acquisition, professional labor, computer time, graphics, and
reporting.
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Defensibilitv. Enforcement and permitting regulations and
procedures require that the boundaries of a WHPA be well
defined and defended against potential challenges and
litigation by parties affected by the delineation. Does the
method used to delineate a WHPA have the scientific basis to
withstand such challenges?
Relevance to Protection Goal. In general, WHPA delineation
will reflect the overall policy/protection goal of a State
program. Selecting a method relevant to this goal is the key
factor in program success.
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4. Fixed Radii & Simp.
Variable Shapes
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PRESENTATION SLIDES
ARBITRARY FIXED RADIUS METHOD
Slide 4.01
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WHPA DELINEATION METHODS
1) ARBITRARY FIXED RADIUS
2) CALCULATED FIXED RADIUS
3) SIMPLIFIED VARIABLE SHAPES
4) ANALYTICAL METHODS
5) HYDROGEOLOGIC MAPPING
6) NUMERICAL FLOW / TRANSPORT MODELS
Slide 4.02
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ARBITRARY FIXED RADIUS METHOD
DESCRIPTION
Circle of specified radius is drawn around a well or we I If i eld
ADVANTAGES
simple, fast, inexpensive way to apply the distance criterion
easily mapped and verified in the field
suitable for physical or microbial threats, or as a
CY^OOCI if& in oorlv/ OT^^it\o_nT \A/LJh^rt ^lAlinootiOft
DISADVANTAGES
does not take site-specific hydrogeological data into
account, and may therefore overprotect or
underprotect depending on hydrogeology
• low defensihilitv
Slide 4.03
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METHODS: ARBITRARY FIXED RADIUS
WHPA BOUNDARY
Slide 4.04
NOT TO SCALE
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ARBITRARY FIXED RADIUS METHOD CASE STUDY
STATE OF FLORIDA
PROPOSED LAW REQUIRES A ZONE WITH 200-FOOT RADIUS TO
BE DELINEATED FOR PUBLIC WATER-SUPPLY WELLS WITH
WITHDRAWALS IN EXCESS OF 100,000 GALLONS PER DAY
PROTECTION ZONE IS TO RESTRICT ANY ACTIVITIES THAT COULD
CONTAMINATE THE GROUND WATER
Slide 4.05
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ARBITRARY FIXED RADIUS METHOD CASE STUDY
STATE OF MASSACHUSETTS
AQUIFER LAND ACQUISITION PROGRAM REQUIRES
DELINEATION OF A WHPA WITH 400-FOOT RADIUS FOR
PUBLIC WATER- SUPPLY WELLS
AREA TO SERVE AS THE FIRST OF THREE ZONES DESIGNED
TO CONTROL LAND USE AROUND WATER-SUPPLY WELLS
Slide 4.06
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ARBITRARY FIXED RADIUS METHOD USED TO
DELINEATE WHPA (ZONE 1) AT FRANKLIN, MA
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PRESENTATION SLIDES
CALCULATED FIXED RADIUS METHOD
Slide 4.08
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WHPA DELINEATION METHODS
1) ARBITRARY FIXED RADIUS
2) CALCULATED FIXED RADIUS
3) SIMPLIFIED VARIABLE SHAPES
4) ANALYTICAL METHODS
5) HYDROGEOLOGIC MAPPING
6) NUMERICAL FLOW / TRANSPORT MODELS
Slide 4.09
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CALCULATED FIXED RADIUS METHOD
DESCRIPTION
Circle with raHiuc cpprifiori fry |jrpo-pi^to^Al-^dtflflfi5is drawn
around well or wellfield
ADVANTAGES
simple to apply, easily mapped and verified
requires limited amount of data, but provides more
accurate coverage
good tie to TOT criterion
DISADVANTAGES
less accurate in many situations because it does
not account for hydrogeological factors that influence
contaminant transport
Slide 4.10
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METHODS: CALCULATED FIXED RADIUS
6r-
c,y
PUMPING
WELL
Q t = n TT H r2
VOLUME VOLUME OF
PUMPED CYLINDER
•n- n H
= 1138 ft
WHERE
Q = Pumping Rate of Well = 694.4 gpm = 48.793.668 ft3/yr
n = Aquifer Porosity = 0.2
H = Open Interval or Length of Well Screen = 300 ft
t = Travel Time to Well (5 Years)
(Any consistent system of
units may be used.)
Slide 4.11
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PRESENTATION SLIDES
CALCULATED FIXED RADIUS EXERCISE
Slide 4.12
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CALCULATED FIXED RADIUS EXERCISE
KENNEDALE, TEXAS
FOUR PUBLIC WATER-SUPPLY WELLS LOCATED IN
CONFINED AQUIFER
VOLUMETRIC FLOW EQUATION AND FIVE YEAR TOT
CRITERION THRESHOLD USED TO DELINEATE WHPAS
Slide 4.13
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N
Trinity -2
water wellp
• ^
CITY OF KENNEDALE WELLHEAD PROTECTION AREAS
Slide 4.14
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CITY OF KENNEDALE PUMPING AND WATER-WELL DATA
WELL
* Paluxy #1
Paluxy #2
trinity #1
^Trinity #2
SCREEN LENGTH
PUMPING RATE
80 ft &9G 4,520,788.8 ft3/yr
80 ft 2,966.123 ft3/yr
175 ft "7^7 13,756,858.3 ft3/yr
175 ft 28,953,048.1 ft3/yr
Aquifer Porosity = .25
Time of Travel = 5 years
Slide 4.15
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Solutions:
Paluxy #1 r =
(4.520.789 ft /vrl f5 vrl
7T (.25) (80 ft)
= 600 ft
Paluxy #2 r =
(2.966.123 ft /vr) (5
7T (.25) (80 ft)
486 ft
Trinity #1 r =
ri3.756.858 ft /vrl (5 vrl
7T (.25) (175 ft)
= 707 ft
Trinity #2 r
(7.581.805 ft /vrl (5 vr)
TT (.25) (175 ft)
= 525 ft
Slide 4.16
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PRESENTATION SLIDES
SIMPLIFIED VARIABLE SHAPES METHOD
Slide 4.17
-------
WHPA DELINEATION METHODS
1) ARBITRARY FIXED RADIUS
2) CALCULATED FIXED RADIUS
3) SIMPLIFIED VARIABLE SHAPES
4) ANALYTICAL METHODS
5) HYDROGEOLOGIC MAPPING
6) NUMERICAL FLOW / TRANSPORT MODELS
Slide 4.18
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SIMPLIFIED VARIABLE SHAPES METHOD
DESCRIPTION
Delineation using "stfmrif|frii7.ediQcms" generated with
analytical methods, with flow boundaries and TOT used as
criteria
ADVANTAGES
if the "standardized forms" have previously been developed
for the region, delineation ifi-fejftjcftfliijrfifi !irtliffif1,gitp -
offers more refined analysis than the fixed-radii methods,
with only a
DISADVANTAGES
this method results in inaccurate delineation if site
conditions depart from local hydrogeological trends
if "standardized forms" have not already been developed
in the region in which the site is located, the cost of
generating the form^14 considerable as it requires
significant site-specific data collection
Slide 4.19
-------
WHPA Delineation Using Simplified
Variable Shapes Method
STEP 1- DELINEATE STANDARDIZED FORMS FOR CERTAIN AQUIFER TYPE
\
02*03
Pumping Rate -
-Various standardized forms are generated
using analytical equations using sets of
representative hydrogeologic parameters.
•Upgradient extent of WHPA is calculated
with TOT equation; downgradient with
uniform flow equation.
STEP 2: APPLY STANDARDIZED FORM TO WELLHEAD IN AQUIFER TYPE
-Standardized form is then applied to
well with similar pumping rate and
hydrogeologic parameters.
LEGEND:
• Pumping Well
I Direction of Ground-water Flow
Slide 4.20
NOT TO SCALE
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4. FIXED RADII AND SIMPLIFIED VARIABLE SHAPES METHODS
4.1 INTRODUCTION
The fixed radius methods are the simplest class of WHPA
delineation techniques. The methods involve defining a
circular area, centered on the well or wellfield, within
which the ground-water supply is to be protected.
The method used to establish the radius of the circular area
distinguishes the two techniques. The arbitrary radius is
based on very generalized hydrogeologic considerations or
expert judgement. The resulting circle is then circumscribed
about a well or wellfield without explicitly considering
site-specific aquifer properties or pumping rate. The
calculated fixed radius method considers pumping rate and
incorporates some information about the aquifer in determin-
ing the size of the delineated circle.
Simplified variable shapes are developed using more sophisti-
cated analytical techniques, but once the standard set of
shapes has been computed they are applied as simply as are
the circles used in the fixed radii methods. The following
sections describe each method, advantages and disadvantages,
and field cases in which the methods have been used to
delineate WHPAs.
4.2 ARBITRARY FIXED RADIUS METHOD
Description
The arbitrary fixed radius method is the simplest method used
to delineate WHPAs. It involves drawing a circle of
specified radius around a well being protected (Slide 4.4).
The radius selected to delineate a WHPA may be arbitrarily
selected. It may be based on state or local regulations,
very generalized hydrogeologic considerations, and/or
professional judgement. For example, the radius selected
could be based on distances previously chosen using different
delineation methods in similar hydrogeologic settings.
Advantages
The arbitrary fixed-radius method is an inexpensive and
simple way to apply the distance criterion. It can be
completed quickly, is easily verified in the field, and
requires little technical expertise. This method can be
adopted as a temporary measure in the early stages of a
particular WHP program until a time when a more sophisticated
4-1
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approach can be adopted and/or more detailed hydrogeologic
data are availabl-e. The approach can be adequately protec-
tive if large distance thresholds are chosen, thus, compen-
sating somewhat for its lack of hydrogeologic precision.
Disadvantages
Due to the lack of scientific basis for choosing a specific
radius, there is much uncertainty in the application of the
arbitrary fixed radius method. This is especially true in
areas where the hydrogeology is anisotropic and hetero-
geneous, and in areas where flow boundaries are located. As
a result, this method may tend to over- or under-protect well
recharge areas. This can lead to increased costs of
purchasing land to be included in a WHPA, and to insufficient
protection of the zone of contribution of a well. In
addition, the lack of technical justification for the
distance criterion gives application of the arbitrary fixed
radius method low defensibility.
Example
In the State of Florida, as part of a proposed law to
protect public water supplies that have an average daily
ground-water withdrawal of at least 100,000 gallons, an area
with a 200-foot radius is to be delineated (Slide 4.5). The
area is established to restrict any activities that could
contaminate the ground water.
As part of the Aquifer Land Acquisition Program in Massa-
chusetts, the State uses the arbitrary-fixed radius method to
delineate the first of three zones designed to control land
use in areas surrounding public water-supply wells (see Case
Study B.5). The area consists of a circle with a 400-foot
radius that is off-limits to activities that could possibly
contaminate the ground water (Slides 4.6 and 4.7).
4.3 CALCULATED FIXED RADIUS METHOD
Description
Delineating a WHPA using the calculated fixed radius method
involves drawing (mapping) a circle with a radius specified
by, for example, a TOT criterion threshold. The radius is
calculated using an analytical equation based on the volume
of ground water that will be drawn to a production well in
the specified time (Slide 4.11). The time period is one that
will allow for cleanup of contaminants threatening the well,
or allows for adequate dilution or dispersion of contam-
inants .
4-2
-------
The analytical equation used to calculate the radius of the
WHPA depends on the data available. For example, if the
effective porosity of the aquifer is known, a simple
volumetric equation is used. If pumping-test data are
available for an unconsolidated, unconfined aquifer, the
radius is determined using the Theis equation.
Advantages
This method is relatively quick and inexpensive compared to
the more complicated delineation methods. It requires
little technical expertise and allows for the delineation of
a number of WHPAs in a short period of time. The calculated
fixed radius method requires more funds than the arbitrary
fixed radius method because it requires more hydrogeologic
data, but it provides greater accuracy and is just as simple
to map.
Disadvantages
The calculated fixed radius method may be inaccurate in many
situations because it does not account for hydrogeologic
factors that influence contaminant transport such as aquifer
anisotropy and heterogeneity, and the presence of flow bound-
aries.
Example
The Florida Department of Environmental Regulations requires
that Zone II of a WHPA be defined as a circle of a radius
calculated using the volumetric equation with a 5 year time-
of-travel criterion (see Case Study B.4). The volumetric
equation:
Qt = nTrHr2
or
Qt
nn-H
where,
Q = well pumping rate (ft3/yr)
n = aquifer porosity
H = open interval (ft)
t = travel time to well (yrs)
r = WHPA radius (ft)
4-3
-------
4.4 CALCULATED FIXED RADIUS EXERCISE
Background
The Texas Water Commission (TWC) delineated WHPAs for four
public water-supply wells in the City of Kennedale, Texas
(Slide 4.14). The TWC selected a 5 year time-of-travel as
the threshold criterion, and the calculated fixed radii
method was chosen to delineate the WHPAs. The volumetric
flow equation was used to calculate the radius of each WHPA
and an additional buffer zone was added to each calculated
radius, bringing the WHPA to a quarter mile radius.
Hvdroqeoloaic Setting
The City of Kennedale derives its water from the Trinity
Aquifer, which is comprised of two water-producing units, the
Paluxy and Twin Mountains Formations. The two zones are
separated by a confining unit, the Glen Rose Formation. The
entire aquifer is under confined conditions, lying under 600
feet of marl, clay, and limestone.
The regional ground-water velocity within the Trinity
Aquifer is estimated to be 2 to 3 feet per year. In the
vicinity of Kenndale, where extensive pumping has lowered
the piezometric surface and induced larger hydraulic
gradients, ground water may be moving 200 to 300 feet per
year towards the pumping centers.
Problem
The hydrogeologic and pumping data used in calculating the
radii are provided in Slide 4.15. Using the volumetric flow
equation,
r =
Ot
n n H
where,
r = protection area radius (ft)
Q = pumping rate of well (ft3/yr)
t = time of travel (years)
n = porosity of aquifer
H = length of well screen (ft)
Calculate the radius for each well.
4-4
-------
4.5 SIMPLIFIED VARIABLE SHAPES METHOD
Description
The simplified variable shapes method for WHPA delineation
provides an alternative to the more simplistic fixed radii
methods and the more complex analytical methods. It provides
a middle ground between these two types of methods in that
its development incorporates analytical methods while its
implementation is similar to that of the fixed radii methods.
In the simplified variable shapes method, "standardized
forms" (Slide 4.20) are generated using analytical methods,
such as the uniform flow equation (see Section 5.4), with
both flow boundaries and TOT used as criteria. This method
attempts to simplify implementation by selecting a few
representative shapes from the large array of potential
possibilities. The appropriate "standardized form" is
selected for hydrogeologic conditions similar to those found
at the wellhead. The standardized form is then oriented
around the well according to ground-water flow patterns. The
variable shapes are calculated by first computing the
distance to downgradient and lateral extents of the ground-
water flow boundaries around a pumping well, and then using a
TOT criterion to calculate the upgradient extent. Standar-
dized forms for various criteria are calculated for different
sets of hydrogeologic conditions. Input data for the
creation of the standardized shapes include basic hydrogeo-
logic parameters and well pumping rates.
Advantages
Advantages of the simplified variable shapes method are that
it can be easily implemented once the shapes of the standar-
dized forms are calculated, and that it requires a relatively
small amount of field data. In addition, relatively little
technical expertise is required to do the actual delinea-
tions. Generally, the only information required to apply the
shapes to a particular well or well field, once the standar-
dized forms are delineated, are the well-pumping rate,
material type, and the direction of ground-water flow. This
method offers a more refined analysis than the fixed radius
method, with only a modest increase in cost; significant data
collection is required (compared to calculated fixed radii)
in order to obtain the set of representative hydrogeologic
parameters needed to calculate the shapes of the standardized
forms and to determine the overall ground-water flow
velocities.
4-5
-------
Disadvantages
The simplified variable shapes method may not be accurate in
areas with many geologic heterogeneities and complex
hydrologic boundaries. If flow directions near a well differ
from those inferred from regional or subregional assessments,
erroneous coverage and insufficient protection result.
Example
An example in which the simplified variable shapes method was
used to delineate the highly prolific chalk aquifer in
Southern England can be found in "Guidelines for Delineation
of Wellhead Protection Areas" (U.S. EPA, 1987a).
4-6
-------
5. Analytical
-------
PRESENTATION SLIDES
ANALYTICAL DRAWDOWN METHODS
Slide 5.01
-------
WHPA DELINEATION METHODS
1) ARBITRARY FIXED RADIUS
2) CALCULATED FIXED RADIUS
3) SIMPLIFIED VARIABLE SHAPES
4) ANALYTICAL METHODS -
DRAWDOWN
5) HYDROGEOLOGIC MAPPING
6) NUMERICAL FLOW / TRANSPORT MODELS
Slide 5.02
-------
ANALYTICAL DRAWDOWN METHODS
DESCRIPTION
Delineation of a WHPA based on specified value of drawdown
criterion
ADVANTAGES
delineation based on site-specific hydrologeological data
these methods provide accurate coverage in cases when
the ZOI of a well is similar to the ZOC (i.e., flat water-
table conditions)
DISADVANTAGES
these methods may be inaccurate in sloping water-table
and anisotropic conditions, where the ZOI of a well does
not closely resemble the ZOC
may overprotect downgradient, and underprotect upgradient
Slide 5.03
-------
4000m
Drawdown
Contour
1m
0 _
.5m
.25m
- 4000m
-4000m
0
4OOOn
LOW PUMPING RATE
Pumping rate = 1500 ro3/day
Transmissivity = 250 m^/day
Storage coefficient = .1
Maximum drawdown = 8.8m
Duration of pumping = 180 days
Slide 5.04
-------
4000m
Drawdown
Contour
0_
- 4000m .
- 4000 m
I
0
4000m
HIGH PUMPING RATE
Pumping rate = 4500 m3/day
Transmissivity = 250 mvday
Storage coefficient = .1
Maximum drawdown = 26.4m
Duration of pumping =180 days
tte,
Slide 5.05
-------
4000m
Drawdown
Contour
O -
4000m
-4000m
4000m
LOW TRANSMISSIVTTY
Pumping rate = 1500 m3/day
Transmissivity =200 nr/day
Storage coefficient = .1
Maximum drawdown = 10.87m
Duration of pumping =180 days
Drawdown contours: .Olm, .025m, .05m,
1m, .2 5m, •5m
.075m,
Slide 5.06
-------
4000m
0 T
-4000m
-40OOm
4000m
jjTJGft TR^tSMTR.^jyTyV
Pumping rate = 1500 m3/day *?
Transmissivity = 2000 m2/day
Storage coefficient = .1
Maximum drawdown = 1.22m
Duration of pumping = 180 days
Slide 5.07
-------
DRAWDOWN METHOD EXAMPLE
OAKLEY, KANSAS rrf 5
AQUIFER DESCRIPTION
• Unconfined Aquifer
• Calcareous Sandstone with some clay, silt, gravel,
cobbles and boulders
• Transmissivity (T) = 20,000 gpd/ft
• Storativity(S) = .12
• Gradient (I) = 10 ft/mile to the east
MODEL DESCRIPTION
• Two Dimensional Finite Difference Model
• 50x50 Grid
• Node Spacing = 660 feet «f»«^> «£ Htr f«-V
• Program locates point at which 0.05 feet of drawdown is achieved
• Variable Pumping Rate of wells is averaged out over one year
RESULTS
Program calculated 0.05 feet of drawdown at a radius of 10,500 ft
Slide 5.08
-------
THEIS EQUATION -t,^c
S =
U =
114.6 Q
T
1.87r2S
Tt
INPUT DATA:
W(u)
Q = 676 gpm
T = 20,000 gpd/ft
s= drawdown (feet)
Q= pumping rate (gpm)
T= Transmissivity (gpd/ft)
S= Storage Coefficient
r= distance from pumped
well to observation well (ft)
t= time (days) - $60 d.
W(u)= Well Function (Appendix C)
Use the Theis Equation, and iterate to find the 0.05 ft drawdown
point.
1. Guess a value of r
2. Calculate u for that radius
3. Read W(u) from Appendix C
4. Calculate drawdown from Theis Equation
5. Estimate a new raduis that will yield a drawdown closer to .05 ft
6. Go to step 2.
7. Repeat until you reach a radius that yields a drawdown of 0.05 ft.
RESULTS
Theis equation calculated 0.05 feet of drawdown at 9,880 feet from
center of we I If ie Id
Slide 5.09
-------
Thomas Co.
Logan Co.
0.05-ft Drawdown
Contour
(Model)
0.05-ft
Drawdown
Contour
(Theis)
City of
Oakley
1 Water
Supply
Well
1 MILE
DRAWDOWN COMPARISON FOR OAKLEY, KANSAS
Slide 5.10
-------
PRESENTATION SLIDES
ANALYTICAL TIME-OF-TRAVEL METHODS
4
•A-'
Slide 5.11
-------
WHPA DELINEATION METHODS
1) ARBITRARY FIXED RADIUS
2) CALCULATED FIXED RADIUS
3) SIMPLIFIED VARIABLE SHAPES
4) ANALYTICAL METHODS -
TIME-OF-TRAVEL
tu an
a»«f«ttr* ; T '/
An* 9
5) HYDROGEOLOGIC MAPPING
£& v» Ct*C rH*' »*~
6) NUMERICAL FLOW / TRANSPORT MODELS
Slide 5.12
-------
ANALYTICAL TIME - OF - TRAVEL METHODS
DESCRIPTION
WHPA delineation based on the maximum time fora
contaminant to reach a well based on regional ground-
water advection patterns and velocities
ADVANTAGES
these methods incorporate varying amounts site -
specific hydrogeological data
considers physical processes and flow velocities
DISADVANTAGES
increased data requirements result in increased
costs
Slide 5.13
-------
TIME OF TRAVEL METHOD CASE STUDY
Brookings County, South Dakota
Brookings County, South Dakota
• Water supply wells draw water from Big Sioux Aquifer
. ZOCs determined for wells; no WHPAs delineated
• TOT equation used to define upgradient extent of ZOC
* Five year and ten year TOT distances computed
• Darcy's Law used to compute TOT distance based on regional
flow 1 gradient (effect of pumping well was neglected)
EQUATION
Darcy's Law
Velocity Definition
K= Hydraulic Conductivity
n= porosity
i= hydraulic gradient
x= distance
t= time (time of travel in this case) »'/» da.
Final Equation
= vt=4!i
x = vt
n
Slide 5.14
-------
TIME OF TRAVEL METHOD CASE STUDY
Brookings County, South Dakota (Com.)
Bruce Well # 1: Aquifer Data
• Aquifer Material: Unconsolidated glacial outwash (sand, gravel)
• Aquifer Thickness: 11 feet
• Aquifer Porosity: 0.20
• Hydraulic Conductivity: 670 ft/day
• Hydraulic Gradient: 0.0017 - Ai» afreet >>«<> e/*
\ ft i ^. \
'*
i*c 4r Lj/m *+* tftA «•» I a *>«
J
5 Year TOT Distance:
x_ ja (670ft/day) (0.0017) (1825days)
n 0.20
= 10,393 feet •* «. m'
10 Year TOT Distance:
y_ Kit
n
(670 ft/day) (0.0017) j3650 days)
0.10
= 20,786 feet ^ 4
Slide 5.15
-------
TIME OF TRAVEL METHOD CASE STUDY
Oakley, Kansas
Oakley, Kansas
• Water-supply wells draw water from Ogallala Formation
• 2 Types of WHPAs delineated -
Overall wellfield protection area:
0.05 ft drawdown contour
less
\ Ctrinf1ont
/
Individual well protection area:
1 80-day time-of-travel distance
\
/
restrictions
restrictions
180-day time-of-travel distance computed
using Darcy's Law for pore velocity based on
gradient across short sections of aquifer
moving rgyiially outwarH frnm wpll
(effect of pumping well considered)
ku~ f .
•»••*
}••*}
** *+
Aquifer Data: C
T = 20,000 gpd/ft
S = 0.12
Q = 300,000 gprii
'/>**
K = 235 gpd/ft
n = 0.15
t = 365 days
i = 0.002
Slide 5.16
-------
DARCY'S LAW APPROACH TO TOT CALCULATION
INCORPORATING EFFECTS OF PUMPING WELL
QL
-------
U =
U =
OL
CD
Ul
00
r •>
TIME OF TRAVEL METHOD CASE STUDY
Oakley, Kansas (Cont.)
X
1.87 S 2
Tt
(1.87) (0.1 2) r2 —
(20,000 gpd/ft ) (365 days)
= (3.07 x10"8) r2
r (ft) s (ft) A s
10 14.46
30 11.83 2.63
50 10.62 1.21
100 8.96 1.66
150 8.00 0.96
200 7.33 0.67
300 6.35 0.98
400 5.67 0.68
500 5.13 0.54
s= 114'6Q W(ll)
T
-i*^ (11 4.6) (208.3 gpm)
' ~ 20,000 gpd/ft 2
s = 1.194W(u)
(ft) Ax (ft) I A
20 0.13
20 0.061
50 0.033
50 0.019
50 0.013
100 0.0098
100 0.0068
100 0.0054
- W(u)
t (days)
0.74
1.6
7.2
12.5
18.4
48.7
70.1
88.3
V =
At =
Ax
At
Ax
K8
n
A x n
v Ki
(0.15) Ax
(31.4 ft/day) i
At = (4.77 x 10 "3) AX
£ t (days)
0.74
2.34
9.54
22.0
40.4
89.1
159
248
-------
o- -
5!
-------
PRESENTATION SLIDES
ANALYTICAL ZONE OF CONTRIBUTION METHODS
Slide 5.20
-------
WHPA DELINEATION METHODS
1) ARBITRARY FIXED RADIUS
2) CALCULATED FIXED RADIUS
3) SIMPLIFIED VARIABLE SHAPES
4) ANALYTICAL METHODS -
ZONE-OF-CONTRIBUTION
5) HYDROGEOLOGIC MAPPING
6) NUMERICAL FLOW / TRANSPORT MODELS
Slide 5.21
-------
ANALYTICAL ZONE OF CONTRIBUTION METHODS
DESCRIPTION
Involves delineating rPghfm.flffi?^°d,*^ujfa£g^^
which water tfi^t is fiyfijfl||^|ly_ftLiiqped from the well flows
ADVANTAGES
incorporate a number of site-specific hydrogeological
parameters
provide excellent protection of water supply
• the most accurale_oiihe analytical methods
DISADVANTAGES
implementation of these methods can be gps^Jy due
to the significant amount of hydrogeological data
required
mapping of topographic divides, recharge areas, and
flow boundaries required
Slide 5.22
-------
.
WHPA Delineation Using the
Uniform Flow Analytical Model
ORIGINAL
PIEZOMETRIC
SURFACE
GROUND
SURFACE
DRAWDOWN CURVE
CONFINED
AQUIFER
IMPERMEABLE
EQUIPOTENTIAL LINES
GROUNDWATER
DIVIDE
(b)
.X
2Kb!
UNIFORM-FLOW
EQUATION
DISTANCE TO
DOWN-GRADIENT
NULL POINT
BOUNDARY
LIMIT
LEGEND:
• Pumping Well
SOURCE: Todd. 1980
Where:
Q = Well Pumping Rate
K = Hydraulic Conductivity
b = Saturated Thickness
i = Hydraulic Gradient
rr = 3.1416
•£00
Slide 5.23
NOT TO SCALE |
-------
Distance
6000
-6000
-6000
Streamline
5 yearZOTs
-------
Distance
6000
-6000
Ol
o
re
-sooo
6000
Units = Meters
EXAMPLE 2 HJ01dLBUMeiM£_BATE, HORIZONTAL WATER TABLE
PUMPING RATE = 150 CUBIC METERS PER HOUR
REGIONAL HYDRAULIC GRADIENT = 0
Slide 5.25
-------
Distance
6000
-6000
xRegional flow line
-6000
ZOC boundary
6000
Units = Meters
EXAMPLE 3 IflW PMMPIMQ RATF, MODERATELY SLOPING
WATER TABLE
DATA
PUMPING RATE = 15 CUBIC METERS PER HOUR
REGIONAL HYDRAULIC GRADIENT = .05
REGIONAL FLOW IS FROM BOTTOM TO TOP OF FIELD
Slide 5.26
-------
I
Distance
Regional Flow Line
6000
-6000
-6000
EXAMPLE 4
wiriH
WATER TABLE
PATF, MODERATELY SLOPING
DATA
PUMPING RATE = 150 CUBIC METERS PER HOUR
HF.GIONAL HYDRAULIC GRADIENT = .05
IS FROM BOTTOM TO TOP OF
FIELD
Slide 5.27
-------
Distance
Regional Flow Line
6000
-6000
-6000
ONGLY SLOPING
CO
rt-
fl]
O
n>
6000
EXAMPLES
DATA
PUMPING RATE = 15 CUBIC METERS PER HOUR
REGIONAL HYDRAULIC GRADIENT = .1
REGIONAL FLOW IS FROM BOTTOM TO TOP OF
FIELD
Slide 5.28
-------
Distance
6000
o
»-»•
05
«-f
o>
o
re
-6000 ' "streamline
-6000 0
-- ZOC boundary uifcfl
EXAMPLE 6 g©W PUMPING RATE , STRONGLY SLOPING
WATER TABLE
6000
Units = Meters
DATA
PUMPING RATE = 150 CUBIC METERS PER HOUR
REGIONAL HYDRAULIC GRADIENT = .1
REGIONAL FLOW IS FROM BOTTOM TO TOP OF
FIELD
Slide 5.29
-------
PRESENTATION SLIDES
ANALYTICAL METHODS EXERCISE
Slide 5.30
-------
ANALYTICAL METHODS EXERCISE
•500
-250
-250
-500
-750
-1000
$«
03
Regional Flow
Discharging Well
250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000
-------
SOLUTION TO ANALYTICAL METHODS EXERCISE
CO
a
-------
5. ANALYTICAL METHODS
5.1 INTRODUCTION
Analytical methods are the most common delineation methods
used when, in more complex hydrogeologic settings, greater
accuracy is necessary than can be obtained from the previous
methods. These methods can define ground-water flow
boundaries and contaminant transport dynamics through the use
of equations representing flow in simple aquifer systems.
These methods are often completed with the aid of computers.
Analytical methods require the input of various hydrogeologic
parameters such as aquifer transmissivity and porosity,
hydraulic gradient, hydraulic conductivity, and saturated
thickness of the aquifer. Costs of using analytical methods
to delineate WHPAs are relatively low, but implementation
costs can be high if site-specific hydrogeologic data must be
developed for each WHPA. If sufficient information is not
available through pertinent local or hydrogeologic reports,
data collection may involve site studies, including test-well
drilling and pump tests.
The analytical methods explained in this section of the
course include calculating drawdown in a well using the Theis
equation (hand calculation) determining an appropriate area
using a volumetric flow equation with a TOT criterion and a
zone of contribution determination with a TOT criterion. The
first and last of these can be simplified by the use of
appropriate computer models which is also discussed. For
applicable ground-water computer models for the criteria and
analytical and numerical methods, consult the OGWP document,
model assessment for delineating WHPAs (EPA, 1988).
Advantages
Most hydrogeologists and civil engineers can understand the
methods and apply them correctly. Also, because these
methods take into account site-specific hydrogeologic
parameters, they provide more accurate representations of the
actual hydrogeologic settings than previous methods.
Disadvantages
The methods use models that generally do not take into
account hydrologic boundaries, aquifer heterogeneities, and
non-uniform rainfall or evapotranspiration.
5-1
-------
5.2 ANALYTICAL DRAWDOWN METHODS
Description
These analytical methods involve delineation of a WHPA based
on a specified threshold value of the drawdown criterion.
These values vary from hundredths of a foot in small aquifers
where the zone of influence (ZOI) is not areally extensive
and the maximum drawdown is small to several feet in regional
aquifers. Analytical methods that calculate drawdown, when
applied properly, can provide accurate descriptions of the
ZOI of a well. Accordingly, these methods should be employed
when delineation of a WHPA based on the ZOI of a well is
appropriate (i.e., horizontal water-table conditions).
Example
The equation most commonly used to calculate drawdown in
homogeneous, isotropic confined aquifers is the Theis
equation. The form of the Theis equation used to compute
drawdown is (Driscoll, 1986):
s . 114.6 0 Wful
where,
s = drawdown, in ft, at any point in the vicinity of a
well discharging at a constant rate
Q = pumping rate, in gpm
T = coefficient of transmissivity of the aquifer, in
gpd/ft
W(u) = is read "well function of u" and represents an
exponential integral
In the W(u) function, u is equal to:
u
where,
= 1.87r S
Tt
S =
T =
t -
distance, in ft, from the center of a pumped well
to a point where the drawdown is measured
coefficient of storage (dimensionless)
coefficient of transmissivity, in gpd/ft
time since pumping started, in days
Values of W(u) for computed values of u can be obtained from
the Well Function table in Appendix C.
5-2
-------
Many computer programs have been designed to solve the Theis
equation and calculate drawdown. One such program, THWELLS
(van der Heijde, 1987), will be used here to demonstrate the
effects of aquifer transmissivity and well-pumping rate, all
other factors the same, on the size of a WHPA delineated on
the basis of the ZOI of a well. THWELLS was developed to
calculate head drawdown or buildup at any location in a
confined aquifer due to the summation of discharge (pumping)
or recharge (injection) of up to 100 wells.
Data input includes the number of wells, aquifer trans-
missivity and storage coefficient, the x and y coordinates of
pumping or injection wells, discharge or recharge rate, and
duration of pumping. Effects of no-flow or constant head
line boundaries can be simulated using image-well theory.
The program outputs the drawdown or buildup at any location
(x,y) in the aquifer as a result of each individual well and
the sum of all effects. The program has options for
determination of head response at a particular time, both
presented in tabular and graphic format.
Slides 5.4 through 5.7 are examples of THWELLS graphic output
to a dot matrix printer. The figures show, in plan view,
contours of drawdown around a single pumping well. Slides
5.4 and 5.5 show the effect of low and high pumping rates,
respectively, on the size of the ZOI. Other factors equal,
the size of a WHPA will increase with increasing pumping
rate.
Slides 5.6 and 5.7 show the effect of low and high trans-
missity, respectively, on the size of the ZOI and the
configuration of the water table. Other factors equal, the
size of a WHPA may either increase or decrease with increas-
ing transmissivity depending on the drawdown threshold chosen
to delineate the WHPA. For example, in Slides 5.6 and 5.7,
the 0.25m drawdown contour moves closer to the well for the
case of higher transmissivity which would result in a smaller
WHPA (if 0.25m were the criterion threshold). However, the
0.01m drawdown contour moves farther from the well, which
would result in a larger WHPA. The data used in each THWELLS
run and the important points of comparison among the four
cases are summarized below:
5-3
-------
SLIDES 5.4 and 5.5
DATA
transmissivity = 250 square meters per day
storage coefficient = .1
contours are .25 meters, .5 meters, 1 meter
. pumping rate in Figure 5.1.1 is 1500 cubic meters per
day
. pumping rate in Figure 5.1.2 is 4500 cubic meters per
day
. maximum drawdown in Figure 5.1.1 is 8.8 meters
. maximum drawdown in Figure 5.1.2 is 26.4 meters
NOTE:
similar contours are found at greater distances from
well in Figure 5.1.2
ratio of maximum drawdowns is equal to ratio of
pumping rates. Pumping rate is directly proportional
to drawdown in Theis equation
a well pumping at a greater rate, all other factors
the same, has a larger ZOI and will require a larger
WHPA to protect the well if a threshold value of the
drawdown criterion is the basis of delineation
5-4
-------
SLIDES 5.6 and 5.7
DATA
. pumping rate = 1500 cubic meters per day
. storage coefficient = .1
8000 meter x 8000 meter field
. drawdown contours are .01 meters, .025 meters, .05
meters, .075 meters, .1 meters, .25 meters, .5 meters
maximum drawdown in Figure 5.1.3 is 10.87 meters
maximum drawdown in Figure 5.1.4 is 1.22 meters
. aquifer transmissivity in Figure 5.1.3 is 200 square
meters per day
. aquifer transmissivity in Figure 5.1.4 is 2000 square
meters per day
all other factors the same, wells in aquifers of
higher transmissivity will create a lower maximum
drawdown. Transmissivity and drawdown are inversely
proportional in the Theis equation
all other factors the same, wells in aquifers with
higher transmissivities will have a larger ZOI (but
delineated WHPAs may be larger or smaller depending
on selected threshold value of drawdown criterion)
wells in aquifers with high transmissivities
generally have a long and flat cone of depression,
while wells in low transmissivity aquifers generally
have a short and steep cone of depression
5-5
-------
A second example is provided showing a comparison between a
WHPA delineated for a wellfield in Oakley, Kansas using a
numerical model and the same WHPA delineated using the Theis
analytical equation (Slide 5.9). A drawdown threshold of
0.05 ft was used to delineate the WHPA. The numerical model
results placed the WHPA boundary at a radius of approximately
11,500 ft from the center of the wellfield. The Theis
solution agreed well with the numerical model, computing the
0.05 ft contour at a radial distance of approximately 9,900
ft from the center of the wellfield (Slide 5.10).
5.3 ANALYTICAL TIME-OF-TRAVEL METHODS
Description
Analytical methods that can be used to delineate WHPAs based
on the Time of Travel (TOT) criterion calculate the travel
time required for a contaminant to reach a pumping well.
This is usually done through the reverse-tracking of a
particle using predicted regional ground-water advection
patterns and velocities. The mapped distance from the well
to the outer edge of the WHPA is the product of the average
ground-water velocity times the TOT criterion threshold
specified by the pertinent regulations. TOT analytical
methods incorporate varying degrees of site-specific
hydrogeologic information and vary greatly in terms of their
complexity. Some of the types of data that are likely to be
required to implement these methods are aquifer porosity,
hydraulic conductivity, regional flow gradient, aquifer
transmissivity and storativity, and pumping and injecting
rates.
An example of a simple analytical method that can be used
with the TOT criterion is the volumetric flow equation. This
equation determines the aquifer volume required to yield the
volume of water removed from the aquifer in a period equal to
the TOT criterion threshold. This method requires aquifer
porosity and pumping-rate data, as well as the open interval
of the well.
Examples
The first example (Slides 5.14 and 5.15) illustrates the use
of Darcy's Law to compute pore water flow velocity and TOT
distance. The method has been used in a number of WHPA
delineations including a project in Brookings County, South
Dakota (Case Study B.I). The method, as employed here, uses
the regional gradient (i) to compute flow velocity and does
not take into account the effects of the pumping well.
Distances were computed for 5-yr and 10-yr TOT thresholds.
5-6
-------
The second example (Slides 5.16 to 5.19) is based on a
method used to delineate small 180-day TOT zones ground
individual wells in an Oakley, Kansas wellfield (Case Study
B.3). More limiting use restrictions were to apply to these
smaller protection zones within the larger WHPA for the
entire wellfield. The Theis equation is used to compute the
drawdown curve with radial distance from a well. This radial
distance is then subdivided into short segments (Slide 5.17),
and Darcy's law is applied to each segment to compute pore-
water velocity and TOT. .Travel times for individual segments
are summed, moving radially outward from the well, until the
cumulative TOT equal 180 days (Slides 5.18 and 5.19).
Another analytical method that incorporates the TOT criterion
is the analytical transport model RESSQ. An introduction to
the model and some example runs are included in the following
section of zone-of-contribution methods.
5.4 ANALYTICAL ZONE OF CONTRIBUTION METHODS
Description
A desirable way to ensure protection of a water-supply well
is to protect the land surface and the subsurface regions
that contribute water to the water supply. This region of
the flow system is called the zone of contribution, or ZOC.
The ZOC includes all recharge areas and subsurface regions
through which water flows to the pumping well. To determine
the entire ZOC of a well or wellfield requires an understand-
ing of the well hydraulics of the system as well as hydrogeo-
logic mapping of topographic divides, recharge areas, and no-
flow boundaries.
One method of defining the ZOC involves the use of the
uniform flow equation to determine the stagnation point
downgradient from a well and the width of the upgradient zone
that contributes flow to the well. This method is discussed
in greater detail in the Delineation Guidelines (EPA, 1987a,
p. 4-14).
The stagnation point or downgradient null point marks the
distance beyond which flow in the aquifer will not be drawn
into the well under the influence of pumping. The boundary
limits of the ZOC in the direction upgradient from the well
define the width of aquifer (given its depth, conductivity,
and prevailing regional (gradient) required to supply flow to
the discharging well. These concepts are summarized in Slide
5.23. The equations employed in this method will be
explained further in the hands-on exercise in Section 5.5,
"Analytical Methods Exercise."
5-7
-------
The sizes of ZOCs can vary greatly. In the case of small
production wells operating in prolific, horizontal water-
table aquifers, the ZOC can be an area with a radius of tens-
of-feet. In the case of a larger well field, the ZOC can
extend miles from the well field and, in the case of the
confined aquifers not necessarily be contiguous with the well
field. Because in some cases it is unrealistic to set aside
such large areas to serve as WHPAs, the entire ZOC of a well
is not normally chosen as the WHPA. Instead, in such cases,
the ZOC is combined with a TOT criterion threshold and the
portion of the ZOC that contributes flow to the well within
that time period serves as the WHPA. These zones of
transport (ZOT) are identified by contours of equal travel
time (isochrones).
RESSO - WHPA Delineation Using Flow Boundary and TOT Criteria
Many analytical methods can be used to delineate WHPAs on the
basis of ZOTs. One such method is the computer model RESSQ
(Javandel, et al, 1984). RESSQ, a semi-analytical model, is
designed to calculate two-dimensional contaminant transport
by the processes of advection and adsorption in homogeneous,
isotropic, confined, and steady-state flow-field aquifers.
To run RESSQ, the following input data are required: aquifer
thickness, porosity, pumping/injection rates, regional pore
water velocity, direction of regional flow, injection
contaminant concentration, and the adsorption capacity of the
rock matrix.
The model produces tabular and graphic output. The tabular
output lists the final destinations and arrival times of
streamlines as well as a contaminant concentration profile
over time for production wells receiving contamination. The
graphic output displays the location of production/injection
wells, with streamlines plotted to depict the flow field.
Time-of-travel fronts may also be displayed.
The user specifies the number of streamlines leaving each
well, the time periods for which the contaminant fronts are
plotted, and the total time of simulation. The ability to
calculate and display chosen time fronts makes RESSQ an
excellent tool for TOT delineation applications.
The following hypothetical situations were developed using
RESSQ in order to demonstrate the effects of pumping rates
and regional hydraulic gradients on the ZOTs of a well. The
examples were developed assuming an isotropic, homogeneous,
confined aquifer with no assimilative capacity, and saturated
5-8
-------
thickness of 10m. Hydraulic conductivity (K) is 100 m/yr,
and effective porosity (n) is 0.1. Six cases were developed
to illustrate the relationship between regional gradient and
pumping rate in determining the size at the ZOT. Three
regional gradients were selected from horizontal to fairly
steep (0, 0.05, 0.1) and, for each gradient, the flow field
was computed for low and high pumping rates (15 m3/hr, 150
m3/hr). Changes in the regional hydraulic gradient were
effected by changing the regional pore-water velocity.
Hydraulic gradient and pore-water velocity are related by the
equations:
V = 3 = Ki
n n
where,
v = pore-water velocity (m/yr)
q = average (regional) ground-water velocity (m/yr)
n = porosity of aquifer = .1
K = hydraulic conductivity = 100 m/yr
i = hydraulic gradient (dimensionless)
By keeping the values of K and n constant, the desired
hydraulic gradient was obtained by entering the corresponding
pore-water velocity value into the model.
The time fronts in each example are plotted for 5, 10, 15,
20, and 25 years. Note the acceleration as flow approaches
the pumping well (i.e., greater distances traversed in
successive 5-yr intervals as flow moves toward well).
The data used in each RESSQ run and the important points of
comparison among the six runs are summarized below:
5-9
-------
RESSO EXAMPLES
EXAMPLE 1: LOW PUMPING RATE, HORIZONTAL WATER TABLE
(Slide 5.24)
DATA
pumping rate =15 m3/hr
regional hydraulic gradient = 0
SHOWS
ground-water velocity increases as the water
approaches pumping center due to increased hydraulic
gradient
straight pathlines, approach well radially
all ZOCs circular with this method of calculations
NOTE
ideal conditions for use of calculated fixed radius
method
method can be applied with high accuracy
5-10
-------
EXAMPLE 2; HIGH PUMPING RATE, HORIZONTAL WATER TABLE
(Slide 5.25)
DATA
pumping rate = 150 m3/hr
regional hydraulic gradient = 0
SHOWS
increased radius of WHPA for a given TOT
ground-water velocity increases slightly as water
approaches pumping center due to increase hydraulic
gradient
straight pathlines, approach well radially
all ZOCs circular
NOTE:
ideal conditions for calculated fixed radius method
method can be applied with high accuracy
5-11
-------
EXAMPLE 3; LOW PUMPING RATE, MODERATE WATER-TABLE GRADIENT
(Slide 5.26)
DATA
pumping rate = 15 m3/hr
regional hydraulic gradient = .05
regional hydraulic gradient flows from bottom to top
of page
SHOWS
NOTE:
ZOCs highly skewed in upgradient direction
stagnation point clearly marked
ground-water velocities greatly accelerated within 5
year TOT boundary
application of calculated fixed radius for WHPA
leads to erroneous coverage - under coverage if
downgradient radius is chosen, over coverage if
upgradient radius is chosen
under these conditions, CFR method is inappropriate,
analytical methods should be used to increase
accuracy of delineation
ZOC is increasingly skewed with increased TOTs.
5-12
-------
EXAMPLE 4: HIGH PUMPING RATE, MODERATE WATER-TABLE GRADIENT
(Slide 5.27)
DATA
pumping rate = 150 m3/hr
regional hydraulic gradient = .05
regional hydraulic gradient flows from bottom to top
of page
SHOWS
pathlines curve slightly (within 25 year TOT limits)
as approach well
ZOC skewed slightly in upgradient direction - degree
of skew increases with increasing TOT
NOTE
in the case of a well with a high pumping rate in an
aquifer with a moderate hydraulic gradient, ZOCs are
nearly circular for TOTs of 5 to 10 years
under these conditions, the calculated fixed radius
methods is appropriate if applied with 5 and 10 year
TOTs. Application to TOTs beyond 10 years results in
increased erroneous coverage
5-13
-------
EXAMPLE 5; LOW PUMPING RATE, HIGH WATER-TABLE GRADIENT
(Slide 5.28)
DATA
pumping rate = 15 m3/hr
regional hydraulic gradient = .1
regional hydraulic gradient flows from bottom to top
of field
SHOWS
ZOC is almost entirely upgradient of pumping center
NOTE
under these conditions, the calculated fixed radius
method results in unacceptable coverage and error
5-14
-------
EXAMPLE 6; HIGH PUMPING RATE, HIGH WATER-TABLE GRADIENT
(Slide 5.29)
DATA
high pumping rate: 150 m3/hr
regional hydraulic gradient = .1
regional hydraulic gradient flows from bottom to top
of field
SHOWS
a high pumping rate reduces the effect of a large
gradient within the 5 yr TOT, but the ZOCs for the
remaining time fronts are skewed such that the
calculated fixed radius method would provide an
unsatisfactory WHPA delineation for TOTs greater than
5 years
NOTE
calculated fixed radius is unacceptable delineation
method if applied under such conditions with TOTs
greater than 5 years
5-15
-------
5.5 ANALYTICAL METHODS EXERCISE
The purpose of this exercise is to employ two analytical
methods to define the boundary of a WHPA. The uniform flow
equation is used to define the boundary of the aquifer zone
contributing flow to a pumping well. Darcy's law is then
used to computer a time-of-travel distance that defines the
upgradient extent of the WHPA for a specified TOT criterion.
Two approaches to applying these methods are presented. The
first approach is based on a method applied in Brookings
County, South Dakota (see Case Study B.l). The approach
requires only three calculations to define the WHPA.
The second approach involves generating a better approxima-
tion to the zone-of-contribution (ZOC) by using the uniform
flow equation repeatedly to compute many points along the
flow boundary. At the completion of the exercise, compare
the WHPAs delineated using these two approaches.
5-16
-------
©-
Approach 1
1) For this exercise, use equations from the Uniform
Flow Analytical Model and the following data:
Q = 46, 170 ft3/day,
i = .001
to compute
a) Distance to the downgradient null point, XL
b) Maximum width of influx zone, 2YL
2) Use the relationship, V=Ki/n, to calculate the
distance to the 5-year time-of-travel line. Porosity
= .20. v^uaacfiir. ,,,4.
110
3) Plot (using graph paper provided, Slide 5.31) the
shape of the ZOC; assume YL is the cross-gradient
distance to the ground-water divide. Then draw the
5-year time-of-travel line as the upgradient boundary
of ZOC to create a 5-year zone-of-transport (ZOT).
J . v/CO * (/.»«X*>*f - *****
Approach 2 y
1) Again using the uniform flow equations, compute the X
and Y coordinates of points along the ground-water
divide for Y = 800, 762, 734, 674, 587, 514, 440, and
293.
Hint: the uniform flow equation along the ground-
water divide reduces to: X^Tjf
,—J *
x = -Y Jcotf (Y/-XL)
where cotangent is in radians *ftf- «•
2) Use the points generated in #2 above, the value for "**
XL computer in Approach 1, #1 and the 5-year time-of- ,.
travel line computed in Approach 1, #2 to delineate **-
the WHPA produced using the uniform flow equations
and a 5-year time-of-travel criterion threshold.
Part 3
1) How do the WHPAs delineated using the two approaches
compare?
5-17
-------
SOLUTIONS:
Approach 1
la) XL =
- Q
27rKbi
XL =
Ib)
*L = ± Q
2Kbi
46,170 ft3/day
2»r(228 ft/day) (110 ft) (.001)
-293 ft
± 46,170 ft3/day
2)
V = Ki
2(228 ft/day)(110 ft)(.001)
J = ±920 ft
(228 ft/day)(.001) = 1.139 ft/day
n .20
Distance to 5-year TOT line = (velocity)(1825 days) = 2,079 ft
3) See Graph (Slide 5.32)
Approach 2
1) Using X = -Y cot (Y/-XL)
for Y = 762:
X = (-762 ft) cot (762 ft/293 ft)
= 1268 ft
X (ft)
Y (ft)
1834
1268
982
606
269
93
-31
-188
800
762
734
674
587
514
440
293
2) See Graph (Slide 5.32)
Part 3
The simpler approach used in Brookings County, SD is also more
conservative (i.e., it protects a large area). For the aquifer
conditions presented here, the two approaches agree well.
5-18
-------
6. Mapping
-------
PRESENTATION SLIDES
HYDROGEOLOGIC MAPPING METHODS
Slide 6.01
-------
WHPA DELINEATION METHODS
1) ARBITRARY FIXED RADIUS
2) CALCULATED FIXED RADIUS
3) SIMPLIFIED VARIABLE SHAPES
4) ANALYTICAL METHODS
5) HYDROGEOLOGIC MAPPING
6) NUMERICAL FLOW / TRANSPORT MODELS
Slide 6.02
-------
HYDROGEOLOGIC MAPPING METHODS
DESCRIPTION
Delineation of WHPAs by mapping TOT and flow boundary
criteria using geological observations, geophysical data, and
dye-tracing methods
ADVANTAGES
well suited to hydrogeologic settings
es, as are found in many glacial and alluvial
aquifers with high flow velocities, and to highly anisotropic
aquifers
DISADVANTAGES
reonire specialized expense in geologic and geomorphic
mapping
on what constitute likely flow
boundaries
less suited to delineatind WHPAs in large or deep aquifers
Slide 6.03
-------
HYDROGEOLOGIC MAPPING
Flow System Boundaries:
Recharge
Impermeable
Flow Divides
Conduit Flow Paths
Slide 6.04
-------
MAPPING TECHNIQUES
GENERAL GEOLOGIC MAPPING
- TOPOGRAPHY
- WATER LEVELS
- WATER QUALITY
- GEOLOGIC CONTACTS
- LINEAMENT ANALYSIS
- AQUIFER TESTS
. GEOPHYSICS
. DYE TRACING
. AGE ASSESSMENT (TRITIUM)
Slide 6.05
-------
WHPA Delineation Using Hydrogeologic Mapping
(Use of Ground-water Divides)
STREAM
VALLEY
/
STREAM
LAND SURFACE
WHPA
WHPA
DRAWDOWN GROUND-WATER
CONTOURS / DIVIDE
LEGEND:
Water Table
Pumping Well
Ground-water Divide
Direction of Ground-water Flow
WHPA
Slide 6.06
-------
GROUND-WATER DIVIDE
+23
+24
+25
Ground-
water divide
+25
+24
+21 +22
+23
Slide 6.07
-------
WATER QUALITY MAPPING:
MOHAWK RIVER BASIN, NEW YORK
WELL FIELD A
MOHAWK
RIVER
WELL FIELD B
..;«..SAND AND GRAVEL .' ' • '. • >•
•• /.'•-•-•••" *"•'»• • ••"..• •/.. ':-'•'-:••„:'
••'..•.• . V'. ; o- • .•-..-•-.• - -« " '-
-------
WHPA Delineation Using Hydrogeologic Mapping
(Use of Geologic Contacts)
STREAM
PUMPING WELL
BEDROCK (NON-AQUIFER
MATERIAL)
ALLUVIAL AQUIFER
Primary WHPA Boundary Drawn as Contact
Between Aquifer and Non-Aquifer Material
NOTE: A secondary protection zone could be delineated based on
the larger area of recharge derived from surface runoff, and
inferred from topography and basin boundaries.
Slide 6.09
NOT TO SCALE
-------
GEOLOGIC CONTACT MAP:
EDWARDS AQUIFER, TEXAS
\RECHARGE
ZONE
UNCONFINED
EDWARDS FORMATION
A.
RECHARGE POND -t
CONFINED
EDWARDS FORMATION
.STREAM
RECHARGE DAM
-A'
o WATER SUPPLY
WELL
PLAN
EDWARDS ' i1 | '| ' |
FORMATION'] • •
RECHARGE
ZONE
A'
^WATER SUPPLY
( WELL
\GLEN ROSE
LIMESTONE
GLEN ROSE
LIMESTONE
SOIL COVER
CONFINING
CLAY UNIT
EDWARDS
FORMATION
CROSS-SECTION
Slide 6.10
-------
Terminology for Wellhead Protection Area
Delineation (Hypothetical Ground-water
Basin in Fractured Rock)
y ' . /
Fractured Rocks
A1
X
Fractured •!
Zone /
\
VERTICAL PROFILE
Stream
A1
PLAN VIEW
SOURCE: Modified from Ouon. 1981
LEGEND:
V. Water Table
w
*>£ Fractures
Ground-water Divide
Slide 6.11
NOT TO SCALE
-------
AQUIFER TEST DETERMINATION
OF AQUIFER BOUNDARIES
._ Lend surface t^
Unconfined • aquifer.* •/ .'' . ^ •. \ +-J- ' »
-_Confining -^ bedi^-_ -3. ^."^
t = O
Discharge (0) = Recharge(R)
t = 1 hr.
Withdrawal (0)- Reduction in storage (As)
t = 6 hrs.
Withdrawal (0) = Reduction in storage (As) + Reduction in discharge (Ao)
t = 24 hrs.
Withdrawal (0): Reduction in discharge (Ao) + Increase in recharge (An)
(Source: Heath, 1983)
Slide 6.12
-------
GEOPHYSICAL METHODS
Elastic-seismic
Electrical
Density-Gravimetric
Magnetic
Slide 6.13
-------
WHPA Delineation Using Hydrogeologic Mapping:
Dye Tracing (Example From Kentucky)
'600-^ Potentiometric surface
„ » Traced flow route
• Sinking spring
—O Spring-fed stream
1. Intermittent stream
^--— Sinking stream
^ , , • Inferred ZOC of spring A based on
mapping of potentiometric surface
A Municipal water supply spring
- — -»»- Inferred direction of ground-water flow
Sinking stream B was found to not be in ZOC of spring A,
although this would be inferred from potentiometric surface.
Modified from Quinlan and Ewers. 1985
Slide 6.14
NOT TO SCALE
-------
AGE ASSESSMENT
EVALUATION OF LEAKINESS OF CONFINING
STRATA
TRACERS
- TRITIUM
- TRICHLOROFLUOROMETHANE (CCI3 F)
Slide 6.15
-------
PRESENTATION SLIDES
MAPPING CASE STUDY AND EXERCISE
Slide 6.16
-------
MAPPING EXERCISE SETTING
BOWLING GREEN, KENTUCKY
PUBLIC WATER SUPPLY DERIVED FROM UNCONFINED
KARST AQUIFER
WHPA DELINEATION STUDY CURRENTLY IN PROGRESS
DYE-TRACER STUDIES COMPLETED TO DEFINE FLOW
ROUTES
FLOW VELOCITY STUDIES COMPLETED FOR SOME
MAJOR FLOW ROUTES
Slide 6.17
-------
SYSTEM
QUATER-
NARY
tr >•
• o a
>• z
tt C
< UJ
- i
iu x
(- O
-------
LOST RIVER BASIN HYDROLOGY
SINKHOLES
SINKHOLE COLLAPSE
INTO CAVE STREAM
; Regolith (Soil)
*»"|j|
T^il Limestone
BASE FLOW
SURFACE
STREAM
CLOGGED
DRAIN
WATER PONDED
BEHIND CAVE
CONSTRICTION
CLOGGED
DRAIN
WATER PONDED
FROM SURFACE
STREAM
FLOOD STAGE
(after Crawford, et al, 1987)
Slide 6.19
-------
LOST RIVER
BASIN FEATURES
Contour interval 10 feet
(after Crawford, et al, 1987)
UNKEN SPRIN
WINDOW
Slide 6.20
Surface Stream
S^2 Intermittent Karst Lake
Intermittent Stream
Hypothesized Route Subsurface
~*— -"">v Stream
O Spring
• Karst Window
City Limits
Water Table Elevation
Oye Trace of Subsurface Stream
Subsurface Stream Flowing
through Mapped Cave
-------
100-
50-
co
O
tl!
10-
I I
5
I I
10
I I I I I I I I I
20 30 40 50 100
200
DISCHARGE (cfs)
TIME OF ARRIVAL OF TRACER vs. DISCHARGE
(after Crawford, et al, 1987)
Slide 6.21
-------
HYDROGEOLOICAL MAPPING EXERCISE
WHPA CRITERIA: FLOW BOUNDARIES
THRESHOLD: BOUNDARIES OF BASIN
METHOD: MAPPING WATER LEVELS AND
GROUND-WATER DIVIDES
USING DYE TRACER INFORMATION AND WATER-LEVEL
MAP DETERMINE BOUNDARIES OF THE GROUND-WATER
FLOW BASIN TO LOST RIVER RISE SPRINGS
Slide 6.22
-------
PRESENTATION SLIDES
GROUP EXERCISE
(MAPPING AND ANALYTICAL METHODS)
Slide 6.23
-------
GROUP EXERCISE
LARAMIE BASIN WYOMING
r -
3 SCENARIO'S
- UNCONFINED, POROUS MEDIA
c - .01$
- CONFINED. POROUS MEDIA
- FRACTURED ROCK, UNCONFINED
EXERCISE FORMAT
- GROUPS OF 4 TO 5
- PRESENTATION OF HYDROGEOLOGIC SETTING
- ASSISTANCE DURING EXERCISE
- SUMMARY FOR EACH SCENARIO
Slide 6.24
-------
WYOMING
LAP AMI £
BASIN
LARAMIE
CHEYENNE
i IOO
MILES
Location of the Laramie Basin and Laramie
Slide 6.25
-------
a>
ro
Geologic cross sections, Laramie area, Albany County, Wyoming.
P4 A'
B
C72
r..n-r CITY SPRINGS
FAULT FAULT
C2I
CI9
HORSE CREEK FAULT
CP I Spring
P8
Spring
-------
R73WIR72W
Pope •
Springs
Soldier /
Springs ./
Cosper-Sotonko Conlocl
Cosper Outcrops To Right
Foult. D-Downthrown Side
U- Upthrown Side
-t i-
Monocline. Arrows Show
Direction Of Dip
-I 1-
Anticline
Ground Woter Flow Directions
In Unfroctured Zones
Ground Woter Flow Directions
Along Tectonic Structures
Areos With Excellent Ground
Woter Development Potentiol,
See Toble 2
Spring
Well, Numbers Correspond To
Toble I
2 Miles
R73WIR72W
Locations of tectonic structures, selected wells and springs, and ground-water flow directions in the vicinity of
i.aramie, Wyoming.
Slide 6.27
/f
-------
EXERCISE I: UNCONFINED POROUS MEDIA (SCENARIO I)
WHPA CRITERIA: TOT
THRESHOLD: 5 YEAR
METHODS: A. CALCULATED FIXED RADIUS
(VOLUMETRIC FLOW EQUATION)
B. UNIFORM FLOW ANALYTICAL MODEL
WITH PORE WATER VELOCITY EQUATION
INPUT PARAMETERS:
WELL = C40
K = 0.70 FT/D
b = 200 FT
S = 0.001
Q = IxlO5 FTVDAY
n = 0.01
H = 50"
Slide 6.28
-------
EXERCISE I & II WORKSHEET
"CTWttH CONFINED AND Ut.CONr.NEO
Of THC CASPER
LINE OF EQUAL ELtVATION IN FEET ABOVE
MEAN SEA LEVEL OF THC POTENTlOMETRIC '
SUflFACE ASSOCIATED WITH THE
CASPER AOUIFER
CASPtR / PRECAMBRIAN CONTAC1
CITY
SPRINGS />
LARAMEE
-------
EXERCISE II: CONFINED POROI
TSCENARIO 2)
WELL C36
WHPA CRITERIA: TOT
THRESHOLD: 5 YEAR
METHODS: A. CALCULATED FIXED RADIUS
(VOLUMETRIC FLOW EQUATION)
B. UNIFORM FLOW ANALYTICAL MODEL
WITH PORE WATER VELOCITY EQUATION
USE WHPAs FROM EXERCISE I AS SIMPLIFED
SHAPES FOR WELL C36
EVALUATE VALIDITY OF WHPAs FROM
EXERCISE I IF DRAWN AROUND WELL C38
(I.e., DO CONFINING CONDITIONS PRESENT AT
C38 ALLOW FOR REINTERPRETATION OF WHPA
BOUNDARIES?)
NOTE: DEPTH TO AQUIFER IS 300 FT
Slide 6.30
-------
EXERCISE III: FRACTURED ROCK AQUIFER
(SCENARIO 3)
CITY SPRINGS
WHPA CRITERIA: FLOW BOUNDARIES
THRESHOLD: ZOC
METHODS: HYDROGEOLOGIC MAPPING
INPUT PARAMETERS:
K = 0.7 FT/D
b = 200FT
S = 0.01
Q = IxlO6 GAL/DAY
n = 0.20
RECHARGE =1.4 IN/YEAR
Prv
HINT: PERFORM MASS BALANCE
Q = RECHARGE RATE X RECHARGE AREA
slide 6.31
-------
EXERCISE III WORKSHEET
LINE OF EQUAL ELEVATION IN FEET ABOVE
MEAN SEA LEVEL OF THE POTENTIOMETRIC
SURFACE ASSOCIATED WITH THE CASPER
AQUIFER
CASPER / PRECAMBRIAN CONTACT
CONTACT BETWEEN CONFINED AND UNCON- 0
FINED PORTIONS OF THE CASPER AOUIFER
AREA IN WHICH THE CASPER FORMATION
IS UNSATURATEO
LARAMIE
CITY
SPRINGS^*
C QUARRY FAULT
a
-------
EXERCISE IA: CALCULATED FIXED RADIUS, VOLUMETRIC FLOW SOLUTION
LINE Of COUAL CLCVATION IN FCII iBOVC
MIAN SCA LCVEl OF TMt POTCNTIOMCTRIC
SUtFACC AS90CMTCO WITH TMt
CASPER AOUIFCft
CASPCR / PRCCAMBRIAN CONTACT
4
CITY -^ '
SPRINGS />
LARAMEE
-------
EXERCISE IB: UNIFORM FLOW ANALYTICAL FLOW MODEL SOLUTION
LINE OF tOUAL ELEVATION IN Hit ABOVE
MEAN SfA LEVEL Of TMt POTENTOMtTOIC
SURFACE ASSOCIATED WITH THE
CASPtR AQUIFER
fAULT
LARAMIE
0 2OOO 4OOO
SCALE (fill)
-------
EXERCISE IB: UNIFORM FLOW ANALYTICAL FLOW MODEL'SOLUTION
-------
EXERCISE HA: SIMPLIFIED VARIABLE SHAPES SOLUTION
LINE OF EQUAL ELEVATION IN FEtT
MEAN SCA IEVIL OF TMt POTCNTX9MCTIIIC
SURFACE ASSOCIATCO WITH THE
CASPER AOUIFCR
FAULT
CASPER / PRECAMBRIAN CONTACT
CITY
S SPRINGS
-------
EXERCISE III: RECHARGE AREA AND DARCY'S LAW SOLUTION
LINE OF EQUAL ELEVATION IN FEET ABOVE
MEAN SEA LEVEL Of THE POTENTIOMETRIC
SURFACE ASSOCIATED WITH THE CASPER
AQUIFER
CASPER / PRECAMBRIAN CONTACT
CONTACT BETWEEN CONFINED AND UNCON
FINED PORTIONS OF THE CASPER AQUIFER
AREA IN WHICH THE CASPER FORMATION
IS UNSATURATED
LARAMIE
I I 1 1 I I
K O O I I
• oof/
HAM /
CITY
SPRINGSyO -i
-------
6. HYDROGEOLOGIC MAPPING METHODS
6.1 INTRODUCTION
In the hierarchy of WHPA delineation methods, hydrogeologic
mapping methods are categorized above analytical methods and
below numerical flow and transport modeling methods in terms
of sophistication and cost.
Hydrogeologic techniques used in field investigations provide
site-specific data and a detailed characterization of the
aquifer. In this sense, the methods provide a more accurate
representation of flow boundaries and aquifer features than
do simple analytical techniques which often require simplify-
ing assumptions (e.g., infinite boundaries).
Field mapping and data collection methods, however, cannot
integrate the aquifer data into a comprehensive picture of
the flow characteristics and expected time-response of the
aquifer as can numerical flow and transport models.
Advantages
Hydrogeologic mapping is well suited to hydrogeologic
settings dominated by near-surface flow boundaries, as are
found in many glacial and alluvial aquifers with high flow
velocities, and to highly fractured anisotropic aquifers,
such as fractured bedrock and conduit-flow karst.
Disadvantages
The method requires specialized expertise in geologic and
geomorphic mapping, plus significant judgment on what
constitutes likely flow boundaries. This method is also less
suited to delineating WHPAs in large or deep aquifers.
6.2 OVERVIEW OF HYDROGEOLOGIC MAPPING METHODS
Hydrogeologic mapping techniques can be employed to locate
physical features for WHPA boundaries. Features such as
ground-water flow system boundaries and principle flow
conduits can in many circumstances be mapped.
Flow system boundaries, which can be mapped by various
methods, are of three types:
Impermeable boundaries,
Ground-water flow divides, and
Recharge boundaries
6-1
-------
thologic changes can present a barrier to flow where an
-quifer is in contact with less permeable material, such as
bedrock or fine-grained deposits. Ground water divides often
coincide with topographic divides and act as an upgradient
limit of a ground-water basin. Recharge boundaries, such as
streams or other surface water bodies, can act as a flow
boundary in shallow aquifers which are in good hydraulic
connection with the surface waters.
In many hydrogeologic settings, flow boundary, and TOT
criteria can be mapped using geological, geophysical, and
dye-tracing methods.
General Geological Mapping Methods
General geological methods include mapping of features such
as topography, water levels, water-quality geologic contacts,
and lineaments. Aquifer water-quality tests will also
provide information on boundaries and the degree of con-
finement.
In simple cases, where topographic divides may safely be
assumed to reflect ground-water divides, ground-water basins
can often be quickly delineated using existing topographic
-=»ps (Slide 6.6).
.. more accurate definition of the ground-water basin can be
developed from water level data from across the basin. Water
levels can be plotted and contoured to determine the location
of ground-water divides, as well as flow directions within
the basin (Slide 6.7).
Water-quality data can be used to delineate the zone of
contribution in some circumstances. For example, infiltering
river water with a higher temperature can be traced to a
well field (Slide 6.8).
Mapping of geologic contacts which act as flow boundaries can
be accomplished using various geological data sources. A
survey of published data may reveal geologic maps of the
study area, which show geologic contacts at the surface and
often include cross-sections illustrating the geologic
relationships at depth (Slide 6.9).
Drilling logs are also a good source of subsurface informa-
tion. Geomorphic features, such as escarpments and valleys,
are often controlled by and therefore indicative of the
underlying geology.
6-2
-------
AH geophysical techniques have certain limitations and their
own particular advantages. The choice of a method depends on
the hydrogeologic setting, the depth to be investigated, the
desired quality of resolution and resources available for
funding.
Dve-Tracinq Methods
Principle flow conduits can be mapped in karst and fractured
bedrock aquifers through the use of dye tracing techniques.
After ground-water drainage basin divides have been deline-
ated from topographic and water-table information, dye
tracing can be used to define ground-water flow patterns, as
well as to quantify flow rates.
Tracing studies involve the injection of a dye or some other
tracer into the ground water through a sinkhole or other
viaduct and monitoring suspected downgradient springs or
discharge areas. Where the tracer is detected, the injection
point is proven to be within the Zone of Contribution (ZOC)
to the monitoring point (Slide 6.14).
The length of time for the tracer to appear is related to the
flow rate. Flow rates may be related to the spring discharge
rate. For a given path, TOT usually decreases as discharge
rate increases.
Age Assessment (Tritium)
An assessment of tritium levels in confined aquifers can be
used to determine age. Higher levels may indicate short
residence time and leakiness of the confining strata.
Another anthropogenic compound, trichlorofluoromethane (CC13
F) has been used as tracer for determining leakage into
confined aquifers. CC13 F is subject to sorption phenomena
that affect its concentration in ground water (Russell and
Thompson, 1983).
6.3 MAPPING EXERCISE
The mapping exercise involves a public water-supply spring in
an unconfined karst aquifer in Kentucky. The Bowling Green,
Kentucky area presented has been studied in great detail as
part of an ongoing karst hydrology research program. A
wellhead delineation study is in progress. Additional
information is provided in a case study found in Appendix B.
6-4
-------
HYDROGEOLOGIC SETTING
The study area surrounding Bowling Green is underlain'by
carbonate rocks of Mississippian Age, predominately the Ste.
Genevieve Limestone, with the St. Louis and Girkin Limestones
occurring in minor portions of the study area (Slide 6.18).
The entire area is a mature karst terrane, exhibiting typical
land form features associated with karst, such as sinkholes,
sinking streams, and springs (Slide 6.19).
Solution enhancement of fractures and joints in the rock has
created large subterranean conduits through which ground
water can flow at high velocities. Such conduit flow can be
several orders of magnitude higher than diffuse flow which
occurs through intergranular pore space.
Flow patterns of ground water in karst aquifers can differ
greatly from those in granular aquifers due to flow through
channels. Furthermore, flow patterns within a single
aquifer may change significantly between normal and high-flow
conditions, because storm water can fill underground
conduits, causing overflow to run off into channels which
normally contain no water. These factors make the prediction
of ground water flow direction difficult.
Flow rates between the major karst features (i.e., lakes,
sinks, spring, and windows) were established as part of a
study. Table 6.1 provides travel time data between selected
points. Note that TOT is dependent upon the stage or water
levels in the cave streams. Even at low stage, however, TOT
across the basin is in the order of days.
METHOD AND CRITERIA SELECTION
Because conduit flow in mature karst aquifers generally does
not follow ground-water flow patterns associated with porous
media aquifers, using methods of wellhead protection based on
simple shapes or analytical flow equations is unlikely to
result in delineation of an effective WHPA.
For example, calculating a fixed radius based on the
volumetric flow equation, or trying to determine the radial
distance at which a certain drawdown occurs may be meaning-
less if a well receives some of its water from a solution
cavity which has its origin a mile or more outside of the
calculated zone of contribution. Also, large supplies of
water are collected at springs, which must also be protected,
but which cannot be evaluated using analytical equations
derived for discharging wells.
6-5
-------
For this reason, hydrogeologic mapping lends itself as the
most useful tool in delineating both WHPAs and protection
areas for springs in mature karst aquifers.
The first step in defining areas to protect wells and
springs used for public water supply is to determine the
boundaries of the ground water basin in which the spring or
well is located. The ground water basin in a karst aquifer
is defined as the entire area which drains to a spring or set
of springs.
Delineation of the ground water basin can be accomplished
through mapping of the potentiometric surface to determine
general flow directions, coupled with dye-flow or other
tracing techniques to better define flow routes.
Ideally, both the potentiometric surface map and the tracing
should be done for normal and high-flow (storm event)
conditions. Having defined the ground water basin and the
general flow patterns within the basin, the next step
involves determination of the contributing area for an
individual well or spring by examining the flow patterns and
potentiometric surface upgradient of the water supply.
Depending on the proximity of the well to the boundary of the
ground-water basin and on flow rates as determined through
dye-tracing, an appropriate delineation criteria may be time
of travel (TOT) or flow boundaries. The ground water divide
would be appropriate for a well located near the edge of the
basin.
EXERCISE
Using the attached worksheet map delineate the boundaries if
the ground-water basin (ZOC) supplying the springs at Lost
River Rise. (Hint: determine location of ground-water
divide). Shown on the worksheet mao are water-level
contours, dye-trace study results and the location of
important hydrologic features.
6-6
-------
TABLE 6.1
TRAVEL TIMES IN HOURS IN THE LOST RIVER BASIN
(From Crawford, et. al., 1987)
BLUE HOLE TO RISE
Date of Trace
11/7/82
9/22/83
3/30/84
6/18/84
7/18/84
Initial
stage
(feet)
6.35
7.49
6.65
6.01
Qi
cfs
12.4
9.2
145
70
29
Centroid
stage
(feet)
6.67
7.55
6.66
5.97
BIG SINKING CREEK
Date of Trace
11/7/82
3/30/84
4/18/84
6/18/84
7/18/84
Initial
stage
(feet)
7.39
6.85
6.8
5.89
Qi
cfs
12.4
130
47
70
25
Centroid
stage
(feet)
7.4
6.87
6.66
5.88
BIG SINKING CREEK TO
Date of Trace
3/30/84
4/18/84
*6/l/84
7/18/84
* Trace started
Initial
stage
(feet)
6.11
5.25
5.86
2.9
Qi
cfs
127
63
105
25
Centroid
stage
(feet)
6.05
5.23
5.86
2.57
Qc
cfs
12.4
10.8
160
70
27
TO RISE
Qc
cfs
12.4
138
50
70
25
BLUE HOLE
Qc
cfs
120
63
105
17
Time of
first
arrival
1*1*3,
68.0
80.5
10.0
16.5
32.5
Time of
first
arrival
185
29.5
48.5
39.25
83
Time of
first
arrival
19.5
27.5
18.5
43
Time of
centroid
87.64
98.56
10.33
19.57
42.5
Time of
centroid
224
32.7
54.7
47.6
102
Time of
centroid
20.8
32.2
22.01
54
wnen Big Sinking Creek ponded.
Results of quantitative dye traces.
6-7
-------
MAPPING EXERCISE
WORK SHEET
(after Crawford, et al, 1987)
<3r
-------
6.4 GROUP EXERCISE
The Laramie basin in Wyoming is used as the setting for these
exercises (Slide 6.25, 6.26, and 6.27). A case study
describing regional and local geology and hydrology is
provided in Appendix B.
Three scenarios have been constructed each with a separate
set of problems. Some of the parameter values presented are
ficticious.
SCENARIOS
Scenario 1. Wells located in an unconfined, porous media
aquifer.
In the Laramie area, the parts of the Casper aquifer
between major tectonic structures can be treated as an
unconfined/porous media aquifer at the scale of a water-
supply well or well field. The wellhead protection area
criteria distance, drawdown, time of travel, and flow
boundaries, are applicable to delineating a protection area
for a well located in an unconfined porous- media aquifer.
Delineation methods that use a fixed radii, simplified
shapes, analytical flow equations, or numerical models can be
used to define a protection area around a well or a spring in
this type of setting.
Delineation methods that take into consideration site-
specific hydrogeologic conditions (i.e. analytical methods
and numerical methods) will define an area for protection
that is somewhat more realistic than the simpler methods that
generate a standard area.
Senario 2. Wells located in a confined, porous media
aquifer with a nearby recharge area.
Another portion of the Casper Aquifer in the Laramie
area is confined. The degree of confinement is such that
most recharge occurs in a nearby unconfined portion of the
aquifer. A confining unit separating a porous media aquifer
from the ground surface provides some protection to the water
source. Therefore, for those cases where the recharge area
is in close proximity to the well, it may be appropriate to
map the recharge area as the WHPA, rather than mapping an
area immediately surrounding the well. This decision would
depend on two factors.
6-9
-------
1. The distance of the recharge area from the
well, and the time it would take a contaminant
released in the recharge area to arrive at the
well.
2. The degree to which the overlying confining
unit protects the aquifer. The protective
capacity of the confining unit depends, in
part, on the presence of fractures, improperly
abandoned wells, and the vertical gradient
across the confining bed. If a number of
fracture zones or other conduits are present it
may be appropriate to map the area around the
well as a WHPA as well as all or relevant parts
of the recharge area.
Scenario 3. Wells and Springs located in close proximity to
a fracture zone.
Fractured-rock aquifers share many characteristics
with conduit karst aquifers. Fracturing has created conduits
through which ground water can flow at high velocities.
Velocities in fractured rocks however do not usually match
the velocity found in karst aquifers because fracture
openings have not been enlarged to the same extent by
dissolution.
Fractured-rock aquifers generally have relatively little
storage capacity in the pore space of the aquifer, compared
to that in porous, granular aquifers. A fracture zone
capable of significant water supply is usually the result of
storage from the matrix rock being discharged to the fracture
system in significant quantities. This is the case with the
Casper aquifer near Laramie.
Because of the rapid, preferred flow through the
fracture zone, the most appropriate WHPA delineation criteria
are probably hydrogeologic mapping of the area supplying the
fracture zone or zone of contribution (ZOC), combined with a
time-of-travel (TOT) calculation to determine a reasonable
WHPA.
6-10
-------
Exercise I.
EXERCISES
Wells located in an unconfined porous
aquifer. (Scenario 1 - Slide 6.29)
media
Using the following aquifer parameters and a TOT
criteria threshold of 5 years, delineate a WHPA
around the pumping well No. C40 using the techniques
of a) Calculated Fixed Radii (Volumetric Flow
Equation), b) Uniform Flow Analytical Model. Use a
TOT calculation to delineate the upgradient extent of
the WHPA. Be careful to take into consideration any
hydrogeologic boundaries that may exist.
K = .70 ft/d
b = 200 ft
S = .01
Q = 1 x 105 ft3/day
n = .01
H = 50'
Exercise II. Wells located in a confined porous media aquifer
with a nearby recharge area (Scenario 2).
a. Use the WHPAs generated in Exercise I as
simplified variable shapes appropriate for the
Casper aquifer in the Laramie Basin. Position
both shapes as WHPAs for Well C36.
b.
Exercise III.
Evaluate the validity of WHPAs delineated in
Exercise I if they were drawn around Well No.
C36. Do the confining conditions present at C36
allow for a reinterpretation of WHPA boundaries?
Wells & Springs located in close proximity to
a fracture zone (Scenario 3).
Using the aquifer parameters given below and the map
given in Exercise I delineate the most appropriate WHPA for
City Springs by:
a. Mapping the area that supplies water
fault zones associated with the spring.
K = .7 ft/day
b = 200 ft
S = .01
Q = 1 x 106 gal/day
n = .2
recharge rate =1.4 in/yr
6-11
to the
-------
Hint: Perform a mass balance on the water discharging
at the spring with water collected in the
recharge area of the spring.
6-12
-------
EXERCISE I & II WORKSHEET
•"*«'• CONriNfO AND UNCONflNCO
pennons or IHE CASPCH AOUI«B
'•••— IINC OF COIMl CLCVATON IN fCCI »80VC
MCAN It* nvtl Of FMt fOTCNTOMtrHIC
JUBfACt USOCIATIO WITH THC
CASPCH
CASPCR / PRCCAMBRIAN CONTACT
CITY
SPRINGS />
LARAMIE
-------
EXERCISE I & II WORKSHEET
AND
or THE CASPIR AOUIFCR
LIHC Of COU»l. ELEVATION IN rCET MOVE
MEAN SEA LEVEL or THE roi
SURrACE ASSOCIATED WITH IMC
CASPER AOUirER
rAULT
C»SPCR / PRCCAUBRIAN CONTACT
LARAMIE
-------
EXERCISE I & II WORKSHEET
LIHC or COUAI CICVATION IN rccr tam
MtAM ICA ItVtl. Of IMt POTCNTlOMCrillC
SURFACE ASSOCIAKO WITH THC
CASPCB AOUirCR
CASPfR / PRCCAU8RIAN CONTACT
CITY
SPRINGS />
LARAMIE
-------
EXERCISE III WORKSHEET
LEGEND
— 7*00
LINE OF EQUAL ELEVATION IN FEET ABOVE
MEAN SEA LEVEL OF THE POTENTIOMETRIC
SURFACE ASSOCIATED WITH THE CASPER
FAULT
CASPER / PRECAMBRIAN CONTACT
CONTACT BETWEEN CONFINED AND UNCON- 0
FINED PORTIONS OF THE CASPER AQUIFER
AREA IN WHICH THE CASPER FORMATION
IS UNSATURATEO
LARAMIE
CITY
SPRINGS jO
\
0 2000 4000
=t=
SCALE.-fltfl)
-------
6.4 GROUP EXERCISE ANSWER
Exercise I. Wells located in an unconfined porous media
aquifer
Aquifer parameters given are:
K = .70 ft/day
b = 200 feet
t = 5 years = 1825 days
S = 0.01
Q = IxlO5 ft3/day
n = .01
H = 50 feet
Aquifer parameters that need to be calculated:
i = 0.06 (estimated from the potentiometric map)
v = Ki = (.70 ft/davl(.06) =4.2 ft/day
n .01
Method A: Calculated Fixed Radius using the Volumetric Flow
Equation
"10779 ft
Qt = *
jrnH >
5 3
rixlO ft /d) (1825d)
JT(.Ol) (50 ft)
2.04 miles
Slide 6.33 shows the fixed radius WHPA.
Method B: Uni'form Flow Analytical Model
Distance to down-gradient null point
2jrkbi
5 3
1x10 ft /d
2JT (.70 ft/d)(200 ft) (.06)
= -1894 ft
Boundary Limit
- ±
2kbi
= +
5 3
1x10 ft d
2 (.70 ft/d)<200 ft) (.06)
= +5952 ft
6-17
-------
Uniform-Flow Equation
- Y = Tan
X
27rkbi
Q
, this equation reduces
to: x = -y cot (y/-XL)
X
-1131
-640
-39.5
995.6
2403
4681
9116
±2000
±2500
±3000
±3500
±4000
±4500
+5000
Distance to 5-year TOT line = (velocity)(3650 days)
= (4.2 ft/d)(3650 days) = 7665 ft = 1.45 mi
Slides 6.34 and 6.35 show WHPAs for the uniform flow equation
solution.
Exercise II.
a. Slide 6.36 shows the positioned WHPA shapes
b. In this exercise a portion of the WHPA, close to the
well, is confined while another more distant portion
is unconfined. In some cases, it may be argued that
the confined portion of the aquifer should be
eliminated from the WHPA. The confining unit must be
able to provide sufficient protection to the
underlying aquifer so that a contaminant release at
the surface could not make its way to the aquifer. A
confined aquifer that is deeper than 300 feet and
does not have fractures or other conduits present «in
the confining unit is mentioned in the Delineation
Guidelines as being relatiely isolated. The
confining unit in the vicinity of Well C-36 is
approximately 300-feet thick and there is no
indication of the presence of fractures or other
conduits.
Exercise III. Map recharge area for a City Springs
Two different methods can be used to map the recharge
area
6-18
-------
Method A. Use the recharge rate of 1.4 in/year and calculate
the area needed to supply a discharge rate of 1 x
106 gal/day.
Recharge rate = 1.4 in/year = .117 ft/yr
Discharge rate =
1 x 106 gal/day x 1.337 X 10"1 ft3 x 365 days
gal year
= 4.9 x 107 ft3/year =
Area = Discharge rate = 4.9 x 10 ft
Recharge rate year = 4 . 2 x 10** ft2
.117 ft
year
AREA = 15.0 miles2
The recharge area is interpreted to lie between faults
leading to spring and upgradient aquifer boundary as shown in
Slide 6.37.
Method B
Using Darcy's law
Q = KIA
where A = bxL, then if T=Kxb
by substitution and rearrangement
Q = TiL
L = _Q
Ti
K = .7 ft/day
i = .06
b = 200 ft
Q = 1 X 106 gal/day x 1.337 x 10"1 ft3 = 1.3 X 105 ft3
gal day
6-19
-------
T = Kb = .7 ft x (200 ft) = 140 ft2/day
day
L = 1.3 x 105 ft3/dav = 1.5 x 104 ft = 3.0 mi
(140 ftz/day) (-06)
L = 3.0 miles
The zone contributing to fracture flow using Darcy's law is
shown in Slide 6.37.
6-20
-------
7. Numerical
-------
PRESENTATION SLIDES
NUMERICAL MODELING METHODS
Slide 7.01
-------
WHPA DELINEATION METHODS
1) ARBITRARY FIXED RADIUS
2) CALCULATED FIXED RADIUS
3) SIMPLIFIED VARIABLE SHAPES
4) ANALYTICAL METHODS
,W «,*"' '<
'•*' Mt to.
5) HYDROGEOLOGIC MAPPING
6) NUMERICAL FLOW / TRANSPORT MODELS
Slide 7.02
-------
NUMERICAL MODELING METHODS
DESCRIPTION
Delineation of WHPAs using rnmpntp^models that approximate
ground-water flow and/or transport equations numerically
ADVANTAGES
• have the potentiallfl^evfiEy. accurate
**- *e f «.iT }V fki* ~
pp applied |Q rifif^yapHtyppgnf hydrogeologic settidgs
ts of ther hydrogeologic system
that affect WHPA size and shape
DISADVANTAGES
of implementation are relatively high compared to other
methods
ceoeidefabJe-eMpacysfi in hydrogeology and modeling is required
to use numerical methods
o
mnkf> numfiriral,
^
Slide 7.03
-------
NUMERICAL GROUND-WATER FLOW AND
CONTAMINANT TRANSPORT MODELING
SIMPLY ANOTHER HYDROGEOLOGIC TOOL
FORCES INTEGRATION OF AVAILABLE
DATA INTO A CONSISTENT ANALYSIS
PROVIDES QUANTITATIVE FRAMEWORK
FOR SYSTEM ANALYSIS UNDER
CHANGED CONDITIONS
ALLOWS BETTER UNDERSTANDING OF
COMPLEX FLOW SYSTEMS
Slide 7.04
-------
TYPES OF GROUND-WATER MODELS
CONCEPTUAL
DESCRIPTION OF KEY AQUIFER FEATURES;
BASIS FOR OTHER TYPES OF MODELS
PHYSICAL (SAND TANK)
NON-SCALED
HYDRAULICALLY-SCALED
ANALOG (fa«l o*> fil'*-'
PHYSICAL ANALOG •~IT"> * '"
VISCOUS FLOW (HELE-SHAW)
ELASTIC MEMBRANE
ELECTRIC ANALOG
CONDUCTIVE PLATE
RESISTOR-CAPACITOR CIRCUIT
MATHEMATICAL
ANALYTICAL '
CLOSED-FORM
SEMI-ANALYTICAL
ANALYTICAL ELEMENT
NUMERICAL
FINITE DIFFERENCE ^.
FINITE ELEMENT ^
BOUNDARY INTEGRAL
Slide 7.05
-------
ANALOGIES TO GROUND-WATER FLOW
VARIABLE
Potential
Quantity
transported
Physical
property
of medium
Relation between
potential and
flow field
Storage
quantity
GROUND WATER
Head, h
Volume
discharge
rate
Hydraulic
conductivity
Darcy's law
q = -K grad h
where q is
specific discharge
Specific storage,
Ss
ELECTRICITY
Voltage, V
Electrical
charge
Electrical
conductivity
Ohm's law
i = - a grad V
where i is
electrical current
Capacitance, C
HEAT
Temperature, T
Thermal
conductivity
Thermal
conductivity
Fourier's law
q = -K grad T
where q is
heat flow
Heat capacity, Cy
—.
a!
-------
Finite-Difference and Finite-Element Discretization Schemes
Fig. 4a. Map view of aquifer showing well field and
boundaries.
Fig. 4b. FJoilfcdjfference grid for aquifer study, where Ax is
the spacing in the x-direction. Ay is the spacing in the y-
directton and b is the aquifer thickness.
7
(Mercer and Faust, 1981)
FJQ. 4c. Finttf>-fl*m*nt rnnfinnrafI^r-. f^n. , -r
.s _i.nnn-firmrnT n9niinnntion for aquifer study where
b is the aquifer thickness.
Slide 7.07
-------
Models Developed by Finite-Difference and Finite-Element Methods
Concepts of (he
physical system
I
Translate to
Partial differential equa-
tion, boundary and initial
conditions
Subdivide region
into a grid and
apply finite-
difference approx-
imations to space
and time derivatives.
Finite-difference
approach
Finite-element
approach
Transform to
Integral equation
Subdivide region
into elements
and integrate
First-order differential
equations
Apply finite-difference
approximation to
time derivative
System of algebraic
equations
Solve by direct or
± iterative methods
Solution
(Mercer and Faust, 1981)
Slide 7.08
-------
STEPS IN DEVELOPMENT AND APPLICATION
OF A HYDROLOGIC COMPUTER MODEL
Definition: MODEL = CODE + DATA
Computer Code
Formulation
Development
V
Verification
1
Hydrologic Process
Code
System
Model
Data
Formulation
Sampling /Testing
I
Parameter Estimation
i
Input Data
Calibration ^
\
Validation^ /,
1
Prediction
Slide 7.09
-------
ITERATIVE MODEL-BUILDING PROCEDURE
DATABASE
DEVELOPMENT
CONCEPTUAL
MODEL
DEVELOPMENT
insufficient
MODEL
CALIBRATION
insufficient
DIAGNOSTIC
CHECKING
AND
SENSITIVITY
ANALYSIS
adequate
calibration
PREDICTIVE
SIMULATION
insufficient
inadequate
calibration
Slide 7.10
-------
DATA REQUIREMENTS FOR PREDICTIVE MODELING OF
GROUND-WATER FLOW AND SOLUTE TRANSPORT
1. PHYSICAL FRAMEWORK
A. GROUND-WATER FLOW
• HYDROGEOLOGIC MAP SHOWING BOUNDARIES
AND BOUNDARY CONDITIONS
• TOPOGRAPHIC MAP SHOWING SURFACE-WATER BODIES
• WATER-TABLE MAP
• BEDROCK CONFIGURATION MAP
• SATURATED THICKNESS MAP
• TRANSMISSIVITY MAP SHOWING AQUIFER AND BOUNDARIES
• SPECIFIC STORAGE MAP OF AQUIFER
• TRANSMISSIVITY AND SPECIFIC STORAGE MAP OF CONFINING BED
• RELATION OF SATURATED THICKNESS TO TRANSMISSIVITY
• HYDRAULIC CONNECTION OF STREAM AND AQUIFER
B. SOLUTE TRANSPORT (IN ADDITION TO ABOVE)
• PARAMETERS THAT COMPRISE HYDRODYNAMIC DISPERSION
• EFFECTIVE POROSITY DISTRIBUTION
• NATURAL CONCENTRATION OF SOLUTE IN GROUND WATER
• FLUID DENSITY VARIATIONS AND RELATIONSHIP TO CONCENTRATION
• HYDRAULIC HEAD DISTRIBUTION (TO COMPUTE VELOCITIES)
• BOUNDARY CONDITIONS FOR CONCENTRATION
Slide 7.11
-------
DATA REQUIREMENTS FOR PREDICTIVE MODELING
(CONTINUED)
2. STRESSES ON SYSTEM
A. GROUND-WATER FLOW
• TYPE AND EXTENT OF RECHARGE AREAS
• SURFACE-WATER DIVERSIONS
• GROUND-WATER PUMPAGE (IN TIME AND SPACE)
• STREAMFLOW (IN TIME AND SPACE)
• PRECIPITATION AND INFILTRATION
B. SOLUTE TRANSPORT (IN ADDITION TO ABOVE)
• SOURCES AND STRENGTHS OF CONTAMINANT SOURCES
• STREAM-FLOW QUALITY
• WATER-QUALITY OF PRECIPITATION
3. OTHER FACTORS
A. GROUND-WATER FLOW AND TRANSPORT
• ECONOMIC WATER-SUPPLY INFORMATION
• LEGAL AND ADMINISTRATIVE RULES
• ENVIRONMENTAL FACTORS
• PLANNED CHANGES IN WATER AND LAND USE
(ADAPTED FROM MOORE, 1979)
Slide 7.12
-------
TYPICAL NUMERICAL MODELING ANALYSES
APPLICABLE TO WHPA DELINEATION
FLOW SYSTEM CHARACTERIZATION
- HYDRAULIC HEADS
- DRAWDOWN DUE TO PUMPING
- FLOW BOUNDARIES
- RECHARGE / DISCHARGE
- SOURCES / SINKS
VELOCITY FIELD ASSESSMENT
- FLOW PATTERNS
- PARTICLE VELOCITIES
- TIME OF TRAVEL
CONTAMINANT TRANSPORT ANALYSIS
- FATE AND TRANSPORT
- ARRIVAL TIME
Slide 7.13
-------
R
FOR WHPA ntri
REVIEW CONDUCTED FOR OGWP BY IGWMC
64 COMPUTER MODELS REVIEWED
OF THE 64 MODELS:
- 27 ARE GROUND-WATER FLOW MODELS
- 37 ARE SOLUTE TRANSPORT MODELS
AND
- 51 ARE NUMERICAL MODELS
• 13 ARE ANALYTICAL MODELS
REPORT PRESENTS:
- DESCRIPTION
- AVAILABILITY
- USABILITY
- RELIABILITY
Source: Model Assessment for Delineating Wellhead Protection Areas,
Office of Ground-Water Protection, EPA, 1988.
Slide 7.14
-------
MODEL SELECTION CONSIDERATIONS
MAJOR CRITERIA IN SELECTING A MODEL FOR A
SITE-SPECIFIC WHPA DELINEATION ARE:
THAT THE MODEL BE SUITABLE FOR
THE INTENDED USE
THAT THE MODEL BE RELIABLE 4 e»f «*n-r
THAT THE MODEL CAN BE APPLIED
EFFICIENTLY
Source: Model Assessment for Delineating Wellhead Protection Areas,
Office of Ground-Water Protection, EPA, 1988.
Slide 7.15
-------
PRESENTATION SLIDES
CHECKPOINTS FOR REVIEWING
A GROUND-WATER MODELING STUDY
Slide 7.16
-------
CHECKPOINTS FOR REVIEWING
A GROUND-WATER MODELING STUDY
HYDROGEOLOGIC SETTING
Aids in evaluation of:
soundness of conceptual model,
reasonableness of parameter ranges,
appropriateness of selected computer code
QUANTITY AND QUALITY OF DATA
Provides basis for reviewing technical approach
CONCEPTUAL MODEL /7*if t**«to wr /*>
INITIAL READING OF MODELING REPORT
PURPOSE t+* ***
f
Sets tone for review
A
Aids in evaluation of:
Preliminary check for technical soundness
COMPUTER CODE
Preliminary judgement regarding appropriate selection
RESULTS
Preliminary judgement regarding success of application;
note problem areas so that possible sources of error can
be identified during detailed review
Slide 7.17
-------
CHECKPOINTS FOR REVIEWING
A GROUND-WATER MODELING STUDY (Cont.)
DETAILED REVIEW OF MODELING REPORT
PURPOSE
Is purpose clearly stated?
Consistent with regulatory requirements of model application?
HYDROGEOLOGIC SETTIN
Regional amd local settings described in sufficient detail?
Strong regional or local controls?
Aquifer boundaries well-defined?
Recharge and discharge areas identified?
Distinctive aquifer features (layering, confining beds, fractures)?
Unusual features requiring simplifying assumptions?
INPUT DATA r*/* /f *-
Data collection procedures followed correctly?
Field and lab test results interpreted correctly?
Significant data gaps requiring simplifying assumptions?
Will data gaps require "expert judgement" data estimates?
Will assumptions or data estimates be verifiable?
Slide 7.18
-------
CHECKPOINTS FOR REVIEWING
A GROUND-WATER MODELING STUDY (Cont.)
CONCEPTUALIZATION
Is conceptual model complete and technically sound?
Conflicts between conceptual model and field data?
CALIBRATION . ,
Is computer code used for model calibration identified?
Is code in public domain (widely used, tested, and accepted)?
fy# *f a>« «4f*4, &**><& iff ye* «**• *• «b'
Were" and code modifications thoroughly tested? * +***'r*-p
Is selected code appropriate for aquifer system?
Is model area clearly identified on a map?
Are starting parameter estimates presented?
Are code operation parameters presented and discussed?
Are simplifying assumptions clearly identified?
Is
Is match wifh cajihrat^p t^rnpts acceptable?
Are final paramelr-vqlMRS
SENSITIVITY ANALYSIS
Were sensitivity analyses performed?
Are sensitivity analyses described clearly and completely?
Does model respond too greatly to changes in parameters?
Does model respond too little to changes in parameters?
V
Slide 7.19
-------
CHECKPOINTS FOR REVIEWING
A GROUND-WATER MODELING STUDY
DIAGNOSTIC CHECKING
Reasonableness of model checked against factors
other than calibration targets?
Are discrfiDancs exlainable and
PREDICTION
Are predictive simulations described in sufficient detail?
Number and range of runs sufficient to meet objectives?
Does range dangerously exceed calibration range?
Is data pre- and post-processing clearly described?
INTERPRETATION
Are results presented and interpreted clearly?
Is interpretation consistent with conceptual model?
Are results presented with appropriate qualifying statements
regarding data limitations, simplifying assumptions,
and limited scope and intent of modeling study?
DOCUMENTATION
Is entire modeling study documented so as to be understandable?
Is study documented sufficiently to support intended purpose?
Are complete records available if more detailed review required?
Is version of source code used in study available?
Are computer copies of final calibration runs available?
Are computer copies of predictive simulations available?
Slide 7.20
-------
PRESENTATION SLIDES
NUMERICAL MODELING
HYPOTHETICAL CASE STUDY
Slide 7.21
-------
HYPOTHETICAL NUMERICAL MODELING CASE STUDY
SINGLE PUMPING WELL IN TYPICAL VALLEY-FILL AQUIFER
DELINEATE WHPA WITH 1000-DAY BUFFER WITHIN ZOC
AQUIFER DATA:
AQUIFER MATERIAL
AQUIFER THICKNESS
VALLEY WIDTH
AQUIFER POROSITY
HYDRAULIC CONDUCTIVITY
(AQUIFER ASSUMED ISOTROPIC)
HYDRAULIC GRADIENT
PUMPING RATE
Glacial outwash (sand, gravel)
200ft
7,500 ft
0.25
100 ft/day
0.005
133,700 cf«l (1 mgd)
Slide 7.22
-------
SITE 1 SITE 2
O O
ALLUVIAL
AQUIFER
=?
QL
(D
SITE MAP FOR HYPOTHETICAL VALLEY-FILL AQUIFER.
EXPLANATION
o
PROPOSED CHEMCIAL PLANT
RIVER
® DISCHARGE WELL
PARTICLE TRACKING ZONE
USED TO DELINEATE WHPA
SCALE
1000
2000 FT
to
CO
-------
HYPOTHETICAL NUMERICAL MODELING CASE STUDY
(CONTINUED)
APPROACH 1
• TREAT AQUIFER AS HOMOGENEOUS
• IGNORE RIVER AND RECHARGE
A) USE ANALYTICAL SOLUTION FOR ZOC AND TOT (RESSQ)
RESSQ INPUT DATA:
AQUIFER THICKNESS 61 m
B)
AQUIFER POROSITY
PORE WATER VELOCITY
TIME OF TRAVEL
PUMPING RATE
0.25
223 m/yr (2 ft/day)
2.74 yr (1000 days)
158 m /hr (1 mgd)
CHECK RESULTS WITH FINITE-DIFFERENCE MODEL (MODFLOW)
AND PARTICLE-TRACKING CODE (GWPATH)
MODFLOW INPUT DATA:
AQUIFER THICKNESS 200 ft
HEAD ON NORTH BOUNDARY 2,000 ft
HEAD ON SOUTH BOUNDARY 1,960 ft
CELL WIDTH IN X-DIRECTION 200 ft
CELL WIDTH IN Y-DIRECTION 200 ft
HYDRAULIC CONDUCTIVITY 100 ft/day
PUMPING RATE 133,700 cfd
GWPATH INPUT DATA:
AQUIFER POROSITY 0.25
Slide 7.24
-------
Distance (feet)
1830
915
\
o
1^-
(A
«-»•
at
3
O
CD
CD
-------
FINITE-DIFFERENCE GRID FOR HYPOTHETICAL VALLEY-FILL
AQUIFER FOR CASE OF HOMOGENEOUS AQUIFER.
EXPLANATION
FINITE DIFFERENCE GRID
INACTIVE CELLS
NO FLOW BOUNDARY
PARTICLE TRACKING ZONE
DISCHARGE WELL
SCALE
1000 2000 FT
>l
O)
-------
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ZONE OF CONTRIBUTION TO PUMPING WELL COMPUTED
llillh'rrn"fpATl1 FOR CASE OF HOMOGENEOUS AQUIFER.
-------
HYPOTHETICAL NUMERICAL MODELING CASE STUDY
(CONTINUED)
APPROACH 2
TREAT AQUIFER AS HOMOGENEOUS
USE FINITE-DIFFERENCE MODEL (MODFLOW)
AND PARTICLE-TRACKING CODE (GWPATH)
MODFLOW INPUT DATA: (gAME-ASuAEEBQACHJ )
AQUIFER THICKNESS
HEAD ON NORTH BOUNDARY
HEAD ON SOUTH BOUNDARY
CELL WIDTH IN X-DIRECTION
CELL WIDTH IN Y-DIRECTION
HYDRAULIC CONDUCTIVITY
PUMPING RATE
200 ft
2,000 ft
1 ,960 ft
200 ft
200 ft
100 ft/day
133,700 CfJ
PLUS
;,
53 RIVER CELLS
AREAL RECHARGE
1.5ft/yr
GWPATH INPUT DATA: (SAME AS APPROACH 1 )
AQUIFER POROSITY 0.25
fi ft)
Slide 7.28
-------
EXPLANATION
FINITE DIFFERENCE GRID
INACTIVE CELLS
RIVER CELLS
NO FLOW BOUNDARY
RIVER
PARTICLE TRACKING ZONE
DISCHARGE WELL
SCALE
I
1000 2000 FT
FINITE-DIFFERENCE GRID FOR HYPOTHETICAL VALLEY-FILL AQUIFER
FOR CASE OF HOMOGENEOUS AQUIFER WITH RIVER AND RECHARGE.
-------
5000.
8
LEGEND
Hydraulic Source
Forward Tracked Path
Hydraulic Sink
Reverse Tracked Path
/*•
Units = Feet
ZONE OF CONTRIBUTION TO PUMPING WELL COMPUTED USING GWPATH
FOR CASE OF HOMOGENEOUS AQUIFER WITH RIVER AND RECHARGE.
-------
HYPOTHETICAL NUMERICAL MODELING CASE STUDY
(CONTINUED)
APPROACH 3
. INCLUDE EFFECTS OF
(CLAY PLUGS)
IGNORE EFFECTS OF RIVER AND RECHARGE
USE FINITE-DIFFERENCE MODEL (MODFLOW)
AND PARTICLE-TRACKING CODE (GWPATH)
MODFLOW INPUT DATA: (SAME AS APPROACH 1 )
AQUIFER THICKNESS 200 ft
HEAD ON NORTH BOUNDARY 2,000 ft
HEAD ON SOUTH BOUNDARY 1,960 ft
CELL WIDTH IN X-DIRECTION 200 ft
CELL WIDTH IN Y-DIRECTION 200 ft
HYDRAULIC CONDUCTIVITY 100 ft/day
PUMPING RATE 133,700 CfS
HYDRAULIC CONDUCTIVITY
OF CLAY PLUG ZON ES 10 ft/day
GWPATH INPUT DATA: (SAME AS APPROACH 1)
AQUIFER POROSITY 0.25
POROSITY OF CLAY PLUGS
0.40
Slide 7.31
-------
////.''////// /D
'//////•• •••'/
//////////,
. .' / f S i s .' ./ >'
' x '////'•'/. V
'////////M
• -•'/. y/
A
m
i
/
X
SITE
>^^
®
d/CITY
ITE 2
/~k
H
/
FINITE-DIFFERENCE GRID FOR HYPOTHETICAL VALLEEY-FILL
AQUIFER FOR CASE OF NONHOMOGENEOUS AQUIFER (CLAY ZONES)
EXPLANATION
FINITE DIFFERENCE GRID
INACTIVE CELLS
CLAY ZONE CELLS
NO FLOW BOUNDARY
PARTICLE TRACKING ZONE
DISCHARGE WELL
fc^Tl*0, .<
SCALE
1000 2000 FT
-------
5000
LEGEND
Hydraulic Source
Forward Tracked Path
Hydraulic Sink
Reverse Tracked Path
Units = Feet
ZONE OF CONTRIBUTION TO PUMPING WELL COMPUTED USING GWPATH
FOR CASE OF NONHQMQPFNFr^0 *^**CP (CLAY ZONES).
-------
5000
CO
LEGEND
A Hydraulic Source
— Forward Tracked Path
• Hydraulic Sink
— Reverse Tracked Path
Units = Feet
ZONE OF CONTRIBUTION TO PUMPING WELL COMPUTED USING GWPATH
FOR CASE OF AQUIFER noNPUfvriviTY REDUCED RY FACIQfirQE 1Q-
-------
5000
s
ZONE OF CONTRIBUTION TO PUMPING WELL COMPUTED USING GWPATH
LEGEND
A, Hydraulic Source
— Forward Tracked Path
• Hydraulic Sink
— Reverse Tracked Path
Units = Feet
FOR CASE nFPiiMPiMf
_CAPTHD
OF 10.
-------
PRESENTATION SLIDES
NUMERICAL MODELING CASE STUDY
FRANKLIN, MASSACHUSETTS
Slide 7.36
-------
NUMERICAL MODELING CASE STUDY
FRANKLIN, MASSACHUSETTS
CITY OF FRANKLIN PROPOSED NEW WATER SUPPLY WELL
DEQE REQUIRES DELINEATION OF THREE ZONES AROUND WELL
ZONE I Immediate area within 400 ft of well
ZONE II Area which supplies water to well under
severe conditions (180 days pumping at
design rate with no recharge)
ZONE III Area beyond Zone II from which surface
water and ground water drains into Zone II
NUMERICAL MODEL DEVELOPED TO DELINEATE ZONE II
AQUIFER DATA:
AQUIFER MATERIAL Glacial outwash (sand, silt, clay)
AQUIFER THICKNESS 43ft at valley center
VALLEY BOUNDARIES bounded by bedrock on all sides
except for narrow neck to East
AQUIFER TRANSMISSIVITY 150,000 gpd/ft near well
(ASSUMED ISOTROPIC) 50,000 gpd/ft near boundaries
HYDRAULIC GRADIENT 0.001 to the East
STORATIVITY 0.02
RECHARGE FROM PRECIPITATION
STREAM ACTS AS CENTRAL DISCHARGE POINT
STREAM MAY ALSO PROVIDE RECHARGE DURING PUMPING
Slide 7.37
-------
Aquifer
Boundary
Equipotential
Line (contour
interval = .5 ft)
FRANKLIN SITE MAP
FRANKLIN-
r\
-------
NUMERICAL MODELING CASE STUDY
FRANKLIN, MASSACHUSETTS (CONT.)
• THREE-DIMENSIONAL FINITE-DIFFERENCE MODEL DEVELOPED
• MODFLOW CODE SELECTED BECAUSE OF ITS ABILITY TO
SIMULATE IMPORTANT AQUIFER FEATURES:
MULTI-LAYERED AQUIFER
IRREGULAR BOUNDARIES
HETEROGENEITY WITHIN LAYERS
INTERACTION WITH SURFACE WATER
AREAL RECHARGE
PARTIALLY PENETRATING WELL
• MODEL SETUP:
3-D Model (2 layers, 21 columns, 27 rows)
Graded grid (50 ft near well, 400 ft near boundaries)
No-flow boundaries around entire aquifer, except for
narrow discharge zone to east
Constant heads at eastern boundary to establish
gradient that produced eastward flow
Slide 7.39
-------
VjNACTIVE CELLS
<10K CONSTANT HEAD CELLS
RIVER CELLS
\" I
LAYER 1
MODEL GRID
Slide 7.40
-------
o
MODEL GRID
-------
NUMERICAL MODELING CASE STUDY
FRANKLIN, MASSACHUSETTS (CONT.)
DATA COLLECTION:
20 boreholes drilled and logged
15 of the boreholes converted to observation wells
5-day pumping test conducted
Estimates of transmissivity and storativity determined
using Jacob's straight-line method and
Theis curve-matching technique
MODEL CALIBRATION:
STEP 1 - Calibrate to static conditions
Input aquifer parameters, recharge and discharge rates
Parameters adjusted in both layers until good match
with observed heads and good water balance achieved
STEP 2 - Calibratelo pumping test conditions
Start with calibrated model from Step 1
Discharge rate of 350 gpm set in pumping well cells
Parameters adjusted until model output matched
observed data satisfactorily
Slide 7.42
-------
NUMERICAL MODELING CASE STUDY
FRANKLIN, MASSACHUSETTS (CONT.)
PREDICTIVE SIMULATION:
JStress period set to 180 davs: re.cha,rge wffi eliminated.
Four scenarios simulated:
SCENARI0 1 - Stream ignored; lower specific yield
SimulatLoiifaUed-after 1?n da.us: excessive dewaterina
SCENARIO 2 - Stream ignored; higher specific yield
' excessive dewaterina
SCENARIO 3 - Stream modeled lower specific yield
Simulation showed all ground water within valley
would flow toward well
SCENARIO 4 - Stream modeled lower specific yield
Simulation showed all ground water within valley
would flow toward well
RESULTS OF STUDY:
Zone II delineated as entire valley in which well is located.
Slide 7.43
-------
MODEL RESULTS AFTER 180-DAY PUMPING
5000 -
4500 -
4000 -
3500 -
3000 -
Site 3
Franklin, MA
2000 -
1500 -
1000 -
500 -
0
1000 1500 2000 2500 3000 3500 4000
SCALE 1r650'
feet
Slide 7.44
-------
MODEL RESULTS AFTER 180-DAY PUMPING PERIOD: LtfYER 2
5000
4500 f-
4000 l-
3500
3000 -
00
2000
1500
1000 ^
500 L
0
Site 3
Franklin, MA
I i
0 500
1000 1500 2000 2500 3000 3500 4000
SCALE 1=650' feet
' '
Slide 7.45
-------
WHPA ZONES DELINEATED FOR FRANKLIN, MASSACHUSETTS SITE
'• Slide 7.46v
_Uji « _^ S
-------
7. NUMERICAL MODELING METHODS
7.1 INTRODUCTION
Numerical methods of modeling ground-water flow and con-
taminant transport lie at the upper end of the spectrum of
WHPA delineation methods in terms of sophistication, data
requirements, and cost.
Numerical methods of simulating flow and transport produce
computer models similar to those developed using analytical
methods. Numerical models, however, are capable of dealing
with more complex hydrogeologic systems and time-varying
pumping rates.
Numerical modeling methods can be used to map criteria such
as drawdown, flow boundaries, and TOT. This is typically
accomplished in a two-step procedure with a flow model being
used to generate a hydraulic head field, and a particle-
tracking or solute-transport code used to aid in outlining
the WHPA.
Sixty-four models (51 of them numerical, 13 analytical)
applicable to WHPA delineation were reviewed for OGWP by the
International Ground-Water Modeling Center (Model Assessment
fo Delineating Wellhead Protection Areas, EPA, 1988). The
report summarizes features and assesses availability,
usability, and reliability of each model.
Major criteria in selecting a model for a site-specific WHPA
delineation are: 1) that the model be suitable for the
intended use, 2) that the model be reliable, and 3) that the
model can be applied efficiently (EPA, 1988).
7.2 FUNDAMENTAL CONCEPTS OF NUMERICAL MODELING
Types of Models
The four basic types of ground-water flow models (Slide 7.5)
are conceptual, physical, analog, and mathematical.
Mathematical models offer the most sophisticated predictive
capability, and among mathematical modeling techniques,
numerical models are the most powerful. After a brief
introduction to the four types of models, the remainder of
this section focuses on numerical modeling techniques.
7-1
-------
Conceptual Models
Conceptual models represent (in a descriptive sense) the
fundamental features and properties of the flow system.
Conceptual models may be based on professional judgement and
previous experience with similar hydrogeologic settings, but
the incorporation of field data will produce a more detailed
and complete conceptualization of the hydrogeologic system.
Conceptual models form the basis for all other types of
modeling, and the importance of formulating a correct con-
ceptual model as a first step to more advanced modeling
cannot be overemphasized.
Physical Models
Physical models use the process of porous media flow to
represent the actual flow conditions. Sand tank models of
ground-water seepage are a common example.
Analog Models
Analog models can be of two types: physical analogs or
electric analogs.
Physical analog models use a physical process that behaves in
the same fashion as flow through a porous medium to mimic
flow conditions. Parallel plate viscous flow (Hele-Shaw)
models and elastic membrane models are some common examples.
Electric and heat analog models use the mathematical
similarity between equations governing conductance of energy
through solids and flow of fluid through a confined aquifer
to represent aquifer conditions.
Mathematical Models
Mathematical models of ground-water flow solve equations
governing porous media flow subject to constraints imposed
by aquifer geometry, boundary conditions, and initial
conditions.
Mathematical models can be set-up, run, and changed much
more quickly and economically than analog models. They can
also represent a wider range of aquifer conditions.
7-2
-------
The equation being solved reflects the complexity of the
conceptualized flow system (i.e. simplifying assumptions
result in simpler equations to solve).
Mathematical models are of two types: analytical and
numerical.
Analytical models are based on exact mathematical solutions
to simpler equations representing idealized aquifer con-
ditions. The method gives highly accurate solutions to a
less accurate representation of the real flow system.
Numerical models are based on numerical approximations to
more complex equations and boundary conditions. The method
gives slightly less accurate solutions to a more accurate
representation of the flow system.
Analytical models (e.g. Theis solution, uniform flow
equation) are often algebraic equations that can be solved
on a hand calculator.
Numerical solution techniques involve the simultaneous
solution of hundreds or thousands of equations and usually
require a digital computer.
Analytical models usually require only a few input parameters
and the form of the equation being solved makes it easy to
see the manner in which the parameters affect the solution.
Numerical require large amounts of data describing aquifer
heterogeneities, location and nature of model boundaries,
and locations and strengths of sources and sinks within the
model domain. A sensitivity analysis is usually required to
determine the effects of given parameters on model response.
Numerical Modeling
Numerical models can be used to simulate steady-state or
transient ground-water flow systems. Steady-state systems do
not change with time; for example, a regional model designed
to represent average annual water levels. Transient systems
vary with time; for example, an aquifer system undergoing
drawdown as the result of one or more pumping wells.
There are several types of numerical techniques employed in
ground-water flow modeling including finite difference
methods, finite element methods, and boundary integral
element methods. Of these modeling methods, finite dif-
ference methods and finite element methods are the most
7-3
-------
widely used, with finite difference models being the most
popular.
Finite difference and finite element methods break-up
(discretize) the flow domain into a set of grid blocks or
mesh cells (Slide 7.7). Equations are written for computa-
tional nodes located at the corners or centers of the blocks
which, when solved, yield the value of hydraulic head at that
location in the flow field (Slide 7.8).
Transient problems require the discretization of time as
well. Initial conditions are specified, and the entire
aquifer problem is solved at each of many short time steps
to produce the solution at some later time.
A 50-column by 20-row finite difference grid would result in
1000 simultaneous equations. Solution of such large sets of
matrix equations requires high-speed computers, especially if
a large number of time steps is required.
Numerical models are very powerful tools due to the wide
range of problems that can be treated.
Numerical models can be used to simulate aquifer conditions
for steady-state and transient cases, incorporating numerous
aquifer layers and other heterogeneities, with a variety of
different boundary conditions, for any specified initial
conditions, with multiple sources and sinks.
Approach to Numerical Modeling
A numerical model should be viewed as a quantitative tool
available to the hydrogeologist to aid in the analysis of
ground-water problems (Slide 7.4).
An aquifer model consists of two components: the computer
code (program) that embodies the mathematical model of the
physical process, and the site-specific data that allow the
model developer to set-up the code to represent that
particular aquifer system (Slide 7.9).
When selecting a code for model development it is wise to
choose a model that has been thoroughly tested and widely
accepted within the ground-water computer modeling field so
that, when results are presented, the code itself is not
called into question. This is especially important in
studies used in support of license or permit applications, or
in court cases.
7-4
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Numerical modeling is useful for preliminary studies
preceding field investigations (i.e. can assist in directing
field data collection activities).
A numerical model can be used at any point in an investiga-
tion to test the current conceptualization of the system, and
to aid in the estimation of aquifer parameters based on
available data.
A numerical ground-water model provides a framework within
which to integrate or synthesize collected data, to aid in
interpretation of field results.
Numerical models are useful for the prediction of system
response at later times for the current set of hydrogeologic
conditions, or to predict aquifer response to changed con-
ditions.
The three most common misuses of models are overkill,
inappropriate prediction, and misinterpretation.
To avoid overkill, the type and complexity of model developed
for a particular problem should be based on the quantity and
quality of available data and on the purpose of the modeling
investigation.
Complex numerical models developed from a sparse data base
may appear impressive, but the necessary incorporation of a
large number of unsubstantiated assumptions may produce
unreliable model predictions.
Inappropriate prediction results from the application of a
model to predict aquifer conditions that are beyond the
capabilities of the code (program) or far outside the range
of conditions"that the model was developed to handle.
Misinterpretation can result from a lack of conceptual
understanding of the specific system model, which can result
in improper utilization of the model, or an inability to
relate model results to the true system. Even worse is no
interpretation; blind faith acceptance of model results.
Application of Numerical Models
Any application of a numerical model to a hydrogeological
problem should follow a set of well-defined steps: data
review, conceptual model development, code selection, model
calibration, diagnostic checking, sensitivity analysis, and
predictive simulation (Slide 7.10).
7-5
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Data for the aquifer system to be modeled should be compiled
and evaluated by checking for completeness and quality. Ob-
vious data gaps or contradictions should be cause for
concern. Numerical models require a large site-specific data
base in order to yield accurate results (Slides 7.11 and
7.12) .
Formulation of an accurate conceptual model of the system is
probably the most important step. If it is wrong, the
numerical model, with all its sophistication, will be wrong
as well.
Codes should be evaluated against the objectives of the
study, and the quantity of available data. The features of
the selected code should match the features of the con-
ceptualized flow system, and the data requirements of the
code should be consistent with the existing data base.
Calibration involves adjustment of model parameters until a
satisfactory agreement is obtained between computed heads
and the heads at selected calibration targets (usually water
levels in wells). Transient calibration matches the
history of response of the aquifer system.
Diagnostic checking involves a "reality check" to see if the
calibrated model makes sense; aquifer parameters should be
within reasonable ranges, the water budget for the aquifer
should match hydrologic observations, and areas at some
distance from calibration targets should be checked to be
sure the water table does not breach land surface.
Sensitivity analyses identify the parameters that exert the
greatest influence on model response by varying each
parameter by a fixed relative amount (e.g. 10 % or 50%) and
recording the change in the response variable (e.g. head). -
Additional data collection focusing on the most sensitive
parameters may greatly improve model performance.
After the model has been calibrated, checked, and run through
a set of sensitivity trials it may be used with some
confidence to make predictions. Predictions are often the
ultimate goal of the modeling study, but they should not be
attempted without careful attention to the preceding steps.
Advantages
This method has the potential to be very accurate, can be
applied to nearly all types of hydrogeologic settings, and
can simulate dynamic aspects of the hydrogeologic system that
affect WHPA size and shape.
7-6
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Disadvantages
Costs are high relative to other methods, and considerable
expertise in hydrogeology and modeling is required to use the
method. The cost may be warranted where a high degree of
accuracy is desired.
Due to limitations on model grid spacing and density,
numerical models are less suitable than numerical methods in
assessing drawdowns close to pumping wells. For this reason,
WHPA delineation in some European countries in recent years
has focused on combining analytical methods for the near-
field and numerical models for the bulk of the protection
area.
7.3 CHECKPOINTS FOR REVIEWING A MODELING STUDY
A report describing the application of a numerical model to a
hydrogeological investigation should be reviewed in two
steps: an initial reading to grasp intent and content of
report, and a detailed review to closely examine approach,
assumptions, and technical issues.
Initial Reading
First establish the purpose of the model application. This
will detemine the level at which certain factors should be
evaluated in the review including appropriateness of selected
modeling technique, reasonableness of simplifying assump-
tions, and interpretation of results.
Review the section describing the hydrogeologic setting being
modeled. Th~is will provide a basis for assessing the
soundness of the conceptual model, reasonableness of
parameter ranges, and appropriateness of the selected
computer code.
Briefly review the quantity and quality of available data.
This will permit evaluation of appropriateness of the
se1ected code.
Skim the conceptual model section checking for completeness
and judging basic agreement with the aquifer setting and
field data.
Identify the code being used and form a preliminary opinion
as to its appropriateness for the particular application.
7-7
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Read the salient points in the results and interpretation
section to determine the degree of success of the applica-
tion. Problem areas should be noted so that possible sources
of error can be identified during the detailed review.
Detailed Review
The detailed review of a model application should be
conducted by moving through the following series of topics
and addressing the listed questions, items, or issues. The
following are questions that should be considered in the
detailed review.
Purpose
Is the purpose clearly stated?
Is the purpose, as stated, consistent with the regulatory
requirements the model application was developed to address?
Hvdrogelogic Setting
Is the regional setting (geology, climate, surface and
subsurface hydrology) described in sufficient detail?
Is the local setting (geology, climate, surface and sub-
surface hydrology) described in sufficient detail?
Are there any strong regional controls on the local setting?
Are there any strong local controls?
Are aquifer boundaries well-defined?
Are recharge and discharge areas identified?
Are there any distinctive aquifer features (layering,
confining zones, fractures)?
Are there any unusual system features (regional, local,
aquifer)?
Will these unusual features require simplifying assumptions
to yield a tractable problem?
7-8
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Data
Were data on which the model is based collected correctly?
Were field or laboratory tests interpreted correctly?
Were any data reduction or parameter estimation procedures
performed correctly?
Are there any data gaps?
Will data gaps require simplifying assumptions?
Will data gaps require parameter estimates based solely on
professional judgement?
Are data gaps serious enough to preclude a reasonable
attempt at model development?
Do data gaps require assumptions or parameter estimates that
are not testable or verifiable?
Conceptualization
Is the conceptual model of the hydrogeologic system complete
enough for the purposes of the study?
Is the conceptualization sound?
Are there conflicts between the conceptual model and
available evidence from field data?
Calibration
Is the code used for model development and calibration
identified?
Is the code in the public domain (or readily available), and
is it widely-used, well-tested, and widely-accepted?
If the code has been modified in any way, are these modifica-
tions clearly described and have they been thoroughly
tested?
If the code is proprietary, is its selection justified on
technical grounds, and has the code been thoroughly tested?
Is the selected code appropriate for the system being
modeled?
7-9
-------
Are the code theory and features described?
Is a description provided of the governing equations being
solved?
Is the area being modeled clearly identified on a map?
Are the starting values of hydraulic parameters and boundary
conditions clearly stated?
Are any other time-stepping or code operation parameters
presented and discussed?
Are simplifying assumptions (due to lack of field data or the
nature of the study) used during model setup clearly
identified?
Are any special simplifying assumptions required to make the
selected code work in this particular case clearly identi-
fied and justified?
Are results of the final calibration run completely presented
and discussed?
Is agreement between model results and calibration targets
good enough given hydrogeologic conditions, model scale, and
purpose of the study?
Are any discrepancies between calibrated heads and target
values satisfactorily explained and justified?
Are parameter values, boundary conditions, and other features
of the calibrated model reasonable and within acceptable
ranges?
Does it appear that individual parameters or, sometimes more
importantly combinations of parameters, have been delib-
erately skewed within their range of reasonable values to
produce a desired or predetermined result?
Sensitivity Analyses
Were sensitivity analyses performed on the calibrated model
to test for robustness and to identify the most sensitive
parameters?
Are the results of sensitivity analyses presented in an
understandable form?
7-10
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Do the sensitivity analyses indicate that model calibration
indicators (usually some measure of residuals between
calculated and target heads) deteriorate rapidly with only
small changes in model parameters?
Do sensitivity analyses indicate that the model does not
respond to changes in parameter values, indicating some
overriding control on the system?
Diagnostic Checking
Was the reasonableness of the calibrated model checked
against factors (e.g. aquifer water mass balance) other than
the calibration targets?
Does the model, although calibrated well, not compare well
with these other factors?
Does the model, with noted discrepancies between computed
values and calibration targets, match well with the bulk of
field observations and water budget estimates?
Are there justifiable explanations for calibration discrepan-
cies that would allow the model to be used satisfactorily
for the purpose of the study?
Prediction
Are all predictive simulations conducted for the study
described in sufficient detail (model setup, input data,
output data, graphical presentation of results)?
Are the number and range of the predictive simulation model
runs sufficient to meet the objectives of the study?
Does the range of runs dangerously exceed the range of
conditions used during model calibration?
Is all pre- and post-processing of data clearly described?
(It is important to know which results are attributable to
the selected code and which are attributable to data
manipulation during post-processing.)
Interpretation
Are model results presented and interpreted clearly in
non-technical language?
7-11
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Is the interpretation of model results consistent with the
conceptual model of the system?
Is the interpretation consistent with the simplicity or
complexity of the model? (It is incorrect to interpret
model predictions in light of features that are not even
incorporated in the model.)
Are model results presented with qualifying statements that
reflect the limitations of the data, the simplifications
inherent in the model, and the limited scope and intent of
the modeling study?
Documentation
Is the entire modeling study documented sufficiently to be
understandable to the reviewer?
Is the modeling study documented sufficiently to support its
intended use (permit application, litigation support, etc.)?
Are complete records of the modeling investigation available
for more detailed review if required?
Is the version of the source code used to develop the model
available?
Are printed and machine readable copies of the final
calibration run available?
Are printed and machine readable copies of all predictive
simulation runs available?
7.4 NUMERICAL MODEL CASE STUDIES
Numerical modeling has been used to delineate Wellhead
Protection Areas (WHPAs) at many sites around the country
including several described in the case studies included in
this manual (Appendix B). The first example presented in
this section, however, is a hypothetical "case study"
designed to illustrate the use of a numerical model in
delineating a WHPA. A comparison is made between the
numerical model results and those obtained using a simple
analytical solution. Emphasis is placed on the flexibility
of the numerical approach and the ease with which hydro-
geologic complexity can be treated and various assumptions
can be tested.
7-12
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A second case study is described in which a numerical model
was applied to an actual site near Franklin, Massachusetts to
delineate a WHPA for the aquifer. The case provides a good
example of the data collection( model calibration, and
predictive simulation steps.
A third case study involving numerical modeling at a site in
Palm Beach County, Florida is not discussed in detail in this
section due to the length and complexity of the case. A
summary of the study, however, is provided in Appendix B
(Case Study B.4). Ground-water flow and transport models
were used to delineate WHPAs based on TOT and drawdown
criteria. Of special interest is the fact that advective
transport travel-time zones were augmented by a factor of 25
percent to account for dispersion effects. This represents a
more sophisticated approach than simple particle tracking
techniques.
7.4.1 NUMERICAL MODELING CASE STUDY 1:
HYPOTHETICAL NUMERICAL MODELING CASE STUDY
The following hypothetical study was developed to demonstrate
the advantages of numerical modeling methods in delineating
WHPAs for complex hydrogeologic settings. While the site
and the data are fictitious, the aquifer setting and the
parameter values used in the demonstration are representative
of real-world values.
A WHPA is to be delineated for a water-supply well in a
typical valley-fill aquifer (Slide 7.22). The protection
area is to provide a 1,000-day travel-time buffer within the
aquifer zone that contributes flow to the well. The results
of the study will have implications for two sites currently
being considered for a new chemical plant. Three technical
experts are hired to delineate the WHPA, and each decides to
take a very different approach to analyzing the site.
The aquifer setting (Slide 7.23) is a broad valley oriented
north-south and filled to a depth of 200 feet with sand and
gravel outwash. Aquifer tests indicate a hydraulic con-
ductivity of 100 feet per day (ft/day), and water level
measurements in wells throughout the valley show a regional
flow gradient of 0.005 to the south. The average porosity
of the aquifer material is 0.25.
The small river running through the valley carries an average
discharge of 1,500 cubic feet per second (cfs). A single
water supply well, located in the center of the study area
near the river, is pumped at a rate of 133,700 cfs (1
7-13
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million gallons per day). For the purposes of this demon-
stration, the well is assumed to draw water from the entire
thickness of the aquifer.
The town being supplied by the well is located south of the
well as shown on the map (Slide 7.23), and the proposed
chemical plant sites are located about 3,000 ft north of
town and 2,000 ft north of the well.
Approach 1
Expert 1 decided to take a simple approach, treating the
predominantly sand and gravel material filling the valley
bottom as a homogeneous aquifer (Slide 7.24). He also
assumed that the river had little effect on the flow system,
and he ignored it in his modeling. He applied the analytical
computer model RESSQ to the study site using the following
data:
Aquifer thickness 61 m (200 ft)
Porosity 0.25
Pore velocity 223 m/yr (2 ft/day, computed
using Darcy's law)
Flow direction South
Time of travel 2.74 yr (1000 days)
Pumping rate 158 m5/hr (133,700 cfs)
The zone contributing ground-water to the supply well within
a 1,000-day time-of-travel distance (Slide 7.25) shows an
area about 350 ft wide and 850 ft long extending north of the
well.
To check his "work, he constructed a simple finite difference
model (Slide 7.26) of the aquifer system and pumping well
using the MODFLOW code (McDonald and Harbaugh, 1984) . He
used the following data:
Aquifer thickness 200 ft
Constant head on north boundary 2,000 ft
Constant head on south boundary 1,960 ft
(these heads produce a regional
gradient of 0.005)
Cell width in x-direction 200 ft
Cell width in y-direction 200 ft
Hydraulic conductivity 100 ft/day
Pumping rate 133,700 cfs
7-14
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Although the problem setup is the same, generating the input
data set for MODFLOW took considerably more time than the
7-line data file required for RESSQ. After computing the
hydraulic heads in the flow field using MODFLOW, he used the
particle tracking code GWPATH (Shafer, 1987) to determine the
zone contributing water to the well within 1,000 days.
GWPATH requires a rectangular computational domain, so data
from the MODFLOW grid cells within the large bold rectangle
shown on Figure 1 were used for the particle tracking study.
He used the head field generated by MODFLOW as input to
GWPATH and assumed a porosity of 0.25. The results of this
analysis (Slide 7.27) were almost identical to the RESSQ
model. Because flow does not move directly south in the
valley, but follows the broad S-shape of the valley, the WHPA
is oriented very slightly north-east. The size of the WHPA,
however, is almost exactly the same as that generated by
RESSQ.
In this simple case there seemed to be little advantage in
using the more sophisticated finite-difference model over
the simple analytical solution. The finite-difference model
took longer to setup and gave almost exactly the same
results.
As a result of the protection area defined by his WHPA
delineation study, Expert 1 recommended Site B for the new
chemical plant.
Approach 2
Expert 2 decided to account for surface hydrology in his
analysis to delineate the WHPA (Slide 7.28). He obtained the
elevation of the water level in the river and the elevation
of the riverbed at numerous points along its course through
the study area. He also obtained records that showed an
average annual rainfall in the area of 54 inches, and
estimated that 18 inches of that amount infiltrated every
year to recharge the ground water system. Since the
analytical model RESSQ cannot treat areal recharge or surface
water bodies, he developed a MODFLOW model of the aquifer.
He used the same data shown in Approach 1, with 53 grid
blocks representing river cells (Slide 7.29), and a recharge
of 18 in/yr.
His delineated area (Slide 7.30) does not differ significant-
ly from those of Approach 1. The moderate amount of"recharge
is transmitted through the highly conductive aquifer without
significantly altering the hydraulic head field established
by the regional flow regime.
7-15
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For this set of aquifer conditions, the regional flow is
moving southward beneath the river, and the zone contribut-
ing flow to the well is relatively unaffected by the presence
of the river and the introduction of recharge. In other
words, the river is not acting as a flow boundary. For this
case, the results natch well with those computed by the
analytical solution employed in RESSQ.
This may not always be the case. Rivers may act as flow
boundaries depending on the properties of the aquifer,
regional flow conditions, rate of recharge, and rate of
pumping (see section below entitled Additional Considera-
tions) .
Based on his study, Expert 2 also recommended Site B for the
new chemical plant.
Approach 3
Expert 3 decided to incorporate subsurface geology into his
delineation study (Slide 7.31). From well borings in the
area, he determined that large zones of low-permeability
material (clay plugs) were located on either side of the
river in the vicinity of the pumping well. Since analytical
solutions cannot treat a nonhomogeneous aquifer, he con-
structed a MODFLOW model of the system (Slide 7.32). Testing
revealed that the hydraulic conductivity of the clay material
was 10 ft/day and its porosity was 0.40. He neglected the
river and recharge, and constructed his model using the same
MODFLOW data set used in Approach 1. In this case, however,
he included low permeability blocks (10 ft/day) to represent
the clay zones. He used GWPATH to perform particle tracking
on the resulting head field, with a porosity of 0.25 for the
sand and gravel material and 0.40 for the clay plugs.
The WHPA he delineated (Slide 7.33) was much different from
those generated in the other approaches. The clay plugs had
two effects on the flow system. First, they diverted
regional flow from the north so that is could only reach the
well within 1,000 days through a narrow section of the
aquifer oriented northeast-southwest between the clay plugs.
In addition, it restricted flow toward the well in the area
just west of the well, causing greater drawdown and a broader
zone of contribution directly around the well.
7-16
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His findings were reported to the appropriate agencies in
time to ensure that Site A was selected for the new chemical
plant. A toxic spill at the plant, were it located at Site
B, would have traveled directly to the water supply well
within 1,000 days.
ADDITIONAL CONSIDERATIONS
Permeability contrasts (like clay plugs) are not the only
ground-water flow system features that can alter the size
and orientation of a WHPA. The orientation of the WHPA can
be altered significantly from that predicted from an
examination of the regional gradient, even in a homogeneous
aquifer.
As an example, consider the MODFLOW model constructed in
Approach 2 above. If a similar model were constructed with
a hydraulic conductivity of 10 ft/day instead of 100 ft/day,
the resulting 1,000-day travel time WHPA (developed using
GWPATH for particle tracking) would be much larger (compare
Slides 7.34 and 7.30). The quantity of flow moving toward
the well under the regional gradient of 0.005 is greatly
reduced, and the well requires a much broader zone of
contribution to receive the 133,700 cfs being withdrawn. The
influence of areal recharge and the resulting flow toward the
river is evidenced in the refraction of the particle paths,
but the well is drawing water from both sides of the river.
The river does not act as a flow boundary for the flow system
in the vicinity of the pumping well.
If, however, the pumping rate is reduced by a factor of ten
to 13,370 cfs, the effect of recharge and flow toward the
river exerts a greater influence on the ground-water flow
system than does the pumping well. The zone of contribution
is largely confined to the region south of the river (Slide
7.35). The river bounds the zone of contribution on the
north, and the axis of the WHPA is oriented northeast in much
the same manner as it was when flow to the well was being
controlled by the low permeability zones (see Approach 3
above).
This demonstrates that many factors, and the balance of
strengths among those factors, must be taken into account to
accurately delineate a WHPA in a complex hydrogeologic flow
system. The U. S. Geological Survey Open File Report 86-543
(Morrissey, 1987) provides an excellent discussion and
numerous modeling examples of the effects of recharge and
rivers on the contributing areas of wells located near
rivers.
7-17
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7.4.2 NUMERICAL MODELING CASE STUDY 2;
NUMERICAL MODEL APPLIED TO A MASSACHUSETTS AQUIFER
The Massachusetts Department of Environmental Quality
Engineering (DEQE) required that three zones be delineated
around a proposed water supply well in Franklin, Mass-
achusetts. The case study is presented in detail in Appendix
B, with only the numerical modeling application designed to
delineate one of the zones discussed here.
The intermediate zone around the well is to encompass the
land area which supplies ground water to a pumping well
under the roost severe recharge and pumping conditions. In
the Franklin case, a computer simulation was deemed necessary
to delineate this zone. The finite-difference ground-water
flow code MODFLOW (McDonald and Harbaugh 1984) was selected
because its features permitted an accurate representation of
the complex hydrogeologic system surrounding the well.
The aquifer is a glacial outwash deposit of sands, silts, and
clays with a maximum thickness of 43 feet at the valley
center. The aquifer is bounded on all sides by bedrock
valley walls or glacial till except for a narrow zone to the
east that connects the aquifer to an adjacent valley (Slide
7.38). Flow is to the east under a gradient of about 0.001.
Transmissivity ranges from about 150,000 gpd/ft near the well
to 50,000 gpd/ft near the boundaries of the aquifer.
Storativity was approximately 0.02.
A three-dimensional model (2 layers, 21 columns, 27 rows)
was constructed with a grid spacing graded from 50 feet near
the water supply well to 400 feet near the aquifer boun-
daries. No" flow boundaries were set around the entire
aquifer except for a narrow discharge zone to the east
(Slides 7.40 and 7.41). Constant heads at this point
established a gradient that produced eastward flow.
The model was first calibrated for non-pumping conditions,
and then for conditions simulating the pumping of wells
under conditions simulating pumping tests previously
conducted to estimate aquifer parameters.
Following calibration, predictive simulations were conducted
for the severe pumping conditions required by DEQE regula-
tions. Four scenarios were simulated: high and low aquifer
storativity ignoring recharge from a surface stream, and high
and low storativity incorporating the effects of the stream
in the model using the river simulation package.
7-18
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The simulations with no recharge from the stream failed due
to excessive dewatering of model cells. The simuTations
with stream recharge predicted that, for both values of
storativity, all flow within the valley would be toward the
well (Slides 7.44 and 7.45}. Zone II was delineated as the
entire valley in which the well was situated (Slide 7.46).
7-19
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8. Comparisons
-------
PRESENTATION SLIDES
COMPARATIVE ANALYSES
Slide 8.01
-------
Interrelationships of WHPA Methods
QUANTITATIVE
ANALYTICAL. NUMERICAL
MODEL
ARBITRARY
FIXED
RADIUS
CALCULATED
FIXED
RADIUS
CALCULATED AREA
EXTENDED TO
BOUNDARY
HYDROGEOLOGIC
MAPPING
ARBITRARY
FIXED RADIUS
WITH EXTENSION TO
BOUNDARIES
(PHYSICAL OR HYDROLOGIC)
PHYSICAL
FEATURES
Slide 8.02
-------
WHPA Comparative Analysis
What is Accuracy?
TooSmall
< Accurate <
RESULTS: Underprotection
Preservation
of Quality
PROBLEMS: Quality Degradation
Too Large
Overprotection
Implementation
00
o
CO
-------
Relationship Between WHPA Delineation Methods and Criteria
=?
a!
-------
PRESENTATION SLIDES
COMPARATIVE ANALYSIS:
KENNEDALE, TEXAS
Slide 8.05
-------
PURPOSE OF CASE STUDY 1
COMPARATIVE STUDY INVOLVING DRAWDOWN
AND TIME-OF-TRAVEL CRITERIA
ILLUSTRATES IMPORTANCE OF BALANCE
BETWEEN PROTECTIVE AND IMPLEMENTABLE
DELINEATION
ILLUSTRATES IMPORTANCE OF UNDERSTANDING
AQUIFER SYSTEM MECHANICS AND WATER
SOURCE TO THE WELL
Slide 8.06
-------
HYDROGEOLOGIC SETTING
- 4 WELLS IN TRINITY AQUIFER
- PUMPING 70.000 - 280.000 GPD PER WELL
- 1.1 MGD COMBINED PUMPAGE FOR 1988
- TWO PRIMARY PRODUCTION ZONES
PALUXY
TWIN MOUNTAINS
- 600-FT CONFINING MATERIALS
Slide 8.07
-------
REGIONAL HYDROGEOLOGIC BOUNDARIES
RECHARGE AREA 20 MILES WEST
- DIRECT INFILTRATION IN OUTCROP AREA
- RECHARGE RATE 1 IN/YR
VELOCITY ESTIMATES
- RANGE 1-2 FT/YR TO 200 FT/YR
Slide 8.08
-------
WHPA CRITERIA AND METHODS
CRITERIA
- DRAWDOWN (5-FOOT CONTOUR)
- TOT (5-YEAR TRAVEL TIME)
METHODOLOGY
- CALCULATED FIXED RADIUS USING THE
VOLUMETRIC FLOW EQUATION
N
Qt
n TT H
- ADDED AN ADDITIONAL BUFFER ZONE
DRAWDOWN MODEL RESULTS YIELD UNREALISTIC
AREA USING 5-FOOT DRAWDOWN CRITERION
THRESHOLD
Slide 8.09
-------
WELLHEAD PROTECTION AREAS
lily of KvnnedOlC
Wclllicod (''election
CALCULATED RADII FOR ALL WELLS LESS THAN 800 FEET
. WHPA ESTABLISHED AT 1,320 FEET
Slide 8.10
-------
PRESENTATION SLIDES
COMPARATIVE ANALYSIS:
BROOKINGS COUNTY, SOUTH DAKOTA
Slide 8.11
-------
PURPOSE OF CASE STUDY 2
COMPARATIVE STUDY OF HYDROGEOLOGIC
MAPPING AND ANALYTICAL METHODS
ILLUSTRATES THE IMPORTANCE OF GROUND-
WATER AND SURFACE-WATER RELATIONSHIPS
AND AQUIFER SYSTEM BOUNDARIES
USES MULTIPLE ZONE DELINEATION WITH
1-FOOT DRAWDOWN CRITERIA
Slide 8.12
-------
HYDROGEOLOGIC SETTING
BIG SIOUX AQUIFER
- UNCONSOLIDATED SANDS AND GRAVELS OF
GLACIAL OUTWASH ORIGIN
- DEPOSITED ON IMPERMEABLE TILL, OR
BEDROCK
- UNCONFINED CONDITIONS
n = .20 - .35
K = 20 - 20,000 gpd/ftz
b = 20 - 60 ft
WELL YIELDS AS MUCH AS 1000 GPM
INDUCED INFILTRATION IMPORTANT ROLE
Slide 8.13
-------
20001
1800-
a.
CD
o
a-
UJ
1600
o
CO
1400-
o
I
1200
1000
R54W
BIG SIOUX AQUIFER
Glacial Till with Gravel Stringers
53
HAMLIN
GEOLOGIC CROSS-SECTION OF BIG SIOUX BASIN
-------
BRUCE WELL NO. 1 SETTING
A) TEN (10) YEAR TIME OF TRAVE!.
B) FIVE (5) YEAR TIME OF TRAVEL
?) WELL
0) ZONE OF CONTRIBUTION
BUFFER ZONE FOR IRRIGATION
AQUIFER AREA
NON-AOUIFER
-------
ANALYTICAL ZONE OF TRANSPORT METHOD
SOLVE UNIFORM FLOW EQUATION
- KEY POINTS ON THE UPGRADIENT DIVIDE
- ESTIMATE DOWN-GRADIENT/CROSS GRADIENT
- LOCATE UPGRADIENT TOT EXTENT
DELINEATE WHPA
Slide 8.16
-------
HYDROGEOLOGIC BOUNDARY EFFECTS
. ADJUST THE ZOC AT INTERSESCTION WITH
THE AQUIFER BOUNDARY
DELINEATE CONTRIBUTING DRAINAGE AREA
SIMILAR ADJUSTMENT FOR IRRIGATION WELLS
Slide 8.17
-------
ZONE OF TRANSPORT METHOD RESULTS
TEN (IO) YEAR TIME OF TRAVEL
FIVE (5) YEAR TIME OF TRAVEL
C) WELL
D ZONE OF CONTRIBUTION
BUFFER ZONE FOR IRRIGATION
AQUIFER AREA
NON-AOUIFER AREA
-------
THEIS ANALYTICAL METHOD
EMPLOY DRAWDOWN CRITERION
DRAWDOWN THRESHOLD = 1 FOOT
THWELLS COMPUTER CODE
T = 55, 128 gpd/ft
S = 0.20
Q = 120 gpm
t = 20 years
GOOD MATCH BETWEEN THEIS AND SIMPLIFIED
VARIABLE SHAPES BUT DOES NOT CONSIDER
BOUNDARY EFFECTS
Slide 8.19
-------
THEIS - IMAGE WELL
BARRIER BOUNDARY EFFECTS RESULT IN
GREATER DRAWDOWN THAN IN INFINITE
AQUIFER
ACCOUNT FOR BARRIERS THROUGH THE USE
OF IMAGE WELL THEORY
- THEIS EQUATION WITH MULTIPLE PUMPING
WELLS
- APPLY LAW OF SUPERPOSITION
PLACE PUMPING WELL (FICTITIOUS IMAGE
WELL) AT THE SAME DISTANCE FROM THE
BARRIER AS THE REAL WELL
USE THWELLS
Slide 8.20
-------
TEN (10) YEAR TIME OF TRAVE
8) FIVE (5) YEAR TIME OF TRAVEL
WELL
D1 ZONE OF CONTRIBUTION
(E) BUFFER ZONE FOR IRRIGATIC
1-Foot Drawdown Contour Using Image Well to
Simulate Impermeable Boundary Effects (t = 20 yr)
IMAGE WELL
Drawdown Contour for
Pumping Well (t = 2"
Comparative analysis between Theis drawdown method and WHPA delineation
methods applied at Bruce Well #1, Brookings County, South Dakota.
8-6
Slide 8.21
-------
PRESENTATION SLIDES
COMPARATIVE ANALYSIS
CYPRESS CREEK WELLFIELD, FLORIDA
Slide 8.22
-------
PURPOSE OF CASE STUDY 3
. COMPARISON OF SEVERAL MODELING AP-
PROACHES USING TIME-OF-TRAVEL CRITERION
THREE APPROACHES CONSIDERED
- VOLUME BALANCE (CALCULATED FIXED
RADIUS)
- RANDOM WALK
- METHOD OF CHARACTERISTICS
CYPRESS CREEK WELLFIELD
. IMPORTANT TO UNDERSTAND SUBTLE DIF-
FERENCES IN NUMERICAL MODEL APPROACHES
Slide 8.23
-------
HYDROGEOLOGIC PARAMETERS
CYPRESS CREEK WELLFIELD
T = 400,000 gpd/ft
b = 500 ft
L = 0.01 gpd/ft3
Q = 2.3 MGD/WELL (13 WELLS)
D = .000001
COMPUTER TIME OF TRAVEL FROM LOCATIONS
IN AQUIFER TO WELLS
RESULTS REPORT SEQUENCE OF TRAVEL
DISTANCE FOR 2-YEAR, 5-YEAR, 10-YEAR TIME
Slide 8.24
-------
2 - YEAR TRAVEL DISTANCE
27
24
21
18
IS
12
EXPLANATION
VOLUME AVERAGE
RANDOM WALK
MOC
12 15 18
X103 FT
21
24
27
Slide 8.25
-------
5 - YEAR TRAVEL DISTANCE
27
24
21
o
o 15
x
12
EXPLANATION
VOLUME AVERAGE
RANDOM WALK
MOC
_L
12
15
X103 FT
IB
21
27
Slide 8.26
-------
10-YEAR TRAVEL DISTANCE
27
21
16
U.
r>
O 15
12
EXPLANATION
VOLUME AVERAGE
RANDOM WALK
MOC
1 t
3 6
I
9
1
12
1
15
X103 FT
1
18
1
21
1 -
24
Slide
1
27
8.27
-------
COMPARISON SUMMARY
. VOLUME BALANCE INTRODUCES GREATER
ERROR WITH TIME
- TRAVEL DISTANCE CONTOURS DO NOT
CONSIDER OTHER WELLS
- 70% OVERLAP AT 10 YEARS
. NUMERICAL MODELS EXHIBIT SUBTLE DIF-
FERENCES
- AVERAGING SCHEMES OF FORMULATION
- GRID RESOLUTION EFFECTS
. MODEL SELECTION CONSIDERATIONS
- AVAILABILITY OF DATA
- COMPUTER FACILITIES
- AQUIFER SYSTEM COMPLEXITY
- CODE FORMULATION, CHARACTERISTICS
Slide 8.28
-------
8.0 COMPARATIVE ANALYSIS CASE STUDIES
8.1 INTRODUCTION
At least six methods are available for use in delineating
Wellhead Protection Areas (WHPAs). These methods span a
broad range of cost and complexity. It is valuable, prior to
designing a WHPA delineation study, to examine comparative
analysis test cases in which several methods are applied to
the same location.
Such studies may be used to assess a number of factors
related to WHPA delineation. Comparison of a WHPA accurately
delineated with a sophisticated method against WHPAs
delineated with simpler methods permit assessment of the
"safety factors" supposedly incorporated in the simple
methods. Similarly, a favorable comparison between simple
and sophisticated methods may indicate that the sophisticated
methods are not worth the extra cost. Comparative analyses
may also be used to assess the impact of different criteria
thresholds selected for a given site.
The following case studies have been selected to illustrate
the use of several methods at a single site. Where appro-
priate, the suitability of the methods applied is discussed.
8.2 COMPARATIVE ANALYSIS CASE STUDY 1:
COMPARISON OF DRAWDOWN AND TIME-OF-TRAVEL CRITERIA
In October, 1987 the City of Kennedale, Texas requested that
the Texas Water Commission (TWC) establish wellhead protec-
tion criteria for their public water supply system. The case
study is presented in greater detail in Appendix B. The
material pertinent to the comparison of two different
criteria for the same system of wells is summarized here.
The City of Kennedale derives its water from the Trinity
Aquifer which is confined beneath 600 feet of limestone,
marl, and clay. TWC first developed a computer model of
drawdown in the confined aquifer using pumping data for the
period 1952 to 1987. The zone of influence (ZOI) was defined
in this case as the 5-foot drawdown contour. Results of the
modeling study showed that the 5-foot drawdown contour was
located at a distance of 20 miles from the Kennedale wells,
encompassing an area that engulfed Fort Worth and extended
into two other counties.
8-1
-------
It was decided that this large zone of influence would not be
appropriate. Water moved very slowly through the confined
aquifer, and a zone of over 1,200 square miles would be
unnecessarily overprotective. It was reasoned that the
distance required for a 5-year time-of-travel to the wells
would provide for sufficient attenuation of any contaminants.
The calculated fixed radius method was used to delineate the
WHPA for each well based on pumping data during the previous
two years. Calculated radii for all wells were less than
800 feet. A buffer zone was added to the calculated radii
and the WHPA for each was established as the zone within a
one-quarter mile (1,320 ft) radius of each well (Slide 8.10).
The large difference in areas between the two methods
described above results from the nature of the aquifer.
Pressure phenomena (i.e. reduction in piezometric surface of
5 ft in this case) can extend to great distances from wells
in confined aquifers. This is true even for relatively low
pumping rates and low flow velocities through the aquifer.
8.3 COMPARATIVE ANALYSIS CASE STUDY 2:
COMPARATIVE ANALYSIS USING THEIS SOLUTION
The Brookings, South Dakota case study (Appendix B) describes
a project in which a modified simplified variable shapes
method was used to delineate a Wellhead Protection Area
(WHPA) for the Big Sioux Aquifer, an alluvial valley-fill
aquifer (Slides 8.14 and 8.15). Hydrogeologic mapping of
topographic divides was also used to define the small
drainage catchments flanking the aquifer that have the
potential to introduce contaminants in a short time through
surface water runoff (Slide 8.18). This second method was
used to delineate a buffer zone surrounding the inner zone
that had been delineated by the simplified variable shapes
analysis. The reader is referred to Appendix B for a
detailed description of the aquifer setting and the methods
used.
To compare a third method with the two actually used in the
Brookings case study, an example was developed using the
Theis well hydraulics equation. The drawdown criterion with
a threshold of 1 foot was selected to delineate the hypothe-
tical WHPA. The computer code THWELLS (van der Heijde, 1987)
was used to solve the Theis equation for a single pumping
well and plot the 1-foot drawdown contour! The following
data for the well identified as Bruce Well 1 were derived
8-2
-------
from the case description in Appendix B, and a pumping time
of 20 years was assumed:
Transmissivity 55,128 gpd/ft
Storage coefficient 0.20
Pumping rate 120 gpm
After 20 years of pumping, the 1-foot drawdown contour is
located at a radial distance of approximately 3,300 feet
from the well. The area encompassed by this contour is
shown on Slide 8.21.
The WHPA delineated using the Theis equation, while over-
protecting slightly south of the well, appears to match the
actual delineated WHPA fairly well, but this is deceiving.
The Theis equation assumes an infinite aquifer, which causes
the 1-foot drawdown contour to extend several thousand feet
into the bedrock material forming the valley wall. This is,
of course, unrealistic. While the Theis-delineated area
appears to match well, it is actually matching a zone that
was added based on geologic mapping and surface water runoff
considerations; not on aquifer hydraulics considerations.
The Theis solution would have been applicable for a well
located in the center of the valley, but valley wall effects
are important for wells located along the edge of the
aquifer. One solution to this problem uses an image well
located on the opposite side of the valley wall from the
pumping well. An image well is a fictitious well, pumping at
the same rate as the real well, and added to the system to
represent the effects of an impermeable boundary (i.e. the
valley wall). The Theis equation for drawdown is solved for
each well and the solutions summed to provide the drawdown
surface for the two-well system.
THWELLS is capable of solving the Theis equation for multiple
pumping wells. The solution obtained for each well is added,
according to the method of superposition, to yield the final
solution. A calculation was performed with an image well
located 2,000 ft from Bruce Well #1 and pumping at the same
rate as the real well. The valley wall is located midway
between the two wells. After 20 years, the one-foot drawdown
contour in the aquifer is located at a radial distance of
9,450 feet from Well #1, extending to the far valley wall
(Slide 8.21).
This computation assumes that the Theis equation applies
accurately to this shallow unconfined aquifer and that the
aquifer is infinite in extent. Both of these assumptions
probably introduce significant error into this simple
8-3
-------
calculation. Nonetheless, the exercise serves to demonstrate
the effort of an impermeable boundary on the drawdown
calculation.
8.4 COMPARATIVE ANALYSIS CASE STUDY 3:
COMPARATIVE ANALYSIS OF TRAVEL-TIME MODELS
In July of 1986, the Florida West Coast Regional Water Supply
Authority (WCRWSA) commissioned a study (Geraghty & Miller,
1986) to demonstrate the use of various modeling approaches
to determine solute travel times in areas affected by water
supply wells. The study was developed for a wellfield
deemed to be representative of those in the region. Proposed
wellhead protection legislation for the State of Florida
would potentially affect privately owned land surrounding
wellfields and the ability for water supply authorities to
acquire land. WCRWSA was interested in determining the
complexity, costs, and limitations of alternative modeling
approaches.
The Cypress Creek wellfield was selected for the study area,
and field parameters and well locations used in the investi-
gation were obtained from a WCRWSA report on the Cypress
Creek field. The following parameters were used as needed in
each of the example models:
Transraissivity (Tx and Ty) 400,000 gpd/ft
Aquifer thickness (b) 500 ft
Leakance (L) 0.01 gpd/ft3
Pumping rate (Q) 2.3 mgd/well
Number of wells 13
Dispersivity (D) 0.000001
Three models were investigated for computing the travel time
of particles moving from discharge points in the aquifer to
pumping wells in the wellfield. In the first and most simple
method, it was assumed that all water discharged from a
pumped well is removed from the soil volume inscribed by a
cylinder with the well at its center, a height equal to the
aquifer thickness, and an effective pore volume equal to the
discharge volume. This is the familiar "calculated fixed
radius method" described in the WHPA Delineation Guidelines
(EPA 1987a).
Two numerical models were also developed with dispersion set
at or near zero (advection-only solute transport), which
permitted comparison of the numerical results with the
simpler calculated radius method. One numerical model used
8-4
-------
the microcomputer version of the Random Walk solute transport
code (Prickett et al. 1981). The model was developed with
the assumption of zero leakance between the aquifer and
underlying units.
The third model was developed using the Method of Charac-
teristics (HOC) solute transport code (Konikow and Bredehoeft
1978). The model incorporated a small leakance representa-
tive of conditions at the Cypress Creek site. This leakance
in the numerical model was expected to have little effect on
the results. Preliminary calculations based on the hy-
draulics of a single pumping well showed that, even with a
head differential of 100 feet between the aquifer and
underlying layers (an unrealistically high amount), the
computed travel distance would be changed by a factor of less
than 0.001 (0.1 percent).
Plots of the 2-year, 5-year, and 10-year travel distances
(Slides 8.25, 8.26, and 8.27, respectively) were generated
for the three models to permit a graphical comparison of the
results. The contours of Model 1 show a series of 13
overlapping circular contours. Each contour represents the
travel distance that would exist had none of the other wells
been present. Since two wells cannot extract water from the
same cylindrical soil volume, the volume error associated
with this approach is simply the amount of circle overlap.
Overlap is minimal for the 2-year travel distance and
increases to nearly 70 percent for the 10-year travel
distance. Additional error is introduced by not accounting
for the deviation from strict radial flow caused by nearby
wells.
The contours for the two numerical models are quite close as
could be expected. In both cases, dispersion was set at or
close to zero. Leakance was incorporated into the MOC
model. However, as expected it had negligible effect on the
computed travel-time distances.
The main difference between the two numerical models is
caused by differences in resolution due to grid refinement
and differences associated with the averaging schemes. The
Random Walk model utilizes an 11 by 11 node grid, with a
node spacing of 3,000 feet., while the MOC model utilizes a
20 by 20 node grid with a node spacing of 1,500 feet.
Discretization error associated with the choice of grid
spacing will therefore be higher with the Random Walk model.
The difference in the graphical representation of the travel
time contours is largely due to the averaging scheme
associated with the MOC model. Particles are associated with
a particular node in the grid if they fall within the square
8-5
-------
area which surrounds the node and bisects the distance from
it to adjacent nodes. In the Cypress Creek example, the
averaging scheme encompasses an area of 1,500 by 1,500 ft.
The Random Walk model tracks particles at 100-ft intervals
and plots their positions directly. This results in a better
defined plume.
It should be noted that the models developed for this
investigation did not consider many factors which would
affect travel distance contours around a well or wellfield,
including regional flow gradient, hydrodynamic dispersion,
or retardation of the moving solute due to adsorption onto
soil material. When regional flow is considered, for
example, the area delineated around the well becomes
elongated and its center is offset from the well in the
direction of flow.
The cost of estimating travel times largely depends on the
availability of data, computer facilities and degree of
model resolution desired. The volume balance (calculated
radius) approach is the least expensive. The only aquifer
parameter required is the effective porosity, and the
calculation is simple.
The two numerical models used in this study are of approxi-
mately equal complexity and require essentially the same data
inputs. The version of Random Walk used in this study could
not handle leakance, but a version is available that adds
that feature. The cost of purchasing, installing and
testing each model is on the order of $500. The labor costs
required to set up each model with site specific data and
appropriate boundary conditions and to perform a sufficient
number of simulations to be confident in the results can
range from $5,000 to $50,000. Additional complexities of the
aquifer system or the type of information required from the
model would place a study at the high end of this range.
For example, the study described here was designed to compare
modeling approaches and not to delineate precise defensible
boundaries. On the course grid spacing of 1,500 by 1,500 ft
well locations were only approximated. A variable mesh grid
would be needed to accurately model the well locations, and a
finer grid would be required to more accurately delineate the
plume boundary. Consideration of spatially varying hydraulic
properties, the inclusion of chemical transport properties,
and more complex boundary conditions might also be required.
In order to be legally defensible, these factors would have
to be considered and would involve additional model setup and
testing costs and additional expenses in obtaining the
required data.
8-6
-------
A. References
-------
APPENDIX A:
REFERENCES
A-l
-------
REFERENCES
INTRODUCTION
U.S. Environmental Protection Agency, 1987a. Guidance for
Applicants for State Wellhead Protection Program
Assistance Funds Under the Safe Drinking Water Act,
Office of Ground-Water Protection, Washington, D.C., 53
pp.
U.S. Environmental Protection Agency, 1987b. Guidelines for
Delineation of Wellhead Protection Areas, Office of
Ground-Water Protection, Washington, D.C., 185 pp.
U.S. Environmental Protection Agency, 1987c. Surface Geo-
physical Technique for Aquifer and Wellhead Protection
Area Delineation, Office of Ground-Water Protection,
Washington, D.C., 48 pp.
U.S. Environmental Protection Agency, 1988. Model Assessment
for Delineating Wellhead Protection Areas, Office of
Ground-Water Protection, Washington, D.C., 210 pp.
FUNDAMENTALS OF GROUND-WATER FLOW
Bear, Jacob, 1980. Hydraulics of Ground Water; McGraw-Hill
Book Co., 1221 Ave. of the Americas, New York, New York
10020, 567 pp.
Bouwer, Herman, 1978. Groundwater Hydrology; McGraw-Hill
Book Co., New York, New York 10020, 480 pp.
Davis, S.N. and R.J.M. DeWeist, 1966. Hvdroaeoloav: John
Wiley & Sons Inc., New York, 463 pp.
Dewiest, R. J.M. (ed.), 1969. Flow Through Porous Media;
Academic Press, New York, 530 pp.
Everett, A.G., 1987. Some Significant Attributes of Aquifers
as Related to Wellhead Protection Considerations. Un-
published Report to the U.S. Environmental Protection
Agency, Office of Ground-Water Protection.
Fetter Jr., C.W., 1980. Applied Hvdroaeoloav; Charles E.
Merrill Publishing Company, Columbus, Ohio, 488 pp.
Freeze, R.A. and J.A. Cherry, 1979. Groundwater; Prentice-
Hall Inc., New Jersey, 604 pp.
A-2
-------
Walton, W.C., 1970. Groundwater Resource Evaluation, Mc-
Graw-Hill Book Co., Inc., 664 pp.
FUNDAMENTALS OF CONTAMINANT TRANSPORT
Cherry, J.A., 1984. Environmental Geochemistry: Short Course
Handbook, Edited by M.E. Fleet, Mineralogical Assoc. of
Canada, pp. 269-306.
Fetter Jr., C.W., 1980. Applied Hydrogeology, Charles E.
Merrill Publishing Company, Columbus, Ohio, 488 pp.
Freeze, R.A. and J.A. Cherry, 1979. Groundwater, Prentice-
Hall, Inc., New Jersey.
Gillham, R.W., and J.A. Cherry, 1982. Contaminant Migration
in Saturated Unconsolidated Geologic Deposits: Geo. Soc.
of America Special Paper 189, pp. 31-62.
LeGrand, H.E., 1965. Patterns of Contaminated Zones of Water
in the Ground: Water Resources Research, Vol. 1, pp. 83-
95.
Miller, D.W., F.A. DeLuca, and T.L. Tessier, 1974. Ground
Water Contamination in the Northeast States: EPA-660/2-
74-056.
National Research Council, 1984. Groundwater Contamination:
Studies in Geophysics Scenes, Geophysics Study Commit-
tee, National Academy Press, Washington, D.C., 179 PP.
Schwille, F. Groundwater Pollution by Mineral Oil Products,
Proceedings of the Moscow Symposium, lAHS-Publication
No. 103, 1975.
U.S. General Accounting Office, 1981. Hazardous Waste Sites
Pose Investigation, Evaluation, Scientific, and Legal
Problems: CED-81-57, Report by the Comptroller General
of the U.S., 65 pp.
Walton, W.C., 1970. Groundwater Resource Evaluation, McGraw-
Hill Book Co., Inc., 664 pp.
FUNDAMENTALS OF WELL HYDRAULICS
Driscoll, Fletcher G., 1986. Groundwater and Wells; Johnson
Division, St. Paul Minnesota, Chapter 9 - Well Hy-
draulics, pp 205-264.
A-3
-------
McWhorter, D., and D. K. Sunada, 1977. Ground-Water Hydro-
logy and Hydraulics: Water Resources Publications, 290
pp.
Theis, C.V, , 1935. The Relation Between the Lowering of the
Piezometric Surface and the Rate and Duration of
Discharge of a Well Using Ground Water Storage:
Transactions, American Geophysical Union, Washington,
D.C., pp. 518-524.
Thiem, G., 1906. Hydrologische Methoden. Leipzig, 56 p.
ELEMENTS OF WHPA DELINEATION
Anderson, M.P., 1984. Movement of Contaminants in Ground-
water: Groundwater Transport-Advection and Dispersion,
Studies in Geophysics: Groundwater Contamination.
National Academy Press, Washington, D.C.
Bear, J., 1979. Hydraulics of Groundwater, McGraw-Hill, Inc.
Fried, J.J., 1975. Groundwater Pollution, Elsevier Scien-
tific Publishing Company, New York, New York.
Quinlan, J.F., and R.O. Ewers, 1985. Ground Water Flow in
Limestone Terranes: Strategy Rationale and Procedure for
Reliable, Efficient Monitoring of Ground Water Quality
in Karst Area, National Symposium and Exposition on
Aquifer Restoration and Ground Water Monitoring,
National Water Well Association, Worthington, Ohio.
ANALYTICAL METHODS
Javandel I., C. Doughty and C.F. Tsang, 1984. Groundwater
Transport: Handbook of Mathematical Models, American
Geophysical Union, Washington, D.C., 228 pp.
van der Heijde, P.K.M., 1987. THWELLS: Calculating Drawdown
from Multi-Well Pumping in a Homogeneous Isotropic
Confined Aquifer: International Ground Water Modeling
Center, Holcomb Research Institute, Butler University,
Indianapolis, Indiana. 82 pp.
A-4
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HYDROGEOLOGIC MAPPING
Crawford, N.C., C.G. Groves, T.P. Fenney, and B.J. Keller,
1987. Agriculture and Urban Nonpoint Source Pollution
Impacts on Karst Aquifers in the Pennroyal Karst Region
of Kentucky: Part I Hydrogeology of the Lost River
Karst Ground-Water Basin, Warren County, Kentucky.
Center for Cave and Karst Studies, Western Kentucky
University, Bowling Green, -Kentucky.
Heath, R.C., and F.W. Trainer, 1968. Introduction to Ground-
Water Hydrology, John Wiley & Sons, Inc., New York, 284
pp; Revised ed. 1981 Water Well Journal, 500 W. Wilson
Bridge Road, Worthington, Ohio 43085.
McGrain, P., and D.G. Sutton, 1973. Economic Geology of
Warren County, Kentucky: Kentucky Geological Survey,
Series 10, County Report 6, 28 p.
Russell, A.D., and G.M. Thompson, 1983. Mechanisms Leading
to Enrichment of the Atmospheric Fluorocarbons CC^F and
CC12F in Groundwater. Water Resources Research. Vol.
16, pp. 145-158.
NUMERICAL METHODS
McDonald, M. G., and A. W. Harbaugh, 1984. A Modular Three-
Dimensional Finite-Difference Ground-Water Flow Model,
U. S. Geological Survey Open File Report 83-875, U. S.
G. S., Reston, Virginia.
Morrissey, D. J., 1987. Estimation of the Recharge Area
Contributing Water to a Pumped Well in a Glacial-Drift,
River Valley Aquifer, U. S. Geological Survey Open File
Report 86-543, U. S. G. S., Providence, Rhode Island.
Shafer, J. M. , 1987. GWPATH: Interactive Ground-Water Flow
Path Analysis, Bulletin 69, Illinois State Water Survey,
Champaign, Illinois.
COMPARATIVE ANALYSES
Geraghty & Miller, Inc., 1986. Travel Time Models for the
Cypress Creek Wellfield, prepared for the West Coast
Regional Water Supply Authority, Clearwater, Florida,
26 pp.
A-5
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Konikow, L. F., and Bredehoeft, J. 0., 1978. Computer Model
of Two-Dimensional Solute Transport and Dispersion in
Ground Water: Techniques of Water-Resources Investiga-
tions of the United States Geological Survey, Book 7,
Chapter 2, 90 pp.
Prickett, T. A., Naymik, T. G., and Lonnquist, C. G., 1981.
A "Random-Walk" Solute Transport Model for Selected
GroundWater Quality Evaluations: Illinois State Water
Survey Bulletin 65, 62 pp.
A-6
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B. Case Studies
-------
APPENDIX B:
CASE STUDIES
B-l
-------
APPENDIX B: CASE STUDIES
The following case studies present actual Wellhead Protection
Area (WHPA) delineation cases, or in the case of two studies,
sites for which WHPAs may eventually be delineated. Table
B-l lists the cases, their status (WHPA delineation completed
or in progress) and the criteria and methods employed or
demonstrated in each.
Cases were provided by regional offices of the Environmental
Protection Agency (EPA), and an attempt was made to present
cases for a range of hydrogeologic settings and a variety of
delineation methods. The case studies provided here are
synopses of the material supplied by EPA regional offices,
and every effort was made to accurately report the methods
and results of each case. Selection of these cases in no way
implies a preferential endorsement of the criteria and
methods used for WHPA delineation in these studies. No
opinion is offered concerning the appropriateness of the
criteria and methods for the sites to which they were
applied, and no attempt was made to correct errors in
implementation and/or reporting of the various methods used.
B-2
-------
TABLE B-l
SUMMARY OF WHPA DELINEATION CASE STUDIES
CASE STUDY/
LOCATION
STATUS
CRITERIA
WHPA DELINEATION METHOD
1. Brookings Co.
South Dakota
In Progress
time of travel
flow boundaries
uniform flow equation
hydrogeologic mapping
(to define hydrogeologic
boundaries)
2. Kennedale,
Texas
Completed
— time of travel
— calculated fixed radii
3. Oakley,
Kansas
Completed
time of travel
drawdown
numerical model
Darcy's law velocity
equation
4. Palm Beach
County, Florida
Completed
— time of travel
— drawdown
— numerical flow model
— numerical transport model
Franklin,
Massachusetts
Completed
distance
flow boundaries
fixed radii
numerical model
hydrogeological mapping
Bowling Green,
Kentucky
In Progress
time of travel
flow boundaries
— hydrogeologic mapping
-------
B.I CASE STUDY; BROOKINGS COUNTY. SD
INTRODUCTION
Brookings County in South Dakota undertook a comprehen-
sive mapping program in 1987 as an initial step in developing
Wellhead Protection Areas (WHPAs). The county first
identified all public municipal and rural water supply
wells. Available information was used to characterize the
Big Sioux aquifer, which is almost entirely unconfined in the
county (see Figure 1) . The uniform flow equation was then
used to generate conservative estimates of the zone of
contribution (ZOC) to each well. This zone was amended with
a buffer zone for irrigation wells, and modified where
hydrogeologic boundaries bisected the calculated ZOC.
PROGRAM OBJECTIVES
The goal of the Wellhead Protection program in Brookings
County was to identify and map zones of contribution to
public water supply wells. Although official WHPAs have not
yet been delineated for the wells studied in this investiga-
tion, it is expected that the ZOCs mapped will be adopted as
WHPAS when it is decided what activities will be regulated,
and how the ordinance will be enforced.
HYDROGEOLOGIC SETTING
Most public water supply wells in Brookings County draw
water from the Big Sioux aquifer, a sequence of unconsol-
idated glacial outwash overlain by minor amounts of alluvial
sand and gravel. Much of the aquifer data used in the study
(Table 1) was obtained from the South Dakota Department of
Water and Natural Resources (DWNR). The saturated thickness
of the aquifer ranges from 20 to 40 feet, but reaches as much
as 60 to 80 feet in parts of Brookings County (DWNR, 1987) .
The aquifer is almost entirely unconfined, with exceptions in
areas where younger glacial till has covered the aquifer as a
result of outwash collapse. Glacial till also forms an
impermeable boundary beneath the aquifer (see Figure 2) .
Where the aquifer is not bounded by till, it is in contact
with less permeable Precambrian or Cretaceous rock. Figure 3
illustrates the general stratigraphic relationships of
geologic units in and around the Big Sioux aquifer.
Wells in the Big Sioux can yield over 1,000 gpm because
of its water-bearing properties. Porosity ranges from 20 to
35 percent, which is typical of glacial outwash deposits.
Values of hydraulic conductivity vary from 20 to 2.0 x 104
gal/day/ft2; and the specific yield is estimated at 15 to 20
percent (DWNR, 1987).
B-4
-------
«!«•<* tlltlltl Mlt«llH4
•S • • 31
R52W
R5IW
R50W
R47W
FIGURE 1 . BROOKINGS COUNTY SATURATED THICKNESS
-------
TABLE 1-SUMMARY OF DATA USED IN EVALUATIONS
WATER
SUPPLY
AURORA
BRKNGS-E
BRKNGS-N
B-D-K RWS
(BRUCE)
B-D RWS
BRUCE
ELXTON
VOLGA
(FUTURE)
WESTERN
ESTATES
WELL
NUMBER
1
1
2
3
3
4
5
6
7
8
9
1
2
3
4
1
2
1
1
2
2
3
4
5-
6
7
1
CAPACITY
(GPM)
90
1000
1400
1400
840
690
255
570
610
490
750
300
250
225
350
110
110
120
90
125
120
150
120
185
185
185
388
-Q"
(CF/D)
17325.00
192500.00
269500.00
269500.00
161700.00
132825.00
49087.50
109725.00
117425.00
94325.00
144375.00
57750.00
48125.00
43312.50
67375.00
21175.00
21175.00
23100.00
17325.00
24062.50
23100.00
28875.00
23100.00
35612.50
35612.50
35612.50
74690.00
SAT THK
"b"
(FT)
20.00
63.00
.'63.00
63.00
37.33
47.33
37.33
37.33
37.33
37.33
37.33
34
34
34
34
20.83
21
11
8
31
17
16
15
30
30
30
18
HYD COND
"K"
(FT/D)
670.00
670.00
670.00
670.00
587
587
587
587
587
587
587
615
571
706 *
582
600
600
670
600
600
480
480
480
300
300
300
533
HYD GRAD
"i"
(FT/FT)
0.0019
0.0013
0.0013 .
0.0013
0.0015
0.0015
0.0015
0.0015
0.0015
0.0015
0.0015
0.0013
0.0013
0.0013
0.0013
0.0017
0.0017
0.0017
0.0023
0.0023
0.0029
0.0029
0.0029
0.0033
0.0033
0.0033
0.0017
B-6
-------
03
2000i
1800-
UJ
o
co
1600-
z
o
1400-
1200
1000
R54W
53
HAMLIN
BIG SIOUX AQUIFER
Glacial Till with Gravel Stringers
FIGURE 2. GEOLOGIC CROSS-SECTION OF BIG SIOUX BASIN
-------
FIGURES.
GENERALIZED STRATIGRAPHIC COLUMN
BIG SIOUX RIVER BASIN
OH
o:
LU
13
o
CO
ID
O
LU
0
<
J—
LU
a:
u
o:
m
cj
UJ
cr
o_
0-20
RECENT ALLUVIUM
0-500
PLEISTOCENE
GLACIAL DRIFT
0-300
PIERRE SHALE
NIOBRARA .
FORMATION
Codell 0-
0-230
CARLILE SHALE
Silt., •and*
and gnavel
indblown
—*ized pantiol
•and and
unetnat i F i ed and
olay with
and
Light- to dank
•hal«t t-hin
and oononet.ion».
to dank gnay to
white chalk with
• i
y
hal
zon
0-300
GRANEROS SHALE
DAKOTA
0—400
SANDSTONE
* «***
•andetone
Dank gnay. oononetion
beaning ehale-
Gnay. oalcaneoue.
1i meetone
Dank qnay,
conbn«t:
5SW3SS-SK
Sjwsga/WB
: i on—bean i ng
ohale.
iLight yellow and
S white eandetonei
£ fine to medium
|. gnained eands
I intenbedded ehalee.
SIOUX
kJ-DMkJkJ^/^i-/ ;^, ;'>::^liKe-P5;iliip^
UUAK I /. i 1 r. i « , • *• • • » - . • JX-. ^ »
NX\NNXV^X .X \.\N.N \?,^?/^?
r ^*>\'^< ^ \' v r ^x^ v ^ ^ "^
i^x» - •'
htoq
B-8
-------
As an unconfined aquifer, the Big Sioux derives its
recharge from infiltration of precipitation and seepage from
surface-water bodies. Quick response of water levels to
recharge events indicates that the aquifer is unconfined and
in good hydraulic connection with the surface. This is an
important consideration in terms of ground-water protection,
as contaminants can quickly leach into the aquifer through
the highly permeable sediments above the water table.
METHOD AND CRITERIA SELECTION
In order to identify the entire ZOC, the criteria
selected were the flow boundaries, and a time-of-travel
criterion for the upgradient limit. Because the County
wanted to delineate WHPAs using only available data a
simplified method of approximating the flow boundaries was
used. The method was adapted from work done in Southern
England and described in "Guidelines for Delineation of
Wellhead Protection Areas", published by EPA, as the
simplified variable shapes method.
The technique involves solving the uniform flow equation
to yield key points on the no-flow boundary or ground-water
divide produced by the pumping well; using the resultant
values to estimate a conservative ZOC down-gradient and
cross-gradient of the well; and using a TOT equation to
define an upgradient extent of the ZOC. The equations
derived from the uniform flow equation are:
27TKbi
and YL = ±
27rKbi
where,
XL = distance to the down-gradient null point beyond
which ground water is not drawn back towards
the well
YL = maximum perpendicular distance to the ground-
water divide from a line extending directly
upgradient of the well
Q = pumping rate
K = hydraulic conductivity
b = saturated aquifer thickness
i = hydraulic gradient
B-9
-------
FIGURE 4.
WHPA Delineation Using the
Uniform Flow Analytical Model
GROUND
Q /-SURFACE
ORIGINAL
PIEZOMETRIC
SURFACE
DRAWDOWN CURVE
CONFINED
AQUIFER
(a)
IMPERMEABLE
EQUIPOTENTIAL LINES
GROUNDWATER
DIVIDE
FLOW
- /LINES
x
Q
X .=-
I
2Kb!
UNIFORM-FLOW
EQUATION
DISTANCE TO
DOWN-GRADIENT
NULL POINT
BOUNDARY
LIMIT
LEGEND:
• Pumping Well
SOURCE: Todd. 1980
Where:
Q= Well Pumping Rate
K = Hydraulic Conductivity
b = Saturated Thickness
i = Hydraulic Gradient
T= 3.1416
NOT TO SCALE
B-10
-------
The physical meaning of the equations is illustrated in
Figure 4. The values used in the equations were taken from
existing records and are presented in Table 1.
The YL value calculated using the uniform flow equation
actually represents the distance to an asymptote which the
ground-water divide approaches at an infinite distance
upgradient of the well. However, to avoid calculating the
coordinates of a series of points along the curve, the YL
distance was assumed to be the cross-gradient distance to the
ground-water divide from the well. This results in the
configuration shown in Figure 5, which is more conservative
than the actual ground-water divide.
Because the uniform-flow equation assumes an infinite
upgradient extent of the ZOC, another method must be used to
define the upgradient extent of the WHPA. For the wells in
Brookings County, calculated distances were based on 5-year
and 10-year travel times. The velocity of ground-water
movement was computed as
V = Ki
The distance was then simply
r = Vt where t = travel time
(Note: The method of computing flow velocity shown above
differs from the method recommended in the WHP Guidance
document. The recommended method incorporates the effect of
aquifer porosity which results in higher computed flow
velocities, and larger WHPAs.)
Hydrogeologic boundaries were also taken into considera-
tion in delineating the ZOC. Where a hydrogeologic boundary
such as a stream, an aquifer boundary or a ground-water
divide intersected the calculated ZOC, such a boundary was
designated as the extent of the ZOC, and "upgradient" areas
were excluded from consideration.
For additional protection, a buffer zone was developed
to protect against the effect of irrigation wells. This
buffer zone was determined by a method developed in Colorado,
where the following relationships apply:
1. The downgradient extent of the buffer zone is twice the
distance from the well to the downgradient null point.
2. The cross-gradient distance from the well to the buffer
zone is twice the distance from the well to the YL distance.
B-ll
-------
3. The buffer zone in the upgradient direction extends
beyond the original delineate boundary an additional 50 feet
for every 100 feet of distance upgradient of the well.
Finally, where the ZOC or buffer zone was intersected by
an aquifer boundary, an area was delineated outside of the
aquifer as a contributing drainage area. Based on topo-
graphy, this area represents the area from which degraded
surface water could quickly enter the ZOC of a well through
surface runoff.
RESULTS
A total of 10 ZOCs have been delineated for 26 wells in
Brookings County. An example of a completely delineated ZOC
and buffer zone, with contributing drainage area is shown in
Figure 5.
B-12
-------
Fig. 5 ZOC and Buffer Zone For Bruce Well No. 1
© TEN (IO) YEAR TIME OF TRAVEL
© FIVE (5) YEAR TIME OF TRAVEL
© WELL
D) ZONE OF CONTRIBUTION
BUFFER ZONE FOR IRRIGATION
c
AOUIFEf! AREA
NOf4-AQUIFER AREA
|\\\\\Vl FUTURE WATER RIGHT AREA
I W
©
B-13
-------
B.2 CASE STUDY: KENNEDALE, TEXAS
INTRODUCTION
The City of Kennedale, in Tarrant County, Texas is
located approximately 15 miles southeast of Fort Worth (see
Figure 1) . In October of 1987 the City requested that the
Texas Water Commission establish wellhead protection criteria
for their public water supply system. The Commission used
available information supplied by Kennedale to delineate
wellhead protection areas for each of five municipal wells
using the calculated fixed radius method described in EPA's
WHPA Guideline document.
PROGRAM OBJECTIVES
In developing groundwater protection goals for the City
of Kennedale, the Texas Water Commission examined potential
sources of groundwater quality degradation and grouped them
according to their origin. The three major groups were:
1) Problems that originate on the land surface
2) Problems that originate in the ground above the
water table.
3) Problems that originate in the ground below the
water table.
A more complete list of identified potential sources is
given in Table 1.
Attention was focused primarily on the third group of
sources, because the 600 feet of confining beds above the
aquifer were considered substantial protection to the
Kennedale wells. Any source of contamination originating
near the surface would be greatly diluted and attenuated
before reaching the confined aquifer. Nor was a protection
strategy developed for the recharge area. The long distance
and slow regional movement of ground water was considered to
provide a sufficient buffer for diluting contaminants.
HYDROGEOLOGIC SETTING
The City of Kennedale derives its water from the Trinity
Aquifer, which is comprised of two water-producing zones, the
Paluxy and Twin Mountains Formations; and a confining unit,
the Glen Rose Formation, which separates the two. The entire
aquifer system is under confined conditions in the Kennedale
B-14
-------
PO'k*
\ \
-------
TABLE 1
Sources of Ground Water Quality Degradation
Ground Water Quality Problems that Originate on the Land Surface
1. Infiltration of polluted surface water
2. Land disposal of either solid or liquid wastes
3. Stockpiles
A. Dumps
5. Disposal of sewage and water-treatment plant sludge
6. De-icing salt usage and storage
7. Animal feedlots
8. Fertilizers and pesticides
9. Accidental spills
10. Particulate natter from airborne sources
Ground Water Quality Problems that Originate In the Ground Above
the Water Table
1. Septic tanks, cesspools, and privies
2. Holding ponds and lagoons
3. Sanitary landfills
4. Waste disposal in excavations
5. Leakage from underground storage tanks
6. Leakage from underground pipelines
7.; Artificial recharge
8. Sumps and dry wells
9. Graveyards
Ground Water Quality Problems that Originate in the Ground Below
the Water Table
1. Waste disposal in well excavations
2. Drainage wells and canals
3. Well disposal of wastes
4. Underground storage
5. Secondary recovery
6. Mines
7. Exploratory veils
8. Abandoned wells
9. Water-supply veils
10. Ground-water development
B-16
-------
DEPTH
FROM
'URFACE
r 0
FIGURE 2. STRATIGRAPH1C UNITS
CITY OF KENNEDALE
PALUXY NO. 3
SP
_100CURVE
-r200
_300
A 00
500
1600
JO
4600
ec
c —«
— «8
C >
-H U
«u Q)
C u
o c
I
igoo
1000
-1100
1200
1300
CJ
-r*
3
CO
c -*
•^ «
e >
C JJ
C C
3
c-
SHORT NORMAL
CURVE
GROUP
Woodbine
Washita
UNIT
CHARACTER OF ROCKS
Medium to coarse sand,
clay, and some lignite
Mainstreet Lro.
Weno Lm.
Pawpaw Fm.
Denton Clay
Fm
Kiamichi Fm.
Fredericks-
burg
Coodland Lm.
Walnut Fm.
Trinity
Paluxy Fm.
Glen Rose Formation
Twin Mountains Fm.
Fossiliferous limestone,
marl, and clay
Fine sand, sandy shale,
and shale
Limestone, marl, shale,
and anhvdrite
Fine to coarse sand,
shale, clay and basal
gravel
B-17
-------
area, lying beneath 600 feet of limestone, marl, and clay. A
summary of the stratigraphic relationships is presented in
Figure 2.
Recharge to the Trinity aquifer occurs primarily through
infiltration in the outcrop area, located about 20 miles west
of the city and covering over 600 square miles. The rate of
recharge is estimated at one inch per year distributed over
the outcrop area. Regionally, ground water within the
Trinity aquifer is moving at an estimated rate of one to two
feet per year toward the east. In the vicinity of Kennedale,
where heavy pumping has lowered the piezometric surface and
thereby steepened the hydraulic gradient, ground water may be
moving at a rate of 200 to 300 feet per year towards pumping
centers.
CRITERIA AND METHOD SELECTION
Before selecting an appropriate method for WHPA
delineation, the Texas Water Commission (TWC) examined
available data on supply well construction, discharge rates,
and hydrogeologic properties of the Trinity aquifer. Using a
computer drawdown model, the TWC simulated the drawdown for
the period 1952 to 1987, and mapped the 5-foot drawdown
contour interval for both the Paluxy and Twin Mountains
aquifers. The area within the approximately 20-mile radius
to the 5-foot drawdown was considered the zone of influence
of the Kennedale wells (Figure 1) . Due to the long pumping
period considered and the hydrogeologic properties of the
aquifer, the resultant zone of influence was very large,
encompassing Fort Worth and extending into two other
counties.
It was decided that the large zone of influence of those
wells would not be appropriate, since the slow groundwater
velocities in the area would also offer protection from
subsurface sources of contamination in the zone of influence
through attenuation of pollutants. A five-year time of
travel was selected as the criteria, and a calculated fixed
radius was chosen as the method to delineate the WHPAs. The
radius which encompassed the 5-year TOT distance was
calculated according to the volumetric flow equation,
*\| n:rH
where
r = radius
Q = pumping rate
t = travel time
n = porosity
H = length of screen
B-18
-------
RESULTS
The final WHPA delineation included an additional buffer
zone which was added to the calculated radius, rounding the
WHPA up to a one-fourth mile radius for each well. The
values used in calculating the radii are given in Table 2.
The mapped WHPAs are shown in Figure 3.
B-19
-------
TABLE 2
HYDROGEOLOGIC DATA USED TO CALCULATE WELLHEAD PROTECTION AREAS FOR KENNEDALE, TEXAS
00
1
to
o
Well ]
Paluxy
Paluxy
Paluxy
Trinity
Trinity
CD
#1
#2
#3
#1
#2
Porosity
.25
.25
.25
.25
.25
Screen
80
80
80
175
175
FY 1986 FY 1987
Length (in gallons) (in gallons)
ft. 25,954,700 41,676,300
ft. 18,220,300 26,152,900
ft.
ft 103,017,700 102,784,900
ft 59,725,700 53,698,100
TOTAL
(in gallons)
67,631,000
44,363,200
—
205,802,600
113,423,800
-------
N
"-Trinity
Poluxy "I
water wells
Trinity "2
water wellp
• ^
FIGURE 3. CITY OF KENNEDALE WELLHEAD PROTECTION AREAS
B-21
-------
B.3 CASE STUDY: OAKLEY. KANSAS
INTRODUCTION
In response to Section 1428 of the Safe Drinking Water
Act Amendment of 1986, the city of Oakley, Kansas initiated
a Wellhead Protection program for its municipal water supply
wells. The City, in consultation with the Northwest Kansas
Groundwater Management District, decided to use a numerical
flow model to generate the area of influence, cone of
depression, and time of travel for each pumping well. The
numerical model also offers Oakley the capability of varying
pumpage rates and grid spacing and the opportunity to refine
the Wellhead Protection Areas (WHPAs) with time.
PROGRAM OBJECTIVES
It was decided by the City management to delineate two
WHPAs: an overall protection area for the well field and a
secondary protection area. The overall protection area
represents the 0.05 foot drawdown area of the Oakley well
field after pumping. The secondary protection area includes
the area around an individual well within a 180 day time of
travel (TOT) distance. More stringent regulations would be
applied to the activities in the secondary protection area
around individual wells.
HYDROGEOLOGIC SETTING
The Oakley, Kansas public water supply wells are
screened in the Ogallala Formation. The Ogallala Formation
is an unconfined aquifer composed chiefly of calcareous
sandstone containing clay, silt, gravel, cobbles, and
boulders of Tertiary age. It is cemented by calcium
carbonate to various degrees. A mature drainage system was
developed upon the underlying bedrock formations before
deposition of the Ogallala formation. Determination of the
width and depth of the principal valleys of that system is
important in delineation of areas of greatest saturated
thickness. Some of these channels provide a medium for
storage and transmission of ground water. In the vicinity of
Oakley, these channels generally trend northeast. The
ground-water gradient (i) is 10 feet per mile, and the flow
direction is inferred to be eastward. The saturated
thickness of the Ogallala Formation in the vicinity of
Oakley, Kansas is approximately 120 feet.
B-22
-------
Pump test data obtained from wells located approximately
six miles from Oakley gave the following aquifer parameters:
T = 20,000 gpd/ft
S = .12
K = 235 gpd/ft2
i = 0.002
METHOD AND CRITERIA SELECTION
The "Basin Aquifer Simulation Model" by T.A. Prickett
and C.G. Lonnquist of the Illinois State Water Survey was
chosen to delineate the WHPAs. The two-dimensional numerical
flow model, capable of outputting the area of influence, cone
of depression, and TOTs was modified by the Northeast Kansas
Ground Water Management District to simulate water table
conditions.
Various assumptions were made because of the model
chosen, limitations of the data, and the hydrogeologic
conditions in the study area. The assumptions are as
follows:
1) The zone of influence (ZOI) and the zone of contribu-
tion (ZOC) are considered the same because the water
table is nearly level in the area and the pumping
regime is relatively small.
2) The aquifer parameters calculated for a well six
miles from the study area are similar to those found
in the WHPA.
3) The total pumpage, for a year, was withdrawn in
equal~ daily increments over the year. In fact, 70
percent of Oakley's total withdrawals are typically
taken in the four months from June through September.
This allows some degree of recovery to take place
during the remaining eight months.
The area around Oakley was represented by a 50 x 50
model grid with node spacing of 660 feet in both the x and y
directions. A recharge boundary was induced along the west
side of the grid by assigning an artificially high storage
value of 3.0 x 1012, and a discharge of 25,410 gallons per
day (gpd) was applied on the east side of the grid to induce
horizontal flow in the model equivalent to the natural flow
resulting from the regional gradient of 0.002.
B-23
-------
TABLE 1
MONTHLY PUMPING RATES FOR OAKLEY,
KANSAS WATER SUPPLY WELLS
(based on 3 year average)
Well No. Pumping Rate (gpd)
1 36,256
4 144,267
5 173,719
6 58,403
7 257,366
8 303,570
B-24
-------
Because of the relative simplicity of the hydrogeology
in the area, it was possible to compare drawdown obtained
with the numerical method against an analytical solution to
the same problem. The numerical model was run assuming
720,000 GPD was pumped for 75 days from the center mode.
These same values were then input into the Theis equation and
the results compared. The result of the numerical model was
in close agreement with that obtained in the Theis eguation.
The model was then considered calibrated.
A three year history of monthly pumping rates from all
Oakley wells was used to estimate discharge values at the
nodes representing pumping wells. Pumping rates used in the
program are shown in Table 1. Because this version of the
model requires constant pumpage, the wells were assumed to
have pumped their total annual amount in equal daily
increments. The model was run for twelve, 30-day time steps
in order to account for one year of pumping. Since Oakley's
total annual withdrawals are not actually pumped in equal
daily increments, it was assumed that a single year's pumpage
would closely enough approximate the results of pumping the
well field for longer periods of time in order to identify
the overall area of influence.
In order to obtain TOT outputs, the program locates the
radius at which the Theis equation computes 0.5 feet of
drawdown; segments that radius into equal increments of width
w with each increment approaching but not exceeding 10 feet;
determines head differences across each increment; calculates
velocity and travel time through each increment (starting at
the well and extending outward) and sums the travel times.
Pore velocity was calculated using Darcy's law and dividing
the darcian flux velocity by the aquifer porosity.
RESULTS
Figure 1 shows the overall WHPA as generated by the
model. It represents the 0.05 feet influence area of the
Oakley well field after pumping their total historical
amounts from their six wells in equal daily increments for
one years time. The radius of the WHPA is approximately
11,500 ft.
Figure 2 shows the secondary WHPAs around each of
Oakley's public water supply wells. The secondary WHPAs
include the area within a 180-day TOT distance from each
well.
B-25
-------
Thomas Co
^m Logan Co.
0.05-ft Drawdown
Contour
City of
oakley
1 Water
Supply
Well
1 MILE
Figure 1. WHPA for Wellfield at Oakley, Kansas
Based on 0.05-ft Drawdown Threshold.
B-26
-------
FIGURE 2. Secondary WHPAs Based on 180-Day TOT Zone
Surrounding Individual Water Supply Wells;
Oakley, Kansas.
THOMAS C
LOGAN CO.
O
EXPLANATION
OAKLEY CITY LIMITS
OAKLEY CITY WELL
SECONDARY WHPA'S BASED ON
A-I80 DAY TOT DISTANCE
o i OOP 2000
SCALE FEET
B-27
-------
B.4 CASE STUDY: PALM BEACH COUNTY, FLORIDA
INTRODUCTION
Aquifer protection programs were initiated in South
Florida in late 1979. In late 1981 the EPA approved and
funded a Wellhead Protection Program for Dade, Broward and
Palm Beach Counties. This project, known as the "State
Biscayne Aquifer Project", was developed by the Florida
Department of Environmental Regulations. The program
consisted of three phases: developing time of contaminant
travel contours around well fields, identifying sources of
contamination within these contours, and developing well
field protection ordinances.
Counties in Florida have the authority to write their
own local rules that specify the types of information needed
and acceptable methods for Wellhead Protection Area (WHPA)
delineation. Palm Beach County, located along the east coast
north of Miami, developed an ordinance requiring that a WHPA
be delineated for each well or well field, and that the
delineation criteria be time of travel (TOT) and/or drawdown.
The criteria threshold values are as follows:
Zone I — 30 day TOT
Zone II —210 day TOT
Zone III — 500 day TOT or 1-foot drawdown contour,
whichever extends farthest from the well/well field
Because the size of the WHPAs change with a change in
pumping rate, the WHPAs are to be updated periodically as
ground-water development continues. The following case study
illustrates how the program was applied in the County.
PROGRAM OBJECTIVE
The objective of the wellhead delineation program for
Palm Beach County was to define, by computer simulation,
contaminant travel time (distance) zones. For the Ordinance,
it was determined that a 30-day (Zone I), 210-day (Zone II)
and a 500-day or one-foot drawdown contour (Zone III) would
be most appropriate. The outer boundary of Zone III was
marked by the 500-day TOT or one-foot contour whichever
extended farthest from the well field. The one-foot contour
zone was defined as an area where the difference in steady-
state water-level elevations between 1984 levels and
predicted year 2010 levels equals or exceeds one foot. Table
1 provides pumping rates for selected well fields.
B-28
-------
»
M
CO
I-
m
m>c
J^ ^i y^
^j 111 nj
to t^m
.w^
grom
omp
WCLLFIELD
I TEBUESTA
2 JUPITER
3 SEACOAST HOOD
4 SEACOAST LILAC
5 SEACDAST RICHARD
6 SEACOAST DIME
7 RIVERA BEACH
B nAUSOUIA
9 CONSOLIDATED
10 CENTURY
II KEADOUBRDDK
12 PBC II
13 PBC 12
14 FBC 13
IS PBC IB
16 PBC 19
17 ROYAL PALM BEACH
IB ACHE
19 PALH SPRINES
20 ATLANTIS
21 LAKE NORTH
22 LANTAHA
23 HAHALAPAII
24 BOYUTON BEACH
25 VILLAGE OF GOLF
26 DELRAY BEACH
27 HIGHLAND BEACH
28 BOCA RATOH
29 PRATT KHITHEY
TOTAL
No. OF WELLS
4
22
14
6
B
9
23
2
3
2
7
7
7
9
13
5
II
II
S
12
4
II
21
3
22
3
SI
6
I»B4
ICFSI
0.97
B.35
11.03
1.44
3.04
1.55
11.20
0.62
0.30
1.46
1.26
0.45
O.B5
2.71
9.36
9.12
1.12
2.22
6.61
0.95
10.12
2.89
1.12
12. IB
0.39
17.30
1.80
44.77
1.51
1 PUMP AGE RATES
(MOD)
0.63
5.40
7.13
'0.93
1.97
1.00
7.24
0.40
0.19
0.94
O.BI
0.29
0.55
1.75
6.05
5.89
0.72
1.43
4.40
0.61
6.54
1.87
0.72
7.87
- 0.25
11. IB
1.16
28.93
0.97
Na. OF WELLS
4
34
14
i
B
9
26
S
3
3
3
7
17
11
28
13
7
11
15
5
12
4
M
40
3
24
3
51
7
eoio pimp AGE
fCFSI
4. IB
31.99
26.62
6.19
5. BO
5.80
18.95
2.74
0.54
2.17
4.64
12.38
21.66
12.38
49.51
20.67
5.38
12.69
9.28
2.07
14.70
3.71
2.94
61.89
0.60
35.59
4.64
89.57
1.69
RATES
(MOD)
2.70
20.67
18.50
4.00
3.75
3.75
12.25
1.90
0.35
1.40
3.00
8.00
14.00
8.00
31.99
13.36
3.4B
B.20
6.00
1.34
9.50
2.40
1.90
39.99
0.39
23.00
3.00
57.BB
1.22
144.87
107.83
473.37
301.89
mz
O
CO
-------
HYDROGEOLOGIC SETTING
The sediments that underlie Palm Beach County consist of
unconsolidated sands, loose- to well-cemented limestones,
moderately indurated sandstones, coquina, and sparry clay
lenses. These sediments are Pleistocene in age and are
considered part of the Pamlico Sands and the Anastasia
Formation.
The surficial aquifer in Palm Beach County is the
saturated portion of these sediments. It is characterized by
large variations in the spatial distribution of porosity and
permeability. Along the eastern part of the county, a zone
of high secondary permeability is known to occur. The
secondary permeability is attributed to dissolution of
calcareous cementing material by circulating ground water.
Western Palm Beach County does not exhibit these extensive
zones of secondary porosity and permeability.
The surficial aquifer in Palm Beach County varies from
west to east, ranging from 140 feet in the west to more than
320 feet thick along the Atlantic Coastline. Aquifer
thickness can be determined with data shown on Figures 1 and
2. While Figure 1 shows the elevation of the water table,
representing the top of the aquifer, Figure 2 shows varia-
tions in the elevation of the base of the surficial aquifer.
Figure 3 shows the inferred distribution of aquifer
transmissivity in the eastern part of the County. Variations
in both transmissivity and specific yield of wells in the
surficial aquifer are related to variations in thickness and
the presence of primary and/or secondary permeability.
Within the thickest zones of secondary permeability,
transmissivity ranges from 100,000 to 2 million gpd/ft.
Lower values", between 50,000 and 100,000 gpd/ft, were
reported for areas along the coast, and in the western half
of the county (Figure 2). Values reported for specific yield
were also highly variable, although a constant value of 0.2
was utilized in the model.
Recharge estimates for the area range from 6 to 12
inches per year (in/yr). Recharge to the aquifer is
accomplished through infiltration of rain waters and leakage
from numerous canals. Leakage from canals tends to reduce
the amount of drawdown observed in the vicinity of pumping
centers, and thus reduces the areal extent of their zone of
influence. This has the additional effect of increasing
travel time, which decreases the size of WHPAs delineated on
the basis of TOT calculations.
B-30
-------
JUNO BC»CM
PH." BEACH
OCLRAV ICACH
BOCA RATON
FIGURE1. ALTITUDE OF WATER TABLE
SURFICIAL AQUIFER
PALM BEACH COUNTY . FLORIDA
B-31
-------
JUNO BEACH
PALM ICACM
OCLRAY 8CACH
BOCA RATON
FIGURE 2. ELEVATION OF BASE OF
SURFICIAL AQUIFER SYSTEM
B-32
-------
JUNO BE*CM
LIMIT OF ZONE
OF SECONDARY
PERMEABILITY
P»IM BC4CM
OELRir BEACH
NOTE . TRANSMISSIVITY VALUES IN MILLIONS
OF GALLONS PER DAY PER FOOT
FIGURE 3.
TRANSMISSIVITY MAP OF
EASTERN PALM BEACH COUNTY
B-33
-------
A numerical model, based on a three-dimensional, finite-
difference computer code developed by the U.S. Geological
Survey, was used to delineate the WHPAs. A numerical
simulation model was selected because of the complex and
dynamic hydrogeologic conditions that occur in the area. In
addition, once a numerical model is calibrated, it can be
utilized to model other hydrologic conditions such as new
sources of ground-water supply, different contamination
problems, and to predict future drawdowns. The computer
methodology required to generate the WHPAs involved a two
step procedure:
1. First the hydraulic head distribution over the model
area had to be simulated and compared to available
head data. The McDonald and Harbaugh (1984) "Modular
Three-Dimensional Finite Difference Ground-Water Flow
Model" (MODFLOW) was used for this computation by
constructing a two-dimensional model of the aquifer
system.
2. The second step involved using the hydraulic head
values obtained from Step 1 as input into a mass
transport program to generate the travel time
(distance) zones. Because MODFLOW does not contain
a solute transport routine, a separate particle-
tracking program, which is a variation of Prickett's
"Random Walk" technique, was chosen to perform Step
2. In order to account for contaminant attenuation
factors such as dispersion and dilution, the model
augments the time interval in question by a factor of
25 percent.
In summary, the generation of travel-time plots involves
the following sequence of events:
1. Compute hydraulic heads
2. Compare to known heads and adjust model inputs
3. Recompute heads with "calibrated" model
4. Calculate ground-water velocities
5. Generate and advance particles through flow field
6. Track particles into well-field areas
7. Delineate WHPAs based on particle travel times
RESULTS
Inputs required by the model include transmissivity,
specific yield, aquifer recharge, aquifer thickness, and
total pumpage of the wellfield. In addition, leakage from
all the major canals was input into the model and adjusted as
part of the calibration process. Finally, the established
B-34
-------
hydrological boundaries for the modeling area were selected
(whenever possible) to reflect actual flow boundary con-
ditions.
The ground-water flow regime was simulated by setting up
two grid systems of square cells for the northern (220 x 136
grid) and the southern (220 x 256 grid) part of the county.
Both grids have the same cell dimensions of 528 feet on a
side.
Table 2 provides a range of WHPA dimensions determined
for the travel-distance zones and one-foot drawdown contour
for each well field. Figure 4 shows that, in general, WHPAs
in the southern part of the county are smaller than those in
the north. This is attributed to the large number of canals
in the south and the greater recharge of water from them
caused by local pumpage. Under similar pumping rates, the
smaller canal recharge in the north results in greater stress
and increased drawdowns in the aquifer.
B-35
-------
TABLE 2.
APPROXIMATE EXTENT OP TRAVEL-DISTANCE ZONES AND ONE FOOT CONTOUR
DO
w
a\
WELLFIELD
NUMBER / NAME. _f_
1 Teguesta
2 Jupiter
3 Seascoast (Hood)
4 Seacoast (Lilac)
5 Seacoast (Richard)
6 Seacoast (Dixie)
7 Riviera
8 Hangonia
9 Consolidated
10 Century
11 Meadowbrook
12 PBC |1
13 PBC #2
14 PBC |3
15 PBC J8
16 PBC «9
17 Royal Palm Beach
18 ACHE
19 Palm Springs
20 Atlantis
21 Lake Worth
22 Lantana
23 Manalapan
24 Boynton
25 Village of Golf
26 Delray
27 Highland
28 Boca Raton
29 Pratt & Whitney
2010
OF WELLS
4 .
34
14
6
8
9
26
5
3
3
3
7
17
11
28
13
7
11
15
5
12
4
11
40
3
24
3
51
7
ZONE 1
RANGE
fFTl
50 / 90
10 / 800
50 / 170
20 / 120
50 / 200
50 / 200
25 / 230
50 / 175
35 / 75
40 / 300
225 / 275
25 / 220
25 / 160
50 / 175
35 / 370
10 / 180
75 / 220
40 / 75
50 / 100
40 / 50
10 / 300
50 / 100
25 / 50
25 / 400
50 / 75
25 / 300
10 / 130
25 / 250
ZONE 2
RANGE
TFTM
270 / 350
40 / 2590
440 / 840
50 / 500
220 / 600
700 / 900
75 / 1150
425 / 625
50 / 150
110 / 1700
1550 / 1700
600 / 1150
150 / 630
300 / 850
280 / 1620
40 / 830
600 / 1190
120 / 370
250 / 675
120 / 300
275 / 1200
250 / 600 ,
50 / 225
225 / 1450
100 / 1150
575 / 1400
250 / 700
100 / 1400
ZONE 3
RANGE
CFT)
550 / 670
100 / 3240
1050 / 1520
175 '/ 600
400 / 960
1050 / 1600
175 / 1710
750 / 1050
85 / 375
200 / 2500
3100 / 3900
690 / 1875
460 / 1060
730 / 1360
425 / 3270
375 / 1570
700 / 1520
260 / 640
500 / 1000
200 / 550
1350 / 1900
500 / 1150
100 / 750
450 / 2550
125 / 2050
750 / 2250
600 / 1100
200 / 2350
1 FT CONTOUR
RANGE
n/a
700 / 1300
650 / 1300
0 / 750
250 / 7000
2000 / 3000
750 / 4500
1000 / 4000
n/a
n/a
n/a
2500 / 4500
250 / 3000
700 / 1300
700 / 2800
500 / 2000
900 / 1500
1000 / 2500
n/a
n/a
1700 / 5000
n/a
n/a
1200 / 10500
n/a
900 / 9000
1500 / 1900
1500 / 5500
n/a
-------
UAH TIN CO.
PALM BEACH co
LOXAHATCHCE NATIONAL
WILDLIFE REFUGE
CVCRCLAOES WILDLIFE
UANACEUCNT AREA
PACK BEACH
£g —'
PALM BEACH CO
BHOWAHO CO
BOCA RATON
FIGURE4. ONE-FOOT CONTOUR ZONE
EASTERN PALM BEACH COUNTY
B-37
-------
B.5 CASE STUDY: FRANKLIN. MASSACHUSETTS
INTRODUCTION
In Massachusetts, the Department of Environmental
Quality Engineering (DEQE) has developed a standard procedure
to be followed by municipalities seeking to develop new wells
for water supply. In addition to a survey of all wells in
the area of interest, a survey of potential sources of
pollution; and a description of the aquifer, the zone of
contribution to the proposed well must be delineated.
The DEQE recognizes three zones around a well, in which
varying degrees of ground water protection are practiced.
The zones are defined as:
Zone I -The immediate area which lies within 400 ft of
the well.
Zone II-The land area which supplies ground water
directly to a pumping well under the most severe recharge and
pumping conditions. The baseline condition is considered to
be 180 days of pumping at design rate without recharge to the
aquifer.
Zone III-The land area beyond zone II from which
surface water and/or ground water drains into Zone II.
Zone II is the most difficult of the three to delineate, so
the State DEQE has set forth guidelines for the acceptable
methods of Zone II delineation. As a minimum effort, a 5-
day pump test must be performed, and drawdown and recovery
data must be collected from an appropriate number of
observation wells. Information on aquifer parameters
inferred from the pump test data is then used to predict the
extent of Zone II as defined above. If the aquifer has a
complex configuration or heterogeneous composition, and
simple analytical techniques cannot accurately reflect the
behavior of the aquifer under pumping conditions, then a
numerical simulation of the aquifer is required.
In the case of Franklin, Massachusetts (see Figure 1) ,
such a computer simulation was deemed necessary. Following a
preliminary survey of existing data, which included published
reports and logs of nearby wells, a field investigation was
undertaken to better define the area's hydrogeology.
Approximately 20 boreholes were drilled and logged, 15 of
them being converted to observation wells. Results of this
investigation and the pump test indicated spatial variation
in aquifer parameters which would require numerical simula-
tion for proper evaluation of Zone II.
B-39
-------
FIGURE 1. FRANKLIN, MASSACHUSETTS SITE MAP
Existing Test Wells To Be
Used As Observation Wells
-------
WELLHEAD PROTECTION OBJECTIVES
The City of Franklin's purpose in initiating the study
was to determine the zones of contribution to their proposed
supply well as defined by the Massachusetts DEQE. These
three zones around a water supply well have been established
to offer varying degrees of protection to the ground water
from potential sources of contamination. Zone I -protects the
area immediately surrounding the well. Zone II includes any
area which directly contributes water to a pumping well.
Zone III is designated in order to protect all areas from
which surface or ground water drains into Zone II.
HYDROGEOLOGIC SETTING
The site of the proposed Franklin water supply well is
located in an alluvial valley of glacial origin. The aquifer
is composed of interstratified sands, silts, and gravels, of
glacio-fluvial origin and is bounded by bedrock and glacial
till. Thickness of the valley sediments reaches a maximum of
43 feet in the central region of the valley and decreases to
as little five feet near the valley walls. The stratigraphy
is not homogeneous. In the area surrounding the test well,
very coarse sands and gravels were encountered from the
surface to the base of the valley. To the north and west,
the sediments thin rapidly and are overlain by fine sand and
silt.
Under static, non-pumping conditions, ground water flows
toward the center of Uncas Brook and out the valley through a
narrow neck of the aquifer, which connects it to another
valley (Figure 2) . Regionally, the general flow is to the
east toward the discharge point, under a hydraulic gradient
of .001 to .002. Transmissivities determined from the 5-day
pump test using Jacob's straight line approximation method
and the Theis curve-matching technique ranged from 145,000 to
188,000 gpd/ft for nearby observation wells, and from 45,000
to 77,000 gpd/ft for outer wells. Values for storativity
ranged from .018 to .035.
METHOD AND CRITERIA SELECTION
The three zones of contribution to a supply well, as
defined by the DEQE, lend themselves to delineation by
certain criteria and methods. By definition, Zone I
encompasses the area within 400 feet of the well, an
arbitrary fixed radius with a distance criteria. Zone III,
the land area from which ground water or surface water drains
into Zone II, is best delineated by mapping of topographic
B-41
-------
FIGURE 2. FRANKLIN AQUIFER
Aquifer
Boundary
Equipotential
Line (contour
interval = .5 ft)
FRANKLINS
r\
B-42
-------
and hydrogeologic divides, which are basically flow boun-
daries.
Zone II is the most difficult to determine, being
defined as the area which supplies water directly to a
pumping well. Little latitude was given to Franklin in
choosing a method and a criteria, as the DEQE requires that
data from a 5-day pump test to be used to project what the
zones of contribution will be after 180 days of pumping at
the design rate without recharge to the aquifer. In
addition, the DEQE requires the use of a computer simulation
of the aquifer if aquifer conditions are too complex for a
simple analytical solution.
Because of the complexity of the hydrogeologic setting,
a numerical model was chosen to simulate ground-water flow
under the required pumping and recharge conditions. The
computer software package, MODFLOW (Modular Three-Dimen-
sional Finite Difference Ground-Water Flow Model) was
selected because of its ability to simulate certain phenomena
recognized at the site, such as a multilayered aquifer,
irregular boundaries, heterogeneity within layers, inter-
action with surface water, a partially penetrating well and
areal recharge.
Model Description
The model simulated the ground-water flow regime by a
two layer, non-uniform grid of 21 columns by 27 rows (Figures
3.A and 3.B). The grid spacing increased from 50 feet near
the pumping center to 400 feet near the model boundaries.
Aquifer boundaries (till or bedrock) were simulated by
inactive cells. Constant heads were assigned to cells east
of the "bottle neck" to drive flow in that direction.
Initial heads" in the aquifer model were assigned according to
water table elevations throughout the area.
In order to calibrate the model, it was necessary to
first simulate non-pumping conditions. Recharge and
discharge rates and aquifer parameters were input to the
model. Values for aquifer parameters were derived from the
results of previous test drilling and the pumping test.
Parameters for both layers of the model were modified until
simulated heads matched observed aquifer heads and a balanced
water budget was achieved.
Further calibration was needed to ensure that the model
would accurately simulate pumping conditions. A discharge
rate of 350 gpm was set in the cells representing the
discharging wells and several runs were made. Output from
the model was compared to data collected during the pump
B-43
-------
M 1-66
M 3-86 • Q
© M 2-88
^r- \V3-i
.3-2* \\ ,
-------
Figure 3.B
LAYER 2
MODE GRID
B-45
-------
Figure 4.A MODEL RESULTS AFTER 180-DAY PUMPING PERIOD: LAYER 1
5000 -
4500 -
4000 -
3500 -
3000 -
500 - -
2000 -
1500 -
1000 -
500 -
0
Site 3
Franklin, MA
0 500
1000 1500 2000 2500 3000 3500 4000
SCALE 1=650' feet
B-46
-------
Figure 4.6 MODEL RESULTS AFTER ISO-DAY PUMPING PERIOD: LAYER 2
5000
4500 \
L
4000
3500
3000
">00
2000
1500
1000
500
i
0
Site 3
Franklin/ MA
j i
j i
0 500
1000 1500 2000 2500 3000 3500 4000
SCALE 1=650' feet
i i
B-47
-------
test, and adjustments were made to certain parameters until
model output matched the observed data satisfactorily.
Following calibration, the model was ready to be used to
simulate the required pumping conditions. In determining the
extent of Zone II, the land area directly contributing water
to the well, the stress period was set to 180 days and the
areal recharge was eliminated. Four scenarios were run in
order to analyze variations in size of the area. In two
runs, the influence of the surface stream was ignored and the
specific yield was modified slightly. The same modifications
for specific yield were again made in two runs in which the
river simulation package was used.
RESULTS
The simulation attempts in which the stream was ignored
failed after a period of 120 days due to excessive dewatering
in the upper layer. Both of the other model runs predicted
that all ground-water flow within the entire valley would be
toward the well. Figures 4.A and 4.B shows the model's
prediction of ground-water elevations after 180 days of
pumping.
As a result of the model simulation, Zone II was
delineated as the entire valley in which the well is
situated. (See Figure 5). Zone III, also shown in Figure 5,
extends to the topographic divide which bounds the Uncas
Brook watershed.
B-48
-------
Figure 5.
WHPA ZONES DELINEATED FOR FRANKLIN, MASSACHUSETTS SITE
B-49
-------
B.6 CASE STUDY; BOWLING GREEN. KENTUCKY
INTRODUCTION
In the Bowling Green, Kentucky area (Figure 1) , water
for public supply is obtained from both springs and wells in
a mature unconfined karst aquifer. Currently, a study is in
progress to address the problem of ground-water protection,
which will include the delineation of Wellhead Protection
Areas (WHPAs). While no actual WHPAs have been defined, the
problem is similar to determining the zone of contribution
(ZOC) to a spring. Much work has been done in the area on
defining ground-water basins and general flow routes using
dye-tracing techniques. Such 'information is useful in
determining the ZOC to a well or spring. The material
presented below has been summarized from a report on the
hydrogeology of the Bowling Green area prepared by Crawford,
et. al. (1987).
HYDROGEOLOGIC SETTING
The study area (Figure 2) surrounding Bowling Green is
underlain by carbonate rocks of Mississippian Age, predomin-
ately the Ste. Genevieve Limestone, with the St. Louis and
Girkin Limestones occurring in minor portions of the study
area (Figures 3 and 4) . The entire area is a mature karst
terrain, exhibiting typical land form features associated
with karst, such as sinkholes, sinking streams, and springs.
Solution enhancement of fractures and joints in the rock has
created large subterranean conduits through which ground
water can flow at high velocities (Figure 5) . Such conduit
flow can be several orders of magnitude higher than diffuse
flow which occurs through intergranular pore space.
Flow patterns of ground water in karst aquifers can
differ greatly from those in granular aquifers due to flow
through channels. Furthermore, flow patterns within a single
aquifer may change significantly between normal and high-flow
conditions, because storm water can fill underground
conduits, causing overflow to run off into channels which
normally contain no water. These factors make the prediction
of ground water flow direction difficult.
METHOD AND CRITERIA SELECTION
Because conduit flow in mature karst aquifers generally
does not follow ground-water flow patterns associated with
porous media aquifers, using methods of wellhead protection
based on simple shapes or analytical flow equations is
unlikely to result in delineation of an effective WHPA. For
B-50
-------
LOCATION OF BOWLING GREEN AND
LOST RIVER KARST GROUNDWATER BASIN,
WARREN COUNTY, KENTUCKY
10 Miles
j
5 1O Kilometers
LOST RIVER
BASIN
BOWLING GREEN ,
FIGURE1. Location of the Loot River Groundwater Basin. Warren County. Kentucky.
B-51
-------
STUDY AREA
Bon liom: Gtologic Mop el Kinlutky
Stun IX.1954, H««ii«d liom Gtok*)< T
Moot o( KinluCk. dolld I927flnd
I9Z9 t>r W n. Jillion
50 MlUS
_J
FIGURE 2. Localion of the study area with respect to regional physiographic setting.
-------
40
GEOLOGY OF THE
LOST RIVER
GROUNDWATER BASIN
WARREN COUNTY. KENTUCKY
GIRKIN
LIMESTONE
STE. GENEVIEVE LIMESTONE
ST. LOUIS
LIMESTONE
FIGURE3. Q.ology of th« Lost Rlv«r QroyndwaUr B««in.
B-53
-------
25
SYSTEM
QUATER-
NARY
cc >•
o cc
> z
a:
CO
CO
MM
SERIES
Holocene
•_ (0
0 C
— i O r—
o o
c o
0 _
o */» m 1m*
• ]»— — !•-! •
^.^S^VrJ-
i i
i i
i i
i i
i i
1C ] Q
I 1
0 1 0|
1 — 1-
1 1
J— *^^1_
Sj^ESE
3=±?=' — , —
S=gfe
T! ' | i-=
FORMATION
OR GROUP
THICKNESS.
IN FEET
Alluvium
0-50
Terrace Deposits
\ O-25
Ste. Genevieve
Limestone
160-2SO
Lost River
Chert Bed
Corydon
Ban cneri
Member
ot. LOUIS
230-3OO
Salem
Warsaw
Limestones
100-160
Fort Payne
Formation
10-15
(exposed)
MAP
SYMBOL
Qal
QTc
Msg
• _ i
MSI
Me f
(VIST
•
FIGURE 4. Stratigraphic Column for the Bowling Green area.
Source: modified from McGrain and Sutton (1973).
B-54
-------
GENERALIZED PROFILE OF LOST RIVER CAVE
UNDER BOWLING GREEN, KENTUCKY
TOXIC AND EXPLOSIVE FUMES FROM
TRAPPED CHEMICALS MAY RISE INTO
HOMES AND BUSINESSES
Lost River
Uvala
Small Hole
Entrance
Bertha
Entrance
Lost River
Blue Hole and
Cave Entrance
\
Livingston
Entrance
Alexander
Entrance
Nashville Road
Sinkhole
Cedar Ridge
Sinkhole
Harvestman
Haven Cave
Entrance
Morgantown Road
Blue Hole
DISTANCE IN MILES
FIGURES. Generalized profile of the Lost River.
-------
example, calculating a fixed radius based on the volumetric
flow equation, or trying to determine the radial distance at
which a certain drawdown occurs may be meaningless if a well
receives some of its water from a solution cavity which has
its origin a mile or more outside of the calculated zone of
contribution. Also, large supplies of water are collected at
springs, which must also be protected, but which cannot be
evaluated using analytical equations derived for discharging
wells. For this reason, hydrogeologic mapping lends itself
as the most useful tool in delineating both WHPAs and
protection areas for springs in mature karst aquifers.
The first step in defining areas to protect wells and
springs used for public water supply is to determine the
boundaries of the ground water basin in which the spring or
well is located. The ground water basin in a karst aquifer
is defined as the entire area which drains to a spring or set
of springs. Delineation of the ground water basin can be
accomplished through mapping of the potentiometric surface to
determine general flow directions, coupled with dye-flow or
other tracing techniques to better define flow routes.
Ideally, both the potentiometric surface map and the tracing
should be done for normal and high-flow (storm event)
conditions.
Figure 6 shows the potentiometric surface and subsurface
flow routes mapped for the Lost River Basin south of Bowling
Green. This information and topographic data that aided in
identifying surface-water flow divides were used to delineate
the boundary of the hydrogeologic system (Figure 7).
Having defined the ground water basin and the general
flow patterns within the basin, the next step involves
determination of the contributing area for an individual well
or spring by "examining the flow patterns and potentiometric
surface upgradient of the water supply. Depending on the
proximity of the well to the boundary of the ground-water
basin and on flow rates as determined through dye-tracing, an
appropriate delineation criteria for the upgradient extent of
the WHPA may be time of travel (TOT) or flow boundaries.
The ground-water divide forming the boundary of the
basin would be appropriate and easy to implement if the well
or spring were located near the edge of the basin. However,
for a well located near the center or at the mouth of a large
basin, enforcing a WHPA that extends to the boundary of the
basin may be difficult.
In such a case, a TOT criterion may be considered to
delineate the upgradient boundary. The problem with this
approach in a conduit-flow karst system is that velocities
are often so high that time-of-travel distances are too short
B-56
-------
19
GROUNDWATER FLOW ROUTES
LOST RIVER GROUNDWATER BASIN
WARREN COUNTY. KENTUCKY
Continuous Water Quality
Monitoring Station
Stage Recorder on Surface
or Subsurface Stream
water Table Elevation in Feet
Groundwater Level Recorder
in Water Well
ell Water Le.el Measured 6y /" Subs
Lambert (1976) or Crawford ** Thr
Subsurface Stream Flowing
ough Mapped Cave
Water Well Intersecting
Subsurface Stream
and Groves (1984)
s*~ Stream Sink
A Recording Precipitation Gauge ..•" Intermittent Stream
O Karst Window » Dye Trace ot
Subsurface Stream
Hypothesized Route ot
Subsurface Stream
Intermittent Karst Lake
Lake or Pond
FIGURES. Qroundwater flow routes of the Lost River Grounidwater Basin.
B-57
-------
61
LOST RIVER RISE
WATER MONITORING STATIONS
LOST RIVER GROUNDWATER BASIN
WARREN COUNTY, KENTUCKY
WAftRCN COUNTY
Basin
Boundary
'- iv-^X. - >
J N - ' (
"-} 7
LOST RIVER BLUE HOLE
u i » .« *
WKU FARM WELL:
MONITORING STATION
BIG SINKING CREEK SWAL
Continuoui water Quality
Monitoring Station
Stage Recorder on Surface or
Subsurface Stream
Groundwater Level Recorder
in Water Well
Water Well Interaoctlng
Subaurface Stream
Bowling Green City Limits
Well: Water Level Meaaured by f Subaurface Stream Flowing
Lambert (1870) or Crawford Through Mapped Cave
and Groves (1084)
Stream Sink
^ Recording Precipitation Gauge ..- Intermittent Stream
O Karat Window
f Dye T
race of Subaurface Stream
Hypothealzed Route of
Subeurface Stream
Intermittent Karat Lake
Lake or Pond
FIGURE?. Lost Rlv«r Groundwater Basin, showing routes of dy« trace*
of subsurface streams.
B-58
-------
to provide an adequate buffer. Data from the Lost River
Basin (Table 1 and Figure 8) indicate that subsurface flow
moves from Big Sinking Creek in the headwater region of the
basin to Lost River Rise at the mouth (a distance of
approximately 10 miles, see Figure 7) in 1 to 10 days,
depending on flow conditions.
Due to the unique nature of karst ground-water flow
systems, special care must be taken in selecting the
criterion, threshold, and method used to delineate a WHPA.
REFERENCE
Crawford, N.C., C.G. Groves, T.P. Feeney and. B.J. Keller,
1987, Hydrogeology of the Lost River Karst Ground-Water
Basin, Warren County, Kentucky, prepared for Kentucky
Natural Resources and Environmental Protection Cabinet
Division of Water Department of Geography and Geology,
Western Kentucky University, Bowling Green, Kentucky.
B-59
-------
66
Date of Trace
11/7/82
9/22/83
3/30/84
6/18/84
7/18/84
BLUE HOLE TO RISE
Initial
stage
(feet)
6.35
7.49
6.65
6.01
Oi
cfs
12.4
9.2
145
70
29
Centroid
stage
(feet)
6.67
7.55
6.66
5.97
BIG SINKING CREEK
Date of Trace
11/7/82
3/30/84
4/18/84
6/18/84
7/18/84
Initial
stage
(feet)
7.39
6.85
6.8
5.89
Oi
cfs
12.4
130
47
70
25
Centroid
stage
(feet)
7.4
6.87
6.66
5.88
BIG SINKING CREEK TO
Date of Trace
3/30/84
4/18/84
*6/l/84
7/18/84
* Trace started
Initial
stage
(feet)
6.11
5.25
5.86
2.9
Oi
cfs
127
63
105
25
Centroid
stage
( feet )
6.05
5.23
5.86
2.57
QC
cfs
12.4
10.8
160
70
27
TO RISE
Oc
cfs
12.4
138
50
70
25
BLUE HOLE
Oc
Cfs
120
63
105
17
Time of
first
arrival
68.0
80.5
10.0
16.5
32.5
Time of
first
arrival
185
29.5
48.5
39.25
83
Time of
first
arrival
19.5
27.5
18.5
43
Time of
centroid
87.64
98.56
10.33
19.57
42.5
Time of
centroid
224
32.7
54.7
47.6
102
Time of
centroid
20.8
32.2
22.01
54
wnen Big Sinking Creek ponded.
TABLE 1. R«
-------
TIME VS. DISCHARGE
BIG SINKING CREEK TO
LOST RIVER RISE
70
300-
200-
100-
50-
O
-C
Ill
5
H
10-
10
I I I I I I I II
20 30 40 50 100
200
DISCHARGE (cfs)
FIGURES. Tlma vs. Discharge: B»g Sinking Crook to Lost RIV«r Rise.
B-61
-------
C. Well Function
-------
APPENDIX C:
VALUES OF WELL FUNCTION
C-l
-------
APPENDIX C.
Values of W(u) Corresponding to Values of// for Theis Noncquilibrium Equation
^XL
.0
2
.3
.4
5
.6
.7
g
'.9 '.'."".'.
2.0
2.1
22
2.3
2.4
2.5
26 ...
2 7
28
29
3.0
3 |
3 2
33
3 4
35
3.6
3.7
3.8
3.9
4.0
4.1
4 2
4.3
4.4
4 5
4.6
4 7
4.8
4 9
50
5.1
NX 10-"
33.9616
33.8662
33.7792
33 6992
33.6251
33.5561
33.4916
33.4309
33 3738
33^ 197
33.2684
33.2196
33.1731
33.1286
33.0861
33.0453
33 0060
32.9683
32.9319
32.8968
32.8629
32.8302
32.7984
32.7676
32.7378
32.7088
32.6806
32.6532
32.6266
32.6006
32.5753
32.5506
32.5265
32.5029
32.4800
32 4575
32.4355
32.4140
32.3929
32.3723
32.3521
32.3323
/vxio-"
31.6590
31.5637
31.4767
31.3966
31.3225
31.2535
31.1890
31.1283
31 0712
3LOI7I
3&96S8
30.9170
30.8705
30.8261
30.7835
30.7427
30.7035
30.6657
30.6294
30.5943
30.5604
30.5276
30.4958
30.4651
30.4352
30.4062
30.3780
30.3506
30.3240
30.2980
30.2727
30.2480
30.2239
30.2004
30.1774
30.1549
30.1329
30.1114
30.0904
30.0697
30.0495
30.0297
/VXIO "
29.3564
29.261 1
29.1741
29.0940
29.0199
28.9509
28.8864
28.8258
28 7686
28.7145
28.6145
28.5679
28.5235
28.4809
28.4401
28.4009
28.3631
28.3268
28.2917
28.2578
28.2250
28.1932
28.1625
28. 1 326
28.1036
28.0755
28.0481
28.0214
27.9954
27.9701
27.9454
27.9213
27.8978
27.8748
27.8523
27.8303
27.8088
27.7878
27.7672
27.7470
27.7271
A'x ID-"
27.0538
26.9585
26.8715
26.7914
26.7173
26.6483
26.5838
26.5232
26 4660
26.4119
26.3607
26.3119
26.2653
26.2209
26.1783
26.1375
26.0983
26.0606
26.0242
25.9891
25.9552
25.9224
25.8907
25.8599
25.8300
25.8010
25.7729
25.7455
25.7188
25.6928
25.6675
25.6428
25.6187
25.5952
25.5722
25.5497
25.5277
25 5062
25.4852
25.4646
25.4444
25.4246
.vx 10 "
24.7512
24.6559
24.5689
24 4889
244147
24.3458
24.2812
24.2206
24 1634
24.1094
24.0093
23 9628
23.9183
23.8758
23 8349
23.7957
23.7580
23.7216
23.6865
23.6526
23.6198
23.5881
23.5573
23.5274
23.4985
23.4703
23.4429
23.4162
23.3902
23.3649
23.3402
23.3161
23.2926
23.2696
23.2471
23.2252
23 2037
231826
23.1620
23.1418
23.1220
,N x in '»
224486
223533
22.2663
22 1863
22 1122
220432
21.9786
21.9180
21.8608
21.8068
•21. mT
21.7067
21.6602
21.6157
21 5732
21.5323
21.4931
21.4554
21.4190
21.3839
21.3500
21.3172
21.2855
21.2547
21.2249
21.1959
21.1677
21.1403
21.1136
21.0877
21.0623
21.0376
21.0136
20 9900
20.9670
20.9446
20.9226
20.901 1
20.8800
20 8594
208392
208194
NX in •
201460
20.0507
199637
198837
19.8096
19 7406
19.6760
19.6154
19.5583
195042
19.4041
19.3576
19.3131
19.2706
19.2298
19 1905
19.1528
19.1164
19.0813
19.0474
19.0146
18.9829
18.9521
18.9223
18.8933
18.8651
188377
18.8110
18.7851
18.7598
18.7351
18.7110
186874
18.6644
186420
186200
185985
18.5774
185568
185366
185168
.v - in •
17.8435
17 7482
17 6611
175811
17.5070
174380
173735
17.3128
jj ?^S7
tii20l6v
^^fca^ -^
iTTTOT
17.1015
17.0550
17.0106
16.9680
16.9272
16.8880
16.8502
16.8138
16.7788
16.7449
16.7121
16.6803
16.6495
16.6197
165907
16.5625
16.5351
16.5085
16.4825
16.4572
16.4325
16.4084
16.3848
16.3619
16.3394
16.3174
162959
162748
162542
162340
16.2142
\x in '
1 5 5409
154456
153586
152785
1 5 2044
15 1354
1 5 0709
150103
149531
14 8990
14 8477
147989
14.7524
14.7080
146654
14.6246
14.5854
14.5476
14.5113
14.4762
14.4423
14.4095
14.3777
14.3470
14.3171
14.2881
14.2599
14.2325
14.2059
14.1799
14.1546
14.1299
14.1058
14.0823
14.0593
140368
140148
139933
13.9723
13.9516
139314
139116
N x in *
132383
13 1430
1 3 0560
129759
129018
128328
127683
12.7077
12.6505
T2 5451
12.4964
12.4498
12.4054
12.3628
123220
12.2828
12.2450
122087
12.1736
12.1397
12.1069
12.0751
1 2.0444
12.0145
.9855
.9574
.9300
.9033
.8773
.8520
.8273
.8032
.7797
.7567
7342
7122
6907
6697
6491
6289
.6091
vx in-'
109357
108404
107534
10.6734
10.5993
10 5303
104657
104051
103479
i!02939
10.2426
10.1938
10 1473
10.1028
10.0603
10.0194
9.9802
9.9425
9.9061
9.8710
9.8371
98043
9.7726
9.7418
9.7120
9.6830
9.6548
9.6274
9.6007
9.5748
95495
9.5248
9.5007
9.4771
9.4541
9.4317
94097
9.3882
93671
93465
93263
93065
N X 1(1 J
86332
8 5379
84509
8 3709
8 2968
82278
8 1634
8 1027
$ Qd ^
^9915]
7 9<»OJ
78914
78449
7.8004
77579
7.7172
7.6779
7.6401
7.6038
7.5687
7.5348
7.5020
7.4703
7.4395
7.4097
7.3807
7.3526
7.3252
72985
72725
7.2472
72225
7 1985
7 1749
7 1520
7 1295
7 1075
70860
70650
70444
70242
70044
\ X III '
63315
62363
6 1494
60695
59955
59266
58621
58016
5 7446
56906
5 6394
55907
55443
54999
54575
54167
5.3776
5.3400
5.3037
5.2687
5.2349
5.2022
5.1706
5.1399
5 1102
5.0813
5.0532
5.0259
49993
4.9735
49482
49236
48997
4.8762
4.8533
48310
48091
4 7877
47667
4 7462
4 7261
47064
N x in '
40379
3 9436
U576
3 7785
3 7054
36374
3 5739
35143
34581
34050
3 3547
33069
32614
32179
3 1763
3 1365
3.0983
30615
30261
29920
29591
29273
28965
2.8668
28379
28099
27827
2.7563
2.7306
2 7056
26813
26576
26344
26119
25899
25684
25474
2 5268
2506S
24871
24679
24491
\ x in '
8229
7371
6595
5889
5241
J645
4092
3578
3098
2649
^ i ^ i
2227
1829
1454
1099
0762
0443
0139
9849
.9573
.9309
.9057
8815
8583
8361
.8147
7942
.7745
7554
.7371
.7194
.7024
6859
6700
6546
6397
6253
6114
5979
5848
5721
5598
5478
^
02194
I860
1 5SJ
1355
1162
1000
OS6M
07465
06471
05620
A t OO A
04S90
04261
03719
03250
02844
02491
02185
01918
01686
01482
01305
.01 149
.01013
008939
007891
006970
006160
005448
004820
004267
003779
003349
002969
002633
002336
002073
OOIS4I
•001635
001453
001201
OOIN8
001021
0
N)
-------
Appendix C Continued
w — U^
52
5.3 ...
5.4
5.5
5.6
5.7
5.8 ... .
59
6.0
6 1
62
6.3
64 ...
6.5
6 6
6.7
68
69
7.0
7.1
72
73
7.4
7.5
7.6.. ..
7 7
7.8
7.9 ... .
8.0
81 . .
82.
8.3.
8.4..
8.5
86
87
88 . .
89
9.0. .
9 1
9.2 .. .
93
94
9.5
9.6 . ..
;vx 10-"
32.3129
32.2939
32.2752
32.2568
32.2388
32.2211
32.2037
32.1866
32.1698
32.1533
32.1370
32.1210
32.1053
32.0898
32.0745
32.0595
32.0446
32.0300
32.0156
32.0015
31.9875
31.9737
31.9601
31.9467
31.9334
31.9203
31.9074
31.8947
31 8821
31.8697
31 8574
31.8453
31.8333
31.8215
31.8098
31 7982
31.7868
31.7755
31.7643
31.7533
31.7424
31.7315
31.7208
31.7103
31.6998
,vx 10-"
300103
299913
29.9726
299542
29.9362
29.9185
29.9011
29.8840
29.8672
29.8507
29.8344
29.8184
29.8027
29.7872
29.7719
29.7569
29.7421
29.7275
29.7131
29.6989
29.6849
29.6711
29.6575
29.6441
29.6308
29.6178
29.6048
29.5921
29.5795
29.5671
29.5548
29.5427
29.5307
29.5189
29.5072
29.4957
29.4842
29.4729
29.4618
294507
29.4398
29.4290
29.4183
29.4077
29.3972
,vxio-"
27.7077
27.6887
27.6700
27.6516
27.6336
27.6159
27.5985
27.5814
27.5646
27.5481
27.5318
27.5158
27.5001
27.4846
27.4693
27.4543
27.4395
27.4249
27.4105
27.3963
27.3823
27.3685
27.3549
27.3415
27.3282
27.3152
27.3023
27.2895
27.2769
27.2645
27.2523
27.2401
27.2282
27.2163
27.2046
27.1931
27.1816
27.1703
27.1592
27.1481
27.1372
27.1264
27.1157
27.1051
27 0946
/vx 10-'-'
25.4051
253861
25.3674
25.3491
25.3310
253133
25.2959
25.2789
25.2620
25 2455
25.2293
25.2133
25.1975
25.1820
25.1667
25.1517
25.1369
25.1223
25.1079
25.0937
25.0797
25.0659
25.0523
25.0389
25.0257
25.0126
24.9997
24.9869
24.9744
24 9619
24.9497
24.9375
24.9256
24.9137
24.9020
24.8905
24 8790
24 8678
24.8566
24 8455
24 8346
24.8238
24.8131
24 8025
24 7920
A'x 10 "
23.1026
23.0835
23.0648
23.0465
230285
23.0108
22.9934
22.9763
22.9595
22.9429
22.9267
22.9107
22.8949
22.8794
22.8641
22.8491
22.8343
22.8197
22.8053
22.7911
22.7771
22.7633
22.7497
22.7363
22.7231
22.7100
22.6971
22.6844
22.6718
22.6594
22.6471
22 6350
22.6230
22.6112
22.5995
22 5879
22.5765
22.5652
22.5540
22.5429
22.5320
22.5212
22.5105
22.4999
22.4895
,vx 10- '•
20 8000
20.7809
20 7622
20 7439
20.7259
20.7082
20.6908
206737
20.6569
20.6403
20.6241
20.6081
20.5923
20.5768
20.5616
20.5465
20.5317
205171
20.5027
20.4885
20.4746
20.4608
20.4472
20.4337
20.4205
20.4074
20.3945
20.3818
20.3692
203568
203445
20.3324
20 3204
20 3086
20.2969
20 2853
20 2739
20 2626
202514
20.2404
20 2294
202186
20.2079
20.1973
20.1869
.vx io-'
18.4974
184783
18.4596
184413
18.4233
184056
183882
18.3711
18.3543
18.3378
18.3215
18.3055
18.2898
18.2742
18.2590
18.2439
18.2291
18.2145
18.2001
18.1860
18.1720
18.1582
18.1446
18.1311
18.1179
18.1048
18.0919
18.0792
180666
180542
180419
18.0298
180178
180060
17.9943
17.9827
179713
17.9600
179488
17.9378
179268
17.9160
17.9053
17.8948
17.8843
,VXIO«
16 1948
16.1758
16.1571
161387
16 1207
16.1030
160856
160685
160517
16.0352
16.0189
16.0029
15.9872
15.9717
15.9564
15.9414
15.9265
15.9119
15.8976
15.8834
15.8694
15.8556
15.8420
158286
15.8153
15.8022
15.7893
157766
157640
15.7516
157393
157272
157152
157034
156917
15.6801
15.6687
15.6574
15.6462
156352
156243
15.6135
15.6028
15.5922
15.5817
.vx 10-'
13.8922
138732
138545
13.8361
138181
1 3 8004
13.7830
13.7659
13.7491
13.7326
13.7163
13.7003
13.6846
13.6691
13.6538
13.6388
13.6240
1 3.6094
1 3 5950
13.5808
13.5668
135530
13.5394
13.5260
13.5127
13.4997
134868
13.4740
13.4614
13.4490
134367
134246
134126
13.4008
133891
133776
133661
133548
133437
133326
133217
13.3109
13.3002
13.2896
132791
.vx 10 •
5896
.5706
5519
.5336
5155
.4978
4804
.4633
.4465
4300
11.4138
11.3978
11.3820
11.3665
11.3512
.3362
.3214
.3068
2924
.2782
.2642
.2504
.2368
2234
.2102
.1971
.1842
.1714
1589
.1464
.1342
.1220
1101
0982
0865
0750
0635
0523
0411
0300
0191
.0083
109976
10.9870
109765
A x 10-'
92871
9.2681
9.2494
92310
9.2130
9 1953
9.1779
9.1608
9 1440
9.1275
9.1112
90952
9.0795
9.0640
9.0487
9.0337
90189
9.0043
8.9899
8.9757
8.9617
89479
8.9343
89209
8.9076
88946
88817
88689
88563
88439
88317
88195
88076
8.7957
8.7840
87725
87610
87497
87386
87275
87166
87058
86951
86845
86740
NX 10 4
69850
69659
6.9473
69289
69109
6.8932
68758
6.8588
68420
6.8254
6.8092
67932
6.7775
6.7620
6.7467
6.7317
6.7169
6.7023
6.6879
66737
6.6598
66460
66324
66190
6.6057
65927
65798
65671
6.5545
65421
65298
65177
65057
64939
64822
64707
64592
64480
64368
64258
64148
64040
63934
63828
63723
vx 10 '
4.6871
46681
46495
46313
46134
45958
4.5785
4.5615
4.5448
45283
4.5122
4.4963
4.4806
4.4652
4.4501
4.4351
4.4204
4.4059
4.3916
4.3775
43636
4.3500
4.3364
43231
4.3100
4.2970
4.2842
42716
42591
4.2468
4.2346
42226
42107
4 1990
4 1874
4 1759
4.1646
4 1534
4 M23
4.1313
4 1205
4.1098
4.0992
4.0887
4.0784
NX io-;
24306
24126
2 3948
23775
23604
23437
23273
23111
22953
22797
22645
22494
2.2346
2 2201
2.2058
2.1917
2 1779
2 1643
2.1508
2 1376
2 1246
2. 1118
20991
20867
2.0744
20623
2.0503
20386
20269
20155
20042
9930
9820
9711
9604
9498
9393
9290
9187
9087
8987
8888
8791
.8695
.8599
VX 10 '
5362
5250
.5140
.5034
4930
4830
4732
4637
4544
.4454
.4366
.4280
.4197
.4115
.4036
.3959
.3883
.3810
.3738
3668
3599
3532
.3467
3403
.3341
.3280
.3221
.3163
.3106
3050
2996
2943
2891
.2840
2790
2742
2694
2647
2602
2557
2513
2470
2429
2387
.2347
N
0009086
00080S6
0007198
0006409
0005708
0005085
0004532
0004039
0003601
.0003211
0002864
0002555
.0002279
0002034
.0001816
.0001621
0001448
0001293
0001 155
0001032
00009219
00008239
00007364
00006533
00005886
.00005263
00004707
00004210
00003767
00003370
.00003015
00002699
000024 1 5
00002162
00001936
00001733
00001552
00001390
00001245
00001115
.000009988
000008948
.000008018
000007185
000006439
-------
Appendix C Continued
~-»»_«
9.7
9.8
9.9
;vxio-"
31.6894
31.6792
31.6690
/vxio-"
29.3868
29.3766
29.3664
yvxio-11
27.0843
27.0740
27.0639
,vxio-'!
24.7817
24.7714
24.7613
,vx 10-"
22.4791
22.4688
224587
.vx ID-'"
20.1765
20 1663
201561
N X 10-'
178739
17.8637
17.8535
N X 10-"
155713
155611
155509
vx to-"
1 3 2688
132585
13.2483
\x 10-*
10.9662
109559
109458
\ x io-1
8.6637
86534
86433
\ x 10-'
63620
63517
63416
\X 10 '
4.0681
4.0579
40479
vx 10- ;
1 8505
1 8412
1.8320
NX ID'1
2269
2231
%
000005173
000004637
NOTE See page 218 for Theis equation and definitions of terms.
Values of IW for,/between I x 10 " and I X 10 'computed b> R G Kaimann assisted h> M M Exans US Geological Survex values for •• bci«ccn I
adapted from Tables of Exponential and Trigonometric Integrals.
From Water Supply Paper 887. U.S. Geological Survc>. 1942
X 10 and 99
-------
D. Conversions
-------
APPENDIX D:
TABLE OF UNITS CONVERSION FACTORS
D-l
-------
UNIT CONVERSION TABLE
1 MULTIPLY
Length
Area
Volume
Velocity
Discharge
Hydraulic
conductivity
Permeability
Transmissivity
ft
mile
ft2
mi2
ft3
gallon
ft/ sec
ft3/sec
gal/min
ft/ sec
gal/day/ft2
ft2
ft2/sec
gal/day/ft
BY
.3048
1.609
.00920
2.590
.02832
.003785
.3048
.02832
6.039 x 10~5
.3048
4.720 X 10"7
.09290
.09290
1.438 X 10"7
TO OBTAIN
m
km
m2
km2
m3
m3
m/sec
m3/sec
m3/sec
m/sec
m/sec
m2
m2/sec
m2/sec
D-2
-------
LIST OF PARTICIPANTS
U.S. ENVIRONMENTAL PROTECTION AGENCY
WELLHEAD PROTECTION AREA DELINEATION TRAINING COURSE
Fairfax, Virginia
August 23 - 25, 1988
PARTICIPANT
NAME
Dale Albeck
\ Greg Anderson
\ Bill Balfour
\ Seymour Bayuk
N
Phil Cherry
Gary Chirlin
Bob Dundas
Jeff Featherstone
Karen Fitzmaurice
AFFILIATION
Broome Co.
Health Dept.
N.Y.S.
Maryland
MDE-Water
Supply
VA Water
Control
Board
Dept. of
Utilities
DE Dept.
of Natural
Resources
Chirlin &
Assoc . , Inc .
DE Dept.
of Natural
Resources
DE River
Basin Comm.
Univ. of KY
ADDRESS
1 Wall Street
Binghamton, NY 13901
201 W. Preston Street
Baltimore, MD 21201
2111 N. Hamilton
Richmond, VA 23230
7409 BNA Blvd. , NW
Glen Burnie, MD 21061
89 Kings Highway
Dover, DE 19901
18 Anamosa Ct.
Rockville, MD 20855
89 Kings Highway
Box 1401
Dover, DE 19901
25 St. Police Dr.
West Trenton, NJ 08628
148 Walton Ave.
AREA CODE AND
TELEPHONE NUMBER
607/772-2887
301/225-6368
804/367-6345
301/760-7740
302/736-4793
301/258-0220
302/736-4793
609/883-9500
606/255-4649
\
Richard Fox
Jim Gerhart
233 Mining and Mineral
Research Building
Lexington, KY 40508
Joint Conserv. Box 254,
Committee Harrisburg, PA 17120
U.S.G.S. 208 Carroll Bldg.
8600 Lasalle Rd.
Towson, MD 21204
717/787-7570
301/828-1535
-------
PARTICIPANT
NAME
Keith Harner
y (fun^V
S Don yfrt»fca>
Cindy Kranz
Ben Lacy
Jill Larson
^/Joseph Lee
v'Ron Lilly
Paula Luborsky
Larry Mata
Cristina Morrison
David Nelms
^/^ Robert Paul
Linda Silversmith
Mary Sitton
Ron Slotkin
AFFILIATION ADDRESS
Dover
Township
WV Health
Dept.
EPA
EPA
EPA
DER
Lord Fx.
Planning
Dist. Comm,
EPA
EPIC
EPA
U.S.G.S.
WV Health
Dept.
League of
Women Voters
of Maryland
EPA
Broome Co.
Health Dept.
N.Y.S
2480 West Canal Rd.
Dover, PA 17315
1800 Washington St . , E
Charleston, WV 25305
1 Wall St.
841 Chestnut St.
Phil., PA 19107
Headquarters
PA DER, BCEC
2nd Floor Exec. House
Harrisburg, VA 17120
103 E. Sixth St.
Front Royal, VA 22630
841 Chestnut St.
Phil., PA 19107
P.O. Box 1575-EPA
Vint Hill Farms Station
Warrenton, VA 22186
Headquarters
3600 W. Broad St.
Room 606
Richmond, VA 23230
1800 Washington ST. , E
Charleston, WV 25305
260 New Mark Esp.
Rockville, MD 20850
P.O. Box 1575
Vint Hill Farms Station
Warrenton, VA 22186
1 Wall St.
Binghamton, NY 13901
AREA CODE AND
TELEPHONE NUMBER
717/292-3634
304/348-2981
215/597-8399
215/597-9058
202/245-3716
717/787-9561
703/635-4146
215/597-2786
703/349-8995
202/475-7057
804/771-2427
304/348-2981
301/294-0566
703/349-8975
607/772-2887
-------
PARTICIPANT
NAME
Bob Thranson
Mary Tieman
AFFILIATION ADDRESS
EPA
Cong.
Research
Service
Headquarters
1507 Baltimore Rd.
Alexandria, VA 22308
AREA CODE AND
TELEPHONE NUMBER
202/382-7103
202/282-5937
Tom Wall
Ava Nelson Zandi
EPA
EPA
401 M St., NW
Permits Div.
(EN-330)
Washington, DC 20460
841 Chestnut St.
Phil., PA 19107
202/475-9515
215/597-9388
-------
SOFTWARE DEMONSTRATED DURING WELLHEAD PROTECTION AREA
DELINEATION TRAINING COURSE
THWELLS
Source: International Ground Water Modeling Center
Holcomb Research Institute
Butler university
Indianapolis, IN 46208
Phone: (317)283-9458 Contact: Stan Williams
i
Use: Drawdown calculations (Theis solution)
Cost: $50
RESSQ
Source: International Ground Water Modeling Cenfer
Holcomb -Research Institute
Butler university
Indianapolis, IN 46208
Phone: (317)283-9458 Contact: Stan Williams
Use: Zone of Contribution, Zone of Transport (Analytical)
Cost: $100
GWPATH
Source: Illinois State Water Survey
2204 Griffith Dr.
Champaign, IL 61820-7495
Phone: (217) 333-6775 Contact: John Shafer
Use: Particle Tracking, Zone of Transport (Numerical)
Cost: $125
-------