UntedSutM
Envwonmafltai Protection
AQ«ney
Offio»Of
Wat«r
(WH-6SOGJ
EPA57IVWI-010
ApriM991
A Review Of Methods For
Assessing Nonpoint Source
Contaminated Ground-Water
Discharge To Surface Water
Printed on.Recycled Paper
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A Review of Methods for Assessing Nonpoint Source
Contaminated Ground-Water Discharge to Surface Water
April 1991
Office of Ground-Water Protection
U.S. Environmental Protection Agency
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! J
i! II
II ' II
ii! a SB. I!
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Table of Contents
.A
. .....
I. ' Introduction ......... .-.- • ; '.*'*• ..... ' '
'. " . / •''.' • ' ' .'.... ~' 1
A. Purpose of -this report .,.....••• ......
-'•'•'' . •'''•-•• • . . 2
. B. Organization of this report ......•••••••••
II Methods for Measuring or Estimating Nonpoint Source Contaminated ^
Ground,- Water Discharge to Surface Water . .......••••••
Studies involving use of seepage meters or mini piezometers ; •
• to measure ground-water discharge to surface water. .. ... ..*.
B- -.' Ground-water quality sampling and ^asurements^of ground- .
' water flow to estimate loading to surf ace . water ..... ' ' '
C Studies involving geophysical techniques to estimate ground- ^
water discharge to surface water ......•>••••••
D. Studies involving hydrograph separation, regression^ :
•. analysis, or mass balance approaches to estimate the
contribution of ground water to stream flow .........
E ' Numerical models of surf ace -water/ground- water interactions . 54'
use types
G studies 'using -environmental isotope methods ^ to estimate the
' ' contri'bution of ground water to stream flow . ...... , • •
Total Maximum Daily L6ad and Waste Load Allocations ......
A.- Statutory and Regulatory Mandate for Determining WLAs and ^ ^ g&
LAs under the TMDL process . . ...... ••.-••
88
B Determining the total maximum daily load ... • . ..... -..
Waste Load Allocation
' .'. , :
D. Summary ..••••••.*'
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niiiiii i1
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Chapter I
Introduction
A. Purpose of this report
This report presents a summary of methods that have been applied to
measure or estimate nonpoint source contaminated ground-water discharge to
surface water. The U.S. .Environmental Protection Agency (EPA) Office of
Ground-Water Protection (OGWP) developed this analysis as part of an effort to
broaden the understanding of the manner in which human activities can affect
water quality in all phases of the hydrologic cycle within a watershed. EPA
undertook this project in response to the-growing awareness tha.t contaminated
ground-water discharge is a significant source of nonpoint source contaminant
Loading to surface waters in many parts of the country. In particular, this
report is intended to stimulate understanding of the methods that may ~be
applied to better account for nonpoint sources of contaminant loading.
'Improved characterization of nonpoint ^source loads to surface water may,' in
turn lead to.more comprehensive approaches for setting total maximum daily
loads for surface waters and waste, load allocation.1 This report provides an
overview of these methods, rather than a manual for employing the methods
presented. Readers who intend to apply the methods summarized here should
study the primary references cited. . ' • .
While ground water and surface water are generally thought of as
separate systems, they are highly interdependent components of the hydrologic
cycle The hydrologic cycle refers to the circulation of water among soil,
ground water, surface water, and the atmosphere. Within a watershed, water
may enter the basin through precipitation, upstream inflow, and ground-water
discharge Water leaves the watershed through downstream -outflow, , •
evaporation, and ground-water outflow (see Figure 1-1). Some,rainwater never
reaches surface water due to the evaporation of intercepted rainfall from
vegetative surfaces and the.soil matrix and transpiration of -water by.plants,
returning water'vapor back into the atmosphere. .
Rainfall that reaches surface water may travel to the stream or lake as
subsurface storm runoff, overland flow, or ground water. In most humid
environments, about 80, percent of rainfall will infiltrate into the s^oil '
-ather than travel by overland flow. Overland flow is more predominant in
semi-arid rangelands, roadways, and*cultivated fields in regions with high
intensity rainfall. Rainfall that percolates into the soil matrix is held by-
capillary forc'es. As the soil moisture increases, older, soil water is
displaced and percolates laterally and/or vertically. Lateral percolation may
eventually enter streams as subsurface storm runoff, while vertical
percolation generally enters the saturated ground-water zone. Ground water
moves more slowly than subsurface, storm runoff and will eventually discharge
' and provide water to streams, wetlands, and lakes.
. i See Chapter 3 of this document for a. discussion of total maximum daily
load and' the waste, load allocation process. , r.
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Host streams and lakes' are surrounded by bank storage zones that
increase during storm events. During a rainstorm, precipitation entering
increase Curing "°™ content which are closer to the stream displaces
«•«. of *£*•?"• s^aeer ^ereby providing the stream with water from bank
Che **fisr ^g^^^e topsoil is underlain by a less permeable
; waterlccumiateTabove that horizon and flows downhill through the
This represents a shorter route to the stream*.
soil.
surface water and the methods that have been developed and applied for
assuring this Kbnpdint source loading to surface water.
In preparing this report, EPA contacted over 100 individuals who are
proKssioniriiterature. .This report represents a synthesis of the
information collected from these sources . .
B. Organization of this report
This report is organized in three chapters. Following this
• K companion volume to this document. , •
::": "2 ' Dunne/Thomas " and Luna B. Leopold: "tfnrff In Environmental
."Planning. W.H. Freeman and Company, 1978, pp. 255-277.
'See "Ah Annotated Bibliography to the ^^
Source Contaminated' Ground- Water Discharge to Surface Water, EPA
006.
il.taiS;;•; iat ;•• i• «• ;, r,;:> .„•• •„:•.•» t j*'r i' ;: ;"" • • . • ..fi• ',.."j :-•. :.• •':;;;• - .• i, •: ; ,:••./ „
ti :::,,!i Illllli:!1!, |:>!; Ui!!!,: luii!!,M1 •.';• ilIilil^i£'[:;>Er;lt^ X ,'i tiH, i:. •: ''H'^Hritii:",!:; !i ''>iii1,';, <, ';]•>-!'i>':'t': <
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Figure 1-1
'•^•/-.V Cfcuria f«ttf to toil :.:/ji> v:V-V-:'"X'.>^t.v':i«V;'.:/SS
•..;./:.•/'.•'•/•; fyauna
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Ill 1 1111
1111
111 111 I I1 II1 111 I
111 111 I I III II
II 111 111 111 I I
Chapter II
Methods for Measuring or Estimating Nonpoint Source Contaminated Ground-Water
Discharge to Surface Water
ill 11. I I Hill I ill !| 1 i1 . • > '••',. •
Introduction
Seven groups of methods have 'tee'n'identifiedin the literature for
measuring or estimating contaminated ground-water discharge to surface water.
Each section of this chapter presents a general description of the method,
assumptionsand limitations for the method, summarizes the data inputs and
output^for the method, describes the environmental settings and contaminant
types th"at"fiavebeen evaluated using the method, and presents a general
evaluation of the suitability of the method for other applications. Each
se'ctionalso" concludes with tables summarizing information presented in the
companion volume to thisdocument,^it Annotated Bibliography to the
LiteratureAddressing Nonpoint Source Contaminated Ground-Water Discharge to
Surface Water,* EPA 450/6-90-006". ^ ; : ' ,
A1 :limiMionl':commdn::'l't'6 '"all of the methods discussed in this report is
the high"degree of uncertainty inherent in the study of ground .water. The
heterogeneity of geologic formations presents a major problem in ground-water
study Fdr eicample, hydraulic'conductivity values can range from 10 cm/s to
less than 10"10 cm/s in different geologic settings. Furthermore, hydraulic
conductivities and other hydrogeologic parameters can vary significantly over
even small distances. Thus, errors inherent in ground-water parameter
estimates can vary by 50 percent or more, whereas an acceptable error for
surface-water work is about 10 percent. As a result, the reader should note
that the methods described in this chapter may inherently encompass broad
ranges of uncertainty in their estimates.
•=-•"••" "gtu:diei involving use of seepage meters or mini-piezometers to measure
ground-water discharge to surface water
The papers cited in this section are summarized in Section I of "An
' Annotated Bibliography of the Literature Addressing Nonpoint Source^
Contaminated Ground-Water Discharge to Surface Water," September 1990, EPA
440/6-90-006 ,'_ .'_' [['''''.' [ , ". ,"'"'''_ 'II''' "J ' ''.'''
i. General description of method •
a. Description of method or procedure
Seepage meters and mini-piezometers may beused to measure the quantity
and quality of ground water discharging to surface water. These methods
ieasurea"point-location" ground-water discharge rate and allow for water-
quality sapling over a very small area at the s»rface-wa"r/sedil!";* . .
interface. In order to characterize larger areas, several measuring/sampling
pointsr';::muit: be selecteH: Areas with different sediment types maybe mapped
and several seepage meters/mini-piezometers installed in each-sediment type.
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The total discharge and loading rate to the surface-water body as a result of
.ground-water discharge can be estimated by applying average measurements per
sediment type to the entire bottom area. Alternatively, reconnaissance over a
large area may be used to identify areas where the greatest quantity of ,
contaminants is entering the surface water body. Seepage meters and mini-
piezometers may then be used to monitor and quantify discharge zones. •
'-.'' Seepage meters and mini-piezometers have been used to investigate -
ground-water discharge into lakes, streambeds, and marine environments They
are best suited for use in moderately permeable soils and relatively quiet
waters but adaptations allow successful use .under more adverse conditions.
They may be used in combination with one another or with piston corers^to
analyze soil permeability, ground-water quality, "*• J«^-WJJJ "j^J"-
An important function of these methods .is to provide field, verification for
. geophysical techniques that may be used to estimate ground-water discharge to
a surface water body (see Section II..C). ' . \
Seepage Meter'
In its simplest form, a seepage meter can be a 55-gallon drum with the
bottom cut off and a vent hole placed in the closed end. The open end pf.the
drum is pushed into the bottom sediments of the surface-water body until only ,
the closed top of the drum is exposed (Lee, 1977), The vent hole remains
unstoppered and the seepage,meter equilibrates with .the sediment environment.
After several days, a collection system consisting of a tube and a deflated
bag is attached to the vent hole (see Figure 2-1). One can use seepage meters
to estimate discharge velocity of ground water tq surface water. Dividing the
collected volume of seepage by the duration of the collection period and by
che area of the seepage meter produces an estimate of ground-water; discharge
•velocity: Multiplying by. the surface area of the stream or lake bottom
estimates the total ground-water discharge rate through that area.
Provided that consideration is given to chemical alteration, seepage.
meters might be used to determine ground-water, quality from collected seepage
samples. Multiplying the measured chemical constituent concentration in the
seepage by .the calculated ground-water discharge rate to the surface-water
body estimates the constituent's loading to the surface water (Goodman et al.,
1989). . . •• •'••'•-.. ' ( - '
Mini-piezometer . • .
'. Description and installation • .
- ' Piezometers are devices consisting of pipes, with slotted tips or well-
points on £he end. They are used to measure hydraulic head in saturated
geologic materials. Piezometers are usually installed: in machine-drilled_
boreholes. Mini-piezometers are similar to piezometers,' but -are.*"!!«• »»~
size and installed manually. A mini-piezometer consists of a —"-«••£«;
tube perforated over a short distance .at ;one end. Nylon mesh covering the
perforated tube keeps sediment from clogging the mini-piezometerTo place a
mini-piezometer, a length of thick-walled pipe, with an inside diameter
slightly larger than the tubing,is hammered into the sediment. A temporary
5 :
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Figure 2-1
water surface
Full section view of seepage meter showing proper
placement m. the sediment. A. 4 liter. 0.017 mm memerane
plastic Baggies Alligator bag (open ,end was heat sealed): B.
rubber-oand wrap; C.' 0.64 cm inside diameter. 6 cm long,.
polyethylene tube: D. 0.79 cm inside diameter. 4,5 cm long,
amoer-tatex tube: F.15 cm "x"5?"cm"diameter epoxy-coatea
cylinder (ena-sectidri ofa"st'eei drum).
Lee "David R.; and John A. Cherry: "A Field Exercise on Ground-Water
Flow Using Seepage Meters and Mini - Piezometers," Tnnmnl of Geo^^g.
Sducacion.. 1978. Volume 27: p. 8.
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plug attached to the end of the pipe keeps sediment from entering the pipe
during placement. . The plug is knocked free before the mini-.piezometer is
inserted to the bottom of the pipe, perforated tip first The mini-piezometer
tube is held in place as the length of pipe is removed .The pipe used in •
installation may be pulled back to expose the perforated section but left in
See to providJ added protection to the tubing. A collection system similar
to the.seepage meter tube and collapsible bag system can be .used to.collect
seepage samples (see figure 2-2).
Mini-piezometer variations .
One difficulty often associated with the installation of mini-
faiezometers is their tendency to move before the sediment collapses around the
' Ptubr« if the tube is pulUd later on. Lee and Welch (1989) have tested a
harpoon piezometer which helps to alleviate this problem (se^Figure 2-3)
-Krbs" on the tip of the piezometer grip the sediment and help to keep the
screen at the desired depth as the driving rod, or pipe, is.withdrawn or if •
the screen in moved during use. _
Another variation of the mini-piezometer is the bundle-type mini-
piezometer, consisting of several small tubes placed within the pipe at one
time The tubes are placed at selected depths to allow detailed vertical
resolution of head and pore-water chemistry at the selected mini-piezometer
location. .If bundle-type mini-piezometers' are placed at selected points along.
a vertical plane, patterns of flow and geochemical processes in the subsurface
are observable. . .
Mini-piezometer measurements
An alternative to direct measurement of ground-water discharge is to use
hydraulic conductivity and hydraulic head data obtained from mini-piezometers
to calculate the ground-water discharge rate to surface water using Darcys
Sw Comparing the Hydraulic head in the mini-piezometer with the hydraulic
htad of the surfac-e-water body determines the hydraulic gradient across bottom
sediments. Hydraulic head differential may be measured using a manometer (see.
Figure 2-4) or a continuous water level recorder (see Figure 2-5). Head
differential is divided by the depth of the piezometer screen below the - ..
. leolment-water interface to obtain the vertical hydraulic gradient Hydraulic
conductivity of the bottom, sediments may be estimated or be ^asured using
either a constant head or falling head test. A constant head test has been
' developed using sections of sediment.cut directly from a thin-walled piston ,
core barrel (Munch and Killey, -1985). Once the hydraulic gradient and^
hydraulic conductivity have been determined, Darcy's Law may be used to
determine the ground-water flux through the sediment (see Section A.i d).
Multiplying the calculated- flux by the surface area of the surface-water
bottom "yields.the ground-water discharge rate to the surface-water body.
'The mini-piezometer yields seepage samples using a syringe or other ^
sampling device Multiplying the measured chemical constituent concentration
'•ItTSHround water by ?he calculated .ground-water "discharge rate yields the
loading rate to surface water. .
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Figure 2-2
II Fill I I,1., (":„;(•',,,"! , I'*
General fea'tures and method of installation of a mmi-
Diezorneter. A. casing driven into the^ sediment: B. plastic tube
with ""'screened1' tip mserteci 'in f^e"'casing;' C, plastic tube is"-a
'{Mzd'rn'eter arid iridi'dales differential .head -(h) with respect to the
surface water: 0. plastic bag attached to the piezometer collects
sediment-pprewster. •„ .ci ' , •
Lee, David R., andJohn A. Cherry: "A Field Exercise on Ground-Water
Flow Using Seepage Meters and Mini-Piezometers," Journal' of Geologic
Education. 1978, Volume 27: p. 7.
i in 11 i
!•;, :tl ..... L 4: ..... M l..i' ...... lie ..... ....... IB; t'lii ..... ill ..... 'i l:> ::: »^!!iJ:::i
.ki!:!!1;, '
i ££ i !», ...... V-ilU .'I.'.'!, '
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Figure 2-3'.'
1/4" O.D.
polyethylene
Cubing
240 ayIon atsh
3/8" 0.0. polyethylene cub*
groove to,fit,.
drive rod
polyethylene tip
*t«inlt««-»tt«l wire
to secure two tubes
Harpoon piezometer tip, screen and tube. Dimensions for the small
type are shown here. The screen is 10 cm iong, has 8 1/4* diameter
perforations and is covered with 3 layers of 240 M«D mesh tightly
rolled around the 3/81 O.D. polyethylene tube to prevent entry of
sediment. The drive rod, not shown, fits loosely in groove. The
•barbs' are folded back before driving in sediment to ensure that
they grip in the sediment. •
Lee, D.L. and S.J. Welch; "Methodology "for Locating and Measuring.
Submerged Discharges: Targeting Tool, Harpoon Piezometer arid More," FOCUS
•Conference on Eastern Regional Ground Water Issues," Kitchener, Ontario,
Canada. October 17-19, 1989.,,p. 8. ' . • • ' .•
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Figure 2-4
•*• -
•'".
'•K.
rubber bulb
B
• ••I !••'
clear »U«iie
••(•r slick
t» III
£•*
The manometer used to measure differential heads in
miniDiezorneters. A. principle of operation: B.- the field ap-
paratus! ": '" :' '.'
'';'''•;' "','"• Laa, ,',Davtd %.., and'John'. A, '.Cherry: "A'Field Exercise on Ground-Water
,'F|,ow Using Seepage Meters and Mini-Piezometers, M journal of Geologic
Education. 1978 ". "Volume' 27r p". .8".' :
10
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Figure 2-5
wartr
levti
rtcoratrsv
Continuous measurement of head differences between
piezometrjc level and river level using two water-level
recorders.
Lee, David R., and Stephen J. Welch: "A Method for Installing and"
Monitoring Piezometers in Beds of Surface Waters," Ground Water. 1989, Volume
27(1): ' p. -89. . -, "- .. ' '
11-
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ill i M IM 11 « 11 nil
In geologic units having permeabilities too low to allow easy withdrawal
of waterfrom a piezometer tip, a piston corer may be used to obtain a
continuous vertical profile of sediment (Lee, 1988). Munch and Killey (1985)
have used a modified piston corer featuring a thin-wall core barrel and
wireline recovery to sample both cohesive and cohesionless sediment frpm
depths up to 30 m below the watertable. The porewater can then be extracted
from the piston core for chemical analysis. .
b. Assumptionsinvolved in using seepage meters and mini-
i i .piezometers
Flow rate is uniform through the sampling interval
Seepage meters and mini-piezometer infer that measured ground-water
quantity and quality are representative .of actual conditions throughout the
stapling interval. The ground-water discharge rate recorded using a seepage
''meteror mini-piezometer represents the average ground-water discharge rate
for thecollection period. If asingle discharge measurement or a series of
discharge measurements recorded over a short time period are used to determine
the ground-water discharge rate to a surface-water body, the calculated
discharge rate may vary from actual rates. • .
Sampled interval_is representative temporally
A series of discharge measurements taken over a short duration can vary.
substantially due to tidal cycles, storm events, and seasonal changes.
Furthermore;seasonal variations within and between years' may be substantial.
It is possible that a series of discharge measurements recorded over a long
duration may' hot be representative of actual conditions if the measurements
were recorded in excessively wet or dry years. ,
Sampling placement is representative spatially
Seepage meters and mini-piezometers"provide ppint measurements that
determine the ground-water discharge rate and.loading rate to a surface-water
body through extrapolation (Goodman et al., '1989). The representativeness of
the sampling locations and the number of locations influence the accuracy of
the"results. For example, Belanger and Connor (1980) not only found
decreasing seepage rates with increasing distance from shore, but also that
ground-water recharge occurred toward the center of East Lake Tohopekaliga.
An overestimation of ground-water seepage would result if seepage meters used
in the study were all located near shore. Conversely, if all the seepage
dgters were located towardthe center of the lake, one would erroneously
conclude thattheentirelake was recharging ground water.
Measured samples are 'repres'enta^i've'bf ground-water dischar&e.
oUalitV " - • ' ,
, „ Measured ground-water quality may not be representative of actual
conditions' because of interactions "occurring at the sediment/surf ace .water
interface Belanger and Mikutel (1985) concluded that direct determination of
water quality using seepage meters overestimated nutrient loading to lakes due
to the enclosure of bottom sediments, which results in anaerobic conditions
12
1 S'i"'",,,' . II i" •!,"!•
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and increased release rates of ammonium, nitrogen, and phosphate. In
addition, seepage .meter or mini-piezometer samples from shallower, shoreline
locations may be influenced by bank storage water. •
c. Limitations of the methods .
Placement on different surface-water bottoms . .
Not all bottom areas of a surface-water body are conducive to
installation of seepage meters or mini-piezometers. Because seepage meters
and mini-piezometers require insertion into bottom sediments, ideal
installation locations-are areas with relatively soft, fairly thick,
moderately permeable sediments containing few cobbles or stones. However,
German has successfully installed seepage meters in cobbles and rocks using
bentonite placement.* ,
Deep surface waters require additional expertise and equipment ..
Seepage meters and mini-piezometers_ located in deep water require scuba
abilities and equipment for installation, sampling,' arid maintenance. Depths
that limit divers' safe performance control installation depths (Woessner and
Sullivan, 1983). Additionally, some bottom locations are not suited to
installation of seepage meters and mini-piezometers.
Strong currents and harsh seasons
Without modification, mini-piezometers and seepage meters should not be
used w-ith strong currents. Acceptable installation locations vary with
seasons in areas due to wave and current action. Additionally, in colder
climates, ice covering surface waters may limit seepage meters and mini-
piezomepers sampling and maintenance activities. .
Sklash has overcome some of these problems.5 In his investigation,
handles placed on seepage meters aided divers in fast currents. Also, once
the seepage meter is placed, bolts are used to clamp it.down 'and ensure its
stability. To protect seepage bags from the elements; Sklash used rapid
disconnects for .the bags and placed rigid containers around'them. . .
Maintenance — . '• ' • • ' ' . •
Seepage meters and mini-piezometers equipped with sample collection
devices require" substantial.maintenance; Without frequent changes, the
increased pressure associated with a full catchment device reduces the amount
4 German, Dave, personal communication, Nonpoint Source Contaminated
Ground-water Discharge to Surface Water Workshop, Chicago, IL, November. 30,.
1989. '-"..'•"'•,'• '''.".-.-'.
5 Sklash, Mike, personal communication, Nonpoint Source Contaminated
Ground-water Discharge to Surface Water Workshop, Chicago, IL, November 30,
1989. ' , , • -•-._.-'•.
','-.' • " . - ' ' 13'' ' - . - • ' ' - .
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of ground-water flow into the seepage meter. The sample collection tubing for
seepage1 ietersIhd mini-piezometers requires regular cleaning or replacement
co preventalgae growth. There may be a need to periodically replace seepage
meters and iinf-piezbmetersdue to wave and current action.
Anaerobic environment within equipment
A final limitation of seepage meters and mini-piezometers is that
anaerobic conditions develop within the seepage meter, altering the chemistry
of the discharging ground water (Belanger and Mikutel, 1985). As a result,
calculated loading rates to surface water, determined using seepage meters,
may not be representativeof actual seepage from the ground water.
d. Representative equations .
Darcy's Law is used to calculate the ground-water discharge rate to
surface water when using .mini-piezometers. The form of Darcy's Law us.ed is:
, Q - K(dh/dl)A / , • \ ' _ | ' . '
where ' '
Q - Ground-water discharge rate [L3/T]
K - " Hydraulic conductivity [L/T]
dh/dl - Hydraulic gradient [L/L] .
* A _r surface area of the bottom of the surface-water body [Lz] .
i;:.,.; ,^,;,,| r^^n ^^^'rVS "£o'" surlace" water " as'"a result "of ground-water discharge is: -
'' ! W'i | j|f!J •,,''':•;* .nSIJ ' IJ IliliV '' : '"„''!'"•' ,'l!! ,,N|1 '""!:!' ' '"« '!' »» ' ' 'lilli ,,'
llll1:1:1!'!" 1 », kJIni "i , "l,.i, ........ ..... 'JiUIHil, ' LJU ""• i ,, ..... !MM" ....... f *' 'TD ^
where , .
LR - Loading rate [M/T]
Q - Ground-water discharge rate [L3/T].
„ '""Chemical cons'tituent coricentration in ground water [M/L ]
' ''"'. .-:^" .^ ...... ... e't ....... ""^""'"Description of field equipment •
Equipment and materials often used for installation, sampling, and
maintenance of seepage meters include:.
open-ended 55-gallon drum with vent hole,
tubing,
- plastic seepage bag,
- ' boat , and • '. •
- scuba gear. ................ • " •'
.typical equipment and materials required for installation, sampling, and
maintenance^ of ............ mini-piezometers include: _ • _ , . , • ,
ffietal pipe,
" "u ' • ...... . ' ' '".'"'
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- end plugs,
- .tubing,
- nylon mesh,
hammer,
sample bag, and
- boat.
For a detailed description -of seepage meters installation -and- sampling, see
Se (W7* installation and sampling of seepage meters in deeper, more
turbulent' water often requires additional equipment.
"-.;"• f. Expertise needed to apply method
Sitine sampling locations requires a sufficient understanding of.
reeionai geology ^hydrology. Extrapolating sampling results also requxres
If «SI iLzometers may be made from a surface platform -as described by Welch
!nd Se"a98?) Se surface platform sits on top. of two -14 foot boats ; and
-
intensive, especially with dive team involvement.
ij_; Data inputs for the method
of sample results to areas with similar sediment
Icnowledge of the spatial ^$^&S
discharge rate.
iii. Outputs from the method- • -
meters and mini -piezometers provide a direct
can provide estimates- of the.' total loading from ground^ater seepage
15
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figure 2-6
SIDE vi£W
plywood box beam on
center joist" only
2x4 joist
platform
eye bolt (3/8 in x 8 m)
joists
aluminum boat
polypropylene
rope (5/6 in dial
PLAN VIEW
20 cm x .20 cm hole
•joist (2x4 mx13 ft
13-4x8 ft 5/8 m thick
T & G plywood)
•14 ft aluminum boat
Side and plan view. Working platform for installing
piezometers and coring sediments from the water surface.
Lee, David R., and Stephen J. Welch: "A Method for Installing and
Monitoring Piezometers in Beds of Surface Waters," Ground.Water•. 1989. Volume
27(1): p. 87.
16
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a.- Ground-water quantity discharge to surface water
wide range of seepage rates can be measured using seepage meters and
rl:;^^^
simple seepage meter described above (Lee, 1977),
b. Ground-water quality discharge to surface water
Seepage meters allow for the collection of samples for water quality
-
•^SS^i^^S^^c..^^.^.^?^^^^.
. iv • Settings in which the method has been applied and _
contaminants .that have been measured using this method
Summaries in Table A-1 describe some of the locations wher* seepage
,25mini-piezometers have.been' used successfully and the. contaminants
met*rs
measured using the- method.
v.
Evaluation of the method
. Seepage meters and mini -piezometers provide a simple d
.extrapolating results to the points of discharge, ,
vi References to annotated bibliography •
' References to the annotated bibliography presented in the accompanying
volume to this document are provided in Table, A- 2.
17
-------
11! I In B Illi • I*
ii Hi I! i!i
i i i i « iliS! i
MI II III !
j »T»UU A-l. ,S««ary of S«Ltl<.Sa In Ht.td« the Hatttod tin Beun Applied ami tin CoHlijiiJnaroU Hea»ur»d.
Location
Author
u i;
r:
fc-
I; -.;-
K
Oiilarlo
SILBS naar LsaralngLon. .
' Ontirto and «t Capa Cod
i:[ :i HasstchusatLs
• Chalk River, Ontailo
. Douglas
••: Key Largo National
- Marine Saucturay, Florida
1 Key Largo National
\ 'Marine Sanctuary, Florida
: OsceoLa County, Florida
Wisconsin
Michigan and Wisconsin
Btovard CouuLy, Florida
Belanger
Upper Great Lakes
Connecting Channels
Orlando, Florida
Brezonik
South Dakota
Colorado
Winter
Floridan Aquifer
Shallow glacial,
glacial bedrock Inter-
face and bedrock units.
Hltratei
(Ontario)
Pesticide*
Heavy M«lal«
Nitrates, selected
cations, total phosphates
.Phosphorous, Hltrogen
Hl.trate, Phosphorous, '
Ammonia;
Chloride
Phosphorous, Chromium,
Lead, Barium, Zinc, Cobalt
Nickel. Phenols
Nitrate
Nitrogen, Phosphorous,
Pesticides
0. R. Lee, S. J. Welch
D. R. Lee
J. B. Hunch, R. W.
G. H. Slnmons Sr.
F. G. Love
G. M. Simwmi Jr.
J. Hetherton
T. V. Belanger
D. F. Hlkutel
I. D. Brock, 0. R. Lee,
D. Janes, D. Hinek
D. A. Cherkauer.
J. M. McBrlde
J. N. Connor. T.V.
EPA Hon Point Source Work
Group •
C. R. Fellows, P. L.
J. Goodman at al.
J. H. LeBaugh, T.C.
Eastern Ontario
D. R. Lee, J. A. Cherry.
F. Plckens
-------
Table A--1. Sunaary of Settings ID Which the Method B«» Been Applied and the Contaminants Measured. (Continued)
Location. •
Aquifer
Contasdnant
Author
tu!.leiu Ontario
Minnesota, Wisconsin
North Carolina, Nova Scotia
Southern Ontario
Barbados, West Indies
SouLliuastern Virginia
Minnesota
Holbrook, Massachusetts '
Ostyre,
Mahantago Creek, •
Gburek,
Pennsylvania
Chicago, Cook County,
Demlssle,
Illinois
Virginia's Eastern Shorn
Sault Ste. .Maria,. Ontario
West tliorton, Hew Hampshire
Lake Mead, Nevada
Sullivan
East Coast 'of Florida
Barbados Aquifer
Shirley. Yorktown,
and Tabb Formations
Manhantago Creek Basin
Cambrian and Ordovician
Aquifers
Tertiary-Cretaceoug
Gale-Hills Formation
Tritium
Phosphate!, Nitrate*,
Ammonia, Chloride • '•
Nutrients '
Nitrogen, Phosphorous
Inorganic Nitrogen.
Phosphorous, Nitrogen
Volatile Organlca and
Inorganics
Nitrogen, Phosphorous
E.P. Metals
Hitrete, Araoonla, Total
Phosphorous
IDS, calciura-iulfate
Phosphate
D. R. Lee, J. A. Cherry •
D. R. Lee
D. R. Lee. H.B.N. Hynea
'j. B. Lewis
W. G. Maclntyre,
• 0. H. Johnson-,
H. G. Reay,
'6. H. Sinmons, Jr.
J. K. Heel. R. M. Brlce
H. R. Herman. D. P.
J. S. Hobin
H. B. Poinke, N: J.
N. J. Gburek et. al.
M. S. Henabry, M.
et el.
G. M. Sinmons, Jr.
S. J. Welch. D. R. Lee
T. C. Winter .'
W. H. Woessner, K. .
C. F. Zlmnerman,
J. R. Montgomery,
P. R.. Carlson
-------
, iij j ] I
!, I i *
i,:! I Nil! ill!
jsri iilj MI
I;;:.: js3 ^
inj.ihi
!i!i Hli 1
!i!l IP! !i i
A 2, Ktil«rwic*s to AmiMtated
= : i
Autliur
Citation
Reference to Annotated
Bibliography
V. B»l*ng«r. D. F. HikuHl
R. Care. T. C. Hlntur
; D. A. CItarkouer, J. H. HcDrlde
, J. H. Connor, T. V. Belanger
to
"
' EPA tlon Point Source Hork Group
C. R. Fellows. P. L. Brazonlk
J, Goodman'et at.
J. H. LaBaugh, T. C. Hintar
"On th« Us* ot S«»p«g» Haters to Estl«*te pp.2-3'
Ground-Witer HutrUnt Loading to Likei,"
Hater Resources Bulletin. 1985, Volume
21(2)! 265-272.
<"An Annotated Blbllogrephy of Devices Developed • p.8 •
'for Direct Measurement of Seepage," U.S. Geological
Survey Open File Report 00-344, I960.
"A Remotely Operated Seepage Mater for Use in Large. pp.9-10
Lakes and Rivers," Ground Hater. 1988, 26(2):
165-171.
"Ground Hater Seepage in Lake Washington and the Upper pp.11-12
St. Johns River Basin, Florida," Hater Resources Bulletin,
1981, 17(5): 799-805,
"Upper Great Lakes Connecting Channel Study, Haste Disposal pp.13-17
Disposal Sites and Potential Ground Hater Contamination.
St. Clalr River," Non Point Source Hork Group Report,
April. 1988.
"Fertilizer Flux into Two Florida Lakes Via Seepage," pp.18-19
Journal ot Environmental Quality. 1980, Volume 10(2):
174-177. .
"Oakwood Lakes - Poinsett: Rural Clean Hater Program pp.20-21
Comprehensive Monitoring and Evaluation Technical Report,
Project 20," Rural Clean Hater Program Comprehensive
Monitoring and Evaluation Technical Report, Project 20,
May, 1989.
"In Impact of Uncertainties in Hydrologlc Measurement on pp.22-23
Phosphorous Budgets and Empirical Models for Two Colorado
Reservoirs," Limnology and Oceanography^ 1984, Volume 29(2):
322-339.
-------
Table A-2.. Kufuruncua t.o Aiuiotateil Blbllogra|>hy (Continued).
Author
Citation
Baferenca to Annotated
Bibliography
D. R. Lee
P. R Lee. S. J. Match
T. D. Brock, D. R. Lee,.
David Janes, David Hinek
'D. R. Leu. J. A. Cherry, J. F. Pickens
D. R. Lee, J. A. Cherry
D. R. Lee
D. R. Lee, II.B.H. Hynes '
J. B. Lewis
"Six In-Sltu Methods for Study of Gcoundwatar Discharge,"
Proceedings of the International Symposium oh Interaction
Sympoiiura on Interaction Between Groundwatar and Surfaca
Hater. 30 May-3 Juna, 1988, Yitad. Sweden, edited by
Patar Dahlblom and Gunner Lindh, Department of Hater
Resource* Engineering, Lund University, Sweden.
"Methodology for Locating 'and Measuring Submerged
Discharges: Targeting Tool, Harpoon Piezometer and
More," FOCUS Conference on Eastern Regional Ground Hater
Issues: October 17-19, 1989, Kitchener, Ontario,
Canada, Co-sponsored by the Association of Ground Hater
Scientists end Engineers., Division of HHHA and Haterloo
Center for Groundwater Research, University of Hatarloo.
"Ground-Hater Seepage as a Nutrient Source to a Drainage
Lake; Lake Mandota, Hisconsln," . , •
"Ground-Hater Transport of a Salt Tracer through a
Limnology and Oceanography. 1980, Volume 25(1):
45-61. .
"A Field, Exercise on Ground-Hater Flow Using
Seepage Metara and Mini-piezometers," Journal'of
Geological Education. 1978, Volume 27: 6-10.
"A Device for Measuring Seepage Flux in Lakes
Lakes and Estuaries," Limnology and Oceanography.
1977, Volume 22(1): 1*0-147.
"Identification of Groundwatar Discharge Zones in a
Reach of Hi1 loan Creak In Southern Ontario," Hatar
Pollution Research Canada. 1976, 13: 121-133.
"Measurements of Ground-Hater Seepage Flux ontq a
Coral Reef: Spatial and Temporal Variations,"
Limnology and Oceanography. 1987, 32(5):
1165-1169. . '
pp.27-29
pp.37-39
pp.6-7
pp.32-34
pp.30-31
pp.24-26
pp.35-36
pp.40-41
-------
S Ii ! i Mil
S!M! MM
»,*-
3
aiBi
T»l)lo A 2. Kaf«r*nea« to Ana«jL«t«J
?! . ! (i : M ! I ,
(Continue*!).
i t
i Ii
111
• III
Author
-, Citation)
Reference to Anraotated
Blbllogcaipby
•*•
4s
iv-
! rt
iiHi
K>
,to
H G. Haclntyre, G. II. Johnson,
!SH G. Reay, G. M Siwmni. Jr.
; J. K lluul , K. M. Uclce
U K. Hoiniaci, D. P. Ostrye,
J. S. Hobin
II. U. Pionke. J. R. Hoover.
R. R. Schnabel, V. J. Gburek.
J, B, Urban, A. S. Rogowokl
' P- E» Ross, M. S. Hanebry.
J. B, Risetli. T. J. Murphy,
: M. Demi55ie County, Illinois
G. M. Simmons Jr.. F. G. Love
G. M. Sinmons Jr., J. Netherton
"Ground-Hater Hon-Polnt Sources of Hutrlants to the
Southern Chesapeake Bay," Proceedings of Ground
Hater Issues and Solution* In the Potoaac River
Bailn/Che»apeake Bay R«nlon. Co-sponsored by the
Association of Ground Hater Scientists and Engineers,
pp. OS-JO*. '
•'Watershed and Point Source Enrichment and Lake
State Index." US EPA, April 1979. EPA-600/3-79-046.
"Use of Seepage Meters to Quantify Ground-Hater Discharge
and Contaminant Flux Into Surface Hater at the Belrd and
McGulre Site (HPL No. 1*)," Proceeding of Third Annual
Eastern Renlonal Ground Hater and Conference. 1986.
p. 472-491.
"Chemlcal-Hydrologic Interactions In the Near-Stream Zone,"
Zone," Hater Resources Research. 1988, Volume 24(7X:
.1101-1110.
"A Preliminary Environmental Assessment of the Contamination
Associated with Lake Calumet Cook Hazardous Haste Research end
Information Center. Illinois State Hater Survey, 1988, HHR1C
RR-019, 88/300.
"Hater Quality of Newly .Discovered Submarine Ground Hater
Discharge Into a Deep (Coral Reef Habitat," (JOA^ Symposium
series for Undersea Research. Volume 2(2): 155-163.
"Groundwater Discharge In a Deep. Coral Reef Habitat:
Evidence for e Hew Blogeochenlcel Cycle?." Diving for
Science...86, Proceedings of the Sixth Annual Scientific
Diving Symposium (1986), Tallahassee, Florida, Charles t.
Mitchell, editor.
pp.42-43
pp.44-46
pp.47-49
pp.50-52
pp.53-55
pp.60-61
pp.62-64
i : r.
-------
Table A-2. References to Annotated Bibliography- (Continued).
Author
Citation
Deference to Annotated
Bibliography
to
OJ
G. M. Simmons, Jt:
G. H, Slnmons, Jr.
S. J. Welch, D. R. Lee
I. C. Winter
W. M, Moessner, K. Sullivan
C. F. Zinroarraan, J. R. Montgomery.
P'; R. Carlson
"Understanding the Estuary Advance* In Chesapeake
Research," Proceedings of a Conference-, March 29-3),
198, Baltimore, Maryland, Chesapeake Research Consortium •
Publication 129. CBP/IHS 24/88.
"The Chesapeake Bay's Hldd.n Tributary: Submarine Ground-
mt-rr P'-"hr''ll*." P™r.«.i»n»« nt Ground Hater Issuas and .
Solutions In the Potoaac River Basln/Chesapaake Bay RaRJon.
Co-sponsored by the Association o{ Ground Hater Scientists end
Engineers, pp. 9-29. t ' ' '.
"A Method for Installing and Monitoring Piezometers in Beds of
In Beds of Surface Haters." Ground Hater. 1989 27(1): 87r90.
•'Geohydrologlc Setting of Mirror Lake. West Thorton, Mew Hampshire,
1984, U.S. Geological Survey Hater Resources Investigation! Report,
84-4266, 61 pp. . • . •
"lisa of Soopage Maters and Mini-piazoneters for Identifica-
tion of Reservoir - Groundwatar Interactions in Lake Mead,
Nevede," Desert Research Institute Hater Resources Canter,
1983. PB 83-22689*. '
"Variability of Dissolved Reactive Phosphate Flux Rates in
Nearshora Estuarlne Sediments." Estuaries. 1985,8(26): 228-236.
pp.36-57
PP;58-59
pp.65-66
pp.67-68
pp.69-70
pp.71-72
-------
Ill
Ground-water quality samplingand measurements of ground-water flow to
estimate loading to surface water
papers cited in thissectionare summarized in Section VIII of "An
Annotated Bibliography of the Literature Addressing Nonpoint Source
Contaminated Ground-Water Discharge to Surface Water," September, 1990, EPA
440/6-90-006. , ;
1. General description of method
Description of procedures
a.
I III n II II I Illl 1 1 I I I ill! 1 I I I } I II i I I II I » ' ,1 , i " „ ' ,'"!,'„ :. ' i, ' ' :
Water-level elevation measurements from piezometers and ground-water
wells provide an indication of the quantity of ground water, discharging to
surfacl water in a watershed. This method uses water-level measurements
obtained from wells located in the watershed to develop a water table contour
glrcy's^Law is then applied to calculate the discharge rate of ground
water to surface water by incorporating estimates of hydraulic conductivity
and the cross -sectional area of the aquifer. By assuming the aquifer
underlying the watershed is homogenous and isotropic, the water-level contour
map can be used to determine flow directions and horizontal gradients in the
basin In a homogeneous, isotropic aquifer, flow lines will be perpendicular
co equipotentials. Hydraulic conductivity can be estimated for a particular
rock or soil type or can be measured in-situ via aquifer tests. Aquifer ••
geometry is' estimated by examining lithologic logs of wells in the watershed. .
Ill I I I I I I II I III I III I I III I II I lull ' ! " ,': Mill,"™". „'!, '' I,!,,," ..... ' j "'' ' ' ''.• ' , ' ' "
This" method is often used in conjunction with other methods, such as
mini-piezometers, seepage meters, tracer studies, isotopic studies, or water
and mass balances analyses to verify study results. This method has been
practiced in loth marine and fresh water environments and has been used on a
large scale, such as in Long Island (Franks and McClymonds) and North Central
Kansas (Spruill) and on a smaller scale such as in South Farmingdale, New York
(Perlmutter and ; X£eber) and the Stockett-Sand Coulee coal field Montana
(Osborne, et.'al.). This method has been used for glacial and dolomite .
aquifers." Contaminants studied include metals , nutrients, and some organic
constituents.
Ground-water samples taken from wells within the basin can be used to
characterize the spatial distribution of ground-water quality as a. means of
estimating nonpoint source contaminant load. To properly characterize ground-
water quality in a drainage basin, potential nonpoint source loading areas •
should be identified and the underlying ground water sampled. Agricultural
areas located on soils allowing rapid infiltration of precipitation are of
particular concern. Such areas are identified from soil and land use ">aps
fHallbere et al. , 1983). Evaluation of ground,wat«r quality beneath nonpoint
source loading areas, over time will indicate qualitatively whether the loading.
tatfto sSpe water, as a result of ground-water discharge, will increase or-
decreasej'iif tKe ^future :_
_ ..... , _. ,.,, .... ..... . , , , ,.. .... . . .,
Ground-water quality in wells adjacent to the s«fa";wat" ^J^"6 Bv
assumed to bi repreVahfiielve of ground water discharging to surface water. By
..... ...... concenfr'ations and the calculated ground-water flux, the-
ng
1(1! ..... .,!.",:• 'i1 Jlilllll i." ..... . ,."" . "i;11: ;. I ',, 1|,,!!l! ..... il vti'l ....... liil'ii1!' I1.1'-"""
. . ' Illl 111 Illlllll I II Mill III ||||I||||||||||||| ll I II III Illl I I I I I II III III I (III
-------
immediate loading rate to surface water from ground-water discharge can be
calculated. . ,
b. Assumptions involved in these methods .
To use Darcy's Law to calculate ground-water discharge to surface water.
it is assumed that the aquifer is. homogeneous', isotropic, of constant
thickness, and that flow is horizontal. The assumption.that the aquifer is
homogeneous and isotropic is necessary to ensure that flow lines are
perpendicular to equipotentials (Perlmutter and Lieber, 1979). _ By assuming a
constant aquifer thickness and horizontal flow, the one-dimensional version of
Darcy's Law can be used. Additionally, .water quality in sampled: wells is
assumed to be representative of the quality of the water discharging to the
stream. ...'"- •
• c. Limitations of the-method .
Aquifer -characteristics
The limitations of this method reflect the natural; variability of
aquifers and the availability of information on aquifer characteristics; 'In
nature, considerable heterogeneity exists and few, if any, .aquifers are
homogeneous, isotropic, and of constant thickness. In a heterogeneous,
anisotropic aquifer, ground-wafer flow is not perpendicular to equipotentials,
and the angle between flow direction and equipotentials is not constant.
Because the predicted flow path length differs from the actual flow path
length, the calculated hydraulic gradients will not be representative of the
actual gradient. Additionally, horizontal gradients determined using wells
screened at different depths below the water table or in different'.geologic
formations may not represent the actual horizontal gradient. Temporal changes
in the hydraulic conductivity due to changes in seepage face from
precipitation events increase the difficulty of estimating an average ground-
water discharge. Hydraulic conductivity also varies spatially and
directionally in a heterogeneous, anisotropic aquifer. It would be difficult,
if hot impossible, to determine an accurate equivalent.hydraulic conductivity
and aquifer thickness for the basin. Because of the difficulties in
determining horizontal hydraulic gradient, hydraulic .conductivity, and aquifer
• thickness, precise determination of ground-Water discharge to surface water is
problematic (Koszalka, 1983). .' .
. • Well installation
Installing the number of wells needed to properly- characterize ground-
water quality in a watershed is resource intensive. As an alternative to
installing costly monitoring wells, existing production, domestic, and stock
wells may be sampled. In many cases, however, these wells.will not be in
optimum locations or open to the geologic, formation of interest.
Additionally, water-quality results can be altered by well construction
- materials, faulty well construction, arid sampling procedures. Consequently,
ground-water quality in the basin may not be accurately characterized, due to
the construction and lo'cation of the well.
25
-------
•
d. Representative equations
Darcy's Law is USed in determining the quantity of flow entering surface
water. The fora of Darcy's Law used is:
.................. ' ..... Q"'- .......... KCdh/dl)A ............... ; ......... " ' ' ......... ;
where ................................................. ' _; ............................................. ,
Q - Ground-water discharge rate (L3/T)
'" ............... ..... "' ....... ! '' £ ........ ' .......... '" ....... "i:i ........ ' ...... '' ' - ": " "v '"Hydraulic conductivity (L/T)
dh/dL - Hydraulic gradient (L/L)
A - Cross sectional area of the aquifer (L2) .
The loading rate 'to' ..... 'surface a/S''rffadt of ground-water discharge', is
determined by multiplying the ground-water discharge rate by the concentrati
of the constituent' in "the^ ground water. _ pie loading rate equation is:
LR - Qc ................... '' "" ...... """ ..... ............ ........... ....... '""•" ............ .
where . ' .
., ,,:,,,;; ,.LR - Loading rate (M/T)
II,".,',! Q " - • Ground-water "discharge rate (L3/T)
: BS;ai;;£'6 ' "' ' ' "'-1"11 " Concentration in ground-water (M/L3)
it III,,,,! I'MJii; ;j]f '! i:;!!;1"'' iiitl. k!.^J'W\-
Jill1 iflilil !*', I 'Will, i"1'1!1!1' liiJI, j,! , IlilEili JH,™ ! l!!lli«! ""
e.Description of field equipment
I'll »l! Illlill '"!"",, "ill 'Ill1'',,," ' ,' I II .1- ,', •, ," "1!" .I',,!, .''I I',!,,-. './.' ,| !':
~ 'l"l After' the" wells 'have been installed, equipment is required 'to"measure
wacer levels and obtain ground-water samples. Suggested equipment includes:
steel tape and chalk or electric well sounder,
*•* 'submersible pump,
,:,',;' " i; ^'pentrifugal pump,
lllilWIIIIIIE'l'iirli L iMni'li! mi/ ill Bii , , nllHIiiJ'!'', U,!",! »' ,',i,'~i, !
-------
determining aquifer characteristics and geometry. Aquifer tests are labor
intensive and sometimes difficult to interpret. Additionally, aquifer
characteristics determined for one portion of a watershed must be extrapolated
to other portions of the watershed (Koszalka et al., 1985).
ii. Data inputs . .
To apply Darcy's Law and estimate the ground-water loading rate for a
watershed, level elevations, hydraulic,conductivity, aquifer geometry, and
chemical constituent concentrations in ground water are needed. Well
construction information is essential to determine the subsurface zones that
.the hydraulic head and water quality measurements represent.
' iii. Outputs from the method
a. Quantity of ground water
" A wide range of ground-water discharge to surface water rates can be
estimated using this method. The factors controlling the quantity of ground-
water discharge to surface water are hydraulic conductivity and gradient. If
the hydraulic conductivity.of the aquifer is low, and the hydraulic gradient
.- across the aquifer is minimal, the ground-water discharge rate to surface
water will also be low. Conversely, a high.ground-water discharge rate to
surface water will occur when the hydraulic conductivity and gradient for an
aquifer are high. • •
', _b. Quality of ground water
• A broad range of loading rates to surface'water'as-a result of ground-
water discharge can be predicted using this :method. The ability to determine
ground-water quality in sampled wells, is limited only by the characteristics
of the well materials and the quantitation limits; for the individual
constituents.
iv Settings in which the method has been applied and .
contaminants that have been measured using this method
Some of the locations where this method has been used and the
contaminants that have been measured using the method are summarized in Table
B-l. -• '. • :. .- ' . •.'- .'.••'
v. Evaluation of the method
Most watersheds contain observation or water supply wells that can1be
used to obtain, water level- elevations., and water quality data making this
method applicable in many locations. The method can qualitatively determine
the amount of -ground-water discharge and the loading rate to surface water
within a watershed. Increasing the number of sampling locations will improve
the predictive capabilities of the method. :
• • „ •• 27 . : '•'•'••
-------
Because the method is often applied with limited knowledge of aquifer
ch,r.cS*i«ics, a large number of sampling points will not necessarily result
f !^Sate Quantification of ground-water discharge or loading rates to
surfacfwate?!comparable qualitative indication of the loading rate to
surface water as" a result of ground-water discharge can be obtained by
o^ervtnrvater-quality crends in the watershed. If, within a watershed
^wtaB^er £ ^dentrations in ground water increase with time, the
fuSre Lading rate to surface water as a result of ground-water discharge can
.116 be expected to increase. In addition-to using the.method to
governing fertilizer and pesticide usage on ground-water
V£. References to annotated bibliography
References to the accompanying annotated bibliography are located in
Table "B-2. ' .'.
11 '' j' ' ' ''
l ill I '..; ''," I :nl: . i: I' f'.-.y
28
!!!!!!!!!'!!!!!!!! "!!''„,' ; T" it
-------
Table H-l. Sunnary of Setting* |D Milcb the Method Baa Been Applied and the ContaaUnantB Maaaured.
Location
Aquifer
Contaminant
Author
Patchogue.
Long Island, Hew "York
Penfield, Hew York
Upper Great Lakes
Connecting Channels
Long.Istand. Haw York
Clayton City, Iowa
Perth,-Australia
Niagara County,
Hew York
Stockett and Sand
Coulee, Montana
Hassau County,
New York
llorth Central Kansas
Lockport dolomite
Shallow glacial, •
glacial bedrock. :
interface. & bid-
rock units
Upper Glacial, .
Magothy. and Lloyd
Galena
'Kootenai Formation,
Morrison Formation
Magothy
Almena,
Kansas Bostwlck,
Cedar Bluff Units
.Nitrate Nitrogen
Sodium Chloride
Zinc, Phenol*,
Phoiphoroua
TDS, Inorganic
M«taU
Nitrates, Herbicide
Pesticides/Bacteria £
.turbidity
Nitrate
Inorganic t Organic
Constituents
Heavy Metals
Cadmium, Chromium
Sulfate," Sodium
Chloride, Calcium
D. Capon*, H. Bautista
L. R. Davis
EPA Hon-Point Source
Group
0. L. Frank*. H. E. McClyioonds
G. R. Hallberj. B. E. Hoyer
E. A. Bettls, III, R. D. Libra
R. E.- Johannes
E. J. Koazaifca. J. E. Paschal
T. S. Miller. P. B. Duran
T. J. Osborn*, J. L. Sonneregger,
J. J. Donovan
N. M. PerLmitter.
H. Lleber
I.'B. Sprulll
Butte. Mead and
Lawrence, South Dakota
Arkansas River Basin
Arsenic,
Selenium
TDS, Salinity.
Chloride
R. L. Stach, R. N. Helgerson.
R. F. Brett, H. J. Tipton.
D. R. Blessel, J. C. Barksen •
J. D. Stoner • '
Schwatka Lake, Yukon
Territory, Canada
Nitrogen, .
Phosphorous
P. H. Whlttield, B. McHaughton.
H. G. Hhltley
-------
I!
T«Mu U Z. HuluruiiLU. lo AuiwUlud Bllil Iojt«|Jrjr
a Guide to Hater-Management Alternatives," U. S. Geological
Survey Professional Paper 627-F, 59p.
"Hydrogoology. Hater Quality, and Land Management In the Big
Spring Basin, Clayton County, Iowa." Iowa Geological Survey,
Open-File Report 83-3, 1983 Report on contract 82-5500-002.
"The Ecological Significance of the Submarine Discharge of
Groundwater," Marine Ecolonv — Progress Series. 1980,
3: 365-373. •
••Preliminary Evaluation of Chemical Migration to Ground Hater
and the Niagara River from Selected Haite - Disposal Sltea."
USEPA. March 1985. EPA 905/4-85-DOi:
"Interaction between Groundwater and Surface Hater Regimes -
and Mine-induced Acid - Mine Drainage in the Stockett-Sand
Coulee Coal Field," Montana Jotnt.Hater Resources Research
Center, 1983, Project No. A-129MONI. Bozeman, Montana.
"Dispersal of Plating Hastes and Sewage Contaminants in Ground
Hater and Surface Hater, South Faraiingdale - Massapequa Area,
Nassau County, Hew York," U.S. Geological Survey Hater Supply
Paper 1879-G.
Reference to Annotated
Blbllogtaphjr
pp.198-199
pp.200-201
pp.202-206
pp.207-209
pp.210-211
pp.212-213
pp.2U-216
pp.217-219
pp. 222-223
w ,
-------
Toblu U 2. Huloruiiuea tu Aiuiotatud Blbl logra|J>y (Colillnuud)
.Author
Citation
Reference to Annotated
Bibliography
T. B. Spruill
R. L. Stach, R. N. Helgerson.
R. F. Bretz. M. J. Tlpton,
D R. BlesseL. J. C. Haiksen
J. D. Stoner
f. II. Whitfieia. B. McHaughton
"Statistical Evaluation of the Effect* of Irrigation on
Chemical Quality of Ground Hater and Ba»e Flow In Three
River Valley* In North Central Kansas." U,'S, GeoloKlcel
Survey Water Reaource Investigation Report 85-*156, 1985.
"Arsenic Level* in the Surface and Ground Haters' along
Hhltewood.Creek, Belle Fourche River, and a portion of
the Chtfyenna River. South Dekota," Completion Report,
Project Number A-OS4-SDAK. Agreement Number .U-3*-0101-60*3,
July. 1978. '
"Disiblved Solid* in the Arkansas River Basin,." Rational,
Rational Hater Sunraary 198*: HvdrolOKtc Eventt. Selected
Hater Quality Trends, and Ground-Hater Reaource*.. U.S.
Geological Survey Hater Supply Paper 2275.
"Indication* of Ground-Hater Influence* on Nutrient Transport
Through Schwatka Lake. Yukon Territory," Hater Resource* Bulletin.
.1982, 18(2): 197 - 203..
pp.224-226
pp.227-228
p. 229
pp.230-232
-------
i!!1! linn 'i!!!!!!1:1)1:1! iiiiiiiiiiiiiio1"1!: I'liiiiiiiggngiiiiii;;:;;!!1«' i iniig ;nfi VCTWWW w inwi nnr WEHM1# f, ,^WWIE?I i!: iiiii'i'f'ii" I'liiini' in11"'!'' iii'iiiS! r1 . !iiiii!i!i; in ifi • riiiiinnn11'' "' "'in ii'" -', :;;•'' ;.<'i: ,< i^: :I: ii'!1'!''" n;; 'iiiii, i;:,,, ''. ,','., n ••' , ,1 , • s , i '••„.:,• 1|:,'L jMW'iiiii: J!'".; , ' '/''.'i;
C. Studies involving geophysical techniques to estimate ground-water
discharge to surface vater
papers cited in this section are summarized in Section II of "An
Annotated Bibliography of the Literature Addressing Nonpoint Source
Contaminated Ground-Water Discharge to Surface Water," September 1990, EPA
440/6-90-006. . .
i. General description of method
a. Description of method or procedure
Ground water discharging to surface water is controlled by the hydraulic
properties of the sediments of the surface-water body and the hydraulic
gradient across those sediments. The sediment hydraulic properties of large .
water bodies, such as the Great Lakes or the Chesapeake Bay, are difficult to
measure due to the depth of the sediments in open water, Standard methods of '
drilling and sediment sampling become slow and costly endeavors in deep
aquatic. . environments . Less costly shipboard geophysical -systems offer a
method that continuously characterizes bottom sediments along the ship's
track. Combining seismic and electrical geophysical measurements provides
data to estimate sediment ' type , thickness, and sequence, as well as relative
vertical hydraulic conductivity. Based on this information, one can calculate
the volume of ground water discharging to surface water.
Geophysical methods have primarily been applied to lakebeds. Bradbury
and Taylor (l9"8~45 'collected' geophysical data at an offshore site in Lake
Michigan with sediment thicknesses ranging from 0.3 to 37 m and water depths
from 2.5 to' 27m. Otherinvestigators have used geophysical techniques in
smaller lakes and in channels connecting the Great Lakes .(see Btadbury and
Taylor, 1984; Cherkauer and Taylor, 1987; Lee,1989, and Taylor and Cherkauer.,
1984). Zektser and Bergelson (1989) have used continuous measurements of
temperature and electricconductivity and continuous seismoacoustic profiling
to detect temperature and salinity anomalies in Lake-Issyk-Kul in the -
southeastern USSR.' One major difficulty associated with geophysical
techniques is the need for field tests to verify the results. Field
verification can be. difficult to obtain in- deep water. ; '
Seismic . . . • '
t
Seismic exploration involves generating seismic waves arid measuring the
time required for the wavesto travel to a series of receiving devices called
geophones. In seismic studies of large, surface-water bodies, a shipboard
seismic profiling system can generate and receive the seismic waves. Seismic
gWes ge'ifg'r'ate'd on board the ship travel downward through the lake bottom
sediment'untilthey reflect off a hard surface and back up through the
sediment to the "ship's geophones. Information on sediment type, thickness,
and sequence can be inferred through interpretation of the travel'times, of the
seismic waves(Taylor and Cherkauer, 1984).
32
-------
Induced Pot?pttal or Electrical Charge
This method involves charging the. sediment with a current, shutting off
the power source, and measuring the rate of current decay. An electrical
array towed behind the boat charges bottom sediments and measures the rate of
current decay. . The relative clay content of bottom sediments can be
determined using this method. These determinations are then used to estimate
the vertical hydraulic conductivity of the sediment. Taylor and Cherkauer
(1984) describe the equations characterizing the use of electrical
conductivity and seismic readings used to estimate seepage (see Section
C.i.d). , .'
Resistivity ' . ... ' . .
Resistivity methods also employ an artificial source of current which
enters the subsurface through point-electrodes. Receiving electrodes, measure
the potentials of the electric flow field, which are influenced by the
composition of the subsurface materials. An electrical array of source and
receiving electrodes towed behind a boat (see Figure 2-7) measures the
resistivity of an induced electrical field in the sediments. -Sediment type, ,
thickness, and sequence affect the configuration of the induced electrical
field. Investigators infer the effective longitudinal conductance of the
bottom sediments through interpretation of the resistivity "of the induced
electrical field.. The effective longitudinal conductance, combined with
sediment thickness information from seismic techniques and clay content
estimates from electrical/resistivity techniques, provides data used to
determine the effective vertical hydraulic conductivity of the sediment
sequence. The effective vertical hydraulic conductivity, the hydraulic
gradient over the sediment sequence (the change in hydraulic head over
distance, measured at various points over a large area or assumed constant
over the study area), and surface area of the water body bottom provide data
to assess the likelihood and quantity of ground water discharging to surface
water (Cherkauer and 'Taylor, 1984).
Temperature and Electrical Conductance ;
Another indirect method for locating ground-water discharge areas
involves measuring temperature and bulk electrical conductance. A sediment
probe with temperature and electrical conductance sensors is towed behind a
'boat along, the bottom of a surface water body. From the-continuous record of.
temperature and conductance, anomalies in temperature and bulk electrical
conductance are located. These anomalies indicate the likelihood of ground-
water inflow. Knowledge of the sediment.type, water depth, and other geologic
or hydrologic information 'concerning the nature of the possible discharge area
may be needed for data interpretation, Investigators may,correlate measured
temperatures and conductivities with other techniques to better characterize
the nature of sediment anomalies (Lee, 1989).
33
-------
Figure 2-7
lirillLiii111, r
S.qna, '•
f*
Block dicgrcrs. of i electriccl
.'In'iiei'd";
Tjtvl,or, Robert W. , and Douglas- S. Cherkauer, "The Application of
Combined'Seismic and Electrical Measurements to the Determination of the
Hydraulic conductivity of a Lake Bed," Cround^Water Monitoring Review, 1984,
Volume 4(4): p. 80.
3A
-------
b.- Assumptions involved in using these models
geismjg
«== ™ -
seismic waves. If the "^^ace the seismic wave may be sufficiently
. 1984) .
bot-:^:^^W^sr^
' gradient is often assumed for the entire body. . .
'" F.I metrical Charge ?T1H ***! stlvitV . • ; _
eal- Conductance
water discharge to the surface-water body (Lee, 198-5).
c Limitations of the methods
35.
-------
• •liiiilillilllilli11 iini ( ii ill in MM i i, MI ,
, ,1 ,:
ana"
lytical results derived from these techniques.
Representative equations
of
S -
where:
Longitudinal electrical conductance .[1/MLT]
Thickness of layer ML]
Electrical resistivity, of layer i [1/MLT].
s -
bl - Thickness of layer
l
nil iiiiiii i in IP i i in
.
(Gherkauer and Taylor):
Kv - (C0bT)/S
where:
y - ' Effective vertical hydraulic conductivity [L/T]
Cv - Total thickness of sediment sequence [L]
ST " . Longitudinal electrical conductance [1/MLT]
c - Scaling factor [1/MLT2].
, Law is as follows:
I, Q - K.dh/dlA
nun in i inn i n in n n mi mi
where:
Grbuhd-water discharge rate [L3/T]
Effective vertical hydraulic conductivity [L/T]
- Hydraulic gradient across the sediment sequence [L/L]
36
ikiV;:,*.!1? i;ii.f':(i:i:i!;^:v:;;^ •'••.•:•/
, llflj||ln!j I i ii Ilin "I11,, ,':!|,il|.' - •!' i • Jl ii, An Kjllj j, '"ll™1 ,'<';,' ' < " i" "' .11'I Vlu! I ll«i '' A III '» i! i 1 |l,
-------
A - Area on bottom of surface-water body with similar-
effective vertical hydraulic conductivity [L2] .
e. Description of field, equipment
These methods usually require a boat, and sometimes a sizeable ship, to
contain and deploy the geophysical instruments and support equipment used to
characterize bottom sediments . Shipboard seismic instrumentation, used to
determine sediment thickness, consists of a high resolution sounder and
rlcoSE? Electrical resistivity and chargeability equipment used to
determine the electrical longitudinal conductance and clay content of a
sedi^nt sequence consists of a long -Iticonductor <^%^f £*' S™~
and/receivine electrodes. The cable is .towed behind the ship. A Lor an
navigation system determines . the location of the ship's position for each
^1 urement ^ A computer stores the position and •-«««•£< f ^ ^
assist in the interpretation of the data (Taylor and Cherkauer, 1984).
.-' ' f. Expertise needed to. apply the methods
The papers reviewed for this report suggest that geophysical methods
require considerable expertise. Prior experience helps., one to properly
coSigure the instruction, conduct .the tests, and interpret the results^
Also because a large boat must be used to house the geophysical system, these.
methods require navigational and piloting skills. , For a more complete
dlsduslion of the expertise required to appLy geophysical methods readers are
re?er«d ?o Taylor and Cherkauer (1984) .Bradbury and Taylor (1989), Cherkauer
and Taylor, and Lee (1985, 1989) . , , _
it. Data inputs for the method
The geophysically determined effective hydraulic conductivity °
' e uanti of
e geop
sediments fs estimated for use with Darcy's Law to determine the quan
ground water discharging to a surface-water body. Addi ^al input data
include a representative vertical hydraulic gradient for the .entire surface
water body and the area of the bottom of the Surface-water body.
, When bottom sediment temperatures and conductivities are used to predict
-ground- water 'discharge .areas to surface water, one^known source^of g«und .
water seepage aids in calibrating the equipment. This- technique is limited to.
general information^ about potential ground-water seepage .zones.
iii . Outputs from the method
" ' .a. Ground-water quantity discharge to surface water ..
- •• Geophysical methods estimate essentially any amount ' °J
Taylor, 1984). .
"• : 37
-------
•'I
b. Ground-water quality discharge to, surface water
techniques ......... do ..... not' ......... Determine "'growid-water ...... quality, but.
presence of
--
; • x;. ••• ' :•; •;/; • ; ', ;. ;;; ; •: • > • ,,= ;. j i ' -ft "f. ;« ..... ,• < , : ' f y > >. ,: "i; M r si ..... .is- * v-j; ;:,; ,j* ft „
£n ^i£li • the ' ,iethod has" been" applied
used.
Table C-l summarizes some of the locations where this method has been
Contaminants that have been measured using the method
measurement. • • .
vi General evaluation of the method
5^^^^^^^r^r^r^^:«=s: »£
(described in Section A o£ this chapter) .provide > ^^ recharge zones
SJ^ss: ss: » ssSLiTSi - ^ - "«^* Z°MS • -£«e-»""
quality can be better protected. .
vii. References to annotated bibliography
References to the accompanying annotated bibliography are provided in
Table C-2. " , - . ' . •
. 38
-------
Table C-l. Suomary of Setting* in
Which the Method Ba. Been Applied and the Contalnant. Measured.
Ontario
Green Bay, Mi
Detroit Metropolitan
Area, HI
Mequon/MI
Great Lakes
Hardwlck and Mew
Braintree,- MA
Dover, NJ
Chalk River
Nuclear - Laboratories,
Ontario
Southeastern
U.S.S.R.
Shallow glacial,
glacial bedrock
interface, bedrock
units
Contaminant
organic solvents
Author
D. R. Lee, S. J. Welch
K. R. Bradbury, . •
R. H. Taylor
D. S. Cherkauer,
R. H. Taylor
D. S. Cherkauer,
B. Zvibletnan
EPA Non Point
Source Group
H. H. Lajpham
D. R. Lee
.• I. S. Zek»ter
G. M. Bergelton
-------
II
i« -I Illl ! II!
111 •ban i i i I • i •• =
C 2. K«tur*M«u« to AamtUt*!
• iilii!! i!
H l!!l!l! i!
- r ": ' = "i l»ISft= -"
Ati'Utor
Citation
Ret«r«ic« to
Mi »
K. R Bradbury
R. H. Taylor
U. S. Churkaiiui
R. H. Taylor
U. S. Cherkauer
B. Zvibleraan
EPA Hon Point Source
Work Group
H. H.
D. R. Lee
R. M. Taylor
D. S. Cherkauer
I. S. Zekster
"Determination of llydrogaolojlc Ptoportles of
Lakebtds Uilng Offshore Geophysical Surveys,"
Ground Hater. 198* Volume 22(6): 690-695".
"G«opliyslcally Determined Ground Hater Flow Into
the Channels Connecting Lakes Huron and Erie."
Proceedings of the Second National Outdoor Action
Conference on Aquifer Restoration. Ground Hater
(tonltorlnn and Geophysical HethpcU, Volume 2.
Presented by the Association of Ground Hater
Scientists and Engineers and EPA/EHSL - Las Vegas.
pp. 779-799.
"Hydraulic Connection between Lake Michigan and a
Shallow Ground-Hater Aquifer." GroundJIater, 1981,
Volume 19(4): 376-381.
"Upper Great Lakes Connecting Channel Study, Haste
Disposal Sites and Potential Ground Hater Contamination
St. Clalr River," Hon Point Source Work Group Report,
April, 1988.
"Use of Temperature Profiles beneath Streams to Determine
Rates of Vertical Ground-Hater Flow and Vertical Hydraulic
Conductivity," Draft Hater Supply Paper No. 2337.
"Method for Locating Sediment Anomalies-in Lakebeda that
that can be caused by Ground-Hater Flow," Journal of
Hydrology. 1985. 79: 187-193.
"The Application of Combined Sei.smlc. and Electrical Measurements
to the Determination of the Hydraulic Conductivity of a Lake Bed,
Ground-Hater Monitorinn Review. 198*. Volume *(*): 78-85.
"Effect of Ground Hater on Lake Hater Quality." Hater'Quality
B..1I.H.. 1r.n...ry. 1OBQ pp in-1"i __ :
74-75
pp.76-78
pp.79-80
pp.81-85
pp.86-87
pp.88-89
pp.92-93
pp.94-95
-------
D Studies involving hydrograph separation, regression analysis, or mass
balance approaches to estimate the contribution of ground water to
istream flow
The papers cited in this section are summarized in Section III of .''An
Annotated Bibliography of the Literature Addressing Nonpoint Source ;
Contaminated Ground-Water Discharge to Surface Water," September, .1990, EPA
440/6-90-006. " . r . , : : .
/' ••-,"-''• . " - -
i. General description of method ,
a. Description of method or procedures
The methods discussed in this section have been applied by investigators
in areas throughout the U.S., in Ontario, Canada, and in the United Kingdom.
Hydrograph separation has been used in conjunction with graphical techniques
to estimate the distribution of ground-water flux to areas of the Great
Lakes 6 Other, investigators have used analysis of conservative tracers along
with hydrograph separation data to estimate ground-water flux ;and contaminant
'loading The regression analysis and soil moisture balance methods rely on
equations developed for specific regions. Arihood and Glatfelter (1986) have
developed regression equations for northern Indiana, while Beyans's (1986)
work was in eastern Kansas. Wilson and Ligon (1979) applied a water balance
model to the Piedmont and Sandhill Regions of South Carolina.
Hvdrograph Separation ' • ' , ,
Precipitation entering a watershed travels to a stream by three main
routes: surface runoff, interflow (or subsurface storm flow), and ground-
water flow. The amount of water contributed to the stream by. each of the
three processes is reflected in the shape of the stream hydrograph, a graph of
stream discharge at a particular point in the watershed versus time. The
hydrograph for a single, short duration precipitation event, occurring over
the entire watershed, follows a general pattern (see Figure 2-8). The
• hydrograph shows a period of increasing stage, or increasing discharge, known
as the rising limb, that culminates in a peak or crest. Following the" peak
discharge, the hydrograph shows a period of decreasing discharge, referred to
as the recession limb. Hydrograph separation techniques are applied to the
recession limb to estimate contributions to stream flow from surface runoff,
'interflow,.and ground-water flow. .
When the hydrograph is plotted on semilogarithmic graph paper (discharge-
on the semilogarithmic y-axis), the recession limb has three identifiable line
segments of different slopes, (see Figure 2-9). The slope of the line segment
immediately after the peak discharge is the steepest and represents
contribution to stream flow as a result of surface runoff and subsurface
-6 Pranckevicius, Pranas, personal communication, Nonpoint Source
Contaminated Ground-water Discharge to Surface Water Workshop, Chicago, IL,
November 30, 1989. ' . '"_••'-
-------
11 111
111
„ ,, ';:::::':. ;'„, ;:H
Figure 2-8
in/ill, i '
-------
Figure 2-9
•otot runoff
Surface runoff plus
subsurface runoff
Surface runoff
f -.1 I
^•Grounawoter runoff
Subsurface runoff
i \ i \
28 29 30 31 I 23 4 5676
August -Septemotr, 1951 .
Senaiibgarithmic plotting of a hydrograph, showing separation of runoff com-
ponents. (Panther Creek at El Paso, Ulinoia.)
Chow/ V.< (ed.-) --^QAA^
Of Applied Hydrology. New York: McGraw-
'•••Hill.
-------
runoff, which includes interflow and ground-water storage depletion. When
surface runoff storage is depleted, the slope of the recession limb flattens.
This portion of the recession limb represents contribution to stream flow as a
resultof interflow and ground-water storage depletion. The slope of the
recession limb of the hydrograph changes again when interflow storage is
depleted and contribution to stream flow is a result of ground-water storage
depletiononly. The ground-water contribution to stream flow is referred to
as baseflow (see Figure 2-8). Surface runoff and interflow are often combined
and'referred to as direct ruhoff. The slope of the final segment of the
recession limb is the ground-water recession constant, K^, for the watershed.
The line segment representing baseflow is extended back in time to a point
under the hydrograph" peak to determine maximum ground-water discharge to the
stream as a result of the precipitation event. The ground-water recession
constant for a watershed and the maximum ground-water discharge rate are used
^n an" empirical formula to estimate ground-water discharge to surface water at
any time after a precipitation event.
0/Brien (1980) has developed a "dynamic method" of hydrograph .separation
, which matches"the hydrograph of an index well with the stream hydrograph to
•determine the moment of maximum ground-water discharge for two small wetland-
controlledbasins in Massachusetts, the advantage of the method is that it is
not rigidly tiedtoground-water stage, and it accommodates variations in
ground-water inflow and loss.in channel storage in response to temperature,
vegetation, stream stage, and change in seasons,, causing shrinking and • .
swelling of the peat and muck in'the wetlands.
Regression Analysis
Equations developed with regression techniques that relate basin
characteristics to baseflow characteristics in gaged streams can be used to
estimate baseflow in ungaged streams. Examples of basin characteristics used
£n the regression"'analysisinclude drainage area of the watershed and flow
duration ratio. The flow' duration for .a stream at a given point in the
vaters'hed is the proportion of time that discharge is less than a specific
dl'scH'arge value. Flow duration is commonly expressed as a curve representing
the percent of 'time discharge is less than an indicated value versus discharge
pf afff gf Che watershed, (see Figure 2-10'). The flow duration ratio is the
20-percent flow duration divided by the 90-percent flow duration.. The
drainage areas of the watersheds and the flow duration ratios are transformed
gp logarithmic units and a regression equation is developed by backward
elimination and maximum R2 improvement procedures. For more information on
-™»^S"aSIisli see'Trl^ooafana Glatfelter (1986) and Bevans (1985).
' Moisture Balance
The ground-water discharge component to a stream can also be estimated
using a soil moisture mass balance approach, where inflow-(precipitation)
equals outflow (baseflow). Soil moisture water balance methods for a
watershed assume that any excess soil moisture below the root zone ultimately
will contribute to baseflow. The soil characteristics of the major soil types
within the watershed are used tq estimate thewater-holding capacity of the
different soil types. Excess soil moisture content below the root zone is
44
-------
Figure 2-10
2
3
50
10
5
i i
<
•
. Maaragua R. at y _-
Maaragua* 138 sq mil./ ~-
•01 ' 52~~i5 10 20 40 60 80 90 95 99
- Percent of time the flow is less than the indicated value
Flow duration curves for the River Maaragua in
humid, centrai Kenya (mean annuai rainfall 60 inchesrand
for the Uaso (River) Nviro in semi-arid, north-central Kenya
(mean annuai Tamfail 3*5 inches). Toe dasned lines indicate
the flow values betow which discharge declines for 10 percent
of the time. The curves were constructed from records for the
period 1956-1970.
' Dunne, T. and L. Leopold. (1978) Uacer i'n Environmental Planning. San
•Francisco: W.H. Freetaan and Co. _•'••; . ,
-------
Ill III III III III 111 11 III I III IIII III I III 11 I III III
predicted1 using precipitation data, the evapotranspiration rate, and estimates
'! of surface runoff for the watershed. The watershed is divided into two zones
based on a predetermined depth toground water from land surface. In the zone
where depth to water from land.surface is less than the predetermined depth,
excess soil moisture below the root zone is assumed to discharge immediately
.".co the stream. In the zone where depth to water is greater than the
i;!S^r''* ::''i:pr^tfetenKne"d depth, excess soil moisture below the root.zone is assumed to
discharge to the stream.in uniform increments, based on the time between •
'^r^c'ipieatioh! events. For more information on soil moisture balance methods,
see Wilson and Ligon (1979).
b. Assumptions involved in using these methods
Hvdrograoh Separation '
Use of hydrograph separation techniques assumes that precipitation
entering a watershed is evenly distributed and o.f the same intensity for the
duration of the storm. Additionally, hydrograph separation techniques assume
cfiicthe semilogarithmic plot of the recession limb of the stream hydrograph
will have three identifiable' segments""of different slopes.
Regression Analysis
An important assumption when usingregression equations to predict
baseflow in unaged streams is that the basin- characteristics used in the
regression analysis are similar to basin characteristics of the unaged stream.
Basin characteristics of concern are (a) .the ground-water gradient, (b) the
direction of theground-water'gradient, (c) the topography of the watershed,
(d)theslopeof the stream channel, and (e) the length of overland flow.
Also the geologic material underlying the basin will influence the shape of
the stream hydrograph (Arihood and Glatfelter, 1986, and Bevans, 1986).
Soil Moisture.Balance
The soil moisture water balance model assumes t'fiat any excess soil
moisture below the root'zone ultimately contributes to baseflow. Excess soil
moisture below the root zone in the zone nearest the stream is assumed to
enter the stream immediately following a precipitation event. Excess soil
moisturebelow the root zone, in the zone farthest from the creek, is assumed
£6" IfeScii the stream."in uniform increments; based on" the time between
precipitation events. Additionally, when the water table.is below the root
zone it is assumed that no evapotranspiration occurs. Ground-water
boundaries are" aMumeV'cV'cVrreipond to "surf ace-water boundaries, and there _
are no losses of ground water to other watersheds (Wilson and Ligon, 1979).
c\ Limitations of the methods
Hvdroeraph Separation
In theory, it is straight forward to separate the recession limb of-a
stream hydrograph into thfie segmentsof different -slopes from which the
quantity of water contributed to the stream by surface runoff, interflow, and
ground-water flow can be determined. In practice, separating the recession
46
-------
of .«.. oiven Sat
arbT<7tnnCevents are not often o? constant intensity or evenly distributed
precipitation events are not t ical watershed,, this is not
and- considering the ^JJ"*™1^ ts o?bank storage will make separating
surprising Af^io5a^' ^orm hydro graph into three segments even more
method.
Regression Analysis
.
basef low redictions.
resulting in inaccurate basef low predictions.
.Mo if f"^e Balance
and
may be inaccurate.
" d. : Representative equations
•„
47
-------
N - A0-2
1 1 1 II I I
where :
• ! i.1,!*;,,,,. ', -I
N - Number of days after the peak when baseflow begins [dimensionless]
A - Watershed area in square miles. [L2].
the equation to determine , the quantity 'of ground water discharging to surface
water at any time after a precipitation event is: .
where:
n
K°
Ground-water flow at time t after the peak discharge'
.......... [L3/T] ' ' „*„, '
Ground- water flow at time t - 0 [L /T]
Ground-water recession constant (derived from the
........ • ........ ''•"" hydro graph)
Time [T] . • , ' • ' . '
Equations for regression analysis and soil moisture balaftce methods are not-
presented here, as the equations are region specific and not universally
applicable. Readers interested in these techniques are advised to read Wilson
and Ligon (1979), Arihood and Glatfelter -(1986) , and Bevans (1.986).
e.
Description of equipment needs
Stream stage data are obtained using a continuous-chart recorder.
Ideally the recorder should be located in a controlled section of the stream
channel so a stream stage/discharge relationship can be developed.
For water balance methods, topographic maps are used to determine'the
a"reaof a watershed. A rain gage can be used to measure precipitati9n; soil
maps are used to determine soil types and to estimate soil properties.
f. Expertise required to apply this method
The greatest difficulty in using this method is in selecting .the portion
Of the baseflow recession hydrograph to use in determining the ground-water
recession constant (Kr) for the watershed. Estimation, of Kr requires
knowledge of basin characteristics and the temporal distribution of
precipitation in the basin as well as considerable professional judgement.
bnce calculated, Kr can be used in the empirical ground-water discharge
formula to determine the quantity of ground water discharging to surface water
in a watershed as a result of a precipitation event.
I I I I Illll "I III II I III I III . V" .III. ". ...' L •• . ',' "'' -j. v-i '. ,_u'' «•
Computer programs, as well as PC-based spreadsheets, are available that
determine equations relating dependent and independent variables tM-micrh
regression analysis. The difficulty in using computer programs to^
the relationship of stream stage to basin characteristics is i
Vhich basin characteristics are appropriate input parameters.
It may be difficult to determine the area over which a regression equation is
I ' ,
' ' ' "; 48
111 ...... Ill illl
^^^ iilllll 111 i
llllllilillllll illllillillllllillii Iliililllillil 1 ll
lllll|i|||l||i|||lllillillilllililii T in
-------
applicable. As with hydrograph separation, this method is best utilized by a
hydrolqgist who is familiar with the subject basin.
• A significant level of effort may be required to use soil moisture
balance models to predict baseflow in a watershed. The upper and lower
watershed zones must be delineated based on estimates of depth to ground water
below land surface. Additionally, surface runoff and evapotranspiration rates
must be estimated for the watershed. Because of a-lack of representative
precipitation measurements, the precipitation entering a watershed often must
be: estimated from precipitation measurements.taken some distance, away. Again,
-familiarity with the hydrologic and geologic characteristics and the temporal
and spatial distribution of precipitation in the subject-basin as well as
surrounding basins.is highly recommended for the successful use of these
models. .
ii. Data inputs for the method
Hydrograph separation techniques requires continuous record of stream
stage or discharge to determine ground-water contribution to stream flow.
Continuous stream stage/discharge data are available for many watersheds .from
the United States Geological Survey. ' •
The drainage area of the watershed must be known to use regression
-equations to determine baseflow in an ungaged stream (Arihood and Glatfelter,
.1986).
Soil moisture balance models require the following data: precipitation
records, water-holding capacity of major soil classes in the watershed, area
of the watershed, and drainable porosity measurements (Wilson and Ligon,
' 1979).
iii. Outputs for the method
a.. Ground-water quantity discharge to surface1 water .
Essentially any quantity of ground-water discharge to surface water can
be predicted using hydrograph separation techniques. If the time.between
precipitation events is sufficiently long,, the predicted ground-water
discharge rate to surface water will decrease over time. The maximum ground-
water discharge rate to surface water will be a function of the length and
intensity of the precipitation event and the amount of ground water currently
stored in the watershed. ...'.;•'
As with hydrograph separation, any quantity of baseflow can be predicted
using, regression- equations and soil moisture water balance models.
b. Ground-water quality discharge to surface water
'Hydrograph ,separation, regression equations, and soil moisture water
.balance methods do not predict the quality of ground water discharging to
. '-' '. : 49 - ..'-••'
-------
surface water. Baseflow determinedusingthese methods can be used in
Conjunction with ground-water quality measurements obtained in wells located
^jicehtto the surface-water body to estimate the ground-water loading rate
to surface water.
iy. Settings in which the method has been applied
Some of the settings in which this method has been used are presented in
Table D-l.
v. Generalevaluation of the method
Hydrograph separation "techniques are an established method for
• estimating the ground-water discharge rate to surface water in a watershed.
The method is well understood, simple to apply, and continuous stream
stage/discharge data are readily available for many watersheds. The key to
' approximating actual ground-water discharge rates to surface water using this
method involves correctly determining the slope of the baseflow portion of the
I!,!! I'1!11',; ,' Secession" lin!b of; the fiyarograpH; Different slopes will produce markedly .
different predictions of ground-water contributions to .stream flow. •
' Baseflow in ungaged streaii:'c'in'1 bV'estimated'"u'sTng'regression.equations..
The equations are developed using regression analysis,, relating drainage basin
characteristicstobaseflow, at gaging stations located in the same region. ,
Because baseflow characteristics are dependent on the geology and geographic
location of a drainage basin, a regression equation developed using drainage
basincharacteristicsfromoneregionshould not be used to predict baseflow
of screams io'cate'S"outside that region. Therefore, accurate estimation of
bas'eHow In ungaged'" streams1" is dependent on the ability of the individual
applying the method to Identify regions having similar-basin characteristics.
Therein liesthe problem-basin characteristics that influence baseflow are a
result ofa combination of components,.some obvious, such as geographic
location, and some not so obvious, such as geology. .Additionally,, the degree
ofihteractibnbetweenthe components affecting baseflow in a drainage basin
is not well understood.' Therefore, the potential exists that regression
equations will be misapplied, resulting in inaccurate baseflow predictions.
Soil moisture balance techniques can be used to estimate baseflow in
unpaged watersheds. Because so many of the input parameters for the model
must be estimated, the error associated with baseflow predictions, made using
this method may be large.
vi. References to annotated'bibliography
References to the accompanying bibliography are summarized in'Table D-2.
50
' ' v'^kjj!:^ ".'. ..I;, •... , • ii jlilill
-------
Tablo U 1. S.«i,«ry of Sittings In HUUh Uio MotlHMl Uau Uum, Applied and the Contaminant. Mua.urod.
Location
Aquifer
Contaalnant
Author
Lincoln, Massachusetts
Northern and
Central Indiana
Upper Coastal Plain
of South Carolina;
North Carolina;
Georgia
United Kingdom
Eastern Kansas
Elliot :Lake, Ontario
Clayton County
Iowa
Clayton County
Iowa
Illinois
Quebec and Ontario
Cedar River Basin,
Iowa-Minnesota
Piedmont and
Sandhill Regions,
South Carolina
Upper Coastal
Plain Aquifer
Galena
Aquifer
Galena
•Aquifer
Cedar River
Basin
Sulfate; Coal
mine drainage
Pyrite, Accessory.
metals, Radlo-
nuclides
Herbicides,
Pesticides", Nitrate.*
and other agricultural
inorganics
Nitrate nitrogen;
Pesticide*
Herbicides
A. L. O'Brien
L. D. Arlhood, D. R. Glatfelter
H. R. Aucott, R. S. Meadows,
G. G. Patterson
M. D. Bako, Ayodela Owoade
Hugh E. Bavaria
D. H. Blowes, R. M. Gillhmm
G. R. Hallberg. R. D. Libra,
E. A. Bettis, III. B. E. Hoyer
R. D. Libra. G. R. Hallberg-
B. E. Hoyer, L. G. Johnson
Michael O'Hearn. James P. Glbb
M. G. Sklaih. R. H. Farvolden
P. J. Squillaca, E. M. Thurman
T. V. Hllson, J.'T. Llgon
-------
! lill! iii
°
- Tublu U .i. Rulai«wti.U'a to Aiuwtatud BII»U«nrai|Jn)r
• illII i!| Ml ! ' _
I 1
I !
I M!Pi ii*
AuUioc
"" - - t. 0. Arlhood, D. R. Glatfelter
M. R. Aucott, R. S. Meadows,
G. G. Patterson
H.D. Bako, Ayodele Owoade
H. E. Bevans
0. H. Blowes. R. H. Gillham
G. R. Hallberg. R. D. Libra,
E. A. Bettis. III., B. E. Hoyer
R. D. Libra, G. R. Hallberg,
B. E. Hoyer, L. G. Johnson
A. L- O'Brien
H. O'Hearn. J. .P. Glbb
H. A. Pettyjon, R. J. Manning
Citation
Reference to Annotated
Bibliography
"Method £or Estlnttinf Low-Flo« Ch«r«ctarl§tlci of
Uiisagad Stcaana In Indiana," U.S. Gaolofical Sucvay,
Op«n-Ftla Report 86-323. 1986.
"Raglonal Ground-Hatar Dlicharga to Larga Strain In
tho Uppar Coaatad Plain of South Carolina and GaorgU."
USGS Hatar Raaourca Invaatlgatlons Report 86-4332, 1987.
"Field Application of a Numerical Method for the Deviation
of Dataflow Racaaalon Constant," Hvdro.loRtcal Process. 1988,
2: 331-336.
"Estimating Stream-Aquifer Interactions In Coal Area»
of Eastern Kansai by u«lng Stremnflow Records," USGS
Hater Supply Paper 2290 (January, 1986).
"The Generation end Quality of Streamflow on Inactive
Uranium Tellings Hear Elliot Lake, Ontario," Journa}. of,
HydrolQKY. 1988, 97: 1-22.
"Hydrogeologlc and Hater .Quality Investigations In the Big
Spring Basin. Clayton County, Iowa," Iowa Geological Survey.
1984, Open-File Report 84-4.
"Agricultural Impacts on Ground-Hater Quality," proceedings of
the Aurlcultural I«pact» on Ground Hater. 1986, National Hat.r
Hell Association. Omaha, Nebraska, pp. 253-273.
"The Role of Ground Hater in Stream Discharges from Two Small
Hetland Controlled Basins In Eastern Massachusetts," Ground Hater.
1980. Volume 18(4): . ,
State Hater Survey Report Number 2*6. 1980 Illinois Institute of
Natural Resources.
"Preliminary Estimate of Regional Effective Ground Hater. Recharge
Rates, Related Streamflow and Hater Quality in Ohio," Hater Resources
Center, Preliminary Estimate of Regional Effective Ground Hatet
Recharge Rates in Ohio. Project Completion Report, 323 pp.. 1979.
l>p.97-9B
pp.99-101
pp.102-103
pp.104-105
pp.106-107,
pp.108-110
pp.111-112
pp.113-114
pp.115-116
pp.J17-119
-------
Tnlilu I) 2. Hutuioncua
Author
I.U Annotated Bllil lugraphy (Contlnuod)
P. J. Squillace, E. M. Ttiurman
t. V. Hilson, J. T. Ligon
Citation
"Surface-Hater Quality of the Cedar River Basin,
Iowa-Minnesota, Hlth Emphasis on the Occurrence and
Transport of Herbicides. May 198* through November
1985." U,S.G.S. Tonic Substances HvdroloKY ProKram.
Abstracts of Technical Heating. PHoenU. Arljtona.
Septimber 26-30, 1968.
"Prediction of Baseflow for Piedmont Watersheds,"
Office of Hater Research and Technology, Hater
Resources Research Institute. Report [lumber 80,
1979, 47 pp.
Refarcnc* to Annotated
pp:120-122
pp.123-125
I/I •
CJ
-------
E. Numeric*! models of surface-water/ground-water interactions
The papers cited in this section are summarized In Sections IV, V, and
VII of "An Annotated Bibliography of the Literature Addressing Nonpoint Source
Contaminated Ground-Water Discharge to Surface Water," September, 1990, .EPA
MO/6 -90 -006.
i. General description of methods
a. Description of method of procedure
................... : " MathematicaF ground-water ..... modelling' simulates ....... an ....... [aquifer or watershed
system using a series of equations governing flow and/or mass balance
nronerties When developing a model, transport properties should be
constructed using a framework of measured variables." Modelling represents a.
SSSSSv. procels of data gathering arid model verification to ensure an
Curate depiction of real world phenomena in the computer simulation Models
should not be used without field, data and ground truthing, and the transient
'conditions of the study locations should be understood and incorporated into •
the analysis. • .
Mathematical ground-water models consist of sets of differential
equations that describe or "govern" ground-water flow and/or contaminant
transport. These equations can be solved to develop an analytical solution
however field situations may be complex and difficult to solve exactly and
the assumptions that must be made to obtain the analytic solution are often
unrealistic arid are not representative of the flow or transport problem under
consideration. In these situations, numerical methods can be used to solve
the differential equations and obtain an approximate solution that can be used
to simulate relatively complex ground-water flow and contaminant transport.
^is process is presented in Figure 2-11. Two popular numerical methods used
Co convert differential equations into algebraic equations are the finite
difference method and the' finite element method. .
To utilize a numerical flow model, a flow system is defined and _
discretized- into a finite number of rectangular blocks, in-the case of finite-
difference models, or triangles or quadrilaterals, in the. case of finite-
element models. Figures 2-12 and 2-13, show finite difference and finite
element representations of an aquifer .bounded on three sides by an
-d o the fo "
eement represen .
boundary (i.e., no flow into or out of the aquifer) -d on the fo ""^ide by
a river into which discharge from the aquifer occurs. Each cell in the flow
reeion is ass'igtwMts' own hydrologic properties based on measurements or
Boundary «'»•«• then
obervations from the flow region being modeled Boundary «££'£»•
IScorporaTe'a Into the numerical model. Typical boundary conditions are
ground-water. divides (no flow), surface-water bodies (fixed head)^ and .
soecified flow. The numerical model is run on a computer, and typically, the
calculated head-'field 'distribution at nodal .points (the intersections of the
Unes delineating the region or centers of the blocks) is compared to the
actual head,field distribution (obtained through measurement of water levels
Swells) in the flow region and, if available, the results »f «£**£"£
Solution (see Figure 2-11). If the predicted and actual head fields are not
1 IfleSnt; 'the model is adjusted by manipulating boundary conditions
54
-------
Figure 2-11
| Set of differential
equations tmatnemaucal
model)
Calculus
tecriniques
Method of finite
differences or
nnite elements
Set of alzeonic
equations (discrete
model)
1
I Analytical solution
! i possible for a limited •
": numoer of casesi .
Compare if
pojsiole
Iterative metnoos
or '
direct metnods
Approximate soluuon
I
i
Compare
*
Compare
Reid'
observations
Relauonships between matneniaucai model, discrete algebraic model, analytical
solution, approximate soluuon. and field observauons.
Wang H.. and M. Anderson. noa^ Tnt-T^duecion to Ground water Modeling;'
Finice Difference and Finite El*mgnc Methods. San. Francisco: W.H. •
Freeman and Co., 237.p. , . - ,
55
-------
mam UBBNEW .a ^:' IB • w$ i nswr dura rt: MB *;t :#* rk-^Kiiw'^sr t. tfa i:i? jf.PftjsHR^i'H^vt.iK w"' i- &•: im"1 vi!air'iii t i;: iKwr
IIH liliis'. '''ii, i»vJp*'! 111*,]::!!!!* '!iii:S,! 'i ,il h(«l'i'1 '''1''! '::!'"..' V'1'^ "'";UJij^Wfr ':' '*"'.•>''L'"11' I!.!'"'•..':• iW(iif^rf •',Vjf.l.,4<','v-iii1. V^.'^'ilF,1'iiji'is?: -i 'WJ'i '
iiiiiili iiliiii'itiiiv'l E'SiilSF' i i i','" !!,!»„ ii i:iiiii,, i; 'I :''': liiiiiiiiiiilNii „ \ I i!!"! !," f::! iii! i' ;li; ,'s ,,'il in< i' 'in'!!, iiui 'iiiiiiiii'": LJ,," l,» ».' !!!•' i' >''' i I1' :,'',•!' I !„: ' ' i Ui'i ,i • >i it • ,„• „ I, ,i: ." l,;""'':;,..' i'lflt 4,!" •'"' ' 11 ' ' 'ii;ii i,.'!1 \ • i, (, iif'1';"1'! iw i'i', j'lHifiii ' Ii i»'' !i! t, " • ,'flii Ii::,,
;'i;| .•,' •>., :ii-!1 •
111 lllllll I II
111 111 I
(111 lllllll I ll
111 111
lllllll HI
! ur ,I
iiiiiii
iiiiiii
iiiiiii
• Figure 2-12
Finm diffn
ib)
• I • I •<••!• • I • i •'•*•* * ' * ' * •><
Js±±±ii±>: : : : : • ^
• V • •• • «•••• «••'••• • • • •
^TTjg^^^^m^^^^mM
i
:
* 5
. Mlllln'ili hl ' ' ' ' I:!' . ' '
Ftmte diffeitnet and fimut ewntnt repraeaaaota of an aauifer. repon.
' laT Mao view of aa«Jitr snowan *«J fteki, obietvaooa weite. ana boundanea.
ib» Fuusi
-------
Figure 2-13
1C)
id Finite diteenae ind w«h i
id) Finite eteoeat mesa «mh mtafnttr eieaenu where 6 is the uuiier thiekaen.
(Adaptea from Mercer ana Fmuit. J980e,»
Wang, H." and M. .Anderson. (1982) Incroduetion to Ground water ModelIrfg:
'.Finite -Difference and' .Finite Element Methods. San Francisco: W.H. .-
Freeman and Co. , 237 p'.
57
-------
ilIiiniiilllfflliaiflllllN Ill lI'IlliKJIilIliliniill IllllllilillVllfin inillllinil'IH • EBSCflNilEnu - :l!'l: I?1!!1 'I!'!!!|:::|":||'I:£.:"I>' "IT11 ':'',!" '!' I!1'
i ,! ',!i|'i,!iill!ii' „„'Ihi,!1
ill'llililllllllllllii ::' ' I'th.;,,1!!'!!!
and/or the hydroTogic'properties of the individual cells. When close
i1'ifglglgfigfi'e IS" reached fietveen predicted and actual head-field distribution-, the
"nioHel Is considered calibrated.
I, VH ,lf: 'S ; •', • 'lillllillllljl: "I!;!! I'mBSWIIIIInll'i;! 'MSii'l,,11
-------
Chemical inputs to the flow region as a result of agricultural or other
practices are assumed from generalized land use (Gburek et al., 1989)., The
input is assumed constant, with time for a given land use for all contaminant
source's within a study region. Instantaneous mixing is assumed to occur in
each cell for each time step. Additionally, in the random walk process .of
transport simulation, it is assumed that dispersion in porous media can be
considered a random process having a normal distribution.
c. Limitations of the models
The major limitation of numerical models is the large amount of data
required to accurately calibrate them. To accurately calibrate a numerical
model information on the spatial and temporal distribution of land use;
recharge, chemical input, hydraulic head, ground-water quality, and surface-
water quality is needed. Also of prime importance is the spatial distribution
of aquifer characteristics. Often, ground-water models do not take into
account- the variable effects of near shore phenomena. Generally, models will
not simulate ground-water quality changes associated with seasons, or reflect
the hydraulic conductivity changes associated with seepage face growth and
capillary response to precipitation. • .
Prior to using a model, the scale and the geographic conditions of the
study area must be incorporated into the model. For instance, fracture flow, .
macropore flow, karst terrain, and anthropomorphic effects on the study area's
ground water may require that adjustments be made to the model's structure,.
Few watersheds have been monitored sufficiently to provide the data needed to
calibrate a.numerical model. Knowledge about one watershed in a region will
assist in characterizing another watershed in the same region, but additional
data probably will be required before the model is considered calibrated and .
can be used for predictive purposes. Without being able to reproduce flow-
field conditions or chemical concentrations, little confidence can be placed
in a model's predictive capabilities. •
An additional limitation of numerical models results from the
uncertainty associated with them. This uncertainty is a result of numerical
models being based on mathematical expressions that are a simplification of.
' the real world and the measurement error associated with input data; This
uncertainty could result in predicted values that deviate'significantly from
the actual flow in the region being modeled. However, proper field data-
collection techniques and the use of well-tested models by experienced
personnel combine to produce reliable predictions in most cases.
d. Representative equations
.The partial-differential equation that describes time-variable .flow in a
heterogeneous, anisotropic two-dimensional aquifer (one in which hydraulic
conductivity varies both in direction and space throughout the aquifer) is:
a/SxdV Sh/8x) '+ a/8y(V 4h/5y) - Ss-6h/5t
'where": . ' \ "••''"
.- K, - Hydraulic conductivity in x direction [L/T] .
•• ; 59
-------
v - Hydraulic conductivity in y direction [L/T]
St - Specific storage [L"1]
h - Hydraulic head [L]
x - x direction [L]
y - y direction [L] ,
t - -Time [T]. .
ill i i i n in i ii ',,,"1,,, ,;, .Hi1 iir i '"Mi1 .•.:;-!•, siiH, ,:"..",:;• i' » :;, lif', 'Mt:,iii.i!iiiihi';i;:r '.; ''iivu,. KS i/^hji't^ u ;n •«": . H lur „" iv,1'1,' • '^~'' n" , *': '
A finite-difference numerical model approximates the above differential
equation using a series of finite-difference equations. The two-dimensional
finite-difference equation for a homogeneous, isotropic medium, where the grid
spacing* in the x- and y- directions are the same and hydraulic conductivity
is constant and isotropic throughout the aquifer (K, - Ky), is:.
where: .
h - Hydraulic head.[L]
T - Transmissivity [L2/T]'
S 1 storativity [dimerisionless] . • '
ti "; "- Time increment [T] -. '•',*•>'
x . width of the grid spacing, where »x ?-*y [L]
i J Column number [dimensionless]
"j _ , "ROW "number "•[dlmensionless] ' ^
k - Time step or iteration index [dimensionless].
Columnand row numbersinthis equation correspond to those in the finite
difference grid presented in Figure 2-14. Nodes (intersections of grids) are
spaced horizontally by *x and vertically by *y. For -the first ^ration or
solution of the equati6n, the modeler estimates the value for the hydraulic
Jeal it eich node The head values of the first iteration (k-1) are used to
calculate the head values for the second iteration (k-2) The equation is
Solvedseveraltimesinthis manner until the difference between the h«-d
values of the final iteration and. the previous iteration is less than a value
specified by the modeler, called a convergence criterion.
The partial-differential equation that describes solute transport in a
two-dimensional, homogeneous aquifer through dispersion and advection is:
- Vx-»c/8x.- »e/«t
dispersion advection
60
-------
Figure 2-14.
j
\
1
(1.
f
a
1)
.4)
(i- "i,j'i
L'-""
U-jijc —
M,;-i)
•(/./)
- •
/>n
•
(i-r I.;')
(5
•
Av'
I' :••
» •
.4)
: >
Finite difference grid showing index numisering convenuon.
Wang H. and M: Anderson. (1982) TnrrodurHon co Ground water 'Mode
"' ^d Tin!-. • ^ »m«r,r Methods.- San Franexsco: W.H.-
• Freeman, and Co. , 237 p..
• 61
-------
where: , ', ,
p^ - Longitudinal dispersion coefficient [L2/T]
Ot - Transverse dispersion coefficient [L2/T]
C - Concentration [M/L3]
V - Averageporevelocity in the x direction [L/T]
x* - /'^"dj-rectipn (direction offlow) [L] .
y - y direction [L]
t - Time [T].
Ill 111' I" I i 111 I i n in the random'walk approach, solute transport in a porous medium is
Illll ii|i " represented by a series" of •equations'^ Dissolved chemical constituents are
iIJII [' ' re'p'res'ented by a finite number of discrete' particles each having a mass
representing a fraction of the total mass of the chemical constituent involved
(Pricket et al.,1981).'The total distance a particle travels between time
steps is: . • ' •
dx - d + d* . ' . •
where: ' , •
dj - Total distance traveled per 'time step {LJ
d. _ •" Distance traveled as a result of advection per time .step [L]
d" - DTs*tance' traveTe'd* as 'a""result:"of dispersion per
time step [L].
The equation representing the distancea particle is transported by advection:
d - vt",
where:
d - Distance particle travels for each time- step [L]
•v - Ground-water flow velocity [L/T]
:.'=:-, v~:".'t: - Time step duration [T] . • ';
•After the particles have been moved advectively, the position of.each
-p-'greicle is adjusted a random amount in any direction to account for
aispersion. The one-dimensional equation representing the influence of
dispersion oh i" particle's position is:
rSii],; r.4* ..^'pjdi/v-t)*" ' .
where:
d* - . Distance traveled as a result of dispersion per
time step [L] ......................... • ................................ ,
........... ..................... ''''''1 .............................
iiiyi - ..................... •.Qrpund-water wlocity [L/T] ^ .(
t - Time step duration [T]
N - - A number between -6 and 6, drawn from a normal distribution
of numbers having a standard deviation of 1 and a mean of
zero [dimensionless] .
Hi i i i 1;
62
-------
The e'quacion determining individual cell concentration for each time step in a
two-dimensional.model is:
where:
Concentration per unit width of chemical constituent [M/L3]
Number of particles in a cell [4imensionless]
Mass per particle [M]
Cell length in x direction [L]
Cell length in y direction [L]
Column number [.dimensionless] , . -•
- Row number [dimensionless]. .
C
n
e.
Description of computer hardware or software needs
55
ars
•hardware includes:
a PC computer with math coprocessor chip and graphics card,
a high resolution monitor (for plotting results on the screen),
a printer, and
a plotter.
Numerous software packages, both in the private an^^ tranter"6
Some of
Lonnquist«, Trescott •« al.9, and the International Ground-Water Modeling
Center at Butler University -in Indiana. .-
7 vonikow -L and J. Bredehoeft.'(1978) Computer model of two-dimensional
solute ^ans^'r^and dispersion in ground water ^S-^^^^'
Techniques of Water Resources Investigations Book 7, Chapter C2, 90 p.
8 Prtckett T and C. Lonnquist. (1971) Selected digital computer
techniques for 'groundwater resource evaluation. Illinois State Water Survey
Bulletin 55, 62 p..-.
» Trescott, P., G. Pinder, and S; Larson. (1976) Finite-difference model
for aauifer simulation in two dimensions with results of numerical
fxperSents. U.S. Geological Survey Techniques of Water Resources
Investigations, Book 7, Chapter Cl, 116 p.
63
-------
f . Expertise needed to run the models
To adeauately simulate1 flow situations using numerical modeling
u ,T° S^^TlL! of
techniques knowledge of
, numerical methods, computer language, and
• these skilUi an intuitive sense, derived
determine if predicted
values are as expected and are correct.
ii. Data inputs for the models •
s for numerical models are the
required.
ill.' Outputs from the models
a. Ground-water quantity discharge to surface water
(cfs) have been simulated (Eddy and Doesburg,
"b. Ground-water quality discharge .to surface water
: Ae W4ch Quantity of ground'-water discharge to surface water, essentially
any conLntratirofVemiLls in both ground water and. surf ace water can be
simulated. •
ivl iettingV'in which the methods have been applied and contaminant
discharge that has been modeled
^ :': Y ^-dei :-'--an:" :'b'e'Calibrated to simulate
With enough information, a numerical m • enough input data,
-S P? S.S^S S^:2^rii Si»uX«ed. 8Con^iMnc
contaminants that have been transported
!!!!B^^^^
IlillilliiL'W^^^^^^^^^^^^^^ ' iii'll!':
IllllijilllllU l/illlllLliir:" , III ;llli'
llllllllIK^^ '!"
lilllilllllllllbul!;"' ihnllFlllli , II Ill1,,'
•i inpip, < i1. iiiiim M1 a]!,,,
, ,
64
;•'! '•«, ,3.:i'i , •• .'•' "iii
-------
v. General evaluation of the method _ .
Numerical models can be used to simulate various nonpoint source loading
scenarios for complex aquifer conditions. Before a numerical model can be
used for predictive purposes, however, a large amount of input data is often
required to properly calibrate the model. .The amount of data required will
depend.on the type'of model used, the objectives of the study, and the level
of accuracy required. Acquisition of the needed data can require considerable
time, expertise, and expense. Because of these constraints, the numerical
model may have limited usefulness in cases where data are scarce and funding
is limited. • . '. •
The numerical model's strength is its usefulness as a screening tool.
Numerical models calibrated to simulate watersheds in different'regions of the
country could be used to assess the general effect of various regulatory
scenarios on ground-water quality in those,watersheds located in those
•regions... • • . , • - - / • • • . -
vi. References to annotated bibliography
• References to the accompanying annotated bibliography are summarized in
Table E-2. ' . ' . • ' • ' V -.
65
-------
• III II-
i mi i i
- - : ] S I
ijjjj i . i
• i!l| 1 II
Ml
I II
I S « I: • I i i»
Wisconsin
Kent, Washington
Pennsylvania
Junaau, Alaska
Northwestern
Indiana
Central Sand Plain,
Wisconsin
Trinmera Rock
and CatskilL
Formations
HendenhalL Basin
Calumet
Aquifer
Organlca, chloroform and tri-
chloro«thyl«n«; zinc
Kitratas
Agricultural chemicals
D. S. Ch«rkau»t, B. R., U»n§«l
C. H. Eddy. J. H. Doaiburg
H. J. Gburak, R. R. Schnabal
S. T. Pott»r
D. I. Siagal
L. R. Hatson, J. M. Fanalaon
C. Zheng, K. R. Bradbury
M. P. Anderson
cr>
isj:
-------
Tufcle K-2. Kofureuces to Annotated Bibliography
Author
Citation
V. K. Barwell, D. R. Lee
D. S. Cherkauer. B. R. Hansel
V. T. Dubinchuk
C. M. Eddy, .J. M. Doesburg
W. J. Gburek. R. 'R. Schnabel
S. I. Potter
T. A. Prlckett, T. G. Nayroik
C. G. Lonnqulst
D. I. Siegel
1. R. Watson, J. M. Fenelson
C. Zheng. K. R. -Bradbury
M. P. Anderson
C. Zheng,: H. F. H«ng
' M. P. Anderson, K. R. Bradbury
"Determination of Horizontal-to-Vertical Hydraulic
Conductivity Ratios from Seepage Measurements on Lake
Beds." Hater Resources Research. 1981. 17: 565-570.
"Ground-Hater Flow into Lake Michigan from Wisconsin."
.Im.rn.l of Hydrology. 1986. Volume 64: 261-271.
"Radon and Radium Discharge to Surface Streams,".
Hater Resources. 1981, 8(1): 102-116, translated
from Vodnye Resursy. •
"Remedial Action Modeling Assessment Western Processing
Site. Kent, Washington." Report prepared for U.S.
Environmental Protection Agency, Region X. Seattle,
Washington 98101. July 1985.
"Modeling the Effect of the Shallow Weathered Fracture
Layer on Nitrate Transport." Unpublished Draft Report.
"A 'Random Walk* Solute Transport Model for Selected Ground
Quality Evaluations." Illinois State Water Survey,
Charapaiun. 1L. 1981. ISWS/BUL-65-81..
"The Recharge-Discharge Function of Wetlands near Juneau,
Alaska: Part I. Hydrogeological Investigations." Ground
Hater. 1988, 26(4).: *27-«<..
"Geohydrology of a Thin Water-Table Aquifer Adjacent to Lake
"Michigan/Northwestern Indiana/: (in press).
"Role of Interceptor Dilches-ln Limiting the Spread of
Contaminants in Ground Water," Ground Water. 1988,
Volume 26(6): 734-742.
"Analysis of Interceptor Ditches for Control of Ground Water
Pollution," Journal of Hydrology. 1988. 98: 67-81. '
Befarenca to Annotated
Bibliography
pp.173-174
pp.175-177 .
pp.178-179
pp.180-181
pp.182-184
pp.185-187
pp.188-189
pp.190-191
pp.192-193
pp.l»4,-196
-------
inn nil
i II I ill
F Studies involving the application of functions estimating nonpoint
source loading to surface water for various .land us.e types
i illii i HI (i
I! lil I Mil 1
Ill I,! ^e" Up1.???1 cfted" Jin 'this section "are summarized in Section VI of "An
Annotated Bibliography of the Literature Addressing Nonpoint Source
Contaminated Grofn^Witer^Dischargeto Surf ace 'Water," September, 1990, EPA
440/6-90-006. '. ' '"' ".
I. General description of method
a. Description of method or procedure •
Nonpoint source loading models combine surface runoff, sediment yield,
aTld ground-water discharge with empirical loading rates to obtain estimates of
nitrogen and phosphorous chemical.concentrations in surface water. Runoff in
the watershed is calculated from daily weather data using the U.S. Soil
donservatibn service's Curve Number Equation Sediment yje"alf "^a*ed .
using" the Universal Soil Loss Equation in conjunction with, the Richardson
daily rainfall erosivity index. Ground-water discharge is calculated from
daily waterbalances for the unsaeurated and saturated zones in a watershed or
by using hydrograph separation techniques. Loading rates for runoff, sediment
yield and ground-water discharge are assigned based on ..land use. Land use is
divided into residential, commercial, industrial, and agricultural categories
Agricultural land is further subdivided bksed on land use crop type and land
management practices. The land use loading rates for runoff, .sediment yield,
and ground-water discharge are summed and multiplied by. the total area of
similar land use in the watershed to obtain the empirical loading rate as a
result of that land use" category". The total nonpoint source loading rate for.
the drainage basin rate is obtained by summing the calculated loading rates
for each land use category (Haith andShoemaker,1987, and Ritter, 1986).
The estimation of ground-water" "discharge from functions is best used in
coniunction with verification methods such as mass arid water balance
ilcliites;ground-water monitoring, piezometer sampling, and seepage-meter
monitoring. Functions'have been used to estimate discharges- in inland
Satersheds in Pennsylvania (Gburek, et. .1.) and Wisconsin (Uttormark, et
•ml ) and in Inland Bays in Delaware (Ritter) and the Chesapeake Bay (Schnabel
and Gburek). Most of the studies utilizing this method have examined nutrient
loadings into surface waters. ;
b. Assumptions involved in using these models .
The inajor "assumption Of "'nonpoint To'ading models is' that the empirical .
loading rates assigned a land use category for runoff, sediment load and
ground-wateroTscharge are representative of actual loading conditions. The
Assigned runoff ,and ground-water discharge loading rates for a land us*
category areassumed independent of topography, soil type, or tillage methods
(Schnabel and"Gburfik, 1983). '
HJJI '"'I1,1! Another assumption 'is 'tna'r'tne transport process'is not scale dependent;
1 lhat is," the"' SSp'SrScal loidlng-rBSrCfor land use «"
-------
• . . c. Limitations of the methods
The ultimate purpose of loading models is to predict the impact various
land management schemes will have on Surface-water quality in a watershed
through use of empirical loading factors. Ideally, loading factors for
various land types, should only be representative of on-field processes, such
as tillage and fertilization practices. In reality, loading factors are a .
combination of on-field and off-field processes. Off-field processes such as
non-crop plant nutrient uptake, deposition of sediment in buffer strips near
streams in the watershed, and mixing of interflow and baseflow components of
'different chemical composition, are included in loading factors.
Additionally, loading factors make no distinction between, flowpaths,
effectively masking the processes which contribute to sediment and chemical
loss from a watershed. As a result, loading factors mask the interaction of
on- and off-field processes and cannot be adjusted to account for individual
changes in either on- and off-field management practices. Thus, as a
predictive tool, loading factors may have limited use.
There was significant uncertainty associated with the input parameters
for the model 'applications referenced in this review. Precipitation and
temperature data were, collected at one or two locations•in a watershed and
were assumed to be representative for the entire watershed (Haith and
Shoemaker 19S7). The shallow ground-water storage value and recession index
were assumed to represent the entire watershed even though several aquifers
• may discharge ground water to surface water. Because of these uncertainties
associated with input values to the model, predicted loading rates to surface
water may not be representative.
d. Representative equations
Ground-water discharge to a surface water is determined using a lumped
parameter water balance model based on daily water balances from the
unsaturated and shallow saturated zones (Haith and Shoemaker, 1987). The
equation describing ground-water discharge is as follows:
• Gt- St-r . : . • • _. ' ...
where: • . .' ' ' ' •
Gt - Ground-water discharge [L3/T] . •
St - Shallow saturated zone moisture content [L ]
r - Ground-water-recession constant, [1/T].
The loading rate to surface water as a result of ground-water discharge is:
LR - Gt-C . . •• . '
i •.-..-•' • ' : J.
where:• • • . . ' ' . -
' LR - Loading rate to surface water [M/T]
' Gt - Ground-water discharge rate to surface water [L /T]
' 'c - Concentration of chemical constituent in ground water
69
-------
"'"iKWiii'lia:.!1''!'!;!''!!1.*1111. IWI frM/l'/'iillOT^ iii 'I '' ,. ill 'I: , ' , ', , '' >, ' f I" T 'Infill!'! murti,"
e. Description of equipment needs
Equipment needed for the methodincludes
•
lllllllllllll
III Illllllll
rain gages", ........................... " ......... ...... ......... " ...... ..... '" .......... ........ "" .............. .' •'
:::; " ..... i:1",; ". continuous' -chart recorder,
Illllllll III • III I I I I I III II I III I II I . 'li"ii"J» ", MM I 111 I ...... II' " ...... !'|i,iii|iii':,' ........ II, V ........ in'l'i,"'! I.. ........... II 'I ..... '» , ''M ' ,, I*1! "i ..... "I ,!„: ,' ..... II' ,' ,: ...... HJIIIIU'I • • ' I , i. , i i1 "
soil maps, . .
v crop distribution maps, and
- land-use distribution maps.
A PC computer-based spreadsheet would be very useful to an application
of the method. ,
f. Expertise needed to use the method
A significant amount of effort 'is required to use this method. The
greatest iRel of effort is required to classify land into the various
. Stories which involves correlating, soil type distribution with land use .
and crop distribution in the watershed. Knowledge of relationships between
soil t^e Land use, and crop distribution within the watershed is usrful.
SSr Se'waSrshed'has been'sectioned into representative land-use categories
and the recession constant has been determined, the method becomes a
Sokkeeptng exercise. A computer spreadsheet can be utilized to multiply and
add the calculated values to estimate the loading rate to surface water.
ii, Data inputs for the model
The model requires data describing land use and soil type distribution
and daily precipitation. The ground-water recession constant can be estimated
using standard hydrograph separation techniques and stream gage data.
iii. Outputs from the model
The" method'' estimates' ..... the" loa ,
ground^ater discharge, sediment load, and surface runoff for various land
The method'' estimates' ..... the" loading rate, to ' surface water as "a result of
uses.
a.
Ground-water quantity discharge to surface water
"The amount of ground-water discharge to surface water predicted by this
method is Tfunction of the recession constant and the storage capacity of the
and thsta are
"-• vba«
small, the predicted discharge rate will be small; conversely, if both are
large, the predicted discharge rate will be large.
b. Ground-water quality discharge to surface water
The chemical constituents commonly modeled using this methor
nitrogen and phosphorous (Haith and Shoemaker, 1987) ThVCOM;n!"-t££ln|r
predicted in surface water using these methods are a function of the loading
70.
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-------
rates assigned to the various land types and land use distribution.
•'
iv. Settings in which the models have been applied and contaminants
that have been modeled
The settings and the contaminants that have been modeled, using this
method are summarized in Table F-l.
v. General evaluation of the method
The method has obvious appeal for many applications because information
concerning land use, soil type distribution, precipitation and temperature
data, and stream stage are readily available for iaost watersheds.
Additionally, the method is relatively easy to use. Once a computer spread.
sheet containing the required inputs has been established for a given
watershed, by inputting weather data, the loading rate to surface water can be
estimated. However, ultimately any model used for management decisions must
be able to predict future loading rates as a result of changes in management
practices. Because loading models rely on a multicomponent loading factor,
the effect of changing one component of the loading factor on surface-water
quality may be difficult to determine, making the models .le;ss suited for
..management applications. ' •
vi. References to annotated bibliography •
References to the accompanying annotated bibliography are 'summarized in
Table F-2.
71
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Table V 2. Kuforunces to Annotated Bibliography
Author
Citation
Reference to Annotated
Bibliography
W. J. Gburek, J. B. Urban
R. R. Schnabel
0. A. Haith, L. L. Shoemaker
"Nitrate Contamination of 'Ground Hater in an Upland
Pennsylvania Hatershed," Proceedings of the Agricultural
Impacts on Ground Mater, A Conference, Omaha, Nebraska,
August 11-13, 1986. pp. 352-380.
"Generalized Watershed Loading Functions for Stream Flow
Flow Nutrients," Hater Resources Bulletin. 1987, 23(3):
pp. 160-162
pp. 163-165
W F. HILLur
R. R. Schnabel. H. J. Gburek
P, 0. Uttormark, J. D. Chapln
. "Nutrient Budgets for the Inland. Bays," Report to Delaware
Department of Natural Resources and Environmental Control,
August, 1986. .
"Calibration of NFS Model Loading Factors," Journal of
Environmental Engineering. 1983.
"Estimating Nutrient Loading of Lakes from Non Point Sources,
Office of Research and Monitoring, 1974, Environmental
Protection Agency report number PA 660/3-74-020.
pp. 166-167
pp. 168- 169
pp. 170-171
-------
:]V^ ^PBSflHIlJ-iflB!If Si|.?f ^OTTOT1?-IB?;;i!'^f • • \;'i•* A';'.• •' • \ <' • •''•':;• •'' •':':!:;i:! -i;i:.,I• '•'W': II1 '••' 1?!
G.'='' ' Studies "us'ing environmental"'' Isotope" methods" to" estimate the' contribution
of ground water to stream flow
papers Sited in this section are summarized in Section XI of "An
«?KiLraphv of the Literature Addressing Nonpoint Source
gSSt:* Discharge to. Surface Water," September, 1990, EPA
440/6-90-006. , : .
i. General description of method
a Description of method or procedure
«opes . con-only used in ,
t. ,.„„,, is fiso^ deuterium (D or H) , ana tritium {i or n; .
Thlse^isTtope0* are all t ideal facers 'for runoff generation studies, due- to
These isotopes are aimos ^ T are constituent parts
KP principal characteristics Qi; sin , ^ L ^ ?he
are altered only by physical processes such as: mixing, diffusion,
dispersion, and radioactive decay.
Both "0 and D are stable isotopes which occur naturally, accounting for.
-
°^£ -SiE^^JS^^^-^^M^ -ef
are about 2000 and 320 ppm, respectively. T is a radiogenic isotope , of
gen whose half -life is in the order of 12.4 years^ T atoms represent an
of thermonuclear devices in 1952, T produced as a by-product of this testing .
has been the dominant source of T in precipitation.
The "tern" "hydrograph separation," discussed in section D of this report
IS OS ve JLU^CVA do ^*»» »•«*«.*-» «-— — * —
different flow paths and have different residence
times". • , .' :
74
iiiiiiiiiiii j i in in iiiiii i, .•
ii5^^^^^^^^^ lilllilHillll' II in Hi Illllililii ill lull I iilill ililHillllililliill ' !!• liaiil •
-------
•1
tracer- based
any' ^during ^Jf^le runoff event is a mixture of
« -new water," which is water from the current rain or snowmelt
"old wat"- which is the subsurface water which existed in the
catchment prior to the "current rain.
'
-old*- and -nlw"' water components are chemically or isotopically
t the stream water becomes "diluted- by the addition of the -new- .-
watr The extent of this dilution is a function of the relative
contributions 'from the -old" and "new" water components,
The precursor to using natural isotopes as tracers in the simple two-
concentrations. of most chemical parameters than -new water? .
• The major problem- associated with separating hydrographs on the basis of
-oS".f r- contribution since the -new' water- P^«J— ^^ ^iTSat of
solutes on its way to • the stream and its chemistry becomes more like that
the -old water". One can, however, derive some valuable information^
'
deposited particulates by overland flow.
During the I960- s, hydrologists began to use- the separation equations
with anthropogenically-produced radioisotopes.
b. Assumptions involved in using the method
- •- «
snowmelt hydrograph can be determined. .
75
-------
illlllllllllli I I 111 I I 1(11 II ill I 1111111
annual sinusoidal cycle with the most depleted values in the winter and the
least depleted values in the summer. Whether the "old" water del values are
constant or cyclical is controlled by the residence time of the "old" water
i, f^jf |fte ,difpee of dispersive flow in the watershed. The "old" water tritium
concentrations, in small watersheds generally show a gradual decrease with
Ctme, reflecting the progressively lower tritium concentrations in recent
(post-1963) precipitation and tritium decay.
The isotopic signature of the "new" water component provides the
,co:E^?:as5 n??ded for the isotopic separation. Although the general seasonal
Y^.Eif.'rlSB,?. In iS6, "9,,« PJ and. T. concentrations in precipitation and the
',,"«.«,,, '",;?,*£?£*?: i£n,I,*,H?,,51 decline in^ tritium levels are documented, it must be "
emphasized that there is no guarantee that the "new" water in an individual
!^^ Ili^^^f^^^r"^^ ..d-.Ipe."n^»-"?.,irh^e.'"?ld" Wer-
Fourassumptions govern the reliability of hydrograph separations using
environmental isotopes:
' • The "new" and "old" water component can be characterized by a
single isotopic value for each component or variations in each
3 Isotopic content can be documented.
• The isotopic content of the "old water" component is significantly
Illililll Ml I in I PI I ill I i I i different from that of the "new water" component.
P » ,','!'
• Vadose zone water contributions to the stream are negligible
. during the event or they must be accounted for (use an additional
tracer if isotopically different from ground water) .•
Surface waterstorage (channel storage, ponds, swamps, etc.)
contributions to the stream are negligible during the runoff
event.
76
r
iiiiiiiiii in in i i 11 i ill
Ulilllill (H (i Ili INI1 i Mill
cJ Limitations of the method ,
I'll. ',.i in.,.!, iiiii.li!!1;. if i; M, iiiniji.!! ef'tix liiiiiiiiiii11 :-i M* «';>!**; • sii ..:: ;' fS1;.*! ".i Kef,, »:;*»*: •I'j"-'!* i. '•«•••„ ... ' . ..';:::'. ;. • ": 'ii
One major assumption in using, environmental isotopes is that the
baseflow represents the "old" water component and the source of ground-water
flow to the stream during storm and snowmelt events is the same as the source
during baseflow conditions. However,, ephemeral springs remote from 'the. stream
""' "or'TC 'ground"-wafer flow sy'ste'as' may 'contribute differently during events
and if their isotopic signatures differ from that of baseflow, the assumed
^old water" isotopic value may be- incorrect. Although the occurrence of such
situations could be tested"by hydrometrie monitoring and isotopic analyses of
in mi Illililll MI i these features, qualification could be difficult.
ill1 ill in inii| in "i i iiiii i i1 i i- i in I, ,, i ' ".LI ',:, '•;;•' •' "'•' .: .,'. .• •.-.' " '• :»;.i* "i-\ •'**••'•
Catchments with significant surface storage cannot be accurately
characterized using isotope hydrograph separation methods. Isotopic
enrichment of surface water in lakes, ponds, and swamps by evaporation may
introduce complications in the simple two component model.
II III 111 III HIM IIIII IIII III III III IIII I II II I IIII III III III II Illililll IIIII II II I II ... .... !,',.* '. . :i . .LI .... .: '.I1 ».. "iT. III. '. . ',..
During some events, the "old" and "new" water isotopic contents may be
too similar for meaningful hydrograph separations. .Considering that
substantial time may be spent waiting for and then sampling an event and
Illililll II III 111 IIIIIIIIII I
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-------
considerable costs "may be incurred for isotopic analyses, it is prudent to
monitor an event using chemical tracers as well as isotope analysis. These
other methods may include: (1) testing for other independent isotopes such as
T rather, than, 180 if 180 is unsuitable and (2) testing for a conservative
chemical constituent, such as silica, or other less conservative parameters
such as electrical .conductivity.
Estimating the actual isotopic composition of the rainfall reaching the
ground surface is complicated in forested catchments because of the
interception loss (by evaporation) from the forest canopy during rainfall.
Evaporation from water, stored on the forest canopy typically occurs at rates
of 0.1-0.5 mm/hr and can account for the loss -of about 20X of the gross _
rainfall. Depending on the ambient relative humidity at the canopy level,
evaporation of 20X of the rainfall could substantially enrich the D or 180
composition of throughfall and net rainfall compared with that of the gross
rainfall usually measured and sampled. This is a po.tentially serious problem
. only when the. gross rainfall is isotopically lighter (more negative in delta
notation; equation [1] below) than the prestorm stream water. , .^
d. Representative, equations ,
' Since D and 180 concentrations in- natural waters .are much smaller than
their common light isotopes (:H and 160) , D and 180 concentrations are _
generally expressed in 'the conventional delta (8). notation as per mil (0/00) •
differences relative to the international. standard, SMOW:
5D or 5180 - (Rsamole - RSMOW) X 1000 [1]
RSMOW .
Analytical precision for 5D and 5180 by mass spectrometry is better than 2 and
0.2X, respectively, with a confidence level of 95Z.
Between storm events-, stream base flow reflects the isotopic composition
of the "old" (stored) water. During storm runoff events, however, the
isotopic character of the stream may be altered by the addition of "new" water
from rainfall^ The r old" and "new" .water contributions at any specified .time
can be calculated by solving the "mass balance equations for the water and
isotopic fluxes in the stream. These equations are expressed as:
' Q8 - Qo + Qn . . . -
C.Q. - C0Q0 +, CnQn ' • . - ;• [-3]-
Oo - CCs - Cn) x 0. - . [*] '
(Co - Cn)
where Q is discharge, C expresses tracer concentration, and the subscripts s,
o, and n. refer to the "stream, "old water," and "new water," respectively. The
utility of the mass balance equations for arty particular storm event is -
controlled mainly by the magnitude of (C0 - C^) relative to .the analytical
error and the recognition of areal and temporal variations in C0 and Cn. The
equations can also provide estimates of- "old" and "new" water percentage
contributions to' throughflow and overland flow. .
- ' ' .' . 77
o
-------
Environmental isotope data can also'used in estimating the areal extent
of overland flow contributing areas and in calculating mean residence time of
the "old" water in the catchment. Assuming that overland flow is generated
entirely as saturated overland flow, the overland flow contributing area is
estimated by the following equation:
Y -
•IS]
where Y is the discharge area expressed"-'as a fraction of the total basin area,
V is the total volume of "new water" which leaves the catchment and Vto is
the total volume of "new water" which falls on the catchment. The mean
residence time of the "old water" in a catchment can be estimated by comparing
the seasonal variations in del values for the precipitation and*h* |«*fflow
or by analyzing the tritium input (precipitation) and output (streamflow)
functions.
e. Description" of'" equipment'' 'heeds
III || II11 || I || Ililllll I Ml 111 " i ,11V" .in i "i": !' , | •: 'I" ii •»!' &, nih;' • u ;<;"" ;|i' iiru, a i, ,i;.,}; f, a•• i;:: |!<: :,:"•' r $ 1 y ar" h 'i y ;',, v, >.| ' „;: < •«; •:" || r I,'. i' i, "I, >...: ,: ; . ,,,!.• i • ' i • i, ', •' "i
in iiiwini ii in 1 1 iiiiiii i iii i ii iiiiiii Af. *;.;-'iv'.'?a^tMi; -i''-^^^'^'^!!!'^*^ ^'i\\.i"^^^^i'Mvi.\ii^ $yKfi.'i-w '•'••' •>••• j • '•>• • ' >•! •• '
Stage or precipitation activated time discrete automatic water samplers are
needed to ensure sampling at the start of an event, .especially for night-time
storms or for remote catchments. Snowmelt lysimeters are needed for sampling
snowmelt. To sample soil water, lysimeters are required. Ground-water samples
are obtained by installing piezometers. Measurements of streamflow from
catchments require weirs with stage recorders.
The concentration^ of "0 and D in" a water sample- are normally measured
using a doubleTcoIIectih-g mass spScCrofltoter which compares the concentration of
18o «r n in the water sample to a standard water. Water samples for T analysis
or D in the water sampl
are measured using a liquid scintillation counter.
f. Expertise required to apply this method
The method" requires knowledge "of basin characteristics and the .temporal
distributionof precipitation and runoff in the basin as weU as considerable
professional judgement.' Site water sampling requires a sufficient
understanding of regional geology and hydrology. •
ilw'rw ''
ii. Data inputs for the method
To determine the "old"'water isotopic value, the samples to be obtained^
« v-fincluoVthe following: ground water at various sites (shallow
soil mb'istiire'-ae1 "seveYal sites (shallow or deep), and
rier ..... stream ......... in ..... the catchment or baseflow in a larger order stream.
ost IsotopiE studies have used either ground water or baseflow to
Characterize the isotopic content of the "old" water. The isotopic value of
streak baseflow is- a good approximation of the isotopic -al-%of,Sround.water
' discharging into the stream. Soil moisture is also appropriate for the "old
water component in certain hydrologic environments.
i;,i ,'.' .ii iiiiiii .i*Hr«'.MHJiiMi»[*:Lffi'iii ..... ;.;' iii'i! ; j'''i ';(«:. iFyiiii ..... »iii:'ii::i":iw:;";iii:!iiiii<. ..... i ..... new ...... s. ..... i ..... -v -t, ...... ,1 ......... Kiiiimi1"!"' t ; • . " •• • • • '_*;.. in1 «.«'
simples are needed when conducting environmental isotope studies
runoff ; i.e., 'one must take as many time discrete samples
liS ;. . M"!,!, ,,; IHIIK I " I" :., "", "ii'ipf !"J". . J • •' !1"!' .I1,!;,1 -IfJ1 (nlf I a1"-;".™,!!>", '."If !,.,ll>'l
.78
. . lirK M';!!,!;
-------
of the precipitation (arid, snowmelt) and the stream as possible. Depending on
the nature of the study, sampling frequency may vary from minutes to day or
loneer depending on the size of the catchment, type of sampling equipment
type of event, and detail desired. Through flow, overland and macropore flow
sources can also be separated.using isotopic methods,
iii. Outputs for the method .
.a. Ground-water quantity discharge to surface water
Essentially any quantity of ground-water discharge - to surface water can
be estimated using isotopic tracer-based hydrograph separation techniques
Isotopes leave signatures of stored water (in the unsaturated and saturated
zones) that can be detected at the discharge points.. Environmental ^otope _
results can be used .to test whether integrated water quality models represent
catchment processes appropriately.
'••'' . b. Ground-water quality discharge to surface water .
Observed contaminant concentrations in surface water can be correlated
with the runoff components Indicated by the isotopic data. For example, if ;
stream flow is found to be dominated by "old" water during a precipitation .
event and observed contaminant concentrations rise above baseflow
' concentrations-, the increased contaminant levels may presumably arise from
subsurface .discharge.
iv. Settings in which the method .has been applied
Some of the settings assessed and the isotopes analyzed in _
representative studies are presented in Table G-l. The predominant conclus-ion
from these studies is that "old" water components normally dominate storm and
snowmelt runoff in humid, headwater catchments. These studies demonstrate how
isotope tracer studies.can improve the characterization of runoff processes
beyond those findings based upon hydrometric and/or hydrochemical data,.
v.
General evaluation of the method
Because isotopic tracers are constituent parts of natural water . _
molecules, they can be used as excellent tracers -of water origin and.movement^
The long term and widespread application of these tracers analyses, will allow
researcLrs to study runoff generation on. scales ranging from »a«°P°5" |°
portions of catchment slopes to first and higher order streams (Sklash 1990).
Several disadvantages may arise, in the use of isotopic tracers, however.
Conditions for thai* use are not met in every event, arid sample «£y™ £
expensive In some catchments, the isotopic content of "old" and "new waters
is not distinguishable in the snowmelt, and variability in the "new water"
isotopic component may decrease the precision of the separation.
79
-------
in in i i in PHI i ill 11 in
vi. References to annotated bibliography
^^ — ^ ^' o;anin annocated bibliography are provided in Table
G-2.
Ill I mi
80
-------
C 1. Suowary of Settings In Milch the Method Uaa Been Applied and the laotopea Heanured
Location
Catclunenl Size (km2)
Isotope
180 D
Author(s)
1 France
2*
E. Crouiet,
P. Hubert, -
P. Ollv., .
E. Sluertz.
A. Horc« (1970)
United Kingdom
1.0
D.S. Blegln (1971)
Mother lands
Canada
650 ha
JO. 5. >.24, 1.76
H.G. Hook. .
O.J. Groanvald
A.E. Bouwn,
A.J. Van Ganswyk (197*)
<, Canada 22, 1.6
5 Canada 73 to 700
6 Canada 1. 1.2. 3.9
* P. Fritz,
• ' J.A.1 Charry,
K.U. Heyer,
H.G. Sklash (1976) .
« H.G. Sfclash.
. R.N. Farvolden,
P. Fritz (1976)
* H.G. Sklash.
R.H. Farvoldan. (1976)
D.J. Bottomley,
0. Craig,
L.M. Johnston (198
-------
t
-------
G 1. S.«ai»ary of Setting lu Milcli th. MoU.od Uaa Boon Applied «nd the I.otope.. Ma.uured
U Location Catchment Size (km2) Isotope Author(s)
' T 180 . D . '
18 Canada ' • 368 * . *
19 Canada . .2.8 * • * ;
20 Sweden ' 4.0, 6.8 .
•21 Swuden . several '
22 . Canada . 10.5 . , *
23 Norway 41 ha . • , • .
,' :•
24 USA'. - *2'-2 . . . *
25 Canada .60 *
26 Canada 10.5 *
P.M. Schwartz (1980)
H.G. Sklash.
R.N. F«rvolden (1980)
A. Rodh* (1981)
A. Rodhe (1984) ,
D.J. Bottoraley, . .
D. Craig,
L.H.- Johnston (1984)
N. Christophersen,
S. Kjiernsrod,
'A. Rodhe (1985)
: R.P.- Hooper,
C.A. Shoemaker (1986),
H.H. Obradovic. .
H.G. Sklash (1986)
A.J. Bottoraley,
0. Craig.
L.M. Johnston (1986)
27
USA
J.R. Lawrence (1987)
-------
l!
=>= Author
Ill B ill
Mil!* I
Citation
Rafarttacv to
Annotated
I i ! Si
H. G. Sklash
M. G. Skiash,
I. D. Moore,
G. J. Burch
R. P. Hooper,
C. A. Shoemaker
P. Maloszewskl,
H. Rauert,
H. Stlchler. ,H. Herrmann
M. G. Sklash,
•R. H. Farvolden
"EnvlroiwwntaL Isotope Studies ot Storm and SnoMnelt
and Runoft Generation," In Surface and Subsurface Processes
in Hydrogeology, H. G. Anderson and T. P. Burt. (ad.).
Joint Hlley and Suns Ltd., Sussex, England. 73 p.-, 1990,
In print.
"Environmental Isotope Tracer Studies of Catchment Proceases:
Tools for Verifying Integrated Hater Quality Models," In: •
Proceedings of the USDA, AIRS-B1, pp. «,59-W. International
Symposium on Hater Quality Modeling of Agricultural Non-point
Sources.
"A Comparison of Chemical and Isotoplc Hydrograph Separation,"
Separation," Hater RasouiVes Research. 1986, pp. 1**4-1«5».
"Application of Flow Models in an Alpine Catchment Area Using
Tritium and Deuterium Data." Journal of Hydrology. 1983. 66:
319-330.
"The Role of Groundwater in Storm Runoff," Journal of Hydrology.
1979, O: *5-65.
p. 289
pp.2B5-286 ; , :
pp.287-288 -[•- '
-------
Chapter III
The Impact of Nonpoint Source Contaminated Ground-Water Discharge
to Surface Water in Water Quality-Limited Water Bodies:
Determining Total Maximum Daily Load and Waste Load Allocations
Introduction'
This chapter provides a general overview of the process for determining
the Total Maximum Daily Load (TMDL) for water quality-limited water bodies and
the allocation of point source waste loads and nonppint source- loads to
achieve the TMDL. . \ , ,
: As,used in-this, chapter, TMDLs are'defined as the assimilative capacity.
of a waterbody, which! is the sum of the individual Waste Load'Allocations
(WLAs) for point sources and Load-Allocations (LAs) for nonpoint sources and
natural background (see 40 CFR 130.2(h)), plus a safety factor. A Waste Load
Allocation is the portion of a receiving water's loading capacity that is
allocated to one of its existing.or future point sources of -pollution (see 40
CFR 130.2(g)). Similarly, Load Allocations (LAs) are the portions of a
receiving water's loading capacity.that is attributed either to one of its
existing or future nonpoint sources of pollution or to natural background
sources (see 40 CFR 130.2(f)).. In sum, the TMDL should encompass the
"contaminant waste loads from point sources and nonpoint sources. However, the
nonpoint source load allocation may be accounted for simply as a component of
background contaminant concentrations. This chapter provides a preliminary
discussion of the rationale for applying the methods described under 2 above
to better measure or estimate the nonpoint source component of the load
allocation under a TMDL. .
Under Section 319 of the Clean Water Act, by August 4, 1988 the States
were required to identify those water bodies that were not expected to attain
•or maintain their respective water quality standards due to point or nonpoint
source loads. In addition, the States were directed to develop a program to
alleviate these problems, by describing how they will utilize the TMDL process
to control nonpoint source pollution in accordance with Section 319 (b) (2)
(B) of the Clean Water Act. This Section calls for "an identification of
'programs to achieve implementation of the best management practices (BMPs) by
the categories, subcategories, and particular nonpoint sources designated
under subparagraph (A)." Subparagraph (A) requires an identification of the
BMPs and measures which will.be undertaken to reduce pollutant loadings
resulting from each category,, subcategory, or particular nonpoint source .
designated under Section 319 (a) (1) (B). Presently, this requirement is the
only regulatory tool available under the Clean Water Act to promote nonpoint
source controls. To date, the Agency has prepared a variety of guidance
documents and models to assist in determining TMDLs as part of the water
85
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quality-based permitting process. l This discussion specifically addresses
the manner in which nonpbint source loads may be accounted for in this
process.
The chapter is organized infour sections. Following this introduction,
Section 2 introduces the regulatory concepts and statutory authorities
theTMDL aidloadallocation processes. Section 2 also- provides a
sumfflary of the status of WIA applications and water quality-based permitting
Section 3 discusses the theory behind the TMDL process and the application of
3?VJ! wIS regard to estimating water quality impacts 'from biochemical oxygen
Demand, nutrients, and toxic substances and provides a limited overview of WIA
modeling approaches. Finally, Section 4 reviews .the applicability of the
lethods described in 2 to supply the data needed to assess nonpoint source
loads as part of a TMDL analysis.
A< Statutory and regulatory, mandate for determining WLAs and LAs under the
" TMDL process • •
"Rationale behind waste load alioc'ffclon and water-quality fcased
i-p-grmitting ' -.'•.-
. , . ,
303ofeCeat,-' IKS"States 'are required to set
!i"ty standard's ^at-protecl the "public -health or welfare, enhance the
ol wfcef; arid serve "the purposes of'the Act for all waters in the
These standards are based on water quality criteria developed by
U S EPA3 and are to guarantee the achievement of a designated use for the
water body. The State may not set a water body's designated use at^less than
fishable/swimmable without performing a use attainability analysis. •
Mill1 III' 111! ti
ill Ill
1 EPA is in the process of,preparing a series of nine Waste Load
Allocation guidance aScumetiits":" Several of those documents that are currently
SvaJiWe1 f?om the Monitoring and Data Support Division/U.S . EPA are cited in
this chapter.
. 2See aiso 48 £E 51400 for the regulations implementing the water
quality standard process.
water quality criteria are developed under Section 304(a) of the
ct; ""^ ^ Criteria for Water 1986.. published May 1987, is the
most recent EPA summary of water quality criteria.
III II III I I I III III I III I II III 111111 I II II I III I II I I II II11 I I III I I II I ' , >'
* Use attainability analyses involve a determination of the level of
aquatic protection that can beachieved for a water body The analysis -
iSsKaei^n assessment of (1) what are the aquatic uses(s) currently being .
achieved in the water body,- (2) what are the potential uses that can be
attained based on the physical, chemical, and Biological <*a""^e £j Jf
Chewater"body;and(3)what are the causes of any impairment of the uses?
T Hn-igal Support Manual: Water Body Surveys and Aegaggmants for
Conducting tTge Attainability Analyses. November 1983. USEPA/OW.
.86
HI ill
II IPl
-------
Sections 302 and 304(1) of the Clean Water Act require the States to
identify those waters for which technology-based effluent limitations are not
sufficiently stringent to attain the water quality standards. The technology-
based limits are mandated under Sections 301 and 307 of the Act and are
implemented by the Agency through the promulgation of industry-specific.
effluent guidelines.5 The States must rank their water quality-limited
stretches for planning purposes and set total maximum daily -loads of
pollutants in the stretches that will achieve the applicable standard.
Finally, the TMDLs are to be converted to wasteload allocations through
modeling and ultimately to water quality-based effluent limitations on
individual point source dischargers in the limited stretch.
ii. Implementing waste load allocations and load allocation in water
quality-limited water bodies
Water quality-based controls are implemented for any stream segment in
which it is know that water quality does not meet applicable water quality
standards, and/or is not expected to meet applicable water quality standards,
even after the application of the technology-based effluent-limitations
required by Sections 301 (B). and 306 of the Clean Water Act (see 40 CFR
130.2(i)). For these segments, water quality-based effluent limits, may be
5 Under Sections "301 and 307 of the Clean Water Act, as amended-in 1972',
.EPA is responsible for promulgating technology-based effluent guidelines, and
applying these guidelines in permits to' industrial point source dischargers.
EPA is to review standards annually and to revise them every three years.
Equivalent technology based standards also apply to municipal discharges;
these have been defined by EPA as secondary treatment of municipal wastewater.
Under the 1972 amendments, industrial point sources were required to
apply the best practicable control technology currently available (BPT) to
their processes by July 1, 1977. BPT was interpreted as involving mainly",
"end-of-pipe" controls that imposed control costs and economic impacts that.
were not "wholly, out of proportion" with water quality benefits. In the
second phase of pollution control,- the Act mandated that industries were to
adopt best available technology economically.achievable (BAT), or, if
feasible, zero discharge, by July 1, 198.3. In contrast, to BPT, BAT was
thought of primarily as in-plant process changes that had been or were capable
of being achieved. Compliance costs were considered in setting BAT, but no
cost-benefit analysis was necessary as with BPT. Finally, new sources were •
expected to immediately, comply with strict standards of performance based on
best available demonstrated control technology (BACT), a standard comparable
to BAT for existing sources. . '••'".'• ' , '
Under the 1977 amendments to the Act, Congress modified the original
technology-forcing approach somewhat to include a new category of control,.
besf conventional pollutant control technology (BCT), to be achieved by July
1, 1984. However, EPA found the BCT cost tests difficult to apply and; as .a
•result, for most industry, categories the BCT effluent limitations are
virtually equivalent to BPT requirements. . • , •
87
-------
rm KV ; ilililii;,!!'11!'1":1!!!;!!!!!!
:;;) liii;!:1:!*1'1!!!*;,;, sir #;(„,;:
I .".MI.; ,„:• is '"Si"* i tf illM!'11 ii" ; I; .'!
Illlil1
imposed on point source dischargers under the authority of Sections 302 and
402 of the Clean Water Act. Water quality-based effluent, limits are derived
co protect water7qualityInthe receiving water regardless of cost or waste
stream cfeaTabilitty. In addition, however, Section 302 of the Act makes
provision for permitees to apply for variances from the water quality-based
effluent limits based upon the "relationship between the economic and social
costsandthebei»:f£fstobeobtained from achieving such limitation."
1 Control programs for nonpoint sources are developed as .part of the
planning processdescribed under Section 319 of the Clean Water Act. In many
cases States do not have certified or established techniques or procedures
for completing load allocations.In those cases, the State should present its
overall schedule form implementing the TMDL process and a schedule with
milestones for establishing the appropriate load allocations. Vntil the load
allocation is approved by EPA, the State should pursue a technology-based
approach. Technology-based controls are to be based upon water quality .
considerations and not just resource protection. For example while
agricultural management activities are directed at minimizing soil erosion for
productivity purposes, the technology-based approach requires the
landowner/operatortoinclude not only productivity based controls but offsite
measures such a filter strips and sediment and water control structures, as
well If BMP implementation is not adequate, the State .-should develop an
action plan to develop additional BMPS, including a schedule to assess the
waceY cjlillity conditions and determine if "standards are being met within an
appropriate timeframe.
ill i i i w in i niiinii n in i i i i n 11 i i i ' i ,«.'
B, Determining the Total Maximum Daily Load
This section presents a brief description of the scientific
Understanding of the processes underlying estimates of total maximum daily .
load Because the approach for assessing water quality impacts from different
categories of contaminants varies, each of three classes- of substances,
biochemical oxygen demand, nutrients, and toxics is discussed separately.
i. Theory behind Waste Load Allocation '
Basic Principles - . '
Qt^ ^— imum "D'aily "Load"assessments provide- information 'to assist in
iffective decisions on levels of treatment required for *««"£•£
of pollutant load. WLAs are water quality oriented and are ^rected^
: ~ ' •---::•; re-iJltiBlTsfeLni a qualitative relationship between a particular waste load and
ics impact on water quality. These relationships make it possible to compare
£^ ::"; Incremental changes in .concentrations of specific constituents in the
water "System; One^is then able to.identify the maximum; waste load
can beDischarged without violating a water quality standard.
IIIH ii "PHI mi"» i iii mi
s Technical Guidance Manual-for Performing Waste Load Allocations.
Guidance.
88
' -
I
-------
.Because of the array of variable elements (e.g:, temperature, stream
flow load level, reaction rates) that must be considered in WLAs,.
computerized mathematical models are generally employed to make the necessary
calculations. Furthermore, the factors and model formats also differ
depending on the water contaminant under investigation. The approaches taken
for each of three-major classes of water contaminants assessed in determining
TljlDLs are discussed below. .
Biochemical Oxygen pemand/Diffiftlved Oxygen
Biochemical oxygen demand (BOP) is a measure of the amount of oxygen
used in stabilizing a biodegradable material. Both carbonaceous organic
compounds (CBOD) and nitrogenous forms (NBOD), such as ammonia and "g-nlc^
nitroeen are subject to bio-oxidation. In most WLA applications, the amount
of oxyge; consumed for biodegradation over a five-day period (BOD5) is used as
the standard measurement. However, fuU oxidation of organic compounds
generally requires in excess of twenty to thirty days for completion. ,
When an organic waste is loaded into a water body, it is subjected to
two processes that influence the transport of the waste: (1) advection which
represents the downstream transport of the waste, load in stream flow, ««M2>Q
dispersion, which encompasses the turbulent and eddying;processes that tend to
mix the waste load with upstream and downstream waters. .Under steady-state
conditions (i.e., constant waste load and stream flow), the. advection and -
dispersion processes can be assumed to be constant. In many WLA. applications,
one may assume steady-state" conditions because critical low-flow conditions
are modeled (e.g., the 7-day,- 10-year low flow period). However, if
conditions vary, the transport processes will also vary.
The biochemical oxygen demand and the resulting dissolved oxygen levels
in the water body are a function of the ability of naturally occurring^
bacteria to decompose the organic waste materials, thereby utilizing the .
oxygen resources of the water body. Replenishment of the oxygen resources in
the water body occurs either through transfer of atmospheric oxygen into the
water column or, to a lesser extent, through oxygen production by aquatic
•plants. .' v ''-.'. ..' . • '
-The interaction of these processes produces the reduction in dissolved.
oxygen levels which is the focus of WIA modeling. The critical factor an the .
• protection of water quality is an understanding of the rate at which _
reaeration takes place and the magnitude of this rate in relation to the rate
of oxvgen consumption.: This relationship is generally expressed in terms of ,
an oxygen deficit, which is defined as the difference in concentration, between
the saturation value and the actual dissolved oxygen concentration.
Allocation. Book
2: Streams and Rivers. Chanter 1,; Biochemical
PB86-178936. September 1983. p.. 2-13.
8 Ibid,, p. 2-19 ^
'. • • ..: .' 39:
-------
i ..... fJutrients__and
The major water body impact associated with nutrient loading is
eutrophication, or enrichment of the biological productivity of the water
•body. Waste load allocations for control of eutrophication are generally
designed to reduce nutrient inputs. This strategy presumes that the nutrient
to be controlled limits the rate of growth and subsequent population of
phytoplankton. It further presumes that reducing the population level of
^_ISikcon win provide the desired control of the complex process of
eutrophication and eliminate undesirable water quality situations such as
algal blooms. Therefore, it should be noted' that WLAs to control
eutrophication in water bodies focus directly on nutrient reductions and
indirectly on phytoplankton and dissolved oxygen conditions that result from
overs timulat ion by nutrients.9
Nutrient levels in water bodies are controlled by external and internal
sources. External sources of nutrients include municipal and industrial point
sources; stream inputs, atmospheric deposition, urban. runoff , ground-water .
discharge ", .......... agricultural ........... drainage", ....... and" other nonpoint sources. Internal
sources include sediment release, biological recycling, and -nitrogen fixation.
Chemicals and Toxic Substances
j*j,|i ji., ._
" ..... ' '"
*iswi!^|Je'':"pr'0!c!edu1re for developing realistic mathematical models for chemical.
S'lts ........ similar "to the mass-balance approach used for other measures of water
............................................ MalityT such' ............. as" ......... biochemical oxygen demand. The main ......... differences involve the .
modeling of processes affecting the chemical constituent. These processes
include chemical partitioning between the soluble phase and adsorption onto
particuiate matter, chemical transfers and kinetics involved in the decay or
volatilization of the constituent, and sedimentation processes. In conducting
WLA for toxic substances, all of these procesises are accounted for in a mass
balance equation. The result is a prediction of chemical concentrations in
the water column, sediment, and, in some cases, in the biota present in the
................................. : ............................. water body. . '
The fundamental transfer and kinetic characteristics are known for a
wide variety of chemicals based upon laboratory analyses. These
characteristics can be combined with other relationships, such as advection
i and dispersion predictions, to account for the manner in which. any material is
transported in a water body.10 .
111111 I 111 ll'I1 Pli 111 _ ! •..'..'.:!. :-' :,",'.''-
J 9- Technical Guidance Manual for Performing Waste Load Allocations. Book
4: Lakes and Impoundments' I cHap'ter 2: Nutrient/Eutrophication Impacts. PBS 6-
178928, August 1983. p. 1-4. ,
i ' 1° Technical Guidance Manual for Performing Waste Load Allocations. Book
4: Lakes.ReservoirsandImpoundments. Chapter 3: Toxic Substances Impact.
EPA 440/4-87-002. .December 1986. p. 6. •
-------
"ii. Waste Load Allocation models: Steady-state conditions
General Approach
Conservation of mass is the fundamental principle which is used as the
basis of all mathematical WLA models of real world processes. All material
must be accounted for whether transported, transferred, or transformed. A
rate equation which conforms to the requirements of mass balance is
'V-dc/dt'- J + *T+. *R + *W
where ;
c - concentration of the chemical .
J[ - transport through the system
f - transfers within the system
R - transformation reactions within the system • .
W - chemical inputs . . , .
V - volume of water body.
•• t - time. •, '
This fundamental model forms the basis for assessing pollutant load to a
.water.system. Most WLA applications also assume steady-state conditions,
thereby'eliminating the need to measure changes in parameters over time. The
simplified steady-state framework for chemical WLA modeling also assumes
complete mixing throughout the water body.
* •• . • " ' v
A steady-state model requires single, constant inputs for effluent flow,.
effluent concentration, background receiving water concentration, receiving
water flow, and meteorologic conditions. As a result, the effects of
variability in nonpoint source and point source contaminant discharge on
receiving water quality cannot be predicted accurately using these steady-
state techniques. Nonetheless, steady-state models provide a relatively
simple and conservative tool for estimating water quality impacts from
contaminant discharges. The specific analytical approaches for steady-state
WLA modeling for BOD," nutrients, and toxic substances are described below.
Biochemical Oxygen Demand and Dissolved Oxygen Profile
A dissolved oxygen profile for a stream reach is based upon a simple
mass balance which accounts for the mass of BOD entering a stream reach, the
.mass leaving the reach, and the biodegradation and reaeration processes that
occur within the reach that result in the oxygen sag. At steady-state, the
following mass .balance applies:11 .' • .
11 Technical Guidance Manual for Performing Waste Load Allocation. - Book
2: Streams and Rivers. Chapter 1: Biochemical Oxygen Demand/Dissolved Oxygen.
September 1983; PB86-178936, p. 2-40.
91
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I III II 11 II
MASS IN - MASS OUT + SOURCES - SINKS - 0
QC. Q:(c+ ac/dx-*x) -*• K.-«VC)-V - K.J-L-V - o
• if U - Q/A and V - A-*x, then:
Q-dC/dx-AX - (Q-*x)-dC/dx - (U-A-*x)-dC/dx - U-V-dC/dx, and'
-U-dC/dx + Km- (C.-C) - Kd-L - 0
• if the oxygen concentration (C) is-expressed in terms
j!!!!!!!!"!!!,,!,"!!', '"[ , •»!,',«„ M«'! ,!",„",!, of oxygen deficit (D) and the saturated oxygen
concentration (Cs) , then C - Cs - D, and
" , -U-d(C,-D)/dx + K.-D - Kd-L - 0
iiiill'ii if!!!1, iijji i 11111,1 iii.i, i n,11 , i iiiiiii i,,in ill i I ,,i , ,, • ' •. : i':
" j "if1 c, is constant over all x, then
U/ dD/dx •«• K«- D - Kd- L - 0
• the rate of change in biochemical oxygen demand
concentration (L) is expressed as: •
L - Lo-e'-*
• therefore ,
U- dD/dx + K.-D - Kd-Lo-
• integrating and solving the equation for the condition
thatTD-pp at x-0 yields the following:
iiiiiiiiiiii i i iiiii in iiiiiii i iiiiiii MI iiiiiii ii j i {-jf«-'jc/U} ji v / (Y -K ^-Ln' f e ' ~"E' */"' - g(-K»-x/U)y
Illliilif illlili l ii ill i'1 ill 1 1 I 1 ....... In 1 1 ...... 1 I ill ii I i ' ..... • .';, ' : •, • :: "
iiiiiiiiiiii 1 I ii nil iiiii i i iiiiiiii i i in i IN iiiiiii 4 . . i i • ',''.•'
where . , ' ......
Q - river flow rate ••
C - concentration of dissolved oxygen entering the segment
Cj » saturation concentration of dissolved oxygen
.................................. [[[ " [[[ i ....... OC - mass of oxygen entering the segment - _
dC/dx - rate of change of oxygen (C) with distance (x) ; equivalent
'. to rate of change with time (t) when converted by velocity
'
-
............. ' ............................... ' ...... F ............. !" ...... « .......... -"'^< • ............... • ....... '; ...... ...... '^ae/aBe;"*"* ...... - ........... change in oxygen concentration during time of passage
[[[ .............................................. ........................................... through segment of length »x
f"f» 'iSi'^iV/iit jja _ • atmospheric reaeration rate coefficient .
.......... : " "'.:: ..... •":1"^ „ BOD" removal" rate ........ coefficient (-K,j) .
liajwMf.^ii •'ws'iik'.i^j n ' ' id ii i1 i i i 111 • L ' * ' •-;.. v ".r =
iE.!''v.ilj;|l!if;(This is a steady-state solution for the oxygen deficit in a stream
- ""• "igmiftic "of teng'tt ''xV'"' The source term for biochemical oxygen demand (L)
::,,:r:,':,,;,,'^SSieF«nES the concentration of BOD within the mixing zone below a P°^
-------
ground- water discharge.
Nutrients
In lakes and estuaries, nutrient inputs may promote increased biological
productivity or eutrophication. Such eutrophication processes depend upon
continual input of nutrients, as a net sedimentation of nutrients occurs over
time This process can be expressed in a general steady-state, mass balance
equation which, assumes a completely mixed water body. The removal rate of the
nutrients is assumed to be proportional to their water concentration, which is
expressed as follows12:
V-dP/dt - EQi-Pi - K.-.p-V - Qp ,
• where ' •
EQ --Pi - the sum of all the mass rates of total nutrients
discharged to the lake from all sources (point source
and nonpoirit source) [M/T] ; Qt - flow [L3/T]; and Pi -
the initial nutrient concentration [M/L3]
p - lake nutrient concentration [M/L3] . ;
V - lake volume [L3]
K,- the net sedimentation rate of the nutrient [1/T]
Q - ' ' • . lake outflow [L3/T] . • "
* '
• assuming steady- state (dp/dt - 0), and letting W - EQt-Pi:
p - W/(Q.+ K.-V)
• if V - A- z {where A- lake surface area and z - mean depth) , then:
p - W/[A-zUQ/V) > K,)]
This expression provides a simple estimate of the ambient, lake water
nutrient concentration given. a loading rate of W. However, the equation does
not provide any indication of the water quality impacts resulting from the
nutrient loading. Such an estimate could be made based upon the ambient
nutrient concentration. .
• . . toxic Substances • ' .
As mentioned above, the modeling approach for toxic substances is
similar to that used for BOD and dissolved oxygen depletion WLAs. One of the
principal differences between the approaches arises in the modeling of the
12 .Technical Guidance Manual for Performing Waste'Load Allocations.....
Book 4: Lakes-and Impoundments. Chapter 2: Nutrient/Eutroohication Impacts,.
PB86-178928. August 1983. p.3-18.
93
-------
various fate processes and reaction rates affecting organic and heavy metal
toxic constituents. Several references list reaction rates for toxic
constituents." If a first-order decay rate estimate for a particular
constituent is available, the following equation for estimating the downstream
concentration of the contaminant may be used:
••o
where
e - c0-e-K<*/u)
C - downstream concentration
C0- concentration at the mixing zone
X - distance downstream of mixing zone,
u - river velocity
K - measured decay rate.
However the fate of many toxic .constituentscurrently is not.well understood
because of the confounding effects of varying temperature, pH, and other
BK|»;!.:^>^vir6nnentaI conditions in a water body. . ' •
Bll, III!: «i;' aW-HltHM.™ yil; 41111 <(»;•; i'*lll; *'- i: i!;'." i i":" n? - K 1> SKS, «:StT'ii/i»;- X OBSaE»l vsiiii It*.::,,;l t" • • •;; ;•.'.' ;«i , /.••.,'..- , .
MIS jf Mini ,i>"!i!!,i ,:B „ n 111 in i ii ii n i i i ii i i minium inn i i i '"lii'i'ihiii'iiiJiiiEi'ii,:. JH^iiHiyiai!!!1''11,,,!',»I'si rfi'ii"»!" i1 SIWIMIIM^^^ '.i i^^wiJi^iiN!11'11*1'J1'1"111""!' "• • s v • » - *• • •' ' ''__-i
FPA*c TMDL euidance for modeling individual toxicants in streams and
:iillllllll||P|||l|i| nilKllllii' lii'lllllh, 'I*If",!!!: , llllllllllllllllll I II II C*ITA. & AiUJl^ ^V*j.Vfc&i*wy. ^.** CT /O«l.«.««w*
i ! I. !i ' ' 'r: ,f:-, i'OL'rs1" r'ecoiJends tine" "following steady-state models: Simplified Lake/Stream'
Analysis (SLSA), Michigan River,Model (MICHRIV), Chemical Transport and
iSalyses Program (CTAP),~ Exposure Analysis Modeling System (EXAMS), and Metals.
Exposure Analysis Modeling System (MEXAMS). All of these models except MEXAMS
can simulate both organic chemical and heavy metal fate and transport in
EPA also recommends these steady-state models for modeling individual
CBXicants in laKe's "and""reservoirs .
In addition to steady-state models, research has continued on the
development of dynamic or continuous simulation models. These modeling
approaches are discussed,below. EPA recommends the following continuous
simulation models for rivers, streams, and .lakes: Estuary and Stream Quality
Model (WASTCX) , Chemical Transport and Fate Model (TOXI^^.L,^a™ei. „
'Transport Model (CHNTRN), Finite Element Transport Model (FETRA) , Sediment
Contaminant Transport Model (SERATRA), Transient One-dimensional Degradation
dnd MigrationModel (TODAM), and Hydrologic Simulation Program-Fortran (HSPF).
All of thesecontinuousmodels are designed for multiple reach, multiple
Source analyses of both ofganics arid heavy metals.
Detailed descriptions of these steady-state and dynamic models are
provided in several of the EPA guidance documents cited in Chapter III of this
document.
^ ''''P!!;1!!1!!!!1! ' , i/nl ', IIUi'linK 'h FI'"':^ "IK, JIM,!!!"'!!,!"1' i llllllllllllllllt i«i' M"'!1 l!i"'i" nil'i"! !!"i|i' iri'l'iVkli'liI 1UIIPIIPI1 Pn^iiAr'iti'PJIPPi'il'l'IS'lPnnPP <" liu li'l'W ^>- L^ •"' '' f""^/io n«J^«.4«>*«v 13/^1
13 For example, see Wager Related Fate of 129 Priority Pol
aa:';:. ;i; JKr^umas f "an? 'Ii:: EPA-440/4-81-014.
'' iiiP1'' * i
:11,, Illliiraii'' \M • ii',; i litK! ('"• m Wl •. ilHIIIIlli;; LWiWfrl ihiPS K^afWfiJfiBI»l /-, i^^ftfflWnp^j \WM\. ^t'\ •. U;.iS i ito iVir,'i: •: "'''JK '::i'i; '''Si t' : i' ••'' r "i;, -'! •.,.. i ' •:' .' :' "' L" \. • ' .".•."'',: f. I' I': • - ' ,:,, \ M
-------
Hi. Dynamic tfasteload Allocation Modeling ... •
At the present time, most States and EPA Regions use steady-state
models which assume the wastewater is completely mixed with the receiving
water and the c6ntaminant source loads are constant, to calculate WIAs for
pollutants This -assumption may be adequate for conventional pollutants
because the greatest environmental impact in the receiving water, such as
severe oxygen depletion, is found downstream of the pollutant outfall.
However for toxic pollutants the highest concentration in the receiving water
(i e near the pollutant outfall) may serve as the critical level for
determining the waste load for the contaminant. As a result, dynamic modeling
approaches are increasingly being applied to better account for variations in
point source loads and variations in ambient water conditions resulting from
changes in nonpoint source loads and other factors.
Dynamic TMDL models calculate an entire probability distribution for
receiving water concentrations rather than a single worst case based on
critical conditions. The prediction of complete probability- distributions.
allows the risks inherent in alternative treatment strategies to be
quantified. The dynamic modeling techniques have an additional advantage over
steady-state modeling in that they determine the entire effluent concentration
distribution required to produce the desired frequency.of criteria compliance.
Continuous or dynamic simulation models use each .day's effluent flow
(Q ) and concentration data (C.) with each day's receiving water flow. (Q.) and
background concentration (C8) to calculate downstream receiving water
concentrations. The model predicts these concentrations in chronological
order with the same time sequence as the input variables. The daily receiving
'water concentrations can then be ranked from the lowest to the highest, without
regard to time sequence. A probability, plot can be constructed from these
ranked values, and the occurrence frequency of any one-day concentration of
interest can be obtained.15
Several methods are available to compute the probability that downstream
toxicants (or effluent toxicity) will exceed criteria. These, approaches
'include an approximate method of moments and numerical integration. The
method of moments is based on the -following equation:
ct - c.- [Q./(Q.-KJ.)] >.c,- [l-(Q./(Q.-*5.»]'
where Ct - downstream concentration of the contaminant- at time .t. Estimates
of the mean and variance of the effluent concentration, effluent flow, and
upstream concentration-can be made by regressing the natural log of each of
these variables against a standard lognormal random variable. More specific
information concerning the variation in each of these terms may also be
applied.
15 Technical Support Document for Water Quality-based Toxics Control.
September 1985, EPA-440/4-85-032. p. 40.
16 Ibid, p. 41.
95
-------
An additional dynamic modeling approach involves the use of Monte Carlo
simulation. MoileCarlo combines probabilistic and deterministic analyses
since ic uses a fate and transport mathematical model with statistically
described inputs. While MonteCarlo simulations require more input data and
calibrationdata than steady-state modeling approaches, they can account for
interactions of time-varying water quality, flow, temperature, and point and
nonpoint source lo'ading terms.
The above discussion presents a brief overview of modeling approaches
for WLAs. More detailed descriptions of the approaches outlined above are
available in the documents summarized in the annotated bibliography which
accompanies this SSport:The following section discusses how information
characterizing nonpoint contaminated ground-water discharge to surface water
may be incorporated in the WLA process.
C Assessment of nonpoint source contaminated ground-water discharge to
surface-water analysis methods as components of waste load allocation
i. UPS loading in current TMDL models
In steady-state TMDL models, all source terms, including NFS loads, are
assumed to be constant. Therefore, one may conclude that NFS loading is
accounted for as a component of ambient water quality conditions. However,
because the application of steady-state models typically focuses only on point
source loads, the contribution of nonpoint source inputs within the water body.
segment of concern may not be adequately assessed. Furthermore, if the WLA is
determined for other than low flow conditions, the NFS load may vary greatly
and a significant contaminant source term may be overlooked.
The need for a more thorough understanding of the change in ambient
water body conditions brought about by contaminated ground-water discharge
increases for dynamic WLA modeling applications. This understanding should
Include an assessment of the magnitude of NFS loading throughout the water
i, body segment of concern and the spatial and temporal variations in that -
loading.
The accuracy of the waste load allocation process is highly dependent on
the quality of the data used for simulation modeling. This data includes
Information concerning the ambient conditions in the water body, spatial and
temporal variations in the source loading terms, and a detailed understanding
of the kinetics of contaminant fate and transport. WLA models should.also be •
calibrated and verified prior to allocating waste loads. Sufficient
historical"data to accomplish these objectives are often lacking, however, or
of the wrong type. Therefore, improved data collection is often needed to
better quantify ambient conditionsand anticipated loadings.
In addition tocharacterizingambient conditions, a firm understanding
of the contaminant source terms should be obtained. .For systems that are not
" See Stream Sampling for Waste Load Allocation Models. EPA/625/6-
86/013.
96
IIIPIll 1 1111 11 111 111 1
'
liilill n n 'Hill
U II II III III
\mm iiiiiiivi iiiiiiiiH
1 i I in i i i 1 1 i ° in ' 'i,-: • , .• , '"; .;.;.;::) ;
, i, •;: ' • . v , ,,
i'i 11,1 liilill 1(11 1 1 . 11 1|| lllllli | 1 |l 111 1 1 1 111 111 (1 ' 1 (111 i1 11(1 111 ill 111 111 1111 1 1 i| II 1 1 1 III li l|il 111 1 1 111 1 1 III „. ;•£,: , . .• 1,; f • ;, •• >':'- :'• ': ' ,j 'I,!" ' ' „
i.n', " ' ',' ' ' '''Jliilli
!l«
il1 ill ill ,'',!< « 'ni'l
-------
in low flow (i e.. near steady-state) conditions, this understanding includes
a quantitative measure of source constituent and concentration levels over
time For point sources, this information is readily available through
analyses of permit conditions or past operating practices. For nonpoint
sources,; however, the amount of information available to characterize the
source terms accurately typically is limited.
A sampling program to support a WLA assessment should, at a. minimum,
Include the following sampling locations within the stream segment: upspream
boundary, point, source, upstream of point source, mouth of any tributaries
entering the segment,.upstream of the tributaries, upstream of any nonpoint
sources? downstream of nonpoint sources, and downstream boundary of segment
In areas where significant nonpoint source loadings are known to exist, both
the flow rate and constituent concentrations should be measured. If this area
is not so large that other water quality changes are likely ^occur during
the travel time through the area, it is reasonable to assume that the^changes
in concentrations are due to the nonpoint sources and to use these differences
as a basis for. estimating the loads." However, if the leveL of nonpoint •
source loading is significant, a. more thorough characterization of the
nonpoint source term may be needed.
• The following section reviews the applicability of the methods described
in 2 above to better characterize nonpoint source loading as part of the TMDL
assessment process.
ii Analysis of contaminated ground-water discharge to surface water
' assessment methods as sources of data for waste load allocation
As described above, there is no single analytical approach to waste load
allocation. The TMDL analysis and the type and amount of data required for an
assessment will differ depending upon the water body characteristics, the
point and nonpoint source contaminant loads, and the level of water quality
impairment. Furthermore, in many situations there may-be no need to
characterize the component of the ambient water contaminant concentrations
contributed by nonpoint source loads.- Such a circumstance may arise if the
nonpoint source load is minimal and limited controls on the point sources
within the watershed will achieve the applicable water .quality standard^ On
the other hand, if nonpoint. sources- contribute a large portion of the ambient
contaminant concentrations in a water body and stringent controls on point
source discharges will not achieve the water quality standard there may be a
. strong incentive to characterize the contaminant load provided by ground-water
discharge to support development of a nonpoint source management strategy
This section discusses the applicability of the various contaminated ground-
water discharge to surface water analysis methods for supporting such nonpoint
source load assessments.
' All of the methods described in Chapter II will provide an estimate of
. 18 sr-ream Sampling for W^e Loa'd Allocation' Applications .. EPA-625/6-
86-013. p. 2-7. , -
97
-------
•f
"*»w, 1
lllllllllliii I'lli'lllii 'llIKi i
^
the loading of nonpoint source contaminants to a water body. However, the
methods differ significantly in the level of effort required, the degree of
specificity ofthecollected data, and the ability to accurately assess
ceiporlland spatial variations in nonpoint source loads. As a result,
different methods may be suitable for different levels of analysis. For
exampleinwa£*rbodies that are severely water quality-limited and that have
high nonpoint source loads, the ability to accurately predict changes in
contaminated ground-water discharge may be critical to support dynamic load
allocation£b"aiirhg:In contrast, for water bodies that are not as severely
water quality-limited, a fundamental understanding of the component of the
water contaminant concentration contributed by ground-water discharge at base
flow or steady-state conditions may be sufficient for determining >:.,:e TMDL.
The following table summarizes four attributes of the contaminated
ground-water discharge to surface-water analysis methods. The
characterizations are very general in nature and are intended to provide only
a "first-cut" assessment ofthevariousattributes of the methods. Because
the categorizationof the methods necessarily combines several different
approaches under onegeneral method heading, a more detailed review of each
method application is needed to better assess the relevance of the approach to
aparticular situation." Nonetheless, this summary- allows one to compare and
contrast the suitability of the methods for specific applications.
The attributes are as follows: (1)-.resources needed to implement the
method- (2) ability to assess spatial variations in ground-water discharge to
"i gcreii ••segment Sr VSESS body; (3) ability to measure changes in ground-water
-fisj^iarge levels over time; and (4) the level of confidence in the method s -
iribifityto provide data that accurately reflects the "true" level of
contaminated ground-water discharge to a water body. The attributes for each
of the methods are ranked relative to one another. A more detailed analysis
acific method" Applications would be needed to provide absolute measures
th'e actr'lb'ute's for each method.
Seepage Meter/
Mini-pjezometer
Hydrograph
• Separation
Total Flux
Measurement
Numerical
Models
Loading'
. Functioni
Geophysical
Methods
Isotopic
Metho
ill iiiiiii
lllllllllliii li
.....
•
Temporal
Change*;
Data
Specificity:
moderate
low
Spatial
Variation: pottfbjy. with no
multiple sample
points
yes
moderate
no
yes
high
yes
yes-
samples
high
low
yes
no
high
yes
moderate
moderate
;IUI!I .,', 'I I' .
moderate to low
high
• yes
moderate.
high
This analysis indicates thatno onemethod may be suitable for all
applications. Nonetheless, one or more of the methods can provide
sufficient data to support load allocations formanyapplications and
98
-------
environmental'settings. ' .
D. Summary
The preceding discussions outlined"several methods that have, been
applied in a varie.ty of environmental settings to assess nonpoint source.
contaminated ground-water discharge to surface water. Each of the methods
is'suitable for different applications and settings and the resources
required to implement each of the methods also differ. An enhanced
understanding of nonpoint source contaminated ground-water.loadings.to
surface water may also improve the total maximum daily load assessment
process in water quality-limited water bodies. These methods can support
point and nonpoint source load allocations by better characterizing the
component of ambient water quality contamination contributed by nonpoint
sources under steady-state conditions and by improving the ability to
characterize and predict changes in-contaminated ground-water loading in
dynamic simulation models. The manner in which several of the methods
described above can .be applied to better account for nonpoint source
loading to a stream is the focus of a companiqn volume to this' document.
•99
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,,j ,„ ji
ii PI ii run" • i1 |M
in
1 Ill
.'rjiAihiiiiiw1 >, i sf .Hill" ' '• 'Hii'iiiiu |! , i ', .', ia.i".,
iil'iliilliillliil!!:!;;!:.' lliHt: •; ,;•; •• 'HI!,iii:' !'."',;" !.("Hi:,,,:r;,j.,'"': Witt'1* IRIIIlh • "i1",!."!'" -' ':.|. '''i! ;„;»?!'
*:, "• • Hi^l •:W 4;;; '= t.'i ill ,.?,;t •.; K:":":K,,-. fe!!"
'??•<• ^a' I',ii'; 'l';;'- .•• "I;
rjiaililli,!.!,.1^ "nllliilJl!1!. .iJi,:!!:'1 'lifliiiliiiK"1'*;1 nJ!"1!",!! ,'M' Illllil^ ".'",»!!S''yiir1,: I',„ /"".i'li!"!!!1!!..1 Hi.!!1!1,!, :'',". 'l|'"'!! i ..':.:i|i"|1'iltii!ll'l|!!lli!:li!i,5!» I J"i '":• i',!ii,!;i"ii!!! '..i",,.i'' '.* *0» •''", 'i, '., ''!',: ', ,'/I!1, !i',"i'|.. ,, J
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