United States
       Environmental Protection
       Agency
Office of Water
4606
EPA 816-R-97-012
October 1997
4>EPA  Delineation of Source Water Protection
       Areas, A Discussion for Managers;
       Part 1:  A Conjunctive Approach for
       Ground Water and Surface Water

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DELINEATION OF SOURCE WATER PROTECTION AREAS,
          A DISCUSSION FOR MANAGERS
                   PARTI:
  A CONJUNCTIVE APPROACH FOR GROUND WATER
             AND SURFACE WATER

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      This document was prepared by Marilyn Ginsberg, Implementation and Assistance
Division, Office of Ground Water and Drinking Water, U.S. Environmental Protection
Agency.

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                              Table of Contents
 INTRODUCTION . .......... . .................................  !

      Purpose of Protection Areas  ........................ ............  J

      Goal of This Document ................... .................. ... 5

 PROTECTION-AREA BOUNDARY DELINEATION .............. .  7

      Introduction .............................................    7

      Combined Ground- Water/Surface- Water Approach ......................  8

      Combined Nested- Watershed Area/Ground- Water Flow Approach ............  11

      Methods for Delineating Ground- Water Boundaries to Protect the Quality
            of Ground- Water Sources Upgradient of Critical-Use Sites ............  11

      Methods for Delineating Surface-Water Boundaries to Protect the Quality
            of Surface- Water Sources Upstream of Critical-Use Sites ............   16

            Streamflow Time-of-Travel Method ..........................   16

            Setback/Buffer-Zone Delineation Method .......................  18

            Nested- Watershed Area Delineation Method .....................  20

      Summary ........... . ............... .  ...................   21

LITERATURE CITED ........................................   22

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                                  INTRODUCTION
       The quality of surface water used for drinking and other purposes is determined by the
 quality of the water that is received from overland flow, upstream surface water and ground
 water. Drinking water withdrawn from surface-water sources, the fishability and swimability
 of surface waters, and ecosystems all rely on the protection of upstream surface-water quality
 and the protection of the quality of the upgradient ground water that discharges to, and
 therefore effects the quality of, upstream surface water. This range of varied uses underscores
 the many different demands on the hydrologic cycle from human activity and ecosystem needs.
 Of particular concern to state and local governments is assessment of the areas which may
 need heightened protection from contamination of the ground water upgradient, and the
 surface water upstream, of specific "critical-use sites" (CRUSs).  Such CRUSs might be, for
 example, surface-water-supplied drinking-water intakes, endangered-species habitats and fresh-
 water fishing areas.

       In protecting CRUSs, it is important to understand the nature of the Zones Of ground-
 water Contribution (referred to as "ZOC"s in this document) to surface water which underlie
 and border rivers, lakes and reservoirs. Although ground water may travel very slowly, all
 flowing ground water that is not transpired by plants, evaporated near the land surface or
 withdrawn by wells, given enough time, ultimately discharges to surface water bodies (Figure
 1). Delineation of a ground-water ZOC within this ground-water continuum is difficult and
 must be based on management needs, in addition to hydrologic and geologic considerations.
 These ZOCs are often areas vulnerable to contamination from human economic activities that
 do not recognize the interaction of the components of the hydrologic cycle. In contrast to the
 difficulty encountered in the delineation of ground-water ZOCs, the areas that contribute
 surface water to rivers,  lakes and reservoirs are usually relatively easy  to delineate.

 Purpose of Delineated  Protection Areas

       Delineating and assessing protection-area boundaries around source  areas of ground-
 water supplies or surface-water supplies provides water-resource managers  with lead time to
 intervene when a  water  supply has been contaminated.  Protection-area boundaries also
 provide some degree of natural remediation of the water. Ground water in most
 hydrogeologic settings undergoes natural remediation over a longer period of time than does
 surface water.  Many of the natural remediation processes present in ground water are similar
to those in surface water.  However,  the slow movement of ground water (generally feet/year,
under natural conditions), hi most non-karst1 settings, provides more time for  natural in-situ
remediation than does the rapid movement of surface water. Natural protection of surface
water depends principally on dilution and on exposure of contaminants  to natural remediation
for periods that, in most cases, do not exceed hours or days. Thus,  these natural processes
should be considered when delineating protection areas.
   1 Karst is a "type of topography that is formed over limestone...by dissolution, and that is characterized by
sinkholes, caves, and underground drainage." (Bates and Jackson, 1984) An aquifer with such features is
informally called a karst aquifer.

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           A
A1
             Land S'jrfaca
          Legend
               Direction of ground-water flow
               Infiltration
Figure 1.   Ground-water flow paths between a ground-water recharge area and a
           stream.  (In this setting the geographic position of the ground-water basin
           boundary approximates that of the surface-watershed boundary.)

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        Such natural processes for ground water begin as the water percolates through the
 unsaturated zone, with some contaminants, such as nutrients, being removed through
 vegetative uptake.  The ground water is also exposed to physical and biochemical processes
 that provide some degree of in-situ remediation,  such as adsorption of contaminants by soils,
 and breakdown of contaminants by chemical reactions and by soil organisms.  Ground water in
 most non-karst settings is similarly afforded in-situ remediation when it reaches the saturated
 zone.  There, ground water: 1) flows slowly enough to allow time for at least partial
 degradation of some contaminants (e. g., by radioactive decay and microbial inactivation),
 2) moves tortuously, making contact with rock surfaces that adsorb contaminants,
 3) undergoes dilution mixing of contaminated and uncontaminated waters as it flows away
 from a contamination source, and 4) flows through the fine pores of an aquifer matrix with the
 resultant sieving (filtering out) of some microbes and particulates. If management decisions
 allow ground-water based protection areas of adequate size, ample time will be available for:
 natural in-situ remediation of many contaminants, deepening or relocating a well threatened by
 the encroachment of contaminated ground water, or taking remedial actions to manage
 contamination.

        Many of the natural remediation processes acting on ground water also act on surface
 water, for example, dilution, dispersion and biological or biochemical inactivation.
 Additionally, such processes as volatilization of VOCs, digestion by protozoa, and photolysis
 may improve water quality,  and contaminant-laden particles may settle out  of a stream and be
 deposited onto the streambed. Surface-water quality is also improved by the deposition of
 particulates filtered out by vegetation intercepted hi the overland flow path. Vegetation also
 slows overland flow, providing more time for overland flow to be recharged to the ground-
 water reservoir.

       In part because of these natural processes, the ground-water and the surface-water
 pathways present very different management challenges. In spite of natural remediative
 processes, once contaminated, the ground-water reservoir may be permanently degraded or
 require costly augmented remediation.  In general, the surface-water pathway allows less tune
 for natural remediation;  however, contaminant spills or discharges into surface water quickly
 move past CRUSs, although perhaps after causing irreparable damage. Therefore, successful
 protection of CRUSs requires the  conjunctive protection of the upgradient ground water that
 contributes to surface water and of the upstream surface water.  Such protection may
 encompass the entire surface watershed upstream of the CRUS (this area is  called the
 watershed area, see Figure 2) and areas of ground-water contribution that may extend beyond
 the upstream surface watershed.

        Where the management goal is protection of surface-water supplied drinking water,
 the CRUS is a drinking-water intake.  The surface area draining to the intake is called the
 source-water protection area (SWPA). In August 1997, the U.S. Environmental Protection
Agency (EPA) stated that for public water systems (PWSs)  relying on surface water, the
 SWPA will "include the entire watershed area upstream of the PWS's intake structure...up to
the boundary of the state borders." (The  EPA also stated that the SWPA for a surface-water

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                     Legend



                     •3  Critical Use Site
Figure 2. Boundary of the watershed area contributing to a critical-use site.




                                            4

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 supplied CRUS [that is, a drinking-water intake] will be delineated topographically.)  For
 settings in which the areas of ground-water contribution to a PWS intake extend beyond the
 surface watershed boundary, complete protection of the drinking-water intake might also
 extend beyond that boundary.  (The EPA encourages states to work cooperatively to protect
 SWPAs extending across state borders, and to consider protecting areas beyond the surface
 watershed boundary, if the ground-water basin boundary is external to the SWPA.) In this
 document, the term source-water protection area is used to identify the area delineated to
 assess and protect not only drinking-water intakes, but also any other type of CRUS.

 Goal of This Document

       The goal of this document is to provide combined ground-and-surface water delineation
 approaches to assist states in determining the areas that should be assessed, in order to identify
 those areas that need heightened management of contaminant sources to help protect CRUSs.
 The first part of this document presents protection-area boundary delineation approaches and
 methods.  The second part of this document (to  be published separately) presents case studies
 demonstrating the development of SWPAs, extended SWPAs and SWPA segments for the
 protection of CRUSs in the Nanticoke-Blackwater River Basins in Maryland and Delaware.

       Presented below are several methods for delineating, for management/assessment
 purposes, the area of ground-water contribution to surface water, the area that supplies surface
 water to a CRUS, and SWPA segments. Approaches to combining surface-water delineation
 and ground-water delineation methods are also described. States and communities can do both
 surface-water and ground-water conjunctive delineation in order to achieve complete
 protection. That is, management to protect the two interrelated water resources is facilitated
 when ground-water protection-area boundaries and surface-water protection-area boundaries
 are combined.

       In the following pages, Part 1 discusses:  1) combined ground-water/surface-water
 approaches to delineating SWPAs that best meet state/local protection needs; 2)  methods for
 delineating a ground-water boundary to protect the quality of the ground-water sources that
 impact drinking water,  riparian habitat and fresh-water recreation areas; 3) methods for
delineating a surface-water boundary to protect the quality of the surface-water sources (rivers,
 lakes and  reservoirs) that impact drinking water, riparian habitat and fresh-water recreation
areas; and 4) methods for segmenting SWPAs to facilitate differential management of potential
contaminant sources.

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                                        PARTI
               PROTECTION-AREA BOUNDARY DELINEATION
 Introduction
                       KEY TERMS, AS USED IN THIS DOCUMENT
  Segment
a subarea delineated within a source-water protection area
  Watershed area
the portion of a watershed  uphill  of a point of interest (for
example, a critical-use site) on a stream;  that portion of a
watershed that drains to a point of interest on a stream
  Buffer zone (or setback)
1) the area between a reservoir and a boundary around, and at
some distance from, the reservoir,  2)  the area within two
boundaries, one on either side of a stream; these boundaries
extend along some portion, or the total length, of the stream
       Under the 1996 Safe Drinking Water Act Amendments, source-water protection areas
(SWPAs) will be delineated for all public water supplies (PWSs).  Some of these are wellhead
protection areas, others are surface-water areas.  In a Wellhead Protection (WHP) Program3,
a wellhead protection area (WHPA) is defined around a public water-supply (PWS) well or
wellfield (a well or wellfield is the critical-use site [CRUS] of the WHP Program); sources of
contamination are managed within the WHPA.  The purposes of the WHPA are to allow
natural remediation of contaminated ground water before it reaches a well, and/or to allow
time to relocate or deepen a well or to implement remediation measures. Most states have
chosen to delineate "tiers" of WHPAs.  That is, the WHP As have inner zones, outer zones
and, in some states, intermediate zones.  Management of contaminant sources becomes
increasingly stringent from the outer to the inner zone.

       A surface-water protection area would also be delineated about a CRUS; and, as in a
WHP Program, sources of contamination would be managed within the SWPA.  A "tiered"
approach to CRUS protection in these surface water areas, therefore, would  be analogous to
the WHP approach.  Tiers of protection about the CRUS would provide the  opportunity for
flexibility while allowing the most protection where it is most needed.  The EPA recognizes
   3Those readers unfamiliar with the Wellhead Protection [WHP] Program or WHP approaches are referred to
"Guidelines for Delineating Wellhead Protection Areas" [U.S. Environmental Protection Agency, 1987a] and
"Guidance for Applicants for State Wellhead Protection Assistance Funds Under the Safe Drinking Water Act"
[U.S. Environmental Protection Agency, 1987b]. Currently, there are forty three states and two territories with an
approved WHP Program.

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that the susceptibility of a PWS to any given contamination source will depend, to a significant
degree, on the location of that contamination source in the watershed area; that is, in some
locations, a source would be a significant threat to a PWS while in other locations, particularly
within a large watershed, the source would be less significant or even non-significant.
Therefore, EPA encourages the segmenting of SWPAs into smaller subunits for the purposes
of source identification and susceptibility determinations.

        The conjunctive use of ground-water protection-area boundaries and surface-water
protection-area boundaries can facilitate implementation of CRUS-protection efforts by
segmenting SWPAs into smaller assessment/management units (that is, segments and
subsegments). States have the opportunity to creatively combine ground-water and surface-
water boundaries to meet state environmental needs.  Various approaches to conjunctively
delineating and segmenting a SWPA may be possible; two are presented below. These are the
Combined Ground-Water/Surface-Water approach and the Combined Nested-Watershed
Area/Ground-Water Flow approach.

Combined Groimd-Water/Surface-Water Approach

         In the "Combined Ground-Water/Surface-Water" approach,  ground-water and
surface-water boundaries define a series of segments that are at increasing distances from the
CRUS. This approach facilitates reduction of contaminant-source controls with increasing
distance from the CRUS.

        In this approach, four different delineation scenarios can occur:  the selected Zone of
ground-water Contribution (ZOC) boundary approximately coincides with the watershed-area
boundary; the selected ZOC  boundary is within the watershed-area boundary; the selected
ZOC boundary is external to the watershed-area boundary; and the selected ZOC boundary is
in-part within, and in part external to, the watershed-area boundary.

       Table 1 presents an example demonstrating this approach to CRUS protection.  This
approach is analogous to the tiered approach many states have chosen for delineating WHPAs.
(In this Table, the ZOC boundary is based on ground-water time of travel [TOT] and has been
given a specific value [10 years], to aid reader comprehension.)

       The delineation approach depicted in Table 1 is equally applicable to protecting
surface-water-supplied drinking-water intakes, endangered-species habitats and recreational
areas.  Protection of drinking-water intakes can be enhanced by calculating  (1) the streamflow-
TOTs and distances needed for sufficient remediation of upstream streamborne contaminants,
and 2) the streamflow TOT available for a water supplier to respond to an upstream
contaminant spill.


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                        LEGEND
                        	Watershed-area boundary
                        — — — — - Watershed boundary
                        — — — 10 year ground-water-time of-
                                travel boundary
                          3|£   Critical Use Site
Figure 3.  Watershed showing watershed-area and 10-year ground-water time-of-travel
          boundaries.
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 Combined Nested-Watershed Area/Ground-Water Flow Approach

          In this approach, segment boundaries are the boundaries of progressively embedded
 (nested") watersheds, delineated at increasing distances upgradient from the CRUS (Figure 4).
 One or more ground-water ZOC boundaries along the stream are superimposed on,  and
 intersect, the nested-watershed boundaries (the intersection of ground-water and nested
 watershed boundaries creates subsegments). This approach facilitates differential management
 of subsurface contaminant sources and surficial contaminant sources.  Figure 5 depicts an
 example segmented SWPA; in this example, the ground-water setback is based on a TOT. In
 this approach, although nested-watershed boundaries are topographically defined, ground-water
 boundaries could be based on the same criteria and thresholds that are used in a state's WHP
 Program.

 Methods for Delineating Ground-Water Boundaries to Protect the Quality of Ground-
 Water Sources Upgradient of Critical-Use Sites

       Protection of CRUSs should recognize that ground water (via base flow to streams) is
 generally a component, possibly a major one (and during  some parts of the year, possibly the
 only component), of streamflow.  Therefore, ground-water quality may significantly impact the
 quality of surface water.

       Defining a ground-water ZOC  is difficult, because with the exception of very, very deep
 water, much of which was emplaced millions of years ago, all ground water not withdrawn by
 wells or lost to evapotranspiration will ultimately be discharged from the ground-water reservoir
 to the ocean or to other surface-water bodies. In any regional setting, the deeper that ground
 water flows into the ground-water reservoir, the further ground water travels before
 discharging, and me greater the stream (the higher the  "order" of the stream in the "nesting"
 hierarchy) to which it discharges (Figure 6). That is, deep ground water will discharge to a
 large regional stream draining a large watershed, and shallow ground water will discharge to a
 local tributary draining a local  "nested" watershed. Thus, not only shallow,  but also deep,
 ground waters will become surface water.  (Conversely, surface water not lost to evaporation,
 runoff to the ocean, or pumping [or other human/animal-induced capture] will recharge the
 ground-water reservoir; this occurs most noticeably during periods of high stream flow.)

      In order to facilitate protection  of water supplies that have a ground-water component,
states and communities may, for management purposes, want to designate a boundary for the'
difficult-to-defme zone of ground-water contribution.  Several such boundaries could be
considered:

           Floodplain boundary setback for perhaps the 20-, 50- or 100-year flood -
           this area would be wide where floodplains are flat or flooding is frequent,
           and narrow where flood plains are steep or flooding is rare.  Although the
           floodplain defines the area over which surface water may infiltrate into the
           ground-water reservoir, the extent of a floodplain is not related to the area through
           which ground water contributes to surface water. Additionally, the selection of one
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      LEGEND
      	Segment boundary
        A-G    Segment Identifier
        $fc    Critical Use Site
Figure 4. Watershed area showing a source-water protection area divided into time-
         of-travel management segments.
                                         12


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      LEGEND
      	Segment boundary
        A-G   Segment Identifier
      	 Ground-water setback boundary
        3j£   Critical Use Site
Figure 5. Watershed an:a showing time-of-travel segment boundaries and a ground-water
         time-of-travel setback from the stream.
                                        13

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                                                                        B
                                                                  ground-water flow path
                                                                in a watershed larger than 'a'
                                                                           Note: diagram has vertical
                                                                              exaggeration
                                                                       Watershed 'b'
                                                                             Watershed 'e'
                                                     Watershed boundary
                                           	•  Sub-watershed boundary
                                           	Lower-rank sub-watershed boundary
Figure 6. A and B show "nested" watersheds. C shows ground-water flow within the
          nested watersheds.
                                           14


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           time-specific floodplain boundary over any other, must be made arbitrarily or be
           based on other-than-hydrologic factors.

       •   Hyporheic-zone boundary setback — this zone may be defined by biological
           parameters, that is, by the presence of certain macro-organisms, or by physical
           parameters; however, the boundary of this zone can vary with the parameter
           used. One parameter is a particular suite of indicator organisms that can be
           withdrawn by wells; these organisms spend part of their life cycle in surface
           water and part in ground water. The delineation of the hyporheic-zone
           boundary may also be defined by the extent of the penetration of surface water
           into ground water as indicated by physical-parameter values in the ground
           water that are similar to the values in the surface water. The size of the
           hyporheic zone can vary seasonally and in response to drought. Research has
           not determined how rapidly the hyporheic zone  is recolonized following the
           episodes of extensive surface-water intrusion into ground water that result from
           periods of flooding.  Although the hyporheic zone might be used to define the
           extent of surface-water intrusion into ground water, this zone is not related to
           the area from which ground water flows towards streams.

       •   Ground-water time-of-travel, and fixed-distance, setbacks — this concept
           relies on the  ability of soil and rock media to improve water quality with
           time and travel distance.  Given the current level of knowledge, specific
           distances needed for ground-water remediation are generally unknown;
           therefore, a fixed-distance or TOT setback has been used (most notably in
           the WHP Program) as a management approach to afford some measure of
           protection via ground-water  flow distance and travel tune.  Because of the
           effect of high-capacity wells on ground-water TOT, states might choose to
           revise TOT boundaries after installation of high-capacity wells in or near
           protection zones.

       •   Ground-water basin boundary — the position of this boundary is determined
           by the hydrologic, geologic and climatic characteristics of the hydrogeologic
           setting and generally fluctuates seasonally. The boundary marks the furthest
           locations from which ground water will flow to a hydraulically connected
           stream.  The  common assumption that the position of the surface watershed
           boundary approximates the position  of the ground-water basin boundary is
           not universally true. Use of this approximation may introduce significant
           error into the estimate of the position of the outermost boundary of ground-
           water flow to a stream.  Communities  with highly valued water uses might
           choose to have hydrogeologic experts accurately determine the boundary of
           their ground-water basin.

       In addition to the  setbacks above, a chemical-standard setback may be a future  option.
Research being performed, for example,  in a karst setting in Florida has shown that, based on
radionuclide information, ground water has contributed to springs and to the Suwannee River.
                                            15

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Such research may someday be helpful in developing a chemical-quality "cutoff" to delineate an
area where ground water and surface water "mix". Managers might choose to consider the
boundary of mis area to be the boundary of the ZOC.  Further research will be needed to
determine if this approach is a reasonable one and if such results would be applicable to other
streams and hydrogeologic settings.

       The reader may note that the ground-water TOT and fixed-distance setbacks are
analogous to the TOT and fixed-radius delineation criteria used in the WHP Program
(U.S. Environmental Protection Agency, 1987a). The reader may also note the analogy between
the chemical-standard or hyporheic-zone setback and the calculated fixed-radius setback that is
used as a delineation criterion in the WHP Program.

Methods for Delineating Surface-Water Boundaries to Protect the Quality of Surface-Water
Sources Upstream of Critical-Use Sites

       Three methods for delineating surface-water areas that contribute water to CRUSs, are
described below. These methods are:  stream TOT, setbacks/buffer zones, and nested-
watershed areas.  The first two methods have been used by states for protecting drinking-water
intakes supplied by streams and reservoirs. The last two  methods are directly applicable to
protection not only of drinking-water intakes, but to other uses deemed critical by resource
managers.  Managers may choose to apply these methods to the protection not only of streams
and reservoirs but to lakes as well, where lake-water quality protection is required for such
critical uses as drinking water, recreation and endangered-species needs.

Streamflow Time-of-Travel Method

       The intent of this method is different than that  of the two that follow. This method is
meant to provide direct protection to the CRUS, rather than protection of the water flowing to
the CRUS. The method does not delineate a protection zone; rather, the method calculates the
TOT of the flow of a stream between a CRUS and a point (such as a monitoring point) upstream
(Figure 7). For a distance between the same two points, TOTs vary with stream-discharge
volume.  It is the Streamflow travel time between the CRUS and the upstream point of interest
that provides the opportunity for managers to protect the CRUS.  The Streamflow TOT method
is often used to  alert a downstream drinking-water supplier that a contaminant spill has occurred
and provides the managers with lead tune to close downstream intakes. The streamflow-TOT
method also facilitates heightened assessment/management of those stream reaches most critical
to protection of drinking-water intakes from upstream, long-term, potential sources of
contamination.

       Generally, the TOT approach is a suitable early-warning method for protecting CRUSs
that can be temporarily isolated from surface-water contamination (for example, by the closing
of a drinking-water intake). However, this early-warning method is of little or no value to
CRUSs such as  endangered-species habitats, that cannot be protected from contaminant
exposure. Particularly sensitive habitats can be destroyed by brief exposure to toxic
contaminants.
                                           16

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                    Legend

                   I  Critical Use Site
Figure 7. Watershed showing points at three different stream times-of-travel (TOTs) to a
          critical-use site.

                                            17

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       At least two sophisticated "early warning" systems, the Ohio River Valley Water and
Sanitation Commission (ORSANCO) along the Ohio River, and the Early Warning Organic
Compound Detection System (EWOCDS) along the lower Mississippi River, have been
established to protect downstream water supplies.  ORSANCO is an interstate commission that
coordinates monitoring for specific organic contaminants hi the Ohio, Allegheny, Monongahela
and Kanawha Rivers in cooperation with local water utilities. ORSANCO notifies downstream
water utilities of detections so that utilities can implement protection measures.  ORSANCO's
monitoring locations encompass six states from Pennsylvania to Illinois. Personnel at water
treatment facilities collect samples directly from raw river feed lines for analysis.  If
contamination above the predetermined action level for a specific chemical is found, downstream
facility operators are notified. ORSANCO uses a flow model to estimate concentrations and
travel times when a notification is issued; potential times of arrival of a spill are provided to the
downstream utilities (Fraser,  K., written communication, 1996).

       EWOCDS was established to provide municipal and industrial water suppliers with early
warnings of contaminant spills on the lower Mississippi River.  The water providers and the
Louisiana Department of Environmental Quality calculate the TOT for the leading edge, peak,
and trailing edge of a spill, based on river velocity data (related to river height) provided weekly
by the Army Corps of Engineers. Through this monitoring and warning program, suppliers are
able to take appropriate measures to avoid intake of contaminated water.

Setback/Buffer-Zone Delineation Method

       Setbacks/buffer zones (Figure 8) are natural or planted, vegetated areas along part or all
of a stream's length. Buffer widths that have been selected by states are generally in the range
of 50-200 ft.  Buffer zones ("green areas") may be intended to serve several functions such as
wildlife habitat, residential or commercial exclusion or source-water protection. Buffer zones
filter out some portion of sediment-borne contaminants. In addition, by slowing down overland-
flow velocity, buffer zones encourage increased infiltration to the ground-water reservoir, where
travel times are longer (but, where contaminant cleanup is more difficult). To some degree,
buffer zones also increase the time available for such processes as photolysis,  evaporation and
plant uptake of contaminants. Buffer zones help to reduce dissolved contaminants entering
streams, and  some research has shown that some forested buffer  zones may be effective in
reducing nutrients.

       The remedial ability of buffer zones may decrease widi tune.  Because the carrying
capacity of moving water is related to its velocity; when overland flow reaches the outer edge of
a buffer zone, the velocity of the water is reduced and sediment is dropped. Thus, with time, a
berm may form along the edge of the buffer z'one.  A berm will cause future contaminant-laden
overland flow to travel parallel to the stream until a topographically low area is encountered.
There, the overland flow will cross the buffer zone and enter the stream; transported with the
overland flow will be its load of contaminants.  Therefore,  maintenance of a buffer zone is
critical to ensuring its effectiveness. The quality of overland flow overtopping buffer-zone
vegetation during a major precipitation event, will not be improved by the buffer zone.
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                    Legend




                   •Sjfr Critical Use Site
Figure 8.  Watershed with a buffer/setback zone for a critical-use site in a stream.




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Nested-Watershed Area Delineation Method

       This method is an outgrowth of the Streamfiow Time-of-Travel method described above.
In the Nested-Watershed Area method, topographic boundaries of progressively "nested"
watersheds (Figure 4) are delineated upstream of a CRUS and divide a SWPA into
assessment/management segments. In this method, the TOT from any point in a nested
watershed to the mouth of that watershed is considered equal to the TOT of the stream as it
flows through the nested watershed.  Stream TOTs are cumulated with decreasing distance to the
CRUS. If the CRUS is located on a stream reach between the mouths of two nested watersheds,
the TOT from the upgradient mouth to the CRUS is based on the relative distances of the CRUS
to the upstream and the downstream mouths.  Augmented management would be necessary for
any potential contaminant source that  occurs hi a nested watershed whose distance from the
CRUS does not provide enough tune for sufficient natural in-situ remediation.

       In this method, although no "credit" is given to overland-flow travel time, the TOT of
surface water at any point on the stream in a nested watershed is considered to be the  TOT of
the stream through the entire nested watershed.  For this reason, EPA recommends that states
delineate as many "levels" of nesting  as is useful for protection purposes.  The greater the level
of nesting, the more the error that is caused by assigning the total-stream TOT to every point on
the stream is reduced.

       The U.S. Geological Survey can provide travel times for many of the streams in large,
and in nested, watersheds in the United States.  States could select the number of levels of
watershed "nesting" that is needed to facilitate the implementation of sufficient
assessment/protection measures.

Summary

       Conjunctive delineation of ground-water protection-area boundaries and of surface-water
protection-area boundaries can facilitate protection of SWPAs.  Delineations and assessments
that lead to management of the quality of ground-water and surface-water resources within
SWPAs can improve the quality of water at such CRUSs as drinking-water intakes, freshwater
recreation areas and endangered-species habitats.
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                            LITERATURE CITED
Bates, Robert L., and Julia A. Jackson, editors, 1984. Dictionary of Geological Terms.
Third edition.  American Geological Institute. Page 280.

Crane, J. J., 1986.  An Investigation of the Geology, Hydrogeology, and Hydrochemistry of
the Lower Suwannee River Basin. Florida Geological Survey Report of Investigations.
No. 96.  205 pps.

U.S. Environmental Protection Agency, 1987a.  Guidelines for Delineation of Wellhead
Protection Areas.  196 pps.  (Reprinted in 1993 as EPA 440/5-93-001.)

U.S. Environmental Protection Agency, 1987b.  Guidance for Applicants for State
Wellhead Protection Program Assistance Funds Under the Safe Drinking Water Act.  53
pps.  EPA 440/6-87-011.
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