Defining the source area of water supply springs - R. Kreye, M. Wei and D. Reksten November 1996

 
Defining the source area of
water supply springs
R. Kreye, M. Wei and D. Reksten
November y 1996

     Hydrology Branch
     Ministry of Environment, Lands and Parks
Canadian Cataloguing in Publication Data
Kreye, R.
   Defining the source area of water supply springs

   Includes bibliographical references: p.
   ISBN 0-7726-2903-X

     1. Springs − British Columbia. 2. Water-supply −
   British Columbia. 3. Watersheds − British Columbia.
   I. Wei, M. II. Reksten, D. III. BC Environment.
   Hydrology Branch. IV. Title.

   GB1198.4.C3K73 1996         551.498   C96-960161-1
Defining the Source Area of Water Supply Springs

Defining the source area of water supply springs
R. Kreye1, M. Wei and D. Reksten,
Hydrology Branch, Ministry of Environment, Lands and Parks

Executive summary
                    Springs are an important source of water supply in British Columbia (BC), and
                    yet little is known about their occurrence, source areas, or sensitivity to impacts
                    from land use activities. An important step in protecting and managing the
                    spring supply is defining the spring’s source area. Spring source areas can be
                    identified and defined using topography, geology, water table contours, water
                    chemistry, spring discharge hydrographs, water balance calculations, and tracer
                    tests. Due to limited data availability for most springs in BC, a combination of
                    these techniques will usually need to be employed.

                    This report presents an approach for defining the source areas of water supply
                    springs in BC. The approach is based on the use of readily available data and
                    limited field investigation. In the approach, the investigator compiles and
                    analyzes data from existing sources and a field investigation to develop an
                    understanding of the hydrogeology of the spring. From this information the
                    location and boundaries of the source area can be interpreted. Source area
                    boundaries are delineated using topographic divides, geologic boundaries, flow
                    system boundaries identified from water table contours, and feature mapping.
                    The interpretation is checked using a water balance calculation. The end result
                    should be technically defensible and include caveats identifying limitations.
                    While the approach and techniques can be applied to a wide range of spring
                    types, they will probably be most applicable to springs associated with shallow,
                    local flow systems, which are common in BC.

                    The approach and techniques were successfully applied to three community
                    springs on Vancouver Island. The source areas for the springs were local in
                    extent, and reasonably well defined by topography. General data limitations
                    were the lack of spring discharge measurements and hydrogeologic information.
                    It is recommended that source area investigations be undertaken on springs in
                    other areas of BC to more comprehensively test the usefulness of the approach.
                    Information gained from source area can be used to help determine appropriate
                    management options for protecting the springs from land use impacts.

1   Water Management, Lower Mainland Region, Ministry of Environment, Lands and Parks

Hydrology Branch, Ministry of Environment, Lands and Parks, 1996                                          i
Defining the Source Area of Water Supply Springs

Acknowledgments
                 The licensees of the three springs used for the case studies were greatly
                 concerned with protecting their water supplies. Jim Lawrence, Obie Olson, Jim
                 Morgan and Stewart Hollingdrake gave freely of their time, for which we are
                 grateful. It is hoped that the work presented here provides the information
                 necessary to ensure their spring-sourced water supplies, as well as all others in
                 the province, are adequately protected. We would also like to acknowledge the
                 reviewers of the draft report for their valuable comments. Greg Blaney, Bob
                 Duncan, Gary Lucas and Jean Wood provided much needed technical support.
                 Finally, without the support of the Hydrology Branch, especially Karen Rothe
                 and Jim Mattison, this work would neither have been undertaken, nor
                 completed.

ii                                        Hydrology Branch, Ministry of Environment, Lands and Parks, 1996
Defining the Source Area of Water Supply Springs

                                                      Contents

1     Introduction .....................................................................................................     1

      1.1 Content of report .......................................................................................          1

2     Spring occurrence and description...............................................................                       2

      2.1 Development of springs..............................................................................               5

3     Literature review .............................................................................................        6

      3.1 Techniques for identifying and defining spring source areas......................                                  6

4     Identifying and defining source areas ..........................................................                       7

      4.1 Compile maps, air photos and data............................................................                     13

      4.2 Data analysis..............................................................................................       14

      4.3 Develop conceptual hydrogeologic model..................................................                          17

      4.4 Delineate source area ................................................................................            18

      4.5 Site investigation ........................................................................................       20

      4.6 Refine conceptual model and source area boundaries ..............................                                 21

      4.7 Evaluate reasonableness of delineated source area..................................                               21

      4.8 Write report ................................................................................................     21

5     Case studies....................................................................................................      22

6     Conclusions and recommendations .............................................................                         23

7     Glossary...........................................................................................................   25

8     Bibliography ....................................................................................................     27

      8.1 Springs .......................................................................................................   27

      8.2 General ......................................................................................................    27

Hydrology Branch, Ministry of Environment, Lands and Parks, 1996                                                             i
Defining the Source Area of Water Supply Springs

                                               List of figures

Figure 1.        Different types of springs (adapted from Davis and Deweist, 1966) .                                       3

Figure 2.        Effect of topography on groundwater flow patterns and location of source
                 areas for discharge springs. ............................................................. 5

Figure 3.        Approach for identifying and defining source areas..........................                             11

Figure 4.        Detailed flow chart of approach for identifying and defining source
                 areas. ...............................................................................................   12

Figure 5.        Relation of catchment area and annual recharge to average spring
                 discharge (from Todd, 1980) ............................................................                 16

Figure 6.        Decision tree identifying appropriate delineation technique for different
                 geologic media and flow types ......................................................... 19

                                                List of tables

Table 1.         Geologic classification of spring types (adapted from Tolman, 1937)                                       4

Table 2.         Techniques for defining source areas................................................                      8

                                           List of appendices
Appendix A.      Peter Springs.................................................................................... A1−1
                 Supply Spring ................................................................................... A2−1
                 Wheelbarrow Springs ....................................................................... A3−1

Appendix B.      Map, air photo and data sources
                 Data summary forms
                 Water chemistry parameters ............................................................ B1−1

ii                                                Hydrology Branch, Ministry of Environment, Lands and Parks, 1996
Defining the Source Area of Water Supply Springs

1       Introduction
                   Springs are an important source of water supply in British Columbia (BC).
                   Approximately 15 percent of all water licenses in BC are on springs, 105 of
                   which are for communitu water supplies (waterworks or water users’
                   communities) and over 6000 for domestic water supplies. These numbers do not
                   include water licenses on streams that are spring-fed or unlicensed water wells
                   that are developed in aquifers associated with springs. Springs can comprise the
                   major or sole source of water supply for larger communities such as Creston,
                   Spences Bridge and Mill Bay. They also provide high quality water for fish
                   hatcheries, commercial water bottling industries and are utilized for irrigation
                   and watering livestock. In many cases, spring waters do not require any
                   treatment to meet drinking water standards. Despite their importance, there is
                   limited information available for springs used for water supplies, the location of
                   their source areas or their sensitivity to land use activities.

                   The source areas of springs need to be defined to enable protection and
                   management under BC legislation, such as the Forest Practices Code (FPC), as
                   well as to support broader Ministry of Environment, Lands and Parks objectives
                   for the protection of spring-sourced water supplies. Source areas could be
                   protected as Community Watersheds or Sensitive Areas under FPC legislation.
                   Preliminary guidelines for management of spring source areas is included in the
                   FPC Community Watershed Manual. Without knowledge of spring source
                   areas, protection and management measures cannot be developed or applied.

                   The knowledge gained from a source area investigation will help guide the
                   development and application of appropriate protective measures for the spring.
                   The compilation of data from all investigations will improve our knowledge of
                   spring-sourced water supplies in BC and help in the development of strategies
                   for more comprehensive management.

1.1     Content of report
                   This report is the result of a study designed to determine available methods for
                   defining the source areas of springs. The report includes background
                   information on the occurrence and characteristics of springs, techniques that can
                   be used for locating and defining source areas, and an approach for
                   investigating and defining source areas. The approach for defining source areas
                   is based on the use of readily available data and a limited field investigation,
                   recognizing that, in most instances, investigators may be unable to employ the
                   drilling and monitoring techniques that are typically required for technically
                   rigorous hydrogeologic investigations.

Hydrology Branch, Ministry of Environment, Lands and Parks, 1996                                        1
Defining the Source Area of Water Supply Springs

                 Appendix A includes three case studies that demonstrate the application of the
                 techniques and the approach. The information presented is intended for use by
                 the professional hydrologist or geomorphologist.

                 The techniques and approach can be applied to a broad range of spring types
                 and geologic environments. However, given the generally limited data
                 availability and proposed level of site investigation, it will be most successful in
                 shallower flow systems. The report does not address the impacts of resource use
                 on springs nor does it propose specific protective measures or management
                 strategies for source areas.

2      Spring occurrence and description
                 Springs can be classified using a number of different criteria. In the literature
                 reviewed, spring classifications are usually based on either physical
                 characteristics or occurrence parameters, such as:

                 •   geology
                 •   magnitude, variation, and permanence of flow
                 •   quality and mineralization of the spring water
                 •   temperature of the spring water.
                                                      (Fetter, 1980; Tolman, 1937; Meinzer, 1923)

                 It is useful to classify springs according to geology, since geology directly
                 governs spring occurrence and water flow to springs. Most springs in BC can be
                 classified according to the categories in Table 1. Figure 1 shows conceptual
                 diagrams of the spring classes.

                 Springs are naturally occurring discharge features of groundwater flow systems.
                 Groundwater flow to springs (and therefore the characteristics of the source
                 area) is governed mainly by three inter-related factors: geology (type,
                 distribution and permeability characteristics of geologic units), topography
                 (landforms and relief), and climate (timing and amount of precipitation).
                 Geology, topography, and climate influence the amount of water that occurs as
                 surface flow versus the amount that infiltrates into the ground as recharge to
                 groundwater. All three factors govern how the subsurface flow system develops
                 and, ultimately, where springs occur. For example, Figure 1-b2 shows that the
                 nature of the geology (permeable sand overlying low permeability till) and
                 relief (shallow slope) allows a flow system to develop in the sand unit.
                 Topography drives the groundwater flow downhill and largely dictates the
                 occurrence of the spring itself. Climate would influence the timing and amount
                 of recharge to the flow system and the volume and variability of discharge.
                 Davis and DeWiest

2                                         Hydrology Branch, Ministry of Environment, Lands and Parks, 1996
Defining the Source Area of Water Supply Springs

Figure 1.        Different types of springs (adapted from Davis and Deweist, 1966).

Hydrology Branch, Ministry of Environment, Lands and Parks, 1996                                        3
Defining the Source Area of Water Supply Springs

Table 1.         Geologic classification of spring types (adapted from Tolman, 1937).

                 Type of spring         Geologic material    Type of porosity                 Setting

                 depression             unconsolidated       primary,               occurs where water table
                 springs                sediments            intergranular          intersects the land surface
                 contact springs        unconsolidated       primary,               occurs at or near base of
                                        sediments            intergranular          underlying confining unit
                 fault/fracture/joint   bedrock              secondary,             occurs along joints,
                 springs                                     fractures              fractures or faults where
                                                                                    they intersect the land
                                                                                    surface
                 karst springs          carbonate bedrock    secondary, solution    occurs where solution
                                                             channels               channels developed in
                                                                                    limestone and dolomite
                                                                                    intersect the land surface
                 lava springs           volcanic bedrock     primary, flow tubes,   occurs where lava tubes,
                                                             interbeds and/or       interbeds and cooling joints
                                                             joints                 intersect the land surface

                 (1966) note that “…a vertical or horizontal variation of permeability is the most
                 common cause of the localization of springs” (p. 63).

                 The hydrology of a spring is intimately related to the flow system. The
                 influence of hydrogeology, topography, and recharge dictates the distribution of
                 hydraulic head within the flow system and, consequently, the flow of water
                 from recharge to discharge areas and to springs. It is the distribution of
                 hydraulic head and configuration of the flow system that defines the flow
                 directions from which the source area for springs can be most directly
                 determined.

                 Unfortunately, hydraulic head measurements near most springs in BC are rarely
                 available for determining hydraulic head gradients and flow directions. In
                 shallow groundwater flow systems however, which are common in many
                 terrains in BC, the flow system and flow directions can be inferred from the
                 local topography and geology. In general, pronounced local relief will affect
                 shallow flow systems, while regional relief will affect more deeper, regional
                 flow systems.

                 The effect of local and regional topography and the concept of shallow and
                 deeper flow systems are illustrated in Figure 2. Local topography produces
                 shallow, local flow systems above a regional flow system. Water that enters the
                 recharge area to a shallow, local flow system discharges at the nearest
                 topographic low. The source area for springs associated with the shallow
                 systems can readily be traced uphill within the local topographic high areas.
                 Springs associated with deeper, more regional flow systems are fed by water

4                                             Hydrology Branch, Ministry of Environment, Lands and Parks, 1996
Defining the Source Area of Water Supply Springs

Figure 2.          Effect of topography on groundwater flow patterns and location of source areas
                   for discharge springs.

                   that infiltrated across the wider area and from areas farther away, beyond the
                   local topographic highs.

                   Geological heterogeneities can similarly have a profound effect on groundwater
                   flow. For deeper, regional flow systems, in areas of low relief, and in karst
                   terrains (where flow typically occurs in discrete channels), the identification of
                   the source area is more complicated and would usually require more detailed
                   hydrogeologic data.

2.1     Development of springs
                   Springs range from disperse, low volume seepage to focused high volume
                   discharge sites. How a spring is developed and the type of waterworks installed
                   may vary, depending on spring flow and the use for which the water supply is
                   intended. Common methods of spring development in BC include:

                   •   digging open drainage channels downhill from the spring to divert and
                       collect the spring flow
                   •   installing drain tiles, pipes, or collection boxes along a seepage face or at a
                       point of spring discharge
                   •   constructing a gravel back-filled and piped drainage trench along the spring
                       line, and
                   •   drilling or excavating wells into the spring discharge area.

                   Supply systems may rely on gravity and natural spring flow or pumps may be
                   employed.

Hydrology Branch, Ministry of Environment, Lands and Parks, 1996                                         5
Defining the Source Area of Water Supply Springs

                 Although the type of works used to develop a spring generally does not affect
                 the source area, the works should be included in the overall protected area
                 specified for the spring. This may include surface water features such as ditches,
                 ponds or dugouts that are integral to the water supply, or engineered structures
                 (see Appendix A: Supply Spring and Wheelbarrow Springs). The type of works
                 may also affect monitoring of spring discharge and water quality, which are
                 important for determining the characteristics of the spring and source area and
                 assessment of land use impacts on the spring (refer to Appendix A: Case
                 Studies).

                 Where there are a number of associated springs, and where it can be determined
                 that they are sourced from the same aquifer, it may be appropriate to consider
                 source area delineation for the group rather than for an individual spring.

                 Finally, development of other waterworks may affect the source area. For
                 example, where the aquifer feeding the spring is influenced by pumping wells,
                 the water table configuration around the wells may change the ambient flow
                 conditions. This could complicate delineation of the source area, or even change
                 the source area over time with continued pumping (see Appendix A:
                 Wheelbarrow Springs).

3      Literature review
                 The literature review for this study discovered little information directly
                 addressing the identification and delineation of spring source areas. Some
                 information is available for karstic springs in Yugoslavia (e.g. Bonacci and
                 Magdalenic, 1993). There are several case studies for mapping spring sources in
                 North America (e.g. Munter et al, 1992; Trudeau et al, 1983). Civita (1995)
                 developed a method for delineating protection zones for springs in the
                 Mediterranean based on an analysis of considerable historical regional data. Its
                 applicability to BC has not been assessed.

                 Risser and Barton (1995) developed a strategy for delineating the recharge area
                 to wells in fractured bedrock which has potential for use for springs in bedrock.
                 While the literature review did not reveal any standardized approaches or
                 methods that could be applied to the range of spring types in BC, it did provide
                 information on general techniques that can be used for investigating the location
                 and extent of spring source areas.

3.1    Techniques for identifying and defining spring source areas
                 There are a number of techniques that can be used to identify and define the
                 source area of a spring (Table 2). These techniques were compiled from case
                 study literature, from techniques used for the source area delineation of wells,
                 and general approaches used for hydrogeologic investigations. Many of the

6                                         Hydrology Branch, Ministry of Environment, Lands and Parks, 1996
Defining the Source Area of Water Supply Springs

                   techniques can be applied using existing data and limited field surveys. The
                   techniques use topographic, geologic, and hydrogeologic (e.g., discharge, water
                   table elevations, water chemistry) data to identify and/or locate either the flow
                   system or spatial characteristics of the source area.

4       Identifying and defining source areas
                   This section presents an approach for applying the techniques presented in
                   Table 2. The approach, as shown in Figure 3 and detailed in Figure 4, is
                   iterative. Although, in theory, the approach applies to all springs (including
                   thermal springs), heavy reliance on existing information and the limited scope
                   of the field investigation suggest that it would be most successfully applied to
                   springs associated with shallow, local flow systems where local topography and
                   geology can be used to locate the source area.

                   The objective of a source area investigation is to define, as closely as
                   possible, the location and extent of the land area that contributes recharge
                   to the groundwater flow system that supplies the spring.

                   To define the source area of a spring the investigator compiles and analyzes
                   data from existing maps and databases, develops a conceptual model of the flow
                   system and flow system boundaries, undertakes a site investigation to verify site
                   specific data, refines and revises the model, and then completes a report
                   documenting the interpretation. The end result should be a technically
                   defensible interpretation of the subsurface flow system and flow system
                   boundaries of the source area, including caveats identifying limitations. Another
                   outcome of the investigation is an understanding of some of the physical and
                   use characteristics of the spring and source area, which can support the
                   development of protective measures.

                   Variable site conditions and limited information for licensed springs in BC
                   make it unlikely that any one of the techniques presented in Table 2 would, by
                   itself, be sufficient to accurately define the source area. However, if the
                   techniques are used in conjunction, a reasonable determination can usually be
                   made. In most cases, insufficient hydrogeologic data will limit the
                   interpretation. It should be emphasized that each investigation will deal with a
                   unique set of data, and therefore, investigators must remain flexible in their
                   approach and in what techniques are most appropriately employed.

                   The case studies in Appendix A illustrate how the techniques and approach are
                   applied.

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Defining the Source Area of Water Supply Springs

Table 2.         Techniques for defining source areas.

Technique           Description/references                                       Notes

arbitrary         designate an arbitrary area      •   different shapes with specific dimensions may be designated
                  around a spring to provide           (e.g., circular, rectangular, or designated by property
                  a zone of protection that            boundaries)
                  may include all or part of       •   is generally not physically based
                  the actual source area
                                                   •   may be appropriate for small domestic springs
                  References: USEPA, 1993          •   can be useful as an interim measure if no other option to
                                                       outline a protection zone
                                                   •   precedence: is commonly used to outline source areas for
                                                       community wells’ protection where no information is
                                                       available

topography        surface elevation contours       •   local topography often controls the direction and gradient of
                  are used to infer the                subsurface flow to springs associated with shallow, near-
                  direction of subsurface flow         surface flow systems
                  and the location of              •   in general, pronounced local relief will indicate a local flow
                  subsurface flow divides              system, while areas of low relief would indicate more
                  References: Kohut, 1985              regional flow systems
                                                   •   flow divides can be defined at different scales (from small to
                                                       large scale maps and air photos down to site level surveys),
                                                       accuracy is scale dependent
                                                   •   assumes flow is perpendicular to the topographic contours
                                                   •   can delineate a source area directly or by deduction from
                                                       delineating adjacent surface watersheds
                                                   •   may not be accurate for karst terrains, areas of low relief, or
                                                       where groundwater pumping has significantly altered the
                                                       water table so that it is no longer a subdued replica of the
                                                       topography
                                                   •   precedence: topography has also been used to delineate
                                                       groundwater flow regions on the Gulf Islands and outline
                                                       source areas for community wells in the Lower Fraser Valley

geology           the type, location and areal     •   the permeability of geologic units and/or differences in the
                  extent of specific geologic          permeability between one unit and another governs the
                  units is used to define the          occurrence of springs and flow to them
                  source area                      •   quantity and variation in flow, and water quality, are
                                                       governed by the characteristics of the geologic units through
                  References: Bonnaci and
                                                       which the water flows
                  Magdalenic, 1993; Munter
                  et al, 1992.                     •   identifying the areal extent and depth of different geologic
                                                       units and interpreting the geology is a critical step in defining
                                                       the source area
                                                   •   a range of reference sources are available for identifying or
                                                       interpreting geology (e.g. surficial geology, landform, terrain
                                                       survey, soils and aquifer classification maps; air photos; drill
                                                       hole lithologies)
                                                   •   in fractured and karstic bedrock, the distribution of discrete
                                                       fractures and dissolution channels through which water flows
                                                       need to be mapped also to delineate the source area

8                                                Hydrology Branch, Ministry of Environment, Lands and Parks, 1996
Defining the Source Area of Water Supply Springs

Technique             Description/references                                     Notes

water balance       use discharge and               •   can indicate the size of the source area, but not the location
                    precipitation data to               or boundaries of the source area
                    calculate the size of the       •   limited by the availability and accuracy of precipitation and
                    source area                         flow data
                    References: Bonnaci and         •   compare temporal variation of spring discharge to
                    Magdalenic, 1993; Munter            precipitation to determine if water is derived from
                    et al, 1992.                        precipitation
                                                    •   provides an estimate only
                                                    •   most useful in context with other techniques
                                                    •   can provide an indication of largest possible size of source
                                                        area

water table         the direction of flow and       •   is a direct method of mapping subsurface flow to the spring
contours            location of flow divides are        and identifying the location and extent of the source area
                    inferred directly from water    •   water table contours can be manually drawn from existing
                    table elevation contours            subsurface water level data points (wells, surface water
                    and the water table                 features)
                    contours are then used to
                    delineate the subsurface        •   water table contours can also be derived through modeling,
                    contributing area or source         calibrated to existing data points
                    area for the spring             •   accuracy is dependent on scale, number of data points and
                                                        how well hydrogeology has been characterized
                    References: Delin and           •   accuracy is often limited by the lack of data points and
                    Almindinger, 1994; Banton           insufficient understanding of the site hydrogeology
                    and Kenrick, 1992.
                                                    •   in many cases the water table is a subdued replica of
                                                        topography and topography can be used to infer subsurface
                                                        flow divides that define the source area
                                                    •   assumes flow is perpendicular to the contours except in:
                                                        fractured bedrock, karst bedrock, and other highly
                                                        anisotropic geologic units
                                                    •   water table contours can change seasonally or under the
                                                        influence of a pumping well(s)

water chemistry     water chemistry can be          •   provides a gross measure of source area location only: local
                    used to infer the relative          versus regional
                    age, origin and history of      •   amount and variation of mineralization (e.g. TDS, specific
                    the water and give general          conductance) are relative indicators of how far and how
                    indication of the location of       deep the water has traveled (water with relatively low TDS
                    the source area                     indicates that the source is nearby and likely from
                                                        precipitation; seasonal variation in water chemistry would
                    References: Kohut, 1985;
                                                        suggest that water is derived from seasonal recharge)
                    Gluns and Green, 1994;
                    Trudeau et al, 1983; Risser     •   may narrow down potential source areas by unique chemical
                    and Barton, 1995.                   constituents of water or by comparison of water chemistry
                                                        with other waters
                                                    •   geology (and land use) can impart a unique chemical
                                                        signature in water (e.g. arsenic from some granitic bedrock,
                                                        elevated calcium from limestone, nitrates from agriculture or
                                                        range land use)
                                                    •   isotope analysis can indicate physical processes water has
                                                        undergone (e.g. evaporation)
                                                    •   water chemistry sampling should include adjacent surface
                                                        waters as well as groundwater sources for comparison

Hydrology Branch, Ministry of Environment, Lands and Parks, 1996                                                     9
Defining the Source Area of Water Supply Springs

Technique            Description/references                                        Notes

spring discharge   the recession curve of a          •   does not identify the location of the source area, only the
hydrograph         spring hydrograph is                  extent and type of protective zones required
                   analyzed to determine the         •   guides the design and dimensions of various types of
                   flow velocity in the spring           protective zones for springs of different sensitivities
                   aquifer; this is used to help
                   define various zones of           •   provides an indication of the estimated time of travel (TOT)
                   protection around the                 of contaminants
                   spring                            •   requires a continuous discharge record of the spring, which
                                                         is not available in many cases
                   References: Civita, 1995;         •   is based on the analysis of springs in the Mediterranean and
                   Johansson, 1987.                      has not been applied in BC
                                                     •   is the only method found that has been specifically
                                                         developed for protecting springs

tracers            dye or other tracers are          •   types include: fluorescent or colour dyes, bromide, and
                   introduced into the up-               radioactive tracers
                   gradient groundwater to           •   can give direction, rate of travel of flow, the location of point
                   determine if flow from that           sources of recharge (karst systems) and with sufficient data
                   location forms part of the            points, the areal extent of the source area
                   recharge to the spring
                                                     •   a comprehensive tracing program requires intensive
                   References: Risser and                sampling and analysis
                   Barton, 1995.
                                                     •   use may be limited by regulation or controversy of
                                                         introduction into or near drinking water sources
                                                     •   long travel times of some flow systems may limit applicability
                                                         in those terrains
                                                     •   most useful in rapid flow systems (e.g. fractured bedrock,
                                                         karst, high permeability unconsolidated deposits)
                                                     •   often used to define point source of recharge in karst
                                                         systems

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Defining the Source Area of Water Supply Springs

                           COMPILE DATA

                          ANALYZE DATA

                      DEVELOP CONCEPTUAL
                     HYDROGEOLOGIC MODEL

                    DELINEATE SOURCE AREA                           SITE INVESTIGATION

                       EVALUATE ACCURACY

                           WRITE REPORT

Figure 3.          Approach for identifying and defining source areas.

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Defining the Source Area of Water Supply Springs

                                     COMPILE DATA

                                     ANALYZE DATA

                    characterize topographic setting
                    •   surface water and watersheds
                    •   other springs/groundwater features
                    •   topographic features (gullies, ridges, etc.)

                    characterize geologic setting
                    •   geologic units and boundaries
                    •   unit materials
                    •   stratigraphy                                                  SITE INVESTIGATION

                                                                                  •   verify existing data
                                                                                  •   acquire new data
                    characterize hydrogeologic setting                            •   identify local scale features
                    •   aquifer                                                   •   survey waterworks
                    •   flow from unconsolidated or bedrock unit?
                    •   discharge/precipitation relationships
                    •   water balance
                    •   water table elevations/contours
                    •   water chemistry

                    identify land use setting
                    •   land use features and boundaries
                    •   vegetation (recharge/discharge features)

                                  CONCEPTUAL MODEL

                    •   flow shallow or deep?
                    •   flow local or regional?
                    •   flow through which geologic deposits?
                    •   discrete or porous flow?
                    •   sources of recharge?
                    •   topography reflection of water table?
                    •   flow boundaries same as geologic boundaries?

                              DELINEATE SOURCE AREA

                              •    topographic divides
                              •    geologic boundaries
                              •    flow system mapping
                              •    feature mapping

                                  EVALUATE ACCURACY

                                     WRITE REPORT

Figure 4.        Detailed flow chart of approach for identifying and defining source areas.

12                                                  Hydrology Branch, Ministry of Environment, Lands and Parks, 1996
Defining the Source Area of Water Supply Springs

4.1     Compile maps, air photos and data
                   The objective of data gathering and analysis is to develop a site specific
                   understanding of how the spring occurs and what physical factors control flow
                   to the spring. Data should be shown on appropriate maps and cross-sections.
                   While the final source area boundaries should be presented on a 1:20 000 TRIM
                   base, larger scale base maps may be appropriate, especially if the spring source
                   area is highly localized (refer to map figures in case studies).

                   Every effort should be made to acquire data from the variety of sources
                   available, since interpretation will often rely heavily on existing data. Data
                   sources include various ministry databases (e.g. WLIS, SEAM, and WELL),
                   other government agencies (Ministry of Health, Ministry of Forests, Ministry of
                   Transportation and Highways), forest licensees, and water purveyors. The site
                   investigation will also generate additional data. Appendix B includes a
                   summary of data sources, and forms that summarize data types.

                   The following features should be identified and mapped:
                   •   the water supply spring(s)
                   •   other spring(s)
                   •   local and regional surface water features and their watersheds (lakes, ponds,
                       streams, etc.)
                   •   other surficial features (gullies, ridges, depressions, topographic divides, etc.)
                   •   distinct forest cover and vegetation types
                   •   geologic units and boundaries (surficial geology, bedrock geology, soils,
                       landforms, etc.)
                   •   land use activities (roads, mines, gravel pits, dumps, clear cuts, range use,
                       agricultural use, etc.)
                   •   wells and other drill holes
                   •   groundwater level elevations
                   •   delineated aquifers
                   •   waterworks

                   The following data should be compiled:
                   •   spring discharge
                   •   water chemistry
                   •   precipitation records
                   •   characteristics of geologic units (material, origin, etc.)
                   •   well lithologies and aquifer materials

Hydrology Branch, Ministry of Environment, Lands and Parks, 1996                                       13
Defining the Source Area of Water Supply Springs

4.2    Data analysis
                 The mapped and compiled data is analyzed to develop an understanding of how
                 the spring occurs, possible sources of recharge, and where flow to the spring
                 may originate. From this information a conceptual model of the flow system
                 and flow system boundaries associated with the spring is developed. Data
                 analysis identifies the topographic, geologic, hydrogeologic and land use
                 settings of the spring, and provides information on the following:
                 •   surficial relief (topography)
                 •   geology (permeability, stratigraphy)
                 •   water table elevation contours for the aquifer supplying the spring
                 •   water balance and discharge / precipitation relationships
                 •   water chemistry

                 Topography

                 Topography often reflects the underlying water table surface and can be used to
                 infer subsurface flow directions and flow divides, especially for shallow flow
                 systems. Two indicators of whether a spring is associated with a shallow flow
                 system are: 1) where the seasonal variation in discharge generally correlates
                 (with a lag time period) with seasonal precipitation patterns; and, 2) where the
                 water quality (as reflected by the specific conductance or total dissolved solids
                 (TDS) (e.g. mineralization)) is relatively fresh (as compared to rainwater) and
                 fluctuates seasonally. Spring discharge from deep flow systems may show little
                 seasonal variation in flow or quality.

                 The degree to which the water table reflects surface topography can be checked
                 by plotting known or inferred water table elevations against surface elevations
                 at those points, for as many points as possible in the area (see Figure 7,
                 Appendix A: Wheelbarrow Springs). A positive correlation indicates that water
                 table elevations reflect surface topography. Subsurface flow is assumed to be
                 perpendicular to surficial contour lines. Groundwater divides are assumed to
                 coincide with topographic divides.

                 Geology

                 Geology and stratigraphy (presented in the form of fence diagrams, cross
                 sections, and isopach maps) identify the location and extent of the type of
                 materials or the aquifer through which groundwater flow to the spring occurs.
                 The porosity, permeability and/or differences in permeability between different
                 geologic units help determine the factors controlling spring occurrence, rate of
                 flow, extent and type of recharge zones, and the potential sensitivity of the
                 spring to impacts.

14                                        Hydrology Branch, Ministry of Environment, Lands and Parks, 1996
Defining the Source Area of Water Supply Springs

                   Groundwater flow in different geologic materials occurs as either porous flow
                   or discrete flow. Porous flow generally occurs in unconsolidated materials or
                   intensely fractured bedrock, and discrete flow in discontinuous fractures in
                   bedrock, along faults and in solution channels (karst bedrock). As geologic units
                   are distinguished by similar properties (e.g. rock type), including hydrogeologic
                   properties, the mapping of geologic units is important for defining the flow
                   system, the aquifer through which flow occurs, and the extent of the source
                   area.

                   Water table contours

                   In unconsolidated deposits and intensely fractured rock, water table elevations
                   and contours reflect groundwater flow directions and, therefore, direction from
                   where spring water originates. Where water table contours are available or can
                   be developed, they are a direct method of identifying the source area
                   boundaries. Water table elevations may be identified on well records or can be
                   taken directly from water level measurements in wells. They can also be
                   inferred from the elevation of surface water features, other springs or seeps, or
                   from diagnostic vegetation associated with groundwater discharge sites. In
                   shallow flow systems, the water table is often assumed to be a subdued replica
                   of surface topography, and as such, water table contours would generally follow
                   topographic contours.

                   Source areas for springs can be delineated by drawing flow lines from the spring
                   perpendicular to the water table contours upgradient, similar to how watersheds
                   are delineated for surface water sources.(see Appendix A: Wheelbarrow Springs)

                   Water balance

                   A water balance provides an estimate of the size of the source area given the
                   spring discharge and amount of recharge in the source area. It is usually
                   calculated on an annual basis. A general water balance equation for a spring
                   source area is:
                                          Q + W = A (P − ET + ∆S)

                   where:     Q = spring discharge
                              W = other discharge in source area (e.g. springs, pumped wells, surface
                                  water flow)
                            A = source area
                            P = total precipitation
                            ET = evapotranspiration
                            ∆S = change in storage
                   If we consider discharge from year-to-year, ∆S can be assumed to be zero if
                   conditions remain constant over a number of years. Where other sources of

Hydrology Branch, Ministry of Environment, Lands and Parks, 1996                                       15
Defining the Source Area of Water Supply Springs

                 discharge, such as well pumping, are absent, W can also be assumed to be zero.
                 Spring discharge is obtained from discharge records, observation, or anecdotal
                 information. Precipitation is estimated from nearby climate station data adjusted
                 to reflect source area conditions, or from regionalized estimates shown on
                 isohyetal maps. Evapotranspiration can be calculated from climate station data
                 using the Thornthwaite method, isohyetal maps of evaporation, or from climate
                 station evaporation data. The size of the source area can then be calculated
                 from:

                                                                                   A (km2) =          Q (dam3)
                                                                                                      P (mm) − ET (mm)

                                          (m3/s ✕ 31 540 = dam3 for annual amounts)
                                          (dam3 [cubic decametres])

                 This relationship between source area, discharge and recharge is demonstrated
                 in Figure 5.

                                                               10 000

                                                                              annual recharge

                                                                                                0.1mm
                                           square kilometres

                                                                1000
                                                                                                       1 mm
                  Source Area of Spring

                                                                                                               10 mm
                                                                 100
                                                                                                                     100 mm

                                                                                                                         1000 mm
                                                                  10

                                                                                                      315 mm

                                                                                   100 ha
                                                                 100
                                                   hectares

                                                                                                   10 L/s

                                                                  10
                                                                        0.1          1           10            100         1       10

                                                                                  L/s                                    m 3/s

                                                                                                Spring Discharge

Figure 5.        Relation of catchment area and annual recharge to average spring discharge
                 (from Todd, 1980).

16                                                                               Hydrology Branch, Ministry of Environment, Lands and Parks, 1996
Defining the Source Area of Water Supply Springs

                   Water chemistry

                   Water chemistry, including seasonal variation, can be used to infer the origin
                   and relative age of water. For example, a spring may show distinct seasonal
                   variability in chemistry that correlates with the seasonal precipitation
                   fluctuation (with a lag time period), indicating that the spring is recharged
                   directly by infiltration of precipitation.

                   Spring water chemistry contains chemical, isotopic, and thermal signatures
                   which may reveal flow paths and history. For example, the amount of total
                   dissolved solids (TDS), in the spring water compared to the chemistry of nearby
                   surface water, rain water, and well water may indicate the relative subsurface
                   residence time and distance groundwater has traveled before discharging as a
                   spring. Spring water with low TDS (slightly higher than rain or surface water)
                   would suggest that the spring water is from infiltration of local precipitation or
                   fresh surface water and that the source area is of local rather than regional
                   extent.

                   The presence of elevated levels of minute chemical constituents, such as
                   arsenic, fluoride, organic acids, and nitrate, in the spring water provides clues to
                   the origin of the spring water and helps define the location of the source area by
                   association with specific geologic units or land use activities. In the semi-arid
                   interior of BC, Kohut (1985) used the isotopic character of spring water to
                   deduce that the source area for Shaughnessy Spring at the Summerland Trout
                   Hatchery included infiltration from surface drainage sources because the spring
                   water showed isotopic evidence that the water had undergone evaporation prior
                   to infiltrating to the aquifer.

                   The specific constituents tested for should be determined in context of the
                   geologic and land use environment of the spring. A common minimum field
                   analysis would include: TDS (or specific conductance), temperature, pH and
                   nitrate-nitrogen. Typical parameters for laboratory analysis are included in
                   Appendix B. Comprehensive historic lab chemistry for a particular community
                   spring may also be available from Ministry of Health’s WSACS database.

4.3     Develop conceptual hydrogeologic model
                   Developing a conceptual hydrogeologic model is a natural progression from
                   data analysis. Data analysis should give an understanding of how the spring
                   occurs, the physical factors governing flow to the spring, the possible sources of
                   recharge, what additional information would be required to clarify the
                   interpretation or distinguish one interpretation from another, and which
                   technique(s) best support source area boundary delineation. The detail of the
                   conceptual model will be governed by data availability, however, the process of
                   developing the model helps to identify additional data needs or limitations of

Hydrology Branch, Ministry of Environment, Lands and Parks, 1996                                       17
Defining the Source Area of Water Supply Springs

                 the final interpretation. In developing the conceptual model, the following
                 questions should be answered:

                 •   What and where are the potential sources of water that supply the spring?
                 •   How and through what geologic unit might water flow to the spring?
                 •   What physical factors (e.g. topography, geology) control flow to the spring?
                 •   Does the water chemistry suggest a local or regional, shallow or deep flow
                     system?
                 •   Does spring discharge or water temperature variability suggest a deep or
                     shallow flow system?
                 •   Does water chemistry suggest what geologic environments or land use areas
                     the flow system may be associated with?
                 •   Does the water balance suggest a large or small source area?
                 •   Are there identifiable recharge and discharge areas?
                 •   What techniques might be suitable for delineating source area boundaries?
                 •   What information is missing and required to confirm the interpretation and
                     delineate boundaries?
                 •   Is there more than one plausible interpretation of the source area?
                 •   What additional information is required to test whether one interpretation is
                     more likely than another?

                 The conceptual model can be illustrated diagramatically or through maps and
                 cross-sections. Rationale supporting the conceptual model, and limitations,
                 should be clearly documented.

4.4    Delineate source area
                 Inferred groundwater flow directions and flow divides mark the location of
                 source area boundaries. Flow system boundaries are identified using:

                 •   water table elevation contours
                 •   topographic divides
                 •   geologic unit boundaries
                 •   feature mapping (e.g. sinkholes, faults, etc.).

                 Figure 6 provides guidance on the most appropriate technique for different
                 types of flow systems. The justification for what techniques are used to
                 delineate the source area boundaries is derived from data interpretation and the
                 conceptual model of the spring.

18                                         Hydrology Branch, Ministry of Environment, Lands and Parks, 1996
Defining the Source Area of Water Supply Springs

                   Of the techniques presented in Table 2, the use of topography, geology, and
                   water table elevation contours, or a combination of these techniques would be
                   most common. Water table elevation contours are usually not available or may
                   be difficult to map without a sufficient number of data points. Where it can be
                   demonstrated that topography reflects the water table surface (see section 4.2),
                   it may be appropriate to use topographic contours to identify inferred flow
                   divides. Where flow occurs in specific and identifiable geologic units, the
                   geologic unit boundaries can also be used to help outline source area
                   boundaries.

                   Feature mapping, utilizing tracers and field mapping, can be employed for
                   refining source area boundaries or for delineating source area boundaries in
                   discrete flow bedrock and / or karstic systems. Tracers are most effective where
                   the source area is very localized and flow to a spring is sufficiently rapid (i.e.
                   travel times of days or weeks rather than months or years) for tests to be carried
                   out. The use of certain tracers may be controversial, especially when introduced
                   into or near active drinking water sources.

                        flow medium              flow type             flow system             delineate
                                                                      characteristics       boundaries using

                                                                     Is the flow system
                                                                   shallow and the water       topographic
                                                                    table a reflection of        divides
                                                                       the topography
                                                                              f   ?

                         unconsolidated                             Is the flow system         water table
                       deposits; intensely         porous           deep or regional in         elevation
                       fractured bedrock                                  nature?               contours

                                                                        Are any flow
                                                                   boundaries consistent        geologic
                                                                     with geologic unit           unit
                                                                        boundaries?             boundary

                                                                    Is flow confined to a        feature
                         fractures faults          discrete           limited number of          mapping
                            conduits
                                                                     discrete channels?

Figure 6.          Decision tree identifying appropriate delineation technique for different
                   geologic media and flow types.

Hydrology Branch, Ministry of Environment, Lands and Parks, 1996                                               19
Defining the Source Area of Water Supply Springs

4.5    Site investigation
                 The site investigation should verify site conditions, gather additional data to
                 further characterize the springs and source area, identify local scale features,
                 and survey the waterworks. In many cases, the mechanism of spring occurrence
                 will not be obvious from an office assessment and can only be determined by
                 site investigation. A site visit also enables spring works to be documented and
                 locations identified for monitoring spring flow and raw water quality. The site
                 visit should confirm and/or support revision of the conceptual model.

                 Site investigations are critical for springs with highly localized source areas.
                 Site surveys should identify local features that may indicate the nature, location
                 and extent of the flow system. Such features as intermittent or ephemeral stream
                 sections, hydrophytic vegetation, seepage faces, and locally defined topography
                 which do not show up on contour maps or air photos are important in
                 delineating the source area boundary. For example, at Peter Springs (see
                 Appendix A) the nature of the flow system could only be determined by
                 mapping site features. This included digging into the spring to identify what
                 materials flow was discharging from, identifying the spring discharge area from
                 the presence of ferns and other hydrophytic vegetation, and field mapping local
                 topography that defines the source area upslope of the spring.

                 In bedrock units, it may not always be apparent if flow is discrete or porous at
                 the spring site. Field mapping should identify other springs or seepage features
                 to verify if intense fracturing (porous flow) is evident, or verify the existence of
                 individual fracture, fault or conduit features.

                 Site-specific maps may be required to accurately identify and depict source
                 areas. Information that should be obtained from the site investigation includes:

                 •   locating the spring site and predicted source area
                 •   verifying the location and characteristics of landforms and surface water
                     features
                 •   verifying or identifying the location and characteristics of geologic units and
                     geologic features
                 •   identifying significant local scale landforms, water courses, land use, and
                     diagnostic vegetation (recharge and discharge sites)
                 •   surveying and identifying the components of the waterworks
                 •   identifying monitoring sites for discharge and water quality sampling
                 •   taking water chemistry samples and discharge measurements (estimate if no
                     other options available) from the spring and other water sources, as required
                 •   interviewing water purveyor / licensee for access to data, spring history, and
                     anecdotal information.

20                                        Hydrology Branch, Ministry of Environment, Lands and Parks, 1996
Defining the Source Area of Water Supply Springs

4.6     Refine conceptual model and source area boundaries
                   Site investigation information should be analyzed and used to support or revise
                   initial interpretations, the conceptual model, and the location of the source area
                   and its boundaries. In some cases a number of iterations of the definition
                   process, including various types of site surveys that build on previously
                   acquired information, may be required to arrive at a final interpretation.

4.7     Evaluate reasonableness of delineated source area
                   There is always a degree of uncertainty associated with delineation of a spring
                   source area because complete information is never available. Ideally, the
                   accuracy of the delineated source area can be evaluated by conducting more
                   extensive site characterization. This, however, is often not practical or
                   necessary. It may be sufficient to conduct further investigation only for those
                   factors or specific areas which were uncertain, or which are vital to the
                   interpretation.

                   The reasonableness of the interpretation should checked by reviewing the
                   consistency of results between the different techniques that were employed. For
                   instance, if water chemistry indicates that the flow system is likely deep and
                   regional, then a locally defined source area using topography would not be very
                   accurate. The water balance provides an estimate of the size of the source area
                   and can be used to evaluate the accuracy of source areas defined using
                   topography, geology or water table contours. A review would be necessary if
                   the size of the defined source area is inconsistent with what can be justified
                   from the water balance.

                   In some cases, the uncertainty may be so great that a source area cannot be
                   reasonably defined. In these cases, the results of the assessment should identify
                   what further information is required and make recommendations on how this
                   information can be obtained. As an interim measure, the designation of some
                   arbitrary fixed area may be appropriate to provide a measure of protection.

4.8     Write report
                   It is important to document the assessment for each spring source area so that it
                   can be reviewed and defended. At a minimum the following information should
                   be included in the report:

                   •   site location
                   •   spring and waterworks description
                   •   topographic setting and nearby surface water features

Hydrology Branch, Ministry of Environment, Lands and Parks, 1996                                       21
Defining the Source Area of Water Supply Springs

                 •   geologic setting
                 •   hydrogeologic setting and groundwater conditions
                 •   interpretation of spring source area
                 •   spring source area description and delineation
                 •   potential impacts to the spring water supply
                 •   summary and conclusions of assessment
                 •   references

                 The case studies in Appendix A show the level of detail and content of spring
                 assessment reports.

5      Case studies
                 Assessments were completed on three community spring sources on Vancouver
                 Island: at Cowichan Lake (Peter Springs); Courtenay (Supply Spring); and Mill
                 Bay (Wheelbarrow Springs) to determine if spring source area boundaries could
                 be delineated using the approach and techniques presented in this report. These
                 springs were chosen because of their different geographic settings and
                 differences in availability and type of data. The case studies are presented in
                 Appendix A.

                 The results indicate that, for these springs, source areas can be identified and
                 defined with reasonable confidence using the described techniques and
                 approach, despite the variations in data type and availability. Data for each
                 spring ranged from limited (Peter Springs) to comprehensive (Wheelbarrow
                 Springs). The source areas for the springs are local in extent, ranging from
                 approximately 1 hectare for Peter Springs to 40 hectares for Supply Spring.
                 Each of the springs are potentially at risk from current or proposed land use
                 activities within the defined source areas.

                 A major reason source areas were able to be defined is that in each case
                 topography could be used to approximate the direction of subsurface flow to the
                 springs. However, geological interpretation, water chemistry, and discharge
                 data were also important and provided a better understanding of spring
                 occurrence and the nature of the source area. As well, none of the assessments
                 could have been completed with adequate confidence without the site
                 investigations. This is especially true for Peter Springs, where the source area
                 was defined on-site rather than at the map scale level.

                 The assessment of Wheelbarrow Springs illustrates that, unlike surface
                 watersheds, spring source areas may change over time. If significant pumping
                 of wells in the source area occurs, the water table configuration upslope of the
                 springs could change, consequently altering source area boundaries.

22                                        Hydrology Branch, Ministry of Environment, Lands and Parks, 1996
Defining the Source Area of Water Supply Springs

                   While the success of the spring assessment relies to a great extent on compiling
                   available information, it was found that the data sources often did not contain
                   adequate or appropriate information for supporting hydrologic investigations.
                   For instance, the water license files and water information data base (WLIS)
                   contain mostly administrative information, and the Engineers Report that
                   accompanies license applications is usually limited. Even so, information from
                   the files and database helped establish an understanding of the waterworks and
                   provided relevant historical information. In some cases discharge estimates
                   were included.

                   The most important data that are generally not available are discharge
                   measurements or estimates, or the date and method of measurement. Discharge
                   measurements support the interpretation of the location, nature and size of the
                   source area and are required for the water balance calculation. The results of
                   these analyses depend on the availability and accuracy of the discharge data.

                   The geographic and hydrogeologic settings of the three case studies represent a
                   limited spectrum of types of springs that may be encountered in BC. How
                   typical these springs and source areas are is unknown. The applicability of the
                   approach to other spring types and to other geographic areas of the province
                   needs to be determined.

6       Conclusions and recommendations
                   The approach presented here for defining the source area of water supply
                   springs depends on the compilation and analysis of existing data and site
                   investigation. The case studies indicate that the approach can be applied and
                   reasonable determinations made. The approach is limited by the availability of
                   existing data, primarily discharge measurements and hydrogeologic
                   information.

                   The absence of information on springs in BC is an indication of the amount of
                   work that needs to be undertaken before effective management and protection
                   of spring-sourced water supplies will become possible. The uncertainty
                   associated with defining source areas using limited information also indicates
                   the importance of monitoring land use activites in source areas and assessing
                   their impacts on the spring supply. The results of this report indicate that a
                   number of areas require further research or development:

                   •   improved documentation of spring hydrologic characteristics during the
                       licensing process and inclusion of this information in appropriate data bases

Hydrology Branch, Ministry of Environment, Lands and Parks, 1996                                       23
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