USA Drinking Water Definition and Model:

Definitions

Adequate Alternative Water Supply: A source of water that currently exists, can be used almost immediately with a minimal amount of effort and cost, will meet the short-term consumptive and hygiene requirements of the existing population of impacted consumers, involves no perceptible change in water quality, and is temporary (until a long-term alternative can be put in place, if necessary).

The intent is that, in the event of a spill which threatens to shut down a water intake, there would be a surface water intake(s) in another location(s) that would not be in the threat zone, or there would be groundwater sources that could be utilized during the threat period, or there would be other drinking water systems that could temporarily provide drinking water to the impacted system.

Community Water System (CWS): A public water system (PWS) that provides water to the same population year-round.

Drinking water resources: Surface water intakes and groundwater-based drinking water supplies supplying potable water for domestic, commercial and industrial users.  Such supplies may provide drinking water for permanent communities (e.g. cities and towns), transient communities (such as campgrounds), or individual domestic supplies for residential consumption.

Environmentally sensitive area (ESA) - Drinking water and ecological resources as generally described by the National Oceanic and Atmospheric Administration (NOAA) (59 CFR 14714).

Filter Criteria: Assessment factors that provide parameters by which the USA candidates can be uniformly assessed for inclusion in the final set of unusually sensitive resource areas.

Hazardous liquid - petroleum, petroleum products or anhydrous ammonia (et. seq. 49 CFR 195.2).

Nontransient Noncommunity Water System (NTNCWS): A PWS that regularly serves at least 25 of the same people at least six months of the year.  Examples of these systems include schools, factories, and hospitals that have their own water supplies.

Pipeline operator - The company, or other entity, which has responsibility for operating and maintaining the pipeline system.

Pipeline system - All parts of a pipeline facility through which a hazardous liquid moves in transportation, including but not limited to, line pipe, valves, and other appurtenances connected to line pipe, pumping units, fabricated assemblies associated with pumping units, metering and delivery stations and fabricated assemblies therein, and breakout tanks.

Public Water Systems (PWS) - A public water system provides piped water for human consumption to at least 15 service connections or serves an average of at least 25 people for at least 60 days each year, and includes the source of the water supply (i.e., surface or groundwater).  PWSs can be community, nontransient noncommunity, or transient noncommunity systems, as defined by the EPA's Public Water System Supervision (PWSS) Program.

Sole Source Aquifers (SSA) - These are areas designated by the EPA (Safe Drinking Water Act, Section 1427) under the Sole Source Aquifer Program as the "sole or principal" source of drinking water for an area.  EPA defines a SSA as one which supplies at least 50 percent of the drinking water consumed in the area overlying the aquifer.

Transient Noncommunity Water System (TNCWS): A PWS that caters to transitory customers in non-residential areas such as at campgrounds, motels and gas stations.

USA candidates: A subset of drinking water and ecological ESAs. These candidates are areas that contain ecological resources that are potentially more susceptible to permanent or long-term environmental damage, regardless of land ownership, management, or proprietorship.

Wellhead Protection Areas (WHPA) - The surface and subsurface land area surrounding a well or well field that supplies a public water system through which, in the event of a release, contaminants are likely to pass and eventually reach the well/well field.

1.1             The USA Concept

Tasked with the responsibility for describing USAs, DOT initiated a consultative process with federal and state regulatory agencies, environmental organizations, the regulated community, and the public. These provided the framework for the proposed USA definition (64 Federal Register 250, pg. 73464).

In general USAs are defined as:

Those definable geographic areas that contain drinking water or ecological resources that by their character are irreplaceable and may be subject to irreparable and irreversible injury or irretrievable loss, if they are exposed to the effects of an accidental hazardous liquids release.

There is an abundance of natural resources that are afforded varying levels of protection under a variety of state and Federal laws.  These include such diverse geographies as federally owned lands (e.g. park, forest, and reserve boundaries), ecological regions (e.g. wetlands, estuaries and river systems), water bodies (e.g. lakes, rivers, drainage basins and groundwater aquifers), cultural resources, and locations of individual species occurrence (e.g. threatened and endangered species). Unusually sensitive areas should not incorporate the entirety of all federally protected natural resource areas.  Rather, the term "unusually sensitive areas" represents a subset of these resources that may be subject to "permanent and long-term environmental damage."  

The USA definition focuses upon those environmental resources that are potentially at risk of such damage and are essential to the protection of human health and the continued viability of ecological resources.  Thus, application of the USA definition, as it is established in this document, specifically identifies drinking water resources that are critical to the uninterrupted delivery of consumable water to public water systems (PWS) and areas critical to the survival and viability of threatened, endangered, and imperiled biological species.

2.0           DRINKING WATER Data Sources and Data Management

All public water suppliers submit compliance and enforcement information to EPA for inclusion in the Safe Drinking Water Information System (SDWIS), as required by the Safe Drinking Water Act (SDWA) Amendments of 1996.  The SDWIS recently replaced the Federal Reporting Data System (FRDS) database.  The Office of Drinking Water maintains and disseminates the data, which is used for the Public Water System Supervision (PWSS) Program.  Data includes, among other things: owner/operator name and address, operational status, location, onsite visits, sources, violations, enforcement and compliance actions, treatment, variances and exemptions, area (county and population) served by the system, and historical information.

Per the EPA, the accuracy of SDWIS classification of Public Water Systems into the three categories of CWS, NTNCWS, and TNCWS is good, but as with any such database the specific accuracy of a particular entry depends on the quality of that state's data input program.

As there are no readily available, national databases on which this filtering criteria could be applied, the existence of adequate alternative sources must be determined on a case-by-case basis for each CWS/NTNCWS, either through the appropriate state agencies or individual Public Water Systems.

3.0           The USA Definition Process

3.1             DERIVING USAs FROM ESAs

The process that should be used for the definition of USAs has been developed through extensive consultation with drinking water and ecological resource experts, government agencies, and other stakeholders. This multi-step process involves the designation and assessment of environmentally sensitive areas (ESAs), USA candidates, filtering criteria and data requirements (Figure 1).  This guidance document identifies ESAs, USA candidates, filter criteria, and data sources that should be used.

Under this process, ESAs include all potential drinking water resources that can be generically considered to be sensitive and would be afforded protection under any number of federal resource protection programs.  In addition to being afforded protection under their individual protective mandates, these resources are also afforded protection under the Oil Pollution Act of 1990 (OPA 90).  As such, these resources are already identified and provided with appropriate response measures through the OPA contingency planning process and may not necessarily need an additional layer of protection as USAs.

From among the ESAs, a subset of USA candidate resources have been identified that are considered to be of greatest significance and potential susceptibility to permanent or long term environmental damage as the result of a hazardous liquid pipeline release.  For drinking water, USA candidates are those resources that are clearly identified as currently providing a potable drinking water source to populations and communities of people, or industrial use.

Filter criteria are applied to the list of USA candidates to identify those areas that are most critical to the maintenance of the health and welfare of humans.  The application of filter criteria produces the final set of USAs.

It is anticipated that pipeline operators will utilize a risk assessment process to consider the potential impacts to USAs that result from a specific pipeline release.  The results of the risk assessment will either lead to implementation of additional protective measures, or reclassification as an ESA (Figure 1).

Figure 1: Schematic of the USA identification process depicting the relationship between ESAs, USA Candidates, Filter Criteria, and USAs.

3.2       THE PROCESS OF IDENTIFYING DRINKING WATER USAs

Drinking water USAs are defined through the stepwise process of defining drinking water ESAs, the selection of USA candidates, and the application of filter criteria to produce the final set of USAs.  This guidance document utilizes a rationale that drinking water USAs should focus upon those identifiable sources of drinking water that are necessary for the uninterrupted consumption by human populations.  This rationale is based upon the high priority of protecting human health.

3.2.1       DRINKING WATER ESAs

For the purposes of this guidance, drinking water resource ESAs include surface water intakes and groundwater-based drinking water supplies supplying potable water for domestic, commercial and industrial users.  Such supplies may provide drinking water for permanent communities (e.g. cities and towns), transient communities such as campgrounds, or individual domestic supplies for residential consumption.

3.2.2       Drinking Water USA Candidates

USA candidates for drinking water resources are a subset of the drinking water ESAs, representing those sensitive areas of greatest significance that are potentially more susceptible to permanent or long term environmental damage from a hazardous liquid pipeline incident.

Drinking water resources USA candidates include the following:

1. Public Water Systems (PWS) (see definition): PWSs include:
   • Community water systems (CWS);
   • Nontransient noncommunity water systems (NTNCWS); or
   • Transient noncommunity water systems (TNCWS),
   as defined by the EPA's PWSS Program;
2. Wellhead Protection Areas (WHPA) (see definition):  WHPAs are geographic areas of varying size and shape, as defined by individual state programs, surrounding existing wellheads.  To date 47 states and 2 territories have identified WHPAs for public drinking water systems.  For states without designated WHPAs, a default WHPA should be used.
3. Sole Source Aquifers (SSA) (see definition).  The sole source aquifer program was established under Section 1424(e) of the Safe Drinking Water Act of 1974.  Under this program aquifers are identified that provide at least one-half of the drinking water consumed in the area above the aquifer, or is the only local or regional source of drinking water. 

3.2.3       Drinking Water Filter Criteria

Filter criteria in the USA identification process are those parameters to be uniformly applied against the USA candidates to arrive at a final set of unusually sensitive areas for consideration in the subsequent risk assessment process.  For drinking water resource USAs, these criteria are to be applied against drinking water USA candidates to determine which areas are most susceptible to permanent or long-term environmental damage from a pipeline spill.  These areas are then classified as drinking water resource USAs.

Three drinking water filter criteria and two notable exceptions have been developed and are further described in the following paragraphs.

Notable Exception 1 - Transient Noncommunity Water Systems

If the public water system is a Transient Noncommunity Water System (TNCWS), the water intakes shall not be designated as USAs

Filter Criterion 1 - Community Water Systems (CWS) and Nontransient Noncommunity Water Systems (NTNCWS) Relying on Surface Water Intakes 

For CWS and NTNCWS that obtain their water supply primarily from surface water sources, and do not have an adequate alternative source of water, the water intakes shall be designated as USAs.

Filter Criterion 2 - Community Water Systems (CWS) and Nontransient Noncommunity Water Systems (NTNCWS) Relying on Groundwater Sources Vulnerable to Contamination

For CWS and NTNCWS that obtain their water supply primarily from groundwater sources, where the source aquifer is identified as Class I or Class IIa (per Pettyjohn et. al., 1991), and which do not have an adequate alternative source of water, the wellhead protection areas (WHPAs) for such systems shall be designated as USAs.

Aquifer Vulnerability Categories

An EPA aquifer vulnerability classification scheme has been developed to aid in distinguishing between differences in the characteristics of various hydrogeologic systems (Pettyjohn et al., 1991; EPA Document: EPA/600/291/043, August 1991).  All aquifers in the United States have been classified into the following nine categories:

1. Unconsolidated (Class Ia): Aquifers consist of surficial, unconsolidated, and permeable alluvial, terrace, outwash, beach, dune, and other similar deposits.
2. Soluble and Fractured Bedrock (Class Ib): Lithologies in this class include limestone, dolomite, and locally, evaporitic units that contain documented karst features or solution channels, regardless of size.  Also included are sedimentary strata, and metamorphic and igneous rocks that are significantly faulted, fractured, or jointed.
3. Semiconsolidated (Class Ic): Semiconsolidated systems generally contain poorly to moderately indurated sand and gravel that is interbedded with clay and silt.
4. Covered Aquifers (Class Id): Consists of any Class I aquifer that is overlain by less than 50 feet of low permeability, unconsolidated material, such as glacial till, lacustrine, and loess deposits.
5. Higher Yield Bedrock (Class IIa): Generally consist of fairly permeable sandstone or conglomerate that contain lesser amounts of interbedded fine-grained clastics and occasionally carbonate units.  In general, well yields must exceed 50 gpm to be included in this class.
6. Lower Yield Bedrock (Class IIb): Most commonly, lower yield systems consist of the same clastic rock types present in the higher yield systems.  Well yields are commonly less than 50 gpm.
7. Covered Bedrock (Class IIc): Consists of Class IIa and IIb aquifers that are overlain by less than 50-feet of unconsolidated material of low permeability.
8. Covered Consolidated or Unconsolidated Aquifers (Class III):  This class includes those aquifers that are overlain by more than 50 feet of low permeability material.
9. Undifferentiated (Class U): This classification is used where several lithologic and hydrologic conditions are present within a mappable area.  This class is intended to convey a wider range of vulnerability than is usually contained within any other single class.
10. Variably Covered Aquifers (Subclass v): The modifier "v" is used to describe areas where an undetermined or highly variable thickness of low permeability sediments overlies the major water-bearing zone.

The geology of the physical system determines vulnerability.  Pettyjohn et. al. (1991, EPA/600/2-91/043) developed the above classification scheme based on an assessment of the vulnerability of surficial and relatively shallow aquifers to contamination from near surface sources of contamination.  The investigation, based entirely on published reports and maps, was an attempt to evaluate all aquifers nationwide on the basis of their reported physical properties and related hydrologic characteristics and behavior.

The maps described by Pettyjohn are regional in nature and provide a broad, generalized overview of aquifer vulnerability and sensitivity.  All class I aquifers and IIa aquifers are considered to be the drinking water resources most vulnerable to contamination, and therefore the objective of this Filter Criterion 2 is to protect systems relying on such sources of groundwater.

The determination of source aquifers for CWS/NTNCWS relying primarily on groundwater can be a complex problem, as no national database directly providing such information is available.  Furthermore, for some CWS and NTNCWS, the depth of the wells or source aquifer is not known.  Such information must be obtained on a case-by-case basis through contacting the appropriate state agencies or, at times, individual Public Water Systems. 

Wellhead Protection Areas

In 1986, Amendments to the Safe Drinking Water Act (SDWA) established the Wellhead Protection (WHP) Program. Under these Amendments, each state was called upon to develop, and submit to EPA for approval, a plan that would protect ground water which supplies wells, wellfields, springs, and tunnels that provide drinking water to the general public. The plan is administered by the EPA Office of Ground Water and Drinking Water.  States and U.S. territories that currently have approved plans are listed by the US EPA web site http://www.epa.gov/OGWDW/wellhead.html.

Wellhead Protection Programs establish Wellhead Protection Areas (WHPAs).  The methods employed to define these areas range from the very simple arbitrary fixed radius method (inscribing a circle around a well location) to more sophisticated analytical methods. Whatever the method, the resulting areas are identified, potential contaminant sources are located, and the areas are managed to protect the drinking water resource.  Additionally, the WHPAs are employed in planning for future development.  Management techniques may range from public education to contingency planning for provision of alternative supplies in the event of contamination.  EPA provides technical assistance to the state in the preparation, approval, and implementation of their plans.

As of January 2000, three states, the Virgin Islands and Northern Marianna Islands did not have Well Head Protection Programs.  For the purposes of applying Filter Criterion 2 at such locations, a default fixed radius of 2000 feet may be employed.

Notable Exception 2 - Community Water Systems (CWS) and Nontransient Noncommunity Water Systems (NTNCWS) Relying on Groundwater Sources of Relatively Low Vulnerability

For CWS and NTNCWS that obtain their water supply primarily from groundwater sources, where the source aquifer is identified as a Class IIb, Class IIc, III or Class U (per Pettyjohn et al., 1991), the public water systems that rely on these aquifers shall not be designated as USAs.

Class IIb, IIc, and III aquifers are considered to be the least vulnerable to contamination by virtue of their hydrogeologic properties (e.g., depth and/or low yield, isolation due to overlying strata, etc.).  Such properties make these aquifers less likely to be impacted by pipeline spills.  The Class U designation was used where several lithologic and hydrologic conditions were used within a mappable area, making a clear designation difficult due to a wider range of vulnerability than is contained within any other single class. 

Filter Criterion 3 - Community Water Systems (CWS) and Nontransient Noncommunity Water Systems (NTNCWS) Relying on Sole Source Aquifers that are Vulnerable to Contamination

For CWS and NTNCWS that obtain their water supply primarily from groundwater sources, where the source aquifer is identified as Class I or Class IIa (per Pettyjohn et. al., 1991), and the aquifer is designated as a sole source aquifer, an area twice the radius of the WHPA, (if the WHPA is fixed-radius), or the WHPA itself, (if the WHPA is zone-defined), shall be designated as an USA.

Sole source aquifers are defined by the EPA as the "sole or principal" source of drinking water for an area, and are defined as aquifers which supply at least 50 percent of the drinking water consumed in the area overlying the aquifer.  Such critical water resources warrant the highest levels of protection.  The EPA Sole Source Aquifer (SSA) program allows individuals and organizations to petition the EPA to designate aquifers as the sole or principal source of drinking water for an area.  The program was established under Section 1424(e) of the Safe Drinking Water Act (SDWA) of 1974.  The primary purpose of the designation is to provide EPA review of federal financially assisted projects planned for an area and to determine their potential for contaminating the aquifer "so as to create a significant hazard to public health". Based on this review, no commitment of federal financial assistance may be made for projects "which the Administrator (of EPA) determines may contaminate such (an) aquifer," although federal funds may be used to modify projects to ensure that they will not contaminate the aquifer.

As of October 1999, EPA has designated 70 SSAs nationwide.  For each designated SSA there is a technical support document which compiles all available technical information for that SSA.  These documents are obtained through the regional EPA offices.  For a National Summary of Sole Source Aquifer Designations as of October 1999, including Federal Register Citations and the availability of Geographic Information System mapping, consult EPA at http://www.epa.gov/OGWDW/swp/sumssa.html.

It should be noted that the list of SSAs in the U.S. is always open for additions, both from the designation of new SSAs as well as existing SSAs being extended based upon approval of new petitions.  Different state and local agencies are at different stages in filing for SSA status.  Significant discrepancies may also arise across governmental boundaries.   An example is in New York, where the SSA boundary corresponds to the county boundary, rather than the hydrogeologic boundary.

4.0  USING A GEOGRAPHIC INFORMATION SYSTEM (GIS) TO IDENTIFY DRINKING WATER USAs

4.1       DATA AND SOFTWARE UTILIZED BY THE DRINKING WATER USA MODEL

The drinking water USA model utilizes the same GIS software package as the ecological USA model, namely, ArcInfo, developed by Environmental Systems Research Institute, Inc. (ESRI), Redlands, CA.

4.1.1   PUBLIC WATER SYSTEMS

Information from databases developed by the state Public Water System Supervision (PWSS) Programs provide the corner stone the model builds its drinking water USA database on.  The data can be obtained through the EPA Office of Drinking Water for each state.

4.1.2   AQUIFERS

The model makes use of "state-accepted" statewide aquifer boundaries.  "State-accepted" refers to publication sources that are widely respected by the state community.  The aquifer boundaries are used to validate the source aquifer attributes of groundwater systems.  The boundaries are also used to assign source aquifers to groundwater systems with unspecified or ambiguous source aquifer attributes.

4.1.3   SURFICIAL GEOLOGY

If available, surface geology maps are used by the model to assist in the Pettyjohn aquifer classification.  Surface geology maps may be used to delineate aquifer outcrop boundaries when no "state-accepted" aquifer boundaries are available.

4.1.4   SOLE SOURCE AQUIFERS

Sole Source Aquifer boundaries are used to provide extra protection for vulnerable groundwater systems that are located within a sole source aquifer. 

Digital boundary data can be obtained by contacting the headquaters of each EPA region.

4.1.5   WELLHEAD PROTECTION AREAS

Most states have a wellhead protection program in place to define protection areas for their groundwater systems.  Delineation methods for wellhead protection areas (WHPAs) vary from state to state.  Some states specify their WHPAs based on a fixed radius in order to generate a protection area.  Other states utilize more complicated methods to create zone-defined WHPAs.  These methods employ numerical transport and hydrogeologic mapping to generate protection areas for groundwater systems.  To date 47 states and 2 territories have identified WHPAs for public drinking water systems.  For states without designated WHPAs, a default WHPA of 2000 feet is suggested by the methodology.

4.1.6   ADEQUATE ALTERNATIVE DATABASE

Data from the Adequate Alternative Database is used in determining which public water systems have no adequate alternative source.  An Adequate Alternative Source (AAS) is defined as an alternative source of water that currently exists, that can be used with a minimum amount of effort and cost, and that will meet the short-term consumptive and hygiene requirements of the existing population.  Information about alternative sources for public water systems is generally not available in PWS databases.  During the pre-processing stage of the pilot test, public water systems were contacted and queried about alternatives in order to compile this information.

4.1.7   HYDROGRAPHY

The drinking water USA uses USGS 1:100,000-scale Digital Line Graph (DLG) information to represent the hydrography (or surface water features) in each pilot test state.  The DLG data are digital representations of points, lines, and areas of planimetric information derived from 30- by 60-minute intermediate scale quadrangle maps.  The data are considered DLG - Level 3 (DLG-3), which means the data contain a full range of attribute codes, have full topological structuring, and have passed certain quality-control checks described in the Federal Geographic Data Committee's (FGDC) Content Standards for Digital Geospatial Metadata.  DLG information is available on the internet at http://edc.usgs.gov/doc/edchome/ndcdb/ndcdb.html.

For the pilot test, the data files were downloaded by file transfer protocol (ftp) in the spatial data transfer standard (SDTS) format.

Another nationwide digital database is currently being developed by USGS and EPA that will soon provide a better representation of statewide hydrography for use in the model.  It is called the National Hydrography Dataset (NHD) and is comprised of the USGS 1:100,000-scale DLGs integrated with reach-related information from the EPA Reach File Version 3 (RF3).  The integration of these two data sets enables the analysis and display of water-related data in upstream and downstream order at an intermediate data resolution scale.  The information is being compiled in hydrologic cataloging units across the United States.  At this time, quality control checks meeting FGDC standards have not been completed for all HUC areas to make statewide applications practical yet.  More information can be obtained from the web site, http://nhd.usgs.gov/.

4.2       STANDARDS IN DATA QUALITY AND CONTENT

The model accepts state Public Water System (PWS) data in a digital format.  The water systems must have valid, (i.e., non-zero), geographic coordinates in order to be input into the model.  The PWS database should indicate the source type of the water systems, (i.e., surface water source or ground water source).  Preferably, the database should also indicate community and non-transient non-community systems and contain well depth information.

In addition, a statewide aquifer map is required to run the model.  If a statewide aquifer map does not exist in digital format, aquifer outcrop and subcrop delineations may be converted into digital format from other "state-accepted" sources, such as surface geology or ground water basins.

If aquifer delineations cannot be inferred and readily converted from existing "state-accepted" data sources, then the model is limited to the source aquifer information that may or may not be present in the state's PWS database.

When "state-accepted" aquifer subcrop delineations cannot be found or inferred from a source that is in a readily convertible format, then the model uses either the aquifer outcrops as an overlay or the depth/source information of nearby wells to determine source aquifers for groundwater wells with unspecified or ambiguous source aquifer attributes.

4.3       SOURCE AQUIFER VALIDATION AND ASSIGNMENT

The greatest challenge the model faces is determining the type of aquifer (vulnerable or non-vulnerable) that each groundwater system sources.  One of the key data used for classifying groundwater wells is the source aquifer information listed for each well.  The model's main process focuses on validating the listed source aquifer information.  When a validation cannot be made due to unspecified or ambiguous listed information, the model attempts to assign a source aquifer to the groundwater system.

The model makes use of a source aquifer lookup table that assigns each groundwater well to one of the standardized aquifer names referenced by the USGS Groundwater Atlases.  The table is necessary because of the variability in the level of geologic detail used in describing the aquifers as well as regional differences in the names of aquifers.  For example, in the case of Texas, 660 separate geologic unit descriptions were collapsed to 23 aquifers names.

The source lookup table for the Texas data is a combination of the Aquifer Code Master Listings from Texas Natural Resources Conservation Commission and Texas Water Development Board.  Each aquifer code is assigned one of 23 aquifer names based on the geologist's interpretation of the aquifer description.  Sometimes a standardized aquifer name cannot be inferred from an aquifer code due to a lack of information in the description for the aquifer code.  This dilemma and the fact that some groundwater wells do not have an aquifer code result in a number of wells that are not assigned a standardized aquifer name.  For these wells, source information, if available, is obtained from the supplemental Public Water System database.  See Figure 6 for an example of the source lookup table used for Texas.

The source lookup table for the Louisiana data is from a unique list of source name descriptions associated with the PWS data.  Each description is then assigned one of 10 standardized aquifer names based on the geologist's interpretation of the aquifer description.

In California, a source lookup table was not used, because the PWS data contained no source aquifer information.

4.3.1   SOURCE AQUIFER VALIDATION

Attributes present in a state's PWS database take precedence over any deductions the GIS model may infer during processing.  The GIS model selects the groundwater wells with source aquifer information from the PWS database and then overlays the "state-accepted" digital aquifer map onto the subset of groundwater wells to verify if the wells fall within their specified source aquifer.

• If a geographic intersection is not verified and the digital aquifer map includes both outcrop and subcrop delineations, then the source aquifer for the groundwater well cannot be validated.
• If a geographic intersection is not verified and the digital aquifer map contains only outcrop delineations, then the well's location and depth are interactively evaluated for concurrence with the outcrop or subcrop description of the source aquifer specified in the PWS database.  The results of the evaluation should be documented for each PWS considered, in order to facilitate any subsequent reviews of the interactive process.   If concurrence is established, then the model infers that the groundwater well sources its specified aquifer.
• If concurrence cannot be established, but the well's depth is greater than 0 and less than or equal to 50 feet, the groundwater well is inferred to draw from a surficial or shallow, permeable aquifer, (Pettyjohn Class I).
• If concurrence cannot be established and the well's depth is unknown, 0 or greater than 50 feet, the model flags the well with "Source Aquifer Cannot Be Determined".

4.3.2   SOURCE AQUIFER ASSIGNMENT

In some cases, the PWS database contains no source aquifer information or the information exists, but it is too obscure to use reliably.  The source aquifer assignment process is only applied to groundwater wells with attributes that fit this description.  As in the source aquifer validation procedure, the GIS model selects the groundwater wells with unspecified or ambiguous source aquifer attributes and overlays the "state-accepted" digital aquifer map onto the subset of groundwater wells to establish a geographic relationship between the wells and aquifers in the state.  Depth information is used to validate deductions made during the source aquifer assignment process.  When depth information is not available, the GIS model relies solely on the groundwater well's location in relation to the aquifers for its deductions.

The source aquifer assignment procedure is as follows for PWS databases that contain no source aquifer information.

• If depth information is available for the top and bottom of the aquifers, then the well's depth is evaluated for concurrence with the prescribed depth range of the aquifer it intersects.  If concurrence is established, then it is inferred that the groundwater well sources the intersected aquifer.  When the digital aquifer map includes both subcrop and outcrop delineations, there is a possibility that the well may intersect more than one aquifer.  If there is concurrence with the depth range of more than one aquifer, then the well is inferred to source the shallowest aquifer for assignment of the Pettyjohn classification.
• When depth information is not available for the top and bottom of the aquifers or depth information is not included in the PWS database, the number of intersected aquifers is evaluated.  If only one aquifer was intersected, then it is inferred that the groundwater well sources the single intersected aquifer.  Otherwise the well is flagged with "Source Aquifer Cannot Be Determined".
• When source aquifer information is included in the PWS database, the model looks at the number of intersected aquifers, the well's depth, and the source aquifers and depth information of the groundwater wells near the well being examined.
• If the well intersects one aquifer, the depth of the well is evaluated for concurrence with the description of the part of the aquifer that was intersected (either the outcrop or subcrop).  If concurrence is established, then it is inferred that the groundwater well sources the intersected part of the aquifer.
• If concurrence cannot be established and the digital aquifer map contains both outcrop and subcrop delineations, the well is flagged with "Source Aquifer Cannot Be Determined".
• If concurrence cannot be established and the digital aquifer map contains only outcrop delineations, the model calculates a search radius based on 1/10^th of the diagonal of the map extent of the intersected aquifer outcrop.  Groundwater wells with source information that fall within the search radius are selected.  If the well has a depth greater than zero, the selected set is limited to only groundwater wells with source information that have depths within a 10 percent range of the depth of the well being examined.  If the well has no depth information, no refinement is made to the selected set.  The GIS model then evaluates source aquifer information for all the wells in the selected set.
• If the well has a depth greater then 0 and at least 90 percent of the wells specify the same source aquifer, the groundwater well is inferred to draw from this aquifer.  If a consensus does not exist for the source aquifers, but at least 90 percent of the wells draw from a vulnerable aquifer (Pettyjohn Class I or IIa) or a non-vulnerable aquifer (Pettyjohn IIb, IIc, or III), then the groundwater well is inferred to draw from the same aquifer type as the 90 percent or greater consensus.  If no consensus can be established, the well is flagged with "Source Aquifer Cannot Be Determined".
• If the well has no depth information, the same conditional tests are applied, but the consensus must be 100 percent.
• If the well intersects two or more aquifers, the model determines the area common to all aquifers that the well intersects.  (See Figure 12.)  The model then calculates a search radius based on 1/10^th of the diagonal of the map extent of the common area, (Figure 13).  Groundwater wells with source information that fall within both the common area and the search radius are selected.  Selection refinements based on depth information and conditional tests of depth and Pettyjohn classification consensus are applied in the same manner as described above when only one aquifer is intersected.
• If the well intersects no aquifers, or concurrence cannot be established from the previous evaluations, but the well's depth is greater than 0 and less than or equal to 50 feet, then the groundwater well is inferred to draw from a surficial or shallow, permeable aquifer, (Pettyjohn Class I).  If the well's depth is unknown, 0 or greater than 50 feet, the model overlays an EPA-approved digital sole source aquifer map onto the well.  If the well falls within a sole source aquifer, the groundwater well is inferred to draw from the sole source aquifer.  Otherwise, the well is flagged with "Source Aquifer Cannot Be Determined".

FIGURE 12: AREA COMMON TO ALL INTERSECTED AQUIFERS

FIGURE 13: SEARCH RADIUS BASED ON 1/10^TH OF DIAGONAL

4.4       DRINKING WATER FILTER CRITERIA

There are three filter criteria and two notable exceptions defined by the methodology.  If a water system is excluded because it does not meet one or any of the criteria described in this section, it is still considered an environmentally sensitive area (ESA) and will be reevaluated in subsequent reruns of the model.  Water systems that are accepted by the model as drinking water candidates, but become disqualified during the filtering process are still considered USA candidates after the model run.  These systems will also have the opportunity to gain USA status in subsequent model reruns.

4.4.1   NOTABLE EXCEPTION 1

Notable Exception 1 identifies public water systems that are transient, non-community water systems (TNCWS).  These systems are not designated as USAs, but remain as USA candidates that will be reevaluated in subsequent reruns.

4.4.1.1      APPLICATION OF NOTABLE EXCEPTION 1 IN THE PILOT TEST

The PWS data for California do not contain specific information regarding the type of supply.  However, some systems indicate the number of people served.  Water systems that indicated they serve less than 25 people are treated as TNCWS by the model.

The PWS data for Louisiana did contain specific information regarding the type of supply.  The field, SYSTEMTYPE, contained a one-letter code denoting whether the system was a CWS, TNCWS, or NTNCWS.

The PWS data for Texas was received in two parts: a public water supply sources ArcInfo point coverage which contains well locations, source aquifer, and source type (ground or surface); and a public water systems data file containing the contact information, a second set of source aquifer information, and the type of supply (CWS, TNCWS, or NTNCWS).  To determine which wells in the point coverage are considered to be TNCWSs, the two data files are related in ArcInfo.  Both files contain a public water system id (PWS_ID), but the water system data file contains multiple records for the same PWS_ID differentiated by plant identifiers (see Table 7).   Unfortunately, the water supply coverage does not contain any plant identifiers.  Because of this incongruity, only records in the water system database where the same PWS_ID lists a unique type of supply (CWS, TNCWS, or NTNCWS) are selected by the model.

4.4.2   FILTER CRITERION 1

Filter criterion 1 identifies surface water systems that have no adequate alternative source of water.  Surface water intakes are traditionally represented by a point location.  In order to provide an area of protection for intakes, all open water features within a 5-mile radius of the surface water system are selected and buffered ¼-mile inland to represent the area of the USA.   All three states contain fields in the PWS point coverages that denote surface water systems, so this criterion was applied equilaterally to the pilot test states by the model.

4.4.3   FILTER CRITERION 2

Filter criterion 2 identifies groundwater systems that are considered vulnerable to contamination.  If a groundwater system sources a vulnerable aquifer and has no adequate alternative source of water, the system is assigned USA status.  The system's WHPA becomes the USA.  If a WHPA has not been established for the system, a protective buffer is generated around the system using a 2000 feet radius, as prescribed by the methodology.  The 2000-feet radius buffer circle becomes the USA.  Groundwater systems sourcing non-vulnerable aquifers remain as USA candidates and are reevaluated in subsequent model runs.

The key to identifying vulnerable groundwater systems is distinguishing those systems that obtain their water from Pettyjohn Class I or Class IIa aquifers.  A primary consideration is the location of the well with respect to the aquifer outcrop or subcrop.  For some aquifers, the aquifer outcrop belt is Class I or IIa, whereas the subcrop belt of the aquifer is Class III, because the aquifer is overlain by a confining unit.

To aid in the process of classifying groundwater systems with a Pettyjohn class, guidelines or screening rules were developed for each state that list the classification for systems based on the location of the well (outcrop/subcrop), well depth, and overlying surface geology.  Below is an example of a guideline for the state of Louisiana.

"4) The Alluvial/Valley Trains aquifer system is composed of Quaternary braided stream deposits overlain, in some areas, by loess deposits.  The aquifer consists of unconsolidated and highly permeable sands.  Wells deriving water from this aquifer are Class Ia USAs and can be no deeper than 250 ft.  When covered with loess, wells are Class Id and can be no deeper than 300 ft., because the loess is an impermeable layer, usually less than 50 ft. thick." 

The guidelines are developed based on the known characteristics, the geographic relationships, and the attribute information of the groundwater wells, the aquifer boundaries, and the surface geology.  Sometimes, all this information is not available to aid in defining a set of screening criteria.  For example, the California PWS data does not provide depth information for wells.  In this case, the guidelines for the pilot test of California were developed solely on aquifer geologic characteristics and the geographic relationship between the groundwater wells and the overlying surface geology maps.

Once the guidelines are developed an ArcInfo lookup table is created based on the information.  The model steps through each record in the guideline table, selecting wells that meet the screening criteria for that record and classifying the groundwater wells accordingly, (see Table 8).

4.4.4   NOTABLE EXCEPTION 2

Notable exception 2 identifies groundwater systems that are not considered vulnerable to contamination.  This identification is based on the Pettyjohn classification of each groundwater system.  This classification is discussed in section 4.3.2. Groundwater wells identified as sourcing a non-vulnerable aquifer are not considered USAs by the model.  They remain as USA candidates, however, and will have the opportunity to gain USA status in later model runs with the advent of updated and more detailed attribute information from the various drinking water data sources.

4.4.5   VARIABLE WATER SYSTEM TYPES

Water system types are generally classed as surface water intakes or groundwater wells.  On occasion, PWS databases may include other types of water systems, such as springs.  These other water system types may be researched to determine whether the state considers their supply to come from a surface or ground water source.  If the source type of a water system cannot be determined, the water system is not considered as a USA candidate, although it remains an Environmentally Sensitive Area (ESA) to be reevaluated in subsequent model reruns.

4.4.6   ADEQUATE ALTERNATIVE SOURCE DETERMINATION

A significant effort was undertaken to contact each public water system that had been assigned a preliminary USA status by the model.  The preliminary status was assigned based on the directives in notable exception 1, filter criterion 1, filter criterion 2, and notable exception 2.  Public water systems that meet these criteria were contacted personally by telephone or fax to ascertain whether they have an alternative source that is "adequate."

The responses to the query ranged from explicit, detailed information to no response at all.  The subjective information relayed through personal contact was manually documented, linked with its appropriate PWS ID number, and entered in Microsoft Access to create the adequate alternative source (AAS) database.  In this way structure was applied to the voluminous amount of information gleaned from the verbal or written communication.  The linked PWS ID number is used as the key index field to join the AAS database with the PWS database.  This enables the AAS information to be applied to the preliminary USAs to determine their final USA status.

For the pilot study, public water systems that stated they did not have an alternative source or that their alternative source could only provide water for periods of one month or less became USAs.  Public water systems that stated they have a source that can provide water for periods longer than one month were not designated as USAs, but remain USA candidates to be reevaluated in later model runs.  When a contact could not be made with a PWS or the information received was too ambiguous to decipher, the PWS is considered to be a USA candidate and has an opportunity to become a USA in future runs of the model.

4.4.7   FILTER CRITERION 3

Filter criterion 3 provides extra protection to groundwater systems that are located within the boundary of a sole source aquifer.  For groundwater systems that are located within a sole source aquifer the model has two options for delineating protection areas depending on the type of WHPA defined for the system.

1. If a groundwater system has a fixed-radius WHPA, then the radius of the WHPA is doubled to provide more protection for the groundwater system.
2. If a groundwater system has a zone-defined WHPA, then the zone-defined WHPA represents the protection area for the system.

For the pilot study both Louisiana and Texas provided fixed-radius WHPAs.  Louisiana designates a 2-mile radius WHPA in unconfined aquifers and a 1-mile radius WHPA in confined aquifers.  Texas has established various fixed-radius WHPAs that are applied directly to each groundwater system through a link on the PWS ID number.  WHPAs were not provided for California at the time of the model run, thus a default fixed-radius of 2000 ft was used to define WHPAs, as described in the methodology.

5.0 LITERATURE CITATIONS

Correll, D.S.  and H.B. Correll.  1975.  Aquatic and Wetland Plants of Southwestern United States.  Environmental Protection Agency Research and Monitoring.

Dobson, A.P., J.P. Rodrieguez, W.M. Roberts, and D.S. Wilcove.  1997.  Geographic distribution of endangered species in the United States.  Science 275:550-553.

Ehrenfeld, D.R., R.F. Noss, and G.K. Meffee.  1997.  Letter to the editor.  Science 276:515-516

Federal Register 1999.  64 FR 250: 73464.

Flather, C.H., L.A. Joyce, and C.A. Bloomgarden. 1994. Species Endangerment Patterns in the United States.   USDA Forest Service General Technical Report RM-241.  Fort Collins, CO.:  U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 

Flather, C.H., M.S. Knowles, and I.A. kendall. 1998.  Threatened and endangered species geography: Characteristics of hot spots in the conterminous United States.   BioScience 48:365-376.

Halls, J., J. Michel, S. Zengel, J.A. Dahlin, and J. Petersen. 1997. Environmental Sensitivity Index Guidelines, Version 2.0. NOAA Technical Memorandum NOS ORCA 115.  Hazardous Materials Response and Assessment Division, National Oceanographic and Atmospheric Administration, Seattle, Wa.  79 pp. + appendices.

Kiester, A.R., J.M. Scott, . Csuti, R.F. Noss, B. Butterfield, K. Sahr, and D. White. 1996.  Conservation prioritization using GAP data.  Conservation Biology 10: 1332-1342.

Scott, J.M., B. Csuti, J.D. Jacobi, and J.E. Estes. 1987. Species richness: A geographic approach to protecting future biological diversity.  BioScience 37: 782-788.

Stein, B.A., L.S. Kutner, and J.S. Adams (eds). 2000.  Precious Heritage: The Status of Biodiversity in the United States. . The Nature Conservancy. Arlington, VA.

The Nature Conservancy (TNC). 1996.  Conservation by Design. The Nature Conservancy. Arlington, VA.

_______.  1997. Designing a Geography of Hope: Guidelines for Ecoregion-Based Conservation in the Nature Conservancy. The Nature Conservancy. Arlington, VA.

Last Update 07/10/2000