Sole Source Aquifer Program | Region 10 | US EPA

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Sole Source Aquifer Program

EPA Contact

Susan Eastman
(206) 553-6249

As of December, 1997, EPA has designated 69 sole source aquifers nationwide. Fifteen of these are in Region 10 (which consists of Alaska, Idaho, Oregon, and Washington). There are currently NO sole source aquifers designated in Alaska.

Recent Progress:
EPA Region 10 signed a new Memorandum of Understanding (PDF) (8 pp, 621K) (MOU) with Federal Highway Administration (FHWA) Washington Division and the Washington State Department of Transportation (WSDOT) on Sept 25, 2014. The MOU expands the list of types of projects which do not have the potential to contaminate a SSA and therefore do not require EPA review.  The MOU also includes additional information about the suite of regulations and policies that govern WSDOT and FHWA’s protection of water quality.

On this page: Designated Aquifers in the Pacific Northwest

Sole Source Aquifer NameStateFR Vol/No/PgFR Date
Spokane Valley-Rathdrum Prairie AquiferWA/ID43/28/556602-09-78
Camano Island AquiferWA47/66/1477904-06-82
Whidbey Island AquiferWA47/66/1477904-06-82
Cross Valley AquiferWA52/95/1860605-18-87
Newberg Area AquiferWA52/191/37215
North Florence Dunal AquiferOR52/194/3751910-07-87
Cedar Valley AquiferWA53/191/3877910-03-88
Lewiston Basin AquiferWA/ID53/191/3878210-03-88
Eastern Snake River Plain AquiferID/WY56/194/5063410-07-91
Central Pierce County Aquifer SystemWA59/1/22401-03-94
Marrowstone Island Aquifer SystemWA59/105/2875206-02-94
Vashon-Maury Island Aquifer SystemWA59/127/3446807-05-94
Guemes Island Aquifer SystemWA62/230/6354512-01-97
Troutdale Aquifer SystemWAE6-1471010-05-06
Bainbridge Island Aquifer SystemWA78/07409/1926203-29-13
Note: Designation of the Eastern Columbia Plateau Aquifer System has been suspended indefinitely.

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The Sole Source Aquifer (SSA) Protection Program is authorized by Section 1424(e) of the Safe Drinking Water Act of 1974 (Public Law 93-523, 42 U.S.C. 300 et. seq), which states:

    "If the Administrator determines, on his own initiative or upon petition, that an area has an aquifer which is the sole or principal drinking water source for the area and which, if contaminated, would create a significant hazard to public health, he shall publish notice of that determination in the Federal Register. After the publication of any such notice, no commitment for federal financial assistance (through a grant, contract, loan guarantee, or otherwise) may be entered into for any project which the Administrator determines may contaminate such aquifer through a recharge zone so as to create a significant hazard to public health, but a commitment for federal assistance may, if authorized under another provision of law, be entered into to plan or design the project to assure that it will not so contaminate the aquifer.”
The Environmental Protection Agency (EPA) defines a sole or principal source aquifer as one which supplies at least 50 percent of the drinking water consumed in the area overlying the aquifer. EPA guidelines also stipulate that these areas can have no alternative drinking water source(s) which could physically, legally, and economically supply all those who depend upon the aquifer for drinking water. For convenience, all designated sole or principal source aquifers are usually referred to simply as "sole source aquifers.”

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Petition for Designation

Although the agency has statutory authority to initiate SSA designations, EPA has a longstanding policy of only responding to petitions. Any person may apply for SSA designation. A "person" is any individual, corporation, company, association, partnership, state, municipality, or federal agency. A petitioner is responsible for providing EPA with hydrogeologic and drinking water usage data, and other technical and administrative information required for assessing designation criteria.

In 1987, EPA published the Sole Source Aquifer Designation Petitioner Guidance to assist those interested in preparing and submitting petitions to EPA regional offices. The document provides procedures and criteria for proposing aquifer boundaries, determining whether an aquifer is the sole or principal source of drinking water, and for evaluating alternative sources of drinking water.

In general, the designation decision process takes a minimum of six months from the time that the petitioner submits a complete petition to EPA. The process may take considerably longer, depending on the technical complexity of the petition, and on the number of petitions that may be undergoing review within the EPA regional office at a particular time.

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Project Review Authority and Coordination

If an SSA designation is approved, proposed federal financially-assisted projects which have the potential to contaminate the aquifer are subject to EPA review. Proposed projects that are funded entirely by state, local, or private concerns are not subject to EPA review. Examples of federally funded projects which have been reviewed by EPA under the SSA protection program include:

  • highway improvements and new road construction
  • public water supply wells and transmission lines
  • wastewater treatment facilities
  • construction projects that involve disposal of storm water
  • agricultural projects that involve management of animal waste
  • projects funded through Community Development Block Grants
EPA has developed Memorandums of Understanding (MOU) with federal funding agencies to establish review responsibilities under the SSA protection program and to list categories of projects which should or should not be referred to EPA for review. MOUs help ensure that projects which pose serious threats to ground water quality "so as to create a significant hazard to public health" are referred to EPA. Region 10 has developed MOUs with a number of federal funding agencies including the Federal Highway Administration, the Department of Housing and Urban Development, and the U.S. Department of Agriculture - Rural Development. We are currently updating and renegotiating these MOUs and, as they are signed, they will be made available We are currently updating and renegotiating these MOUs, all current information can be found on the Groundwater Protection Unit Homepage.

Most projects referred to EPA for review meet all federal, state, and local ground water protection standards and are approved without any additional conditions being imposed. Occasionally, site or project-specific concerns for ground water quality protection lead to specific recommendations or additional pollution prevention requirements as a condition of funding. In rare cases, federal funding has been denied when the applicant has been either unwilling or unable to modify the project.

Whenever feasible, EPA coordinates the review of proposed projects with other offices within EPA and with various federal, state, or local agencies that have a responsibility for ground water quality protection. Relevant information from these sources is given full consideration in the sole source aquifer review process and helps EPA to understand local hydrogeologic conditions and specific project design concerns. Project review coordination also helps ensure that SSA protection measures support or enhance existing ground water protection efforts, rather than duplicate them.

To have a project reviewed by us ensure your project meets two criteria:
  1. Be in the review area of the SSA. The review area consists of both the aquifer boundary AND the source area of the SSA as delineated in the GIS maps on this website. 
  2. The project receives federal funding. The SSA program has no statutory authority to review a project unless it is receiving federal funding.
If your project meets these criteria please submit a completed Region 10 SSA check list (RTF) (2 pp, 69K) by email to Susan Eastman (  Projects submitted without a checklist or via hardcopy may have a delayed review time

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Public Awareness and Participation

SSA designations help increase public awareness on the nature and value of local ground water resources by demonstrating the link between an aquifer and a community's drinking water supply. Often, the realization that an area's drinking water originates from a vulnerable underground supply can lead to an increased willingness to protect it. The public also has an opportunity to participate in the SSA designation process by providing written comments to EPA or by participating in an EPA-sponsored public hearing prior to a designation decision.

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Resource Characterization

Important information on the boundaries, hydrogeologic materials, and water use patterns of an area's aquifer must be documented by a petitioner seeking SSA designation. Following EPA's technical review of a petition, this information is summarized by the Agency in a technical support document that is made available for public review. Following designation, a Federal Register (FR) notice is published to announce and summarize the basis for EPA's decision.

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Limitations of the Program

Sole source aquifer designation provides only limited federal protection of ground water resources which serve as drinking water supplies. It is not a comprehensive ground water protection program. Protection of ground water resources can best be achieved through an integrated and coordinated combination of federal, state, and local efforts such as called for under the Comprehensive State Ground Water Protection Program (CSGWPP) approach. For example, local wellhead protection programs designed to protect the recharge areas of public water supply wells should work in concert with contaminant source control and pollution prevention efforts being managed at various levels of government. This coordination ensures that all ground water activities meet the same protection goal without duplication of time, effort, and resources.

Although designated aquifers have been determined to be the "sole or principal" source of drinking water for an area, this does not imply that they are more or less valuable or vulnerable to contamination than other aquifers which have not been designated by EPA. Many valuable and sensitive aquifers have not been designated simply because nobody has petitioned EPA for such status or because they did not qualify for designation due to drinking water consumption patterns over the entire aquifer area. Furthermore, ground water value and vulnerability can vary considerably both between and within designated aquifers. As a result, EPA does not endorse using SSA status as the sole or determining factor in making land use decisions that may impact ground water quality. Rather, site-specific hydrogeological assessments should be considered along with other factors such as project design, construction practices, and long-term management of the site.

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Contact Us

For more information on the Sole Source Aquifer Program in Region 10, contact:

Susan Eastman

Call toll-free from AK, ID, OR, and WA at 1-800-424-4EPA

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