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Contact EPA Pacific Southwest Groundwater

Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

Ground Water

Ground Water Quick Finder
Ground Water Home Class V Wells Cesspools in Hawaii Onsite Sewage Treatment Permits Sole Source Aquifer Source Water Protection Tribal Water Protection Underground Injection Wells

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Sole Source Aquifer

The EPA's Sole Source Aquifer (SSA) Program was established under Section 1424(e) of the Safe Drinking Water Act (SDWA.) Since 1977, it has been used by communities to help prevent contamination of groundwater from federally-funded projects. It has increased public awareness of the vulnerability of groundwater resources. The SSA program allows for EPA environmental review (PDF) (1pg, 34K) of any project which is financially assisted by federal grants or federal loan guarantees. These projects are evaluated to determine whether they have the potential to contaminate a sole source aquifer.

In Region 9, nine sole source aquifers have been designated:

Sole source aquifer map for California, Arizona
Sole source aquifer map for Guam and Hawaii
Sole source aquifer map for Guam and Hawaii


Click here for a national layer including all available coverage for Sole Source Aquifers (SSA) that can be used in Geographic Information Systems (GIS)

State Sole Source Aquifer Name Federal Reg. Cit Publ. Date Map
AZ Upper Santa Cruz & Avra Basin Aquifer 49 FR 2948 01/24/84 KMZ
PDF (1 pg, 1.3M)
AZ Bisbee-Naco Aquifer 53 FR 38337 09/30/88 KMZ
PDF (1 pg, 175K)
CA Fresno County Aquifer 44 FR 52751 09/10/79 KMZ
PDF (1 pg, 1.3M)
CA Santa Margarita Aquifer, Scotts Valley 50 FR 2023 01/14/85 KMZ
PDF (1 pg, 434K)
CA Campo/Cottonwood Creek 58 FR 31024 05/28/93 KMZ
PDF (1 pg, 321K)
CA Ocotillo-Coyote Wells Aquifer 61 FR 47752 09/10/96 KMZ
PDF (1 pg, 337K)
GU Northern Guam Aquifer System 43 FR 17867 04/26/78 KMZ
PDF (1 pg, 400K)
HI Southern Oahu Basal Aquifer 52 FR 45496 11/30/87 KMZ
PDF (1 pg, 716K)
HI Molokai Aquifer 59 FR 23063 04/20/93 KMZ
PDF (1 pg, 146K)

A map of all nationally designated SSAs is also available on the Source Water Protection Publications Database.

For more information, please contact the Ground Water Office at
415-972-3971 or visit the national EPA Sole Source Aquifer Program site.

Outreach Documents

Sole Source Aquifer Fact Sheet (PDF) (1pg, 34K)

For Project Planners: What to submit for EPA review of proposed projects (PDF) (1pg, 34K)

Contact Information

See the Sole Source Aquifer section of the Ground Water contacts page.

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