Mormon Island Auxiliary Dam Modification Project Complete, Parking Lot and Public Trail Reopens

The Bureau of Reclamation announces the completion of Safety of Dams modifications to Mormon Island Auxiliary Dam (MIAD) and the reopening of public parking at Mormon Island Cove, near Sophia Parkway, and public access across the crest of MIAD between Folsom Point and Sophia Parkway.

Located between Folsom and El Dorado Hills along Green Valley Road, MIAD is an important component to the Folsom Facility, which includes Folsom’s concrete and left and right wings dams and eight earthfill dikes, each of which serves to impound water to create Folsom Reservoir. Completing this project significantly enhances the continued safety of the communities downstream of MIAD.

The MIAD Improvement Modification Project was part of Reclamation’s Dam Safety Project, approved in 2007. Through the project, Reclamation has worked to reduce hydrologic (flood), seismic (earthquake) and static (seepage) risks at the Folsom Facility. In June 2010, Reclamation issued a Record of Decision for the MIAD Improvement Modification Project, selecting Alternative 4, Cellular Open Excavation and Overlay. The work was completed in two phases:

  • Phase 1 began in October 2010 and was completed in February 2013. The work consisted of one 50-foot by 50-foot trial excavation and five 150-foot by 50-foot excavations to bedrock that were backfilled with concrete and highly compacted soil to provide strength and eliminate foundation movement during a seismic event.
  • Phase 2 began in the fall of 2013 and has now been completed six months earlier than expected. The work consisted of increasing the mass of MIAD by strategically placing layers of sand, gravel and crushed rock on the downstream side of the dam and installing a system of filters and drains. This essentially allows any internal seepage within the structure to drain appropriately.
  • Please visit to view the MIAD Record of Decision and other related documents.