Farmington Dam Repurposing Project

A long-term groundwater overdraft exists in the eastern San Joaquin County California which has resulted in lowering ground levels below the City of Stockton and has allowed the intrusion of saline water to portions of the aquifer. The 315,000 residents of Stockton and the surrounding 398,000 acres that comprise the local agricultural economy rely heavily on the safety of the groundwater aquifer and the stability and reliability of surface water supplies to further prevent saline intrusion.

To solve the water supply reliability and safety of water issues, Stockton East Water District (SEWD) and the United States Army Corps of Engineers (USACE) have analyzed options to modify the Farmington Dam from solely flood control to a permanent water supply storage dam with flood control. Back in 1998, the USACE prepared a reconnaissance-level design report that identified modifications needed to facilitate permanent water supply storage at Farmington Dam.

Farmington Dam has a flood control capacity of 52,000 acre-feet at pool elevation 156.5 feet. The proposed project would increase the total reservoir capacity to 112,000 acre-feet which includes 60,000 acre-feet for water supply and 52,000 acre-feet for flood control by raising the dam crest 11.5 feet.

The Project will generate multiple benefits, including providing additional water supply storage for municipal and agricultural demands. Key points are the following:

·         New source of stored water with 60,000 acre-feet permanent water supply storage for municipal and agricultural water users by raising the dam 11.5 feet.  The new source of water will potentially directly benefit all the 315,000 residents of the City of Stockton and 140,000 acres of agricultural land.

·         Additional capacity for flood control by keeping the existing flood control volume and adding additional capacity for control if necessary

·         Overcoming groundwater depletion with additional capacity to percolate into the overdrawn groundwater aquifer which will aid in repelling saline intrusion and ensure a safe water supply for residents and local crops.

·         Existing water rights applications will be perfected to allow for the annual storage of water, when available, and unused water from existing Central Valley Project contracts can be transferred for carryover storage.

The Project would construct a 40-foot deep slurry cutoff wall along the entire length of the dam with an upstream clay berm about 10 feet thick to minimize seepage, improve two, 500-foot sections of the dam foundation, replace the existing 95-foot broad crest weir spillway with a 200-foot wide ogee spillway, and add the necessary modifications for seismic control.

An Engineering Technical Memorandum to review and update aspects of the 1998 initial study was completed on November, 2015.  The memorandum listed an estimated cost for the Farmington Dam Retrofit Project of $158.1 Million.  SEWD is requesting the Farmington Dam Retrofit Project be considered for inclusion within the 2024 Water Resources Development Act (WRDA) bill to direct the USACE to re-evaluate the feasibility of the project. General inquiries can be sent to SEWD’s General Manager, Justin Hopkins, at jhopkins@sewd.net.