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Eastern San Joaquin Groundwater Basin Groundwater Management Plan Northeastern San Joaquin County Section 8 Groundwater Banking Authority 133 Integrated Conjunctive Use Program all water diverted through Strawberry (Pinecrest) Reservoir and Lyons Reservoir in excess of the required in-stream flows. The amount of water available annually is dependent upon the natural flow of the South Fork of the Stanislaus River which has an average annual yield of approximately 100,000 af including 24,000 af combined storage in Strawberry and Lyons Reservoirs (http://www.tuolumneutilities.com/uwmp.pdf, 2000). TUD is currently evaluating the possibility of replacing the existing Lyons Dam to create a larger reservoir to provide enough water for future development. The current capacity of Lyons Reservoir is 6,219 af, and the current spillway elevation is 4,214-ft. TUD has contemplated either a 25,000 af or 50,000 af reservoir with surface elevations of 4,285-ft and 4,328-ft respectively. Both options would be located 800-ft downstream of the current dam. The estimated cost of a new 50,000 af reservoir is $26 million. A map of the 50,000 af option is shown in Figure 8-19. SEWD has expressed interest in partnering with TUD for supplemental water supplies from the Lyons Reservoir enlargement (http://www.cserc.org/news/newsletter/2003winter/Lyons.html, 2003). 8.3 Groundwater Recharge Components For planning purposes, the following descriptions represent the final use of water. The components include groundwater recharge infrastructure and improvements, drinking water treatment facilities, and agency conjunctive use programs. 8.3.1 Farmington Program In 1997, the USACE completed the Farmington Dam and Reservoir Conjunctive Use Study, which evaluated potential structural and operational changes at Farmington Dam and Reservoir as part of a conjunctive use program. The study found that long-term storage at Farmington Reservoir is not cost-effective; however, operational modifications and the construction of groundwater recharge facilities are cost-effective. Consequently, the USACE, SEWD, and local water interests embarked on the development of a groundwater recharge program. In 1999 the U.S. Congress authorized up to $25 million for construction of groundwater recharge and conjunctive use projects in Eastern San Joaquin County. In 2001, SEWD completed the Farmington Groundwater Recharge/Seasonal Habitat Study (Farmington Study) to evaluate the physical and financial feasibility of a groundwater recharge program in Eastern San Joaquin County. Through pilot testing, the study team found that the most effective area for groundwater recharge is the area bounded by Highway 99, Jack Tone Road, the City of Manteca, and the Mokelumne River. A map of the general area is shown in Figure 8-20. The Farmington Study also explored the feasibility of various recharge techniques and concluded that the most efficient method of groundwater recharge in Eastern San Joaquin County is the use of field flooding, recharge basins, and excavated pits. Each method varies in average water depth from a few inches to several feet. Figure 8-21 illustrates the various methods of recharge used in the Farmington Program. Existing structures and improvements such as flood detention basins, quarry excavations, canals, and clarifiers can also be easily modified and incorporated in to the project. In November of 2003, the District received $1.3 million from the DWR for a Proposition 13 grant to complete the first pilot project facilities adjacent to the SEWD Treatment Plan. The pilot project is a permanent facility consisting of one 19-acre pond and three recharge basins totaling 35 acres. These facilities are expected to recharge 7,000 af/yr. In February of 2004, the pilot project was named the Water/Environment Project of the Year, 2003, by the American Society of Civil Engineers.