Los Banos Creek Recharge and Recovery Project

The Project entails using existing gravel pits (basins), designated as the Central Basin and the Southern Basin, to capture, store, recharge, and bank CVP and Warren Act water and/or Los Banos creek flood waters. The Central Basin is approximately 85 acres and has the capacity to store approximately 1,000 acre-feet. The Southern Basin is approximately 51 acres and is expected to store approximately 800 acre-feet upon completion of mining operations. The Basins will serve four purposes: 1. Surface Water Storage Conveyed using the DMC, CVP and Warren Act water will be stored during the winter months and returned to the DMC in the spring to serve agricultural demand. Some of the return water may be exchange with Reclamation to serve agricultural demands from the San Luis Canal. CVP water may be transferred to SLWD from other CVP contractors for short term storage, and the return transfer will take place in a subsequent water year, typically the next water year. In most cases the transfer(s) will be conducted using the Accelerated Water Transfer Program. 2. Groundwater Recharge The Central Delta Mendota Groundwater Sustainability Agency is developing groundwater management policies. It is expected that policies will be developed to encourage recharge and other actions that will improve groundwater sustainability. The basins will be operated to achieve both their maximum storage and recharge potential. Assuming a conservative daily infiltration rate of 0.5 inches per day, the Central Basin can recharge over a 90-day period approximately 242 acre-feet. Using the same assumptions, the Southern Basin can recharge approximately 208 acre-feet. Evaporation losses will be calculated using data from the California Irrigation Management Information System and deducted from the daily surface volume to calculate net recharge. SLWD will consider transfers of surface water for recharge by other contractors to help improve basin wide groundwater sustainability. These types of transfers for recharge will typically be conducted by CVP water contractors within the Delta Mendota Sub-Basin. 3. Groundwater Recovery When drought conditions occur, SLWD may extract, or effectively recover, a portion of the water recharged in the Central and Southern Basins and introduce the water into the Delta-Mendota Canal. Recovery of the recharged water will comply with the Delta-Mendota Subbasin Groundwater Sustainability Plan, limited to avoid significant and unreasonable impacts, as defined under the Sustainable Groundwater Management Act (SGMA) of 2014, and at least 5% of all water recharged will remain in the aquifer and will not be recovered. Recovered water will be used within the SLWD boundaries (which is wholly within the Central Delta Mendota Groundwater Sustainability Agency boundaries). All water recovered and introduced into the DMC will comply with all relevant standards and monitoring protocols established for the introduction of pumped water into the DMC. 4. Flood Water Capture Los Banos Creek is prone to flooding. During a declaration of flood emergency or when the State of California Governor’s office issues Executive Orders such as N-4-23 and N-7-23 the basins may be used to divert flood water. DMC Diversions Under the Project, CVP and/or Warren Act water will be conveyed through the DMC and diverted into the Central Basin or the Southern Basin at three locations. The first point of diversion will be constructed at approximately mile post MP 80.03-L where a new storage and recovery pump system will be installed to lift water from and return water to the DMC from the Central Basin. The second point of diversion will be constructed at approximately mile-post MP 80.03-R where a second new storage and recovery pump system will be installed to lift water from and return water to the DMC from the Southern Basin. The third point of diversion is at the existing diversion structure near Check 15 at mile post MP 79.60-R (Los Banos Creek) which will gravity flow water from the DMC into Los Banos Creek where a weir and diversion structure will be constructed to divert flows into the Central Basin. Los Banos Creek Diversions Flood water flowing in Los Banos Creek may be diverted downstream of the DMC siphon crossing where the aforementioned weir and diversion structure will be constructed to divert flows into the Central Basin. Flood waters will only be diverted under the previously stated conditions. Under the Project, the weir and diversion structure would be constructed and the capacity to divert flood waters would increase. Conveyance and Infrastructure The Project would include constructing the following infrastructure and conveyance components: • Construct a 30 to 50 cfs water transfer facility between the Central Basin and the DMC. • Construct a 30 to 50 cfs water transfer facility between the Southern Basin and the DMC. • Construct a weir in Los Banos Creek downstream of the DMC siphon crossing and the existing Vulcan haul road crossing to facilitate convey water into the Central Basin from Los Banos Creek to capture water released from the DMC or flood flows; • Construct a diversion structure on the right bank of Los Banos Creek immediately upstream of the newly constructed weir to convey water flowing in Los Banos Creek into the Central Basin. The Project also includes contouring of the of the bottom of the existing pits being used for the Central Basin and the Southern Basin to facilitate the evacuation of the storage space. There will be no excavation work to create water storage space as the storage space was effectively created through past mining operations. Reshaping and stability improvements to the banks of the basins will also be performed.