City of Los Banos Basins and Stormwater Capture Project

City of Los Banos Basins and Stormwater Capture Project

The proposed Project would construct a basin for the purposes of surface and storm water capture as well as for incidental groundwater recharge with approximately three internal cells. The basin would provide multiple benefits in terms of storage, recharge, and re-regulation of various City and GWD water sources and possess a combined storage capacity of approximately 500 AF. GWD operates two canals near the Project site: the San Luis Canal bordering the site on the west and the Santa Fe Canal to the east. The San Luis Drain, which is part of the U.S. Bureau of Reclamation (USBR) Central Valley Project (CVP), is situated between the Santa Fe Canal and the Project site. From either canal, GWD could physically deliver floodwaters, storm drainage, CVP and local surface water supplies, or other existing water supplies from the Mendota Pool on the San Joaquin River. The proposed Project would be surrounded with low lying embankments to contain the water supplies. The site would be separated into multiple cells with an interconnection between the cells, as well as have a connection at the northerly end to return water supplies to the San Luis Canal. The separation of the basin into three cells separated by levees would allow for access, installation, and repair of existing and future utilities that cross the site, in addition to access for operation and maintenance. The Area of Potential Effect (APE) for biological and cultural surveys is identified as approximately 180 acres with the multi-cell basin accounting for approximately 160 acres. Based on the canal water surface elevation compared to the proposed ground surfaces, turnouts to the property would require pumping plants to deliver the supplies. The basin would allow GWD to divert flows off either canal when there are capacity limitations in the canals or extra supplies, temporarily storing water on the site for later use, as well as perform groundwater recharge activities. The City has multiple existing stormwater discharge outfalls to the San Luis Canal upstream and adjoining the Project site. Diverting these flows to the Project site can reduce the peaking flows in the canal, which would reduce possible downstream flooding and provide capacity flexibility for GWD operations. The detention basin would contain the following components: • Basin embankment heights would be less than six feet above the existing ground surface; • Turnouts on each side of the property, one from the Santa Fe Canal and one from the San Luis Canal; o Major components of the turnouts would include a concrete structure, pumping plants with electrical motors, metering, discharge pipeline and outlet structure; • Excavation would be balanced on site, if possible; • Inter-basin cells connection structure; and • Return flow structure and pipeline to the San Luis Canal. The USBR San Luis Drain encroachment would be constructed with bore and jack or open cut methods. The discharge carrier pipeline would likely be cased with a steel pipeline sleeve. The City is in the process of developing other projects for sewer and drinking water pipelines that would also cross the drain and canals, however the turnout and pipeline off the Santa Fe Canal would likely be further south and may or may not be combined with other projects with one encroachment process. Due to budgetary processes and funding limitations, it is likely that the project will be constructed in phases, with the embankment earthwork, connections to the San Luis Canal and inter-basin structures being constructed first, then pump and electrical work, and the easterly turnout off the Santa Fe Canal constructed at a later date than the rest of the Project. Construction Schedule Construction of the Project is expected to be completed in phases, totaling nine to 12 months. Initially, the proposed basin embankments/cells, structures off the San Luis Canal, and basin inter-connection structures would be constructed over the course of approximately six months. The Project includes mobilization, site preparation, and berm construction surrounding the basin; earthwork and structures placement; Project turnouts, metering stands, and inter-basin and basin outfall structures. New berm construction would be less than six feet, measured from the exterior toe to the top of the new levee. The Project would include approximately three ponds/cells within the detention basin separated by berms. A 15-foot-wide drive/access road would be constructed to surround the basins. The proposed road would not require any special surfacing and would be used for maintenance access and operations. After construction completion, performance testing and demobilization would occur. At a later date, installation of the pumping plant and electrical service for the turnout off the San Luis Canal, crossing the USBR San Luis Drain (once federal approvals are obtained), and construction of an additional turnout and pump station off the Santa Fe Canal are proposed to be constructed, over about a three-month period. Equipment Construction equipment would likely include, but not be limited to, the following types: • Excavators; • Backhoes; • Graders; • Skid steers; • Loaders; • Hauling trucks; • Scrapers; • Sheepsfoot compactors; • Dozers, • Large tractor and large discing unit, • Water trucks supplying water for dust control and conditioning soil for compaction; and • Large watercannon and hoses. Post-construction activities would include system testing, commissioning, and site clean-up. Construction will require temporary staging and storage of materials and equipment. Staging areas would be located onsite within the identified APE or at the City of Los Banos wastewater treatment plant property. Operation and Maintenance Management and operations of the basin would include monitoring existing nearby wells and flows in and out of the basins, plus estimated recharge quantities will be maintained to assist with City understanding and management of the groundwater levels and recharge. The City’s operation of the basin would be consistent with the City’s other similar facilities in that groundwater conditions would be monitored to minimize negative impacts on the surrounding areas (such as nearby wells, crops, and the existing wastewater treatment plant). Discing, mowing or spraying weeds will likely be required, as well as occasional grading of embankment roadways.

Los Banos

Merced

Northern California

Merced