The Coachella Valley Water District (CVWD) proposes to consolidate the sanitation system at the Oasis Gardens MHP into CVWD’s sanitation system, and upgrade Lift Station 55-21 (LS 55-21). The project has two components: installation of sewer lateral pipelines at Oasis Gardens MHP and upgrade of facilities at LS 55-21. The Oasis Gardens MHP has a population of approximately 500. The purpose of the project is to consolidate a community that currently relies on septic systems to CVWD’s sewer system. Many communities in the Coachella Valley served by onsite septic systems do not have the resources to properly maintain these systems, often resulting in system failure and causing public health and safety issues. MHPs tend to have a higher number of persons per household than other residential communities, resulting in frequent system failures and surfacing wastewater causing public health, aesthetic, water quality, and other issues. The Coachella Valley relies almost entirely on groundwater for potable water supplies. Failure of septic systems and potential contamination of surface waters has the potential to infiltrate the groundwater supplies and impact CVWD’s water supplies. The Oasis Gardens MHP Sewer Consolidation Project Phase 2 will help to minimize risk to public health and water quality for the MHP and the Coachella Valley.
The MHP component consists of installation of 270 linear feet (LF) of 6-inch PVC sewer lateral piping within the Oasis Gardens MHP to connect with CVWD’s sewer main within Polk Street. The project will convert 77 mobile homes from septic systems to CVWD’s sewer system. The nine communal septic systems currently used by the 77 mobile homes will be left in place and abandoned per State of California and Riverside County requirements. Lateral pipelines would be installed via open-trench construction. A 6-inch cleanout would be located at each of the nine connection points. Surface restoration would occur after backfilling is complete and include roads and walkways and landscaping. Construction would take place over the course of one month.
The lift station component involves improvements at CVWD’s existing LS 55-21 site. The existing Polk Street sewer pipeline is tributary to LS 55-21 and discharges to CVWD’s Water Reclamation Plant 4 (WRP-4), which operates under a National Pollutant Discharge Elimination System (NPDES) permit issued by the Colorado River RWQCB and adopted May 19, 2017 (R7-2017-0006) for discharge into the Coachella Valley Stormwater Channel. LS 55-21 currently does not have enough capacity to service the project and other planned development. LS 55-21 pumps and motors would be upsized as part of the project to serve the new additional flows and all electrical equipment, including the emergency generator, would be replaced. Construction at LS 55-21 would be completed in three phases. The first phase of construction will involve construction of new facilities and adjustments as needed. The second phase of construction will involve removal of existing facilities and switchover from existing to new equipment and facilities. The third and final phase of construction will involve performance testing/checks and acceptance testing. The activity at LS 55-21 would take place over the course of approximately 12 months.
The increase in flow capacity at LS 55-21 would require additional power for the upsized pumps and motors. Electrical service from Imperial Irrigation District (IID) would need to be increased from 200A to 400A and the existing pole mounted transformer (75 kilovolt-ampere [kVA]) would require replacement with a pad mounted transformer estimated at 225kVA. IID would be notified during design of the increase in power required. The estimated additional amount of energy consumed by the upgraded LS 55-21 pump station would be 8,400 kWh per year.
Air pollution from construction of the project was estimated in October 2021. All emission levels were lower than local significance thresholds. Prior to grading or excavation, the Construction Contractor would be required to prepare a Fugitive Dust Control Plan, subject to the approval of CVWD and South Coast Air Quality Management District (SCAQMD), to comply with SCAQMD Rule 403 and Rule 403.1, which would reduce emissions of dust and particulate matter during construction.
A Biological Resources Technical Study was prepared for the project in October 2021. The study found the project sites are entirely developed, comprised of irrigated residential lots, paved roads, the lift station facility, and other buildings, with ornamental vegetation. No special-status wildlife species were determined to have potential to occur within the project sites. Improvements to the lift station facility may hinder wildlife during temporary impacts associated with construction but would not create any additional permanent barriers or obstacles to wildlife movement. The project sites are within the boundaries of the Coachella Valley Multiple Species Habitat Conservation Plan and Natural Community Conservation Plan but are not located within or adjacent to a conservation area associated with the Coachella Valley Multiple Species Habitat Conservation Plan. Both project sites are developed and improved and therefore this project is not subject to the Coachella Valley Association of Governments Local Mitigation Development Fee. Measures necessary for compliance with CFGC 3503, CFGC 3503.5, and the MBTA would be implemented by the project, which would minimize potential temporary construction-related impacts on nesting birds that may be present during the bird nesting season.
A Cultural Resources Study was prepared for the project in October 2021. The project would not have a significant effect on historical or archaeological resources and no adverse effect on historic properties under Section 106 of the National Historic Preservation Act. The project would implement a measure for the unanticipated discovery of cultural resources during project development as a standard construction practice, and would also adhere to regulations regarding the unanticipated discovery of human remains.