2025 Urban Water Management Plan

Section 7 2025 Urban Water Management Plan Water Supply Reliability Assessment City of Pleasanton Public Draft | May 2026 7-3 EKI Environment & Water, Inc. regulatory constraints from the Coordinated Operations Agreement; operational constraints due to the Endangered Species Act; emergency management constraints necessary to prepare for potential Delta outages or interruptions from floods, earthquakes, and other risks; and impacts from subsidence. Further, Zone 7 and other SWCs are currently working with DWR and other key stakeholders to address the many complex issues undermining the Delta through the proposed DCP, as discussed in Section 6.8.1.1. The proposed new diversion structure in the northern Delta provides alternative intakes in case the Delta is affected by an earthquake, levee failure, or some other catastrophic event that impacts water quality and prevents pumping from the Delta. The DCP would also provide alternative intakes that could be used to minimize harm to endangered and threatened species in the Delta. DWR is working closely with regulatory and natural resource agencies to address regulatory uncertainty and protect the Delta ecosystem using an adaptive management framework based on the best available science. With these benefits, the DCP is expected to significantly alleviate constraints on SWP operation and provide more water supply reliability. 7.1.1.1.2 Water Quality Until the DCP is constructed and operational, there continues to be water quality concerns associated with transport through the Delta. In 1982, DWR formed the Interagency Delta Health Aspects Monitoring Program to monitor water quality in the Delta and protect human health. The program was renamed the Municipal Water Quality Investigations Program in 1990. From a municipal water supply perspective, water quality issues in the Delta are associated with salinity from seawater intrusion, wastewater effluent discharges, agricultural drainages from the island surfaces, and recreational activities. Water quality issues of specific concern to Zone 7 are: • Algal byproducts: Parameters of concern include compounds that cause taste-and-odor (T&O) and algal toxins. T&O is primarily a problem in the warmer months, when algal blooms may be present. It can affect supplies from the Delta and from Lake Del Valle (which stores SWP water). Algae produce geosmin and 2-methylisoborneol, which are key T&O-causing compounds in surface water supply. Algal toxins derived from blue-green algae can also be a concern. Zone 7’s ozonation facilities (installed at DVWTP and Patterson Pass Water Treatment Plant [PPWTP]) effectively treat algal byproducts. Without ozonation, high levels of algal byproducts in both Delta and Lake Del Valle supplies may necessitate temporarily switching to groundwater supplies; blending of sources is also an option depending on the source of algal byproducts and severity. • Total and dissolved organic carbon (TOC/DOC): Zone 7 treats organic carbon with coagulant and disinfectant chemicals, and therefore higher levels of organic carbon increase costs. In addition, TOC and DOC help form disinfection byproducts (DBPs), which are regulated compounds in drinking water. Historically, Zone 7’s WTPs have managed high TOC/DOC by increasing coagulant dosages. However, this operational change results in greater sludge production and limits plant production. The use of ozone reduces coagulant and chlorine demands, thus reducing typical chlorination DBPs; however, formation of ozonation DBPs, such as bromate, will need to be controlled. • Turbidity: Like TOC/DOC, turbidity affects the amount of chemicals used in treatment and Zone 7’s ability to meet drinking water standards. It can also reduce the production capacities of Zone 7’s WTPs, requiring increased groundwater production under high demands. Coagulant dosages can be adjusted to address high turbidity (which can happen after big storms), but if filters require more frequent backwashing, then production may decrease. • Salinity or Total Dissolved Solids (TDS): Salinity has significant impacts on SWP operations and the availability of water. To meet the salinity objectives in the Delta, water exports from