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SFPUC outlines Lake Merced role in local groundwater and recycled‑water projects
Summary
Assistant General Manager Steve Ritchie told commissioners how four interrelated projects — Westside recycled water, San Francisco groundwater supply, regional groundwater storage and Daly City's Vista Grande drainage project — collectively influence Lake Merced levels and water quality; staff noted Lake Merced is listed as impaired under Clean Water Act section 303(d).
At a March 26 meeting, Assistant General Manager for Water Steve Ritchie presented how Lake Merced is central to several local water‑supply and stormwater projects and explained how those projects interact to shape lake levels and water quality.
Ritchie reviewed four projects: the Westside Recycled Water Project (which would irrigate large parks and shift groundwater uses), the San Francisco Groundwater Supply Project (proposing about 4 million gallons per day from the Westside Basin), a Regional Groundwater Storage and Recovery Project (a conjunctive‑use, dry‑year supply estimated at about 7.2 MGD), and Daly City’s Vista Grande Drainage Basin Improvement Project (which would restore watershed flows into Lake Merced). He told the commission these projects taken together are expected to produce a net effect close to the lake’s present average level (about 6.0 feet in city datum); individually, projects can push the lake level higher or lower.
Commissioners pressed staff on how lake elevations are reported. Ritchie explained the presentation used "city datum," which differs from the 27‑foot figure referenced previously (a separate datum such as NAVD); he said the operable range under study is roughly 5–9 feet city datum and that CEQA analysis will examine environmental impacts of various operating ranges.
On water quality, Ritchie said Lake Merced is listed as impaired for low dissolved oxygen and high pH under the Clean Water Act's 303(d) listing, which constrains permitting for the Vista Grande project because returning new runoff to an already‑impaired water body would constitute a new discharge. Ritchie said the agency has not detected lead accumulation in the fish tissue to date, and staff plan an ecological risk assessment as part of any cleanup.
Ritchie summarized the interdependence of the projects: "When you put the three of those together, it's basically they counteract each other and we have a net, you know, reasonable effect on the lake." He also said the Vista Grande project’s EIR will analyze target lake levels and that SFPUC will participate as a responsible agency in that environmental review.
Ending: Staff said they will complete responses to comments on the groundwater project environmental impact report by year end and bring proposals back to the commission; commissioners encouraged continued public participation through the EIR process.
