State Water Board staff seek input on proposed urban stormwater infiltration policy

Welcome to the State Water Board's public meeting on the proposed urban stormwater infiltration policy, Amanda McGee, senior engineering geologist and Storms Unit lead in the State Water Resources Control Board's Division of Water Quality, told attendees at the start of a virtual workshop.

Staff framed the workshop as an early-input meeting rather than a decision session and asked stakeholders to provide written and verbal comments during the informal comment period. "Are we including too much? Are we not including enough?" Kelly Rodman, a water resource control engineer in the storms unit, asked attendees as she outlined the draft policy's scope and components.

The proposal seeks to encourage capture and infiltration of urban stormwater while protecting groundwater quality and beneficial uses, staff said. Officials tied the policy to statewide water-supply goals and drought planning, noting the Governor's 2022 California Water Supply Strategy goal to increase annual water supply by 500,000 acre-feet and the Department of Water Resources' 2020 Water Resilience Portfolio as background for prioritizing stormwater capture.

At the workshop staff identified barriers the policy aims to address: regulatory inconsistency across permits and local ordinances; unclear siting and design guidance for infiltration systems; concerns about potential adverse impacts to groundwater, including drinking-water aquifers; and the absence of standardized, statewide pretreatment and long-term operation-and-maintenance (O&M) requirements. Staff said there are already thousands of urban infiltration systems statewide and that the policy will focus on systems in 2020 census-defined urban areas.

Staff described the kinds of systems likely to be covered: dry wells, infiltration basins and galleries, regional infiltration projects, infiltration trenches, and large-scale bioretention or bioinfiltration projects designed to intentionally infiltrate significant volumes from larger catchments. Staff said the policy is not intended to add requirements for small-scale residential systems such as single-home bioswales or impervious driveways.

To manage groundwater-protection risks, staff proposed a risk-based approach linked to land use and subsurface conditions. Examples discussed included: low-risk land uses (residential, open space, small commercial and parking lots); medium-risk (commercial areas larger than about 5 acres of impervious surface, roads with light-to-medium traffic, transit stations); and high-risk land uses (many industrial facilities, equipment storage and maintenance sites, high-traffic roads, solid-waste handling and transfer stations). Staff said some land uses would likely be prohibited where minimum setbacks cannot be met or where pretreatment cannot adequately address contaminants of concern.

Staff highlighted minimum setback concepts to protect groundwater and drinking-water wells. Based on literature and guidance from the Division of Drinking Water, staff proposed a 100-foot minimum horizontal setback from water-supply wells as a likely standard and described a 250-foot setback for localized active contaminated sites to reduce the risk of mobilizing subsurface contaminants. Staff said flexibility would be available when a geotechnical or engineering analysis demonstrates an alternative setback will not harm groundwater quality.

Industrial sites and the Industrial General Permit (IGP) were singled out as areas needing coordination; staff said they are working with IGP permit writers to address pretreatment, good housekeeping, spill containment/response, and legacy contamination when siting infiltration systems in industrial areas.

On operations and monitoring, staff said the policy will aim to set minimum pretreatment and O&M standards scaled to the risk category so infiltration systems continue to function as designed and protect groundwater quality. Existing systems will generally be evaluated for exemption from new requirements, staff said, though failing systems or systems demonstrably degrading groundwater would need to be addressed.

Staff also described outreach plans, including early outreach to tribal nations and historically underserved communities in accordance with AB 52, AB 2108 and the board's Racial Equity Action Plan. Staff noted co-produced resources such as a story map on stormwater capture and a separate story map on race and stormwater management prepared by economist Megan Kung and the Los Angeles Regional Water Quality Control Board.

Workshop logistics and next steps: staff said this meeting and a duplicate February 6 meeting will cover the same material; the informal comment period for initial scoping comments closes at noon on February 24, 2025; a CEQA scoping session focused on the scope of environmental review will be held March 12 at 10 a.m.; and staff plan to release a draft policy in late 2025 followed by public workshops on the draft. Staff asked participants to submit written comments to the Storms inbox email and to use the Q&A and “raise hand” features for verbal comment during the webinar.

The workshop was described as informal stakeholder engagement only; no formal board action was taken or expected during the session. Amanda McGee noted meeting participation skewed toward consultants, with roughly 55% of registrants identifying as consultants and broad geographic representation across Southern California, the Central Valley, the San Francisco area and the Central Coast.