Expert panel urges regional A‑minus‑R rulemaking; board hears widespread public comment

A statewide expert panel convened by the State Water Resources Control Board recommended on June 16 that regulators use an A minus R (applied minus removed) metric on a three‑year rolling average as the preferred way to link farm nutrient management with potential groundwater discharge, urging regional boards to set iterative targets and pair any limits with outreach and technical assistance.

The recommendation, delivered by panel chair Dr. Daniel Gistler, follows a 10‑month process of 21 meetings that included plenary sessions, listening sessions and working groups. The panel told the board that A minus R is more directly related to potential nitrate discharge than the previously suggested A/R efficiency ratio and that initial limits should be regionally tailored and phased in — for example beginning near the 80th–90th percentile of current practice so regulators can focus on higher outliers first. “As a panel we recommend implementing increasingly strict targets and limits using an iterative approach,” Dr. Gistler said during the presentation.

Why it matters: Nitrate pollution from fertilizer and irrigation is a leading cause of unsafe drinking water in parts of California. The panel’s technical guidance is intended to give regional water boards a consistent metric while recognizing agricultural and hydrologic diversity across the state.

What the panel recommended and why: The experts concluded that A minus R is preferable because it better estimates the mass of nitrogen potentially available for leaching to groundwater. Where crop‑specific removal coefficients are lacking, the panel advised temporary use of applied‑only measures while developing alternative reporting approaches. The panel also recommended: - Using three‑year rolling averages to smooth year‑to‑year variability caused by weather or pest events; - Allowing regional boards to set targets and limits appropriate to local crops, soils and climate; - Applying discount factors for organic amendments (compost) based on plant‑available nitrogen (C:N guidance); - Supporting models as a supplemental tool where coalitions and regions have capacity; and - Crafting alternative reporting pathways and technical assistance for small diversified farms, nurseries and specialty operations.

Public response and board reaction: The panel’s findings drew more than 20 public commenters in Sacramento. Environmental and community groups pushed the board for enforceable interim limits in basins with strong data, arguing residents already face health risks from contaminated groundwater. Industry representatives, coalition managers and nursery groups urged regional flexibility and alternative reporting rules, warning of implementation costs and data challenges for small or diversified operations.

Board members acknowledged the report’s technical depth and pressed staff and the panel on next steps. Division of Water Quality staff recommended a near‑term workplan: (1) workshops with regional boards for technical exchange, (2) data standardization and quality‑management work to make existing coalition and grower data comparable, and (3) a public rulemaking path to propose options where a regulatory change is warranted. Several board members stressed urgency for regions with strong data (for example parts of the Central Valley and certain basins in the Central Coast), while also saying any legal or policy direction should allow regional tailoring.

Notable public points: Peter Dremmyer, policy director for Yusefed Rivers Alliance, told the board that declines in spring‑run Chinook counts underscore the importance of water flows and habitat protections, saying, “what we need to do is we need to frontload the water more.” Coalition representatives from the Central Coast said some growers and third‑party coalitions will face high compliance costs if strict numeric limits take effect quickly; community and environmental groups said public‑health harms and existing groundwater impacts require enforceable action where the data show it.

Next steps: Staff told the board they intend to hold workshops with the regional boards and interested parties to evaluate which panel recommendations can be implemented administratively (data harmonization, sampling protocols), and which will require regulatory action. The board signaled it wants to return early next year with a clearer proposed path forward, including timelines for data standardization and options for potential regulatory changes.

Ending: The panel report gives the State Water Board a technical pathway to link farm nutrient management with enforceable groundwater protections while preserving regional flexibility. The process ahead will be technical and political: staff, regional boards, growers, environmental groups and communities all emphasized they want to move quickly but responsibly to protect drinking water and agricultural viability.