The Windrock Creek GSA on Nov. 20 voted to adopt the board option to set groundwater-level minimum thresholds using a 5% domestic-well impact metric and approved an updated representative monitoring-site (RMS) network intended to improve coverage where domestic wells exist.

Becky Fairbanks, the GSA project manager, introduced the topic and said Department of Water Resources (DWR) comments required the agency to specify how many domestic wells would be impacted at each MT. Laura Foglia of Larry Walker Associates described the consultant work: updated monitoring-network selection, a domestic-well inventory and a domestic-well risk assessment that informed MT options.

Foglia said the team narrowed the inventory and assumptions to focus the risk assessment. "This leaves us with 360 total domestic wells in the basin that need to be included in the risk assessment," she reported, noting limitations in older state well-log records and that some pre-1980 wells were excluded as likely inactive.

The consultant presented three protection options — measures based on the fifth, tenth or fifteenth percentile of nearby shallow wells — and a second criterion based on a fixed buffer below historical lows (historical low minus 20 feet). Foglia told the board the recommended approach is to use whichever criterion yields the deeper (more protective) threshold for each representative monitoring site.

On mitigation cost, Foglia used a low-end estimate of about $30,000 per well to deepen or replace domestic wells and ran scenarios: at current MTs roughly 53 wells appeared at risk (rough order-of-magnitude mitigation cost ~$1.6 million); raising protection decreased that count (e.g., 38 wells and about $1.14 million under a different option).

Following the consultant recommendation and advisory-committee input (the WAC favored 5%), a motion to adopt the 5% MT option passed by voice vote and the board approved the updated 10-well RMS map. Staff will develop mitigation protocols and a verification process to determine when a dry-well claim is attributable to GSA management rather than other causes (such as local geology or pump failures).

Next steps: staff will use the updated inventory and monitoring network to operationalize MTs and to draft mitigation procedures for future board review.