Butte County advances pilot groundwater recharge projects using reverse tile drains and floodwater triggers

GeoSyntec project manager Joe Turner and county staff briefed the Butte County Water Commission on pilot groundwater-recharge work funded by the VINA SGMA grant, describing field tests, geophysical surveys and early monitoring results.

The presentation described two complementary goals: a water-supply feasibility study and on-the-ground recharge pilots intended to identify one or two sites with feasible designs and reliable infiltration. "The first pilot study that we just started this week is using what we call reverse tile drain," Turner said, explaining the method places perforated horizontal pipe roughly 12 feet deep to inject water below crop root zones so fields are not flooded. Turner added, "We are seeing the water recharging is hitting the groundwater."

Why it matters: the pilot work is meant to generate the site-specific infiltration rates, volumes and monitoring data that grant writers and project sponsors need to pursue larger, full-scale projects. Staff said a county resolution and implementation plan will define precipitation-based "triggers" under new water code 1242.1 to coordinate diversion of imminent flood flows for recharge, and that the team hopes to present that resolution to the Board of Supervisors in December.

What the team did and found: GeoSyntec combined literature and data review (soils maps, statewide airborne electromagnetic surveys, SGMA data) with TTEM geophysics at three initial sites, cone-penetrometer tests, hydrologic profiles and small-scale infiltration tests. Turner described pilot installations near the county surface impoundment and adjacent tile-drain tests and stilling wells to measure how quickly water moves from the surface to groundwater. He reported some infiltration tests above 10 feet per day and explained that, by comparison, "1 foot per day is good" for a basin infiltration approach.

Location and partners: Turner and staff said the currently running tile-drain pilot is on private property just south of Comanche Creek, south of Chico, where a cooperating landowner allowed pilot pumping. Staff identified Dylan McGregor as the county GSA program manager administering certain GSA services under a three-way cost-share agreement among Wyandotte, Vina and the County of Butte.

Legal, quality and operational constraints: Commissioners raised concerns about sediment, water quality and permitting. Turner said surface- and groundwater sampling will be part of the pilot and that using treated wastewater would require water-board permits and additional studies; for floodwater diversion the State Water Board's current approach is less restrictive when systems remain significantly above the groundwater. Jim Graden, a domestic well owner and Vina Basin stakeholder, urged the Commission not to overlook the Lindo Channel feasibility project and emphasized the DWR grant's legal-implications task on water rights; Graden reported preliminary infiltration findings "on the order of 100 feet per day" for the Lindo Channel and asked that water-rights issues be fully vetted before project implementation.

Next steps: staff said the pilot studies are intended to produce the quantitative infiltration and monitoring data needed to write project descriptions for future grants and to inform a county-level implementation plan tied to precipitation-based triggers (example discussed: a 2-inch precipitation forecast over five days as a possible trigger to coordinate with public works). Staff will continue coordination with public works on notice procedures and monitoring design and expects to bring the proposed resolution to the Board of Supervisors if conditions warrant.

Ending: The Commission received the update, discussed operational questions and water-rights concerns, and invited continued public engagement as the pilot studies and the DWR component 5 legal analysis proceed.