Commission approves zoning change to require groundwater monitoring where solar array piers are close to water table

The Douglas County Commission voted Jan. 22 to adopt a text amendment to the county zoning regulations that requires initial and ongoing groundwater monitoring when metal support piers for solar energy conversion systems (solar farms) would be installed within four feet of the shallowest annual groundwater level.

Mary Miller, county city-county planner, briefed the commission on staff research and the planning commission’s recommendation. Staff initially recommended denial, concluding that zinc released by corroding galvanized piers tends to bind to soil and is normally immobile in Douglas County soils; the planning commission recommended approval on a precautionary basis. Miller told commissioners that no documented cases were found of galvanized pier corrosion causing groundwater contamination in the studies staff reviewed, but the planning commission asked staff to propose regulatory language that would require monitoring where piers are close to groundwater.

Under the adopted text amendment, applicants for a conditional use permit for a solar energy conversion system must include an existing-conditions site plan that shows estimated groundwater levels and the location of any piers expected to lie within four feet of the shallowest groundwater depth. If piers are within that threshold, the operator must submit a groundwater-monitoring plan prepared by an appropriate hydrogeology expert. Monitoring wells will measure zinc concentrations upstream and downstream of the project and at private wells within a quarter mile if levels indicate a potential problem. Monitoring is annual by default and increases to semiannual sampling if zinc in monitoring wells reaches or exceeds 5 milligrams per liter (the EPA’s non-enforceable secondary recommendation for aesthetics).

Supporters of the amendment urged a precautionary approach. Dan Fuller, the applicant who requested the amendment, said he was concerned about the number of galvanized piers and local shallow groundwater in areas proposed for solar projects. Speakers from Sustainability Action Network and local residents also urged monitoring wells to protect neighbors’ drinking water.

County staff said the requirement would not apply retroactively to approved and vested solar projects; new monitoring requirements would apply to future CUPs or to projects that seek amendments after their CUPs expire. The planning commission unanimously recommended approval of the amendment; the Board approved the text amendment and adopted the related resolution.