Midpeninsula Regional Open Space District (District) Preserves contain extensive groundwater systems. The District’s acquisition and restoration of domestic land parcels in the Preserves has resulted in abandoned wells. To protect water quality in California, inactive wells are decommissioned to reduce the potential for the transfer of surface contaminants to groundwater. The District has followed state and county regulations to properly decommission 10 wells since spring 2021.
The District has identified 37 remaining wells in the Open Space Preserves (Figures 1 and 2) that meet Santa Clara Valley Water District’s (Valley Water) and San Mateo County Health Groundwater Protection Program’s definitions of abandonment and require decommissioning. Beginning summer 2023, the District will contract with a C-57 licensed drilling company to continue decommissioning wells in Open Space Preserves across the mid- to northern Santa Cruz Mountains Region. The drilling company will work with the counties to obtain permits and to assess how to appropriately decommission each of the wells, which could vary based on the geologic setting, well type, and other factors that influence decommissioning protocols. Trucks will be used to prepare the wells for decommissioning, and a cement truck or crew using hand tools will fill each well casing with a cement-based mixture to a depth compliant with county regulations—typically from the bottom of the well to 5 feet below ground surface. The remaining casing, pump, cement pad, and wellhead will be removed. The small (5 foot by 5 foot) disturbance area will be leveled, and soils will be left at-grade.
Most of the abandoned wells are adjacent to established roads. None of the work will impact streams or ephemeral channels, and minor vegetation removal will be limited to clearing existing roads that lead to the well sites. Biological surveys conducted prior to each well’s decommissioning will ensure the avoidance of rare plant species, bird nesting, and bat habitat. There are no known contaminants or septic tanks near the wells.