Conservation director outlines plan to plug suspected lake leak, avoid dyke excavation

County staff described technical plans June 8 to identify and stop a suspected leak in a lake intake structure that has not been used since about 1979.

According to the conservation department staff, the system includes a 30‑inch intake that transitions down to a 15‑inch outflow and an 8‑inch drawdown structure believed to discharge to the lake. Engineers and DNR biologists have inspected the site. The proposed initial approach is to put an inflatable plug into the 8‑inch outlet on the lake side, remove the existing 15‑inch plug and observe whether the leak stops. If the plug halts the leak, staff plan to reduce the 30‑inch intake to approximately 14–15 inches, elbow the line, and bag and concrete the lower column so it seals at lake level.

Staff noted they have procured an inflatable sewer bladder and plan a dive operation; the tentative date mentioned in the meeting was the 22nd. The goal is to avoid digging through the dyke, which engineers said would raise risk and complexity. County staff said the system has not been used since 1979 and that modern pumping technology could draw the structure down if needed in the future.

Supervisors asked practical questions about how to place concrete and shore the new connection while preventing bleed through into the existing outflow. Staff said the engineers will stage small pours to achieve an initial seal and then pour the remainder once the initial seal is confirmed.

Next steps: staff will coordinate divers, finalize staging and materials, and report back after the plug test and any subsequent work.