I found this info on the PA fish commissions website:
December 19, 2007
Cumberland County, PA – The Pennsylvania Fish and Boat Commission (PFBC) is currently drawing down Opossum Lake, a 59-acre lake near Carlisle, in the interest of public safety, state officials announced today.
The lake will be drawn down to 14 feet below normal pool. The drawdown will occur at a rate of two to three feet per week as conditions allow.
The lake was temporarily at normal pool for geotechnical monitoring conducted by the Friends of Opossum Lake, the PFBC, and the Department of Environmental Protection, for the purposes of measuring water infiltration of the dam in determining future repairs.
The jointly funded study will help to establish the best course of action for rehabilitating or replacing the earthen embankment. A series of piezometers, devices that measure water pressure, were installed in holes drilled into the dam breast. Over the spring and summer months of 2007, the water level in the lake was raised incrementally with readings taken at regular intervals. Now that sufficient data has been gathered to help isolate the source(s) of water infiltrating the dam breast and the water’s pathway through the dam, the lake is currently being drawn down in the interest of public safety.
The data collected from the geotechnical monitoring will be used by engineers to come up with a final design and cost estimate for repairs. The current preliminary estimate for rebuilding the 46-year-old lake is approximately $3.6 million – part of a $105 million statewide backlog of major impoundment upgrades needed on state-owned dams the Commission manages. Opossum Lake is emblematic of many of those aging dams: built to the standard of the day, they are reaching the end of their useful lifespan and need to be reconstructed to modern safety standards.
