Lake Bonita is located on the Mount McGregor Correctional Facility in Wilton, New York. The 60-acre lake is retained by an earthen dam, located at its northern end. The lake serves as a water supply for the Correctional Facility and forms the headwaters of Beaver Brook, which begins at the dam and flows from south to north towards its confluence with Stony Brook. Water flows from Lake Bonita, over a concrete ogee spillway, at the east end of the dam, into the creek.

An evaluation of the concrete spillway indicated that it did not meet current standards for stability as required by the NYSDEC.

McMahon & Mann retained a driller to drill borings and install piezometers through the embankment to allow an evaluation of the earthen embankment. McMahon & Mann also prepared plans (in accordance with the New York State Office of General Services (OGS)) to replace the reinforced concrete spillway and monitored its construction for OGS and the New York State Department of Corrections. Construction included chemical grouting to seal the rock foundation and the connection between the spillway and the existing earthen embankment.