Lake Whetstone Dam internal seepage collection system evaluation

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Montgomery Village Avenue is the dam for Lake Whetstone and contains an internal drainage system to collect and filter seepage. Seepage occurs in all dams. Modern earth embankment dams, like the Lake Whetstone Dam, are designed with internal drainage features to collect seepage passing through the dam. Uncontrolled or unfiltered seepage creates dam instability and concern for dam health and function. Therefore, assurance of the proper performance of the dam internal seepage collection system, including its toe drain, is critical for the stability of the dam.

Montgomery County Department of Environmental Protection (DEP) conducts routine inspections to Lake Whetstone and the dam. Recent inspection has found Lake Whetstone’s toe drain pipe has corrosion. DEP has retained Gannett Fleming, Inc. to evaluate the Lake Whetstone Dam internal seepage collection system. This evaluation is the first phase of the toe drain repair project.

The evaluation work includes:
•    Drilling of soil borings
•    Installation of monitoring instrumentation in the dam, and
•    Pressure washing and video inspection of the internal metal drain pipes.

Drilling on the crest and slopes of the Lake Whetstone Dam will start soon, pending approval of the Maryland Department of Environmental. Field work is scheduled to begin at the end of the month and will take place between 7 a.m. and 5 p.m. on weekdays. Work will be completed in about four weeks. One lane of Montgomery Village Avenue will be closed during drilling equipment unloading and setup time on the crest of the dam, to provide sufficient space and a safe working environment. Lane closure will only be 3 to 5 days during the working period and won’t be full work hours of each day.

The Montgomery County Department of Transportation (DOT) approved the Maintenance of Traffic (MOT) plan designed by Gannett Fleming, Inc. to control traffic in the road during the lane closure.