WATER - COVERED SURVEYS
The leak detection method for water-covered surveys is the most sensitive in locating leaks. When a leak is present in the water-covered geomembrane, electrical current paths through the liner are detected using a leak detector box and survey probes. Safety harnesses and life vests may be required depending on the application. Four types of water-covered surveys are provided: wading, tow, side-slopes, and plummet.
SHALLOW - WATER WADING SURVEYS
The wading survey method is suitable when the liquid level in the impoundment is approximately 6 to 32 inches at the shallowest end of the cell. BLD personnel would wade in the liquid using a 9-feet probe stick and scan the floor area. Once a section has been surveyed, de-watering may be required to continue the survey process. The leaks are pinpointed and are marked by using weighted bags with floats attached by a string. The leaks are also marked on the slopes as a second reference point.
DEEP - WATER TOW SURVEYS
The tow survey method is practical when the liquid level in the impoundment is greater than 32 inches or if a high amount of sediment is present. BLD personnel and an assistant would stand on opposite banks of the impoundment and drag a sensor across the cell floor. The distance to the leaks are measured and documented. They are also referenced to a mark on the nearest respective side-slopes.
SIDE - SLOPE SURVEYS
The side-slope of an impoundment may be surveyed by using either a 9-feet or 20-feet probe stick. BLD personnel would stand on the slope near the water line and scan the side-slopes down to the toe line. The leaks are documented and marked on the side-slopes with a reference direction and distance.
VERTICAL WALL PLUMMET SURVEYS
Geomembrane-lined tanks, vaults, or vertical walls can be surveyed using the plummet survey method. Depending on the vertical height, a 9-feet probe stick, 20-feet probe stick, or plumb bob probe may be used for the leak detection survey. The leaks will be marked on top of the walls with a reference point and a distance to the leak.