Ponds lined with an exposed geomembrane commonly experience uplift pressure from gases. These pressures can uplift the geomembrane in the form of “bubbles” or “whales”. This paper draws on results from previous studies to evaluate the transmissivity requirements for underdrains to relieve gas pressure, and presents a method to calculate the force required to move geomembrane gas bubbles laterally when underdrains are not present or functioning. A method is presented to estimate the unbalanced hydrostatic force, caused by a sloped pond bottom, which would be exerted on a geomembrane bubble. Recommendations are presented for minimum reliable pond bottom slopes to induce bubbles to move to the perimeter slope where they can be vented. The paper is concluded with a summary of practical design and operational considerations for dealing with gas pressures below exposed geomembrane pond liners.
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