In 1971,twenty circular aquaculture ponds were constructed for the W.K.Kellogg Biological Research Station in Hickory Corners,Michigan.The 30.5-m-diameter research ponds were lined using a 0.51-mm-thick fish-grade PVC geomembrane.Over the years the ponds became congested with dense,persistent stands of cattails,trees,and other vegetation,which required the ponds to be cleared and relined in September 2000 in order to allow the initiation of new experiments.The lack of holes in the exhumed geomembrane suggests that it resisted biological attack from microorganisms and also root penetration.Laboratory testing shows that the tensile behavior of the nearly 30-year-old PVC geomembrane is within current specifications for new 0.51-mm-thick PVC geomembranes.Test results also indicate that performing laboratory tests at in-situ moisture conditions provides a better estimate of the field properties of PVC geomembranes than desiccating the material prior to testing,as is required by ASTM Standard Test Methods.
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