Abstract: The invention is a monitoring well cover with a generally planar lid, a generally cylindrical rim, and one or more generally cylindrical skirts. The lid has threads on its side to secure the lid to the rim. The rim has an L-shaped upper edge for receiving and sealing tightly with the lid and has snaps positioned around its lower edge for receiving and sealing tightly with one of the skirts. The skirts each having flanges positioned around their upper ends and snaps positioned around their lower ends such that the first of the skirts may seal tightly with the rim and each subsequent skirt may seal tightly with the skirt preceding it. The lid, the rim, and the skirt are all constructed from a fiber reinforced, heat stabilized, high strength thermoplastic.