The cell-house site in Berlin, N.H., was part of a chlor-alkali plant associated with a pulp and paper mill on the bank of the Androscoggin River (fig. 1). The chlor-alkali plant used elemental (liquid) mercury in the papermaking process. Mercury was released and seeped into the overburden and underlying fractured bedrock as a result of this process and represents a risk to human health and the environment. The extent of mercury contamination in the bedrock and mechanisms of transport to the riverbank are unknown.