SUBMARINE GROUNDWATER DISCHARGE BENEATH EASTERN CASCO BAY, MID-COAST, MAINE

Hydrographic studies in several locations within eastern Casco Bay suggest that ground water is discharging through the seabed, creating layers of anomalously fresh water in the bottom most meter of the water column. Deep-water areas of Quahog Bay continuously revealed bottom water up to 5 psu fresher when compared to overlying waters. Locations in Quahog Bay and Harpswell Sound were monitored with multiple CTD lowerings on several time scales during a three-month period in the summer of 2002. Moreover, salinity anomalies were both geographically and temporally persistent. Similar intensive hydrographic studies in nearby Harpswell Sound showed little evidence for widespread submarine groundwater discharge. Our working hypothesis is that submarine groundwater discharge originates from fractured bedrock aquifers beneath Quahog Bay. Quahog Bay is underlain by the gneisses of the Late Ordovician to Early Silurian East Harpswell Group. Harpswell Sound is underlain by the schists of the Middle Ordovician Spring Point and Cape Elizabeth Formations.