WETHERSFIELD COVE, HARTFORD, CT – A 300 YEAR URBAN POLLUTION RECORD

Wethersfield Cove is a small (750 m diameter), shallow (5 m) pond connected through a narrow opening with the Connecticut River. It is located just south of Hartford in the old settlement of Wethersfield, directly downstream of a major waste water treatment plant of Hartford. The cove used to be an arm of the Connecticut River, but was cut off in 1692 during major floods. The connector to the current river has been maintained over the years. Two sediment cores were taken in the cove (61 cm, WC-2; 83 cm, WC-3) that consisted of fine dark mud with a profound diesel smell. These samples have been analyzed for Mercury with a Milestone DMA-80 analyzer. The Hg concentrations range from 400-500 ppb in the top 20cm, whereas the lower core sections have values of 2000-3000 ppb Hg. These are unusually high levels of contamination, although Woodruff and Martini and their students (UMass and Amherst College, MA) have documented similar Hg enrichments in Connecticut River coves further south. Coastal coves and marshes along central and eastern Long Island Sound have commonly peak concentrations of 400-500 ppb Hg. What could be the reason for these unusually high Hg concentrations in these Connecticut River coves? Possibly, only very fine-grained sediment is trapped in the coves versus coarser, less Hg-rich sediment in more dynamic environments. In western CT, marshes and river sediments have tens of ppm of Hg as a result of pollution from the historic hatting industry in Danbury and surroundings. Hartford has no known connection with that source, so presumably an alternative pollution source was present. I speculate that the Hg-enriched sediment resulted from a mercury spill from the Dutch Point-South Meadows (HELCO) power plant just north of the cove. This plant (1928) was one of the first to use mercury vapor in a binary cycle with steam as a working fluid, which is thermodynamically advantageous. This type of plant leaked a fair bit of mercury and had to be resupplied periodically. There is a poorly documented incident that in the early 1960s a large barrel with liquid mercury was spilled into the river during resupply. The fate of that mercury is unknown but would have been gradually transported downstream with fine-grained sediment. I will present full chemical data (DMA-80; XRF) on these cores with preliminary ages.