Flax Pond
Harwich, MA.
Flax Pond is a fifteen-acre (6 hectare) pond in Harwich, Massachusetts that has been heavily impacted for decades by leachates from an adjacent landfill and unlined septage holding lagoons. By 1989 the pond was closed to recreation and fishing because of contamination caused by the daily intrusion of 295 m3(78,000 gallons) of leachate from the landfill (Horsley et al., 1991). The pond had low oxygen levels, high coliform counts, excessive sediment build up, and organic pollutants in the water column including volatile organic compounds (VOCs). Macro-benthic organisms were absent from many of the bottom sampling stations. Flax Pond had unusually high sediment concentrations of total phosphorus (300 times greater) and iron (80 times greater) compared with other Cape Cod ponds (K.V. Associates, 1991). Ammonia levels in the sediments were found to be as high as 8,000 mg/kg. The pond is delineated into an eastern zone and a western zone; the cloudier eastern zone is the predominant zone of impact from the landfill. The pond had a maximum depth of 6 meters and stratifies in its western end.
In the autumn of 1992 construction of the first Restorer was completed and anchored in the eastern end of Flax Pond. It employed a windmill and solar panels for electrical generation and was capable of circulating through its nine cells up to 380 m3 d-1 (100,000 gallons per day) of water drawn from the bottom of the pond. The first three cells were filled with semi-buoyant pumice rock that supported diverse benthic life including freshwater clams of the genera Unio andOnodonta. A slow release form of a clay-based soft phosphate was added to the media cells in the Restorer. Bacterial augmentation and mineral enrichment in the first three cells was frequent. The final six cells supported over two dozen species of terrestrial plants on racks. The Restorer was not operated during the winter months to allow the pond to freeze completely.
The impact of the Restorer on Flax Pond must be set against the background of the significant loading of pollutants into the pond resulting from leachate from the nearby landfill. Between 1990 and 2000 approximately 964,000 kg of alkalinity, 142,000 kg of iron, 44,940 kg of ammonia, and 1,095,680 kg of dissolved solids have entered Flax Pond via groundwater contamination. Given these levels of contamination we would expect significant deterioration of water quality, biological activity, and increases in sediment levels.
Despite the onslaught of groundwater contamination, Flax Pond has maintained its biological health over the course of the last decade. This is in part the result of the Restorer and in part the result of the cleaning up of the nearby unlined septage lagoons in the early 1990s. Ammonia levels in sediments have not significantly increased; the pH of the water and sediment has hovered around neutral; dissolved oxygen at sediment levels has increased; and organic sediment levels have been reduced. The pond supports healthy fish populations, water quality has been maintained to allow irrigation of a nearby cranberry bog, and microbial and macroinvertebrate activity in sediments has increased.
