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Can a Sewage-Contaminated Aquifer Naturally Clean Itself?

Areal View of the Sewage Disposal Beds and the Gravel Pit with the Tracer Test Sampling Array
Areal view of the sewage disposal beds and the gravel pit with the tracer test sampling array on Cape Cod, Massachusetts. Ashumet Pond is to the right, and the disposal beds are on the upper left. The disposal beds are the source of a subsurface plume of contaminants that's more than 6 kilometers long.

The answer may be yes, but it might take much longer then scientists originally guessed. U.S. Geological Survey (USGS) scientists are studying the natural restoration of an aquifer that was contaminated by 60 years of land disposal of treated sewage. Studies at the abandoned sewage-disposal facility at the Massachusetts Military Reservation on Cape Cod have shown that:

  • The natural cleanup in the aquifer on Cape Cod is taking longer than USGS scientists had expected.
  • Although the natural ground-water flow has flushed away some contaminants in the aquifer under the disposal area, continuing biodegradation of organic materials associated with the aquifer sediments is maintaining low oxygen levels and elevated pH.
  • Some contaminants, such as phosphorus and zinc, are expected to remain at elevated levels in the sewage-contaminated zone for many years because of the persistent low oxygen levels and elevated pH.
  • Geochemical models developed for the studies at the site predict that restoration to pre-contamination conditions may take many decades.

The Department of Defense is using the predictions of the long natural-cleanup time to develop plume-management strategies that protect the environment and drinking-water supplies in the Cape Cod sole source aquifer.

References

Natural restoration of a sewage plume in a sand and gravel aquifer, Cape Cod, Massachusetts, by D.R. LeBlanc, K.M. Hess, D.B. Kent, R.L. Smith, L.B. Barber, K.G. Stollenwerk, and K.W. Campo

Evolution of a ground-water sewage plume after removal of the 60-year-long source, Cape Cod, Massachusetts--Changes in the distribution of dissolved oxygen, boron, and organic carbon, by L.B. Barber and S.H. Keefe

Evolution of a ground-water sewage plume after removal of the 60-year-long source, Cape Cod, Massachusetts--Fate of volatile organic compounds, by K.W. Campo and K.M. Hess

Evolution of a ground-water sewage plume after removal of the 60-year-long source, Cape Cod, Massachusetts--Inorganic nitrogen species, by R.L. Smith, B.A. Rea Kumler, T.R. Peacock, and D.N. Miller

Evolution of a ground-water sewage plume after removal of the 60-year-long source, Cape Cod, Massachusetts--pH and the fate of phosphate and metals, by D.B. Kent and Valerie Maeder

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