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Student Guide | Cape Cod | Everglades | Los Angeles | Download PDF

Cape Cod:

Introduction

Reading

Focus Question

The Interested Parties

Cape Cod's Unique, "Absorbent" Geology

Where Do Cape Codders Get Their Water?

Porosity, Permeability, and Ground Water

The Massachusetts Military Reservation - An Environmental Dilemma

The Facts About Septic Tanks, and Other Threats to the Cape's Ground -Water Quality

Ground-Water Cleanup - No Easy Task

The USGS's Toxic Substances Hydrology Program, or "How We Learned About the Ashumet Valley Sewage Plume"

The Harwich Solar Aquatic Septage Treatment Plant - the Neighbors May Have One Answer

Glossary

The USGS's Toxic Substances Hydrology Program, or "How We Learned About the Ashumet Valley Sewage Plume":

Government and university scientists are using the sewage plume created by the Massachusetts Military Reservation (MMR) sewage treatment plant on Cape Cod as a field laboratory. They are studying how toxic chemicals move in ground water. For 50 years, treated sewage disposed on the reservation has leached into the sand and gravel aquifer below. To figure out how and where this sewage affects the quality of the ground water, scientists have drilled a "well field" or set of narrow wells. These wells enable them to pump ground- water samples for examination.

To study the Ashumet Valley plume, the USGS scientists have dug more than 300 sampling wells. They began the study after State and Federal officials became concerned that sewage disposal was contaminating shallow aquifers. At one of their first test wells, dug in 1979, 10,000 feet away from the sewage treatment plant, water foamed when it came out of the ground. The USGS scientists knew they had discovered a problem.

To decide where to place the sampling wells, they had to hypothesize about what chemicals in the treated sewage would move in the aquifer and where the contaminated ground water would move. Then, using topographic and water table contour maps to guide them, they dug wells downgradient - along the downward slope of the water table - below the suspected source of contamination. To gather information about the shape, content, and movement of the plume, they kept digging groups of sampling wells until they found clean, uncontaminated water.

By sampling ground water in the area for several years, scientists have been able to describe accurately the sewage plume. The Ashumet Valley plume is more than 2 miles long. However, the plume is only 75 feet thick. It is overlain by as much as 40 feet of uncontaminated ground water. The plume moves 0.9 to 1.5 feet per day southward toward Nantucket Sound. The plume contains high concentrations of boron (found in household cleaners), chloride, nitrogen (a byproduct of decomposing organic material), and detergents, which cause the water to foam. Approximately 2.6 billion cubic feet of the Cape Cod sole-source aquifer have been contaminated by the treated sewage from the MMR.

Can the Ashumet Valley plume story have a happy ending? Perhaps. In late 1996, proposals were being prepared to contain the Ashumet Valley plume and other plumes on the MMR with extraction wells.

Tying theory to reality: the USGS uses experimental wells in the area of the Ashumet Valley sewage plume. Tying theory to reality: the USGS uses experimental wells in the area of the Ashumet Valley sewage plume. (Photo by D. LeBlanc, USGS, 1985)

Chemical Concentration
Source of water samples taken in 1979 Chloride
(milligrams / liter)
Boron
(micrograms / liter)
Nitrogen
(milligrams / liter)
Treated sewage released at the MMR 33 510 19
Contaminated ground water 3,000 feet from the sewage disposal site 28 280 16
Uncontaminated ground water in the area 8 7 0.4
This table shows the levels of ground-water contamination caused by sewage. Soils may be able to trap some contaminants, but they cannot turn sewage into pristine ground water.
Year-Round Population, 1980-2010, by Community*

Federal Census year-Round Population Projected Population
Community 1980 1990 1994 (est) 2000 2010
Barnstable 30,698 40,949 42,579 46,417 51,684
Bourne 13,874 16,064 16,646 17,891 19,061
Falmouth 23,640 27,960 28,949 30,157 31,701
Mashpee 3,700 7,884 9,540 10,945 14,088
Sandwich 8,727 15,489 17,755 19,587 23,720
TOTAL 80,639 108,346 115,469 124,997 140,254
*From Cape Cod Commission, Barnstable County Population 1980-2010.

Use these data to help you answer the Focus Question. By what percentage is the total population of the upper Cape likely to increase during the next decade? Where will the population jumps be the largest? how are the areas with the fastest growing demand for clean water affected by the ground-water contaminant plumes?
Community 1990 Federal Census Year-Round Population* Projected Peak Summer Population*
Barnstable 40,949 81,800
Bourne 16,064 37,900
Falmouth 27,960 69,300
Mashpee 7,884 25,800
Sandwich 15,489 29,200
TOTAL 108,346 244,000
*From Cape Cod Commission (Cape Trends, 3rd edition, 1996)

By what percentage does the Upper Cape's population increase during the summer? How many ways does the increase in population affect the water supply? How does the increase in population change the quantity or the effects of contamination in the ground water?
Use this map as a decision making tool as your group identifies potential ground-water contamination sources
Use this map as a decision making tool as your group identifies potential ground-water contamination sources (Ryan, 1980)
Sewage plume in ground water downgradient from Otis Air Force Base in 1983.
Sewage plume in ground water downgradient from Otis Air Force Base in 1983. A shows the water-table contours and the location of sampling wells. B shows the distribution of boron, in micrograms per liter. C shows the distribution of detergents, in milligrams per liter. D shows the distribution of volatile organic compounds, in micrograms per liter (Hess, 1986).

Why did different contaminants have different concentrations in the plume? Consider such factors as the solubility of the contaminants and when they were released. For example, in 1964 new biodegradable detergents replaced the nonbiodegradable detergents being used at the time.

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Student Guide | Cape Cod | Everglades | Los Angeles | Download PDF

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