Sewage-Contaminated Ground Water:
(Cape Cod, Massachusetts)

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Treated wastewater disposal beds, which created a large subsurface plume of contaminated ground water

A view of the side of a trench cut into the Cape Cod aquifer showing what is commonly referred to as a "homogeneous" aquifer. Studies of the distribution of the horizontal conductivity resulted in a range of conductivity from 0.02 to 0.34 centimeters per second, which demonstrated that the aquifer is not homogeneous

Multilevel monitoring wells being prepared for installation prior to a large-scale natural-gradient tracer test above a plume of sewage-contaminated ground water

An array of several hundred multilevel wells were installed in an abandoned gravel pit. The array of wells was used to conduct a natural-gradient tracer test. The results of the test provided information on how contaminants are transported in ground water

A close-up of the ports of a multilevel well that's part of the large-scale tracer-test array at the site. Each port is covered with a nylon mesh.

Color-coded tubes sticking out of the top of a multilevel monitoring well. Each tube is connected to a port on the side of the well.

Winter-time view of multilevel well sampling array. There are over 10,000 subsurface sampling ports

A tracer solution (bromide, lithium, fluoride, and molybdate) was injected into three wells at the start of a large-scale (280 meters) natural-gradient tracer test (circa 1985 to 1986)

A special sampling apparatus was designed to collect samples from multi-level monitoring wells during large-scale natural-gradient tracer tests. Each well has up to 15 sampling ports

During the first large-scale natural-gradient tracer test conducted at the site, wells from the array of over 600 multilevel wells were sampled about once a month (circa 1985 to 1986)

USGS scientists monitored the first large-scale natural-gradient tracer test conducted at the site for over 17 months (circa 1985 to 1986)

The thousands of sampling ports in the subsurface sampling array used for the large-scale, natural-gradient tracer test created a mind-boggling number of water samples. In later stages of the test over 4,000 samples were collected during sampling field trips (circa 1985 to 1986)

Areal view of the sewage disposal beds and the gravel pit with the tracer test sampling array. Ashumet Pond is to the right

The gravel pit on the Massachusetts Military Reservation, Cape Cod, where USGS and other scientists have conducted over 50 tracer tests involving reactive and non-reactive solutes, microspheres, and deactivated microorganisms

The over 10,000 subsurface sampling ports in the three-dimensional array have been used to conduct over 50 tracer tests

Sample-freezing drive shoe before application

Field crew working to cap the bottom of the core liner after a successful coring attempt with the sample-freezing drive shoe

Sample-freezing drive shoe and frozen core after extraction from a borehole

Closeup of the sample-freezing drive shoe with core frozen inside

A handful of sand from aquifer sediments on western Cape Cod, MA. The surfaces of these quartz grains are covered by coatings containing iron and aluminum oxides and silicates. Arsenic in the coatings can be released by changes in chemical conditions

Setup for the electrical resistivity tomography (ERT) that USGS scientists used to monitor the injection of a saline tracer. The yellow cables are ERT cables. Metal pipes indicate the location of sampling sites. Boreholes are encased in white PVC pipes

Setup of an in-well diffusion sampler that is used for monitoring volatile organic compound (VOC) concentrations in ground water. In-well diffusion samplers consist of a polyethylene tube filled with deionized water and sealed at both ends. Sampling using the in-well diffusion samplers was compared to samples collected by traditional pumped-sampling methods in 89 monitoring wells on Cape Cod, MA

USGS scientists conducting a tracer test where clean, oxygenated groundwater was injected into an anoxic zone beneath the sewage infiltration beds. The tracer test was part of a study of the natural restoration of a subsurface sewage plume after the use of the infiltration beds (the source of the plume) was discontinued

Divers from the USGS Science Center for Coastal and Marine Geology, Woods Hole, MA, assisted with the installation of wells designed to better understand the upward hydraulic gradients beneath Ashumet Pond, Cape Cod, MA

Seepage meters were deployed to measure fluxes of water and associated phosphorus concentrations discharging into Ashumet Pond, Cape Cod, MA. A National Association of Geoscience Teachers student intern is connecting a seepage bag to the meter

USGS scientists installing diffusion samplers used to monitor the performance of a reactive barrier designed to remediate a phosphate plume discharging to Ashumet Pond, Cape Cod, MA

USGS scientists installing an experimental horizontal well to test its usefulness for monitoring the performance of a reactive barrier that was installed to remediate a phosphate plume discharging to Ashumet Pond, Cape Cod, MA

The sediment along the shoreline of Ashumet Pond, Cape Cod, MA, before the installation of a permeable reactive barrier to remediate a plume of sewage discharging to the pond. The black color of the sediment is the result of manganese in the plume precipitating to manganese oxide when ground water with very little dissolved oxygen encounters the oxygen rich pond water

Shortly following the installation of a permeable reactive barrier, the sediment along the shoreline of Ashumet Pond, Cape Cod, MA, turned red, indicating the oxidation of the iron filings in the barrier. The barrier was constructed to remediate a phosphate plume discharging to the pond

A USGS scientist is monitoring a bladder used to hold the injection fluid during a single-well tracer test designed to study the transport on ammonium in ground water on Cape Cod, MA. The bladder is placed in a small pool of water to control the temperature of the injection fluid during the test

Filling a 200-liter, gas-impermeable bladder with a tracer solution of ¹⁵N-enriched ammonium as part of a multiple-well, natural-gradient tracer test designed to assess the nitrification of ammonium in a sewage plume on Cape Cod, MA

A tracer solution of ⁵N-enriched ammonium was injected upgradient of several multilevel sampling wells during a natural-gradient tracer test designed to assess the fate and transport of ammonium in a sewage plume on Cape Cod, MA

Single-well tracer tests, which involve injecting a tracer into one port on a multilevel sampling well and then monitoring the same well for the tracer, were one of several tools used to study the fate and transport of ammonium in a sewage plume on Cape Cod, MA

Multiple-well natural gradient tracer tests, which involve injecting a tracer in an upgradient well and then monitoring downgradient wells for the tracer, were one of several tools used to study the fate and transport of ammonium in a sewage plume on Cape Cod, MA

Vertical cross sections through the wastewater (treated sewage) plume on Cape Cod, MA, showing the distribution of dissolved ammonium (NH₄⁺ ) in micromoles per liter (µmol/L) during 1994. Small dots indicate data points. The cross-section shows a cloud of NH₄⁺ in the center of the wastewater plume that is moving much slower than ground water