RECIRCULATING WELLS PILOT TESTS 
at
SD-5 SOUTH 

WILLEY PLAYGROUND, BRIARWOOD

Overview
A recirculating well pilot test is planned for the downgradient portion of contamination associated with the SD-5 South plume. This plume is located under the Briarwood section of Mashpee; it contains volatile organic compounds (VOCs) and ethylene dibromide (EDB). The test wells will be located at the Willey Playground, at the corner of Hillside and Highland Avenue.

The objectives of the pilot test are:

• Determine if recirculating well technology can effectively reduce the level of VOCs which are found in the SD-5 plume to less than 1 part per billion (ppb), and EDB to less than 0.02 ppb.
• Assess the effectiveness of recirculating well technology versus extraction, treatment, and reinjection (ETR) technology - also known as "pump and treat".

How does Recirculating Well Technology work?
Recirculating wells technology is a recently developed method of treatment for volatile organic compounds (VOCs) in groundwater. They are being used at several locations throughout the United States.

Unlike "pump and treat" technology, recirculating wells do not extract water for treatment. Instead, the water is treated in the ground. By removing VOCs from water while it remains within the aquifer, this technology minimizes effects on groundwater levels and bodies of water in the area.

Once the recirculating well is installed in the ground, groundwater enters the well casing at the lower end of the well. A pressurized stream of air is injected into the water, causing air bubbles to rise up through the well. As the bubbles rise, they collect VOCs from the groundwater. This system works because VOCs readily transfer from water into air. The VOC vapors are carried to the surface where they enter an activated carbon filter system. The filter removes the vapors from the air by capturing them in the carbon. Water is continuously pumped up into the well and discharges directly back into the aquifer, creating a zone of circulation in the vicinity of the well. This maintains equilibrium in the aquifer and avoids drawdown of the water table.

EDB contamination will be treated using carbon filtration and biological degradation.

What Will the System Look Like?
Two recirculating wells will be installed along with about 30 monitoring wells. These will be used to track the effectiveness of the system. Two structures housing carbon treatment equipment and air blowers will be installed on concrete pads on the site. These structures will be about 10 feet high and 10 to 20 feet wide. A gravel work surface and access road may be necessary as well.

Why Locate the System at Willey Park?
Willey Park has been proposed as the best location to conduct this pilot test because it is located over the center of the SD-5 plume where concentrations are greater than 10 ppb, the highest in the plume. This area provides sufficient space for installation of the system along with up to 30 monitoring wells which will be used to evaluate the system's performance. In addition, access to this property could be obtained in a reasonable time frame. Although other sites were assessed, no other met the needs of the pilot test project.

When Will the System Be Installed?
The pilot test will consist of four phases:

•  Planning and design. 
• Construction and installation. 
• Operation and maintenance 
• Evaluation of pilot test

A summary of activities and requirements is presented below.

1. Planning and Design
The Air Force hopes to begin installing the system in November, 1996.

Plans and engineering designs for the SD-5 recirculating wells pilot test have been prepared and are currently being reviewed. Identification of suitable locations for the test, the property access process, and site verification are part of this phase of work.

Initial site access is being sought at this time to collect groundwater and geological samples and install up to eight monitoring wells. The Air Force has received permission to conduct the pilot test at this location from the Briarwood Homeowners Association.

2. Construction and Installation
Data from the first monitoring wells will confirm the location of the plume and provide detailed geologic data for final design. Access to drilling locations may require some clearing of trees and shrubs. Because the site is a playground, measures will be taken to eliminate the potential for unsafe conditions. These measure may include the placement of temporary security fencing to prevent access to the site by unauthorized persons. It is likely that, for safety reasons, access to the playground area will be restricted during this phase.

Drilling to collect these samples and install the monitoring wells may take three to four weeks. Drilling will occur during daylight hours on weekdays and possibly on Saturdays during early to mid November. Weekend work may be necessary in order to install the wells before the onset of winter weather. Noise associated with this activity will be similar to, or less than, that associated with typical road maintenance.

Drilling and system construction and installation will occur in early December and will conclude in early March with the start of system operation. Work will normally be conducted during daylight hours.

Some moderate noise levels similar to that associated with typical road maintenance will be experienced during drilling and well installation.

3. Operation and Maintenance
The pilot test will initially take place over a six month period, from March until early September 1997.

The pilot test will involve recirculating contaminated water through the recirculating well system and treating the effluent air with a carbon filter system. The treatment sheds will be constructed using noise reduction insulation to minimize noise levels.

Wells will be located at depths of from 40 to 140 feet, and water will enter the wells at varying depths.

Soils in the area are mainly fine to coarse-grained sand, with a 35 to 40 foot layer of very fine sand, silt and/or clay located about 80 feet under the surface. The plume is located at a depth of about 65 feet underground and extends down to about 125 feet in depth. It is 500 feet wide at this point.

Normally, personnel will be present at the site three times a week for a few hours a day (typically on Mondays, Wednesdays, and Fridays). Personnel will also be at the site during normal working hours for 10-15 days of each month to collect water samples. In the event maintenance is required, efforts will be made to confine the presence of personnel at the site to hours of 7:00 AM to 7:00 PM.

4. Evaluation of Pilot Test
Upon completion of the pilot test:

• The system will be expanded to become a plume-wide response action, or 
• The system will be shut down, all wells abandoned, and the site restored to its original character, or
• The test will be extended to obtain further information in order to make a decision on expansion of the recirculating wells system as part of a plume wide response action. 

At the end of the test the system may be held on standby for a period of months pending a decision on whether or not to implement recirculating well technology on a plume-wide basis.

How Will It Be Determined That the Test Is Successful?
If VOCs in the zone of recirculation are found to have been reduced to less than 1 ppb, the recirculating well technology will be considered a success.