The most common method of treating groundwater, known as "pump and treat," is to extract the water, treat it at the surface, and return the treated water to the aquifer. There are various ways to return treated water to an aquifer, one of which is through reinjection wells. Systems using reinjection wells are known as extraction, treatment, and reinjection (ETR) systems. A typical ETR system has three basic components:

Schematic of an ETR System

1. Contaminated groundwater is pumped from the aquifer through extraction wells. This requires placing extraction wells in different locations and at different depths to capture the plume.
2. The extracted water is then treated at the surface. At the MMR, the treatment system is activated carbon. Carbon has the ability to adsorb or capture passing organic molecules and hold them in pores within the carbon granule. When contaminated groundwater is pumped through a filter of carbon granules, most of the organic contaminants become trapped on the surface of the carbon. Eventually the carbon fills up and must be replaced. Used carbon is sent off-Cape to be recycled.

3. After being tested, the treated water is returned to the aquifer through reinjection wells. Returning the water to the aquifer helps to control plume migration and reduces the disruptive effects of extraction on the groundwater hydrology.

Design Considerations

ETR groundwater collection systems usually consist of a line or fence of wells placed around the contaminated area or in the path of the groundwater flow. Reinjection wells generally are placed beyond or near the edges of the groundwater plume. The specific arrangement of extraction and reinjection wells is determined using groundwater flow information and computer modeling. Modeling and other tools enable hydrogeologists to design the most effective system, including the number of wells, depths, spacing, and pumping or reinjection rates. Engineers design the appropriate treatment plant, which can be located away from the extraction and reinjection wells. At the MMR, treatment is typically achieved by passing the contaminated groundwater through granular activated carbon. Performance monitoring evaluation wells and sampling of both the incoming groundwater and the outgoing treated groundwater are used to check the effectiveness of the treatment system.

Use at Other Locations

ETR is the most commonly used treatment technology for contaminated aquifers. It has been proven effective over a wide range of site conditions and contaminants.