The Remediation Process
The process for selecting a clean-up technology for the site is called a feasibility study (FS). The FS considers a variety of factors in selecting a remedy, including:
- Protection of people's health.
- Protection of the local ecology.
- Available technologies and the likelihood of success.
- Short- and long-term effectiveness of technologies.
- Acceptability to the public and regulatory authorities.
- Cost of the remedy versus reduction of risk.
A remedy selected in the FS must at a minimum be protective of people and the environment based on the exposure of human or ecological resources to the contamination. This is usually accomplished by requiring the clean up to meet standards — such as federal or state drinking water standards — for the groundwater at the site or at locations where exposure could occur, such as private wells.
Available Clean-up Technologies
Some of the available technologies for the site include:
- “Skimming” oil from wells as it accumulates.
- Excavating contaminated material and either treating or landfilling it.
- Pumping groundwater and oil for separation and treatment above ground.
- Applying heat to the aquifer to improve the removal of the oil.
- Using surfactants (a type of soap) to help the oil flush out of the soil.
- Natural attenuation, which is a process where natural bacteria is used to break down contaminants.
Each technology has limits to its effectiveness and practicality and must be evaluated with the data from the site.
Protection of People and the Environment
A critical part of assuring protection of people and the environment is to understand the risk that the site poses to humans and the ecology. At the Cass Lake site, the primary concern for human health is exposure to the contamination that may enter a private drinking water well. The ecological concern is that contaminants may enter a surface water body, like a stream or lake, and cause damage to wildlife or plants.
Current Human or Ecological Exposures
The remedial investigation includes a review of all wells within a 1 mile radius of the site. No wells exist within ½ mile of the site in the direction the groundwater flows. The contamination from the oil spill extends only about 200 hundred feet from the spill itself. (See Figure 6). Therefore, no humans have been exposed to any site contamination. Monitoring wells are in place to detect if any contamination is moving toward any private wells.
The ecological concern is that oil or dissolved contaminants may enter a surface water body, like a stream or lake, and cause damage to wildlife or plants. Similar to the human exposure concern, the monitoring shows that the contamination is not entering a surface water body. The nearest potential surface water is Spike Lake, which is ½ mile away and well beyond the limits of contamination.
The Monitoring Program for the site is crucial to providing the data needed to continue to verify that there is no human or ecological exposure at the site. The monitoring data is also necessary to complete the FS. The monitoring program includes:
- Collecting groundwater samples from the monitoring wells at the site.
- Measuring and removing the thickness of the oil that accumulates in the wells.
- Measuring the properties of the oil that determine its ability to move (viscosity).
- Measuring the groundwater flow direction and velocity.
- Tracking the potential movement of the oil and dissolved contaminants in the aquifer.
Frequently Asked Questions