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Analysis of alternatives for Cleaning Up Flowing River Site

Alternative #1: Provide Security

Brief Description

This alternative is used as a baseline against which to compare other alternatives. It allows for continuous monitoring of site conditions; action can be taken if conditions change. It includes fencing the contaminated area and erecting signs to indicate potential health hazards.

Advantages

  • Because no threat to drinking water exists (the deep aquifer is not connected to the shallow aquifer), funds for this site may be used for more hazardous sites.

  • The fence prevents direct contact with contamination.

Disadvantages

  • It does not address the contamination.

  • Contaminated water may continue to move toward the flowing river.

  • Asbestos particles may be released during windy weather if erosion continues to occur.

  • The site is not available for future use.

Alternative #2: Only Cap

Brief Description

This alternative places layers of waterproof material like clay and plastic over the contamination. It reduces the amount of water reaching the contamination, and the contamination is slowed from moving and reaching water sources.

Advantages

  • A short period of construction is required, so the site is addressed quickly.

  • This technology is inexpensive, reliable, and commonly used. It will last with proper maintenance.

  • The cap will reduce the rate at which the contamination in the shallow aquifer will move toward the flowing river.

Disadvantages

  • The cap does not neutralize or eliminate the contamination.

  • The cap requires maintenance and monitoring and is not always 100% effective.

  • It limits the site's reuse; in order to maintain the cap, nothing can be built on top of it.

Alternative #3: Cap, Air Stripping, Chemical Precipitation

Brief Description

This alternative uses a cap to address soil contamination, as described in alternative #2.

Air stripping and chemical precipitation of contaminated water requires building a large tower on the site and drilling wells into the aquifer. Contaminated water is pumped to the top of the tower where the volatile pollutants can evaporate and form into a gas. The gas is then filtered through a layer of carbon to remove the contaminants.

After air stripping, the water is treated by chemical precipitation to remove heavy metals. Chemicals are added to the water to create a sludge. The water is filtered from the sludge, treated, and pumped back into the environment. The sludge is sent off site to a licensed disposal facility.

Advantages

  • The cap addresses the asbestos. See discussion of capping advantages in alternative #2.

  • This technology effectively removes most of the contamination from the shallow aquifer over 2-10 years.

  • Most of the contamination is addressed through treatment, without having to move it from the site.

  • An air stripper is relatively easy to operate and is not technically complex.

  • Metals and PCBs are captured in the sludge. A licensed off-site facility can contain the sludge through extensive controls.

Disadvantages

  • See the discussion of capping disadvantages in alternative #2.
  • The air stripping tower needs to be monitored carefully to ensure that any contamination released into the air meets State standards.

  • Air stripping is 90% efficient and the tower needs to be monitored to prevent releases of contaminants.

  • Contaminated sludge needs to be disposed of properly offsite.

Alternative #4: Incineration, Air Stripping, and Chemical Precipitation

Brief Description

This alternative involves digging up and burning contaminated soils at high temperatures in an on-site incinerator. The incinerator destroys TCE and PCB contamination. The remaining ash containing heavy metals is shipped off site to a landfill.

As described in alternative #3, air stripping and chemical precipitation of contaminated water require building a large tower on the site and digging wells into the aquifer. Contaminated water is pumped to the top of the tower where some of the pollutants can form a gas that may be filtered through carbon. Heavy metals are removed from the water by chemical precipitation.

Advantages

  • The site is "clean" and available for reuse.

  • The incinerator destroys at least 99.9999% of the organic (burnable) contaminants in the soil.

  • An air stripper is relatively easy to operate.

Disadvantages

  • Stringent permits are required to operate an incinerator. Hazardous emissions from incinerators have been associated with health risks, so careful monitoring is required.

  • Public resistance from incineration often occurs. Treatment residuals from the incinerator must be managed and disposed of.

  • Air stripping is 90% efficient. The air stripping tower needs to be monitored carefully to ensure that any contamination released into the air meets State standards.

  • Asbestos is not addressed.

Alternative #5: Complete Excavation

Brief Description

This alternative requires digging up a large volume of the contaminated soil and shipping it to an off-site hazardous waste facility.

Groundwater contamination is treated on site with an air stripping and chemical precipitation, as described in alternative #3.

Advantages

  • This technology removes contaminated soil completely in a short period of time and requires no future maintenance.

  • An air stripper is relatively easy to operate and is not technically complex.

  • The site is safe for future use.

Disadvantages

  • Trucks that carry contaminated soil (and those that deliver clean backfill) drive through town. A risk that something could go wrong during the removal and export of soil exists, which could result in public exposure to the contaminants through the air. Concerns may be raised over odor caused by excavation and transporting contaminated soil.

  • Contamination is not addressed or treated on-site, but is passed elsewhere.

  • Dust from excavation activities must be controlled.

  • Roads may need to be repaired.

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