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Environmental Site Remediation System Design

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Environmental Site Remediation System Design

There are two basic ways to remove environmental contamination.

• Mass Transfer
  • Pump and Treat
  • Vapor Extraction
  • Over-excavation

• Contaminant Degradation
  • Bio-degradation
  • Air Sparging
  • Chemical-degradation

Mass Transfer

Pump and Treat

During Pump and Treat, contaminated groundwater is pumped from the site and is treated to remove the contaminant, prior to disposal or recharge. It has been found that because of the generally low mass transfer rates, Pump and Treat is usually not an effective way to remediate petroleum hydrocarbons.

Pump and Treat can be an effective way to control dissolved hydrocarbon plumes if their migration would poses a hazard.

Vapor Extraction

During Vapor Extraction, air is vacuumed from the soil and is treated to remove contaminant vapors. In this way, it is like Pump and Treat, but usually the mass transfer rate is much greater. Additionally, vapor extraction helps to augment bio-degradation by removing CO2, thereby recharging the formation with Oxygen. We have found that at many sites that the amount of hydrocarbons recovered as Carbon Dioxide exceeds that recovered as product vapor.

There are a number of factors to consider when designing a Vapor Extraction system.

• Concentration of contamination in soil vapor.
• Expected flow rates.
• Expected vacuums values.
• Area of influence.
• Available maintenance.
• Conduits to surface, i.e. excavations, wells, French drains, etc.

Contaminant Degradation

Bio-degradation

During Bio-degradation, living organisms, usually bacteria, break down the contamination. The activity of these bacteria is controlled by the concentration of contaminants and by the presence of electron acceptors that allow the bacteria to oxidize the contaminants. In most sites, these electron acceptors have been depleted and it may be necessary to augment them to restart or to continue active bio-degradation.

Natural Attenuation

If the amount of electron acceptors at a site is found to be sufficient to degrade the contamination before it can endanger health or the environment, then nature can be left to take care of the problem on its own. In order to do this safely; it is necessary to have sufficient information about the site to determine the risk.

Enhanced Attenuation

Bio-degradation may be speeded or enhanced by physically adding nutrients of some form or another or by removal of some inhibitor. In the case of petroleum hydrocarbons, amount of oxygen is usually the limiting nutrient. While with chlorinated hydrocarbons, the presence of oxygen limits the bio-degradation. Chloroinated hydrocarbons require some method of oxygen removal must. Therefore, depending on the compounds to be degraded, Oxygen may need to be added or removed. This is usually accomplished by or part of other processes or types of degradation and/or mass transfer.

Air Sparging

One of the most effective electron acceptors is Oxygen, which is also the most quickly depleted. Air Sparging is one of the more effective and least expensive methods of replacing the consumed Oxygen. This process is greatly enhanced by the removal of Carbon Dioxide at the same time.

During Air Sparging, clean compressed air is injected into the formation through sparging wells.

Chemical-degradation

At most, sites chemical-degradation of the contamination is not an important factor.