Soil Excavation

Soil excavation is a straightforward remediation method that effectively removes impacted soils, eliminating the spread of contaminants to other media and receptors. Conditions for successful soil excavating (i.e., shallow depth of soil contamination, limited prohibitive infrastructure in areas to be excavated, etc.) are evaluated to determine the effectiveness of implementation.

Bioremediation

Certain compounds found in petroleum can be degraded by bacteria. Aerobic bacteria have been effective in reducing concentrations of petroleum constituents but may be limited by the availability of oxygen. Dissolved oxygen levels can be depleted, leaving anaerobic conditions unless supplemental oxygen is added. Bioremediation can occur by allowing indigenous bacteria, to degrade most petroleum contaminants to carbon dioxide and water. The passive alternative is also referred to as natural attenuation. If dissolved oxygen concentrations are sufficient, the passive alternative can be actively enhanced by simply injecting additional bacteria into the subsurface. A more aggressive technique would involve injection of bacteria and/or nutrients in targeted areas. In certain instances, the addition of oxygen by means of air sparge points or injection of oxygen releasing compounds may be used to further enhance bacterial populations.

Natural Attenuation

Natural attenuation can be applied at moderately contaminated sites as a low-cost remedial approach in the absence of an active remediation system. The natural attenuation approach involves allowing existing sorbed- and dissolved-phase contaminant mass to be left in-situ where it is degraded by natural processes in the subsurface, including biodegradation, volatilization, advection, and dispersion. Natural attenuation does not provide control of dissolved- and vapor-phase contaminant migration and therefore may not be appropriate in scenarios where on- and off-site receptors could be impacted. In addition, natural attenuation requires site monitoring over potentially long periods of time, offsetting potential costs savings.

Air Sparging and Soil Vapor Extraction

The combination of air sparging (AS) of the saturated zone and soil vapor extraction (SVE) in the vadose zone is a treatment technology that has proven to be effective on MTBE, benzene, toluene, ethylbenzene, and xylenes (BTEX) under the proper lithologic conditions. In general, this technology involves forcing air into the saturated zone to volatilize contaminants out of solution. The vapor-phase contaminants are then removed via extraction wells that induce air flow through an applied vacuum. The contaminated vapors can be treated using vapor-phase granular activated carbon (GAC) vessels or catalytic oxidation

Subsurface air permeability must be sufficient to cost-effectively (relatively low pressures/vacuums and air flows) deliver and remove air and produce an effective radius-of-influence (ROI).

Dual Phase Extraction

Dual-phase extraction (DPE) can be used as a primary remediation technique in shallow, low-yield aquifers. The technique entails using a high-vacuum pump configured with an air/water separator to recover liquid and vapors simultaneously, remediating both dissolved-phase and vapor-phase contaminants. When a recoverable amount of liquid enters an extraction well, the pump removes it by vacuum. When no liquid is present in the well, the pump removes vapors. In addition to providing mass recovery by removing contaminants in the dissolved phase, recovery of liquids provides hydraulic control to prevent further dissolved-phase contaminant migration. The recovery of liquids also creates a cone of depression allowing treatment of materials normally in the saturated zone by the vapor extraction process. The vacuum created by the high-vacuum pump acts on the soil contamination by reducing the air pressure in the subsurface, thus increasing volatilization rates. The vacuum also induces a flow of air through soil pore spaces thereby moving the vapor-phase contaminants toward the extraction wells.

Pump and Treat

Pump-and-treat remediation systems are relatively easy to install and typically consist of a pump, or pumps, and a treatment system designed to remove groundwater contaminants. Typical systems designed to remediate petroleum constituents include top-loading or electric submersible pumps that transfer groundwater from recovery wells to the treatment system. The treatment system may include an oil/water separator to collect separate-phase liquids (SPL), an air stripper, and/or GAC filtration vessels. In some cases, groundwater can be effectively treated simply by passing the extracted water through GAC vessels.