Soil and groundwater remediation and cleanup may be required to facilitate development of land for residential, commercial/industrial, or other land use. Soil cleanup may also be required to mitigate impacts for existing land use, or to mitigate impacts to groundwater and/or surface water. Groundwater remediation may be required to reduce concentrations of various compounds below regulatory agencies specified threshold levels or to prevent the potential impact on a receptor such as a stream or drinking water well. The following summarizes some of the methods applied by ART to remediate soil and groundwater:

Excavation and Disposal/Treatment
Typically the “baseline” for soil remediation, ART will often remove contaminated soil through excavation and then transport it off-Site for disposal at a landfill. As part of excavation projects, ART can develop the planning documents required by regulatory agencies. These documents include grading plans, air quality monitoring programs, health and safety plans, storm water pollution prevention plans (SWPPP), and comprehensive sampling plans.

Soil Vapor Extraction
Volatile compounds, such as gasoline and solvents, can be remediated through vapor extraction. Wells installed in the vadose zone are used to apply a vacuum and extract volatile vapors from the subsurface.

Dual-Phase Extraction
This technology involves the extraction of groundwater to lower water levels within a well, and then vapor extraction to remove volatile vapors from the dewatered sediments. The technology can be effective for volatile compounds such as gasoline or solvents in tightly compressed soils.

In-Situ Chemical Oxidation
This technology involves injection of chemical oxidants such as peroxide, ozone, or permanganate into the soil and groundwater to facilitate chemical transformation of contaminants. The technology is suited well in situations where chemicals are recalcitrant to biodegradation, either due to their chemistry and the aquifer conditions or due to elevated chemical concentrations. Chemical oxidation can be used for solvent and hydrocarbon contamination, and can be favorable when significant concentrations of contaminants are present that will prevent successful bioremediation. Chemical oxidants can be injected into the subsurface using Geoprobe borings and injection wells.

In-Situ Chemical Reduction
Contaminants in the subsurface can also be remediated through chemical reduction. An example is hexavalent chromium, which can be reduced in-situ to the less toxic and less soluble trivalent chromium precipitates. Chemical reduction is done through injection of compounds such as sodium thiosulfate, calcium polysulfide, and ferrous sulfate.

In-Situ Bioremediation/Biodegradation
In-situ bioremediation/biodegradation is commonly the most cost-effective means for treatment of soil and groundwater impacted by contaminants. It involves the natural degradation of chemicals as result of aerobic and/or anaerobic processes. Even metals can be treated by stimulating microbial activity in the subsurface. Although most contaminant plumes are undergoing bioremediation naturally, injection of materials into the subsurface may be necessary to accelerate the process. In some cases, natural bioremediation/biodegradation may be stalled because one or more limiting elements, such as oxygen, nitrate, and sulfate, have been completed exhausted by the microbial population. The oxygen is paramount for aerobic degradation, and the nitrate and sulfate for anaerobic processes. Materials such as ethanol and essential nutrients can be injected into the subsurface to facilitate natural remediation of chemicals in soil. Oxygen may also be introduced to through various mechanisms including sparging and oxygen release compound (ORC). Nitrate, sulfate, and other key elements for anaerobic degradation are usually injected in solutions.

Hydraulic Control
Experience has shown that little contaminant mass is typically removed using groundwater extraction, and thus pumping groundwater is used primarily today for hydraulic control in cases where contaminants are migrating off-site at unacceptable rates. ART has experience designing, installing, and operating hydraulic control systems. The design typically involves aquifer testing and numerical modeling. The system operation will include extraction wells, conveyance piping, and potentially above-ground treatment. Treated groundwater is either discharged under appropriate permit to a sewer system, storm drain, or surface water, or re-injected to the aquifer.

Natural Attenuation
Natural attenuation is the collective term for the various processes, like sorption, dilution, dispersion, and natural biological degradation, whereby contaminants are prevented from spreading in the subsurface. Due to the high costs to remediate chemicals in the subsurface to their low remedial goal concentrations, most remedial programs involve natural attenuation to some degree. In some cases, natural attenuation may the primary remedial measure selected. In other cases, natural attenuation is selected as the final remedial option following completion of more aggressive measures such as source removal and hot spot groundwater cleanup. Approval of natural attenuation remedial measures by regulatory agencies typically requires evaluation of the Site to demonstrate a thorough understanding of hydrogeology, contaminant distribution, and contaminant fate and transport. Fate and transport analysis may require modeling and risk assessment. Long-term monitoring

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