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Sub-slab depressurization (SSD) - An effective technology in eliminating hazardous vapor intrusion


Sub-slab depressurization (SSD) systems have proven to be an effective and cost- efficient approach in addressing the risks associated with radon gas intrusion in residential properties (Environmental Protection Agency (EPA, 1993). SSD systems have also been identified as an effective tool in eliminating the risks associated with vapor intrusion (VI), which results from contaminant sources, primarily volatile organic compounds (VOCs), which are present in soil, or migrate in groundwater located below adjacent and/or nearby buildings.

The concern regarding VI among state regulators has been steadily increasing, as the awareness of risks resulting from exposure to contaminants volatilizing and entering residences and buildings has increased. Where VI is a problem, air quality can be adversely impacted, resulting in increased health risks to the occupants. This concern is magnified when a release to the environment involves chlorinated solvents, such as perchloroethene (perc) from dry cleaning and/or manufacturing facilities.

Recently enacted changes in regulatory standards in 2006 and 2008 have addressed these concerns, in part by lowering the regulatory cleanup standards and goals designed to be protective of indoor air. As a result, there have been significant reductions in chlorinated VOC clean-up standards. For instance, the Mass. Department of Environmental Protection (MADEP) regulatory standard, which is protective of indoor air for the dry cleaning chemical perc, was reduced from 3,000 parts per billion (ppb) to 50 ppb in groundwater. The result of this reduction has been to increase the overall number of dry cleaning facilities, which trigger a reporting obligation from a "reportable release" when undergoing a "due diligence" environmental assessment.

Regulatory "action level" criteria for contaminants constituting a threat to the health of occupants for indoor air have also been significantly reduced in the past year. The concentration of perc in indoor air previously considered as "background" is now greater than the "action level," which constitutes a threat to the health of the occupants. These changes have brought about a dramatic increase in the need for remedial actions needed, in order to eliminate the VI pathway exposures.

SSD systems have increasingly become the technology of choice to address a VI problem, because they are effective in reducing up to 99.9% of chlorinated solvent contamination in indoor air (Folkes, 2002), can be installed at a modest cost into pre-existing buildings (a $2,000 system is usually sufficient for a residence), has low operational costs (typically a 90 to 150 watt fan), and an operational lifespan of 5 to 15 years for the fan motors, which are easily replaced when they wear out. These systems are also very similar to those utilized for treating radon gas problems. The systems can be installed unobtrusively, and do not generate any noise within the occupied spaces. A "U-tube" manometer displaying a differential in the water column is the only indication that the system is operating. The fans are mounted on the exterior of the building where the decreased noise levels do not pose a problem to the occupants.

Norfolk Ram Group, LLC recently installed a two part SSD system at an office building located in Medford, Mass. The system was placed down-gradient of a former dry cleaner facility where perc had migrated into the groundwater located beneath the building. Perc vapors were detected in the indoor air, at levels which exceeded the DEP Imminent Hazard criteria. The SSD system was installed over a period of several days at a cost of $10,000, and depressurized an area of approximately 4,500 s/f. Post installation indoor air samples have demonstrated a reduction of perc in indoor air below laboratory detection limits. In one area, perc concentrations were reduced from 18.8 μg/m3, which exceeded an "Imminent Hazard" action level, to below laboratory detection limits (< 3.4 μg/m3). The SSD system is anticipated to run continuously for many years, with reasonable electrical consumption costs, and with minimal required maintenance.

In short, SSD systems can be a highly effective, cost-efficient approach to addressing VI problems. By freeing up resources to address the releases, SSD systems allow engineers to continue to work towards long-term solutions to these problems.

Recent Changes in Hazardous Waste Regulations

The Massachusetts Department of Environmental Protection has implemented final regulations to the Massachusetts Hazardous Waste Regulations (310 CMR 30.000) which became effective on May 1, 2009. The revised regulations include eleven changes in the requirements governing waste oils and other regulated recyclable materials, as well as the adoption of the EPA's federal exclusion for medicinal nitroglycerine.

A summary of the significant changes are listed below:

  • Adoption of a revised definition of oil and used waste oil to include spent parts washer solvents not otherwise regulated by US EPA to be regulated as waste oil;
  • Definition of "crimes of moral turpitude" and requirement for disclosure to MassDEP by applicants and licensees of any crimes involving fraud, misrepresentation or deceit as well as any crime that adversely reflects on the applicant or licensee's competence to transport, use, collect, store, treat or dispose of hazardous waste;
  • Adoption of the EPA exclusion for medicinal nitroglycerine allowing for disposal of finished dosage forms (tablets and capsules) as a non-hazardous waste and eliminating the requirement for "triple rinsing" of empty packages to be considered as "RCRA empty";
  • Clarification that shipments of regulated recyclable materials sent off the site of generation must go directly to the appropriate authorized facility and remain loaded on the transporter's vehicle at all times until delivered to the point of destination;
  • Clarification for signage requirements in areas of hazardous waste accumulation to include lettering "HAZARDOUS WASTE" in capital letters at least one inch high;
  • Clarification for transporters of off-specification used oil fuel to a Class B(3) facility licensed to burn used oil fuels for the production of heat or power;
  • Clarification that a marketer of specification used oil fuel may ship to another marketer licensed with a Class B(3) recycling permit in addition to other persons licensed to burn that fuel.

If you are a hazardous waste transporter or your facility generates regulated recyclable materials and waste oils these revisions to the Massachusetts Hazardous Waste Regulations 310 CMR 30.000 may be applicable to your continued regulatory compliance status. Norfolk Ram Group, LLC can review these changes with respect to your facility and provide recommendations for changes in your operations and procedure to assure your continued regulatory compliance with 310 CMR 30.000

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