June, 2001

Engineered Barrier and
Institutional Controls as Remedial Action

 Leggette, Brashears & Graham, Inc. has successfully completed Remedial Investigation (RI) and Feasibility (FS) Studies under state and federal Superfund programs for sites ranging from retail gasoline stations to complex industrial facilities. One of the keys to developing cost-effective remedial action alternatives is the consideration of engineered barriers and institutional controls as risk reduction measures.

In 1999, LBG was retained to conduct a comprehensive RI/FS of an active plastic manufacturing facility in central Massachusetts. The 10-acre site is located in a mixed-use area with a residential population of more than 3,500 within one-half mile. The site is also located near several wetlands, abutted by a stream, and less than one-quarter mile from a potential water supply aquifer. A prior property transaction assessment resulted in the discovery of chlorinated volatile organic compounds (CVOCs), primarily trichloroethene in ground water.

The RI included the use of more than 25 soil borings and 50 ground-water observation wells in a multi-layer unconfined aquifer and a bedrock aquifer to delineate the horizontal and vertical extent of CVOCs. More than 25 soil gas and indoor air samples were also collected to evaluate the potential migration of CVOCs from shallow ground water to on-site manufacturing buildings and nearby private residences. In addition, drinking water samples were taken from nearby private water supply wells drawing from the bedrock aquifer.

Results of the RI documented that CVOC concentrations in soil were below detection levels or risk standards throughout the site. However, CVOCs were detected in soil gas up to 600-feet from the site. In addition, dissolved CVOCs were detected up to 450-feet and 750-feet downgradient of the site in the water table and deep overburden aquifers. CVOCs were also found in ground water more than 1000-feet downgradient of the site in the bedrock aquifer. A detailed exposure assessment and risk characterization demonstrated that cumulative risks were acceptable for all current and future scenarios except on-site building exposure to CVOC vapors from ground water and for future potable use of off-site ground water.

A detailed FS was performed to identify a remedial action to reduce CVOC concentrations in ground water and reduce the potential risk from ground-water vapor migration to indoor air and potable water use. Ground-water pump and treat, air sparging/vapor extraction, in-situ bioremediation, reactive treatment walls, natural attenuation, and engineering and institutional controls were considered in the FS. None of the active remedies was found to meet the technical feasibility requirements for a permanent solution. In addition, The life-cycle cost of the remedies ranged from $450,000 for in-situ bioremediation to over $1,500,000 for ground-water pump and treat.

However, LBG demonstrated that engineering controls consisting of sub-slab depressurization for the on-site buildings and replacement of off-site private wells with municipal water service, supported by ground water use restriction, would result in elimination of potential risk under current and future use scenarios. The time frame to implement engineering and institutional controls was substantially less and the life cycle cost with annual monitoring of natural attenuation resulted in savings of up to $1,250,000. The selected remedy was approved by the Massachusetts Department of Environmental Protection and the remedy design is under development.

For more than 57 years, Leggette, Brashears & Graham, Inc. has provided state of the art consulting services to our clients. The bulk of our work is repeat business from customers who have benefited from the value-added services we provide. If you would like more information on how LBG can add value to your ground-water or environmental project, please contact your local LBG office for assistance.