Cambridge Environmental uses computational, statistical, and graphical tools to analyze data with efficiency and intelligence. We identify patterns and inconsistencies in complex sets of data, use fundamental chemical and physical principles to build robust models, and thereby solve the problems at hand.

1. In a recent project, Cambridge Environmental designed a soil gas model to estimate exposure to chemicals volatilizing from an underground plume into indoor air in a residential community. A large spill of petroleum products had migrated from storage tanks some distance beneath a common area and several neighborhood homes. The petroleum products had floated on the groundwater surface and become smeared throughout a soil zone due to fluctuations in groundwater levels. The regulatory authorities were concerned about the potential for off-gassing of benzene, toluene, ethylbenzene and xylene (BTEX) vapors from the plume or smear zone, through the soil, and into the neighborhood homes, and indicated that use of EPA’s default models for vapor transport from groundwater or product plumes through soil into homes resulted in vapor concentration estimates in neighborhood homes that were unacceptably high.
   
   We performed and documented a statistical analysis of the vapor measurements that showed there was no difference in measured BTEX concentrations between homes above the plume and those not above the plume, even though such background concentrations were larger than the 10–6 “acceptable risk” level. We then designed and implemented a simple spreadsheet model that simultaneously incorporated all the physical processes considered by the EPA default models, including the variation of soil water content with depth and air infiltration into a house, while additionally including the effect of the smear zone of petroleum hydrocarbons and dampening of off-gassing due to infiltration of rainwater. Applying this model to the site soil data, we found that the estimated indoor air concentrations due to the plume were negligibly small and presented no additional unacceptable risks. We demonstrated that a more sophisticated view of physical forces could indeed be modeled simply, practically, and conservatively. The effort was successful, since infiltration of vapors was subsequently not considered important by the regulatory authorities.
   
   
2. A recent project completed for a chemical manufacturer involved a lawsuit filed by a volunteer fireman who had responded to a chemical spill caused by a leaking tanker truck. The fireman claimed that exposure to fumes caused him permanent injury. Cambridge Environmental estimated the chemical concentrations likely to have resulted from the incident, and showed that these concentrations were insufficient to cause the alleged health effects. Based in part on the strength of our analysis, the manufacturer reached a favorable settlement with the plaintiff.
   
   
3. In recent years, the U.S. EPA has developed guidance for performing multi-pathway risk assessments for waste incinerators. We have been assembling methodologies for performing such assessments for several years, and have previously incorporated many of the methods into other risk assessments. In one particular project, we proposed to EPA a protocol for the most complete multi-pathway assessment to date, including a complete uncertainty analysis. In addition, we have performed detailed quantitative analyses, including the necessary data, of the methods required. We expect to implement this protocol, or a similar one, at a future date.

   The analyses that we prepared for this project were incorporated into comments to the U.S. EPA on several of their draft guidance documents. All are quantitative, involve analysis of current literature, and incorporate uncertainty estimates. They include:
    

   • Analysis of available air dispersion models for application to multi-pathway assessments at our client's site (which is situated in complex terrain), together with suggested alternatives to result in substantial improvements;
   • Dose-response analysis for carcinogenic and non-carcinogenic effects;
   • Estimation of emission rates, based on application of a statistical model to an existing database; and
   • Evaluation of: PCDD/PCDF vapor-particle partitioning under ambient conditions and in combustor plumes; vapor uptake by plants; beef and cow bioconcentration/biotransfer coefficients; wet- and dry-deposition coefficients; and water/sediment partitioning models.

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