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WHAT ARE THE BEST MEANS TO ASSESS SITES AND MOVE TOWARD CLOSURE, USING APPROPRIATE SITE SPECIFIC RISK EVALUATIONS?
Citation:
WEAVER, JIM W., D. C. DIGIULIO, AND J. T. WILSON. WHAT ARE THE BEST MEANS TO ASSESS SITES AND MOVE TOWARD CLOSURE, USING APPROPRIATE SITE SPECIFIC RISK EVALUATIONS? Presented at 18th National Tanks Conference, Memphis, TN, March 20 - 22, 2006.
Impact/Purpose:
To inform the public.
Description:
To facilitate evaluation of existing site characterization data, ORD has developed on-line tools and models that integrate data and models into innovative applications. Forty calculators have been developed in four groups: parameter estimators, models, scientific demos and unit conversions. These have been used to couple ORD field research and observations to practical tools for site managers. Most noteworthy are calculators for borehole concentration averaging, uncertainty in contaminant transport, uncertainty in vapor intrusion assessment and plume diving. There is no generally accepted standard practice to evaluate exposure to vapors that intrude into living spaces. ORD has developed a method to install a probe through the sub-slab of a building and sample the vapors in the unsaturated zone beneath the building. ORD has also developed a method to assess vapor intrusion that is appropriate for individual buildings at sites containing petroleum hydrocarbons. The method compares samples from indoor air and sub-slab samples. It is very difficult using conventional site characterization approaches to evaluate natural anaerobic biodegradation of MTBE to TBA. Recent ORD research has shown that anaerobic biodegradation of MTBE can be recognized from a shift in the ratio of 13C to 12C (δ13C) in the MTBE remaining. Contaminant plumes have been observed to dive deeper into aquifers in response to a variety of factors. Conventional monitoring wells can miss these plumes. Flow in aquifers, influenced by infiltration and varying hydraulic properties was used to estimate the amount that plumes sink into aquifers. An on-line model (http://www.epa.gov/athens/onsite) was developed to estimate how deep to place monitoring points. Site characterization tools, including electrical resistivity probes and pneumatic hydraulic conductivity testing, were used to identify preferential flow paths for diving plumes in aquifers.