Pinnacle Engineering has significant experience utilizing forensic techniques, including Compound Specific Isotope Analysis (CSIA) methodology, in environmental studies. CSIA is frequently applied to carbon isotopes, and is considered an accepted scientific technique applicable on a routine basis for analyzing these chlorinated compounds. CSIA provides data and information independent of concentration; it measures the types of molecules that make up a volatile organic compound (VOC), whereas concentration-based analysis measures the number of those molecules. The natural abundance of δ13C is ~ 1%, and δ12C ~ 99%, and the CSIA forensic analysis focuses on determining the isotopic ratio as the ratio of the concentration of compound with δ13C to the concentration of the compound with δ12C.
In one recent study, Pinnacle used CSIA to separate nearby sources of VOCs in soil and groundwater from elevated soil vapors detected beneath a client’s facility. Pinnacle conducted a Phase II Environmental Site Assessment, in which evaluations of potential recognized environmental conditions (RECs) revealed limited and minimal soil impacts with chlorinated solvents, including Tetrachloroethene (PCE) and Trichloroethene (TCE) in the areas at the site with identified RECs. Groundwater was not encountered in these early investigations due to shallow bedrock conditions, and soil vapor intrusion (SVI) risks were deemed to be low based on soil conditions encountered. However, based on historical chemical use of surrounding businesses and known long-term soil and groundwater remediation systems near the site, coupled with the state regulatory authority’s renewed focus on SVI at chlorinated solvent sites, the State requested further investigation, including sub-slab sampling beneath the client’s building and the sampling of adjacent residences. Based on these results, the State deemed the site to be contributing to the regional groundwater plume and soil vapor impacts.
Pinnacle conducted additional investigations in response to the State’s claims, including on- and off-site groundwater sampling, and deep and shallow soil vapor sampling, the regulatory driver for potential SVI. Scientifically, this investigation utilized CSIA to differentiate carbon isotope ratios for PCE and its degradation compounds, and compared this data spatially upgradient and downgradient of the property. When chlorinated VOCs degrade in the environment, the ratio of stable isotopes changes, and the extent of degradation can be predicted from that change. With time and differing sources, these isotopic ratios differ, resulting in the ability to differentiate individual spills of the same chemical. Based on the results of this forensic investigation, Pinnacle was able to distinguish sources and obtain an agreement from the State that the client was not a contributor to the larger, regionally expansive soil and groundwater contaminant plumes.