Technical memorandum: Compound specific isotope analysis, Oak Grove Village well site OU1, Franklin County, Missouri

A study involving Compound Specific Isotope Analysis (CSIA) of trichloroethene (TCE) in groundwater at the Oak Grove Village (OGV) Well Site was conducted by the U.S. Environmental Protection Agency (EPA) in 2014 in an effort to fingerprint the source(s). This technical memorandum, written as a joint effort between HydroGeoLogic, Inc. (HGL) and the U.S. Geological Survey (USGS) Central Midwest Water Science Center (Schumacher, 2019), documents the procedures and analysis of the CSIA investigation.

CSIA is an analytical method that measures the isotopic ratios of naturally occurring stable isotopes in specific chemical compounds in environmental samples. CSIA using primarily the ratio of carbon ¹³C/¹²C (δ¹³C), known as 1-D CSIA, has been used for decades in evaluating degradation pathways of organic compounds, including chlorinated solvents such as TCE. Ratios of stable chlorine isotopes ³⁷Cl/³⁵Cl (δ³⁷Cl) also have been used with carbon isotopes, collectively known as 2-D CSIA, and most recently isotopes of hydrogen ²H/¹H (δ²H) have been added, collectively known as 3-D CSIA, in attempts to further determine source, transport, and fate of compounds such as TCE (Ertl et al., 1998; Hunkeler et al., 2011; Kuder et al., 2013; McHugh et al., 2011; Shouakar-Stash et al., 2003; EPA, 2008; and van Warmerdam et al., 1995.