Total Petroleum Hydrocarbons in Groundwater—Evaluation of Nondissolved and Nonhydrocarbon Fractions

Total petroleum hydrocarbons (TPH) in groundwater samples are commonly extracted and analyzed for comparison to regulatory standards and for forensic evaluation of the source of spilled petroleum. While this procedure is normally intended to provide information on hydrocarbons dissolved in water, several complicating factors exist. In this study, the significance of reported TPH values is evaluated for a suite of surface water, interstitial, and groundwater samples by comparing analytical data obtained on unfiltered water, filtered water, and water from which nonhydrocarbons were removed by treatment with silica gel. Results indicate that standard measurements of TPH in groundwater not only include dissolved petroleum hydrocarbons, but commonly also include contributions from: (1) hydrocarbons sorbed on particulate matter; (2) droplets or micellular forms of liquid hydrocarbon contamination; (3) biogenic hydrocarbons; (4) contamination by field or laboratory equipment; and (5) dissolved polar organics (nonhydrocarbons), which may be naturally occurring or derived from spilled petroleum products. These factors complicate the regulatory and forensic interpretation of standard TPH data for groundwater samples.