material as the likely source of the PAHs. Concentrations of PAHs in soil at these levels could pose potential direct-exposure concerns, even if the bioavailability of the PAHs is relatively low. Volatile components of petroleum that are not specifically identified as target indicator compounds in Figure 2-3 but reported as separate compounds by the laboratory using Method 8260 or similar methods can in general be ignored (e.g., hexane, methylbenzenes, alkanes, alkenes, alkyl benzenes and other aromatics not specifically identified as target indicator compounds; refer to Section 2.10 and NEIWPCC 2003). These compounds are included under the umbrella analysis for TPH in general and do not need to be evaluated (or even reported) separately. This is based on the assumption that the toxicity factors selected for TPH are adequately conservative for the mixture of compounds present in fuels beyond the target compounds noted in Figure 2-3 (refer to Appendix 1, Chapter 6). Soil, groundwater and soil gas samples must always be tested for TPH (or equivalent) in addition to targeted, individual chemicals. Laboratory analysis for TPH as gasolines and middle distillates is generally carried out using gas chromatography, modified for "gasoline-range" organics ("Volatile Fuel Hydrocarbons") and "diesel-range" organics ("Extractable Fuel Hydrocarbons"), respectively (e.g., EPA Method 8015). Refer to the Hawai‘i DOH Technical Guidance Manual for additional information on laboratory methods. Analysis for TPH as residual fuels up to the C40 carbon range can be carried out by gas chromatography, infrared absorption, or gravimetric methods. The latter methods are rarely used, however, due to their inability to discriminate the type of the petroleum present and interference with organic material in the soil. Analysis of soil gas for TPH is also sometimes reported as “Total Volatile Hydrocarbons” or “TVH.” Consult a laboratory with expertise in analysis of total hydrocarbon fractions in soil gas for additional information. As discussed in Appendix 1, environmental screening levels for TPH were developed by assigning representative fate and transport properties and toxicity factors to surrogates for each TPH category and applying the same models and approaches as used for the target, indicator compounds (refer to Appendix 1). The following carbon range fractions were targeted:
C5-C8 aliphatics; C9-C18 aliphatics; C19+ aliphatics; and C9+ aromatics.
Pacific Basin Edition (Fall 2012)
2-16
Volume 1