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Figure 1: Approach to estimate TPH cancer risks and noncancer Hazard Indices using component and mixture fraction methods. Whole mixture toxicity data are not available for the many, highly variable TPH mixtures of concern that are found at different sites, and as a result, both MADEP and TPHWG have proposed a fractional and subsequent surrogate/component-based approach for the risk assessment of TPHs. This figure shows that following the measurement of TPHs in either soil or water, both MADEP and TPHWG recommend that exposure estimates be developed for each fraction. Relying on surrogates for each fraction, Figure 1 shows that whole mixture risk assessments can be done using data directly on the mixture of concern, on a sufficiently similar mixture, on a mixture’s fractions, or on a subset of its components.