(a) For each individual COC for which PCLs have been developed in response to §350.71(k) of this title (relating to General Requirements), the person shall establish the critical PCL. The critical PCL is the lowest PCL for a particular environmental medium considering all the exposure pathways for which a PCL is developed in accordance with §350.75(i) of this title (relating to Tiered Human Health Protective Concentration Level Evaluation) and/or §350.77 of this title (relating to Ecological Risk Assessment and Development of Ecological Protective Concentration Levels).
(b) If the critical groundwater PCL, or an attenuation action level developed in accordance with §350.33(f) of this title (relating to Remedy Standard B), is greater than the aqueous solubility limit for that COC, then the COC should be addressed as NAPL should any NAPLs be present.
(c) If the critical PCL for a COC established in subsection (a) of this section is less than the method quantitation limit as defined in §350.4 of this title (relating to Definitions and Acronyms) or background concentration for that COC as determined in accordance with §350.51(l) and (m) of this title (relating to Affected Property Assessment), then the greater of the method quantitation limit or background concentration is the critical PCL for that COC.
(d) As an additional requirement, the critical PCL and any attenuation action level must ensure that the explosive vapor provisions set forth in §350.31(c) of this title (relating to General Requirements for Remedy Standards) are met.

Source Note: The provisions of this §350.78 adopted to be effective September 23, 1999, 24 TexReg 7436