(a) Medium specific concentrations (MSCs) for ingestion of surface water and groundwater, and soil ingestion along with inhalation of volatiles and particulates are calculated according to the procedures specified in subsections (b)-(d) of this section based on residential exposure factors. MSCs are subject to additional numeric criteria and adjustments of §335.559 of this title (relating to Medium Specific Requirements and Adjustments for Risk Reduction Standard Number 2). The derivation of all equations is presented in §335.567 of this title (relating to Appendix I).
(b) For a contaminant which is a carcinogen, the MSC is the concentration which represents an excess upper bound lifetime cancer target risk (TR) of 0.000001 (also expressed as one in one million) for Class A and B carcinogens, or 0.00001 (also expressed as one in 100,000) for Class C carcinogens due to continuous lifetime exposure as calculated using the equations and factors listed in paragraphs (1) and (2) of this subsection.
  (1) Water MSC for ingestion, in units of milligrams per liter (mg/L):
Attached Graphic   (2) Soil MSC for ingestion with inhalation of volatiles and particulates, in units of milligram per kilogram (mg/kg):
Attached Graphic (c) For a contaminant which is a systemic toxicant, the MSC is the concentration to which human populations (including sensitive subgroups) could be exposed by direct ingestion or inhalation on a daily basis without appreciable risk of deleterious effects during a lifetime. The MSC is calculated using the equations and factors listed in paragraphs (1) and (2) of this subsection.
  (1) Water MSC for ingestion in units of milligram per liter (mg/L):
Attached Graphic   (2) Soil MSC for ingestion with inhalation of volatiles and particulates, in units of milligram per kilogram (mg/kg):
Attached Graphic (d) Examples of unadjusted MSCs, standards, and criteria are listed in §335.568 of this title (relating to Appendix II. Examples of Medium Specific Concentrations, Standards, and Criteria for Health-Based Closure/Remediation). The commission will revise Appendix II on an annual basis to reflect newly promulgated standards and MSCs based on current toxicological data.

Source Note: The provisions of this §335.558 adopted to be effective June 28, 1993, 18 TexReg 3814.