Section 250.304. MSCs for groundwater

(a) A person shall implement a remedy under the Statewide health standard that is protective of human health and the environment.

(b) The MSCs for regulated substances in groundwater are presented in Appendix A, Tables 1 and 2. The methodology used by the Department for calculating MSCs in groundwater is detailed in subsections (c)—(f).

(c) The MSCs for regulated substances contained in groundwater in aquifers used or currently planned to be used for drinking water or for agricultural purposes is the MCL as established by the Department or the EPA as established in § 109.202 (relating to state MCLs, MRDLs and treatment technique requirements) and Health Advisory Levels (HALs) set forth in Drinking Water Standards and Health Advisories, EPA Office of Water Publication No. EPA 822-R-09-011 (October, 2009). For a regulated substance where no MCL has been established, the MSC is the lifetime HAL for that compound. For a regulated substance where neither an MCL nor a lifetime HAL has been established, the MSC is the lowest concentration calculated using the appropriate residential and nonresidential exposure assumptions and the equations in § § 250.306 and 250.307 (relating to ingestion numeric values; and inhalation numeric values). New or revised MCLs or HALs promulgated by the Department or the EPA shall become effective immediately for any demonstration of attainment completed after the date the new or revised MCLs or HALs become effective.

(d) For regulated substances contained in aquifers not used or currently planned to be used, the MSCs in Appendix A, Tables 1 and 2 are calculated by the following:

(1) For volatile organic regulated substances with an attenuation factor of less than 20, as calculated by the methodology in paragraph (7), ten times the appropriate residential or nonresidential MSC for groundwater in aquifers used or currently planned to be used containing less than 2,500 mg/l total dissolved solids.

(2) For volatile organic regulated substances with an attenuation factor of greater than or equal to 20, as calculated by the methodology in paragraph (7), 100 times the appropriate residential or nonresidential MSC for groundwater in aquifers used or currently planned to be used containing less than 2,500 mg/l total dissolved solids.

(3) For semivolatile organic and inorganic regulated substances, regardless of the attenuation factor, 1,000 times the appropriate residential or nonresidential MSC for groundwater in aquifers used or currently planned to be used containing less than 2,500 mg/l total dissolved solids.

(4) For benzene, 100 times the appropriate residential or nonresidential MSC for groundwater in aquifers used or currently planned to be used containing less than 2,500 mg/l total dissolved solids.

(5) For regulated substances with no calculated attenuation factor because of a lack of data in Howard, P. H., R. S. Boethling, W. F. Jarais, W. M. Meylan and E. M. Michalenko. 1991. Handbook of Environmental Degradation Rates. Lewis Publishers, Inc., Chelsea, MI., the appropriate residential or nonresidential MSC for groundwater in aquifers used or currently planned to be used containing less than 2,500 mg/l total dissolved solids.

(6) For minimum threshold MSCs, 5 micrograms per liter in groundwater shall be used.

(7) The attenuation factor (AF) for an organic regulated substance shall be calculated according to the following formula:

AF = K x KOC

Where:

K = degradation coefficient = 0.693

T_1/2

T1/2—half-life of organic regulated substance in groundwater as reported in Howard, P. H., R. S. Boethling, W. F. Jarais, W. M. Meylan and E. M. Michalenko, 1991. Handbook of Environmental Degradation Rates. Lewis Publishers, Inc., Chelsea, MI.

KOC—organic carbon partitioning coefficient (See Appendix A Table 5).

(e) If the groundwater in aquifers used or currently planned for use at the site has naturally occurring background total dissolved solids concentrations greater than 2,500 milligrams per liter, the Statewide health standard for a regulated substance dissolved in the groundwater may be adjusted by multiplying the MSC for groundwater in aquifers by 100. The adjusted Statewide health standard shall then be used in calculating the soil to groundwater pathway numeric value as specified in § 250.308 (relating to soil to groundwater pathway numeric values).

(f) In addition to the requirements in this section, the MSCs are further limited by solubility as identified in Appendix A, Table 5. The solubility limits are derived from the references in subsection (g), which are keyed to the numbers in Table 5. The following procedure was used to determine the appropriate solubility value for each regulated substance: where multiple sources are cited in Table 5, the value for the solubility limit is the median of the values in the indicated references.

(1) Using the hierarchy established in subsection (g), the first two references were consulted. If the solubility values agreed within 5%, the selected value is the lower of the two values.

(2) If the values in step (1) did not agree within 5%, the next references in order were consulted until two values that did agree within 5% were found. The selected value is then the median of all the values consulted.

(3) If none of the values in all of the references in subsection (g) agreed within 5%, the selected value is the median of all values in all references.

(g) The references referred to in subsection (f) are:

(1) Lide, D. R., ed. 1996. CRC Handbook of Chemistry and Physics, 77th Edition. CRC Press.

(2) Budavari, S., ed. 1996. The Merck Index, 12th Ed. Merck and Co.

(3) Perry, R. H., et al. 1997. Perry’s Chemical Engineer’s Handbook, 7th ed. McGraw-Hill, New York.

(4) Howard, P. H. 1991. Handbook of Environmental Fate and Exposure Data for Organic Chemicals. Vol. III Pesticides, Lewis Publishers.

(5) Verschueren, K. 1977, Handbook of Environmental Data on Organic Chemicals, Van Nostrand Reinhold.

(6) MacKay, D., et al. 1997, Illustrated Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals, 5 Volumes. Lewis Publishers, New York.

(7) Montgomery, J. H. 1991, Groundwater Chemicals Desk Reference, Vol. II. Lewis Publishers and Montgomery, J. H., and L. M. Welkom. 1990, Groundwater Chemicals Desk Reference Vol I, Louis Publishers.

(8) Milne, G.W.A., ed. 1995, CRC Handbook of Pesticides, CRC Press, Inc.

(9) National Library of Medicine (Grateful Med), Hazardous Substances Databank.

(10) EPA. 1994, Superfund Chemical Data Matrix. Office of Solid Waste and Emergency Response, EPA 540-R-94-009.

(11) Mabey, et al. 1982, Aquatic Fate Process Data for Organic Priority Pollutants, SRI. EPA Contract Nos. 68-01-3867, 68-03-2981.

The provisions of this § 250.304 amended November 23, 2001, effective November 24, 2001, 31 Pa.B. 6395; amended January 7, 2011, effective January 8, 2011, 41 Pa.B. 230. Immediately preceding text appears at serial pages (285766) to (285768).

Notation

Authority

The provisions of this § 250.304 amended under sections 104(a) and 303(a) of the Land Recycling and Environmental Remediation Standards Act (35 P. S. § § 6026.104(a) and 6026.303(a)).

Cross References

This section cited in 25 Pa. Code § 250.303 (relating to aquifer determination; current use and currently planned use of aquifer groundwater); 25 Pa. Code § 250.308 (relating to soil to groundwater pathway numeric values); 25 Pa. Code § 250.312 (relating to final report); 25 Pa. Code § 271.1 (relating to definitions); and 25 Pa. Code § 287.1 (relating to definitions).