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SRP Community RelationsSite Information ProgramHudson Chromate Project Basis & BackgroundPart 1

 

Summary of the Basis and Background of the Soil Cleanup Criteria for Triavalent and Hexavalent Chromium (September 19988)
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I. Executive Summary

NEW JERSEY DEPARTMENT OF ENVIRONMENTAL PROTECTION
SITE REMEDIATION PROGRAM
SEPTEMBER 18, 1998

I. Executive Summary

In response to requests by the regulated community as well as interested citizens in Hudson County, The New Jersey Department of Environmental Protection (Department) prepared several draft documents concerning suggested soil cleanup criteria for trivalent and hexavalent chromium. These documents were made available to the regulated community as well as other stakeholders as part of an informal interested party review in September 1995. In addition, a several of informal public meetings were held in Hudson County along with informal meetings with interested environmental groups and Hudson County chromium responsible parties. As a result of this process, the Department received approximately 1,000 pages of written comments from twelve (12) interested parties.

The Department has reviewed the comments from the interested party review, conducted additional research and reviewed additional scientific literature in an effort to develop reasonable, clear and predictable soil cleanup criteria for the remediation of chromium contaminated sites in New Jersey. This effort has culminated in a series of soil cleanup criteria for trivalent and hexavalent chromium. This document summarizes the basis and background of the development of these criteria. The Department will begin a formal rulemaking effort for the development of soil cleanup standards in 1999. The soil cleanup criteria for chromium discussed in this document will be part of the rulemaking effort. The Department will use the new chromium soil cleanup criteria as guidance in the interim.

Because of the technical nature of the text, a glossary of terms has been provided as Attachment 1 to facilitate the reading of this document.

Whenever a site is investigated or remediated, there are two options available with respect to soil cleanup criteria. One option is to use the already available generic numbers that apply to all sites within New Jersey. The other option is to develop an alternative number that incorporates site-specific conditions and information or recent scientific developments. Such a number is more formally known as an Alternative Remediation Standard and is in accordance with Public Law 1997, Chapter 278 (Brownfield and Contaminated Site Remediation Act, N.J.S.A. 58:10B). These two options existed for the current chromium soil cleanup criteria and will exist for the new chromium soil cleanup criteria.

Soil cleanup criteria have been developed for two (2) valence states of chromium: trivalent chromium (Cr+3) and hexavalent chromium (Cr+6). Different criteria have been established due to the differing toxicity and solubility between the two valence states.

From 1993 until September 3, 1998 the soil cleanup criterion for Cr+3 had been 500 parts per million (ppm or mg/kg) and had been based on an allergic contact dermatitis health endpoint. As this health condition results from short-term or acute exposures to chromium, the same criterion was applicable to both residential and nonresidential land use scenarios. On September 3, 1998, the Department proposed to delete this criterion and establish a soil cleanup criterion based on a soil ingestion exposure pathway using United States Environmental Protection Agency (USEPA) exposure pathway models, exposure assumptions, and toxicology data. This resulted in a new residential soil cleanup criterion of 78,000 ppm for Cr+3. Using USEPA models and assumptions, there is no unacceptable risk from Cr+3 exposure under the nonresidential land use scenario. As such, the Department chose not to regulate Cr+3 under a nonresidential land use scenario.

Simultaneously with the Department's proposal of this soil cleanup criterion, the USEPA toxicology database known as the Integrated Risk Information System (IRIS) was modified with respect to Cr+3. Recalculation of the Department's proposed 78,000 ppm Cr+3 criterion using the new USEPA toxicology data yields a value of 120,000 ppm Cr+3. The Department now proposes to use this value as the Cr+3 soil cleanup criterion.

Currently, only toxicological information for Cr+3 via the ingestion pathway is found IRIS. Therefore, the Department is only proposing a soil cleanup criterion for Cr+3 based on the soil ingestion exposure pathway. It is important to note that the 120,000 ppm Cr+3 criterion for the residential land use scenario and the finding of no unacceptable risk from Cr+3 exposure under a nonresidential land use scenario are only applicable to insoluble forms of Cr+3.

The soil cleanup criterion for Cr+6 of 10 ppm was also established in 1993 and was also based on an allergic contact dermatitis health endpoint. As this health condition results from short-term or acute exposures to chromium, the same criterion would be applicable to both residential and nonresidential land use scenarios. On September 3, 1998, the Department proposed to retain soil cleanup criteria based on this exposure pathway; however, the new generic soil cleanup criterion was expected to increase. In addition, the Department also proposed to establish Cr+6 soil cleanup criteria for the following exposure pathways:

  • Soil ingestion
  • Inhalation of soil particles
  • Impact of soil contamination on ground water quality

For the soil ingestion and inhalation soil exposure pathways, the Department again proposed to establish soil cleanup criteria using USEPA exposure pathway models, toxicology data, and exposure assumptions (substituting New Jersey specific data where applicable). As the existing toxicology data for the ingestion and inhalation exposure pathways were based on long-term or chronic exposures to Cr+6, different criteria could be developed for residential and nonresidential land use scenarios.

Again concurrent with the Department's proposal of the above, the USEPA modified the IRIS database which affected inputs potentially used in developing soil cleanup criteria for both the soil ingestion and soil inhalation pathways. The Department had proposed on September 3, 1998 to use as Cr+6 criteria 390 ppm and 10,000 ppm for the soil ingestion pathway under the residential and nonresidential land use scenarios, respectively. The Department has recalculated the affected criteria and determined that the Cr+6 criteria for the soil ingestion pathway should be 240 ppm and 6,100 ppm for the residential and nonresidential land use scenarios, respectively. Comparison of the derived values using the new IRIS data led to the conclusion that the preliminary value of 20 ppm Cr+6 originally proposed for the inhalation pathway leading to a cancer health endpoint on September 3, 1998 would still be the most protective for a nonresidential setting. Regarding the residential land use scenario, the Department still proposes to use the Cr+6 USEPA soil screening level (USEPA 1996) for the inhalation pathway. Consequently, the Department is not altering its September 3, 1998 proposal for establishing criteria with respect to the Cr+6 inhalation pathway.

For the impact to ground water exposure pathway, the Department proposed on September 3, 1998 and will continue to propose the use of USEPA exposure pathway models and the Department ground water quality standard for Cr+6 to develop a site-specific cleanup criterion. Due to highly variable soil conditions throughout the State, it is not possible at this time to develop a generic soil impact to ground water cleanup criterion for Cr+6. As the ground water quality standard for Cr+6 is the same throughout the state, different soil cleanup criteria cannot be developed for residential and nonresidential land use scenarios.

The proposed soil cleanup criteria for Cr+6 for the various exposure pathways follow. Please note that the numbers provided below are either derived by the USEPA or calculated using standard USEPA equations and assumptions.

Exposure Pathway Residential Nonresidential Comments
Ingestion 240 ppm 6,100 ppm  
Inhalation 270 ppm 20 ppm
Preliminary
1,2
Impact to Ground Water Site Specific 3,4
Allergic Contact Dermatitis Under Development 1,3

1 Exposure models and assumptions have been established or are being finalized; development of a generic soil cleanup criterion is currently being conducted.

2

Due to the effects of vehicular traffic, the nonresidential land use scenario cleanup criterion will be lower than the residential land use scenario cleanup criterion. The nonresidential land use cleanup criterion is preliminary and presumes a site size of 2 acres.

3

Soil cleanup criterion will be the same for both residential and nonresidential land use scenarios.

4

Due to highly variable soil conditions throughout the State, it is not possible at this time to develop a generic soil impact to ground water cleanup criterion for Cr+6.

The Department is recommending the release of these cleanup levels in the form of Soil Cleanup Criteria guidance prior to a rule making proposal as soil cleanup standards. Please note that all the soil cleanup numbers presently being used in site remediation are "guidance" and are awaiting formal adoption via the rulemaking process. The Department will begin a formal rulemaking effort for the development of soil cleanup standards in 1999. In addition, the Department will release these new criteria in response to the large number of written requests to both the Department and the Governor's Office to finalize soil cleanup numbers for chromium.

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