The Department of Environmental Protection (Department) has continually refined its guidance for chromium soil cleanup levels based upon changes and developments in the applicable science (Table 1).
Table 1. History of Chromium Soil Cleanup Levels in New Jersey
Initially the Department used a 100 milligram total chromium per kilogram of dry weight soil (mg total Cr/kg DW soil, equivalent to parts per million or ppm) action level prior to 1989. This action level was based on a multiple of the maximum New Jersey background total chromium soil concentrations derived from Rutgers University data and also took into account qualitative toxicological information.
The Department established subsequent guidance on a chromium cleanup level in 1989 with a value of 75 mg total Cr/kg DW soil to preclude allergic contact dermatitis (ACD) in more than 10 percent of a sensitized population. This number was based on the work of Bagdon (1989) and a risk assessment conducted for the Department by Environmental Science and Engineering, Inc. (NJDEP, 1989). Its initial application was site-specific for the chromate production waste contaminated sites in Hudson County. It is important to note that the USEPA does not use the ACD endpoint as a basis for determining the need to remediate a site.
The Department developed this guidance on the basis of a 10 milligrams of hexavalent chromium per kilogram of dry weight soil (mg Cr+6/kg DW soil) cleanup level. However, the lack in confidence of a hexavalent chromium (Cr+6) analytical method for soil caused the Department to rely on the use of total chromium data. Based on an analysis of the available data (NJDEP, 1989), the Department estimated that the 95 percentile of the sample distribution of the ratio between Cr+6 and total chromium in chromate ore waste residue was 0.14. Consequently, the target level of 75 mg total Cr/kg DW soil was not expected to result in a Cr+6 level greater than 10 mg Cr+6/kg DW soil in soil samples. Eventually this action level supplanted the earlier 100 mg total Cr/kg DW soil value for use statewide.
In 1993 the Department further refined the earlier guidance and began using the values of 10 mg Cr+6/kg DW soil and 500 milligrams of trivalent chromium per kilogram of dry weight soil (mg Cr+3/kg DW soil). The endpoint was ACD and based on the work of Bagdon and Hazen (1991). The Department's Division of Science and Research indicated that a 10 milligram Cr+6 per liter solution (mg Cr+6/l) would cause ACD in 10 percent of a sensitized population. Making a conservative assumption that all the Cr+6 was extractable, the Division of Science and Research determined that this was equivalent to 10 mg Cr+6/kg DW soil. The 500 mg Cr+3/kg DW soil number was based on information in Bagdon and Hazen (1991) that trivalent chromium (Cr+3) was less potent than Cr+6 by a factor of 50 relative to ACD. This guidance was in place until September 3, 1998.
Concurrent with this change was a shift in the Department's position on measuring hexavalent chromium directly. As a result of Department investigations, modifications in the analytical methodology were made. This along with greater experience in using the methodology increased the Department's confidence in measuring Cr+6 concentrations in soil directly. Consequently, the Department determined that the use of total chromium as a surrogate was no longer necessary.
Subsequent research, discussions with the responsible parties and other stakeholders, and the impact of recent legislation (Hazardous Discharge Site Remediation Act, N.J.S.A. 58:10B) have led the Department to consider changing the minimum elicitation threshold (MET) for ACD from 10 to 25 mg Cr+6/l. The Department has now completed it's evaluation of the human health study conducted by ChemRisk - - McLaren/Hart and James Nethercott, M.D. (1995), and the Department formally proposes to use 25 mg Cr+6/l as the MET.
Another development is that the Department no longer considers the conservative assumption of 100% extractability as necessarily appropriate based on its experience with chromium contamination and in particular the solid chromate production waste found in Hudson County. The Department intends to institute a protocol that will assess the extractability and therefore availability of Cr+6 in a fluid media. The specifics of the protocol are described below.
In response to information requests from the regulated community, the Department developed several draft basis and background documents to communicate the Department's current thinking on the chromium issues. The Department held an informal interested party review (IIPR) of these same documents in September 1995. As part of this outreach effort, a series of public meetings were held. These included meetings held at St. Aedan's School and St. Michael's Methodist Church in Jersey City. A meeting with interested environmental groups was also held as well as a meeting with the Hudson County chromium responsible parties (AlliedSignal, Inc.; PPG Industries, Inc.; and representatives of Occidental Chemical Corporation). The large response (from 12 separate entities totaling approximately 1,000 pages of written comments) generated by this IIPR caused the Department to further investigate many of the aspects of the chromium issues and in many cases revise the Department's original position. This document constitutes in part the Department's response to those comments.
In the past, much of the Department's attention has appeared to focus on the ACD endpoint. This is because the Department believed that the ACD related cleanup criterion would dictate where it was necessary to remediate. However, with the adjustment for extractability, it is likely that other human health endpoints such as cancer (air inhalation pathway) may determine the remediation goal. Of course ecological, ground water, and surface water impacts must also be evaluated when determining if remediation is required.
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