In May 2017, the Wisconsin Department of Natural Resources (DNR) proposed new guidance for assessing residual contamination levels (RCLs) for select carcinogenic polycyclic aromatic hydrocarbons (cPAHs) in soil. The proposed guidance includes a modified spreadsheet that incorporates information from a reassessment of DNR’s soil standard calculation process conducted by the Wisconsin Department of Health Services (DHS).
As of this writing, DNR is reviewing public comments on the proposed guidance, RR-079 "Calculating Soil RCLs for PAHs Wis, Admin. Code § 722.11(1)".
Here are highlights of the proposed guidance.
DNR Proposed Guidance on Seven cPAHs
There are hundreds of PAH compounds in our environment. Commonly released through automobile exhaust, industrial emissions, and smoke from burning wood, charcoal, tobacco, and other organic materials, PAHs can be found in our air, soils and water.
One particular cPAH – benzo[a]pyrene – is a primary driver for soil remediation work at many redevelopment sites. Six other cPAHs have toxicity that is assessed relative to benzo[a]pyrene.
DNR’s proposed guidance presents an alternate methodology for assessing seven cPAHs:
EPA Exposure and Toxicity Updates
In March 2017, DNR updated the RCL spreadsheet used to assess soil contamination to reflect updated information from Environmental Protection Agency (EPA). Updated exposure assumptions used to calculate residual contamination levels (RCLs) included an increase in the average body size of adults and children (weight and surface area) and a decrease in the average length of time people live in the same residence. The incorporation of the updated exposure assumptions resulted in an increase of approximately 10 percent for all compounds with direct contact RCLs.
EPA also completed a reassessment in the relative toxicity value of benzo[a]pyrene, resulting in a determination that this compound is not as toxic as previously calculated. As a result of EPA’s relative toxicity value recalculation, DNR’s RCL for nonindustrial direct contact for benzo[a]pyrene increased from 15 ppb to 115 ppb.
DHS Concludes cPAHs May Be Assessed Together
The guidance DNR proposed in May 2017 incorporates an additional modification to the assessment process for seven cPAHs. In 2016, at the request of DNR, the DHS conducted a reassessment of the DNR’s RCLs for PAHs.
DHS concluded that it is reasonable and protective of public health to assess cPAHs in soil solely using a cumulative risk approach. A cumulative approach sums the individual excess cancer risks of the cPAHs present in a soil sample and compares the summed value to a threshold for acceptable cumulative excess cancer risk, such as 1-in-100,000 (i.e., 1x10-5). The rationale for the conclusion regarding the cumulative approach is that PAHs only occur in the environment in mixtures and have similarities in their modes of carcinogenic action.
Proposed Alternative Risk-based Assessment Spreadsheet
DNR’s current soil assessment and clean up criteria appear in chapter NR 720, Wis. Admin. Code section NR 720.12 contains procedures for assessing the risks of individual compounds and the cumulative risks to public health. Assessment of both the individual compound and cumulative risks are required under Section NR 720.12.
Section NR 722.11(1)(b) allows DNR to grant approval for other methods of risk assessment under certain circumstances. Based on the conclusions of the DHS reassessment, the proposed guidance offers the alternative of using a modified RCL spreadsheet that evaluates only the cumulative risk of seven cPAHs. Asessment of cPAHs on an individual compound specific basis would not be required using this cumulative approach.
Each soil has had its own history. Like a river, a mountain, a forest, or any natural thing, its present condition is due to the influences of many things and events of the past. Charles Kellogg, The Soils That Support Us, 1956
The alternative cumulative spreadsheet may be used if attaining individual direct contact RCLs is not practicable. The goal of the alternative cumulative spreadsheet is to maintain protection of public health while allowing assessment methods that take into account the most current EPA and DHS information on RCLs and human exposure.
Other Risk Assessment Procedures Remain Unchanged
The proposed guidance addresses only the seven designated cPAHs in nonindustrial settings. At this time, DNR has not proposed to change:
- The overall cumulative risk assessment required for all carcinogenic, direct contact risk compounds
- The assessment procedures for other cPAHs (e.g., naphthalene and 1-methylnaphthalene)
- The RCLs for Industrial direct contact
- Groundwater protective RCLs
The Remediation and Redevelopment program will be posting the final guidance once it is approved. The alternative spreadsheet and recommendations for how to use it are currently being finalized.
If approved, the proposed alternative assessment may facilitate redevelopment of sites with lower levels of cPAHs for nonindustrial uses. Such sites are often found in urban areas such as Milwaukee, Madison, and Green Bay.
Background Study of Soils in Milwaukee
A forthcoming study is currently underway to further define actual, infield background levels of PAHs. The study is being conducted by DNR in conjunction with the UW Extension Service. More than 300 soil samples will be collected at sites in Milwaukee County parks in 2017, and samples will be collected in areas that have not been disturbed since at least 1937.
The study results will help to assess atmospheric deposition of PAH compounds and may provide additional data to guide next steps in assessing PAH contamination in soils.
To receive emails from the DNR’s Remediation and Redevelopment program, including updates on the proposed guidance and the background study, sign up on the DNR’s website.