Risk-based site evaluation guidance

The Minnesota Pollution Control Agency has developed guidance outlining a risk-based approach to decision making during site investigation and remedy selection under the state's Superfund and Brownfields Programs. The Risk-Based Site Evaluation (RBSE) Manual provides a tiered process for making decisions based on an evaluation of risks to human health and the environment. MPCA staff with expertise in risk assessment, soil physics, hydrogeology, and remediation technologies have developed the following risk guidance.

The RBSE manual includes individual documents describing the process of site characterization, community involvement, evaluating the risk to human health and the environment posed at a site, and how to address that risk. Working drafts of the manual documents are maintained here.

What's new

October 2016: Draft SRV related documents

The MPCA’s VIC, RCRA and Superfund programs are seeking stakeholder input regarding the October 2016 draft SRV related documents listed above. Please submit your comments to SRVcomments.pca@state.mn.us by December 2, 2016.

Note: Some of the SRVs did change due to a change in the definition of a VOC based on EPA’s recommendation. This revision was completed to ensure we were both consistent with EPA and with our intrusion screening values (ISVs) used to investigate vapor intrusion sites. Background threshold values (BTVs) for arsenic and BaP have not changed. All changes are shown on the “Comparisons” tab in the SRV Spreadsheet.

The MPCA will be hosting a stakeholder meeting on October 31, 2016. Details regarding this meeting will be announced later in October.

Timeline for SRV revisions

June 2015 SRV stakeholder meeting presentations

September 2015 community stakeholder information session

October 2016 SRV related document stakeholder meeting presentations

September 26, 2014: Interim Policy on Implementing MDH’s Revised cPAH Guidance

Background

The Minnesota Department of Health’s (MDH) “Guidance for Evaluating the Cancer Potency of Polycyclic Aromatic Hydrocarbon (PAH) Mixtures in Environmental Samples” is available at the hyperlink below.

This guidance recommends a revised method to evaluate carcinogenic PAHs (cPAHs) using relative potency factors (RPF) instead of potency equivalence factors (PEF) and an alternative surrogate mixture method using 7X the concentration of benzo[a]pyrene (BaP). Six new cPAHs have been added to the list to analyze and ten have been removed.   

MPCA Interim Policy

Although it is MPCA's practice to adopt MDH's guidance, since laboratory analytical methods are not available to analyze the six additional cPAH compounds added to the RPF list, it is not feasible at this time. MPCA and MDH are working together to develop analytical methods for the new cPAH compounds. Once analytical methods have been established MPCA will re-evaluate the feasibility of implementing this guidance. Until then, MPCA will continue to use the PEF method to evaluate human health risks from cPAHs. 

September 26, 2014: Interim policy on implementing new lead blood level

Summary

  • 5 µg/dL is currently recommended by CDC and MDH as the blood lead level that triggers the need for medical and prevention actions when observed in a child’s blood sample.
  • 10 µg/dL is currently recommended by EPA to be used in their lead models to determine a soil reference value (SRV) for lead. EPA is revising some of the parameters used in their models based on new scientific data; those revisions will include the incorporation of CDC’s new blood lead level. Based on EPA’s initial assessment of the revisions, the SRVs are not expected to change significantly. 
  • The use of 10 µg/dL in EPA’s models does not conflict with the use of 5 µg/dL for medical and prevention actions, given the different purposes of these uses. 
  • To maintain program consistency, MPCA will continue to use the current EPA lead models and EPA-recommended lead blood level to derive SRVs until new versions of the EPA models are available.

Background

On January 4, 2012, the Center for Disease Control’s (CDC) Advisory Committee for Childhood Lead Poisoning Prevention (ACCLPP) released a report regarding children blood lead levels (BLL). ACCLPP recommended eliminating the use of the term “blood lead level of concern” and replace it with the term “blood lead reference level” since they determined there was no safe level of lead exposure. They also recommended the use of a blood lead reference level of 5 µg/dL (opposed to the previously recommended 10 µg/dL) in children to trigger medical and prevention actions. 

The Minnesota Lead Poisoning Prevention Act (Minnesota Statutes 144.9501-144.9512) is intended to prevent and decrease elevated blood lead levels of children and pregnant women. This rule provides blood lead levels that trigger certain medical and prevention actions and a time frame to take those actions. On April 16, 2014, the Commissioner of Health (MDH) revised the definition of an elevated blood lead level from 10 µg/dL to 5 µg/dL based on CDC’s findings.

This Minnesota statute also states that once an elevated blood lead level of a child or pregnant women is established at a residence, bare soil at the residence or a play area is considered contaminated if it contains lead equal to or above 100 mg/kg. This value is based on an earlier version of EPA’s lead model, is not intended to be used as a soil cleanup value and is not used by MDH as a soil cleanup value. If soils with lead above 100 mg/kg are observed at a residence by MDH, action is taken to cover that soil to eliminate exposure.

MPCA uses EPA’s child lead model to derive the residential lead soil reference value (SRV) and adult lead model to derive the industrial lead SRV. In some cases, MPCA also allows site specific lead modeling to derive a site specific lead SRV. In these cases MPCA may use professional judgment to determine a “do not exceed” level. 

On March 15, 2013, MPCA requested guidance from MDH regarding the most appropriate lead blood level to use in deriving statewide and site specific SRVs.

MDH guidance

MDH responded to MPCA’s request on March 25, 2013, stating that they recommended the use of CDC’s lead reference level of 5 µg/dL for the purpose of modeling exposure levels and pathways and developing cleanup guidance. This advice was not given to pertain specifically to EPA’s lead models. MDH did not evaluate EPA’s lead models or the exposure parameters they use to calculate SRVs. 

Additional information from EPA

EPA’s Superfund program announced that they did not recommend using CDC’s new 5 µg/dL blood lead level in the current version of their child lead model (Integrated Exposure Uptake Biokinetic or IEUBK) or their Adult Lead Model. They will be releasing a new version of the child lead model (IEUBK) that contains revised exposure parameters based on new scientific data in addition to CDC’s new blood lead level. Preliminary results from EPA’s revised model show that residential lead SRVs may not decrease and if they do decrease that decrease will not be as significant as it would be using the current model and the new CDC lead blood level. At this time it is not clear what EPA will advise regarding the Adult Lead Model or how it may impact the industrial SRV. 

MPCA policy decision

Lead SRVs are currently 300 mg/kg for Residential and 700 mg/kg for Industrial both derived using EPA’s lead models and a blood lead level of 10 µg/dL. MPCA will continue to use 10 µg/dL to derive lead SRVs and for site specific lead modeling. However, responsible parties must be aware that MPCA will be adopting the new lead blood level for the residential lead SRV once EPA releases the new version of the child lead model (IEUBK). MPCA will also be adopting any changes EPA recommends regarding the Adult Lead Model that may result in a change in the industrial SRV once those are released. Responsible parties may be required to perform additional lead clean up based on these changes.

The use of 10 µg/dL in EPA’s model does not conflict with the use of 5 µg/dL for medical and prevention actions. A model estimates values based on assumptions (exposure parameters) that are put into the model. If these assumptions are not reasonable the value the model produces will also not be reasonable. With EPA’s version currently available for use it is not reasonable to use a blood lead level of 5 µg/dL. Per CDC and MDH it is reasonable to use a 5 µg/dL blood lead level from an actual blood sample to trigger the need for medical and prevention actions.

Current RBSE manual documents