In our April 28th blog, So Now…How Clean is Clean?, we “introduced” the changes to Michigan’s Cleanup Criteria under Part 201 of Public Act 451. In that blog, we mentioned that the vapor pathway received considerable attention. We now have some additional details regarding evaluation of the vapor pathway under Part 201.
In this blog, I will touch on some of the points discussed at a recent conference where Abigail Hendershott of the Michigan Department of Environmental Quality (MDEQ) provided some insight. Here is a link to her PowerPoint presentation titled “Vapor Intrusion Emerging Concepts.”
Tiered Approach to Vapor Assessment
Going back to our April 28th blog, we mentioned that there are 30 pages (and more than 50 equations) in the new criteria package related to the vapor pathway. Also, as mentioned several times by the MDEQ Remediation and Redevelopment Chief, Bob Wagner, future “disputes” regarding vapor results at your site will have to focus on the values used in the criteria calculation algorithms – that is, focus on the site-specific inputs in the equations for the new tiered vapor intrusion (VI) approach to “how clean is clean.”
- VI Tier 1 – Generic Screening Levels: These criteria are generated using very conservative assumptions (sandy soil, basement present, groundwater in contact with a basement/sub slab, etc.). This is, basically, the traditional Johnson-Ettinger model approach, and if you do not exceed these screening levels, you are “clean.”
- VI Tier 2 – Generic Residential Criteria Facility Specific Data: These criteria are calculated based on more facility-specific data (soil type, depth to groundwater, etc.). In Tier 2, you will be able to begin to tailor the VI assessment with the collection of site-specific data to support the vapor assessment. If the vapor data are less than the calculated Tier 2 criteria, the site is considered clean, regardless of land use.
Summa Canisters set up on a project site to collect a sub slab sample and a duplicate in the background and an indoor air sample in the foreground (Photo Credit: Dragun Corporation).
- VI Tier 3A – Facility-Specific Land Use & Building Specs: Under the Tier 3A assessment, the MDEQ will require information such as land use, building type, foundation type, plus the same information that is requested in a Tier 2 assessment. Since land uses other than residential generally have less conservative exposure assumptions and building-specific characteristics may prohibit VI, the calculated Tier 3A criteria may create another off ramp for the VI pathway evaluation.
- VI Tier 3B – Site-Specific Data: In the MDEQ presentation, there wasn’t much discussion on Tier 3B assessments. As I understood, a Tier 3B assessment will require the same as Tier 3A above, but it will also require information relating to site-specific controls and mitigation measures that could limit VI.
Eventually, the MDEQ will have an on-line calculator that will allow you to enter the data that you gather, and it will “spit out” a result (i.e., a Tier 2 screening level) instantaneously. However, based on what we heard, the MDEQ is not yet comfortable in releasing this calculator.
The evaluation of the VI pathway has been a consideration in the past, but it is now becoming a mandatory evaluation that will impact subsurface investigations (including Phase II Environmental Site Assessments), Due Care Evaluations, and Response Action Plans.
Finally, we’ll mention the MDEQ has scheduled several “Public Rollout Meetings” to explain the new Part 201 Rules. These meetings began on May 31st and complete on July 13th.
As always, if you have any questions or need assistance, please feel free to contact me (jbolin@dragun.com) at 248-932-0228, Ext 125.