This question was sent to PADEP who provided the following response:
DEP establishes Act 2 Statewide health standard cleanup values for soil and groundwater, known as Medium-Specific Concentrations (MSCs), using a variety of risk- and health-based methods. For instance, many groundwater MSCs are adopted from U.S. EPA’s drinking water standards. Other MSCs are calculated by DEP to protect human health at acceptable risk levels (e.g., a cancer risk of no more than 1 in 100,000).
For site-specific standard cleanups, remediators may develop a risk assessment that uses data specific to the site, and therefore it may differ from attainment of the Statewide health standard MSCs. Risk assessments must demonstrate acceptable cumulative risks, meaning that health effects of all contaminants from both soil and groundwater and through all exposure pathways must be examined. Risk assessments must also consider all potential human receptors (e.g., workers and contractors, as well as nearby residents if contamination has migrated to homes, parks, etc.).
An alternative approach with the site-specific standard is known as “pathway elimination,” meaning that the remediator implements measures to prevent people from being exposed to contamination. These measures commonly include constructing a cap at the surface so people won’t touch or ingest contaminated soil and dust, prohibiting groundwater use, and sometimes installing systems to mitigate vapor intrusion in buildings. The determination that pathway elimination remedies are “safe” relies in part on the remediator following best practices and standard guidance. DEP reviews plans and specifications for the work (submitted in an Act 2 cleanup plan), DEP reviews documentation for the remedy completion (submitted in an Act 2 final report), and DEP inspects the installation work and subsequent maintenance of the remedy. In addition, DEP oversees the execution of an environmental covenant recorded on the property deed to ensure future maintenance of the remedies. In some cases, testing is also performed to verify that the remedy is effective.
Lastly, while the focus of Act 2 cleanups is on the protection of human health, they must also address potential ecological exposures. Contamination that affects certain sensitive ecological receptors, such as threatened and endangered species, must be addressed in the cleanup. This can also be accomplished through a risk assessment or remedial measures.