PEM staff were tasked to perform a Screening Level Human Health Risk Assessment (SLHHRA) for three Installation Restoration (IR) sites at Marine Corps Air Ground Combat Center (MCAGCC) Twentynine Palms, CA for the purpose of fulfilling requirements for site closure. The three sites contained residual petroleum and metals contaminants as a result of former airfield activities. Contaminants of concern included volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), and select metals.
The screening process involved compiling all historical soil data for the three sites and applying updated risk-based screening values in the assessment. In addition, a conceptual site model (CSM) was developed for each site to depict the potential exposure pathways. The CSM displays the relationship between the sources of contamination that were released into the outdoor environment at the primary source area and the potential for direct (ingestion, dermal absorption, or inhalation of particulates) or indirect (inhalation of vapors released from the soil) exposure by individuals accessing or working at the site. During the screening process, background concentrations for naturally-occurring metals such as arsenic, chromium, and lead were compared with detected concentrations to determine whether they were representative of background.
Results from the SLHHRA resulted in a NFA determination from the regulatory agencies for one of the sites.
RESULTED IN A NFA DETERMINATION FOR ONE SITE