Client Profile
Property and underground storage tank (UST) owner at an active historical retail fueling station, convenience store, and automotive service station
Project Profile
Two petroleum product releases were identified at an active fueling station property. One unleaded gasoline release was identified during a PADEP compliance inspection performed following vapor intrusion complaints from neighboring property owners. Soil and bedrock aquifer groundwater was impacted due to a mechanical failure of a product line. Also, light non-aqueous phase liquid (LNAPL) was encountered in the bedrock aquifer groundwater. Forensic analysis of the LNAPL determined that the LNAPL remained from a tetraethyl lead (TEL) dominant gasoline release that occurred prior to 1985. The leaded gasoline release originated from an unknown source and was unrelated to the more recent release of unleaded gasoline. The two releases applicable to this site are addressed under the Pennsylvania Land Recycling and Remediation Standards Act (Act 2), but with separate regulations issued pursuant to the Act 2 legislation: the unleaded gasoline release (25 PA Code §245) and the leaded gasoline release (25 PA Code §250).
Letterle performed an environmental site characterization to assess the extent of soil and groundwater quality impact in response to both known releases on-site to the extent practical to date. The site-specific standard (SSS) was selected for soil and groundwater. A risk assessment (RA) was conducted with the assumption that institutional controls would be implemented to eliminate several exposure pathways associated with both known releases at the site. The RA concluded that upon implementation of the proposed institutional/engineering controls, there would be no current or future unacceptable risk to ecological or human health receptors related to both releases.
Project Summary
An initial assessment and emergency mitigative measures were completed inclusive of installation of multiple sewer line running traps (to mitigate vapors), vapor intrusion screening, indoor air sampling for multiple off-site properties, and extensive preferential pathway evaluations of sanitary and storm sewer networks and other underground utility lines. Results suggest that the sanitary and storm sewer networks are interconnected, possibly due to breakage/deterioration of the lines. LNAPL was manually recovered via bailing techniques from site monitoring wells as an interim remedial action. Subsequently, recovery events were discontinued, and LNAPL thickness remained stable or decreased in site monitoring wells over time.
The site characterization activities included a sensitive receptor survey, soil boring advancement, soil sample collection, monitoring well installations, groundwater monitoring, sub-slab vapor pin installations, aquifer characterization (slug testing), and laboratory analysis of soil, groundwater, stream surface water, LNAPL, indoor air, and sub-slab vapor samples. Downgradient stream characterization for RA purposes included calculating stream velocity, cross-sectional area, and discharge rate. Geophysical surveys utilizing very low frequency (VLF) electromagnetic and ground penetrating radar (GPR) / time-domain electromagnetic (EM) techniques were conducted to assess for potential bedrock fractures and anomalous areas (e.g., potential unknown USTs), respectively. A comprehensive conceptual site model was produced. Fate and transport analysis, which was completed using Visual MODFLOW for the impacted bedrock aquifer, indicated which parameter plumes would migrate off-site. A detailed assessment of preferential pathways in the RA report ultimately determined that concentrations in the sanitary and storm sewer networks are not site-related. The risks and hazard indices were calculated in the RA for multiple on-site and off-site receptors. The total risks and hazard indices were calculated to be below the benchmark values of 1×10-4 and 1.0, respectively for all evaluated on-site and off-site receptors.
Project Results
A Remedial Action Completion Report requesting a Release of Liability for the unleaded gasoline at the site will be submitted as per 25 PA Code §245. A Final Report requesting a Release of Liability for the TEL dominant leaded gasoline at the site will be submitted as per 25 PA Code §250. Identified future exposure pathways will be eliminated via an Environmental Covenant (EC) that is intended to be comprehensive in nature. The EC will state that groundwater may not be used as a water supply for any purpose now or in the future and will require vapor intrusion mitigation and/or assessment measures for a future building that may be constructed on-site. The implementation of the EC will render the potential exposure pathways incomplete and will not require additional remedial actions.
