Source Removal at a Florida Fuel Station

In February 2017, our team at Advanced Environmental Technologies(AET) initiated a project at a fuel station located in Quincy, FL, aimed at the replacement of a submersible transfer pump (STP) sump for the 15,000-gallon regular unleaded underground storage tank (UST). While executing the sump replacement, we encountered petroleum-impacted soil, prompting closure assessment sampling. Analysis revealed concentrations of benzene exceeding the 0.007 mg/kg Soil Cleanup Target Level (SCTL), leading to the submission of a Discharge Reporting Form (DRF) to the Florida Department of Environmental Protection (FDEP). Consequently, we excavated 45.75 tons of petroleum-impacted soil surrounding the sump.

Following FDEP approval, our team conducted soil borings around the UST utilizing a DPT drill rig. Soil borings were advanced to depths ranging between 20- to 45-feet below surface level. Analysis of the samples revealed no soil contamination in the unsaturated zone. The soil lithology comprised gray to orange stiff clay down to approximately 34-feet below surface level, transitioning to clay with sand stringers, with groundwater encountered at about 37-feet below surface. Subsequently, in April, we installed three monitoring wells and conducted groundwater sampling, all of which reported contaminant concentrations below detection limits or respective Guideline Cleanup Target Levels (GCTLs).

Returning to the site in September 2018, we advanced a soil boring adjacent to the previous sample location, with laboratory results showing levels below detection limits for all constituents analyzed. However, in October 2018, a soil sample from 2-feet below surface level exhibited benzene above the SCTL. Further analysis using Synthetic Precipitation Leaching Procedure (SPLP) indicated potential leachability to groundwater, prompting the submission of a Remedial Action Plan (RAP) to the FDEP.

Upon RAP approval in June 2019, we removed approximately 5.42 tons of petroleum-impacted soils from an area measuring 5-feet by 8-feet on the north side of the UST. Utilizing a vacuum truck, we excavated to 3-feet below the surface to minimize UST damage, with soil samples collected for screening. Post-excavation, the area was treated with Petro-Clean by Alabaster Corporation™ which contains a proprietary blend of pH neutral surfactants and several strains of safe, non-pathogenic micro-organisms. The excavation area was then backfilled with clean sandy soil, followed by repaving with 8-inches of 4,000-psi fiber mesh concrete.

All onsite vapor readings were below 100-ppm, with laboratory soil samples being collected for BTEXD+MTBE analysis from each sidewall at approximately 1.5-feet below surface level and from 3-feet below surface level at the bottom of the excavation area. Laboratory data indicated a benzene concentration of 0.011 mg/kg in the sample collected from the north side wall. The sample was subsequently analyzed using SPLP, in which a benzene concentration of 1.4 µg/L was detected. All other concentrations of were either below laboratory detection limits, or below their respective SCTLs. Utilizing FDEP guidelines, the November 2011 Rounding Analytical Data for Site Rehabilitation Completion Memorandum, the benzene concentration of 1.4 µg/L rounded down to 1 µg/L, satisfying the benzene GCTL.

Subsequently, the FDEP granted No Further Action (NFA) status and issued a Site Rehabilitation Completion Order (SRCO) in February 2020, with proper abandonment of monitoring wells completed by March 2020.