Project Location: Shell Genes Northside, Tallahassee, FL
Client: Rhodes-Boone Partners LP
The site is an operating retail petroleum station selling unleaded gasoline. In April 1990, inventory reconciliation records indicated a release of approximately 900 gallons of unleaded gasoline due to a flex line failure attaching the tank pumps to the distribution lines. A Discharge Reporting Form (DRF) was submitted, and immediate response actions included emptying three underground storage tanks (USTs) and excavating 320 cubic yards of contaminated soil for off-site treatment.
Between 1992 and 1995, contamination assessment activities revealed elevated organic vapor analyzer (OVA) readings exceeding 1,000 ppm at 25 feet below land surface near the former USTs. In 1997, the site was converted into a convenience store, with four USTs removed and replaced by two new tanks. A total of 37 monitoring wells were installed, and groundwater sampling showed contaminant concentrations above Groundwater Cleanup Target Levels (GCTLs) both onsite and offsite, extending at least 800 feet from the site. Assessment ceased in 1995 due to legislative changes and did not resume until NOVA, formerly MAS Environmental, began work in 2016.
Beginning in 2016, NOVA, formerly MAS Environmental, conducted extensive environmental assessment and remediation activities. Groundwater sampling in December 2016 from 11 monitoring wells identified exceedances of GCTLs. In June 2017, two new deep wells were installed using sonic drilling at depths of 70 and 80 feet below land surface. In April 2018, an additional well (DW-32) was installed, and four wells were sampled, with exceedances found in two.
In September 2018, NOVA submitted a Pilot Test Plan, later revised under a new purchase order in October 2019. In early 2020, site surveys were conducted to assess monitoring wells, many of which were dry, obstructed, or inaccessible. In May 2020, 18 wells, including two deep wells, were sampled, with six showing exceedances of GCTLs. Continued contamination was confirmed in both shallow and deep groundwater zones.
In October 2020, ground-penetrating radar and metal detection were used to locate and tag wells, and three replacement wells were installed. In November 2020, 26 wells were sampled, with nine showing exceedances of GCTLs. Groundwater sampling in September 2022 included 21 wells, though several were inaccessible. Analytical results again identified nine wells with exceedances.
In January 2023, NOVA prepared a new Pilot Test Plan for Air Sparge and Soil Vacuum Extraction (AS/SVE). Pilot test wells were installed in August 2023, and a mobile AS/SVE system was tested. In November 2024, NOVA performed a chemical oxidizer injection pilot test. Baseline groundwater sampling from three wells showed exceedances of GCTLs and Natural Attenuation Default Concentrations (NADCs). A total of 1,000 gallons of Klozur® CR slurry was injected, and post-injection sampling in December 2024 showed decreases in petroleum constituents with supporting field measurements confirming oxidizer activity.
NOVA concluded that oxidizer injection is a viable remediation method and recommended a 10-foot radius of influence for full-scale design, phased implementation, quarterly sampling, and additional injections. Recommendations also included forensic analysis, installation of a new well, and evaluation of a nearby contaminated facility.
Services Provided: Environmental Consulting
