Plumes under adjacent properties typically require additional logistics, permissions, and often increase the time and effort to complete remediation. In worst case scenarios, these properties can completely prohibit remediation offsite. Vertical well point arrays lead to poor coverage around buildings and roads and require unwanted trenching. Large horizontal remediation wells provide options for these sites, but installation has typically been too expensive for smaller sites. The Shell Florida Hospital Site utilized compact nested horizontal wells to perform biosparging under three adjacent properties funded by the PRP program. The more cost-effective remedy was applied to a hydrocarbon plume that was approximately 16,600 sf and 120 ft in length. Directional drilling allowed seamless and easy installation from a more convenient location which traversed under two adjacent properties with significant site structures, and one property with a resistant owner. Installation incorporated 16 well screens to provide maximum control utilizing two bores and was completed quickly in only five days. After the December 2021 startup, biosparge system influence was observed within the first month and excellent reductions as reported in laboratory data to below GCTLs within the first quarter at key monitoring wells. The system continued to operate until April 2024, when system decommissioning and Natural Attenuation Monitoring (NAM) Only was approved by the regulatory authority. The obstacles, benefits, specifics of installation, and results will be discussed in this presentation.
