Remediation Status: Site closed

Why the technology was selected:
Due to the low contaminant concentrations present in groundwater, monitored natural attenuation was selected as the groundwater remedy. It was believed that contaminant source removal (excavation of contaminated soil and septic tank cleanout) would result in a drop in contaminant concentrations in groundwater and that groundwater remediation would not be necessary.

Next Steps:
A Site Rehabilitation Completion Report will be issued for the site.

Cost to Design and Implement:
All technologies: Design: $9,700 Implementation: $136,800

Why the technology was selected:
The decision was made to clean out the septic tank because PCE, TCE and cis 1,2-DCE were detected in a wastewater sample collected from the tank and most of the groundwater contaminant plume was located in the area under and downgradient of the drainfield. The decision was made to excavate soil because drycleaning operations had ceased in early 2005 and the building that formerly housed the drycleaning operation was accessible. Also, there is a shallow water table at the site and most of the contaminant mass was sorbed on an organic-rich sand at 3-4 ft BLS.

Date implemented:
November 2006.

Final remediation design:
Clean out septic tank. Excavate contaminated soil beneath facility floor slab and from area outside service door.

Results to date:
Approximately 1000 gallons of sludge/wastewater were vacuumed from the septic tank and hauled offsite for property disposal. The concrete floor was removed from the inside of the building and mini-excavator and mini-front end loader were used to first excavate a trench 3 feet wide by 5 feet deep along the southern and eastern extent of contamination and the trench was filled with flowable concrete (5-to-1 sand-to-cement mixture to stablize the building structure. After the flowable fill was allowed to cure overnight, the excavation inside the building continued. Approximately 65 tons of soil were removed from the area beneath the facility floor slab and the excavation was backfilled with clean fill and a new floor slab was poured. The soil excavation area outside the service door was approximately 6 feet by 6 feet. Contaminated soil was excavated to a depth of 5 ft BLS. Because of the presence of numerous utility lines, much of the soil had to be hand excavated. Approximately 68 tons of contaminated soil was excavated from this area and the area was backfilled with clean fill. Confirmatory soil sampling and groundwater monitoring have demonstrated that the site has met the No Further Action criteria (without institutional or engineering controls).

Next Steps:
A Site Rehabilitation Completion Report will be issued for the site.

Cost to Design and Implement:
All technologies: Design: $9,700 Implementation: $136,800