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Envirocon was awarded a competitively bid contract for the remediation of 1.9 miles of the Middle Reach of Chattanooga Creek. The Chattanooga Creek was contaminated with coal tar from a former coking facility. This project was performed for a PRP Group as part of a Superfund site remediation program.
Envirocon and Barge Waggoner Sumner Cannon, Inc. (BWSC) formed an integrated team to provide turn-key design and remedial action services for the removal of impacted sediments from the creek. BWSC, with assistance from Envirocon, performed the remedial design during the first phase of the project.
The second phase of the project included all remedial activities for the creek. Envirocon's approach for diversion of the creek, which is 40- to 70-feet wide, included a series of pumps and piping systems to divert the main channel flow and to maintain the footprint of the diverted creek bed from minor groundwater and run-on infiltration. The creek was being dammed using earthen dams to stop the flow of main channel. Damming the creek was performed in sections or "reaches" providing two dewatered reaches at one time, thus allowing for optimal use of the equipment and work area. By drying two areas at once, the process provided a dried area to proceed with excavation while the pumping system was reconfigured allowing excavation to continue without stoppage.
Approximately 108,000 tons of coal tar sediments were excavated from the 1.9-mile span of creek. Two load-out areas were set up, each consisting of two excavators, both of which were capable of maneuvering in the potentially soft creek bottoms. This first excavator was used for locating, excavating, and stockpiling coal tar material. The second excavator was tasked with load-out operations. Following excavation of the coal tar, the sediments were transported to a pre-constructed 200-foot by 200-foot drying bed. The base of the drying bed was constructed of clay with a perimeter 3-foot berm to prevent run-on/run-off. Over the clay base, a 40-mil HDPE geosynthetic liner was placed, followed by a 6-inch layer of sand with 4-inch HDPE drain piping and sumps imbedded in the sand. Non-woven geotextile was placed over the sand layer, which was topped with gravel to facilitate drainage and promote drying. The drying bed included a leachate system where liquid was collected by pumping to an oil/water treatment system. The coal tar was then treated in the drying bed with 10% lime kiln dust (LKD) to stabilize the material. The LKD was mixed with the coal tar using an SS250, which blended the material and promoted drying.
A specific mix design for stabilizing the coal tar was not provided for this project so Envirocon developed an approach based on a local supply of LKD reagent. The two major performance criteria to be verified and tested under our QA/QC program included passing TCLP and the paint filter test.
Upon completion of the stabilization activities, the dried/stabilized materials were moved to a staging area and verification sampling was performed to ensure acceptance criteria prior to load out. The stabilized coal tar material was then loaded into haul trucks and transported to a Subtitle D landfill.
Once EPA approval was obtained for each reach, bank stabilization occurred. Approximately 12,000 cubic yards of backfill material was placed.
During the course of the impacted sediment removal, a non-aqueous phase liquid (NAPL) was discovered penetrating the bottom of the creek bed. As there was fractured limestone beneath the creek bed, it was impractical to try to capture the NAPL, so the USEPA and the PRP group elected to seal the bottom of the creek with AquaBlok®, which is a bentonite clay surrounding a core of pea gravel. The creek bed containing the NAPL was initially covered by a 12-inch layer of compacted clay, followed by a 6-inch layer of AquaBlok®, and topped with a 6-inch layer of clay. This modified restoration method was used to seal 5,750 of the approximately 10,000 linear feet of the Chattanooga Creek.
Following completion of all remedial activities, restoration of the site included re-vegetation of impacted creek banks, seeding disturbed areas with native grasses, and placement of rip rap at areas prone to erosion along the creek. Upon inspection approval by the PRP group and the USEPA, all dam materials were removed, pumping and piping systems taken down, and the drying bed dismantled and hauled to the Subtitle D landfill.
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