CODE removed ~1,500 cy of coal tar impacted soil and installed a sheet pile barrier adjacent to an elevated portion of the I-95 at the Del-Marva Electric MGP Site adjacent to the Christiana River in Wilmington, Delaware. The project was particularly challenging because site groundwater was located at 18 inches below ground surface. In addition, a portion of the excavation was conducted in a swale.

To facilitate excavation, CODE successfully designed/installed a very aggressive dewatering system that was operated on a 24 hour/day basis. By project end, over 150,000 gallons of water had been removed from the excavation and transferred to a series interconnected FRAC tanks. Water from the FRAC tanks was pumped through an on-site treatment system prior to discharge. The on-site water treatment system consisted of a carbon unit for organics and a US filter vessel for metals.

35' deep sheet pile was driven down to grade in a 70' x 60' rectangular cofferdam. Following sheet pile and dewatering system installation, CODE excavated MGP-contaminated soil to approximately 10 fbgs. Excavated soils were direct-loaded into staged transport vehicles for off-site treatment at a permitted thermal desorption facility.

The remediated excavation was backfilled with ¾” stone to within three feet of grade. A geotextile layer then was installed followed by PA 2A Modified backfill - placed to within three inches of grade and compacted to 95%. The sheet pile barrier was removed and a stormwater diversion system installed prior top-dressing the excavation with 3" of clean stone.