Significant Project Features
- Excavation of 23,800 CY of sediment at Willetts Creek, utilizing temporary diversion barriers
- Mechanical dredging of 29,800 CY of sediment in Lake Capri
- Onsite metals stabilization of cadmium and chromium using Sevenson’s proprietary MAECTITE® treatment process to stabilize 1,600 CY of material, saving $144,600
- Off-site T&D of 63,300 tons of material
- Extensive restoration to upland and wetland including plants, seeds, and sod
- Completed over 20,000 workhours without a lost-time incident
History & Location Details
The remedial area is the site of the former Dzus Fastener Co. Willetts Creek, Lake Capri and the surrounding areas were contaminated with heavy metals. Schools and homes sit along the creek in this neighborhood. Both topographic and hydrographic surveys were performed. Major COCs include cadmium and chromium. Sevenson’s scope of work under this contract included soil excavation, sediment dredging, installation of temporary diversion barriers to divert creek flow (enabling sediment removal), stabilization of materials impacted by heavy metals, and management of transportation and disposal activities.
Site preparation included installation of WWTP which consisted of a 20,000 gallon pre-treatment influent weir tank, inclined plate clarifier and 200 gpm chemical feed pumps, bag filtration, and a 21,000 gallon post-treatment frac tank. The WWTP was designed to suspend solids and specific soluble and insoluble metals. Solids containing the metals of concern (cadmium and chromium) settled to the bottom and the clarified water passed through. It was set up in the east of the High School parking lot in the grass area, where it remained for both the creek excavation and dredging of Lake Capri. Sevenson installed bypass piping along the entire length of the creek in order to divert the flow for sediment excavation, backfill and restoration. Sevenson installed a supersack/sandbag temporary diversion barrier in order to remove impacted sediment and soil of the creek bed. This project required Sevenson to perform a stream bypass. Water was forced into an HDPE diversion pipe, which conveyed it around the work area by an 8-inch electric pump and two back-up 18-inch diesel bypass pumps.
Sediment excavation of Willetts Creek began in the northernmost area of the creek and progressed south. The excavation depths in Willetts Creek ranged from 1.5 feet to 2 feet below ground surface along the western bank and ranged from 6 inches below ground surface along the shoreline of Lake Capri to 2.5 feet below ground surface in the deepest part. Dredging was accomplished using a barge-mounted Komatsu LF excavator with an environmental bucket with a hydraulic environmental lid. 23,800 CY of sediment was transported to the TFS in off-road trucks and stabilized, then loaded for offsite T+D. In Lake Capri, Sevenson employed mechanical dredging in combination with an outer silt curtain moon pool in order to prevent sediment from migrating from the work area. 18,400 CY of dredged sediment was loaded into barge scows and transported to the shore for offloading into off-road trucks, which transported the material to the TFS at the High School or the upstream sediment processing and load out area. Sevenson was prepared to blend the sediment with Portland cement for loading and offsite T&D at Burlington County Sanitary Landfill.
Sevenson implemented MAECTITE® to stabilize 1,600 CY of RCRA metals-contaminated material. This proprietary reagent effectively rendered hazardous material non-hazardous, achieving a substantial cost savings for the client (treated material was sent offsite for disposal at a non-hazardous rate of $74/CY versus a hazardous rate of $180/CY). Treating metals-impacted material using MAECTITE® realized a costs savings of approximately $144,600.
Placement of backfill materials was performed using dedicated clean equipment in order to prevent any possibility of cross contamination. Sevenson self-performed backfill, stone and riprap placement and subcontracted upland and wetland planting, seed, and sod installation.