Significant Project Features:
- Bio-polymer slurry trenching method collection trench
- 310-feet in length and up to 38-feet deep.
- Backfilled with ½” Washed Gravel encapsulated with non-woven Geotextile.
- Contained 2 sump locations.
- Each sump location contained a 20-inch ID stainless steel .020-slot well screen and riser.
Background:
The site, originally a 150-acre sand and gravel quarry, began receiving industrial and solvent recycling wastes in the late 1960’s and early 1970’s. Complaints from local residents eventually led to investigations and closure by the EPA. The site was put on the National Priority List (NPL) for superfund sites in 1984 and over 200,000 gallons of liquid waste was removed. The EPA’s Record of Decision (ROD) for the Site included:
- The continued removal of buried waste
- The installation of a fence around the heavily contaminated areas of the site
- The installation of groundwater interceptor trenches for the collection and treatment of site groundwater
Project Objectives:
Geo-Solutions was contracted to install a groundwater interceptor trench by the bio-polymer slurry trenching method to provide groundwater collection and treatment, in conjunction with several existing trenches, to intercept contaminated ground water traveling from the waste areas to surrounding fresh water sources.
Description of Work:
The interceptor trench was 310 lineal feet long and excavated 38 feet deep to the existing confining clay layer. Bio-polymer slurry was produced in Geo-Solutions’ high speed/high shear colloidal batch plant and piped to the trench via hoses. The 4-foot wide trench was excavated using a CAT 385 excavator equipped with Geo-Solutions’ custom-made long-front attachment and trenching bucket.
Non-woven filter geotextile was placed in the trench to completely encapsulate the ½-inch size washed gravel backfill. The trench contained two extraction sumps. The sumps were excavated to a total depth of approximately 38 feet below ground surface with a precise 1 to 1 slope from trench bottom to sump bottom. The sumps consisted of 20-inch ID stainless steel .020-slot well screens and risers.
Work also included:
- Work platform preparation
- Trench spoils transportation and disposal at on-site disposal area
- Site grading and restoration
- Site stabilization and final seeding
- Down-well pumps and piping
- Electronic control panels
- Flow meters, valves, piping, and plumbing
- New 6-inch diameter HDPE force main piping
Project Challenges:
- To achieve the objective of the project, Geo-Solutions monitored the slurry properties continuously during construction to prevent premature slurry degradation. Geo-Solutons modified the standard chemistry of the fresh slurry to compensate for the constant influx of contaminated groundwater.
Due to the absence of clay key in some areas, the trench alignment was changed to follow the existing clay seam and ensure the trench was properly keyed into the confining layer.
- Limited work area created issues with maneuverability of equipment along the trench. Critical planning was used in order to have multiple pieces of heavy equipment maneuver safely in a small area and remain on schedule.
- The project was completed on schedule with zero health and safety related incidents.
