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Scope of Work:
¨ General site preparation included clearing and grubbing, topsoil stripping, constructed haul roads, and stabilized site entrances. Due to the close proximity of residential properties, over 4,000 feet of security fence was installed to protect the work area. Erosion control around the pond and stream included 4,000 sand bags and 3,000 feet of silt fence / hay bale barrier.
¨ Diversion of the existing stream flowing into and out of the pond implemented a dual flow design. Flow into the pond was blocked with an engineered barrier berm. All pumps were placed just above the barrier.
o The baseline system diverted an average daily flow of 4,000 gpm utilizing one 10” submersible pump connected to a 12” steel diversion line.
o The high flow, backup system was required to handle a maximum flow of 18,000 gpm based on a 10 year, 2 hour storm event. The high flow design included two additional 10” pumps connected to separate 12” lines.
o All three diversion lines ran 1,200 feet and beneath three major roads to the discharge area.
o The entire system was powered with a 750KW Genset equipped with a silencer for noise reduction.
¨ Contaminated water generated as a result of pond decanting and sediment dewatering was pumped via 4” pumps to the on-site water treatment system. The 100-gpm system consisted of one 50,000 gallon influent tank, two 50,000 gallon effluent holding tanks, one 1,000 lb. organoclay primary filter, two 10,000 lb. carbon polishing units, and bag filter cartridges for particulates. Additionally, the entire area was surrounded with a 1,100’ concrete barrier wall for site security.
¨ Over 7,500 tons of TSCA and non-TSCA sediment was removed using low ground pressure (LGP) excavators equipped with either a standard boom or long reach boom. Saturated sediments were stockpiled in a designated treatment area for gravity drainage and solidification prior to loadout. Pelletized quicklime, delivered in super sacks, was used as the solidification agent since it could be handled in small volumes with minimal dust generation.
¨ A multi-layered design was used during backfill placement. First, a 1’ layer of cushion sand was spread across the entire basin. The cushion sand was then covered with geotextile and variations of crushed stone and rip rap, depending upon location. Additionally, a 20’ diameter duck island was constructed in the middle of the pond. All backfill placement was performed using LGP dozers and backhoes.
¨ Additional site restoration included the installation of 450’ of gabion baskets around most of the perimeter, installation of an 18’ dock, and topsoil and seeding of grassy areas.