Beneath the facility, a chlorinated solvent spill was contaminating groundwater, which had previously been addressed with a series of underdrains and a collection system, now failed. Aztech won a competitive bid to install a new groundwater collection and treatment system (GCTS) and a sub-slab depressurization system.
The existing groundwater collection system used 24-inch clay stormwater pipe (now cracked) leading water to a manhole sump where it was pumped to an air stripper. The entire system needed rebuilding to comply with the more stringent requirements of the new tenants.
Aztech excavated a 12-foot deep trench alongside the old clay collection pipe, and placed 220 linear feet of six-inch high-density polyethylene (HDPE) perforated collection pipe wrapped in filter fabric and set in a graded bed of crushed stone. The pipe design required a 0.5% pitch over the entire length, which necessitated dewatering and shoring for the length of the project.
To ensure a safe working environment Aztech utilized four (4) eight-foot by twenty-foot steel trench boxes that were stacked in pairs to provide adequate protection to personnel and equipment. The excavation had to be dewatered continuously in order to install the required crushed stone sub-base and to carry the proper grade along the extent of the trench. Compaction testing was carried out to verify that the proper quality control parameters were met. Upon completion of the collection pipe installation, Aztech backfilled and compacted the trench to grade in preparation for follow up paving and striping.
The collection pipe drained by gravity into a six-foot diameter, 18-foot deep concrete collection sump. To accomplish such a deep excavation, Aztech brought in a 80,000 lb. excavator. Plans called for the installation of a 12’ X 12’ x 20’ slide rail shoring system to stabilize the opening. Each eight-foot wall section weighed close to ten tons, requiring a 70,000 lb. loader to move the boxes from the staging area to the excavation where the excavator carefully and precisely placed them into position.
With the slide rail system the inner and outer panels lock together under external pressure, making a solid walled enclosure. Once the slide rail shoring system was installed Aztech dewatered the excavation and installed a crushed stone sub-base and geotextile layer. The twenty-ton concrete structure was quickly and safely lowered into place with precision and backfilled per the customer’s specifications.
To install the manhole components Aztech executed a confined space entry per Occupational Safety and Health Administration standards. The well components included two submersible pumps, schedule (SCH) 80 poly-vinyl chloride (PVC) pipe, valves, floats and wiring. Once the manhole components were installed the control and power wiring were terminated in the GCTS building.
Within the sump, the collected water was pumped back to the filtration system through a new force main. The force main design incorporated HDPE pipe in a dual containment configuration in which two-inch standard dimensional ration (SDR) 11-inch pipe was installed inside of four-inch SDR-17 pipe using centralized fittings. Aztech fabricated and welded the specialty piping onsite using butt-fusion HDPE welding equipment. The force main was installed below the frost line and routed from the manhole to the GCTS building, a total of 330 linear feet, pitched back to the sump, in the event of a failure. Conduits were installed in the same trench along with a road rated pull box. The trench was backfilled and compacted to grade in preparation for follow up paving.
Aztech replaced the old direct-vent, air-stripper system with a new, combination stripper/carbon-filter treatment system. To comply with New York State Department of Environmental Conservation requirements, Aztech utilized a 250 gallon per minute portable air stripper system in order to bypass the existing system during the upgrades.
Aztech demolished a portion of the concrete slab in the GCTS building to accommodate pipe and conduit penetrations and to install a new concrete equipment pad for the new carbon units. Aztech installed a new air stripper, blower, duct heater, carbon filtration vessels and controls. In the new system, the air stripper uses high velocity air to volatilize the organic compounds, where they are captured and treated through an activated carbon filter. Prior to completion Aztech also replaced the existing four-inch SCH 40 PVC effluent pipe with a new SDR-17 HDPE line.