project located at 534 W. 29 St. in New York City. On this particular project, the required drawdown was greater than the typical 15 ft (4.6 m) of suction lift, so a vacuumed can pump system was utilized. The tubing was connected to a vacuumed perimeter dewatering wellpoint system, which is a predrainage system that is installed prior to the start of excavation for the underpinning of the adjacent structures and for the overall foundation. Each well- point, which was composed of a PVC pipe that was 1.5 in (38 mm) in diameter by 25 ft (7.6 m) long, was drilled to a depth of about 23 ft (7 m) using a hollow stem auger and was installed around the perimeter at a center- to-center spacing of about 7.67 ft (2.3 m). In lieu of a traditional perimeter collection header, and to allow for greater flexibility for the contractor, the wellpoints were inter- connected to a modified vacuum can pump system utilizing ¾ in (19 mm) drop tubes that were “spaghetti” around the perimeter. th tubing had to be buried prior to the installation of the mud-slab, waterproofing, rebar and final slab. The drop tubing provided considerable flexibility in such tight quarters and was directed to a centralized manifold that was left in place throughout construction. A well-planned and well-executed approach to the construction dewatering program was essential for the success of this project. Reeder St., Elmhurst, Queens, N.Y. Other projects may have larger footprints, but can provide a host of other obstacles. One example is a project that was recently completed on Reeder St. in the Elmhurst section of Queens, N.Y. This site has a subway tunnel running beneath it, an inconsistent soil profile across it and lateral artificial recharge of the groundwater from leaks in nearby water mains. Due to the underground subway running under the northeast side of the site, the dewatering Wellpoint dewatering system setup minimized. The modeling of the dewater- ing plan also had to assure the developer that the required drawdown could and would be achieved. To mitigate the diverse geology (e.g., sands with layers of clay and silt) and the issues relating to the lateral seepage of water, the dewatering contractor implemented a series of low sump collection systems, which were outfitted with electric submersible pumps at strategic locations throughout the excavation area. The sumps were interconnected with gravel-toed and drainage-toe ditches. The predrainage wellpoint system, combined with the sumps and the contractor’s continuous around-the-clock monitoring of all dewater- ing operations, allowed for a successful construction dewatering operation. 416-420 Kent Ave., Williamsburg, Vacuum can wellpoint pump system The drop tubing provided many advantages, including not having to anchor the header onto adjacent buildings (which can be a legal concern), flexibility if relocation of the tubing was needed during underpinning, and drawdown to nearly the bottom of the screen at the end of the wellpoint to maximize drawdown. To counteract the uplift pressures, this project also required that the dewatering system remain in operation until the first-floor slab was completed, which meant that the 92 • DEEP FOUNDATIONS • MAY/JUNE 2017 Centralized manifold system system was designed to be installed in and operated from the side of the property opposite the tunnel. Understandably, subsidence of the tunnel was also a major concern for the owner and the contractor. The dewatering contractor utilized sophisticated groundwater modeling technology to show the subway regulatory agencies that, by concentrating the dewatering away from the subway, any potentially negative impacts on the subway structure from the dewatering could be Brooklyn, N.Y. The water’s edge of the East River in Williamsburg, Brooklyn, N.Y., is witnessing an increase in mixed-use developments, where developers are purchasing water- front properties in an area once lined with industrial manufacturing plants. Many of these sites are underlain by contaminated soil and, correspondingly, with con- taminated groundwater. Most of these sites have been designated by the federal government as brownfield projects. Developers that have purchased these parcels of land take on not only the task of development but also of remediating the
