4-Stage Wellpoint Dewatering Project

Thompson Pump Company, the industry leader in providing pumps for dewatering applications, was involved recently in an extensive, five month unique project in Fairfax, South Carolina. Don Polzin from Thompson Pump in Charleston, South Carolina worked closely with the general and site contractor to dewater three acres of land for a press board plant. The plant's foundation was going to be a structure 40-feet wide, 150-feet long, and contain 300,000 pounds of steel, but before this extensive structure could be constructed, an area fifty-two feet below natural ground elevation needed to be cleared and dewatered. In order to complete this project, Thompson Pump installed wellpoint systems in four stages, utilizing 13 pumps and pumping an average of 1.3 million gallons a day.

Installation of the first stage of this project took three days and utilized two 8-inch wellpoint systems with Thompson 12-inch Rotary pumps and one backup pump. Following a week of pumping and excavating, the area was 18-feet deeper and ready for stage two. Stage two involved installing two 450' x 8" systems with a Thompson 12-inch Rotary pump on each system and another backup pump. After a week with the stage two pumps functioning, another 18-feet of earth was excavated, totaling 36-feet of depth.

The site contractor had initially planned for this to be a three stage project at a target depth of 47-feet. Stage three started successfully with two 350'x 6" systems utilizing Thompson 12-inch Rotary. Despite the pumps being placed at a depth of 36-feet and discharging through 500' of Thompson galvanized pipe, the pumps quickly reached the original target depth of 47-feet. However at 44-feet an unexpected challenge was confronted. A very soft, impermeable layer of clay five feet thick was shelving water past the wellpoints and un-stabilizing the banks of the final cut. It took some time to install some more shallow points, jet in some sand wicks, and find a successful cure for this challenge. The cure was to install a rocked French drain around the grade perimeter of the final slope. A Thompson 4-inch vacuum-assisted pump and one backup pump kept the French drain sumped out at its lowest point. The clay layer made the center of the excavation floor unstable and un-suitable for building. To remedy this, a fourth stage welIpoint system was installed that solidified the excavation floor. Utilizing one Thompson 12-inch rotary pumping against 50-feet of static discharge head and 540-feet of discharge piping, stage four had the area dewatered and ready for building within a week.

After the area was cleared to 52-feet below natural ground elevation, a two foot layer of stone was poured across the entire excavation floor and a one foot mud mat was laid. Six weeks after this point, the stage four system was buried in concrete and the pump was removed. Twelve weeks after stage four was removed, the stage one pumps were pulled and removed.

At the completion of the press board plant project, 195 million gallons had been pumped by Thompson Pump through 3,150-feet of wellpoint system and 3,600-feet of Thompson galvanized discharge pipe.