During 2010 DTD completed two projects requiring horizontal dewatering wells. Both projects were designed to lower the water table for excavation purposes. One project dewatered for a source-removal excavation at an Air Force Base, while the other dewatered contaminated groundwater prior to a construction excavation.
The first project included a series of six horizontal wells set beneath an area targeted for the subgrade construction of a commuter train terminal. The terminal required excavation to almost 40 feet below grade in an area where the water surface was approximately 20 feet below grade. Traditional dewatering from within the excavation was not an option because the groundwater was contaminated from a nearby service station.
The six ~300 ft horizontal wells were fanned out beneath the terminal area at a depth of approximately 50 feet bgs and passing beneath a busy commuter highway near Washington DC. The wells operated for approximately 16 months removing approximately 10,000,000 gallons of water and lowering groundwater almost 25 feet. The excavation contractors unfamiliar with the dewatering going on beneath there feet commented on how dry the excavation was!
The second project dewatered a 66 acre area and allowed excavation of a pit 40 feet deep for the removal of contaminated soils at an Air Force Base. The pit was dewatered with two ~1,100 ft long horizontal wells set just below the bottom of the excavation. These wells have removed approximately 16,000,000 gallons of groundwater and lowered the groundwater by tens of feet a a distance of several hundred feet. All this in just 9 months of operation.
Both projects have exceeded their dewatering design expectations, pulling more water and expressing a larger than expected radius of influence.
For more information on using horizontal wells for dewatering, please contact dan AT horizontaldrill.com.