Flexible Drainage Sock Pipe up to 10” in diameter can be installed in a single pass under the water on a precise grade using the DeWind One-Pass Trencher. With the aid of dual automatic laser levels mounted on the Trencher boom, flexible drainage pipe can be installed on the exact grade to facilitate proper gravity drainage of failing slopes, dams, tailings piles and ponds. The One-Pass Trenchers can install miles of deep drainage pipe down steep slopes on perfect grades. The drainage pipe is installed under the water table without the need to install construction-dewatering systems. Unlike excavators that must dig mass excavations to install deep drainage pipe the One-Pass technique installs the pipe without an open excavation and there are minimal spoils produced during the installation process. Due to the minimal disturbance to the soils during the installation process there is little or no site restoration required.