ABSTRACT
Due to the vast uncertainty associated with subsurface water, the design of a dewatering system (Figures 4.1 and 4.2) involves a considerable amount of intuition and guesswork. Determining the depth to drill the dewatering wells, based upon the determination of the depth of the water table relative to the depth of the excavation, is relatively easy and will likely take care of 98% of the water. Unfortunately, 98% is not satisfactory and that remaining 2% needs to be addressed. The majority of the sources for this rogue water are difficult to identify as the soil borings may not disclose a layer of free-flowing sand trapped above a clay or impermeable rock layer. Rain water that reaches the sand layer will run right through the sand over the top of the clay or rock, through the lagging, and into the excavation.
