Water Well Journal
Issue link: http://read.dmtmag.com/i/440561
W hile not a favorite topic of those who supply water to communities, businesses, and homes, the fact is sometimes mistakes made in the design of a well can and often do result in rapid deterioration of the well. Such situations can cause much frustration, but they also can be the catalyst for the introduction of new technology as part of the solution. While none of this is rocket science, care- ful attention to detail during well design and construction can minimize problems in the future. This article will present a brief case history of a poorly designed well and the rehabilitation program used to restore the well to service. The Well A freshwater well named PW-4 was originally constructed in 2006 in an alluvial (sand, gravel, silt and clay) aquifer known to contain chloride-impacted groundwater resulting from operations by a previous owner of the property. Geometric mean chloride concentration was 224 mg/L (essentially 224 parts per million), and total dissolved solids were 799 mg/L. PW-4 was constructed using 20-inch outside diameter, 5/16-inch wall mild steel (ASTM A53 Grade B) casing in a 28-inch borehole. The louver screen, with 0.125-inch slot, extended from 175 to 415 feet below ground surface (bgs). Static water level was 122 feet bgs, and when pumped at 2000 gallons per minute, the well had a specific capacity of 44. The vertical turbine line shaft pump (14-inch diameter) failed after just seven years. A video survey showed extensive corrosion of the casing (Figures 1 and 2), including complete loss of the casing in the deepest portions of the well due to corrosion, and in addition, no filter pack could be seen in the well. The damage to the casing was extensive enough to cause concern about the integrity of the casing, and the lack of filter pack virtually guaranteed the well would be likely to pump significant amounts of sand. In fact, the pump had failed because of sand production. The decision was made not to pump the well until an analysis of options was made. The main criteria in the analysis were cost, specific capacity, and the pump. (It was preferred the well would continue to use a vertical turbine line shaft pump, rather than a submersible unit.) The Rehab Both replacement and rehabilitation of the well were con- sidered. Ultimately rehabilitation was selected, primarily due GOING GLASS Rehabilitation of a freshwater supply well using a high-strength low-alloy liner and glass beads. By Robert M. St. Louis and Jofree Duran Rehabilitation of a freshwater supply well using a high-strength low-alloy liner and glass beads. GOING GLASS continues on page 26 Glass beads being installed between existing casing and liner. Note the 18-inch bullnose on top of the liner and the wooden frame constructed to contain the glass beads. GOING GLASS Twitter @WaterWellJournl WWJ January 2015 25