Consideration Factors of Production-Well Rehabilitation Assessment on Guam
Wednesday, December 5, 2018: 3:00 p.m.
Exhibit Hall- C4 & C5 (Las Vegas Convention Center)
Currently, Guam Waterworks Authority (GWA) produces 90% of the 45 MGD potable water from its main source, the Northern Guam Lens Aquifer (NGLA). GWA is currently managing 100 to 120 deep vertical production wells in this aquifer to meet the demand. However, many of these production wells are deteriorating from age with more than 50 years in operation, thus lifespan exceeded, maintenance is no longer economically viable, and production has become unsustainable. The NGLA is a composite to complex karst aquifer with a thick vadose zone, forming an uplifted plateau (> 60 m), and a highly anisotropic and permeable porous media. This aquifer bears a meteoric recharged freshwater lens atop saltwater, divided by a volcanic basement of 7 aquifer basins that form basal and parabasal zones with varying lens thickness in different regions. On Guam, rehabilitation of abandoned production well sites is a promising way of keeping freshwater production without further developing new well sites. However, some of rehabilitated production wells drilled adjacent to the old wells have resulted in severe reduction of water production. To investigate this issue, case study wells were chosen, and their construction, operation and rehabilitation history were analyzed. Based on the analysis, main consideration factors of production-well rehabilitation assessment were categorized.