First Artificially Filter Packed Slant Well
Municipal Water District of Orange County (MWDOC) has conducted detailed investigations to determine the feasibility of providing an ocean water desalination supply source in south Orange County utilizing slant well technology. The Doheny Ocean Desalination Project (formerly South Orange Coastal Ocean Desalination Project), consists of a phased study into the feasibility of obtaining desalination feed water supply from subsurface intakes at Doheny State Beach in Dana Point, California. The project, which originated with MWDOC, is now managed by the South Coast Water District (SCWD).
In 2005, GEOSCIENCE began a multi-phase study on potential subsurface intakes, beginning with a comprehensive literature review and initial screening of subsurface intakes. Following this review, GEOSCIENCE located and designed construction of four exploratory boreholes on Doheny beach using the sonic drilling method, two of which were completed as nested monitoring wells. Initial modeling provided further screening of potential subsurface intakes and a 350 ft long angled well (slant well) 23 deg below horizontal was constructed.
The slant well, which began pumping in 2006, was the first successfully constructed artificially filter packed slant well completed below the ocean floor and produced approximately 3 mgd for two years during pilot testing. To assess the feasibility of this alternative, GEOSCIENCE developed and calibrated a variable density groundwater model that incorporated comments from a peer review panel of experts in the field of groundwater modeling, as well as feedback from the San Juan Basin Authority and other agencies. Data from this long term test is currently being used to design the full scale 30 mgd feed water supply consisting of seven 800 ft slant wells and two standby wells. The groundwater modeling work determined the potential yield of a slant well intake system, predicted water quality variations with time, and simulated effects on groundwater levels in the onshore ground water basin.