National Institute for Water Resources, Water Resources Research Institute Program
9/01/07 - 12/31/08
There is a heavy reliance on salinity-versus-depth profiles from deep monitor wells for the regulation ground-water withdrawals in some locations in Hawaii. Because of possible intraborehole flow effects, however, salinity profiles from deep monitor wells may not accurately reflect the salinity distribution with depth in the aquifer. Borehole geophysical logging in Hawaii has shown some evidence for subtle intraborehole flow in some cases. The definitive question then becomes: "Is this subtle flow sufficient to invalidate the depth-salinity profiles that are being observed?" Or: "Is the flow great enough that the observed salinity profile in the wellbore is substantially different than in the adjacent aquifer?" A final question concerns the management intent and use of these monitor wells: "Are salinity profiles sufficiently invalid that they can't be used to monitor long-term changes over years to decades?" - which is the timescale that is anticipated for saltwater intrusion in response to pumping. Thus far, this topic has not been dealt with comprehensively in the published literature.
Evaluate the potential for intraborehole flow to result in inaccurate or misleading information being used for ground-water management in Hawaii.
Two approaches were used: (1) evaluating and summarizing existing work to date; and (2) consulting with experts in borehole geophysical logging to design a strategy for further field work. Results were published in the USGS Scientific Investigations Report series.
Click here to view the related publication: CP-2010-01