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CHAPTER 2 <br />KONA TODA Y <br />Groundwater. On the Island of Hawaii, groundwater is the primary source of drinking water. In <br />Kona, groundwater occurs as both basal groundwater' and high-level groundwater2. The basal <br />lens in Kona is relatively thin and inconsistent due to the low rainfall input and the lack of a <br />geological "plug" that could slow the leakage of the groundwater at the coastline.3 Consequently, <br />wells drawing from basal groundwater in Kona are susceptible to salinity if they are drilled too deep <br />or if they are over -pumped. In the 1990's, exploratory wells drilled above the 1,600 -foot elevation <br />encountered high-level groundwater 25 to 460 feet above sea level. Better understanding and <br />protection of the high-level groundwater is important, since it has a significant potential for serving <br />Kona. <br />Three possible geologic structures that could impound high-level <br />water. (A) buried dike complex; (B) buried fault system, (C) buried, <br />massive lava flows. Oki, Delywn, 1999. <br />nn , <br />KAMM <br />..wn. m• . N\ \ <br />.x• wvs\ � \\�2 <br />T„w.•��!. •'Ixwe1.em:�� KEAUHDU <br />�� owfS 4 <br />I <br />I I <br />•a I <br />•.�nl a <br />�.�. .-. .,.,....... \.. y.,rw KEALAKEKIIA <br />Water level contours in the high-level aquifer. Bauer, Glenn, <br />September 2003. <br />1 Basal groundwater is freshwater "floating" atop deeper seawater. The freshwater forms a "lens" that extends below sea <br />level in a phenomenon described by the Ghyben-Herzberg Principle. For every foot of fresh water above sea level there are <br />40 feet below sea level. <br />2 High -Level ground water refers to potable water sources that are impounded by a relatively impermeable geologic <br />structure such as dikes or clay soils. <br />3 For example, on 0`ahu, eroded sediment that has accumulated at the coastline is relatively impermeable and holds back <br />the groundwater, enabling a larger lens of water to form. <br />2-4 KONA CDP <br />