Geology and Stream Infiltration of North Halawa Valley, Oahu, Hawaii

A geohydrologic investigation of North Halawa Valley, Oahu, Hawaii, and its stream was undertaken in response to concern that runoff from the H-3 highway draining into the stream might seep into the ground and seriously contaminate potable water pumped at a nearby skimming well.

North Halawa Stream flows over highly weathered alluvium or highly weathered basaltic basement for almost its entire course. Measurements of discharge at selected points along the stream indicate that infiltration occurs along some reaches. The infiltration of water from North Halawa Stream varies with season and stage. Water lost by the stream probably passes into and out of a perched aquifer in the alluvium of North Halawa Valley. Some of the water could pass from the alluvium to the basal aquifer from which the skimming well draws its water.