Findings are recorded of a six-year investigation of pollution hazards involved with the use of septic tanks and drainfields in the Spokane Valley of eastern Washington. The geological setting of the study area was investigated by gravimetric and refraction seismic methods. The results of these studies indicated a generally simple, U-shaped valley incised in ancient granitic and metamorphic rocks. Valley fill materials appear to be almost entirely glaciofluvial sands and gravels. Previously postulated basalt flows and Latah clays are probably not present in significant amounts. Drilling and sampling of local drainfields revealed that the upper moist and wet valley fill materials pass into dry sands and gravels at depth. This phenomenon prompted a postulate that drainfield fluids must be moving laterally rather than vertically. Confirmatory laboratory measurements of soil moisture tension showed all of the soils, at depth, to be in a state of high moisture deficiency. Routine geophysical logging of monitor wells indicated that moisture movement and variations were confined to upper soil layers. Infiltration tests substantiated other findings concerning the movement of soil moisture. Extensive sampling and analysis of surface and ground waters revealed no evidence of ground-water contamination. Surface waters are generally of good quality east of Spokane but are seriously degraded in the immediate Spokane area. (Author)