IRRIGATING WITH MUNICIPAL SEWAGE EFFLUENT IN A RURAL ENVIRONMENT

Between 1968 and 1988, tertiary treated sewage effluent from the South Lake Tahoe, California area was pumped from the Tahoe basin, stored in a multi-use recreation reservoir in a neighboring county, and utilized as agricultural irrigant in that county. A comprehensive monitoring program for surface and groundwater in the irrigation area was not implemented until 1980. The holding reservoir repeatedly proved of inadequate size, resulting in spills to an adjacent creek or the use of irrigant at sub-optimum times. The number of acres available for effluent irrigation decreased substantially during the study period. The amount of effluent irrigant used per acre was significantly higher than the original, anticipated application rates, resulting in demonstrable impacts on surface and groundwater. These impacts, while of no immediate public health concern, were not an intended outcome of the project and were substantially avoidable with better planning. In this rural, near-pristine environment, all but the most minimal impact was unacceptable to local citizens. In response, important changes were implemented as part of a major program change in 1989. Nonetheless, significant concerns exist and should be addressed. Recommendations for improvements to the program and for future avoidance of unnecessary impacts on surface and groundwater are discussed.