Delineation of areas for terrestrial disposal of waste water

The disposal of municipal, industrial, and livestock waste waters into the Snake River and its tributaries is the source of a serious surface‐water pollution problem in the southern part of Idaho. At places waste water is also a threat to the groundwater resource. Renovation, particularly with respect to organic and nutrient constituents, through irrigation with coincidental crop fertilization and groundwater recharge is proposed for hydrogeologically suitable portions of the Snake River plain, instead of expensive tertiary or sometimes secondary treatment. The region near Idaho Falls and Blackfoot has been used as a case study area to establish the methodology for selecting the most suitable terrestrial disposal sites. The procedures used are sufficiently straightforward; thus they are readily adaptable to other larger areas. Safeguarding surface water and groundwater resources, providing for maximum probability of proper renovation of waste water, and minimizing design and supervision requirements are conditions that must be satisfied by any terrestrial waste water disposal project. The criteria for selecting sites that meet these conditions for proper disposal and renovation include gently sloping topography, a thick subsurface section of unconsolidated, unsaturated porous medium, a surficial mantle of high sand‐silt content, and a well‐understood shallow groundwater flow system. When evaluation and mapping apply to these criteria in the area around Idaho Falls and Blackfoot, Idaho, the delineation of sections of land where successful terrestrial disposal of waste water can be expected is facilitated. The delineation of such areas permits municipalities to identify sites for terrestrial disposal of domestic waste water, and it provides industry with the opportunity to select locations for future plants from which terrestrial disposal of waste water is anticipated; such planning is essential in eliminating the nutrient enrichment of surface water bodies in the future.