AWWA MTC69740

The Central Shoshone County Water District (District) serves potable water in rural Northern Idaho near the City of Kellogg. The State of Idaho has designated the water source as groundwater under the direct influence of surface water (GWUDI). Consequently, the District is implementing a treatment facility to comply with the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). Membrane filtration was selected as the core treatment process and three suppliers participated in a competitive procurement pre-qualification pilot study. Several factors related to the pilot study created a ripple effect that influenced procurement specification of the membrane system and facility design. Each supplier started their pilot work at different times resulting in a limited window of data where all three pilot units were operated at the same time. The pilot study duration was also less than typical, and repeatability of the efficacy of cleaning cycles could not be verified. An attempt was made to simulate a high turbidity event during the pilot study similar to the event that led to state designation of the water source as a GWUDI. The short duration of the pilot study also limited observation of the impact of seasonal temperature extremes on membrane performance. Process definition from the pilot study shaped the design. The backwash, chemically enhanced backwash or maintenance clean and recovery protocols used in the pilot study also played a significant role in the design of the facility. The selected site is not served by a sanitary sewer and the climate, topography and soils are not compatible with evaporation or percolation beds for wastewater disposal. Consequently, recovery or disposal of backwash and cleaning wastes were critical design factors. For this reason, backwash water is recovered to minimize the quantity of residuals requiring disposal. The broad range of water demands and seasonal water temperatures led to development of multiple criteria for design flux rates and redundancy requirements. Includes tables, figures.