AWWA WQTC55015

This project examined the survival of a variety of health-related microorganisms in the face of natural bacterial, geochemical, and physical processes that may occur in the recharge zone of an aquifer storage and recovery (ASR) well. Bench-scale beaker studies were performed to determine the effect of total dissolved solids (TDS) and temperature on survival of several organisms. Three model TDS levels and two temperatures were evaluated: 500, 3,000, and 10,000 mg/L TDS at 20 degrees and 30 degrees C each. These conditions were established using NaCl and sterile distilled water. The organisms evaluated consisted of 2 individual organisms and 3 populations. The individual organisms were MS-2 bacteriophage and PRD-1 bacteriophage. Microbial populations evaluated were fecal coliforms, enterococci, and coliphage, all isolated from natural surface waters. Samples were taken from the survival experiments at varying intervals for a period of 0 to 100 days, until the endpoint of less than 0.5 viable organisms per ml was reached. For each organism, the inactivation over time was determined using established media culture (bacteria) or agar overlay plaque analysis (bacteriophage). Preliminary results revealed extensive survival times of all bacteriophage groups and fecal coliforms, in excess of 6 weeks. Reactors with the higher salinity conditions (3,000 and 10,000 mg/L TDS) supported survival better. The enterococci population was rather sensitive, with organisms in the low-saline 500 mg/L conditions exhibiting a greater than 99.9% extinction by one day. Enterococci in other conditions experienced reduced die-off rates but were overall much more sensitive than fecal coliforms or bacteriophage. However, to evaluate the survival of these microorganisms in actual environmental conditions, the naturally-occurring physical, biological, and chemical conditions found in the Floridan aquifer, natural waters must be investigated. On-going research will examine inactivation rates in lower TDS ranges, from 100 - 1500 mg/L, the survival of organisms in natural vs. artificial water, and field monitoring of ASR sites for microbial detection. These data will help determine the potential adequacy of natural aquifer conditions within a recharge zone around an ASR well for inactivating microorganisms introduced from surface water. Includes 7 references, figures.