LIQUID PHASE RADON REMOVAL USING GAC   The overall purpose of this research is to determine the design and operational criteria for the removal of radon from groundwater systems by GAC adsorption. The three key factors that must be resolved are the determination of the capacity and EBCT of GAC for radon removal, the evaluation of radioactive build up on the GAC including the ramifications of this build up on disposal and worker safety issues, and the development of overall system design. This research will provide utilities of all sizes with the information they need to assess the potential of GAC treatment for radon removal. The three objectives are:   1. Determine Carbon Requirements   The research will allow for the detailed evaluation of GAC's capacity to remove radon in community water system applications. We will determine if GAC has a practical capacity for radon, and how water quality parameters impact that capacity. This portion of our research effort will provide an estimate of carbon life for different water qualities and will assess what, if any, pretreatment requirements exist. Another integral part of this research objective is a detailed evaluation of required empty bed contact times for different radon influent levels and required percent removals. For both the capacity/water quality relationship studies and the EBCT determinations, different types of carbon will be tested as well.   2. Determine Build Up of Radioactivity on the Carbon   This objective of determining the extent of radon progeny, as well as naturally occurring uranium and radium build up on the GAC is important because of its implications for proper handling and disposal of the material, as well as worker safety considerations. Potential build up on pretreatment devices will also be addressed.   3. Determine Overall System Design   The research includes an extensive design phase as well as field verification of the design in order to provide utilities with overall system selection guidance. We will address regulatory requirements, pretreatment requirements, options, and recommended methods; contactor type, size, number, carbon type; hydraulic loading rates and required contact times; materials of construction with respect to worker exposure to radioactivity; headloss and pump requirements; side stream treatment, handling, and disposal issues; and post treatment issues such as disinfection and pH adjustment. By meeting these three objectives, a sound approach to the design and operation of a GAC facility for radon removal can be accomplished.