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Attachment A Area of Review Methods Application Requirements Give the methods and,if appropriate,the calculations used to determine the size of the Area of Review (fixed radius or equation). The area of review shall be a fixed radius of 1/4-mile from the well bore,unless the use of an equation is approved in advance by the Director. Approach A single Area of Review (AOR) was developed for the STIG-LEC facility wells because of the relatively small dimensions of the overall site. The AOR considered the maximum potential injection rates for the STIG-1 and LEC-1 wells over the next 30 years (the life expectancy of the power plants). This approach provided the'worst case scenario' for assessing potential impacts of the injection process over time because it focused the injection on two wells. Results for 10 years,the duration of the permit request,are also considered. Although specific assessment of injection at LEC-2 was not directly conducted,its role as a backup well was considered as part of the overall injection scheme at the STIG-LEC. Methodology Three independent methods are available to decide the appropriate size of the area to be surveyed to assess the possible impact of the proposed use of an injection well on underground sources of drinking water (USDWs). Those methods are the fixed radius method,the volumetric method,and the pressure build-up method. The results from applying each of those methods to determine an appropriate-sized AOR for the NCPA STIG-LEC facility are described below. It was assumed that the fully permitted injection rates for the STIG-1 (200 gallons per minute [gpm]) and LEC-1 (225 gpm) wells were achieved 24 hours per day,365 days per year for the next 30 years. Injection was assumed to occur from a single point located at the center of the facility. Formation properties used for the calculations were taken from the original permit application and subsequent testing activities performed during mechanical integrity testing (MIT). Original data for the permit was collected through research on nearby wells, geophysical logging,and injection testing. Permeability is one of the parameters critical for determining long term pressure increases. Due to the nature of evaluating pressure response to injection,combined with minor differences in testing procedures and initial reservoir conditions,results of the tests have varied as shown in Table A-1. The original value of permeability and net sand thickness based on perforated intervals was selected to provide the most conservative estimated distances for the AOR. SAC/371322/082550016(ATTACHMENT-A.DOC) A-1