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ATTACHMENT A:AREA OF REVIEW METHODS TABLE A-3 Volumetric Calculations Summary including Dispersion for 30 Years Variable Description Value R Radius of Invaded Zone,feet 1,604 ftp D Dispersion Coefficient, feet 3 ft R' Radial Distance with Dispersion,feet 1,763 ft *Based on 30 years of future injection Zone of Endangering Influence The primary concern related to pressure increases around an injection well is the endangerment of USDW. This occurs when the pressure increases in the injection zone to levels that exceed the pressure in upper zones. This pressure difference can drive water from the injection zone into shallower zones through conduits described above. The ZEI is the area over which the increased pressure in the injection zone could push injected or native fluids into an overlying USDW. In the case of the STIG-LEC site,the only identified conduits through which fluids could migrate from the injection zone to a USDW,are test holes or oil and gas wells present in the area. No faults have been identified in the immediate vicinity of the site. In order for the boreholes to pose a threat to any USDW,the pressure increase in the injection zone must be greater than the required pressure to displace the drilling fluid left in the hole. In order for drilling fluid to be displaced,the hydrostatic pressure and gel strength of the mud must be overcome (Johnston and Knape, 1986). Therefore,the allowable pressure increase in the formation can be calculated using the following equations: Allowable — PH +PG where PH = (.052)(H)(10mua) and P _ 0.0033(GS)(H) G D A-4 SAC/371322/082550016(ATTACHMENT-A.DOC)