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� AMBRIA <br /> 13. Mass balance calculation of the substance treated versus that remaining, <br /> As noted above, detectable concentrations of TPHg, benzene, and MTBE were only left in place <br /> in the vicinity of the northwestern former USTs at the site Soil samples have not been collected <br /> from tlus area since at least 1998 Recent (2004) soil analytical data collected from the <br /> northeastern UST area and its associated piping and dispensers did not contain detectable levels <br /> of TPHg, benzene, and MTBE No other recent data is available for the northwestern UST area <br /> for preparation of mass balance estimates in soil Current groundwater concentration data <br /> indicates background levels have been attained at the site, therefore no mass remains in <br /> groundwater at the site <br /> 14. Assumptions, parameters, calculatwns and model used in risk assessments, and fate and <br /> transport modeling; <br /> See Appendix D-VLEACH Model <br /> 15 Rationale why conditions remaining at the site will not adversely impact water quality; , <br /> health,or other beneficial uses;and <br /> • Separate-phase hydrocarbon has never been present beneath the site or in site wells <br /> • TPHg and BTEX have not been detected in groundwater at the site since at least October <br /> 2003 - n o l- &M,Pe fCtj - D LA- zD D 3 3 k a4 V_S& J,)4 may/L_ <br /> • MTBE levels have been below detection limits in groundwater for at least the last three <br /> quarters July 2005 data had a 12 ppb detection of MTBE in one well and no MTBE <br /> detected in the other two site wells <br /> 16. WET or TCLP results - dAr141�-�� �1 '� (', .vr� <br /> Not available <br /> 0323 11 <br />