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Mr Don Rodgers Project 2613-100 01 • May 1, 1997 Page 2 Between September 17 and October 11, 1996, EMCON observed the drilling of six soil borings (B-IR through B-6R) One soil boring was converted to monitoring well MWA R, three soil borings were converted to dual completion vapor extraction wells VW-1 through VW-3, and one soil boring was converted to a single vapor extraction well VW-4 (EMCON, Preliminary Investigation and Evaluation Report, February 5, 1997) The results of this investigation indicated the following • The majority of residual hydrocarbons were detected in the viciruty of the former USTs and dispenser islands Residual hydrocarbons were detected in each boring, except from soil samples collected from boring B-6R The highest concentrations were detected approximately 10 feet below ground surface (bgs) near the former USTs Total oil and grease was detected in the soul sample collected near the former UST cavity (located near the building) at a concentration of 10,000 parts per million Polychlornnated bi-phenyls, TPHD, and chlorinated hydrocarbons were below laboratory detection limits in all soil samples analyzed from soil borings B-2R and B-6R • Groundwater was encountered at approximately 31 to 38 feet bgs On September 30, 1996, static groundwater was measured at 26 44 bgs in monitoring well . MW-1R Groundwater elevation is consistent with groundwater elevations measured at adjacent properties • TPHG, benzene, toluene, ethylbenzene, and total xylene (BTEX) isomers, and methyl tert-butyl ether (MTBE) compounds were detected in monitoring well MW-1 R TPHG and benzene were detected at concentrations of 33,000 parts per billion (ppb) and 1,400 ppb, respectively MTBE was detected at a concentration of 550 ppb GROUNDWATER MONITORING- FIRST QUARTER 1997 On February 24, 1997, an EMCON technician was on site to measure depth to groundwater and collect a groundwater sample from well MW-1 R for subjective and laboratory analyses Floating product was not observed in groundwater monitoring well MW-1 R (see Table 1) EMCON used these data to evaluate changes in concentrations of dissolved gasoline hydrocarbons in the groundwater and changes in the gradient and direction of groundwater flow beneath the site EMCON's sampling and analysis procedures are presented in Appendix A The groundwater elevation in well MW-1R and elevations obtained from monitoring wells MW-3, MW-5, MW-6, and MW-7, installed by ARCO as part of the assessment conducted at the former ARCO Service Station (east of the site), were used to evaluate the gradient and direction of groundwater flow beneath and in the vicinity of the site (see Table 1) On February 24, 1997, the SA(�\Pi2\,2613\26131o00IBS-97\prc 1