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Mr Dora Rodgers Project 792774 01000000 November 19, 1999 Page 2 Between September 17 and October 11, 1996, EMCON observed the drilling of six soil borings (B-1R through B-6R) One soil boring was converted to monitoring well MW-1R, 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 • With the exception of soil samples collected from boring B-6R, residual hydrocarbons were detected in each boring The highest concentrations were detected approximately 10 feet below ground surface (bgs) near the former USTs Total oil and grease was detected in the soil sample collected near the former UST cavity (located near the building) at a concentration of 10,000 parts per million Polychlorinated bi-phenyls, TPHD, and chlorinated hydrocarbons were below laboratory detection limits in all soil samples analyzed from soil borings B-2R and B-6R • TPHG, benzene, toluene, ethylbenzene, and total xylenes (BTEX) isomers, and methyl tert-butyl ether (MTBE) were detected in the groundwater sample collected from monitoring well MW-1R 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: THIRD QUARTER 1999 On August 18, 1999, an IT technician was on site to measure depth to groundwater and collect a groundwater sample from well MW-1R for subjective and laboratory analyses Floating product was not observed in groundwater monitoring well MW-1R (see Table 1 and Appendix A) IT used these data to evaluate changes in concentrations of dissolved gasoline hydrocarbons in the groundwater IT's sampling and analysis procedures are presented in Appendix B A groundwater sample was collected from monitoring well MW-1R and was analyzed at Sequoia Analytical in Sacramento, California The groundwater sample was analyzed for TPHG using U S Environmental Protection Agency (USEPA) Modified Methods 8015, and for BTEX and MTBE using USEPA Method 8020 Copies of the chain-of-custody records and laboratory analysis reports are presented in Appendix C The results of laboratory analyses indicated that dissolved hydrocarbons were present in the monitoring well TPHG was detected at a concentration of 2,820 micrograms per liter (µ&/L), BTEX was detected at concentrations of 360 Rg/L, 35 8 µg/l, 116 µg/L, and 125 �tg/L, respectively, and MTBE was detected at 248 pg/L using USEPA Method 8020. Results of laboratory analyses are presented in the Table 1 CP\C\Arch►ve\Rodgers\Qtrly\RDGRQ399 doe-98ft 1 rr Corporation