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BACKGROUND Site investigations have been performed under the present on the Lopez property WaterWork regulatory oversight of PHS/EHD and the concluded that the extent of the TVG plume had RWQCB beginning in 1987,with PHS/EHD been defined to the south, east, and northeast, and performing the lead role as the local implementing also suggested that the plume may be due to an agency(LIA) In this section, a brief summary of offsite source Based on the results presented work performed at the Site is presented The (WaterWork, 1989), PHS/EHD directed TVG to various features, borings,and monitoring wells begin quarterly monitoring and monthly water- discussed are shown on the Site Plan presented in level measurements Plate 3 Quarterly monitoring began in third quarter 1989 1987 TO 1994 INVESTIGATIONS and in the first quarter 1991 report WaterWork �(o� l�yf# recommended active pump and treat remediation TVG rformed re at of the two gasoline USTs at well MW-4 Quarterly monitoring continued (5,06y and 10,00 gallons) in February 1987, through second quarter 1991 when continuous under the oversight of PHS/EHD Impacted operation of a low flow(1 8 to 2 0 liters per conditions were encountered and PHS/EHD minute)pump and treat system began in May directed TVG to perform a soil and groundwater 1991 Operation of the pump and treat system and investigation of the extent of impacted conditions quarterly monitoring continued through the second quarter 1994 when these activities ceased with the Exceltech installed and sampled 3 monitoring concurrence of PHS/EHD and RWQCB wells(MW-1, MW-2, and MW-3) in August 1987 Soil samples(nine)and groundwater samples were RAH INVESTIGATIONS analyzed for total petroleum hydrocarbons as gasoline(TPHg),total petroleum hydrocarbons as In June 1994, PHS/EHD requested that TVG diesel (TPHd),benzene,toluene, and xylenes perform additional investigation of the extent of (BTX) None of the analytes were detected above TPH-impacted soil RAH Environmental(RAH) their respective reporting limits and a northeasterly drilled and sampled seven borings(SB-1 through flow direction was determined PHS/EHD SB-7) and collected grab samples of groundwater directed TVG to install a downgradient well through the augers after reaching depths of 20 feet (MW-4) bgs(RAH, 1995a) Only three of the sixteen soil samples analyzed contained detectable ' Exceltech installed well MW-4 and sampled all concentrations of TPHg(5 1 through 2,700 four wells in January 1988 Detectable milligrams per kilogram (mg/kg)),all three hydrocarbons were present only in well MW-4 and samples from the angle-boring SB-1 (Plate 4) a westerly groundwater flow direction was Prior to submitting the above report to PHS/EHD, determined Exceltech reported the presence of a TVG performed additional investigation of the gasoline dispenser to the north on the Lopez extent of impacted soil and groundwater beneath property and suggested it may be a contributing the forklift shop offsite source PHSIEHD directed TVG to define the extent of the groundwater plume to the east, In February 1995, RAH hand augered three soil west, and northwest of well MW-4 borings(HA-1 to HA-3) in the fork lift shop to depths of approximately 16 feet bgs Soil samples WaterWork installed and sampled wells MW-5 (two per boring) were collected from the auger and MW-6 in March 1989 Detectable bucket and groundwater samples were collected hydrocarbons were present only in well MW-4 and from open boreholes TPHg was only detected in a variable westerly flow direction was determined the soil and groundwater from borings HA-1 and WaterWork reported that a 500-gallon UST was HA-2 RAH concluded that the lateral extent of L 1300001387371WP\38737N19 Harding Lawson Associates 3