ARCHIVED REPORTS_XR0012607 - Laserfiche WebLink

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RIB" Decembc: IS, 1991 ` Dormer Unocal Bladon 2859. Stoclrton, California --- A Y, r Applied GeoSysterns began,""environmental investigation in conjunction with unde reolor d- storage tank removal in ,1%Iarch and April 1988. During this investigation, a g S ist observ�cl rcrnoval of site underground storage tanks and collected soil samples for laboratory analysis of hydrocarbons. Results of aaalyses indicated tltat hydrocarbons were present in the sol! underlying the tank cavity (Applied GeoSysterns, April 2.8, 1988, Report No. tale3SOS 1). III Jane 1988, we ir;stalled eround-water monitoring wells MW-1 throueh iVi1Y 3 (Applied GeoSysterns. July 28, 1988, Report No. 38012-2). Results indicated a further investigation of ground water down-gradient was wa-ranted. Therefore,in August 1989,two groundwater wells were installed offsite to delineate dissolved hydrocarbons (applied mo GeoSvstems, December 12. 1990, Report No. 38012-5). In response to the detection of hydrocarbons in soil and ground water. Applied GeoSystems began periodic monitoring of the 7round water in June 1988. Results of Previous monitoring events indicated that dissolved hydrocarbons were detected in water samples coliected from the fiva wells; tite ltigltest concentranoils of ltycrucarbons were detected ill well iV11V-2. We evaluated the direction of ground-water flow to be northeast from June 1988 to May 1990 (before the wells were dry). The average gradient was 0.002. The direction of ground water flow for yiMay 30. 1990, was to the northeast as shown on Plate 2. GROUND-WATER SAMPLING A RESNA technician was onsite August 25, 1991, to collect groundwater samples front wells MW-4 and ivi%V-S for subjective analysis using procedures summarized in an attachment to this report. The technician noted 'to subjective evidence of hydrocarbons in the two wells. Cumulative results of subjective analyses are presented its fable I. The technician purged wells ,IMW-4 and and collected water samples for laboratory analyses. A Chairs of Custody Record was initiated in the field and accompanied the samples to the laboratory. A copy of that record is attached. The methods of ground-water sampling are discussed in an attachment to this rr:port. The purge water was stored onsite in properly labeled 17-E steel drums pending the results of laboratory analyses. At Unocal's request, drummed water was subsequently removed and disposed of by Armour Petroleum Fairfield. California. on September ?. 1991. Service and Equipment Corporation of LABORATORY ANALYSES AND RESULTS The water samples were submitted for analyses of total petroleum hydrocarbons as gasoline (TPHg)using modified Environmental 1't .section Agency(EPA) Method 8015 and benzene. toluene, ethvlbenzene, and total sylerte isomers (BTEX) using EPA Method 602. Laboratory analyses were performed Applied Analytical Environmental Laboratories in ns3on;5 � NOW