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. Date June 6, 2040 ARCO QUARTERLY GROUNDWATER MONITORING REPORT i I Facility No 2130 Address 7906 EI Dorado Street, Stockton, California ARCO Environmental Engineer Paul Supple Consulting Co/Contact Person IT Cor oration/David Foley Consultant Project No 803879 00010000 Primary Agency/Regulatory ID No Mike Infuma, San Joaquin County Public Health Services WORK PERFORMED THIS QUARTER (First 2000) 1 Groundwater samples were collected from monitoring wells MW-1 through MW-7 and MW-10 and submitted for laboratory analysis 2 IT compiled and evaluated groundwater monitoring data 3 IT conducted routine operation and maintenance of the air bubbling system to increase dissolved oxygen (DO) levels in the wells at the site and, thereby, help to promote biodegradation of hydrocarbon-impacted groundwater 4 IT shut down the sod vapor extraction(SVE) system in the fourth quarter 1997 due to low influent sod vapor concentrations The system remained down this quarter due to low hydrocarbon concentrations in the influent sod vapor The heating elements in the Katox 100000 Catalytic Oxidizer faded in January 1999 Additionally, higher groundwater elevations have limited the amount of available screen 5 IT submitted a letter on September 21, 1999, requesting a change in the groundwater monitoring requirements Oxygenate results dating back to November 1997, show that methyl tert butyl ether (MTBE) is the only oxygenate detected in groundwater samples, and MTBE concentrations are consistently below 10 micrograms per liter Therefore, the discontinuance of oxygenate analysts by USEPA Method 8260, was proposed Future monitoring events would utilize USEPA Method 8020 for MTBE analysis WORK PROPOSED FOR NEXT QUARTER (Second 2000) 1 The next sampling event is tentatively scheduled for June 2000 Groundwater samples from wells MW-1 through MW-7 and MW-10 will be collected and analyzed for total petroleum hydrocarbons as gasoline (TPHG) using U S Environmental Protection Agency (USEPA) Method 8015, for benzene, toluene, ethylbenzene, and total xylenes (BTEX), and methyl tert-butyl ether (MTBE) using USEPA Method 8020, and for oxygenates tertiary butanol, MTBE, di-isopropyl ether (DIPS), ethyl tertiary butyl ether (ETBE), and tertiary amyl methyl ether (TAME) using USEPA Method 8260 2 The SVE system will be pulsed on a periodic basis (one week per month) 3 operation of the air bubbling system will continue to increase DO levels at the site The low flow system will operate on a continuous basis CP1N\CamPk\Data\ArcfvvelAxo121301Qtrly12130Q100 DOC-97w 2 IT Corporation 06/06/00