SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

f ;JHfd-2y-1953 17.53 FROM TO 12094640138 P.03 ' 1 e y �:r 1l�ra!'lyCCY S1 'r 4445 Per mr.q Avenue.SttaekW.CEditmla It was not requested and Aegis did not intend to conduct any of the subsurface investigations at the site by methods other than the above. Monitoring wells MW-1, MW-2, and MW-3 were installed on site in July 1990; penetrating from 15 to 20 feet into the saturated zone. Aegis prepared the workplan for the installation of well MW4 in responso to a letter from the SJCEHD to Shell, dated October 7, 1991, requesting "repeatable sampling from a monitoring well downgradient from the probable source.' Well MW-4 was installed in December 1991 after review and approval of the workplan by the SJCEHD. The estimated groundwater flow direction at the site has been consistently to the east- northeast, placing MW-4 approximately 20 feet downgradient of the location of soils indicating the highest concentrations of hydrocarbons during the removal of the farmer underground fuel tanks. Well MW-4 penetrates approximately 10 feet into the saturated zone as estimated from average static depths to groundwater from July 1 to present. The soils beneath the former tanks in the vicinity of the petroleum hydrocarbons indicated during sampling were vented during a vapor extraction pilot test performed at the site from early December 1991 to February 1992. Air monitoring data indicated petroleum hydrocarbons in concentrations of up to 5,500 parts-per-million volume were removed from soil. The deepest soil sample analyzed from the boring f6r MW-4 (29,5 feet below surface) was below the detection limits for all petroleum hydrocarbons tested. The deepest soil sample analyzed to date from the site (t(llected at 35 feet below surface in the boring for MW-1) was also below the detection limits for all petroleum hydrocarbons tested. To date, eighteen soil borings have been drilled and sampled on site at locations surrounding the former tanks, product piping, and fuel dispensers. The borings ranged in depth from 21 to 51 feet below surface. Hydrocarbons have not been indicated by laboratory analysis above the respective detection or reporting limits in any soil samples collected from below the top of the saturated zone. The investigations have been documented by Aegis in reports dated November 15, 1989, June 14, 1990, March 5, 1991,. and April 27, 1992. Aegis would be pleased to provide additional copies of the reports If for any reason they are not currently in the SJCEHD project file. The October 8, 1992, monitoring event represents the fourth consecutive quarter the samples collected from all four monitoring wells on site have indicated concentrations below the respective detection limits for all petroleum hydrocarbons tested. The tank repair and replacement history and the cross section requested in the December 9, 1992, letter will be included with the first quarter 1993 quarterly monitoring report, egoy SY.ITR -z- yy