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CALIFORNIA GEOPHYSICAL GROUP, INC. P.O. Box 691, Poway, CA 92074 Tel: (619) 486-1323 1 of 4 Pages FAX: (619) 484i�6 WORK PLAN 7 "tA FOR CASCO SERVICE STATION MAR 1 1 1193 749 E. CHARTER WAY STOCKTON, CALIFORNIA ENVIRONMENTAL HEALTH December 11, 1991 PI.1IIT�S �1�fCE SITE HISTORY On November 14, 1989 three underground tanks were removed from the site in accordance with the Tri-Regional regulations. Testing of the soil samples taken around the old tanks indicated. the site had been contaminated with gasoline. The excavation site was backfilled with the original soil plus soil from a new excavation. The site was then remodeled and placed back in service. A work plan for assessing the contamination of the site was sent to the the San Joaquin Health Department of Dec. 29, 1.989. The plan was accepted and a special well permit was issued on Jan. 19, 1990. Drilling and sampling according to the work plan began on Jan. 22, and finished on Jan 26, 1990. A Site Assessment report was submitted to San Joaquin County Health on February 9, 1990. On October 1, 1990 we began quarterly sampling but by that time the water table had dropped below the bottom of the wells and has remained below the wells to this time. In April 1992, we drilled three additional wells at the site into and well below the water table. The results of this work were reported in our Site Assessment of April 30, 1992. SCOPE OF WORK During the quarterly measuring event of January 1993, we discovered about 3 inches of floating product in MW-5. Using the CONCAWE formula H = h x (pw-po)/Po, where H is the thickness of the plume on the water table, h is the measured depth of floating product in the monitoring well, pw is the density of water and po is the density of the floating product, we calculate the plume thickness to be about 0. 75 inches thick. In an effort to remove some of this product now we propose to pump about 55 gallons of product from the well at a rate of about 2 GPM. We will then allow the formation to recover for �►- at least 48 hours and if floating product is still present we will repeat the original operation. If after two pumpings floating product is present we will assess the value of continuing this process .