SITE INFORMATION AND CORRESPONDENCE FILE 1

Home Browse Search

CALIFORNIA GEOPHYSICAL GROUP , INC . P . O . Box 578341 , Modesto, CA 95357 Tel : (209) 527- 1247 May 25, 2001 Fax : (209) 527-4810 Public Health Services San Joaquin County 304 East Weber Ave. 3 floor Stockton , CA 95202 Attn : Mr. Mike Infurna RE : Darpetro , Inc. USA Service Station , 749 E. Charter Way, Stockton , CA, Site No. 1060 This site has MtBE in the groundwater. During 2000, we tested the tank installation and reported it to the EHD of San Joaquin County. No leaks were found in the tanks or in the piping connected to the tanks. We also had a CPT rig drill a hole just north of the tank and took discrete water samples. No MtBE was found at 39 feet, however, at 50 and 60 feet below the surface MtBE was found . This was reported in our Drilling Activity Report dated December 14, 2000. There was MtBE in the quarterly monitoring water at BM-3 and BM-2 prior to the drilling of B-3 . Wells BM-2 and BM-3 are completed to a depth of 50 feet. Also in our May 7 , 2001 Quarterly Monitoring Report, we found well BM-3 had MtBE and TBA in the groundwater. TBA and MtBE have been in this well water since January 1998. However, we recorded in the May Report that there was no gasoline TPH or BTEX chemicals in the BM-3 water. We believe that MtBE alone without gasoline indicates that the MtBE has not come from the tanks or pipes , which are about 20 feet north of BM-3 . We, therefore , believe that the MtBE and TBA is arriving at well BM-3 from stations west of this site. The groundwater gradient has flowed to the northeast and east-northeast since April 1992 and the average gradient if 0. 004 Ft/Ft. In 1993 when we did the hydraulic conductivity test the water was 53 feet bgs. The water table has risen to about 32 feet bgs since 1998 and is now in a different soil layer, possibly the hydraulic conductivity has changed . The closest station to the west-southwest is 100 feet from well BM-3. The average linear i velocity of the groundwater has been 0. 10 Ft/day, therefore , it takes about 1000 days or i 2 . 7 years to flow from the nearest station to well BM-3 . In June 1995, we drilled two hydropunch wells around the Sun Gardens Property west of this station . Hydropunch borings HP-1 and HP-2 found gasoline coming from the stations west of the Sun Gardens property. Well BM-9 has had TPH and BTEX concentrations since it was drilled in September 1994. We recorded in October 2000 and February 2001 that MtBE had arrived at well BM-9 and there was an indication that it may have arrived at that well in July 1998 and July 1999 . This well has had TBA since it was first tested in October 1997 . {