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- E _ . NVIROl� 1vIENTAL HEALTH JEPARTMENT PauIN SAN JOAQUIN COUNTY p CO ?� y Donna K. Heran, R.E.H.S. Unit Supervisors 0 / < Director 304 East Weber Avenue, Third Floor Carl Bergman, R.E.H.S . Laurie A. Cotuna, R.E.H.S. Stockton, California 95202-2708 Mike Huggins, R.E.H.S ., R.D.I. cg4Foeei�P • Program Manager Telephone: (209) 468-3420 Douglas W. Wilson, R.E.H.S. Margaret Lagorio, R.E.H.S . Fax: (209) 464-0138 Robert McClellan, R .E.H.S. Website: www.sjgov.org/ehd/ Jeff Carruesco, R.E.H.S . DAVID GUARDINO AND PAT GUARDING JUN 2 7 2006 GUARDING AND CRAWFORD CONSTRUCTION 517 W FREMONT ST STOCKTON CA 95201 RE: GUARDINO AND CRAWFORD SITE CODE: 1112 517 W Fremont St, Stockton CA 95201 San Joaquin County Environmental Health Department (EHD) has reviewed Fourth Qmarter Monitoring Refiort 2005 dated April 123 2006 prepared by your consultant, Advanced GeoEnvironmental, Inc. (AGE) . The groundwater contamination plume has remained centered around monitoring well MW-1 located approximately 7 feet south of the tank excavation and near the piping trench. The recent analytical results of MW-1 groundwater samples were 32,000 micrograms per liter (ug/1) total petroleum hydrocarbons as gasoline (TPH-g) and 8,600 ug/l benzene. The only other well with contamination detected was MW-2 at 7.7 ug/l benzene and "non-detect" for TPH-g. The remaining six monitoring wells, MW-3 to MW 8, were all "non-detece' for all analytes including TPH-g, aromatic hydrocarbons, 5 oxygenates, :and 1 ,2-dichlotoethane and 1 ,2-dibromoethane. The highest contaminant concentrations in MW-1 were recorded in November 2000 at 120,000 ug/1 TPH-g and 18,000 ug/l benzene. The concentrations rose again in September 2005 to 85,000 ug/l TPH-g and 40,000 ug/l benzene (the highest for benzene) . Historical groundwater low elevation was approximately 55 feet below surface grade (bsg) in 1978 according to San Joaquin County Flood Control Lines of Equal Depth to Groundwater in Spring 1978. Groundwater flow direction was toward the northwest in the past, but has shifted toward the east and northeast the last few quarters. Results of historical quarterly samplings of the monitoring wells since July 1999 indicate the core of the groundwater plume to be in the immediate area of MW-1 . One lateral edge of the plume extends to approximately MW-2 where the concentrations have declined significantly since 1999. Results of deep grab groundwater samples collected by cone- penetrometer testing boring CPT1 at 33, 55, and 80 feet below surface grade (bsg) in October 2004 were "non-detect" for all analytes . The groundwater plume appears to be defined both laterally and vertically. The bottom of the tank excavation in June 1989 was approximately 13 . 5 feet bsg, and 4. 5 feet bsg in the piping and dispenser area. Although neither odor not discoloration was noted in the three soil samples (2 tank pit and 1 piping samples); the analytical results of soil sample #2 (south) were 68 kg/mg TPH-g, and from soil sample #3 (piping) the results were