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Groundwater investigation Report 1 • Country Club Drain System Project City of Stockton Municipal Utilities Department October 2 2003 Page 6 ' The investigation included the advancement of 15 borings (GP-1 through GP-15) with direct push technology (Geoprobeo) along portions of the MUD storm drain located along Country Club Blvd and Plymouth Road Four borings were advanced downgradient of the Exxon Mobil site, eight borings were advanced crossgradient and downgradient of the Shell Oil site, one boring was advanced upgradient of the Shell Oil site, and two of the borings were advanced at the south end of Plymouth Road None of the borings advanced in the area of the Exxon Mobil site were placed next to existing monitoring wells ' Three of the borings advanced in the area of the Shell Oil site were placed near existing monitoring wells Boring GP-12 was advanced near MW-9, GP-10 was advanced near MWA, and GP-9 was advanced near MW-08 ' The soil borings were hydraulically advanced using a 1 75-inch diameter bit Before advancing each boring, the bit and associated push rods were thoroughly cleaned using laboratory-grade, non-phosphate detergent and delonized water and double-rinsed with deioriized water Upon completion of the dnlling ' and sampling, the borings were grouted with neat cement to within 18 inches of the ground surface The remainder of the boring was filled to the surface with soil from the borings and capped off with an asphalt hole patch The locations of the borings are shown on Figure 2,Appendix A ' 3 31 Groundwater Sampling Groundwater samples were collected from all borings The samples were collected using a push-type ' groundwater sampler The sampler has a sealed, retrievable stainless steel screen The sampler was pushed in a closed position in the borings to groundwater The sampler push rod was then retracted exposing approximately four feet of intake screen Groundwater flowed hydrostatically from the formation into the intake screen A groundwater sample was retrieved from within the screen with a length of clean, 3/8-inch diameter polytygon tubing equipped with a check valve at the bottom The tubing was moved up and down by hand to draw groundwater up inside the tubing The groundwater 1 samples were discharged directly from the tubing into laboratory supplied sample containers The sample containers were labeled, stored in a cooler chilled with Blue Ice, and delivered, under chain-of-custody procedures, to Argon Laboratories for analysis ' 3 4 LABORATORY ANALYSES Groundwater samples were analyzed for BTEX, and selected gasoline oxygenates/additives (TBA, MTBE, di-isopropyl ether [DIPE], ethyl tertiary-butyl ether [ETBE], TAME, 1,2-dichloroethane [1,2- DCA],and ethylene dibromide [EDB]) by EPA Method 8260B 4 0 INVESTIGATION RESULTS ' 4 1 FIELD OBSERVATIONS Condor observed the advancement of 15 direct push borings at various locations along the MUD storm ' drain Borings were advanced to depths ranging from 14 to 20 feet bgs, with the majority of the borings advanced to 14 or 16 feet bgs GP-7 was advanced to 20 feet bgs and GP-12 was advanced to 18 feet bgs Water samples were collected from approximately five feet below the first encountered groundwater First groundwater was encountered at an average depth of approximately 9 2 feet bgs Boring locations are shown on Figure 2, Appendix A 4 2 LABORATORY ANALYTICAL RESULTS ILaboratory analytical results indicate TBA was detected in groundwater samples collected from two . borings (GP-10 and GP-11) at concentrations of 600 and 52 gg/L Both of these locations are in the V j �� CONDOR