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i i Mr.Jeffrey M.Baker,RE Baseline Assessment for Soil Boring and Monitoring Well Installation April 30,2004 �.- Page 2 Soil Boring Installation and Soil Sampling On November 21, 2003, Delta Environmental Consultants Inc. advanced soil borings B-1 through B-4 (Figure 2). Soil boring B-1 encountered refusal at approximately 10 feet below surface grade (bsg), B-2 at approximately I1 feet bsg, and B4 at approximately 10 feet bsg. Soil Boring B-3 was advanced to 30 feet bsg as planned. A soil boring log was only prepared for B-3 Enclosure C). Soil Borings B-1, B-3, and B4 were grouted and B-2 was comp]. On December I and 3, 2003,Delta returned to the site with a Sonic drill rig and advanced four soil borings,three of which were converted to groundwater monitoring well 3 (B-2, MW-1, MW-2 and MW-3). Soil boring B-2 was advanced to 30 feet bsg and MW-1 through MW-3 o 60 feet bsg. Soil samples collected for lithologic description were screened for volatile organic vapors usir.g a photo-ionization detector (PID) and recorded on the boring logs presented in Enclosure C. The results fort a highest concentrations are as follows: MW-1 at 30 feet bsg was 28 parts per million volume(ppmv), at 35 feat bsg was 37 ppmv, at 40 feet bsg was 18 ppmv, and at 45 feet bsg was 15 ppmv. Groundwater was encountered at approximately 50 feet bsg. The PID readings for the soil screening for M:WA were the highest recorded and the only ones that appeared to be greater than background levels. They were above the threshold established in the Baseline Conditions Requirements provided by Tesoro and USA. As a result,groundwater monitoring wells were installed at the site. Locations of the soil borings and additional monitoring wells are shown on Figure 2. Soil samples were collected at five-foot intervals and logged to the total deptb drilled. Soil types encountered were classified using the Unified Soil Classification System, Visual/Manual Method, and recorded on the soil boring logs. Field methods and procedures used by Delta during installation of the soil borings are summarized in Enclosure B. Soil boring logs are presented in Enclosure C. Soil samples were selected from the borings for chemical analysis,based on field screening results, depth of soil samples, and soil lithology. Samples were submitted tc Kiff Analytical LLC. (Kiff), Davis, California for analysis of benzene, toluene, ethylbenzene, and total xy enes (BTEX), 5 oxygenenates, and total petroleum hydrocarbons (TPH) in the gasoline range using EPA Me hod 8260B, and TPH in the diesel range using EPA Method 8015 modified. Soil samples were collected using the procedures described in Enclosure B. Soil sample laboratory analyses results are summarized in Table 1 and the laboratory reports presented in Enclosure D. Monitoring Well Installation The monitoring wells were constructed of 2-inch diameter flush-threaded, Schedule 40 PVC casing. They have approximately 5 feet of screen above the water table a d 10 feet beneath the water table. All wells were screened with 0.020-inch slotted casing. The annular space of the well was backfilled with Lonestar No. 3 sand to approximately two feet above the screened section. Following the installation of the filter pack, each monitoring well was surged with a surge block to set the lter pack material. Additional sand was added to the annulus when required to maintain the filter pack over the top of the well screen. A two-foot thick bentonite seal was placed above the filter pack. The remaining annulus as filled with cement/bentonite slurry (grout), mixed in accordance with SJCHD specifications, to approximately six inches above surface grade. The surface was completed with an 8-inch traffic rated well box set in co erete. The well construction details are included in Enclosure C.