ARCHIVED REPORTS XR0010914 - Laserfiche WebLink

Home Browse Search

f. The excavation was backfilled in May 1994 subsequent to collection of stockpile soil samples for single-sample-composite analyses in order to detect residual TPH-g and TRPH-d analytes. Favorable results (all analytes were nondetectable) allowed for stockpile backfill, approved in a letter dated May 10, 1994 from SJCPHS EHO Specialist Michael Collins to Mr. Dwight Davis of the Pegasus Group. ` Hydropunch' Sampling - April 8, 1994 €' Under the supervision of Specialist Collins, three Hydropunch'boreholes (HP-1, HP-2, and HP- `"' 3 shown on the Site Sketch, Figure 2 and the Ground-Water Gradient Map, Figure 3) were drilled near the north, east, and west flanks of the overexcavation. Borehole soil samples were `'- togged at five-foot intervals by the W.W. Irwin, Inc. field geologist; the samples were chilled and retained for laboratory analyses, but the analyses were not required by the SJCPHS-EHD. Ground water was encountered at an average depth of 23.7 feet bsg. When analyzed, the ground-water samples collected from HP-1 and HP-2 revealed BTEX analytes in nondetectable or fractional concentrations; the sample from HP-1 exhibited 86 µg1.0 t` of TPH-gasoline. The sample collected from HP-3 exhibited a benzene concentration of 160 jcg/C, prompting the SJCPHS EHD to order the completion of three monitoring wells for ground- water direction and gradient determination, and possible definition of the contaminant migratory path. Drilling, Sampling, and Completion of Three Monitoring Wells On June 6, 1994, soil borings 4, 5, and 6 were drilled and completed as ground-water monitoring wells MW-4, MW-5, and MW-6. This sequence of well numbers was selected by the field geologist in order to avoid confusion regarding the previous Hydropunch'numbers HP- 1, HP-2, and HP-3. All monitoring wells were drilled, sampled, and completed in order to 'i determine the horizontal and vertical extent of soil and ground-water contamination and to allow ? ! for calculation of the ground-water flow direction and gradient. The monitoring well locations are depicted on the Site Sketch, Figure 2. W.W. Irwin, Inc. of Merced served as the environmental consultant while Woodward Drilling Company of Rio Vista drilled and completed the wells to a total depths of 30 feet. Collected soil samples were placed in an ice chest chilled to 4°C and dispatched to Sherwood Labs. Inc. of Hilmar using appropriate chain-of-custody procedures. Each sample collected to a depth of 20 feet was analyzed for the presence of Total Petroleum Hydrocarbons as gasoline (TPH-g) by modified EPA Method 801515030, Total Recoverable Petroleum Hydrocarbons as 1 diesel (TRPH-d), and the volatile aromatics benzene, toluene, ethylbenzenc, and total xylenes (BTEX) by EPA Method 8020. Detectable, primarily fractional BTEX analytes were detected only in soil samples collected from MW-6. The highest TPH-g result was 39 mg/kg, revealed in the sample collected from MW-6 at 15 feet bsg. TRPH-d results were nondetectable except for 8 mg/kg of weathered diesel revealed in the sample collected from MW-5 at 5 feet. k W.W. Irvin, Inc. Project No. 33016.04 <__/ January 1995 3