ARCHIVED REPORTS XR0010909 - Laserfiche WebLink

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Each sample collected from HP-7, HP-8, HP-9, and HP-10 was analyzed for the presence of Total Petroleum Hydrocarbons as gasoline (TPH-g) by modified EPA Method $01515030, Total Recoverable Petroleum Hydrocarbons as diesel (TRPH-d), and the volatile aromatics benzene, toluene, ethylbenzene, and total xylenes (BTEX) by EPA Method 8020. All soil analytical results are listed in Table 1. Detectable, primarily fractional BTEX analytes were detected only in soil samples collected from _. HP-7 at 15 feet, and from HP-9 at 15 feet. The highest TPH-g result was 3 mg/Kg, revealed in the sample collected from HP-9. TRPH-d results were wholly nondetectable. _ Hydropunch' ground-water samples were collected from HP-7 at 19 feet; from HP-8 at 21.5 feet; from HP-9 at 23.5 feet; and from HP-10 at 21.5 feet bsg. Boring logs of HP-7, HP-8, HP- 9, and HP-10 are included within Appendix B. HP-9 yielded the only sample impacted with elevated concentrations of TPH-g and benzene. Table 2 lists the analytical results of the _- Hydropunch' ground-water samples submitted to Sherwood Labs. New monitoring wells MW-7 and MW-8 were developed on July 7, 1995 using sterile, polyethylene bailers. Bailing removed turbid water from the wells until clear water appeared. The monitoring wells were sampled after a minimum of 40 gallons were bailed and the ground- water levels had recovered to at least 90% of their static levels. SITE GEOLOGY The site is located within the delta region of the San Joaquin River on Fourteen-Mile Slough. + The surface elevation is about nine feet above Mean Sea Level (AMSL). The slough is situated adjacent to the project area at an elevation below the former underground storage tank invert. � ) The lithology encountered during the drilling of soil borings and HydropunchesTm (prior to completion as monitoring wells MW-4 through MW-8) consisted predominantly of black-gray, micaceous, organic, clayey silt to the total depth in each well of approximately 30 feet below surface grade (bsg). Ground water was encountered in the five, on-site monitoring wells during - the October 18, 1995 monitoring activity at an average depth of 15.63 feet below the tops of the well casings. Generally, the quality of the water is considered poor. GROUND-WATER MONITORING I.A Ground-Water Sounding Monitoring wells MW-4, MW-5, MW-6, MW-7, and MW-8 were again sounded on October 18, 1995 utilizing a Keck Tm interface probe; the W.W. Irvin, Inc. staff geologist intercepted the a piezometric surface at an average depth of 15.63 feet below the tops of the well casings (see W.W. rrn n, Inc. Project No. 33016.07 December 1995 4 I ; I 1