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II Mr. Harlin Knoll February 15, 2000 Page 3 of 4 the former USTs to the south and west. Residual contamination in the soil appears to attenuate I'I rapidly, as no contamination was detected in any soil samples collected from 15 feet bgs or below. An estimated 1,300 cubic yards of soil between the depths of approximately 6 and 13 feet bgs has been impacted beneath the site. The estimated area of sc it contamination is shown on Figure 3. 3.2 Groundwater Contamination Groundwater beneath the affected soil has been impa ted by petroleum hydrocarbons and the oxygenated fuel additive MTBE. The lateral extent of shallow groundwater contamination beneath .� I the site is largely defined to the north and the south, but has not been fully defined to the west or the east. The estimated extent of dissolved petroleum hydrocarbon constituents in groundwater is shown on Figure 4. 4.0 WORKPLAN 9 r remove residual soil contamination from the approximate area We propose using an excavator to depicted on Figure 3. Excavation will continue laterally until field evidence indicates that the majority of contaminated soil has been removed. Excavation will proceed vertically to an estimated ;r depth of approximately 13 feet. Soil excavation will be performed by Oil Equipment Service, a Division of Keith A. Tallia, Inc. Ground Zero anticipates that approximately 1,100 cubic yards of clean overburden soil will be removed prior to excavating contaminated soil. The clean soil will be stockpiled separately from the contaminated soil and confirmation soil samples will be collected at a frequency of one 2:1 'f composite sample per 100 cubic yards of excavated soil Documented clean soil will be utilized as backfill. The anticipated stockpiling location is shown o i Figure 5. Approximately 1,300 cubic yards of contaminated soil is expected to be removed. The contaminated soil will be temporarily stockpiled on site on 6-mil plastic sheeting and confirmation soil samples will be collected at a frequency of one 2:1 composite sample per 100 cubic yards of excavated soil. Contaminated soil will be aerated un er a permit for uncontrolled soil aeration . issued by the San Joaquin Valley Unified Air Pollution Control District (APCD). The anticipated III area for soil aeration is shown on Figure 5. Ground Zero anticipates collecting 12 confirmation soil amples from the sidewalls and floor of the excavation to document the removal of impacted soil. In addition, one groundwater sample will be collected from the excavation pit. Samples will be analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX) using EPA method 8020, total petroleum hydrocarbons as gasoline (TPHG) and diesel (TPHD) using EPA 8015 modified, and gasoline xygenate additives using EPA 8260. Upon completion of the excavation, Oil Equipment Service will line the bottom and the sides of the excavation with Typar filter fabric prior to backfilling the excavation with crushed rock to approximately one foot above the static groundwater level. Another layer of fabric will be placed on top of the crushed rock prior to placing and mec anically compacting the remainder of the .I G:Mata1GROL NDZEIMANSER\Manser 2linterimwp.doc I�