ARCHIVED REPORTS XR0012602 - Laserfiche WebLink

Home Browse Search

Julian Muno•t. tiT'fS4 nsSOCIATIS February 10, 198!3 t' A continuous. cement slab was encountered at the bottom of the excavation at a 3.5 feet (Figure 1). Steel anchors attached to the depth of about 1slab stabilized the former tanks and prevented thea, from floating. The extent of the slab was determi;ted by probing with the clamshell and a backhoe. Along the east, west and soutn sides, the slab extends almost to the edges of the excavation, 1 to 2 feet pant the outer limit of the forger tanks. The northern edge of the slab was inferred from the location of the former northern tank. The thickness of the slab could not readily be determined. SUBSURFACE MATERIALS Silty clays of low estimated permeability occur from ground surface to tile bottom of the excavation at about 14 feet. These fine-grained soils would retain water or fugitive hydrocarbons in t .L backfilled tank pit or in the perched water. The low-permeability 50115 open excavation creat`_ug a basin of f ground water and diesel fuel away from the should also retard the migration o excavation. No permeable materials were encountered above about 17 feet in any of the arentl discontinuous zone of silty sand occurred adjacent borings. An app Y from 17.5 to 21.5 feet below grade in the boring of MW-3- SOIL AND BACKFILL SAMPLING Native soil samples were collected along the southern half of the excavation and pea gravel samples were collected to characterize the northern half of the excavation. Two samples of the pen gravel were collected and submitted to Brown and Caldwell Analytical Laboratories of Emeryville, California (B&C) for compositing and hydrocarbon analysis. Locations of the samples, labeled TP-B-2 and TP-B-3, are shown on Figure I. The samples were collected.....by.._driving..steam cleaned brass tubes into the pea gravel and then hermetically sealing the tubes With aluminum foil plastic end caps avid- duct- tape. The tubes were immediately labeled and refrigerated in preparation for delivery under chain of custody to B&C.