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RECENT WORK On July 15 1999 we drilled one monitoring well The monitoring well (BM-12) was drilled to a depth of 60 feet below the surface (bgs) One foot of sloughing material fell into the well before the casing was landed The slotted 2 inch casing extends from 29 to 59 feet bgs Blank 2 inch casing extends from 29 feet to the surface Number 3 sand was placed opposite the slotted casing and 3 feet above the slotted casing A hydrated bentonite transitional seal was placed between 26 and 29 feet and from 26 feet to the surface the annulus was filled with hydrated cement A steel traffic box was placed over the well This well was then developed by removing about 50 gallons of water At that time the pumped water was free of silt and sand and most of the clay The well casing was surveyed to sea level through the Stockton City BM-29 ' On July 16, 1999 we drilled one deep boring (B-3) to attempt to find the vertical limas of the contamination This boring was drilled to a depth of 80 feet bgs Soil samples were taken every 5 feet and the samples from 60 feet to 80 feet were tested by a mobile laboratory on site for this work Because contamination was found, we had the laboratory test some of the soil samples for diesel No diesel was found We performed this test because the deeper level tests had a high amount of compounds which could have been diesel The boring was partially abandoned since the driller did not have any more augers to go deeper We backfilled this hole with hydrated bentonite chips from 80 to 45 feet We then constructed a vapor extraction well (VW-7) in the remainder of the boring Slotted casing was set between 45 and 15 feet bgs and blank casing was set between 15 feet and the surface Number 3 sand was placed opposite the slotted casing and to 14 feet Above the sand a hydrated bentonite transition seal was placed between 14 and 12 feet bgs The remainder of the annulus was filled with hydrated cement The well is protected with a steel 18 inch manhole All the drill cuttings were placed in steel drams and are being removed to a landfill within a few weeks See Bonng Logs and Cross-section Figure 1 GEOLOGY The site and all nearby terrain are underlain by non-manne fine grained sediments which are tentatively assigned to the Modesto Formation of Pleistocene age ( USGS Bulletin 1470 Marchand and Awordt, 1981) Although the Modesto is typically composed of coarser-grained material such as sands and gravels it is reasonable on the basis of stratigraphic position, to consider these finer-grained sediments to be a distal portion of the large alluvial fans which make up the Modesto The materials penetrated in this sites borings are chiefly clay, silty clay and clayey silt Sandy strata, although present, are relatively minor and are silty or clayey and fine- grained Bedding is absent or non-distinct but appears to be essentially honzontal The soil unit found in most of the bonngs at 60 feet is a clay or a silty clay It is a silty clay in the area around the former tank pit and becomes a pure clay at wells BM-8 and BM-7 as well as VW- 7 W7 A silty clay is more permeable than pure clay The silty clay unit found at 60 feet in the former tank area must extend down below the 60 foot level and interconnects with silty clay lenses where 4 II I