SITE HISTORY - Laserfiche WebLink

Home Browse Search

w Ms. Laurie Cotulla July 25, 1989 Page 9 La of this letter report. Each sample tube was labeled on site to show the date, project number, sample location, and depth interval. The sealed soil samples were stored on ice in a closed ice chest and protected from meltwater. `"` Visible signs of hydrocarbons or hydrocarbon odor were noted. Periodically during the continuous sampling, relative hydrocarbon vapor concentrations were measured using a Bacharach brand combustible gas vapor analyzer. The readings were recorded on the borehole 4.6 log. The three selected soil samples were transported and delivered by Brown and Caldwell 1.+ personnel under proper chain-of-custody to Eureaka Laboratories, Inc. (Eureka), a DHS- certified laboratory located in Sacramento, California. The samples were analyzed for petroleum hydrocarbons using EPA Method 8015, modified, and BETX using EPA 8020. `.9 Monitoring Well Installation and Development. The monitoring wells were designed in the field by the on-site geologist. Monitoring wells were installed in each of the boreholes by +.0 inserting 4-inch-inside-diameter, schedule 40 PVC flush-threaded casing with 20 feet of 0.020- inch machine-slotted casing beneath the blank casing. The slotted casing extends at least 15 feet below and 5 feet above the groundwater surface in order to accommodate for fluctuations L, in the groundwater table. Bottom caps were installed at the bottom of each well. To gravel pack the wells, clean No, 1C sand was poured directly through the annulus between the casing and the auger as the auger was removed from the boreholes. The sand extends to approximately 2 feet above the slotted interval. A 2-foot-thick bentonite seal was placed immediately above the sand and hydrated. The remaining annular space was filled through L, a tremie pipe with a bentonite cement slurry under the direction of the County. A locking cap was installed at the top of the casing of each well. Each well was fitted with an at- grade locking steel box. Following installation, each well was developed using a PVC bailer. The wells were developed until relatively sediment-free water was produced. Water generated from the development process was contained on site in properly labeled drums pending laboratory results. ARCO is responsible for the disposal of the water. When the RWQCB deems that monitoring groundwater quality is no longer necessary, ARCO will be responsible for the proper abandonment of the wells. All downhole drilling equipment was steam cleaned prior to use at each borehole. All soil and groundwater sampling equipment was washed with laboratory detergent and tap water, and then rinsed with deionized water prior to each use. As described in the Background section of this report, the geology underlying the site is a sequence of sand, silt, and clay. Groundwater occurs in a continuous layer of silt at approximately 11 feet below ground surface. _ BROWN AND CALDWELL 723 S STREET SACRAMENTO,CALIFORNIA 95814-7092•(916)444-0123