Laserfiche WebLink
3.0 Investigation Procedures <br /> 3.1 Drilling <br /> On October 16 and 17, 1989, five soil borings were drilled <br /> to a depths ranging from 11 to 29 feet below grade. Four of <br /> the borings were completed as groundwater monitoring wells <br /> (MWl to MW4). Drilling was conducted with a B-61 rig using <br /> eight inch diameter (O.D. ) hollow-stem augers. The drilling <br /> was performed under the direction of a field geologist who <br /> maintained a continuous log of the material encountered <br /> using the unified Soil Classification System (Appendix I) . <br /> ; L The well borings were drilled in numerical order with well <br /> MW1, initially believed to be in the down gz:oundwater <br /> gradient direction, being the first well completed. Because <br /> no indications of hydrocarbon contamination were detected by <br /> field inspection during drilling of this well, the next <br /> boring SB1 was drilled on the opposite (northerly) side of <br /> the tank pit. Slight to moderate diesel odor was noted in <br /> this boring between 5 and 11 feet below grade. As such, the <br /> gradieL.It was anticipated to be in this direction. To <br /> provide for down gradic- . definition of the contamination <br /> wells MW2 and MW3 were installed to the north and northeast <br /> of the former tank pit. The relative groundwater elevation <br /> was calculated by monitoring depth to water and surveying <br /> wellhead elevations after the installation of each well. <br /> This data confirmed that the groundwater flow at the time of <br /> drilling was to the north. Well MW4 was located as close as <br /> possible to the suspected source of soil contamination <br /> between the former u/g tank and product line location. <br /> Because there were a number of u/g utilities whose exact <br /> r location was not known the drilling locations were severely <br /> limited. <br /> The wells were construnted of two inch diameter flush <br /> ' threaded F480 PVC screen/casing. No glues or solvents were <br /> is used in well construction. Monterey silica sand (#3) was <br /> placed in the annular space around the 0.020 inch slotted <br /> � - screen. A two foot bentonite seal was placed above the <br /> :.; sandpack prior to surface sealing with neat cement. <br /> Specific well construction details are presented in <br /> Appandix 2. The soil soil boring was abandoned by filling to <br /> glade with neat cement. The location of the four wells and <br /> one soil boring is shown an Figure 3. The drill cuttings <br /> were stored on an asphalt surface adjacent to the former <br /> tank pit and covered with plastic sheeting. <br /> Subsequent to completion, the wellheads were surveyed to a <br /> common datum and groundwater levels monitored to determine <br /> the site specific: groundwater gradient. Depth to <br /> groundwater was measured in accordance with WaterWorks <br /> Groundwater Monitoring Protocol (Appendix II) . The wellhead <br /> survey and groundwater monitoring data are presented in <br /> .,r Table 1. <br /> 2 <br />