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i File No.2070-2 19 December 1991 ^-^\ Page 4 borings (see Appendix III for boring logs). Two inch diameter, schedule 40 PVC well casing was then installed and the wells constructed as detailed in the well construction diagram of Figure 3. Soil cuttings derived from the drilling of the well borings were containerized in 55-gallon drums. The drums were stored on the site pending laboratory analyses determining whether soil contamination was detected. Static groundwater level measurements were then obtained for all five onsite monitoring wells(the two newly-installed ACG wells and the three existing ESE wells). Calculations indicated that the local groundwater gradient tended toward the east/northeast (see Appendix V for groundwater - gradient calculation procedure). Following well development (see Appendix VI for monitoring well development procedure), groundwater samples were obtained from MW-4 and MW-5 (see Appendix VII for groundwater sampling procedure) and analyzed by a State of California certified analytical laboratory for the presence of TPI?, AVO's and lead. Detectable levels of AVO's (benzene, toluene and xylenes) were detected in the groundwater sample obtained fzomitIW-4. The groundwater sample obtained from h4W-5 exhibited ro detectable levels of TPH, AVO's or lead. To aid in the estimation of a lateral "zero line"of groundwater contamination, ACG installed two, additional monitoring wells at the subject property, thus bringing the tots! of onsite monitoring wells to seven (see Appendix IV for applicable well permits). Monitoring well 6 (MW-6) was installed on 15 February 1990 at a location up-gradient from the source of the contamination (see Figure 2). Monitoring well 7 (MW-7) was installed on 21 February 1990 at a loc=ation down-gradient from the source of the contamination. Both wells were advanced to a depth of 55 feet utilizing eight inch, hollow stem, flighted augers driven by a truck-mounted drill rig. Subsurface soil conditions were logged by an onsite geologist during advancement of the well borings (see Appendix III for boring logs). Two inch diameter schedule 40 PVC well casings were then installed and the wells constructed as detailed in the well construction diagram of Figure 4. Soil cuttings derived from the drilling of the well borings were containerized in 55-gallon drums. The drums were stored on the - site pending laborato►y analyses determining whether contamination was detected. Following well development (see Appendix VI for monitoring well development groundwater samples were obtained from MW-6 and MW-7 see A ,p pro cedure), Appendix ater sampling procedure) and analyzed by a State of Cali16mia certifiedanalyticalfor the presence of TPH AVO's and lead. Aaalysis of a groundwater sample obtained from MW-6 : detected no TPH, AVO's or lead. MW-6, therefore, allowed an up-gradient "zero line" of contarninatl-on to be estimated and subsequently is the up-gradient control well. A groundwater sample obtained from MW-7, however, exhibited detectable levels of AVO's. Since MW-7 was intended to be the down-gradient control well, it was decided to re-sample MAV-7 in oder to corroborate the first sample results. However, the second groundwater sample obtained from MW- 7 also exhibited detectable levels Of AVO's. Since both groundwater analyses of MW-7 had detected contamination, iY1W-7 could not be utilized as a control well for the down-gradient direction of the contaminantplume. Therefore, on 4 September 1990,MW-li was installed on the subject property approximately 100 feet down-gradient from MW-7 (see Figure 2 for location and Appendix IV for applicable well permit). MW-8 was ANDERSON of CONSULTING . ��. GpOLIP - +aim Ems.