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" MANS, N 1 File No.2070.2 19 Dscember 199I - Pare 4 borings (see Appendix III for boring logs). Two inch diameter, s:h�Jt0e 40 PVC well casing was then installed and the well;,constructs: as detaif6' in the well construction diagram of Figure 3. Soil cuttings dedveu from'the drilling of the well borings were containerized in 55-gallon drums.. The drums wern 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 tha local groundwater gradient tended toward the east/northeast (see Appendix V for groundwater gradient calculation procedure). PAlowing 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 TPN, AVO's and lead. Detectable levels of AVO's (tenzene, toluene and xylenes) were detected in the groundwater sample obtained from MW-4. The groundwater s:*nple obtained from MW-5 exhibited no detectable levels of TP.H, AVO's or lead. To aid in t',.e estimation of p lateral "zero line"of groundwater contamination, ACG installed two, additional monitoring wells at the subject pronerty, thus bringiag the total of onsite monitoring wells to seven (see Appendix IV for applicable well permits). Monitoring well 6 evnV-6) was installed on 15 February 1990-it a location up-gradient from the source of the contamination (see Figure 1, 2). Monitoring well 7(MW-7) was installed on 21 February 1990 at a location 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 truce:-mounted drill rig. ;Subsurface soil conditions were logged by an onsite geologist during advancement of,he well borings (see Appendix III for boring logs). Two inch diameter schedule 40 ki_4 well cas"ngs were then installed and the wells constructed as detailed in the we!'construction diagram of Fixture 4. Soil cuttings derived from the drilling of the well b&ings were containerized is 55-gallon drums. The drums were stored on the site pending laboratory analyses determining wheu%er contamination was detected. Following well development (see Appendix VII for monitoring well development procedure), grot%ndwater samples were obtained from MW-6 anal MW-7 (see Appendix VII for groundwater sampling procedure) and analyzed by a State of California certified analytical laboraiury for the presence of TPH, AVO's and lead. Analysis of a groundwater sample obtained from MW-6 detected, no TPH, AVOV's or lead. M45, therefore, allowed an up-gradient "zero lists" of contamination to he estimated and subsequently is the up-gradient consrol well. A groundwater sample obtained, from MW-7, however, exhibited detectable levels of AVD- Since n ord was intended to be the down-gradient control well, it was decided to re.-sample MW-7 in order to corroborate the first sample results. However, the second groundwater sample nbtaincd from MW- 7 also exhibited detectable levels of AVO's. Since both groundwater analyses of MW-7 had detect+ contamination, MW-7 could not be utilized as ,i control well for die down-gradient direction of the contaminant: plume. Therefore, on 4 September 1990,MW-3 was installed on the subject property approximately 200 feet down-gradient from MW-7 (see Figure 2 for location and Appendix 1V for applicable well permit). MW-13 was LANDERSON CONSULTING :- Group