22 ATTACHMENT 02 - Laserfiche WebLink

The borehole for MP-I was terminated at a depth of 29.5 feet below ground surface (BGS), while the borehole for MP-2 was terminated at a depth of 17 feet BGS. These termination depths coincide to app-.oximately 15 feet below the proposed building pads. Findings from the soil sampling program revealed soil profiles consisting of sandy silt and silt with sand units at both locations. Based on the relatively unifomi and fine-grained nature of the underlying soils,single probes were installed at both locations. The probes were constructed of 1-inch diameter, Schedule 40 polyvinyl chloride (PVC) slotted (0.02-ioch machine slot) and blank casing. The slotted intervals for MP-1 and MP-2 were placed from 16.5 to 26.5 feet BGS and eight to 17 feet BGS, respectively. Coarse sand (#3) was placed around the slotted intervals, followed by hydrated bentonite chips to within approximately two feet of ground surface. The upper two feet of the boreholes were backfilted with compacted soil. The tops of the probe casings at ground surface were fitted with labcock valves to facilitate monitoring. Please refer to the soil boring logs in Appendix B for graphic illustrations of the probe construction characteristics. The probes were allowed to stabilize for one week after installation, whereupon a monitoring event was performed by EBA on October 18,2012. The monitoring event encompassed initially' measuring static pressure conditions using a Magriehelic pressure gauge, followed by purging one probe volume equivalent from each probe. Methane, carbon dioxide and oxygen concentrations were measured during the course of purging using the RK1 Eagle Series portable methane meter. A final reading was also measured upon conclusion of the purging process. The corresponding data was recorded on a field data sheet. A copy of the field data sheet is enclosed in Appendix C. RESULTS AND FINDINGS ' Findings from the monitoring activities performed during the course of drilling and one week following the probe installation revealed no indications of methane being present on the Property in the areas of the proposed building pads. Since the Landfill has existed for over 60 years, sufficient time has elapsed to allow for LFG to migrate into the area, if such conditions were going to occur. Thus,the absence of methane negates this concern_ Other variables that should provide ongoing protection include the fine-grained nature of the soils underlying the building pads and the fact that active LFG collection is currently performed at the Landfill and will continue as such for the foreseeable future. Based on these circumstances,further assessment of potential LFG migration issues associated with the proposed development is not considered warranted. RECOMMENDATIONS Since findings from the investigation confirmed the absence of LFG in the area of the proposed building pads, provisions should be made to properly destroy the LFG monitoring points under permit from the Zone 7 Water Agency. A rotary auger drill rig should be used to remove the probe casing and annular materials (i.e., sand and bentonite chips). Upon removal of these materials,the boreholes should be backfilled with neat cement but in accordance with Zone 7 Lpmpect,19691,PaparttRepert 10 13 11 aix 2 E " )