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1 Table 5 ' Phase II Preliminary Analytical Results VOC Concentrations From Phase II Temporary Well Samples February 24,2012(µg/L) Well ID DCDFM PCE TCFM Total VOC MW-9A 0.11(trace) ND 1.4 1.51 MW-10A 1 0.91 1.4 0.24(trace) 2.55 MW-11A I ND ND ND 0.49 Notes: A trace concentration is one measured between the laboratory's Method Detection Limit(MDL)and Practical Quantitation Limit(PQL). It is symbolized by a"j"in the laboratory report. ' µg/L: micrograms per liter. (1): Total VOC concentration does not include perceived field/laboratory contaminants carbon disulfide and acetone. ' (2): Sample also contained benzene,cis-1,2-dichloroethene,and bromoform(field contaminant associated with water introduced to facilitate drilling). ' 4.4.4 Phase II Permanent Monitoring Well Construction The results of the Phase II temporary well samples provided the additional data to better extrapolate VOC concentrations and assess the extent of the release. As a result, permanent monitoring wells were constructed at these locations between March 12 and 15, 2012, in accordance with the EMP workplan and under the supervision of a ' State of California Certified Engineering Geologist and a representative from the County of San Joaquin Environmental Health Department. ' The Phase II temporary well materials were removed and the borings were reamed to 10-inches in diameter to accommodate permanent well installation. Groundwater monitoring wells were constructed using flush-threaded, 2-inch diameter, Schedule 80 PVC casing. The well screen consists of 0.020-inch wide machine cut slots. A sounding tube consisting of flush-threaded, 1-inch diameter, schedule 80 PVC casing was installed ' within the same borehole. All well materials, including blank and factory-slotted casing, were virgin, decontaminated, and factory sealed. All well materials were covered in plastic or similar protective materials when delivered to the site and remained so until used in construction. All well casing is flush-threaded, including the bottom cap at the base of the wells. No ' glues or solvents were used to connect the casing. Centralizers were not used on the casing, as allowed by State standards, because the wells were installed inside hollow stem augers. The driller suspended the casing from the top during construction to ' ensure that the casing remained straight and centered within the augers. ' Based on the grain size distribution of the shallow, perched aquifer encountered in past site investigations, inert, washed and graded No. 2/12 Monterey sand was used as the filter pack material in wells MW-9A, MW-10A, and MW-11A. Well filter pack sand was 1 placed in the annulus by slowly pouring the sand down the auger flights because water EMP Report—Phase IIGeo-Loic Page ■ 11 ' Corral Hollow Sanitary Landfill w s s o c i ATE sg August 21,2012