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A10/71-51-1c <br /> o SB23- This five-foot soil boring was added in order to determine any <br /> potential shallow soil contamination in the area around MW7 where <br /> an underground tank was removed <br /> Soil and groundwater sampling involved the following activities in the indicated sequence <br /> 9 P 9 9 q <br /> o Measurement of water levels of twelve existing groundwater monitoring wells <br /> (MW1 to MW12) using an electronic water level meter Table 1 in Appendix <br /> C presents the water level measurements <br /> o Purging and sampling of existing monitoring wells When these were done, <br /> it was discovered that only the following wells were not dry MW7, MW10, <br /> MW11, and MW12 All the rest were dry due to the lowering of <br /> groundwater elevation <br /> o Drilling of 11 new soil boreholes and converting six of these boreholes into <br /> groundwater monitoring wells The new wells are MW13, MW14, MW16, <br /> MW19, MW20, and MW24 <br /> o Development of six new groundwater wells, <br /> 1 o Measurement of water levels in the new and old wells, <br /> 1 o Sampling of newly-installed wells <br /> During the week of October 25, 1993, Caltrans surveyed all the new wells including the <br />' wells at Stockton Yard (See Table 2 in Appendix C) The older existing wells were not <br /> included in the survey <br /> 4 2 SOIL SAMPLING AND DRILLING METHODS <br />' The following procedures were used for advancing the borings to collect soil samples and <br /> for the installation of monitoring wells Each of the drilling site was clearly marked with <br /> a white spray paint Drilling activities were performed utilizing a Mobile Drill B-61 equipped <br />' with approximately ten and eight-inch outside and inside diameters, continuous flight, <br /> hollow-stem augers The hollow stem augers were steam-cleaned before use and in <br /> 12 <br />