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YVATC 1117 Lone Palm Avenue, Suite B
<br /> Modesto, CA 95351
<br /> www.atcassociates.com
<br /> 209-579-2221
<br /> Ass o c i are s I N c . Fax 209-579-2225
<br /> Environmental, Geotechnical and Materials Engineers
<br /> From November 10 to November 12, 2004 and November 15 to November 17, 2004, an ATC
<br /> geologist supervised the installation of monitoring wells MW5 through MW12. Soil samples
<br /> were collected from the boreholes of MW5 , MW6, MW7, MW8, MW9, MW10, MWl 1 , and
<br /> MW12 and selected soil samples were submitted for laboratory analyses. Each well was
<br /> constructed with 2-inch diameter PVC casing, with MW8, MW9, MW10, and MWl l extending
<br /> to a depth of 65 feet bgs in the shallow groundwater bearing zone, MW5, MW6, and MW12
<br /> - extending to a depth of 90 feet bgs in the intermediate groundwater bearing zone, and MW7
<br /> extending to a depth of 121 feet bgs in the deep groundwater bearing zone.
<br /> - Monitoring wells MW5, MW6, MW8, MW9, MW10, and MW12 were developed on December
<br /> 22 and 23, 2004. An obstruction encountered in MW7 at approximately 64 to 65 feet bgs
<br /> prevented development of this well. MW l l was purged dry after removing 0.5 gallons of water.
<br /> Efforts to develop this well using a bailer revealed the presence of grout inside the well and the
<br /> j I total depth of the well was measured to be approximately 58 feet.
<br /> On December 22 and 23, 2004 monitoring wells MWl through MW12 were surveyed relative to
<br /> _ NAD 83 and NGVD29 for position and elevation and groundwater samples were collected from
<br /> MWl through MW6, MW8, MW9, MW10, and MW12. Petroleum hydrocarbon constituents
<br /> were detected in soil samples collected from the boreholes of MW5 through MW9 and MW12.
<br /> Groundwater samples were not collected from MW7 and MWl l due to an obstruction in MW7
<br /> and grout infiltration in MWll . Petroleum hydrocarbons were detected in the groundwater
<br /> samples collected from MWl through MW6, MW8 through MW10, and MW12. The results of
<br /> � - the subsurface investigation activities are presented in ATC ' s Subsurface Investigation Report,
<br /> dated July 25 , 2005 .
<br /> -_ On April 7, 2005 , an ATC geologist supervised the destruction of MWl l and the installation of
<br /> replacement monitoring well MW11R to a depth of approximately 65 feet bgs using 2-inch
<br /> diameter schedule 40 PVC casing. Refer to ATC' s First and Second Quarter 2005 Monitoring
<br /> - Report, dated October 10, 2005, for additional information.
<br /> P From September 25 to 30, 2006, an ATC geologist supervised the installation of monitoring
<br /> wells MW13 , MW14, and MW15 . MW13 and MW14 were installed off-site to the east and in
<br /> the northern portion of the site, respectively, to evaluate the lateral extent of impacted
<br /> groundwater in the shallow zone. Monitoring well MW15 was installed on-site downgradient
<br /> from the source area to evaluate the vertical extent of impacted groundwater. Each well was
<br /> I constructed with 24rich diameter PVC casing, with MW13 and MW14 extending to a depth of
<br /> E J approximately 60 feet bgs in the shallow groundwater bearing zone, and MW15 extending to a
<br /> depth of approximately 151 feet bgs in the deep groundwater bearing zone. Monitoring wells
<br /> t MW13, MW14, and MW15 were developed and sampled on November 9 and December 7, 2006,
<br /> respectively. The results of the subsurface investigation activities are presented in ATC' s
<br /> Subsurface Investigation Report, dated December 20, 2006.
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