|
1117 Lone Palm Avenue, Suite B
<br /> Modesto, 95351
<br /> www.ateassociates.com
<br /> 209-5757 9-2'^ i
<br /> Ass o c I ATE s i N c . Fax 209-579-.
<br /> Environmental, Geotechnical and Materials Engineers
<br /> From November 10 to 12 and 15 to 17, 2004, an ATC geologist supervised the installation of
<br /> monitoring wells MW5 through MW12. Soil samples were collected from the boreholes of MW5,
<br /> MW6, MW7, MW8, MW9, MW10, MWl 1 , and MW12 for purposes of logging soil type, and selected
<br /> soil samples were submitted for laboratory analyses. Each well was constructed with 2-inch diameter
<br /> PVC casing, with MW8, MW9, MW 10, and MWl l extending to a depth of 65 feet bgs in the shallow
<br /> groundwater bearing zone, MW5 , MW6, and MW12 extending to a depth of 90 feet bgs in the
<br /> intermediate groundwater bearing zone, and MW7 extending to a depth of 121 feet bgs in the deep
<br /> groundwater bearing zone.
<br /> Monitoring wells MW5, MW6, MW8, MW9, MW10, and MW12 were developed on December 22 and
<br /> 23, 2004 . An obstruction encountered in MW7 at approximately 64 to 65 feet bgs prevented
<br /> development of this well. MW11 was purged dry after removing 0 .5 gallons of water. Efforts to
<br /> develop this well using a bailer revealed the presence of grout inside the well and the total depth of the
<br /> well was measured to be approximately 58 feet.
<br /> On December 22 and 23, 2004, MW l through MW12 were surveyed relative to NAD 83 and NGVD29
<br /> for position and elevation and groundwater samples were collected from MWl through MW6, MW8,
<br /> MW9, MW10, and MW12 . Petroleum hydrocarbon constituents were detected in soil samples
<br /> collected from the boreholes of MW5 through MW9 and MW12. Groundwater samples were not
<br /> collected from MW7 and MWll due to an obstruction in MW7 and grout infiltration in MW11 .
<br /> Petroleum hydrocarbons were detected in the groundwater samples collected from MWl through 1 )
<br /> MW6, MW8 through MW10, and MW12. The results of the subsurface investigation activities are
<br /> presented in ATC ' s Subsurface Investigation Report, dated July 25 , 2005 .
<br /> On April 7, 2005, an ATC geologist supervised the destruction of MW11 and the installation of
<br /> replacement monitoring well MW11R to a depth of approximately 65 feet bgs using 2-inch diameter
<br /> schedule 40 PVC casing. Refer to ATC' s First and Second Quarter 2005 Monitoring Report, dated
<br /> October 10, 2005, for additional information .
<br /> From September 25 to 30, 2006, an ATC geologist supervised the installation of MW13 and MW14 to
<br /> approximately 60 feet bgs, and MW 15 to approximately 151 feet bgs. To evaluate the lateral extent of
<br /> j impacted groundwater in the shallow zone, MW13 was installed off-site to the west and MW14 was
<br /> installed in the northern portion of the site. Monitoring well MW15 was installed on-site downgradient
<br /> from the source area to evaluate the vertical extent of impacted groundwater. The results of the
<br /> subsurface investigation activities are presented in ATC 's Subsurface Investigation Report, dated
<br /> December 20, 2006.
<br /> SELECTED MONITORING WELL CONSTRUCTION INFORMATION
<br /> i
<br /> Groundwater monitoring wells associated with the subject site (Figure 3) are screened at various depth
<br /> intervals. The vadose zone generally extends to approximately 44 to 47 feet bgs. The saturated
<br /> subsurface is roughly differentiated by three zones identified as a shallow groundwater zone, an
<br /> intermediate groundwater zone, and a deeper groundwater zone. MWl , MW2, MW3 , MW8, MW9,
<br /> S:\Environmental\28349\comparative study.doc 2 ATC ,associates Inc.
<br />
|