|
16
<br /> the shallow groundwater bearing zone, MW5, MW6, and MW12 extending to a depth of 90 feet bgs
<br /> in the intermediate groundwater bearing zone, and MW7 extending to a depth of 121 feet bgs in the
<br /> deep groundwater bearing zone.
<br /> Monitoring wells MW5, MW6, MW8, MW9, MW 10, and MW 12 were developed on December 22
<br /> and 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
<br /> the well was measured to be approximately 58 feet.
<br /> On December 22 and 23, 2004 monitoring wells MW1 through MW12 were surveyed relative to
<br /> NAD 83 and NGVD29 for position and elevation and groundwater samples were collected from
<br /> MW1 through MW6, MW8, MW9, MW10, and MW12. Petroleum hydrocarbon constituents were
<br /> detected in soil samples collected from the boreholes of MW5 through MW9 and MW12.
<br /> Groundwater samples were not collected from MW7 and MW11 due to an obstruction in MW7 and
<br /> grout infiltration in MW 11. Petroleum hydrocarbons were detected in the groundwater samples
<br /> collected from MW1 through MW6, MW8 through MW10, and MW12. The results of the subsurface
<br /> investigation activities are presented in ATC's Subsurface Investigation Report, dated July 25, 2005.
<br /> ' On April 7, 2005, an ATC geologist supervised the destruction of MW 11 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 /> SAMPLING ACTIVITIES
<br /> The depth to water was measured in MW1 through MW10, MW11R, and MW12 (Figure 3) on
<br /> ' September 28, 2005. All of the monitoring wells except MW7 were purged and sampled on
<br /> September 28, 2005. A submersible pump separated from its tether and sank to the bottom of MW7.
<br /> Attempts to retrieve it on September 28, 2005, were unsuccessful. The submersible pump was
<br /> retrieved on September 30, 2005, and MW7 was purged and sampled on October 7, 2005. Prior to
<br /> collection of groundwater samples, the depth to water was measured in the wells and the pH,
<br /> electrical conductivity, and temperature were measured in groundwater purged from the monitoring
<br /> ' wells and recorded. A minimum of three well casing volumes were purged from each monitoring
<br /> well prior to sampling. The wells were allowed to recover and samples were collected from each well
<br /> using disposable polyethylene bailers.
<br /> The groundwater samples collected from each well were submitted to State-certified Argon
<br /> Laboratories (Environmental Laboratory Accreditation Program Certification. No. 2359) in Ceres,
<br /> California for chemical analyses of total petroleum hydrocarbons quantified as gasoline (TPHg)
<br /> utilizing EPA Method 8015M; and benzene, toluene, ethylbenzene, and xylenes (BTEX), methyl
<br /> tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE) di-isopropyl ether (DIPS), tertiary
<br /> amyl ether (TAME), tertiary butyl ether (TBA), 1,2-di chloroethane (1,2-DCA), and 1,2-
<br /> dibromoethane (EDB) utilizing EPA Method 8260B. Groundwater well purge and sample logs are
<br /> included in Attachment 1.
<br /> s:\enviromental1283491reports12005 3QMR.doc 2 ATC Associates Inc.
<br />
|