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a v1117 Lone Palm Avenue, Suite 8 Modesto, CA 95351 www.atcassociates.com 209-579-2221 A S S O C I A T E S I N C . Fax 209-579-2225 Environmental, Geotechnical and Materials Engineers 2. 1 Drilling Activities From September 25 to 30, 2006, an ATC geologist supervised the installation of MW13 and MW14 to approximately 60 feet bgs, and MW15 to approximately 151 feet bgs. Woodward Drilling, California License C57 710079, installed MW13 and MW14 utilizing a hollow stem auger drilling rig, and MW15 utilizing a mud rotary drilling rig. The locations of the monitoring wells are shown on Figure 3 . The borehole for MW13 was logged based on the drill cuttings . Soil samples were collected from the borehole of MW14 at five-foot intervals in stainless steel sampling tubes from 5 feet bgs to approximately 60 feet bgs. The borehole for MW15 was drilled within ten feet of MW6, consequently the lithology previously logged for MW6 is assumed to be similar for MW15 to 85 feet bgs . Lithologic characterization below 85 feet bgs was based on drill cuttings and information provided by the drillers based on drilling rig response during the drilling. The cored samples and drill cuttings were characterized, for soil type, moisture content, and visual evidence of petroleum hydrocarbons . A photo-ionization detector (PID) was used as a field-screening device for the detection of petroleum hydrocarbon vapors in drill cuttings and cored samples. A field geologist logged drill cuttings and soil samples utilizing the Unified Soil Classification System. Descriptions of soil types encountered and sample collection intervals are included on the well logs contained in Appendix A. 2.2 Groundwater Monitoring Well Construction The monitoring wells were installed to further assess the lateral and vertical extent of petroleum hydrocarbon impact to the subsurface and to provide measurement points for the determination of groundwater flow direction and hydraulic gradient. Monitoring wells MW13 and MW14 were installed to a depth of 60 feet bgs and were each constructed with approximately 45 feet (surface to 45 feet bgs) of blank 2-inch diameter Schedule 40 PVC casing and approximately, 15 feet of slotted (0 . 020-inch slots) 2-inch diameter Schedule 40 PVC well screen. The annulus of the screened portions of MW13 and MW14 was backfilled with a #3 sand filter pack from approximately 42 to 60 feet bgs. Monitoring well MW15 was installed to a depth of 151 feet bgs. Because this well was installed in an area of known groundwater contamination, as evidenced by historical laboratory analytical results of groundwater samples collected from MW6, an 8 %/ inch diameter steel conductor casing was installed to a depth of 136 feet bgs. The steel conductor casing was installed to minimize contaminant migration from above. The bottom of the conductor casing was placed in the top of a clay layer that extended from approximately 136 to 141 feet bgs . Monitoring well MW15 was constructed with approximately 141 feet (surface to 141 feet bgs) of blank 2-inch diameter Schedule 40 PVC casing and approximately 10 feet of slotted (0 . 020-inch slots) 2-inch diameter Schedule 40 PVC well screen. The well screen of MW15 was set in a sand layer that was encountered from approximately 141 feet bgs to the terminal depth of the boring at 5:\Enviromental\28349\reports\sum.doe 3 ATC Associates Inc.