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' Mountain House Storm Water Detention Basin Page 3 WKA No. 6504.05 October 7, 2005 4.1 Soil Boring On September 12, 2005, four soil borings, subsequently converted into monitoring wells, were advanced at the locations shown on Figure 2. The borings for monitoring wells MW 1 through MW3 were advanced to a depth of approximately 30 feet bgs. The boring for monitoring well MW4 was advanced to approximately 60 feet bgs. Each soil boring was drilled using a BK-81, truck-mounted drilling rig, advancing 8-inch diameter, hollow-stem augers operated by V& W ' Drilling Inc. of Isleton, California. During drilling and at approximately 5-foot intervals, soil samples were collected for lithologic description. The soil samples were collected with a modified California split spoon sampler. At each sampling interval, the sampler was driven 18 ' inches into the bottom of the borehole and then extracted. Subsurface materials encountered were described and recorded using the Uniform Soil Classification System (USCS). Boring logs of the materials encountered and samples collected during drilling are included in Appendix B. 4.2 Monitoring Well Construction and Sampling 4.2.1 Monitoring Well Construction ' Each soil boring was converted into a monitoring well upon reaching terminal depth of exploration. All four wells were constructed of 2-inch diameter, Schedule 40, polyvinyl chloride (PVC) well casing and slotted pipe (well screen). The well screen openings were machine- slotted 0.010-inch. The wells were constructed with#2/12 sand for a filter pack placed in the annulus of the screened interval. A bentonite seal using 3/8-inch chips was placed in the annulus above the screened interval and a grout of Type 1/11 neat cement was placed in the well annulus above the bentonite seal. The PVC well casing was also fitted with a locking well cap. Each well was secured at the surface with a locking, stove-pipe, steel protective casing surrounded by a concrete apron at its base. Three concrete-filled metal bollards were placed around each well vault to.provide protection from future on-site traffic. The monitoring wells were constructed in ' a manner so they could be used for long-term monitoring. Well construction details are summarized in Table 1. Typical well construction details are shown on Figure 4. WALLACE KUHL Rcycme p.ipor S ASSOCIATES INC.