SITE INFORMATION AND CORRESPONDENCE

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Mr. Benjamin Hall - 3 - • 25 September 2000 Installation Workplan and a Monitoring Well Installation Report of Results. The following items will need to be addressed: • For the well placement at the 1 Mgal storage pond, the two downgradient wells must be located within 30 feet of the toe of the pond berm. The upgradient well should be located upgradient of the pond berm to allow collection of groundwater samples upgradient of the storage pond. • The workplan describes soil sampling but does not specify the sampling interval. The goal of the groundwater monitoring program is to monitor the first saturated zone. Samples shall be collected for lithologic description at minimum five-foot intervals. It is noted that the sampling hammer should be dropped 30 inches for a standard penetration test (ASTM D1586-99). • Well development shall be performed no sooner than 24-hours after the well grout (cement/bentonite slurry)has been installed in accordance with the Department of Water Resources California Well Standards, Bulletin 74-90. This is considered especially important to protect the surface seal of the wells. • Permits from the San Joaquin County Environmental Health Department must be obtained prior to . installation of groundwater monitoring wells. • If conditions in the borehole allow, it is recommended that the sand pack be surged prior to installing the bentonite seal. • The following comments on the well construction methods are provided: — If site specific conditions allow, well screen length should be 20 feet long to allow for variation in the depth to groundwater. If a slip cap is used on the bottom of the well casing, it must be secured using stainless steel screws. — The workplan states a six-inch diameter auger will be used to drill the soil boring (nine inch in Table 3) and a six-inch well casing will be installed in the boring. Department of Water Resources California Well Standards, Bulletin 74-90 requires a minimum two-inch thick gravel pack. In addition, the well casing could not be installed in the specified hollow stem auger. — Musco should ensure the driller is aware of the possibility of well casing damage caused by well grout heat of hydration. If you have any questions, or want to schedule a meeting to discuss these issues or the cleanup and abatement order being developed,please telephone me at (916) 255-3116. J� TIMOTHY R.O'BRIEN Waste Discharge to Land Unit San Joaquin River Watershed cc: Mr. Mike Huggins, San Joaquin County Environmental Health Department, Stockton Mr. Richard Stratton, HDR, Folsom CWmj _Filalt(l MusD 010915WR lilac