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Woolsey Oil Company 07/23/01 San Joaquin County 3 3. Summary/Conclusions, page 5: The conclusion that, based on the contaminant concentration gradient, there is a substantial vertical flow component to the deeper than 75 foot section of the aquifer is questionable, due to the suggested issue of cross -contamination from the smear zone down into the boring. Groundwater sampling and a directional flow analysis along the screened interval in the new proposed deep well should provide that verification. 4. Recommendations, page 5: We agree with the recommendations presented in the text, with the following modifications: • For a deeper groundwater monitoring well screened from 85-100 feet, use a properly designed, pre - packed well screen to minimize the effects of the heaving sands on the installation; • Sample all wells quarterly for hydrocarbons and oxygenates for a minimum of one year; • Use a directional flow meter to evaluate vertical flow direction along the length of the well screen; • Take extra caution while constructing the deeper well, to prevent cross -contamination; and • Begin the additional characterization of the lateral and vertical extent of the contaminant plume, if warranted, after the first quarter of the deep well groundwater monitoring (versus after the proposed one year study). 5. The Attachment A drill logs are hard to read, use an atypical method for describing depths of the logged soil types (e.g., drill log description says 41/49.5-51/54.5'), use a non -Munsell Soil Color classification, and do not have a key for the despription abbreviations. Provide the descriptions and abbreviations key and explain the unusual description of soil type depths. The log shows a soil type is present from 41-54.5'. It appears this soil type is logged only from the 18" long core taken from 49.5- 51'. If so, why were the cuttings from the auger not used to log the sample? By 15 September 2001, please provide a work plan to install the monitoring well and responses to the Investigation Report comments. Attachment 1 and 2 provide general guidance for work plan and report preparation. If you have any questions, you may contact me at (916) 255-3050. hAS L.L. BARYON, R.G. Associate Engineering Geologist cc: Mr. Michael Infurna, San Joaquin County Environmental Health Services, Stockton Mr. Patrick Riddle, Law Offices of Patrick D. Riddle, Acampo Mr. Gregory Stahl, Ground Zero Analysis, Inc., Escalon