SITE INFORMATION AND CORRESPONDENCE

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+ V Clayton ENVIRONMENTAL CONSULTANTS Mr. Donald C. Lewis August 9, 1990 Page 2 collected. Following removal of the septic tank, and the oil contained in this septic tank, Clayton removed additional soil from beneath and adjacent to this tank. No soil was left in the excavation which exceeded 80 ppm of oil and grease or 3.6 ppm of gasoline. • Although monitoring well MW-3 was destroyed during excavation, the excavation was sealed with quarry gravel and clean clayey soil from a depth of 11 feet below ground surface (bgs) to a depth of 7 feet bgs before stockpiled (aerated) soils were placed in the excavation. Clayton does not feel that this abandoned monitoring well will provide a conduit for migration of contamination based upon the fact that the source (soil) of contaminant has been removed. • Soil sample MN-2 was analyzed for oil and grease by EPA Method 418.1. Although the results of this analyses were not listed in the table on page 4 of our report, the result was included in the laboratory analysis (Appendix C). This sample contained less than 10 parts per million (ppm) of oil and grease. • During development of monitoring wells MW-2 and MW-3, tap water was introduced to facilitate development. This is an accepted and recognized practice when initial (development) pumping dewaters the well casing and sufficient water is not recharged into the well. Sampling of these two wells was conducted two days after development. No tap water was introduced during the purging and sampling process. In addition, with regard to field sampling procedure for wells that recover slowly after purging (resulting in the well being evacuated and recharging slowly), sampling is commonly acceptable if the water in the well recovers to 80% of the initial volume. This was indeed the case for wells MW-2 and MW-3, although field pH and conductivity readings were not taken. • All three original wells were surveyed by a licensed land surveyor, Tronoff and Associates of San Francisco, California. Three point problems were utilized to calculate the required groundwater flow direction and gradient, as discussed on page 3 of Clayton's Report No. 29531.00, dated April 26, 1990. • A well to replace the destroyed well, downgradient of the excavation, has been discussed and is planned. Concentrations of oil and grease ranging from 20 parts per million (ppm) to 80 ppm in the soil were left in the excavation. This is acceptable and within the guidelines of the California LUFT manual. Additionally, at these levels we believe the hydrocarbons will be remediated inplace via passive biodegradation. Post closure monitoring of the onsite wells may be advisable. The monitoring should be terminated if no 29531-Mtr