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n. C. PERCOLATION TEST RESULTS Percolation testing was conducted on October 9, 2001 under U.S.E.P.A. and San Joaquin County Environmental Health guidelines. One perc test boring of 42 in. and one test boring of 20 in. was prepared in each of the three parcels. The 42 in. boring represents the maximum depth of standard leachline trenches, while the 20 in. perc tests represents percolation of a filter bed. After completion of the test borings, the bottom and sides were scarified to open smeared soil surfaces. This is a critical procedure and must also be done at the time of leachline or filter bed emplacement. The test borings were then pre-saturated with six inches of clear water. After 24 hrs, all the water had seeped away in each of the six borings. Approximately six inches of head water was maintained during the entire four-hour test. As illustrated on the attached FIELD PERCOLATION TESTING REPORTS, the perc rates for all six test borings shows exceptional percolation considering the clay soils. This phenomenon has been observed often and can be attributed most likely to macro and microscopic cracking, which is indicative of clay soils. Four of the perc rates slowed over the 4-hr test interval and two ' became faster, indicating soil saturation did not occur in all six borings. The 20 in, perc tests reveal a consistently slower perc rate than the 42 in test depth of approximately 4 min/in. The perc test results are summarized below for each of the three Parcels: . . RCQLATYDN, TAT �RSVLTS PARCEL No 42" PERC RATE IN MINIINCH PARCEL No 20"PERC RATE IN MINANCH Parcel 1 7.9 min/in Parcel 1 11.5 min/in Parcel 2 10.7 min/in Parcel 2 14.3 min/in Parcel 3 8.1 min/in Parcel 3 12.5 min/in I D. GROUNDWATER INFORMATION Groundwater depths and elevations are illustrated on maps published by the San Joaquin County Flood Control and Water Conservation District. However, due to the variability in groundwater elevations in the Tracy area, groundwater lines are not drawn for this area. The last map denoting lines of equal elevation for the Tracy area was published in 1992 and indicate the general groundwater flow to be in a northeasterly direction, toward the San Joaquin River. This directional flow is confirmed by a contaminate plume originating from the Tracy Defense Depot. As with all groundwater tables, there will be fluctuations in elevation. Attached well logs indicate a water table depth of 21 ft at the corner of Linne and Banta Roads in 1987, which is r probably near to what it is today. It is highly probable there has not been dramatic fluctuations in groundwater elevation under the subject property for many years. The critical issue regarding the groundwater elevation is there must be sufficient distance between the bottom of a leachline trench and the highest anticipated depth to groundwater for sufficient treatment of bacteria and 4 valley;QgResearch