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kn KLEINFELDER <br />6.2.4.3 Settlement <br />Asbestos waste placed in the landfills was not compacted which is why differential settlement <br />can be observed in some of the landfill areas, particularly WMU-C and D. Additional <br />settlement is anticipated for an unknown time into the future. The surface impoundments will <br />also experience cap settlement. <br />In a report dated September 18, 1990, Kleinfelder presented the results of an assessment of the <br />surface impoundment sediment with respect to cap settlement. Eight sediment samples were <br />collected and the thickness of the sludge was also assessed. Kleinfelder estimates that the <br />sediment is 25 feet thick at the east end of the impoundments and thins to approximately 5 feet <br />thick at the western ends. <br />Consolidation tests (ASTM D-2435) were run on 7 of the samples. Test results were then used <br />to estimate potential settlement. If a 2 -foot thick soil cap were placed on the sediment, surface <br />settlement was estimated to range from one to six inches. If the impoundments were <br />backfilled with soil to the surrounding berm grade, estimated settlement would range from one <br />to twelve inches. <br />The effects of settlement will be controlled by filling settled areas. This activity will occur on <br />a yearly basis after closure and is discussed in the chapter on postclosure maintenance. <br />6.3 DRAINAGE PLAN <br />i - <br />Control of drainage is an important part of the overall closure plan. Proper drainage reduces <br />the chance for erosion damage to the WMU caps. The drainage design will also allow J -M <br />Mfg. to control drainage that may be contaminated with asbestos. <br />6.3.1 Background <br />An existing channel passes through the J -M Mfg. site and is used by J -M Mfg. for discharge <br />of storm water runoff. The channel ultimately discharges to French Camp Slough. The <br />channel is also used for drainage by two significant upgradient neighbors, the Stockton <br />Metropolitan Airport (northwest corner) and the planned Stockton Business Park. <br />CR14-92-12 Page 30 of 39 24-220109-1709 <br />Copyright 1992 KLeinfeider, Inc. <br />