CORRESPONDENCE_1984-1989 - Laserfiche WebLink

Home Browse Search

Mr. Greg Basso -2- 21 April 1989 run at different compactions on aliquots of a soil sample which is representative of the site soils. Sufficient tests must be run in order to plot a curve which describes the relationship between compaction and permeability. The permeability -density relationship must be described in this manner each time there is a significant change in the engineering properties of the soils used for construction. In this manner the soils engineer may determine that these soils, when compacted to a certain density at some moisture content over optimum, will achieve a certain permeability. This relationship may then be utilized by taking numerous, comparatively inexpensive, density tests of the liner during construction to demonstrate that the .appropriate density was achieved for the desired permeability. In order to monitor changes in soil type, spot checks should be incorporated into the construction quality assurance (CQA) plan. variations in soil properties such as visual appearance, grain size distribution, plasticity index, liquid limit, optimum moisture and maximum dry density should be checked. The criteria by which variations in each parameter are judged significant also need to be established in the CQA plan. Subchapter 15 also requires that the permeability be deter- mined by appropriate field test methods. This is an important step in the construction quality assurance (CQA) process. Clod size and strength have a major impact on hydraulic defects and permeability of the liner. The only effective test for permeability, which measures the effect of clods is an in-situ test. The in-situ test with which we are most familiar is the Sealed Double Ring Infiltrometer. Other tests, such as the Air Entry Permeameter, have also been demonstrated to be effective measures of in-situ permeabil- ity. The total thickness of the liner is uncertain due to the absence of survey data on the liner subgrade for comparison to the final grade survey. However, the liner thickness determined from the liner borehole exceeds the minimum required by Subchapter 15. Since the clay liner on WMU D-88 is not a mandatory requirement of Subchapter 15, we can approve this waste management unit for waste disposal. However, we cannot recognize the full attenuation that would be provided by a 4 - foot thick, 1.0 x 10-6 cm/sec liner without proof that the liner in WMU D-88 has an in-situ permeability of 1.0 x 10-6.