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November 18, 1996 Geotechnical Study Evaluation Page 4 Paae 3: "Fill Recommendations" Dependent upon the results of the additional amended stability analyses indicated by our adequacy concerns, the recommendations for maximum slope angle, compaction densities and material placement techniques may prove to be inappropriate. At this point, we cannot complete an overall opinion concerning their efficency. However, the recommendations concerning lifting, scarifying, benching, and compaction agree with prudent earthwork construction practice. Maxim Technologies reconsidered and restated its recommendations concerning the use of filter fabric above basal boulder rubble blankets beneath reclaimed fills. Maxim has specified that where used as a drainage blanket, coarse boulder rubble should be fabric shielded to prevent invasion of fines into the drainage blanket. In situations where the boulder rubble is being used to increase the frictional bond of the basal layer of the fill "it is important that rock be incorparated into a soil matrix to assure that any voids between rock are filled to prevent migration of fines." We agree with these statements. However, in the final design specifications of the permit more detail will be necessary. First, how will the two differing situations be identified and projected under reclaimed conditions? Often, after backfilling, previously well-0rained situations develop ground water saturated conditions. Further, specification for fabric installation over coazse boulder rubble materials will require allowances to avoid over stressing the fabric's tear resistance. Repeatedly a[ coal mine sites, underdrains have been compromised when fabrics failed between a coazse underdrained matrix and overlying fine grained soils. The fabric is incapable of bridging the matrix voids in the boulder rubble. At a minimum, properly graded finer grained filter layers should be placed to support the filter fabric. P In their original geotechnical engineering report, Maxim Technologies reported that several soils exhibited volumetric expansion (under 500 psf fixed loads) of up to 13 percent, and these soils were correctly termed "highly expansive." Further, the author appropriately commented: "Clearly, most of the clays on this site would be considered sensitive to loss of strength andlor volume change upon increases in moisture content or pore pressure. In our earlier adequacy memorandum we observed: "...upon reclamation of [he surface facilities, extensive soil materials will be unavoidably exposed to the elements. In their reclaimed configuration, swelling and low-strength soils will be unconfined and exposed to extensive moisture. In this configuration, materials will exhibit their swollen, deteriorated 'ultimate' plastic regime strengths. Reclaimed facilities will have to be designed and analyzed with this fact in mind. The appropriate material strengths will have to be used in determining the slope stability of reclaimed facilities, cuts and fills." Further, the author observed that the expansive soil materials will likely significantly degrade in performance if wetted. One of the anticipated wet azeas in which Maxim projects the likelihood of encountering significant ground water is in the area of the portal bench, where the highest cuts and slopes are projected to be constructed. In our eazlier adequacy comments we commented: "....extensive detail will have to be provided to describe the collection and diversion of these ground waters and the long term stabilization of the potentially affected 80 foot high cut slopes and 50 foot high fill embankments. This will constitute both a significant operational facility and reclaimed configuration design challenge."