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~: . September 30, 1986 2 863-2032 it should be noted that both the allowable soil bearing capacity and settlement estimates are based on the assump- tion that the soil conditions beneath the tank are essentially the same as those encountered at DH-81. During installation, the soils encountered in the tank excavation should be carefully observed. If any soft, highly organic or otherwise deleterious soil or material is encountered, this condition should be brought to our attention immedi- ately so that if necessary, modifications to the design recommendations can be made. We understand that the tank will be underlain by a minimum of 12 inches of 3/4 inch minus granular material. This material will be contained by a steel ring wall which will have a slightly larger diameter than the steel tank. Prior to placing the ring wall and granular materials, we recom- mend that the in-situ colluvial soils beneath the tank be proof-rolled and compacted to a density of at least 958 of the Standard Proctor maximum dry density (ASTM 698). This will provide a further check on the presence of soft or deleterious soils and will help insure that the soil beneath the tank is uniformly stiff. We further recommend that the granular fill placed beneath the tank be free draining and that positive drainage be provided underneath this fill away from the tank and tank pad area. This precaution will reduce the likelihood of deleterious movements underneath the tank due to freeze thaw action. Ponding of water underneath the tank is potentially a problem because of the low permeability of the colluvial soils and the steel ring wall which will surround the tank. If you have any questions concerning the recommendations in this letter please feel free to contact us, Yours very truly, GOLDER ASSOCIATES ~(~cl¢,aS~ ~C.o~ Michal Bukovansky Princi al /~~~~~v "ri~/JR~lit/ Ronald E. Versaw Associate MB:REV:tls Golder Associates