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-_..,;.x,~.~... ~ ~ • STEEPEN ROBERTSON AND KIRSTEN Consulting Engineers and Scent~sts MEMORANDUM TO: Mike Young - BMRI FROM ~~ave Hallman - SRK DATE: October 27, 1993 RE: DRAINAGE BLANKETlLINER COVER LAYER PERM~ABII,ITY Additional laboratory permeability testing has been conducted on samples of the drainage blankedliner cover layer material (Material Type 2) which was placed prior to utilization of the screening plant currently on site. The samples consisted of the six-inch interval samples from arrPC t t t to ~~ ,...+ ~, ~-..~,~._,, :- .~-, ^---.-.-.:_- ~._.. - -- - The interval samples ..- --.. _.. __.._.. -.....__ ~r.,... from each acre were blended to result in a typical material representative of tlhe material placed in each acre. The samples were screened to remove all + 3: inch particles in order to create a gradation which is suitable for the pet7tteability testing equipment in the lab. Gradations for the composite samples (attached) indicate that the samples contain 19.6 - 26.7% finer than the No. 200 sieve. The samples were prepared at densities of approximately I15-117 pcf rto simulate field conditions. Recent density measurements in the Type 2 material indicates that this density is higher th2.n tvpic~~!y r'chie:•ed during the construction and should result in pemneabilities which are lower than those of the actual material on the liner. The laboratory tests resulted in permeabilities of I.5 x 10'5 cm/sec to 4.9 x 10'5 cm/sec (see attached). These values are approximately an order of magnitude higher than those obtained in the field using the BAT equipment. This is attributed to several reasons; the BAT equipment was developed for clayey soils and the material tested is a silty sand, and the BAT equipment is only applicable for soils with permeability less than 1 x 10' cm/sec. Thee Type 2 material exhibits permeabilities which approach or in some cases possibly exceeds the upper bound limit of the equipment and the material is ouite drv which may be affective the resuUts. rnn~~rierat.t:• more reuabttny is placed on the laboratory permeability measurements. Thei BAT equipment is considered to be reliable for testing the clay liner material (material Type 3). The laboratory permeability data indicates that the Type 2 material tested exhiCits a sufficiently high permeability for the drainage layer to function as intended. DH:Ip Attachments S.a'~a.. ~.ooe~..c~ arc -._ ~U S i..cc X2,2 ~c_,-. ...ace Sue- . ~_a..-.:oce ~o~,~~aac 5227. U.S.A