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-2- this value would correspond to a permeability of approximately lE-(~3 CM/SEC." No reference is cited for these "accepted relationships." Sherard.(1963) gives a probable permeability range for SM Classified soils as 9.7ff-09 CM/SEC to 4.8E-04 CM/SEC and states that the relative permeability of this type soil is "semipervious to impervious." Wilum and Starzewski (1972) list typical values for coefficient of permeability for silty sand, a description which would encompass SM type soils, as 1E-03 to 1E-04 CM/SEC. It is my opinion that unless you are dealing with clean Sands or gravels (which we re not), or unless you have a hydrometer analysis of particles within the soil smaller than .074 mm diameter (which we do not), that any attempt to relate grain-size distribution to permeability is tenuous. Two lab-tests for permeability were performed on SM type soil excav ted from test pits within the borrow area. Permeabilities of these soil sam les were found to be 5.0E-03 CM/SEC and 1.7E-03 CM/SEC (Appendix D.l, 112 pe mit, November 1488). These test results are encouraging, however, two l~b permeability tests are insufficient to characterize the 600,000 yar s of material that comprise the sub-drainage layer. In situ permeabilit testing within bore holes drilled in the borrow area (BH-2 and BH-3, Append x E, 112 Permit, November 1988), gives permeabilities ranging from 1.0E-04 C /sEC to 7.4E-06 CM/SEC. Hopefully, borrow material exhibiting the lower pe meability would not h=~~e met "type 2" specifications, and would not have been used in placement of the sub-drainage layer, but there is no way of knowing this. I would recommend that samples of the sub-drain layer material be sub ected to additional laboratory scale, constant head permeability analysis, t provide reliable data on the permeability of this vital drain layer materia . Giroud and Bonaparte (1989) report that with good quality control d ring geomembrane installation, one hole per acre i5 typical. They also ote that most defects are small (0.1 square cm.), but that larger holes ar occasionally observed. Based on the assumption that a single synth tic liner flaw of .1 sq. cm. exists for each acre of liner, the calculations ubmitted with the SRK technical memorandum state that the total seepage for he pond will be 9,460 gallons/year. However, utilizing Table 2.3 from the PA document "Design and Construction of RCRA/CERCLA Final Covers," whi h lists calculated flow rates for composite liners, you would come up with total seepage of 183,648 gallons/year from the pond. This is a rate 19 times greater than that used by SRK, and assumes that the sub-drainage la er is functioning to limit the applied hydrostatic head to one foot (an assumption that T am not presently comfortable with), and that the compacted s it portion of the composite liner has a permeability of 1E-06 (based on permea ility measurements made during construction quality control (Appendix A, Construction Report), I am comfortable with this assumption). It must be noted that the flow rate for seepage of 183,648 gallons/year assumes a poor hydraulic seal between the geomembrane and the soil; if a good seal xists, then seepage from the pond could be as low as 36,730 gallons/year. (This is still 4 times greater than the figure supplied by SRK. If we give the pond design the benefit of the doubt in each case (i.p. a single liner flaw of .1 sq. cm. per acre, upper limit of 1 foot hydrostatic head applied to the liner, a compacted sub-soil permeability of lE-0~ CM/SEC, and a good hydraulic seal between the sub-soil and the geomembrane), the result is a total of 34,375 cu. feet. of seepage over an eight year Pond life.