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. ' <br />Memo to Berhan Keffelew 2 February 8 1995 <br />The anticipated flow through the upper geomembrane into the leak <br />collection gravel is estimated below: <br />Known: Surface area of pregnant solution storage area (from As-Builts) <br />= 614,129.3 sq. ft. = 14.1 acres. <br />A conservative estimate of the head that may be applied to any <br />flaw that may exist in the upper geomembrane can be made by <br />taking the average of the elevation difference between the <br />bottom of the pregnant solution recovery sump and the lower <br />anchor trench, i.e.: <br />9360' - 9225.5 64.5' <br />Average head = 4.5' 2 - 32.2 ', 9.84 meters (m) <br />A geosynthetic liner installe th a onstruction <br />Quality Assurance can be expected to have one small cm or <br />.00001 m) hole per acre (ref.l). So we can anticipate 14 sma <br />Fiot~`~o be present in the upper liner of the pregnant solution <br />storage area at the Cresson Phase 1 pad, and can calculate an <br />anticipated flow rate to the leak collection gravel: <br />If it is assumed that the holes are sufficiently widely spaced <br />that leakage through each hole occurs independently from the <br />other holes, that the head of the liquid ponded above the liner <br />is constant, and that the material that underlies the <br />geomembrane has a large hydraulic conductivity (offers no <br />resistance to flow through a hole in the geomembrane), the <br />following equation can be used to calculate flow through <br />geomembrane defects: <br />q = Ce a (2gh)0.5 (ref. 1) <br />where q is the rate of flow (m3/s); CB is a flow coefficient <br />with a value of approximately 0.6; a is the area (m2) of a <br />circular hole; g is the acceleration due to gravity (9.81 <br />m/s2); and h is the head (m) above the liner. <br />Plugging in the site specific values yields: <br />q = (.6)(.00001)(2.9.81.9.84)0'5 = .000083 m3/s <br />_ .0219 gal/sec = 1892 gal/day <br />With 14 total flaws or holes, a flow of 26,490 gal/day to the <br />leak collection layer can be anticipated. Theoretically, in <br />order to avoid flooding the leak collection sump, and imposing <br />a head of greater than two feet on the composite liner, the <br />sump needs to be pumped at approximately 10 hour intervals. <br />