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a geotextile filter fabric. This: concept is shown on Figure <br />• 2. , <br />It is our understanding that the Colorado Mined Land <br />Reclamation Division requires the elimination of the collection <br />and discharge pipes discussed in our earlier report as <br />components of the subdrain system. We suggest you consider <br />replacing the pipe components of the subdraius with a roc4: <br />drain consisting of ,t graded aggtoyate. The rock dr•ri 1. ~:hould <br />be a clean ayg rr_yate of limited :•i zr• distribution wrdl•~~~~.~ <br />with a geotextile filter fabric. The size of the rock ,Irwin <br />should be about four (4) cubic f~•L•t f:er linear ll,ut of ,iraiu. <br />The rock drain should be locatod at the downhill edyo L~•i the <br />blanket drain and graded to outlet downhill and beyond I:he <br />toe of the slope. The rock dr~ir concept is shown on Ptgut L: <br />• 3. The rock drain material fur the collector/conduct should <br />be graded aggregate which will I~t uv;de ad c•y u,.tc nurmL .ii il:t ~~ <br />for drainage of the seepage water. We suggest that yon <br />consider grading for the roc}. drain material with the maxim wn <br />aggregate size of about one (1) to one and one half (1.5) inch <br />with no material passing a Numbet 4 sieve size. The rock <br />drain does not replace the drain blanket concept as di::cussod <br />in our previous report, but replaces only the drain pier <br />portion of the drain system. The rock dram should be graded <br />to a slope of at least four (4) percr.nt and discharged beyond <br />the toe of the slope. For ease of construction and maintenance <br />-3- <br />1485021GE <br /> <br />~lambrrt ana ~,ssoriate~' <br />CONSUL LNG GEO tEGMN~CAI ENGIN EERS AND <br />M ALERiAL TESTING <br />