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- 14 - <br />• should extend from the embanbrent tce a distance of 1 1/2 times the <br /> embankment height for heights ~~reater than 10 feet. Thickness of the <br />blanket should be at least 2 feet. The toedrain should also be <br />provided with a minimum 4-ind~ diameter perforated pipe sloped at a <br />minimum 1~ grade to gravity outlet. The blanket and tce drain mater- <br />ial should consist of a granular soil meeting graded filter criteria <br />with less than 58 passing the #200 sieve. <br />For impoundments located within the lower area along the river, <br />seepage analysis should be performed to determine required drainage <br />within embanlanent and foundation soils. We anticipate that for a <br />relatively impervious e~ankn~ent section, a tce and blanket drain <br />should be adequate at runoff ponds #2 and #3. Permeability rates of <br />in-situ granular soils have not been determined. Based on general <br />• properties of the soils, we estimate permeabilities to range between <br />approximately 10-3 to 10'5 czn/sec. for natural silty to clayey <br />sands and 10'1 to 10-2 csn/sec. for the coarse alluvial soils. <br />Exploratory holes drilled in proximity to the fresh water pond #2 <br />indicate shallow sand and silt depth and ground water table. Impound- <br />ment depth is anticipated to be approximately 15 feet. For these <br />ocnditions, we anticipate a semi-impervious sail liner or impervious <br />synthetic liner will be required to reduce seepage rates to tolerable <br />limits. If this is required, on-site clay soils obtained in the <br />higher plateau area should be suitable for use as liner material. A <br />tce and blanket drain will pr+obabl}• also be required for a homogeneous <br />type embanlarent. <br /> <br />