ARCHIVED REPORTS_1981 - Laserfiche WebLink

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ENVIRONMENTAL ASSESSMENT NATURAL ENVIRONMENT Topography Use of the site for a sanitary landfill operation would ultimately result in creating an earth covered terrace ranging 0 to 10 feet higher than the present level of Harney -Lane. It would be rectangular in shape; approximately 5,100 feet long by 2,500 feet wide. The top surface would be quite flat and inclined slightly toward the north to promote surface runoff. The periphery of the mound would be inclined from existing grade to the mound's top surface grade at approximately 2:1 (horizontal:vertical) slope or less. While this probably would not be visually obnoxious after revegetation, it nevertheless, would clearly stand out as an unnatural topographical feature. The significance of this topographical impact would be purely a matter of observer opinion. Tree plantings properly located to obscure the unnatural visual appearance could probably mitigate this impact satisfactorily. It should be noted that the final surface elevation will continue to settle with time as decomposition and compaction progress. Typically the amount of settling is variable and can only be predicted roughly. This generally results in formation of an irregular or lumpy sur- face which needs to be graded periodically to promote rapid drainage and prevent ponding of precipitation. Soils A section cut through the upper portion of the earth's crust would reveal several kinds of earth materials. At the bottom, solid, hard rock which is relatively unchanged is called bedrock. It grades upward into a zone where the rock has become decayed and has disintegrated into clay, silt, sand, gravel, and pebbles. This material above bedrock is called regolith. The top layer of the regolith, which in California rarely exceeds a foot or two in thickness, is what is commonly referred to as topsoil. This relatively thin surface layer is a dynamic natural body in which plants grow and is composed of mineral and organic materials and a multitude of tiny soil organisms essential to the development of topsoil. These organ- isms which live in the soil are responsible for converting the infertile mineral materials into fertile topsoil. Without the fertile topsoil it is difficult to establish vigorous and persistant vegetation. The process, however, requires hundreds of years to produce a single inch of thickness. Topsoil is a valuable natural resource which requires hundreds or even thousands of years to form. It cannot be replaced by infertile, mineral subsoil and then expect subsequent revegetation after closure of the landfill to flourish as it would in the natural topsoil. In effect, existing topsoil would be irretrievably lost if it is mixed in and buried :�I