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<br />v 11--5 <br /> <br />Another assumptioh, based on recent experinece in Boulder, is that sed- <br />iment removal from the sedimentation basins would be self-supporting_ <br />The materials removed can be sold as fi 11, topsoi I, or aggregate for <br />concrete, depending on their composition. <br /> <br />SECONDARY BENEFITS <br /> <br />The secondary or auxiliary benefits are not easi Iy measured in terms of <br />dollars, but they can be so measured if time is taken to get the facts, <br />utilizing suitable experts in many disciplines. <br /> <br />Auxiliary benefits are numerous_ A significant list can be prepared on <br />most urban areas by engineers, urban planners, and sociologists. The <br />following partial tabulation is presented for Lena Gulch. <br /> <br />I. Lowered ground water table <br />2. Controlled rising ground water table after urbanization <br />3. Reduced street maintenance cC6tS <br />4. Reduced street construction costs <br />5. Improved movement of traffic <br />6. Improved public health environment <br />7. Lower cost open space <br />8. Lower cost park areas and more recreational opportunities <br />9. I mp roved qua 11 ty of stream <br />10. Opportunities for close-in solid waste disposal sites <br />II. Opportuni ties for lower bulld'ing construction cost <br />12. Opportunities for creating new water supplies <br />13. Opportunities for lower insurance I"ates on private <br />and Federal levels <br /> <br />These factors were considered in the unit cost prices and the estimation <br />of various schemes, but do not affect the costs significantly from alter- <br />native to alternative. The following paraqraphs provide further comments <br />on a selected number of these benefits. <br /> <br />1. Groundwater Control. The Lena Gulch basin has some high ground water <br />problems in regard to development of subdivisions for residential homes. <br /> <br />A problem area is not always apparent prior to urbanization, yet, after <br />development Is completed, the percolation from lawn irrigation some- <br />times exceeds the aquifer's capacity to carl"Y water off. The I-esult <br />is an increase in groundwater storage ,,'ith a rising water table. Sump <br />pumps Installed to keep a basement dry nearly always discharge to a <br />sanitary sewer, increasing the load on the sewerage system. <br /> <br />A storm sewer into which the developer daylights subsurface drains to <br />control groundwater elevations provides many benefits. These benefits <br />