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08/22/95 TUE 09:49 FAX WOODWARD CLYDE [ j015 <br /> CITY OF EUGENE <br /> STORMWATER MANAGEMENT PROGRAM <br /> STANDARDS FOR NEW DEVELOPMENT <br /> PUBLIC WORKS ENGINEERING DIVISION August 21,1995 <br /> Maintenance of Facilities for Stormwater Quality and Quantity Control <br /> Issue: Following the presentation of the comparison between on -site and regional <br /> stormwater control facilities in Technical Memorandum #5, additional concern was raised <br /> regarding the maintenance of these facilities. <br /> 1.0 INTRODUCTION <br /> Regular maintenance of a stormwater control facility is an important factor in meeting its <br /> flood control and water quality improvement objectives. The failure of a facility to meet the <br /> water quality objectives is less easily detected than failure to meet the flood control goals. <br /> Thus, planned and scheduled maintenance programs are more effective in insuring that both <br /> goals are met than responding to citizen complaints or isolated problems. The effort required <br /> to maintain a system of stormwater control facilities depends on the number and type of <br /> facilities used. This memo presents an overview of the typical maintenance requirements for <br /> a variety of stormwater control facilities and the differences between systems of on -site <br /> versus regional controls. <br /> 2.0 MAINTENANCE REQUIREMENTS <br /> Infiltration Facilities. Infiltration facilities include controls such as infiltration trenches, <br /> infiltration basins, concrete grid pavement systems, and dry-wells or sumps. These facilities, <br /> which have both flood control and water quality benefits, are designed to intercept surface <br /> runoff and allow it to enter the underlying soil. Infiltration basins and trenches are not as <br /> common in western Oregon as regions which have more sandy soils. Monthly inspections <br /> should be made for the basins and trenches following construction and twice annually during <br /> normal operation (Portland, 1995). The City of Portland inspects their sumps every three to <br /> five years, although this period may be too long. The necessary maintenance activities <br /> include maintaining the adjoining vegetation, cleaning debris, and removing sediment to <br /> prevent clogging. The sediment removal frequency will depend on the runoff quality. Tilling <br /> of the surface soil layer in an infiltration basin is another possible maintenance activity. The <br /> ui <br /> q equipment required a ment for maintaining infiltration facilities includes mowers, 4Mscrapers, and <br /> other sediment removal equipment. <br /> Detention Basins. Detention basins include controls such as wet ponds and dry extended <br /> detention ponds. These facilities serve to reduce peak runoff rates and remove pollutants <br /> from stormwater through settling. These facilities should be inspected at least annually. <br /> Maintenance of detention ponds includes removing accumulated sediment from the bottom, <br /> removing debris and/or dead vegetation from the water, and maintaining the surrounding <br /> pmj91l 945 042othask0200Isfandard/mammc. doc <br />