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FLSA ASSOCIATES,INC. INITIAL STUDY/ENVIR <br /> JULY 2000 ONMENTAL DOCUMENTATION <br /> STOCKTON METROPOLITAN AIRPORT <br /> SPECIAL PURPOSE PLAN <br /> C) Substantially alter the existing drainage pattern of the site or area,including <br /> through the alteration of the course of a stream or river,in a manner which <br /> would result in substantial erosion or siltation on-or off-site? <br /> Less than significant impact. The proposed project will not result in substantial <br /> alteration to the surrounding surface drainage conditions that would result in <br /> F substantial erosion or siltation. A Master Plan of Storm Drains has been prepared <br /> for the SPP that provides for the conveyance and storage of surface runoff of the <br /> "design storm." A series of detention basins,storm drain pipes, and curbs/gutters(or <br /> temporary surface ditches)will be used to accommodate peak detention needs. <br /> Ultimately, runoff will be conveyed into New Weber Slough, Mansville Ditch, and <br /> related storm channels. With these interim and ultimate improvements, surface <br /> drainage conditions will be mitigated,and erosion/siltation will be negligible. <br />€ 'F Erosion and siltation control measures included in the Airport Master Plan EIR will <br /> apply. <br /> FAirport Master Plan Mitigation: <br /> Mitigation Measure DW-2; Implement measures to minimize the attraction of <br /> waterfowl to detention facilities. <br /> Fd) Substantially alter the existingdrainage I; pattern of the site or area,including <br /> through the alteration of the course of a stream or river, or substantially <br /> # increase the rate or amount of runoff in a manner which would result in <br /> F flooding on- or off-site? <br /> F <br /> Less than significant impact. The drainage patterns associated with the Special <br /> Purpose Plan will be substantially similar to the patterns previously included in the <br /> Master Plan design. Minor changes to detention basin sizes and locations will be <br /> required. The overall rate of runoff,diversion of flow, etc.,will generally reflect <br /> F those conditions identified in the Master Plan. <br /> Airport Master Plan Mitigation: <br /> I Mitigation Measure DW-1: Develop and implement a comprehensive drainage plan. <br /> e) Create or contribute runoff water which would exceed the capacity of existing <br /> F' <br /> or planned stormwater drainage systems or provide substantial additional <br /> sources of polluted runoff? <br /> Less than significant impact. The proposed Special Purpose Plan will not result in <br /> F substantial alteration to the surrounding surface drainage conditions that would <br /> substantially increase runoff and result in flooding on-or off-site when compared <br /> with the previous Master Plan. <br /> Storm runoff from the roadway surface may contain pollutants such as oil, grease <br /> and petroleum products, but the amount of contaminants is expected to be minimal. <br /> It is unlikely that the pollutants will percolate into the groundwater. Grading of the <br /> F site may cause some siltation, but this can be controlled by adherence to mitigation <br /> measures contained in the Master Plan EIR. <br /> F <br /> F <br /> 7/20100(P:1SJC030Tnvironmentat\iniiial studympd) <br /> 37 <br />