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38 <br /> concentrated in a swale, from adjoining development and <br /> achieve reductions in pollution discharges . <br /> Within the University Lake Watershed (ULW) District, an <br /> area of land or buffer zone along perennial and <br /> intermittent streams shall be required to remain in its <br /> natural state, unless the area is subject to serious <br /> erosion, in which case an erosion resistant vegetative <br /> cover shall be established and maintained. Perennial <br /> streams are those streams shown in solid blue on the <br /> USGS quadrangle maps for Orange County. Intermittent <br /> streams are those streams shown by broken blue lines on <br /> the same maps. <br /> 6.25.5. 1 Calculation of Buffer Zone Width <br /> Width; i.e. , distance from the stream bank to the edge <br /> of the buffer, is a critical factor in determining the <br /> effectiveness of a buffer zone. An equally important <br /> determinant in pollutant removal in a buffer zone is <br /> travel time; i.e. , the greater the time allowed for <br /> runoff to travel through a buffer, the greater the <br /> opportunities for pollutant removal through <br /> sedimentation, filtration, absorption, and seepage into <br /> the soil profile. <br /> Monitoring studies of highway runoff have shown that <br /> pollutant removal in grass swales is at a maximum after <br /> a 15-minute travel time. Based on this standard, Table <br /> 6.25 .5 was derived to provide a sliding scale for buffer <br /> zone widths based on slope and vegetative cover. <br /> TABLE 6.25.5 REQUIRED BUFFER ZONE WIDTHS <br /> ALONG PERENNIAL AND INTERMITTENT STREAMS <br /> IN UNIVERSITY LAKE WATERSHED <br /> Type of Groundcover <br /> Grass Woods <br /> Slope (Ft) (Ft) <br /> -.. <br /> 2% to 4.9% 100 50 <br /> 5% to 6.9% 150 100 <br /> 7% to 9 .9% 150 100 <br /> 10% to 14.9% 200 100 <br /> 15% or greater 250 150 <br />