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27 <br /> PRELIMINARY STORMWATER & DRIANAGE STUDY <br /> Project Name: Annandale at Creek Wood <br /> Project Number: 12-017 <br /> Report Date: August 31, 2012 <br /> Purpose: The purpose of this report is to investigate preliminary requirements for <br /> stormwater management associated with development of the subject property. <br /> SITE DESCRIPTION: <br /> Project Location: 2520 Whitfield Road <br /> Chapel Hill, NC. <br /> It is located in Orange County north of Whitfield Road and East of NC86. <br /> Site Size: 36.46 acres by survey. <br /> Soil Types: EnC— Enon loam, 6 to 10% slopes—Group C <br /> EnB—Enon loam, 2 to 6% slopes—Group C <br /> HrC—Herndon silt loam, 6 to 10% slopes—Group B <br /> TaD—Tatum silt loam, 8 to 15% slopes- B <br /> GeC—Georgeville silt loam, 6 to 10% slopes—Group B <br /> GeB—Georgeville silt loam, 2 to 6% slopes—Group B <br /> Watershed: WS-IV NSW/Jordan Lake <br /> River Basin: Cape Fear River Basin <br /> Site Characteristics: The site is a heavily wooded, 36.46 acre tract bisected by two streams running <br /> south to north which merge in the middle of the site. Slopes vary on the site, <br /> with some slopes of 25% present; however, most slopes appear to average <br /> 5%-8% based on LIDAR topography. <br /> Drainage All runoff from the edges of the site drain toward the two streams located on <br /> Characteristics: the site and exit at roughly the midpoint of the northern property line. It should <br /> be noted that this site is a portion of a much larger drainage basin that <br /> incorporates portions of a large commercial area located immediately south of <br /> 1-40. <br /> PROPOSED DEVELOPMENT: <br /> Proposed Usage: The proposed development consists of 11 lots of a minimum of 2 acres in size <br /> with the remainder being placed in open space/buffer area (see attached). <br /> Lots will be accessed via two public roads, one located at the eastern extreme <br /> of the site and another located at the western extreme; thus, preserving the <br /> stream and buffer area by not providing a roadway crossing. <br /> Additionally, the owner proposes to restrict impervious area to roughly 14%, <br /> which is less than the 15% required for an exemption from peak flow <br /> attenuation requirements; however, the site would still require peak flow <br /> attenuation if increases in runoff produced in the 1-year storm exceed 10%. <br /> Additionally, the site's location in the Upper New Hope Sub-Watershed will <br /> likely require the use of some treatment for nutrient reduction. Therefore, this <br />