Orange County NC Website
Browse       Search
22 <br />Recharge for the Morgan Creek basin (upstream from White Cross and Chapel <br />Hill) is higher than any other basin, explained in part by the soil properties in this <br />area that allow high infiltration rates (sometimes known as "Chapel Hill gravel"). <br />The Haw River basin (Bingham. Township and the northwestern edge of the <br />County) and New Hope River sub-basin (northern and eastern Chapel Hill) has <br />the lowest recharge, the latter largely due to the presence of Triassic <br />sedimentary rocks and soils with low infiltration capacities. <br />Finally, the report offers a method of using the recharge rate data for ground <br />water management planning. The ultimate limit on ground water availability is <br />the rate of recharge, i.e., the amount that can be sustainably withdrawn without <br />averdrafting the supply. Twa examples are provided that offer ways to translate <br />the recharge rate data on a basin-by-basin approach to determine the recharge <br />area needed and~the sustainable lot size, given a known water demand. <br />In summary, the report found that there are significant reserves of ground water <br />in the County, but that the rate of recharge varies from one geographic area, to <br />another. Although ground water supplies are currently sufficient, the report <br />notes the critical importance of proper management, conservation and planning <br />for, use of ground water supplies for the future. <br />B. 2001 Ground Water Resource Investigation <br />Where the ].996 Recharge Rate report looked at the County's ground water <br />availability using, streamflaw records by basin, the 2001 Resource Investigation <br />augments this report with actual well data. <br />The new report provides a baseline on well yield in the County, from data <br />gathered from 649 wells. These data include yield, depth, diameter, location, <br />casing depth, and water level. Table 3 on page 11 of the USGS report offers a <br />synapsis of the water availability findings. <br />Well yield (in gallons per minute) ranged dramatically, as has been known for <br />many years by those involved in well drilling and. inspection. The lowest yield <br />well in the,600-plus sample produced only 0.1 gallons per minute (gpm), while <br />the high yield well produced 240 gpm. The average well in the sample was much <br />lower, however, averaging 17.6 gpm. <br />The depth for wells in the sample likewise varied signifcantly, from a minimum <br />of 24 feet to a maximum of 805 feet. The average well depth was 208 feet. <br />The well ,yield and well depth findings allowed USGS to perForm sensitivity <br />analysis to see what type of correlation well yield had to construction practices <br />and siting of wells -and to well yield per foot of depth. <br />15 <br />