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<br />1 EXECUTIVE SUMMARY <br />HSI GeoTrans conducted a hydrogeologic investigation of the proposed Alphin <br />subdivision site, which is located on the northeast side of Charles Town Pike (Route 9) <br />across from the intersection with Hampton Road (Route 738) southeast of Wheatland in <br />Loudoun County. The proposed conventional A-3 subdivision includes 31 individual home <br />lots on 135 acres. The hydrogeologic study was conducted in compliance with County <br />requirements to evaluate the adequacy of the available groundwater supply to meet the needs <br />of the proposed residences. <br />Based on the results of literature review, drilling test wells on nine lots, aquifer testing, <br />groundwater quality analyses, and evaluation of potential drawdowns and water-quality <br />impacts, we conclude the following. <br />(1) The groundwater supply available at the site is adequate to support the proposed <br />development of 31 homes. <br />(2) Drawdowns to result from long-term domestic well pumping at the subdivision will <br />probably not exceed 5 to 10 feet at a distance of 500 feet beyond the site perimeter, and <br />will decrease with distance from the extraction wells. <br />(3) The required water demand for 31 residences is estimated conservatively to average 8.6 <br />gpm based on a daily consumption of 400 gpd per home for 31 homes (Virginia State <br />Board of Health, 1982). Test wells completed on five of the nine lots where drilling <br />occurred yield in the range of 10 to 20 gpm. These yields individually exceed the <br />projected, time-averaged, total water demand of the entire proposed subdivision. <br />(4) The estimated rate of recharge to groundwater by infiltrating precipitation at the <br />proposed 135-acre subdivision site (time-average value of 70 gallons pe minute, gpm) <br />greatly exceeds the estimated water demand associated 31 domestic wells (time- <br />average value of 8.6 gpm). <br />(5) Existing groundwater quality at the site is generally good. Trihalomethanes, <br />volatile organic chemicals, pesticides, herbicides, and PCBs were not detected at <br />levels of concern in groundwater sampled from the any of the test wells. <br />Groundwater sampled from most of the test wells contained undesirable natural <br />levels of iron, manganese, and turbidity. Nitrate-nitrogen was not detected (<0.5 <br />mg/L) in six of the eight groundwater samples. No Primary Drinking Water <br />Standard were exceeded in any of the samples. <br />P: W LPHA' WLPHQJ FQdAL REPORT. WPD <br />JANUARY 1999 1 <br />