A New Water Supply for the Alexandria Water Company

Abstract

RARELY in these times does the opportunity come to promote, plan, construct and operate an entirely new water supply system. In the past several years, the Alexandria Water Co., serving Alexandria and the surrounding area of Virginia, has had that opportunity. In the resultant new 4-mgd. plant are several novel features which may be of special interest to the water works profession. A number of factors created the need for a new water supply. Alexandria's former supply had been secured from Cameron Run, a stream with a rather small drainage area of 33 square miles. At the headwaters, on Holmes Run, was an impounding reservoir holding 817 mil.gal. Continuing growth in the area was rapidly populating the watershed. More important, it was found that trunk and intercepting sewers laid adjacent to the streams constituting the source of the water supply were materially depleting the reservoir and streams through infiltration. In dry periods such infiltration might seriously reduce the safe yield of water below the amount required to serve even the existing service area. In addition, the growth of adjacent Fairfax County was being retarded by the lack of an adequate water supply system. To expand the service area throughout the southern part of Fairfax County would require a substantial additional source of water. Well yields were not satisfactory except in limited areas and even in those areas a dry period might well demonstrate their inadequacy. In the area under consideration, there were three streams which were considered for development the Accotink, Pohick and Occoquan Creeks. The first of these streams was already in limited use as a source of water for Fort Belvoir, located at the confluence of Accotink Creek and the Potomac River. Both the Accotink and Pohick Creeks have small drainage areas, and the amount of storage which would be necessary to provide a dependable supply for the area made both these streams uneconomical of development except as an addition to the existing supply. Furthermore, any new development would have to provide for considerable future growth in the area to be served.