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     Potomac River at Chain Bridge, at Washington, D.C.
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     Water-quality data were collected at this river location from 
  1973 to 1994 by the U.S. Geological Survey as part of the National 
  Stream Quality Accounting Network (NASQAN), composed of 618 stream
  monitoring stations in the United States.  

     This NASQAN station is located at river mile 115.9 on the 
  western edge of the District of Columbia, and its watershed 
  includes drainage in the states of Virginia, Maryland, West 
  Virginia, and Pennsylvania.  
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  WATERSHED ATTRIBUTES:

    Drainage area (square miles)............................11,570 

    Population density, 1990 (no. persons per square mile).....162   
 
    Land cover, 1987 (percent of basin area) 
       Urban.................................................... 5   
       Crop and Pasture........................................ 38
       Forest...................................................42        
       Other....................................................15

  NASQAN STATION ID:  01646580
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 Photograph by R.B. Alexander, September, 1996