Summary of the National Atmospheric Deposition Program/National Trends Network intersite-comparison program, November 1978-November 1989

Abstract

Intersite-comparison studies have been used since November 1978 to assess the accuracy and precision of pH and specific-conductance measurements made by National Atmospheric Deposition Program and National Trends Network site operators. Between November 1978 and June 1980, the first four intersitecomparison studies were administered by the Illinois State Water Survey Central Analytical Laboratory, Champaign, Illinois. The U.S. Geological Survey assumed responsibility for the program in October 1981. Twenty-four intersite-comparison studies were completed as of November 1989. The pH and specific-conductance measurements made during intersite-comparison studies were primarily evaluated using two methods of analysis. The first method of analysis evaluated site-operator reported values in terms of the measurementaccuracy criteria established by the Network Operations Subcommittee. The measurement-accuracy criteria for pH are ±0.10 unit if the most probable pH value is 5.0 or less or ±0.30 unit if the most probable pH value exceeds 5.0. In every intersite-comparison study except study 22, the median pH was less than 5.0. The measurement-accuracy criteria for specific conductance are ±4.0 microsiemens per centimeter of the most probable value. The second method of analysis evaluated the differences between site-operator reported values and network median values.