TM95-01 National Water Quality Laboratory Alkalinity Reanalysis Policy

This memorandum presents a new policy statement for reanalysis of alkalinity in water samples. Because alkalinity is not a stable constituent, alkalinity measurement in the field are more accurate than alkalinity measurements in the laboratory. Therefore, the National Water Quality Laboratory (NWQL) will no longer perform routine reanalysis of alkalinity. NWQL alkalinity methods are I-2030-85 and I-2034-86 (Fishman, 1993, p. 9-12; Fishman and Friedman, 1989, p. 55-58, respectively). The lab codes and test ID's for methods I-2030-85 and I2034-86 are lab codes 0070 and 1270 and test ID's 90410A and 90410B. As described in the method documents, alkalinity is susceptible to substantial change between time of collection and time of laboratory analysis. These changes are more rapid once the sample bottle is opened. The alkalinity of some samples may change appreciably within hours. Therefore, alkalinity should be determined as an on-site parameter at the time of sampling for the greatest accuracy. In addition, the U.S. Environmental Protection Agency (1992) states that environmental alkalinity measurements require immediate analysis. This indicates laboratory measurements of alkalinity may not accurately represent the alkalinity at the time of collection. Based on the sources, laboratory alkalinity values should be used only as qualitative checks or as determinations of sample stability during transit. The laboratory alkalinity should be published only as a last resort (R.J. Pickering, U.S. Geological Survey, written communication, Quality of Water Branch Technical Memorandum No. 82.06, 1982).