WATER-QUALITY DATA: Publication of Water Temperatures March 13, 1975 QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 75.15 Subject: WATER-QUALITY DATA: Publication of Water Temperatures The question of publication of negative water temperatures in Geological Survey basic-data reports has recently been raised by some WRD District personnel. This memorandum is to provide guidance to Districts in deciding whether or not to publish negative temperatures. Review of pages D-143 through D-182 in the 49th edition of CRC's Handbook of Chemistry and Physics provides a basis for evaluation of freezing point depression associated with increased concentrations of various chemical constituents. As an example, concentrations of potassium chloride (KCl) and sodium chloride (NaCl) are used to illustrate the freezing point depression. Solute concentrations of 10,000 milligrams anhydrous KCl or NaCl per 1,000 grams (approximately 1 litre) solution will result in a depression of the freezing point by 0.46 or 0.59!C, respectively. The relation between solute concentration and freezing point depression is linear to concentrations of 30,000 milligrams/litre of KCl and NaCl. Supercooled conditions can exist in streams characterized by turbulent flow conditions, but generally this condition alone will not result in temperatures colder than -0.1!C. In summary, conditions may be found in which water temperatures of less than 0!C are measured. Negative values of water temperature in the range of 0!C to -1.0!C should be published in Survey basic data reports after they have received a thorough review and their accuracy verified. Any values less than -1.0!C are highly questionable and should be published only after a complete check of the calibration of equipment used and discussion with the respective Regional Water Quality Specialist. R. J. Plckering WRD Distribution: A, B, FO-L, PO