In Reply Refer To: September 19, 1980 EGS-Mail Stop 412 Quality Water Technical Memorandum No. 80.27 Subject: WATER QUALITY -- New Parameter Codes for pH, Alkalinity, Specific Conductance, and Carbonate/Bicarbonate Beginning October 1, 1980, the field and laboratory values for the subject constituents will be entered into WATSTORE under separate parameter codes. In addition, a more careful distinction than has been made in the past will be made of the methods used to determine alkalinity and carbonate/bicarbonate ion concentrations and of the assignment of parameter codes to values obtained by those methods. Either by request from the field or by necessity for quality control checks, the National Water Quality Laboratories (NWQL) often measure pH, specific conductance, and alkalinity even though field values may be reported on the log-inventory form. Both values need to be stored, and parameter codes are being established for that purpose. The measurement of alkalinity, bicarbonate, and carbonate and the reporting of those measurements are complicated by a mixture of problems including past field measurement methods that may have produced less accurate data than those that could be acquired through incremental titration and parameter codes that were not sufficiently descriptive to allow certainty in their use in WATSTORE. This memo is intended to specify acceptable field measurement methods and clarify the assignment of parameter codes. Prior to 1964, the accepted procedure for determination of hydroxide, carbonate, and bicarbonate ions was to titrate with a standard acid to fixed endpoints at pH 10.4, 8.3, and 4.5. The concentrations of the ions were equated to the volume of a standard acid added to the sample after conversion to proper reporting units. In 1964, Barnes (WSP 1535-H, 1964) showed that the actual stoichiometric endpoints of the bicarbonate portion of the titration could vary between pH 5.38 and 4.32, depending on the temperature and ionic strength of the sample. This kind of endpoint variability can be expected with respect to the other two ions, the chemical principles Barnes used in his arguments apply to those endpoints as well. It is quite clear from this work that titration to fixed endpoints yields measures of hydroxide, carbonate, and bicarbonate that are probably in error by variable and indeterminate amounts. The only acceptable method for measuring these constituents is to titrate in increments of acid small enough to accurately distinguish the inflection points of the pH vs. acid-volume curve, which are the stoichiometric endpoints. Titration to fixed pH endpoints is still in common use in water-quality work; however, and many WRD field personnel continue to use the method in the field because they have received no directions to discontinue its use. Since 1964, the measurement of "alkalinity", as defined by the acid needed to drive the sample pH to 4.5, has been made extensively. Our files now contain hundreds of thousands of measurements made by titration to pH 4.5. The method is recognized by EPA and USGS, as well as by other organizations devoted to methods standardization, and the term "alkalinity" has been attached to this measurement so frequently that the term and the measurement are now virtually inseparable. The different measurements and parameters that may be derived from titration of a sample with a standard acid are illustrated in the enclosed figure. The dots on the curve are the inflection points, the true stoichiometric endpoints of the titration of hydroxide (OH), carbonate (C03), and bicarbonate (HC03). In this example, the inflection points are all at pH's greater than the previously accepted endpoints 10.4, 8.3, and 4.5, but they could as easily be less than those values. It can be seen that l) volume A correctly represents OH(-), but volume B does not, 2) volume C correctly represents C03(-2) CO3(2_), but volume D does not, 3) volume E correctly represent HCO3(-) but F does not, 4) G correctly represents the alkalinity due to C03 and HC03- but H does not, 5) volume I represents the alkalinity as now accepted by common use, namely, the acid needed to drive the sample pH to 4.5. It is also clear that the measurements represented by volumes B, D, F, and H are those most commonly reported and that they are not rigorously correct. In accordance with the foregoing analysis, after October 1, 1980, 1) data will no longer be entered from the field under parameter codes 71830, 00445, 00440, and 00430; these codes will henceforth be used only for data retrieval; 2) values of OH(-), C03(-2), and HC03(-) will be entered only if they are determined by incremental tltration to the inflection points and expressed only as mg/L of the ion; new paramenter codes have been requested for these latter determinations and will be transmitted to you along with the approved field procedures as soon as they are available; 3) values of alkalinity by titration to pH 4.5 obtained in the field and lab will be entered under parameter codes 00431 (field) and 00410 (lab). In addition, 4) specific conductance values determined in the field and will be entered under parameter codes 00094 (field) and 00095 (lab) and 5) pH values determined in the field and lab will be entered under parameter codes 00400 (field) and 00403 (lab). R. J. Pickering Enclosure Distribution: A, B, S, PO, FO Key Words: Water quality, analytical methods, data handling, field measurements, parameter codes, pH, specific conductance, alkalinity, carbonate, bicarbonate, hydroxide. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - In Reply Refer To: October 8, 1980 EGS-Mail Stop 412 Memorandum To: Distribution From: Chief, Quality of Water Branch, Reston, Virginia Subject: Water Quality--Quality of Water Branch Technical Memorandum No. 80.27 The figure enclosed in the subject memorandum was incomplete. Please substitute the enclosed figure in your copy of Quality of Water Branch Technical Memorandum No. 80.27. R. J. Pickering Enclosure Distribution: A, B, S, PO, FO