Programs and Plans--Quality assurance of water quality data; Standard Reference Water Sample Program In Reply Refer To: September 9, 1980 EGS-Mail Stop 412 QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 80.25 Subject: Programs and Plans--Quality assurance of water quality data; Standard Reference Water Sample Program The Division's Standard Reference Water Sample (SRWS) Program, which has been in operation for seventeen years, has provided the Geological Survey with valuable information on the precision of data produced by participating laboratories, including those of WRD and its cooperators, using a variety of analytical methods. By combining the information from all labs, it is possible to get an estimate of the general precision of water quality data as a whole. Over the years the program has expanded; from inclusion of only common inorganic constituents to inclusion of trace metals and nutrients as well. The attached report, which expands the area of investigation into organics and represents another milestone in the program, is provided for your information. Your attention is drawn to two items in Table 1: (a) the good agreement in results between the two USGS central laboratories (labs numbered 039 and 050), and (b) the availability of precision data based on a number of laboratories employing a variety of analytical systems. R. J. Pickering Chief, Quality of Water Branch Enclosure WRD Distribution: A, B, S, FO, PO REPORT OF ANALYTICAL EVALUATION PROGRAM STANDARD REFERENCE WATER SAMPLES Insecticide No. 1 and Herbicide No. 1 July 1980 PARTICIPATING LABORATORIES U.S. Geological Survey COLORADO, Denver: McAvoy (050) GEORGIA, Doraville: Erdmann (039) Other ARKANSAS, Little Rock: Arkansas Department of Pollution Control and Ecology CALIFORNIA, Oakland: East Bay Municipal Utility District CALIFORNIA, Los Angeles: Water Quality Laboratory CALIFORNIA, La Mesa: San Diego Water Laboratory FLORIDA, Tampa: Hillsborough County Env. Prot. Commission GEORGIA, Atlanta: Natural Resources Env. Prot.Division IOWA, Des Moines: University Hygienic Laboratory MARYLAND, Annapolis: Water Resources Laboratory NEVADA, Reno: Nevada State Health Labs SOUTH CAROLINA, Columbia: Water Resources Commission VIRGINIA, Richmond: Division of Consolidated Laboratories PURPOSE AND PLAN As a means of providing an independent and objective evaluation of the water quality data published by the U.S. Geological Survey and other cooperating laboratories, standard reference water samples are prepared and distributed at regular intervals. The program has included standard reference water samples for major constituents, trace metals, and nutrients. Because of the increasing demand for pesticide analyses, it was deemed important to expand the program to include both insecticide and herbicide reference water samples. These were preliminary samples and were prepared in an attempt to determine if pesticides would remain stable for a period of time in a natural water matrix. A detailed report on stability will be prepared at a later date. This report summarizes the analytical results submitted by 13 laboratories for Insecticide and Herbicide Reference Water Sample No. 1. Preparation Of Samples Approximately 55 gallons of tap water were collected in a steel container on February 14, 1980, and cooled to 4 degrees C. Organochlorine and organophosphorus insecticides, and chlorinated phenoxy herbicides dissolved in acetone were added dropwise, with stirring to the water. After mixing, the sample was packaged in l-liter glass bottles and stored in the dark at 4 degrees C. The samples were packed in ice prior to distribution. Two bottles were sent to each participant; one sample was for determination of insecticides, and the second sample for determination of herbicides. The samples contained the following constituents: Insecticide Sample No. 1 Aldrin Heptachlor DDT Lindane Diazinon Mirex Dieldrin Ethyl parathion Herbicide Sample No. 1 2,4-D 2,4,5-T Silvex Dichloroprop (2,4-DP) STATISTICAL EVALUATION A statistical evaluation of the data has established the most reliable estimate of the true value for each of the various constituents determined. Reported values of "less than" were considered as "not determined" and hence do not enter into the computation of the means, standard deviations, etc. Mathematical computations are the same as those used previously for similar Standard Reference Water Samples of this type. The mean and standard deviation were calculated for each determination. Outlying values were rejected on the basis of statistical tests as outlined in ASTM Recommended Practice for Dealing with Outlying Observations (1969 Book of ASTM Standards, Part 30, p. 429-445). REPORTED VALUES AND METHODOLOGY Table 1 which follows shows the reported value for each determination by each participating laboratory and the overall means and standard deviations generated to four decimals. Reported values have not been rounded off. If it was not indicated on the report form that an insecticide or herbicide was "Not Detected" or "Not Determined", a blank space was left in Table 1. Tables 2, 3, and 4 give a summary of the methodology used by each laboratory.