CORRESPONDENCE_1987-1991 - Laserfiche WebLink

Home Browse Search

Mr. Tom Horton Project 939-02.31 December 4, 1991 Page 3 Historical summaries of the analytical data are presented in Tables 1 and 2. In some instances, analytical data were available for monitoring events conducted before the 1-year WQPS monitoring program. These data are also presented in Tables 1 and 2 and were used, together with the WQPS monitoring program data, to establish WQPS for the site. STATISTICAL DEVELOPMENT OF WQPS The statistical method selected for WQPS development is the tolerance interval method. This method is used to estimate the highest value (and the lowest value, in the case of pH) of each parameter that a downgradient well or downstream surface-water point can exhibit and still be reasonably attributed to natural variability, given the historical chemical characteristics of background ground and surface water. These highest and lowest val- ues, or tolerance limits, are the proposed WQPS. A tolerance interval establishes a concentration range that contains a specified proportion, or coverage, of the population with a specified confi- dence limit. The coverage and confidence limit were chosen at 95 and 95 percent, respectively. Tolerance limits were calculated using the historical background mean (x) for each parameter, the standard deviation (s) of the background data, and a tolerance factor (K) specific to 95 percent cover- age and a 95 percent confidence limit. Tolerance factors are listed in Introduction to Statistical Quality Control (D.C. Montgomery, John Wiley Publishing, New York, 1985). The tolerance limits were calculated as fol- lows: upper tolerance limit = x + (K)(s) lower tolerance limit = x - (K)(s) [for pH only] The calculated tolerance limits (WQPS) for ground and surface water are presented in Tables 3 and 4, respectively. The tables also show the num- ber of samples included in the calculations and the mean, standard devia- tion, and the tolerance factors used in calculating each tolerance limit. One requirement of the tolerance interval method is that more than 50 percent of the data points be greater than zero. The data for carbonate alkalinity, sulfate, total organic carbon (TOC), and manganese for well G-1, and nitrate-nitrogen and sulfate for S-1 and S-2 do not meet this requirement. Therefore, EMCON recommends that the WQPS for these PJ9\939\9390231 i