Streamline - Fall 2012 - (Page 31)
Ergs, Joules & Such
BY JOHN E. REGNIER, NRWA
Notes on Energy Savings for the Rural Water Community and Maybe Others
IN OUR CONTINUING review of NRWA White Papers, I thought this month we would look at the topic of Compliance Data Variability. This refers to the variation in results of determinations of the amount of a contaminant in water sampled from a specific entry point to the distribution system of a water supplier. This is a subject of critical importance to water systems as these results (normally the average of four quarterly samples) are used to judge whether a system is in regulatory compliance and may be the basis for requiring expensive treatment. NRWA has investigated this topic thoroughly with four White Papers being generated and a peer reviewed summary paper currently undergoing consideration by the American Water Works Association for possible publication in Journal AWWA. The four NRWA White Papers are: Reliability of Laboratory Data Generated For Compliance With Drinking Water Regulations by Charles Philips; Applicability of Laboratory Data Generated for Compliance With Safe Drinking Water Regulations by Charles Phillips; Water Quality Compliance Decisions Based on Four Quarterly Measurements by Charles Phillips and Harry Chemylinski; and Required Number Of Samples For Acceptable Precision of Compliance Data Means by Harry Chemylinski and Edwin L. Sensintaffar.
Due to the importance of this topic to water systems, I felt that a summary of these papers would be important and the following bullet points summarize the key findings. Please keep in mind that variability in this context refers to total variability in the individual results making up a mean, not just analytical variability in the laboratory. • The latest data used in this evaluation and the most reliable were taken from EPA’s second Six-Year Review Database which provided over 900 sets of four or more samples from specific system entry points. • Although the database contained a wealth of entries, the majority were non-detects with positive results being available only for a limited number of contaminants; 10 were selected for statistical analysis. • The principal statistical parameter used in the analysis was the 95 percent confidence interval (CI) of the mean which is the range of values around a calculated mean that one can be 95 percent certain includes the true value of the contaminant concentration. • The average value for the CI for all 970 data sets analyzed was 105 percent of the mean. In other words, on average when a system receives or calculates a mean of four quarterly sample analyses, they can only be 95
percent certain that the real value of the concentration is the mean +/- 50 percent of the mean. • Perhaps even more startling is the additional finding that when the mean is at or near the MCL, the average CI is 193 percent of the mean. Under these conditions, on average, a system manager could only be 95 percent confident that the true concentration is somewhere between about zero and twice the mean value. • Theoretically, it should be possible to improve this situation by additional sampling, but additional evaluation of the data showed that for numerous contaminants the additional number of samples is too large to be practical. • Stay tuned for more on this critical issue and be as sure as possible of contaminant concentrations before taking any corrective action. This article ran in Energy Conservation Newsletter, Volume 4, Issue 8, August 2012. Contact John E. Regnier, NRWA, at firstname.lastname@example.org or (334) 462-1541.
Table of Contents for the Digital Edition of Streamline - Fall 2012
From the President
From the Executive Director
A Day ( or Two) in the Life of a Circuit Rider
The Necessary Evolution of Water and Wasterwater Utilities
Craig-New Castle PSA: One Small System's Giant Leap into the Future
Poor planning on your part does not constitute an emergency on our part
Extra Highlights from 2012 VRWA Conference
Virginia Department of Transportation Work Zone Traffic Control Update
FOG (Fat, Oil and Grease): Sewer Public Enemy No.1
The Inspector Found What?
Ergs, Joules & Such
Understanding your Job as a Board or Council Member?
Throwing My Loop
Do You Know What Your VRWA Benefits Are?
Welcoming New Members
Board Of Directors
Index to Advertisers/Ad.com
Streamline - Fall 2012