What is the standard used to post advisories?
During August of 2002, the standards were changed to the following: “A public advisory is recommended if the arithmetic mean of the two samples at a site exceeds 104 CFU/100ml, or if the running geometric mean of the arithmetic means of all samplings at a site within 30 days exceeds 35 CFU/100ml. The public advisory recommendation will remain in effect until these criteria levels are met through resampling.” In other words, two samples are taken at each site. If the average count is 104 colony forming units per 100 ml of sample, a public advisory is recommended. If not, all the averages at the site within the last 30 days are subjected to a statistical analysis. If this statistical average is 35 CFU/100 ml or more, a public advisory is recommended. If a public advisory recommendation is in effect, the site is resampled every day or two until the above criteria are met. The “running geometric mean” statistic plays down one or a few very high or very low readings. If only one site in a b
