The log mean for the past 30 days of data for each sampling station is calculated for total coliform, fecal coliform or E. coli and enterococcus bacteria. Sampling data that are influenced by rainfall are excluded.
The 30 day log mean is applied to the tables below to arrive at a grade. Since a grade is generated for each of the 3 types of bacteria tested at each station, the lowest of the three grades is used as the assigned grade.
If there are less than 4 test results in a 30 day period for any of the 3 bacteria tests, the results are considered insufficient to assign a grade. If all 3 bacteria tests fall into this category the sampling station is assigned an "ID" (insufficient data to assign a grade).
The table for E. coli is used in place of Fecal Coliform for sampling data from the Department of Health Service's due to the method of testing performed.
A <=500 (org/100ml.)
B 501 - 1000
C 1001 - 2000
D 2001 - 3000