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a. Interpretation of Standard Methods SM 9222 , B.6, 20`x' Ed. and EPA 1600, Appendix B . calculations : CFU/ 100 mL= C x 100 V Where, CFU/ 100 mL = Number of enterococci or fecal coliform colony forming units per 100 mL of sample. C = Total number of positive colonies counted on all acceptable dilutions. V = Total volume, equal to the sum of all acceptable dilutions (sample volumes used, in mL (i) When one dilution in a series has a count within the ideal CFU range (see above): ( 1 ) Use the count from the dilution that is within range to calculate the final result in the equation above . (ii) When more than one dilution in a series has an acceptable count within the ideal range use the applicable method below. Since this calculation is not a laboratory sample replicate, do not use an "A" qualifier. ( 1 ) SM 9222D - Use the sum of all dilutions within the ideal range and the sum of the counts from all dilutions in the ideal range in the equation above . (2) EPA 1600 - Independently calculate a final value for each dilution within the ideal range in the equation above and report the average of these values. (iii) When no dilutions fall within the ideal range : ( 1 ) For both methods : A `B" qualifier is not required if all dilutions were less than the lower acceptable limit (20 CFUs), and one of the dilutions was 100 mL. For this situation, report the calculated value from the 100 mL dilution without a "B" . (2) SM 9222D - Use the sum of all dilutions in the equation to calculate the final result. Include dilutions that have a zero count. Report the final result with a `B" qualifier. (3 ) EPA 1600 : (a) If all counts are under the lower acceptable limit (20 CFUs) or are both above and below the limit, choose the dilution with the count that is closest to the ideal range to calculate final result and report with a "B" qualifier. (b) If all counts are above the upper acceptable limit (60 or 80 CFUs), use -the dilution with the smallest volume filtered to calculate final result and report with a `B" qualifier. (iv) If counts from all dilutions are zero : ( 1 ) For SM 9222D- Use " 1 " as the total number of colonies counted and include all dilutions in the equation to . calculate final result. Report with a "U" qualifier. (2) For EPA 1600 - Use " I " as the total number of colonies counted and use only the highest filtration volume as total volume in the equation above to calculate final result. Report with a "U" qualifier. (v) If there are >200 target colonies in all dilutions : (vi) For both methods - Use the upper limit of the ideal range (60 or 80) and the smallest filtration volume in mL to calculate an estimated final result. Report with a "Z" qualifier. (vii) If there are >200 non-target colonies, or if the colonies are not distinct enough to count (confluent growth) kin all dilutions : ( 1 ) For both methods = Report as "No Result" with a "Z" qualifier. 8 . Use of Dilution Factor (DF) field a. Use the following equation to determine dilution factor for all samples : DF = 100 V Where, DF = Dilution Factor V = Total volume (sum of dilutions in mL used in final calculation) 9 . Verification a. Frequency (i) Independently verify at least 10 isolated colonies from a positive sample per month. (ii) Verify atypical colonies of different morphological types to check for false negatives. (iii) Also, verify any ambiguous colonies as needed. Revision Date: 02/09 DEP Agreement No. G0353, Attachment J, Page 11 of 14