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C. DEFINITIONS OF TERMS PART I Page l0 Permit No. CO-0044776 9. "Thirty day average" means, except for fecal coliform bacteria, the azithmetic mean of all samples collected during a thirty consecutive-day period. For fecal colifotm bacteria, it is the geometric mean of all samples collected in a thirty day period. The permittee shall report the appropriate mean of all self-monitoring sample data collected during the calendaz month on the Discharge Monitoring Reports. Samples shall not be used for more than one reporting period. 10. "Visual" observation is observing the discharge to check for the presence of a visible sheen or floating oil. 11. "Water Quality Control Division" or "Division" means the state Water Quality Control Division as established in 25- 8-101 et al.) 12. For fecal coliform bacteria concentrations, the thirty day and seven day averages shall be determined as explained in defmitions '~ and • above, respectively, except that the geometric mean shall be used instead of the arithmetic mean. .The geometric mean may be calculated using two different methods. For the methods shown, a, b, c, d, etc. aze individual sample results, and n is the total number of samples. Method l: nrw Geometric Mean = (a*b*c*d*...) "*" -means multiply et Geometric Mean = antilog ([log(a)+log(b)+log(c)+log(d)+:..]/n ) Graphical methods, even though they may also employ the use of logarithms, may introduce significant error and may not_be used. In calculating the geometric mean, for those individual sample results that aze reported by the analytical laboratory to be "less than" a numeric value, the numeric value shall be used in the calculatons unless the result is "less than 2.2". If the result is "less than 2.2", use a value of I in the calculations. If all individual analytical results for the month aze reported to be less than numeric values, then report "less than" the largest of those numeric values on the monthly bMR. Otherwise, report the calculated value. For any individual analytical result of "too numerous to count" (TNTC), that analysis shall be considered to be invalid and another sample shall be promptly collected for analysis. If another sample cannot be collected within the same sampling period for which the invalid sample was collected (during the same month if montlily sampling is required, during the same week if weekly sampling is required, etc.), then the following procedures apply: i) A minimum of two samples shall be collected for coliform analysis within the next sampling period. ii) Ifthe samplin frequency is monthly or less frequent: For the period with the invalid sample results, leave the spaces on the corresponding DMR for reporting coliform results empty and attach to the DMR a letter noting that a result of TNTC was obtained for that period, and explain why another sample for that period had not been collected. :,. Amendment No. 1 Issued z~~~• ` ~ Effecrive ~~ n ~ ~~~~