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PART I Page No. 10 Permit No.: CO-0042161 C. DEFINITIONS OF TERMS • 1. "Composite" sample is a minimum of four grab samples collected at equally spaced two hour intervals and proportioned according to flow. 2. "Continuous" measurement, is a measurement obtained from an automatic recording device which continually measures provides measurements. 3. "Chronic lethality" occurs when a statistically significant difference, a[ the 95% confidence level, occurs in the chronic test between the mortality of the test species in ]00~ effluent (the chronic IWC = 100%) and the control. 4. "Daily Maximum limitation" means the limitation for this parameter shall be applied as an instantaneous maximum (or, for pH or DO, instantaneous minimum) value. The instantaneous value is defined as the analytical result of any individual sample. DMRs shall include the maximum (and/or minimum) of all instantaneous values within the calendar month. Any instantaneous value beyond the noted daily maximum limitation for the indicated parameter shall be considered a violation of this permit. 5. "Fecal coliform bacteria" thirty (30) day and seven (7) day averages shall be determined as explained in 11. and 12. below, 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. are individual sample results, and n is the total number of samples. (I/n) Method 1: Geometric Mean = (a*b*c*d*...) "*" -means multiply • Method 2: Geometric Mean = antilog ([log(a)+log(b)+log(c)+log(d)+...]/o ) 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 are reported by the analytical laboratory to be "less than" a numeric value, the numeric value shall be used in the calculations unless the result is "less than 2.2". If the result is "less than 2.2", use a value of 1 in the calculations. If all individual analytical results for the month are reported to be less than numeric values, then report "less than" the largest of those numeric values on the monthly DMR. 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 anotlter 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 monthly 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) If the samplinr; 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. • If the sampling freguencv is more frequent than monthly: Eliminate the result of TNTC from any further calculations, and use all the other results obtained within that month for reporting purposes. Attach a letter noting that a result of TNTC was obtained, and list all individual analytical results and corresponding sampling dates for that month.