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November 28, 1997 Mr. John Hazdaway page 2 2) In relation to the four-times-per-day diurnal monitoring that is done twice per year, this monitoring only needs to be done in Arequa Gulch, immediately downstream of point OOlA. And, the pH monitoring that is supposed to be done at half-mile intervals only needs to be done at the time of day that routine pH monitoring is ordinarily done. The pH recovery information provided by this monitoring will be factored into the Colorado Ammonia Modeling sepazately from the diurnal variability information. 3) The monitoring required for the ammonia study (except for the half-mile interval monitoring described above) can be done at the same point that monitoring is currently being done for other permit monitoring requirements - at point OOIA. This point is in fact "in stream", but is also considered to be the facility's "dischazge point". 4) With respect to pH measurement, the equipment and calibration procedures you intend to use aze fairly standazd and aze approved. In order to avoid freezing the pH probe, samples may be collected and analyzed in a vehicle provided it is done relatively quickly and the sample temperature does not appreciably increase. 5) In relation to the downstream half-mile interval pH monitoring requirement, since you have an access problem and the total length of the stream below dischazge point OOIA is less than one mile long, monitoring the flow at point AG2.0 is an acceptable alternative. Also, from prior discussions we have had, it seems likely that the pH level in the stream should have reached an equilibrium point by the time it reaches point AG2.0. Since the whole point of the downstream pH monitoring is to determine what the equilibrium pH is, and to provide some assessment of where equilibrium is reached, monitoring at point AG2.0 will be satisfactory if in fact pH has reached an equilibrium at this point. However, even if pH has not reached equilibrium by point AG2.0, the confluence with Cripple Creek is only a short distance downstream. This limits the extent to which downstream pH stabilization needs to be assessed. And, because of the additional dilution provided by this stream, it is likely that ammonia limits based upon the protection of only Arequa Gulch stream standards will be more stringent than those based upon the protection of Cripple Creek standazds. Still, the potential change in pH and temperature characteristics between Arequa Gulch and Cripple Creek could complicate matters. If the pH and temperature chazacteristics aze significantly different, the resulting allowable instream total ammonia concentrations in Cripple Creek might be much lower than the allowable concentrations in Arequa Gulch. This could potentially outweigh the increased dilution provided by Cripple Creek.