Excerpt from Predicting Effects on Fish of Fire Retardants in Streams

In recent years, fire retardant materials applied by aircraft have become important in the control of range and forest fires. The number of fire retardant drop missions flown rose from virtually zero in the mid-1950's to nearly in 1971 and involved some 17 million gallons of material (assuming an average drop of gallons). Use of sodium calcium borate was discontinued in the early l9oo's because it was heavy, expensive, and a soil sterilant. More effective retardant salts, ammonium phosphates and sulfates, have been used for more than a decade. In general, they are fertilizers and produce beneficial results unless a dosage is too heavy.

Wildfires may occur in areas where lakes and flowing streams contain valuable game fish. Fire retardants are concentrated aqueous solutions of chemical materials. Since at some concentration, most soluble chemicals will injure or kill fish, the possibility of damage to fish exists because retardants can be dropped directly into the body of water in which they live.

The purpose of this report is to provide a method of estimating whether fish kill is likely to result from a particular release of retardant. The approximate length of the affected zone of a stream can be calculated. Accuracy of the result is expected to range between plus or minus 75 percent, which is not precise, but can be of considerable value. This figure is the result of estimating the probable uncertainty of each item or source of data required for a computation, and then tracing the cumulative effect of these uncertainty values through the computation procedure outlined in this report. Where two Or more values are combined or interact arithmetically, the uncertainty of the result is identified by finding the square root of the sum of the squares of the individual uncertainties of the values being combined.

It would be important to know, for example, whether a given event would be likely to damage only a few hundred feet of a stream or its length to the next major conflu ence. The estimation system would make possible a judgment before the drop mission is ordered as to whether the immediate fire control need is great enough to warrant pos sible consequences. Preseason determination of stream discharge rates and velocities would make potential damage appraisal a simple matter.

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