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Show Salt Lake City Watershed Management Plan ' 99 NUTRIENTS AND TURBIDITY Analysis of turbidity, nitrate, and phosphorous failed to reveal any statistically significant trends. Grab sample total phosphorous data has on occasion exceeded 0.05 mg/ 1 ( State water quality standard) 15 in all the canyons. Emigration Canyon and Parley's Canyon have experienced frequent exceedences of the state standard for phosphorous. Grab sample ammonia ( NH4) data has on occasion exceeded state standards for cold water fishery ( use classification 3A) in all of the canyons. Un- ionized ammonia toxicity is dependent upon the temperature and pH of the waterbody. 16 A summary of ammonia exceedences is provided on Table 8. State criteria includes two different levels for ammonia dependent upon exposure time ( 4 day average and 1 hour average). Because the samples are independent grab samples, the more stringent 4- day average criteria is assumed, however we have no evidence that this data accurately represents a 4 day average. Often the analysis detection limit used in the lab has been greater than the allowable for the cold water fishery use classification. Table 8 Grab Sample Ammonia Data Above 4- day Average 3a Use Standards CANYON Exceedances during the last 10 years of 3A Cold Water Fishery 4- day Average Ammonia using grab sample data. City Creek Canyon 02/ 24/ 95, 3/ 27/ 96, and 4/ 11/ 96 Emigration Canyon 6/ 1/ 93, 2/ 24/ 95,4/ 11/ 96 and 7/ 11/ 96 Parleys Canyon 9/ 8/ 95, 4/ 11/ 96, and 9/ 8/ 96 Millcreek 5/ 26/ 93 Big Cottonwood Creek 3/ 4/ 92, 3/ 15/ 95, and 6/ 13/ 95 Little Cottonwood Creek 3/ 27/ 96, 4/ 11/ 96, 5/ 15/ 96,10/ 23/ 96, and 11/ 15/ 96 Page 23 |