1986-12-31_REPORT - C1981008 (3)

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section for discussion purposes. Upon comparison of the historic data collected from site SW-N3 to the agricultural use standards, it is apparent that manganese (Mn) has commonly exceeded its standard of 0.2 mg/l since mining began in 1980 (see Table 12). On occasion, cadmium (Cd) and lead (Pb) have exceeded their respective standards but these few exceedences are anomalous. It is impossible to know if molybdenum (Mo) exceeds its standard of 10 ug/l because the laboratory detection limit has routinely been 200 ug/l . Despite these few exceedences, the agricultural suitability of Tuttle Draw for irrigation is questionable. The mean SAR and conductivity for site SW-N3 between May and September for the period of record are approximately 0.6 units and 1700 umhos/cm at 25°C, respectively. According to Agricultural Handbook No. 60 published by the Department of Agricultural (1969) , this water poses little to no sodium hazard for irrigated crops. - However, because of its relatively high salinity, the water cannot be used on soils with restricted drainage. With adequate drainage, special management for salinity control may be required and plants with good salt tolerance should be selected. With regard to the suitability of Tuttle Draw for livestock drinking water, the mean water quality for the period of record measured at SW-N3 is well within the recommended limits for the principal salts and TDS as shown on Table 13. In light of the previously discussed seasonal flux of water quality measured at SW-N3, these period-of-record mean values are also weighed against typical mean summer (June-September) and winter (November-February) values obtained during 1985 and early 1986 as presented in Table 13. Despite the range in concentrations, all of the principal salts and TDS are still well within the livestock drinking water limits. 38