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• equal proportions. Major cations are sodium (Na), calcium (Ca), <br />and magnesium (Mg), in about equal proportions. Plotted on Figure <br />3.3-16 are the major ions from the two Alkali Creek monitoring <br />stations on two separate dates. These data are representative of <br />data taken during the monitoring program. The figure shows that <br />there is little change in water type between seasons or between <br />stations. <br />Water quality of Alkali Creek is generally good, with the exception <br />of nitrate and selenium. Trace metals are generally quite low in <br />concentration. This was the reason that some parameters were <br />deleted from the monitoring program with the approval of MLRD. <br />Additional deletions may be made in the future. <br />Total dissolved solids (TDS) from Alkali Creek are higher than that <br />of the Colorado River. The average TDS concentration at the <br />upstream site on Alkali Creek was 795 mg/1 for seven samples. The <br />• average concentration at the downstream site was 1099 mg/1 for 10 <br />samples. Alkali Creek has a substantially higher TDS than the 377 <br />mg/1 TDS of the Colorado River as reflected in Table 3.3-6 for 796 <br />samples over a 37 year period. However, flow weighing the con- <br />tribution to TDS of the two sources, mainstem of the Colorado River <br />and Alkali Creek, indicates that Alkali Creek increases Colorado <br />River TDS only about 0.02 percent (0,0002). The average TDS at <br />Colorado River monitoring site CR-2 is 437 mg/1 for the quarterly <br />monitoring program since June, 1983. <br />Figure 3.3-17 shows seasonal TDS values on Alkali Creek and the <br />Colorado River, which are inversely proportional to flow. During <br />late spring/early summer when flows are high, TDS values are low, <br />and during base flow periods, TDS values are high. The USGS <br />classifies water with a TDS concentration of 1000-3000 mg/1 as <br />slightly saline, which includes the downstream site on Alkali <br />Creek, which averages 1118 mg/1. Based on salinity hazards <br />classifications established by NTAC, 1968, water with a TDS range <br />of 1000-2000 mg/1 may have adverse effects on many crops and <br />NCEC - Coal Ridge #1 3-47 ABC/1145/900301 <br />