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. Little variability between the seasons for pH was detected at SW-N103. During irrigation, pH <br />averages 7.84 and ranges from 6.84 up to 8.10 units. After the irrigation season, pH averages 7.88 <br />and ranges between 7.50 and 8.06 units. <br />Similar to previously discussed surface water monitoring sites, the mean of TDS during the <br />non-irrigation season was more than double (3,135 mg/I) the mean for this constituent during the <br />irrigation period (1,371 mg/I). Again, the higher levels ofthe major ions in Calamity Draw atthis site <br />after irrigation stops explains this trend. <br />At site SW-N 103, both TSS and Fe averaged higherduring the irrigation period (57.0 mg/1 and 1.46 <br />mg/I, respectively) than after irrigation has ceased (39.4 mg/I, TSS and 1.05 mg/I Fe). The mean <br />value of Fep was slightly higher (.04 mg/1) during the non-irrigation period compared to the average <br />Fe (.02 mg/I) determined for the irrigation season. As seen for all previously discussed sites, MnT <br />averaged consistently higher (1.24 mg/I) afterthe irrigation season ended than during the irrigation <br />period (.33 mg/I). <br />West Lateral IrrigationDitch - Flowand WaterQuality. The West Lateral irrigation ditch is part <br />• of the Colorado Co-operative Company's main ditch system that originates on the San Miguel River <br />just upstream of Cottonwood Canyon (about 12 mites upstream of Naturita). Construction of the <br />main ditch commenced in 1896, and water began flowing to the First Park area (see Map 2.04.7-1) <br />via the ditch in the spring of 1904 (Mercer, 1967). The main ditch, as well as the main laterals, is <br />basically an unlined open-channel excavated in shallow soils and sandstone. Where the ditch <br />crosses drainages, pipes and aquaducts have been constructed to carry the flow. The main ditch <br />has an average gravity run of four feet per mile from the San Miguel River to the First Park area <br />(Mercer, 1967). For a more historical discussion on the Colorado Co-operative Company's <br />development ofthe regional ditch system, the readershould referto Section 2.04.3, Site Description <br />and Land Use Information. <br />The West Lateral splits off the main ditch near the northern boundary of the Nucla Townsite. The <br />West Lateral follows aridge-top course westward from Nucla to the main north-south county road, <br />then winds south and southwest until the conveyed irrigation water is used by the various <br />shareholders located along the ditch's course. Atotal of 18 diversions have been identified on this <br />lateral; many consist of wooden "splitte boxes" that divert a consistent proportion of the irrigation <br />• water from the lateral to fields via small ditches and channels. Some diversions simply consist of <br />(Revised 6/28/01) 2.04.7-28 <br />