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I I I I I I I I I I I I I I I I I I I average annual diversion for the Longmont Supply and Oligarchy ditches are 4046 acre-feet and 7349 acre-feet, respectively. Approximately 90 percent of the irrigation land for the Longmont Supply and Oligarchy ditches are located below McCall Lake. Thus, the historic diversions and demand for water downstream of McCall Lake would indicate that Options 2,4,5 and 6 are viable. D. Water Quality 1. Raw Water Quality at McCall Lake Two McCall Lake water samples were collected on October 7, 1987 by the City of Longmont's Water Quality personnel and selected water quality tests were per- formed to determine the suitability of releasin9 lake water for irrigation use. Table 5.8 summarizes the results of the surface and subsurface McCall Lake water quality tests. The water in McCall Lake will be released for 1) irrigation of City Parks, 2) released to downstream irrigation users on the Longmont Supply or Oligarchy Ditches in exchange for diversion of St. Vrain Creek at the North and South pipeline diversion points, or 3) released into Union Lake and exchanged from Union Lake to the North and South Pipeline or Buttonrock Reservoir. In all sce- narios, the ultimate use of McCall Lake water will be for irrigation. The tolerance of crops to salinity is an important parameter in determining the suitability of water for irrigation use. The concentration level of total dissolved solids (TDS) is directly related to water salinity. The TDS tolerance level to achieve 100 percent crop yield for crops such as potatoes, onions, beans, carrots and lettuce is between 600 to 700 mg/l. For crops such as corn, alfalfa, pasture grass, the TDS limit approaches 900 to 1000 mg/l. For bermuda grass, barley, hay, wheat, the TDS limit is over 3500 mg/l. The TDS levels measured in McCall Lake were approximately 1000 mg/l which would indicate that the TDS level may be harmful to some crops. The TDS levels -20-