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<br />Water samples will be taken at numerous sites for determination of sodium ions <br />and total dissolved solids. Well water will be blended as necessary to assure <br />that project water meets Rio Grande Compact requirements before delivery to the <br />Rio Grande at the outfall of the channel. <br /> <br />III. AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES <br /> <br />A. Wetlands and wetland habitat. <br /> <br />1. Studies. The FWS stated in its 1969 Coordination Act Report that <br />the project would affect 100,000 acres of existing wetlands within project <br />boundaries. The Bureau conducted a broad land-cover and land-use analysis of <br />the land within project boundaries in 1977, which indicated about 40,000 acres <br />of wetlands were within the 138,500 acres of project-included lands. <br /> <br />More detailed studies indicated that between 26,000 and 47,000 acres of wetlands <br />and wetland habitat were present depending on the year the analysis was made. <br />The primary difference between these two wetland acreages was in the delineation <br />of ephemeral wetlands. <br /> <br />In 1978 the FWS initiated the National Wetlands Inventory for the San Luis <br />Valley and Closed Basin Division wetlands under a memorandum of agreement with <br />the Bureau. The inventory indicated that 43,122 acres of wetlands were present <br />within the proposed project boundary. These wetland acreages are similar to <br />those of the Bureau studies and have been accepted for use in this supplement. <br /> <br />Wetlands and wetland habitat in some parts of the project will be affected where <br />existing ground water tables are less than 2-1/2 feet. Lowering of the water <br />table through pumping of the unconfined aquifer will alter existing vegetation. <br />An increase in loss of free-standing water .due to seepage will also occur in <br />some areas. <br /> <br />Map overlays of the top of the unconfined aquifer in relation to the natural <br />ground surface were developed for 1978-1980 using ground water depth readings <br />from observation wells scattered throughout the project. Ground water table <br />maps of this nature were used to determine the potential effects of lowering the <br />water table on existing vegetation and general location of wetlands and wetland <br />habitats. These overlays also indicated the seasonal variation in water tables <br />and the general trend toward deeper water tables. <br /> <br />Readings from about 60 observation wells were used. The shallowest and greatest <br />readings, regardless of date, during a given year were plotted on overlays on <br />USGS 7.5-minute topographic bases. In general, the shallowest water table <br />depths occurred during late winter and spring before the growing season and <br />increased total evapotranspiration, while the greatest water table depths <br />occurred in the late summer and fall. <br /> <br />Using data supplied by the Bureau, the USGS conducted computer modeling analysis <br />of the Closed Basin to develop the well field systems to be installed for proj- <br />ect pumping. The analysis also provided estimated drawdown of the existing <br />unconfined aquifer in 2-foot increments within the project boundaries after more <br />than 50 years of pumping. <br /> <br />f <br /> <br />...., ~ -"".... j.'" <br />(, . . l;. . <br />J ,. ,).... <br />