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2 Estimating Economic Impacts 01 Salinity.., Salinity Damage Levels ~ r..o CD ~ The salinity levels of the Colorado River, in this study, are taken from the Colorado River Simulation System (CRSS) developed by the Bureau of Reclamation. The flow-weighted average annual estimates cover the period from 1985 to 2010. Under the 1987 version of the CRSS simulation used in this study, salinity below Hoover Dam is projected to go from its 1986 value of about 542 mgIL TDS to about 790 mgIL TDS by 2010, Below Parker Dam salinity is projected to increase from about 542 mgIL TDS in 1986 to about 822 mgIL TDS by 2010. At Imperial Dam, salinity will rise from about 579 mgIL TDS in 1986 to about 958 mgIL TDS by 2010. These are the present and future saJinjty level estimates used in this report. Another group of saJinjty values also are used for comparison. These are the ten-year average (1976-1985) levels of saJinjty at the reservoirs: 652 mgIL TDS at Hoover; 678 mgIL TDS at Parker; and 767 mgIL TDS at Imperial. These levels are considered more representative of past and probable future conditions in the river, Salinity levels for major metropolitan areas in the Lower Colorado River Basin are much more difficult to estimate. Almost all metro- politan water supplies of Colorado River water are blended with local ground or surface water, or with imported surface water. Further, salinity or TDS is not a very frequently measured water quality parameter of municipal supply. Using the best available data, the authors can provide estimates of current water supply average TDS for broad metropolitan areas. These averages range from 405 mgIL to 579 mgIL TDS for a 1986 current value; and from 450 mgIL to 767 mgIL TDS for the ten-year average value. There are various levels of concentration at or above, which salinity in water can cause som~ type of economic damage. In agriculture that level is where a decline in crop yield begins to occur. For households the damage level is de- pendent on the type of household item subject to corrosion or scale from contact with saline water (water pipes, hot water heater, etc.) and some- times on the type of treatment the homeowner gives the water. For water and wastewater utilities the level is where salinity begins to reduce the useful life of facilities and equipment. For industry there are known TDS limits for particular processes, above which levels water treatment is necessary, and industry must pay the costs of treatment. In addition, other economic costs to industry can result, not from actual corrosion or scale, but from regulation of permissible TDS levels in discharge water that can affect the useful life of the water, i.e., num- ber of times the water is used. In such cases industry must pay additional costs, either fo: greater quantities of water or for water treat- ment. Salinity Effects vs. Salinity Damages Earlier attempts to measure the effects of salinity have treated such effects as absolute, That is, the physical effects of salinity levels in reducing crop yields, in corroding and thus reducing the useful life of water-using household devices, etc., have been measured against an "ideal" saJinjty level at which no physical effect is apparent. Then these physical effects are described in economic terms, such as the value of reduced crop production and the monetary costs of more frequent replacement of washing machines, household piping, etc, Such an ap- proach can be misleading, This measurement of physical and economic effects of salinity in water supply against an ideal water supply appears to have been taken with lit- tle justification. It may reflect merely an assump- tion that saline water has deleterious effects which logically should be measured against a standard of pristine water whose salinity level is below the threshold that causes measurable effects. However, such pristine water is not always found in nature and certainly is rarely found in waters that have been subjected to the impacts of human activity. This leads to a fundamental question under- lying this study, a question whose answer has a major influence on the study findings, yet one that cannot be answered solely through engineer- ing or economic analysis. That is, which physical and economic effects of saline water should be termed "damages"? The question of effect versus damage relates not only to water source, but to the cause of the salinity, the use to which the water is put, and