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Summary of Major Findings 3 I-' CD CD '-~ / whether the use is appropriate or well-managed. In direct answer to the question, "Should every negative salinity effect be considered a damage? ," it is the judgment of the authors that each negative impact should not be, and could not be, considered a damage, Instead, the im- pacts of current salinity should be compared with those of a baseline salinity level that can be justified as a basis for comparison. By using one or more selected baseline salinity levels a potential problem is avoided: that of measuring damages against an idealized water supply that rarely exists in nature and could never be achieved technologically or economically for most water supplies, Measur- ing against such a water supply would exaggerate the true damage figure. Instead, it is proposed to measure the physical and economic effects of two or more water supplies - one with current salinity levels and another one or two with selected baseline salinity levels - and subtract the latter from the former. The difference in the economic effects, or costs, between two or more salinity levels has been selected in this study as the appropriate measure of salinity "damages." The selection of appropriate baselines has been a matter of intense discussion among the authors, with the Bureau of Reclamation, and with the Work Group of the Colorado River Basin Salinity Control Forum, Agreement was reached regarding the selection of two baselines which, in conjunction with a current salinity level would bound the range of salinity damages. They are: 334 mg/L TDS and 500 mg/L TDS. The first, 334 mg/L TDS, was determined by EP A to be the River's natural TDS level caused by natural point and diffuse sources at Hoover Dam based on the 1942-1961 hydrologic record. The second is the EP A Secondary Drinking Water Standard of 500 mg/L TDS, the standard widely used by various health agencies as well as by EPA, Damages to Agriculture The authors recognize that salinity damage to agriculture can involve more than a reduction in crop yield or in acreage planted. However, such other damage categories as labor costs, resulting from a need for more frequent irrigations or from the need to clean drain tiles, and capital costs for automated irrigation equip- ment or for installation of drains are fairly site- specific. Research on these questions revealed that it is not possible to quantify, let alone project, the amount of the costs in a basinwide perspective, or to separate that portion of costs attributable to salinity damage from costs in- curred by good farming practice, Review of ex- isting studies and interviews with knowledgeable persons in Lower Basin agricultural areas revealed that the attribution of such costs to salinity alone is unrealistic. In keeping with the guiding dictum, the authors have chosen to focus on crop yield, crop acreage, and cropping patterns because these are consistently and regularly reported throughout the basin and are most clearly re- lated to salinity. The nine crops selected for the computer program rcpresent an average 80 per- cent of crop value for the affected areas. Eight of these commonly grown crops have salinity damage thresholds that are below the CRSS projected level of TDS for the Colorado River at Parker and Imperial Dams, Theyare Lettuce (555 mg/L TDS); Carrots (427 mg/L TDS); Oran- gesrrangerines (725 mg/L TDS); Grapefruit (768 mg/L TDS); Onions (512 mg/L TDS); LemonslLimes (768 mg/L TDS); Table Grapes (640 mg/L TDS); and Avocados (427 mg/L TDS). Alfalfa hay at (853 mg/L TDS) is above the level at Parker, but below the projected level at Imperial Dam. The annual dollar losses to these nine crops that may be fairly attributed to the salinity of Colorado River irrigation water ranged from $112.8 million to $122,5 million (based on the ten-year average salinity levcl) subject to varia- tions due to non-water factors such as weather, pests, and crop market prices. Damages to Households As noted, damages to households depend on a number of factors that are related to salinity or that can be aggravated by salinity, First among these is water hardness which, for the Colorado River, is directly proportional to salinity, con- stituting 49 to 53 percent of the TDS value, in parts per million. It is water hardness that can cause scale, nOliceable erfec[s on cleaning, and