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<br />Chapter 3 <br /> <br />The soluble mineral content of saline formations is variable and can be significantly different <br />within one stratigraphic unit. The determination of the soluble mineral content of surficial soils is <br />highly dependent upon the sampling and analytical methods used. The effects of contact time and <br />sediment to water ratios on rate and extent of dissolution are extremely important. Since much of <br />the salt is dependent upon sediment load, contact time and sediment to water ratio must be <br />considered. Laronne[ IS] recommends a sediment to water ratio of 1 percent. This ratio allows for <br />greater dissolution of salts and a better estimate of salinity contributed from erosion. <br /> <br />EFFECTS OF WATER QUALITY ON WATER USERS <br /> <br />Economic <br /> <br />Estimating Economic Impacts of Salinity of the Colorado River[16] updated the economic impacts <br />of salinity in the Colorado River Basin and developed a method of forecasting economic impacts <br />as salinity levels rise and water use changes in <br />the future. The first objective of the study was <br />to update, revise, clarify, and refine the <br />estimates of economic damages from salinity <br />that had been described in earlier studies[17,18]. <br />Figure 4 shows the relative impact of salinity on <br />water users in the Lower Colorado River Basin. <br />The study estimated damages were $311 million <br />per year based on 1976-85 salinity levels in the <br />Lower Basin and 1986 dollar values. During <br />this period, salinity averaged 767 mg/L at <br />Imperial Dam. <br /> <br />Salinity Costs by Sector <br /> <br /> <br />M&I (3%) <br /> <br />Household <br />(50%) <br /> <br />The second objective of the study was to <br />provide a better means of estimating present and Figure 4.-Salinity costs by user group. <br />future salinity damages through the deve!cpment <br />of a comprehensive computer program. Damages for 1976-85 were estimated by the study to be <br />$3 1 I million per year, but as salinity levels increase to more normal levels, damages (figure 5) <br />will also increase. Sensitivity analysis[19] using the damage model showed that damages (or the <br />value of salinity control) increase with salinity. <br /> <br />In 1995, the salinity at Imperial Dam was 803 mg/L. Figure 5 shows that at this level of salinity, <br />damages exceed $750 million per year. As salinity approaches the salinity standards levels <br />(879 mg/L at Imperial Dam), damages are projected to increase to about $1 billion per year. <br />Without further salinity controls to offset development, damages will increase another quarter of a <br />billion dollars per year. <br /> <br />Using a relatively conservative analysis, the benefit of salinity control was estimated to be <br />$340 per ton (1994 dollar values). In comparison, the cost of salinity control generally ranges <br />from $20 to $100 per ton. <br /> <br />14 <br />