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w (;) N -t incurring additional costs. These alternatives include drain installation, ditch lining, land leveling, deep plowing, planting bed modification, sprinkler and drip irrigation, and increased irrigation frequency. (5) The last alternative is to plant salt tolerant crops. An economic loss would usually occur since many salt tolerant crops ordinarily produce a lower economic return. Municipalities could: (1) Do nothing and the residents would consume more soap and detergents or purchase home softening units or experience accelerated frequency of replacement of water facilities. (2) Build central water softening plants. (3) Develop new, less mineralized water supplies. Industrial users could combine more extensive treatment of their water supply with the purchase of additional makeup water based upon the economics of prevailing conditions. The required mineral quality levels are maintained in boiler and cooling systems by periodically adding an amount of relatively good quality water (makeup water) and discharging from the system an equal volume of the poorer quality water (bl owdown), The cost of applying each of the alternative remedial actions was determined, and the least costly alternative selected for subsequent analyses. For industrial use, an estimate of required makeup water associated with salinity increases was selected to calculate the penalty cost. Municipal damages were estimated by calculating the required additional soap and detergents needed, physical damages to facilities, and the cost of central softening. Economic studies were intended to provide a basis for assessing the economic impact of a change in salinity levels. Water quality, water use patterns, and economic conditions were projected and appropriate discounts made to arrive at representative values. Direct penalty costs were then aggregated for the entire impact area. Because of the interdependence of numerous economic activities, there exist indirect effects on the regional economy stemming from the direct economic impact of salinity upon -agricultural water users. These effects, termed indirect penalty costs, can be determined if the interdependency of economic activities is known. A simple ratio of direct to indirect impacts was used based on the EPA study wherein an "input-output model" was developed to follow changes affecting any agricultural industry through a chain of transactions in order to identify secondary or indirect effects on the economy stemming from the direct economic costs of salinity. The economic validity of salinity reduction measures is dependent upon the extent to which damages to water users are reduced or the usefulness of the waters is increased. Similarly, water uses and projects which cause salinity levels to rise must be considered as imposing costs or damages on the system which must be offset by benefits or controls. An example of economic effects of salinity increases on irrigated crops in the Colorado River Basin is described below. Po-Chuan Sun's 1972 study2 provides a means of estimating the direct salinity effect per mg/l. Utilizing a regional economic model for 469,200 acres results in an estimated $16 per acre reduction in net farm income or a penalty effect of 5 cents per mg/l per acre per year. The Lower Colorado River Basin was divided into three study areas: Southern California, Lower Main Stem, and the Gila area. Within these study areas, irrigation districts or Bureau of Reclamation projects were identified as representative and for which information regarding crop value was available. A summary of the estimates for each area is given in Table 7. The total direct salinity impacts are $66,900 per mg/l on an annual basis for 1,076,800 acres or an average of $0.0621 per acre per mg/l per year, The indirect effects were estimated to be 62 percent of the direct effects, The total impact of salinity upon the agricultural users of the Lower Basin is estimated to be $108,400 per mg/l per year in 1972 dollars. Household damages due to salinity have been estimated by a number of researchers. An array of the calculated costs is shown in Table B. The Orange County and the Black and Veatch studies are the most complete of those available. F rom these two studies and other information available from various salinity reports, an estimated value for each of the household items was 2Sun, Po-Chuan, An Economic Analysis of the Effects of Quantity and Quality of Irrigation Water on Agricultural Production in Imperial Valley, California, an Unpublished Ph. D, Dissertation, University of California~ Davis, 1972. 31