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, (0 Ul l';;' 1-' , , ;>j-'< VII. CONTROL OF SALINE POINT SOURCE GROUNDWATER DISCHARGES A. Determining Technical Feasibil ity The proper design of a facility for controlling point source saline groundwater discharges requires data collection about the origin of the groundwater, how and where it discharges, the water itself, and terrain of the surrounding area. First, a reconnaissance level investigation should be made to determine if more detailed studies are warranted. Measurements should be taken to determine the rate of waterflow, any variation in quantity of flow, and electrical conductivity (concentration of total dissolved solids [TDS]). The area surrounding the discharge point should be inspected to see if a tract of flat land exists large enough for an evaporation pond. Soil texture on the proposed site should be noted. Apparent depth of soil and existence of rock outcrops. should also be noted. If reconnaissance investigations indicate a control project may be feasible, more detailed studies can be made. This would entail gathering additional information for the items discussed above. B. Determining Economic Feasibility Public Law 92-500, Clean Water Act of 1972, states that salinity standards must be met. This should be done in the most economic manner technically feasible. -': An economic analysis should include an accurate determination of the project cost-effectiveness as well as local and downstream economic benefi ts. Cost-effecti veness rel ates the total annual cost of a project to the expected reduction in salt concentration as measured at Imperial . Dam, California. Cost-effectiveness is an efficient yardstick to measure and compare salinity control projects having equivalent downstream benefits and can be applied to other agency programs and basinwide efforts as well. Economic benefits are generally described in terms .Of an incremental economic detrimental value related to salt concentration changes at Imperial Dam. The economic detriment (or benefit) at Imper- ial Dam is a composite value representing annual damages to downstream municipal, industrial, and agricultural users in the United States. This study uses an economic detriment value of $425,000 per mg/1 per year based on $343,000 per mg/l per year (22) and indexed to 1979 dollars. ',' J '1 , < -,., '{ 1 >1 The computed reduction in salinity, as a result of each project, is the annual sum of the positive effects of removing a given number of tons of salt and the negative effects of detaining a given number of acre-feet (ac-ft) of water. The removal of salt reduces the salt load, while the loss of water raises the TDS concentration. The net effect will be a lowering of the concentration if the amount of salt lost is high in relation to the amount of water detained. Reductions in salt concentra- . tions at Imperial Dam resulting from each project were computed using data from Table E (7). -1 ., J 19 ",,- ,~" ;,,:;;;-$,CiJ.;'~,'%, .;-. -