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00301 t:s:"'~~.~~::~:/" ;~.- \~ ~~:I"~IY.'.<,,! '~jh:t( .. Alternatives to deal with the salinity- toxlcs.drainage problem En the San JoaquIn Valley Include source control, groundwater management, drainage.water reuse, water treatment and off.site disposal. Kesterson Reservoir and plugging of drain lines in the Westlands Water District that were contributing drainage flows to the reservoir (Letey et al. 1986). Subsequently, three federal agen- cies (Bureau of Reclamation.. Fish and Wildlife Service and Geological Sur- vey) and hvo California resource agen- ci~s (Department of Water Resources, and Fish and Game) jointly established a Snn Joaquin Valley Drainage Pro~ gram in 1984. The goal of the program was to develop short- and long-range pl,ms for solving the salinity-toxics- drainage problems of the western San Joaquin Valley. Constraints were placed on the de- ,'elopment of the plans. Specifically, all alternative plans mllst meet California's water-quality objectives, and focus on in-valley solutions (San Joaquin Valley Drainage Program 1990). The latter constraint eliminated the option of completing the drain as originally planned or any other dis- posal to a bay or tht.:' ocean. These con- straints made it "lithe more difficult for the West Side to nchie,'e salt balance. Assessing the alternatives Several management options have been proposed to deal with the salinity- toxics-drainage problem in the San Joaquin Valley. Eight technical commit- tees (comprised of individuals from UC, federal and state agencies, and the pri- vate sector) recently syntllesized the present state of knowledge concerning the following options into a series of reports (San Joaquin Valley Drainage Implementation Program 1999). Source control. Source control re- quires the farmer to apply water uni- formly across the field and accurately control the volume applied. Fanners can gain greater coiilrol by switching from surface irrigation to sprinklers to microirrigation systems, thereby reduc- ing the volume of drainage water imd subsequent costs to dispose of it. Grow- ers must carefully evaluate the trade- offs between the increased costs associ- ated with source control - such as, for example, installing microsprinklers - and the benefits associated with lower costs for water and drainage disposal. Groundwater management A rise in water-table elevations results from an imbalance between the water appli- cation (irrigation and precipitation) and water extraction (crop evapotrans- piration and pumping). Groundwater management entails increased pump- ing for irrigation to lower the water table and reduce drainage volume. During drought years, farmers have pltmped more to compensate for re- duced surface-water supplies, and in turn lowered water tables. in principle, this practice could be continued during years of plentiful surface-water supplies. However, its success requires coordi- nated regional management and com- pliance. A long-term consequence is that pumping accelerates the exploita- tion of high-quality groundwater. Rather than discharging salts and chemicals through drainage systems, the chemicals move downward with the water toward the zone from which the water is pumped. Pump- ing increases the rate at which good quality water is replaced by poor quality water. 46 CALIFORNIA AGRrCUL TURE, VOLUME 54, NUMBER 2 , Land retirement Fields can be re- moved from agricultural production and converted to other uses, releasing the irrigation waters for other useS. As a voluntary program, growers with high water tables and low agricultural productivity would be most likely to agree to retire their land. These farms are likely to be located in lower eleva- tions near the trough of the West Side, which could receive lateral flows from up-slope irrigation. A negative conse- quence is the probability that with a . high water table, water will migrate to fue soil surface by capillary action, transporting and depositing salts and toxic elements, The resulting landscape would be sparsely vegetated, promoting erosion and degrading wildlife habitat.. Drainage water reuse, While drainage water may be reused for irri- gating salt-tolerant crops, even those have upper limits and leaching of salts from the root zone will be required. Indeed, if irrigation waters are very sa- line, relatively high leaching fractions may be required because Salts are placed back into the soil and salt bal- ance is not achieved. A hazard of us-, ing drainage water for irrigation is the destruction of the soil's physical prop- erties, threatening the viability of agri- culture. For example, crust can form on the soil surface resulting in poor in- filtration, which in turn impedes leaching of saitsand promotes their accumulation in the soil. Amendments such as gypsum can mitigate physical deterioration of the soil but are costly to the farmer. Water treatment Water can be treated to remove total salinity and se- lenium. Reverse osmosis (RO) is the most promising treatment technology, but is constrained by high cost and diffi- culties with safe disposal of the brine. The value of treated water could offset Some of the treahnent costs, and a water trade with the urban sector, which can afford to pay more for water, could en- hance the feasibility of RO treatments. Treating drainage water to remove only selenium would still leave a very saline water. Nevertheless, it would increase the options for disposing of