INTRODUCTION 



Statement of the Problem 



Agricultural drainage and associated salinity and toxic element problems affect areas of 

 the San Joaquin Valley, some moderately and others severely. The widely publicized selenium 

 toxicity problems at Kesterson Reservoir heightened public awareness of this problem. 



Backlund and Hoppes (1984) indicate that 1.5 million acres (0.6 million hectares), equal 

 to 27%, of the 5.6 million acres (2.3 million hectares) of irrigated lands in the San Joaquin Valley 

 are affected by shallow ground water to within five feet of the land surface and that 2.3 milHon 

 acres (0.9 million hectares), or 41%, are affected by water quality problems, including salinity, 

 pesticide residues, nitrates and toxic elements. 



Figure 1.1 (San Joaquin Valley Drainage Program (SJVDP), 1989) delineates areas in 

 the west side of the San Joaquin Valley having water table depths from to 5 feet and from five 

 to 20 feet. Subsurface drainage in these areas began in the 1950's. The Northern (least water 

 quality impact) and Grassland Subareas have opportunities to discharge their irrigation return 

 flows into the middle reaches of the San Joaquin River. As water quality objectives for the river 

 grow more stringent, drainage from the two northernmost subareas will need to be increasingly 



reduced. 



In contrast, the Westlands Subarea has no surface drainage outlet. Drainage waters are 

 accumulating in the vadose region. The Tulare and Kern Subareas are located in a hydrologically 

 closed basin with limited opportunities to discharge drainage into the lake beds. The SJVDP 

 (1989) has enumerated numerous management options for drainage and drainage-related 

 problems, e.g., selenium and salts. A combination of viable in-valley drainage management 

 options is being sought to determine the best management practices (BMP). One of the most 

 effective BMPs is source control with improved water management practices. But, even with 

 source control BMPs, a residual of drainage waters containing elevated concentration levels of 

 TDS and toxic elements will still need to be treated, or disposed, or both. This drainage problem 

 is most critical in the Westlands, Tulare and Kern Subareas. 



In the 1970's, the Tulare Lake Drainage District constructed two evaporation pond 

 facilities and Carmel Ranch one pond with a total surface area of over 3,000 acres (1200 hectares) 

 to dispose of over 15,000 ac-ft/yr (18.5 million m') of drainage collected from over 27,000 acres 

 (66,700 hectares) of tile-drained fields (Department of Water Resources (DWR), 1988). Between 

 1981 and 1985, 24 more evaporation ponds were constructed. Most are located in the Tulare and 

 Kern Subareas with several as far north as in the Grassland Subarea. 



Earlier, concern focused on potential seepage of hypersaline waters from ponds into 

 usable ground waters and adjacent lands. Since the Kesterson Reservoir crisis, the emphasis has 

 shifted toward potential bioaccumulation of selenium and other constituents in the aquatic food 

 chain and toxicity to birds attracted to the ponds. Several ponds have either exceeded the soluble 

 thresholdlimitconcentration of 1,000 |ig/L selenium or begun toexhibittoxicity problems similar 



to those at the Kesterson Reservoir. 



Aside from the highly visible concerns of bioaccumulation and hydrogeology, the 

 following management-oriented questions need to be addressed to fully evaluate the efficacy of 

 evaporation ponds: 



• How long can ponds effectively operate? What variables and conditions would Hmit their 



operation? 



• At what levels of salinity do evaporites begin to precipitate'' What kind of salts, how much 

 and from where? How does the initial inflow chemistry influence evaporite formation? 



• What parameters affect evaporation rates of pond water? How do salinity, wind speed, 

 wave action, temperature, turbidity, and thin surface salt crusts influence evaporation 

 rates? 



piige 1.15 



