SECTION 8 



MAGNITUDE OF SALT LOAD 



Introduction 



In the previous interim report (Tanji and Grismer, 1989), a brine chemistry 

 model (C-Salt) was utilized to simulate the sequence and quantities of salts precipitating 

 as pond waters are evapoconcentrated up to a 50-fold decrease in volume. This report 

 takes another approach in assessing the magnitude of salts accumulating in 

 evaporation ponds. The primary data used herein are from the Central Valley Regional 

 Water Quality Control Board (Westcot et al., 1988) and the Department of Water 

 Resources (1988) that were summarized in the interim report. 



Unit Values 



The 27 evaporation ponds have a total pond surface area of about 7,070 acres 

 annually receive about 31,900 ac-fl of subsurface drainage from about 56,500 acres of tile- 

 drained fields containing about 810,000 tons of salts (TDS). These data are transformed 

 into unit values as follows: 



unit tile effluent = ^^ yin^"^^*" = 4.51 ft/yr (8.1) 



7 070 ac 



The unit tile effluent is the average annual surface depth of drainwater disposed 

 into the ponds. 



unit pond surface = -g -^^ — = 0.125 (8.2) 



56 500 ac 



The unit pond surface is the acres of pond surface for each acre of tile-drained 

 field. 



unit field drainage = ^^ 56 500 a^^' = ^'^^ ac-fVac-yr (8.3) 



The unit field drainage is the average annual quantity of subsurface drainage 

 water collected from the fields and disposed into ponds. 



. „^^ ^ _ , , 810 OO P tons/yr , . o * / ro a\ 



unit TDS from fields = — rg con o^ = ^"^-^ tons/ac-yr (8.4) 



56 500 ac 



This unit TDS is the average annual quantity of salts collected in the tile 

 effluents from the fields. 



810 000 to ns/yr nc a i i t\ lo c\ 

 unit TDS into ponds, concentration basis = s^gooac-fVyr ^ tons/ac-ft (8.5) 



This unit TDS gives the average annual salt accumulation discharged into the 

 ponds. 



, , . 81 OOP ton&/>T ,,C4 / /fi c^ 



unit TDS into ponds, weight basis = q q-jq ^c ^ tons/ac-yr (8.6) 



This unit TDS is the average annual weight of salts discharged into the ponds. 



page 8.1 



