In the San Joaquin Valley, water levels in evaporation ponds change seasonally . They 

 are typically high in winter and low in summer (Tanji and Grismer, 1989). Since the capacity 

 of the evaporation ponds have to satisfy the highest water level to avoid overflow to adjacent 

 areas, pond capacity has to be determined using the highest water inflow rather than the yearly 

 averaged value. Pond volume must also be calculated to deal with major storm events and 

 prolonged high rainfall years. 



Shape 



The major factor influencing the shape of an evaporation pond is the environmental 

 impact. Since wildlife are attracted to evaporation ponds, the reduction of shoreline (the 

 reduction of access to contaminated water) is desirable. Although the circular shape poses the 

 least shoreline per unit area compared to square and rectangular shapes, the circular shape 

 would not make efficient use of land because most fields are rectangular in shape. If land wasted 

 is not a constraint, the circular shap>e is the best option environmentally. Otherwise, the square 

 shape is recommended since the shoreline per unit area is less than that of rectangular shapes 

 (Department of Water Resources, 1988). 



Depth J V- o 



According to the Department of Fish and (^me the recommended minimum depth is 2 



feet to discourage wildlife use. Bonython (1965) found that the variation with depth can be 



virtually neglected evaluating the result of Ferguson (1952) and Block etal., (1951). Ferguson 



has shown that evaporation in a pond with a depth of 40 inches is 4 % less than a 6 inch deep pond, 



and the evaporation from a 1 inch deep pond is 4 % greater than a 6 inch deep pond. Thus, the 



influence of depth on evaporation may be largely ignored. 



Cells 



As explained in the previous sections, cells contribute to maximizing evaporation and 

 salt precipitation by allowing mixing of waters to control solute concentrations. Cells with gates 

 are essential for regulating solute concentrations and thus maximizing efficiency of evaporation 

 ponds. 



Embankment 



The current design based on the specification of the Department of Agriculture-Soil 

 Conservation Service is adequate relative to evaporation but not to discourage wildlife usage. 

 The current design criteria include: 



Top width At least 14 feet 



Freeboard 1.6 feet or the maximum wave ramp 



Inside Slope 6:1 



Outside Slope 2:1 



T.inintT and Intprcentx)r Drain • ,, /• ui r 



Impermeable linings such as concrete and asphalt are not economically feasible for 

 evaporation ponds. Tanji and Grismer (1989) estimated that seepage from a typical San Joaquin 

 Valley evaporation pond is approximately 1 foot per year using existing soil materials for a pond 

 bottom. Interceptor drains would be desirable to reduce contamination of groundwater ftx)m 

 seepage. Tanji et al. (1985) suggested installation of tile drains underneath ponds instead of 

 around the perimeter and pumping seepage back into evaporation ponds. 



Best Management Options 



Possible management options to sustain evaporation and precipiUtion rates include: 

 1 Use of green dyes to increase evaporation. 



2. Monitor the salinity of eflHuent to each cell to determine when effluent should be 

 transferred to a higher concentration cell. 



page 9.4 



