EXECUTIVE SUMMARY 



OVERVIEW 



This report contains information and data on site-specific field and laboratory studies on 

 the physical and chemical efficacy of evaporation ponds. Data were collected from the Pryse, 

 Peck and Barbizon evaporation pond facilities. The main goal of disposing saline tile drainage 

 effluents into ponds is the evaporation of the impounded waters. A number of climatic, physical 

 and chemical factors affect evaporation rates. The nature of salts (evaporites) deposited in ponds 

 are strongly influenced by the chemical composition of the tile drainage effluent. The extent of 

 evaporite precipitation is influenced by the degree of evapoconcentration of the impounded 

 waters. Of particular concern is the accumulation of toxic trace elements in the pond facilities. 

 The design and operational management of the ponds may influence evaporation rates. 



The following presents highlights on the physicochemical efficacy of agricultural evapo- 

 ration ponds. Some of the data were collected over a three-year period (1986-89), while others 

 were collected only in 1989. 



▲ Pond Waters - Salinity and Major Solutes 



• The average electrical conductivity (EC) of tile drainage discharged into Pryse pond was 

 29.7 dS/m (mmhos/cm), Peck pond, 10.4 dS/m, and Barbizon pond, 8.4 dS/m. 



• The ECs in Cells 1 and 2 in Pryse pond ranged from a minimum of 25.6 to a maximum 

 of 175 dS/m. On a meq per liter basis, waters in Pryse pond are classified as NaCl-Na^SO^ 

 type. 



• The ECs in Cell 1 through Cell 6 in Peck pond ranged from a minimum of 8.3 to a 

 maximum of 109 dS/m. Waters in Peck pond are Na^SO^ type. 



• The ECs in Cells A, B and C, separated by wind-break berms, in Barbizon pond ranged 

 from a minimum of 8.8 to a maximum of 48.3 dS/m. Waters in Barbizon pond are the 

 NajSO,-NaCl type. 



▲ Pond Waters • Trace Elements 



• The concentration of trace elements reported herein is the total dissolved concentration 

 in ng per liter (ppb) for arsenic (As), molybdenum (Mo) and selenium (Se) and mg per liter 

 (ppm) for boron (B). 



• The average influent concentration of B was 9.3 ppm in Pryse pond, 7. 1 ppm in Peck pond 

 and 3.5 ppm in Barbizon pond. The average As and Mo data reported herein are 

 consistently greater than those reported by the Central Valley Regional Water Quality 

 Control Board. 



• Using chloride (CD as a nonreactive parameter to estimate the degree of evapoconcen- 

 tration in ponds (ECF), the measured concentration of B in all ponds increased in direct 

 proportion to CI. 



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