concentrations between 

 tile drainage systems 

 within major tiled 

 areas and between 

 major tiled areas. 

 Nitrogen concentra- 

 tions ranged from 2 to 

 400 mg/l in drainage 

 collected from individ- 

 ual tile systems over 

 the entire area; phos- 

 phorous concentrations 

 ranged from 0.01 to 

 6.6 mg/l. Tile flows 

 ranged from no flow to 

 more than 1,600 gallons 

 per minute during 

 summer months. Samples 

 collected from individ- 

 ual systems ranged in 

 TDS from 1,320 to 

 1^,630 rag/l in a given 

 month. Most systems in 

 the central area 

 discharged effluent with TDS 

 3,500 mg/l. Several samples 

 tile system in the San Luis 

 100,000 mg/l at low flow. 



JUN JUL AUG SCP OCT NOV DEC 



1967- 68 



FIGURE 12- SEASONAL VARIATIONS OF DISCHARGE, 



NUTRIENT CONCENTRATIONS, AND TOTAL DISSOLVED SOLIDS 



concentrations exceeding 

 collected from an experimental 

 Unit Service Area exceeded 



Composited Drainage 



The variability of discharge, nutrients, and TDS in compos- 

 ited drainage from major tiled areas was much less than that 

 observed in individual systems. 



Tile Drain Discharge . Discharges varied between major areas 

 The highest discharges were noted in the Byron-Westley area, 

 which for the I967-68 period averaged 2.3 acre-feet per year 

 (Table 11). This amounts to more than twice that of the 

 Gustine-Mendota area, which had the next highest quantity of 

 discharge . 



Nitrogen . Nitrogen content in the composited drainage from 

 the central area averaged three times more than in drainage 

 from any other major tiled areas. The average nitrogen 

 value was 32.8 mg/l. (A value of 21 mg/l had been predicted 

 for the entire Valley.) The higher nitrogen concentrations 

 in the tile discharge from the central area greatly 

 influenced the overall nitrogen concentration in the compos- 

 ited drainage of the Valley. However, the low nitrogen 



52 



