Second piece, with union attached, is 

 threaded onto the shaft (figure 8). As the 

 extension brings the height of the stand- 

 pipe above the surface of the stream, water 

 then is easily removed from the chamber of 

 the pipe with a small bilge pump. 



Obtaining a Dissolved Oxygen Siumple 



After the water has been evacuated from 

 the St andpipe , the key inserted, and the 

 sleeve turned to the open position, ground 



CORD FROM CONDUCTIVITY BRIDGE 



V.ATER LEVEL 



STANOPIPE CAPPED AKD 

 NOT IN OPERATION 



""-SS) 



'PEAN'F^' 



^ 



Figure 8. — On the left, the standpipe is in nonoperation 

 position. On the right, the standpipe is in op- 

 erationaposition, with the conductivity cell in 

 the standpipe and with cord leading from the cell. 



water seeps into the chamber of the stand- 

 pipe and fills it. The temperature of the 

 water in the standpipe is recorded, the 

 valve is closed, and a sample of water for 

 oxygen determination is drawn off with a 

 suction bottle as is shown in figure 9. The 

 Sample then is allowed to siphon back into 

 tinted flasks for "setting" in the manner 

 commonly employed in the Winkler method 

 (American Public Health Association, 1947). 

 This process is repeated if a larger sample 

 of water is needed. When water is being 

 drawn , the valve always is 

 closed to keep sediment out of 

 the standpipe and to prevent 

 vacuuming the particles sur - 

 rounding the base of the stand - 

 pipe . Another essential pre - 

 caution is to avoid jarring the 

 sta ndpipe . These precautions 

 are deemed necessary to avoid 

 disturbing the natural struc- 

 ture of the streambed and 

 causing surface contamination 

 of the groundwater sample. 



Percolation Tests 



On the basis of the behav- 

 ior of a Salt Solution in a 

 standpipe that has been cali- 

 brated for apparent velocity 

 in the laboratory, velocities 

 are ascertained by corapcirable 

 behavior of a salt solution in 

 a standpipe in the field. 



Figure 10 illustrates the 

 use of the conductivity bridge 

 and cord. At Mill Creek, a 

 plastic cell was used instead 

 of the regular glass cell to 

 avoid breakage from rough treat- 

 ment, which is unavoidabile 

 under conditions in the field. 

 The conductivity bridge is 

 operated most conveniently from 

 the bank of the stream. This 

 operation from a remote loca- 

 tion requires a much longer 

 cord than normally is supplied 

 with the instruments. With the 

 longer cord, however, it is 

 advisable to use a cell with a 

 const £Uit of one-tenth of that 

 normally used, to reduce the 

 percentage error of increased 

 resistance resulting from the 

 use of the longer cord. 



STANDPIPE IN OPERATION 

 Vi.!TH EXTENSION ATTACHED 



14 



