PCWA-L 467.pdf - PCWA Middle Fork American River Project ...

230
MEASUREMENT OF STAGE AND DISCHARGE
solution is diluted to 2,000 mL with pure water. The concentration of
the resulting solution is computed by use ofequation 34. The process
is repeated twice, each time using the solution last obtained, as indicated
in the following flow chart:
c"
20 mL of (200x 10")
iLgiL dye solution
2,000 mL total solution
I
20 mL of (2x 10 6 )
JLg/L solution
2,000 mL total solution
I
20 mL of 20,000
Vg/L solution
2,000 mL total solution
160 (200x 10 6 )
The solution obtained, with concentration equal to 200 fLglL, is
referred to in this manual as a working standard solution because
any lesser concentration that may be desired can he prepared from it
by one additional serial dilution. For example, a dilution ratio of
1/200 will provide a solution with a concentration as low as 1 f.Lg/L. No
dilution ratios of less than 11200 should ever be used. The working
standard solution should be stored for future use. Experience has
indicated that standard solutions of 200 or more iLg/L when properly
stored in hard glass dark bottles out of direct light will keep for
periods ofat least 6 months. There is evidence, though not conclusive>
to indicate that very weak standard solutions tend to deteriorate or to
adhere slightly to the bottles in which they are stored.
The stored working standard solution may be used for periodically
checking the fluorometer calibration to determine if changes in the
calibration have occurred, and enough ofthe standard solution should
be retained for future use ifthe same dye lot from the manufacturer is
to be used for discharge measurements, New sets of standard solutions
should be prepared after 6 months to avoid the risk ofdecay of
fluorescence in the stored standard solutions. In addition, new sets
should also be prepared when new batches of dye are to be used for
discharge measurements because the dyes received from the manufacturer
may vary from batch to batch.
Ir the fluorometer calibration is known to be linear, from previous
tests using standard solutions made with distilled or unchlorinated
tap water, only a limited few concentrations need be prepared and
tested for the discharge-measurement calibration of the fluorometer.
The concentrations prepared should approximate the plateau concentration
expected in stream samples that will be taken during the
discharge measurement.