3.1. Flow rate test
The minimum flow rate required to maintain a formalin treatment concentration of
1500 ~1 1-l f 10% for a 15 min exposure was 7.6 1 min-’ (Fig. 1). Flow rates of 1.0
and 3.8 1 min- ’ did not produce or maintain the desired treatment concentration over the
15 min exposure period. Formalin concentrations peaked at 1020 ~1 1-l (sample time
25 min) and 1339 ~1 1-l (sample time 15 min) in the 1.0 and 3.8 1 min-’ flow rates,
respectively, and were slowly diluted out of the system over the remaining 60 min
sampling period. In the 7.6 and 15.1 1 min- ’ flow exposures, formalin treatment
concentrations of 1500 ~1 1-l were maintained for at least 10 min of the 15 min
exposure periods. The formalin concentration reached approximately 1400 ~1 l- ’ within
5 min in these tests and was maintained for at least 10 min. The concentration had
decreased sharply to 160 ~1 1-l at the 20 min sample time and the remaining traces of
formalin were quickly flushed from the system. The mean relative standard deviation of
the triplicate water samples withdrawn at 5, 10, and 15 min into the treatment was 4.9%
+7.3. We feel that this validated the precision of the sampling technique.