2-10. OPERATING PROCEDURES (Cont'd).
Chlorine residual test
(1) Rinse test tube (1) with
sample water. Fill to line with
(2) Add one DPD tablet (2)
Install cap (3) and shake test
tube until tablet dissolves.
(3) Remove cap (3).
(4) Place test tube in reader (4)
at back of comparator (5), in a
(5) Match sample color to color
standard. Move sample tube
from behind one clear window
to behind other until color match
(6) If color is darker than 1.0
ppm Cl (2.0-10.0 ppm CI), place
(7) Move sample tube from one
position to another until color
match is made. If color of test
the result is average of the two values. Record as ppm Cl residual chlorine
(8) If color is darker than 5.0 ppm Cl color standard, amount of chlorine present cannot be measured
accurately with one DPD tablet (2). Add an additional DPD tablet to test tube (1), install cap (3) and shake until
tablet dissolves. Repeat step (6).
(9) Rinse test tube (1) with treated water and store in test kit.
Determine chlorine dosage requirement by subtracting ppm of source water chlorine residual from the desired
chlorine residual (as prescribed by TB-MED-577) For example
Desired Chlorine Residual
Source Water Chlorine Residual
Chlorine Dosage Requirement
If the chlorine dosage requirement is 2 ppm, for example, find a dosage ppm of 2 in2-11 table 2-2. If the dosage
requirement is 2 ppm and the hypochlorination unit will be run at 50 gpm, 7.5 ounces of 70% calcium hypochlorite will be
mixed with 5 gallons of water