Dechlorination of Highly Chlorinated Water - Disinfection of Pipelines and Storage Facilities Field Guide - page 93

Table 7-1 Nonchemical dechlorination methods

Method of Discharge Dechlorination Effectiveness Notes

Retention in holding tanks Chlorine (0.5-2.0 mg/L) reduced in several

hours to a few days. Chloramines take three
to four times longer.

Land application/flow
over pavement or gravel

Chlorine (1.2 mg/L) at 300 gpm reduced to
1.0 mg/L in 500 ft. Chloramines (1-2 mg/L)
at 300 gpm needed 2,414 ft to reduce the
residual below regulatory requirements.

Groundwater recharge/
percolation into groundwater
basins

Very effective but groundwater must be
carefully monitored. Only approved in
limited areas.

Through natural
obstructions (hay bales)

May be effective but control is difficult. A
crude technique that has limited application.

Storm sewers Chlorine demand may not be high enough

to eliminate a residual prior to discharge to
the receiving waterway. May be acceptable
depending on the circumstances.

Sanitary sewers The method most used by water utilities.

Must have a sewer entry point near the
location of discharge. Need authorization
from the sewage agency. Backflow
prevention must be practiced.

ascorbate (NaC 6 H 7 O 6 ). A comparison of these chemical dechlori-
nation agents is provided in Table 7-2. The amount of dechlorina-
tion chemical needed for water with a 100 mg/L chlorine residual
for each 100 ft (30 m) of pipeline is given in Tables 7-3 and 7-4.

Chemical Feed Techniques
There are several methods commonly used for feeding dechlo-
rination chemicals in the field. Some of these may require the
availability of electricity. Portable generators can provide elec-
tricity in areas where it may not be readily available.

Gravity feed method. The gravity feed method typically
involves adding dechlorinating solution from a container
equipped with a spigot that is placed above the water flow path.