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10.10 CHAPTER TEN

sufficient TOC removal was not accomplished through the treatment process, the rule re-
quired water systems using surface water or groundwater under the direct influence of
surface water to practice enhanced coagulation, i.e., additional removal of organic pre-
cursor materials, unless the system could meet at least one of six alternative compliance
criteria. The MCLs for the chlorinated DBPs, total trihalomethanes (TTHMs), and sum
of five haloacetic acids (HAA5) are computed as a running annual average (RAA) of all
monitoring stations under the Stage 1 DBPR.
The Stage 2 DBPR will maintain the MCLs established under the Stage 1 Rule, but
the chlorinated DBPs, TTHMs, and HAA5 will now be regulated on a locational running
annual average (LRAA) basis. Each location, selected under a new monitoring plan in-
tended to use monitoring sites where high levels of DBPs occur, must meet MCLs of 80
and 60/xg/L for THMs and HAA5, respectively, 6 years after the rule is promulgated.
Additionally, after the first 3 years, the Stage 1 DBPR monitoring locations must meet
limits of 120 and 100/xg/L for THMs and HAA5, respectively, as LRAA in addition to
meeting Stage 1 limits of 80/60 as RAA.

Groundwater Disinfection Rule
Federal regulations require all surface water and GWUI systems to practice disinfection
and maintain a chlorine residual in the water entering the distribution system; but there
is no federal requirement for groundwater systems to practice disinfection. Many states
have gone beyond the federal requirements and currently require all or certain classes of
public water systems to practice chlorination.
The proposed Ground Water Rule (GWR) was published in the Federal Register on
May 10, 2000, and is expected to be promulgated in final form during the fall of 2003.
This rule is intended to protect the public from consuming contaminated drinking water
from groundwater sources by identifying which source waters are subject to fecal conta-
mination and then specifying corrective action. The rule will apply to approximately
157,000 public water systems using groundwater. Disinfection is not mandatory but may
be required for vulnerable systems.
The GWR relies on five key components to accomplish its objectives:
• Sanitary surveys that will identify deficiencies in water systems
• Hydrogeologic sensitivity studies for systems that do not disinfect
• Source water microbial monitoring for some systems
• Corrective action if deficiencies are identified
• Compliance monitoring for groundwater systems that disinfect to ensure they achieve
a minimum of 4-log inactivation and/or removal of viruses

CHEMICAL OXIDATION TREATMENT

Oxidation-reduction (redox) reactions form the basis for many water treatment processes
addressing a wide range of water quality objectives. These may include removal of iron,
manganese, sulfur, color, tastes, odor, and synthetic organics (herbicides and pesticides).
A redox reaction consists of two half-reactions: the oxidation reaction, in which a sub-
stance loses, or donates, electrons; and the reduction reaction, in which a substance gains,
or accepts, electrons. An oxidation reaction and a reduction reaction must always be cou-
pled because free electrons cannot exist in solution and electrons must be conserved.