Possible Monitoring Requirements for the
Disinfectants and Disinfection by-Products
          (D/DBP) Regulations



                        January 1993
     The monitoring requirements presented in this report were
developed by EPA before a negotiated D/DBP rule was considered.
The framework described herein may substantially change as a
result of the negotiated rulemaking process.  Nevertheless, the
monitoring strategies described herein, particularly as they
pertain to reduced monitoring for smaller systems and systems
less vulnerable to exposure from DBPs, may be useful to consider
in developing various monitoring options during the negotiated
rulemaking process.

     Monitoring requirements for four trihalomethanes (THMs) were
promulgated in 1979 [44 PR 68264].  They apply to all systems
serving 10,000 or more people that disinfect the drinking water
source.  All four regulated THMs must be measured.  Depending on
certain system criteria and prior monitoring results, each system
must collect from one to sixteen samples each year.  The
requirements discussed in this report parallel the THM monitoring
requirements, but differ in two important ways.  First, some
systems may not have to measure all of the disinfectants and
disinfection by-products that may be regulated under the D/DBP
rule.  Second, monitoring frequencies may be longer than one year
(i.e., less than one sample per year) for some small or very
small systems.

     The last draft of these possible monitoring requirements was
prepared in June 1991 by combining the trihalomethane monitoring
requirements with certain features of the 1991 Standardized
Monitoring Framework [56 FR 3526 and 30266] and with a
consideration of how to measure residual disinfectant
concentrations and other indicators of disinfection by-product
formation potential.  This draft of the requirements factors in
suggestions received on the 1991 draft from EPA, State, and other
commenters.  Although the Agency is considering ways to improve
the Standardized Monitoring Framework, the requirements in this
paper have not tried to anticipate the effect these changes may
have, nor the effect the negotiated rulemaking process may have.


     The Disinfectants and Disinfection By-Products Rule may have
monitoring requirements for disinfectants and for organic and
inorganic by-products of disinfection.  The requirements may

apply to over 50,000 public water systems that use disinfection -
including those that purchase water from other systems.
EPA estimates that about 90% of the systems affected may be
very small ground—water systems that serve less than 500 people.
Because of characteristics unique to most of these systems (low
variability of the already low organic content in the source
water and small distribution systems), EPA may require fewer
samples to characterize disinfectant and disinfection by—product
(DBP) occurrence at very small systems. In addition, some of
these systems that demonstrate low probability of significant
by—product formation may qualify for monitoring waivers for some
Approximately 80% of the U.S. population is currently served
by about 3000 large systems that disinfect. These systems must
comply with the monitoring requirements of the trihalomethane
rule (40 CFR 141.30]. To do so, they have selected sample
collection points, designed compliance monitoring procedures, and
are now paying about $65 per sample for measurement of THMe. The
monitoring requirements as presented here would result in
additional analytical costs for these systems. Most of the new
costs are anticipated to result from measurement of haloacids
($200), chloral hydrate ($75), and chlorine dioxide ($50) (prices
are per sample). Costs for measurement of other by—products,
disinfectants, and some surrogates also have been estimated
(Table 1). In addition to absorbing the same per sample
analytical costs as large systems, small systems (serving
populations of less than 10,000) may have to set up sample
collection and data reporting procedures to meet the new
monitoring requirements.
Possible Conditions of th. Monitoring R.auirem.ntp
1. The D/DBP rule will specify minimum monitoring
requirements, but EPA may allow systems to ask to
sample more frequently or at more locations to
determine compliance. To obtain approval for this, the
system must submit a map of all sampling locations,
reasons for the frequency selected, and the formula
that will be used to calculate a running annual average
concentration for each organic by-product and an annual
average concentration for each disinfectant and
- inorganic by-product. This plan, when approved by the
State, must be used to measure all disinfectants and
by-products for which the system must monitor.
2. A system using ground water under the direct influence
of a surface water may have the same requirements as a
surface water system.


ANALYTE OR PARAMETER                       COST($)/SAMPLE

Source Water Quality Indicators
Total Organic Carbon (TOC)                 $ 35 - 45
Ultraviolet (UV) Absorption                < 10
Bromide                                      20-30
Total Organic Halogen (TOX)                  65 - 100
Formation Potential Studies (FP)            150 - 500

Organic t Inorganic By-Products
Trihalomethanes (THMs)                      $  65
Haloacetic Acids (HAAs)                       200
Chloral Hydrate (CH)                          75
Brornate, Chlorate, Chlorite ($25 each)        75

Chlorine                                   $ 10 - 25
Chloramines                                < 10
Chlorine Dioxide                             50
(includes Chlorite & Chlorate)

3. When monitoring is less frequent than quarterly or less
than four samples are collected per sampling period,
the system may be able to select a sample point and
time that are expected to produce the highest
concentration of by-product, which is defined as at
remote points in the distribution system during the
month of warmest water temperature. -
4. A ground-water system may (unless th State objects)
elect to determine compliance for organic disinfectiøn
by-products with one annual formation potential sample.
SummarY of Comoliance Xonitorin Reauirements
Despite some comment to the contrary, EPA is not
planning to adopt the Standardized MonitoringFramework (the
Framework) per se for this rule, ‘since to do-eo-vould -delay
initial monitoring until January 1999 for ey te as that now
disinfect. Instead EPA -is considering phasing-in initial
monitoring beginning on January 1, 1997. Although the
Framework does not apply to the disinfectants and
disinfection by-products, the moi itOring requfrenents
described herein fit relatively.we’11? itWiItit. Feetures of
the Framework that are compatible with (aitd have been -
incorporated into) the monitoring requirements presented in
this paper include:
1. Monitoring is a system responsibility unless the State
accepts responsibility.
2. Waivers (by Rule, by Us6 ’ and by sueceptibility) are
granted by the State. They are used to permit no or
reduced monitoring.
3. There are always base aonitoting requir aent& thata
system must comply with whenever a waiver is not
obtained or renewed.
4. The initialmonitoring peridd begins on a January 1st.
5. States submit to EPA a sampling schedule to-phase-in
the initial monitoring reqüi-reaentsj- phase—in by system
size is not required. -
Anol :her feature of the Framework -included i-n this draft ‘of
the D/DBI ’ monitoring requirements is the adoption of the
three—yeur cycle for phasing-in initial monitoring, and for
setting :,epeat and reduced monitoring frequencies.

1. In general, all systems using a chemical disinfectant
may be required to monitor for the disinfectant and
possible by-products. A system cannot receive a waiver
from disinfectant monitoring but may obtain waivers
from some or all by-product monitoring. Possible
exceptions to the prohibitions on waivers for
disinfectant monitoring are that systems using ozone
may not be required to measure ozone residuals under
the monitoring requirements discussed herein.
Groundwater systems that use only ultraviolet (UV)
radiation may not be subject to any monitoring
requirements. Instead, these systems may have
monitoring requirements to characterize the
effectiveness of UV disinfection under the Ground-Water
Disinfection Rule.
2. Systems that annually conduct monitoring of total
organic carbon (TOC), bromide, and UV absorbance (all
relatively inexpensive), or other indicators of
by—product formation potential, may be able to obtain a
waiver from some by-product measurements.
3. Systems with certain types of pM control, or that can
demonstrate predictable by-product formation
correlations with other by-products or parameters, may
receive a waiver from some or all by-product
4. Systems with compliance samples that are reliably and
consistently below a “trigger” percentage of the
maximum contaminant level (MCL) for certain
disinfection by-products may be able to obtain a waiver
from some by-product measurements.
5. Waivers to allow reduced monitoring frequencies may be
required to be renewed regularly. They are not
automatically granted when prior monitoring data show
levels below the trigger concentration. To qualify for
r uced monitoring, the State must not object, and
th.r. must be no significant change in source water
quality or treatment during the waiver period.
6. Possible waiver criteria that would allow systems to
avoid monitoring for some or all disinfection
by-products are listed in Table 2. Possible criteria
for reduced frequency monitoring waivers for chioral
hydrate, haloacetic acids and trihalomethanes are shown
in Tables 3 and 4.

Systems may be allowed to avoid measuring some DBPs if one
or more of the following criteria are met, subject to State
approval. A waiver generally must be renewed every year or at
the end of the reporting period.
1. Raw water aualitv . If the source water (or water prior to
disinfection) falls below certain levels x, which are to be
determined for certain combinations (to be determined], of the.
following parameters:
TOC < “x”
UV absorbance c “x”
then monitoring for certain DBPs may be waived.
2. Other water cuality criteria . If the criteria. lov (to be
determined) are met for any of the DBPS specified, then
monitoring for those DBPB ia not required.
waiver For Raw Water Crit.ria Finished Water Crit.ria
Haloacetic Acids (Acids) < T% MCL
Bromate Bromide < - No use of OZOflQ
Chloral Hydrate (chloroform] < T% MCL
The quantities “x” and --”T%” are currently upapeci ied .
3. Surrogates in finished water . If the ratio of ?I’HX/TOX is
(required relationahip to be determinedi and pH and temperature
are within (range to be determined] and (range to. be determined),
respectively then DBP monitoring is not required.
4. Membrane treatment . If certain membrane processes are used,
no DBP monitoring is required. -

(Based on 1979 T 4 Rule)
System Size: PoDulation > 10.000
Water Source: Surface Water Ground Water
Sample Location: All samples taken at the 40 FR 141.30 THM
Sample Frequency: 4/quarter 4/qtr, or one Fr/qtr
Reduction Criteriab:
Annual average Annual average CX% )ICL or
CX% FrC X% M L
1 smpl/quarter 1 smpl/quart.r
worst-case sample) (worst—case sample)
Compliance: See text and Figure 1.
This is a formation potential (FP) sample with criteria as yet unspecified.
b Assumes no significant change in treatment or source water quality, and that
the State does not demur. Significant is a term and 1% a quantity yet
t ô—b —d.t rmInAd -

System Size: Pomulation < 10 .000
Water Source: Surface Water Ground Water
Sample Location/Time: Worst-case sample Worst—case sample
from distribution from distribution
system system
Sample Frequency: 1 sample/quarter 1 sample/year
Reduction Criteria’: Annual average Each sample
<50%MCL0r <50%XcLfor3yrs
< 25% MCL or one sample
< 25% MCL for 1 yr
Reduced’Frequency: 1/yr or 1/3 yrs, 1/3 yrs or 1/9 yrs,
respectively respectively
Compliance: See text and Figures 2 and 3.
Assumes no significant change in trea ent or source water
quality, and that the State does not demur. significant
is a term yet to-be-determined,

The monitoring requirements for the organic by-products -
chioral hydrate, haloacetic acids and trihalomethanes - have
been divided first by population served, and second by type
of source water used (ground or surface water).
1. Initial monitoring at large systems is at the same
frequencies and sample points used for trihalomethane
compliance sampling. Large systems are defined as
serving a population of 10,000 or more people (Table 3
and Figure 1).
2. Initial monitoring at small systems requires only one
sample per sampling period, which is quarterly for
surface water systems and annually for ground water
systems (Table 4 and Figures 2 and 3).
3. Reduced monitoring eligibility is predicated on
worst-case samples. Since most systems are very small
ground-water systems (the majority with populations
less than 500) with low and relatively constant
concentrations of precursors in the source water, they
are likely to meet this eligibility requirement.
The disinfectants are chlorine, chlorine dioxide and
chloramines; the inorganic by—products are bromate,
chlorate and chlorite (Table 5).
1. Disinfectant residuals are measured at least monthly at
representative locations in the distribution system
under the Surface Water Treatment Rule (SWTR). The
same monitoring is expected to be required under the
Ground-Water Disinfection Rule (GWDR) for those systems
that must disinfect distribution systems. If a system
is not using a chemical disinfectant under the GWDR,
these monitoring requirements may not apply.
2. Monitoring requirements for inorganic by-products are
identical to those for the disinfectants.
3. Msasurem nts of free chlorine may be required to
determine compliance with the chlorine MCL; however,
total chlorine measurements may be used instead. Many
systems measure total chlorine residual under the SWTR.
4. Total chlorine measurements may be used to determine
compliance with the chioramines MCL.

Initial Monitoring
4 samples/qtr for 1 yr
T samples/qLr
fi sample/qtr I
Figure 1

Initial: I sample/qtr
for lyr
I 1 sample/qti I
1’ sample/yr I
1! sarnple/3 yrs
Figure 2

Ii sample/9 yrs ft sarnple/3 yrs ]
50% MCL
for 3 yrs?
Figure 3

Water Source and System Size: Pertinent systemsc
Sample Location: Representative locations in
the distribution system’
Sample Frequency: 1/month’
Compliance: Running annual average of
monthly values must be < MCL.
If more than 1 sample is taken
per month, the monthly mean
values are averaged.
‘As free chlorine - analysis performed at water system.
Compliance may also be determined using total chlorine
b Compliance determined using combined chlorine measurements.
To be defined; possibilities include — only systems using ozone
will monitor for bromate; only systems using chlorine dioxide
will monitor for chlorine dioxide or chlorite.
d Monitoring for disinfectant residuals is already required under
the surface water treatment rule, and is anticipated under the
ground-water disinfection rule.

5. Sampling location, minimum sampling frequency, and
calculations required for determining compliance with
the disinfectant and inorganic, by-product MCLs are
specified in Table 5.
1. The possible dates of the disinfectant and disinfection
by-product monitoring requirements and the anticipated
actions under the GWDR (Table 6) assume promulgation by
June 30, 1995, or the DIDBPR an4 August 3 , 1996, for
the GWDR.
2. For systems that are disingec ing at,çha ç4ns of
promulgation, the initial D/DBP monitoring period may
be complete by December 31 ,, 1998g if the SMP,is not
followed, and December 31, 2001, if the SMP is followed
completely. -For the GWDR, ,the 4nitial. monitoring
period may begin on March 1, 1998, for monitoring only
and January 1, 1999, for compliance with performance
Monitoring data for by-product4 -collected up to twelve
months before monitoring is required. may be accepted
provided the State,Ldoes net object, an4 treatment and
source water quality have not significantly changed.
3. Phase-in periods for systems.that begin disinfection
after promulgation may be as followB.
a. Fo community water systems, initial D/DBP
monitoring may be -cqaplet;by December 31, 2001., if
the SXF is not followed, and December 31, 2004, if
SM? is followed.
b • For non-tr;ns ie t, •noncommw*tty.
initial monitoring may becomp] .ete by December 31,
2004, if the SM? is not followed. If the SM? is
followed, the initial monitoring period would be
complete by December 31, 2007.
4. Tbsse monitoring requirements-can accommodate any
combination of regulatory MCL options. Regulatory
options include, but are not limited to, setting MCLs
for each c taminant, setting MCI.s for, total T1 Is and
total haloacetic acids, or .setting a-combination of
single-contaminant and multiple— contaminant MCL5.

Promulaation : June 30, 1995 August 31, 1996 (1)
Effective Date : January 1, 1997 March 1, 1998
System. Currently Disinfectina :
Comply with disin- NA January 1, 1999 (4)
fect ion performance
Complete initial December 31, 1998 (2) NA
D/DBP Monitoring
December 31, 2001 (3)
Systems That Beam
Disinfection After 7/1/95 :
Conunity Systems:
Begin Disinfection: NA March 1, 2001
Complete initial December 31, 2001 (2) NA
D/DBP Monitoring:
December 31, 2004 (3)
Woncoaaunity S ys tea.:
Begin Disinfection: NA March 1, 2003
Complete initial December 31, 2004 (2) NA
D/DBP Monitoring:
December 31, 2007 (3)
(1) - Assumes promulgation date of August 31, 1996, and certain
requirements in rule. Dates and requirements may be changed.
(2) — Schedule applicable if Standardized Monitoring Framework
(SM?) not followed (i.e., if initial D/DBP monitoring must be
completed les. than three year. after rule becomes effective).
Date is first SM? period final date after rule becomes effective.
(3) — Schedule applicable if SM? followed fully (i.e., if initial
D/DBP monitoring must be completed during first complete three
year SM? period following effective date of rule).
(4) - Ground water systems disinfecting when GWDR promulgated
will have until January 1, 1999. to meet disinfection performance
requirements, although GWDR monitoring will begin March 1, 1998.

Compliance may be determined by comparing the running annual
average of prior sample measurements to each MCL. The running
annual average requirement may apply to whatever combination of
single-contaminant MCLs or group MCLs (e.g., total haloacids)
that EPA adopts in the final rule.
Therefore, for systems serving less than 10,000 people, EPA
may consider determining compliance for trihalomethanes, chloral
hydrate, and haloacids as follows. A sample is collected in the
first year that a system qualifies for a reduction in sampling
frequency to less than quarterly. Depending on the result of
this measurement, one of three repeat sampling schedules applies:
1. If the result is less than the MCL but above one or
more of the trigger concentrations, the sampling
frequency stays at or increases to the next higher
frequency (Table 4), depending on whether the system
was at a lower frequency prior to the sample result.
2. If the result is less than the MCL and meets the
trigger concentration criteria, the next sample is
collected at the reduced monitoring frequency (Table
3. If any measurement exceeds the MCL, the system must
immediately increase its monitoring to at least
quarterly to compute a running annual average. If
appropriate, the state may require the system to take
more immediate corrective action to assure compliance.
The system is not in violation until two quarterly
annual average calculations exceed the XCL (Figure 4).
If any sample concentration exceeds 4 times the MCL, a
violation may be considered to have occurred.
Note that compliance with disinfection requirements (Table 5) is
always checked by monthly monitoring of both disinfectants and
inorganic disinfection by-products except for bromate.
Z t I ii iM
To further develop and impr’ve the compliance monitoring
requirements for this rule, EPA believes the following issues and
problems will require attention.
1. EPA has suggested several parameters or correlations
with treatment processes or with occurrence of other
disix fection by-products as ways to waive a system from
some by—product monitoring.

Result Yes
 4 X MCL? > _Violation
Collect Samples
• Average
< Trigger?
Figure 4

a. We need to carefully discuss and determine the
reasonableness of this approach.
b. Information must be obtained so that cutoffs can
be proposed:
i. for the indicators of source water quality
listed in Table 2, and
ii. for the reduced monitoring trigger
concentrations in Tables 2, 3 and 4.
c. We must determine whether EPA can obtain enough
data to support use of surrogate indicators to
grant monitoring waivers.
d. We should consider whether EPA should offer
systems the option of performing simulated
distribution system studies to support waiver
2. For large systems, the monitoring requirements
presented here for’ all by-productm -are identical to the
requirements of the 1979 THX Rule.
a. EPA must determine whether’ this amount of
monitoring is sufficiently predictive, and yet
b. We must consider whether EPA should modify these
monitoring requirements to permit more flexibility
in initial or repeat monitoring. Specifically:
i. for initial monitoring EPA might consider
allowing a t angeóf 2—4 ’saaples per quart.r
rather than requiring 4 samples per quarter;
ii. for repeat or reduced monitoring, EPA could
allow less frequent monitoring when a systam
is reliably and consistently below some
percentage of the MCL. For example, if for
three years a system is below a trigger
percentage of the MCL, the sampling frequency
could be reduced to once every three years.
3. When less than four sample. per sampling period ar.
collected, or when the sampling frequency is less than
quarterly, EPA may require that compliance with an P1CL
be based on a worst-case sample.
a. EPA must determine whether it is cost—effective
for a system to select a worst-case site and time
for monitoring.

b. EPA could consider limiting the options of
collecting only one sample per sampling period, or
permitting less than quarterly monitoring to only
small or very small systems.
C. In Table 4, EPA defined the small system group as
those serving populations of less than 10,000
people. Three other ways in which EPA might
define this group are: only nontransient,
noncommunity systems; only systems serving fewer
than 500 people; or only systems serving fewer
than 3,300 people. There are other possibilities
for defining this class of “small” systems, and
the merits of each must be carefully considered.
d. EPA should consider whether it is reasonable to
ever permit less than one sample per year per PWS
under any conditions. Requiring at least one
sample per year would increase the monitoring load
at small systems from that presented in Table 4.
4. If EPA fully adopted the Standardized Monitoring
Framework (SM?) nine—year compliance cycle, initial
monitoring for systems that currently disinfect would
occur from 1999 to 2001. Initial monitoring for
community water systems that begin disinfection under
the GWDR would occur from 2002 to 2004. Conformance
with the SM? rather than the dates shown earlier in
this paper would result in a two—year delay for systems
now disinfecting, with a 10 month delay for others.
Non-transient noncommunity systems would begin
disinfection in March 2003, and initial D/DBP
monitoring under SMF would run from 2005 until 2007.
This represents almost a two year delay. We should
carefully consider whether the monitoring requirements
should fully conform to the Framework’s nine—year
compliance cycles, given that this may give systems the
option to delay monitoring two years after an MCL
becomes effective.
5. For small systems that are monitoring the organic
by—products - chloral hydrate, trihalomethanes or
haloacetic acids - less frequently than quarterly, EPA
is suggesting that one sample exceeding an MCL is not a
violation until the average of this sample plus the
next three quarterly samples exceeds the MCL. This
proposal would treat small systems more like large
systems in that an MCL violation would not be based on
a single, worst-case sample.
a. All parties must consider whether this is a
reasonable approach.
b. We could consider other options such as allowing

this approach only for some of the organic
by-products listed above, based on the relative
health risk.
6. Compliance determinations need to be more thoroughly
developed so that the conditions are complete, clear
and reasonable. The conditions for determining
MCL-compliance need to cover cases when worst-case
samples are collected, and when sampling is less
frequent than quarterly.

Ref erenc..
Code of Federal Regulations: Title 40, Protection of
Environment, Parts 100 to 149, Revised as of July 1, 1992.
Federal Register: U.S. Environmental Protection Agency. National
Interim Primary Drinking Water Regulations; Control of
Trihalomethanes in Drinking Water; Final Rule; Vol. 44, No. 231,
Thursday, November 29, 1979 - Part III. (44 FR 68264]
Federal Register: U.S. Environmental Protection Agency. National
Primary Drinking Water Regulations - Synthetic Organic Chemicals
and Inorganic Chemicals; Monitoring for Unregulated Contaminants;
National Primary Drinking Water Regulations Implementation;
National Secondary Drinking Water Regulations. Vol. 56, No. 20,
Wednesday, January 30, 1991 — Part II. (56 FR 3526]
Federal Register: U.S. Environmental Protection Agency. Drinking
Water; National Primary Drinking Water Regulations; Monitoring
for Volatile Organic Chemicals; MCLGs and MCLs for Aldicarb,
Aldicarb Sulfoxide, Aldicarb Sulfone, Pentachlorophenol, and
Barium. Vol. 56, No. 126, Monday, July 1, 1991 —Part XII. (56 FR
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