A. The following
requirements establish the minimum allowable disinfectant residuals for each
type of system.
1. For systems that are
utilizing surface water sources, or sources determined to be groundwater under
the direct influence of surface water, one of the following options must be
implemented to meet the minimum residual requirements.
a.0.2 ppm residual for free chlorine or 0.5
ppm for total chlorine or
b.0.1 ppm
residual for free chlorine or 0.25 ppm for total chlorine provided the
requirements in Section C items 1-5 of this attachment are met or
c. HPC of <500 cfu/ml.
2. All groundwater systems serving
water to the public that contains chlorine or chloramines as a chemical
disinfectant or oxidant on a continuous basis must use one of the following
criteria for minimum residuals.
a.0.1 ppm
residual for free chlorine or
b.0.05 ppm for free chlorine if qualifying
criteria in section C items 3-5 of this attachment are met or
c. HPC of <500 cfu/ml.
B. If a system is
required to disinfect under an Administrative Order (AO), the requirements
listed in the AO will supersede any requirements for minimum residuals
established in this attachment.
C.
In order for a system to maintain the lower minimum residual requirement for
free or total chlorine (referred to in A, items 1.b. and 2.b.), the following
criteria must be met:
1. Any public water
system using surface water or ground water under the direct influence of
surface water must meet or exceed all CT inactivation requirements in 179 NAC
13., Tables 13.1 to 13.8 at all times through the treatment process in order to
utilize the lower requirements of A, item 1.b.
2. Any public water system using surface
water, or ground water determined to be under the direct influence of surface
water, must maintain effluent turbidity levels of less than or equal to 0.3 NTU
in 95% of all readings, and at no time exceed 1 NTU. A system may submit a
study to the Department showing that turbidity values in excess of the
specified turbidity limits are a direct result of the treatment process and do
not represent a threat to public health. The Department will review the study
to determine the nature of the high turbidity levels and if they pose a threat
to public health.
3. The system
must demonstrate that the field test method being used can consistently,
reliably, and precisely measure residuals less than or equal to the specified
limit being used.
4. The system
must document that the manufacturer's recommendations for calibration or
standardization are being done according to manufacturer's specifications and
frequency, and make this information available for review during sanitary
surveys.
5. The system must
demonstrate that there is no interference with the testing method, or document
that interference has been corrected for. This can be done by any one of the
following methods:
a. Demonstration through
historical source water data (a minimum of 12 months of data, or at least four
quarterly samples for non-transient non-community systems) that no interference
listed under the manufacturer's instructions is present in the
system.
b. Sampling for applicable
interferences once each day that a residual disinfectant compliance sample(s)
is taken to obtain a correction factor to be added to all residual compliance
samples taken that day.
c. Using an
EPA approved method that provides a correction for interference as part of the
procedure, and documenting all corrections.
d. Adjusting all results based on stable
historical data and adding the maximum interference obtained, with the
Department's approval.
D. Disinfectant residuals must be at or above
the required minimum residual limits in at least 95% of all distribution
residuals taken for the month. If the system fails to meet the 95% requirement
for two consecutive months, or for >= 50% of the previous 12 consecutive
months, the system will be deemed to be in violation of prescribed treatment
techniques and will be issued a Treatment Technique violation.
