The board adopts and incorporates by
reference 40 CFR
, which set forth maximum
contaminant levels for turbidity, except for the following changes:
(a) The terms "one turbidity unit" and "1
NTU" mean 1.0 nephelometric turbidity unit, and the terms "five turbidity
units" and "5 NTU" mean 5.0 nephelometric turbidity units for the purposes of
replaces 40 CFR
(a) (1) : "For systems using
conventional filtration or direct filtration, the turbidity level of
representative samples of the system's combined filtered water must be less
than or equal to 0.5 NTU in at least 95% of the measurements taken each month,
and may not at any time exceed 1.0 NTU."
The following replaces
(a) (2), and is also added at the end
of 40 CFR
(a) (1) and 141.551: "For systems
using conventional filtration or direct filtration, the turbidity level of
representative samples of a system's effluent from individual filters, measured
at a point prior to mixing with effluent from other filters or other sources,
may not exceed 0.5 NTU in at least 95% of the measurements taken each month,
and may not at any time exceed 5.0 NTU. This requirement is not violated if the
turbidity reading for the effluent from each individual filter is the first
reading of the month that exceeds 0.5 NTU and the individual filter is taken
off-line within 24 hours after the sample analysis that shows the
The first sentence
in 40 CFR
is replaced with the following
sentence: "Your system must meet three strengthened combined filter effluent
The department may invalidate a turbidity measurement based on documentation
that demonstrates the exceedance was caused by turbidimeter performance
difficulty or sample site location problems and that the measurements were not
indicative of true water quality. If the department invalidates the turbidity
reading on one of these bases, the turbidity reading may not be included in the
95% compliance calculations required under this rule.
Mont. Admin. R.
NEW, 1977 MAR p. 1187,
Eff. 12/24/77; AMD, 1982 MAR p. 594, Eff. 3/26/82; AMD, 1991 MAR p. 1492, Eff.
8/16/91; AMD, 1994 MAR p. 2131, Eff. 8/12/94; TRANS, from DHES, 1996 MAR p.
1499; AMD, 2000 MAR p. 3400, Eff. 12/8/00; AMD, 2005 MAR p. 257, Eff.
75-6-103, MCA; IMP,