Wisconsin Administrative Code › Department of Natural Resources › NR 800 - Environmental Protection - Water Supply › Chapter NR 810 - Requirements for the operation and maintenance of public water systems › Subchapter III - Toolbox Options for Meeting Enhanced Treatment for Cryptosporidium Requirements › Section NR 810.45 - Additional filtration toolbox components

Current through June 24, 2024
(1) BAG OR
				  CARTRIDGE FILTERS. Public water systems receive Cryptosporidium treatment
				  credit of up to 2.0-log for individual bag or cartridge filters and up to
				  2.5-log for bag or cartridge filters operated in series by meeting the criteria
				  in pars. (a) to (j). To be eligible for this credit, water suppliers for
				  systems shall report the results of challenge testing that meets the
				  requirements of pars. (b) to (i) to the department. The filters shall treat the
				  entire plant flow taken from a surface water or GWUDI source.
(a) The Cryptosporidium treatment credit
				  awarded to bag or cartridge filters shall be based on the removal efficiency
				  demonstrated during challenge testing that is conducted according to the
				  criteria in pars. (b) to (i). A factor of safety equal to 1-log for individual
				  bag or cartridge filters and 0.5-log for bag or cartridge filters in series
				  shall be applied to challenge testing results to determine removal credit.
				  Systems may use results from challenge testing conducted prior to January 5,
				  2006 if the prior testing was consistent with the criteria specified in pars.
				  (b) to (i).
(b) Challenge testing
				  shall be performed on full-scale bag or cartridge filters, and the associated
				  filter housing or pressure vessel, that are identical in material and
				  construction to the filters and housings the system will use for removal of
				  Cryptosporidium. Bag or cartridge filters shall be challenge tested in the same
				  configuration that the system will use, either as individual filters or as a
				  series configuration of filters.
(c) Challenge testing shall be conducted
				  using Cryptosporidium or a surrogate that is removed no more efficiently than
				  Cryptosporidium. The microorganism or surrogate used during challenge testing
				  is referred to as the challenge particulate. The concentration of the challenge
				  particulate shall be determined using a method capable of discreetly
				  quantifying the specific microorganism or surrogate used in the test; gross
				  measurements such as turbidity may not be used.
(d) The maximum feed water concentration that
				  can be used during a challenge test shall be based on the detection limit of
				  the challenge particulate in the filtrate, including filtrate detection limit,
				  and shall be calculated using the following equation:
Maximum Feed Concentration = 1 x 104 x (Filtrate Detection
					 Limit)
(e) Challenge
				  testing shall be conducted at the maximum design flow rate for the filter as
				  specified by the manufacturer.
(f)
				  Each filter evaluated shall be tested for a duration sufficient to reach 100%
				  of the terminal pressure drop, which establishes the maximum pressure drop
				  under which the filter may be used to comply with the requirements of this
				  chapter.
(g) Removal efficiency of
				  a filter shall be determined from the results of the challenge test and
				  expressed in terms of log removal values using the following equation:
LRV = LOG10(Cf)-LOG10(Cp)
Where:
LRV = log removal value demonstrated during challenge
					 testing; Cf= the feed concentration measured during the challenge test; and Cp=
					 the filtrate concentration measured during the challenge test. In applying this
					 equation, the same units shall be used for the feed and filtrate
					 concentrations. If the challenge particulate is not detected in the filtrate,
					 then the term Cp shall be set equal to the detection limit.
(h) Each filter tested shall be challenged
				  with the challenge particulate during 3 periods over the filtration cycle:
				  within 2 hours of start-up of a new filter; when the pressure drop is between
				  45% and 55% of the terminal pressure drop; and at the end of the cycle after
				  the pressure drop has reached 100% of the terminal pressure drop. An LRV shall
				  be calculated for each of these challenge periods for each filter tested. The
				  LRV for the filter (LRV filter) shall be assigned the value of the minimum LRV
				  observed during the 3 challenge periods for that filter.
(i) If fewer than 20 filters are tested, the
				  overall removal efficiency for the filter product line shall be set equal to
				  the lowest LRV filter among the filters tested. If 20 or more filters are
				  tested, the overall removal efficiency for the filter product line shall be set
				  equal to the 10th percentile of the set of LRV filter values for the various
				  filters tested. The percentile is defined by (i/(n+1)) where i is the rank of n
				  individual data points ordered lowest to highest. If necessary, the 10th
				  percentile may be calculated using linear interpolation.
(j) If a previously tested filter is modified
				  in a manner that could change the removal efficiency of the filter product
				  line, challenge testing to demonstrate the removal efficiency of the modified
				  filter shall be conducted and submitted to the department.