Nebraska Administrative Code › Topic - HEALTH AND HUMAN SERVICES SYSTEM › Title 179 - PUBLIC WATER SYSTEMS › Chapter 25 - LONG TERM 2 (LT2) ENHANCED SURFACE WATER TREATMENT › Section 179-25-021 - ADDITIONAL FILTRATION TOOLBOX COMPONENTS

Current through June 17, 2024
021.01 Bag and
				Cartridge Filters
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
				  following criteria. To be eligible for this credit, systems must report the
				  results of challenge testing that meets the requirements of 179 NAC 25-021.01
				  items 2 through 9 to the Department. The filters must treat the entire plant
				  flow taken from a surface water or ground water under the direct influence of
				  surface water source.
1. The
Cryptosporidium
treatment credit awarded to bag or cartridge
				filters must be based on the removal efficiency demonstrated during challenge
				testing that is conducted according to the criteria in 179 NAC 25-021.01 items
				2 through 9. 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 must 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 179 NAC 25-021.01 items 2 through
				9.
2. Challenge testing must 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 must be challenge
				tested in the same configuration that the system will use, either as individual
				filters or as a series configuration of filters.
3. Challenge testing must 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 must 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.
4. The maximum feed water
				concentration that can be used during a challenge test must be based on the
				detection limit of the challenge particulate in the filtrate (i.e., filtrate
				detection limit) and must be calculated using the following equation:
Maximum Feed Concentration = 1 x
				  104 x (Filtrate Detection Limit)
5. Challenge testing must be conducted at the
				maximum design flow rate for the filter as specified by the
				manufacturer.
6. Each filter
				evaluated must 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.
7. Removal efficiency of a
				filter must 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
				  must be used for the feed and filtrate concentrations. If the challenge
				  particulate is not detected in the filtrate, then the term
				  Cp must be set equal to the detection limit.
8. Each filter tested must be
				challenged with the challenge particulate during three periods over the
				filtration cycle: within two 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 must be calculated for each of these challenge periods
				for each filter tested. The LRV for the filter
				(LRVfilter) must be assigned the value of the minimum
				LRV observed during the three challenge periods for that filter.
9. If fewer than 20 filters are tested, the
				overall removal efficiency for the filter product line must be set equal to the
				lowest LRVfilter among the filters tested. If 20 or more
				filters are tested, the overall removal efficiency for the filter product line
				must be set equal to the 10th percentile of the set
				of LRVfilter values for the various filters tested. The
				percentile is defined by [i/(n+1)] where i is the rank of n individiual data
				points ordered lowest to highest. If necessary, the
				10th percentile may be calculated using linear
				interpolation.
10. 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 must be conducted and submitted to the
				Department.