40 CFR § 141.715
Microbial toolbox options for meeting Cryptosporidium treatment requirements
June 9, 2020
(a)
(1) Systems receive the treatment credits listed in the table in paragraph (b) of this section by meeting the conditions for microbial toolbox options described in §§141.716 through 141.720. Systems apply these treatment credits to meet the treatment requirements in §141.711 or §141.712, as applicable.
(2) Unfiltered systems are eligible for treatment credits for the microbial toolbox options described in §141.720 only.
(b) The following table summarizes options in the microbial toolbox:
Microbial Toolbox Summary Table: Options, Treatment Credits and Criteria
Open Table
| Toolbox Option | Cryptosporidium treatment credit with design and implementation criteria |
|---|---|
| Source Protection and Management Toolbox Options | |
| (1) Watershed control program | 0.5-log credit for State-approved program comprising required elements, annual program status report to State, and regular watershed survey. Unfiltered systems are not eligible for credit. Specific criteria are in §141.716(a). |
| (2) Alternative source/intake management | No prescribed credit. Systems may conduct simultaneous monitoring for treatment bin classification at alternative intake locations or under alternative intake management strategies. Specific criteria are in §141.716(b). |
| Pre Filtration Toolbox Options | |
| (3) Presedimentation basin with coagulation | 0.5-log credit during any month that presedimentation basins achieve a monthly mean reduction of 0.5-log or greater in turbidity or alternative State-approved performance criteria. To be eligible, basins must be operated continuously with coagulant addition and all plant flow must pass through basins. Specific criteria are in §141.717(a). |
| (4) Two-stage lime softening | 0.5-log credit for two-stage softening where chemical addition and hardness precipitation occur in both stages. All plant flow must pass through both stages. Single-stage softening is credited as equivalent to conventional treatment. Specific criteria are in §141.717(b). |
| (5) Bank filtration | 0.5-log credit for 25-foot setback; 1.0-log credit for 50-foot setback; aquifer must be unconsolidated sand containing at least 10 percent fines; average turbidity in wells must be less than 1 NTU. Systems using wells followed by filtration when conducting source water monitoring must sample the well to determine bin classification and are not eligible for additional credit. Specific criteria are in §141.717(c). |
| Treatment Performance Toolbox Options | |
| (6) Combined filter performance | 0.5-log credit for combined filter effluent turbidity less than or equal to 0.15 NTU in at least 95 percent of measurements each month. Specific criteria are in §141.718(a). |
| (7) Individual filter performance | 0.5-log credit (in addition to 0.5-log combined filter performance credit) if individual filter effluent turbidity is less than or equal to 0.15 NTU in at least 95 percent of samples each month in each filter and is never greater than 0.3 NTU in two consecutive measurements in any filter. Specific criteria are in §141.718(b). |
| (8) Demonstration of performance | Credit awarded to unit process or treatment train based on a demonstration to the State with a State- approved protocol. Specific criteria are in §141.718(c). |
| Additional Filtration Toolbox Options | |
| (9) Bag or cartridge filters (individual filters) | Up to 2-log credit based on the removal efficiency demonstrated during challenge testing with a 1.0-log factor of safety. Specific criteria are in §141.719(a). |
| (10) Bag or cartridge filters (in series) | Up to 2.5-log credit based on the removal efficiency demonstrated during challenge testing with a 0.5-log factor of safety. Specific criteria are in §141.719(a). |
| (11) Membrane filtration | Log credit equivalent to removal efficiency demonstrated in challenge test for device if supported by direct integrity testing. Specific criteria are in §141.719(b). |
| (12) Second stage filtration | 0.5-log credit for second separate granular media filtration stage if treatment train includes coagulation prior to first filter. Specific criteria are in §141.719(c) |
| (13) Slow sand filters | 2.5-log credit as a secondary filtration step; 3.0-log credit as a primary filtration process. No prior chlorination for either option. Specific criteria are in §141.719(d). |
| Inactivation Toolbox Options | |
| (14) Chlorine dioxide | Log credit based on measured CT in relation to CT table. Specific criteria in §141.720(b) |
| (15) Ozone | Log credit based on measured CT in relation to CT table. Specific criteria in §141.720(b). |
| (16) UV | Log credit based on validated UV dose in relation to UV dose table; reactor validation testing required to establish UV dose and associated operating conditions. Specific criteria in §141.720(d). |
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