Section 611.1017  Requirements for Microbial Toolbox Components:  Pre-Filtration Treatment Toolbox Components

a)         Presedimentation.  A supplier receives 0.5-log Cryptosporidium treatment credit for a presedimentation basin during any month the process meets the criteria in this subsection (a).

1)         The presedimentation basin must be in continuous operation and must treat the entire plant flow taken from a surface water or groundwater under the direct influent of surface water source.

2)         The supplier must continuously add a coagulant to the presedimentation basin.

3)         The presedimentation basin must achieve both of the following performance criteria:

A)        It demonstrates at least 0.5-log mean reduction of influent turbidity.  This reduction must be determined using daily turbidity measurements in the presedimentation process influent and effluent, and it must be calculated as follows:  log₁₀ (monthly mean of daily influent turbidity) - log₁₀ (monthly mean of daily effluent turbidity); and

B)        It complies with Agency-approved performance criteria that demonstrate at least 0.5-log mean removal of micronsized particulate material through the presedimentation process.

b)         Two-Stage Lime Softening.  A supplier receives an additional 0.5-log Cryptosporidium treatment credit for a two-stage lime softening plant if chemical addition and hardness precipitation occur in two separate and sequential softening stages prior to filtration.  Both softening stages must treat the entire plant flow taken from a surface water or groundwater under the direct influent of surface water source.

c)         Bank Filtration.  A supplier receives Cryptosporidium treatment credit for bank filtration that serves as pretreatment to a filtration plant by meeting the criteria in this subsection (c).  A supplier using bank filtration when it begins source water monitoring under Section 611.1001(a) must collect samples as described in Section 611.1003(d), and it is not eligible for this credit.

1)         A well with a groundwater flow path of at least 25 feet receives 0.5-log treatment credit, or a well with a groundwater flow path of at least 50 feet receives 1.0-log treatment credit.  The groundwater flow path must be determined as specified in subsection (c)(4).

2)         Only a well in granular aquifers is eligible for treatment credit.  A granular aquifer is one comprised of sand, clay, silt, rock fragments, pebbles or larger particles, and minor cement.  A supplier must characterize the aquifer at the well site to determine aquifer properties.  A supplier must extract a core from the aquifer and demonstrate that in at least 90 percent of the core length, grains less than 1.0 mm in diameter constitute at least ten percent of the core material.

3)         Only a horizontal or vertical well is eligible for treatment credit.

4)         For a vertical well, the groundwater flow path is the measured distance from the edge of the surface water body under high flow conditions (determined by the 100 year floodplain elevation boundary or by the floodway, as defined in Federal Emergency Management Agency flood hazard maps) to the well screen.  For a horizontal well, the groundwater flow path is the measured distance from the bed of the river under normal flow conditions to the closest horizontal well lateral screen.

5)         The supplier must monitor each wellhead for turbidity at least once every four hours while the bank filtration process is in operation.  If monthly average turbidity levels, based on daily maximum values in the well, exceed 1 NTU, the supplier must report this result to the Agency and conduct an assessment within 30 days to determine the cause of the high turbidity levels in the well.  If the Agency determines that microbial removal has been compromised, it may, by a SEP, revoke treatment credit until the supplier implements corrective actions approved by the Agency to remediate the problem.

6)         Springs and infiltration galleries are not eligible for treatment credit under this Section, but are eligible for credit under Section 611.1018(c).

7)         Bank Filtration Demonstration of Performance.  The Agency may, by a SEP, approve Cryptosporidium treatment credit for bank filtration based on a demonstration of performance study that meets the criteria in this subsection.  This treatment credit may be greater than 1.0-log and may be awarded to bank filtration that does not meet the criteria in subsections (c)(1) through (c)(5).

A)        The study must follow an Agency-approved protocol and must involve the collection of data on the removal of Cryptosporidium or a surrogate for Cryptosporidium and related hydrogeologic and water quality parameters during the full range of operating conditions.

B)        The study must include sampling both from the production wells and from monitoring wells that are screened and located along the shortest flow path between the surface water source and the production wells.

BOARD NOTE:  Derived from 40 CFR 141.717.

(Source:  Amended at 44 Ill. Reg. 6996, effective April 17, 2020)