Current through Register Vol. 48, No. 38, September 20, 2024
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.
