Section R. 325.10611j - Enhanced treatment for Cryptosporidium; microbial toolbox; pre-filtration treatment toolbox componentsRule 611j.
(1) Presedimentation is a pre-filtration treatment toolbox component. Subpart H supplies that are subject to R 325.10611d receive 0.5-log Cryptosporidium treatment credit for a presedimentation basin during any month the process meets all of the following criteria:(a) The presedimentation basin shall be in continuous operation and shall treat the entire plant flow taken from a surface water or GWUDI source.(b) The subpart H supply shall continuously add a coagulant to the presedimentation basin.(c) The presedimentation basin shall achieve either of the following performance criteria: (i) Demonstrates not less than 0.5-log mean reduction of influent turbidity. This reduction shall be determined using daily turbidity measurements in the presedimentation process influent and effluent and shall be calculated as follows:log10 (monthly mean of daily influent turbidity) - log10 (monthly mean of daily effluent turbidity).(ii) Complies with department-approved performance criteria that demonstrate not less than 0.5-log mean removal of micron-sized particulate material through the presedimentation process.(2) Two-stage lime softening is a pre-filtration treatment toolbox component. Subpart H supplies receive an additional 0.5-log Cryptosporidium treatment credit for a 2-stage lime softening plant if chemical addition and hardness precipitation occur in 2 separate and sequential softening stages before filtration. Both softening stages shall treat the entire plant flow taken from a surface water or GWUDI source.(3) Bank filtration is a pre-filtration treatment toolbox component.Subpart H supplies using bank filtration when they begin source water monitoring under 40 CFR §141.701 (a) shall collect samples as described in 40 CFR §141.703 (d) and are not eligible for this credit. The department adopts 40 CFR §141.701 and 40 CFR §141.703 by reference in R 325.10720b.Subpart H supplies receive Cryptosporidium treatment credit for bank filtration that serves as pretreatment to a filtration plant by meeting all of the following criteria: (a) Wells with a groundwater flow path of not less than 25 feet receive 0.5-log treatment credit; wells with a groundwater flow path of not less than 50 feet receive 1.0-log treatment credit. The groundwater flow path shall be determined as specified in subdivision (d) of this subrule.(b) Only wells in granular aquifers are eligible for treatment credit.Granular aquifers are those comprised of sand, clay, silt, rock fragments, pebbles or larger particles, and minor cement. A subpart H supply shall characterize the aquifer at the well site to determine aquifer properties. Subpart H supplies shall extract a core from the aquifer and demonstrate that in not less than 90% of the core length, grains less than 1.0 mm in diameter constitute not less than 10% of the core material.(c) Only horizontal and vertical wells are eligible for treatment credit.(d) For vertical wells, 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 horizontal wells, 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.(e) Subpart H supplies shall monitor each wellhead for turbidity at least once every 4 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 subpart H supply shall report this result to the department and conduct an assessment within 30 days to determine the cause of the high turbidity levels in the well. If the department determines that microbial removal has been compromised, the department may revoke treatment credit until the subpart H supply implements corrective actions approved by the department to remediate the problem.(f) Springs and infiltration galleries are not eligible for treatment credit under this rule, but are eligible for credit under R 325.10611k (3).(g) The department may approve Cryptosporidium treatment credit for bank filtration based on a demonstration of performance study. This treatment credit may be greater than 1.0-log and may be awarded to bank filtration that does not meet the criteria in subdivisions (a) to (e) of this subrule. The bank filtration demonstration of performance study shall meet both of the following criteria:
(i) The study shall follow a department-approved protocol and shall 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.(ii) The study shall include sampling both from the production well or wells and from monitoring wells that are screened and located along the shortest flow path between the surface water source and the production well or wells.Mich. Admin. Code R. 325.10611j