Ala. Admin. Code r. 335-7-6-.23
Current through Register Vol. 42, No. 12, September 30, 2024
Section 335-7-6-.23 - Pre-Filtration Treatment Toolbox Components(1) Presedimentation. Systems receive 0.5-log Cryptosporidium treatment credit for a presedimentation basin during any month the process meets the following criteria: (a) The presedimentation basin must be in continuous operation and must treat the entire plant flow taken from a surface water or ground water under the direct influence of surface water source.(b) The system must continuously add a coagulant to the presedimentation basin.(c) The presedimentation basin must achieve the following performance criteria: 1. Demonstrate at least 0.5-log mean reduction in influent turbidity. This reduction must be determined using the daily average turbidity measurements taken every four hours in the presedimentation process influent and effluent and must be calculated as follows: log10 (monthly mean of daily influent turbidity) - log10 (monthly mean of daily effluent turbidity).2. Comply with Department-approved performance criteria that demonstrate at least 0.5-log mean removal of micron sized particulate material through the presedimentation process.(2) Two-stage lime softening. Systems receive 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 ground water under the direct influence of surface water source.(3) Bank filtration. Systems receive Cryptosporidium treatment credit for bank filtration that serves as pretreatment to a filtration plant by meeting the following criteria. Systems using bank filtration when they began source water monitoring under rule 335-7-2-.17 must collect samples as described and are not eligible for this credit. (a) Wells with a ground water flow path of at least 25 feet receive 0.5-log treatment credit; wells with a ground water flow path of at least 50 feet receive 1.0-log treatment credit. The ground water flow path must be determined as specified in subparagraph (3)(d) of this rule.(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 system must characterize 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 10 percent of the core material.(c) Only horizontal and vertical wells are eligible for treatment credit.(d) For vertical wells, the ground water 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 ground water flow path is the measured distance from the bed of the river under normal flow conditions to the closest horizontal well lateral screen.(e) Systems 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 system must 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 system implements corrective actions approved by the Department to remediate the problem.(f) Springs and infiltration galleries are not eligible for treatment credit under this section, but are eligible for credit under rule 335-7-6-.24.(g) Bank filtration demonstration of performance. The Department may approve Cryptosporidium treatment credit for bank filtration based on a demonstration of performance study that meets the following criteria. This treatment credit may be greater than 1.0-log and may be awarded to bank filtration that does not meet the criteria in subparagraphs (3)(a) - (e) of this rule. 1. The study must follow a Department-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.2. The study must include sampling both from the production well(s) and from monitoring wells that are screened and located along the shortest flow path between the surface water source and the production well(s).Ala. Admin. Code r. 335-7-6-.23
New Rule: Filed December 18, 2007; effective January 22, 2008.Author: Dennis D. Harrison
Statutory Authority:Code of Ala. 1975, §§ 22-23-33, 22-23-49, 22-22A-5, 22-22A-6.