Maximum Turbidity Levels and Monitoring Requirements and Filter Backwash Recycling

PURPOSE: This rule establishes maximum contaminant levels and monitoring requirements for turbidity. (1) Applicability. This rule applies to all public water systems that use surface water or ground-water under the direct influence of surface water. (2) Enhanced Turbidity Requirements. (A) Maximum Turbidity Levels. 1. Turbidity must be equal to or less than 0.3 turbidity units in at least ninety-five percent (95%) of the measurements taken each month; and 2. There must be no more than one (1) turbidity unit in any one (1) measurement. (B) The frequency of sampling shall be as set forth in 10 CSR 60-4.080(3). (C) Reporting to the Department. 1. If at any time the turbidity exceeds one (1) nephelometric turbidity unit (NTU) in representative samples of filtered water in a system using conventional filtration treatment or direct filtration, the system must inform the department as soon as possible, but no later than the end of the next business day. 2. If at any time the turbidity in representative samples of filtered water exceeds the maximum level set by the department under subsection (2)(F) of this rule for filtration technologies other than conventional filtration treatment, the system must inform the department as soon as possible, but no later than the end of the next business day. (D) Filtration Sampling Requirements for Surface Water Systems 1. A public water system using surface water or groundwater under the direct influence of surface water that provides conventional filtration treatment must conduct continuous monitoring of turbidity for each individual filter using an approved method in 10 CSR 60-5.010 and must calibrate turbidimeters using the procedure specified by the manufacturer. Systems must record the results of individual filter monitoring every fifteen (15) minutes. 2. If there is a failure in the continuous turbidity monitoring equipment, the system must conduct grab sampling every four (4) hours in lieu of continuous monitoring, until the turbidimeter is repaired and back on-line. A system has a maximum of five (5) working days after failure in the continuous monitoring equipment to repair the equipment before the system is in violation. With department approval, systems serving less than ten thousand (10,000) people may be granted up to fourteen (14) days to repair the equipment before the system is in violation. (E) Lime Softening. 1. A system that uses lime softening may acidify representative samples prior to analysis using a protocol approved by the department. 2. Systems that use lime softening may apply to the department for alternative exceedance levels for the levels specified in 10 CSR 60-7.010(6)(B) if they can demonstrate that higher turbidity levels in individual filters are due to lime carryover only and not due to degraded filter performance. (F) Filtration Technologies Other Than Conventional Filtration Treatment. 1. A public water system may use a filtration technology other than conventional filtration if it demonstrates to the department, using pilot plant studies or other means, that the alternative filtration technology, including direct filtration, in combination with disinfection treatment that meets the requirements of 10 CSR 60-4.055, consistently achieves 99.9 percent removal and/or inactivation of Giardia lamblia cysts and 99.99 percent removal and/or inactivation of viruses, and ninety-nine percent (99%) removal of Cryptosporidium oocysts, and the department approves the use of the filtration technology. 2. For each approval, the department will set turbidity performance requirements that the system must meet at least ninety-five percent (95%) of the time and that the system may not exceed at any time at a level that consistently achieves 99.9 percent removal and/or inactivation of Giardia lamblia cysts, 99.99 percent removal or inactivation of viruses, or both, and 99 percent removal of Cryptosporidium oocysts. (3) Filter Backwash Recycling. (A) Applicability. Any water treatment plant proposed for construction or major modification for a surface water or groundwater under the direct influence of surface water or direct filtration treatment and that will recycle spent filter backwash water, thickener supernatant, or liquids from dewatering processes must be designed to meet the filter backwash recycling requirements of this section. (B) Reporting. A system must notify the department in writing if the system recycles spent filter backwash water, thickener supernatant, or liquids from dewatering processes. This notification must include, at a minimum, the following information: 1. A plant schematic showing the origin of all flows which are recycled (including, but not limited to, spent filter backwash water, thickener supernatant, and liquids from dewatering processes), the hydraulic conveyance used to transport them, and the location where they are reintroduced back into the treatment plant; and 2. Typical recycle flow in gallons per minute (gpm), the highest observed plant flow experienced in the previous year (gpm), design flow for the treatment plant (gpm), and department-approved operating capacity for the plant where the department has made such determinations. (C) Treatment Technique Requirement. Any system that recycles spent filter backwash water, thickener supernatant, or liquids from dewatering processes must return these flows through the processes of a system’s existing conventional or direct filtration system or at an alternate location approved by the department. (D) Record Keeping. The system must collect and retain on file recycle flow information for review and evaluation by the department. This information shall include, but may not be limited to: 1. A copy of the recycle notification and information submitted to the department under subsection (3)(B) of this rule; 2. A list of all recycle flows and the frequency with which they are returned; 3. Average and maximum backwash flow rate through the filters and the average and maximum duration of the filter backwash process in minutes; 4. Typical filter run length and a written summary of how filter run length is determined; 5. The type of treatment provided for the recycle flow; and 6. Data on the physical dimensions of the equalization and/or treatment units, typical and maximum hydraulic loading rates, type of treatment chemicals used and average dose and frequency of use, and frequency at which solids are removed, if applicable. AUTHORITY: section 640.100, RSMo 2016.* Original rule filed May 4, 1979, effective Sept. 14, 1979. Amended: Filed April 14, 1981, effective Oct. 11, 1981. Amended: Filed July 12, 1991, effective Feb. 6, 1992. Amended: Filed Feb. 1, 1996, effective Oct. 30, 1996. Amended: Filed Dec. 15, 1999, effective Sept. 1, 2000. Amended: Filed Jan. 16, 2002, effective Nov. 30, 2002. Amended: Filed March 17, 2003, effective Nov. 30, 2003. Amended: Filed June 13, 2018, effective Feb. 28, 2019. *Original authority: 640.100, RSMo 1939, amended 1978, 1981, 1982, 1988, 1989, 1992, 1993, 1995, 1996, 1998, 1999, 2002, 2006, 2012, 2014.