(1) The maximum contaminant level for turbidity, applicable only to public water systems which use water obtained in whole or in any part from surface water sources, shall be measured at representative entry point(s) to the distribution system, and shall be:

1. (a) One turbidity unit, (one NTU, Nephelometric turbidity unit) as determined by a monthly average rounded to the nearest significant whole number pursuant to 310 CMR 22.08(3) except that five or fewer turbidity units may be allowed if the supplier of water can demonstrate to the Department that the higher turbidity does not do any of the following:

   1. 1. Interfere with disinfection;
   2. 2. Prevent maintenance of an effective disinfectant agent throughout the distribution system; or
   3. 3. Interfere with microbiological determinations.
2. (b) Five turbidity units, as determined by the arithmetic mean of two consecutive daily samples pursuant to 310 CMR 22.08(3).

(2) All analyses shall be conducted in accordance with the following methods:

1. (a) Nephelometric Method 2130B, "Standard Methods for the Examination of Water and

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Wastewater", American Public Health Association, 14 Edition, pages 132-4, 18 , edition

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(1992), 19 edition (1995), or 20 edition (1998), American Public Health Association, 1015 Fifteenth Street, NW., Washington, DC 20005. The cited methods published in any of these three editions may be used. In addition, the following online versions may also be used: 2130 B-01, 9215 B-00, 9221 A, B, C, E-99, 9222A, B, C, D-97 and 9223 B-97. Standard Methods Online are available at http://www.standardmethods.org. The year in which each method was approved by the Standard Methods Committee is designated by the last two digits in the method number. The methods listed are the only Online versions that may be used; or (b) Nephelometric Method, Method 180.1, "Methods in the Determination of Inorganic Substances in Environmental Samples" EPA-600/R-93-100, August 1995, Available at NTISPB94-121811. (c) GLI Method 2, "Turbidity" November 2, 1992, Great Lakes Instrumentation, Inc., 8855

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North 55 Street, Milwalkee, Wisconsin (d) Hach FilterTrak Method 10133. A description of the Hach Filter Trak Method 10133, “Determination of Turbidity by Laser Nephelometry”, January 2000, Revision 2.0, can be obtained from; Hach Co., P.O. Box 389, Loveland, CO 80539-0389, telephone: 800-227- 4224. (e) Styrene divinyl benzene beads (e.g. AMCO-AEPA-1 or equivalent) and stabilized formazin (e.g. Hach StablCal™ or equivalent) are acceptable substitutes for formazin.

(3) In no event shall the frequency of sampling be less than as set forth in 310 CMR 22.08(3)(a) through (d):

1. (a) Community water systems subject to 310 CMR 22.08 shall commence sampling by not later than June 24, 1977 and shall take at least one sample per day thereafter. All samples shall be taken at representative entry point(s) to the distribution system.
2. (b) Non-community water systems subject to 310 CMR 22.08 shall commence sampling by not later than June 24, 1979 and shall take at least one sample per day thereafter. All samples shall be taken at representative entry point(s) to the distribution system.
3. (c) If the result of a turbidity analysis pursuant to 310 CMR 22.08(3)(a) and (b) indicates that the maximum contaminant level has been exceeded, the sampling and measurement shall be confirmed by resampling as soon as practicable and preferably within one hour. If the repeat sample confirms that the maximum contaminant level has been exceeded, the supplier of water shall report to the Department by the end of the next business day. The repeat sample shall be the sample used for calculating the monthly average pursuant to 310 CMR 22.08(3)(a) and (b). If the monthly average of the daily samples exceeds one turbidity unit, or if the average of two consecutive daily samples exceeds five turbidity units, the supplier of water shall notify the public pursuant to 310 CMR 22.16.
4. (d) If the Department determines that a reduced sampling frequency in a non-community system will not pose a risk to public health, it can reduce the required sampling frequency. The option of reducing the turbidity frequency shall be permitted only in those public water systems that practice disinfection and which maintain an active residual disinfectant in the distribution system, and in those cases where the Department has indicated in writing that no unreasonable risk to health existed under the circumstances of this option.