(2) The minimum number of samples to be collected from the distribution system and examined each month should be in accordance with the number on the graph in Figure I, for the population served by the system. For the purpose of uniformity and simplicity in application, the number determined from the graph should be in accordance with the following: For a population of 25,000 and under-to the nearest 1; 25,001 to 100,000—to the nearest 5; and over 100,000-to the nearest 10.

(3) In determining the number of samples examined monthly, the following samples may be included, provided all results are assembled and available for inspection and the laboratory methods and technical competence of the laboratory personnel are approved by the reporting agency and the certifying authority:

(i) Samples examined by the reporting agency.

(ii) Samples examined by local government laboratories.

(iii) Samples examined by the water works authority.

(iv) Samples examined by commercial laboratories.

(4) The laboratories in which these examinations are made and the methods used in making them shall be subject to inspection at any time by the designated representatives of the certifying authority and the reporting agency. Compliance with the specified procedures and the results obtained shall be used as a basis for certification of the supply.

(5) Daily samples collected following a bacteriological unsatisfactory sample as provided in paragraphs (b) (1), (2), and (3) of this section shall be considered as special samples and shall not be included in the total number of samples examined. Neither shall such special samples be used as a basis for prohibiting the supply: Provided, That (i) when waters of unknown quality are being examined, simultaneous tests are made on multiple portions of a geometric series to determine a definitive coliform content, (ii) immediate and active efforts are made to locate the cause of pollution, (iii) immediate action is taken to eliminate

the cause, and (iv) samples taken following such remedial action are satisfactory.

(b) Limits. The presence of organisms of the coliform group is indicated by samples examined shall not exceed the following limits:

(1) When 10 ml standard portions are examined, not more than 10 percent in any month shall show the presence of the coliform group. The presence of the coliform group in three or more 10 ml portions of a standard sample shall not be allowable if this occurs:

(i) In two consecutive samples;

(ii) In more than one sample per month when less than 20 are examined per month; or

(iii) In more than five percent of the samples when 20 or more are examined per month.

When organisms of the coliform group occur in three or more of the 10 ml portions of a single standard sample, daily samples from the same sampling point shall be collected promptly and examined until the results obtained from at least two consecutive samples show the water to be of satisfactory quality.

(2) When 100 ml standard portions are examined, not more than 60 percent in any month shall show the presence of the coliform group. The presence of the coliform group in all five of the 100 ml portions of a standard sample shall not be allowable if this occurs:

(i) In two consecutive samples;

(ii) In more than one sample per month when less than five are examined per month; or

(iii) In more than 20 percent of the samples when five or more are examined per month.

When organisms of the coliform group occur in all five of the 100 ml portions of a single standard sample, daily samples from the same sampling point shall be collected promptly and examined until the results obtained from at least two consecutive samples show the water to be of satisfactory quality.

(3) When the membrane filter technique is used, the arithmetic mean coliform density of all standard samples examined per month shall not

exceed one per 100 ml. Coliform colonies per standard sample shall not exceed %0 ml, 100 ml, 200 ml, or 100 ml in:

(i) Two consecutive samples;

(ii) More than one standard sample when less than 20 are examined per month; or

(iii) More than five percent of the standard samples when 20 or more are examined per month.

When coliform colonies in a single standard sample exceed the above values, daily samples from the same sampling point shall be collected promptly and examined until the results obtained from at least two consecutive samples show the water to be of satisfactory quality.

§ 72.204 Physical characteristics.

(a) Sampling. The frequency and manner of sampling shall be determined by the reporting agency and the certifying authority. Under normal circumstances samples should be collected one or more times per week from representative points in the distribution system and examined for turbidity, color, threshold odor, and taste.

(b) Limits. Drinking water should contain no impurity which would cause offense to the sense of sight, taste, or smell. Under general use, the following limits should not be exceeded:

Turbidity-5 units.

Color-15 units.

Threshold odor number-3.

§ 72.205 Chemical characteristics.

(a) Sampling. (1) The frequency and manner of sampling shall be determined by the reporting agency and the certifying authority. Under normal circumstances, analyses for substances listed below need be made only semiannually. If, however, there is some presumption of unfitness because of the presence of undesirable elements, compounds, or materials, periodic determinations for the suspected toxicant or material should be made more frequently and an exhaustive sanitary survey should be made to determine the source of the pollution. Where the concentration of a sub

stance is not expected to increase in processing and distribution, available and acceptable source water analyses performed in accordance with standard methods may be used as evidence of compliance with these Standards.

(2) Where experience, examination, and available evidence indicate that particular substances are consistently absent from a water supply or below levels of concern, semi-annual examinations for those substances may be omitted when approved by the reporting agency and the certifying authority.

(3) The burden of analysis may be reduced in many cases by using data from acceptable sources. Judgment concerning the quality of water supply and the need for performing specific local analyses may depend in part on information produced by such agencies as (i) the U.S. Geological Survey, which determines chemical quality of surface and ground waters of the United States and publishes these data in "Water Supply Papers" and other reports, and (ii) the U.S. Public Health Service which determines water quality related to pollution (or the absence of pollution) in the principal rivers of the Nation and publishes these data annually in "National Water Quality Network." Data on pollution of waters as measured by

carbon chloroform extracts (CCE) may be found in the latter publication. (b) Limits. Drinking water shall not contain impurities in concentrations which may be hazardous to the health of the consumers. It should not be excessively corrosive to the water supply system. Substances used in its treatment shall not remain in the water in concentrations greater than required by good practice. Substances which may have deleterious physiological effect, or for which physiological effects are not known, shall not be introduced into the system in a manner which would permit them to reach the consumer.

(1) The following chemical substances should not be present in a water supply in excess of the listed concentrations where, in the judgment of the reporting agency and the certi

Based on temperature data obtained for a minimum of five years.

(iii) In addition to the sampling required by paragraph (a) of this section, fluoridated and defluoridated supplies shall be sampled with sufficient frequency to determine that the desired fluoride concentration is maintained.

§ 72.206 Radioactivity.

(a) Sampling. (1) The frequency of sampling and analysis for radioactivity shall be determined by the reporting agency and the certifying authority after consideration of the likelihood of significant amounts being present. Where concentrations of Ra-226 or Sr-90 may vary considerably, quarterly samples composited over a period of three months are recommended. Samples for determination of gross activity should be taken and analyzed more frequently.

(2) As indicated in § 72.205(a), data from acceptable sources may be used to indicate compliance with these requirements.

(b) Limits. (1) The effects of human radiation exposure are viewed as harmful and any unnecessary exposure to ionizing radiation should be avoided. Approval of water supplies containing radioactive materials shall be based upon the judgment that the radioactivity intake from such water supplies when added to that from all other sources is not likely to result in an intake greater than the radiation protection guidance 1 recommended by

'The Federal Radiation Council, in its Memorandum for the President, September 13, 1961, recommended that "Routine control of useful applications of radiation and Footnotes continued on next page

the Federal Radiation Council and approved by the President. Water supplies shall be approved without further consideration of other sources of radioactivity intake of Radium-226 and Strontium-90 when the water contains these substances in amounts not exceeding 3 and 10 μμc/liter, respectively. When these concentrations are exceeded, a water supply shall be approved by the certifying authority if surveillance of total intakes of radioactivity from all sources indicates that such intakes are within the limits recommended by the Federal Radiation Council for control action.

(2) In the known absence of Strontium-90 and alpha emitters, the water supply is acceptable when the gross beta concentrations do not exceed 1,000 μμc/liter. Gross beta concentrations in excess of 1,000 μμc/liter shall be grounds for rejection of supply except when more complete analyses indicate that concentrations of nuclides are not likely to cause exposures greater than the Radiation Protection Guides as approved by the President on recommendation of the Federal Radiation Council.

§ 72.207 Recommended analytical methods.

(a) Analytical methods to determine compliance with the requirements of these Standards shall be those specified in Standard Methods for the Examination of Water and Wastewater, Am. Pub. Health Assoc., current edition and those specified as follows:

(1) Barium: Methods for the Collection and Analyses of Water Samples, Water Supply Paper No. 1454, Rainwater, F. H. & Thatcher, L. L., U.S. Geological Survey, Washington, D.C.

(2) Carbon Chloroform Extract (CCE): Manual for Recovery and Iden

Footnotes continued from last page

atomic energy should be such that expected average exposures of suitable samples of an exposed population group will not exceed the upper value of Range II (20 μμс/day of Radium-226 and 200 μμc/day of Strontium90)."

'Absence is taken here to mean a negligibly small fraction of the above specific limits, where the limit for unidentified alpha emitters is taken as the listed limit for Radium-226.

tification of Organic Chemicals in Water, Middletown, F. M., Rosen, A. A., and Burttschell, R. H., Robert A. Taft Sanitary Engineering Center, PHS, Cincinnati, Ohio.

Radioactivity:

Laboratory

(3) Manual of Methodology, Radionuclide Analyses of Environmental Samples, Technical Report R59-6. Robert A. Taft Sanitary Engineering Center, PHS, Cincinnati, Ohio, and Methods of Radiochemical Analysis, Technical Report No. 173, Report of the Joint WHO-FAO Committee, 1959, World Health Organization.

(4) Selenium: Suggested Modified Method for Colorimetric Determination of Selenium in Natural Water, Magin, G. B., Thatcher, L. L., Rettig, S., and Levine, H., J. Am. Water Works Assoc. 52, 1199 (1960).

(b) Organisms of the coliform group. All of the details of techniques in the determination of bacteria of this group, including the selection and preparation of apparatus and media, the collection and handling of samples and the intervals and conditions of storage allowable between collection and examination of the water sample, shall be in accordance with Standard Methods for the Examination of Water and Wastewater, current edition, and the procedures shall be those specified therein for:

(1) The Membrane Filter Technique, Standard Test, or

(2) The Completed Test, or

(3) The Confirmed Test, procedure with brilliant green lactose bile broth, 3 (4) The Confirmed Test, procedure with Endo or eosin methylene blue agar plates. '

4

"The Confirmed Test is allowed, provided the value of this test to determine the sanitary quality of the specific water supply being examined is established beyond reasonable doubt by comparisons with Completed Tests performed on the same water supply. or

"The Federal Radiation Council, in its Memorandum for the President, September 13, 1961, recommended that "Routine control of useful applications of radiation and atomic energy should be such that expected average exposures of suitable samples of an exposed population group will not exceed the upper value of Range II (20 μμс/day of Radium-226 and 200 μμc/day of Strontium90)."