Wisconsin Administrative Code
Department of Natural Resources
NR 800 - Environmental Protection - Water Supply
Chapter NR 809 - Safe Drinking Water
Subchapter I - Maximum Contaminant Levels, Monitoring and Analytical Requirements for Primary Drinking Water Contaminants
Section NR 809.31 - Distribution system microbiological contaminant monitoring requirements

Universal Citation: WI Admin Code ยง NR 809.31

Current through August 26, 2024

(1) ROUTINE AND REDUCED MONITORING.

(a) Monitoring site plans. Water suppliers for all public water systems shall collect total coliform samples at sites which are representative of water throughout the distribution system according to a written sample siting plan. These plans are subject to department review and revision. Monitoring required by this section and s. NR 809.32 may take place at a customer's premise, dedicated sampling station, or other designated compliance sampling location. Routine and repeat sample sites and any sampling points necessary to meet the requirements of s. NR 809.325 shall be identified in the sampling plan.

(ag) Action after total coliform positive sample. Following any total coliform-positive sample taken under the provisions of this section, water suppliers shall comply with the repeat monitoring requirements and E. coli analytical requirements in subs. (2) and (4).

(ar) Transition from total coliform rule to revised total coliform rule.
1. Water suppliers of public water systems, including seasonal systems, shall continue to monitor according to the total coliform monitoring schedules that were in effect on March 31, 2016, unless any of the conditions for increased monitoring in sub. (2m) are triggered on or after April 1, 2016, or unless otherwise directed by the department.

2. Beginning April 1, 2016, the department shall perform a special monitoring evaluation during each sanitary survey to review the status of each public water system, including the distribution system, to determine whether the public water system is on an appropriate monitoring schedule. After the department has performed the special monitoring evaluation during each sanitary survey, the department may modify the public water system's monitoring schedule, as necessary, or it may allow the public water system to stay on its existing monitoring schedule, consistent with the provisions of this section. The department may not allow public water systems to begin less frequent monitoring under the special monitoring evaluation unless the public water system has already met the applicable criteria for less frequent monitoring in this section. For seasonal systems on quarterly or annual monitoring, this evaluation shall include review of the approved sample siting plan, which shall designate the time period(s) for monitoring based on site-specific considerations (e.g., during periods of highest demand or highest vulnerability to contamination). The water supplier of the seasonal system shall collect compliance samples during these time periods.

(b) Monitoring frequency at community water systems. Water suppliers for community water systems shall take water samples for coliform determination at regular intervals, and in a number proportionate to the population served by the community water system. Water suppliers required to collect multiple samples each month shall sample at geographically representative locations and on dates evenly spaced during the month. The minimum sampling frequency shall be as set forth in the following table:

Population served:

Minimum number of samples per month

25 to 1,000 (Not serving a municipality)

1

25 to 1,000 (Serving a municipality)

2

1,001 to 2,500

2

2,501 to 3,300

3

3,301 to 4,100

4

4,101 to 4,900

5

4,901 to 5,800

6

5,801 to 6,700

7

6,701 to 7,600

8

7,601 to 8,500

9

8,501 to 12,900

10

12,901 to 17,200

15

17,201 to 21,500

20

21,501 to 25,000

25

25,001 to 33,000

30

33,001 to 41,000

40

41,001 to 50,000

50

50,001 to 59,000

60

59,001 to 70,000

70

70,001 to 83,000

80

83,001 to 96,000

90

96,001 to 130,000

100

130,001 to 220,000

120

220,001 to 320,000

150

320,001 to 450,000

180

450,001 to 600,000

210

600,001 to 780,000

240

780,001 to 970,000

270

970,001 to 1,230,000

300

1,230,001 to 1,520,000

330

1,520,001 to 1,850,000

360

1,850,001 to 2,270,000

390

2,270,001 to 3,020,000

420

3,020,001 to 3,960,000

450

3,960,001 or more

480

(c) Monitoring frequency for coliforms at non-community water systems. The monitoring frequency for total coliforms for non-community water systems, notwithstanding pars. (dg) and (dr), is as follows:
1. A water supplier for a non-community water system using only groundwater and serving 1,000 persons per day or fewer shall monitor each calendar quarter that the non-community water system provides water to the public.

2. A water supplier for a non-community water system using only groundwater and serving on average more than 1,000 persons per day for any month shall monitor at the same frequency as a like-sized community water system, as specified in par. (b), except that the department may reduce the monitoring frequency, in writing, for any month the average daily population served is 1,000 persons or fewer per day.

3. A water supplier for a non-community water system using surface water, or groundwater under the direct influence of surface water as defined in s. NR 809.04 (40), in total or in part, shall monitor at the same frequency as a like-sized municipal community water system, as specified in par. (b). GWUDI public water systems shall begin monitoring at this frequency beginning 6 months after the department determines that the groundwater source is under the direct influence of surface water.

4. The water supplier for a transient non-community water system serving a school shall sample for coliform bacteria in each calendar quarter during which the public water system provides water to the public, unless the department, on the basis of sub. (2m), determines that more frequent monitoring is appropriate. Transient non-community systems serving schools are not eligible for reduced monitoring under par. (dg) of this section.

(de) Annual site visits. Beginning no later than calendar year 2017, transient non-community systems on annual monitoring, including seasonal systems, shall have an initial and recurring annual site visit by the department that is equivalent to a Level 2 assessment or an annual voluntary Level 2 assessment that meets the criteria in s. NR 809.313 (2) to remain on annual monitoring. The periodic required sanitary survey may be used to meet the requirement for an annual site visit for the year in which the sanitary survey was completed. Transient non-community systems with little-to-no distribution system may, at the discretion of the department, be exempt from the annual site visit requirements in this section, and still remain on annual monitoring.

(dg) Criteria for annual monitoring at transient non-community systems. Beginning April 1, 2016, the department may reduce the monitoring frequency for a well-operated transient non-community ground water system serving 1,000 persons per day or fewer from quarterly routine monitoring to no less than annual monitoring, if the transient non-community system demonstrates that it meets the criteria for reduced monitoring in subds.
1. to 4., except for a transient non-community system that has been on increased monitoring under the provisions of sub. (2m). A transient non-community system on increased monitoring under sub. (2m) shall meet the provisions of sub. (2m) (b) to go to quarterly monitoring and shall meet the provisions of sub. (2m) (c) to go to annual monitoring.

1. The transient non-community system has a clean compliance history for a minimum of 12 months.

2. The most recent sanitary survey shows that the transient non-community system is free of sanitary defects or has corrected all identified sanitary defects, has a protected water source, and meets approved construction standards.

3. The department has conducted an annual site visit within the last 12 months and the water supplier has corrected all identified sanitary defects. A Level 2 assessment that meets the criteria in s. NR 809.313 (2) may be substituted for the department annual site visit.

4. The public water system is not a school.

(dr) Seasonal system requirements.
1. Beginning April 1, 2016, all water suppliers of seasonal systems shall demonstrate completion of a department-approved start-up procedure, which may include a requirement for start-up sampling prior to serving water to the public.

2. Seasonal systems shall be monitored every month that they are in operation unless they meet the criteria in subd. 2. a. to c. to be eligible for monitoring less frequently than monthly beginning April 1, 2016, except as provided under par. (ar).
a. Seasonal systems that are monitored less frequently than monthly shall have an approved sample siting plan that designates the time period for monitoring based on site-specific considerations (e.g., during periods of highest demand or highest vulnerability to contamination). Water suppliers of seasonal systems shall collect compliance samples during this time period.

b. To be eligible for quarterly monitoring, seasonal systems shall meet the criteria in sub. (2m) (b).

c. To be eligible for annual monitoring, seasonal systems shall meet the criteria under sub. (2m) (c).

3. The department may exempt any seasonal system from some or all of the requirements for seasonal systems if the entire distribution system remains pressurized during the entire period that the seasonal system is not operating, except that seasonal systems that are monitored less frequently than monthly shall be monitored during the vulnerable period as designated by the department.

(e) Sample collection time intervals. Water suppliers for public water systems shall collect samples at regular time intervals throughout the month, except that for public water systems which use only groundwater and serve 4,900 persons or fewer, may collect all required samples on a single day if the samples are taken from different sites.

(eg) Minimum required number of samples after MCL violation or treatment technique trigger. Water suppliers shall take at least the minimum number of required samples even if the public water system has had an E. coli MCL violation or has exceeded the coliform treatment technique triggers in s. NR 809.313.

(er) Sampling in excess of requirements. Water suppliers may conduct more compliance monitoring than is required by this section to investigate potential problems in the distribution system and use monitoring as a tool to assist in uncovering problems. Water suppliers may take more than the minimum number of required routine samples and shall include the results in calculating whether the coliform treatment technique trigger in s. NR 809.313 has been exceeded only if the samples are taken in accordance with the existing sample siting plan and are representative of water throughout the distribution system.

(f) Special purpose samples. Special purpose samples such as those taken to determine whether disinfection practices are sufficient following pipe placement, replacement or repair, may not be used to determine whether the coliform treatment technique trigger has been exceeded. Repeat samples taken pursuant to sub. (2) are not considered special purpose samples, and shall be used to determine whether the coliform treatment technique trigger has been exceeded.

(g) Analyses required after turbidity exceedances at selected systems. A water supplier for a public water system that uses surface water or groundwater under the direct influence of surface water as defined in s. NR 809.04 (40), and does not provide filtration in compliance with s. NR 810.29, shall collect at least one sample in the distribution system near the first service connection each day one or more turbidity measurements of the source water obtained as specified in s. NR 810.38 (1) (c), exceeds 1 NTU. This sample shall be analyzed for the presence of total coliforms. The water supplier shall collect this coliform sample within 24 hours of the first exceedance unless the department determines that the water supplier, for logistical reasons beyond their control, cannot have the sample analyzed within 30 hours of collection. Results from this coliform monitoring shall be used to determine whether the coliform treatment technique trigger has been exceeded in s. NR 809.313.

(2) REPEAT MONITORING.

(a) If a routine sample is total coliform-positive, the water supplier for a public water system shall collect a set of repeat samples within 24 hours of being notified of the positive result. The water supplier shall collect no fewer than 3 repeat samples for each total coliform-positive sample found. The department may extend the 24-hour limit on a case-by-case basis if the water supplier has a logistical problem that is beyond its control in collecting the repeat samples within 24 hours. In the case of an extension, the department shall specify how much time the water supplier has to collect repeat samples. The department may not waive the requirement for a water supplier to collect repeat samples in this paragraph or pars. (b) to (c).

(b) Unless the provisions of subds. 1. and 2. are met, the water supplier shall collect at least one repeat sample from the sampling tap where the original total coliform-positive sample was taken, and at least one repeat sample at a tap within 5 service connections upstream and at least one repeat sample at a tap within five service connections downstream of the original sampling site. If a total coliform-positive sample is at the end of the distribution system, or one service connection away from the end of the distribution system, the water supplier shall take all required repeat samples. However, the department may allow an alternative sampling location in lieu of the requirement to collect at least one repeat sample upstream or downstream of the original sampling site. Except as provided in subd. 2., public water systems required to conduct triggered source water monitoring under s. NR 809.325 shall take ground water source samples in addition to repeat samples required under this paragraph.
1. A water supplier may propose repeat monitoring locations to the department that the water supplier believes to be representative of a pathway for contamination of the distribution system. A water supplier may elect to specify either alternative fixed locations or criteria for selecting repeat sampling sites on a situational basis in a standard operating procedure (SOP) in its sample siting plan. The water supplier shall design its SOP to focus the repeat samples at locations that best verify and determine the extent of potential contamination of the distribution system area based on specific situations. The department may modify the SOP or require alternative monitoring locations as needed.

2. A water supplier of a ground water system serving 1,000 or fewer people may propose repeat sampling locations to the department that differentiate potential source water and distribution system contamination (e.g., by sampling at entry points to the distribution system). A water supplier of a ground water system with a single well required to conduct triggered source water monitoring may, with written department approval, take one of the repeat samples at the monitoring location required for triggered source water monitoring under s. NR 809.325 if the water supplier demonstrates to the department's satisfaction that the sample siting plan remains representative of water quality in the distribution system. If approved by the department, the water supplier may use that dual purpose sample result to meet the monitoring requirements in both s. NR 809.325 and this section.
a. If a dual purpose repeat sample taken at the monitoring location required for triggered source water monitoring is E. coli-positive, the public water system has violated the E. coli MCL and shall also comply with s. NR 809.325 (2) (e). If a water supplier takes more than one repeat sample at the monitoring location required for triggered source water monitoring, the water supplier may reduce the number of additional source water samples required under s. NR 809.325 (2) (e) by the number of repeat samples taken at that location that were not E. coli-positive.

b. If a water supplier takes more than one repeat sample at the monitoring location required for triggered source water monitoring under s. NR 809.325 (2). and more than one repeat sample is E. coli-positive, the public water system has violated the E. coli MCL and shall comply with s. NR 809.327.

c. If all repeat samples taken at the monitoring location required for triggered source water monitoring are E. coli-negative and a repeat sample taken at a monitoring location other than the one required for triggered source water monitoring is E. coli-positive, the public water system has violated the E. coli MCL, but is not required to comply with s. NR 809.325 (2) (e).

3. The department may review, revise, and approve, as appropriate, repeat sampling proposed by water suppliers under subds. 1. and 2. The water supplier shall demonstrate that the sample siting plan remains representative of the water quality in the distribution system. The department may determine that monitoring at the entry point to the distribution system, especially at ground water systems without disinfection is effective to differentiate between potential source water and distribution system problems.

(c) Water suppliers at ground water systems may use a repeat sample, taken at the source or all of the sources serving the location of each routine positive sample, to meet the requirements of both this paragraph and s. NR 809.325 (2) (d). In cases where more than one source serves the location of the routine positive sample or samples, repeat samples shall be taken from each of the sources to satisfy the requirements of this paragraph and s. NR 809.325 (2) (d).

(d) The water supplier shall collect all repeat samples on the same day, except that the department may allow a water supplier for a public water system with a single service connection to collect the required set of repeat samples over a 3-day period or to collect a larger volume repeat sample in one or more sample containers of any size, as long as the total volume collected is at least 300 mL.

(e) If one or more repeat samples in the set is total coliform-positive, the water supplier shall collect an additional set of repeat samples in the manner specified in pars. (a) to (d). The additional set of samples shall be collected within 24 hours after the water supplier is notified of the positive result, unless the department extends the limit as provided in par. (a). The water supplier shall repeat this process until either total coliforms are not detected in one complete set of repeat samples or the water supplier determines that the coliform treatment technique trigger specified in s. NR 809.313 has been exceeded and the water supplier notifies the department as specified in s. NR 809.80 (2). If a trigger identified in s. NR 809.313 is exceeded as a result of a routine sample being total coliform-positive, water suppliers are required to conduct only one round of repeat monitoring for each total coliform-positive routine sample.

(f) Water suppliers collecting samples on a quarterly or annual frequency shall conduct additional routine monitoring the month following one or more total coliform-positive samples regardless of whether the positive samples resulted in a Level 1 treatment technique trigger. Water suppliers shall collect at least three routine samples during the next month, after consultation with the department, except that the department may waive this requirement if the conditions of subd. 1., 2., or 3. are met. Water suppliers may either collect samples at regular time intervals throughout the month or may collect all required routine samples on a single day if samples are taken from different sites. Water suppliers shall use the results of additional routine samples in coliform treatment technique trigger calculations under s. NR 809.313 (1).
1. The department may waive the requirement to collect 3 routine samples during the next month the public water system provides water to the public if the department performs a site visit before the end of the next month the public water system provides water to the public. Although a sanitary survey need not be performed, the site visit shall be sufficiently detailed to allow the department to determine whether additional monitoring or any corrective action is needed. The department may not approve an employee of the public water system to perform this site visit, even if the employee is an agent approved by the department to perform sanitary surveys.

2. The department may waive the requirement to collect 3 routine samples during the next month the public water system provides water to the public if the department has determined why the sample was total coliform positive and establishes that the water supplier has corrected the problem or will correct the problem before the end of the next month the public water system serves water to the public. In this case, the decision to waive the following month's additional monitoring requirement will be documented in writing, signed by a qualified department official, and made available to the public. The written documentation shall describe the specific cause of the total coliform positive sample and what action the water supplier has taken or will take to correct this problem.

3. The requirement to collect 3 routine samples during the next month the public water system provides water to the public shall not be waived solely on the grounds that all repeat samples are total coliform-negative. The water supplier shall collect at least one routine sample before the end of the next month the public water system serves water to the public and use it to determine compliance with the treatment technique trigger for total coliforms in s. NR 809.31, unless the department has determined that the water supplier corrected the contamination problem before the water supplier collected the set of repeat samples required in pars. (a) to (e) and all repeat samples were total coliform negative.

(g) After a water supplier collects a routine sample and before learning the results of the analysis of that sample, if the water supplier collects another routine sample from within 5 adjacent service connections of the initial sample, and the initial sample after analysis is found to contain total coliforms, then the water supplier may count the subsequent sample as a repeat sample instead of as a routine sample.

(h) Results of all routine and repeat samples not invalidated by the department shall be included in determining whether any coliform treatment technique triggers specified in s. NR 809.313 have been exceeded. If any trigger has been exceeded, water suppliers shall complete assessments as required in s. NR 809.313.

(2m) INCREASED MONITORING.

(a) Increased monitoring requirements for public water systems on quarterly or annual monitoring. Except as specified in pars. (d) and (e), water suppliers at public water systems on quarterly or annual monitoring that experience any of the events identified in subds. 1. to 4. shall begin monthly monitoring the month following the event. A water supplier at a public water system on annual monitoring that experiences the event identified in subd. 5. shall begin quarterly monitoring the quarter following the event. The water supplier shall continue monthly or quarterly monitoring until the requirements in par. (b) for quarterly monitoring or par. (c) for annual monitoring are met. A public water system on monthly monitoring for reasons other than those identified in subds. 1. to 4. is not considered to be on increased monitoring for the purposes of pars. (b) and (c).
1. The public water system triggers a Level 2 assessment or two Level 1 assessments under the provisions of s. NR 809.313 in a rolling 12-month period.

2. The public water system has an E. coli MCL violation.

3. The public water system has a coliform treatment technique violation.

4. The public water system has two coliform monitoring violations in a rolling 12-month period, or is a non-community public water system and has one coliform monitoring violation and one Level 1 assessment under the provisions of s. NR 809.313 in a rolling 12-month period for a public water system on quarterly monitoring.

5. The public water system has one coliform monitoring violation for a public water system on annual monitoring. For transient non-community public water systems, the department may elect to not count monitoring violations under sub. (9) if the missed sample is collected no later than the end of the monitoring period following the monitoring period in which the sample was missed. The water supplier shall collect the make-up sample in a different week than the routine sample for that monitoring period and shall collect the sample as soon as possible during the monitoring period, except that this is not allowed under par. (c). This authority does not affect the provisions of sub. (9) and s. NR 809.312 (2).

(b) Requirements for public water systems on increased monitoring to return to quarterly monitoring. The department may reduce the monitoring frequency for a public water system on monthly monitoring triggered under par. (a) to quarterly monitoring if the public water system meets the criteria in subds. 1. and 2.
1. Within the last 12 months, the public water system shall have a completed sanitary survey or a site visit by the department or a voluntary Level 2 assessment by a party approved by the department, be free of sanitary defects, and have a protected water source.

2. The public water system shall have a clean compliance history for a minimum of 12 months. For transient non-community public water systems, the department may elect to not count monitoring violations, as allowed under sub. (9), if the missed sample is collected no later than the end of the monitoring period following the monitoring period in which the sample was missed. The water supplier shall collect the make-up sample in a different week than the routine sample for that monitoring period and should collect the sample as soon as possible during the monitoring period, except that this is not allowed under par. (c). This authority does not affect the provisions of sub. (9) and s. NR 809.312 (2).

(c) Requirements for systems on increased monitoring to qualify for annual monitoring. The department may reduce the monitoring frequency for a transient non-community public water system on increased monitoring under par. (a) if the transient non-community public water system meets the criteria in par. (d) and the criteria in subds. 1. and 2.
1. The department shall conduct an annual site visit and the water supplier shall correct all identified sanitary defects. The water supplier may substitute a voluntary Level 2 assessment conducted by a party approved by the department in place of the department's annual site visit in any given year.

2. The water supplier shall have in place or adopt one or more additional enhancements to the water system barriers to contamination in subds. 2. a. to 2. e.
a. Cross connection control, as approved by the department.

b. Regular visits by a circuit rider approved by the department.

c. Continuous disinfection entering the distribution system and a residual in the distribution system in accordance with criteria specified by the department.

d. Demonstration of maintenance of at least a 4-log removal or inactivation of viruses as provided for under s. NR 809.327 (4).

e. Other equivalent enhancements to public water system barriers to contamination as approved by the department.

(d) Allowance for transient non-community water systems to monitor annually.The department may allow water suppliers at transient non-community water systems to monitor annually for total coliform and E. coli following conditions that would require increased monitoring under par. (a), provided the water supplier meets the requirements of subd. 1. or 2.
1. For water systems that began operation and conducted coliform monitoring prior to April 1, 2016, the water supplier shall have done all of the following:
a. Completed all required total coliform monitoring in the previous calendar year.

b. Received a sanitary survey within the previous 5 years.

c. Corrected all significant deficiencies or is following a department agreed upon schedule for correcting all significant deficiencies.

d. Received a level 2 assessment within 30 days of any level 1 assessment trigger identified after April 1, 2016, and corrected all sanitary defects or is following a department agreed upon schedule for correcting all sanitary defects.

e. Completed all repeat sampling requirements associated with any total coliform positive identified after April 1, 2016.

f. Had no E. coli MCL exceedances in the previous 2 years.

2. For public water systems that began operation or began coliform monitoring on or after April 1, 2016, the water supplier shall meet all of the requirements of subd. 1 and shall have completed at least one year of coliform monitoring at a frequency of no less than quarterly.

(e) Allowance for non-transient non-community water systems to monitor quarterly.The department may allow a water supplier of a non-transient non-community water system to monitor quarterly for total coliform and E. coli following conditions that would require increased monitoring under par. (a), provided the water supplier meets the same requirements specified for transient non-community water systems in par. (d) 1. a. to f.

(3) INVALIDATION OF TOTAL COLIFORM SAMPLES.

(a) A total coliform-positive sample invalidated under this subsection does not count towards meeting the minimum monitoring requirements of this section.

(b) The department may invalidate a total coliform-positive sample only if the conditions of subd. 1., 2. or 3. are met.
1. A certified laboratory establishes that improper sample analysis caused the total coliform-positive result.

2. The department, on the basis of the results of repeat samples collected as required by sub. (2) (a) to (e), determines that the total coliform-positive sample resulted from a domestic or other non-distribution system plumbing problem. A sample may not be invalidated by the department on the basis of repeat sample results alone, unless all repeat samples collected at the same tap as the original total coliform-positive sample are also total coliform-positive, and all repeat samples collected at a location other than the original tap are total coliform-negative. The department will not invalidate a total coliform-positive sample on the basis of repeat samples if all the repeat samples are total coliform-negative, or if the public water system has only one service connection.

3. The department has substantial grounds to believe that a total coliform-positive result is due to a circumstance or condition which does not reflect water quality in the distribution system. In this case, the water supplier shall still collect all repeat samples required, and shall use them to determine whether a coliform treatment technique trigger in s. NR 809.313 has been exceeded. To invalidate a total coliform-positive sample under this paragraph, the decision with the rationale for the decision shall be documented in writing, approved by a qualified department official and available to the public for inspection. The document shall state the specific cause of the total coliform-positive sample, and what action the water supplier has taken or will take, to correct this problem. The department may not invalidate a total coliform-positive sample solely on the grounds that all repeat samples are total coliform-negative.

(c) A laboratory shall invalidate a total coliform sample if the sample produces a turbid culture in the absence of gas production using an analytical method where gas formation is examined for, example, the Multiple Tube Fermentation Technique, produces a turbid culture in the absence of an acid reaction in the Presence-Absence Coliform Test, or exhibits confluent growth or produces colonies too numerous to count with an analytical method using a membrane filter, for example, Membrane Filter Technique, except that a laboratory shall not invalidate a total coliform sample if total coliforms are detected. If a laboratory invalidates a sample because of such interference, the water supplier shall collect another sample from the same location as the original sample within 24 hours of being notified of the interference problem, and have it analyzed for the presence of total coliforms. The water supplier shall continue to re-sample every 24 hours and have the samples analyzed until a valid result is obtained. The department may waive the 24 hour time limit on a case-by-case basis. Alternatively, the department may implement criteria for waiving the 24-hour sampling time limit to use in lieu of case-by-case extensions.

(4) E. COLI testing.

(a) If any routine or repeat sample is total coliform-positive, the water supplier shall analyze that total coliform-positive culture medium to determine if E. coli are present. If E. coli are present, the water supplier shall notify the department by the end of the day when the water supplier is notified of the test result, unless the water supplier is notified of the result after normal department business hours, in which case the water supplier shall notify the department before the end of the next business day.

(b) The department may allow a water supplier for a public water system, on a case-by-case basis, to forgo E. coli testing on a total coliform-positive sample if that water supplier assumes that the total coliform-positive sample is E. coli positive. Accordingly, the water supplier shall notify the department as specified in par. (a) and the provisions of s. NR 809.30 (2) apply.

(5) GROUNDWATER SYSTEM RAW WATER SAMPLING. In addition to sampling from the distribution system, each water supplier for a public water system providing disinfection shall obtain at least one sample every 3 months from each well prior to the point of treatment. For public water systems which have more than one well in the same location and utilizing the same aquifer, the supplier of water may sample only one of the wells each time on an alternating basis. If a well has a high potential for contamination, the department may, in individual cases, require more frequent sampling.

(6) SURFACE WATER SYSTEM RAW WATER SAMPLING. At surface water facilities, the microbiological quality of the source water shall be monitored sufficiently to maintain quality control of the treatment process. Water suppliers shall establish a schedule for each plant, subject to review and modification by the department.

Note: Generally, enumeration methods such as membrane filter, numeric enzyme substrate, or 5 tube fermentation tests and heterotrophic plate counts of the raw, settled and finished water on an established schedule will be necessary to meet this requirement.

(7) HETEROTROPHIC PLATE COUNTS. At all waterworks which have a potential for high total bacteria levels because of the water quality, the method of treatment, chemical addition or other cause, the department may require heterotrophic plate counts pursuant to an established schedule. Analyses shall be conducted in accordance with the analytical requirements in s. NR 809.311 (1), Table F.

(9) MONITORING VIOLATION.

(a) Failure to take every required routine or additional routine sample in a compliance period is a monitoring violation.

(b) Failure to analyze for E. coli following a total coliform-positive routine sample is a monitoring violation.

(10) REPORTING VIOLATION.

(a) Failure to submit a monitoring report or completed assessment form after a water supplier properly conducts monitoring or assessment in a timely manner is a reporting violation.

(b) Failure to notify the department following an E. coli-positive sample as required by sub. (4) in a timely manner is a reporting violation.

(c) Failure to submit certification of completion of department-approved start-up procedure by a seasonal system is a reporting violation.

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