BACTERIOLOGICAL SAMPLE SITING PLAN
The Coliform Sampling Rule (15A NCAC 18C .1534) requires that a Sample Siting Plan for the collection of routine
total coliform samples be developed by each water system. These plans are subject to State review and revision.
Each water system must submit a copy of their plan to the appropriate Public Water Supply Section Regional Office
as soon as possible. A duplicate of the plan must be kept on site and made available for review by the Regional
Office staff during system inspections.
The plan should specify the locations of routine samples that are “representative” of the water supplied to every
customer. Sampling sites should be selected carefully to represent the varying conditions that occur within the
distribution system. It is important to identify and include areas that may adversely affect the microbiological quality
of the water such as low pressure zones, areas of low velocity, cross connections and dead-end lines.
Factors to consider when preparing a Site Sampling Plan must include:
• Location and type of water sources, treatment facilities, storage tanks, booster pump stations, blowoffs/flushing
points, hydrants and critical valves.
• Distribution system’s configuration and location of mains, branch lines, service connections, loops, dead-end
pipes, sites of deteriorating water lines, and interconnections with purchase water systems.
• Cross-connection hazards and shared connections.
• Pressure zones and areas of low water pressure.
• Areas of low-velocity water movement
• Varying population densities
• Water Age
• Avoid undesirable conditions such as swivel type faucets, leaky faucets, faucets near or below ground, faucets
with threads on the inside of their spouts, and faucets with aerators.
A properly completed Sample Siting Plan will include the following:
1. System information – at a minimum, provide the following information:
• System name
• County location
• Seven-digit PWSID number
• System type
• Contact information for the owner and the administrative contact
• Total number of service connections
• Population count
• Minimum number of required routine samples (based on population – see Table 1 below)
• List of routine sample location codes with corresponding addresses or site description
• Frequency of required monitoring
• Sample collection schedule
• Monthly rotation cycle
• Treatment plant description and type of disinfectant used
• Date plan was prepared (and revision date, if applicable)
• Name and telephone number of the person who prepared or revised the plan
2. Distribution system map – at a minimum, include the following:
• Layout of distribution system’s piping
• All water sources and entry points into the distribution system
• Treatment facilities, including booster stations
• Storage tanks and reservoirs
• Hydrant locations
• Dead-end mains and known trouble areas
• Maximum Residence Time (MRT) sites and other areas with high water age
• Locations of the routine bacteriological sampling sites
Number of Sites and Sample Location Code Requirements:
• A minimum of five sites must be identified for small systems required to collect one routine sample per
monitoring period. Larger systems that collect two or more samples per month must identify at least two to three
times the number of sampling sites as required according to the system’s population. (See Table 1 and Table 1
Notes below for required number of routine samples based on population). For systems with less than five (5)
service connections, all service connections must be identified as a sample site.
• A location code must be developed for each sampling location. The codes must be three digits using letters,
numbers or a combination of both (for example: ABC, 123, or 1B3). Note: If there is a need for repeat
sampling, the upstream-downstream sample location codes may have to be uniquely created at the time of
collection if no routine sampling sites are located within 5 service connections upstream and downstream of the
• Address information or a site description must be provided for each location code.
Routine Total Coliform Monitoring Frequency for Community Water Systems
Minimum Number of
Population Minimum Number of
Samples per Population
Served Samples per
25 to 1,000* 1 59,001to 70,000 70
1,001 to 2,500 2 70,001 to 83,000 80
2,501 to 3,300 3 83,001 to 96,000 90
3,301 to 4,100 4 96,001 to 130,000 100
4,101 to 4,900 5 130,001 to 220,000 120
4,901 to 5,800 6 220,001 to 320,000 150
5,801 to 6,700 7 320,001 to 450,000 180
6,701 to 7,600 8 450,001 to 600,000 210
7,601 to 8,500 9 600,001 to 780,000 240
8,501 to 12,900 10 780,001 to 970,000 270
12,901 to 17,200 15 970,001 to 1,230,000 300
17,201 to 21,500 20 1,230,001 to 1,520,000 330
21,501 to 25,000 25 1,520,001 to 1,850,000 360
25,001 to 33,000 30 1,850,001 to 2,270,000 390
33,001 to 41,000 40 2,270,001 to 3,020,000 420
41,001 to 50,000 50 3,020,001 to 3,960,000 450
50,001 to 59,000 60 3,960,001 or more 480
* Includes public water systems that have at least 15 service connections, but serve fewer than 25 persons. Reference §141.21 (a)(2)
TABLE 1 NOTES: (Requirements for Non-Community Systems)
Non-community groundwater systems with < 1,000 population [except ground water under the direct influence of
surface water (GWUDI) systems]: Collect one routine sample per quarter. [§141.21(a)(3)(i)]
Non-community groundwater systems with > 1,000 population (except GWUDI systems): Sample monthly
according to the table above for community water systems. [§141.21(a)(3)(ii)]
Non-community surface water systems: Sample monthly according to the table above for community water
Non-community GWUDI systems: Sample monthly according to the table above for community water systems.
Important Notes on Routine Monitoring: [Section .1534, §141.21(a)]
Routine samples should be collected at representative sites throughout the distribution system. Each routine
sample should be collected from a different sampling site. The sampling sites should be rotated each
Systems required to collect 6 or more routine samples per month MUST spread the collection of those samples
throughout the month at regular intervals. Only those groundwater systems having populations of 4,900 or less
(where 5 or less routine samples are required per month) may collect all samples on the same day if they are
taken from different sites.
Systems are encouraged not to wait until the last week of the month to collect samples in case a problem should
arise with the sampling or laboratory analyses, which may result in late reporting of results to the State.
Repeat Samples and Next Month’s Routines
Frequency Following a Total Coliform- Positive Routine Sample
No. Routine No. Repeat No. Routine
Samples per Samples* Samples the
Month Next Month
1 or less 4 5
2 3 5
3 3 5
4 3 5
5 or more 3 See Table 1
* The number of repeat samples to be collected for each total coliform-positive routine sample. Reference §141.21 (b)
Important Notes on Repeat Monitoring: [Section .1534, CFR 141.21(b)]
If any routine sample is total coliform-positive, a set of repeat samples must be collected for each positive
Each set of repeat samples must be collected within 24 hours of being notified of the positive result.
A set of repeat samples must have at least the following: one sample collected from the same location (Repeat-
Original Tap) as the previous positive, one sample collected within five (5) service connections upstream
(Repeat-Upstream) of the previous positive location, one sample collected within five (5) service connections
downstream (Repeat-Downstream) of the previous positive location, and if the population is less than 1,001, an
additional sample must be collected anywhere in the distribution system to help identify the problem, i.e. a total
of four (4) samples.
If any repeat sample collected is total-coliform positive, an additional set of repeat samples must be collected, as
described above. This process must be continued until either total coliforms are not detected in one complete
set of repeat samples or your system determines that the MCL has been exceeded and notifies the State.
For systems required to normally collect less than 5 routine samples per month/quarter, 5 routine samples must
be collected the next month following a positive routine sample.
Submittal of Your Bacteriological Sample Siting Plan:
Please submit your plan to the appropriate Regional Office. Regional Office information is provided below. If you
have already submitted your plan, please review it to make sure it complies with the requirements of this letter and
submit a modified plan, if applicable.
If you have questions or need assistance, please contact your Regional Office at:
Swannanoa Regional Office Fayetteville Regional Office Mooresville Regional Office
2090 U.S. Highway 70 225 Green Street, Suite 714 610 East Center Avenue, Suite 301
Swannanoa, NC 28778 Fayetteville, NC 28301 Mooresville, NC 28115
Phone: (828) 296-4500 Phone: (910) 433-3300 Phone: (704) 663-1699
Fax: (828) 299-7043 Fax: (910) 486-1858 Fax: (704) 663-3772
Raleigh Regional Office Washington Regional Office Wilmington Regional Office
3800 Barrett Drive 943 Washington Square Mall 127 Cardinal Drive Extension
1628 Mail Service Center Washington, NC 27889 Wilmington, NC 28405-3845
Raleigh, NC 27699-1638 Phone: (252) 946-6481 Phone: (910) 796-7215
Phone: (919) 791-4200 Fax: (252) 975-3716 Fax: (910) 350-2004
Fax: (919) 788-5349
Winston-Salem Regional Office
585 Waughtown Street
Winston-Salem, NC 27107-2241
Phone: (336) 771-5000
Fax: (336) 771-4631