Section 380. Bacteriological quality

A. Analytical methodology.

1. The standard sample volume for the coliform test shall consist of 100 milliliters, regardless of the analytical method used.

2. Owners need only to determine the presence or absence of total coliforms and E. coli; a determination of total coliform density is not required.

3. The time from sample collection to initiation of test medium incubation shall not exceed 30 hours.

4. Owners are encouraged but not required to hold samples below 10^oC during transit.

5. If water having residual chlorine (measured as free, combined, or total chlorine) is to be analyzed, sufficient sodium thiosulfate (Na₂S₂O₃) shall be added to the sample bottle before sterilization to neutralize any residual chlorine in the water sample.

B. PMCLs for microbial contaminants.

1. A waterworks is in compliance with the PMCL for E. coli unless any of the conditions identified in this subdivision occur. A violation may pose an acute risk to public health and is a Tier 1 condition requiring public notification as described in 12VAC5-590-540 when:

a. A repeat sample following a total coliform-positive routine sample is E. coli positive;

b. A repeat sample following an E. coli-positive routine sample is total coliform positive;

c. The owner fails to take all required repeat samples following an E. coli-positive routine sample; or

d. The owner fails to test for E. coli when any repeat sample tests positive for total coliform.

2. Compliance shall be determined with the PMCL for E. coli for each monitoring period for which monitoring for total coliforms is required.

C. The best available technology, treatment techniques, or other means available for achieving compliance with the PMCL for E. coli shall be:

1. Protection of wells from contamination by coliforms by appropriate placement and construction;

2. Maintenance of a disinfectant residual throughout the distribution system;

3. Proper maintenance of the distribution system including appropriate pipe replacement and repair procedures, main flushing programs, proper operation and maintenance of storage tanks and reservoirs, continual maintenance of positive water pressure in all parts of the distribution system, and an approved cross connection control program;

4. Filtration and disinfection of surface water or surface influenced groundwater; and

5. Disinfection of groundwater using strong oxidants such as chlorine, chlorine dioxide, or ozone.

D. A total coliform-positive result is indicative of a breakdown in the protective barriers and shall be cause for repeat monitoring and special follow-up action to locate and eliminate the cause of contamination.

1. For each routine sample found to be total coliform positive, the waterworks owner shall collect a set of three repeat samples within 24 hours of being notified of the positive result. The commissioner may extend the 24-hour limit on a case-by-case basis. For groundwater waterworks, the requirements of 12VAC5-590-379 shall also apply, and all repeat samples must be analyzed for E. coli using one of the analytical methods in 40 CFR 141.402(c).

a. The owner 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 five 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 owner must still take all required repeat samples.

b. The owner shall collect an additional set of repeat samples if one or more repeat samples in the current set of repeat samples is total coliform positive. The owner shall collect the additional set of repeat samples within 24 hours of being notified of the positive results, unless the commissioner extends the limit as provided in this section. The owner shall continue to collect additional sets of repeat samples until either total coliforms are not detected in one complete set of repeat samples or the owner determines that a coliform treatment technique trigger specified in 12VAC5-590-392 B has been exceeded as a result of a repeat sample being total coliform positive and notifies the appropriate ODW field office. If a trigger identified in 12VAC5-590-392 B is exceeded as a result of a routine sample being total coliform positive, an owner is required to conduct only one round of repeat monitoring for each total coliform-positive routine sample.

c. If the owner collects a routine sample before learning the results of the previous routine sample, and the sample is taken within five service connections of the initial routine sample, then the owner may count the subsequent sample as a repeat sample when the initial sample results are found to be total coliform positive.

d. If one or more repeat samples taken at the monitoring location required for triggered source water monitoring are E. coli positive, the waterworks has exceeded the E. coli PMCL and must comply with the groundwater system treatment technique requirements specified in 12VAC5-590-421.

e. 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, then the waterworks has exceeded the E. coli PMCL. However, the owner is not required to collect five additional source water samples from the same source within 24 hours of learning the E. coli-positive result.

f. The waterworks owner shall collect all repeat samples on the same day, except the commissioner may allow a waterworks with a single service connection to collect the required set of repeat samples over a three-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.

g. If a repeat sample taken at the monitoring location required for triggered source water monitoring is E. coli positive, the waterworks has exceeded the E. coli PMCL and must collect five additional source water samples from the same source within 24 hours of learning the E. coli-positive result.

2. Results of all routine and repeat samples not invalidated by the commissioner shall be used to determine compliance with the PMCL for E. coli and whether a treatment technique trigger specified in 12VAC5-590-392 B has been exceeded.

3. Special purpose samples, such as those taken to determine whether disinfection practices are sufficient following pipe placement, replacement, or repair, and samples taken before start-up of a seasonal waterworks, shall not be used to determine compliance. Repeat samples are not considered special purpose samples.

E. A total coliform-positive sample invalidated under this paragraph does not count towards meeting the minimum monitoring requirements of this section. To invalidate a total coliform-positive sample under this subsection, the written decision and rationale shall be reviewed, approved, and signed by the commissioner. The commissioner shall make this document available to EPA and the public. The written documentation shall state the specific cause of the total coliform-positive sample and what action the owner has taken, or will take, to correct this problem. The commissioner shall not invalidate a total coliform-positive sample solely on the grounds that all repeat samples are total coliform negative.

1. The commissioner may invalidate a total coliform positive sample if any of the following conditions are met:

a. The laboratory establishes that improper sample analysis caused the total coliform-positive result;

b. The commissioner, on the basis of the results of repeat samples collected as required by subdivision D 1 of this section determines that the total coliform-positive sample resulted from a domestic or other nondistribution system plumbing problem. The commissioner cannot invalidate a sample on the basis of repeat sample results unless all repeat sample(s) 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 (e.g., the commissioner cannot invalidate a total coliform-positive sample on the basis of repeat samples if all the repeat samples are total coliform negative, or if the waterworks has only one service connection); or

c. The commissioner has substantial grounds to believe that a total coliform-positive result is due to a circumstance or condition that does not reflect water quality in the distribution system. In this case, the waterworks owner shall still collect all repeat samples required under subdivision D 1 of this section, and use them to determine whether a coliform treatment technique trigger in 12VAC5-590-392 B has been exceeded.

2. A laboratory must invalidate a sample because of sampling interference (i.e., turbid culture in absence of (i) gas production, or (ii) acid reaction; exhibition of confluent growth; or production of colonies too numerous to count). The waterworks owners shall collect a replacement sample from the same location within 24 hours, and have it analyzed for the presence of total coliforms. The waterworks owner must continue to resample within 24 hours and have the samples analyzed until they obtain a valid result. The commissioner may waive the 24-hour time limit on a case-by-case basis.

F. Escherichia coli (E. coli).

1. If any routine or repeat sample or replacement sample is total coliform positive, the waterworks owner shall analyze that total coliform-positive culture medium to determine if E. coli are present. If E. coli are present, the waterworks owner shall notify the appropriate ODW field office by the end of the day when the waterworks is notified of the test result, unless the ODW's field office is closed, in which case the appropriate ODW field office must be notified before the end of the next business day.

2. The commissioner has the discretion to allow a waterworks, on a case-by-case basis, to forgo E. coli testing on a total coliform-positive sample if the owner assumes that the total coliform-positive sample is E. coli positive. Accordingly, the owner must notify the appropriate ODW field office as specified in subdivision 1 of this subsection and the provisions of subdivision B 1 of this section apply.

G. Groundwater sources.

1. Groundwater sources shall be disinfected in accordance with 12VAC5-590-1000 when the total coliform geometric mean of 20 or more raw water samples measured by a method yielding a multiple-portion decimal-dilution (MPN) result is greater than three. The value 1.0 shall be used to represent a negative coliform result in the calculation of the geometric mean.

2. Groundwater sources containing a total coliform geometric mean of 100 or more organisms per 100 milliliters or with more than 10% of these samples exceeding 100 organisms per 100 milliliters constitutes unacceptable contamination for disinfection treatment only.

3. Groundwater sources shall be disinfected in accordance the requirements of 12VAC5-590-1000 when the source water quality contributes to the waterworks' failure to meet the bacteriological PMCL specified in subsection B of this section.

4. Groundwater sources shall be disinfected in accordance with 12VAC5-590-421 A 1 d when the results of source development samples specified in 12VAC5-590-840 B 11 indicate the presence of E. coli in two or more samples.

5. Groundwater sources shall be disinfected in accordance with 12VAC5-590-421 A 1 d when the results of raw water monitoring conducted in accordance with 12VAC5-590-425 indicate the presence of E. coli in two or more samples during any running six-month period.

H. Groundwater systems conducting source water monitoring as described in 12VAC5-590-379 shall determine the presence or absence of E. coli. All samples shall be analyzed in accordance with 12VAC5-590-440 by the Division of Consolidated Laboratory Services (DCLS) or by a laboratory certified by DCLS for drinking water samples.

Historical Notes

Derived from VR355-18-004.05 § 2.5, eff. August 1, 1991; amended, Volume 09, Issue 17, eff. June 23, 1993; Volume 19, Issue 24, eff. September 10, 2003; Volume 28, Issue 05, eff. December 7, 2011; Volume 33, Issue 03, eff. November 2, 2016.

Statutory Authority

§§ 32.1-12 and 32.1-170 of the Code of Virginia.