9 Va. Admin. Code § 25-260-170
Current through Register Vol. 41, No. 6, November 4, 2024
Section 9VAC25-260-170 - Bacteria; other recreational watersA. The following bacteria criteria (counts/100ml) shall apply to protect primary contact recreational uses in surface waters, except waters identified in subsection B of this section: In freshwater, E. coli bacteria shall not exceed a geometric mean of 126 counts/100ml and shall not have greater than a 10% excursion frequency of a statistical threshold value (STV) of 410 counts/100 ml, both in an assessment period of up to 90 days.
In transition and saltwater, Enterococci bacteria shall not exceed a geometric mean of 35 counts/100ml and shall not have greater than a 10% excursion frequency of a statistical threshold value (STV) of 130 counts/100ml, both in an assessment period of up to 90 days.
1. See 9VAC25-260-140 C for boundary delineations for freshwater, transition and saltwater. 2. In VPDES discharges to freshwater, bacteria in effluent requiring disinfection shall not exceed a monthly geometric mean of E. coli bacteria of 126 counts/100ml. Alternative performance standards may be established where an approved long term control plan establishes an alternative level of disinfection for a combined sewer system. In VPDES discharges to transition and saltwater, bacteria in effluent requiring disinfection shall not exceed a monthly geometric mean of enterococci bacteria of 35 counts/100ml.
B. The following bacteria criteria per 100 ml (CFU/100 ml) of water shall apply: E. coli bacteria shall not exceed a monthly geometric mean of 630 CFU/100 ml in freshwater.
Enterococci bacteria shall not exceed a monthly geometric mean of 175 CFU/100 ml in transition and saltwater.
1. See 9VAC25-260-140 C for boundary delineations for freshwater, transition and saltwater.2. Geometric means shall be calculated using all data collected during any calendar month with a minimum of four weekly samples.3. If there is insufficient data to calculate monthly geometric means in freshwater, no more than 10% of the total samples in the assessment period shall exceed 1173 E. coli CFU/100 ml.4. If there is insufficient data to calculate monthly geometric means in transition and saltwater, no more than 10% of the total samples in the assessment period shall exceed 519 enterococci CFU/100 ml.5. Where the existing water quality for bacteria is below the geometric mean criteria in a water body designated for secondary contact in subdivision 6 of this subsection that higher water quality will be maintained in accordance with 9VAC25-260-30 A 2.6. Surface waters designated under this subsection are as follows: 9 Va. Admin. Code § 25-260-170
Derived from VR680-21-02.2, eff. May 20, 1992; amended, Virginia Register Volume 14, Issue 4, eff. December 10, 1997; Volume 19, Issue 7, eff. January 15, 2003; Volume 20, Issue 9, eff. February 12, 2004; Volume 26, Issue 12, eff. February 1, 2010; Amended, Virginia Register Volume 35, Issue 22, eff. 6/24/2019.Statutory Authority: § 62.1-44.15 of the Code of Virginia; Clean Water Act ( 33 USC § 1251 et seq.); 40 CFR Part 131.