9VAC25-260-170. Bacteria; other recreational waters

A. 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: a. (Reserved) b. (Reserved) c. (Reserved)