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Pathogen Indicator Study Raw Data

The raw data are available at the link below.  When reviewing the data there are two important considerations to keep in mind: one is related to the differences in the sensitivity and accuracy of the analytical methods and the other is EPA’s acceptable risk levels and corresponding criterion.

Analytical Method:

Fecal coliform bacteria are enumerated using a membrane filter method, whereas E. coli and Enterococcus measured using a Most Probable Number (MPN) approach.  The membrane filter method provides actual counts of the number of colonies that develop on a Petri plate.  The E. coli and Enterococcus analyses are performed using the Colilert and Enterolert Quanti-Tray methods respectively.  The concentration of the target indicator is determined based on the number of positive reactions using a Most Probable Number (MPN) statistical table provided by the manufacturer. 

Quanti-Tray methods are more sensitive than the membrane filter media. There is usually higher recovery with MPN procedures versus Membrane filter procedures because the MPN procedures are less harsh and allow for the resuscitation of stressed or injured bacteria.

SC Current Standard:

In Regulation 61-68, Water Classifications and Standards, the current South Carolina state standard for fecal coliform bacteria for freshwater is “Not to exceed a geometric mean of 200/100 ml, based on five consecutive samples during any 30 day period; nor shall more than 10% of the total samples during any 30 day period exceed 400/100ml.”

EPA Bacteria Criteria Information:

EPA’s acceptable risk levels are based on the number of occurrences of gastroenteritis in swimmers engaged in full body immersion.  The EPA acceptable range is from 8 illness per 1000 swimmers (0.8%) to 10 illnesses per 1000 swimmers (1.0%).

EPA considers States that use an illness rate of 1.0% or less for fresh waters to have criteria as protective of human health as the 1986 bacteria criteria (Water Quality Standards For Coastal Recreation Waters, Considerations for States as They Select Appropriate Risk Levels, EPA September 2006, EPA-823-F-06-012 (http://www.epa.gov/waterscience/beaches/rules/bacteria-risk-level-factsheet.htm#whatdoes); Implementation Guidance for Ambient Water Quality Criteria for Bacteria, USEPA November 2003 Draft; Federal Register: November 16, 2004 (Volume 69, Number 220),Rules and Regulations, pp 67217-67243, page 67232 (http://www.epa.gov/EPA-WATER/2004/November/Day-16/w25303.htm).  All of the ranges cited below are considered by the USEPA to protect primary contact recreation and support the swimmable goal of the Clean Water Act.

For Enterococci EPA would accept a geometric mean within the range from 33 to 54 per 100 ml based on established illness rates, and/or a single sample maximum value within the range of 62 to 247 per 100 ml depending on the established illness rates and frequency of use for full body contact recreation.

For E. coli EPA would accept a geometric mean within the range from 126 to 206 per 100 ml based on established illness rates, and/or a single sample maximum value within the range of 236 to 940 per 100 ml depending on the established illness rates and frequency of use for full body contact recreation.

Enterococci Criteria (Parameter Code=50589)

Risk Level  (Illnesses per 1000 swimmers)

Geometric
Mean Density
(per 100 ml)

Single Sample Maximum Allowable Density (per 100 ml)

Designated Beach (75th Percentile)

Moderate Full Body Contact Recreation (82nd Percentile)

Lightly Used Full Body Contact Recreation
(90th Percentile)

Infrequently Used Full Body Contact Recreation
(95th Percentile)

8

33

62

79

107

151

9

42

79

100

137

193

10

54

101

128

175

247

 

E. coli Criteria (Parameter Code=31633)

Risk Level  (Illnesses per 1000 swimmers)

Geometric
Mean Density
(per 100 ml)

Single Sample Maximum Allowable Density (per 100 ml)

Designated Beach (75th Percentile)

Moderate Full Body Contact Recreation (82nd Percentile)

Lightly Used Full Body Contact Recreation
(90th Percentile)

Infrequently Used Full Body Contact Recreation
(95th Percentile)

8

126

236

299

409

576

9

161

301

382

523

736

10

206

385

489

668

940

 

Because of the variability of water concentrations of the various indicators, getting exact values was not always possible.  The following REMARK abbreviations are used in the raw data spreadsheet;

EST = Estimated value
GT = Greater than the numeric RESULT indicated
LT = Less than the numeric RESULT indicated

Raw Pathogen Indicator Study Data (xls)

Contact

David Chestnut (803) 898-4066