Bacteriological surveys are the collection of water samples from all shellfish growing areas. A minimum of six sets of water samples are collected from each sampling station in each growing area on a random schedule to access the overall quality of the waters for classification. Waters are classified as either Approved, Conditionally Approved or Prohibited based on the analysis of the data collected from each sampling station.
Approved shellfishing waters must meet a bacteriological standard over the survey period of a median or geometric mean of not more than 14 MPN/100ml and a 90th percentile not to exceed 43 MPN/100ml.
Hydrographic and Meteorological Survey
A summary of the meteorological conditions that have an effect on a growing area must be made within the sanitary survey report. Rainfall and the resultant runoff can cause fecal coliform counts to increase within shellfish growing waters. Climate and weather can affect the distribution of pollutants or can be the cause of pollutant delivery to a growing area. Prevailing winds can determine the distribution of pollutants in a growing area. Rainfall patterns and intensity can affect water quality through pollutant delivery in runoff or cause flooding which can affect the volume and duration of pollutant delivery. All of these factors must be evaluated as part of the overall sanitary survey and classification of shellfish growing areas.
An evaluation of the hydrographic factors that may affect the distribution of pollutants throughout the area must be made. Examples of hydrographic factors are tidal amplitude and type, water circulation patterns, and the amount of fresh water. These factors, along with water depths and stratification caused by density (salinity and temperature) differences, and wastewater and other waste flow rates are used to determine dilution and time of transport.
Tracer dye studies provide site-specific dilution, dispersion and time of travel information. These are required at each wastewater treatment plant that has a direct discharge into shellfishing waters to determine the proper "closed safety zone" around each outfall pipe.
For more information about the shellfish growing water shoreline surveys, contact the Shellfish Sanitation Office at 252-726-6827.
|N.C. Division of Marine Fisheries • 3441 Arendell Street • Morehead City, NC 28557 • 252-726-7021 or 800-682-2632 |