When sampled correctly, a INCREMENT sample will provide results that are at, or very close to, the mean of the parameters being measured. To verify the accuracy of the sample results, the DU should be sampled in triplicate, and the percent Relative Standard Deviation (%RSD) calculated for each parameter. The results are in control (i.e. the variability has been properly captured) if the %RSD < 20%. (The lower the %RSD, the better.) Figure - DU when the is flowing. When the water is flowing, the DU can be situated at the downstream end of the silt curtain since any pollutants leaking out will flow through the DU. The sample bottle is moved throughout the entire DU, providing each drop of water an equal opportunity of being sampled. Figure - Typical layout (standing Control Station DUs should be established fifty (50) feet away from the Impact Station. The intent of the Control Stations is to document the ambient conditions in the general vicinity of the project. In addition, the Control Stations should be situated such that they will detect any contributions from related sources that could impact sample results. Triplicate samples means three separate samples taken sequentially. It does not mean one large sample split into 3 parts (split samples), nor does it mean three samples taken simultaneously (co-located samples). Red Flags samples”, and spots” are terms that are generally used when sampling – “Grab “Outliers” “Hot is not representative. When sampling procedures or data analyses include these terms, care should be taken to ensure that the data are accurate. The work area is 10 feet from the toe of the active Activity Decision Unit boundary. A vessel/barge may be operated outside of the isolated and confined in-water work area only if it is surrounded by a boom.
When sampled correctly, a INCREMENT sample will provide results that are at, or very close to, the mean of the parameters being measured. To verify the accuracy of the sample results, the DU should be sampled in triplicate, and the percent Relative Standard Deviation (%RSD) calculated for each parameter. The results are in control (i.e. the variability has been properly captured) if the %RSD < 20%. (The lower the %RSD, the better.) Figure - DU when the is flowing. When the water is flowing, the DU can be situated at the downstream end of the silt curtain since any pollutants leaking out will flow through the DU. The sample bottle is moved throughout the entire DU, providing each drop of water an equal opportunity of being sampled. Figure - Typical layout (standing Control Station DUs should be established fifty (50) feet away from the Impact Station. The intent of the Control Stations is to document the ambient conditions in the general vicinity of the project. In addition, the Control Stations should be situated such that they will detect any contributions from related sources that could impact sample results. Triplicate samples means three separate samples taken sequentially. It does not mean one large sample split into 3 parts (split samples), nor does it mean three samples taken simultaneously (co-located samples). Red Flags – “Grab samples”, “Outliers” and “Hot spots” are terms that are generally used when sampling is not representative. When sampling procedures or data analyses include these terms, care should be taken to ensure that the data are accurate. The work area is 10 feet from the toe of the active Activity Decision Unit boundary. A vessel/barge may be operated outside of the isolated and confined in-water work area only if it is surrounded by a boom.
20150618AMAP-Guidelines-DQO-format-TT4.docx