2C, Storm Water Ponds Maintenance Program

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Environmental Risk Assessment Overview In determining the most appropriate management method for dredged material, an evaluation of the reasonable Likelihood for a given pollutant to be present in the material must be made. A determination as to whether a pollutant has `reasonable likelihood' is done through a combination of empirical and technical evaluation of the sediment to be dredged, which may include sampling and analysis. The following methods are used in preparing a risk assessment for the proposed dredging material: grain size analysis past industrial activities /sources of pollutants sampling and analysis of pollutants likely to be present Together, these methods characterize the dredged material. In addition to characterizing dredged material, any non exempt discharge from a project and /or management unit requires complete characterization. Characterization of effluent from the dredge project site and/or management unit(s), if proposed, are described in Chapter 4 of this document. Exempt discharges are described in Chapter 5 of this document. An evaluation of the reasonable likelihood for a given pollutant to be present in the material must be made, so that the proper management method for the material can be determined. Grain size analysis Begin the dredge site risk assessment by determining whether the material to be dredged is predominantly sand, gravel or pebble, or is comprised of other materials. Dredge material that is predominantly sand, gravel or pebble is unlikely to be contaminated, as pollutants do not generally adhere to these types of particles, and are therefore not incorporated into the sediment. Dredge materials that are primarily sand are unlikely to be contaminated and do not require additional chemical evaluation, and can proceed to permitting. To demonstrate that dredged material from a given project or site is predominantly sand, 93 percent of the dredged material must be coarser than silt; i.e. only seven percent of the dredged material can be silty materials that are finer than sand. To make this determination, the following procedure must be used: a. Conduct a sieve grain size analysis using ASTM Method C -136 for the gradation analysis and ASTM Method D -2487 for classification. b. Determine the minimum number of samples required using Table 6, based on the total amount of material to be dredged. c. Conduct the analysis using the following US Standard sieves: 1", 3/8 #4, #10, #100, and #200. d. Report the results for each of the discrete sample locations as a mass percentage of retained sediments. If 93 percent or more of the dredged material is retained on a #200 sieve, that is, the material is coarser than silt, the dredged material is unlikely to be contaminated, and does not require additional evaluation. Dredged material not excluded from additional analysis, as determined using the grain size analysis described above, must be more thoroughly characterized by evaluation of past industrial activities and analysis of dredged material for any pollutant has a reasonable likelihood to be present in the dredged material. Continue the evaluation as described by the following sections. Analysis of base -line and additional sediment parameters are described in the following chapter. 10 In projects where more than 93 percent of the dredged material is coarser than sand, additional evaluation is not required. Managing Dredged Materials in the Minnesota Pollution Control Agency State of Minnesota June 2009