Water Quality Criteria
Excerpted from the Southeastern Regional Implementation Manual (SERIM)
22.214.171.124 Screen to Determine WQC Compliance
A screening method utilizing sediment chemistry can be used to determine compliance. The screen assumes that all of the contaminants in the dredged material are released into the water column during the disposal operation (see Section 10.1.1 of the 1991 Green Book). If the numerical model predicts that the concentration of all COCs released into the water column are less than the applicable WQC, the marine WQC LPC is satisfied.
The model needs to be run only for the COC that requires the greatest dilution. If the contaminant requiring the greatest dilution is shown to meet the LPC, all of the other contaminants that require less dilution will also meet the LPC. The contaminant that would require the greatest dilution is determined by calculating the dilution that would be required to meet the applicable marine WQC. To determine the required dilution (Dr), the following equation is solved for each COC:
Dr = (Cs-Cwq) / (Cwq - Cds) [Eq. 3-1]
Cs = concentration of the contaminant in the dredged material elutriate, expressed as micrograms per liter (μg/L) as determined by either equation 3-1 below or by elutriate chemical analytical results discussed in Section 126.96.36.199.
Cwq = applicable marine WQC (EPA WQC or state WQS), in (μg/L)
Cds = background concentration of the constituent at the disposal site water column, in μg/L
NOTE:Dilution is defined as the volume of ambient water in the sample divided by the volume of elutriate water in the sample.
Note that most contaminant results are reported in micrograms per kilogram (μg/kg) dry weight. To convert the contaminant concentration reported on a dry-weight basis to the contaminant concentration in the dredged material, the dry-weight concentration must be multiplied by the mass of dredged-material solids per liter of dredged material:
Cdw = contaminant concentration in dredged material, reported on a dry-weight basis (μg/kg)
ns = percent solids as a decimal
G = specific gravity of the solids. Use 2.65 if site-specific data are not available.
A table showing each contaminant and the dilution required to meet the WQC should be provided with the analysis. Alternatively, a module in the STFATE model can be used. The module requires the solids concentration (g/L), which is the term in brackets in Equation 3-2 above multiplied by 1000.
The concentration of the contaminant that would require the greatest dilution is then modeled using a numerical mixing model. Model input parameters are specific to each proposed dredging project and each ocean disposal site. Standard STFATE input parameters for each disposal site are being developed with each ODMDS-specific SMMP. They are included in Appendix G along with additional guidance on model usage. The key parameters derived from the dispersion model are the maximum concentration of the contaminant in the water column outside the boundary of the disposal site during the 4-hour initial-mixing period or anywhere in the marine environment after the 4-hour initial-mixing period. If both of these concentrations are below the applicable marine WQC, the WQC LPC is met and no additional testing is required to determine compliance with the WQC. If either of these concentrations exceeds the WQC, additional testing is necessary to determine compliance with the WQC, as described in the next section.
Citation: USEPA/USACE. 2008. Southeast Regional Implementation Manual (SERIM) for Requirements and Procedures for Evaluation of the Ocean Disposal of Dredged Material in Southeastern U.S. Atlantic and Gulf Coast Waters. EPA 904-B-08-001. U.S. Environmental Protection Agency Region 4 and U.S. Army Corps of Engineers, South Atlantic Division, Atlanta, GA. http://www.epa.gov/region4/water/oceans/documents/SERIM_Final_August 2008.pdf