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Designing a Dredging Sediment Sampling and Analysis Plan

By following this guidance and TOGS 5.1.9 In-Water and Riparian Management of Sediment and Dredged Material (821 KB PDF), as appropriate, applicants proposing to dredge should be able to create an approvable sediment sampling plan. A flowchart has been provided, to allow the applicant to easily follow the sediment sampling plan process.

The applicant is encouraged to contact NYSDEC Region 2 at any point during the sediment sampling plan design phase and the application processes. Staff can address problems and concerns relating to the application, the design of the sediment sampling plan, and analysis of sediment samples.

For handy reference, the Checklist, Flowchart, and Balduck's Method table are available in a PDF (270 KB).

Checklist

The following steps should be taken in designing an approvable sediment sampling plan. This is part of the reference PDF (270 KB) available.

  1. Prepare a plan view of the proposed dredge area and provide proposed project depth.
    1. Use a recent (less than five years old) bathymetric survey of the project site.
    2. Determine total area to be dredged and total volume of sediment to be removed.
  2. Determine the number of samples to be collected based on the total area to be dredged by using Balduck's Method.
  3. Identify sites for core sampling using the guidance for identifying core sampling sites.
  4. Plan to drive cores six inches below project depth. Definitions of dredging and sampling depths.
  5. Create a compositing scheme for core samples; compositing will reduce the overall number of samplings to be analyzed.
    1. Samples in a composite should represent sediments taken from approximately the same depth and from the same geographic area within the dredging area.
    2. Composites should be comprised of no more than three samples.
      1. Core material above the project depth will be composited.
      2. Core material below the project depth (additional six inches) will be composited separately.
    3. Cores from areas known or suspected to consist of impacted sediments (e.g. outfall or spill areas) are not to be composited with cores from other areas.
  6. Submit complete Sediment Sampling and Analysis Plan to the NYSDEC (c/o Dredge Team; 47-40 21st Street 4th Flr; Long Island City, NY 11101) for review and approval. Sediment sampling should not commence until plan approval is received.

Sediment Sampling Plan Process Flowchart

The flowchart allows an applicant to assess whether they may be exempt from submitting a sediment sampling plan. This is part of the reference PDF (270 KB) available.

Flowchart of Sediment Sampling Plan Process

Balduck's Method

This table identifies, by total dredge area, how many samples are required. This is part of the reference PDF (274 kb) available.

Balduck's Method for identifying how many samples are required by total dredge area
Total Dredge Area
(sq. yds)

No. samples
Df = 1

No. samples
Df = 2

No. samples
Df = 3

5,000 - 10,000 5 - 6 10 - 12 15 - 18
10,000 - 20,000 6 - 7 12 - 14 18 - 21
20,000 - 30,000 8 - 9 16 - 18 24 - 27
30,000 - 50,000 9 - 10 18 - 20 27 - 30
50,000 - 65,000 11 22 33
65,000 - 85,000 12 24 36
85,000 - 100,000 13 26 39
100,000 - 130,000 14 28 42
130,000 - 160,000 15 30 45
160,000 - 200,000 16 32 48
200,000 - 230,000 17 34 51
230,000 - 280,000 18 36 54
280,000 - 330,000 19 38 57
330,000 - 380,000 20 40 60
380,000 - 440,000 21 42 63
440,000 - 500,000 22 44 66
500,000 - 580,000 23 46 69
580,000 - 650,000 24 48 72
650,000 - 750,000 25 50 75
750,000 - 830,000 26 52 78
830,000 - 930,000 27 54 81
930,000 - 1,030,000 28 56 84
Df equals 1 for sites:
  • with no previous sediment data; and
  • no suspected likelihood of appreciable contamination.
Df equals 2 for sites:
  • with no previous sediment data; but
  • where there is a likelihood of contamination based on history of surrounding land uses (e.g., heavy industry), spills, observed environmental stresses; and dredging has occurred within the last five years; or
  • near particularly sensitive features, e.g., water supply intakes, unique habitats.
Df equals 3 for sites:
  • with documented contamination from past sediment data; or
  • in areas of established fish advisories or spills or site-specific contamination of concern (e.g., copper, mirex, dioxin, PCB's) in the drainage basin; or
  • where there is a likelihood of contamination and dredging has not occurred in the last five years.

Identifying Sites for Core Sampling

  • Sites should be spread over the entire area to be dredged.
  • Sampling should be skewed towards
    1. areas that are shallow relative to the project depth
    2. areas adjacent to sewer outfalls or other sources of runoff

Definitions of Terms for Dredging and Sampling Depths

Dredging Depth -- proposed depth for dredging project

Overdredge -- additional depth for dredging allowed below project depth due to technical limitations of the accuracy of the dredging equipment. No more than one foot of overdepth will be acceptable.

Project Depth -- dredging depth plus overdredge (i.e., dredging depth + one foot)

Exemptions from Testing

Projects meeting any of the following conditions may be excluded from chemical testing*:

  1. The quantity of material to be removed is less than 1,500 (<1500) cubic yards.
  2. Material to be dredged is equal to or more than 90% sand and gravel.+
  3. Site was appropriately sampled in the past five years and contamination was not a concern.+

* Applicant should confirm exclusions from chemical testing with NYSDEC staff.

+ Applicant must provide documentation of recent grain size analysis to be exempted by #2 or results of pertinent prior chemical analyses to be exempted by #3.

Core Material Below Project Depth

Sample core material collected six inches below project depth will be composited separately from the material above project depth. The additional material from this six inches of core will be used to characterize the sediments which will remain at the water-sediment interface post-dredging. If these sediments are appreciably contaminated, project plans may require dredging to a shallower or deeper depth to avoid disturbance to the contaminated layer. If dredging to the depth of the contaminated material cannot be avoided, placement of a clean cap (armoring) over the sediment in question may be necessary to prevent dissolution of contaminants into the water column.