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 (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 process. Staff can address problems and concerns relating to the application, the design of the sediment sampling plan, and analysis of sediment samples.
For reference, the Checklist, Flowchart, and Balduck's Method table are available in a PDF.
Checklist
The following steps should be taken in designing an approvable sediment sampling plan. This is part of the reference PDF available.
- Prepare a plan view of the proposed dredge area, including project depth.
- Use a recent (e.g., less than 6 months old) bathymetric survey of the project site.
- Determine the total area to be dredged and the total volume of sediment to be removed.
- Identify the locations of outfalls or other known sources of pollution, including historical spill areas.
- Determine the number of core samples to be collected based on the total area to be dredged using the Balduck's Method.
- Identify locations for core sampling using the guidance for identifying core sampling locations.
- Plan to drive cores one foot below project depth. Definitions of dredging and sampling depths.
- Cores will be separated into two segments, a segment homogenized over the project depth and a segment representing the next six inches to be exposed after dredging. The remainder of the core can be excluded from further analysis.
- Individual cores should not be homogenized if color, odor, grain size, total organic carbon (TOC), or likelihood of contamination differs among horizons. In such cases, horizons should be analyzed separately.
- Create a compositing scheme for core samples; compositing will reduce the overall number of samples to be analyzed.
- Samples in a composite should represent sediments with similar characteristics (e.g., grain size, TOC, color) taken from approximately the same depth and geographic area within the dredging area
- Composites should be comprised of no more than three samples.
- Core material above the project depth will be composited separately from core material below project depth (next 6 inches of sediment to be exposed).
- Cores from areas of known or suspected contamination (e.g., proximity to outfall or historical spill areas) are not to be composited with cores from other areas.
- Submit a complete Sediment Sampling and Analysis Plan to the NYSDEC via email at r2dredge@dec.ny.gov for review and approval. Sediment sampling should not commence until the sediment sampling plan is reviewed and approved by NYSDEC.
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.
Balduck's Method
This table identifies, by total dredge area, how many core samples are required. This is part of the reference PDF available.
| Total Dredge Area (sq. yds) |
No. samples |
No. samples |
No. samples |
|---|---|---|---|
| 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 the history of surrounding land uses (e.g., heavy industry), spills, observed environmental stressors; 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, spills, or site-specific contamination concerns (e.g., copper, mirex, dioxin, PCBs) in the drainage basin; or
- where there is a likelihood of contamination and dredging has not occurred in the last five years.
Identifying Locations for Core Sampling
- Locations should be spread over the entire area to be dredged.
- Sampling should be skewed towards
- areas that are shallow relative to the project depth
- areas affected by specific contamination (e.g., proximity to outfalls or historic spill areas)
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 dredging equipment. No more than one foot of overdredge 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*:
- The quantity of material to be removed is less than 1,500 (<1500) cubic yards.
- Material to be dredged is equal to or more than 90% sand and gravel.+
- 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 the project depth represents the area to be exposed after dredging and will be composited separately from the material above the project depth. If the sample representing the area to be exposed is appreciably more contaminated than pre-dredge conditions, the following options may be implemented to prevent the dissolution of contaminants into the water column;
- dredge to a shallower depth to avoid the contaminated sediment
- dredge to a deeper depth until cleaner sediments are exposed
- dredge to a deeper depth and place a clean cap over the contaminated sediment.
