Section 7 Effect Analysis: Turbidity in the Greater Atlantic Region
Guidance for action agencies on how to address turbidity in their Effects Analysis.
Turbidity (an optical quality of light transmission through a fluid containing sediment particles most often measured as nephelometric turbidity units) and Total Suspended Sediment concentration (TSS, a gravimetric measure of particles in suspension generally measured as milligrams per liter) are not directly comparable without calibration of instrumentation to in situ sediments (Davies-Colley and Smith 2001, Clarke and Wilber 2008).
Effects of the actions described below will vary based on site-specific conditions (Wilber and Clarke 2001). If information is available on how conditions (e.g., bathymetry, currents) and material (e.g., sand versus silt) may influence turbidity and re-suspended sediment at a site, action agencies and applicants should consider it in addition to the general guidance provided below. Understanding how local conditions influence turbidity and re-suspended sediment, and using site-specific information in the consultation is encouraged. Assessing exposure of listed species to elevated levels of turbidity or TSS concentration requires an understanding of the sources (e.g., dredge type), factors that influence the duration and intensity of exposure (e.g., sediment type and/or current), as well as the individual species tolerance to the anticipated level of exposure at a given life stage. After reviewing the available studies relative to the ESA-listed species in the Greater Atlantic Region — Atlantic salmon, Atlantic sturgeon, shortnose sturgeon, large whales, and sea turtles — we believe the effects of turbidity and suspended sediment are greatest for fish species. For all fish species in which effects to early life stages have been measured, it is clear that eggs and larvae are the most sensitive to suspended sediments and sediment deposition. The deposition of sediment from dredging or other human activities can be harmful to eggs and larvae through burial or encasement of eggs in fine particles occupying interstitial spaces, and these earlier stages are unable to avoid this stressor because of their limited mobility.
To complete the Turbidity section of your Effects Analysis, use the appropriate language from the Species and Action tables below. Note: These numbers are based on situations where no overflow from the dredge occurs.
Species Turbidity Thresholds
High TSS levels can cause a reduction in DO levels. Earlier life stages of Atlantic salmon require dissolved oxygen levels at saturation, whereas adults can tolerate lower levels closer to approximately 5.0 mg/L (NMFS 2009). Newcombe and Jensen (1996) demonstrated that behavioral changes for both adult and juvenile salmonids began to occur at relatively low TSS levels at around 20 mg/L after one hour of exposure (avoidance response). If animals remain exposed to elevated TSS levels, sub-lethal effects began to occur and major physiological stress occurred at approximately 1,100 mg/L after 24 hours of exposure. Lethal effects could begin to occur at TSS levels of 3,000 mg/L and higher after 24 hours of exposure. Servizi and Martens (1992) observed the cough frequency of juvenile coho salmon significantly increased at 240 mg/L after 24 hours of exposure. Additionally effects that last longer than 24 hours reduces tolerance to TSS levels to about only 50 mg/L (Johnson 2018). Mortality for eggs/larvae can occur at anywhere between 10 mg/L and 120 mg/L depending on the duration of exposure (Wilber and Clarke 2001). The turbidity plumes caused by dredging are generally expected to last for less than 24 hours. While the increase in suspended sediments may cause Atlantic salmon to alter their normal movements, these minor movements will be too small to be meaningfully measured or detected. TSS is most likely to affect Atlantic salmon if a plume causes a barrier to normal behaviors. However, we expect adult and juvenile salmon to swim through the plume to avoid the area with no adverse effects.
High TSS levels can cause a reduction in DO levels. Both Atlantic and shortnose sturgeon may become stressed when dissolved oxygen falls below certain levels. Jenkins et al. (1993) observed that younger shortnose sturgeon experienced high levels of mortality at low dissolved oxygen levels while older individuals tolerated those reduced levels for short periods of time. Tolerances may decline if chronic exposure to low dissolved oxygen levels occurs. Johnson (2018) recommends that sturgeon should not be exposed to TSS levels of 1,000 mg/L above ambient for longer than 14 days at a time to avoid behavioral and physiological effects. During times when early life stages could be present in an action area, it is recommended that they be exposed to less than 50 mg/L of TSS. While the increase in suspended sediments may cause Atlantic and shortnose sturgeon to alter their normal movements, these minor movements will be too small to be meaningfully measured or detected. TSS is most likely to affect sturgeon if a plume causes a barrier to normal behaviors. However, we expect sturgeon to swim through the plume to avoid the area with no adverse effects.
No information is available on the effects of TSS on juvenile and adult sea turtles. While the increase in suspended sediments may cause sea turtles to alter their normal movements, these minor movements will be too small to be meaningfully measured or detected. Sea turtles breathe air, and would be able to swim away from the turbidity plume and would not be adversely affected by passing through the temporary increase in TSS. TSS is most likely to affect sea turtles if a plume causes a barrier to normal behaviors. However, we expect sea turtles to swim through the plume to avoid the area with no adverse effects.
No information is available on the effects of TSS on whales. While the increase in suspended sediments may cause whales to alter their normal movements, these minor movements will be too small to be meaningfully measured or detected. Whales breathe air, and would be able to swim away from the turbidity plume and would not be adversely affected by passing through the temporary increase in TSS. TSS is most likely to affect whales if a plume causes a barrier to normal behaviors. However, we expect whales to swim through the plume to avoid the area with no adverse effects.
TSS levels are shown to have adverse effects on benthic communities when they exceed 390.0 mg/L (EPA 1986). It is anticipated that there will be a temporary impact on the availability of prey species within the area of direct impact; however, it is anticipated that this area will be recolonized within a short period of time after the completion of the project. Because the habitat disturbance would affect a relatively small amount of the action area and because of the temporary nature of the disturbance, the project is expected to result in negligible reductions in benthic shellfish and infaunal organisms that serve as prey for ESA-listed species.
Total Suspended Sediment Levels and Plume Distances for Various Actions
Turbidity and Total Suspended Sediment Effects
|Hopper Dredging||Hopper dredges re-suspend sediment when the suction draghead(s) make contact with the substrate and during release of overflow waters, which generally occurs through the bottom of the vessel’s hull. Hopper dredges have a large range in capacities and different draghead configurations. Plumes generated during hopper dredging of sandy entrance channels will have very different spatial and temporal characteristics than those created in silt-laden harbors. Near-bottom plumes caused by hopper dredges may extend approximately 2,300 to 2,400 feet (701-731 meters) down-current from the dredge (ACOE 1983). According to Wilber and Clarke (2001), suspended sediment plumes can extend 3,937 ft (1,200 m). TSS concentrations may be as high as several hundred mg/L near the discharge port and as high as several tens of mg/L near the draghead. In a literature review conducted by Anchor Environmental (2003), near-field concentrations ranged from 80.0-475.0 mg/L. TSS and turbidity levels in the near-surface plume usually decrease exponentially with increasing time and distance from the active dredge due to settling and dispersion, quickly reaching ambient concentrations and turbidities. In almost all cases, the majority of re-suspended sediments resettle close to the dredge within one hour, although very fine particles may settle during slack tides only to be re-suspended by ensuing peak ebb or flood currents (Anchor Environmental 2003). The TSS levels expected for hopper dredging (up to 475.0 mg/L) are below those shown to have adverse effect on fish (typically up to 1,000.0 mg/L; see summary of scientific literature in Burton 1993; Wilber and Clarke 2001).|
|Cutterhead Dredging||Cutterhead dredges use suction to entrain sediment for pumping through a pipeline to a designated discharge site. Production rates vary greatly based on pump capacities and the type (size and rotational speed) of cutter used, as well as distance between the cutterhead and the substrate. Sediments are re-suspended during lateral swinging of the cutterhead as the dredge progresses forward. Modeling results of cutterhead dredging indicated that TSS concentrations above background levels would be present throughout the bottom six feet (1.8 meters) of the water column for a distance of approximately 1,000 feet (305 meters) (ACOE 1983). Elevated suspended sediment levels are expected to be present only within a 984.3 to 1,640.4 foot (300-500 meters) radius of the cutterhead dredge (ACOE 1983; LaSalle 1990; Hayes et al. 2000, as reported in Wilber and Clarke 2001). TSS concentrations associated with cutterhead dredge sediment plumes typically range from 11.5 to 282.0 mg/L with the highest levels (550.0 mg/L) detected adjacent to the cutterhead dredge and concentrations decreasing with greater distance from the dredge (Nightingale and Simenstad 2001; ACOE 2005, 2010, 2015b). The TSS levels expected for cutterhead dredging (up to 550.0 mg/L) are below those shown to have adverse effect on fish (typically up to 1,000.0 mg/L; see summary of scientific literature in Burton 1993; Wilber and Clarke 2001).|
|Mechanical Dredging||Mechanical dredges include many different bucket designs (e.g., clamshell, closed versus open bucket, level-cut bucket) and backhoe dredges, representing a wide range of bucket sizes. TSS concentrations associated with mechanical clamshell bucket dredging operations have been shown to range from 105 mg/L in the middle of the water column to 445 mg/L near the bottom (210 mg/L, depth-averaged) (ACOE 2001). Furthermore, a study by Burton (1993) measured TSS concentrations at distances of 500, 1,000, 2,000, and 3,300 feet (152, 305, 610, and 1006 meters) from dredge sites in the Delaware River and were able to detect concentrations between 15 mg/L and 191 mg/L up to 2,000 feet (610 meters) from the dredge site. In support of the New York/New Jersey Harbor Deepening Project, the U.S. Army Corps of Engineers conducted extensive monitoring of mechanical dredge plumes (ACOE 2015a). The dredge sites included Arthur Kill, Kill Van Kull, Newark Bay, and Upper New York Bay. Although briefly addressed in the report, the effect of currents and tides on the dispersal of suspended sediment were not thoroughly examined or documented. Independent of bucket type or size, plumes dissipated to background levels within 600 feet (183 meters) of the source in the upper water column and 2,400 feet (732 meters) in the lower water column. Based on these studies, elevated suspended sediment concentrations at several hundreds of mg/L above background may be present in the immediate vicinity of the bucket, but would settle rapidly within a 2,400- foot (732 meter) radius of the dredge location. The TSS levels expected for mechanical dredging (up to 445.0 mg/L) are below those shown to have adverse effect on fish (typically up to 1,000.0 mg/L; see summary of scientific literature in Burton 1993; Wilber and Clarke 2001).|
|Beach Nourishment||Wilber et al. (2006) reported that elevated total suspended sediment (TSS) concentrations associated with an active beach nourishment site were limited to within 1,312 feet (400 meters) of the discharge pipe in the swash zone (defined as the area of the nearshore that is intermittently covered and uncovered by waves). Another study, conducted 5 years later, found that the turbidity plume and elevated TSS levels were expected to be limited to a narrow area of the swash zone up to 1,640 feet (500 meters) down-current from the discharge pipe (Burlas et al. 2001). Considering beach nourishment materials consist primarily of coarse sands, plumes from the discharge should settle rapidly and not affect large areas. Based on this and the best available information, TSS concentrations created by beach nourishment operations along an open coastline are expected to be between 34.0-64.0 mg/L; limited to an area approximately 1,640 feet (500 meters) down-current from the discharge pipe; and, settle within several hours after discharge cessation. The TSS levels expected for beach nourishment (up to 64.0 mg/L) are below those shown to have adverse effect on fish (typically up to 1,000.0 mg/L; see summary of scientific literature in Burton 1993; Wilber and Clarke 2001) and benthic communities (390.0 mg/L (EPA 1986)).|
|Off-shore Disposal||During the discharge of sediment at offshore disposal sites, suspended sediment concentrations have been reported as high as 500.0 mg/L within 250 feet (76 meters) of the disposal vessel and decreasing to background levels (i.e. 15.0-100.0 mg/L depending on location and sea conditions within 1,000-6,500 feet (305-1981 meters) (ACOE 1983). Multiple characterizations of disposal plume spatial and temporal dynamics have been conducted by the USACE New England District, providing an extensive body of knowledge on all aspects of off-shore disposal (e.g., Fredette and French 2004, SAIC 2005). TSS concentrations near the center of the plume created by the placement of dredged material have been observed to reach near background levels in 35-45 minutes (Battelle 1994 in ACOE and EPA 2010). The TSS levels expected for off-shore disposal (up to 500.0 mg/L) are below those shown to have adverse effect on fish (typically up to 1,000.0 mg/L; see summary of scientific literature in Burton 1993; Wilber and Clarke 2001).|
|Pile Driving and Removal||The installation of piles will disturb bottom sediments and may cause a temporary increase in suspended sediment in the action area. Using available information collected from a project in the Hudson River, we expect pile driving activities to produce total suspended sediment (TSS) concentrations of approximately 5.0 to 10.0 mg/L above background levels within approximately 300 feet (91 meters) of the pile being driven (FHWA 2012). Using a clamshell to extract piles allows sediment attached to the pile to move vertically through the water column until gravitational forces cause it to slough off under its own weight. The small resulting sediment plume is expected to settle out of the water column within a few hours. Studies of the effects of turbid water on fish suggest that concentrations of suspended sediment can reach thousands of milligrams per liter before an acute toxic reaction is expected (Burton 1993). The TSS levels expected for pile driving or removal (5.0 to 10.0 mg/L) are below those shown to have adverse effect on fish (typically up to 1,000.0 mg/L; see summary of scientific literature in Burton 1993; Wilber and Clarke 2001) and benthic communities (390.0 mg/L (EPA 1986)).|
|Jet Plow Technology||Jet plow technology has been shown to minimize impacts to marine habitat caused by excessive dispersion of bottom sediments, but some increased turbidity and resuspension of sediments can be expected. Based on the Applied Science Associates, Inc. (ASA) model used by the ESS Group, Inc. (2008), the maximum suspended sediment concentration at 20 meters (65 feet) from the jet plow is 235.0 mg/L, with concentrations decreasing to 43.0 mg/L within 200 meters (656 feet) from the plow. Based on the model used by the ESS Group, Inc., and information provided by Upstate NY Power Corp (the permit applicant), elevated levels of suspended sediment are predicted to return to ambient conditions within 24-48 hours after plowing operations. The TSS levels expected for jet plow technology (up to 235.0 mg/L) are below those shown to have adverse effect on fish (typically up to 1,000.0 mg/L; see summary of scientific literature in Burton 1993; Wilber and Clarke 2001) and benthic communities (390.0 mg/L (EPA 1986)).|
|Dewatering Dredged Sediment||The release of effluent during the dewatering of dredged sediment may temporarily increase suspended sediment concentration, thus elevating turbidity in the receiving waterbody. However, by discharging effluent through a fabric filter, hay bales, or a vegetated buffer strip prior to the effluent entering the receiving waterbody any remaining sediment in the effluent will be trapped or be allowed to settle out of suspension, whereby eliminating listed species exposure to elevated concentrations of suspended sediment.|
Creating an Effects Determination
For each stressor:
- Establish if individuals (or essential features of critical habitat) will be exposed to the effect/stressor and if so, which individuals (i.e., life stage, species) or aspect of critical habitat;
- Use the guidance documents, including the tables above, to identify the stressors associated with the activities under consultation. The “Effects of the Action” section should be organized by effect/stressors, which may result from multiple activities (e.g., you may have subheadings for water quality and vessel traffic and all activities resulting in those stressors would be discussed under those headings);
- Explain the consequence of that exposure;
- Each stressor must be analyzed for its additive effect to the existing conditions (aka “baseline conditions”), and a declarative statement must follow each effect determination; and
- As appropriate, conclude that the activity will have effects that are discountable (extremely unlikely to occur) or insignificant (unable to meaningfully measure, detect or evaluate) or wholly beneficial (positive effects with no associated negative effects) and, consequently, the action is not likely to adversely affect listed species or critical habitat, and incidental take is not anticipated to occur.
Example of Effects Determination
Potential Water Quality Effects
The installation of the steel pipe piles will disturb bottom sediments and may cause a temporary increase in suspended sediment in the action area. Using available information collected from the Tappan Zee Bridge Replacement Project (FHWA 2012) over the Hudson River, we expect pile driving activities to produce total suspended solids (TSS) concentrations of approximately 5 to 10 mg/L above background levels within approximately 300 feet (91 meters) of the pile being driven. The small resulting sediment plume is expected to settle out of the water column within a few hours. Studies of the effects of turbid water on fish suggest that concentrations of suspended solids can reach thousands of milligrams per liter before an acute toxic reaction is expected (Burton 1993). The TSS levels expected for pile driving (5 to 10 mg/L above ambient or background conditions) are below those shown to have adverse effect on fish (typically up to 1,000 mg/L; see summary of scientific literature in Burton 1993; Wilber and Clarke 2001) and benthic communities (390 mg/L (EPA 1986)). As explained above, we expect few, if any, Atlantic sturgeon to forage in the action area. As the TSS levels will not reach levels that are toxic to benthic communities, the proposed action is extremely unlikely to result in reductions in the quality or quantity of sturgeon prey currently available. TSS is most likely to affect sturgeon if a plume causes a barrier to normal behaviors. However, the increase in TSS levels expected for pile driving (5 to 10 mg/L above ambient or background conditions) is so minor that any effect of sediment plumes caused by the proposed action on sturgeon movements or behavior will be undetectable; we expect sturgeon to either swim through the plume or make small evasive movements to avoid it. Based on the best available information, the effects of re-suspended sediment on sturgeon resulting from pile installation when added to baseline conditions will be too small to be meaningfully measured or detected and are, therefore, insignificant.
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