Summary
Some segments of the Lake Source Cooling (LSC) intake and outfall pipelines will be buried within Cayuga Lake's bottom sediments. To maintain recreational use of the lake and meet navigational safety guidelines, these pipelines will not protrude above the sediment surface in places where the water depth is less than 2.7 meters (m) or 9 feet (ft) at mean summer lake level. In deeper water, the intake pipeline will lie on the sediment surface. Approximately 4,650 cubic meters (6,100 cubic yards) of Cayuga Lake sediments will be disturbed to install the LSC intake and outfall pipelines below the sediment surface in shallow water and accommodate a transfer barge area near the shoreline.
In 1994 and 1996, LSC researchers conducted investigations of the quality of Cayuga Lake sediments in the vicinity of the proposed LSC aquatic pipeline routes. Sampling and analysis provided required information for the engineering and construction plans, and for the joint state and federal permits required to conduct dredge operations in the navigable waters of the United States (6 New York Code of Rules and Regulations [NYCRR] Part 608, §401 and §404 Clean Water Act, and §10 Rivers and Harbors Act).
The results of these studies indicate that most of the sample sites contain concentrations of heavy metals corresponding to the New York State Department of Environmental Conservation (NYSDEC) sediment category of Class B (moderately contaminated). Trace concentrations of organic compounds were also detected, but were within NYSDEC Class A (uncontaminated) sediment guidelines. Because of the presence of these heavy metals, the sediments will be removed from the lake using state-of-the-art closed bucket dredging equipment and transported to an upland disposal site under applicable 6 NYCRR Part 360 (solid waste disposal) guidelines. This expensive option was selected as most protective of Cayuga Lake's food web and human uses. LSC researchers propose the use of best management practices (BMPs) for containing sediment-related turbidity within the construction area. These BMPs will minimize the potential for harm to human lake users and the aquatic food web during sediment excavation.
The results of sediment quality investigations support the conclusion that construction and operation of the LSC system will have minimal impacts on the Cayuga Lake ecosystem or human uses of the lake. Temporary increases in water column turbidity in the immediate area of the excavation during installation of the intake and outfall pipelines will be the most significant sediment-related environmental impact. Because of the elevated concentrations of heavy metals, efforts will be made to minimize the resuspension of sediments, and consequently, the potential for human and aquatic organism exposure to toxic substances. The hard water nature of Cayuga Lake should minimize release of soluble metals during excavation. BMPs (closed bucket dredging, silt curtains, and removal of the sediments from the lake) are proposed to minimize the potential for bottom sediments to be suspended in the water column outside of the immediate excavation area. No adverse impacts on drinking water quality are projected. Rooted aquatic plants and algae (macrophytes) and benthic invertebrates will be physically disturbed as a result of the pipeline installations, but communities are expected to quickly re-establish.
Temporary increases in turbidity in the immediate vicinity of the intake and outfall are possible during periodic pipeline pigging operations for mussel control. No adverse impacts on drinking water quality are projected.
2.3.5.1 Existing Conditions.
Segments of the LSC intake and outfall pipelines will be installed within Cayuga Lake's bottom sediments. The proposed method of construction involves excavating the sediments using a closed-bucket dredge and removing them from the lake for upland disposal. In this section of the Draft Environmental Impact Statement (DEIS), we discuss the potential impacts of disturbing the lake bottom sediments during construction and operation of the LSC system and mitigating measures that will lessen these impacts.
The proposed dredge area will extend 137 meters (m) or 450 feet (ft) (outfall pipeline) and 275 m (900 ft) (intake pipeline) from the shoreline, and has been divided into five zones (Figure 2.3.5-1). An estimated 4,650 cubic meters (6,100 cubic yards) of sediments will be disturbed in order to install the pipelines below the sediment surface and accommodate a transfer barge area for dredging operations. Water depths within this area range from 0 to approximately 5 m (16 ft). To maintain recreational use of the lake and meet navigational safety guidelines, the intake and outfall pipelines will not protrude above the sediment surface in places where the water depth is less than 2.7 m (9 ft) at mean summer lake level (based on United States Geological Survey [USGS] datum 382.4 ft above mean sea level [AMSL]).
Cayuga Lake sediments in the proposed LSC excavation area consist of fluvial silt, sand, clay, gravel, shale fragments, and detrital organic particles. This composition reflects near-shore fill as well as sediment transport from the southern tributaries, including Renwick Brook, which enters the lake just south of where the pipelines would be installed. With the exception of the immediate near-shore area, sediment texture in the proposed dredge area is classified as a silt loam, with more than 70 percent silt-sized particles (0.05 millimeters [mm]).
The texture of soil near the shoreline (within 30 m [100 ft]) is composed of larger particles, as reflected in its classification as loamy sand. More than 50 percent of the sediment particles in this near-shore area are classified as gravel (size class 100 mm), with greater than 25 percent sand-sized particles (2 mm). Shale fragments and organic particles (primarily wood) of varying size are common. Detailed results of the physical characterization of lake sediments in the proposed dredge area are included in Appendix C-12, Sediment Quality Investigations.
2.3.5.1.1 Regulatory Approaches to Sediment Quality and Disposal Options.
Sediment quality criteria are under development at both the state and federal level. These criteria are designed to protect against adverse effects of sediment-based chemicals on various receptors: benthic aquatic organisms (through direct exposure), water column aquatic organisms (through partitioning of chemicals first from the sediment to the overlying water and then from the water column to the aquatic organism), humans (through ingestion of water and fish), and wildlife (through ingestion of water and fish).Predicting the impact of sediment contamination on receptors is a complex task. Sediments vary in texture (particle size distribution) and chemical composition, which affect the equilibrium partitioning and thus the biological availability of individual contaminants. Water chemistry of the aquatic system further affects the partitioning and biological availability of contaminants.
Sediment quality guidelines have been developed to meet two interrelated objectives: to determine when sediments are contaminated (which can be used to define the limits of remedial action), and to determine options for handling and disposal of sediments removed from aquatic systems. Sediment contamination is typically defined with respect to the impairment of specific uses of the water body (toxicity to benthic organisms, toxicity to water column organisms, or food web accumulation of contaminants that would restrict the use of the water body for human or wildlife consumption). Appropriate disposal options are those that would not cause or contribute to an impairment of use.
2.3.5.1.1.1 Federal Guidelines.
At the federal level, the United States Environmental Protection Agency (USEPA) and the U.S. Army Corps of Engineers (USACOE) have developed a testing manual entitled Evaluation of Dredged Material Proposed for Discharge in Waters of the U.S. - Testing Manual, commonly referred to as the Inland Testing Manual. The publication presents a tiered decision-making framework for evaluating and drawing conclusions on the environmental impacts associated with sediment disturbance activities. The manual provides a tiered approach to projecting the environmental impact of sediment dredging and the options for sediment disposal.Tier One requires the review of existing available information on the quality of the sediments in question. If the existing information is not adequate to determine the environmental impacts associated with the disturbance of the sediments, then the applicant proceeds to Tier Two. Tier Two requires an evaluation of whether the proposed action will cause or contribute to toxic conditions for aquatic life (both benthic and water column organisms). The Tier Two evaluation is completed by investigating the chemical quality of the sediments in question and comparing the results to state or federal water quality criteria and/or applicable state regulatory guidance. The Inland Testing Manual outlines Tier Three and Four investigations for unusual circumstances when additional data are required. The manual also provides guidance regarding the minimum criteria for defining the impact and terminating the investigation.
Existing data on the sediments of Cayuga Lake were not sufficient to determine the impacts associated with the proposed LSC in-lake construction activities. We consequently completed Tier Two activities, measuring the chemical concentrations in sediment and comparing the results to applicable state guidelines, to complete the DEIS and related permit applications.
2.3.5.1.1.2 New York State Guidelines.
In New York State, two guidance documents have been developed for screening aquatic sediments and defining appropriate disposal options. The first is the New York State Department of Environmental Conservation (NYSDEC) guidance document Technical Guidance for Screening Contaminated Sediments (NYSDEC 1994a), which defines sediment criteria to protect human health, aquatic and benthic organisms, and wildlife. The benthic organism criteria were developed based on empirical correlation between the presence and diversity of benthic organisms and the concentration of chemicals measured in a variety of sediments. Criteria to protect water column organisms, human health, and wildlife were developed based on equilibrium partitioning models and risk assessment. Results of the LSC sediment sampling and analysis were compared to these criteria.The second applicable NYSDEC document, entitled Interim Guidance: Freshwater Navigational Dredging (NYSDEC 1994b), was used to select appropriate disposal options for excavated sediments. This guidance document tabulates maximum contaminant levels of selected chemicals used to assign sediments to one of three classes: Class A (uncontaminated), Class B (moderately contaminated), or Class C (hazardous). Each of the three classes has defined acceptable disposal options.
2.3.5.1.2 Results of 1994 and 1996 Sediment Quality Investigations.
Our knowledge of the existing sediment quality in the proposed LSC dredge area is based on investigations conducted by the LSC research team in 1994 and 1996. The results of these investigations are discussed below and presented in their entirety in Appendix C-12.2.3.5.1.2.1 1994 Sediment Investigation.
Sediment samples were collected by box core on July 21 and 22, 1994 in the region where sediments would be excavated to install LSC pipelines. The box core sampled the upper 20 centimeters (cm) of the sediment profile. These samples were analyzed for Target Compound List analytes (as provided in Comprehensive Environmental Response, Compensation, and Liability Act [CERCLA] [1980]), total organic carbon, and acid volatile sulfides (AVS) in order to evaluate the chemical quality of the material. The entire data set is presented in Appendix C-12. The analytical results are summarized in Table 2.3.5-1. An illustration of the locations of the 1994 sediment sampling sites (P1 and P4) is shown in Figure 2.3.5-2.The 1994 Cayuga Lake sediment data indicated that the content of Target Compound List chemicals in the sediment was low. No organic compounds were detected at concentrations above the analytical limits of detection achieved by the laboratory that conducted the analyses.
The trace metal content of sediment samples was also low. The concentrations of total metal analyses for cobalt, copper, lead, nickel, and zinc ranged from 1.16 micromoles per gram (µmol/g) to 1.35 µmol/g. Acid volatile sulfides were analyzed as well, because their relationship to concentrations of metals is an indicator of the potential for exposure of benthic organisms to potentially toxic concentrations of some divalent metals. When the ratio of metals to AVS is greater than one, biological toxicity may occur (DiToro et al. 1991). The molar ratios of total metal to AVS were calculated and range from 0.0711 to 0.0653. The AVS calculations indicate that the potential for toxicity to benthic and water column organisms from the metals detected in the Cayuga Lake sediments in 1994 is low.
The 1994 sediment quality investigations provided a useful data set on which to base further investigation strategies. However, the data set was not adequate to support the application for dredge/fill permits for the LSC project. Sampling and analysis was conducted on the upper 20 cm of the sediment profile, not through the dredging depth (2-3 m [6-10 ft]). The analytical limits of detection achieved by the laboratory for certain compounds were not low enough to compare the results to the NYSDEC disposal guidelines. The 1996 sediment quality investigation was designed as an extension of the earlier work to address these remaining uncertainties. A research laboratory (Battelle Marine Sciences Laboratory of Washington) was contracted to perform low-level analyses of heavy metals.
2.3.5.1.2.2 1996 Sediment Investigation.
Sediment samples were collected by split-spoon and hand core on June 18, 19, and 20, 1996. LSC researchers circulated a document entitled Sediment Sampling and Analysis Protocol (Stearns & Wheler 1996) through several NYSDEC offices (NYSDEC Division of Water, Bureau of Environmental Protection, and Office of Sediment Assessment and Management) for review prior to the sampling and analysis. This document (included in Appendix C-12) was used as a guideline for the 1996 sediment investigation and provides detailed descriptions of the equipment and methods used for the sampling events.Six sampling sites (SS1-SS6) along the proposed pipeline route (subsurface section) were selected for sampling by split-spoon core (Figure 2.3.5-3). The number and locations of sampling sites were determined based on the NYSDEC's Interim Guidance: Freshwater Navigational Dredging (1994b), and input from the NYSDEC Office of Sediment Assessment and Management. In addition to the length, the anticipated width and depth of the area to be disturbed were factored into the final number of split-spoon core composite sample sites. Split-spoon core samples were taken to a depth of 3 m (10 ft) at Site SS5, and to a depth of 2 m (6 ft) at Sites SS1 to SS4, and SS6. The core sample depths represent the anticipated dredging depths for each section of the excavation (zones A-D in Figure 2.3.5-1).
Three additional hand core sample sites (HC1-HC3) along the pipeline route (subsurface section) were selected for sampling surficial sediments (Figure 2.3.5-3). These sites were located at sufficient distances from the split-spoon core sites to obtain samples with no disturbance to the top layer of sediments. The top meter of sediments was anticipated to represent a "worst case" scenario, as it is comprised of approximately 60 to 100 years of sedimentation (assuming a sedimentation rate of 1.0 to 1.6 centimeters per year [cm/yr]), and therefore likely contains elevated concentrations of these substances associated with industrial activity and/or atmospheric deposition. Hand core samples were collected at Sites HC1-HC3 to a depth of 1 m by a diver guiding a core sampling tube into the sediments in a manner that ensured capture of the finest surficial material.
Split-spoon core samples were analyzed by Quanterra, Inc., of Pittsburgh, PA. Quanterra is a New York State Department of Health (NYSDOH) and NYSDEC Analytical Services Protocol (ASP) certified laboratory. Analytical results were generated in support of both this DEIS and a combined state and federal permit for dredge/fill operations in the navigable waters of Cayuga Lake (6 New York Code of Rules and Regulations [NYCRR] Part 608, §401 and §404 Clean Water Act, and §10 Rivers and Harbors Act).
Hand core samples were analyzed by Battelle Marine Sciences Laboratory of Sequim, WA. Battelle has a documented history of proficiency in analyzing for very low chemical concentrations in freshwater sediments and has provided analytical services to the USACOE and the USEPA.
2.3.5.1.2.2.1 NYSDEC Sediment Screening Guidance.
The NYSDEC provides regulatory guidance thresholds for sediments contaminated with nonpolar organic compounds and heavy metals (NYSDEC 1994a: Technical Guidance for Screening Contaminated Sediments). These regulatory thresholds have been developed to protect four uses of surface water resources: human health, wildlife health and reproduction, benthic and water column organisms (acute toxicity), and benthic and water column organisms (chronic toxicity).
The most stringent criteria (lowest allowable contaminant levels) are developed to protect human health. Human health bioaccumulation can result from contaminants entering the primary consumer level of the aquatic food web, bioaccumulating or bioconcentrating among the predatory species, and finally entering the human body through ingestion of fish flesh. Wildlife bioaccumulation is a result of ingestion by terrestrial predatory species of aquatic organisms and affected water-containing organic compounds, and may have such effects as reproductive failure. Acute toxicity to benthic aquatic life is a result of exposure to lethal concentrations of contaminants and causes mortality to the exposed organism. Chronic toxicity to benthic aquatic life is a result of sublethal exposure of organisms to contaminants over time to cause effects such as reproductive failure (NYSDEC 1994a).Risks associated with exposure to metals (inorganic compounds) are addressed in NYSDEC guidance with two separate thresholds for protection: the "lowest effect level" and the "severe effect level." The severe effect level corresponds to acute toxicity thresholds for aquatic organisms, while the lowest effect level "indicates a level of sediment contamination that can be tolerated by the majority of benthic organisms, but still causes toxicity to a few species" (NYSDEC 1994a).
The NYSDEC has also published guidelines for the management of sediment materials in its 1994 Interim Guidance: Freshwater Navigational Dredging (NYSDEC 1994b). These guidelines provide a sediment classification system and associated disposal options that are based on measured chemical concentrations. Class A sediments are considered "clean" and suitable for most uses, including in-lake disposal. Class B sediments are moderately contaminated with organic and/or inorganic compounds that have the potential for negative environmental and human health impacts. Class B sediments are generally considered unsuitable for in-lake disposal. Several options are available for upland disposal of Class B sediments, including use as daily cover at a 6 NYCRR Part 360 (NYSDEC)-approved sanitary landfill, as an amendment to road-base aggregate, or as a fill material at local approved disposal sites. Class C sediments are considered hazardous and must be disposed of at an NYSDEC-approved hazardous waste facility.
The Interim Guidance: Freshwater Navigational Dredging recommends composite core-style sediment sampling to the anticipated depth of dredging. The split-spoon samples were obtained to the anticipated dredge depth, mixed to form a composite, and analyzed by a New York State-approved laboratory in accordance with the interim guidance document.
2.3.5.1.2.2.2 Split-Spoon Core Samples - Analysis by Quanterra, Inc.
Organic compound (pesticide, polychlorinated biphenyls [PCB]) analysis results from Quanterra, Inc., are presented in Table 2.3.5-2. The full laboratory report from Quanterra is also presented in Appendix C-12. Analyses of individual compounds at each sampling site indicate that the sediments exceeded some NYSDEC thresholds (see Table 2.3.5-2). Organochlorine pesticides are persistent in character and were commonly used during the post-WWII period in the United States until the early 1960s. It is not uncommon to find trace residuals of these compounds in soils and sediments, especially in watersheds with agricultural land use, such as those in the Cayuga Lake basin.Compounds were detected in the 2- and 3-m composite core samples in concentrations that exceeded human health bioaccumulation thresholds, and in some cases, exceeded the higher thresholds for benthic life chronic toxicity and wildlife bioaccumulation. These compounds included tetrachlorodiphenylethane (DDD), dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethylene (DDE), dieldrin, endosulfan I and II, total chlordane, heptachlor, heptachlor epoxide, methoxychlor and total hexachlorocyclohexanes, also known as benzene hexachloride (BHCs). None of the 2- and 3-m composite core samples exceeded the NYSDEC Class A sediment criteria for any of the measured organic compounds. Additionally, Cayuga Lake fish flesh contamination monitoring does not detect pesticides or PCBs in concentrations above the NYSDEC human health bioaccumulation guidelines. The fish flesh contamination monitoring results are consistent with the 1996 sediment analysis, which did not detect PCBs above the analytical limits of detection.
Inorganic compound (metal) analysis results from Quanterra are presented in Table 2.3.5-3. Trace metals were detected at all sampling sites. Metals are part of the natural soil matrix, so their detection at low levels in sediments is to be expected. Elevated concentrations can reflect industrial inputs through effluent discharges, watershed runoff, and atmospheric deposition. Concentrations of certain metals were above the NYSDEC 1994 Interim Guidance: Freshwater Navigational Dredging thresholds for Class A (clean) sediments and/or the Technical Guidance for Screening Contaminated Sediments "lowest effect level." The NYSDEC "lowest effect level" thresholds for antimony, cadmium, copper, iron, mercury, and nickel were exceeded at nearly every site. NYSDEC Class A (uncontaminated) sediment thresholds for cadmium, copper, and mercury were exceeded at nearly every site as well.
An estimate of the concentrations of metals in the Cayuga Lake sediments that will be removed during installation of the LSC in-lake pipelines is provided in Table 2.3.5-4. This table was prepared to support an evaluation of upland disposal of removed sediments. Results of samples through the dredging depth (SS1 - SS6) are included in this calculation.
Laboratory analytical results (presented in Appendix C-12) include measurements of total Kjeldahl nitrogen (TKN), ammonia-N, and chemical oxygen demand (COD) concentrations in lake sediments. The average sediment ammonia-N concentration for all sample sites was 26.8 milligrams per liter (mg/l), which meets the NYSDEC Class A sediment (uncontaminated) limit of <40 mg/l. The ammonia-N concentration at all sample sites ranged from 3.4 to 45.8 mg/l. The standard deviation for ammonia-N at all sample sites is 16.44 mg/l and the standard error is 6.21 mg/l. The average COD for all sample sites was 72,683 mg/l. The average TKN concentration for all sample sites was 412 mg/l.
2.3.5.1.2.2.3 Hand Core Samples - Analysis by Battelle Marine Sciences Lab.
The results of Battelle Marine Sciences Laboratory's organic compound (pesticide, PCBs, and semi-volatile organic) analysis are presented in Table 2.3.5-5. Some polycyclic aromatic hydrocarbons (PAHs) exceeded NYSDEC thresholds at all three hand core sites, but most notably at sites HC1 and HC3. BHCs (hexachlorocyclohexanes) slightly exceeded NYSDEC thresholds at site HC3. The organochlorine pesticides aldrin and dieldrin slightly exceeded the NYSDEC human health bioaccumulation thresholds at site HC1.Inorganic compound (metals) analysis results from Battelle are presented in Table 2.3.5-6. Trace metals were detected at every hand core site. NYSDEC thresholds were exceeded for a number of metals at each site. The NYSDEC "severe effect" and Class B sediment thresholds for lead were exceeded at site HC2, the station closest to the shoreline.
Results from Battelle differ from those reported by Quanterra for two reasons. First, the samples analyzed by Battelle were taken from different locations than those analyzed by Quanterra (see hand core sample sites in Figure 2.3.5-3). Second, the Battelle samples were 1-meter composites, which theoretically represent about 60 to 100 years of sedimentation and impacts from the modern industrial era. In contrast, the Quanterra samples were diluted to a greater extent due to the mixing of 2 to 3 m of sediment core, and thus would include a higher percentage of deposition from pre-industrial years.
2.3.5.1.3 Results of Other Sediment Investigations.
Historical data on lake sediments were reviewed as part of the preparation of this DEIS. This assessment included a review of published and archived results of sediment surveys and benthic investigations previously conducted on the lake. Several investigations have been conducted over the past 30 years, and are discussed below. A recent survey, a cooperative sediment coring effort between USGS, Cornell University, Hobart William Smith Colleges, Syracuse University, Tompkins County Water Quality Coordinating Committee, and the U.S. Department of Energy, was conducted in July 1994. Analysis of these cores is in progress.In 1986, the Environmental Measurements Laboratory of the U.S. Department of Energy and the Center for Climatic Research conducted a study of the sediments in Cayuga Lake (Heit et al. 1986). This research was designed to determine the deposition of polycyclic aromatic hydrocarbons in the sediment. Cores were collected and dated, historic changes were recorded, and pollution trends were established.
The New York State Electric and Gas Corporation (NYSEG) obtained lake sediment cores along the southeastern shoreline of Cayuga Lake in 1973 (NUS Corporation 1973). This was done to evaluate baseline environmental conditions to support an environmental evaluation of a nuclear power plant proposed for Cayuga Lake.
In 1973, a graduate thesis on Cayuga Lake aquatic plants incorporated sediment sampling (Vogel 1973). Grab sediment samples were collected at 33 locations on the lake. Sediment analyses revealed that southern lake sediments are comprised of 10 to 20 percent clay, 45 to 85 percent silt, and up to 80 percent sand. These findings are generally consistent with the geotechnical findings of the 1994 and 1996 sediment investigations. The samples were also tested for pH, percent organic matter, available phosphorus, nitrate nitrogen, total nitrogen, potassium, magnesium, calcium, manganese, iron, aluminum, and zinc.
Ludlam's 1964 research on the sediments of Cayuga Lake revealed that the lake sediments are patterned as banded pairs that are usually deposited on the lake bottom on an annual basis. The pairs of bands were approximately 2 cm (0.78 in.) thick in the top 1.5 m of the sediment cores, and were comprised of alternating pale and dark bands. Grain size differences between the bands were slight and no differences between microfossils were noted. Local environmental conditions, such as weather and sedimentation rates, determined the formation of up to six distinct facies of banded sediments that could be identified within the pairs.
2.3.5.1.4 Results of Biological Investigations in the Littoral Zone.
The benthic community of macrophytes (rooted aquatic plants and algae), and invertebrates will be disturbed during excavation activities inthe littoral zone necessary to install the LSC intake and outfall pipelines. Historical data on the benthic community were reviewed as part of the preparation of this DEIS. Additional data were collected during the LSC field investigations in 1994, 1995, and 1996.2.3.5.1.4.1 Benthic Invertebrates.
Benthic invertebrates spend all or most of their existence at or near the lake bottom sediments. The most common benthic taxa are crustaceans, insect larvae, oligochaetes, and molluscs. Benthic invertebrates transform the fine particulate detritus they utilize for food into animal protein that can be used for other animals higher in the food web. The 1994 monitoring program was designed to assess the benthic invertebrate fauna living near the LSC intake and outfall.The benthic fauna of Cayuga Lake have been surveyed several times in the past (Birge and Juday 1919; Henson, Bradshaw, and Chandler 1961; Dahlberg 1973; and Oglesby 1978), but a quantitative comparison of those studies with the data collected in July 1994 is not straightforward for two reasons. First, previous authors concentrated on macrozoobenthos and did not enumerate small cladocerans and copepods. However, the majority of organisms collected in the July 1994 sampling event were small cladocerans and copepods. Second, each researcher used a different taxonomic level of identification. For example, Dahlberg (1973) identified most taxa to species level, whereas the inventory for 1994 identifies taxa to subclass or a higher taxa.
A total of 17 major taxa were identified in samples collected on July 22, 1994 (Table 2.3.5-7). Table 2.3.5-8 provides a listing of zooplankton taxa found in Cayuga Lake during the summer of 1994. Littoral sites P1 and P2 had 13 and 11 taxa, respectively. Profundal sites P3 and P4 had 13 and 14 taxa, respectively. Eleven taxa were collected at Station R1. The limited data set suggests that the number of taxa is higher and individuals are more evenly distributed among taxa around the P3 and P4 sites. Densities were definitely greater in the littoral than in the profundal sites.
In the littoral sites (less than 4.5 m depth), harpacticoid copepods were by far the most numerous (79 to 86 percent). Next in prevalence were ostracods (5.0 to 5.6 percent), and benthic cladocerans (2.9 to 4.9 percent). Cyclopoid copepods, nematodes, and chironomids were less abundant.
In general, the benthic communities are more dense and diverse in shallow water than in deep water, probably due to the higher quantities of nutrients and higher microhabitat diversity created by standing macrophytes (Thorpe and Covich 1991). In Cayuga Lake, the proportion of harpacticoid copepods, chironomids, and oligochaetes declined sharply with depth. D. affinis and M. relicta were absent from the littoral zone samples.
2.3.5.1.4.2 Rooted Aquatic Plants and Algae (Macrophytes).
Macrophytes in the dredging region consist primarily of common northeastern United States submergent rooted aquatic plants and algae. As part of the LSC field investigations, we collected samples in several locations in the littoral region where the LSC pipelines will be buried. No rare species were found. Water milfoil (Myriophyllum spicatum) and water weed (Anacharis canadensis) were moderately abundant at the sample stations, with notable populations of pond weed and water celery (Najas flexilis, Potamogeton pectinatus, Potamogeton pusillus, and Vallisneria americana) present as well.
2.3.5.2 Impacts of the Proposed Action.
The proposed method of handling displaced sediments is to remove them from the lake with a closed bucket dredge, transport them to the shoreline, and haul the sediments (after partial dewatering) to an NYSDEC-approved on-shore disposal location. To minimize any additional disturbance of sediments, only the first 30 m (100 ft) of the trench from the shoreline will be backfilled with clean fill after the pipelines are installed. The remainder of the trench will be allowed to fill with sediment, which will accumulate during the normal siltation process of the lake.
Sediment excavation can potentially affect the physical, chemical, and biological character of the dredging area and adjacent aquatic environment. The removal or relocation of bottom sediments causes physical alterations of the lake's bathymetry. The suspension of sediments in the water column during dredging could cause additional physical alterations. The resulting turbidity reduces light penetration and can locally increase water temperature. The temporal and spatial extent of elevated suspended solids in the water column depends onthe sediment texture (particle size distribution), lake current velocity, and the efficacy of mitigating measures such as silt curtains and timing of dredging activities.
Physical impacts may have associated biological impacts as well. Sediment excavation removes habitat and destroys benthic biotic communities. Decreased light penetration temporarily alters the environment for benthic and water column photosynthetic organisms (plants and algae).
Chemical impacts result from the release of contaminants adsorbed to sediment particles or present in the pore water to the water column during dredging activities. Partitioning of organic compounds between the sediment and the water column depends on the relative affinity of each chemical for the aqueous or organic phase (commonly indexed by the octanol-water partition coefficient), the relative concentration of the chemical in the lake water and sediments, and the properties of the lake water such as pH, temperature, hardness, dissolved and particulate organic carbon and alkalinity. The amount of metals released and their biological availability also depends on the nature of the disturbance and the properties of the lake water. Each metal sulfide oxidizes at a different rate, and each solubilized metal has a unique affinity for repartitioning onto solid phase particulates in the water column and lake bottom.
Once released into the water column, the sediment chemicals may produce biological impacts, which could vary depending on the resulting concentration (after dilution and dispersion) and the temporal and spatial extent of elevated concentrations. Biological exposure and the potential for related impacts depends on the assemblage of organisms present and their vulnerability to the individual contaminants. Exposure to both dissolved and particulate contaminants in the water column is possible, depending on the feeding habits of the organisms.
Swimming and other water contact recreation will not occur within the construction zone during installation of the LSC pipelines. Therefore, the potential impact on the human population is ingestion of sediment contaminants in drinking water drawn from the lake. Filtered water supplies could be affected by soluble contaminants; unfiltered water supplies could be affected by both soluble and particulate contaminants. The severity of potential adverse impacts on drinking water quality depends on the magnitude of the chemicals released, the dilution and transport mechanisms to the water intakes, and the effectiveness of the proposed best management practices in containing contaminants within the construction area.
The impacts discussed are limited to the construction phase of the LSC project. During the operations phase, the mussel control efforts could present one additional potential impact. The pigging operation to control the growth of exotic mussels may have a short-term, but recurrent, impact on turbidity in the immediate vicinity of the intake and outfall structures. Temporary increases in turbidity are projected to be associated with the high velocity water discharge created by the pigging operation designed to scour the interior of the pipelines of mussels and other biofouling organisms.
2.3.5.2.1 Spatial Extent of the Excavated Region.
The region where the intake and outfall pipelines are to be buried will extend into the lake approximately 137 m (450 ft) for the outfall pipeline and 275 m (900 ft) for the intake pipeline. These distances are determined by the depth of overlying water necessary to meet navigational safety guidelines. See Figure 2.3.5-1 for an illustration of the spatial extent of the region to be excavated. The 76 m (250 ft) of the dredged area nearest the shoreline (Zone A) will be 3 m (10 ft) deep by approximately 21 m (70 ft) wide. In this area, the intake and outfall pipelines will be installed parallel to each other. The pipelines diverge near the end of Zone A, with the outfall pipeline aligned west for an additional 84 m (275 ft) out into the lake, and the intake pipeline aligned north for another approximately 238 m (780 ft). The total area to be excavated is approximately 6,900 square meters (74,000 square ft.). The sediment volume to be disturbed is estimated at 4,650 cubic meters (6,100 cubic yards).2.3.5.2.2 Physical Impacts.
The primary physical impact of the excavation activities will be temporary increases in water column turbidity. The closed bucket dredge will minimize sediment loss to the water, but we anticipate that some turbidity will be created. Light penetration will be temporarily diminished. Localized temperature increase from the increased turbidity is possible as well. Silt curtains will be employed to contain suspended sediments within the construction zone and allow them to resettle within the construction zone.Secondary impacts will include minor bathymetric changes caused by the construction activities. The top of the intake and outfall piping will be installed at or below the original lake bottom evaluation. The trench will be backfilled with clean fill within 30 m (100 ft) of the shoreline, but the remainder will be allowed to fill with sediment during the normal siltation process of the lake.
The post-construction sediment particle size distribution gradient in the excavated area will be different than the original configuration. Sediments that are disturbed or inadvertently released from the closed bucket dredge will settle through the water column at different rates, depending on their density. Larger, heavier particles will settle first. Smaller, finer sediments will settle from the water column last, blanketing the lake bottom. The finest sediments will contain the highest percentage of contaminants. This is primarily a function of the high cation exchange capacity of the smaller particles.2.3.5.2.3 Chemical Impacts.
Short-term chemical impacts may be associated with the construction activities, as the sediments are removed from the lake to enable installation of the intake and outfall pipelines.Results from laboratory analyses indicate that concentrations of pesticides, PCBs, and semi-volatile organic compounds in most of the samples are near or below NYSDEC thresholds for Class A (uncontaminated) sediments. Thresholds of potential concern to human health and food web bioaccumulation are not exceeded. We therefore conclude that toxicity to water column organisms and adverse impacts on drinking water quality from elevated concentrations of organic compounds will not occur as a result of the proposed sediment excavation.
Analytical results further indicate that concentrations of heavy metals in the sediments warrant an NYSDEC classification of "B" (moderately contaminated). The potential for the heavy metals to adversely impact the food web and drinking water quality of the lake depends on their concentration after dilution and transport to receptors, and their biological availability. Measurement of heavy metals and AVS present in surface sediments in the littoral region indicated that the concentration of AVS was sufficient to prevent biological availability of the heavy metals to benthic organisms. However, as sediments are disturbed and come into contact with the well-oxygenated Cayuga Lake water column, the sulfide complexes that bind heavy metals and render them biologically unavailable may be oxidized. This chemical oxidation process may result in the release of metals to the water column.
The chemical equilibrium model MINEQL+ (Schecher and McAvoy 1992) was used to evaluate the speciation of metals potentially mobilized from Cayuga Lake sediments as a result of the dredging operations. The composition of major solutes in Cayuga Lake water was used as input to the model. Since measurements of soluble metals in the water column are not available, the calculations were made assuming that each metal was at a concentration of 1 x 10-8 molar (M). For most metals, this assumption would overestimate the actual concentrations. A water column temperature of 10°C was assumed.
Results of the chemical equilibrium modeling analyses are summarized in Table 2.3.5-9. Trace metals in the lake water are largely associated with carbonate complexes. This is typical of high alkalinity hardwater lakes such as Cayuga. Most metals exhibit relatively low concentrations of the aquo (uncomplexed) form. This analysis suggests that if trace metals are mobilized from the sediments as a result of the dredging operations, they will generally not be in a biologically available form. Exceptions to this pattern occur for zinc (Zn2+) (100 percent of this metal is predicted to occur in an uncomplexed form); and silver (Ag+) (30 percent of this metal is predicted to occur in an uncomplexed form). The uncomplexed form of these metals are considered biologically available.
Because of the uncertainties in predicting the partitioning and biological availability of sediment metals, we have decided to remove the sediments from the lake and to employ methods of handling designed to minimize contact between sediments and the overlying water. Consequently, we project no adverse impacts of sediment metals on aquatic organisms or drinking water quality as a result of the LSC dredging activities.
Concentrations of TKN in the water column will increase temporarily during construction and system startup, but will return to background as sediments settle and soluble nitrogen disperses in the lake. Ammonia concentrations will also increase temporarily, but the concentration of ammonia in the water column following initial dilution will fall below toxicity thresholds for aquatic organisms. The COD results indicate that disturbance of the near-shore sediments may result in a limited temporary increase in oxygen demand during LSC construction. No adverse impact on the aquatic biota is projected.
2.3.5.2.4 Biotic Impacts.
Biotic impacts of the sediment excavation will result from the physical removal of habitat, release of chemicals in the sediment and pore water to the overlying water, and suspension of sediments and resultant turbidity. Temporary productivity increases may occur as some portion of nutrients currently held in sediments becomes available as a result of sediment disturbance during construction and startup. Motile organisms such as fish will avoid the region of elevated turbidity associated with the construction activities. The silt curtains will prevent migration of fish into the impacted area.2.3.5.2.4.1 Benthic Invertebrates.
Installation of the subsurface segments of the LSC pipelines in Cayuga Lake will temporarily disturb benthic invertebrate communities in the immediate area. One hundred percent mortality of benthic invertebrates in the dredged area can be assumed to occur as a result of trauma and/or burial during construction activities and the LSC system startup. However, these communities should re-establish themselves quickly following disturbance based on the high population density in adjacent areas and the animals' short generation time.2.3.5.2.4.2 Rooted Aquatic Plants and Algae (Macrophytes).
Macrophytes along the pipeline routes will be removed during construction. Additionally, increased turbidity and resulting sedimentation may affect the environment for macrophytes a short distance beyond the limits of construction. However, plant and algal communities should re-establish themselves quickly following construction disturbance.2.3.5.2.4.3 Toxicity to Water Column Organisms.
Chemicals adsorbed to sediment particles or present in the pore water may be released to the overlying water column during dredging activities. Water column organisms such as phytoplankton and zooplankton that cannot avoid the construction region could potentially be exposed to soluble or particulate contaminants that are currently held in the sediments. The proposed action to use a closed bucket dredge will minimize this potential release.Concentration of chemicals that would be released in the water column, their chemical state, and biological availability cannot be quantitatively predicted. However, we are able to draw qualitative conclusions by comparing the sediment concentrations to known benthic life criteria (assuming that water column organisms can tolerate short-term exposure to comparable levels) and by examining available equilibrium partitioning data.
Concentrations of organic compounds measured during the 1996 sediment investigations were below benthic life chronic toxicity thresholds in most cases (see Tables 2.3.5-2 and 2.3.5-5). Furthermore, due to the well-documented hydrophobic nature of the compounds (McLachlan 1996; Somasundaran, Healy, and Feursteneau 1964; Sherma 1995; Scamehorn, Schecter, and Wade 1982; Smith, Hale, and Greaves 1993), concentrations of dissolved nonpolar organic compounds in the water column following sediment disturbance are not expected to be at concentrations that would adversely impact the biota.
The proposed mitigating measure of sediment removal with a closed bucket dredge minimizes the potential for adverse environmental impact. Therefore, although concentrations of some heavy metals were measured in excess of NYSDEC guidance values, we project that the sediment removal activities will have no long-term adverse impact on the biota. This conclusion is based on the concentrations of metals in the sediments, which in most cases are within 20 percent of the Class A guidelines, and the limited region of disturbance.
2.3.5.2.4.4 Impacts on Drinking Water.
There are several individual homes and seasonal cottages in the vicinity of the proposed dredge site that may draw water from Cayuga Lake. According to Mr. Kevin Kauffman, Executive Director of the Bolton Point Water Plant in Ithaca, several dwellings in the 1200 block of East Shore Drive may draw water from this region of the lake (see Figure 2.3.5-4). Based on the concentration of chemicals in the sediments and the fact that best management practices will help to contain turbidity within the excavation region, there will be no adverse impact on drinking water quality resulting from installation of the LSC pipelines.
2.3.5.3 Mitigating Measures.
Measures to reduce impacts related to sediment disturbance have been incorporated into plans for construction and operation of the LSC system. Measures will be employed to minimize increases in turbidity, minimize turbidity outside of the construction corridor, and minimize disturbance to aquatic life during both construction and operation of the system. During operation of the LSC system, a diffuser incorporated into the outfall pipe will limit impacts related to sediment disturbance.
2.3.5.3.1 Turbidity Minimization During Construction.
In order to minimize the disturbance of sediments, and thus minimize turbidity increase, we propose to utilize environmental dredging equipment (mechanical type) to remove the sediments in the areas described in Section 2.3.5.2.1 of this report. This equipment would include an environmental trenching bucket. The bucket design incorporates modifications from the traditional bucket that enable it to achieve a high solids-to-liquid ratio and secure closure of the mouth through electronic sensors and compressible seals. This type of equipment has been successfully implemented during dredging operations to minimize turbidity increases. The environmental trenching bucket has been demonstrated to reduce construction turbidity levels up to 90 percent, as compared to conventional trenching methods (Hempel 1993).To further address the potential increases in turbidity, silt curtains will be utilized to limit (to the greatest extent possible) the turbidity increases to the construction corridor. Silt curtains will most likely consist of floating booms anchored with heavy steel rods or some other means (Figure 2.3.5-5). A woven calendared monofilament geotextile composed of polypropylene filaments with an apparent opening size of 0.21 mm (70 sieve) will be specified. This mesh size will contain sediment particles in the size range greater than 0.21 mm. Based on the sediment texture data collected as part of the LSC field investigations (presented in Appendix C-12), the mesh would retain up to 83 percent of the near-shore sediment material (coarser grained) and 2 percent of the deeper sediments (finer grained).
To further define the appropriate selection of silt curtain material, design parameters will be considered. Soil retention, permeability, anticlogging, survivability, durability, and application filter requirements will be evaluated. These design criteria will be addressed to balance the need for sediment retention with the need to withstand the lake currents.
Any sediment particles inadvertently suspended during the closed bucket dredging operation will resettle through the water column at different rates based on specific gravity and water depth. Based on the results of the hydrometer analyses of the six sediment samples (presented in Appendix C-12), the settling velocities for the sediment particles ranged from 1.66 x 10-4 to 1.0 x 10-1 cm/s. Up to 60 percent of the near-shore sediment material would settle in less than one hour (assuming a 10-ft water depth), whereas up to 33 percent of the deeper (finer-grained) sediments would settle in less than one hour (assuming a 10-ft water depth). Up to 75 percent of the deeper (finer-grained) sediments would settle in less than one day (assuming a 10-ft water depth).
2.3.5.3.2 Material Handling Procedures.
To control potential impacts to the environment in the areas surrounding the access points to the lake and the transportation routes, we propose the use of lined rolloffs for placement of the dredged material and transportation to an approved disposal site. Based upon the solids content of the dredged material following placement in these lined rolloffs, physical methods, such as solidification, could be employed to increase the solids content to a level suitable for transport and disposal, if necessary. In an effort to reduce potential water quality impacts, any water removed from the rolloff containers following dredging will be pumped to a temporary sediment basin, as indicated on Figure C-16-45 in Appendix C-16. This basin will act to retain sediments prior to the release of the water to the ground surface. This basin will be constructed of a ring of haybales overlain with filter fabric.
2.3.5.4 Unavoidable Impacts.
The results of both the 1994 and 1996 sediment quality investigations support the conclusion that temporary increases in water column turbidity in the immediate area of the pipeline excavation activities will be the most significant sediment-related unavoidable environmental impact. However, this impact will be mitigated to the extent possible by using closed bucket dredging, silt containment curtains, and other environmentally sound in-lake construction approaches. Sediments will be removed from the lake for upland disposal. Elevated turbidity will temporarily decrease light penetration. No long-term impacts on algal or macrophyte communities are likely to occur as a result of construction.
A temporary increase in water column turbidity in the immediate area of the LSC outfall following the LSC system startup is anticipated. Macrophytes and benthic invertebrates will be physically disturbed as a result of the pipeline installation, but communities should quickly re-establish themselves.
Finally, the resuspension of some sediments with elevated concentrations of heavy metals during construction could potentially cause or contribute to toxicity to water column organisms. This potential impact is difficult to quantify, however, as we cannot accurately predict the amount of metals in the sediments that would be biologically available. Based on the measured concentrations of metals in the near-shore sediments, and the chemical nature of Cayuga Lake water, we project that the excavation of sediments to install the LSC pipelines will not create elevated concentrations of soluble or particulate metals. The proposed method of sediment excavation using a closed bucket dredge and disposal on land will minimize this potential impact. No impact on drinking water quality is projected.
