Summary
Zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena bugensis) are two species of freshwater mussels found in Cayuga Lake. These species have spread throughout lakes and waterways in the northeastern U.S. and are notorious for their tendency to colonize on water intake pipes, boat hulls, and docks. If mussels colonize on the Lake Source Cooling (LSC) intake pipes and associated facilities, they will increase pipe roughness and reduce flow through the lake water pumps.
Based on the LSC research results, it is anticipated that zebra mussels will not colonize to any significant extent within the LSC system. However, quagga mussels are more tolerant of the colder temperatures that exist at the depth of the LSC intake, and are expected to colonize the intake, heat exchangers, and associated piping in the LSC system. Quagga mussel colonization is not anticipated to occur at rates that typically occur in warmer, shallower waters. Controls will be necessary to prevent quagga mussel colonization from impeding the operation of the LSC system.
Various strategies to control mussels, including both chemical and nonchemical forms, are available. No single control will protect all components of the LSC system, so a combination of controls have been considered. Controls that would prevent settlement of mussels on a majority of the LSC system components are all chemical in nature (e.g., chlorine and copper ion generation). Reactive controls allow mussel fouling to occur between treatments and can be chemical (e.g., oxidants and nonoxidizing organic molluscicides, pH depression) or nonchemical in nature (e.g., pipeline pigging, manual cleaning, and thermal treatment). Each control strategy has associated benefits, costs, and risks.
The mussel control strategy to be employed for the LSC system will include: (1) the physical pigging of the intake and outfall pipe, as needed (twice per year maximum); (2) manual cleaning of the outfall diffuser nozzles and heat exchangers as necessary; and (3) annual system shutdown, during which the temperature of the water within the heat exchange facility and associated piping will be raised to about 38°C (100°F). Established mussels will be killed by exposure to this elevated temperature. The thermal treated water will be blended with lower temperature lake water prior to discharge to the lake. This control strategy will rely on infrequent mechanical controls and temperature manipulation to control mussels. Cornell has selected a nonchemical control strategy to minimize any potential secondary environmental impacts associated with mussel control.
Remote operated underwater video cameras will be employed to monitor the rate of mussel colonization of the intake structure and pipes. The heat exchangers and other on-shore facilities will be designed to biomonitor mussel colonization. In this manner, control measures can be employed only when necessary.
Zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena bugensis) are two species of nonindigenous freshwater mussels currently present in Cayuga Lake. These species are collectively referred to as Dreissena. In 1986, zebra mussels were first identified in North America in Lake St. Clair, and since that time have rapidly spread to all the Great Lakes and their connecting waterways, the Finger Lakes, and many major rivers in the Northeast (Ohio Sea Grant 1993). The Lake Source Cooling (LSC) researchers expect that zebra mussel populations peaked in Cayuga Lake during the summer of 1996, and that quagga mussel populations will increase over the next few years.
Dreissena can attach to most solid surfaces and readily colonize water intake pipes, boat hulls, docks, and natural surfaces. These species could potentially colonize within the LSC facilities, constricting flow, increasing headloss and pumping requirements, and impacting the operation of the LSC system. Control measures to prevent or remove Dreissena colonization will be necessary to prevent operational impact to the LSC system.
In addition to Dreissena's potential impacts to LSC operation, their presence can also impact water quality. Dreissena graze on several species of algae and can remove phytoplankton from the water column (Ohio Sea Grant 1993).
This section of the Draft Environmental Impact Statement (DEIS) discusses the status of Dreissena in Cayuga Lake, and presents the strategy that will be used to control mussel colonization in the LSC system. This section also presents an assessment of potential impacts of this strategy on Cayuga Lake and measures that will be taken to mitigate potential impacts.
2.3.6.1 Existing Conditions.
2.3.6.1.1 Distribution and Abundance of Dreissena.
The recent spreadof Dreissena throughout North American water bodies has prompted research designed to explain the environmental limitations of these mussels and the conditions under which they proliferate. Table 2.3.6-1 lists the water quality characteristics of water bodies where zebra mussels are likely to persist, with corresponding ranges found in Cayuga Lake. These water quality conditions may not exist at all depths and locations within a water body or at all times of the year. However, if they generally exist in the shallow areas of a water body during some period of the year, colonization is likely, as is distribution to deeper, colder areas via current dispersion and gravity settling. Quagga mussels also thrive under the conditions indicated in Table 2.3.6-1, except that their reproductive temperature limit is lower (about 8°C, 46°F) and their preferred temperature range is wider (4°C to 20°C, 39°F to 68°F) (Ohio Sea Grant 1994). The following paragraphs discuss the environmental limitations of mussels in greater detail and point out some exceptions to these limits.Salinity is a key factor in limiting colonization of Dreissena in estuarine and marine environments, but with the low salinity in freshwater lakes, it plays a small role.
For freshwater alkaline lakes, such as the Great and Finger Lakes, temperature (and indirectly, depth) plays a key role in the colonization of Dreissena and can differ from one water body to another. Evidence in literature indicates that zebra mussels reproduce at temperatures as low as 2.5°C (37°F) (Mills et al. 1993). The presence of small zebra mussels (<5 millimeters [mm], <0.2 inch [in]) was detected at deep water sites in Lake Ontario, suggesting successful reproduction. In general, density of mussels decreases with depth. Due to sub-optimal temperatures and low food availability at the depth of the LSC intake (76 meters [m], 250 feet [ft]), it is not expected that zebra mussels will reproduce at the intake depth at any significant rate. Evidence from a 60-m (197-ft) depth intake for a water works facility in Lake Constance indicated no zebra mussel colonization in the intake, even with their presence in shallow areas of the lake (Walz 1978). Quagga mussels are not present in Lake Constance (Walz 1996). Quagga mussels reproduce at low temperatures (Smythe 1996a).
The growth of settled mussels is also limited by temperature. Experiments by Walz (1978) indicated that no positive growth occurred in zebra mussels exposed to 4.5° to 5.5°C (40° to 42°F) water drawn from a 60-m (197-ft) depth in Lake Constance. Food availability presented the limiting growth factor at this depth. Poor growth of zebra mussels also occurs when temperatures are greater than 28°C (82°F), and no survival at temperatures greater than 32°C (90°F) (Claudi and Mackie, 1994) (Ohio Sea Grant 1993).
Local studies in Lake Ontario found adult mussels (>10 mm, >0.4 in) in deep, low temperature water (Mills et al. 1993). As Mills et al. (1993) indicated, adult size quagga and zebra mussels are found in Lake Ontario at depths ranging from 25 to 110 m (82 to 360 ft), with the total numbers and size decreasing with depth. Adult quagga mussels were also found at a depth of 130 m (427 ft). At the 75-m (246-ft) depth in Lake Ontario and a water temperature of 5.4°C (42°F), 156 quagga mussels were collected with sizes ranging from 4 to 23 mm (0.16 to 0.91 in), and 84 zebra mussels were collected with sizes ranging from 4 to 20 mm (0.16 to 0.79 in) (samples collected by dredging). At the 25-m (82-ft) depth in Lake Ontario and a temperature of 8.4°C (47°F), 929 quagga mussels were collected with sizes ranging from 4 to 30 mm, and 3,142 zebra mussels were collected with sizes ranging from 2 to 25 mm (Mills et al. 1993). These data suggest that quagga mussels are more abundant at depth than zebra mussels, possibly outcompeting them for available food. Zebra mussel populations have peaked in Lake Ontario, while quagga mussel populations are increasing and have yet to peak. According to Mills (1996a), the quaggas are displacing zebras at depths greater than 25 m (82 feet) in Lake Ontario, with the percentage of quaggas increasing since his 1993 studies. Mills (1996b) expects that quaggas will ultimately be the dominant species in the Great Lakes and Finger Lakes. These data also suggest that quagga mussels will successfully reproduce and grow at the anticipated depth and temperature of the LSC intake.
The minimum pH tolerance for reproduction of Dreissena appears to be 7.0 (Maryland Sea Grant 1993; Claudi and Mackie 1994). Successful reproduction requires a pH range of 7.4 to 8.7 based on laboratory studies (Sprung 1987). In Cayuga Lake, with a pH range of 7.9 to 8.7 at a depth of 60 m (197 ft), pH is not expected tobe a limiting variable.
Abundant calcium is necessary for shell development and tissue maintenance in Dreissena. Good growth of mussels will occur at calcium concentrations of greater than 35 milligrams per liter (mg/l), but growth is precluded at concentrations less than 4 mg/l (EPRI 1992). Levels of 43 mg/l were sampled from Station P4 in Cayuga Lake, suggesting that calcium is abundant for Dreissena growth and will not be a limiting variable.
The potassium level of Cayuga Lake is reported at 2.6 mg/l (Dahlberg 1973). Potassium levels of greater than 100 mg/l are lethal to adult zebra mussels (Maryland Sea Grant 1993) and prevent settlement of veligers (immature mussels) at 50 mg/l (Claudi and Mackie 1994), but this level is very uncommon for freshwater lakes. Ammonia is also toxic to zebra mussels at levels of about 2 mg/l (Maryland Sea Grant 1993). Ammonia levels in Cayuga Lake are generally less than 0.16 mg/l.
Dissolved oxygen concentrations of less than 2 mg/l are lethal to zebra mussels. The hypolimnion of Cayuga Lake is well-oxygenated on a year-round basis, with levels of 10 to 13 mg/l detected at a depth of 60 m (197 ft).
2.3.6.1.2 Status of Dreissena in the Cayuga Lake Ecosystem.
Zebra mussels were first identified in Cayuga Lake in 1991 and quagga mussels were first identified in 1994 (Mills et al. 1995, in review). Zebra mussels are now widely distributed throughout the lake, with dense populations noted in the shallower near-shore areas. Existing water treatment plants, utilities, and other users withdrawing water from shallow depths (<10 m, <33 ft) have found it necessary to employ control measures to minimize or prevent fouling by mussel colonization.During the summer of 1995, mussel colonization experiments were performed at Stations S11 and P2 in Cayuga Lake in support of LSC by Ichthyological Associates, Inc. Polyvinyl chloride (PVC) and high density polyethylene (HDPE) pipe plate racks were suspended in the lake. One plate rack with 12 plates (three PVC, nine HDPE; see Figure 2.3.6-1) was deployed at Station P2 at a 2 m depth, and another was deployed at Station S11 at a depth of 61 m (200 ft). A pipe-style apparatus (see Figure 2.3.6-1) was deployed at 7.5-m (25-ft), 10-m (33-ft), and 30-m (98-ft) depths at Station S11, and at a 2-m (7-ft) depth at the pile cluster near Cayuga Lake inlet. See Figure 2.3.6-2 for locations. In general, colonization was heavy at the 2-m (7-ft) depth for both the pipe and plate-style apparatus and for both PVC and HDPE. The pipe apparatus retrieved from Station S11 was analyzed for mussel densities (Table 2.3.6-2). At increased depths, colonization decreased markedly.
Although the 1995 study showed a general pattern of decreased colonization with depth, the populations may not stay consistent because quagga mussel populations in the lake had peaked at the time of the study.
2.3.6.1.3 Life Cycle of Mussels.
In the northeastern U.S. and southern Canada, reproduction in adult zebra mussels (>8 mm, 0.3 in) occurs throughout the warm water months (late spring through summer). Generally, zebra mussel eggs and sperm begin to be released when the water temperature reaches 12°C (54°F), with peak activity occurring when temperatures reach 15° to 17°C (59 to 63°F). This typically occurs around the early to mid-part of June (Claudi and Mackie 1994) and can vary from year to year and from water body to water body. Mussel larvae generally grow to a size that allows them to settle by gravity in late June and July and, if temperatures allow, may rapidly grow to adult size (8 to 10 mm) and contribute to a late summer or early fall reproduction cycle. Egg and sperm release tends to cease in late September to mid-October in the northeastern U.S. (Claudi and Mackie 1994). A single mature female mussel can produce more than 1 million eggs in a spawning season (Ohio Sea Grant 1994).The larval life cycle for zebra mussels typically lasts about four weeks. There are five distinct stages that occur in the larval cycle: (1) egg; (2) embryo; (3) veliger; (4) pediveliger; and (5) post-veliger (settling). The veliger stage is associated with initial shell development and free swimming by means of the velum. The development of a foot initiates the post-veliger stage.
In the northeastern U.S. and southern Canada, zebra mussel veligers require about three to five weeks' growth to reach a size that allows them to settle by gravity. Colder water temperatures can reduce growth rates and extend the period required for a mussel to reach a settleable size. Settlement and attachment usually occur in late June to late August and are associated with a veliger size of around 175 to 200 microns (µm) (6.8 to 7.9 mil). If amussel veliger does not find a firm object to which it can attach, it generally dies. It is estimated that only 1 to 3 percent survive to adulthood (Ohio Sea Grant 1994). Mussel attachment to surfaces is more likely to occur in areas with low water velocity (<1.5 meters per second [m/sec], 4.9 feet per second [ft/sec]), where mussels have a greater opportunity to attach to a surface. Because of the short residence time within the LSC system, mussels that attach to surfaces within the facility should not produce veligers that will mature to a size that would enable them to attach inside the facilities prior to being discharged.
Zebra mussels grow rapidly, as much as 25 mm (1 in.) in their first year, but typically around 15 to 20 mm (0.6 to 0.8 in.). They grow another 12 to 25 mm (0.5 to 1 in.) in their second year. Growth rates are dependent on water conditions, especially temperature. Quagga mussels grow up to 20 mm (0.8 in.) in their first year. Zebra mussels may live four to six years, but generally survive only two years. An adult mussel can filter up to one liter of water per day (Ohio Sea Grant 1994).
Dispersal of mussels occurs by a variety of mechanisms. Generally, in the presettling stage, mussel veligers are moved with water currents based on prevailing current directions. Once they reach a size at which they can settle by gravity, the mussel veligers drift down and with currents until they encounter a suitable attachment surface. Adult mussels can translocate either by crawling, which can occur at rates up to several meters per day (Maryland Sea Grant 1993), or by moving with currents after detachment. Translocation of adult mussels is more common in fall and winter months (Claudi and Mackie 1994). To a lesser extent, waterfowl and other aquatic organisms also assist in the dispersal of mussels.
Mussels attach to surfaces by secreting a tuft of fibers known as byssal threads (collectively forming a bysuss) from a gland near the foot of their shells. The threads have an adhesive disk at their end that attaches to surfaces by secreting a protein adhesive. To detach, the mussels secrete enzymes that break the byssal threads near the foot. Byssal threads are regenerated after detachment (Claudi and Mackie 1994).
Zebra mussels will colonize on any hard surface, and can reach densities of up to 30,000 to 70,000 mussels/m2 (2,800 to 6,500 mussels/ft2) under certain conditions. Zebra mussels will also colonize soft, silty lake bottoms where harder objects are deposited to serve as substrate (Ohio Sea Grant 1994). Zebra mussels also will attach to one another, growing to thicknesses of up to 150 mm (6 in.) (O'Neill 1996). Although limited data are available, quagga mussels are more likely to grow in single layers and produce more patchy distributions than zebra mussels (Smythe 1996b). Quagga mussels can grow on the soft silty bottom sediments of lakes (Ohio Sea Grant 1994).
2.3.6.1.4 Implications for the LSC System.
The LSC system may be impacted by the presence of Dreissena in Cayuga Lake, and controls will be necessary to prevent operational difficulties due to colonization. Because of the cold temperatures of the intake water (4 to 6°C, 39 to 43°F), significant reproduction and growth of zebra mussels are not anticipated in the vicinity of the intake. While data are limited as to the extent of reproduction of quagga mussels at the depth and temperatures of the LSC intake, it is anticipated that reproduction and growth will occur, but not at rates typically seen in shallower, warmer waters. However, mussels of a settleable size can also be transported to the area of the intake by storms and currents from shallower near-shore areas, where they are more prevalent. These mussels may be drawn into the system. Once mussels are in the LSC system, there are a number of areas where they might attach. Any area of the system in which water velocity is low (<1.5 m/sec, <4 ft/sec) is susceptible to mussel colonization. Low velocities will occur in several areas of LSC during low cooling demand periods. However, high velocities can be maintained through the heat exchangers by staging their operation, thus discouraging mussel colonization on these critical surfaces.The portions of the LSC system that run from the heat exchange facility (HEF) to the outfall may be particularly susceptible to mussel colonization as temperatures will have been raised to levels more conducive to mussel growth (12°C to 13°C, 54°F to 55°F), and will be maintained at these levels year-round. Any settleable-stage veligers that reach this area will find an environment conducive to attachment and growth if no controls are employed. Due to the periodic low velocities and the length of the intake piping, settlement may occur in this area prior to reaching the HEF.
The water in the intake piping will be at temperatures consistently near 4°C (39°F) which is an environment that may limit growth of quagga mussels and limit survival of zebra mussels. At the anticipated temperatures of the intake water, it is not expected that rapid colonization of Dreissena will occur within the intake piping. However, some colonization will probably occur, mainly by quagga mussels, and could impact LSC operation.
Reproduction of adult mussels within the LSC system will not be a source of veligers that attach to system surfaces, as detention times within the LSC system are anticipated to be about one to six hours, depending on flow rates. Veligers produced within the system will be carried to the outfall and discharged before reaching a size at which they can attach, unless they encounter a quiescent area inside the system where oxygen and food is sufficient for growth.
The colonization of mussels on the intake piping can decrease pipe diameter and increase pipe roughness, potentially increasing pumping head requirements and reducing flow from the lake water pumps. Increases of pipe friction coefficients of 9 to 16 percent over a two-year period have occurred in shallow intakes (<13 m, <44 ft) in Lake Erie due to mussel growth, resulting in about a 10 percent reduction in flow capacity (Sarrouh and Ramadan 1994).
2.3.6.2 Impacts of Proposed Action.
2.3.6.2.1 Change in Habitat.
Dreissena are generally considered nuisance organisms, creating fouling problems for a variety of lake uses, including recreation, industrial withdrawals, and water supply. Because of their nuisance characteristics and their ability to rapidly alter the food web, management efforts emphasize eliminating mussels rather than accommodating and enhancing their growth.The LSC system will impact Dreissena habitat in both a positive and negative manner. The off-shore facilities will temporarily disrupt Dreissena colonization areas during construction, but will provide a permanent hard surface for attachment on the exterior of piping. Dreissena withdrawn from the lake that settle within the LSC system will be removed from the system by periodic control measures (to be discussed in Section 2.3.6.2.2).
Due to the high density (8 to 1,322 mussels/m2 in 1995) of mussel populations in Cayuga Lake, the biomass of Dreissena in the lake will be essentially unchanged due to construction and operation of LSC.
2.3.6.2.2 Mussel Control Practices.
Although Dreissena are relatively new to North America, they have been identified in many water bodies in Europe for years. Because of the rapid reproduction, growth, and spread of Dreissena in North America, much was learned in a very short period of time as to how to control mussel infestations in utilities and other industries. There is also a body of literature based on European experiences with control of Dreissena. Through an extensive literature search, interviews, and visits to facilities employing mussel control programs, LSC researchers identified available control strategies and evaluated them for their applicability to LSC.Table 2.3.6-3 lists available control strategies that were considered and evaluated for potential application to LSC. These control strategies were evaluated based on their:
· efficacy
· impact on Cayuga Lake
· costs
· ability to be permitted
· impact of mussel control system failure
· ability to monitor performance
· adaptability
· impact to LSC components or operationBecause no single technology was capable of protecting all components of LSC, a combination of controls was selected.
2.3.6.2.2.1 Proposed Mussel Control Strategy for LSC.
The mussel control strategy for the LSC system shall consist of the following treatments:· pipeline pigging of intake and outfall
· thermal treatment of on-shore facilities
· manual cleaning of diffuser nozzles, seal pit, and heat exchangers
· foul release coatings on the seal pitEach of these treatments is described in more detail in the following sections:
2.3.6.2.2.1.1 Pipeline Pigging.
Pipeline pigging involves forcing a flexible plug through pipelines to remove fouling that accumulates on interior pipe surfaces. It is not a preventive measure, but rather a corrective measure used after settlement and colonization have occurred. Historically, pigging has been used extensively in the drinking water supply field for removal of iron tuberculation from water distribution mains to restore hydraulic capacity. More recently, it has been utilized to effectively remove colonized zebra mussels from intakes and outfalls in the Great Lakes and Finger Lakes regions. Pigging is also used in marine environments to remove barnacles or other marine foulants from intakes and outfalls. The gas and oil industry has also used pigging for maintenance of transmission lines, with pigging lengths extending for miles. Pipeline pigging has proved very successful in cleaning pipelines colonized by zebra mussels.Pigging involves applying a differential pressure across a short length flexible plug (typically through pumping) to force it through the pipe. The plug (called a pig) is sized to have slightly larger diameter than the pipeline to be cleaned, which causes the pig to come in direct contact with the pipe wall or foulant. Where heavy fouling exists, generally a series of pigs is necessary for effective cleaning. The first pigs are low density (generally porous polyurethane) to determine the extent of fouling and to prevent the pig from becoming lodged in the pipeline. If an obstruction is encountered, the low density pig will deform, which allows it to continue to pass. Successively higher density pigs are then passed if increased level of cleaning is desired or required. Open pores remain on coated pigs to allow equal pressure throughout the pig. For cleaning rigid metal or concrete pipes, the final pigs can be fitted with wire brushes or other hard abrasive coatings to increase the level of cleaning.
Where fouling is minimal, the first foam pig may provide a sufficient level of cleaning. Pigs are forced to the end of pipelines and are recoverable and reusable if not damaged during the cleaning process. With proper pig core design, pigs will float to the water surface after exiting the pipe.
Mussels dislodged by the pig are carried along the pipeline by the jetting action of water moving past the pig as it moves along the pipeline. Minimum recommended velocities during a pigging operation are 0.6 to 0.9 m/sec (2 to 3 ft/sec). Observations of pigging for mussel removal indicate that the pig can pulverize some of the mussels' shells to much smaller pieces. Some material may remain in the pipe after cleaning; therefore, shells will be flushed prior to bringing the facility back on line.
Removed mussels or mussel remnants may be left behind the pig and may resettle (dead) onto the pipe. Further flushing is recommended to remove these mussel remnants. A flushing velocity of 1.25 m/sec (4.1 ft/sec) is recommended to resuspend detached adult mussels. Lesser velocities would be required to resuspend mussel remnants.
The LSC pigging operation is anticipated to be employed as monitoring indicates the need, up to twice per year, to remove established mussels from the intake and outfall pipelines. The lake water pumps are designed so that water can be reversed up to 1.6 cubic meters per second (m3/sec), or 26,000 gallons per minute (gpm) from the outfall to the intake to force a pig through the intake pipe. The outfall diffusers are designed such that they can be temporarily capped during the pigging operation, and a hinged flapper at the end of the outfall can be secured open to pass the pig. Minor piping adjustment at the seal pit would also be performed to pressurize the outfall for pigging. Pig launching points for the outfall and intake are located within the HEF. After each section is pigged, high velocity >1.25 m/sec, (>4.1 ft/sec) flushing would be performed to remove mussel remnants.
LSC researchers anticipate that two passes of a pig per section (intake and outfall) will be used to provide the desired degree of mussel removal. The intake and outfall piping are designed to accommodate the anticipated level of mussel fouling that will occur between cleanings.
2.3.6.2.2.1.2 Thermal Treatment.
As discussed in Section 2.3.6.1.1, Dreissena do not survive in water bodies where the temperature is above 32°C (90°F). Thermal treatment (high temperature) of mussels has been effectively employed by a number of industrial water users. Exposure of adult zebra mussels to 34°C (93°F) for 419 minutes will provide 100 percent mortality when zebra mussels are acclimated to 5°C (41°F). Longer contact time is required for mussels acclimated to higher temperatures. Contact time for 100 percent mortality is reduced to 116 minutes at 37°C (100°F) and requires even shorter contact times at higher temperatures (Claudi and Mackie, 1994). Studies by Spidle et al, 1995 indicate that the upper thermal limit of quagga mussels is lower than that of zebra mussels. Therefore, thermal treatment to kill zebra mussels will provide effective control of quagga mussels.Because of the difficulties in raising the temperature of off-shore facilities, thermal treatment is only considered for treatment of on-shore facilities, where water can be recirculated through heat exchangers for temperature elevation.
The advantage of thermal treatment is that it has minimal environmental impact, as heated water can be blended with lake water to acceptable temperatures prior to discharge, and requires minimal system shutdown time to achieve treatment.
2.3.6.2.2.1.3 Manual Cleaning.
Manual cleaning, including hydroblasting, abrasive blasting, and wire brush cleaning, is used by many utilities to remove mussel infestations. Manual cleaning is a corrective measure that is proposed for use on the small diameter outfall diffuser nozzles in conjunction with the pigging operation and the heat exchangers. The heat exchangers will be designed so they can be disassembled for manual cleaning. Wire brushes would be employed to remove established mussels on and in the diffuser nozzles.2.3.6.2.2.1.4 Coatings.
Because mussels must attach to a surface in order to propagate, significant efforts have been made by many researchers to create a surface that would minimize the level or strength of attachment. These efforts involve placing coatings on the wet surface of various facility components. Several coatings are available, including toxic antifouling coatings and nontoxic foul release coatings.
Antifouling coatings generally release a mussel toxin at the surface of the coating that prevents attachment. The coatings are generally copper-based and have been effective in controlling mussel colonization. High zinc paints and tributyl tin oxide (a biocide) paints have also been used; however, there may be toxicity issues related to their use. Some copper-based epoxy paints have been approved for use by the United States Environmental Protection Agency (USEPA) and New York State Department of Environmental Conservation (NYSDEC). The main disadvantages of toxic coatings are the release of these toxins into the environment and the need for maintenance (recoating).The intake screens at New York State Electric & Gas (NYSEG) Greenidge Station on Seneca Lake are coated with EPCO-TEK 2000, a copper-based epoxy paint. The coating does release a minor amount of copper, but is considered by the manufacturer to be nonablative (i.e., it does not wear away). It has been in service in Seneca Lake for about two years and has maintained the intake screens mussel-free during that period. Areas adjacent to the coated screens that did not receive coatings are completely infested with mussels (as evidenced by underwater video of the intakes).
Based on his studies with a variety of coatings and materials, Mackie (1990) reported that the best products for resisting zebra mussel infestations over the short term are those with copper as a component, especially EPCO-TEK 2000.
Foul release coatings are generally nontoxic and create a surface that may foul with zebra mussels, but the strength of attachment is minimized. As with any coating, foul release coatings require periodic maintenance, involving both cleaning and recoating. The use of nonablative or foul release coatings is proposed to coat the concrete of the seal pit located within the HEF.
2.3.6.2.2.2 Regulatory Procedures for Mussel Control Strategies.
2.3.6.2.2.2.1 Pipeline Pigging.
During pigging operations for the intake, water will be withdrawn from the outfall and pumped back through the intake in a reverse flow manner. Generally, intake pigging will be performed in the late spring and fall or winter when cooling demands are low and the lake is isothermal; therefore, no thermal impact will occur at the intake region. However, if intake pigging is performed during stratified periods, particularly summer months, warmer surface water will be discharged at the intake. Due to the short-term, low volume nature of this potential discharge and the significant tempering available from the intake region, we do not foresee any regulatory procedures for permitting short-term reverse flow discharges. Remote operated underwater video will be employed to determine when pigging will be required, and to assess the performance of the pigging operation. Although the degree of fouling is uncertain, we estimate that the quantity of shell discharge that could be anticipated is in the range of 10 to 50 cubic yards/ year.2.3.6.2.2.2.2 Thermal Treatment.
Water in the HEF will be heated to a temperature of about 38°C (100°F) and circulated within the HEF to kill mussels. Blending lake water with thermal treated water will reduce temperatures to acceptable levels prior to discharge.Although not proposed for the LSC system, direct discharge of high temperature water may be permittable, with proper monitoring, due to the rapid mixing of return flow with ambient lake water created by the outfall diffusers (see Section 2.3.2, Thermal Characteristics), and the low volume of water within the treated section.
2.3.6.2.2.2.3 Manual Cleaning.
Manual cleaning of mussels is employed extensively by many facilities to remove established mussels from critical areas of facilities. For LSC, manual cleaning is proposed for the diffusers and on-shore plant facilities, when necessary. Minimum growth area is available on the diffusers for mussel colonization; therefore, minimal removal of mussels back to the lake will occur due to manual cleaning. No permit issues are anticipated for manual cleaning.2.3.6.2.2.2.4 Coatings.
Nonablative or foul release coatings are proposed for use in LSC, specifically to critical fouling areas, such as the seal pit. No special regulatory issues are anticipated for use of these coatings.2.3.6.2.2.2.5 Future Regulatory Issues.
If the mussel control strategy were to change in the future due to poor performance of the strategies proposed here, the first consideration would be to increase the frequency of cleanings in conjunction with the proposed controls. If a preventative or reactive chemical treatment is proposed in the future, it would require a modification to the LSC State Pollutant Discharge Elimination System (SPDES) permit, which includes a public notification and comment period.2.3.6.2.3 Impacts of Mussel Control Practices on Uses of Cayuga Lake.
During cleaning operations, the area near the outfall and intake will be cleared of boat traffic to accommodate the cleaning personnel (including divers) and their water craft, and to allow pigs to float to the lake surface after exiting the pipes. An anticipated 150-ft radius area around the intake and 150-ft radius around the outfall will be cleared of boat traffic during the cleaning operation. The anticipated duration of impact to boat traffic is one to two days per year, corresponding to cleaning of the facilities.
2.3.6.3 Mitigating Measures.
The use of pipeline pigging and manual cleaning to remove established mussel colonies on the intake and outfall piping and the diffusers is a proven technology for control of mussel fouling. It is a reactive control that allows subsequent mussel fouling to occur between treatments. There are other preventative control technologies available for better protection of these components, but most are chemical in nature. Oxidants, such as chlorine, oxygen scavengers, or nuisance chemicals (such as copper-ions), effectively prevent or remove mussel colonization. These preventative control chemicals would be injected either continuously or periodically into the intake water and discharged back to the lake. Oxidants would require deactivation prior to discharge. The preventative controls, while permittable with proper operation, have the potential to be toxic to other nontarget organisms in the lake. If the procedure is not properly controlled, it could cause environmental impact to the lake on accidental discharge.
Chemical reactive controls are also available for reactive treatments and include oxidants, organic molluscicides, and oxygen scavengers. These chemical reactive treatments can cause impacts to nontarget organisms.
The use of thermal treatment is proposed for on-shore facilities due to its low environmental impact and short duration treatment periods. Accidental discharge of high temperature water can also be effectively mitigated by the rapid mixing with ambient water afforded by the outfall diffuser design (see Section 2.3.2). The use of pipeline pigging and thermal treatment will not introduce any toxic chemicals into the intake or outfall during the cleaning operation. The use of pipeline pigging and manual cleaning, combined with design of system components to allow fouling, effectively mitigates toxicity issues related to mussel control of the intake, outfall, and diffusers.
2.3.6.4 Unavoidable Impacts.
Because mechanical reactive controls are being used to eliminate preventative chemical controls, the discharge of mussel shells back to the lake during pipeline pigging operations is unavoidable. This will have no significant environmental impact as mussel shell quantities are expected to be low. The short-term, infrequent increase in turbidity in the vicinity of the intake and outfall by mussel shell discharges during pigging is also unavoidable, but will not affect drinking water quality due to its distance from drinking water intakes (approximately 8,000 and 1,600 ft from the intake and outfall, respectively).
