Zebra mussels attach themselves to hard surfaces by using a tough elastic fiber tipped with an adhesive, similar to that of barnacles. Once attached, the mussels can form a dense colony within the water intake pipe. The waterline is an ideal habitat providing a continuous source of food and oxygen while carrying away mussel wastes, and protecting the mussels from predation and storm waves.
Once the waterline is infested, zebra mussels can colonize from the mouth of the intake to the plumbing inside the house. Since mussel spawning takes place when the lake waters are above 50 °F, homeowners on infested waters should assume that their intake may take in mussel larvae during much of the year.
Water System Protection
To protect a system from zebra mussels, the homeowner should think of their system in two parts: an offshore component (from the end of the pipe or foot valve in the water to the pump on shore), and an onshore component (from the pump to the plumbing in the house, including any storage tank). Generally, the offshore component will be the most difficult and expensive part to protect against mussel clogging, but may be the least difficult section to clean out if infested. The onshore component will, in most cases, be the simplest and least expensive section to protect, but the most difficult and costly to clean. Cleaning mussels from inside the household plumbing is very difficult, if not impossible.
Onshore Component Protection
First and foremost, mussels should be kept out of the onshore component of the water system. Zebra mussels larvae range from about 70 microns (.00275 inch) and larger. An in-line filter for the onshore component is a viable, relatively inexpensive, and easily accomplished, utilizing a "whole house" in-line filter capable of filtering 250 - 400 gallons per day and capable of removing all particles larger than 40-50 microns (about .002 inch). This is installed on the incoming water line at the pump prior to the in-house plumbing. There are a number of filter types, but all need periodic replacement or cleaning. The time between cleanings depends on the amount of silt, algae, and mussel larvae at a specific location and during the year. Filters cost between $50 and $100, plus installation.
Another way to prevent clogging of the onshore component is to install an in-line chlorine injector after the pump and before the water enters the in-house plumbing. Such systems add a small amount (about 0.25 parts per million) of potable chlorine (comparable to that added to municipal water) to the incoming water when the pump runs. This amount, added each time water is drawn from the lake or river, will kill zebra mussel larvae and adults and keep the plumbing mussel free. (Check with your local Cornell Cooperative Extension or health department office for guidelines.) Chlorine injection systems cost between $400 and $1000. A chlorinator will not keep shells or fragments from clogging faucets, and should be used in conjunction with a filter for best results.
Offshore Component Control Alternatives
The most popular method for attempting the control of zebra mussels in the offshore component is to keep them from entering the pipe by the use of strainers or filters. The common screen mesh openings on intake pipes keep out leaves and debris are 0.25 to 0.50 inches in diameter. Since zebra mussel larvae can be as small as 70 microns (.00275 inch), these strainers are ineffective as a control strategy.
Several water intake filters have been developed and tested recently and have proven to be effective. Water is pulled through a fine filter screen and/or bonded sand/composite filter (50 microns or less absolute). These units may be effective if they are backwashable and maintained on a regular basis. The units may clog under turbid (cloudy water) conditions and may create a habitat suitable for mussel growth on the inside of the housing if they are not maintained regularly. Taste, odor and bacteria may be a problem if the population is allowed to grow extensively inside the housing or in the area around the filter.
If lake residence is only used on weekends, there is a possibility that very little needs to be done. During the week while the pipe is not used, oxygen in the line may be depleted enough to kill mussel larvae. Since no testing has been done to date on residential water systems, homeowners are advised that this approach is risky and may result in pipe clogging, particularly at the end of the line. If the end of the pipe can be inspected (try tying a line to the pipe end and attach a buoy), bedding foam wrapped several times around the end of the pipe has been used by many residents on Seneca and Keuka Lake with reported good success. Some filter experts say the foam methods cannot reliably filter water to the required levels to remove larvae. Without further testing, the foam method should be considered a backup option along with other methods and practices.
Another option is to install a second waterline to the lake. Perhaps the simplest and cheapest available methods is installing a T-valve before the pump and installing a second line into the lake (See illustration on previous page). The method of control would involve alternating the use of the pipe every two weeks. The ends of the waterlines may be susceptible to clogging, so regular inspection (monthly) may be needed. A line and buoy tied to the end of the waterline would allow for easy raising and inspection of the intake. After the water has cooled to around 50 degrees in the late fall, only one waterline would need to be used. Use of the foam method described above help keep the end of the pipe mussel-free.
Many untested offshore filters are being marketed. Before buying, consider how well the filter will be protected from rapid clogging by silt, algae, debris, and mussels. Filters in metal, plastic, or other containments to protect the filters from the elements may actually foul more quickly. Homeowners considering these systems should ask how, when, and where the systems were field tested; who has had one in the water for a reasonable length of time; and what will the seller do when the system clogs. Testing should be done in the spring and fall when mussel larvae, algae, and silt are in the water; not winter when there is little threat to intakes.
Placing the water intake in over 60 feet of water affords some protection. The majority of zebra mussels are found in shallower waters. Depth is no guarantee of protection but, if used with other methods, the amount of maintenance could be reduced. Another exotic mussel starting its invasion of U.S. waters, the quagga mussel, is found much deeper than the zebra mussel and could become a problem for deep, unprotected water systems.
Sand Filtration for Offshore Control - The most common form of sand filter, the enclosed or manufactured sand filter is a sand-filled concrete or steel box with a perforated pipe in its center. The box is placed on the bed of the lake with the pipe connected to the intake pipe. There is no top on the box, allowing for water infiltration downward through the sand into the pipe. A different, and more difficult approach for source filtration makes use of buried intakes or sand filters. One form, the infiltration gallery, consists of porous intake pipes laid in trenches in the bed of a lake, backfilled with sand and gravel. A pump draws water down through the fill, removing zebra mussel larvae and other particles. Another form of intake filtration, the raised fill sand filter, replaces the trenches with a shallow layer of gravel placed directly on the bed of the lake, upon which the perforated pipes are placed. The pipes, in turn, are covered with a raised fill of sand and gravel. This raised fill sand filter functions the same as an infiltration gallery, with water drawn through the sand and gravel into the pipes, filtering out mussels and other particles. All sand based filtration systems should be constructed with backwash capability to avoid compaction of the sand and reduction of flow rate.
The environmental impacts of sand filter alternatives (siltation impact during construction and disturbance of natural bottom habitat) can be minimized or mitigated. All three structures will require permits from NYS DEC. A non-environmental drawback is the high cost of construction for the last two options.
Mechanical Remediation of Clogged Intakes - Another approach for the offshore component is to allow a certain amount of clogging, followed by periodic mechanical cleaning of the pipes. (Remember, the onshore component is always protected by its own filtration and/or chlorination system.) To facilitate mechanical cleaning, it is advisable to install a cleanout at the shore end of the intake pipes. Mechanical cleaning alternatives include:
- Snaking pipes which are short enough and have easy access from the shore end.
- Suffocating mussels by sealing pipes off long enough for the water to lose its dissolved oxygen - Since this means not using the pipe for a number of days, systems should have dual pipes installed beforehand.
- Periodically flushing intake pipes with hot water or steam.
- Use a two line system.
- A last resort for extreme situations is removal and replacement of clogged piping -This is still cheaper than cleaning out the plumbing in the house.
If you want more specific details on the different types of zebra mussel control systems, contact your local Cornell Cooperative Extension (CCE) office and ask about three publications: the New York State Sea Grant Coastal Resources Fact Sheet, 1996 entitled "Control of Zebra Mussels in Residential Water Systems" by Charles R. O'Neill, Jr.; "Stop! No Zebra Mussels Allowed"; and the Zebra Mussel Product Information List by Peter Landre, CCE.
Regulations on Installation of Zebra Mussel Protection Devices
The work that needs to be done to install an offshore component for protection against zebra mussels may require a permit from the New York State Department of Environmental Conservation (DEC) if you intend to disturb the near shore area or the lake bottom. Your regional DEC office can help you with permit requirements. Call or write to the Regional DEC office for help. The following list describes the regulated activities:
- Excavation, fill and placement of materials in navigable waters, which includes streams and lakes
- Disturbance of the bed or bank of a protected stream
- Filling, excavating, and construction in a protected wetland
- Excavation, dredging and construction within a Natural Protective Feature or Structural Hazard Area of a Coastal Erosion Hazard Area
- Any discharge of chemicals such as chlorine or hot water to surface waters
Can I get a permit in less time?- In NYS DEC Region 8, a Standard Activity Permit has been developed for several generic systems that are used to protect residential water intakes from zebra mussel colonization. The systems that are covered by the Standard Activity Permit are:
- Beach wells, drilled or driven wells in the nearshore area at or below the mean high water line (MHWL)
- Infiltration galleries in the nearshore area or in the lake bottom. Area of disturbance less than either 50 or 150 square feet below MHWL.
- Combinations of beach wells and infiltration galleries that extend out into the lake. Area of disturbance less than either 50 or 150 square feel below MHWL.
- Minimize disturbance to the nearshore area and lake bottom with a system that will reasonably meet your needs. The project can be done without placing motorized equipment in the water.
- Restore surface contours of the lake bottom and nearshore areas.
- Prevent/control erosion during the site work, reseed/revegetate immediately.
- Not place extensive amounts of fill in the lake.
Do I Need Other Permits or Approvals?- You may need to obtain a permit from the U.S. Army Corps of Engineers for excavation and fill in a regulated Federal wetland. When you apply to the New York State Department of Environmental Conservation, they will send one set of the applications to the Corps of Engineers.
You should also check with your local government, the county and/or State Health Department. The Regional office for Yates County is (315) 789-3030. The Health Department can give you advice on how to protect your water supply and ensure its use for drinking and cooking. They can also help you determine if your water supply is far enough away from your sewage wastewater disposal system to avoid contamination.