West Nile Virus & Massachusetts Public Drinking Water Systems

Basic information to assist in the decision-making process regarding applying pesticides to public drinking water sources

Municipal officials may be deciding to use pesticides to control mosquitoes consistent with the Massachusetts Department of Public Health's (DPH) "Surveillance and Response Plan to Reduce the Risk of West Nile Virus Transmission and Human Encephalitis" (updated in 2008).  Discharge of pesticides into public surface water drinking sources and their tributaries requires prior written authorization from the Massachusetts Department of Environmental Protection's (MassDEP) Drinking Water Program. Pesticide use is not allowed in Zone I of a public groundwater source. This Fact Sheet will provide you with basic information to assist in the decision-making process regarding applying pesticides to public drinking water sources.  MassDEP anticipates it can respond in a timely manner to requests for authorization to apply larvicides or adulticides to public surface drinking waters.

Background on the West Nile Virus

West Nile virus (WNV) is a rare disease caused by a virus. WNV grows in birds, and is transmitted from bird to bird and from birds to humans by mosquitoes. Horses bitten by mosquitoes carrying WNV can also become sick. DPH has developed a surveillance and response plan to reduce the risk of West Nile Virus transmission and human encephalitis. It focuses on surveillance and preventative measures such as larviciding of the primary breeding habitat in catch basins and other areas where stagnant water collects. DPH provides daily West Nile surveillance updates at its web site (see contacts below). DPH also has fact sheets with detailed information on protective measures for individuals to follow.

Mosquito Pesticides (Larvicides and Adulticides) Are Regulated in Massachusetts

Pesticides and pesticide application in the Commonwealth are regulated by the Massachusetts Department of Food and Agriculture (DFA), Pesticide Bureau (see the Massachusetts Pesticide Control Act, MGL Chapter 132B). The Act conforms to the Federal Insecticide, Fungicide, and Rodenticide Act, Public Law 92-516, as amended. The Pesticide Bureau issues certification and licenses to applicators. Only certified and licensed individuals may commercially apply pesticides within the Commonwealth. The DFA provides certification training for municipal employees, including local Department of Public Works, to certify them to apply larvicides. By law, all pesticide applications must follow the instructions provided on the pesticide label - - this is both State and Federal law.  Mosquito pesticide controls fall into two basic types: larvicides and adulticides.  Larvicides kill mosquito larvae, are typically bacterial-based and are routinely applied to catch basins.  Adulticides are less common and are typically used only when adult mosquito populations reach nuisance and health concern levels.

Mosquito Control in Massachusetts

As of summer 2008, 186 of the 351 cities and towns in Massachusetts are members of Mosquito Control Districts (MCD). Mosquito Control Districts are overseen by the 3-member State Reclamation and Mosquito Control Board (SRMCB). MCDs monitor mosquito levels, bird mortalities, and use integrated pest management techniques to control mosquitoes. For the 165 municipalities not currently within a MCD, the Massachusetts legislature has empowered the local Board of Health through Chapter 252 Section 5B to determine whether mosquitoes within their municipality pose a public health threat and take appropriate actions, subject to state and federal law and regulation. DPH provides daily surveillance reports to assist municipalities with monitoring West Nile Virus. If your municipality is not a member of a MCD, but is interested in joining one, contact the SRMCB for assistance (see contact number below).

Public Surface Water Systems

There are over 1,600 public drinking water systems (PWS) in Massachusetts. Application of a pesticide to any surface water of a public water source or its tributaries requires the prior written authorization of the Department of Environmental Protection Drinking Water Program (see 333 CMR 13.03(16)). No pesticide application may be made in violation of the regulations, rules or statutes of the Department of Environmental Protection (see 333 CMR 13.03(21)]) and, additionally, no aerial applications may be made within 400 feet of a surface water supply (see 333 CMR 13.05(3)(c)(5)).

For the location of PWS surface waters in your community, contact the local PWS, local Board of Health (BOH) or the regional MassDEP office.

In order to apply to DEP for review of pesticide application to a public surface water source or tributary, the proponent should submit a letter to the DEP Regional Office, Drinking Water Program, with a copy to the local BOH and Water Supplier documenting:

  • The mosquito surveillance results (mosquito larvae counts, infested birds or horses, etc.);
  • Written findings from the local Board of Health determining there is a public health threat and ordering application of pesticides;
  • The pesticides proposed to be used along with the method of application; and
  • Map depicting the location of the surface public water source (and tributary if the tributary is to be treated) and the geographic area to be treated.

Public Groundwater Systems

The Zone I of a PWS (the most protected area, immediately surrounding a well; its radius is based on usage) may only be used for purposes directly related to the provision of public water, which have no impact on water quality (see 310 CMR 22.21(3)(b)). Pesticide application is banned from this area.

The Zone II of a PWS is the primary recharge area of the well.  There are specific chemicals that may not be used in the Zone II of a PWS due to their chemical characteristics and toxicity, or have been restricted due to groundwater concerns.  Those chemicals are not found in the pesticides approved by the DFA for use to reduce mosquitoes. If interested, the list (some are pesticides) can be obtained by contacting your MassDEP Regional Office Drinking Water Program or the DFA website .

Check with your local PWS, local Board of Health or the MassDEP Regional Office for locations of Zone Is and Zone IIs in your community.

Private Water Systems

Private property owners and private well owners may ask to be excluded from mosquito control applications (see 333 CMR 13.04). This may be done by contacting the clerk of the municipality in which the application may occur, by certified letter, with the person's name, address, telephone number and the name(s) of all abutters, and defining the program from which exclusion is requested.

Contact for West Nile Virus & Massachusetts Public Drinking Water Systems

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