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Groundwater Monitoring

The Vermont Agency of Agriculture initiated the Pesticide and Groundwater Monitoring Program in 1986. The Pesticide and Groundwater Monitoring Program was founded to investigate the quality of groundwater and drinking water for Vermont farms and their neighbors with drinking water supplies adjacent to agricultural lands because of concern for the potential for groundwater contamination by pesticides and other agricultural chemicals.

The Agency has sampled more than 1,900 private drinking water supplies in 186 towns representing all of Vermont’s fourteen counties.  Farm owned wells account for approximately 63% of all drinking water wells sampled.  Non-farm, neighboring wells account for 35%.  The final 2% of wells includes the 21 public water supplies and other small-scale public systems also sampled by the program.  The types of water supplies sampled as part of the Monitoring Program include: drilled, driven point and dug wells and springs, ponds, streams or lakes used as drinking water supplies for human or livestock consumption and irrigation.

A major portion of the sample collection and laboratory analyses conducted by the Agricultural Water Quality Monitoring Program is paid for by the registration fees collected from companies that sell pesticide and fertilizer products in Vermont.  All sample collection work is done by Agency of Agriculture and Vermont Association of Conservation District field staff.  The work of sample analysis is conducted by the Agency of Agriculture and the Department of Environmental Conservation Laboratories.

The Pesticides and Groundwater Monitoring Program tests wells in agricultural areas to help farmers learn about practices that prevent pesticide leaching and conserve the nutrients in fertilizers and manure in the soil.  The water quality information provided by this program also helps farmers decide if tillage practices and crop rotations are working to reduce the amounts of nutrients and pesticides lost to groundwater or surface run-off. Sharing this information with farmers, agricultural dealers, landowners, conservation organizations and other departments of state government helps to improve agricultural practices, protect groundwater, raise public awareness and provide for clean drinking water and a healthy environment in Vermont.

History of the Program

The primary focus of the Pesticide and Groundwater Monitoring Program is testing for corn herbicides because, with the exception of chemicals used for cooling towers and water treatment, corn herbicides are applied more than any other group of pesticides.  In an average year, approximately 76% of all pesticides used outdoors in Vermont are herbicides applied to land used for growing silage or sweet corn. 

The Pesticide Monitoring Program also tests groundwater for nitrate (a source of nitrogen) which is associated with fertilizers, manure, compost or septic systems.  Excess application rates of manure, compost or fertilizer and faulty septic systems can cause nitrate to reach groundwater by leaching downward through the soil.

The focus on corn herbicides and nitrate in groundwater and drinking water has been maintained as a priority since the program was established in 1986.  As the Agricultural Water Quality Program has evolved and grown over the past 25 years, the Agency of Agriculture has continued to expand the scope of the Pesticide and Groundwater Monitoring Program to include other classes of chemicals, crop types, land use categories and surface water.  

Program Growth & New Projects

In addition to farm and non-farm neighbor wells, the Agricultural Water Quality Program conducts several other projects that sample both groundwater and surface water adjacent to land uses where pesticides, manure and fertilizers are applied.  These projects include farm operations that are inspected for Accepted Agricultural Practices (AAPs), Medium and Large Farm Permits (MFOs & LFOs) and Best Management Practices (BMP & NRCS EQIP) Cost Share Grants.  The Pesticide and Groundwater Monitoring Program also test wells and streams on golf courses, at fruit & vegetable farms and along highways, electric power lines and railroads that receive right-of-way (R-O-W) permits from the Agency of Agriculture and the Vermont Pesticide Advisory Council.

To support these additional types water quality monitoring projects, the Agency of Agriculture expanded the capability of the laboratory to test for many new herbicide and fungicide compounds.  The Agency has also added the technology to test for the breakdown products of these pesticide compounds in the environment.  Through cooperation with the Department of Environmental Conservation and the Department of Health, the Agency of Agriculture can conduct special investigations to test for phosphorus in surface waters and bacteria in both drinking water and surface water.

Drinking Water Standards

Drinking water standards and health advisory levels are set by the Federal Environmental Protection Agency (EPA) and the Vermont Departments of Health and Environmental Conservation.  Drinking water standards set an allowable limit of a substance in drinking water.  This limit is a health-based value on a lifetime exposure from drinking two (2) quarts of water each day for seventy (70) years.

Table #1 provides the trade names, common names, use category and drinking water standards for the chemicals tested for by the Agency of Agriculture.  These compounds are selected for testing because they are the herbicides and fungicides most commonly used in Vermont.

Table 1.  Priority Compound List




Standard / Advisory





                      3 ppb




                      10 ppb




                        6.5 ppb




                        1.5 ppb




                    70 ppb




                      2 ppb




                      2 ppb




                      10 ppb




                      2 ppb




               2,000 ppb




                      4 ppb




                  280 ppb




                        5 ppb




                    700 ppb




                    10 ppm

Notes:  Categories of Use:  A = Agriculture, R = Rights-of-Way, T = Turf & Golf Courses
Abbreviations:  ppm = parts per million = 1/10,000%, ppb = parts per billion = 1/10,000,000%

Farm & Non-Farm Drinking Water Well Data

Nitrate Results

Long-term monitoring results for Vermont demonstrate that the occurrence of nitrate (nitrogen) in groundwater and surface water is far more common than the detection of pesticides. The Agency's Monitoring Program indicates that low levels of nitrate in Vermont's groundwater are common in agricultural areas.   Historical data for the last ten years (2001-2010) indicate that approximately 11% of the wells tested had high levels of nitrate that exceeded the standard at some point in time.

To evaluate progress and the effectiveness of current agricultural management practices that may influence groundwater or surface water quality, the Agricultural Water Quality Program instituted the practice of tracking water testing results based on the most recent 5 year sampling period.  Each 5 year timeframe includes first time testing of new wells and the repeat testing of wells that are already part of the program.  The Agency of Agriculture started using this indicator in 2005.   Table # X shows the trend for significant improvement in the number of farm and non-farm wells with elevated nitrate concentrations.  The data for these rolling five year periods indicate that awareness of water testing results, nutrient management practices, farm permitting and the site remediation practices adopted by farm operators and the AAFM have a positive impact on water quality in Vermont.

5 Year Rolling Averages for Wells with Nitrate Detections Above 10 ppm

History of Nitrate Violation Rate Above 10 ppm Standard


14 %


14 %


12 %


11 %


 7 %


 5 %


Herbicide Results

The detection of herbicides in Vermont groundwater is uncommon. Long term historical data for pesticide detections indicate that only 9% of the wells ever sampled have tested positive for herbicides or fungicides.  For the most recent ten years of sampling (2001-2010) the detection rate for herbicides dropped to 5%. 

Table X+2 contains the results for both nitrate and herbicide sampling conducted between 2006 - 2010.   675 individual wells were tested during this most recent 5 year period.  The nitrate results show that 30 wells exceeded the drinking water standard of 10 ppm at some point in time.  This represents a current nitrate violation rate of 5%.  The herbicide results show that 39 wells had a positive detection for one or more herbicides.  This represents a detection rate of 6% for the reporting period.  It is important to recognize that  there were zero (0) drinking water wells with a detection of herbicide that exceeded a state or federal drinking water standard.  This represents a current herbicide violation rate of 0%.

Distribution of Herbicide & Nitrate Detections

Based on the current and long term data, the Agency of Agriculture considers nitrate, rather than pesticides, as the primary groundwater contaminant of concern for agricultural water quality in Vermont.  The Agency of Agriculture conducts both surface water and groundwater sampling projects and water quality investigations as part of a unified Agricultural Water Quality, Farm Permitting and Resource Management Program.  The recognition of nitrate in groundwater as a significant agricultural water quality concern stimulated the merger of program priorities and water sampling activities between the Pesticide Program and the Agricultural Non-Point Source Control Program.  The Agency of Agriculture now conducts surface water and groundwater sampling projects and water quality investigations as part of a coordinated Agricultural Water Quality and Resource Management Program.

Distribution of Nitrate - N Detections 2006-2010

Distribution of herbicide Detections 2006-2010

Sources of Assistance

The Vermont Agency of Agriculture (AAFM) and the Association of Conservation Districts (VACD) have field staff  available to work with well owners and agricultural landowners on water sampling, well construction, manure and silage storage systems, control of barnyard and milk house wastes, soil testing, nutrient management planning, preventing  soil erosion, stream bank restoration and other watershed conservation practices.

The State of Vermont provides this technical assistance through the AEM Program (Agricultural Environmental Management).  Field staff conduct site inspections and use a series of worksheets to help make a water quality evaluation of farms. These worksheets cover topics such as well construction, the storage of pesticides, fertilizers and manure, fuel tanks, barnyards, silage bunkers, septic systems, field buffers and nutrient management plans.  For assistance with testing your drinking water or evaluating and correcting the sources of nitrate or herbicide in your drinking water well(s), you may contact one of the regional Conservation District offices and talk with an Agricultural Resource Specialist (ARS) staff or the Vermont Agency of Agriculture.

Additional information about the Pesticide and Groundwater Monitoring Program or Vermont’s Agricultural Water Quality Program is available by contacting us here:

  • Vermont Agency of Agriculture (802) 828-2431
  • Pesticide & Groundwater Monitoring Program (802) 828-3473 

Vermont Association of Conservation Districts -

  • Franklin County District (802) 524-6505
  • Orleans County District (802) 334-8325
  • Otter Creek District (802) 388-6746
  • Windham County District (802) 254-5323