Delaware Department of

Groundwater Monitoring Program for Pesticides

Delaware’s Reliance on Healthy Groundwater


In Delaware, approximately 65 percent of the population obtains its drinking water from groundwater. For residents of southern New Castle County, Kent, and Sussex counties, groundwater is the sole source of drinking water. Much of the drinking water in these areas is provided by shallow private wells of less than 75 feet, drawing from the water-table aquifer.


How Pesticides Can Reach Groundwater


A pesticide can be defined as any chemical used to control pests; this includes herbicides, insecticides, and fungicides. Pesticides are used to control nuisance organisms and to increase crop yields; therefore pesticides are a beneficial component of Delaware’s agricultural industry. However, the potential exists of adversely affecting the environment and human health. When pesticides are applied, whether it is on a farmer’s field or around a residential home, there is a chance that some of the product may run off the soil’s surface or leach down through the soil to eventually reach the water held in the ground. In Delaware, the water table is very high; this means that the distance from the soil surface to the groundwater is relatively small. The high water table and the characterizations of the subsurface soil are factors conducive for contaminant migration into groundwater. So monitoring the groundwater for the presence of pesticides is particularly important for the state.


Groundwater Monitoring


The Delaware Department of Agriculture’s Pesticide section began monitoring the state’s shallow groundwater for pesticides in 1995. Since then, the Department has collected more than 1000 individual groundwater samples from over 220 domestic, agricultural, and monitoring wells. Individual samples have been screened for up to twenty-two different pesticides that are commonly used in agriculture and the commercial industry. These include alachlor, atrazine, carbofuran, chlorothalonil, chlorpyrifos, cyanazine, diazinon, dicamba, dieldrin, glyphosate, lambda-cyhalothrin, lindane, malathion, metolachlor, metribuzin, pendimethalin, picloram, simazine and the compound 2, 4-D. The majority of the wells tested negative.

Read a summary of the 2018-2019 sampling season by clicking on the link below. You can also access the Geographic Information System database, which shows the locations of all the monitoring wells, by clicking the link below.

Having an active monitoring program is the best way to evaluate the health of the state’s groundwater. Collecting and analyzing groundwater data allows the DDA to detect contaminants before they become significant, as well as measure its progress in its efforts to protect the state’s groundwater.


If you would like further information, please email Chris Wade.

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