When it comes to pesticides, trickle-down is bad economics.
Farmers can use simple strategies to keep pesticides in the field and out of groundwater, Bryan Swistock, a Penn State Extension water resources specialist, said during a recent webinar.
Pesticides can get into groundwater by running off into surface water, leaching through the soil, or falling into improperly built wells.
Farmers should avoid applying pesticides near streams and lakes. “There’s a very strong connection between groundwater and surface water,” Swistock said.
Farmers can also use buffers and cover crops to minimize runoff, and integrated pest management can provide some alternatives to pesticides, he said.
Farmers should consider backflow protection mechanisms when filling pesticide tanks.
Otherwise, farmers may accidentally send the mix of pesticide and water back into their pond, killing their fish, Swistock said.
“I’ve had multiple cases of that occur over my experience with Extension,” he said.
Groundwater usually moves downhill like surface water, so it’s best to site anything that can contaminate groundwater downhill from a well.
Contamination risk areas include barns, septic systems, fertilizer and pesticide storage, and manure storage, Swistock said.
Obviously, siting is mostly a consideration for new construction, but “you can certainly control where you’re storing and mixing pesticides,” he said.
Ideally, sprayed pesticides will fall directly on the plant, but soil is the second-best landing place.
When pesticides land on the soil, microbes and chemical reactions can break them down. “The soil is often your best friend,” Swistock said.
Pesticides that land on hard surfaces like sidewalks can easily run off into surface water, he said.
Pesticides move quickest through soils that are coarse, sandy and shallow with low organic matter.
Pesticides are most likely to move if they have a long half-life, are highly water soluble and are used at a high rate, Swistock said.
Shallow groundwater, heavy rainfall shortly after spraying and limestone bedrock also make contamination more likely, he said.
Farmers can control some of these risks by applying pesticides at dry times.
“If we have multiple choices of pesticides, let’s look for the ones that have less risk for the water,” Swistock said.
Soil and surface water are easier to contaminate than groundwater, but they are also easier to clean.
If soil becomes contaminated, it can be removed for hazardous waste disposal or remediated on site. Often, groundwater must be pumped to the surface, cleaned and put back in the ground, Swistock said.
Wells are a particularly troublesome path for groundwater contamination in Pennsylvania.
Pennsylvania has about 1 million private water wells, second only to Michigan, but is one of the few states that does not regulate such wells, Swistock said.
About 80 percent of Pennsylvania’s wells are missing at least one key contamination safeguard, such as a sealed cap on top, he said.
A grout seal, sometimes lacking, is a cementlike material around the well casing, the well’s vertical tube.
The grout seal prevents water from flowing down the casing and contaminating the groundwater, Swistock said.
Old, hand-dug wells are particularly concerning. “They are almost like an open hole in the ground,” he said.
These wells may be wide enough that animals or people could fall into them. Disused wells need to be decommissioned properly, which includes filling the bore hole, Swistock said.
Farmers should avoid using pesticides, fertilizers and other potential contaminants within 100 feet of well heads.
“Even 50 feet is better than nothing,” he said.
If that protection area extends across a property line, the farmer should talk to the adjacent landowner.
In a study, the U.S. Geological Survey found a measurable level of pesticide in half of the Pennsylvania private water wells tested. But the pesticides rarely exceeded drinking water standards, Swistock said.
When Penn State studied 700 wells in the state a decade ago, only three wells had pesticide levels above drinking standards, he said.
Those three well owners did not know about the problem. “That’s not unusual,” Swistock said.
Because pesticides do not affect taste or smell, well owners probably would not know they have a problem unless they test their water.
Most well owners with some other contamination problems, such as coliform bacteria and lead, did not know of their problems either, Swistock said.
A relatively small number of wells had nitrates, but a larger percentage of people knew about the problem. “There’s a lot of education around nitrates,” he said.
Atrazine was one of the pesticides USGS found most frequently in Pennsylvania groundwater. That’s a common finding in such studies, as atrazine is mobile and heavily used, Swistock said.
No matter which pesticides farmers use, they can take precautions to prevent contaminating the water they and their neighbors drink.