As Waterborne approaches its 33^rd anniversary, we thought it would be interesting to recall our “early days” and the extensive fieldwork we conducted to address concerns about the potential for groundwater leaching associated with labeled uses of pesticides.

Waterborne, as a company, managed and completed over 30 separate studies assessing potential leaching to groundwater from normal uses of crop protection chemicals. Until the mid 2000’s, two types of studies were required by the USEPA: “prospective” and “retrospective” groundwater studies.

Prospective groundwater (PGW) studies were multi-year studies that included site selection, site characterization, instrumentation, application of a tracer (KBr) and the pesticide product of interest, sampling of soil and water for two or more years, followed by reporting. These studies were labor-intensive during the site selection, characterization, and instrumentation phases prior to application. Following the application, the first month of soil and water sampling was also intensive before settling into monthly sampling afterward.

Sites were selected in typically worst-case environments where the potential for leaching through the soil column to the saturated zone was highest. The sites often had sandy, sandy loam, or loamy sand soils with depth to groundwater (saturated zone) of 10-30 feet. The tracer (KBr) was applied, and its progress leaching through the unsaturated zone was tracked until it achieved “breakthrough” into the saturated zone.

These expensive studies were required by the USEPA to address specific concerns about select active ingredients whose environmental fate profiles indicated a potential for leaching. These studies provided a strong environmental fate database, which was used to create the SCI-GROW simulation model being developed for regulatory purposes.  They also served as a validation dataset for more advanced simulation models like PRZM.

Retrospective groundwater studies were also required by the USEPA during this time, although less often. These studies typically involved the sampling of existing wells (primarily drinking water wells) to assess whether the product of interest was detected. Fewer of these studies were required, but Waterborne conducted several on regional and national scales. The wells were selected in areas vulnerable to leaching and sampled monthly or quarterly for a year or so.

It’s been more than a decade since PGW field studies were required by USEPA, as USEPA has relied on modeling to assess potential groundwater risks from the labeled uses of pesticides.  While not common, the Terrestrial Field Dissipation (TFD) guidance does have a leaching module using lysimeters as an option that Waterborne can support if questions around leaching are to be evaluated.  For groundwater modeling, USEPA originally had the screening-level model SCI-GROW (now archived), a regression model developed from 13 prospective groundwater monitoring studies. Currently, USEPA uses the PWC (Pesticide in Water Calculator) with six standard groundwater scenarios in regions with leaching potential (DELMARVA, GA, NC, WI, and two in FL). Modeling groundwater concentrations takes significantly less time and is much more cost-effective than running PGW studies.

An additional advantage of modeling is the ability to estimate the long-term leaching effects of pesticide use over a 30+ year simulation.  Waterborne has the ability to refine groundwater modeling using spatially explicit modeling with more soil and weather combinations than available in standard scenarios in both the USA and Europe. This spatially distributed landscape modeling (SDLM) is useful in identifying areas vulnerable to leaching if groundwater monitoring is required. USEPA has stated that they are developing new groundwater scenarios that will cover a much wider range of spatial variability and leaching potential.

Waterborne looks forward to the release of new groundwater scenarios by USEPA.