Pesticide Case Study
Chemical Integrity: Pesticides Case Study

Reduced Atrazine Concentrations in Upper Big Walnut Creek Linked to Watershed Restoration Efforts (2/10/05 version)


The Upper Big Walnut Creek watershed serves as a drinking water source for the City of Columbus and surrounding communities. The presence of the agricultural chemical atrazine in the source water helped prompt the development of the Upper Big Walnut Creek Water Quality Partnership in 1997. The partnership includes diverse representation from local farmers, the City of Columbus, Ohio Farm Bureau, County NRCS and SWCD offices, state government, and many other organizations. The goal of the Upper Big Walnut Creek Water Quality Partnership is to protect the water resource quality of the Big Walnut Creek watershed. To help achieve water quality goals, the partnership has promoted the use of Environmental Quality Incentive Program (EQIP) funds and newer Conservation Reserve Enhancement Program (CREP) funds to support voluntary and innovative restoration and protection strategies throughout the watershed. To help assess the impact of these programs, a comparison of water quality between the Big Walnut Creek watershed and Upper Scioto River watershed was conducted. Future studies will attempt to assess the effectiveness of the EQIP and CREP programs more definitively.


The Upper Scioto River and Big Walnut Creek flow through similar primary land cover of row crop agriculture in central Ohio. Soils in the watersheds vary slightly, with more limestone bedrock in the Upper Scioto River and more shale bedrock in the Big Walnut drainage. Both watersheds are used for drinking water supply and both water sources have problems with seasonal atrazine runoff. Due to differences in the two waterway reservoir systems, there is a difference in how runoff can affect the water quality of the reservoirs. In the Big Walnut, the Hoover reservoir can contain up to 20 billion gallons of stored water. The Griggs and O 'Shaughnessy reservoirs together hold only 3 billion gallons of Upper Scioto River water. As a result the larger capacity of Hoover reservoir, problems in water quality can really linger. The long time that a pollutant stays in Hoover is a primary reason why the Big Walnut partnership was formed.

Water Quality Sampling

Comparison of atrazine concentrations in the Upper Scioto River with those in the Upper Big Walnut Creek may demonstrate whether the management practices used in the Big Walnut EQIP project (which have not been used in the Upper Scioto River) are making a difference in atrazine run-off. However, each year the weather and runoff patterns present a unique set of variables to consider, and the 2002 season was no exception. Rainfall June 5-6, 2002, was nearly two inches across the region. Basin-wide corn planting and atrazine spraying likely had occurred by this time in both watersheds. Since there are differences in rainfall and farm activities in the two watersheds, only a general comparison is possible.

Atrazine runoff in the Upper Scioto River occurred quickly following the June 2002 rain events, spiking to nearly 20 ppb in samples taken at several water quality monitoring sites on June 10th. In contrast, atrazine values rose to less than half the Upper Scioto levels in samples taken from Big Walnut Creek and tributaries. For example, atrazine levels in Duncan Run, a tributary to Big Walnut, were12 ppb sample shortly after June 5th, while at the same time the Upper Scioto samples were analyzed at 25 ppb. The pulse of atrazine moved rapidly down the Upper Scioto reaching the Dublin Road Water Plant intake by June 10th. A powdered activated carbon feed treatment system was initiated and an atrazine maximum contaminant level exceedance was averted. By August 21, 2002, no powdered activated carbon treatment had been necessary for atrazine removal in the Hap Cremean Water Plant, which treats the Hoover reservoir drinking water supply . Concentrations in Hoover Reservoir stayed below the 3 ppb maximum contaminant level for the rest of the season.

Preliminary Results

There are uncontrollable variables between watersheds, however the data seem to indicate that significant atrazine runoff occurred as expected in the Upper Scioto River system (due to rain and crop planting schedules), but was much less for the Upper Big Walnut Creek, as observed by the lower atrazine values in the tributaries and Hoover reservoir. This has resulted in considerable dollar savings because the use of powdered activated carbon was reduced for the Hap Cremean Water Plant, as compared to prior years.

Additional Studies

The following projects have been initiated to help determine the effectiveness of agricultural management practices implemented in the Big Walnut Creek watershed, and their applicability in other watersheds.

  • In 2002, a USEPA research grant was awarded to the Ohio River Valley Sanitation Commission (ORSANCO) to develop a methodology to characterize environmental and water quality benefits of agricultural management practices. The approach is to model pesticide runoff loads to Hoover Reservoir, based on watershed conditions such as soil types, land cover and precipitation, and type and extent of agricultural management practices used in the drainage basin. Water quality data acquired through the City of Columbus monitoring program will be used in this model to determine "before" and "after" effects of the management practices.
  • The Source Water Protection Initiative (SWPI) is being conducted by the Agricultural Research Service (USDA-ARS) and is funded through the America's Clean Water Foundation. This research will examine the effects of both currently used conservation practices (e.g., voluntary, incentive-based Farm Bill programs) as well as some that are more innovative and untried. This will entail an intensive quantification and qualification of watershed conditions (e.g., soil type, farm management, etc.) across multiple sub-watershed spatial scales. The purpose is to look at the individual effects of specific conservation practices, as well as their relative impacts when used in combination. This will be accomplished through paired comparisons of water quality in watersheds that have these conservation practices with those that do not (control group).

The Big Walnut Creek watershed is one of three watersheds included in the Source Water Protection Initiative. Also, the NRCS led Conservation Effects Assessment Program (CEAP) has designated the Upper Big Walnut as one of twelve "benchmark watersheds" and will cooperate in this ARS study. The results will likely be used to guide future decisions regarding the availability and funding allocations for USDA conservation programs.

  • In addition to the above-mentioned evaluation projects, the collaboration between the City of Columbus water department and local farmers and agricultural representatives is going to be documented in a new guidance document on how public water supply systems can build partnerships with the agricultural community.


Substantial amounts of funding have been dedicated to reduce atrazine loadings to the Big Walnut, and similar funding proposals are in place for the Upper Scioto. From 1998 to 2002, the USDA's Environmental Quality Incentives Program (EQIP) has implemented management practices (MPs) on more than 23,000 Upper Big Walnut cropland acres at a cost of approximately $1.2 million. Beginning in 2002, federal, state and local funding became available for Upper Big Walnut riparian corridor protection through the Conservation Reserve Enhancement Program (CREP) and will exceed $13 million over the life of the program. This is in addition to past and continued local and state funding for water quality monitoring and funding from USEPA. The Upper Scioto watershed has received state funding for a watershed coordinator to develop a state endorsed watershed action plan.

Watershed Coordinator

For more information regarding the Upper Big Walnut Creek Water Quality Partnership please contact Gregg Sablak at the Delaware Soil and Water Conservation District:

(740) 368-1921 ext. 109 or


Upper Big Walnut Creek Watershed Water Quality Management Plan:

"A Tale of Two Watersheds: Big Walnut Creek and the Scioto River" (Dan Binder, City of Columbus)