EPA Summary:

Big Darby Water Quality "Fair to Good"

The much-anticipated report from the Ohio EPA’s ambitious Total Maximum Daily Load (TMDL) study of Big Darby Creek and its tributaries is taking longer than expected to complete. In the interim, the agency has issued a general summary of the water quality conditions in the Darby basin.     Full report   

The summary supports DCA’s view that the Darby watershed, though one of the midwest’s best systems, is suffering from chronic stresses that have led to a slight decline in species diversity and a moderate decline in species abundance.

The summary describes water quality in both Big Darby and Little Darby as "fair to good." In the past, most agency and non-agency accounts of Darby water quality have used terms such as "excellent" and "exceptional."

The summary announced that chemical testing by the EPA found "gross contamination of the water column from point sources such as Honda and Plain City." Even more troubling, testing found "many exceedences" of standard levels for bacteria and nutrients throughout Big and Little Darby. In fact, many nutrient values exceeded the 75th, 90th, or 95th percentiles for Eastern Corn Belt streams. These findings are consistent with data collected by Metro Parks, which showed high nitrate levels in Battelle-Darby metro park. The EPA noted that nutrient loads were higher during rain events.

The summary also describes a trend toward a "hardening" of the Darby watershed. Hardening occurs when human activities pave surfaces or speed drainage in a watershed. The EPA report cites roadwork, residential development, ditch maintenance, channelization, filling of wetlands, removal of riparian buffers, and increases in winter plowing as contributing to more rapid stormwater runoff. If widespread, all of these processes can cause erosion and damage in-stream habitat. The summary also notes that this process results in a more rapid loss of water during drought.

The EPA document also summarizes the biological performance of Big and Little Darby. In 2001, Big Darby reached full attainment of its "aquatic life use" at 11 of 17 sites sampled. Little Darby reached full attainment at 8 of 11 sites.

The EPA cautions that the summary is "very general in scope," and it "should not be used as a mechanism to draw conclusions about specific causes and sources of pollution in the Darby Creek basin." It promises that these will be discussed in its final report, which now is projected for late 2003.

Despite this caution about identifying sources, the agency describes Darby as "an aquatic system threatened by urbanization, and excess nutrient load, bacterial contamination from diffuse sources such as failing on-lot waste treatment systems, discharges from wastewater treatment facilities, agricultural runoff and chemical spills."

by John Tetzloff