Impact of agrichemical facility best management practices on runoff water quality
Water quality effects of structural and managerial BMPs implemented at an agrichemical mixing and handling facility, located in an agricultural watershed in Virginia, were investigated in this study. The measured water quality parameters include two commonly used pesticides (atrazine and metolachlor), nitrogen (N), and phosphorus (P). BMPs implemented include: pesticide mixing and loading concrete pad with a sump and pump fitting; a variety of runoff diversion structures to divert the rooftop runoff away from the critical areas; structures to contain transport of chemicals to the drainage leaving the facility; and recycling of rinsate by applying it on the agricultural land. Concentration of pesticides and nutrients were measured at the facility outlet as well as the outlet of the main watershed in which the facility was located. Implementation of BMPs resulted in drastic reduction in mean concentrations of the two pesticides in the stream leaving the facility as well as in the main watershed stream. Maximum atrazine concentrations in the drainage leaving the facility reduced from 17,389 mug/l during the pre-BMP period (1986-1988) to 1,452 mug/l during the post-BMP period (1989-1996). The post-BMP mean concentrations of atrazine and metolachlor at the facility outlet were reduced by 94% (2690 mug/l to 166 mug/l) and 91% (4579 mug/l to 402 mug/l), respectively. The corresponding post-BMP reductions in concentration at the main watershed outlet were 52% and 78% for atrazine and metolachlor, respectively. Nonparametric trend tests results indicated statistically significant downward trend and reduced post-BMP concentrations of the two pesticides at the facility as well as the watershed outlets. Impact of BMPs on the nutrient concentrations were not clear due to large nutrient contributions from animal production activities in upland areas of the watershed Results from this study will provide needed impetus for implementation of BMPs at other agrichemical mixing and handling facilities in Virginia as well as other states to drastically reduce the transport of pesticides and nutrients to surface water bodies.