This slide presentation describes a case study of a backflow contamination situation that occurred when a lawn care company employee inserted a garden hose into a 200 gallon tank to fill it, having just added 9 quarts of the herbicide 2-4-D to the tank. When the Lousiville Water Company crew turned off the water main for scheduled maintenance work, the 2-4-D was back-siphoned into the distribution water main. Details are given of how the water company handled the situation, which included: determining the type of chemical that caused the contamination; locating the source of the contaminate; determining the extent of the contamination; notifying businesses in the impacted area; contacting the Health Department; flushing the water system; and, outlining the costs involved in the effort.