An apparatus and related method for fracturing a formation penetrated by a well comprises a frac pressure pump, a frac fluid source, and a proppant supply source. The frac pressure pump is connected to the well. The frac fluid source is connected to supply a stream of frac fluid to the frac pressure pump. The proppant supply source has a proppant receiver, a positive displacement pump, and at least an inlet into the proppant supply source. The at least an inlet is connected to one or more liquid hydrocarbon sources to supply liquid hydrocarbons to proppant in the proppant supply source. The positive displacement pump is connected to pump proppant into the stream of frac fluid before the frac pressure pump. Fluid lines connecting the frac pressure pump, the well, and the frac fluid source have isolation valves spaced so that the volume of fluid containable between any set of neighboring isolation valves is less than or equal to 500 L.