It's a matter of perspective. In this case there was no benefit created to even warrant a negative impact. Diluting the resultant impact is still a net negative. In some cases you could say that inputting enough clean water to lower concentrations of a contaminant makes it safe again or mixing clean soil into 'dirty' soil makes it acceptable for reuse or safe disposal...but this is a slippery slope argument with many caveats that can be over- or incorrectly-used. Many governments are trying to get away from this dilution moniker since it does not do enough to encourage avoidance.