Wastewater containing mostly soil and sand presents different needs than water containing oily substances. Oils and other hydrocarbon contaminants can originate from vehicle surfaces, processing, or maintenance activities.

In these cases, relying solely on solids sedimentation may not be sufficient. Separation of the oily component and the specific characteristics of the contaminant must also be considered.

Correctly identifying the substances present is therefore the first step in avoiding a common mistake: designing the system based on the available technology rather than the wastewater to be treated.

A truly efficient system follows the opposite path. First, the process, the type of contamination, and the objectives to be achieved are analyzed; then the most appropriate technologies are identified.

Contaminant concentration also makes a difference.

Knowing the type of contaminant is not enough. Two systems can produce wastewater containing similar substances, but in very different concentrations.

A washing system used occasionally does not operate under the same conditions as a system continuously traversed by heavy vehicles. As the number of cycles increases, the amount of material transferred to the water increases, changing the load the treatment system must withstand.

Weather conditions can also rapidly change the situation. During very rainy periods, for example, vehicles can transport greater quantities of sludge. During dry periods, however, the presence of soil and dust may prevail.

For this reason, sizing must take into account actual operating conditions and potential peaks in use. A properly designed system must maintain reliable performance even as the contaminant load increases.