The AJM EnviroSEP in conjunction with a first flush system is a commonly approved process for storm water management from open areas.
 

Contaminated yards should install first flush systems

When pollutants deposited on exposed areas are dislodged and entrained by the rainfall run off process, the storm water that initially flows off the area will be more polluted than that which runs off later. This initial run off can be considered as a cleansing stream.

First flush systems are designed to capture, isolate and treat this cleansing stream whilst allowing subsequent runoff to be flowed directly to storm water drains.

There are many factors that determine whether or not a first flush is appropriate such as; the mobility of the pollutants, the size and drainage characteristics of the catchment area and the nature or porosity of the ground. It is essential that each case is individually assessed and designs are approved by an appropriate authority.

Once a first flush is accepted as a suitable storm water pollution control device, a cleansing rain fall level will be applied. This is typically between 10 and 20mm. The capacity of the first flush collection tank must be greater than this level, multiplied by the area of the catchment.

How the First Flush works

When the rain starts, the storm water runs into the first flush collection pit via a storm water bypass pit. Once the first flush pit is "full" the water will backflow to the bypass pit and flow directly to storm water drains.

The rain gauge will prevent the pump from operating whilst it continues to rain. After the rainfall has ceased, the water in the first flush pit is pumped to the EnviroSEP or other appropriate treatment device where the pollutants are removed.

The water treated by the EnviroSEP is discharged either to storm water drains or sewer depending on local requirements and the nature of the pollutants concerned.