When a WSP is preceded by a septic tank, how is it sized?

The correct approach to sizing a wastewater stabilization pond (WSP) when it is preceded by a septic tank involves using the daily flow of wastewater. In this context, the sizing requirement of "60 times daily flow" refers to the volume capacity necessary to effectively treat and manage the effluent that has undergone initial treatment in a septic tank.

This sizing standard is based on the assumption that the septic tank will remove a significant portion of the solids and reduce the organic load in the effluent. As a result, the WSP can be smaller than it would need to be if it were handling the raw waste directly. The higher multiplier of 60 ensures that there is adequate retention time within the WSP for settling and biological treatment, allowing for greater efficiency in reducing pollutants before the treated effluent is discharged or reused.

This practice aligns with guidelines and standards that prioritize effective wastewater treatment and environmental protection, supporting the overall design principles used by septic installers. Other options, although they represent potential sizing calculations, do not meet the established guideline of 60 times the daily flow necessary for adequate WSP sizing in the context of prior septic tank treatment.