Separator tank

A separator tank for separating and trapping contaminants in rainwater and runoff is disclosed. According to one embodiment of the present invention, the separator tank comprises a container having a bottom wall, side wall, and top wall defining an internal chamber; an insert located inside of the internal chamber, the insert comprising a weir defining an intake area between the weir and the side wall; and a round-edged orifice positioned within the intake area; an inlet conduit for introducing an influent liquid into the intake area; wherein the weir is positioned such that the weir induces the influent liquid to flow in a swirling motion within the intake area. According to another embodiment of the present invention an insert for a separator tank is disclosed. The insert includes a weir defining an intake area for receiving an influent liquid; and a round-edged orifice positioned within the intake area.