25 October 2004
Figure 8-8. Inlet Device Schematic
Source: Tyack & Fenner, 1997. In EPA, 1999b.
Most Appropriate Uses. This technology may be used by itself or in
conjunction with other stormwater management devices as part of an overall stormwater
control strategy. Hydrodynamic separators are ideal for areas with limited land
availability. In addition, hydrodynamic separators can be placed in almost any location
in a system, making them ideal for use in potential stormwater "hotspots" (areas where
higher concentrations of pollutants are more likely to occur; e.g. gas stations).
Decreasing land availability for the installation of large stormwater management
facilities is fueling the need for solutions such as hydrodynamic separators.
Cost Data. Costs are influenced by several factors including the amount of
runoff to be treated, the amount of land available, and any other treatment technologies
that are presently being used. Capital costs can range from ,300 to ,000 per pre-
cast unit. Units that are site-specifically designed typically are more costly. Total costs
for hydrodynamic separators often include pre-design costs, capital costs, and operation
and maintenance costs.
Maintenance Issues. Proper maintenance of a hydrodynamic separator
involves frequent inspections throughout the first year of installation to ensure that
sediments are removed before the unit's sediment capacity is reached. Sediment depth
can be measured using a "dip stick" or rod. Subsequently, sediment removal may be
performed with a sump-vac or vacuum truck, depending on which type of separator is
used. After the first year of installation, inspections can be scheduled according to
observed rates of sediment accumulation. In general, hydrodynamic separators require
a minimal amount of maintenance, but lack of attention will lower their overall pollutant