About the ADS Water Quality Unit & Infiltration System
General Information Performance Data Water Quality Treatment Process Design


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Design

The ADS Water Quality Unit & Infiltration System is a treatment train that consists of a water quality unit (WQU) that provides pretreatment through the process of sedimentation, and an infiltration unit (IU) that performs much like a leach field. Both units are made of high-density polyethylene (HDPE) pipe and are designed to bear loads consistent with those experienced by parking lots. The design is completed by the system manufacturer in accordance with local watershed conditions and target treatment objectives.

The WQU is constructed from a 60-inch diameter HDPE pipe with a series of weirs for removal of coarse solids and floatables. The IU consists of three, 40-foot sections of 48-inch diameter, perforated HDPE pipe, laid over an infiltration base composed of two feet of bank run gravel. The top and sides of the excavation basin are wrapped in non-woven geotextile to protect the system from the migration of fine particles from the surrounding soil. The bottom of the treatment unit should not be lined to prevent premature clogging of the system from fines carried by runoff.

A three- to five-foot separation from seasonal high groundwater tables (as designated by regulations) and a proper sandy subbase are necessary to prevent groundwater contamination.

Stormwater flows of one cubic foot per second (cfs) enter the treatment train through the WQU and then flow into the IU. Flows exceeding one cfs bypass the WQU and flow directly into the IU, which prevents the re-suspension of solids. During channel protection volume (Q2) events, stormwater bypasses the WQU and fills the IU, which typically drains over a 24- to 48-hour period. During ten-year (Q10) events, stormwater bypasses the WQU, fills the IU, and then discharges directly to the surface, largely bypassing treatment.