Evaluation of Stormwater Permeable Rapid Infiltration Barriers for use in Class V Stormwater Injection Wells;Draft Final Research rept

摘要

Stormwater injection wells are widely used as stormwater management systems. These wells may act as a low resistance conduit for contaminants transported by stormwater to enter groundwater. This paper summarizes the testing of a natural filtration medium, referred to as a Stormwater Permeable Rapid Infiltration Barrier (SPRIB), that has been proposed as a potential retrofit option for stormwater injection wells in Spokane, Washington because of its theoretical contaminant attenuation capabilities and its good hydraulic properties. This medium was tested in the laboratory and at a field site using near field-scale columns to determine its useful life span in terms of metal (Cu, Pb, and Zn) removal capacity and maintenance of acceptable infiltration rates. After a series of simulated storm events, the SPRIB demonstrated contaminant concentration reduction rates of total metals greater than 99% and soluble metals from 91 to 98% Surface clogging of the columns by stormwater particulate matter was shown to be the limiting factor in the useful life span of an unmaintained SPRIB. Based on the observed linear decline in infiltration rates due to sediment loading, the predicted life span of SPRIB is 20 to 22 storms (roughly 6 months in the Spokane area) before infiltration falls below acceptable rates (8 to 12 in/hr). A significantly longer life span is expected if pretreatment for suspended solids or periodic SPRIB maintenance is performed.