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Water Quality Pretreatment - Hydrodynamic Separator vs. Isolator Row (Chamber Infiltration System)

Water Quality Pretreatment - Hydrodynamic Separator vs. Isolator Row (Chamber Infiltration System)

Water Quality Pretreatment - Hydrodynamic Separator vs. Isolator Row (Chamber Infiltration System)

Hello Everyone,

I have some questions that I was hoping to rely on some experience regarding long-term performance for the two aforementioned pretreatment devices. Perhaps also some design pointers.

I work for a multidisciplinary firm in Southern California and we have lots of public education projects. Maintenance, as with most clients, is a serious concern for installed BMPs for these school districts and maintaining these types of systems is new for many of them. For discussion, let's set up the hypothetical scenario that we have a proposed volume-based BMP in which we elect to do subsurface plastic chambers and therefore are required to install pretreatment at some level for suspended solids and pollutant removal from stormwater runoff prior to infiltration in the chamber system. I have been in numerous conversations with manufacturers regarding these products that often lead to their recommendation of installing one or the other, not both. But I feel these conversations are usually driven by the products that they have available for sale rather than what is best for the project and our clients.

Hydrodynamic Separator - manhole with separation chambers/screens/baffles to separate solids and hydrocarbons from the first flush
Isolator Row - initial chamber row for incoming flows (hydraulically), usually double lined at bottom with geotextile fabric, also meant for removing solids and hydrocarbons from the first flush

My questions:

1. From a design standpoint, in terms of pollutant removal, is there better performing device between the two?
2. From a maintenance standpoint, it appears both require a vacuum truck to flush and vac out the collected solids at some frequency. Logic tells me it would be easier to do this from a manhole versus a potentially long isolator row, in which you would need to flush from one end and vac out the solids from an inspection port at the other. Also, the likelihood that all the solids would be cleaned out from the isolator row seems unlikely. Also, it seems likely that the fabric underneath the isolator row could eventually become silted up therefore reducing the infiltration of the chamber system.

Any insight on this topic would be greatly appreciated. Does anyone have constructed experience either bad or good for these two pretreatment devices or even subsurface plastic chamber systems in general?

Thanks in advance,

RE: Water Quality Pretreatment - Hydrodynamic Separator vs. Isolator Row (Chamber Infiltration System)

Every propriety product is going to have it's own unique treatment efficiencies. Be sure to use a product that is certified in CA (if required).

As for maintenance, all options are easy to maintain, if they are actually maintained at recommended intervals. I'd guess the isolator rows become more of a challenge when they are neglected.

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