Wednesday, November 18, 2015

A Simple Design for Stormwater Compliance - New Homes

This design is for new single family homes, or small commercial properties, up to about 10,000 s.f. of impervious surface (rooftops and driveways). You will find that the cost is as low as any approved stormwater management method, plus you will collect about 20 gallons/square foot of impervious surface.

Sizing the Infiltrator Below-Ground Tank

You'll need 1 for every 1800 square feet of impervious surface.  If you have a fraction the round up (e.g. 4100 s.f. / 1800 = 2.27; you'll need 3)  The dimensions are 14' long x 5' wide. They can be buried 6" - 48" deep.

Infiltrator tanks do not require gravel backfill or other soil amendment, provided that the soil is no more than 70% clay. Interconnect the tanks with 1" - 2" flexible PVC.

In-Tank Prefilter

The 4" Purain filter is suitable for about 1800 square feet also. Plan on a filter in each tank.

This means that you will need a manhole for each tank. If you have 3-5 tanks and don't want so many manholes, then choose a single, larger, Purain HD for direct burial.


Pipe from the downspouts to the tank location with SDR 35 pipe. If you have multiple filters, you'll need a header at the tank to distribute the water.


A submersible pump with a floating filter intake will send the water to your irrigation system. A pressure-activated pump will start whenever the irrigation heads open, and also if you have a hose connection. They will also start and run continuously if you have a leak in your irrigation system. We can also synchronize the pump start with the irrigation controller. We can put a timer switch next to a hose connection. We like the second method a little better, but either can be best.

The pump will need a floating filter intake, as shown in the photo, to maximize water quality.

Standby Connection

Two common methods are a pressure regulating valve (PRV) or a solenoid valve. Either is acceptable in residential systems. Solenoid valve systems cost a little less conserve city water pressure better; PRV's are more readily available, last longer, and easier to service.

Standby Connection Protection

Most municipalities are currently requiring an RPZ backflow preventer or air gap at a standby connection, unfortunately. We have new evidence that the rainwater does not contain any known contaminants, and would love to discuss this with your plumbing inspector. We would recommend a dual check valve, if that is typically an acceptable level of protection for a residential irrigation system. Dual check valves can be buried, which makes them easier to install. RPZ backflow preventers must be installed inside, or in an above-ground insulated and heated enclosure. Air gaps require re-pumping and therefore waste energy.

Georgia Water Tanks provides design assistance and on-site installation supervision for all packages.


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