Take Control Underground Stormwater Management

by Mary Angle, EcoRain Systems, Inc.

These tanks are AASHTO H25 load rated for use under driving surfaces. Built in 2009, this CVS Pharmacy parking lot in Del Rey Beach, Fla., has a 15,516 cubic feet detention tank system for exfiltration to the ground water.

There are many ways to skin a cat when capturing, detaining and/or reusing storm water in underground cisterns. Product selection can include Plastic Chambers, Corrugated Metal Pipe and concrete Vaults/Arches.

All of these products have applications where they excel and have advantages over their competition.

When comparing products consider the location, cleanliness of the water – water quality, water reuse or ground water recharge, cost, warranty, maintenance, load requirements and certification. Some municipalities require American made and third-party verification.

Plastic chambers are the best product for use in cities - areas where there is limited land. When selecting a plastic chamber manufacturer, cost can vary due to shipping, assembly, gravel fill and installation. If assembly is needed, ask the supplier for an assembled cost. Always check the load rating for plastic chambers.

At a naval base in Jacksonville, Fla. a reuse tank captures water used to wash helicopters.

While most are at least AASHTO H-20, some will require additional costly steps to achieve it. Be sure to ask for certified testing that proves the rating. The ICC certifies EcoRain Tanks under strength and plumbing codes.

Plastic chambers are lightweight and easy to install by hand, especially in tight areas. Water must be filtered before entering the plastic chambers, which eliminates the need for maintenance within the chambers. Some chambers have cleanout channels or baskets. Wrap plastic chambers in liners when the goal is either to detain water for controlled release or reuse water for toilets or irrigation.

Corrugated metal pipe is advantageous in rural areas where land is still available – it can be a cost savings to use more land area to capture the intended volume. Large corrugated metal pipe requires the use of heavy equipment, and lots of gravel, which may increase installation costs. They may or may not need filters, and if large enough, maintenance workers in Hazmat gear can enter the tubes. Corrugated metal pipes are not usually used for controlled release or water reuse. Concrete arches and vaults are best used in applications where a load rating higher than AASHTO H-25 is required.

Concrete vaults require the use of heavy equipment, and usually will not need water filtration. The downside to no water filtration is that sediments build up in the bottom and require constant cleaning. When using a concrete vault, the inside will need periodic cleaning due to the anaerobic environment.

Between 2006 and 2008 EcoRain Systems installed tanks along a 2.6-mile bioswale at the Los Angeles International Airport runway.

For all product categories, manufacturers have experienced failures in their systems and 99 percent of this is due to either the design or the installation. Consult with the manufacturer on design – ensure design follows the manufacturer's procedures before bidding or installation.

When considering one product over another, do not ask the competition. Rumors abound. Ask each manufacturer to discuss their advantages and pitfalls. Ask for references and for installations that have longevity.

I have worked for a chamber supplier for 10 years and have seen many new products on the market. It can be a challenge to know which product to use – but the bottom line is: after due diligence, the landscape architect will specify to use the product that best fits their needs.