Phoenix lies within the Sonoran Desert and most of the region receives less than 10 inches of rainfall per year, so managing ALL of our water resources has always been critically important. In the early 1970s, the City of Phoenix instituted a drastic change in stormwater policy by requiring all new development to capture, retain, and infiltrate the 100-year, 2-hour storm event (approximately 8,000 cubic feet/acre) on site within 36 hours. With that first step, the other cities in the Phoenix Metropolitan Area followed suit and grading designs in the Valley were forever changed. Out of those new policies was born the need for a different method of disposal, because it was quickly discovered the infiltration capacity of surface soils degrades quickly, leaving impounded stormwater sitting for days and even weeks.
Enter engineered drywells…Drywells get their name because they are normally “dry” and are only “wet” during a rainfall event. The key to drywell performance lies in its ability to bypass the upper layers of soil (0’ – 25’), which are often consolidated and impermeable. Torrent Resources, an Arizona based contractor that specializes in the design and installation of their own brand of engineered drywell known as a MaxWell®, can drill past poorly drained surface soils and complete the drywell at depths up to 180’. Typically however, Arizona drywells don’t go much deeper than 60’ before they get into well-drained material such as sand and gravel. And unlike fine grained surface soils, these materials are capable of transmitting stormwater into the vadose zone at exceptional rates.
With the advent of the engineered drywell, considered a Class V – Underground Injection Control Well by the EPA, regulations governing their installation, operation, and closure were necessary. The Arizona Department of Environmental Quality (ADEQ) proposed and adopted regulations in 1988, thereby setting up the framework for the regulation of engineered drywells in Arizona. Following these new state statutes, local governments began to create their own policies and guidelines for the use of engineered drywells.
During this time, Torrent Resources was right there to support these local agencies in crafting policies that were user friendly, yet protective of our valuable groundwater aquifers. Now, cities such as Phoenix, Chandler, Gilbert, Tempe, Goodyear, etc. each have their own set of rigorous drywell policies that govern everything from design and location to performance and registration. The use of engineered drywells in the Valley has become a given and civil engineers have been specifying engineered drywells for the disposal of stormwater for decades.
As counties and cities in other states, California for instance, begin to embrace drywells as an effective infiltration best management practice (BMP), they need not contemplate a drywell as some new thing that must be “figured out” in order to create regulations for their use. They can look to Arizona Cities and Torrent Resources to help craft policies that will be both user friendly and protective at the same time.
Stay tuned to see how the stormwater retention policies and engineered drywells have helped keep Arizona’s aquifers full.