Aqua Tech has been selling and operating large subsurface drip disposal systems (SDDS) for decades.
Here’s one. The 400k gallons per day of treated sewer effluent for Cave Springs, Arkansas, irrigates a golf course.
The Cave Springs Wastewater Treatment Plant went online in January of 2008 and has been running ever since.
And Aqua Tech has been operating the system along with this very large and sophisticated subsurface drip dispersal system for much of that time.
We also operate another eight drip systems in Northwest Arkansas.
After decades of operating several subsurface drip systems, we’re still big fans.
Here are some reasons we continue to recommend subsurface drip disposal:
Drip systems are easy to install.
Unlike traditional drain fields or chamber systems, SDDS don’t require major excavation or backfill. The flexible drip tubing can be vibraplowed into undisturbed dirt from a spool to a depth of around 8″1.
Subsurface drip systems can be installed in shallow soil.
Because they slow-rate apply water just below the soil’s surface, they can overcome some limiting conditions such as shallow depth to bedrock.
Drip disposal can be installed just above a seasonal high-water table2.
With the right level of pretreatment, some states allow as little as 6″ of separation between the bottom of the drip line and a seasonally wet soil layer.
Subsurface drip disposal fields can be smaller than traditional drain fields.
Aqua Tech’s wastewater systems clean the water before it reaches the ground. This means the dispersal system doesn’t have to do the cleaning.
The absence of organics in the discharged effluent eliminates the possibility of field failure3.
Because they’re shallow buried at the root line, up to 80% of the water is taken up into the grass cross and disposed via evapotranspiration. This takes some of the burden for water absorption off of the soil.
Drip systems can be configured for non-discharge or beneficial reuse applications.
Perhaps the greatest concern associated with the disposal of domestic wastewater into a subsurface disposal system is over nitrogen. When nitrate concentrations over 10 mg/L reach the aquifer, public health is threatened. If high concentrations of ammonia nitrogen reach a surface water way, environmental health can suffer. Fortunately, plants need nitrogen and phosphorus. Drip systems can be designed to eliminate the risk of contamination by these nutrients by distributing treated effluent to a crop at the rate of agronomic uptake per the table below. Between evapotranspiration and agronomic uptake of nutrients, drip systems can be configured to eliminate potential discharge of wastewater to the environment4
- Varies by region. ↩︎
- Subject to design, environmental, and regulatory conditions. ↩︎
- Matejcek et al (2000) found that dispersal systems with a mass loading of .0015 lb/sf/day or less did not fail. Cited in Connecticut DEEP Guidance for Design of Large-Scale On-site Wastewater Renovation Systems ↩︎
- Other surface discharge systems such as spray or overland flow can serve this same function although they usually require more space and are more expensive than SDDS. ↩︎