We received this question during a recent webinar and thought it would be helpful to discuss here.
When urine is diverted from feces by even a few inches, the feces remain free of urea from urine, and therefore free of the ammonia that soon develops through urea hydrolysis. It is this ammonia that prevents feces from being a viable food source for invertebrates such as worms, nematodes, and other organisms that consume plant litter and animal dung.
Biochemically, just a few inches of separation is enough. This is similar to humans and other mammals: when bears squat to poop and pee in the forest, they do not pee directly on their poop. That small separation is enough for the soil ecosystem to process the two waste streams differently.
In a practical toilet setting, most parks locate the urine drainfield 5–10 feet from the toilet, as long as this meets the requirements of permits or engineering reports. These typically require separation distances from surface water, often 50–200 feet, and from groundwater, often around 4 feet.
Urine is generally diverted into a shallow drainfield. Toilet Tech offers three packages of components for urine drainfields: the simplest is a perforated pipe; the mid-range option is an EZflow product, with perforated pipe surrounded by engineered media; and the third option is EZflow paired with a FLOUT mechanical dosing tank, which fills to a set level and then empties the tank in one dose.
Federal agencies tend to review and approve their own designs. Some state agencies do the same or obtain engineering reports. Private installations generally follow local county codes for drainfield design.
Daily urine flow at the average backcountry toilet, typically 1–20 gallons, is very low compared with residential drainfields, which may be designed for around 1,000 gallons per day. As a result, it is usually straightforward to meet county codes for drainfields. Idaho and British Columbia have also developed urine-diversion-specific drainfield permitting pathways.
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