The gravel in the drainfield maintains the struc­ture of the trenches and helps distribute the effluent to the infiltrative soil surfaces. Also, the porosity of the gravel provides temporary stor­age capacity during peak flows.


Engineer Randy May believes there are a number of things wrong with the use of gravel in drain- fields. Although the gravel maintains the struc­ture of the trenches, it also is filling % of the available storage capacity in the drainfield with rock. The gravel itself provides little treatment of effluent and, moreover, may cause compaction in the trench bottom due to its weight and fines (if present) in the gravel. (See p. 22 regarding shallow drainfields, which use no gravel, and p. 23 regarding Infiltrator” Chamber Leaching Systems.)


there are two brilliant things about a properly functioning gravity-fed septic


•the power is gravity, the earth’s magnetic force — pulling water and wastes downward. no pumps, no electricity.

•the cleansing agent is the earth, where microorganisms, naturally present in the soil filter, feed on and purify septic tank effluent, including disease- causing organisms.

it is an elegant design, working silently underground, and requires only a minimum of maintenance to keep it functioning. it is practical, functional, and ecological. it’s worth knowing how to be an intelligent steward of this living system.


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