Sand Filter Septic System

Sand Filter Septic System

Septic tanks with gravity flow drainfields have been used for many years in areas not served by public sewers. Unfortunately, not all soil and site conditions are well suited for these conventional systems. To protect public health and water quality, alternative systems are often used in areas where conventional systems cannot assure safe sewage treatment.

The intermittent sand filter is one alterative, which:

  • Can be constructed above or below the ground.
  • Provides a high level of wastewater treatment.


The following information will help you understand your sand filter system, and keep it operating safely at the lowest possible cost.

Sand Filter Septic System — Aberdeen, WA — Stangland Septic Service

A typical sand filter system has four working parts:

  1. The septic tank.
  2. The pump chamber with the pump.
  3. The sand filter.
  4. The disposal component including a drainfield (or possibly a mound) with its replacement area.
Sand Filter Septic System Installation — Aberdeen, WA — Stangland Septic Service

The Septic Tank

Septic Tank Installation - Sand Filter Septic System — Aberdeen, WA — Stangland Septic Service

The typical septic tank is a large buried container made of concrete, fiberglass or polyethylene. Wastewater from your home flows into the tank. Heavy solids settle to the bottom where bacterial action partially decomposes them. Most of the lighter solids, such as grease and oils, rise to the top and form a scum layer.


The wastewater leaving the septic tank is a liquid called effluent. It has been partially treated but still contains disease causing bacteria and other pollutants. From the tank, the effluent flows by gravity into the pump chamber.

The Pump Chamber

Pump Chamber - Sand Filter Septic System — Aberdeen, WA — Stangland Septic Service

The pump chamber is a concrete, fiberglass or polyethylene container that collects the septic tank effluent. The chamber contains a pump, pump control floats, and a high water alarm float. The pump action may be controlled either by the use of control floats or by timer controls. Control floats are set to turn the pump “ON” and “OFF” at levels for pumping a specific volume of effluent per dose. Timer controls are set to produce both the length of the dose and the interval or rest period between doses.


The high water alarm float starts an alarm to warn you of any pump or system malfunction. If pump timer controls are used, the alarm also will warn you of excessive water use in the home. The float is set to start when the effluent in the pump chamber rises above the “ON” float. The alarm should consist of a buzzer and an easily visible light. It should be on an electrical circuit separate from the pump.


The pump discharge pipe should have a union and valve for easy removal of the pump. A piece of nylon rope or other noncorrosive material should be attached to the pump for taking the pump in and out of the chamber.

The Sand Filter

Sand Filter - Sand Filter Septic System — Aberdeen, WA — Stangland Septic Service

The typical sand filter is a PVC lined or concrete box filled with a specific sand material. A network of small diameter pipes is placed in a gravel-filled bed on top of the sand.


The septic tank effluent is pumped under low pressure through the pipes in controlled doses to insure uniform distribution. The effluent leaves the pipes, trickles downward through the gravel, and is treated as it filters through the sand. A gravel underdrain collects and moves the treated wastewater to either a second pump chamber for discharge to a pressure distribution drainfield or to a gravity flow drainfield. The second pump chamber may be located in the sand filter.

The Drainfield

Drain-Field Sand Filter Septic System — Aberdeen, WA — Stangland Septic Service

The drainfield receives the treated sand filter effluent for disposal. It has a network of pipes placed in gravel-filled trenches 2–3 feet wide or beds (up to 10 feet wide) in the soil. The effluent leaves the pipes, trickles downward through the gravel, and into the soil.


Every new drainfield is required to have a designated replacement area. This area is similar to the size of your existing drainfield. It must be protected should the existing system need an addition or repair.
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