Septic System and Drainfield Experts

King County Homeowners guide to How Septic Systems Work

by Lillys Septic Tank Pumping, Installation & Repair Service

The Septic Tank, Pump Tank and The Drainfield are what make up the Typical single family Septic System. Your Septic System will include the septic and pump tank (if a pressure system) that are concrete or fiberglass rectangles or cylindrical. The Tanks are buried and sit approximately one to two feet below the surface unless risers are installed that bring the lids to the surface for easy maintenance and pumping access. All of the drainswithin the home lead to the septic tank, so every drop of water that is used in the house goes into the septic tank.

When the wastewater enters the the tank it then separated into three parts, the scum layer which consists of fats, oils and greases.

The sludge layer that consists of the heavier solids that sink to the bottom and then the natural bacteria action produces digested sludge and dangerous gases. The mid water layer is simply suspended solid particles and wastewater.

Homes built up until about 1975 usually have single compartment 750 gallon Tanks and those built after 1975 typically will have a two compartment 900 to 1000 gallon tank. Homes built after 1990 will most likely be a pressure distribution system and will also have a 1000 gallon pump tank with a effluent pump to pressure the wastewater to the drainfield.

The Single Compartment Septic Tank:

There are some old wives tales or beliefs that “if a Septic Tank is working properly, you never have to pump it). This is absolutely false and negligent and will cost you thousands of dollars if you do not pump the septic tank regularly. Pumping should be performed every 3 years for a single compartment Tank and 3 to 5 for a 2 compartment Tank, depending on usage and habits.

If the Septic Tank is not pumped regularly the solids will accumulate until eventually they are pushed out the outlet pipe and into the drainfield. Because there is no wall for further treatment and separation, single compartment Tanks are at higher risk of this situation than a 2 compartment Tank. When Solids are pushed into the drainfield the soil and drain lines will become clogged and will not allow the water to dissipate into the soil, sending it to the surface or back into the house. This is when you will have raw sewage backed up into the bathtub or shower and the toilet, causing a health risk for your family. When the sewage water surfaces in the yard you are not only putting your family at risk, but you are risking your pets and neighbors as well. If the scum level reaches 24 inches you are risking the drainfield damage, that is why it is so important to inspect the Septic System yearly and pump a Single compartment Septic Tank every 3 years.

~Following is a cross section of the single compartment Septic Tank~

Double compartment septic tank anatomy:

All Septic Tanks need to be pumped every 3-5 years, depending on the tank size, the amount of solids entering the tank and the habits of the users. The only sure way to know is to have the Septic Tank inspected annually. By measuring the sludge and scum layer thickness it can be determined when the Septic Tank needs to be umped.

The Septic Tank should be pumped whenever the bottom of the scum layer is 12 inches thick. The scum layer can move to the second compartment through crossover baffle. The 2 compartment Tank has a wall in the center of the tank separating it into 2 compartments. The 1st compartment holds the 3 layers and the 2nd compartment should only be wastewater, although it often has scum and sludge as well at the end of the pumping schedule.

~The diagram below is a cross section of a 2 compartment Septic Tank~

Wastewater leaving the septic tank is a liquid called effluent. While it has received some treatment in the tank, it is still unpleasant smelling and contains disease organisms, organic wastes and other pollutants. This effluent requires proper treatment and disposal otherwise there can be significant environmental and public health problems. Discharging effluent onto the ground or into surface and ground water is against Washington State Law and King County Board of Health Codes.

There are many different pretreatment units that are installed today to further treat the effluent prior to hitting round water. Lillys Septic System Service has diagrams and information on these pre treatment units at the website listed at the end of this article.

~ Following are some pictures of some plugged drainlines and surfacing sewage ~

Pump Tanks:

Most systems installed in King County since 2000 include a pump tank. The pump tank contains a submersible sewage pump, high water alarm float and on & off floats. If the system is hooked up to a timer the pump will be activated at specific times for a specific amount of time to pump the effluent out to the drainfield. If the system is on demand, whenever the water level rises and reaches the “on” float level the pump will be activated to pump the effluent to the drainfield, once the water level reaches the “off” float level the pump will turn off until the water rises again to the “on” float level. If you have a pump failure or plugged drainfield and the water cannot leave the Pump Tank a high water level alarm float is installed, if the water level rises to the alarm float an alarm will sound. Your alarm is located on the pump control panel on the side of the house near the septic tanks, under the kitchen sink or in the garage. The location of the alarm device should be known by the homeowner (see your as-built for information for details). Once this alarm is activated there is some emergency storage space before the wastewater over flows out the top of the lids or backs up into the house.  The alarm can be deactivated but will not solve the problem. You should immediately begin emergency water conservation measures and call a Lilly’s Septic Tank Service at 425-432-3084 to send a technician out to troubleshoot the situation.

~Following is a typical Pump Tank ~

The Drainfield:

The drainfield is generally located in a stretch of lawn in the back or side yard of a property. The size and type of drainfield depends on the estimated daily wastewater use of the house hold, the more bedrooms a home has them larger the drainfield will need to be. The drainfield is mad up of gravel lined trenches with either corrugated pipes or pvc pipes with holes drilled for the water to disburse through. The water flows from the septic tank to a D-Box and is then directed evenly to each line in the field. the water flows out of the holes in the lines and into the gravel underneath, where it filters through to the soil where further treatment happens naturally prior to the water entering the ground water.

Your Septic System is your Largest underground investment.

Your septic System should be treated as though your home depends on it, It Does! The Septic Tanks and drainfield area should be protected from Cars being parked on it, any type of structure such as carports, decks sport courts or sheds. You will not want to put down any type of landscape plastic or allow farm animals to graze in the area as they can compact the soil creating possible drainfield failure or broken lines. The best solution over your septic system is simply lawn, roots from shrubs and trees can also be detrimental to the drainfield area as the roots can intrude into the lines or the septic tank and cause blockages. Your property will also require a “Reserve area” in case your Septic System fails and a new drainfield must be installed.

~Following is a diagram of a typical septic system~

Lilly’s Septic Tank Service has been providing Expert Septic System Service to King county Homeowners since 1990 including - Maple Valley, Enumclaw, Black Diamond, Ravensdale, Covington, Kent, Auburn, Renton, Issaquah, Renton.

Learn more about your Septic Tank System at the Septic System and Drainfield Experts main website at:  www.LillySeptic.com