Septic tanks are installed on, with a few exceptions, all septic systems. A septic tank is a dual-chamber, single tank made of either concrete or plastic. Septic tanks accept raw sewage from the source (house). Water enters the tank in what is called a baffle. The baffle guides the sewage coming into the tank deeper into the tank. This allows the separation of solid material to begin.
Heavier types of solids, along with older solids, that have been inside the tank a while, sink to the bottom. This layer of solid material is called sludge. Lighter and newer solids float to the top of the tank. This layer of solids is called scum.
Between the scum and sludge layers is wastewater without any solids; commonly known as the clear layer. Inside the tank, is a hole that separates the two chambers. This partition has about a 4” round hole half way down. This hole allows the clear water, with no solids, to flow into the next chamber. This chamber is storage for water to be dispersed into the drainfield, (sometimes known as the leach field). On the outlet side of the septic tank, is another baffle. This serves two purposes. First, we attach a filter inside the baffle; this prevents any solids that have made it into the second chamber from going out into the drainfield. The baffle also serves as a way to draw water from the middle layer to exit into the drainfield. This side of the septic tank is supposed to be free of solids, but the baffle acts as insurance.
Over time, sludge layers and scum layers settle and will build up into thicker deposits. These deposits are why it is a good idea to pump your septic tank at least once every three years. If these deposits get too thick, they can make their way into the liquid chamber and eventually out into the drainfield, or plug up the filter if one is installed. Solids will plug up the drainfield and prevent it from dispersing water into the ground. This can cause flooding at the tank and make a mess of the site.
Dose tanks are installed on all pressurized drain fields but can also serve other purposes. Generally, these tanks are also made of concrete or plastic. Wastewater flows from the outlet side of the septic tank into the dose tank. The dose tank serves as a sewage pump and control tank. The sewage pump and its controls are placed inside of the tank. As wastewater flows into the tank the water level rises. Floats are installed to turn the pump on and off at certain water levels. When the water level reaches the designated level, the float turns the pump on. The pump will then discharge the water out into the drainfield.
As the pump runs, the water level lowers until it reaches the designated level in which the float turns the pump back off. There is also a high level alarm float, this float serves as a warning to the homeowner when the water level is getting too high and something has probably gone wrong.
The high level alarm is attached to a box that sounds a siren and light, either at the surface or in the house. The dose tank has a vent pipe at the surface that allows air to vent into and out of the system as the water level rises and falls. Dose tanks also have an electrical control box for managing the floats and pump so they work on a timer. All pressure systems work on timed doses to prevent overdosing the drainfield at peak times.
Gravity Septic System Drainfields
Gravity septic systems are the oldest type of legal solutions for disposing of wastewater onsite; they also have the advantage of a lower initial cost. Gravity septic systems use gravity to move wastewater throughout the system. It works like this, water flows out of the septic tank and into a pipe that leads to a distribution box. The distribution or “D” box is made of either concrete or plastic. Wastewater goes from the “D” box into the drainfield. Gravity drainfields can be installed in many ways. The most common is pipe and aggregate. We transform the pipe coming from the “D” box into perforated pipe. The perforations allow water out of the pipe and into the aggregate surrounding the pipe. We use a specific sized, washed aggregate, (either stone or other material), this allows water to penetrate into the ground below. As water settles to the bottom of the aggregate, it meets the soil and begins soaking into the ground. Another option, recently available, is our EZ Flow product. EZ Flow replaces the stone as aggregate. EZ Flow has studies that show evidence of a 20-30% longer lifespan than normal gravel. The reasoning is the Styrofoam product is manufactured to eliminate fines; stone tends to have stone dust, fines, broken smaller pieces no matter how it is washed or which size it is. These fines settle to the bottom of the stone installation and can help clog the infiltrative surface over time. EZ Flow prevents that from happening.
LPP Septic System Drainfields
Low Pressure Pipe drainfields are 12’ wide trenches with aggregate and pipe. The pipe is pressurized with a pump located in the dose tank. The pipe has small holes on the bottom that allows water to enter the aggregate. The water filters through the aggregate and into the surface of the soil, at that point, the water begins to soak into the soil. The fact that the pipe is pressurized means water will come out of all the holes in the pipes at the same time. This
causes the entire drainfield area to receive an equal amount of wastewater at once. The pipe leaves the dose tank and leads into a manifold. The manifold has the lateral pipes attached to it, and when the pump comes on, it pumps water to the manifold and out of the laterals. LPP technology is extremely effective, but these types of systems generally do not have as long of a lifespan as a gravity septic system or mound septic system.
Mound Septic System Drainfields
Mounds are the dreaded, “hill in the yard”. They are pressurized by a pump just like an LPP. The pipe leaves the dose tank and leads to a manifold, at which all of the lateral pipes are attached. The laterals with the holes are placed inside an aggregate bed. This pump allows the entire drainfield to receive water to all the holes at the same time. This is called equal distribution. Mounds are constructed by placing a layer of sandy fill under an aggregate bed with laterals inside. Then the aggregate (stone) bed is covered with sandy fill.
It is very important to maintain a mound septic system’s grass. It is not a good idea to allow a lot of foot traffic or activities to happen on the mound system. Anything that allows the soil to be removed from the sides and/or top of the mound will cause premature “blow outs”. Blow outs are areas where sewage begins to surface. Since the mound is above the ground, it erodes soil a lot easier if proper maintenance isn’t performed. Walking up and down the mound can cause soil to erode also. All of these reasons make it very important to have a good, mowed grass surface on the mound area.
Innovative / Alternative Septic Drainfields
There are many technologies that utilize methods of treating wastewater before it reaches the ground. This is becoming more common in our area due to our environmentally sensitive location and regulations. There are too many methods of I/A systems to describe, but here are the two main categories.
Nitrogen Reduction Units:
Nitrogen reduction units are a way of reducing the nitrogen content in wastewater along with other pollutants. Nitrogen is one of the major sources of pollution infecting our waterways. DNREC has approved regulations that are the beginning of requiring nitrogen reduction on septic systems located anywhere near a water source that is in close proximity to our Inland Bays or the Chesapeake Bay. The units have filters that sit inside the liquid chamber of septic tanks. The basic process involves wastewater being introduced at the top of these filters which settles down to the bottom. Some of the wastewater from the bottom goes out toward the drainfield/dose tank, and some of the wastewater goes back to the top of the filter. Oxygen is pumped into the filter to help the tank accomplish the denitrification process. The oxygen comes from a pump at the surface. We typically place the pump inside of a waterproof container and locate it directly above the septic tank.
Peat systems are a way of reducing bacteria in wastewater along with other contaminants. A peat system is a plastic container that contains peat moss. Wastewater is pumped into the top of the container. Wastewater then soaks down through the peat moss to the bottom of the container. The bottom of the container has holes allowing water out of the container. The container usually sits on a aggregate bed. As water leaves the peat unit, it enters the aggregate bed. We also use peat systems in place of sand mounds as peat systems take up much less room than a sand mound.