A septic mound is also referred to as a raised sand bed. This type of septic field is a hybrid between the conventional and classic way we think of septic fields. Mounds use washed concrete sand to raise the elevation of the pipes that distribute effluent, allowing for a vertical separation from any bad layers found in your onsite soils. This separation insures that we have at least 36” of travel for the effluent to achieve treatment before it enters the soil, making its way to your limiting layer (the layer that stops effluent from easily migrating further down).
A soil texture such as clay or silty clay with a platey structure will always require the installation of a sand mound. When properly installed, a mound can be contoured to match and blend in with your landscape. An average size* for a sand mound is 130’ end to end and sits around 3 feet high on average. It must sustain grass coverage, which needs to be cut just like your lawn to allow breathability. With a 3 to 1 slope on either side of the highest point, mounds are safe to mow even with a ride-on lawn mower.
One thing to keep in mind with mounds is that they will always stay a consistent width, however the overall length may change when dealing with larger flows of water.
At-Grade Septic System
The at-grade septic system is the newest in the family of treatment fields. The main thing to keep in mind is that to install this field, it requires effluent to be treated. It must also be installed in treed area that has a layer of LHF in the soils. LFH is a layer of decomposed organics from leaves, shrubs, bark that has been built up over many years and is special to the treatment of effluent as the effluent travels downwards.
The composition of the field itself is two rows of 1” pressurized pipe that is held approximately 6” off the ground with spikes and clips. By code, we must install a row of arc chambers over each row of piping. These arc chambers protect the 1” lines and help evenly distribute effluent over what we call the soil infiltration area. Because the piping is pressurized, we insert small holes called orifice holes. These holes spray effluent directly to the underside of the arc chamber, which splashes and deflects the flow evenly before it reaches the ground surface. The width of the arc chambers can vary from 18” to 36” in width. Just like the raised sand mounds, the width will stay consistent but the overall length changes with larger flows of water. Finally, we cover the entire area of the arc chambers with approved bark mulch. The thickness of this mulch must be at least 9” after settlement has occurred from install. As you can imagine, we need quite a lot of mulch – in most cases, about 125 cubic yards is needed to complete an install.
Pressure Trench Septic Field
A pressure trench septic field follows the same concept of a conventional leach field that most people associate with septic. It is typically installed over a large flat area and does not protrude above surface. The use of gravity-fed effluent is no longer common practice, however the process of excavating a trench no deeper than 36” is still used.
Piping is pressurized in a way that the effluent is evenly distributed over the length of the trench by using a consistent length of 1” piping, called laterals. The laterals are then fed effluent via a delivery line connected to the center of the laterals. Once completed, the system will deliver effluent evenly over the trench bottom or soil infiltration area.
One argument I get all the time is that there was nothing wrong with those old siphon systems that gravity fed into a 4” lateral. We never had problems with over saturated fields or high water alarms in the tanks due to pump issues. My answer is common for everyone: we know how to treat our environment properly now. We introduce effluent at the proper elevation and don’t over saturate one area. Those old fields may have “worked” but they risked contaminating the ground and groundwater. Also, we build bigger houses now that produce a lot more water and we often have specialized water treatment units in our house such as reverse osmosis and iron filters. These units can triple the amount of water sent into your septic system.
*The total area required can be decreased with a package treatment plant