We stick by our motto: “Gravity is Our Goal!” We want to design for you the least expensive, least complicated and longest lasting type of septic system allowed by state and local codes. The less you have to pay for the system, the happier we are. Since 1990 we have been designing everything from simple gravity-flow systems, to complicated high-volume commercial systems. Whether it is a conventional gravity system, or a more complex alternative system, we want to design a system for you that will meet your needs for years to come and provide customer service that will make you feel like family and give you peace of mind.
The type of septic system we can design for you depends on several factors. Primarily, the depth of soil above a restrictive layer (“hardpan”, clay, water, etc.) on your property determines the type of system that will be allowed. Septic system types in Washington State are classified as follows:
Gravity is our goal! Standard gravity septic systems are the simplest and least expensive type of system allowed in Washington State. A standard gravity septic system consists of a septic tank, a distribution box, and drainfield laterals (or trenches). We try to design for you a standard gravity septic system if it is possible. Typically, septic system drain fields are installed at a depth of 12 inches. The installation depth can vary, depending on site conditions. The amount of undisturbed, native soil beneath the drainfield trench and above the restrictive layer (“hardpan”, clay, water, etc.) is known as “vertical separation”. To meet code, a standard gravity septic system must have at least 36 inches of vertical separation. To simplify things, a minimum of 48 inches of soil (vertical separation + trench depth) is usually needed on a relatively flat grade to be able to design a standard gravity system.
If your soil isn’t deep enough for a standard gravity system, the next best thing is a standard pressure distribution septic system. A standard pressure distribution septic system consists of a septic tank, a pump tank (also known as a “wet well”), an effluent pump, a timed dosing panel, a pressure manifold, and pressure distribution laterals (or trenches). A standard pressure distribution septic system spreads the effluent out over the entire infiltrative surface of the drainfield with each dose. Typically, pressure systems are set up to dose the drainfield 6-12 times daily. To meet code, a standard pressure distribution septic system must have at least 24 inches of vertical separation, or a minimum overall depth of 36 inches of native, undisturbed soil.
If there is less than a minimum overall soil depth of 36 inches, then an alternative-type septic system must be used in order to protect the marine shorelines, lakes, streams, and drinking water aquifers from the dangerous vectors and pathogens that can be found in sewage. There are many types of alternative septic systems, including aerobic pretreatment systems with pressure distribution, aerobic pretreatment systems with drip irrigation, bottomless sand filters, Glendon Biofilter mounds, and many others. With shallow soils there are usually other concerns such as high water tables, poor quality soil, wetlands, etc. Site conditions will usually dictate what type of alternative septic system is needed. Typically, an aerobic pretreatment system with pressure distribution is the least expensive and longest lasting alternative-type septic system. Typically, aerobic pretreatment systems, drip irrigation systems, and sand filters are setup to dose the drainfield 6-24 times daily, depending on the type of system. To meet code, an alternative septic system must have a minimum of 12 inches of vertical separation. The minimum overall depth of native undisturbed soil for these systems ranges between 18 and 24 inches.