Earthwise Excavation...From the ground down.

Septic Systems

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HISTORY

Hello and welcome,
This site is being constructed to assist you in understanding the basic concepts of onsite sewage treatment systems. Prior to the mid seventies the majority of systems that were installed were basically just trying to dispose of the households waste water. But over the years, given the increasing density of single family homes out in the rural areas in the Northwest, we were negativity impacting our groundwater, streams and lakes. This was the impetus for stricter control and standards and rightly so since untreated sewage can contain e-coli, fecal coliforms, to just name a few of the pathogens.

Today onsite sewage treatment systems are designed to be state of the art, meeting EPA's treatment standard one. This far exceeds the standards for sewage treatment plants and replenishes existing groundwater systems. This decentralized form of treatment is of greater benefit to the surrounding ecosystem than that of sewers. But of course things need to be working properly, which is probably why you are reading this. The added complexity of today's systems belies a need for periodic maintenance and monitoring for proper operation. All to often we wait till sewage is surfacing on the ground before we try and figure out what's down there.

That is the purpose of this site. To share what we have learned over the years of working in the business. For knowledge is golden.

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BEGIN

The main focus of this site will be for systems not older than 1980. This will include but not limited to: Low Pressure Distribution systems
Sand Filters
Mound systems
Aerobic treatment units
Drip systems
Pump tanks
Septic tanks
Gravity fields

1. What kind of system do I have?

If you are unsure the first step is to locate your "asbuilt drawing". This is a drawing made of your system components by your system designer after installation but prior to backfill. This is different than the system design drawings for it reflects how it was built. Hence the name "asbuilt" This drawing is typically on file with your local health department, which is best located with your property parcel number. This is also called the Property Tax Number. Your address does not always stay the same so it is best to have your parcel number when calling to obtain the drawing. Your local health officer will be able to tell what type of system you have and send you a copy of the drawing. The accuracy of the drawings are for the most part approximate depending on the system designer.


2. Why are there so many different types?

Each system is designed to be site specific, taking into account soil depths, soil types, land topography and restrictive site conditions such as wells, waterways and cut banks. In the State of Washington the requirement is that untreated effluent pass through 36 inches of soil before encountering high ground water tables.

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SEPTIC TANK


The septic tank is the first step in the process, which is to separate the solids from the influent stream. This is done by slowing the velocity of the influent to allow greases and oils to float to the surface. This also allows any solid matter to settle to the bottom. It is in here that the anaerobic bacteria break down any organic materials. Greases and oil, sheer volume of matter, introduction of toxins all play a part in hindering the productivity of the bacteria, this accounts for the periodic need for septic pumping. There are two chambers in the septic tank with baffles in place to assist this process. As the wastewater exits the septic tank it passes through a filter places in the outlet baffle as an added pre caution against the passage of solid matter. From here the wastewater is called effluent and goes to the pump tank.

 

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PUMP TANK

The pump tank is designed to allow for retention of the effluent in the specified dose volume for your system. (I.e.; 90 gallons per dose) There is a pump at the base, along with float controls, which are actuated by water level in the chamber. If there is a malfunction and the effluent rises above the normal retention volume the alarm will be actuated. There is enough capacity above the alarm float for storage of one day's volume of effluent. Under normal conditions the pump is actuated by a float control to pump a dose volume of effluent to the sand filter. The effluent is pumped through a transport pipe into a network of distribution pipes in the Top gravel layer of your sand filter.

Rates

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SAND FILTER

The sand filter is constructed as follows, starting from the Top down. Nine inches washed gravel on the Top in which a network of distribution pipes is installed. This network consists of 1 ¼ in. PVC laterals with 3/16 in. holes drilled at preset spacing to allow for equal distribution of effluent in the sand filter. Under this gravel layer is twenty-four inches of graded sand, which provides a medium for the aerobic bacteria to further breakdown, and filters the effluent. And on the very bottom is two layers of gravel in which is installed another network of collection pipes. These pipes collect the filtered effluent and transport it to a central pump basin. This pump is installed, along with float controls, alarm etc., in much the same fashion as the pump tank. All of these layers are surrounded on all sides except for the Top by a thirty mil PVC liner. This is done to protect the ground water from being contaminated by effluent and vice versa. From her the effluent is once again pumped via a transport pipe to the drainfield.

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MOUND SYSTEMS


Mounds are constructed on Top of the existing soil after it has been prepared with moldboard plowing. They are constructed with a sand media with a depth of one to three feet deep. On Top of this sand a gravel bed is constructed in which small diameter pipes are installed with pre-drilled holes. Upon receiving a dose of effluent from the pump tank, the lateral pipes disperse the effluent evenly over the Top of the sand bed. The sand media and the underlying soil provide treatment of the effluent prior to dispersal into the groundwater table. This whole "mound" of sand is covered over with sandy loam cover material to provide protection.

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DRIP


This drainfield design uses small diameter polyethylene tubing with emitters installed directly into the soil. The emitters are spaced twelve to twenty four inches apart with tubing runs spaced twenty four to thirty six inches apart. This typically allows for a area reduction of 20 to 40% and still provides excellent treatment. The system is connected to both a supply and a return line which allows for timed flushing of the system. All effluent passes through a 100 micron filter which is also connected to the return line for flushing. This system can be used with or without pretreatment. This system has a very low impact installation method and can be installed without removing the majority of the typical undergrowth or landscaping.


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GRAVITY FIELDS

This is the standard type of dispersal system used in the majority of Onsite Sewage Treatment systems. Drainfield trenches have a four inch perforated pipe installed in gravel twelve inches deep. The trench width will vary between twenty four and thirty six inches wide. The pipe is held six inches up from the bottom of the trench and is covered with two inches of gravel. Today the gravel is covered with filter fabric with older systems having used biodegradable covering techniques. These trenches were installed level following ground contours. On sloping sites more than one trench would be used interconnected with solid overflow pipes. Each trench designed to fill up before spilling over into the next trench below.
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DESIGN


This is the conceptual drawings of the Onsite Sewage Treatment System designed specifically for a parcel of land. These drawings are used as a communication tool in regards to proposed system components and their location. Typically these drawings are created by a drainfield designer after a site visit and test holes, revealing soil depth and type have been dug. The resulting information is used to design a system that meets current code requirements. Some Health districts allow installers to design repair procedure for failing systems, but for the most part designers perform all the work. The design must meet minimum health code requirements but no restrictions on the maximum. This situation can create questionable design methodologies and incur extra expenses due to installation costs. Speak to more than one designer as well as industry technicians

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CONSTRUCTION

The first step in the installation process is to obtain the required installation permit. For new construction this can only be done if there is a valid building permit for the site This process varies from county to county so we have outlined the different procedures in the following list:

Island County 3-5 working days
The installer fills out a permit application called the "start card" and submits to the area's designated Health officer. A reconstruction meeting is conducted by either phone or a onsite meeting depending on the system complexities

King County 2-4 weeks
The installer calls the system designer for a "stub out release" certificate. This is an onsite inspection of the site conducted by the designer after the foundation is installed. There needs to be a plumbing stub outlet in place so the tank location can be inspected. The installer then sends this certificate along with the permit application, copy of the building permit, and the permit fees to the Health Department. A Health officer will review the paperwork and after approval will send to the permitting office. This office will send out the permit once all paperwork has been verified

Snohomish County 3-5 working days
The installer calls the system designer to schedule a reconstruction conference. The system designer schedules either an onsite meeting or a phone conference depending on the system complexity. After this meeting the Health officer will send out the permit

After receivable of the permit to install, installation is scheduled. Consideration is given to the weather depending on site conditions and prerequisites. On the day of installation the equipment and crews will typically be onsite early morning to prepare the site. All the system materials will be brought onsite with trucks. The tanks will be brought with a boom truck to place in the excavated hole. Each tank will displace approximately 7 cubic yards. After installation the tanks will be partially backfilled and will need to be filled with water. This is for stability, since tanks can "float" out of wet soils and for hydrostatic leak testing. The tank depth is dependent on the plumbing stub depth which should be as shallow as possible. This is due to concerns of groundwater infiltration over the long term into the tanks through seams and joints. Protect your investment and keep your plumbing stub high.

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MAINTENANCE

Maintenance of an Onsite Sewage Treatment system is relative to the type of system in use. The common maintenance task shared by all systems is pumping of the septic chamber or chambers. This is typically done every three years but is very dependent upon household usage. This procedure involves gaining access to the septic tank for pumping and cleaning of solid matter.

After a septic tank is pumped there is a period lasting one to three months where the full effectiveness diminishes. This is due to a loss of the anaerobic community that had established itself in the tank. Make sure that you really do need your tank pumped by checking your sludge and mat depths prior to scheduling. Given low organic matter loading of a septic tank, the pumping cycle could extend out ten years or more.

Operational checks of your system should be performed at least every three years. Just as any machinery, regular maintenance and system checks are vital to longevity. The more complex your system is, the more often operational checks should be performed. More and more systems these days have monitoring required but monitoring alone is not a full operational check.

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MONITORING

Monitoring that is done of an Onsite Sewage Treatment system should consist of the following: An inspection of the septic tank sludge and mat levels and inspection of the drainfield infiltrate conditions. This done typically through access and inspection ports at ground surface. Should your system not have these points, they can be installed during the preliminary inspection to provide for future access.

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SERVICE


We provide a full range of service for all Onsite Sewage Treatment systems. This includes repair, maintenance, monitoring, pumping, retrofitting, and installation. The primary focus of Earthwise Excavation is serving the Onsite Sewage Treatment community in King, Kitsap, Island and Snohomish counties. We have been providing Top quality service, innovation and guarantees since 1987

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AEROBIC TREATMENT UNITS


There are a myriad of different manufacturers each with there own "mousetrap". Some of the current units being used in this area are the FAST system, the Geoflow system, the Nibbler system, and the Whitewater system. The very basic concept of these units is aeration of the effluent after the septic tank and prior to the absorption field. This is done typically with small air compressors and circulation of the effluent within the chamber through some form of turbidity enhancer. Most of the manufacturers also pass the finished product past ultraviolet light to kill off any remaining life. Other systems use chlorine tablets. This technology is still considered relatively new to the industry. Consult your local health department for the current list of approved systems.

The advantages to these systems are their ability to handle larger volumes of higher effluent strengths than conventional systems. Also it is less costly for repair should the system fail due to overuse. Disadvantages are higher operating and maintenance costs due to 24hr a day air compressor (small and quiet), ultraviolet light bulb replacements, and venting issues. There is no question that these units are perfect for some situations, but we feel that they are not yet a blanket alternative to secondary treatment.