Do It Yourself

The Do-It-Yourself Septic System

            You can avoid the cost of hiring a septic designer and excavator, but don’t let friends convince you that these jobs are without value.  Be aware that like buying property this aspect of homesteading, if not handled with cold reason and great care, could ruin many Thanksgiving dinners and many restful nights sleep. 

          Why not do it yourself?  Doing anything yourself can be heroic or crazy depending on the outcome, I have seen more than one home-site ruined forever by sloppy excavation, poor water well placement and the dozens of other pitfalls awaiting an eager baron or baroness heading up the country with a heart full of dreams.   

            Homeowners can save money and prove to their friends that they have mastered this aspect of house construction.  However, be warned that a few down days with a rented backhoe can quickly eat up any anticipated saving by doing-it-yourself.  Remember also that digging up a power line and darkening your block cannot only embarrass you but it could cost you more in repairs than your project budget.

            The skills of an experienced septic designer or excavator increase in value with smaller sites and in poor soil conditions.  If you know in your heart that you lack these skills, don’t risk your peace-off-mind. 

            The site evaluation is step one: Get a scale map of your property if you don’t have one. A scale drawing is usually needed as part of an application for a septic system.  Usually the map is drawn by a professional septic designer and submitted to the local permit department.  A very small site can be classified as a difficult one due to a cramped layout.  The other factors that make a site difficult can be poor or shallow soil, high water table, excessive slope or other general conditions.  A water well must have a  minimum distance from the drainfield even if the well is on a nearby property.  A neighbours’ house already in place must be mapped and often included in the design process due to the presence of a well which will restrict the septic or the presence of a septic system which could restrict well placement. 

            Design and construction will be cramped on small lots.  With small lots, every inch of space is needed.  A survey is required to ensure that setbacks from property lines are met.

Local Counties will usually require a package of forms and information explaining the process. The helpfulness of local inspectors is generally better in the rural counties.

            Important note: The site should not be cleared, scraped, levelled or otherwise disturbed until the details of the site layout have been figured out.  If a water well is required on the site, it should be located only after a place has been found for the septic system.  

            The map is vital.  The map must show the location of the test pits. Most local departments require this evaluation to be done by a licensed person.  Also, the surrounding conditions are shown in scale including property lines, buildings, wells, pipes, paved areas, surrounding septic systems if known, roads, easements, trees and banks, You must also show slope direction, drainage ways, surface water, and surrounding land uses.  Go to your local records to see what your inspection department requires here and to see if you can make your own map.

            The test pits and site exploration are by backhoe.  A minimum of Two 9-foot deep pits are required by authorities on each new lot in most counties.  The pits or “test holes” have replaced the traditional percolation or “perc” test that used to be common in most areas. Today, the soil expert must have one or two pits dug with a back-hoe, wide enough and sloped so that he or she may walk down into them and sample the soil in the side walls.  This is a better evaluation because you can see the soil changes in texture, structure or modeling and seasonal high water.

            Design the drainfield as big as required by the soil analysis test.  This size is based on soil type and house size. The soil expert will pay particular attention to the soil found at a depth of three to six feet below the finish grade at the location of the future drainfield.  This is the soil that will receive the bulk of the “sewage effluent ” and provide final treatment.  Although the test pits can be dug by hand, very few homeowners are willing to take this task on when a few minutes with a back-hoe solves the problem..

            Back-hoe operators generally charge $100 per hour or so depending on driving distance, and whether the test holes will lead to a construction job on the property. Also, don’t forget that someone can fall into the pits and the property owner is usually liable so plan to have them filled in as soon as you can.  Cover the pits with plywood and place barriers around them if you are forced to wait until a local authority has checked them. You may be able to open and close them at one time if  the site can be approved.  Unlicensed equipment operators can usually dig the pits for you but only experienced people should locate the drainfield area and arrange the parts of your site to your best advantage.

            When you stop exploring soil and begin construction, there is often no going back.  The site at this point may be ruined forever by getting it wrong.

            Drainfield location is desired downslope from the tank, for a gravity system.  Whatever soil is in this location, will likely be where the drainfield will have to be.  It is a lot easier to move downslope from the house to a better drainfield location.  If you must place the drainfield up-slope from the obvious location, a pump may be required to “lift” the sewage.  A sewage pumping system may increase the cost of the septic system..

            On a larger property, if the test holes show a poor soil type (usually clay, gravel restrictive soil, solid rock or water), another pit or two or three could be dug to get a better location for the drainfield. In most counties this is customary and not considered deceptive.  Local inspectors will only evaluate what you show them and your job is to put the best appearance on your property for the evaluation.  Finding a favourable location for the drainfield and then sizing it to match the ability of the soil to absorb water is the job of the soil expert.  In most counties this expert is a consultant to the property owner and is known as a designer, an engineer or a soil scientist.

            Soil classification is next.  Be aware that the ability to determine such qualities as “soil texture” and “soil structure” comes with experience.  If you blow the soil classification, you may wind up with less or more drainfield than you need, or a system failure.

The most restrictive soil type should guide your choice in the case of mixed or confusing soils.  Most test pits involve a number of soil types within each pit.

            Drainfield, and septic tank size: The drainfield and tank size is not dependent on the number of bathrooms or fixtures only in the home, most jurisdictions use the number of  bedrooms to determine the amount of sewage that may be sent to the drainfield.  Once you have decided what type of soil is found under your future drainfield, look up the drainfield area required for your house size in the New Private Sewage System Standard of Practice for Alberta, this can be accessed from a qualified installer or possibly from the County. 

            Drainfield layout requires equal sized trenches, for a gravity system.  From the septic tank, at least two equally sized trenches or lines must be designed.  A single drain line is no longer advised.  The separation of flow into two, three or more lines is accomplished with a distribution box or D-box to split the flow.  In the D-box pipes are equipped with simple flow control valves in the form of eccentric plugs that evenly split the flow between lines.  The effluent flows downhill from the tank outlet, through the D-box and down to the individual trenches where it spills out onto the floor of each trench where final treatment starts in the soil at that location.

            Your local inspection department rules.  Your county inspection department has rules and guidelines to follow.  Sometimes rules are the same as provincial guidelines, but sometimes more restrictive rules special to your county must be followed.  These rules include depths and setbacks and construction details.  Such things as how far you can place the drainfield from a water well, a building, a water line, the septic tank, or even a tree.  They will specify how deep the trenches can be (usually no deeper than three feet total from final grade down to the floor of the trench).  The key to getting the correct results from your inspection department people, is to present your ideas clearly and completely in your drawings.

            There is often some back and forth with this department.  You may be asked several times to return with fresh drawings to meet all of the site requirements and rules that the department has on its books.

            Before you begin drawing your project, you should have all the regulations.  This may be in the form of a two-page handout or a thick ordinance of dozens of pages.

            Complete the drawings and the other paper work that goes with your application.  A complete set of drawings for a three-bedroom house on a reasonably simple site will probably be complete in two pages.  The level of detail required may depend on the inspector’s preference.  All buildings, walkways, property lines, retaining walls and the location of the original test holes must be shown.

            You now must wait for the permit to be approved before going on to the construction phase.  Ask local inspection agency what the customary time frame is for permit application review, usually at least two weeks.  Local authorities will approve your drawings, usually with a dated signature.

            Construction should usually begin within one year of that date to avoid starting from scratch with a new fee.  You should get a copy of the permit in the mail once the drawings are approved. You must follow all the notes and details on the drawings exactly.  Look for and follow the printed instructions and any special notes that local inspector adds to the permit face.  Local authorities will inspect your work before anything is covered so plan your job carefully.

            The layout stage of the job transfers the design to the ground. The Layout of all parts of the system must be projected onto the ground.  A long (100 feet plus) tape, a twenty-five-foot tape, stakes and spray paint are the tools of choice.  You must be deliberate here because ground that has been excavated cannot generally be filled in and reused without problems.  The system will only work if the bottom of the trench sits in undisturbed ground and dead level.

Be careful not to begin excavation until local inspectors have approved your plans, no mater how eager you are to get started.  If the inspector requires layout changes, he or she will not listen to excuses such as “we had to get the backhoe back, so we started without the permit.”

            Elevations are critical for all components.   A tripod mounted transit or level or a laser construction level device will be helpful and necessary.  The laser is the newest and generally easiest to use device for constructing everything to the correct level.  With the special level rod, an assistant may walk around and find the elevation of any point of the system within sight of the tripod mounted unit by listening for a series of beeps when the rod is at a predetermined level. 

This tool is particularly useful to ensure that the trenches are not over excavated.  Constant attention to elevation is the key to a successful job.

            The older technology such as a surveyor’s transit may be used, but don’t attempt construction with a standard construction bubble type level.  The level measuring tools are available anywhere to rent.  The inspector must be called for a final inspection of the job before any backfilling occurs.  However, the tanks, pipes and vaults should be backfilled around their sides during construction, and be insulate all areas with less than 4 feet of cover.

            Gravity system preparation.  A poly D-box is usually placed between the septic tank and the drainfield and the effluent lines are pushed into the seals around its perimeter to ensure distribution between the two or more trenches.  Although all the other pipe joints are glued together, where the lines enter the tank and D-box, the pipes are pushed into the special seals without glue.  Plastic rotatable flow control seals are placed into the pipe ends in the D-box to evenly distribute the flow between the trenches.

            The plans must address the difference in elevation between the sewer line leaving the house, the septic tank, the D-box, the effluent lines to the trenches and all of the trenches themselves.  All of these elevations must be in relation to the final, or finish grade of the site which in this case is almost flat.

            Distribution must be even: The flow control valves are set by pouring a bucket of water into the D-box and rotating the seals to make the opening in each seal break the surface at the same elevation.  This evenly distributes the flow between the two or three outlet lines leading to the trenches.  The inlet to the d-box does not have a flow control seal.

The sandy dirt around the pipes has been walked and compacted during construction to ensure that the lines will not be disturbed during backfilling.  Good contractors pay a lot of  attention to detail.  This attention by some excavators distinguishes the best from the rest.  Skill and attention to details will help you more than anything else to ensure that the septic system will not  within its useful life.

            Never Underestimate the Importance of Details: In most modern gravity septic systems, the sewer line must pass through the foundation wall about ten inches below the finish grade.  Just outside the wall of the house, a sweep and riser and a cap, allow the sewer line to be “snaked” out all the way to the septic tank without working from the crawl space or basement.  This is a good maintenance feature.  An important point here is that the sewer line should not pass through the foundation below the footing.  A sewer line that passes through the foundation wall below the footing is generally  much too deep to meet the depth requirements for the drainfield that local health will require in a gravity system.

            The plans for most systems call for an invert (bottom of the pipe) elevation of no more than thirteen inches below grade.  Contractors who leave this detail to the plumber may wish they had not.  Raising the house plumbing, or lowering the septic tank are expensive ways to “fix” this problem.

            Without the professional knowledge of the various details of designing and building your septic system, you may wind up spending a dollar to save a dime.  If you are doing the work yourself, you may not take advantage of all the detailed tricks of the trade that only come to excavators who have learned to successfully complete job after job.  Sometimes a project is better left to those who can make it look simple.

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