How To Build A Septic Tank System

How To Build a Septic Tank System

The Think Tank - Septic Design Forum

for systems other than for the average home - jump To: septic systems for churches and theaters septic systems for waterfront lots and tight sites septic systems for the small shop or office septic systems for larger rural homes septic systems for commercial wineries car washes and kennels etc. Introduction: 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 Thanksgiving dinner and many restful nights sleep. How to build a septic system? It's all here. Why not do it yourself? Doing anything yourself can be heroic or crazy depending on the outcome. In more than 20 years spent designing site layouts and septic systems in the scenic countryside of beautiful Washington State, 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 entire 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-of-mind. The site evaluation is step one: Get a scale map of your property if you don't have one. The scale drawing below is from an application for a septic system that was drawn by a professional septic designer and submitted to the local health department. The site, classified as a difficult one, is for a small lot in a rural subdivision with a community water system (tank in distance). At least a water well does not have to be worked into the layout. The closest neighbor's house can be seen in the photo to the left. The dirt dug from the two test holes can be seen at the back of the lot at the edge of the farm field above and on either side of the green power transformer. The site is ready for the site evaluation with local health. Design and construction will be cramped. With small and tight lots, every inch of space is needed. A survey is usually advised to ensure that setbacks from property lines are met. Note the red survey steak marking the lot corner pin behind the transformer. Local health will usually provide a package of forms and information explaining the application process. The helpfulness of health inspectors is generally better in the rural counties, but they will not tell you how to build a septic system. That information follows; Important note: The site should not be cleared, scraped, leveled 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 witched or located only after a place has been found for the septic system. Besides the description of soil texture and depth, the site evaluation usually has a scale hand drawn map. The map must show the location of the test pits. Most health 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. You can go to your local health records to see what your health department requires here and to see if you can make your own map. The test pits and site exploration are by backhoe. A couple of 6 foot or deeper pits are usually required by local health 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 or more pits dug with a back-hoe 5 or more feet deep, and wide enough and sloped so that he or she may walk down into them and sample the soil in the side walls. Soil stability and safety are always considered for the inspectors and for casual members of the public. Kids are drawn to equipment and holes in the dirt. Leaving the holes open for later inspection is inferior to having local health attend the site inspection and close things up in a single trip for the backhoe. The site evaluation by backhoe is a better test than the old perc test because it allows a wider look at the soil. Soil classification is next. The soil classification system used in most places in the USA (and in some other countries), is called the US Department of Agriculture Soil Conservation Classification System. 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. More drainfield means needless expense. Less drainfield means early failure, usually with guests over. The most restrictive soil type found in any of the pits in the area of the drainfield should guide your choice in the case of mixed or confusing soils anywhere within the drainfield area. Most test pits involve four or more soil types as you look down through the soil profile within each pit so study the soil directly below where the drainfield will be (between 36 inches and 48 inches below grade usually). You are now ready to determine the area of trench needed for your home. Remember, dig a couple of six foot holes at each end of your drainfield area and check the soil type. How to use the chart: In spite of what you think, the drainfield size is not dependent on the number of bathrooms or fixtures in the home. Almost all health departments use the number of bedrooms in a home as a way to size drainfields. The number of people in the house (usually two to a bedroom), and their usual daily water use (usually sixty gallons per person per day), is how the flow rate is established. This flow rate of about three hundred sixty gallons of water use per day inside a three bedroom house determines the amount of sewage that must 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 chart below and you have the required drainfield size. Note: The chart below was compiled from the rules of various states and many years of practical experience. Your county may have very different sizes and by law you must use the chart from your local health department. Drainfield Size Chart Soil Class USDA Soil Type: take a soil sample 5 ft below grade in drainfield area by digging a person sized test pit at each end 2 Bedroom House 240 gallons of sewage/ day 3 Bedroom House 360 gallons of sewage/ day 4 Bedroom House 480 gallons of sewage/ day Commercial Projects for every 100 gallons of sewage/ day # 1 Coarse Sand - most sand soils will require pressure distribution and 200 sq ft gravel or 10 six ft vaults or 16 four ft vaults 300 sq ft gravel or 14 six ft vaults or 22 four ft vaults 400 sq ft gravel or 18 six ft vaults or 28 four ft vaults 84 sq ft gravel or 3.6 six ft vaults or 5.6 four ft vaults # 2 Medium Sand 240 sq ft gravel or 12 six ft vaults or 20 four ft vaults 360 sq ft gravel or 16 six ft vaults or 25 four ft vaults 480 sq ft gravel or 21 six ft vaults or 33 four ft vaults 100 sq ft gravel or 4.3 six ft vaults or 6.7 four ft vaults # 3 Fine Sand - Loamy Coarse Sand - Loamy Med Sand 300 sq ft gravel or 10 six ft vaults or 16 four ft vaults 450 sq ft gravel or 15 six ft vaults or 24 four ft vaults 600 sq ft gravel or 20 six ft vaults or 32 four ft vaults 125 sq ft gravel or 4.1 six ft vaults or 6.5 four ft vaults # 4 Very Fine Sand - Loamy Fine Sand - All Loams 400 sq ft gravel or 14 six ft vaults or 22 four ft vaults 600 sq ft gravel or 20 six ft vaults or 32 four ft vaults 800 sq ft gravel or 26 six ft vaults or 42 four ft vaults 167 sq ft gravel or 5.4 six ft vaults or 8.4 four ft vaults # 5 All Silt Loams of Good Structure 540 sq ft gravel or 18 six ft vaults or 28 four ft vaults 800 sq ft gravel or 26 six ft vaults or 42 four ft vaults 1070 sq ft gravel or 35 six ft vaults or 55 four ft vaults 223 sq ft gravel or 7.2 six ft vaults or 11.2 four ft vaults # 6 Other Silt Loams - All Clay Loams - All Clays Note: some clays may not qualify for any system 1200 sq ft gravel or 39 six ft vaults or 62 four ft vaults 1800 sq ft gravel or 60 six ft vaults or 94 four ft vaults 2400 sq ft gravel or 78 six ft vaults or 122 four ft vaults 500 sq ft gravel or 16.0 six ft vaults or 25.0 four ft vaults bed type drainfields allowed if the soil type is fine sand or coarser - pressure distribution required with all bed designs and if soil is extremely gravelly or very gravelly plus a sand lining may be required under the drainfield one square foot of drainfield is measured like a carpet looking down from the top - "sidewall" is not considered although some health departments continue to give "credit" for up to 6 inches of sidewall calculated by measuring the perimeter of the bed or trenches - using sidewall confuses calculations and has been discredited due to the fact that water in soil seldom moves sideways except when saturated Return to Drainfield Design Return to Site Evaluation "Perc Test" Drainfield layout requires at least 2 equal sized trenches. From the septic tank 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 (sewage that has gone through the septic tank) 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 treatment starts in the soil at that location. Don't forget, the individual trenches are NOT sloped, but are dead level from one end to the other. Your local health department rules. Your county health department has rules and guidelines to follow. Sometimes rules are the same as state 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 (usually 100 feet), a building (usually 10 feet), a water line (usually 10 feet), a stream, pond or lake (75 to 100 feet), the septic tank (generally 5 feet), or even a tree (5 to 50 feet depending on species) cuts and banks (varies state to state, and county to county) are spelled out. They will specify how deep the trenches can be (usually no deeper than three feet max from final grade down to the floor of the trench), and even whether you may use the plastic vault technology shown here. The key to getting the correct results from your health department people, is to present your ideas clearly and completely in your drawings. There is often some back and forth with the health 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 must have all the rules from local health. This may be in the form of a two-page handout or a thick ordinance of dozens of pages. By the way, a square foot of gravel in a drainfield is measured like a carpet, covering a 12 inch by 12 inch piece of ground, except the gravel is one foot thick. Therefore, a drainfield trench "covering" 300 square feet, is a pit, three feet wide and one hundred feet long, with a foot deep of gravel in the bottom. (In reality, you will use two trenches at 50 feet long each.) The gravel is covered with a tough but thin fabric to keep the dirt out called filter fabric. The whole thing is buried with a cover (backfill) of one to two feet of native soil. The thickness of backfill depends on the desired trench depth. The "gravel" is not really gravel at all, but a uniform clean washed rock with granules one and a half inches in diameter known to a gravel pit operator as "inch-and-a-half drainrock". PVC Vault Technology: You may in most areas substitute rows of plastic chambers instead of the old school leachfield gravel. Infiltrator® and Hancor® are two companies who supply this product shown to the right. The vaults hook together like a freight train and are very easy to transport and build. Excavators and installers usually prefer the vaults over drainrock once they have tried them. Most health jurisdictions are recognizing the value and efficiency of the vault technology and the use of vaults is becoming widespread across the USA. Gravel is used for geometric reasons and can be cheaper particularly if the job is close to the supply. Also, some health inspectors give "credit" for the increased storage capacity of the vaults over gravel systems. Each foot of standard 3 x 1 ft vault yields around 10 gallons of storage. A linear foot of 3 ft wide gravel trench yields less than half of that even with the highest quality drainrock. You may get 400 Sq Ft of "credit" for our trench that actually contains only 300 Sq Ft of ground. This may save vital space on a tight site. Vaults now come in several widths, lengths and heights. However, the standard width is a little less than three feet wide (but generally 3 feet is the width used for design and space planning) and two standard lengths 6 and 4 feet. Various heights and capacities are now available. In most counties, in most states, the new plastic vault technology has replaced the traditional gravel drainfield. Although, the Septic Design CD available on this site provides for both gravel and vault drainfields. Eventually the vaults will become the standard drainfield type. Notice that the vaults provide treatment with less area depending on the soil type. Usually local health will allow a quarter to a third less drainfield with the vaults. This is because of the superior storage volume provided by the vaults compared to drainrock. The Septic Design CD available on this web-site allows you to create plans that may be modified and edited to meet the needs of your local health department whatever they are. Often a few simple notes or other changes can satisfy the specific rules of most health jurisdictions.

Study the drawings shown here. Drawings tell others how to build a septic system. These two sheets represent the complete drawing set for a three-bedroom house on our model property. The level of detail required may depend on the inspector's preference. However, all buildings, walkways, property lines, retaining walls and the location of the original test holes must be shown.

Time To Apply for the Permit Now Make Your Application to Local Health: You now must wait for the permit to be approved before going on to the construction phase. Ask local health what the customary time frame is for permit application review. Local Health Will Approve Your Drawings usually with a signature and a date. 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 health adds to the permit face. Local health will inspect your work before anything is covered so plan your job carefully. Time To Start Building the Septic SystemThe 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. Before you begin, be sure that the drawing is accurate and that it matches the site exactly. Compare the site drawing on your approved design to a plat map of the site to make sure that the drawings match and show the correct scale. On the drawings, add up all strings of dimensions to make sure that a critical measurement has not been missed. Find and mark the corners of the property. Do not use existing fences or the advice of neighbors unless you are sure of the property lines from a legal survey. Here, the construction crew is checking the location of the third trench. 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 health has 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. The tripod on the sidewalk on the left side of this picture is a laser level device. 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 by listening for a series of beeps. 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. Older technology such as a surveyor's transit may be used, but don't attempt construction with a standard construction bubble type level. These tools are available anywhere to rent. The health 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. The crew is using the top of the septic tank in the foreground as a work table . Notice the difference in elevation between the top of the tank and the surface of the nearby sidewalk. This tank will be less than a foot underground. Pipe Slope and Type for Proper Drainage. A word here about pipes and drainage. PVC (polyvinyl chloride) pipe comes in a variety of sizes and types. Pipes in a gravity system are 4 inch diameter. ASTM 3034 or ASTM Schedule 40 are both good for sewer lines between the house and the tank. These pipes can not be crushed by stepping on them. ASTM 2729 (perforated drainfield pipe is made of this stuff) and ASTM CL160 (known as Class-160) are too thin to stand up to being driven over with a car, etc when placed in shallow trenches. Some counties allow the thin wall pipe between the tank and the drainfield. The "building sewer" must be sloped (sometimes called fall) at between 1/8" per foot and 1/4" per foot (in other words the pipe must drop at least one inch for every 8 feet of sewer line and not more than one inch for every 4 feet). Less slope and the flow is too slow to clear the pipe. More slope and the water theoretically drains off too quickly and the solids will become stranded and cause a blockage. This idea of maximum slope no greater than 1/4" per foot has been challenged, and an engineering justification seems around the corner, but almost all health departments require this minimum slope and will require "stair stepping" down steep slopes. Do not ignore the minimum slope requirement for any reason, or the spot will become a perpetual problem in the system. If the yard down to the tank from the house slopes too much, the sewer may be dropped straight down in a series of drops followed by pipe slope runs to the next drop. The drops are good places for cleanouts. Remember also that any right angle bends in the sewer pipe are not allowed when changing direction in the sewer, down or side-to-side. Always use two 45 degree "elbows" or "90 degree sweeps" instead of a 90 degree elbow to allow proper cleaning with a snake or roto-rooter. Also put in a clean-out (sweep "T" with a riser and cap) to direct a snake (a metal probe for cleaning out blockages from the surface) toward the tank every 50 feet (100 feet absolute maximum) in the sewer line. Clean-outs and 45 degree elbows are not needed in the effluent line although some health departments want them there anyway. If the ground slopes towards the house from the drainfield area, or if the site is flat, you may need a pump in the tank to deliver the effluent to the proper elevation. After the septic tank, and after the D-Box all the way to the drainfield, the slope may be as little as 1/64" per foot if the excavation is expert. The effluent line has no solids in it so the slope is only required to keep the pipe clear of liquid. The effluent line may drop down at any angle for the same reason. All effluent lines must drain fully and not have a "sag" in the line that could cause pools to form and in cooler climates cause a line freeze. Click here or here for more about freezing septic systems. This view of the site clearly shows the layout. The septic tank can be seen on the right of the view between the first trench and the patio. On this job, and normally, the septic tank is delivered from the tank manufacturer and lowered from the truck into a hole prepared by the excavator. The tank hole has a flat floor at the exact depth. Call the tank supplier to get the exact tank height and depths of the inlet and outlet. In rocky ground, two or three inches of pea gravel may be needed to protect the tank bottom. The septic tank is often the first thing to be added to a new house site. A concrete tank in our area runs about $550 delivered up to 40 miles, and further for a few dollars more. Fiberglass tanks and ribbed polyethylene septic tanks are not usually advised as they are not only more expensive but they may not be sturdy enough to do the job. Flexible tanks tend to distort over time particularly when they are pumped out. Don't trust a tank that can't safely be filled with water in the parking lot without distorting or leaking. Steel tanks are still used in remote, colder locations such as Alaska, but sewage is corrosive to steel. Metal components have a limited life in septic systems and should be avoided if possible . In the view to the left, the backhoe is working on the third trench. The vaults are in place in the first two trenches and the vault units seen near the backhoe are waiting to go into the third trench when it is finished. The site is being watered with the hose as work progresses. The site may need to be sprinkled for a day or more prior to construction for the same reason. Although this keeps dust down, the primary reason for adding water to dry soil is to provide proper moisture for compaction of the dirt around the pipes and parts. Water is usually used to soak the sides of the tank to compact the soil and fill in voids to avoid sink holes in the lawn. Very wet or very cold weather is not the time to build a septic system. Good excavators avoid working in extreme conditions except in emergencies. Working in poor weather usually involves return trips to smooth and refinish surface grades. Before the vaults are placed in the trench, the side walls of the trench are roughened with a garden rake. This important step prevents the formation of bacterial scum on the trench walls called "smearing" which can cause early failure of the drainfield. In some areas, the excavators weld teeth to the side of the backhoe bucket to do this job in one pass. Septic systems are plumbing systems. In this view, the concrete D-box has been placed where it belongs and the effluent lines are being pushed into the seals. 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. Older construction methods require lines to be sealed into D-boxes and tanks with concrete grout. To the left bottom of the view, the yellow plastic rotatable flow control seals are waiting to be placed into the pipe ends to evenly distribute the flow between the trenches. Next to the excavator is the level rod for checking the level of the D-box and the pipes. The system works because of the difference in elevation between the sewer line leaving the house, the septic tank, the D-box, the effluent lines to the trenches and the floor elevations of all of the trenches themselves. These final elevations must be from the plans. The finish grade and backfill will have to cover everything at the required depth when you are done. Often the top of the septic tank is used as a datum or benchmark. The floor of a well house, an existing slab, any reasonably immovable object will qualify as a benchmark. Property corners on a site can change elevation.

Distribution must be even. The D-box is ready to go. The flow control has been set by pouring a bucket of water into the 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 three outlet lines leading to the three trenches. The inlet to the d-box is on the right and does not have a flow control seal.

The sandy dirt around the pipes has been walked and compacted to ensure that the lines will not be disturbed during backfilling. The backfill will form a slight hump over the drainfield so that eventual settling will not cause low spots over the drainfield over time. Note the expandable urethane foam sealing the effluent line at the top of the view where the northeast effluent line disappears into the vault. This attention to detail 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 fail within its useful life of fifteen to twenty-five years. Most Owners' say at the first meeting with the designer "I don't want to have to mess with it." They will call the contractors back to the site at the first sign of trouble. Doing it yourself won't hand you this option.

Finishing the Job: Final backfilling after the final health department inspection will require special attention to soil moisture and soil compaction as well. Some excavators will "Walk" the trenches with the rear wheel of the backhoe, but this may collapse the vaults if done too aggressively. The soil must be slightly damp and not wet. If soil compaction is ignored, the lawn will settle, sink-holes can appear, and the tank itself may shift during a heavy storm. Backfilling may have to happen even though the site is soaking wet or frozen. A visit later in the year may be required to fix the dips prior to the laying of sod. Weather conditions should be considered in all excavation projects. Putting off the job may be easier in the long run than fighting the elements. Good excavators avoid working in the worst weather unless the client understands the risks and is willing to pay extra for precautions. Remember, slightly damp (not wet, not bone dry) ground is the easiest to work with.

Never Underestimate the Importance of Details: This image shows a clean-out. The sewer line to our project shown here just outside the house passes through the foundation wall about ten inches below the finish grade. The sweep and riser and cap (shown here white), allow the sewer line to be "snaked" out all the way to the septic tank without working from the crawl space, a good maintenance feature. Note the 45 degree elbow below the cap, directing the cleanout downstream toward the tank. This clean-out if placed near the driveway can be used as an RV dump as well. back to pipe slope

The important point here is that the sewer line should not pass through the foundation below the footing. The example in the small inset photo shows the wrong way to do this. That sewer line in the inset photo is much too deep to meet the depth requirements for the drainfield that local health will require.

How to Design the Grade Elevations of the Septic System: The plans for our example on the right called for an invert (bottom of the pipe) elevation at the outside wall of no more than thirteen inches below finish grade. Contractors who leave this detail to the plumber may wish they had not. Redoing the house plumbing is one fix and shaving dirt off the surface of the yard is the other. In most health regulations, the floor of the drainfield trench can not be deeper than 3 feet from finish grade of the yard.

On a mostly level site, set your depth at the drainfield trenches first. Starting with the floor elevation of the lowest trench we work our way upstream to the invert elevation of the effluent line into the highest trench (8 inches above the floor of the highest trench) back along the effluent line with minimal slope up to the D-Box (add 3 inches for drop inside this box.) From the inlet of the D-Box we follow the effluent lines up to the septic tank outlet. Don't forget to add pipe slope between the D-Box and the septic tank (minimal slope to fully drain) plus 3 more inches for drop inside the tank bringing us up to the septic tank inlet invert elevation. From this septic tank inlet elevation we figure the route up to the house foundation following proper sewer slope. This gives us the pipe invert elevation of the sewer leaving the house as shown in the above photo to inform the plumbers.

Some old school excavators will try to justify a deeper excavation for freeze protection. In several years of occasionally hard freezes in central Washington State (we see 25 below on rare nights), I have never seen a sewer line freeze that was built at the proper slope however shallow. Tanks too are safe from freezing even when placed slightly above ground such as under a deck. Water lines however are buried at 3 to 4 feet in northern areas to prevent freezing. Sewer lines and septic tanks follow a different set of rules than water lines because septic system lines are seldom deeper than a foot or 2 below grade.

Pressure systems however are protected from freezing in a slightly different way. I favor full drainback of all transport lines, manifolds and even laterals. In vault type drainfields the one inch diameter lateral lines are strapped to the underside of the vaults with zip ties. Enough downward pointing orifices must be provided for complete lateral drainage. If you are not following all of these technical suggestions, consider hiring a good professional designer for drawing up your plans, particularly if you are required to provide pressure distribution.

Much further north, things are different. Tanks are insulated with foam insulation, deeper systems are allowed and heating elements are sometimes added. Vast areas of the planet are unsuitable or poor for septic. Solid rock, for instance, or permafrost will not provide safe treatment. However the places people chose to live, in most cases are suitable places for septic already. And if not, technology steps in, on marginal and fringe areas with more complex (and expensive) septic systems.

Get answers to your septic questions on our forum Click Here Costs: With constantly changing cost of oil and fuel, costs are going up generally. Excavators run equipment all day and therefore have increasing fuel bills. Septic systems have many parts made of plastic (petroleum based) and these parts are often manufactured far away and are trucked to the site. Designers and regulators spend time in the field and a lot on the road often to remote sites in trucks. Septic is likely the only choice for sewage treatment from wilderness to farm to resort and even within some city limits. Mostly experts rather than homeowners are required to design systems in most areas. As long as full time public health is available in your county, you will likely not be able to avoid getting a permit. Public health fees for permits to build septic systems are like taxes and they help to fund public health services. The cost of public health is seldom figured into construction. Fees or taxes if you prefer are due with your permit. Local health also manages a huge database of systems and sets design and construction standards for a large and broad industry, and a green one at that. Licenses for qualified excavators, designers, inspectors, pumpers and other waste managers are administered at state and local levels through local boards of health and many state level relationships. To determine the retail cost of your drainfield, figure that 4 foot plastic vaults will cost $85 in place, and drainrock type drainfields in place will cost roughly $4 per square foot (drainrock is $15-20 / ton delivered with a cubic yard of drainrock representing about 1.2 tons of material). The tank is about $600 delivered - 1000 gal should be plenty, but some health departments require larger tanks, presumably to accommodate the negligent homeowner who thinks pumping is not required - ever. Larger tanks add a dollar per gallon. Plastic tanks will cost you a lot more whether you go for one of the many flimsy ones or one of the good few. Some jobs require a D-Box with fittings and seals for about $50 total. Gravel and foam peanut drainfields require filter-fabric to keep dirt out of the drainrock before backfilling at $30 to $50 depending on trench length (fabric is not needed with vaults.) Excavation costs another $1 - 2,000 for pipe laying, sewer line excavation final backfilling and other tasks, or a lot more depending on job layout and slopes. Pipe is usually ASTM 3034 or the heavier Schedule 40 at $15 - $25 per 10 ft piece. Forget about using ASTM 2729 as a money saving move - too flimsy. Click here for further cost estimates. Additional Tips on the Site Evaluation: For digging test holes, backhoe operators generally charge between $300 and nothing depending on driving distance, and whether the test holes will lead to a construction job on the property. Shop around. Remember also 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 local health has checked them. You may be able to dig and fill them in at the same time if health department personnel show up for a site evaluation with all parties present (the designer, excavator, local health inspector and owner). The designer sets up this meeting. The owner does not have to be at the meeting and can be represented by the designer. However, many designers (and I am one) prefer to have the owner there if the designer and owner (or developer) have only met on the phone. Checks for the permits and the designer's fee can be secured by the designer and building plans and preferences and site planning ideas can be shared. How Long Should a Site Evaluation Take?: The site evaluation on a normal simple lot should take about an hour or two total. Each six foot deep hole takes five minutes or less to dig, ten minutes to log and study and five minutes to fill in. Health personnel should show up once the two to four holes are dug and should only be on the site for ten to twenty minutes if all goes well. Difficult soils and sensitive areas can involve many more holes and can take much more than twice as long for all parties. Beyond the site evaluation, the designer should spend at least an hour or two more on the site to locate surrounding wells, locate all buildings, structures, trees, shorelines, banks, map contours, roads, easements, fences, power lines and all underground utilities (although the excavator is generally responsible to call for locating underground utilities). Unlicensed equipment operators can usually dig the pits for you but only experienced people can locate the drainfield area and arrange the parts of your site to your best advantage. Any county licensed excavator knows how to build a septic system so even though you know what you are doing, don't forget to listen when you get the chance. Who Can Evaluate the Site? In most counties this expert is a consultant to the property owner and is known as a state or county licensed designer, a state licensed engineer or soil scientist. Who can perform evaluations depends on the state rules. Homeowners can often build the system but few jurisdictions allow owners to evaluate the site. In the past, and in some counties today, local health sanitarians will do this for you and hand you the drainfield location, trench length and tank size. Your local health department will tell you over the phone who can evaluate the site or even send you a list of qualified people. Details and Equipment: Each professional evaluator has slightly different preferences as to equipment. Besides the usual clipboard and assortment of pens, pencils and maps, our methods rely on 6 pieces of equipment to study the site: 1) a handpick, 2) a 25 ft tape to measure depths within the soil profile, 3) a Rolatape® measuring wheel for distances (much superior to a 200 ft tape measure), 4) a Sunco® clinometer, indispensable for quickly measuring and estimating slopes, banks and levels, 5) a spray bottle of ammonia based window cleaner used to moisten soil samples for checking texture as well as for general hand cleaning and, 6) a digital camera. Lately I have been using a seventh item. The GPS removed from the suction cup on my windshield to grab a location of a test hole, a water well or the high spot on a site. These locations can be typed later into Google Earth and transferred to a site plan. This saves vast amounts of time on a large site with scattered landmarks, poorly marked corners or a large number of test holes. The Garmin and the ruler on Google Earth are accurate enough for most septic work. For more accurate locating you will hire a surveyor. This is one of the few jobs where a true 4 wheel drive SUV is the correct vehicle for the job. Most pickups have too much wheelbase and rear overhang to get around on some sites. You will have to be able to go anywhere the backhoe goes with all of your equipment sometimes in deep mud. Where to Look: Drainfield location is generally downslope from the tank. In our example, there is little extra space on the site so the drainfield location is more or less fixed. Whatever soil is found in this location, will have to be accepted as a given. You may find that there is not enough area on a tight site for the drainfield and the required replacement area. It is then up to the owner to scale back the project by dropping a bedroom, one space in the garage or the spot for a future pool. Do not expect local health to allow you to trim even a few inches off one of the the trenches to make the drainfield fit in a tight spot unless such relaxations are customary. The work of health inspectors is public, very public. The behavior of health inspectors is under constant and sometimes unsympathetic review by neighbors, developers and their local politicians. Inspectors who give out too many favors will eventually have to face charges of playing favorites. On a larger property, if the test holes showed a poor soil type (usually silty or restrictive soil, solid rock or water in the test hole), another pit or two or three could be dug to get a better location for the drainfield. Fill in the poor test pits before local health sees them. In most counties this is customary and not considered deceptive. Local health will only evaluate what you show them and your job is to put the best appearance on your property for the evaluation in the location where you want the drainfield. Finding a favorable 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. Do not worry about the soil expert tearing up the site during the exploration phase. As with medical diagnostics, the knowledge gained will outweigh the risk. The Last Word is Have Fun But Be Cautious. Every site has its own special qualities and potential traps. Without the 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 miss an important detail like getting a final inspection tag for the system from the inspector to prove compliance with all standards. Tricks of the trade only come to designers and excavators who have learned to successfully complete job after job. Sometimes a project is better left to those who can make it look simple. However if you DO do-it-yourself, and it all works out, every plumbing moment in your day will be that much more satisfying. Last Revised: 01/29/2010 How to Build a Septic Tank System Copyright © 2000-2010 ECO-NOMIC INC. All rights reserved. Send comments to:

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