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How To Build Septic Tank Systemsin 6 easy steps

The Think Tank ­ Septic Design Forum

for systems other than for the average home ­ jump To:

septic systems for churches and theatersseptic systems for waterfront lots ­ tight sitesseptic systems for small shops ­ officesseptic systems for larger rural homesseptic systems for commercial wineries ­ car washes ­ kennels etc

Introduction: You can avoid the cost of hiring a septic designer and excavator, but don't let friends convinceyou that these jobs are without value. Be aware that like buying propertythis aspect of homesteading, if not handled with cold reason and greatcare, could ruin Thanksgiving dinner and many restful nights sleep. How

to build septic tank systems? It's all here.

Why not do it yourself ? Doing anything yourself can be heroic or crazy depending on theoutcome. In more than 25 years spent designing site layouts and septic systems in the scenic countryside ofbeautiful Washington State, I have seen more than one home­site ruined forever by sloppy excavation, poor waterwell placement and the dozens of other pitfalls awaiting an eager baron or baroness heading up the country with aheart 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 bydoing­it­yourself. Remember also that digging up a power line and darkening your block cannot only embarrass youbut 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 soilconditions. If you know in your heart that you lack these skills, don't risk your peace­of­mind.

1. The site evaluation is step one: Get a scale map of yourproperty if you don't have one. The scale drawing below is from an application for a septic tank system that wasdrawn by a professional septic designer and submitted to the local health department. The site, classified as adifficult one, is for a small lot in a rural subdivision with a community water system (tank in distance). At least awater well does not have to be worked into the layout.

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The closest neighbor'shouse can be seen in thephoto to the left. The dirt dugfrom the two test holes can beseen at the back of the lot atthe edge of the farm fieldabove and on either side of thegreen power transformer. Thesite is ready for the siteevaluation with local health.Design and construction willbe cramped. With small andtight lots, every inch of spaceis needed. A survey is usually

advised to ensure that setbacks from property lines are met. Note thered survey steak marking the lot corner pin behind the transformer.Local health will usually provide a package of forms and informationexplaining the application process. The helpfulness of healthinspectors is generally better in the rural counties, but they will not tellyou how to build septic tank systems. That information follows;

Important note: The site should not be cleared, scraped,leveled or otherwise disturbed until the details of the site layout havebeen figured out. If a water well is required on the site, it should bewitched or located only after a place has been found for the septicsystem.Besides the description of soil texture and depth, the siteevaluation usually has a scale hand drawn map like the oneabove. The map must show the location of the test pits. Most healthdepartments require this evaluation to be done by a licensed person. Also, the surrounding conditions are shown in scale including propertylines, buildings, wells, pipes, paved areas, surrounding septic systemsif known, roads, easements, trees and banks. You must also showslope direction, drainage ways, surface water, and surrounding landuses. You can go to your local health records to see what your healthdepartment 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 pitsor "test holes" have replaced the traditional percolation or "perc" test that used to be common inmost areas. Today, the soil expert must have one or two or more pits dug with a back­hoe 5 ormore feet deep, and wide enough and sloped so that he or she may walk down into them andsample the soil in the side walls. See the video clip above right.Soil stability and safety are always considered for the inspectors and for casual members of the public. Kids aredrawn to equipment and holes in the dirt. Leaving the holes open for later inspection is inferior to having local healthattend the site inspection and close things up in a single trip for the backhoe. If the holes must be kept open, say fora later visit by local health, barricade or safely cover the holes to keep the public out.The site evaluation by backhoe is a better test than the old perc test because it allows a wider look at the soil.

2. Soil classification is next: The soil classification systemused in most places in the USA (and in some other countries), is called the US Department of Agriculture SoilConservation 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 moredrainfield than you need. More drainfield means needless expense. Less drainfield means early failure, usually withguests over.The most restrictive soil type found in any of the pits in the area of the drainfield should guide your choice in the caseof mixed or confusing soils anywhere within the drainfield area. Most test pits involve four or more soil types as youlook down through the soil profile within each pit so study the soil directly below where the drainfield will be (between36 inches and 48 inches below grade usually).

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3. You now determine the area of trench foryour home: Dig a couple of six foot holes at each end of your drainfield area andcheck the soil type.How to use the chart: In spite of what you think, the drainfield size is not dependent on the number of bathroomsor fixtures in the home. Almost all health departments use the number of bedrooms in a home as a way to sizedrainfields. The number of people in the house (usually two to a bedroom), and their usual daily water use (usuallysixty gallons per person per day), is how the flow rate is established. This flow rate of about three hundred sixtygallons of water use per day inside a three bedroom house determines the amount of sewage that must be sent tothe drainfield. Once you have decided what type of soil is found under your future drainfield, look up the drainfieldarea required for your house size in the chart below and you have the required drainfield size. Note: The chart belowwas compiled from the rules of various states and many years of practical experience. Your county may have verydifferent sizes and by law you must use the chart from your local health department.

Drainfield Size ChartSoilClassUSDA

Soil Type: take asoil sample 5 ftbelow grade indrainfield area bydigging a personsized test pit ateach end

2 Bedroom House240 gallons ofsewage/ day

3 Bedroom House360 gallons ofsewage/ day

4 Bedroom House480 gallons ofsewage/ day

CommercialProjects for every100 gallons ofsewage/ day

# 1 Coarse Sand ­most sand soils willrequire pressuredistribution if gravel ispresent and/or the lot issmall

200 sq ft gravel or10 six ft vaults or16 four ft vaults

300 sq ft gravel or14 six ft vaults or22 four ft vaults

400 sq ft gravel or18 six ft vaults or28 four ft vaults

84 sq ft gravel or3.6 six ft vaults or5.6 four ft vaults

# 2 Medium Sand 240 sq ft gravel or12 six ft vaults or20 four ft vaults

360 sq ft gravel or16 six ft vaults or25 four ft vaults

480 sq ft gravel or21 six ft vaults or33 four ft vaults

100 sq ft gravel or4.3 six ft vaults or6.7 four ft vaults

# 3 Fine Sand ­ LoamyCoarse Sand ­Loamy Med Sand

300 sq ft gravel or10 six ft vaults or16 four ft vaults

450 sq ft gravel or15 six ft vaults or24 four ft vaults

600 sq ft gravel or20 six ft vaults or32 four ft vaults

125 sq ft gravel or4.1 six ft vaults or6.5 four ft vaults

# 4 Very Fine Sand ­Loamy Fine Sand ­All Loams

400 sq ft gravel or14 six ft vaults or22 four ft vaults

600 sq ft gravel or20 six ft vaults or32 four ft vaults

800 sq ft gravel or26 six ft vaults or42 four ft vaults

167 sq ft gravel or5.4 six ft vaults or8.4 four ft vaults

# 5 All Silt Loams ofGood Structure

540 sq ft gravel or18 six ft vaults or28 four ft vaults

800 sq ft gravel or26 six ft vaults or42 four ft vaults

1070 sq ft gravel or35 six ft vaults or55 four ft vaults

223 sq ft gravel or7.2 six ft vaults or11.2 four ft vaults

# 6 Other Silt Loams ­ AllClay Loams ­ All

1200 sq ft gravel or 1800 sq ft gravel or 2400 sq ft gravel or 500 sq ft gravel or

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Clays Note: some claysmay not qualify for anysystem

39 six ft vaults or62 four ft vaults

60 six ft vaults or94 four ft vaults

78 six ft vaults or122 four ft vaults

16.0 six ft vaults or25.0 four ft vaults

bed type drainfields allowed if the soil type is fine sand or coarser ­ pressure distribution required with all beddesigns and if soil is extremely gravelly or very gravelly plus a sand lining may be required under the drainfieldone square foot of drainfield is measured like a carpet looking down from the top ­ "sidewall" is not consideredalthough some healthdepartments continue to give "credit" for up to 6 inches of sidewall calculated by measuring the perimeter of thebed or trenches ­ usingsidewall confuses calculations and has been discredited due to the fact that water in soil seldom moves sidewaysexcept 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 nolonger advised. The separation of flow into two, three or more lines is accomplished with a distribution box or "D­box" to split the flow. In the D­box pipes are equipped with simple flow control valves in the form of eccentric plugsthat evenly split the flow between lines. The effluent (sewage that has gone through the septic tank) flows downhillfrom the tank outlet, through the D­box and down to the individual trenches where it spills out onto the floor of eachtrench where treatment starts in the soil at that location. Don't forget, the individual trenches are NOT sloped, but aredead level from one end to the other.Your local health department rules. Your county health department has rules and guidelines to follow. Sometimesrules are the same as state guidelines, but sometimes more restrictive rules special to your county must befollowed. These rules include depths and setbacks and construction details. Such things as how far you can placethe 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 trenchescan be (usually no deeper than three feet max from final grade down to the floor of the trench), and even whetheryou may use the plastic vault technology shown here. The key to getting the correct results from your healthdepartment people, is to present your ideas clearly and completely in your drawings. There is often some back andforth with the health department. You may be asked several times to return with fresh drawings to meet all of the siterequirements 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 atwo­page 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 pieceof ground, except the gravel is one foot thick. Therefore, a drainfield trench "covering" 300 square feet, is a pit, threefeet wide and one hundred feet long, with a foot deep of gravel in the bottom. (In reality, you will use two trenches at50 feet long each.) The gravel is covered with a tough but thin fabric to keep the dirt out called filter fabric. Thewhole thing is buried with a cover (backfill) of one to two feet of native soil. The thickness of backfill depends on thedesired trench depth. The "gravel" is not really gravel at all, but a uniform clean washed rock with granules one anda half inches in diameter known to a gravel pit operator as "inch­and­a­half drainrock".

PVC Vault Technology: Youmay now in most areas substitute rows of plasticchambers instead of the old school leachfield gravel.Infiltrator® and Hancor® are two companies whosupply this product shown to the right. The vaults hooktogether like a freight train and are very easy to transportand build. The green pipes are inspection/squirt ports forthe homeowner looking into the drainfield especially iftrouble occurs down the road. The ports are also usedfor periodic squirt testing and are cut down to the finishdepth after the drainfield is backfilled. Constructiondetails for this house and dozens of other systemsare shown in our drawings.Excavators and installers usually prefer the vaultsover drainrock once they have tried them. Most healthjurisdictions are recognizing the value and efficiency ofthe vault technology and the use of vaults is becomingwidespread across the USA. Gravel is used forgeometric reasons and can be cheaper particularly if thejob is close to the supply. Gravel is also used if livestock or vehicular traffic could invade the drainfield. Drainrock is alittle more robust than most vaults.Also, some health inspectors give "credit" for the increased storage capacity of the vaults over gravel systems. Each

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linear foot of standard vault in the ground yields around 10 gallons of storage. A linear foot of 3 ft wide graveltrench yields less than half of that even with the highest quality drainrock. You may get 400 Sq Ft of "credit" forour 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 feetwide (but generally 3 feet is the width used for design and space planning) and two standard lengths 6 and 4 feet.

Time To Prepare the Drawings:The Septic Design CD available on this web­site allows you to create plans that may be modified and edited tomeet the needs of your local health department whatever they are. Often a few simple notes or other changes cansatisfy the specific rules of most health jurisdictions, but notes and requirements must usually be typed onto theplans. Drawings are the language of construction of anything. Besides, this is not your grandfathers septicsystem. Our drawings talk the new lingo.

Study the drawings shown below. Permit drawings also tell others how to build septic tank systems. These twosheets represent the complete drawing set for a gravity design for the three­bedroom house on our model propertyshown below. 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.

4. Time to apply for the permit: Now Make Your Applicationto Local Health: Submit your plans at the counter of the local health department. You will have to fill out theapplication form and pay the permit fee. The example septic system drawings for r our model property are shownbelow. You now must wait for the drawings to be reviewed and approved before going on to the constructionphase. Ask local health what the customary time frame is for permit application review. It should not take more thantwo or three weeks at the most to receive the approved construction permit in the mail unless there is a localbacklog, a staff shortage or a deliberately slow process in your area.

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Local Health Will Approve Your Drawings usually with a signature and a date. Construction should usually beginwithin one year of that date to avoid losing the permit and having to start from scratch with a new fee. You should geta copy of the permit in the mail once the drawings are approved. You must follow all the notes and details on thedrawings exactly. Look for and follow the printed instructions and any special notes that local health adds to thepermit face. Local health will inspect your work before anything is covered so plan your job carefully. Click on thedrawings for a close­up. You will naturally apply your logo and address on the plans.The left hand drawing shows the Site Plan with all of the required information in scale. The drawings are forprinting on standard 8.5 x 11 copy paper. This format is the most handy size for filing and favored by healthdepartments for storage convenience. Some health departments have gone all electronic and our drawings convertinto PDF files with ease. Click on the drawings above to see them in PDF format.

Using the Gravity Drawing Archive:The drawing on the right above is our drawing GTGV3WDD from our CD for gravity septic designs. You can see itin our archive about half way down on the page under the topic "Vault designs using 3 trenches only." Once youhave a plan view layout for your system, find the matching detail page for your trench cross section, trench layoutand standard notes.

5. Finally it's time to start building the septic tanksystem:The layout stage of the job transfers the design to the ground.Excavation is like sewing. The Layout of all parts of the design (thepattern) must be projected onto the site (the cloth) and cutting in morethan once will increase wastage. If there was a caution for youngexcavators it would be never to over excavate. Measuring twice andcutting once applies here. Before you begin, be sure that the drawingis accurate and that it matches the site exactly. Compare the site planon your approved design to a plat map of the site if you have to, tomake sure that the drawings match and show the correct scale. On theapproved drawings from the health department, add up all stringsof dimensions to make sure that a critical measurement has not beenmissed. Always find and mark the corners of the property. Do not useexisting fences or the advice of neighbors unless you are sure of the

property lines from a legal survey.Here in the image to the left, the construction crew is checking the location of the third trench. A long 200 foot

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tape, a Lufkin® twenty­five­foot tape, wooden stakes and a red rattle can of spray paint are the tools of choicefor this stage. Gravity systems will only work well if the bottom of the trench sits in undisturbed ground and is level.Sewer slope does NOT apply in the drainfield. Level means dead level. Read this caution again if you are not withme.Be careful not to begin excavation until local health has approved your plans, no mater how eager you are to getstarted. Even though you have applied for and paid for a permit ­ If the inspector has not approved the design, theymay require layout changes. He or she will not listen to excuses such as "we had to get the backhoe back, so westarted without the permit." RULE: Once you have applied, listen to the inspector and follow all instructions, orstart reading this page again from the top.

Measure Twice Cut Once: The tripod onthe sidewalk on the left side of the picture to the right is a laserlevel. This tool has been around for twenty years and developed withpublic money. Do not begin this job without one. With the special levelrod, an assistant may walk around the site and find the elevation ofany point of the excavation within an inch (2 cm) anywhere withinsight of the tripod by listening to a beep from the box on the rod whenyou are "on elevation."This tool (the laser level) is particularly useful to ensure that thetrenches are not over excavated. Constant attention to elevation isthe key to a successful job. Older leveling technology such as asurveyor's transit may be used as long as you know how to use it,but don't ever think you know how to build septic tank systems with astandard construction bubble type level. I do not care if your level is20 feet long. Laser levels and all the needed tools are availableeverywhere to rent. Once you are done excavating, the health inspector must be called for a final inspection of the job. Then backfillingoccurs. The tanks, pipes and vaults can and should be backfilled around their sides during construction though.More counties are requiring leak testing of the tank these days. Vacuum testing, pressure testing or water testing ofall tanks may be required in your area. Backfilling around the sides of concrete tanks may be postponed until thefinal inspection to check for leaks if desired by the county inspector. Most plastic tanks will distort under such stressand must be backfilled at the same time as they are filled with water for the first time.In the picture to the right, the crew is using the top of the septic tank in the foreground as a work table and a datum.Notice the difference in elevation between the top of the tank and the surface of the nearby sidewalk (hint ­ about afoot or 30 cm.) This tank will be less than a foot underground when the lawn is planted.

Pipe Slope and Type forProper Drainage: A word hereabout pipes and drainage. PVC (polyvinyl chloride)pipe comes in a variety of sizes and types. Pipes in agravity system are either 4 inch diameter. ASTM 3034or 4 inch diameter ASTM Schedule 40. These pipetypes are both good for sewer lines between thehouse and the tank. These pipes can not be crushedby stepping on them. ASTM 2729 (perforateddrainfield pipe is made of this thin stuff) and ASTMCL160 (known as Class­160) are too thin to stand upto being driven over with a car, etc when placed inshallow trenches (a normal condition in modern septicsystems.) Some counties allow the thin wall pipebetween the tank and the drainfield ­ we do not.Pipe Slope: There are only 2 pipe slopes used in septic systems, the sewer slope (contains "solids") andeffluent line slope (no solids.) The "building sewer" must be sloped (sometimes called fall) at between 1/8" perfoot and 1/4" per foot. In other words the pipe must drop at least one inch for every 8 feet of sewer line, and notmore than one inch for every 4 feet all the way to the septic tank. Less slope and the flow is too slow to clear thepipe. More slope and the water theoretically drains off too quickly and the solids will become stranded and cause ablockage. This idea of maximum slope no greater than 1/4" per foot has been challenged recently, but anengineering justification is required to allow this in practice. Almost all health departments require this minimumslope of 1/4" per foot and will require "stair stepping" down steep slopes. However, do not ignore the minimum slope

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requirement in a sewer line for any reason, or that spot on your property will become a perpetual problem in thesystem. Effluent lines can slope less than the sewer, and more. They can "fall" with as little as 1/64th of an inchper foot (experienced excavators only) and effluent lines drop at any maximum slope you choose.Drainfield Slope: It never hurts to remind everyone learning how to build septic tank systems, that the drainfieldtrenches and beds whether vaults or gravel are built dead flat with no slope at all end­to­end or side­to­side.Some ancient drainfield plans call for a slope in the drainfield, but this practice went out with the manufacture of claysewer pipe. Resist the advice of friends and neighbors to put a slope in the drainfield. Trenches can naturally be atdifferent elevations based on the ground contours, but each trench or bed (leaching bed) should be level within aninch up or down over the entire bed or each individual length of trench. Your system will last longer.If the yard down to the tank from the house slopes too much, the sewer must be dropped straight down in a seriesof drops followed by proper sewer slope to the next drop. The drops are good places for cleanouts. Remember alsothat any right angle bends in the sewer pipe are not allowed when changing direction in the sewer, down or side­to­side. Always use two 45 degree "elbows" or "90 degree sweeps" instead of a 90 degree elbow to allow propercleaning with a snake or roto­rooter. Also put in a clean­out to direct a snake (a metal probe for cleaning outblockages from the surface) starting at the outside of the house toward the tank every 50 feet (100 feet absolutemaximum) in the sewer line. Clean­outs and 45 degree elbows are not needed in the effluent line. If the groundslopes towards the house from the drainfield area, or if the site is flat, you may need to pump the effluent from theelevation of the septic tank up to the drainfield (or leach bed.)After the septic tank, and after the D­Box all the way to the drainfield, the slope may be effluent line slope, as littleas 1/64" per foot. This requires expert excavation practice. The effluent line may drop down at any angle. All effluentlines must drain fully and not have a "sag" in the line that could cause pools to form and in cooler climates cause aline freeze. Click here or here for more about freezing septic systems.

This view of the site shows thelayout:

The septic tank can be seen on the right of the view between the firsttrench and the patio. On this job, and normally, the septic tank isdelivered from the tank manufacturer and lowered from the truck into ahole prepared by the excavator. The tank hole has a flat floor at the exactdepth. Call the tank supplier to get the exact tank height and depths ofthe inlet and outlet. In rocky ground, two or three inches of pea gravelmay be needed to protect the tank bottom. The septic tank is often thefirst thing to be added to a new house site.A concrete tank in our area runs about $550 delivered up to 40 miles, andfurther for a few dollars more. Fiberglass tanks and ribbed polyethyleneseptic tanks are not usually advised as they are not only more expensivebut they may not be sturdy enough to do the job. Flexible tanks tend todistort over time particularly when they are pumped out. Don't trust atank that can't safely be filled with water in the parking lot withoutdistorting 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 shouldbe 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 andthe vault units seen near the backhoe are waiting to go into the third trench when it is finished. The site is beingwatered with the hose as work progresses. The site may need to be sprinkled for a day or more prior to constructionfor the same reason. Although this keeps dust down, the primary reason for adding water to dry soil is to provideproper moisture for compaction of the dirt around the pipes and parts. Water is usually used to soak the sides of thetank to compact the soil and fill in voids to avoid sink holes in the lawn. Very wet or very cold weather is not the timeto build septic tank systems. Good excavators avoid working in extreme conditions except in emergencies. Workingin poor weather usually involves return trips to smooth and refinish surface grades and is more expensive.Before the vaults are placed in the trench, the side walls of the trench are roughened with a garden rake. Thisimportant step prevents the formation of bacterial scum on the trench walls called "smearing" which can cause earlyfailure of the drainfield. In some areas, the excavators weld teeth to the side of the backhoe bucket to do this job inone pass.

Septic systems are plumbing systems:In this view, the concrete D­box has been placed where it belongs and the effluent lines are being pushed into theseals. Although all the other pipe joints are glued together, where the lines enter the tank and D­box, the pipes arepushed into the special seals without glue. Older construction methods require lines to be sealed into D­boxes andtanks with concrete grout. To the left bottom of the picture to the right, the yellow plastic rotatable flow control sealsare waiting to be placed into the pipe ends to evenly distribute the flow between the trenches. Next to the excavatoris the level rod for checking the level of the D­box and the pipes. The system works because of the difference in

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elevation between the sewer line leaving the house, the septic tank, theD­box, the effluent lines to the trenches and the floor elevations of all ofthe trenches themselves. These final elevations must be taken from theapproved plans (see above.) The finish grade and backfill will have tocover everything at the required depth when you are done. Often the topof the septic tank is used as a datum or benchmark. The floor of a wellhouse, an existing slab, any reasonably immovable object will qualify as abenchmark but many of these things are built after the septic. Propertycorners on a site can change elevation.

Distributionmust be even: The D­box is ready to go. The flow control has been set by pouring abucket 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 linesleading to the three trenches. The inlet to the d­box is on the right anddoes not have a flow control seal.The sandy dirt around the pipes has been walked and compacted toensure that the lines will not be disturbed during backfilling. Thebackfill will form a slight hump over the drainfield so that eventual settlingwill not cause low spots over the drainfield over time. Note theexpandable urethane foam sealing the effluent line at the top of the viewto the left where the northeast effluent line disappears into the vault. Thisattention to detail by some excavators distinguishes the best from therest. Skill and attention to details will help you more than anythingelse to ensure that the septic system will not fail within its useful life offifteen to twenty­five years. Most Owners' say at the first meeting with thedesigner "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.

6. Finishing up, final inspection & backfill: Final health sign­off can be obtained only after calling the local health department for a final inspection. They will tellyou to fix anything you missed based on the approved plans. Hopefully you followed the plans closely. After all, youspent the time and money getting the plans and getting them approved.Some installers do not always follow all the notes and details. Some self installers eitherforget or avoid the final health inspection, or getting a health permit at all. This once wasconsidered heroic behavior. However, these days people are not getting away with thesecareless practices in most jurisdictions. Appraisers, lenders and insurance companiescheck for permits before writing loans and policies. With us pulling out of a deep recession littered with distressed and poorly managed property, there is a renewed interestin these companies only underwriting solid property value. Missing permits identify riskyproperty ­ do not gamble with the value of your dream.Backfilling will require special attention to soil moisture and soil compaction as well. You should backfill andcompact the sides of tanks, vaults and pipes as you build, mostly by filling in layers and compacting by walking alongthe fill areas until it "feels" solid. Some excavators will "Walk" the trenches with the rear wheel of the backhoe, butthis may collapse the vaults if done too aggressively. The backfill soil must have no stones, be slightly damp and notwet. If soil compaction is ignored, the lawn will settle, sink­holes can appear, and the tank itself may shift during aheavy storm.Backfilling may have to happen even though the site is soaking wet or frozen. A visit later in the year may berequired to fix the dips prior to the laying of sod. Weather conditions should be considered in all excavationprojects. Putting off the job may be easier in the long run than fighting the elements. Good excavators avoidworking 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 to theright shows a clean­out. The sewer line to our project shown here justoutside the house passes through the foundation wall about ten inchesbelow the finish grade. The sweep and riser and cap (shown herewhite), allow the sewer line to be "snaked" out all the way to the septictank without working from the crawl space, a good maintenancefeature. Note the 45 degree elbow below the cap, directing the cleanoutdownstream toward the tank. back to pipe slope

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The important point here is that the sewer line should not pass through the foundation below the footing. Theexample in the small inset photo shows the wrong way to do this. That sewer line in the inset photo is much toodeep to meet the depth requirements for the drainfield that local healthwill require.Side note: A cleanout identical to this one is often provided beside thedriveway or near the RV parking area to act as an RV dump.

How to Design the GradeElevations of Septic Systems:The plans for our example on the right called for an invert (bottom ofthe pipe) elevation at the outside wall of no more than thirteen inchesbelow finish grade. Contractors who leave this detail to the plumbermay wish they had not. Redoing the house plumbing is one fix andshaving dirt off the surface of the yard is the other. In most healthregulations, the floor of the drainfield trench can not be deeper than 3feet from finish grade of the yard.On a mostly level site, set your depth at the drainfield trenches first. Start from the floor elevation of the lowesttrench (remember ­ in most jurisdictions NO deeper than 36 inches from finish grade.) Remember too, thefloor of trench has NO SLOPE and is dead flat end to end. The 4 inch diameter effluent line pipe enters the drainfieldtrench with the "invert elevation" (bottom of the pipe) 6 inches to 8 inches above the floor of the trench. Next the D­Box is located upstream of the drainfield. All effluent lines must drain fully into the drainfield from the D­Box.Always avoid "bellies" or dips in the effluent lines which will trap effluent. To inspect long lines, pour 5 gallons ofwater in the top of a dry line to yield an equal volume into a bucket at the bottom.Now determine the invert elevation of the effluent line that enters the highest trench (8 inches above the floor of thehighest trench.) Place this effluent line with minimal slope up to the D­Box which will now fix the elevation of the D­Box. Add 3 inches for drop inside this box. From the inlet of the D­Box we follow the effluent line up to the septictank outlet following the same effluent line slope rule. This will determine the outlet elevation, and therefore thevertical placement of the septic tank. Between the outlet and the inlet of the tank, add 3 more inches for theinternal working of the septic tank. This brings you up to the septic tank inlet invert elevation. From this septic tankinlet elevation we figure the route up to the house foundation following proper sewer slope. This gives us the pipeinvert 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 ofoccasionally hard freezes in central Washington State (we see 25 degrees F below zero on rare nights), I havenever seen a sewer line freeze that was built at the proper slope however shallow. Tanks too are safe from freezingeven when placed slightly above ground such as under a deck. Water lines however are buried at 3 to 4 feet ormuch more in northern areas to prevent freezing. Sewer lines and septic tanks follow a different set of rules thanwater 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 alltransport lines, manifolds and even laterals. In vault type drainfields the one inch diameter lateral lines are strappedto the underside of the vaults with zip ties. Enough downward pointing orifices must be provided for complete lateraldrainage. If you are not following all of these technical suggestions, consider hiring a good professional designer fordrawing 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 andheating elements are sometimes added. Vast areas of the planet are unsuitable or poor for septic. Solid rock, forinstance, or permafrost will not provide safe treatment. However the places people chose to live, in most cases aresuitable places for septic already. And if not, technology steps in, on marginal and fringe areas with more complex(and expensive) septic systems.

Costs: With constantly changing cost of oil and fuel, costs are going upgenerally. Excavators run equipment all day and therefore have increasing fuel bills.Septic systems have many parts made of plastic (petroleum based) and these partsare often manufactured far away and are trucked to the site. Designers andregulators 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 resortand even within some city limits. Mostly experts rather than homeowners are requiredto design systems in most areas. As long as full time public health is available in yourcounty, you will likely not be able to avoid getting a permit. Public health fees forpermits to build septic systems are like taxes and they help to fund public healthservices. The cost of public health is seldom figured into construction. Fees or taxesif you prefer are due with your permit. Local health also manages a huge database ofsystems 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

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state and local levels through local boards of health and many state level relationships. Drainfield Cost: To determine the retail cost of your drainfield, figure that 4 foot plastic vaults will cost $65 in place ifan excavator does it. Older style drainrock type drainfields in place will cost roughly $4 per square foot (drainrock is$15­20 / ton delivered with a cubic yard of drainrock representing about 1.2 tons of material). Drainrock, $300 for a360 sq ft (typical 3 bedroom) drainfield plus $250 for delivery (depending on distance from the pit regardless of whois driving the dump truck.) You must include the cost of digging out the drainfield area, placing and shoveling rockand placing and assembling the perforated pipes (this is mostly equipment and shovel time.) Some rock is lost by allgood excavators who leave the bottom of the pile on the ground.The Septic Tank: The standard tank is about $650 delivered. 1000 gal should be plenty, but some healthdepartments require larger tanks, presumably to accommodate the negligent homeowner who thinks pumping is notrequired ­ ever. For larger tanks add a dollar per gallon so a 1250 gallon (next size up) is $650 + $250 = $900.Plastic tanks will cost you a lot more whether you go for one of the many flimsy ones or one of the good few.Because of their weight, concrete tanks are always regional. However, many new plastic tanks are competing for asprouting national market. This website is not confident that plastic tanks are ever superior to standard concretedesigns except in a few rare instances ­ fly­in or winter­road locations for instance.Other Items: Some jobs require a D­Box with fittings and seals for about $50 to $100 total depending on the numberof outlets. Gravel and foam peanut drainfields require filter­fabric to keep dirt out of the drainrock before backfilling at$30 to $50 depending on trench length (fabric and center pipes are not needed with vaults for standard gravitysystems like this one.) Excavation costs another $1 ­ 3,000 for digging the tank hole, pipe laying, sewer lineexcavation final backfilling and other tasks, or a lot more depending on job layout and slopes. Pipe is usually ASTM3034 or the heavier Schedule 40 at $15 ­ $25 per 10 ft piece. Forget about using ASTM 2729 for your sewers as amoney saving move ­ too flimsy. Your tank may need two plastic or concrete access risers and a filter. $200­ $280.Click here for further cost estimates.

Additional Tips on the Site Evaluation (Perc Test):For digging test holes, backhoe operators generally charge between $300 and nothing depending on drivingdistance, and whether the test holes will lead to a construction job on the property. Shop around. Remember alsothat someone can fall into the pits and the property owner is usually liable so plan to have them filled in as soon asyou can. Cover the pits with plywood and place barriers around them if you are forced to wait until local health haschecked them. You may be able to dig and fill them in at the same time if health department personnel show up for asite evaluation with all parties present (the designer, excavator, local health inspector and owner). The designer setsup 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 onlymet on the phone. Checks for the permits and the designer's fee can be secured by the designer and building plansand 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 anhour or two total. Each six foot deep hole takes five minutes or less to dig, ten minutes to log and study and five to15 minutes to fill in or more depending on surface finish, sod replacement, irrigation repairs and any unexpectedfindings. Health personnel should show up once the two to four holes are dug and should only be on the site for tento twenty minutes if all goes well. Difficult soils and sensitive areas can involve many more holes and can take muchmore than twice as long for all parties. Beyond the site evaluation, the designer should spend around an hour ormore 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 responsibleto call for locating underground utilities).Unlicensed equipment operators can usually dig the pits for you but only experienced people can locate thedrainfield area and arrange the parts of your site to your best advantage. Any county licensed excavator knows howto build septic tank systems so even though you know what you are doing, don't forget to listen when you get thechance.

What if My Site Fails the Evaluation?!: The site evaluation can show that you have a "difficult site." Hereis some advice about proceeding with your project in spite of finding "problems" during your site evaluation.

Who Can Evaluate the Site? The local health department is qualified, but in many states healthinspectors will no longer perform your assessment. In most counties these days, the expert is a consultant tothe property owner and is known as a state or county licensed designer, a state licensed engineer or a registeredsoil scientist. Who can perform evaluations depends almost exclusively on the state rules. Homeowners can often

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build the system but few jurisdictions allow owners to evaluate the soil because of the potential risk to public health.In the past, and in some counties even today, local health inspectors (sanitarians) will do this for you and hand youthe drainfield location, trench length and tank size. Your local health department will tell you over the phone who canevaluate the site or even send you a list of qualified people. Most local health departments have the rules and theapplication forms available online.

Where to Put the Drainfield: Drainfield location is generally downslope from the tank. Our exampleabove is a tight site. There is little extra space on the site so the drainfield location is more or less fixed. Whateversoil is found in this location, will have to be accepted as a given. You may find that there is not enough area on atight site for the drainfield and the required replacement area. It is then up to the owner to scale back the project bydropping 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 fitin a tight spot unless such relaxations are customary. The work of health inspectors is public, very public. Thebehavior of health inspectors is under constant and sometimes unsympathetic review by neighbors, developers andtheir local politicians. Inspectors who give out too many favors will eventually have to face charges of playingfavorites. My 25+ years of practice in various jurisdictions has never caught a health inspector trying to pull off anyserious shenanigans. On a larger property, if the test holes show poor soil (usually silty or restrictive soil, solid rock or water in the testhole), another pit or two or three is dug to get a better location for the drainfield. Fill in the poor test pits before localhealth sees them if you want. In most counties this is customary and not considered deceptive. Local health willonly evaluate what you show them. Your job is to put the best appearance on your property for the evaluation inthe location where you want the drainfield. Finding a favorable location for the drainfield and then sizing it to matchthe 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, theknowledge gained will outweigh the risk.

The Last Word is Have Fun But Be Cautious. Every site has its ownspecial qualities and potential traps. Without the knowledge of the various details of designing and building yourseptic system, you may wind up spending a dollar to save a dime. If you are doing the work yourself, you may missan important detail like getting a final inspection tag for the system from the inspector to prove compliance with allstandards. Tricks of the trade only come to designers and excavators who have learned to successfully complete jobafter job. Sometimes a project is better left to those who can make it look simple.However if you DO do­it­yourself, and it all works out, every plumbing moment in your day will be that much moresatisfying.

Last Revised: 10/25/2012 How to Build Septic Tank SystemsCopyright © 2000­2012 ECO­NOMIC INC. All rights reserved.

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