Individual Home Sewage Treatment Systems

AE892 (Revised)

Thomas F. Scherer Extension Agricultural Engineer

North Dakota State University, Fargo, ND

Reviewed and reprinted October 2015 Contents

Introduction...... 3 House Plumbing for Sewage...... 4 Septic Tanks...... 6 Sizing...... 6 Location and Installation...... 7 Construction...... 8 Inlet and Outlet Baffles...... 9 Access Holes in Septic Tanks...... 9 Holding Tanks...... 10 Pumping Stations...... 11 Sizing...... 11 Sewage Pumps...... 12 Pump Controls...... 13 Septic Tank Outlet Sewer...... 13 Soil Absorption Systems...... 14 Absorption Trenches...... 14 Trench Construction...... 15 Rock-filled Trenches...... 15 Gravelless Trenches...... 17 Effluent Distribution...... 18 Drop Boxes...... 18 Distribution Boxes...... 20 References Absorption Beds...... 21 North Dakota State Plumbing Code, Chapter 62-03.1-03, 2001, North Sewage Mounds...... 22 Dakota State Plumbing Board, Sizing...... 25 Bismarck, North Dakota. Construction...... 27 Design Manual: Onsite Wastewater Treatment and Disposal Systems, Lagoons...... 28 1980. Report number EPA-625/1- 80-012, Environment Protection Alternate Septic Systems...... 29 Agency (EPA), Office of Water Pro- Filtration Systems...... 29 gram Operations, Washington DC. Alternative Drainfields...... 29 Onsite Wastewater Treatment Systems Manual, 2002. Report Appendix: Percolation Test...... 30 number EPA/625/R-00/008, Environmental Protection Agency (EPA), National Risk Management Research Laboratory, Cincinnati, OH. Residential Onsite Wastewater Treat- ment Systems: An Operation and Maintenance Service Provider Program, 2005. MWPS (Midwest Plan Service), 122 Davidson Hall, Iowa State University, Ames, IA.

2 his publication contains information on the design, installation and maintenance Tof individual home sewage treatment systems. It is meant to be a homeowner reference document. An individual sewage system both treats and disposes of household wastewater. If a homeowner understands how the various components of a home sewage system work, then a properly designed and installed system will function for many years with a minimum of maintenance and upkeep. Home wastewater enters the septic tank, which separates solids from liquids. Solids are held in the septic tank and liquids are conveyed to the final soil treatment site. The septic tank is a “bioreactor” where microorganisms break down organic matter in the wastewater to liquids, gases and solids. Gases are vented off through the house vent stack. Solids are composed of both scum and sludge. Scum is lighter than water and floats to the surface in the septic tank. The solid parts are heavier than water and sink to the bottom of the tank. Bacteria feed on the wastes and the fraction that can’t be decomposed is “sludge.” Sludge accumulates in the bottom of the septic tank and must be removed periodically. The five parts of a sewage disposal system are: (1) the house plumbing, (2) the sewer line from house to septic tank, (3) the septic tank, (4) the septic tank outlet sewer pipe, and (5) the final soil treatment unit, which may be a soil absorption unit or lagoon. All individual sewage treatment systems must comply with requirements in the North Dakota State Plumbing Code. In some counties, a permit is required before constructing a new home sewage treatment system or when repairing an existing system. Before construction begins, check with your local zoning administra- tor, sanitarian or health department. Whether you need a permit or not, concern for basic human health demands that the location of individual home sewage system components meets certain requirements. For example, keep the septic tank and soil absorption unit at least 100 feet away from any private well that is less than 100 feet deep, and at least 50 feet away from wells more than 100 feet deep. Generally accepted safe distances are shown in Table 1. When the sewage treatment system is installed, make a map of the installation. Measure and record distances from the septic tank, septic tank cleanout and drainfield to aboveground features such as buildings, fence corners or large trees. Then after the area has grassed over, you still can find the component parts of the septic system.

Table 1. Separation distance between the septic system components and water sources (all distances in feet). Well less Well more than 100 than 100 Distribution Treatment Property feet deep feet deep device area lines Buildings Building Sewer 100 50 - - - - Septic Tank 100 50 5 10 10 100 Distribution Device 100 50 - - 10 20 Treatment Area 100 50 5 - 10 10 Well (shallow) - - 100 100 NA NA Well (deep) - - 50 50 NA NA Pressure Water Line - - 10 10 NA NA Suction Water Line - - 50 50 NA NA Surface Water Bodies NA NA 100 100 NA NA NA – not applicable

3 House Plumbing for Sewage

he house plumbing system in- Tcludes waste pipes, vent pipes and water traps (Figure 1). House plumbing and home sewage treatment systems must comply with the North Dakota State Plumbing Code. Following this code ensures that a plumbing system will be safe and operate properly. Waste and vent pipes usually are the same pipe, with wastewater flowing downward and gases rising in the pipe. A 3- or 4-inch vertical pipe serves as the main stack to carry wastes, water vapor and gases from the house. The main stack also acts as a vent for gases that collect in the septic tank. Gas from a septic tank has a bad odor, may cause serious illness, and in some situations, can be explosive. In cold weather, the gases exiting from the stack contain water vapor that will form a frost layer that can get thick enough to close off the end of the stack. Excessive snow on the roof also can block the vent stack. Closing off the vent stack will prevent fixtures from draining properly. The vent stack extending above the roof should be insulated to help prevent frost and snow from closing it off. A water trap must be installed in the drain line between each fixture and the main stack. The trap prevents sewer gases from coming into the house through the fixtures. Without a vent pipe, a full flow of wastewater in the drain line could siphon water out of the traps and let sewer gases into the house. Sometimes, during very windy

Figure 1. House plumbing includes waste and vent pipes, as well as plumbing fixtures. 4 conditions, wind pressure on the House sewer pipe should insulation over the pipe during vent stack can force sewer gas have a slope between 1 percent the installation process. The rigid through the trap. Proper venting and 2 percent. This is around a foam insulation should extend installed according to the plumb- 1- to 2-inch drop in 8 feet. On too at least 1 foot on either side of ing code will prevent this problem. flat a grade, the liquid will slow the pipe. Insulation generally is Adequate cleanouts are down, allowing the solids to settle not needed if the house sewer necessary in the stack so the out in the sewer pipe. On too is more than 4 feet below the plumbing and sewer line can steep a grade, the liquids will ground surface. be serviced and cleaned. One flow away from the solids. Don’t make sharp bends in cleanout should be installed at the The sewer line from the house the house sewer system. When base of the stack and a second to the septic tank may be plas- 45- or 90-degree bends are at the point where the sewer line tic sewer pipe with glued joints necessary, use long sweep (long leaves the house. One cleanout or cast iron with stainless steel radius) elbows to allow a plumb- may be enough if the stack is near clamps or leaded joints. If using er’s snake to get through the the point where the house sewer plastic pipe, the pipe must have a sewer line. If long sweep elbows leaves the building. pressure rating equal to Schedule are not available, use several Cast iron or copper drain 40 or greater. The joints must be 22- and half-degree elbows. systems may be found in older glued so they are watertight and Never, under any circum- homes. Most new homes use resist root penetration. stances, allow basement plastic sewer pipe listed in the The house discharge sewer footing drains to discharge plumbing code. When working in must be at least 4-inch diam- into the house sewage sys- older homes, avoid direct copper eter pipe. This pipe must have a tem. This water will overload the to iron pipe connections since uniform slope with no high or low septic system. It can cause the pinhole leaks may develop in the spots. A common place for frost water and sewage to back up into iron due to galvanic action. Use to accumulate in the house dis- the house. Run basement footing insulated connectors between charge sewer pipe is just after the drain water to a sump. Install a copper and iron pipe to reduce pipe passes through or under the sump pump and pump the water this problem. basement wall. Where the house out away from the drainfield. sewer pipe is above the frost line, this problem can be corrected by putting 2-inch-thick rigid foam

5 Septic Tanks

eptic tanks have been used Sfor on-site wastewater treatment for more than 120 years. A septic tank can have single or multiple compartments. Single- and two-compartment septic tanks generally are used with individual home sewage treatment systems. Household wastewater enters the septic tank through the house discharge sewer pipe (Figure 2). After passing through the inlet baffle, the solids separate from the liquid as the sewage flows slowly through the septic tank. Some solids settle to the bottom of the tank and others float in the scum layer at the top. Bacterial action partially Figure 2. Typical septic tank. Sludge builds up in the bottom and scum decomposes the solids. floats on the liquid surface. The material in the septic tank separates into three distinct layers: 1. A top layer of floating scum 2. A middle liquid zone tarians call effluent on the ground Sizing 3. A bottom layer of sludge surface “day lighting.” Human Septic tanks are rated accord- The scum layer consists effluent on the ground surface ing to liquid-holding capacity, not primarily of cooking fats and can be a source of dangerous total capacity. The liquid capacity oils, soap scum and products of water-borne diseases and proof a septic tank is the volume of decomposition that are lighter duce offensive odors. The effluent effluent it holds below the tank than water. The greatest amount must be delivered to a properly outlet. Liquid capacity often is of bacterial action occurs in the designed and constructed drain- called the “working capacity” of a sludge layer, which consists of field or lagoon for treatment. septic tank. For a house, the re- solids heavier than water. All household wastewater quired working capacity is based The liquid discharged from a must go to the septic tank. House- on the number of bedrooms, not septic tank is called effluent. Ef- hold wastewater sometimes is the number of people in the house fluent from a properly maintained referred to as “black water” or at the time of construction. Each septic tank is slightly cloudy and “gray water,” depending on which bedroom can hold two people, contains fine suspended solids, appliance or fixture it came from. so the standard three-bedroom bacteria and nutrients. Sep- No matter the source, do not let house could have six people gen- tic tank effluent must not be water and other similar wastes erating household wastewater. discharged directly to the bypass the septic tank. Grey water ground surface or into sur- containing soap or grease sent face waters. Professional sani- directly to a drainfield will plug the soil pores quickly.

6 Location and ground surface. A shallow sep- Installation tic tank and drainfield provides The septic tank should be easy access to the component at least 10 feet away from the parts, plus the drainfield is more house. The tank should be aligned efficient at treating effluent. For straight out from the point where new houses, the North Dakota the discharge sewer line leaves Plumbing Code recommends us- the house. Installing the tank so ing a basement sump (Figure 3) Table 2. Recommended it is level, with no slope in any designed to handle wastewater if septic tank liquid capacities. direction, is important. For pump- the septic tank and drainfield can Minimum ing and cleaning, the septic tank work by gravity and the home has Working should be situated near a drive- basement toilets and fixtures. For Capacity way or other access road. Most these types of systems, the sewer Minimum for Homes Working with Garbage septic pump trucks carry between pipe leaves the house through Number of Capacity* Grinders# 50 and 100 feet of hose, so the the basement wall. The sump lifts Bedrooms (gallons) (gallons) tank should be accessible from the water to the sewer pipe. If the 3 or less 1,000 1,500 this distance. Select a location house sewer pipe is less than 4 1,250 1,750 away from high vehicle traffic 4 feet below ground surface, it 5 1,500 2,000 areas. Never locate septic tanks needs to be insulated in the trench *Working capacity is the tank volume under sidewalks or patios where below the outlet. An additional internal for frost protection. Ready-to-in- volume equal to 20 percent of the the tank is inaccessible for pump- stall basement wastewater sump working capacity is needed for floating ing. stations are available in most scum storage. #Garbage grinders require septic A home sewage treatment home supply or hardware stores. tanks with about 50 percent greater system works best and is more Having the lift pump in the volume and often a second compartment is required. easily maintained if both the septic basement has some major ad- tank and drainfield are near the vantages. First, that allows the

Figure 3. Shallow septic tank installation. 7 wastewater from the upper part at a shallow depth. In areas where Construction of the house to flow by gravity to the water table can rise above the Septic tanks are built using the septic system. This has proven top of the septic tank, homeown- corrosion- and decay-resistant to be valuable during a flood or ers must seal around the inlet and materials. If installed properly, power outage. Second, the hom- outlet pipe holes, any joints, the they will be watertight for a long eowner doesn’t need a lift station septic tank cover and manhole ac- time (30 years or more). Precast that pumps all the effluent from a cess so they are watertight. reinforced concrete tanks are the house. Third, a basement sump Wastewater from the house most common. However, tanks only turns on when basement and bacterial action usually also may be constructed using fixtures are used. Last, it’s acces- provide enough heat to keep the poured-in-place concrete or built sible for maintenance and repairs. septic tank from freezing, even from concrete blocks with the Many older houses have a when located above the frost cores filled with concrete rein- septic tank installed lower than depth. When the top of a septic forced with rebar. Concrete block the basement floor level. New tank is installed within 2 feet of the tanks must be sealed with at least houses can have a deep septic ground surface, covering the top two coats of concrete plaster. tank, providing a high water of the tank with 2 inches of rigid Fiberglass and durable plastic table is not present (Figure 4). foam insulation board will help re- septic tanks also are available. If suitable slope is not present, a tain heat in the septic tank. When- They must be installed by care- lift-pump station must be installed ever the system is built above frost fully following the manufacturer’s at the outlet side of the septic tank depth, laying all sewer pipes at a instructions so they will withstand so the drainfield can be installed uniform grade with no high or low soil and water pressure. spots is very important.

Figure 4. Deep septic tank installation. Suitable for use where a high water table is not present. Always check with the tank manufacturer to make sure the tank has the load- bearing capacity to handle the soil overburden. 8 Septic tanks should be de- Baffles must be durable and ground level, extensions must be signed for a liquid depth of not corrosion-proof. Durable concrete, attached to the top of the tank to less than 3 but not more than 6 fiberglass or plastic are excellent bring the cover within 12 inches of 1/2 feet. The horizontal distance materials. Never use steel baffles, the ground surface. In high water between the inlet and outlet of as they will corrode quickly. If table areas, the extensions and rectangular tanks should be about baffles are bolted in place, use cover must be watertight. If the three times the width of the tank. only stainless steel bolts. manhole access is at ground level, Incoming solids will settle out The bottom of the inlet baffle it should have a locking bracket in this distance and not flow out should be at least 6 inches below or be chained shut with a padlock to the drainfield. Circular tanks the liquid surface when the tank is (Figure 5). should have at least a 5-foot full. The bottom of the outlet baffle To check the septic tank’s inside diameter. should be at least 18 inches below operation, the tank should have The liquid depth in a septic the liquid surface. The top of the two inspection ports, each 4 to 6 tank is the distance from the outlet baffles must be open and extend inches in diameter. One should pipe to the bottom of the tank. The no closer than 1 inch to the tank be over the inlet baffle and one septic tank inlet should be at least cover. This is necessary for proper over the outlet baffle (Figure 2). 3 inches above the outlet. The venting of gases from the tank. This allows for easy inspection tank must have room above the to determine if sewage is flowing liquid level for scum accumulation. into or out of the tank properly A minimum of 20 percent of the Access Holes or if plugging has occurred. The tank’s liquid depth should be left in Septic Tanks inspection ports must be capped as freeboard between the outlet Access to septic tanks is at or just above ground level. The level and the cover of the septic required for inspection and pe- caps prevent gas from escap- tank. For most manufactured riodic cleaning. One manhole at ing and children from dropping tanks, this will be about 12 inches. least 15 inches in diameter must objects into the tank. be on the top of the tank. The Septic tanks must be cleaned manhole should have a concrete regularly to remove the sludge Inlet and cover with an earth covering of that accumulates in the bottom of Outlet Baffles at least 6 inches, but not more the tank. Note that the manhole, Inlet and outlet baffles are criti- than 12 inches. If the top of the not the inspection ports, must be cal parts of a correctly installed tank is more than 12 inches below used for cleaning the tank. For septic tank (Figure 2). The inlet baffle directs incoming sewage downward into the liquid zone of the septic tank. The outlet baffle allows sewage effluent to flow out of the liquid zone, retaining the scum in the tank. Many new septic tanks have a removable filter incorporated into the outlet baffle. The filter prevents nondecompos- able materials (condoms, sanitary napkins and other items) from reaching the drainfield. Baffles may be constructed as an integral part of the septic tank or fastened to the tank after construction. Four-inch diameter plastic tees often are used as baffles (Figures 2, 3 and 4). Figure 5. Methods of securing a manhole cover to prevent unauthorized entry. 9 most houses, cleaning every three be pumped on a regular basis, The cover must have a lock or be years is satisfactory. However, a and reducing daily water use in chained shut to prevent children house with a garbage grinder that the house will contribute to lower or other unauthorized individuals the occupants use may require a annual pumping costs. from entering it (Figure 5). one- to two-year cleaning interval. The holding tank must be Since the tank is watertight, it Garbage grinders increase the watertight and hold at least 400 could try to float out of the ground organic matter flowing into the gallons for each bedroom in the right after being pumped if the septic tank. house. However, for any house, local water table is within 3 feet of the minimum tank size should the ground surface. In locations hold at least 1,000 gallons. For a with high water table conditions, Holding Tanks common three-bedroom house earth anchors may be necessary. Some houses are in areas occupied by four people, a 1,200- Keeping the tank above the water where a septic tank and drainfield gallon tank will provide about table and pumping sewage from will not work. Locations with a six to 10 days worth of storage. the house if necessary usually are high water table, bedrock close The holding tank must be situ- best. to the surface and very small lots ated so it is accessible to a pump Installing a meter to measure with insufficient drainfield area are truck under all weather condi- water flow into the house, and the most common reasons. Often tions and where accidental spills thus the amount of water flowing the only option is to use a holding during pumping will not create a into the holding tank, may be nec- tank for household wastewater nuisance. The tank must be level essary. By periodically checking (Figure 6). People with holding and placed on firm, settled soil the water meter, you will be able tanks must practice good water capable of bearing the weight of to determine when the tank is full. conservation so the tank doesn’t a full tank. The riser of a holding A better method would be to use fill quickly. Holding tanks have to tank must come to the surface. a high-water alarm. These can be either electronic with a remote reader in the house or a floating indicator that protrudes above ground surface.

Figure 6. Holding tank for household effluent. Must be pumped on a periodic basis (usually every two weeks to a month).

10 Pumping Stations

umping stations are required P in situations where the effluent cannot flow by gravity and must be lifted to a destination. Many new houses are using lift stations in the basement, and outside the house the wastewater flows by gravity through the septic tank to the drainfield. Many manufacturers make complete ready-to-install pump stations for basements. Many older on-site systems have pumping stations that pump all the water coming from a septic tank to the drainfield (Figure 7). Pumping is required with a deep septic tank installation and shallow soil absorption unit or when the soil absorption unit is at a higher elevation than the septic tank. A mound soil absorption system will require a pumping station. A pumping station consists of two main parts — the watertight tank and the pumping system that in- Figure 7. Septic tank effluent pumping chamber. Working capacity cludes the pump, on/off switches, should equal about one-fourth the daily sewage volume. Reserve plus alarm system and wiring. working capacity should equal about one day’s sewage volume. This allows time to correct any pumping problems.

Tanks The tank containing the pump A reasonable reserve capacity is off setting. Ranges of 12 inches must be watertight. If not, ground three-quarters of the daily esti- to 30 inches are common. The water may seep into the tank mated wastewater volume. following table gives some capaci- and the excess water easily will For example, a three-bedroom ties of circular tanks in gallons per overload the drainfield. Whether house with a design volume of foot of depth. the pumping station is in the base- 450 gallons per day (gpd) requires ment or outside, the tank should a tank with a working volume Inside Diameter Gallons per foot have enough volume below the of about 110 gallons (volume (inches) of depth inlet pipe to hold about a day’s between pump-on and pump-off) 18 13 worth of wastewater. The tank and a reserve capacity of about 24 23 should hold about one-fourth the 330 gallons. The working volume 30 36 36 53 plus reserve capacity equals daily wastewater volume between 42 72 the on and off levels of the pump about 450 gallons, or one day’s 48 94 controls. Some reserve capac- amount of wastewater storage. 60 147 ity in the pumping tank must be Pump controls often have a 72 212 available in case of pump failure. limited range between the on and

11 The capacity of rectangular tanks. Sump pumps sold in home When choosing a pump for a tanks in gallons per foot of depth supply and hardware stores for mound soil absorption system, can be calculated by multiplying basement drain water are not size the pump for a delivery of length in feet by width in feet by recommended for use in sewage about 7.5 gpm per 100 square 7.5. For example, a rectangular lift stations. Pedestal sump pumps feet of rock bed area. For exam- tank with an inside width of 4 feet with an open motor should not be ple, a mound for a three-bedroom and inside length of 5 feet has used except in an emergency. house has about 300 square feet a capacity of 4 x 5 x 7.5, or 150 All lift pumps are designed to of rock bed area, so the pump gallons per foot of depth. With be submersible. Pump bodies are should have a flow rate around a 12-inch on-off setting for the commonly made from cast bronze, 27 gpm. The pump must have this pump, this tank would handle a cast iron and plastic. All bolts, nuts capacity at the required head. The three-bedroom house easily. A and screws are stainless steel. required head will be the eleva- circular tank would need a diam- The pump must be set on a con- tion difference in feet between the eter of at least 48 inches, but if the crete block or pedestal in the tank pump discharge and the mound, on-off setting were 30 inches, a bottom so grit and other solids are plus friction loss in the pipe, plus 30- to 36-inch diameter tank could not drawn into the pump and sent 5 feet. For mound systems, use be used. to the drainfield. a minimum of 1½-inch diameter Pumping station tank materi- Pump capacity is rated by how plastic pipe. At a pumping rate als include concrete (similar to much flow rate can be produced of 27 gpm, the friction loss in the holding tanks), concrete culvert versus the amount of head (verti- pipe will be about 5 feet of head sections and complete, ready-to- cal lift plus friction losses) it is loss per 100 lineal feet of pipe. install plastic units. Metal tanks do lifting. For example, a pump with not last very long because effluent a 3/4 horsepower motor might is very corrosive. Installations with pump 40 gallons per minute (gpm) Example: A pump must an open bottom, such as concrete against a lift of 15 feet. With a lift be selected to lift 27 gpm culvert sections, must have a of 25 feet, the same pump will of effluent from a pump watertight, cast-in-place concrete have a flow rate of only 15 gpm. chamber to a mound for floor. All joints between culvert Flow rate usually is not a limit- a three-bedroom house. sections must be sealed so they ing factor in pump selection when The mound is 200 feet are watertight. Flotation may be a pumping to trenches or an absorp- from the pump tank and problem with precast tanks under tion bed. However, the maximum 10 vertical feet above the high water table conditions. Under lift capability of the pump may be elevation of the pump this condition, soil anchors may a limiting factor. Always determine discharge. The pump be required to prevent upward the vertical lift by measuring from must overcome a head movement. the pump discharge to the pipe of 10 feet (for elevation A secure manhole cover outlet in the drainfield. Select a difference) + 10 feet (for must be located on the top of the pump with a maximum lift capa- friction loss) + 5 feet = pumping tank. The cover must be bility at least 5 feet higher than 25 feet. The chosen pump lockable to prevent children from this elevation difference. Use a must deliver about 27 removing the cover. 1¼-inch or larger diameter flex- gpm at about 25 feet of ible plastic pipe from the pumping head. station to the drainfield. The plastic Sewage Pumps pipe must be buried below frost Many manufacturers make lift depth with a uniform grade back Install the pump with a union pumps specifically for sewage to the pumping chamber. In the or quick disconnect coupling near effluent. Lift pumps must be winter, the water in the line should the top of the pump tank. This durable and corrosion-resistant drain back to the pump station makes installation and removal of with sealed motors and electrical to prevent freezing. Low spots in the pump easier. Do not install a connections. They must be able to shallow buried pipe will freeze. check valve in the outlet pipe from withstand the acidic and corrosive the pumping station. If the pump environment present in sewage has a built-in check valve, remove

12 it. Loop the outlet pipe with a piggyback into the control cord ¼‑inch weep hole drilled at the plug. A weatherproof box outside Septic Tank low point of the loop. The weep the pumping tank must be used hole allows the water in the pipe for an electrical outlet to serve the Outlet to drain back to the pump tank pump. after the pump shuts off. Pumps must have a failure Sewer alarm system to warn the home- ■ Pump Controls owner if the pump stops pumping. he outlet sewer pipe carries All wastewater pumps need The alarm system senses pump Tsewage effluent from the to be turned on and off based on failure when water rises above septic tank to a pump chamber the liquid level in the tank. The the pump-on control. The sensor or the drainfield. The outlet sewer most common pump on/off control is another mercury level control pipe must be watertight where it is a mercury level control switch switch in a watertight bulb. It usu- leaves the septic tank and at least sealed in an effluent-resistant ally is set 3 to 6 inches higher 4 inches in diameter. Plastic pipe plastic or rubber bulb (Figure 8). than the pump-on water level sen- (either PVC or ABS) should be The length of the cord between sor. The pump failure alarm circuit schedule 40. Plastic pipe with thin- the attachment point and the mer- should be installed on an electri- ner wall thickness often will slump cury bulb determines the water cal circuit separate from the pump. when the soil settles. Lay the pipe level where the pump turns on A homeowner can select from at a minimum grade of 1/8 inch and off. among several alarm methods per foot. No maximum grade is A licensed electrician must in- to warn of pump failure. Remote required for the outlet sewer pipe stall all electrical wiring for a pump alarms, located in a convenient since it carries only liquid. The station. Electrical outlets must not place in the house or garage, outlet sewer pipe must be laid be installed inside a pump tank. are common. They can be pro- to grade with no low spots where State plumbing code requires grammed to make a sound similar effluent can collect and freeze. all electrical connections to be to a smoke detector, flash a light outside the pump tank. On/off or call a telephone number. Many control switches commonly use alarms are at the pump tank on piggyback plugs where the control a pole and use either a light or cord plugs into an electrical outlet buzzer to warn of pump failure. and the pump electrical cord plugs Some use a light aimed at a win- dow in the house.

Figure 8. Liquid level pump controls. All electrical connections must be outside the pumping chamber and at ground surface.

13 Soil Absorption Systems

he soil absorption system has system. The infiltration rate of the least 24 inches (2 feet) below the Tto work all year. That means soil usually was given in “minutes trench bottom. However, 36 inches it must infiltrate effluent during per inch” or mpi. The lower the or more of separation between wet springs and cold winters. mpi, the higher the infiltration rate. the high water table and trench Effluent from the septic tank is However, percolation tests have bottom is preferred. Trenches are about 99 percent water but it also proven to be unreliable in many most suitable for soil textures with contains biological material (small situations. Currently, many local percolation rates of 60 minutes particles). Additional treatment of health districts require a regis- per inch (mpi) or less (Table 3). the biological material occurs in tered soil classifier to determine Trenches may be used on 61 to 90 the soil absorption system (Figure the texture of the soil and local mpi soils, providing a high water 9). The area of soil absorption groundwater hydrology for de- table does not exist and adequate must be sized so it can infiltrate sign purposes. Percolation tests trench length is used. For soils the daily wastewater flow from still are accepted in some health with percolation rates of 61 to 90 the house, as well as effectively districts or if a house lot has been mpi, increase the trench area by decompose the biological materi- created with fill soil. The proce- 25 percent over the area required als in the effluent. dure for doing a percolation test is for a soil with a 60 mpi percolation The ability of the soil to treat in Appendix A. rate. For soils with percola- and infiltrate the effluent is based tion rates greater than 90 on the texture and local hydrology mpi, trenches should not be at the depth where the effluent Absorption Trenches used as a soil absorption will be introduced to the soil. In Trenches are the most com- system without consulting the past, a “percolation” test was mon and effective drainfield. They the local health sanitarian. performed and the results were can be used in areas where the The square footage (length used to size the soil absorption historic high water table is at and width) of required absorp-

Figure 9. Location of the biological treatment area under a drainfield.

14 tion trench for a given house and ■ Trench Construction where effluent enters the trench. A lot is based on the daily average Trenches are constructed with trench can be 200 feet long if the wastewater flow and soil texture a backhoe. Commonly, a 24- to effluent is delivered to the center. at the depth of the trench bottom. 36-inch-wide bucket is used. On sloping ground, trenches must If the soil texture is a mixture, for A wider bucket makes a wider follow the contour of the slope so instance a fine sand with some trench that increases the trench the bottom of the trench is level silt mixed in, design for the finer bottom area and reduces the along its full length (Figure 10). soil. Be sure to construct at least length of trench. Do not allow any Never construct trenches in this amount of absorption trench. wheel tracks in the trench since loam or clay loam soils under wet Many homeowners and installers the compaction will seal the sur- conditions. At the depth where the feel this is more trench than they face, greatly reducing the effec- trench bottom will be, obtain a soil require and install less trench to tiveness of the absorption trench. sample and the soil wetness. If the save money. This usually ends up The bottom of each trench soil can be rolled into a thread 1/8 being false economy. The system must be level throughout its full inch in diameter without breaking, fails within a number of years and length. A level trench bottom al- it is too wet to dig trenches. Wet then additional work must be done lows effluent to infiltrate uniformly soil will compact and smear, seal- to upgrade the system. Recom- for its entire length. If the trench ing the trench and greatly increas- mendations for trench bottom area bottom has any slope, all the ef- ing the chance of failure. If the soil are based on a long-life treatment fluent will collect at the low spots. is dry enough for construction, it system, not a temporary solution. This can lead to premature failure will crumble when you try to roll it Built into the trench bottom area or day lighting of effluent. In most into a thread. requirements is reduced infiltration situations, the maximum length Rock-filled Trenches capacity through time due to the of any one trench should not be Trenches using crushed rock accumulation of biological mate- more than 100 feet from the point for overburden support may be rial in the trench bottom. constructed 18 to 36 inches wide

Table 3. Effluent loading rate of an absorption trench based on soil texture. A registered soil classifier should determine the soil texture at the depth where the bottom of the trench will be located. Percolation Depth of rock below the distribution pipe Rate Soil Texture (minutes/inch) 6” 12” 18” 24” Square feet of trench bottom per bedroom Sand and loamy sand 1 to 5 125 100 85 70 Sandy loam 6 to 15 190 150 125 110 Fine sand, very fine sand, loam 16 to 30 250 200 165 145 Silt and silt loam 30 to 45 300 240 200 170 Clay loam, sandy clay, silty clay loam 45 to 60 330 265 220 190 Clay 60 to 120 650 515 440 375 Trench bottom area loading rate, gal/ft2/day Sand and loamy sand 1 to 5 1.2 1.5 1.8 2.1 Sandy loam 6 to 15 0.8 1.0 1.2 1.4 Fine sand, very fine sand, loam 16 to 30 0.6 0.75 0.90 1.05 Silt and silt loam 30 to 45 0.5 0.63 0.75 0.90 Clay loam, sandy clay, silty clay loam 45 to 60 0.45 0.57 0.68 0.80 Clay 60 to 120 0.23 0.29 0.34 0.4

15 and 6 to 48 inches deep. The it drainfield rock). Washed rock is rate and lead to premature failure. depth of crushed rock is depen- important because most rock has The depth of soil cover over the dent on the depth of the trench fine clay attached. When un- rock will depend on the depth of (Figure 11) and distribution pipe. washed rock is used, the clay will the distribution pipe. In the trench, use ¾- to 2½-inch be washed off by the effluent and Four-inch diameter plastic diameter crushed rock that has end up in the bottom of the trench. sewer pipe with ½-inch diameter been washed (some suppliers call This can reduce the infiltration or larger holes spaced 12 inches apart or closer is used for distribution pipe (Figure 12). It is available in home supply and hardware stores. The distribution pipe can have a slight slope (1- to 2-inch drop in 100 feet) to help distribute the effluent over the full length of the trench. The pipe should have at least 2 inches of crushed rock over it. The rock under the pipe distributes effluent over the trench bottom and sidewalls, allowing the liquid to infiltrate into the soil. The pipe is oriented in the trench with the holes downward. When using pipe with a double row of holes, place the pipe with the holes downward in a 5 o’clock and 7 o’clock position. The rock must be covered to prevent soil from seeping in and plugging the spaces between the rocks (Figure 13). Several products can be used. The most common is red rosin paper or a geo- Figure10. Trenches constructed on the contour of a slope. The bottom textile fabric. A 4- to 6-inch layer of the trenches must be level. of hay or straw also can be used. Don’t use plastic (black or clear) to cover the rocks in the trench. After covering the rock, backfill the trenches with earth. Overfill the trenches with 4 to 6 inches of backfill to allow for settling.

Figure11. Cross section of a rock-filled absorption trench.

16 Figure12. Gravel-filled trench with plastic drop box in the foreground. Figure13. Gravel-filled trench covered with geotextile fabric.

Gravelless Trenches Gravelless trench systems use plastic pipe or chambers (Figures 14 to 17) instead of crushed rock for overburden support. No rock is required in the trenches with these products. Gravelless systems are becoming more common because they can be installed with a smaller crew, require less heavy equipment and provide greater effluent storage volume in the trench. Like any trench system, Figure 14. Cross section of a gravelless trench design using plastic the trench bottom must be level pipe (10- or 12-inch outside diameter) encased in a geotextile fabric for good distribution of effluent. sock. Trench bottom area is determined from Table 3 using the 6 inches of gravel column. Both the pipe and chamber system designs could put in three trenches each of just more than 3 feet. This is use an equivalent of a 3-foot- 100 feet long or four trenches equivalent to a 3-foot-wide trench wide trench. For example, say we each 75 feet long. because the biomat treatment want to install a gravelless trench The gravelless pipe system area forms on the sock on the system for a three-bedroom house uses plastic corrugated pipe outside of the pipe and increases with a silt loam soil at the bottom covered with a nondegradable the infiltration area. The chamber of the trench. From Table 3, the geotextile fabric sock. It can be system also has a maximum buri- necessary bottom area would be installed in trenches a minimum al depth of 4 feet. The chamber 300 square feet per bedroom for a of 18 inches wide to a maximum design has various permutations total of 900 square feet. Using an depth of 4 feet. The outside that range in width from 18 inches equivalent trench width of 3 feet diameter of the pipe is 12 inches, to 3 feet. Selection is based on requires 300 feet of trench. We which provides a circumference site requirements and soil texture.

17 ■ Effluent Distribution Most trench drainfields have two to four separate trenches requiring some method of equitably distributing the effluent between the trenches. Two methods commonly used are drop boxes and distribution boxes. Drop boxes are used on sloping land where the trenches are aligned with the contour of the slope (Figure 9). Distribution boxes are used on level land where the elevations of all the trench bottoms are about the same.

Figure 15. Cylindrical gravelless pipe in shallow trenches. Drop Boxes Note the geotextile cover. Drop boxes are the preferred method of effluent distribution and may be used on near-level or sloping terrain (Figures 18, 19 and 20). Drop boxes commonly are made from concrete or plastic. They have an inlet, two outlets that distribute the effluent to the trench and an outlet that takes the overflow to the next drop box. The inlet and outlets commonly are 4 inches in diameter to accommodate plastic pipe. Drop boxes allow a trench to be utilized fully before any effluent goes to the next trench. Drop boxes are required Figure 16. Cross section of a gravelless trench design using a for trench systems installed on plastic chamber (sometimes called a chamber unit). hillsides. Even distribution of effluent over the entire drainfield is very important. Otherwise, all the effluent would collect in the low spots and overload the soil. If a trench becomes overloaded and effluent is coming to the surface, the outlets from the drop box can be blocked to allow the trench time to recover its ability to infiltrate effluent.

Figure 17. Chamber-type gravelless system being installed on a very small house lot. Normally the chambers would be used in trenches. 18 Figure 18. Drop box showing inlet and outlet pipe elevations.

Figure 19. Location of drop boxes used for effluent distribution to an absorption trench system.

19 Distribution Boxes Distribution boxes are used only on level terrain (Figure 21). Distribution boxes normally are made from concrete or plastic. They have an inlet and usually three outlets for each of the absorption trenches. The inlet and outlets commonly are 4 inches in diameter to accommodate plastic pipe. All of the outlets from the distribution box are set at the same elevation, thus having a base under the box of crushed rock or gravel to keep it level is very important. However, in practice, due to frost action or flooding Figure 20. Concrete drop boxes used to distribute conditions, keeping all outlets at effluent to absorption trenches. Note that the the same elevation throughout distance between the trenches is 6 feet, the minimum separation distance. The trench on the right has been the life of the system is virtually backfilled and the trench on the left is ready to be impossible. If the box gets tilted, covered with hay, straw, untreated building paper or the trench served by the low- a geotextile fabric.

Figure 21. Distribution box used for effluent distribution to an absorption trench system. 20 est outlet will receive the great- Absorption Beds The absorption bed should be est amount of effluent. For this dug with a backhoe. No wheeled Absorption beds basically are reason, distribution boxes may be or tracked equipment should be rectangular pits dug into the soil used only where the elevation of driven on the bottom of the bed. (Figure 22). Depending on the the lowest trench is high enough The bottom of the absorption bed house lot, depths can range from to back effluent up to the distribu- must be level in all directions. 1 to 4 feet. They cannot be used tion box without surface seepage A minimum of 6 inches of rock in locations having slopes greater occurring. should be placed in the bottom of than 6 percent. Absorption beds A common sign of problems the bed. Use washed rock that is are not as effective at treating with a distribution box is if the soil ¾ to 2½ inches in diameter. The effluent as trenches because the gets soggy over one trench but rock must be washed to remove absorption bed has less sidewall stays dry over the others. To check clay particle. When unwashed area for infiltration. Therefore, for this problem, open the top of rock is used, the clay will be about 25 percent to 50 percent the distribution box and check the washed off by the effluent and end more bottom area is required than water flow to the outlets. You may up in the bottom of the bed. This for trenches. Even with the larger have to dig around the box and can reduce the infiltration rate and bottom area requirement, absorp- level it again. After leveling the lead to premature failure. tion beds require less total yard box, the outlet going to the trench The pipes within absorption area than trenches and can be that was soggy can be plugged beds are normally 4-inch diameter used on small house lots. Soil tex- temporarily (two to four weeks) so perforated plastic. The pipes must ture and the number of bedrooms the trench can be rested. be level, 4 to 6 feet apart and 1½ in the house determine the neces- to 3 feet from the edge of the bed. sary bottom area of an absorption The pipes normally are joined bed (Table 4).

Figure 22. Absorption bed construction and layout. 21 at the ends to form a continu- sell and Richard Witz designed On low infiltration rate soils, the ous loop, although they can be in 1947 at North Dakota State basal area must be large enough terminated as shown in Figure University. Through the years, the to allow percolation of the daily ef- 22. A four-way tee will distribute design parameters and shapes of fluent volume into the soil surface. the effluent but a distribution box mounds continually have changed In high water table conditions, also can be used. All joints must as more research information the elevated bed allows biologi- be glued. Washed rock then is became available. Present param- cal treatment to take place before placed over the distribution pipe eters for mound design allow for the effluent infiltrates to the water to a depth of 2 to 4 inches. After higher water usage and differ- table. the distribution pipe is covered ent construction techniques than Effluent is pumped to a mound with rock, a soil separator must be many earlier designs. system and distributed across placed above the rock. Any of the A sewage mound is a special the rapid infiltration bed under following materials are acceptable: drainfield design used in locations pressure (Figure 25). The effluent a 4- to 6-inch layer of hay or straw, with high water tables (within 2 is pumped to the mound through untreated building paper (called to 3 feet of the surface) and slow 1½-inch diameter or larger plastic red rosin paper) or a geotextile infiltration rate soils. A sewage pipe. The pump tank should be specifically designed for drain mound takes advantage of the large enough and the pump con- fields. Cover the bed with 6 to 18 higher infiltration rate of surface trols set so a dose equal to about inches of topsoil and form a crown soils, compared with subsurface one-fourth of the daily wastewa- to account for any settling and soils. A sewage mound is con- ter volume is discharged to the also allow the bed to shed water. structed above the existing ground mound when the pump starts. A Shallow absorption beds often will surface. A mound is basically a three-bedroom house has a de- have a permanent mound. Don’t high infiltration rate bed set on sign load of 450 gpd, so the pump plant trees or shrubs on top of the top of a sand fill that has been should discharge about 110 gal- absorption bed. spread over the existing ground lons per dose. This provides a rest (Figure 23). The high infiltration period between doses and allows rate bed can be constructed using the effluent to infiltrate before the Sewage Mounds clean rock or gravelless systems next dose. In addition, it increases Sewage mounds can trace (Figure 24). The area where sand pump life. Frequent starting and their origins to the first “NODAK” makes contact with the existing stopping of a pump will reduce the mounds that J. Clayton Rus- ground is called the basal area. life of the motor.

Table 4. Effluent loading rates for absorption beds based on soil texture. A registered soil classifier should determine the soil texture at the depth where the bottom of the bed will be located. Percolation Bottom Area Rate Loading Rate Per Bedroom* Soil Texture (minutes/inch) gal/ft2/day square feet Sand and loamy sand 1 to 5 1.0 150 Sandy loam 6 to 15 0.65 230 Fine sand, very fine sand, loam 16 to 30 0.5 300 Silt and silt loam 30 to 45 0.40 375 Clay loam, sandy clay, silty clay loam 45 to 60 0.35 430 Clay 60 to 120 0.18 830 *Based on 150 gallons per day per bedroom

22 Figure 23. Construction features of a sewage mound.

Figure 24. Cross section of a sewage mound showing two types of gravelless leaching systems. 23 Figure 25. Septic tank, pumping chamber and sewage mound.

Sewage mounds always The distribution pipes must where the effluent enters the should be designed with a pres- have a ¼-inch diameter hole pressurized distribution system surized effluent distribution every 40 inches in the bottom of from the pump delivery pipe. To system (Figure 26). A pressurized the pipes. The pipe joints and end protect from freezing conditions, distribution system evenly distrib- caps must be glued. Otherwise, the distribution pipe and delivery utes the effluent over the entire they will pull apart during con- pipe must be designed to drain basal area and helps prevent struction, under pressure or later when the pump is off. This can be overloading in any one spot under from settling and frost heave. The accomplished by using a ¼-inch the mound. The plastic pipes pipes are connected at the center diameter weep hole in the delivery can be set in either a rock bed or pipe in the pump tank. inside gravelless pipe. Gravelless pipe manufacturers make products specifically for use in sewage mounds. The pressure distribution system is constructed from either 1¼- or 1½-inch PVC pipe. Pipe diameter is important because too large a diameter (such as 2 inches) could result in uneven distribution of the effluent. For a sewage mound requiring a 6-foot or narrower rapid infiltration area, two parallel pipes are used. For a sewage mound requiring a 7- to 10-foot-wide rapid infiltration area, three parallel pipes are used. When using plastic gravelless systems instead of rock, the pressure distribution pipe is attached inside the chamber or pipe. Figure 26. Pressure distribution system using two parallel pipes with a center feed. The pump in the pump chamber supplies effluent under pressure.

24 ■ Sizing The basal area of the mound Example: for a three-bedroom house producing (contact area of the fill sand with 450 gallons per day of effluent, the contact area the existing soil) determines all between the fill sand and the existing ground should the other mound design parame- be between 1,800 feet2 (450 gpd ÷ 0.25 gpd/feet2) ters. The basal area is determined and 2,250 feet2 (450 gpd ÷ 0.20 gpd/feet2). Figure by the texture of the existing soil. 27 shows a mound for a three-bedroom home. The For slowly permeable clay and basal contact area for this mound on level ground is clay loam soils, use a design ef- 2,150 square feet. The amount of clean, washed sand fluent loading rate of from 0.20 needed is about 72 cubic yards. to 0.25 gallon per day per square foot.

Figure 27. Sewage mound on flat terrain. The dimensions were calculated based on the effluent from a three-bedroom house with the mound built above a clay-loam to clay soil.

25 The rapid infiltration area is keep the effluent distribution pipe Mounds should be located determined using the intake rate width at 4 to 6 feet. For our three- on flat areas or the crests of hills; of medium sand. Medium sand bedroom home example, the rock however, they can be built on slop- has a loading rate of 1.2 gallons bed or gravelless systems will be ing terrain (Figure 28). However, per day per square foot. Using the about 375 feet2 ÷ 6 = 63 feet long. soil texture and percolation rate three-bedroom home example, A 6-foot-wide rock bed 12 inches will determine the maximum slope. the required rock bed area is 375 thick will require about 14 cubic For example, if the soil texture of feet2 (450 gallons per day ÷ 1.2 yards of washed rock. For gravel- the topsoil is clay loam with a per- gallons/day/feet2). If a gravelless less systems, two rows of plastic colation rate of 120 mpi, then the system is used instead of rock, chamber or two rows of gravel- ground slope should not exceed it needs to be sized to provide less pipe, each 63 feet long, are 3 percent (3-foot vertical drop in 375 feet2 of rapid infiltration area. required. 100 feet). If the percolation rate is For soils with low permeability, between 60 and 120 mpi, then the

Figure 28. Sewage mound on sloping terrain. For most soils, the maximum slope should be no greater than 6 percent (6-foot vertical drop in 100 feet). The dimensions were calculated for the amount of effluent from a three-bedroom house with the mound built above a clay-loam to clay soil.

26 ground slope should not exceed 6 Once the surface is prepared, no or straw, untreated building paper percent, and if the percolation rate wheel traffic can be allowed in the (red rosin paper) or a geotextile is 30 mpi or less, then mounds basal area. Wheel traffic will seal material designed for septic sys- can be constructed on slopes up the soil. Do not work in wet soil tem drainfields. to 12 percent. conditions because wet soil will For gravelless distribution, When a mound is constructed compact, smear and seal the soil. place the gravelless pipe or cham- on a slope, only the sand-soil Next comes the fill sand. The ber on top of the level sand. Place contact area under the distribu- fill sand should be washed and the distribution pipe in the gravel- tion area (rock bed or gravelless) checked to be sure it contains less carriers and connect to the and down-slope from there can no more than 10 percent delivery pipe from the pump tank. be considered basal area. Under fines. To test, put 2½ inches of Double-check all connections. Test sloping soil conditions, the ends sand in a quart jar and add water the pump and distribution system and up-slope portion of the mound until about three-quarters full. before covering. Cover the grav- receive very little effluent and Cover and shake to mix the sand elless system with a geotextile do not contribute to the area of and water. Let the mixture stand fabric and put a cap of heavy soil infiltration. for an hour and measure the silt on top (Figure 24). ■ Construction and clay accumulation on top of Cap the mound with a loam the sand. If the depth is ¼ inch or loamy sand soil (Figures 23 Mounds require very diligent or less, the sand is clean enough and 24). Make the cap 12 inches and careful construction practices. for use in the mound. This test high at the center of the bed and 6 Mounds have been known to fail should be done before the sand is inches high at the end of the bed. due to two main causes — too delivered to the site. Pit run sand Taper the cap down the sides of small of a basal area for the efflu- varies widely, even from the same the mound. ent flow from the house, and poor area of a pit, and should not be Last, cover the mound with 6 construction practices. To ensure used. inches of good top soil and seed a mound works as planned, Place the clean sand start- to grass. Don’t plant trees or construction practices must be ing at one end and work toward shrubs on top of the mound. Wa- followed very closely. Plus, the ho- the other end. Drive on top of the ter-tolerant shrubs may be planted meowner must use water wisely. sand as you progress. Shape the around the base. Permanent lawn The first step in mound con- sand with a backhoe with tracks sprinkler systems should not struction is to mow the grass or or a crawler tractor but make sure be installed near enough to the vegetative cover over the basal you have at least 6 inches of sand mound to throw water on it. area to a maximum 2-inch height under the tracks. Wheeled ve- Construct mounds to follow and remove all the cuttings. Then hicles should not be used for this the contour of the existing ground. dig in the effluent line from the operation. Do not allow the tracks Never place a mound in a low pumping station. The line must to run directly on the earth. After area where water will accumulate. be installed below frost level forming with the tractor blade, If the mound is on sloping ground, or sloped uniformly back to the level and do the final shaping by use a berm on the uphill side to pumping chamber so it drains hand. The top of the sand bed divert runoff water around the after the pump shuts off. The ex- should be level the full length of mound. Mounds can be construct- cavated trench must be backfilled the mound. ed to complement your landscap- and the soil firmly compacted to For rock beds, a trench about ing design. Shrubs at the base of prevent effluent from flowing along 12 inches deep and 6 feet wide the mound will use water and help the pipe. should be formed the required trap snow. If the mound is built in Ground preparation comes length on top of the sand. Place the fall, it should be covered with next. The ground must be ripped 6 inches of ¾- to 3-inch diameter straw or hay the first winter to or scarified with a chisel plow or rock in the trench. Place the pres- prevent freezing. the teeth from the backhoe bucket. sure distribution pipe on the rock and cover with 2 inches of rock. Cover the rock with one of the following: a 4- to 6-inch layer of hay

27 Lagoons

mall lagoons (Figure 29) can freeboard of 2 feet. The sides Sbe used to contain septic of the lagoon should have a 3-1 system effluent in some locations. slope or more. A circular 3,000- Lagoons are a viable option when square-foot lagoon with 3 feet the nearest neighbor is at least a working depth and 3-1 side slopes quarter of a mile away. Lagoons would have a 62-foot diameter at should be constructed only in its working depth and a 74-foot di- high clay content soils. A lagoon ameter at the top of the dike. The should act as a container and not lagoon also may be square as an infiltration galley. The water or rectangular. in a lagoon should be removed by A lagoon must be fenced to evaporation. exclude children and animals. An- The lagoon surface area nual maintenance requires check- should be sized at about 1,000 ing for damage and to make sure square feet per bedroom. A animals are not burrowing into the lagoon serving a three-bedroom sides of the lagoon. Cattails and house needs about 3,000 square other plants in the lagoon help feet of water surface area. The la- use the nutrients in the water, but goon should have a working depth their roots can create channels for of about 3 feet and a minimum water to seep away.

Figure 29. Cross section of a small farm lagoon sized to handle the sewage effluent from a typical three-bedroom home.

28 Alternative Septic Systems

omeowners have many alter- Filtration Systems Alternative native methods for treatment H Filtration systems physi- Drainfields and disposal of wastewater from a cally trap suspended solids in the Most alternative drainfields are house. Some alternative systems wastewater and provide a me- variations of the trench, absorp- replace the septic tank or modify dium to speed up the process of tion bed and mound systems out- the operation of the septic tank decomposition. They are like mini lined in this publication. At-grade to speed up or improve the initial versions of a typical municipal systems are used in high water treatment of the household waste- waste treatment system. Filtration table areas, areas with shallow water. Some alternative methods systems can be part of the septic bedrock or other infiltration prob- to the traditional drainfield improve tank or just downstream from lems. They are a combination of the infiltration of the treated water. the septic tank. Sand filters have trench and mound technology. The Many of these alternative systems been used for many years and trench bottom is ground surface. are designed as complete pack- they can be configured as single- The vegetation is removed and ages. pass (waste flows through only the ground is roughed up or scari- Generally, alternative systems once) or multiple-pass systems. fied where the trench bottom will are more expensive than tradition- Filtration systems that use peat be. Then gravel is added and the al systems and practically all of have come on the market in the distribution pipes are laid in place them require electrical power on last 10 years and are used as a and covered with gravel and then a continuous basis. However, in single-pass system. Other filtration a layer of topsoil. some locations where a traditional systems use artificial or synthetic Alternating drainfields is septic system cannot be installed, materials to filter the effluent and another method of distributing they provide a viable alternative. treat the biological solids. These wastewater. Two drainfields are If you are in a health district with mostly are multiple-pass systems. constructed. Each has about 50 on-site septic system rules, check In some parts of the U.S., artificial percent to 100 percent of the area with your local health sanitarian wetlands have been used to treat needed for the house. While one before installing an alternative household wastewater. However, drainfield is in use, the other is system. Some may not be ap- research on artificial wetlands in resting. Typically, one will be used proved. In areas with no sanitar- the northern-tier states has not for about two years, then the hom- ian, check with the North Dakota been successful. eowner will switch to the other. A Health Department’s Environmen- Except for some single-pass special box with a two-way valve tal Health Section. Some of the filtration, all the others have to use or sliding gate controls the flow more common alternative systems a pump to circulate the effluent for from the septic tank. are listed here. multiple passes. Use of a pump on Drip irrigation is being used a continuous basis increases en- to distribute treated wastewater ergy costs and requires an alarm in some parts of the U.S. The drip system. Often the systems cannot lines usually are buried about 1 be operated unless the pump is foot below the soil surface. Drip working. lines can plug very easily, so the wastewater must be treated, filtered and chlorinated before it is pumped to the drip lines. These systems can be very expensive both to install and maintain.

29 Appendix: Percolation Test

Percolation tests are made at locations where and bottom of the holes with a knife or nails driven the water table is at least 2 feet below the surface into a board to counteract the sealing action of the or where the drainfield will be constructed in “fill’ spade or auger. Clean out the loose dirt in the bot- soil. The percolation test helps determine the ability tom of the hole. Place 2 inches of coarse gravel in of a soil to absorb effluent. The rate of water drop in the hole. a test hole determines the percolation rate (Figure 2. Carefully pour at least 12 inches of water into the 30). A fast drop indicates a high percolation rate hole. Add water through a hose connected to a fun- while a slow drop indicates slow percolation. Soils nel. The bottom of the hose should rest on the top that have slow percolation rates need large soil ab- of the rock to prevent washing of the soil in the test sorption areas to treat a given quantity of effluent. hole. Washing will loosen fine materials and seal Prior to running a percolation test, make soil the hole. Keep water in the hole at least four hours borings to a depth of at least 5 feet to determine (overnight would be better). Refill if necessary to the soil texture (amount of sand, silt and clay) at keep the water at the 12-inch level. In clay soils, potential locations for the drainfield. Then choose water must be kept in the hole at least 12 hours the location with the best soil characteristics. for soil swelling to take place before measuring the Generally, soils with higher sand content are better percolation rate. choices for the drainfield area. Once a location is 3. Do the percolation test. Adjust the water level so selected, dig at least three holes at opposite ends it is about 6 to 8 inches above the gravel layer. of the site and do a percolation test in each hole. Measure the water level from a fixed point every The following steps outline the procedure used 30 minutes or as often as required and calculate in running a percolation test: percolation rate in minutes per inch. The percola- 1. Dig a 6- to 8-inch diameter hole to the depth tion rate is calculated by dividing the time interval in of the proposed drainfield. Roughen the sides minutes by the water level drop in inches.

Example: If the water level takes 34 minutes to drop 1c inches, the percolation rate is: 34 minutes = 30.2 mpi 1c inches

Refill the hole as required. Calculate the percolation rate for each reading. Continue taking readings until three percolation rates vary by no more than 10 percent. For example, if you had three readings of 28.4, 27.4 and 29.5 mpi, 10 percent would be about 2.8 mpi, which means they are within 10 percent of each other. Use the slowest value for each test hole to get the average percolation rate for designing the soil absorption field.

Example: Test 1 Test 2 Test 3 Use Hole 1 28.4 27.4 29.5 29.5 Hole 2 31.1 32.8 33.5 33.5 Hole 3 33.4 34.1 32.9 34.1 Figure 30. Soil percolation test hole and water Average 32.4 level measuring apparatus.

30 Notes

31 Use the space above to make a map of your house, septic tank and soil absorption system components and well. Include distance to septic tank and soil absorption components from two fixed points, such as the corners of the house.

Installing Contractor ______Address ______Telephone ______

System Description Gravity ______Pressurized ______Septic Tank ______gallons Manhole ______Inspection Ports ______Pumping Chamber ______gallons

Soil Absorption System (Number of Feet, or Area Covered) Trenches ______Mound ______Bed ______Other ______Depth ______ft

Accessories Distribution Box ______Drop Boxes ______Pump ______GPM at ______feet of head

The NDSU Extension Service does not endorse commercial products or companies even though reference may be made to tradenames, trademarks or service names. NDSU encourages you to use and share this content, but please do so under the conditions of our Creative Commons license. You may copy, distribute, transmit and adapt this work as long as you give full attribution, don’t use the work for commercial purposes and share your resulting work similarly. For more information, visit www.ag.ndsu. edu/agcomm/creative-commons. For more information on this and other topics, see www.ag.ndsu.edu County commissions, North Dakota State University and U.S. Department of Agriculture cooperating. North Dakota State University does not discriminate on the basis of age, color, disability, gender expression/identity, genetic information, marital status, national origin, public assistance status, race, religion, sex, sexual orientation, or status as a U.S. veteran. Direct inquiries to the Vice President for Equity, Diversity and Global Outreach, 102 Putnam, (701) 231-7708. This publication will be made available in alternative formats for people with disabili- ties upon request, (701) 231-7881. 2.5M-8-06, 600-10-15