L-5230 2-99

On-site treatment systems

Constructed absorption Two-compartment field

Figure 1: A system. Constructed Bruce Lesikar Extension Agricultural Engineering Specialist The Texas A&M University System

constructed wetland system for domestic nutrients, organic matter, sus- is designed to mimic the natural wetland treatment processes by pended solids and ; and A Mother Nature. This system uses plants and microbes to improve ✓ A land application system, which the wastewater quality. disperses the wastewater into the soil for final treatment and Natural wetlands generally have visible water in the system. However, disposal/reuse. for those at homes, the water flows beneath the soil surface, which limits Constructed wetland systems contact between residents and wastewater. should be designed and built to blend The constructed wetland waste- removing the settling solids and into the home’s landscaping. The best water treatment system has three floating solids (oils and greases) way to achieve this goal is to deter- main components that work together from the wastewater; mine where the wastewater treatment to purify wastewater: system will be located before the ✓ A constructed wetland, which is a house is built. Effective planning ✓ A septic tank, which is an bed of graded stone, with water before building the house simplifies enclosed watertight container that beneath the surface, where aquatic the system and helps you enjoy it. provides primary treatment by plants are grown. It removes For example, a key factor in deter- two compartments, should be sized whether or not your system appropriately to allow enough time for uses gravity or a pump to move the the settling solids to separate from the water between the system components wastewater. is the location and elevation of the Upon leaving the septic tank, plumbing exit from the house. If the wastewater enters the wetland. It is plumbing exit is too low, you will need believed that entering the to install a pump to lift the wastewater wetland are removed from the water back to near the ground surface to have by microbes living on the surfaces of a gravity flow system. the and plant . The plants Also, the pipes transporting the provide to the bed and remove wastewater must be installed with a some of the nutrients. Other processes slight slope to help wastewater flow such as filtering, microbial decomposi- through the system. If the yard slopes tion and attachment to particle surfaces in the same direction as the wastewa- also help remove pollutants. The ter flow, the wetland will be near the longer the water is detained in the soil surface, thus increasing its wetland, the more pollutants are aesthetic value. removed and the better the quality of water leaving the wetland. The wetland consists of a bed of graded stone where aquatic plants are After flowing through the gravel, grown. The wetland cell is generally wastewater exits the wetland through a an earthen basin lined with compacted water-level control sump. The sump Constructed native , bentonite clay, concrete, allows the water level to be adjusted, PVC, hypalon or PondGard Ethylene because the wetland water level must wetland systems Propylene Diene Terpolymer (EPDM) be lower than the media surface to Rubber. The bed itself is usually prevent odors. should be gravel but can be any porous material The water then flows into the soil that resists being corroded or dis- designed and built absorption field, the last treatment solved by wastewater. stage. If it cannot enter the field by to blend into the The media bed has devices to gravity, it enters a collection tank and home’s landscaping distribute wastewater entering the is pumped to the absorption field, system and to collect wastewater where the soil absorbs it. Microbes and leaving it. The water to be treated plants growing in the soil use the flows horizontally through the bed, remaining nutrients in the water. remaining below the gravel surface. Plants in the wetland must be able Design to survive in a saturated medium. All components of the wetland Although soft- and hard-tissue plants system must be designed properly. can be used, some experts believe that This fact sheet focuses on the wetland. hard-tissue plants are better because For information on septic tank sizing they may provide a pathway for oxygen and land application systems, see the to enter the wetland during winter and Extension publication L-5227, “Septic reduce the need for plant maintenance. Tank/Soil Absorption Field.” However, residents prefer soft-tissue plants because they generally have Wetland systems remove biologi- flowers and are colorful. Remember cal materials, , that if you use soft-tissue plants, your nutrients and pathogens from the system may need more maintenance. wastewater. To determine a wetland’s size, consider: Treatment ✓ of the system, which affects how fast it removes Wastewater is treated by the septic nutrients; and tank first. The tank, which should have Cleanout Adjustable standpipe

3/8 inch pea gravel

1% bed slope 4 inch inlet 4 inch outlet pipe pipe

Figure 2: A constructed wetland is a bed of graded stone where water flows be- neath the surface and plants grow on top.

✓ Amount of waste. A wastewater land’s performance and sizing. The treatment system must be de- depth of a wetland can vary, but it Plants in the signed to treat the most waste- generally ranges from 1 to 2 feet. A water that a residence generates. 1-foot-deep wetland has double the wetland must be able surface area for the same storage This information is used in an volume as a 2-foot-deep wetland. to survive in a equation to determine the hydraulic retention time, which is the amount of The wetland should have enough saturated medium time the wastewater needs to stay in the cross-sectional area for water to flow wetland. It is generally expressed in into it. Water flows through the wetland days. The longer the wastewater stays in by passing from one pore space to the the wetland, the more time that mi- next while remaining below the surface crobes and plants have to treat the of the gravel. If the total cross-sectional water. Generally, the water needs to stay area of pore spaces is too small, waste- in the wetland system for 2 to 3 days. water cannot enter the gravel and the water level rises to the surface of the The relationship between how wetland, causing odors. much water is stored and how long it stays in the wetland determines how One way to determine if you have much surface area the system needs. enough cross-sectional area to accept In general, a constructed wetland in the flow of wastewater is to divide the Texas needs about 1 square foot of length of the wetland by its width. surface area for every gallon of That calculation gives you the wetland wastewater it receives a day. A length-to-width ratio, which should wetland for an average three-bedroom range from 2 to 3. house producing 300 gallons of An example: Say you need a wet- wastewater a day would need a surface land to be 360 square feet. You could area of 300 square feet. build it 3 feet wide by 120 feet long, Physical limitations, such as wet- but that would give a length-to-width land depth, bottom slope and length-to- ratio (120 divided by 3) of 40 — way width ratio, also can affect the wet- too high. If you built it 12 by 30 feet (divide 30 by 12), the ratio would be every 2 to 3 years, depending on the 2.5 — which falls into the accepted size of the home and the number of range of between 2 and 3. people living there. If an effluent filter is located at the exit of the septic tank, When enlarging the wetland, keep clean the filter periodically. the length-to-width ratio relatively constant by extending both the width Here’s how to take proper care of and the length. If it stays relatively the constructed wetland: constant, the flow per unit of cross- ✓ Manage the wetland as a rock sectional area increases less than if the garden. To keep it looking good, wetland size were increased by adding remove dry material as plants length only. freeze in the winter. Gravity pulls the water through ✓ Keep the pore spaces in the media the wetland. The slope of the wetland open. Removing plant roots from bottom also helps the water move the wetland helps maintain the through the wetland. In residential The longer pores needed for the water to systems, the slope could be used to flow through the wetland bed. To help flush solids from the pore spaces the wastewater stays do this, remove plants from the in the media. Common slopes in wetland and replant. Manage the residential systems can range from 0 in the wetland, water level to help break down to 1 percent. Bottom slopes for the fixed film on the media. Also, the more time that municipal systems need to be designed prevent soil from entering the based on hydraulic loading rates. microbes and plants wetland, because soil can fill the pores. If the media is filled with have to treat the water How to keep it working soil or solids, you will need to Each of the constructed wetland remove the media and replace system’s three main components — with clean media. the septic tank, constructed wetland ✓ Control the water level. You may and land application system — has its need to adjust the water level in own maintenance requirements. See the wetland so that it is below the the Extension publication, L-5227, media surface. When it is too “Septic Tank/Soil Absorption Field,” close to the gravel surface, the for tips on how to maintain the septic wetland smells bad. Lowering the tank and land application system. outlet pipe in the water level In general, maintain the septic control sump will lower the water tank periodically to make sure solids level in the wetland and prevent are removed efficiently. Pump the tank odors..

The On-Site Wastewater Treatment Systems series of publications is a result of collaborative efforts of various agencies, organizations and funding sources. We would like to acknowledge the following collaborators: Texas State Soil and Water Conservation Board USEPA 319(h) Program Texas On-Site Wastewater Treatment Research Council Texas Agricultural Extension Service Texas Natural Resource Conservation Commission Texas Agricultural Experiment Station USDA Water Quality Demonstration Projects Texas On-Site Wastewater Association Consortium of Institutes for Decentralized Wastewater Treatment USDA Natural Resources Conservation Service Produced by Agricultural Communications, The Texas A&M University System All publications in the On-site Wastewater Treatment Systems series can be downloaded free from the World Wide Web at: http://agpublications.tamu.edu/pubs/ewaste

Educational programs of the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin. Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the Department of Agriculture. Chester P. Fehlis, Deputy Director, The Texas Agricultural Exension Service, The Texas A&M University System. 30,000 copies, New ENG For Sale Only $1