Wastewater Treatment Engineering & Design Resources
Effective design and engineering are essential to the long-term performance of onsite wastewater treatment systems. This resource hub provides industry professionals with technical guidance, design references, and engineering tools to support the planning and development of reliable onsite systems. From site evaluation and hydraulic considerations to treatment component selection and system sizing, these materials are intended to help engineers, designers, and practitioners create solutions that protect public health and preserve water quality across a wide range of conditions.
A properly functioning system begins within the building itself, where the drain, waste, and vent (DWV) plumbing system collects and transports wastewater from fixtures such as sinks, toilets, and laundry to the treatment train. Approximately 80% of household water use becomes wastewater, which contains organic matter, nutrients, and other contaminants that must be properly conveyed to the septic tank for initial pretreatment. However, not all flows should enter the system—sources such as roof drainage, sump pumps, swimming pools, and air conditioning condensate are not considered wastewater and should be excluded to prevent system overload and reduced treatment performance.
Once wastewater enters the septic tank, separation begins through natural buoyancy processes that divide solids, liquids, and floating materials into distinct layers. This initial stage reduces the load on downstream components and supports effective treatment in the soil absorption area. In more advanced configurations of onsite wastewater treatment systems, additional pretreatment may be incorporated to further improve effluent quality and reduce pollutants before dispersal.
These advanced processes can include aerobic treatment units (ATUs), media filters, constructed wetlands, and disinfection systems. ATUs introduce oxygen to support aerobic bacteria, which accelerate the breakdown of organic material and improve treatment efficiency. Media filters and wetland systems provide biological treatment through attached growth and natural processes, while disinfection technologies such as ultraviolet light or chlorine help reduce pathogens when environmental or regulatory conditions require higher levels of treatment.
Where gravity flow is not possible, pump tanks and control systems are used to move effluent between components or distribute it evenly across the soil treatment area. These systems ensure consistent dosing and help maintain long-term performance, particularly in sites with elevation challenges or pressurized distribution requirements.
Together, these components form an integrated approach to onsite wastewater treatment systems, where proper design, installation, and maintenance are critical to protecting water quality, preventing system failure, and ensuring compliance with environmental and public health standards.
NOWRA
- Recommended Guidance for the Design of Wastewater Drip Dispersal Systems (PDF)
- NOWRA Standard of Practice: Decentralized Wastewater Treatment – Soil-Based Treatment System “Selection and Design” (DOC)
- A Homeowner's Onsite System Guide and Record Keeping Folder (PDF)
US Environmental Protection Agency (EPA)
- EPA Decentralized Wastewater Home Page
- Onsite Wastewater Treatment and Disposal Systems Manual (PDF) - This manual provides supplemental and new information for wastewater treatment professionals in the public and private sectors, expanding upon the design manual listed below.
- Design Manual: Onsite Wastewater Treatment and Disposal Systems (PDF) - This design manual provides technical information for those involved in the design, construction, operation, maintenance and regulation of onsite wastewater treatment and disposal systems. It does not contain standards for those systems, nor does it contain pertinent rules or regulations
- EPA's Class V Well Program
- EPA Region 1 Innovative Technology Inventory
- Source Water Protection Practices Bulletin: Managing Septic Systems to Prevent Contamination of Drinking Water
- Industrial Wastewater Treatment Technology Database
Technology Fact Sheets:
- Aerobic Treatment (PDF)
- Evapotransportation (PDF)
- Low Pressure Pipe Systems (PDF)
- Mound Systems (PDF)
- Septage Treatment/Disposal (PDF)
- Septic System Tanks (PDF)
- Septic Tank Effluent Screens (PDF)
- Septic Tank Leaching Chamber (PDF)
- Septic Tank Systems for Large Flow Application (PDF)
- Septic Tank-Soil Absorption Systems (PDF)
- Small Diameter Gravity Sewer (PDF)
- Types of Filters (PDF)
- Control Panels (PDF)
- Recirculating Sand Filters (PDF)
- Septic Tank Polishing (PDF)
Wastewater Technology Fact Sheets:
- Disinfection for Small Systems (PDF)
- Free Water Surface Wetlands (PDF)
- High-Efficiency Toilets (PDF)
- Intermittent Sand Filters (PDF)
- Ozone Disinfection (PDF)
- Package Plants (PDF)
- Sewers, Pressure (PDF)
- Ultraviolet Disinfection (PDF)
- Wetlands: Subsurface Flow (PDF)
Water Efficiency Technology Fact Sheets:
- Composting Toilets (PDF)
- Incinerating Toilets (PDF)
- Oil Recirculating Toilets (PDF)
Water Environment Research Foundation (WERF)
- Qualitative Tools to Determine the Expected Performance of Wastewater Soil Treatment Units
- Performance and Costs for Decentralized Unit Processes
- Performance Dynamics of Trace Organic Chemicals in Onsite Treatment Units and Systems
- Development of Design Criteria for Denitrifying Treatment Wetlands
- Nitrogen Removal and Sustainability of Vertical Flow Constructed Wetlands for Small-Scale Wastewater Treatment: Recommendations for Improvements
- Influent Constituent Characteristics of the Modern Waste Stream from Single Sources
- State of the Science: Review of Quantitative Tools to Determine Wastewater Soil Treatment Unit Performance
- Hydrologic Bioretention Performance and Design Criteria for Cold Climates
- Factors Affecting the Performance of Primary Treatment in Decentralized Wastewater Systems
- Guidance for Evaluation of Potential Groundwater Mounding Associated with Cluster and High-Density Wastewater Soil Absorption System
- Organic Wastewater Compounds, Pharmaceuticals, and Coliphage in Groundwater Receiving Discharge From Onsite Wastewater Treatment Systems Near La Pine, Oregon: Occurrence and Implications for Transport
- Micro-Scale Evaluation of Phosphorus Management: Alternative Wastewater Systems Evaluation
- Performance of Engineered Treatment Units and Their Effects on Biozone Formation in Soil and System Purification Efficiency
- Decentralized Wastewater System Reliability Analysis Handbook