less stringent treatment standards compared to reuse or point source discharge. This may reduce the cost, size, and complexity of the treat - ment plant if soil-based dispersal is specified. 4. Understand Site Conditions The final step in the site analysis is to understand the specific site conditions. Common site conditions under consideration in the design process are site layout, soil conditions, elevation, temperature, power availability, noise, and odor. • Site layout – Site layout will help the design engineer determine the treatment and discharge options available. Sites with limited space for soil dispersal may be forced to discharge to a point source which may lead to tighter effluent requirements. • Soil conditions – Soil type, percolation rate, and depth to restrictive layers, help the engineer determine the options for soil dispersal or even soil treatment. • Elevation – Elevation is a parameter that is used in the aeration design of an aerobic treatment system. Higher elevations have lower oxygen concentrations compared to sea level which requires additional air to be introduced to the system to meet the oxygen requirement for the system. • Temperature – Wastewater temperature is factored into the design, es - pecially in colder climates. Colder temperatures lead to slower biologi - cal reaction rates, which may lead to increased treatment system size. • Power Availability – The voltage, phase, and frequency available at the site is required to select the equipment, which includes pumps, blowers, mixers, etc. • Noise – Noise may be a concern with larger treatment plant equip - ment like blowers. Understanding the facility type and potential noise concerns will help the engineer design a system that reduces these is- sues. Site placement of the treatment plant and equipment away from people is a simple solution. Sound attenuating structures or structures that redirect noise are commonly used as well. Another option is the use of silencers on blowers. • Odor – Like noise, odor control should be a step in the design process to ensure that odors are appropriately handled. Carbon vent filters or mulch beds are two examples of cost-effective solutions to reduce odor concerns. Since every onsite project is different, the site conditions will change and must be addressed on a case-by-case basis.
Conclusion The challenge presented with onsite wastewater treatment plant design is the variation between projects. Following the four basic steps listed above is a useful tool for design engineers to gather the crucial site- specific information for their project. The key to a properly designed treatment plant is to understand and determine the input and output parameters. Before the engineer can jump into the process design, they must first perform a thorough site analysis. Flow rate determination is the first step that will ensure an appropriately sized system. Accurate design values for influent characteristics will ensure the treatment plant is sized appropriately. Assessing the different discharge methods will lead to the effluent treatment criteria of the project, which then drives the treatment process selection. Finally, an understanding of the unique site conditions will improve the overall design and efficiency of the system. After these steps are completed, the design engineer should have sufficient information for the accurate design of the treatment plant. This upfront analysis will lead to an efficiently designed treat - ment plant that is catered to meet the needs of the project. CHRIS STRYCHARZ, P.E. joined Infiltrator Water Technologies in 2015 after gradu - ating from the University of Connecticut with a BS in Civil and Environmental Engineering. Starting his career as a Project Engineer, Chris worked in the Technical Services Department and contributed to the R&D of new products. In 2019, Chris took on a new role as the Western Region Engineered Systems Consultant, where he was responsible for providing sales and technical assistance for commercial and decentralized onsite wastewater systems. As of 2022, Chris began a new role as a Wastewater Engineer assisting in the design of onsite wastewater treatment facilities. Chris is a registered PE in the State of Connecticut and recently received his Master of Engineering degree from the University of Connecticut.
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