by Bill Nestor

Design and construction of sewer systems can include environmentally-safe innovations.

Most homeowners would choose to live within neighborhoods that provide unique streetscapes, people-oriented walkways and interesting architecture. Instead, many developments offer little privacy, green space or landscape sculpting. Rick Harrison, the author of Prefurbia: Reinventing the Suburbs from Disdainable to Sustainable, and his team have spent 30 years designing more than 700 innovative neighborhoods in 46 states and 14 countries. More communities across the U.S. are becoming aware of Rick Harrison's vision and expertise and are actively taking part in planning committees and discussions about Prefurbia. Prefurbia incorporates Harrison's green neighborhood design thoughts, innovative ideas, techniques and methods.  

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A sanitary and storm water sewer system with homes that include basements

“Prefurbia is a balance of design elements that address economic, environmental and existence—the human desire for self-worth, and space. [These are] the three Es of sustainability,” states Rick Harrison, president of Rick Harrison Site Design Studio, a planning firm, and Neighborhood Innovations, LLC, a technology and educational firm. “It's about designing every home location to enhance the quality of life through new design methods made possible by the advanced technology in today's digital age.” 

Harrison's suggestions, initiatives and experience have specific relevance to pump system professionals and the design and construction of sewage systems. 

 

Sustainability and Sanitary Sewers

 

Sanitation is one of the world's largest problems, especially as populations grow faster than economies. A popular method to remove of human waste has been gravity through sewer pipes. Pump and system professionals can create the most economical and efficient design by understanding gravity systems.

Sewer pipe is expensive, anything that can be done to lessen the sewer length while designing a neighborhood municipal system will be a savings, but a lot more makes up sanitary sewer construction costs than the pipe installed. The type of soils on the site (sand, clay, rock), the depth of these substrates and slope of the land further influence the cost.

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Low-pressure sewer system with grinder pumps at each home

Conventional sanitary sewers are most often placed on an exact slope and in a straight line. To make a bend or change in di-rection, they will typically use a manhole. Manholes are expensive, and to access the sewer line underground, it is most practical if the pipe is perfectly straight between two manholes. 

Storm sewer systems and conventional sanitary sewers share some components. Both require manholes and pipes. Both use gravity, but storm sewers are designed to flow quickly to make sure that the development does not flood. Storm sewer design is also unpredictable with unknown volumes of water, so they are typically over-engineered. 

Sanitary (gravity flow) systems are much different. The volume of sewage going through the pipe can be more accurately es-timated, and the sewage must flow at a steady but slow rate. Sewage can contain material that can be abrasive causing premature wear if allowed to rush through the system. The regulations for sanitary sewers restrict the pipes to a fairly low slope, as a steep slope would cause it to flow too fast.

It is more cost-effective to create a sustainable design around the physical limitations of the land during the planning stage than to make changes that cut into profits or cause undue increases to homebuyers' costs later. In some situations, the depth of the sewer may need to be lower than the destination elevation or the land may be blocked by a hill. To get the sewage elevated to a higher point so it can continue a downhill path, a costly lift station, essentially a sewage elevator, may be required. They need to be extremely reliable and also have an energy source. Plans and designs featuring gravity that reduces or eliminates lifting sewage dramatically lower costs.

Homes are connected to the sewer system by a lateral, which is typically a smaller (around A 4-inch diameter) and lower-cost pipe connecting directly to the main sewer pipe using a tee connection or directly into a nearby manhole. The deeper the pipe, the more complex and expensive the entire system becomes. If the homes are slab on grade, the system should not require excessive depths.

If basements are introduced, the entire system becomes about 10 feet deeper and the cost to construct the sewers rises, par-ticularly for areas in which tough soil conditions and/or rock needs blasting for construction. 

It gets even more expensive if large storm sewer pipes each with manholes and inlets need to be constructed. Pump and system professionals serve as valuable resources in keeping down costs by paying attention to details and components proposed in the planning stage to create feasible and affordable sewer system designs that follow nature's patterns of surface flow.

 

Low-Pressure Sewers

 

A pressurized sewer can be a viable option, especially when difficult soils, slopes and/or a plan introduce a lot of interesting geometry. Pressurized systems need no manholes or lift stations. The pipe can be shallow and can bend easily. 

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