Low Pressure Sewer Main

[H2OEngnr]

I'm designing an access road for a 10-acre lot in an area served by a low pressure sewer system. A 6" pressure sewer runs parallel to the state road that I am pulling my access road from and the owner would like to install a branch main in the access road to accomodate the future development of the parcel. The lot has a base density of 1-unit/per acre and a max of 5-units/acre with one unit having a flow projection of 250-gpd. Aside from pipe material specifications the only information the county can supply is that all grinders attached to the system must be either Myers or Barnes Simplex or Duplex grinder pumps. They can not or will not tell me the pressure in the main at the point of interconnection. It is the intent of the developer for each lot owner to have ther own private grinder pump (inferring a minimum of 10 individual pumps). Any suggestions where I should go from here?

 

[francesca]

Model their system and calculate the pressure at the point of interest.

 

[bimr]

There are several methods available for low pressure sewer systems. Grinder Pump Systems and Step Systems are the most common.

You are going to have to find out what the operating pressure is in the force main. If the operating pressure is less than say 60 psi, then you will be able to pump directly into the force main from the project using the standard lps system components. If the pressure in the force main is higher than that, you are going to have to do more design work.

Grinder pump manufacturers like e/one use a progressive cavity pump high head low flow pump. The pumps are rated for 60 psi operation.

http://www.eone.com/downloads/products/lps_design_manual.pdf

Step systems consist of a filtered effluent pump (Orenco) within a wetwell. This type of system settles solids on site in a septic tank and pumps gray water (effluent) through small collection pipes to further wastewater treatment. Orenco step system also uses high head pumps.

http://www.orenco.com/ccs/ccs_caseStudy.asp