Large On-Site Septic Design Guides For Systems With 10,000+ GPD Daily Wastewater Flow

[deactivated]

Our company recently got a request to design a very large on-site septic system that will handle a wastewater flow that is about 10,000 gpd. The soil scientist is currently modeling K-sat values for us. The water table in this area will be high. Our company has only designed a large system such as this once and it was over 15 years ago and the engineer involved is no longer with the company so I am trying to learn as much as possible about large septic system designs before I start working on this project next year.

I know that I need to do mounding analysis and I have already acquired free software that I can use at work. I have only designed small septic systems that handle a daily wastewater flow of 360 gpd to 480 gpd and those were based on county recommendations from the health department. What I'm looking for is some design guides and/or good examples online that I could research and follow along as I am designing my system. I am particularly looking for guides dealing with very shallow water tables. We have plenty of area for our septic system but since the seasonal high water table is expected to be high, I have some concerns about designing a safe system. If anyone knows of great design guides for large on-site septic systems, please let me know.

Thanks

 

[dik]

With the effluent outflow, you may be looking at some sort of proprietary 'raised bed' type of construction due to the high water table. What type of system are you looking at and where are you roughly located? For flows of that magnitude, the work may have to be reviewed/approved by a State environmental agency and not local. If memory serves, in Ontario, anything larger than 10,000 l/day required MOE involvement and not the local jurisdiction.

Dik

 

[bimr]

http://www.eng-tips.com/viewthread.cfm?qid=158023

http://www.eng-tips.com/viewthread.cfm?qid=372733

http://www.eng-tips.com/viewthread.cfm?qid=294920

http://www.eng-tips.com/viewthread.cfm?qid=202178

http://www.eng-tips.com/viewthread.cfm?qid=166229

 

[darthsoilsguy2]

In Vermont and likely in your jurisdiction, such a system would require a hydrologist perform a hydrogeological study on the site. perhaps that is the soil scientist you're referring to. if your jurisdiction requires such and you pick a good one, they will be the best resource for you since they will have been involved in many projects of similar flow. Also in Vermont but perhaps less likely in your jurisdiction.... such a system would require an indirect discharge permit which would trigger environmental impact studies on downgradient streams (i think the trigger is around 6500 GPD here). You definitely should check out the jurisdictional permitting requirements if you haven't already and look for red flags. A stream study can add a whole year to the project schedule if the project greenlight occurs after the observation window has passed. Apologies for such a regional-specific post, wastewater design is very jurisdictionally driven.

 

[EdStainless]

There has been a lot of work out of U of Minn on septic systems, including very large systems. Check with them.

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P.E. Metallurgy, Plymouth Tube

 

[Ron]

With a 10,000 gpd flow, I would look toward a small package treatment plant. There are extended aeration plants in this size that require little maintenance and you don't have to worry about a drain field. In fact, the effluent could be used as irrigation for the green space on the site.

 

[tkall]

You don't mention anything about treatment requirements so it is not clear whether or not a treatment system is required. When you say the soil scientist is "modeling" saturated hydraulic conductivity values, do you mean you are trying to determine an application rate based on a computer model? If so, bad idea. For the daily flow you indicate I suggest at least one basin flooding test to determine the long term clear water acceptance rate of the soil. Also, in all the time I have done this work I have found groundwater mounding analysis to be useless. The key in drainfield design is the method of wastewater application to the soil. A system this size needs to be pressure dosed to achieve uniform distribution and to maintain unsaturated soil conditions. I will mention my software which is available at not cost to you on the web. It is called Squirt and it was written specifically to aid in the design of large pressure dosed systems. find it at

http://www.squirtonsite.com

 

[nackra]

I used references from Small Flows for design of on-site systems:

http://www.nesc.wvu.edu/wastewater.cfm