Septic System

jbos333 · May 11, 2008, 09:15:20 AM

Hi, all. I was wondering if anyone out there knows the maximum distance away from the house that the septic tank can go and still work properly. I am in the process of planning a spot on my land for a permanent house, but I am still kinda up in the air on it. Meanwhile, I can get a good deal on a 3 bdrm. septic now, and tie it in to my existing pole building for a toilet/shower, etc. But of course it won't be a good deal if I have to do it twice!

glenn kangiser · May 11, 2008, 09:48:26 AM

Depends ...on a lot of factors. Putting the system deeper will allow more distance.

1/4 inch per foot grade from the inlet of the septic up to the house without popping out of the ground is normal. Materials approved for use withing walls are approved to and above the surface of the ground also (Sch. 40 ABS- cast iron - maybe other materials). Also seems the inspectors prefer 12" cover, but I found the above wall approved materials were approved by the code during a fight with an inspector - I won at that time.

In some situations they allow a bit less slope w/ 1/8" being a minimum with special approval.

The above is from what I learned about 30 years ago. Scott should know if that is still correct.

May 11, 2008, 10:11:13 AM

I'm not aware of a maximum distance. Codes are different in every area so you'll need to see what your locals say. So long as you have fall I'd say you could go as far as you want. But, pipe is not cheap anymore so you'll want to stay as close as you can. Also until it gets to the tank it's a sewer so it will need to be tested the same as the house. Cleanouts are required every 100'.

Redoverfarm · May 11, 2008, 05:21:42 PM

Probably should contact the local regulatory agency as it varies from state to state. WV the tank has to be 25' from the house and the field has to be 100 feet from a well. This is depending on the amount of land. Less than two acres there has to be a additional 10,000 sq ft set aside suitable for additional system should the first fail. All flat perkble land wouldn't be a problem but in the mountains withthe steep elevation. Here the Health Dept is the agency. Three bedroom has to have 180' feet of drain field.

Daddymem · May 12, 2008, 08:12:41 AM

Talk to the locals to see if they have regulations covering that. As far as engineering is concerned, no distance is theoretically too far. I would however, suggest steeper pipe slopes the further you go so enough energy is there to keep paper goods traveling down the pipe all the way to the tank. We generally design for 2 feet per second velocity in full pipes which generally will scour sediments and move the paper goods along (look up Manning's equation if you really want to). Normal practice is 1/4" per foot (2%) but if I have to go down to 1/8" per foot (1%) I do. If I was going far away I'd hold the 2% as a minimum and if I could add some steep sections in between (use a couple 45 angles) I would to get the stuff moving fast again.

May 12, 2008, 10:02:19 AM

Good info Daddymem. Thanks.

Does the 1/4 inch give the 2 feet per second? or are you going to make me figure out the equation (like I could) ? hmm

Daddymem · May 12, 2008, 11:50:41 AM

The 2 fps actually calculates out to roughly half a percent slope for 4" pvc. But since that is for pipes flowing full, we bump it up and use 1/4" per foot where possible and set the lower limit at 1/8" per foot to put us above the 2fps when those pipes aren't running full. We could sit there and calculate the actual velocity for a given flow and slope and pipe diameter etc etc etc but much easier to hold fast on 1/4" and 1/8" used sparingly. It also depends on the use. A single family home with a slug down the pipes every once in a while versus a gravity line tied to a number of homes that can get several slugs in a row. I have put in 8" lines at much lower slopes because I knew there would be scour from many slugs coming down the pipe.

I believe around here the numbers come from ~~mafia~~ plumbers code where smaller pipes than the 4" for residential and 8" for commercial we'd see outside the building around here. I think it just carried over to our rule of thumb book.

glenn kangiser · May 12, 2008, 11:51:43 AM

Thanks, Daddymem.

jbos333 · May 12, 2008, 04:31:43 PM

Thanks everyone for the input. I shouldn't have any problem with too little pitch; I have at least a 25-30 ft elevation change between where I would like to put the house and where the septic can be used now for my utility building. That is over a distance of about 400 ft. Of course, I might rethink the location of the house later due to 400 ft+ of extra road, pipe, electric etc. and just put it close to where my current road ends, near my existing building/electric etc. But what fun would that be?

May 12, 2008, 05:45:21 PM

With steep slopes you want to be absolutely sure you have an inlet tee in the tank. The purposed of the tank is to settle out solids, don't want splashing around to disturb the quiescent upper and lower zones in the tank.

StinkerBell · May 12, 2008, 09:21:34 PM

We just put our septic tank and field in last summer. We are getting ready to put our building/home up on our property. The one think NetHog (hubby) has gone on about, is that the building can not (should not) be more then 5 feet away. I do believe that has to do with code.
But out tank to the dbox to the field is a different matter.

davidj · May 12, 2008, 10:09:31 PM

Is it normal to use 3" or 4" for the section from the house to the tank? It'll just be 30' or so and only one bathroom.

glenn kangiser · May 12, 2008, 11:14:55 PM

I may be wrong, Stink, but I thought 5' was a minimum distance to the tank with more being OK.

This one shows 10 feet minimum to the tank - more is ok http://www.inspect-ny.com/septic/A75Fig2.jpg

Quote from another place:
How far can septic tank be from house?

Answer

You will need to check your local codes, but here in Indiana it is a ten feet minmum.

This one shows 5 feet minimum from a building -- more is OK http://extension.missouri.edu/xplor/envqual/eq0401.htm

glenn kangiser · May 12, 2008, 11:16:32 PM

Quote from: davidj on May 12, 2008, 10:09:31 PM
Is it normal to use 3" or 4" for the section from the house to the tank? It'll just be 30' or so and only one bathroom.

I'm sure that a small place like that would only require 3" based on fixture units for sizing -- going from memory though.

May 13, 2008, 08:12:50 AM

Around here it is 10' for tanks. That is based on the ~~mafia~~ plumber's union who set up the code. You would have to pay a plumber to install the tank within 10 feet of any building if it wasn't in the State Sanitary Code anyways.

3" should suffice, but if you have any inclination at all for expansion of flows a 4" would be a good choice for minimal cost increase. A 3" pipe gives you 7 square inches of available flow area, a 4" pipe gives you 12.5 square inches of available flow area or over 1-3/4 times the area of a 3" plus you will gain the extra air flow venting the septic tank through the house.

Hey, that brings up another issue. Make sure you have a positive (negative?) slope down to that remote tank to allow it to vent back through the house (no low spots), if not put a vent on the tank itself.

glenn kangiser · May 13, 2008, 08:29:56 AM

Good idea. I may add one to my tank as our place is a bit spread out and I somehow sometimes manage to send a full load down the line.

Thanks, Oh great sewer engineer.

ScottA · May 13, 2008, 01:54:29 PM

Check your codes. In some areas 4" is required outside the structure. I'd also recomend 4" since it's alot harder to stop it up and easier to clear if it does.

Okie_Bob · May 15, 2008, 07:38:30 AM

Hey, you guys managed to totally confuse me on this. I always thought that the 1/4" per foot rule was not to be exceeded either way?
In other words, you should not exceed 1/4" drop per foot or make it less than 1/4" per foot?

Reason being that if your line was too steep (greater than 1/4" per foot), the liquids would run too fast leaving the solids behind with nothing to wash them on down the line.
Less drop than 1/4" per foot and you didn't get enough velocity and the solids would not move down the line.
From what I read above, this is apparently not true? Help me out here.
Also, why would anyone run 3" pvc when 4" is literally only a few cents per foot more costly?
Okie Bob

ScottA · May 15, 2008, 08:10:29 AM

I've heard that too Bob. Way it was explained to me was that rule applied to old clay and cast iron pipe that was not as smooth on the inside. PVC is very slick on the inside. My rule of thumb is 1/8" per foot inside the house. 1/8" -1/4" per foot outside but don't have an issue going steeper if needed.

Redoverfarm · May 15, 2008, 04:40:41 PM

I personally would never run anything less than a 4" Sch 40 pipe. I think it is alright to increase the drop if it is before the tank. Common if the tank is considerable feet/inches from the primary 1/4"-1' line. No way the solids would not slide. That's just MO but some say I am FOS. But I have never had a problem with 1/4"-1' or maybe just a tad more but it's easier to use this ratio when figuring the drop.

May 15, 2008, 07:42:07 PM

I like the 1/4 per foot normal with the 45 degree drops as Daddymem recommended on long runs if necessary for bigger drops. It is easy to do that way.

Okie_Bob · May 16, 2008, 07:54:18 AM

Thanks Scott. Never thought of clay or cast iron...personally prefer 4" sched 40 pvc also.
BTW, where in Okla? I was from Yukon area, lived in Tulsa, Norman and Okie City before moving to TX
Okie Bob

ScottA · May 16, 2008, 09:15:32 AM

Bob we are about 50 miles east of Tulsa. I've lived in Texas as well. Plano and Dallas.

Daddymem · May 16, 2008, 12:49:17 PM

The slope confusion happens when you compare septic system design vs sewer system design. The principles are the same, it is the use that changes how they work. In municipal system design you would be concerned with too steep slopes that would allow the liquids to outrun the solids and end up with buildup in your pipes, but that is because you typically have long runs of 300' between manholes. In septic systems you are usually close enough to the end point that steep slopes don't matter as much, the kinetic energy from the flush is enough to keep the solids going the short distance. My rules of thumb used is shoot for 1/4" per foot if possible, under no circumstances go below 1/8" per foot, and start being concerned in the 5-6% slope. (we actually do all these in % slopes typically, the plumbers use the x"/foot). But as always, the circumstances can change the actual design.