Chambered/domed system in leach field?

Anyone here with experience with the plastic domes that bury in place of perforated pipes with gravel or shredded tires? I have a situation where I will need a large surge capacity and thought that was a good way to get it instead of installing a LOT more pipe in a LOT more feet of trench.

I will be installing two septic tanks. One will be a standard gravity flow system and the other will have a demand pump on the last chamber to pump the water uphill to where the gravity tank outputs to the input of the leach field.

I have been advised that the lower and upper pump settings should be set as far apart as is practical to minimize the number of times the pump cycles. The one septic guy I discussed the installatlion with disagreed with me on this point: Since in "normal" use the output chamber overflows to the leach filed in a per flush or per bath or per laundry load manner there is not a huge volume all at once AND the output chamber stays full to the overflow point all the time. When pumping the output up hill with maximized volume per cycle you pump the output tank way down each time. I thought there should be an extra chamber or another tank that would receive the normal output and store it for "batch" pumpouts. The septic tank would then work just like in a "normal" gravity setup. This would still leave the problem of handling the surges during pumpout which is why I was considering the domed plastic chambers, for their surge capacity.

Thoughts?

Pat

Pat,

I think you are asking about "infiltrator". This is a ventilated plastic dome shaped piece that looks like a coffin lid with louvers all over it. The pieces are snapped together and are used to replace a conventional drain/leach field.

We've got a 90 foot long run of it that has been installed for 2 years (full time use for 1 year). It seems like it would be difficult to use as a holding tank since it is designed to be self draining. Sort of like putting one leach field in front of another.


Steve

Steve, I sometimes am less than clear. I want the "Infiltrator" type leach field for its great surge capacity so that when the holding tank (between septic tank and leach filed) pumps out it won't overwhelm the leach field. The final stage of the septic system would gravity flow to the holding tank. I will be pumping the contents of the holding tank uphill to the leach field.

I was concerned that a "standard" leach fiield would not work well with a "batch" system as they typically get supplied one shower, flush, or load of washing at a time not 500 gallons every few days.

Pat

What does your county health department say about Infiltrator fields? Are they approvable? Do they have any good or bad experience they can relay to you? Call them from a friend's cell phone, if you are worried about drawing their curiosity, [img]/forums/images/icons/wink.gif[/img] but they may have some knowledge to impart.

Get a copy of your state or county septic tank ordinance and/or design manual if they have one. Usually a lot of good design information in there, and no rocket science.

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I was concerned that a "standard" leach fiield would not work well with a "batch" system

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The Pennsylvania septic tank code has some good information about design of pumped/batched septic systems. I don't recall if it is available on line, but you can call them and they will send you a copy.

Typically, batched systems use two leach fields with a dosing valve or siphon to alternate between the two fields. The PA pressure system design put the holes on top of the drain pipes. They used custom hole sizing and spacing, with the holes hand drilled in the pipe to get the required discharge rates. I seem to rember using something like eight 3/8 inch holes per pipe leg. The pipes were sloped to drain back down to the wet well after the pumps shut off, so that solids wouldn't collect.

The concept of this whole thing was that the volume of the pipe was small compared to the volume of pumped effluent, so the pipes more or less filled up at once and all the orifices discharged at once. This was supposed to prevent overloading the near end of the field.

The piped system used the drainfield gravel to hold the surge volume. The volume of air space in the rock is pretty substantial. The biggest advantage to the Infiltrator, IMO, is that it saves on rock.

With an occasional use system, I'd feel safe eliminating the double tile field and dosing siphon, as the drain field can dry out between dosings. Your health department may feel otherwise.

Currmudgeon, A good question. A couple years ago when I was looking into all of this the DEQ (Department of Environmental Quality) allowed them and If I recall correctly there was consideration for allowing fewer linear feet of leach lines but I don't think that is "good" for all areas. Lots of changes in approval system. Now instead of perk tests they do site soil evaluations. I am grandfathered because I had a PE perk my site and got it registered with DEQ before changes due to inside info of impending change. He is a civil eng specializing in waste water treatment projects usually much much larger that a residential system but the young lad moonlights for "fishing" money.

The infiltrator's surge capacity is way ahead of gravel since the gravel system only has its interstecies for temp storage unlike the infiltrators unencumbered volume.

Pat

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He is a civil eng specializing in waste water treatment projects usually much much larger that a residential system but the young lad moonlights for "fishing" money.

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Sounds like an old f(r)iend of mine. Septic tanks built his garage.

Currmudgeon, Wow, what a fantastic undertaking. In a Disney movie, "Fantasia", I saw a broom fetch water but to have septic tanks, even working in groups, build a garage is really something my fiend, err ahh friend!

As you can see, I won't be raking in any extra coin as a comedian.

Pat (declining to make any "gas" puns... too obvious)