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Question DetailsAsked on 12/5/2017

Conflicting opinions on Presby Enviro Septic inspection...

Inspector states leach field is in “fair condition” due to gray discoloration of sand 1/2 up pipe and retaining effluent 1/4 up the pipe

The installer of this system explained that: gray sand is due effluent washing over and something about iron? And that finding effluent/water in the first drain tube of the Presby system is NORMAL. He also told me that once the first pipe fails, the remaining pipes continue to work

Inspector only dug up the first drain pipe of the Presby system.

Anyone with experience with this type of septic who can offer their advice/understanding would be greatly appreciated!

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3 Answers

0
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From what I see on their website, the Presby Enviro System is just a typical perforated pipe septic leach field with a fancy name appealing to greenies - and I can't say I like the design because the exit holes are awfully small (so prone to grease blockage, which is actually something they tout, which is not a good thing), and it is designed to trap the filtered grease and solids inside or in filter fabrics right outside the pipe, whereas a normal properly designed septic system leach field uses a properly graded fill extending typically 6-12 inches all around the pipe to filter and biologically treat that material over a much larger capture/contact volume before the leachate goes into the native soil.


As to the gray sand - it is gray because it is in an anaerobic environment and also because it has a fair amount of partly biodegraded toilet paper and grease in it. It is oxygen deficient most of the time when field is wet and not dried out from lack of use - so does not turn yellow or orange like if exposed to oxygen - and that is its normal appearance. Does turn "rusty" orange or reddish if it dries out - like in only seasonally used cabins and such, but drying out is actually bad for the field because it promotes iron and manganese-eating bacterial growth (the rusty orange material that clogs water pipes in hard water areas) and promotes hardening and matting of the bacterial mass, which reduces the necessary water exfiltration. The healthiest leach field is usually one with a constant and steady water usage well within its design capacity coming into it, not saturated from rain or high groundwater, and with a low grease and chemical content in the source sewage.


Regarding the "fair" classification - except for very new or basically unused leach fields, an inspector is not going to rate it "excellent", so 'fair" indicates it passed inspection and is working acceptably. Different states have different designations for inspections, but generally "excellent" or "good" would be a newer or rehabbed field, "fair" would be normal, "poor" or "marginal" would mean it is nearing its functional life (so needs rehabbing or replacement) or has operational or layout problems, "unsatisfactory" or "defective" would be a fail. A "poor" or "marginal" rating may, if your area requires inspections reports be filed with the govenrment environmental or water quality agency, result in a requirement for more frequent inspection until it is eventually failed and has to be replaced or rehabbed.


The sand 1/2 up pipe - if you mean the sand is filling the pipe half way then three normal causes for that:

1) leachate pipe is broken and letting soil in


2) the filter fabric was not put around the pipe properly so the backfill is filtering into the pipe - which reduces its effectviveness by blocking off half the exit holes.


3) If the sand is grit coming into the system from the tank with the effluent as he indicated (meaning the sand depth would be more in the manifold and inlet ends of the pipes that further down the pipes), that does happen to a limited extent with grit and solids carried in suspension past the septic tank, but if a significant infilling in manifold and into the leach field drain pipes then the tank baffles are not working right or the tank is being allowed to overfill with solids (not being pumped often enough), so they are migrating out of the tank into the leach field - not something you want as it fills the pipes with sludge and grit and shortens the life and reduces the leaching capacity fo the field.


He should have checked what the composition of this grit is - if basically silt size, then pretty normal. If sand size then something is not stopping that coarser material from getting in there or it is getting in through the leach field pipe - presence in just one pipe would indicate probably the latter, if uniform in all then either the filter material around the pipes is too coarse for the soil around it, or your septic tank is letting too many solids through (in which case presumably the outlet end of the tank would be overly full of solids, up to the outlet assembly).


Hopefully the report gave some guidance on pumping out frequency - can sometimes (especially with larger - 500-1000 gallon say - tanks), for a couple living in an area with decent soil drainage might go 5-10 years between pumpings of the tank, sometimes a single elderly person (very low sewage/water passing into system) can go as much as 10-20 years between pumpings, or almost indefinitely even if the tank is almost full because the excess just starts filling the leach field pipes, which can hold quite a bit of solids if the water flow into the system is low.


In less permeable soil or with a less well built system, and with typical say 4 person family 3-5 years is more common pumping cycle, and for very large family or one with a lot of cooking producing a lot of grease, or using the garbage disposal for all waste food instead of just what cannot be scraped off into the trash, pumping is sometimes needed as often as one year or less. I have seen houses with multi-generational family occupancy of say 7-10 people who do a lot of deep frying or oil/grease cooking in woks or such with the grease going down the drain (as opposed to into tin cans to congeal and go out with the trash as you should) needing pumping every 4-6 months and shorten a typical 20-30 year leach field life to just 5 years or so before it plugs off.


The pipe being 1/4 full of leachate is normal to very good. A leach field should not run pipe-full except maybe if it is getting overloaded with water in very heavy rains or sometimes if it was improperly built so it freezes to the bottom of the field, 1/4-1/2 full would normally be considered properly graded and functioning correctly. How full the pipes are is also largely a function of when the last water came into the field and how much water - test it right after several large wash loads and it will normally be more full than first thing in the morning or at the end of an empty-house daytime period. And of course, if the leach field pipe has a distinct slope to them, then one end or the other will typically stand full much or most of the time, with the other end dry.


The comment by the installer is a common one - if the system is built right, with the inlet of all pipes off the manifold at the same elevation, then all the pipes should (in theory) take a roughly equal amount of the flow - one pipe should not plug up before the others. Granted, in low-flow or surge-flow systems (which most household systems are) in reality the pipes nearest the inlet to the manifold get more flow and certainly more solids until they start plugging off, then the others pick up the flow - which is why manifolds should be fed from the center or better yet at at two third-points from the tank, though a great percentage feed only from one end.


From the snapshot you give, and with the fair rating, I see nothing to worry about - check if the report indicated if the tank was overfull of solids so needed pumping or had damaged/missing baffles, and at next pumping out be sure those are inspected for being intact and in place. Below are a couple of graphics with typical tank cross-section showing what the bafles do and where they normally are located in the tank - sometimes they are heavy duty screen or much more commonly solid plastic/metal, sometimes concrete depending on tank construction. The much less effective type are like the first image, where they just use pipes to draw the effluent off below the outlet scum level, but do not have a solid bottom baffle (typically about 2/3 of the way to the outlet end) to keep most of the settleable material out of the second half of the tank so it does not make it to the leach field.


http://www.aoseptic.com/septicacademy...


http://www.co.thurston.wa.us/health/e...


Answered 11 months ago by LCD

0
Votes

thanks for the input! To clarify, the sand being “gray” and discolored was the inspectors reasoning for the fair rating and stated that it appeared the leach field was likely slowly down/halfway through its life. The system is only TWO years old. The septic tank is also only 2 years old, in great condition, and he recommended pumping that in 2 years from now.

Answered 11 months ago by Ashcarb87

0
Votes

Sounds like you are in great shape.


On the gray thing - unless you have odd water or soil chemistry or odd chemicals coming through from the house, the sludge in septic tanks that I have seen (in several states) has all been gray to blackish, so I wonder just how many jobs he has been on. His color "rule of thumb" might be an urban legend sort of thing. When I was doing septic system design and evaluations as a state licensed designer and inspector and testing arbitrator, I think that was the area in construction (along with foundation failures) where there were the most urban legends and invalid rules of thumb and such. Some were pretty useful for ballparking designs, some based on some fact or science but might not have been quite true, and some were just out in left field and flat out wrong from an engineering or scientific point of view, so the color thing might be coming from there.


On the "sand" or grit issue - because the width of the pipe increases rapidly as you move up from bottom toward top, for an assumed relatively constant amount of sludge-forming (grit, paper fibers, grease, hair, anything else suspended in the flow from the tank), initially it will fill the bottom of the pipes pretty quickly, then slower and slower till it reches the half-full point. From there on not only is it going to fill in more pipe height each year because of the decreasing width as you fill the top half of the pipe, but you are alos blocking more and more of the perforations or holes in the pipe so less and less goes into the surrounding soil, and the biologic processing of the sludge is reduced more and more. Therefore, once the pipes are about half full of sludge it is assumed the field will start failing to do its job pretty soon so that is commonly cuase for a "poor" or "marginal" rating, and about time to either jet the pipes out to clear out the sludge and grease and such, or totally rehab or replace the field, depending on whether it is still taking the water well, whether you have a suitable nearby spot for a new leach field, etc.

Answered 11 months ago by LCD




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