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WASTEWATER TREATMENT BASICS
WINTERIZE A BUILDING
Building an ice rink over the septic field: this article explains the problems that may occur during & after constructing an ice rink or similar structure atop a septic leach field or soakaway bed. Some interesting arguments in support of temporary covers over a drainfield are presented by an ice rink supply company. This article discusses the effects of a plastic cover (such as a ice rink, tarps, tents) on the evaporation and transpiration functions of a conventional or aerobic drainfield.
The article emphasizes that even if the cover is to be just temporary and during frozen-ground conditions, you should not drive construction equipment, or other heavy machinery over the septic drainfield in the course of building, grading or leveling soil or similar site work for any purpose except during original construction of the drainfield. Our page to photo shows a temporary-structure type ice rink of the type that some readers want to construct atop a septic field or soakaway bed.
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It might be possible to place an ice rink atop a septic drainfield area without the rink cover and components or skaters themselves damaging the drainfield. And at least one ice rink expert weighs in pointing out that by keeping rain and snow off of the drainfield the septic field performance might be helped even though evaporation and transpiration are temporarily stopped.
[Click to enlarge any image]
Photo at above left: a NiceRink™ ice skating rink installed in a level area, photo used with permission. [Click to enlarge any image]
But as we warn in the discussion below, if the process of building the ice rink includes driving equipment over the ice rink area or drainfield there is a risk of costly damage to the septic system.
Generalizing the Reasons to Keep Equipment, Grazing Animals, Paving, Coverings and What Have-You Off of Septic Drainfields
Reader Question: I would like to put a skating rink in my yard over the septic field (mid-Dec. to mid-March, i.e. northern Illinois) because it is the flattest part of my yard. I read everywhere on the internet and your site that one shouldn't put "anything" on top of a drainage field, at least the channels where the pipes ("tiles") are buried.
Photos provided by NiceRink www.NiceRink.com and are used with permission.
My question is exactly how a skating rink can damage field. Has research been done on this specific situation? Is the problem of a skating rink perceived or real? I haven't read of a failure due to a skating rink, though skating rink are relatively rare. I thought about the various issues: weight and permeability. Are there others?
For weight, the additional water (ice) weight is equivalent to, say, 2"-4" extra inches of dirt. Is this considered too much? In more northerly climates that are habitable, there are equivalent thick layers of snow and ice lying on fields for two or three months.
There is a liner over the field; does a liner prevent air exchange over this 3 month period? Note that there is effectively no precipitation during three months (so no clogging of interstitial space), as the liner captures all the snow and rain.
You probably noticed a thread of rationalizing. If I'm wrong about the above is there any way to mitigate the effects? Can you point me to other resources? Can I monitor the underground in some way? I'm handy with electronics and sensors in general. If it helps answering the questions, the lot has at least 2 feet of permeable dirt over clay, and the lot handles consecutive days of heavy rainfalls well.
My county health dept. will probably put the worse light on my plans for liability (theirs) reasons. So I wanted an unbiased opinion.
Reply: worries arise if building a skating rink atop a septic drainfield
Regarding your assertion and question
Of course not. The number of possible SNAFUs humans can come up with is near infinite. We are not likely to find a study of skating rinks over septic drainfields because of their rarity. And some reasons for their rarity may be founded in common sense: the various objections to placing anything over a drainfield or soakaway bed can be generalized so that a requirement that experts explicitly address everything imaginable that one could place and should not place in that location is, with respect, well I'll leave out the adjective.
The reasons to stay off of a drainfield in just about all regards are outlined at SEPTIC FIELD FAILURE CAUSES
I hope you'll read that article and invite you to ask me further questions if it is unclear or incomplete.
You'll see that the character of the activities that ruin a drainfield or leachfield are not innate in the invading item itself and not necessarily just weight - I agree with you that a couple of inches of water, as a weight source ought not to harm a drainfield any more than a foot of snow that later is wet by rain and then freezes would be expected to damage the field.
The damage for the sort of project you describe is more likely to be in the process of building something and in how it compacts the soil, interferes with transpiration and evaporation, or damages piping.
Consider my snowfall example. Each flake falls gently onto the ground, with an impact velocity and mass that is nothing short of trivial insofar as it might compact soil below. Subsequent rain that falls onto the area adds weight to the snow if it doesn't melt it, but again the soil compaction effects are nil.
Equipment to build something is a different matter however. For example, a backhoe, lawnmower, grazing cattle, machinery used to pave, or machinery used to grade and level for a skating rink all involve weight, movement, and soil compaction.
Beyond disturbing soil, compacting it, possibly crushing or breaking a pipe, construction of something over a drainfield also may result in the impervious layer concern.
Certainly placing a plastic skating rink liner over the ground completely stops any soil transpiration and evaporation when the soil is otherwise able to conduct those processes. And paving, ice, most dense plantings, or tarps, plastic sheeting's, beach blankets, bingo boards, or whathaveyou also, to the extent that they close off or seal a surface, interfere with seasonal evaporation and transpiration.
Now I'll agree with you that wet then frozen snow is about the same effect as water frozen to make a skating surface. And once frozen I'm doubtful that the Weight of a couple of people skating, the septic-field-skaters-club for example, is likely to be harmful. But how are we building the skating rink? How are we keeping water in it? How are we freezing the water? What are we doing to the normal growth of grass we'd like to have there during the baseball season?
You'll be gratified to know that a few people have written about the effects of urbanization or human activities on septic drainfields and related infrastructure systems and on the effects of wet soils and similar worries though I can't find anyone specifically addressing a plastic-lined skating rink.
Reader follow-up: pursuing a way to build something over the drainfield
I'm impressed with your dedication in replying in detail, and, of course, adding to the public's knowledge of septic fields. And thank you for your patience in addressing someone who really wants a skating rink in their backyard, and letting me reach conclusions on my own.
I'm replying and forgive me if I'm repeating some ideas of the original mail.
I realize that a full-time cover of the field, like paving, would be bad. So my question was really about the time limits of a temporary cover. Compared to a summer stormy period of a week, say, when there is no evaporation, three months of cover seems like a long time in comparison.
I had previously built my rink on a septic field on my other property with no problems visible on the surface. The unknown is the long term effects underground. (Can the decline of a field be measured in any way by sensors or probes?)
I noticed dampness on the ground everywhere under the liner when I took it off after three months; I wasn't sure if it was snow melt from 20' away or condensation from the evaporated waste water. The water just smelled like dirt. The dampness evaporated in a day (in March).
My chief concern was the transpiration aspect. Your web answer was that lack of evaporation may cause spreading of the dirty water outside the designated range. Is it possible to engineer a ventilation system under the liner (e.g. some large perforated half-pipe)? You can tell I really like that septic field location for a skating rink.
My skating rink is 40'x60', based 2'-high pressure-treated boards, some plastic brackets and a large liner (see for example nicerink.com -- you may remove this url) to keep the water in during thaws in Northern Illinois. No heavy equipment involved.
I have a front yard that can fit this 40'x60' rink but it has a grade of 2 1/2' over the footprint :(. So if all avenues are exhausted for the backyard scheme, then I have to level the front yard with grading machinery (next summer). Obviously I have to ask the County first. You may include any portion of this as you see fit.
Reply: possible approaches to skating over the drainfield
I very much appreciate polite healthy debate - which is how working together we're smarter than anyone (individual). When I first read your original email my reaction was the expected one - aw gee, just keep off the field and stop being ridiculous. But taking time to write detail also forces time for reflection. I understand that the project you want to undertake is one that indeed permits some argument pro and con.
If we ignore the question of reasonable costs for a moment, I'd agree that it is probably possible to design a septic wastewater treatment system that can be paved-over, by a combination of protection from compression damage of equipment used to build above along with a (in my opinion too costly) network of pipes and vent fans and monitors to handle transpiration/evaporation, or by making a design that supports the used-surface off of the ground entirely.
About evaporation/transpiration: the role it plays in conventional and aerobic septic systems for disposing of a portion of wastewater effluent is significant, but almost certainly varies significantly seasonally. As implied in our earlier conversation, when the ground surface is frozen or covered with snow and ice in a northern climate, surely there is no significant level of evaporation/transpiration going on. So that component of the wastewater treatment process must be seasonal.
While you might find only limited moisture under a plastic cover over a drainfield, such that it evaporates in 24 hours after being un-covered, that's the tip of the iceberg of the issue. When we seal a surface against evaporation of moisture from soil into air we are stopping the disposal of the entire quantity of moisture that would have moved up through soil and into the air over the time period for which the cover was in place.
That septic effluent quantity is certainly more than just the moisture found under the cover when it's opened. Why? Open soil with a relative humidity difference between soil top and air over the soil, acts as a pump moving moisture from ground to air. When we cover the ground we turn off the pump, so to speak.
So the total disposal loss during field cover-time is not measured by just moisture you see when the cover is removed. About the soil compression and drainfield damage problem, I argued previously that the construction phase, driving equipment over the drainfield, is what one must avoid completely to avoid damaging the drainfield. Equipment heavier than a conventional residential lawnmower risks soil compression and pipe damage - effects that may not be immediately visible but that have the results of not only contaminating the environment with inadequately treated septic effluent, but also shortening the functional drainfield life and thus incurring the significant cost of drainfield replacement earlier than otherwise.
How to measure this? One could make test excavations and actually measure soil compression and soil percolation rates before and after driving over a drainfield, but the thinking in such an approach is hard for me to understand unless we first, established that soil properties are uniform throughout the drainfield and second, tested the soil compression effects on a very small drainfield area so that we don't risk paying the high and early costs of having to completely replace a drainfield because of an experiment in damaging it.
That sort of experiment more fittingly belongs in the academic realm where someone obtains funding to test soil effects and percolation rates without jeopardizing an individual property owner's savings account. If nevertheless you intend to fund such research, try contacting experts (see next paragraph) to get help forming a valid experimental design. You might get somewhere by contacting a septic design engineer or one of the advanced wastewater treatment fellows like Anish Jantrania (search InspectApedia.com).
The advantage of using a local design engineer is that s/he may be known to the local approving BOH authorities and thus your design has a chance of approval.
Depending on the design cost to continue to use a conventional septic drainfield but to protect it from damage and permit it to function normally while temporarily covering it for any purpose, skating or otherwise), it may be less expensive to design an alternative, small-footprint wastewater treatment system that frees-up the space you want to use for non-wastewater-treatment purposes.
The question of why you want to skate over the septic fields (can we all it the scatological skating society?) has not been raised. I have to presume that you want a skating area and that there is no other space available that could be used without intruding on the septic field. I suspect that if one compared the total costs involved, using a different property area would be more appealing.
Advantages of & Suggestions for Placing an Ice Rink Over a Septic Field - NiceRinks™ over a Septic/Leeching Field
We asked for comment from Jim Stoller, President of NiceRinks™, a Genoa City Wisconsin company that provides outdoor ice rink supplies such as rink boards and ice rink liners. Mr. Stoller makes some interesting points that suggest that an ice rink liner over a septic field in winter may actually improve septic system performance.
Photo at left: a NiceRink™ ice skating rink installed in a level area, photo used with permission.
Watch out: while we agree with the points made in the comments below, readers should not forget that driving equipment over a drainfield, such as a backhoe or small dozer or even a large tractor used to level the surface is likely to cause costly damage. Keep equipment off of the septic fields.
Mr. Stoller generously replied as follows:
Tips for Avoiding Damage to A Soakaway Bed or Septic Field Caused by an Ice Rink
If you are going to test that advice anyway, here are some further considerations.
Although a temporary ground cover such as an ice rink liner over a septic field should not itself damage the field when used during frozen-ground conditions, to take the best care of the septic system the property owners/managers should keep these warnings in mind
Comparing Soil Loading of Dry Snow, Water, Wet Snow on Ground Surfaces such as Leachfields & Earth Loading Weights of Ice Resurfacing Machines & Snow Blowers
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