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Question DetailsAsked on 2/28/2017



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2 Answers


Presuming this is out in the boonies - no public sewer within a mile or so, because usually for this large a septic load building if there is public sanitary sewer within reasonable reach (commonly defined as about 1/2 to 1 mile) you will be required to hook up to that - which can be pricey if a long run or uphill so it requires a lift stations as well. However, certainly more trouble-free, and avoids the problem of having to rehabilitate/relocate the leach field every 10-25 years as the existing one reaches capacity.

It is also possible that a septic system will not be allowed, for zoning reasons or failure to pass percolation tests or because your site is in a natural drainage area, and that they will require primary or even a primary and secondary treatment system and possibly chlorination before the effluent is discharged to a leach field or spreading ground.

Also, this may very well rate as an LCSS - Large Capacity Septic System - under EPA regulation, so the regulatory requirements may be tougher than a normal septic system, including provisions for retention of any leakage or overflow in the event of a system failure so the efflulent/sewage cannot make it to public lands or drainages.

Your architect should be able to help you out with finding a designer and contractor and rough costing. Most likely, if this is new construction (as opposed to refurbishing an existing building for this use) your site Civil Engineer can also design and certify the septic system and give you a cost estimate, and provide recommendation on construction contractor if not done by the General Contractor for the job. Otherwise Septic Tank would be the Search the List category to find contractors to do the installation.

Bear in mind the location has to be selected, and in some areas pre-approved, based on soil stratigraphy and permeability testing using small borings and/or test pits - BEFORE construction starts. Also, the tank (usually) and leach field (always) has to be certain distance from property lines in most areas, and from other leach fields (commonly 50-100 feet away if level or uphill from other one) or wells (typically 100-200 feet in any direction) in all areas, so commonly once a rough location for the building is laid out, the septic system testing is done BEFORE finalizing the building locatiuon - because while the building can be moved around on the site, the septic system HAS to be installed in a suitable swoil and topographic condition.

And for this big a school - I would recommend allowing land with suitable soil/percolation test for at least a 100% oversizing of the field area to allow for expansion. For such large facilities, sometimes a second leach field is initially installed and blanked off so all that is needed is an hour or less plumbing to change from the existing to new field. Sometimes an entire duplicate system with tank and all is installed as a ready-to-use backup, which can also be used during system maintenance, because it is real hard to work on s leach field when there is sewage flowing in, but you also can't readily ask 180 boys to just "hold it" and the kitchen and laundry and such to shut down for a number of hours while work is done on the system.

Also, to prevent problems with the system, unless you have two parellel systems (the way I would design it), it is common to have an overflow septic tank with alarm (there are several types of alarm a large system like this should have BTW) to handle flow if the primary tank overfills or the outlet becomes clogged, because that many peopel in the building cause a MAJOR amount of sewage popping to the surface - or dramatic backup into the building - if the outlet capacity becomes blocked.

Also - generally for a commercial system like this you will have above-ground access to the tank (not buried hatches) because it will need more frequent pumping than a normal tank, and of course a much larger tank as well (or commonly a series of parallel smaller tanks).

You will also need a separate grease separator for the kitchen, and almost always also a separate solids holding tank/digester for the kitchen waste too, which will need more frequent pumping out than the septic tank (commonly every couple of months or less for that size unit) - otherwise the grease and biologic load will overwhelm and plug up your sanitary waste leach field in no time. IN ADDITION, it is VITAL that the kitchen not use a grinder or garbage disposal system to dispose of kitchen waste food - everything that can be scraped off into trashcans to go to the dumpster should be, because kitchen loading, especially of grease and vegetable matter, can kill the life of a septic system - I have seen brand new septic systems reach their effective life in only a year or two because the kitchen was using a garbage disposal/grinder as their routine means of kitchen waste disposal.

IF you will have chemistry/biology lab or infirmary that waste discharge needs to be specially handled too, because chemicals and lab equipment cleaning chemicals can also kill a septic system. You will also have to get written guidelines fro the design engineer regarding disposal of cleaning/antiseptic/antibiotic/etc wastes from those areas because they can kill the biologic activity which makes a septic system work to dispose of the waste materials - especially disinfectants (including bleaches and steerilization fluids used in toilets and shower rooms and such), and most especially antibiotics and medical disinfectants.

Ditto to solvents, oils, etc from maintenance shop and any equipment or automotive shop or classroomslabs.

Talk to the engineer about placement too - which of course topography may control to a large extent - but if all possible the septic system should not be uphill of the building in case of overflow, should not be under parking lots though sometimes the leach field has to go there (makes it expensive to digs it up to rehab it, and eliminates the possibility of converting to a mound system if required in the future if land is limited). If under parking lots it has to be deeper than nusual to prevent pipe crushing and compaction of the leach field soils. Also, while it is not uncommon to put leach fields under playing fields, again it has to be deeper, and the weight of maintenance equipment has to be limited and signage posted. Gang mowers and such are fine - but utility tractors and trucks and such should be kept off unless the leach field is put about 3-4 feet deep instead ofthe usual 18" or so. And of course, if put under playing fields due to space limitations, it the field ever become oversaturated due to it getting clogged up with grease or nearing its useful life, or due to oversaturation by heavy rains or rapdi snowmelt, the sewage can break through to the surface and make the field unusuable. And of course, if it needs to be dug up then you have repair of the playing field to pay for too, so siting the septic system(s) is more important than most people realize.

Costs can be all over the place with large systems like yours - but I would be very surprised to see if less than around $50,000 - and $100,000 or more would not surpise me - potentially substantially more if a package treatment system has to be put in to pre-treat the waste (in an above-ground package treatment plant) before discharge. I have been involved in jobs this saize and smaller where the package plant ran into the half million and above range because the discharge was going into wetlands, so early-on determination of what is going to be required should be a priority as it can at times affect the overall economics of the project. You may be lucky and there will be no issues or large costs, but I would not count on that without the preliminary design and percolation testing to back that assumption up.

Answered 3 years ago by LCD



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Answered 3 years ago by Member Services

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