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Do-It-Yourself Septic Plans


"Some states regulate small commercial septic systems like

home systems. Some states have separate rules for the commercial systems. Some states have no rules for small commercial systems"

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Septic Systems for Commercial Wineries  Car Washes Kennels etc.






Introduction: The following article applies to the drawing template package sold here from 

The drawing templates are in both standard PDF and CAD (What is a CAD Drawing?) These drawings will enable you to prepare a set of construction drawings of your project for your property. Before beginning construction, every business owner, excavator or designer in the septic industry must hand in clear, proper scale drawings to get approval to build a septic system for a commercial enterprise in the country away from municipal sewers. Important; In most areas the owner of property can prepare drawings and build his or her septic system. State and local laws tell you if you can do this yourself or if you must hire an expert. Read this disclaimer before getting started too. If you are unclear about your rules, call your county or parish health department and ask them for the rules in your area.

Commercial Wineries, Car Washes Kennels

and other rural farming and business operations often need a way of getting rid of non-domestic or industrial sewage.

Domestic sewage comes from kitchens and washrooms used by people and is different from the wastewater from small farm and small industrial operations.

The car wash shown here has 4 self-serve bays and a single automatic bay. The maximum design capacity negotiated with local health was 12 manual washes and 6 automatic washes per hour of operation. At 10 hours of operation per day, the capacity is 2230 GPD. Whether you can combine this industrial wastewater with the wastewater from the toilet and sink in the managers private bathroom is up to the state and local rules. 

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In many states like Florida these types of facilities are regulated like domestic septic systems by local health with oversight from the state. The industrial systems in Florida are at the time of writing designed following mainly the same rules as domestic systems based on the total gallons per day (GPD) of combined wastewater going through the system.

More often domestic and industrial flows are not combined and separate septic tanks and often separate drainfields are required for domestic and industrial wastewater.

Many states have no regulations at all for non-domestic septic systems. Some states are reluctant to regulate such small systems in farming areas in what usually is a rare situation.

Sometimes without rules or guidelines state departments of environment or ecology will assume authority over design based on a lack of policy. Bottom line - ask local health. Always give them a set of the system plans even if they do not regulate non-domestic septic systems. This courtesy will help you avoid an embarrassing visit from the state later, and we all know that eventually new rules will be written and the permit fees will be required.

Calculating Flow Volume and Waste Strength: Depending on the type, car washes use between 12-14 gal (self serve) to 11.1 gal (automatic) per car. Semi-trucks use up to 40 gal including trailer. It takes between 4-20 minutes for one vehicle and the method of calculating GPD is simply to multiply time per wash with gallons per wash for hours of operation. Most car wash managers will usually discuss these things to get details from a local operation. Not all car washes are trying to save water so you may notice a range of water use.

Most septic systems can not tolerate the gravel that results from car washes. Most sewage pumpers will not service a septic tank containing gravel. Even before hitting the septic tank, vehicle wash requires an oil and gravel separator to protect the system. Gravel is best scooped out of the separator with a back hoe and requires a traffic bearing top that is removable in pieces by a back hoe operator at the time of service.  

Most agricultural operations like wineries do not have steady flows and instead produce wastewater only at certain times of the year. The bottling phase of wine making involves washing and cooling with high flows. During the crush, high strength wastewater is produced with high BOD due largely to sugars and high organic content. A rule of thumb could be a liter of wine annually produces a gallon of sewage or 12 gallons per case. A winery producing say 1000 cases per year would yield 1000 x 12 = 12,000 gal per yr or about 33 GPD. Because of the high waste strength and the peaks arriving during one or two months with long resting periods, it would be prudent to ignore the GPD of this system and size the tanks and drainfield based on a compromise of say gallons per month or 1 GPD for each case produced per year. It is advised to base the size on the use of the vault type drainfield rather than gravel because of the larger storage capacity of the vaults per foot compared with gravel. The storage or surge capacity of each PVC vault is 43.5 gallons.

Our 1000 GPD test system in a loam soil with vaults would have 84 of the 4 foot units for a drainfield of around 1000 sq ft of drainfield with a storage capacity of over 3,600 gal. The surge capacity for this system will account for a multitude of sins such as high waste strength and a few peak days. To further support the the drainfield size, it is understood that this non-residential drainfield will be resting most of the year. The separate domestic system will account for several full-time employees, the tasting room, any additional food service and possibly a caretaker or owner's home. Disposal of the non liquid part of the winemaking operation, the marc and lees including pulp, seeds, dead yeast cells and fermentation waste will have to be composted, land filled or otherwise removed from the site and care should be taken during wash down to screen this indigestible waste from entering the system.

Septic Systems for Commercial Wineries Car Washes Kennels etc. have certain common parts not usually found on purely domestic systems. For instance a trench drain like the one shown here to the right is the way cleaning and waste water is flushed into the septic system. Floors are built with a slight slope into the drains. The drains themselves are sloped into the main sewer and through the outside wall into the tanks. A oil/ water separator proceeds the septic tank where cars and vehicles are washed. The dimensions and slopes of the drains are clearly shown in the plans. The best layouts for commercial operations are simple and linear where possible.

Roof drains and stormwater should always be directed away from the trench drains. If not, then the volume of water must be included in the flow calculations for the system.

Dog kennels are usually located away from built-up areas due to the noise. The municipal facility below is for a population of about 12,000 people. It contains seven separate kennels with both inside and outside spaces for each dog. The building contains a single toilet and sink connected to the separate domestic tank and drainfield.

Determining the size of the (sewage load) for the sep-arate non-domestic kennel septic system is determined by only two factors; the cleaning schedule and rainfall. The inside floor of the facility slopes gently toward the pens inside. Washing the facility down begins inside and continues outside to a trench drain along left side of the row of kennels at the edge of the grass. 

Keep storm water out of the system as much as possible. The roof gutter on the pen side collects rainwater and directs it away from the pens. The pens are open to the sky to promote natural disinfection by sunlight so all of the rainwater falling on them winds up in the non-domestic septic tank. The building is in an area with less than a foot per year of rainfall. Severe storms seldom drop more than an inch and a half of rain per day. In this case the outside pen area is about 200 sq ft so the total volume of water into the system in a severe storm  condition would seldom exceed 120 gal on any day.

If the rain water volume exceeds half of the capacity of the system then a roof should be put over the pens to direct runoff water away from the septic system. You will negotiate conditions with the local health department using historic weather data for your area if any open areas drain into the septic system.

Wash down is determined by the output volume of the pressure washer and the time taken to wash each kennel inside and out. The daily wash-down of the pens uses about 20 gallons per each of the 7 kennels totaling 140 GPD.

Therefore with the stormwater above, the Total System capacity is 260 GPD.

This view of the rear of the facility shows the pens and the drain along the right. The traffic bearing lids for the two separate septic systems are seen in the parking lot.

The two drainfields are separate from each other as required in this jurisdiction and they are in the grass exercise area to the right of the view. The replacement areas for each system are adjacent to their respective drainfield areas.

Dog waste by the way has an unusual characteristic. It all floats. Dog waste will not sink in the water in the tank and decompose and therefore has to be periodically pumped out.

Lets discuss filtering: All domestic and non-domestic septic tanks should have a plastic mesh filter at the outlet of the tank. Nothing will drop the waste strength of septic tank effluent easier and cheaper than a cartridge type mesh filter with 1/8 inch openings. If the system is not serviced, the blockage will come at the filter not the drainfield. Hosing the filter off into the tank is a simple annual 5 minute ritual that will include a visual inspection of the outlet baffle and scum layer.

To the right is a 15 inch dia PVC bio-type filter about to be installed at the outlet of a new larger commercial septic tank. You can see the tools, fittings and the filter sleeve to the left of the filter. The filter sleeve laying on the tank will form the outlet baffle keeping scum out of the drainfield. You can see the quarter sized inlet holes encircling the filter sleeve at the correct outlet height. This is a custom item with several details that must be specified in the system plans.

Non-domestic systems should use filters to lower waste strength and to protect the drainfield. The design of the one shown uses a cluster of small diameter mesh tubes to yield a huge filter surface. The handle is glued to the filter at a convenient height for removal once the riser height is set.

The picture to the right shows the filter in place in the tank. The 15 inch dia filters usually require two people to extract them from the tank. A more practical size for a smaller operation is a 12 inch diameter which would be plenty of filter for most domestic and non-domestic operations of less than 4000 GPD. Multiple smaller diameter filters can be ganged onto a manifold if more capacity is needed but each filter would likely require its own riser. 

If the waste strength leaving the tank is still too high, one approach often taken by regulators and designers is to simply enlarge the drainfield. Oversized drainfields seldom work well under normal flows and require precious space on the site.

You may need a pre treatment device or advanced treatment unit (ATU) to knock down the waste strength before it reaches the drainfield. Most ATUs are packed bed filters like the one pictured below. An eco-nomic approach would be to size each part of the system to match the volume and strength of the wastewater. Adding proprietary devices to a system is sort of a last resort for the GTO System which is based on the use of off-the-shelf parts. A generic recirculating gravel filter will treat just about any organic substance and reduce nitrogen to boot.

Types of ATUs: The designs for standard ATUs were developed early in the last century and are refined now as intermittent sand filters and recirculating gravel filters. GTO systems include modern sand and gravel filter designs. However some of the new and slick products out there are superior to standard filters in some situations.    

The example right shows a cluster of large above ground textile filters utilizing underground recirculation tanks which send the effluent over the filter multiple times before directing it to the drainfield. The filters and recirculation tanks are located between the septic tanks and the drainfields.

What Does the Drawing Package Contain? The package shows a variety of designs for septic systems for commercial wineries, car washes, kennels and other situations where wastewater is generated and must be treated and released.

The package shows you how to prepare the drawings you will need for your project. Learn how to show such things as tank size, trench drains, gravel and oil separators, ATUs, building location, drainfield design, construction and pipe details and all the other notes and instructions required to fully describe your project. The package contains both PDF and editable DXF drawings as well as instructions and photos to illustrate the work and special GTO spreadsheets in Excel format for calculating the design of all pressure pumping systems large and small.


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A Septic System for the Small Office  - Last Revised: 11/11/2016
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