The first set of graphic standards for septic system design in the USA is known as the GTO System.
Every health department in the country has different rules for designing septic systems. There are no uniform standards to guide engineers, designers and property owners in this important work. . .until now.
This page is an introduction to the GTO System explaining how it is used to develop a set of drawings for a specific parcel of rural property.
This 3 bedroom system being squirt tested here was designed as a GTO System using our design software
An Introduction to the GTO System and how to use the Drawings to prepare a Set of Septic System Plans
Welcome – To design a septic system, the 2011 GTO System (Generic Treatment Option) and your computer are all you need to prepare the plans. You now have the tools to design a septic system for 99% of homes in most counties and parishes in the USA and many other countries. The GTO System is universal because it works with any editable CAD program and contains all the CAD drawings and detailed instructions you will need to design for any septic situation. The parts that go into the GTO System are off-the-shelf and available at local hardware stores. Specialized parts like pumps, control panels and floats on which all systems depend, are available online. Concrete septic tanks and pump chambers are available across the country at reasonable cost in and near all large rural communities.
How to Prepare a Set of Pressure System Plans
A Site Plan is
First and contains all buildings with their sewer connections to the system. The site plan must show the layout of the property and the septic system in scale. This map of the site must show soil log locations, wells, water mains, surface water, driveways and any site details affecting the septic system along with all major site dimensions.
Every site is different. We offer many examples of site plans for sale in our various packages like this one. But no template for this page is possible. You must create an accurate site plan to include in your plan set. Study this example site plan for the Rookie septic system design. You will need to show the number of bedrooms on the site plan. This is how to determine the size of the drainfield based on daily sewage flow and the absorptive ability of the local soil.
Our website, eco-nomic.com contains the information you need to get the right sized and type of drainfield for your septic project. Your local health department has the rules and regulations being enforced for your area. A hundred foot tape and an hour on the ground with a survey map of the property is the first step to prepare your plans using your CAD program and our site plan template.
The Cross Section-
(Page 3) is next:
Page 3 in the Rookie plan set to the right is a cross section of the system or a view from the side. It shows the pump chamber and the drainfield. The difference in height between the water level in the pump chamber and the top of the drainfield laterals shows the real work to be done by the pump. This pumping height plus the length and diameter of the transport line have a huge effect on the strength you will want in your pump. We will explain how pump selection is made when we cover septic pressure system calculations a little later.
For now, you must choose the cross section drawing from the GTO Drainfields to match your system. The Rookie System shows a 1000 US gal septic tank followed by a 1250 gal pump chamber. The system uses an economical centrifugal pump pressurizing a traditional gravel bed type drainfield. The one-foot deep sand lining underneath the drainfield qualifies this combination as a bottomless sand filter. The soil under this site is gravelly and the site is dead level. If your site is sloping with loamy soil, you will be able to find the right combination of tanks and drainfield (probably shallow trenches) to match your site conditions. With your drawing program and our CAD drawings, you can make any changes to your drawing set to match all of your local area rules.
Septic Tank and Pump Chamber -(Page 4) is next:
Page 4 in our example plan set shows the septic tank and the pump chamber. You will find all of the possible tank combinations from the GTO Tanks. The Rookie system shows a standard 1000 US gallon septic tank and a standard 1250 US gallon pump tank. The minimum tank sizes are dictated by state and sometimes by local health regulations. Your local health department should give you the minimum sizes over the phone. In the Rookie System, the pump chamber contains a day’s worth of emergency storage volume in case of a power failure or the need to order a new pump. The pump is water-cooled and must be submerged all of the time. This is how the minimum water level (pump off elevation) is determined for the pump chamber.
The Drainfield - (Page 5) is next:
There are hundreds of possible drainfield and lateral design combinations and sizes. The GTO Drain-fields Page of the GTO System covers the spectrum of drainfield types from trench systems to beds, large and small, lined and unlined including mounds. You can choose old school gravel or the newer PVC vaults. Assume that you will be adding or subtracting length from our standard designs.
The Rookie System utilizes a 48 x 10 foot wide bed-type drainfield. The contact area of this bed with the native gravelly soil is 480 sq ft (looking straight down.) At 120 GPD (gallons per day) per bedroom, the capacity of the system is 4 bedrooms. Drainfield capacity is based on its ability to absorb water without backing up. Capacity goes up with size. If a bedroom is added to the house, and the drainfield is not enlarged to match, a drainfield failure is in the future sooner rather than later.
The image to the right and below shows a ten foot wide gravel bed drainfield undergoing a final inspection and squirt test.
This drainfield was selected for the Rookie System because a supply of drainrock was available at a nearby gravel pit.
The drainrock is called "inch-and-a-half." This drainfield type is a bottomless sand filter.
Local health will often dictate the best drainfield type to use in your situation. The GTO System has them all in a range of sizes. We have gravel (like this one) and the newer plastic vaults.
Adding a bedroom or two to the system capacity for future growth on the property is relatively cheap insurance up front, before construction begins. It is costly and difficult to do this after the fact with pressure systems. Plan ahead!
Construction Details - (Page 6) the last page in the pressure set:
Match your system details with your drainfield type from the GTO Drainfields. The details are important to make sure your drainfield meets local regulations. Also, inspection ports and visual access to the working drainfield will be done through inspection ports. The design of the ports is shown on Page 6 for the range of drainfield types.
A drainfield cross section showing plumbing connections in the drainfield, media type and depth is a part of any complete plan set. Correct and functional details are important to the treatment performance of the system and indirectly to the durability of the drainfield for the years to come.
All of our details have been field tested over many years of experience. John Glassco, the software developer is a former health inspector, a licensed septic designer and a licensed specialty excavator. Nothing is shown on these plans that has not been approved for construction and field tested.
The Cover Page - (Page 1) has some important information for the owner:
Now that your design is finished, it is time to fill in all the instructions to the homeowner and print out the set of plans. This cover page is from the GTO Drainfields. Except for filling in the titles, dates and drawing numbers, the plan set is almost complete. Print the set on 8.5 x 11 bond using the landscape layout. The drawings will appear at the correct scale. You will of course replace our logo and address with your own to give your work a professional appearance.
You must type an important number in Section 6 of the cover page to match the system calculations. This is the total hours per day the pump will run with the system operating at full design capacity. In operating pressurized septic systems, the accumulating total pump run time is displayed in the panel on the odometer-like elapsed time counter.
System Calculations used to take hours to perform with a hand calculator. Now designers of pressure systems use computer spreadsheets like the one on the right.
The GTO System provides these Windows® Excel® compatible spreadsheets for sale on our website with detailed instructions for performing the calculations in pressurized designs. Excel spreadsheets are in use everywhere. Our septic design spreadsheets can be adapted to any spreadsheet program if you already use another brand of spreadsheets in your home or business computer.
Many septic system designers already have their own apps or spreadsheets supplied by pump manufacturers for selecting pumps. Manufacturer’s spreadsheets are generally primitive, and they are restricted from being used to compare pumps from other manufacturers. The GTO System Engineering Spreadsheets are universal and do not suffer from these limitations. Our spreadsheets will be useful for calculating septic system pressures for your septic system designs for years to come. The rules of hydraulics are not likely to change any time soon.
Preparing Gravity Septic System Plans:
By far, the bulk of septic systems throughout the world are gravity systems. Many jurisdictions allow homeowners to prepare their own plans. The example to the right is Page 1, or the site plan for a standard gravity septic system.
Besides the application forms, gravity septic system plans usually have only 2 pages; a site plan and a detail sheet.
The GTO System is mostly for preparing plans for pressurized systems, trenches, beds, mounds and sand filters. It contains limited information on preparing gravity septic plans.
However, our other products like our packages for Larger Rural Homes and Tight Sites and Waterfront Lots and Small Shops and Offices contain a variety of systems including both pressure and gravity designs. Every site is different and the GTO System covers the range of system types for every possible site condition.
Designing septic systems is a new and growing business in most rural areas. New septic regulations are coming to a county health department near you. Whether you are a bright new face, or an old hand in the septic system design game in your area, the GTO System will help your expand your business skills. Knowledge and research in this industry is advancing daily. New products are showing up all the time. We are keeping up and proud to be a part of this growing industry with the GTO System.
John Glassco, Software Developer – Owner, Eco-nomic Inc.
Last Revised: 10/05/2012
all words and images copyright © 2011-2012 ECO-NOMIC INC. All rights reserved.