Long-term Acceptance Rate (LTAR) - What does it mean?

If you don't really want to know what LTAR is, and just want to find out how to increase it, reduce your drain field size, increase bedrooms, or increase lots,add a pool feel free to skip to the bottom and get in touch. 

The Long-Term Acceptance Rate (LTAR) or loading rate is one of the most significant metrics regarding septic design and installation that home builders and developers should understand.

To oversimplify it, "Good soil" will have a higher LTAR while "bad soil" will have a lower LTAR.

Class I soils - Sand, Loamy sand -  .9 - 1.0 gpd/ft^2

Class II soils - Sandy Loam, Loam - .7 - .8 gpd/ft^2

Class III soils - Sandy Clay Loam, Clay Loam, Silt Loam - .5 - .6 gpd/ft^2

Class IV soils - Silty Clay Loam,  Sandy Clay Loam, Clay, Silty Clay - .1 - .4 gpd/ft^2

So what does LTAR mean and what influences it?

The units used for LTAR or Long-term acceptance rate are gallons per day (gpd) per sq ft (ft^2). (i.e. .15gpd/ft^2)

That means that a soil assessor based on experience and an assessment of soil characteristics believes that the soil can receive .15 gallons of septage per day per sq ft of soil indefinitely.

Let's break that down in an example.

A builder wants to build a 4 bedroom home. Septic systems are designed to handle 120 gallons per day per bedroom. So, 480gpd for a 4 bedroom home.

If your soil was given a .15gpd/ft^2 LTAR then you will need 3200 sq ft of drain field area for your primary drainfield. (480/.15=3200)

In SC rules require a 50% repair area equaling 1600 sq ft. In total, you will need 4800 sq ft of suitable area on your property for a drain field in this scenario. In NC you need a 100% repair area, meaning you would need 6400 sq ft of total suitable area for drain field.

Clay soils are assessed an LTAR between .1 and .4 depending on their characteristics.

.15gpd/ft^2 is a pretty low LTAR.

A .3gpd/ft^2 LTAR would need half as much area compared to a .15gpd/ft^2 LTAR.

Are there ways to increase your LTAR and still have a septic system that will not fail and get overly saturated? Yes!

LTAR can be increased at the soil assessors discretion when the wastewater is treated before being put in the soil. Treatment breaks down the nutrients and gunk in the septage that would otherwise contribute to soil pore clogging. If we remove the nutrients and suspended solids then the soil can accept the wastewater at a higher rate.

In North Carolina the onsite wastewater rules are written such that you can automatically decrease the size of your drain field when you add treatment. You can also decrease set backs to water features, ditches, drainage etc.

In South Carolina, the rules don't allow for this kind of automatic decreasing of drain field size and set backs. Working with a creative soil classifier who understands and has experience with the how soil's ability to accept wastewater increases when the wastewater is treated can deliver a similar result.  Soil classifiers can use their best professional judgement to increase the LTAR within the particular soil category at their discretion.

i.e. SC rules state that clay soils will be assigned an LTAR of .1 to .4 gpd/ft^2. A soil assessor can't change the category of soil on the property, but they can increase the LTAR within the range allowed by the state rules.

Have you made it this far? 

The confidence soil assessors have in their LTAR is related to how confident they are in the treatment of the waste water and the long-term operations and maintenance of the wastewater treatment and disposal method. That's where AQWA comes into play. We provide the most robust, durable, dependable treatment system on the market as well as providing the best after-sales operations, maintenance, and service.

No other treatment and service provider has a track record or as much performance data as we do which means we empower soils pros and engineers to reach for the highest and best results for their clients.

Email Michael to get a list of soil professionals and engineers we work with who really understand wastewater treatment and soils and can push the envelope on your project to get the highest and best results.

Thanks for Reading! Email me (Michael) at mclayton@aqwa.net or call 252-292-1667