How to minimize your risk by reducing Allowable Leakage Rates 
Learn effective strategies to lower ALR and minimize environmental risks with our comprehensive guide on engineered containment systems. 

By Jimmy Youngblood

22 May 2024

5 Min read

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How to minimize your risk by reducing Allowable Leakage Rates 

While every effort is used to stop a pond or waste containment facility from leaking and contaminating the surrounding ground water or soil, the truth is, nothing is impermeable. When designing and constructing a pond, engineers will calculate the Allowable Leakage Rate (ALR) in an impoundment with leak detection layers, the ALR must remain below acceptable thresholds to reduce risk to the environment, ensure continuous production and avoid paying penalties.

Often regulatory bodies will require an ALR to be specified, and if it exceeds the acceptable threshold, action will need to be taken.

In 2009 the Geosynthetic Institute published GRI White Paper #15 Survey of U.S. State Regulations on Allowable Leakage Rates in Liquid Impoundments and Wastewater Ponds. The survey intended to report the “state-of-the-practice insofar as regulatory guidance for maximum allowable leakage from liquid impoundments and wastewater ponds.”  The survey found that the allowable leakage rates is extremely varied.  Various leakage amounts and suggested response action plans (RAP’s) for landfills are measured in gallons per acre per day (1.0 gallons/acre-day or the equivalent of 10 litres/hectare-day)

According to the paper:

Various Leakage Amounts and Suggested Response Action Plans (RAP’s) for Landfills

(a) “de minimum” leakage = 10 lphd (~ 1.0 gpad) 

  • the vapor diffusion through perfect geomembrane with no flaws ranges from 0.2 to 20 lphd (~ 0.02 to 2.0 gpad); i.e., this represents the perfect liner 

(b) typical action leakage rate (ALR) = 50 to 200 (~ 5.0 to 20 gpad) 

  • continue monitoring 

  • assess liquid characteristics 

  • compare to primary leachate 

(c) typical intermediate leakage rate (ILR) = 200 to 1000 (~ 20 to 100 gpad)  

  • stop adding waste 

  • continue monitoring and testing of liquid characteristics 

(d) typical rapid and large leak (RLL) > 1000 lphd (> 100 gpad) 

  • remove the overlying waste 

  • repair leak(s) 

Note: All the above RAP-values are for illustration only; they must be site specifically determined. Also note that the U.S. EPA only requires the establishment of an action leakage rate (ALR) value.  The survey shows there is disparity in the regulations, and not all states specify allowable leakage rates:   

  • Sewage and/or wastewater ponds - 19 (48%) States have regulations: 

  • Other liquid impoundments - 9 (18%) States have regulations 

  • Municipal and Industrial Lagoons - 2 States have regulations 

  • Livestock waste control - 2 States have regulations 

  • Earthen impoundments - 1 State has regulations 

  • In-situ leach mines - 1 State has regulations 

  • Metal laden seepage water - 1 State has regulations 

  • General aquifer - 1 State has regulations 

  • Leakage collection pond - 1 State has regulations 

  • States that do not specify leakage rate in regulations - 9 (18%) States have regulations 

The ARL is determined based on the type of facility and level of risk leakage poses to the environment, particularly in oil & gas brine ponds. The maximum allowable leakage is determined by the environmental consequences the leakage will have but should nonetheless be a quantifiable value. Without which you cannot determine and manage the risk.  

In order to measure leakage, you need to install a double liner system with some kind of leak detection layer in between. This could be a geonet. In some cases, sand or gravel is used, but this is not ideal. You do not want gravel next to a plastic liner, as you may end up with even more leaks. Furthermore, if you have a foot or two of soil or gravel this reduced the capacity of your pond. 

Whereas a geonet liner paired with a primary liner allows you to catch and measure leakage with minor risk of seepage into the environment.

If you exceed the ALR you must stop production or face fines for each day you are over the accepted threshold.

The importance of leak location  

 It is not enough to just install a high-quality liner. You also need to conduct a leak survey to make sure there are no holes in your lining. Humans are not perfect, and mistakes happen. If you have a construction site that is 20 to 30 acres, that is a lot of room for something to go wrong. You do not know if something was dropped on the liner or if a rock pulled up and created a hole. The hole might not be visible to the naked eye, but once you have 30 feet of brine on top of that lining, the resulting pressure means even the tiniest hole is going to create a big problem.  

So, you must have a way to test for leaks in the lining during and after installation. One of the ways we do this is with electrical leak surveys, and conductive spark testing. Electrical leak surveys find holes before the lining is put into service.  

In Texas for example, regulatory bodies do not specify what the ALR should be, but they do require you to have one. You will not be able to get a permit without one, and the rates can vary from one project or application to another.  

Once the project is completed, you need the right Construction Quality Assurance process in place to make sure you monitor the lining consistently for leaks and can take action to keep the ALR down.  

Conductive is used as well, if the bottom of your lining is conductive, you can not only pick up that there is a leak but also pinpoint where the leak is, minimising the risk that you will exceed your ALR.