LNAPL - Light Non-Aqueous Phase Liquids

What Is A Light Non-Aqueous Phase Liquid?

LNAPL, or a light non-aqueous phase liquid, is a liquid that is less dense than water and is also classified as a NAPL. Non-aqueous phase liquids can dissolve in water very slowly over time. In fact, not only does it take a long time for a NAPL to dissolve, but when introduced to water, an apparent distinction and separation will occur. The separation between the LNAPL and water is often called a physical interface.

Light non-aqueous phase liquids are less challenging to remediate than dense NAPLs because they tend to rest on top of groundwater, but this is only sometimes the case. Where DNAPLs will sink in water and essentially bury deep in the subsurface below groundwater, traveling vertically and horizontally until eventually coming to rest after creating a complex network of vertical drops and horizontal runs - LNAPL generally is only found in a few places.

An LNAPL is, as its name suggests, a "light" NAPL. Having a specific gravity less than water, it will float when introduced to water or groundwater plumes. What this means for remedial sites is that LNAPL will be brought lower and lower beneath the subsurface.

One of two things will happen once a light NAPL contaminates a site. If the amount of contamination is relatively small, the contaminant may stop before reaching the water table. However, if enough of the contaminant is released, it will most likely reach the water table and pool up on top of the groundwater.

When this contaminant reaches the edges of the groundwater, it will fall alongside the groundwater and collect in the soil above, beside, and even below the water table.

One of two things will happen once a light NAPL contaminates a site. If the amount of contamination is relatively small, the contaminant may stop before reaching the water table. However, if enough of the contaminant is released, it will most likely reach the water table and pool up on top of the groundwater.

If Light Non-Aqueous Phase Liquids Are Left Untreated

What can happen if left untreated is that eventually, as the contaminant pool ages, it will dissolve and break down over time. What was once a connected pool and network of contamination will become stand-alone pools. After a prolonged period, these stand-alone pools will eventually weather away.

However, the soil and groundwater will be heavily contaminated, and the health and safety of humans, plants, and animals will be threatened until contaminant levels are returned to normal.

Examples Of LNAPLs

Many hydrocarbons, in general, are considered LNAPLs, but some of the most common LNAPLs are petroleum products. Arguably most often, when a site is contaminated by light NAPLs, it's because of petroleum-based effects.

• Gasoline
• Diesel
• Kerosene
• Chlorinated Hydrocarbons

Non-Aqueous Phase Liquid

Non-aqueous phase liquids aren't easily dissolved in or mixed with water. Over time a NAPL can solubilize (dissolve) into any present water source, but it takes time. There are generally two classifications of NAPLs. Light non-aqueous phase liquids - which you know about now - and dense non-aqueous phase liquids, which we'll cover below.

Dense Non-Aqueous Phase Liquids

A DNAPL is exactly the opposite of an LNAPL. Where light NAPLs will rest on top of groundwater, and form a physical interface between the surface of the water and the body of the contaminant, dense NAPLs will sink in water.

DNAPLs are much harder to remediate because characterizing those types of contaminations is much more difficult due to the nature of those chemical compounds.

Many types of DNAPL are considered chlorinated solvents.

Treating Your Hydrocarbon (LNAPL) Contamination

Successfully handling your contamination is incredibly important if you want to achieve No Further Action (NFA) closures for your site, and there are many different ways to do this.

When dealing with light non-aqueous phase liquids, you'll generally face hydrocarbons. More often than not, the contaminant will be a petroleum-based pollutant. Still, regardless of the type of contaminant, you can go about treating your property in several ways - as long as you have an effective reagent.

Below we'll cover some common ways to treat sites plagued with these contaminants.

Pumping The Contaminant Out

One way to deal with these types of contaminants is to access the surface of the groundwater and skim (pump) out the topmost layers. While we wouldn't recommend this method, it's a quick way to remove a large amount of any present LNAPLs due to the very nature of these contaminants.

However, the drawbacks with this method are that more than just skimming out the contaminant pools on top of the water table is needed, considering the contaminant is still soaked into the soil directly above, around, and - quite often - underneath the groundwater as well.

For this reason, other methods are expected to be used in conjunction with any pumping services.

In-Situ Remediation

Arguably the most efficient and cost-effective method for treating these contaminants - and generally any contaminant - is in-situ remediation. In-situ remediation is a fancy way of saying remediation is in place, as you don't have to excavate and remove contaminated soil off-site. Because of this, you can forgo the costs of excavation, handling, and disposal.

In-Situ remediation generally has two technologies that are used - which are also used in ex-situ remediation.

These two technologies involve in-situ chemical oxidation and in-situ chemical reduction. Chemical reduction involves introducing reductants to reduce the concentrations of any present contaminants, making them easier to break down. Chemical oxidation involves introducing oxidants into the contaminated soil to change chemicals into less toxic ones and destroy as much of the present contaminants as possible.

When these two - chemical reduction and chemical oxidation - are used together, they form a reaction called a "redox" reaction. When a redox reaction is created, that is when these two processes are the most effective, as one can reduce them, and the other can destroy them. What is left can then help the development of any present native microorganisms, which will encourage plant growth, effectively getting your site back to normal.

While we won't cover each method used for in-situ remediation, we will cover some of the most common techniques you'll see.

Soil Mixing

Soil mixing is a technique where excavators blend contaminated soil with remedial reagents. We've been in the environmental industry for over two decades, and this method has stood out head and shoulders above all others.

Soil mixing is so effective because your lead environmental specialist can drive the excavator while a team of specialists administers the required reagents. These reagents are used to destroy any present contaminants.

While soil mixing occurs, your specialists can ensure that all of the contaminated materials make good contact with the required reagents to ensure maximum effectiveness. While other methods are also effective, this would be our primary method on most sites if given a chance.

Environmental Drilling

Many forms of environmental drilling can easily clean up even the worst contaminants. However, DP drilling is one of the quickest and most cost-effective methods.

The main reason this drilling method is better than the more traditional rotary drilling method is that with DP drilling, there is no need to deal with and remediate contaminated drill cuttings. Contaminated drill cuttings caused by rotary drilling aren't an issue with DP drilling.

With any form of drilling used, the goal is to get the tooling down to the desired levels to administer the required reagents.

Remedial Services With A Small Impact

Many forms of remediation can be used on sites where minimal impact is required. Whether it's a laundromat and remediation is needed indoors or the contamination is less than 12 feet from the surface, services exist to treat the site. High-pressure handheld remedial tools can be used to treat these types of situations, and for more information regarding these methods, check out our page on hand lances.

Well Injections

If your environmental consultant or previously used remedial companies have installed monitoring or recovery wells, well injections can be used to treat contaminants, whether light or dense NAPLs.

Ex-Situ Remediation

Ex-situ remediation is a fancy way of saying remediation that occurs out of place. Generally, with ex-situ remediation, remediation can begin once a site investigation has been carried out, and your remedial professionals have determined the dimensions of any present contaminants.

During ex-situ remediation, you'll generally have an excavator remove all contaminated material, and they can do one of two things.

Treat the soil at a different location on the site, or load it up and deliver it so it can either be treated and returned or disposed of and replaced.