Quality Assurance and Quality Control in Site Remediation

A well-crafted remedial design is crucial for successful remediation projects, but its actual effectiveness in performing as planned depends in large part on strict adherence to the design during field implementation. Quality assurance/quality control (QA/QC) measures are essential in ensuring the design is executed correctly in the field, acting as a safety net to identify and address inconsistencies before they escalate into larger issues or result unplanned variances in remedial performance down the road.

Why QA/QC Matters

There are many variables at play when implementing a remedial design and field conditions are rarely perfect or predictable (i.e., expect the unexpected!). QA/QC measurements provide multiple lines of evidence that remedial amendments are being applied correctly, uniformly and according to plan. This allows for real-time adjustments to be made to dosing rates and amendment distribution, potentially avoiding over-dosed or under-treated areas.

More rudimentary QA/QC measurements that have been used for a long time to support in-situ remediation include:

Mass tracking: Tracking the masses of amendments and/or fill material used
Visual assessment: Inspection of mixtures of remedial amendments and native soil or imported sand backfill
Field monitoring: Visual checks for remedial amendment presence at nearby monitoring wells and/or measurements of water levels and geochemical parameters

However, a relatively new, semi-quantitative method that was developed in-house by VEI is also available to provide more objective data:

Amendment quantification: Real-time, field deployable methods for quantifying amendment concentrations in soil mixtures

More details on the specifics of the QA/QC dye testing methodology in relation to remedial amendment quantification are presented at the end of this article (for the super inquisitive), but let’s jump into a couple of actual case studies where it was used to illustrate usefulness of this technique and the data it can provide.

Case Study #1 – QA/QC Testing for Ex-Situ Soil Mixing

VEI was tasked with “seeding” native soil with a powdered activated carbon (PAC)-based remedial amendment at the low weight percentage of 0.26%. Unlike in many permeable reactive barrier (PRB) applications where the backfill is delivered to the site in truck loads of known mass, in this instance, the mass of soil used for mixing and backfilling was only estimated in real-time by the excavator operator. The combination of the low target concentration, the use of site soil as backfill and non-quantitative soil mass information made advanced QA/QC measures key for remedial success.

Excavation seeding to backfill an excavation to prevent contaminant rebound in groundwater

Completing an excavation “seeding” project whereby a remedial amendment is mixed with imported sand fill and used to backfill an excavation to prevent contaminant “rebound” in groundwater

After each stockpile was mixed with the remedial amendment, five samples were tested on-site with VEI’s proprietary dye-testing method to allow the quantification of PAC-based amendment in each of the soil samples. Through this process both the average concentration and uniformity of mixing was investigated.

As indicated by the red points in Figure 1 below, five out of the eight amended backfill stockpiles required re-mixing to fall within the targeted concentration range of 0.22% to 0.32% by weight. In each instance, the initial average concentration was above the target range, meaning that too much amendment was added to those stockpiles by the excavation contractor or else the mass of the stockpiles was overestimated.

Figure 1 PAC based remedial amendment concentrations in backfill stockpiles

Figure 1: Average PAC-based remedial amendment concentrations in each backfill stockpile showing elevated readings (red) in piles that required re-mixing

After adding additional soil and re-mixing of each of the stockpiles all of the samples tested fell within the target of ±20% of the average concentration (as shown in Figure 2 below), indicating that the piles were sufficiently mixed to uniformity, and also met the targeted loading rate (the black dots in Figure 1 above).

Figure 2 QAQC testing demonstrating uniformity assessing variability remedial amendment concentrations

Figure 2: QA/QC testing used to demonstrate uniformity by assessing the variability of remedial amendment concentrations in multiple samples from each stockpile

Without these QA/QC measurements, the remedial amendment would have been used up prior to completing the project – either leading to cost overruns to purchase more amendment or resulting in treatment “dead zones” after the amendment ran out.

But It’s Not Only for Ex-Situ Applications

QA/QC testing is not limited to ex situ approaches as illustrated in Case Study #1 above. It can also be a valuable tool for in-situ injection applications.

For these projects, standard QA/QC methods include mass tracking of amendments, monitoring injection pressures and flow rates, and monitoring for evidence of amendments in neighbouring monitoring wells. By adding QA/QC boreholes, the project team can better investigate amendment distribution in the subsurface, particularly the vertical distribution – something that is not possible using monitoring well observations.

For activated carbon (AC)-based amendments, a visual assessment of absence/presence can be beneficial, but going a step further to perform the semi-quantitative dye testing method on soil samples retrieved from the boreholes allows for the detection of much lower concentrations of AC in soil (i.e., <0.1% by weight).

VEI has invested considerable time developing and improving this dye testing methodology to be able to perform QA/QC testing of the much more complex subsurface environment with its many, varied soil types, as illustrated in the following case study.

Case Study #2 – QA/QC for an Injected PRB

This is a recent case study where dye testing was completed during the installation of a Trap & Treat® BOS 100® PRB with subsurface soil types ranging from sand to silty clays. The first step in the process was to lay out the PRB injection grid in Environmental Site Model (ESM) software. ESM is a super-powerful interactive tool that VEI uses to track site characterization data and remediation progress.

Screenshot of the PRB injection grid laid out in ESM

Background boreholes were advanced and sampled for use in characterizing soil conditions prior to remedial injections and to perform calibration testing using the different soil types encountered.

After completion of the remedial injection program, QA/QC boreholes were then advanced at six locations throughout the PRB area. QA/QC dye testing revealed that BOS 100® was detected in 100% of the boreholes sampled and throughout the entire targeted vertical injection interval of 3.0 to 5.7 meters (m) below ground surface. The figure below shows the average BOS 100® concentrations at 0.3 m intervals along the alignment of the injected PRB.

Figure 3 BOS 100 loading across targeted vertical depth injected PRB based on soil sampling and QAQC dye testing

Figure 3: BOS 100® loading across the targeted vertical depth of an injected PRB based on soil sampling and QA/QC dye testing

These results showed excellent evidence that the BOS 100® was well distributed in the subsurface and in accordance with the remedial design.

As such, it’s no longer necessary to have to only rely on field monitoring, visual assessment of uniformity and mass tracking data. These case studies clearly demonstrate that VEI’s proprietary QA/QC dye testing is a valuable, semi-quantitative tool that provides an additional line of evidence to verify that in-situ remediation programs are completed according to plan.

For those of you who are exceedingly curious, feel free to continue reading more about the nuts and bolts of the QA/QC dye testing methodology. Otherwise, thanks for reading and feel free to reach out to us to enquire how we can assist you with your in-situ remediation challenges!

What Exactly is QA/QC Dye Testing in Relation to Remedial Amendment Quantification?

Previous QA/QC testing for AC-based remedial amendment admixtures were limited to mass tracking, visual assessment and indirect monitoring only. Therefore, way back in the summer of 2019, VEI initiated a research and development project into a real-time, field deployable method for quantifying AC-based amendment concentrations in soil matrices, taking advantage of AC’s high organic compound absorption capabilities. This was driven by the desire to achieve more precision in the field implementation of remedial programs.

The proprietary method eventually developed in VEI’s in-house laboratory essentially involves mixing a set volume of a known concentration of dye solution with set mass of soil containing an AC-based remedial amendment. After waiting a set period of time, the dye solution is decanted off, filtered, flocculated (if necessary), and the percentage of transmissivity of a specific wavelength of light passing through the dye solution is measured. The measured concentration of dye before and after exposure to the AC is compared to site-specific calibration curves to accurately translate the degree of dye adsorption of the mixture to the corresponding AC concentration in the soil mixture.

As of August 2021, the methodology was fully functional and used for the first time by VEI at a trenched PRB site in Calgary. The new QA/QC test proved to be sufficiently portable and rapid that it could be used to perform uniformity and concentration checks in real-time in the field. Detection limits varied based on the type of AC-based amendment and the specific characteristics of the soil/sand media but were consistently below 0.75% by weight. Fast forward to 2025, and continuous refinements and improvements in the test method have resulted in achievable detection limits of below 0.10% by weight! The method has also been modified for use on other adsorbents, such as Fluoro-Sorb®, a form of modified clay adsorbent used to treat perfluoroalkyl and polyfluoroalkyl substances (PFAS) in-situ.