Interpreting Results and Making Informed Decisions in Groundwater Monitoring

The ability to accurately interpret the results of groundwater tests is essential for making informed decisions that protect our environment and public health. This article delves into the interpretation of common substances monitored in groundwater, including Volatile Organic Compounds (VOCs), Semi Volatile Organic Compounds (SVOCs), and Per- and Polyfluoroalkyl Substances (PFAS), and the decision-making processes driven by this data.

Understanding VOCs in Groundwater

Volatile Organic Compounds are common contaminants in groundwater. They include chemicals like benzene, toluene, ethylbenzene, and xylene (BTEX), often found in industrial solvents and petroleum products.

When interpreting VOC levels, it’s crucial to compare the concentrations against regulatory standards, such as those set by the Environmental Protection Agency (EPA). For example, the EPA’s maximum contaminant level (MCL) for benzene in drinking water is 5 parts per billion (ppb). Levels exceeding this threshold indicate a potential health risk and necessitate remedial action.

The Impact of SVOCs

Semi Volatile Organic Compounds, though less volatile than VOCs, are equally concerning. These include compounds like naphthalene and phenols, commonly originating from industrial discharges and pesticide runoff.

SVOCs tend to adhere to soil particles, making their migration slower but persistent. Interpreting SVOC data involves assessing both concentration levels and the extent of spread. Remediation strategies might involve soil excavation or in-situ treatment methods.

PFAS: The Emerging Contaminant

PFAS, often referred to as “forever chemicals,” are a group of man-made compounds used in various industrial applications and consumer products. Due to their persistence and bioaccumulation potential, PFAS are particularly concerning.

Interpreting PFAS levels involves understanding both individual compound concentrations and total PFAS burden. With evolving regulations, and new groups of PFAS constantly being discovered and researched, it’s important to stay updated on guideline values. The EPA finalized MCL’s for PFAS in drinking water in April of 2024, with levels for PFOA and PFOS set at 4 parts per trillion (ppt). Other PFAS, such as PFNA, PFHxS and “GenX Chemicals” are set at 10 ppt.

Data-Driven Decision Making

The interpretation of groundwater contaminants drives critical decisions in environmental management. For most contaminants, exceeding regulatory thresholds often triggers site investigations to determine the contamination source and extent. Remediation decisions are based on factors like contaminant type, concentration, and site characteristics.

Now that PFAS standards are set, facilities such as wastewater treatment plants and landfills must comply with the new limits over the next few years. As these facilities are investigated, sites where PFAS levels are over the limits will require long term monitoring, upstream investigations, and extensive remediation plans until the sites are below the thresholds. Throughout this investigative process, the industry is working hard to develop cost effective remediation plans for these “forever chemicals”.

Conclusion

Interpreting groundwater monitoring data is a nuanced and critical process. Understanding the implications of various contaminants like VOCs, SVOCs, and PFAS is key to making informed decisions for environmental and public health protection.

Utilizing passive groundwater sampling methods in your groundwater monitoring can ensure accurate and timely data, allowing you to make decisions quicker and move faster to act. The low cost of passive sampling can also free up more funds to allocate towards remediation and compliance.

Schedule a free consultation to learn more about how passive groundwater sampling equipment from EON can help you make better decisions while saving time and money.

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The Importance of Proper Data Analysis in Groundwater Monitoring

Groundwater monitoring is a critical aspect of environmental assessment, resource management, and contamination cleanup efforts. Accurate data analysis not only informs stakeholders of current conditions but also guides remediation and protection strategies. This article delves into the best practices and challenges in analyzing data from groundwater samples, with a focus on the treatment of passive samples.

Best Practices in Data Analysis

Groundwater monitoring data offers a snapshot of the subsurface environment’s health. Best practices in data analysis involve:

  • Temporal Consistency: Regular sampling provides a timeline of data that can reveal trends.
  • Spatial Accuracy: Precise location mapping ensures data relevance to specific contamination sites or aquifers.
  • Analytical Precision: Utilizing accredited laboratories and validated methods for analysis guarantees the reliability of data.

However, challenges abound. Data variability due to seasonal changes, cross-contamination risks during sampling, and the complexity of subsurface geology can skew results. Addressing these requires a methodical approach to sampling and analysis.

Groundwater monitoring projects encounter a variety of contaminants ranging from volatile organic compounds (VOCs) to heavy metals and emerging contaminants like PFAS and 1,4 Dioxane. Each type of contaminant presents unique challenges and considerations in data analysis, often requiring specialized approaches to ensure accurate assessment and interpretation.

Volatile Organic Compounds (VOCs)

Challenges:

  • Sample Preservation: VOCs are prone to evaporation and degradation. Therefore, maintaining the integrity of the sample from the field to the laboratory is crucial.
  • Detection Limits: Many VOCs are harmful at very low concentrations, necessitating highly sensitive analytical methods.

Considerations:

  • Method 8260: This is a standard EPA method for analyzing VOCs using gas chromatography/mass spectrometry (GC/MS).
  • Low-Flow Sampling Techniques: These can be used alongside passive sampling to reduce disturbance of the sample and prevent loss of VOCs.

Heavy Metals

Challenges:

  • Particulate Association: Metals can be present in dissolved form or bound to particles, and distinguishing between these forms is essential for accurate risk assessment.
  • Oxidation States: The toxicity and mobility of metals can vary significantly with their oxidation state, which can change during sampling and storage.

Considerations:

  • Sequential Extraction Procedures: These are used to differentiate between the speciated forms of metals.
  • Acidification: Adding acid to samples can preserve metals in their dissolved state for analysis.

PFAS

Challenges:

  • Diverse Chemical Properties: These contaminants have a wide range of chemical properties and behaviors in the environment, making standardized analysis difficult.
  • Difficulty to Destroy: PFAS are widely known as “forever chemicals” due to their lack of degradation and difficulty to destroy. Reliable and cost effective remediation methods are currently non-existent and are a focus for many environmental companies today.
  • Unknown Health Impacts: The health impacts of many emerging contaminants at trace levels are not well understood, complicating risk assessment.

Considerations:

  • Advanced Analytical Techniques: Techniques such as liquid chromatography-tandem mass spectrometry (LC-MS/MS) are often required for these contaminants.
  • Low Cost Investigation: Due to the low MCLs announced by the EPA for PFAS in drinking water, it is important that companies find technologies and adopt practices that decrease the cost of determining if PFAS is present. This will allow the allocation of more funds toward site remediation and cleanup.

Nutrients (Nitrogen, Phosphorus)

Challenges:

  • Biological Activity: Nutrients are subject to biological uptake and transformation, which can rapidly change concentrations.
  • Eutrophication Risk: Elevated levels can lead to eutrophication, and pinpointing sources is essential for mitigation.

Considerations:

  • In Situ Sensors: These can provide real-time monitoring of nutrient levels.
  • Isotopic Analysis: Nitrogen and phosphorus isotopes can help trace nutrient sources and pathways.

Organic Matter

Challenges:

  • Complex Mixtures: Natural organic matter consists of complex mixtures of thousands of different chemicals, complicating analysis.
  • Interference with Contaminant Measurements: Organic matter can bind with contaminants, affecting their detection and interpretation.

Considerations:

  • Total Organic Carbon (TOC) Analysis: This provides a measure of the organic content in a sample and can be a proxy for organic matter.
  • UV-Visible Spectroscopy: This can help characterize organic matter and understand its interactions with contaminants.

Proper data analysis begins with your sampling method and choosing the method that best suits the contaminates you are dealing with.

Passive Sampling: Revolutionizing Groundwater Data Collection

Passive groundwater sampling is an innovative method that offers several advantages over traditional techniques like pump-and-purge or low-flow sampling. This method uses a no-purge approach, allowing for the collection of samples without the need to remove large volumes of water. This reduces sample turbidity and avoids the disruption of the natural chemical conditions of the groundwater.

Benefits of Passive Sampling:

  • Cost-Effectiveness: Reduces time in the field and the volume of water needing disposal or safe storage.
  • Data Integrity: Minimizes disturbance to the water column, leading to representative samples that do not bias the sample.
  • Enhanced Safety: Lowers the risk of exposure to contaminants for field technicians.

Data Interpretation: Navigating the Complexities

Proper interpretation of groundwater data from passive sampling is paramount. It involves understanding the geochemistry of the site, the behavior of contaminants, and the potential for biodegradation or natural attenuation. Analysts must consider:

  • Contaminant Distribution: Recognizing the heterogeneous distribution of contaminants can affect sampling strategies.
  • Geochemical Indicators: Parameters such as pH, redox potential, turbidity, and conductivity can provide insights into subsurface conditions.
  • Time-Series Analysis: Evaluating changes over time can help distinguish between transient spikes and stable contamination levels.

Advancing Groundwater Monitoring with Passive Sampling

By offering an accurate representation of in-situ conditions, passive sampling can equip you with the data necessary to make informed decisions about remediation efforts and groundwater management.

The analysis of groundwater data, particularly from passive samples, is a cornerstone of effective environmental stewardship. Adhering to best practices in sampling and analysis, and overcoming the inherent challenges, ensures the protection of this vital resource for future generations.

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Collecting Groundwater Samples for PFAS Analysis

Bench and field scale studies indicate that dual membrane passive diffusion bags may be a viable and readily available technology for the collection of groundwater samples of per- and polyfluoroalkyl substances.

The Military Engineer Magazine – By Paul Caprio, PG, S.SAME, Erica Thiekman, M.SAME, and Steven Gragert, CHMM

Due to the historical use of aqueous film forming foam with per- and polyfluoroalkyl substances (PFAS), the Department of Defense (DOD) is currently managing a growing number of sites with known or suspected contamination. Groundwater monitoring for PFAS at these locations is conducted using low-flow well sampling procedures, which employ portable pumps, dedicated tubing, real-time water quality measurements, and may require management of investigation-derived waste.

A research team comprising EA Engineering, Science and Technology Inc. PBC, EON Products Inc., and the Omaha District of the U.S. Army Corps of Engineers evaluated the effectiveness of Dual Membrane Passive Diffusion Bag (DMPDB) technology to collect representative groundwater samples for PFAS analysis. Although passive sampling groundwater technologies have been routinely used for more than 20 years at DOD sites for volatile organic compounds, metals, and inorganic analysis, their reliability for monitoring PFAS in groundwater is the subject of ongoing bench scale and field study research.

CURRENT ALTERNATIVES

There are several passive samplers under evaluation for the collection of groundwater samples for PFAS analysis. These include grab samplers for instantaneous recovery; sorption-type samplers where contaminant mass accumulated over a known duration is used to calculate concentration, and equilibrium-type samplers that reach and maintain equilibrium with the sampled medium.

Traditional PDBs consist of semi-permeable membrane bags filled with deionized water. The bags are placed in the saturated screen intervals of groundwater monitoring wells where molecules diffuse across the membrane pores into the smaller until the concentration equalizes between the groundwater and the outside of the sampler. The single polyethylene diffusive membrane utilized in traditional PDBs is permeable to non-polar volatile organic compounds but not to other common analytes.

It has been well documented that the collection of groundwater samples using passive samplers results in both significant cost and time savings relative to other common sampling techniques, due to lower equipment and labor costs. Passive samplers also lower the chance of cross-contamination, allow for depth-specific profiling and generate less investigation-derived waste. This is of particular concern at PFAS sites where treatment and disposal techniques are still evolving. Additionally, several passive sampling technologies yield very low turbidity sample aliquots, which is vital for reduced matric interference during laboratory analysis. Equilibrium-type samplers allow for sample aliquots to be collected directly in the field and prepared using conventional methods. Conversely, sorptive samplers require additional preparatory work to extract target chemicals from the sorptive media prior to analysis.

TECHNOLOGY DESCRIPTION

DMPDBs apply the same concept as PDBs, but utilize two membranes with different diffusion capabilities to expand the analyte list beyond volatile organic compounds. None of the DMPDB materials are considered to be sources of PFAS. The upper membrane, made of polyamide, has larger pores and is hydrophilic; this facilitates diffusion of polar and larger molecules into the sampler, such as metals, cations, anions, and 1,4-dioxane. PFAS, which consists of carbon chains bonded to fluorine atoms with hydrophilic polar functional groups, are both polar and relatively large compared to volatile organic compounds. They pass through the upper membrane of the DMPDBs. The lower membrane, made of high-density polyethylene, has smaller pores and is hydrophobic. It is permeable to relatively small volatile organic compound molecules.

This lower membrane also prevents water from escaping the smaller, serving as a sample reservoir. Suspension tethers are typically made of polypropylene=braided cord manufactured without PFAS and are dedicated to each well.

BENCH SCALE TESTING

In 2017, a bench scale study evaluated the ability of DMPDBs to collect representative PFAS samples in a controlled environment using a polyvinyl chloride test chamber filled with a known volume of PFAS-free water that was spied with eight PFAS — including long-, medium-, and short-chain substances — at target concentrations of 20-30 ng/L. The liquid was mixed and allowed to stabilize for six days. The first test consisted of nine samplers that were allowed to equilibrate with the tank water for 21 days (three DMPDBs) and 41 days (six DMPDBs) prior to sample collection.

A second test was performed for tank concentrations between 1- ng/L and 10-ng/L and a residence time of 21 days. A pair of control samples were taken from the chamber port during each retrieval event. All the samples were analyzed for the eight PFAS using a modified Method 537.

FIELD STUDY METHODS

Side-by-side samples were collected from 10 wells with known PFAS impacts at a DOD facility using PMPDB and low-flow purge techniques. DMPDBs were filled with PFAS-free primer water, installed in one mobilization, and allowed to equilibrate for 21 days. This duration was applied based on the shorter of the two durations used during bench scale tests (21 days and 41 days), where comparable results were observed. There is no maximum known timeframe for retrieval. A sample of the water used to fill the PMPDBs was collected to confirm it was PFAS-free. A single DMPDB was placed in the center of the screen of each well, and two DMPDBs were deployed in tandem in two of the wells.

After 21 days, the DMPDBs were retrieved from each well and sampled. High-density polyethylene tubing and a submersible pump were then deployed to purge and collect another sample using low-flow procedures. Flow flow, DMPDB, and field quality control samples were packed in ice and shipped to a DOD-accredited analytical laboratory for analysis in accordance with Quality Systems Manual Version 5.3 Table B-15 for 24 PFAS.

DATA AND RESULTS

Some apparent stratification was observed in one of the two wells with tandem DMPDBs. As a result, only the lower DMPDBs were used for comparison to low flow samples for consistency. PFAS were reported in 126 pairs of the 240 pairs of results that were analyzed. All pairs with detections were used for compassion on a 1:1 regression plot, with low-flow results on the x-axis and DMPDB results on the y-axis. However, only pairs with results greater than five times the reporting detection limits were used for relative percent difference analysis to eliminate artificially high results produced from comparing low values.

This process also was used to analyze results from a set of low-flow field duplicate samples collected during the field event for comparison, and for field study results less than 200 ng/L, which are more representative of values within the range of existing screening levels.

REAL-WORLD APPLICATION

DMPDB PFAS results correlated well with the bench scale and field study samples. They were comparable to the low flow field duplicate sample, and did not produce any results that affected comparisons to screening levels. Additionally, DMPDBs appeared to produce consistent results for both long- and short-chain substances, indicating that it may be suitable for PFAS sampling in future projects — although it may be better suited for sites with regular sapling events to eliminate the need for two mobilizations.

The cost benefits of DMPDBs were not evaluated in this effort. However, studies performed by both the Interstate Technology & Regulatory Council in 2004 and DOD’s Strategic Environmental Research & Development Program/Environmental Security Technology Certification Program in 2014 indicated that the cost savings associated with switching from low flow to equilibrium passive samplers can be expected in the range of 40 to 70 percent for long-term monitoring programs.

This article was written by Paul Caprio, PG, S.SAME, Erica Thiekman, M.SAME, and Steven Gragert, CHMM, and published by The Military Engineer magazine. To read the original article, click here.

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Groundwater Remediation for Environmental Safety

For farmers, landowners, businesses and local governments, groundwater is an essential resource. If local groundwater is not properly protected and managed, contamination can quickly become a common environmental problem that will reduce or eliminate the ability to use the resource and require remediation to restore its value.

Groundwater Remediation for Environmental Safety - EON Products, Inc.

Groundwater remediation is the process of managing and reversing the effects of contamination in the underground water supply that may be caused by industrial, agricultural, or consumer activities. Contaminants may include oil, chemical solvents, fertilizers, heavy metals, and other potentially dangerous substances. Often released into the environment by runoff or discharge into streams, lakes, rivers and oceans, the contaminants can find their way into the food chain and cause long-term contamination of wildlife, farm products, and ecosystems. If ingested, many of these pollutants can cause illness or be fatal to human health.

Although groundwater quality is highly influenced by geologic processes, human activity is a strong factor as well. Proper storage and disposal of potential pollutants, proper land use management, runoff management, and protection measures around wellheads and sinkholes can help protect water quality and prevent contamination.

Because groundwater contamination can become both an expensive and safety issue, it can be considered a legal risk within many industries. Therefore, it is important to utilize advanced remediation technologies to properly manage and solve contamination problems wherever they exist. 

Groundwater Remediation for Environmental Safety - EON Products, Inc.

When it comes to achieving basic groundwater remediation, EON Products understands the importance of high quality and easy-to-use tools. Our remediation products are designed to effectively remove dangerous materials, including hydrocarbon contaminants, from groundwater, while minimizing cost and wastewater disposal to ensure project success for the end user. Our products include passive and active groundwater remediation skimmers, spill kits and absorbent materials, DNAPL and LNAPL recovery systems and sparging systems. 

With our passive skimmers, absorbent socks and pneumatically-operated pumping systems, the user can collect and eliminate light non-aqueous phase liquids (LNAPLs), such as hydrocarbon containments, resulting from tank leaks, dry cleaners, spills, or other discharge events. 

For more information on our groundwater remediation products, contact our team today. 

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