Passive Soil Vapor Sampler with Constrained Membrane Uptake
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Solution Overview
Problem
Existing passive soil vapor sampling devices lack accurate and precise quantification of volatile organic compound (VOC) vapor concentrations due to uncontrolled uptake rates and site-specific variations in soil porosity and moisture, limiting their use beyond screening purposes.
Innovation Solution
A fully passive sampling device with a sorbent medium and a membrane that constrains uptake rates to match or exceed vapor delivery rates, using mathematical models to ensure consistent quantification, and incorporating methods for optimal deployment and analysis to measure VOC vapor concentrations below the ground surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the uptake rate of the sampler is increased to detect low VOC concentrations, then the sensitivity is improved, but the starvation effect worsens causing inaccurate quantification
Solution Approach 1:
The patent applies parameter changes by systematically varying the membrane permeability coefficient (Km) and membrane thickness (Lm) to achieve an optimal uptake rate. The design equation Lm/Km = f(C, Deff, r) provides a quantitative relationship that allows selection of membrane parameters to constrain uptake rates within a specific range (10^-6 to 10^-4 cm³/s), resolving the contradiction between sensitivity and accuracy by finding the optimal parameter combination.
Solution Approach 2:
The patent introduces a mathematical model as an intermediary between the sampler design and field conditions. The model incorporates soil effective diffusion coefficient (Deff), void space concentration (C), and geometric parameters to predict uptake rates. This intermediary allows designers to account for site-specific variations in soil porosity and moisture without requiring direct measurement of uptake rates in the field, enabling accurate quantification across different environmental conditions.
2Measurement precision
If the uptake rate is constrained to minimize starvation effect, then quantification accuracy is improved, but the sampling duration must be extended to detect low concentrations
Solution Approach 1:
The patent applies dynamics by making the sampler design adaptable to different field conditions through the design equation. Rather than using a fixed uptake rate, the system allows dynamic selection of membrane parameters (Lm, Km) based on expected VOC concentrations, soil properties, and desired sampling durations. This dynamic approach enables optimization of the balance between uptake rate control and sampling time for each specific application.
Solution Approach 2:
The patent applies preliminary action by calculating and selecting appropriate membrane parameters before field deployment. The design equation allows practitioners to pre-determine the optimal membrane thickness and permeability based on anticipated conditions, eliminating the need for trial-and-error field testing. This preliminary design phase ensures the sampler is pre-configured to achieve both accurate quantification and practical sampling durations for the specific application.
3Device complexity
If existing passive samplers are used without controlling uptake rate, then device complexity is reduced, but measurement precision deteriorates due to uncontrolled uptake rates
Solution Approach 1:
The patent maintains relatively simple sampler structure while achieving controlled uptake rates through careful selection of membrane parameters (thickness Lm and permeability Km). The design equation provides a straightforward method to calculate appropriate parameters based on desired uptake rates and field conditions, avoiding complex active pumping systems or multiple components. This parameter-based control achieves measurement precision without significantly increasing device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution allows for accurate and precise measurement of VOC vapor concentrations, minimizing the 'starvation effect' and providing reliable data for human health risk assessments, with the ability to detect low concentrations within practical sampling durations.
Implementation Method 1
relies on diffusion and permeation only with no power, pumping or forced advection
Implementation Method 2
relies on diffusion and permeation only with no power, pumping or forced advection
Implementation Method 3
The sorbent medium is suitable to retain and recover the target analytes
Data Source
AI summary
A device and method to quantitatively measure concentrations of volatile organic compound vapors below the ground surface using a preferably “fully” passive device that is placed in a drilled or bored hole for a specified period of time, wherein the sampler constrains the uptake rate to match values that minimize or eliminate the starvation effect and provide acceptable sensitivity for most soil types as calculated via mathematical models.