Permeation is the passage of contaminants through porous and non-metallic materials. Permeation phenomenon is a concern for buried waterlines where the soil is contaminated with organic compounds, due to spills or leaks of underground storage tanks. Permeation cases in polyvinyl chloride pipes (PVC) have been already reported in US. OBJECTIVES 1) Track solvent permeation in PVC pipes due to organic solvents with NIRS 2) Predict permeation susceptibility of new PVC pipes with NIRS LABORATORY SET UP Tracking permeation in PVC pipes with NIRS Pipes - Three kinds of pipes (Same diameter, different company) in duplicates - Same length (12.5 cm) and PVC surface exposed to solvent - Pipes sealed with two glasses and epoxy, and soaked in 1 liter Teflon-lid jars Solvents - Pure: Gasoline (9 months soaking), benzene (11 days), and toluene (11 days) - Aqueous solutions of benzene and toluene: 20%, 40%, 80%, and 100% saturated solution (7 months soaking) Laboratory reference data - Moving front location (mm): Pure toluene and benzene - Weight gain (g/cm and %): Pure toluene and benzene - Time (days): Gasoline, aqueous solutions Outer wall Inner wall Moving front Prediction of new PVC pipes permeation susceptibility with NIRS Pipes - 58 pipes from 5 major manufacturers - Six commercial diameter sizes: ½”, ¾”, 1”, 1+ ¼”, 1+ ½”, 2” and 3” - Three 12.5 cm samples from each pipe were cut for the study - Each sample was scanned six times, covering the whole surface Laboratory reference data - Slope k (mm/h 1/2 ) of the line from the moving front test using pure toluene. Millimeters versus square root of time provided straight lines with R 2 > 99% (linearized permeation rate) NIRS SPECTROSCOPY Spectrometer: - Foss NIRsystems ® 6500 (Foss-NIRsystems, Silver Spring, MD) Chemometrics: Calibration models 1) Tracking of permeation: Partial Least Squares (PLS) with cross validation 2) Prediction of permeation susceptibility: PLS and Locally Weighted Regression with Principal Component Regression (LWR-PCR); validation with ¼ of the scans non accounted in the calibration, combinations of 25, 50 and 75 neighbors or objects and 5 to 15 principal components. Spectra pretreatments 1) Tracking of permeation: Raw, first and second Savisky-Golay derivatives 2) Prediction of permeation susceptibility: Raw, first and second Savisky-Golay derivatives, and Standard Normal Variate (SNV) for LWR models Model evaluation: Statistic parameters - Number of Principal Components (PCs) - Coefficient of determination (R 2 ) in % - Standard Error of Cross Validation (SECV) for permeation tracking, Standard Error of Prediction (SEP) for prediction of permeation susceptibility - Relative Performance Determinant (RPD) as the ratio of the standard deviation of the reference data over the SEP/SECV - Standard Error of the Laboratory (SEL) Software - The Unscrambler ® v.9.5 for PLS models - MATLAB ® v and PLS_toolbox v for LWR-PCR - SAS v.9.1 for SEL RESULTS Tracking permeation in PVC pipes with NIRS The best PLS models for pure solvent were the following: Best PLS models with aqueous solutions: Toluene: R 2 = 94.5 %, SECV = days, RPD = 4.12 (raw spectra) Benzene: R 2 = 95.1 %, SECV = days, RPD = 3.99 (first derivative) Both benzene and toluene: R 2 = 90.8 %, SECV= days, RPD = 3.25 (raw spectra) Prediction of new PVC pipe permeation susceptibility with NIRS - Reference data showed low error (SEL = mm/h 1/2 ) - The best PLS models gave the following statistics - The poor results of PLS models were due to a strong clustering among pipe types during the principal component analysis (PCA) - LWR-PCR improved the results substantially. Best models were achieved when SNV was applied, and worse results when spectral data was treated with second derivative. SEP values from SNV models are represented in a surface plot, as combination of number of objects and number of principal components. ACKNOWLEDGEMENTS Iowa State University gratefully acknowledges that the Awwa Research Foundation is the joint owner of the technical information upon which this manuscript is based. Iowa State University thanks the Foundation for its financial, technical, and administrative assistance in funding and managing the project through which this information was discovered. The comments and views detailed herein may not necessarily reflect the views of the Awwa Research Foundation, its officers, directors, affiliates, or agents. The findings described here are preliminary in nature and are subject to revision. A final project report will be published by AwwaRF. - There was not a best unique solution. Better combinations have SEP values between and mm/h 1/2 CONCLUSIONS - NIRS tracked permeation by toluene and benzene in PVC pipes with provided reference data (mm, weight gain (%), and weight gain (g/cm)) with PLS models - Saturated solutions of toluene or benzene provided models with rough screening accuracy when days of soaking were used as reference - Permeation by gasoline could be modeled with PLS using days of soaking with good accuracy - Permeation susceptibility was poorly predicted by traditional PLS due to pipe type clustering in the PCA - LWR-PCR provided accurate models, with best results when SNV was applied to spectra. Best models gave a RPD higher than 7 and SEP lower than mm/h 1/2 Measurement of Organic Solvent Permeation through PVC Pipes with Near Infrared Spectroscopy L. Esteve Agelet 1 C. R. Hurburgh 1 Jr. F. Mao 2 S. K. Ong 2 and J. A. Gaunt 2 Department of Agricultural and Biosystems Engineering 1 Department of Civil, Construction and Environmental Engineering 2 Iowa State University © 2006 Iowa State University and AwwaRF