Principles and Practices for Petroleum Contaminated Soils

Edward J. Calabrese, Paul T. Kostecki

• Publisher: Routledge
• Year: 2019
• Print ISBN: 9780367450144
• eBook ISBN: 9781351422024
• Edition: 1
• Topic: Tecnologia e ingegneria
• Subtopic: Agricoltura

Principles and Practices for Petroleum Contaminated Soils includes some of the best research and practical work done by top researchers in the field-both in industry and academia. It covers fundamental and advanced topics, such as analysis and site assessment, techniques (e.g., vacuum extraction, asphalt incorporation), and case studies. The book will interest anyone working with contaminated soils, ground water, and underground storage tanks. It will also be a valuable reference for regulatory personnel and environmental consultants at all levels.

Part I: Analysis & Testing

CHAPTER 1

Analysis of Petroleum Contaminated Soil and Water: An Overview

Thomas L. Potter, Mass Spectrometry Facility, Massachusetts Agricultural Experiment Station, University of Massachusetts, Amherst

Introduction

Spills and leaks of petroleum products including gasoline, diesel fuel, and lubricating and heating oil often result in the contamination of soil and water. Analyses required to evaluate the extent of such releases and the threat they present to public health and the environment take a variety of forms. Analytical objectives are also diverse and often poorly specified. They range from a simple assessment of “presence or absence” to determination of the concentration of certain toxic substances these products contain. The least specific and most general analytical approach to the problem involves some form of “total petroleum hydrocarbon” (TPH) measurement. In contrast are analyses which are focused on selected target compounds.

Methods^{1, 2, 3} and ⁴ which are commonly used for petroleum contaminated soil and water analysis were developed by the U.S. Environmental Protection Agency (EPA). Various modifications of well-known EPA techniques such as “Modified Method 8015”⁵ also see wide application. It should be emphasized that the EPA methods have their origin in techniques developed by the agency for compliance monitoring in certain regulatory programs. The methods were not specifically developed for the analysis of petroleum contaminated soil and water, nor have they been systematically evaluated for this purpose.

In this review, the “state of the art” of petroleum contaminated soil and water analysis is discussed with emphasis on the EPA Methods.^{1, 2, 3, 4}, and ⁵ Examples demonstrate that the methods can be used effectively but problems do arise. The need for method development is emphasized.

The Problem Defined: Petroleum Product Chemistry

The source material for nearly all petroleum products is crude oil. Initial processing involves distillation into a series of fractions characterized by distillation temperature ranges and pressures. In general, the lighter fractions (lower boiling) represent gasoline-range material. The intermediate or middle distillate fractions represent feedstock for diesel and jet fuels and “light” heating oils. The residuum in this process serves as heavy fuel oils or other products. The trend from gasolines to the residual fuels is from the highly volatile to the nonvolatile, recognizing that in this case volatility is functionally defined.

Beyond distillation, numerous refinery processes are utilized to optimize the yield of certain products and to achieve desired product characteristics. The result is that some products may have little resemblance to the distillate fractions obtained in the initial crude oil processing. Gasoline is probably the best example. This product is blended from numerous refinery streams, and various additives are used to meet engine performance criteria.

Regardless of production modes or producers, most products are exceptionally complex materials with a wide range of physical and chemical properties. Gasoline, diesel fuel, and related products may contain hundreds or even thousands of individual constituents with boiling point distributions on the order of hundreds of degrees Celsius. Further, several chemical classes are usually represented, including paraffins, olefins, aromatics, heteroaromatics, and polar hydrocarbons containing oxygen, nitrogen, and sulfur. In turn, each class of compounds is characterized by various homologous series within which structural, enantiomeric, and other types of isomerism are exhibited. The higher alkyl substituted homologs also predominate.⁶

Another significant characteristic of the products is that their composition is variable. This is primarily in terms of the relative amounts of the various hydrocarbons the products contain. Relative product composition may also change dramatically after release into the environment. Processes responsible include volatilization, dissolution, and biotic and abiotic degradation. Each process influences to greater or lesser degree certain compounds or groups of compounds, and the rates of change are a function of environmental conditions.

These factors and others make petroleum product residue analysis in soil and water a formidable analytical challenge. They require that analytical methods be broad in scope. Where target compound analyses are involved there is also need for very high degrees of analytical selectivity and specificity. Compounds must be able to be detected in the presence of numerous potential interferences, and considering the toxicity of many petroleum constituents, high sensitivity is needed. Detection limits in the 1 to 10 micrograms per liter per component must be routinely achieved.

“Total Petroleum Hydrocarbons”

In light of the physical and chemical complexity of petroleum products, the analytical process is often reduced to the measurement of indicator parameters. Measurements of this type focus on determination of TPH. EPA methods include Method 413.1: “Oil and Grease” and Method 418.1: “Total Recoverable Petroleum Hydrocarbons.”¹ These methods are similar to other well-known techniques.

Methods Description

Methods 418.1 and 413.1 specify the extraction of hydrocarbon residues from solids and water using an organic solvent, trichlorotrifluoroethane. After extraction the sample is discarded and the solvent treated with silica gel to remove interfering “humic” materials. Solvent concentration using rotary thin film evaporation and other techniques follows.

In Method 418.1, measurement of the “total hydrocarbon” content is performed using an infrared spectrophotometer set at 2930 cm^-1. Petroleum hydrocarbons, namely n-paraffins, exhibit a strong adsorbtion band at this wavelength. This is due to the presence of -CH²- groups in the molecules. Total hydrocarbon concentration is expressed relative to the detector response to a standard mixture containing a fixed ratio of aromatic and paraffinic hydrocarbons, or to a petroleum product reference sample.

With Method 413.1, the total hydrocarbon content in solvent extracts may be determined gravimetrically. In this case the solvent is completely evaporated and the residue weighed.

Applications

A distinct advantage of the TPH approach is that instrumentation costs are modest and extensive technical training of analysts is not required. This translates to low cost. Excellent measurement precision (i.e., reproducibility) can also be obtained. Unfortunately, there are some important limitations. Measurement accuracy may vary widely, depending on the products involved and the extent of post-release chemical changes (weathering) which may have occurred. Even more significant is the uncertainty that the use of data obtained from analyses of this type may introduce into risk assessment and management schemes.

Specific problems relate to the fact that a significant portion of the more volatile compounds in gasoline and light fuel oil may be lost in the solvent concentration step. This is especially so with gravimetric techniques. With residual fuels and other “heavy distillates,” low recoveries often result for another reason. This is because many of their constituents are poorly soluble in trichlorotrifluoro-methane and are not effectively extracted.

Another problem, at least with the infrared procedures, is in the selection of standards. The relative response of an infrared spectrophotometer to a hydrocarbon mixture is a function of the relative amounts of aromatic and aliphatic hydrocarbons it contains and the wavelength setting. At 2930 cm^-1, the wavelength specified in Method 418.1, detector response is only obtained for compounds which have a -CH²- group. In short, the method has very poor sensitivity for aromatics.

A related issue is that hydrocarbon mixtures used for instrument calibration have constant composition (in terms of aromatics/paraffins content), whereas the relative composition of petroleum products and their residues are highly variable. This may introduce substantial uncertainty into measurements. Attempts have been made to compensate by using samples of petroleum products as standards and in some cases by artificially weathering them.⁷ However, there has been no systematic evaluation of the relative effect of this approach on method precision and accuracy. Some improvement is expected, but the choice of product “standards” and the extent to which laboratory “weathering” should be carried out are complex variables. Various data show that the aromatics content of products may vary by at least a factor of two and after release the relative composition of residues is highly variable, depending on numero...

Table of contents

• Cover
• Title Page
• Copyright Page
• Dedication Page
• Preface
• Contents
• Part I: Analysis & Testing
• Part II: Environmental Fate and Modeling
• Part III: Remediation
• Part IV: Health Assessment
• List of Contributors
• Index