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API Publ 4593-1994: Technical Guidance for Sampling and Analysis of Petroleum Hydrocarbons in Contaminated Soils
Comprehensive Overview of Scope, Analytical Methods, Quality Assurance, and Compliance Considerations
Scope and Purpose of API Publ 4593-1994
API Publication 4593 (1994) provides comprehensive technical guidance for the assessment, sampling, and analysis of petroleum hydrocarbons in soil matrices. Developed by the American Petroleum Institute (API), this publication addresses the need for standardized procedures to evaluate the extent of contamination from petroleum releases, including crude oil, gasoline, diesel, and lighter-end fuels. While the document is not a formal consensus standard, it serves as a key reference for environmental professionals conducting site investigations and remediation at petroleum-impacted sites.
The publication covers: (1) project planning and sampling strategy development, (2) field sample collection, handling, and preservation techniques, (3) laboratory analytical methods for total petroleum hydrocarbons (TPH) and individual target analytes (e.g., BTEX and PAHs), and (4) data quality objectives (DQOs) and quality assurance/quality control (QA/QC) protocols. It is applicable to a wide range of soil types and contamination scenarios and is frequently cited by regulators and industry as a benchmark for defensible site characterization.
Technical Requirements and Analytical Methods
Field Sampling and Preservation
API 4593 emphasizes that sample integrity begins in the field. Sample containers must be of appropriate material (amber glass for VOCs), free of interfering contaminants, and sealed immediately. Headspace must be minimized for volatile organic compounds (VOCs). Samples are to be stored at 4°C in the dark and shipped to the laboratory within 48 hours. A chain-of-custody record is required for all samples. The publication recommends collecting sufficient mass for multiple analyses and for matrix spike/matrix spike duplicate (MS/MSD) quality control samples.
Laboratory Analytical Methods
The publication describes several analytical approaches depending on the target analytes and data quality needs. Table 1 summarizes the primary methods referenced in API 4593 for petroleum hydrocarbon analysis in soil.
| Method | Analytes | Preparation / Cleanup | Detection |
|---|---|---|---|
| EPA Method 5035 / 8260B | BTEX, gasoline-range organics (GRO) | Methanol extraction, purge-and-trap | GC/MS |
| EPA Method 3540C / 8270C | PAHs, diesel-range organics (DRO) | Soxhlet extraction, silica gel cleanup | GC/MS |
| EPA Method 3580A / 8015B | TPH (diesel and heavier fractions) | Dilution or solvent extraction | GC-FID |
| Modified EPA 1311 (TCLP) | Leachable petroleum fractions | Leaching procedure | GC-FID / GC-MS |
For TPH quantification, API 4593 advocates using a cleanup step (e.g., silica gel) to remove biogenic interferences from natural organic matter. The publication also includes guidance on method detection limits (MDL) and reporting limits appropriate for risk-based screening.
Quality Assurance and Quality Control
A critical component of the publication is its detailed QA/QC section. Required QC elements include: laboratory method blanks, laboratory control samples (LCS), MS/MSD, surrogate standards, and field duplicates. Acceptance criteria for precision (relative percent difference, RPD) and accuracy (percent recovery) are provided. The document recommends initial calibration with five concentration levels and continuing calibration verification (CCV) every 10 samples.
Tip: Use certified reference materials (CRMs) for the specific fuel type suspected at the site. Matching the analytical standard to the contaminant source improves accuracy in TPH quantitation.
Warning: Natural organic matter (humic acids) can produce elevated TPH results if silica gel cleanup is omitted. API 4593 stresses the importance of cleanup for soils with high organic carbon content.
Implementation Highlights and Best Practices
Successful implementation of API 4593 guidance requires careful alignment of site objectives with analytical capabilities. For example, if the goal is to assess human health risk from inhalation, VOC analysis via EPA Method 8260B (low-level) should be prioritized. If ecological risk is the primary concern, PAH analysis using EPA Method 8270C may be more appropriate.
Subsampling homogeneity is a known challenge in petroleum-contaminated soil analysis. The publication recommends collecting at least three discrete aliquots from each sample jar and, if feasible, performing total solids correction to report concentrations on a dry-weight basis. Data evaluation should include comparison against applicable regulatory screening levels (e.g., EPA RSLs, state-specific cleanup goals).
For sites with multiple contamination sources, fingerprinting techniques—such as calculation of alkane ratios or PAH diagnostic ratios—can aid in source apportionment, although such interpretation is beyond the core scope of API 4593.
Success: Laboratories that follow the QA/QC protocols in API Publ 4593 consistently achieve defensible data that withstand regulatory scrutiny during site closure negotiations.
Compliance and Regulatory Alignment
API Publ 4593-1994 does not supersede any federal or state regulations but is widely recognized as a “good practice” document. In many jurisdictions, using methods and protocols consistent with API 4593 can satisfy the analytical requirements of corrective action rules (e.g., TCEQ, NJDEP, CalEPA). The publication aligns with the U.S. EPA’s SW-846 methods and incorporates many of the same quality control criteria, making it compatible with federal RCRA and CERCLA site assessments.
Users should note that some regulatory programs have specific requirements for TPH analysis (e.g., Massachusetts MCP provides its own method). API 4593 should be supplemented with state-specific guidance where applicable. The document also references earlier ASTM guides (e.g., ASTM E1912) and remains consistent with the later ASTM D5769 and D7353 standards.
Important: This publication is from 1994. Analysts should verify that the cited method numbers and acceptance criteria remain current. Many EPA methods have been updated (e.g., 8260C vs. 8260B); ensure the laboratory uses the most current version unless otherwise required by statute.
Frequently Asked Questions
Q: What is the difference between API Publ 4593 and an ASTM standard?
A: API 4593 is a publication (guidance document) rather than a formal consensus standard. It provides recommended practices and procedures but does not go through the same balloting process as ASTM standards. However, it is widely referenced in environmental contracts and regulatory guidance as an authoritative source for petroleum hydrocarbon analysis in soil.
A: API 4593 is a publication (guidance document) rather than a formal consensus standard. It provides recommended practices and procedures but does not go through the same balloting process as ASTM standards. However, it is widely referenced in environmental contracts and regulatory guidance as an authoritative source for petroleum hydrocarbon analysis in soil.
Q: Can API 4593 be used for groundwater sampling?
A: The publication’s focus is on soil matrices. While some of the analytical methods (e.g., EPA 8260B) are also applicable to groundwater, the sampling and preservation guidance is specifically written for soil. For groundwater, refer to API Publication 4592 or EPA guidance for sample collection.
A: The publication’s focus is on soil matrices. While some of the analytical methods (e.g., EPA 8260B) are also applicable to groundwater, the sampling and preservation guidance is specifically written for soil. For groundwater, refer to API Publication 4592 or EPA guidance for sample collection.
Q: Does API 4593 include risk-based screening levels?
A: No. API 4593 does not specify cleanup or screening levels. It focuses solely on sampling and analysis procedures. The data generated using its protocols can be compared against risk-based values from the EPA, state agencies, or API’s own Risk-Based Decision Making (RBDM) publications.
A: No. API 4593 does not specify cleanup or screening levels. It focuses solely on sampling and analysis procedures. The data generated using its protocols can be compared against risk-based values from the EPA, state agencies, or API’s own Risk-Based Decision Making (RBDM) publications.
Q: Is the “scan” version of this publication still acceptable?
A: Yes. The “scan” refers to a digitized copy of the original 1994 print document. The technical content remains unchanged. However, users should ensure they have the complete document, as missing pages could affect method understanding. The publication has not been revised, so it represents the state of practice as of 1994.
A: Yes. The “scan” refers to a digitized copy of the original 1994 print document. The technical content remains unchanged. However, users should ensure they have the complete document, as missing pages could affect method understanding. The publication has not been revised, so it represents the state of practice as of 1994.
— 2026