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API RP 1604-1996: Recommended Practice for Closure of Underground Petroleum Storage Tanks – Technical Overview
Guidelines for Safe and Compliant Decommissioning of Underground Storage Tank Systems
API Recommended Practice 1604, first published in 1996 and reaffirmed in subsequent years, provides comprehensive guidelines for the closure of underground storage tanks (USTs) that have contained petroleum products. The document establishes a uniform set of procedures to ensure that tank systems are decommissioned in a manner protective of human health and the environment. This article examines the scope, key technical requirements, and compliance aspects of API RP 1604‑1996 (the “1996 scan” edition).
1. Scope and Purpose
API RP 1604-1996 applies to UST systems used for storing petroleum substances, including gasoline, diesel, fuel oil, and used oil. It covers both single‑wall and double‑wall tanks, as well as associated piping and dispensers. The recommended practice is intended for use by owners, operators, environmental consultants, and regulatory personnel involved in the closure phase of a UST’s lifecycle.
The document addresses two primary closure methods:
- Removal – excavating the tank and appurtenances for disposal or recycling.
- Abandonment in Place (AIP) – leaving the tank in the ground after cleaning and filling with an inert solid material.
Each method has specific prerequisites regarding subsurface conditions, structural integrity, and regulatory approval.
Tip: Even if local regulations allow abandonment in place, API RP 1604 recommends removal wherever feasible, as it eliminates future liability and permits thorough site assessment beneath the tank.
2. Technical Requirements and Procedures
2.1 Pre‑Closure Planning
Before any closure activity, the standard requires compiling as‑built records, waste manifests, and leak‑detection history. The local regulatory authority must be notified, and a pre‑closure site assessment should be conducted to establish baseline conditions. All tanks must be emptied, and vapours must be controlled to safe levels before cutting or removing.
2.2 Tank Removal
Where removal is elected, the following steps are outlined:
- Emptying and Cleaning: Remove all product, sludge, and residuals. Cleaning must be performed according to API 1604 recommended practices, including atmospheric testing for lower explosive limit (LEL).
- Disconnection: Isolate piping and electrical connections.
- Excavation: Expose the tank, avoiding damage to adjacent structures.
- Removal: Lift the tank and transport for disposal at an approved facility.
- Site Assessment: Collect soil and groundwater samples from the excavation area per the prescribed sampling plan.
2.3 Abandonment in Place (AIP)
AIP may be considered when removal would pose unacceptable risks (e.g., structural collapse, high water table) or when local ordinances permit. The standard specifies:
- The tank must be thoroughly cleaned and determined to be structurally sound.
- All product lines must be removed or sealed.
- The tank must be filled completely with an inert material (e.g., cement slurry, sand) to prevent future collapse.
- All openings (fill pipes, gauges, vents) must be permanently sealed.
- A site assessment is required at the perimeter of the tank and, if possible, beneath the tank using sidewall samples or soil borings.
2.4 Site Assessment and Sampling
API RP 1604‑1996 provides detailed guidance on the number and location of soil and groundwater samples. The table below summarizes the minimum requirements from the 1996 edition.
| Parameter | Removal Closure | Abandonment in Place |
|---|---|---|
| Soil samples – below tank | At least 1 per 10 ft of tank length; from the base of the excavation | As close to tank bottom as possible (sidewall push or auger hole) |
| Soil samples – piping runs | At least 1 per 50 ft of trench | Same as removal |
| Groundwater samples | If water is encountered; at least 1 per tank footprint | If water is encountered; at least 1 up‑gradient and 1 down‑gradient |
| Analytical tests | Total petroleum hydrocarbons (TPH), BTEX, and applicable state parameters | Same as removal |
Important: The 1996 edition predates many modern risk‑based corrective action (RBCA) frameworks. Practitioners should verify that the sampling plan meets current state or local requirements, which may be more rigorous.
3. Compliance and Documentation
Compliance with API RP 1604‑1996 is not mandatory by default, but the recommended practice has been adopted or referenced by many states and local authorities. Documenting adherence to the standard can demonstrate due diligence and may expedite regulatory closure.
3.1 Reporting Requirements
The standard specifies that a closure report be prepared containing:
- Site map and photos
- Pre‑closure inspection results
- Cleaning and removal/AIP procedures
- Sampling methodology and analytical results
- Conclusions and recommendations
Records must be maintained for a period consistent with local regulations (typically at least 3 years or as specified by the implementing agency).
3.2 Training and Qualifications
API RP 1604‑1996 emphasizes that closure activities be performed under the supervision of a qualified environmental professional. Personnel involved in tank cleaning and removal should have training in confined space entry, hazardous waste operations, and emergency response.
Best Practice: Even if using a later edition of API RP 1604 (e.g., 2015 reaffirmed), the core principles of the 1996 edition remain relevant. Align closure plans with the latest state guidance and incorporate new analytical methods where beneficial.
3.3 Regulatory Interface
The United States Environmental Protection Agency (USEPA) underground storage tank closure regulations (40 CFR Part 280 Subpart G) require closure assessment similar to that described in API RP 1604. Many states have authorized programs that directly cite or endorse API RP 1604. The 1996 scan edition remains a widely recognized baseline, although practitioners should consult the most recent edition for updates on abandonment criteria and sampling protocols.
Caution: Failure to comply with applicable regulations may result in civil or criminal liability. API RP 1604‑1996 is a guide, not a substitute for independent legal and regulatory review.
Frequently Asked Questions
Q: Can all underground tanks be abandoned in place per API RP 1604‑1996?
A: No. The standard restricts abandonment in place to tanks that are structurally sound, thoroughly cleaned, and where removal is unfeasible due to safety risks or regulatory constraints. Many jurisdictions prohibit AIP for tanks that have ever leaked or are located in sensitive environments.
A: No. The standard restricts abandonment in place to tanks that are structurally sound, thoroughly cleaned, and where removal is unfeasible due to safety risks or regulatory constraints. Many jurisdictions prohibit AIP for tanks that have ever leaked or are located in sensitive environments.
Q: What are the most significant changes in later editions of API RP 1604?
A: Later editions (e.g., reaffirmed in 2005 and 2015) include updated references, clearer language on risk‑based sampling, and alignment with contemporary vapor intrusion assessment methods. The 1996 edition lacks certain provisions for vapor monitoring and may not reference modern analytical test methods (e.g., TPH‑GC).
A: Later editions (e.g., reaffirmed in 2005 and 2015) include updated references, clearer language on risk‑based sampling, and alignment with contemporary vapor intrusion assessment methods. The 1996 edition lacks certain provisions for vapor monitoring and may not reference modern analytical test methods (e.g., TPH‑GC).
Q: Is API RP 1604‑1996 still accepted by regulators?
A: Many regulators still accept the 1996 edition as a recognized industry standard, though they often require compliance with more current state release‑detection or sample‑analysis protocols. Always confirm with the local implementing agency which edition is accepted before commencing closure work.
A: Many regulators still accept the 1996 edition as a recognized industry standard, though they often require compliance with more current state release‑detection or sample‑analysis protocols. Always confirm with the local implementing agency which edition is accepted before commencing closure work.