The El Segundo Bottom


Why the name “El Segundo”?  The answer is rather simple; the El Segundo Bottom was first installed at Chevron’s El Segundo Refinery. In an effort to limit potential seepage from the floors of old storage tanks into ground water, Chevron’s El Segundo Refinery, designed a system with multiple layers of containment. Chevron was the first petrochemical company in the United States to adopt a standard for double bottoms. This standard was cutting edge engineering in the 1970’s and positioned Chevron as one of the nation’s most environmentally conscious companies.

The Original Design:

  1.  A tank contractor will slot the shell of the existing storage tank approximately 3-4 inches above the existing bottom.
  2. The existing bottom will be freed of sharp edges and welds.
  3. A geo-textile fabric is then laid over the bottom, to protect the liner from damage.
  4. A liner is then installed over the top of the existing bottom and geo-textile fabric. The liner is then anchored to the shell or bottom.Concrete is placed over the liner accounting for the appropriate floor slope.El Segundo Bottom
  5.  Leak detection grooves are formed or cut, in a spoke pattern, from the center of the tank to the shell, where they tie into leak detection ports welded to the dead shell section.
  6. Once the concrete has sufficiently cured, a new bottom will be installed over it. The new bottom will extend beyond the tank shell 2-3”. The new floor shall be installed in accordance with API 650 and API 653.
  7. All shell penetrations in the lowest shell course, which no longer meet API 650 spacing requirements, shall be raised, trimmed, or adjusted by adding reinforcement.

 How it Works:

  1. If the bottom of the tank begins to leak
  2. Product travels down to the concrete and into leak detection ports
  3. The tank will have periodic checks of leak detection ports, or will have product sensors installed to notify tank owner of a leak.
  4. Product will then be trapped by the liner
  5. If for any reason the product breaches the liner the original bottom is still in place to contain the product.
  6. Once a leak has been detected, the tank can be cleaned and gas freed and the bottom can be repaired or replaced. Note; there is no risk of environmental contamination because all leaking product is contained by the El Segundo Bottom.


Over the years there have been multiple variations of the El Segundo Bottom. In most cases, the industry simply calls these double bottoms.

  1. Concrete will often be replaced by sand and slotted and sleeved pipes will replace the leak detection groves.
  2. Sand or concrete may be used without the installation of the liner, when the original bottom is intact.
  3. Note: All repairs must be made in accordance with API 650 and API 653 regardless of style.

If your company is in need of a new bottom or you are looking to install an El Segundo style bottom, please contact Advance Tank and Construction and we will assist you in the process. From conception to completion we can take care of all of your tank needs.