Buried Tanks Cause Wet Basement or Crawl Area

Buried components near the building foundation can cause or increase foundation leaks and wet basements or crawl areas.

When roof spillage or surface runoff land near a building foundation wall, objects buried close to the structure, such as a buried oil tank or septic tank or even a large boulder or in-sloping solid rock, or even burrows from a gopher or groundhog all form a ready cavity or hole that helps catch and accumulate water that then can penetrate the foundation wall or leak up through the basement or crawl space floor.

Buried Septic Tank or Oil Tank Near Foundation Contributes to Water Entry

Question: could my buried oil tank be causing basement water entry?

2019/02/06 Maggie said:

I have an underground oil tank, not used for 30 years. I didn’t know it was there when I bought the house. It is buried in the driveway.

A leak in the basement has been going on for a few years. Now that I know the tank is on the other side of the wall. Is the tank causing the leak in the basement? Thank you

This question and reply were posted originally

at OIL TANK LIFE, ABOVEGROUND

[Click to enlarge any image]

Reply: Why Water Leaks Through a Foundation Wall Near a Buried Oil Tank

Maggie

I would not say the tank is the prime or only cause of basement water entry but there is no doubt that an oil tank buried close to a building wall can contribute to water entry through or under the foundation wall in that area. I have personally seen and verified that phenomenon.

Watch out: If you see basement or crawl space water entry and if you see that there is a wet area along a foundation wall that is localized and that appears to be in the same location as an outdoor object that is buried close to the building, that's a strong suggestion that the excavation for the buried oil tank, septic tank, boulder, or other object is serving as a water catchment that collects and aims water at the building.

The oily stain in th the mortar joint in the concrete block foundation wall shown above was a telltale indicator of an improperly abandoned oil storage tank outside the wall. The tank had leaked oil.

Our photo below, taken at the same location but close to the crawl space floor, shows active water entry along with old heating oil.

How a buried septic tank or oil tank close to a foundation contributes to localized water entry

1. There is a water source near the building foundation wall, usually roof gutter overflow, spillage, or a downspout not directed away from the home, occasionally in-slope grade towards the wall, and very rarely, an underground water source.
2. Water isn 't being directed away from the building because of defects in point No. 1
3. Water filters down through soil, hits the original excavation made for the buried tank, finding a more-easy path downwards towards the foundation that it would in nearby areas that don't have a ready excavation and object buried near the building.
4. Enough water accumulates to overwhelm a footing drain (if present and if still working after 30+ years, which would be rare);
5. Accumulated outside water finds its way inside through the foundation wall or under the wall and up at the floor/wall joint inside.

Watch out: water from roof spillage or surface runoff will also follow trenches dug to route piping such as oil piping from a buried oil tank (shown below) and also buried water entry lines or sewer lines or buried electrical wiring.

How to Stop Foundation Leaks Near Buried Oil Tanks, Septic Tanks, Boulders, etc.

You do not normally have to remove the buried object, and in fact doing so risks leaving a new excavation of less-compacted soil that sill catches water and aims it at the foundation wall.

1. Fix the roof drainage. The solution to this problem is usually as simple as fixing and maintaining the roof gutters and downspouts. Be sure the downspout empties more than 10 ft. from the building and into an area that continues to drain away.
   
   See details at GUTTERS & DOWNSPOUTS
2. Fix surface grading: On occasion we also need to re-grade around the building to direct surface runoff away from the structure.
   
   See details at GRADING, DRAINAGE & SITE WORK
3. Desperate measures: Rarely we need to remove the buried object, fill and compact soil in the hole, or pump bentonite clay around the foundation wall.
   
   See BASEMENT WATERPROOFING for more suggestions.

You should also check the following:

• Is the oil tank empty?
• If the buried oil tank was not properly abandoned (by emptying it and filling it with sand) it should be so treated.
  
  See OIL TANK ABANDONING PROCEDURE
• Did the oil tank leak oil?
  
  Confirm by test and inspection that there is no oil in the tank
  
  See OIL TANK LEAK TEST METHODS
• If the underground tank leaked oil it'll need to be removed and the contaminated soil removed
  
  See OIL TANK LEAK TEST METHODS
  
  

For more examples of building oil or water leaks traced to a buried oil tank see

OIL TANK, BURIED, ADVICE

For clues indicating that there may be a buried oil tank near a building see

OIL TANK, BURIED, FINDING

For a discussion of just how close a septic tank may be to a building see

CLEARANCE DISTANCES, SEPTIC SYSTEM

If you see animal or other holes in the ground surface near the point of water entry

see GOPHER HOLE DAMAGE

This article series discusses methods for preventing wet basements by attention to multiple best construction practices, including the basics of foundation damp proof coating or waterproofing, poor site drainage, bentonite clay for basement waterproofing, foundation membranes to prevent leakage, foundation drain tiles, proper backfill, and proper finish grading.

...

Continue reading at EXTERIOR WATER SOURCE ELIMINATION or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

GUTTERS & DOWNSPOUTS

Or see these

Basement / Crawl Area Dry-Out Articles

• BASEMENT DE-WATERING SYSTEMS
• BASEMENT LEAKS, INSPECT FOR
• BASEMENT WATERPROOFING
• CRAWL SPACE DRYOUT
• EFFLORESCENCE SALTS & WHITE DEPOSITS
• FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
• FOUNDATION WATERPROOFING
• FOUNDATION WATERPROOFING: CRACK SEALANTS
• FOUNDATION WATERPROOFING SEALANTS
• GEOTEXTILES & DRAINAGE MATS
• GRADING, DRAINAGE & SITE WORK
• PLUMBING LEAK DETECTION & SHUTOFF DEVICES
• WATER BARRIERS, EXTERIOR BUILDING
• WATER ENTRY FROM BURIED TANKS
• WATER ENTRY in BUILDINGS - home
• WET BASEMENT PREVENTION
• WET, DEFINITION OF

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING LEAKS & WATER ENTRY

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