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I didn't find a similar topic on the site. I'm a first-time home owner who just closed on a property. While under contract, the seller had to remove an old UST (Underground Storage Tank) for an oil furnace. They left before being able to fill the hole, so now it's on me. It's about 15' by 20' and approximately 3' to 4' deep at the shallowest part, 5' at the deepest.

The tank was right alongside the house, so the hole has exposed some foundation. The area is dry, on high-ground, but I've read online that I need to do my homework on selecting fill so I don't negatively effect the construction. Nothing too organic, I assume? I want to restore landscaping in the area, so I do want some topsoil on top, but what should go underneath? Is there something specific I should be looking for? I'm in the mid-Atlantic region if it matters!

Much thanks in advance! I look forward to the conversation!

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    Was the removal inspected and certified? Is there any underground drainage system visible against the foundation adjacent to the hole? Or just soil all around. Usually you just get "clean fill", maybe for free, dug up from local construction sites, and add top soil.
    – jay613
    Commented Oct 13, 2023 at 17:50
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    Before you fill in the hole, better find out if the company that removed the tank was licensed for it. If it is discovered at a future time that they did not certify the tank as intact and the soil as free of contamination, you may have to pay for many bore holes and soil tests. Taking soil samples now while the hole is open is trivial and comparatively inexpensive. See for example this mid-Atlantic company blog about it (no connection): currenenvironmental.com/blog/oil-tank-removal-new-jersey
    – MTA
    Commented Oct 13, 2023 at 18:08
  • Hey guys! Thank you for your replies. The removal was not only inspected and certified but overseen by a township inspector! The tank DID have pinholes on it, but soil samples came back clean. The area received a tremendous amount of rain between the tank removal and our closing date, however, and the seller's landscaping company, who was going to come and backfill / reset paving stones, canceled on them multiple times. That's what has left me with the hole now as the new home owner. The seller gave me a very sizeable credit to do the work, though. I just want to make sure I get it done right!
    – Chris
    Commented Oct 16, 2023 at 12:29

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From your description of the tank's removal, I assume that the soil cut from the hole is long gone and you're shopping for dirt. Without knowing more about your foundation (specifically, whether it's a good idea to compact soil beside it), you can't go wrong with uniformly graded sand. The uniformly graded sand will settle to its natural density in less than a year. I'm tempted to suggest clean 3/4" crushed rock (the clean indicates that rock particles finer than 5/8" have been sifted out of this product), because it instantly settles to 95% maximum density without any compaction effort whatsoever. The problem is that I wouldn't be surprised if garden soil particles from above trickle into this soil's structure, resulting in the surface soil sagging slowly over time.

Since this is a garden which I assume isn't grass, you may not care about the soil surface sagging as the underlying soil naturally settles over time. In this case, your criteria for selecting fill should avoid highly expansive soil and soil with high frost heave susceptibility, as these soils can ramp up seasonal horizontal loads against the surface of your foundation. The International Residential Code's Table R405.1 will steer you away from such soils. Your intuition on the organic soil is correct, where this table lists it with medium susceptibility to frost heave and highly expansive.

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  • This is perfect, thank you so much for your reply! Awesome information popham, and I think 3/4" crushed rock is going to be the way to go for me! I don't know if it's appropriate for me to ask a follow-up / semi-related question, but now that the tank has been removed, the removal company also left a small 2"x4" rectangular penetration in my basement. It's where the supply and return pipes entered the home. It looks like there's an all out WAR on the internet concerning masonry caulk... how can I patch this hole in my cinderblock? Thanks again!
    – Chris
    Commented Oct 16, 2023 at 12:25
  • @Chris, use hydraulic cement.
    – popham
    Commented Oct 16, 2023 at 16:59
  • Thank you again!
    – Chris
    Commented Oct 16, 2023 at 17:37
  • @Chris, it's 3/4" clean crushed rock that has that compaction property. This crushed rock has the particles smaller than 5/8" sieved away.
    – popham
    Commented Oct 16, 2023 at 17:41
  • Indeed, noted! I appreciate your expertise again! Don't want the whole garden sinking next year!
    – Chris
    Commented Oct 16, 2023 at 17:43

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