Backfill and Compaction After Pool Removal: What to Ask For
The fill that replaces a pool matters as much as the demolition. This guide covers what to ask for on backfill and compaction, and why each item matters years later.
Short answer: If anything may be built over the old pool, ask for engineered fill: clean material placed under an engineer’s supervision, tested against a lab standard, with a signed report. Non-engineered fill can settle. No Mid-Atlantic code we found sets one compaction percentage for every pool fill, so your permit office decides.
What is the difference between engineered and non-engineered fill?
ASTM, the standards body, describes engineering fill as soil compacted to a dense state so it has satisfactory strength, compressibility and permeability. Engineered fill is built to a written target and checked against it. Non-engineered fill is soil or stone that goes into the hole without that testing. Both can look the same from the lawn.
Some offices treat the two differently. As our guide to full, partial and abandoned-in-place removal explains, one Maryland county ties engineered fill to building near the pool. This guide covers what sits behind that choice.
Why do filled-in pools settle?
Settling means the fill sinks over time, and it matters most when one part sinks more than the part beside it. Loose fill holds more air spaces and compresses under its own weight, rain and anything built on top. ASTM notes that heavier compaction effort leaves fewer air voids and less compressibility.
Latham’s installation guide for the Corinthian 12 says excavated soil used as backfill in a shell’s hole will settle. That is a different hole, but it shows the same principle.
What are the ASTM D698 and D1557 tests?
Both are laboratory methods. A sample of the actual fill soil is packed into a small mold with a weighted rammer, at several moisture levels. The results show the soil’s maximum dry density and the moisture level where it packs best. Fill placed in the ground is later measured and expressed as a percentage of that laboratory maximum. The two methods differ in how hard the rammer works.
| Method | Common name | Rammer | Compactive effort |
|---|---|---|---|
| ASTM D698 | Standard Proctor | 5.5 lbf, dropped 12 inches | 12,400 ft-lbf per cubic foot |
| ASTM D1557 | Modified Proctor | 10 lbf, dropped 18 inches | 56,000 ft-lbf per cubic foot |
Because the efforts differ, “95 percent” or “90 percent” means nothing until the test is named. ASTM says codes may direct which of the two is used. Both methods apply to soils with 30 percent or less of their mass retained on a three-quarter-inch sieve, so a fill full of large chunks falls outside what the tests describe. We read ASTM’s own pages for these standards, not the full standards.
What is a compaction test or geotechnical report, and who orders it?
A compaction report records tests on fill after it is placed. One field method, described in ASTM D6938, uses a nuclear gauge to measure in-place density and moisture. A geotechnical engineer takes a wider view: the soil, the fill and what it can support.
The pages we read tie the work to the project. Prince George’s County requires a subgrade inspection before structural fill goes in and a certified compaction report, approved by its inspector, before the final inspection. The sources do not say who must hire the engineer or testing firm. Settle that in your contract.
Does any local code set a compaction percentage?
The only pool-specific figure we found is in Prince George’s County, Maryland’s Building Bulletin 2013-01: 95 percent of ASTM D-698, for a pool with a building planned over it or within five feet, with a soil engineer supervising and a certified report. That is one county’s requirement, not a regional rule.
The pool and demolition permit pages we read for Fairfax County, Prince William County, D.C. and one more Maryland county do not mention fill or compaction. For Loudoun County, Arlington and West Virginia, call the permit office before work starts. Ask how your own office treats fill for a pool.
Why does debris-free fill matter?
Prince George’s bulletin states that no construction debris is allowed in fill for an abandoned pool. It does not say why. Our reading is that the lab tests above describe soil, and a fill of mixed rubble cannot be checked against them in the same way. Ask your contractor what is in the fill and where the removed material went.
How should the filled area drain?
Prince George’s County requires the pool bottom to be opened or broken and inspected before backfill when a pool is abandoned in place. Ask whether the floor will be opened, whether you can see it inspected before fill goes in, and how the final grade sheds water. If the pool must be emptied first, see our guide to draining a pool safely.
Can you build on a filled-in pool, or put in a new pool?
Sometimes, and the answer comes from your permit office and an engineer, not from the contractor alone. Tell everyone about your plans before the hole is filled.
A new fiberglass pool needs a different excavation. Latham’s guide describes a hole dug close to the shell’s size, a compacted bed of sand or clean gravel, no excavated soil as fill, and a sump pipe or daylight drain. It does not describe setting a shell into a filled pool, so ask your installer. See replacing a concrete, gunite or vinyl pool with fiberglass and why a shell cannot sit over a concrete pool.
What should you get in writing and keep?
- Fill material: type, source, and a statement that it contains no demolition debris or trash.
- Placement method: how the fill is placed and compacted, as described by your contractor or engineer.
- Test results: the lab standard named (D698 or D1557), the target percentage, the field results and who ran the tests.
- Inspection sign-offs: the pre-fill inspection, any fill inspection and the final inspection.
- As-built record: a sketch of the pool’s footprint and depth, distances to the house and property lines, and what remains below the fill.
Keep the set with your permit papers and hand it to the next owner or to anyone designing a future addition, deck or pool.
Questions to ask any contractor
- Will the fill be engineered, and who is the engineer?
- What material is going in, and where does it come from?
- Which lab standard and target apply, and who set them?
- Who hires the testing firm, and will I receive the full report?
- Which inspections happen before and after the fill?
- How will water drain from the area, and what is the final grade?
- Will the report support a future addition or pool? Can I have that in writing?
Last reviewed October 2026 by Calm Water Pools.
Related guides
- How to verify a pool removal contractor
- How long pool removal takes, and the best season
- Partial vs full pool removal
- What affects the cost of removing an inground pool
- Replace a concrete, gunite or vinyl pool with fiberglass
- Can you put a fiberglass pool over a concrete pool?
- How to safely drain a fiberglass pool
Thinking about removing or replacing an old pool in Maryland, D.C., Northern Virginia or West Virginia? See how Calm Water Pools coordinates removal and replacement or call 240-372-4440.