New Castle County, Delaware
The soil mapped across New Castle County is predominantly classified well drained. Below is what that classification means for a basement, what it does not mean, and what the three repairs it points to cost here.
34% of the county’s mapped soil area falls in classes the USDA describes as wet enough to need artificial drainage for ordinary use. Saturated soil against a foundation wall is what creates hydrostatic pressure.
Linear extensibility 1.9% in the top metre — low. Volume change in this soil is negligible.
Shallowest annual water table maps at about 125 cm (4.1 ft) below the surface — water table below basement floor. A typical US basement floor sits just under 200 cm, which is also the deepest the soil survey reports.
Source: BasementSoil physiographic region model — region “Atlantic coastal plain”. Not a soil survey of this county. Why.
What the ground here is made of
Atlantic coastal plain. Unconsolidated sands and clays at low elevation
Extremely variable over short distances: sand and saturated clay side by side. A county figure means less here than anywhere else we cover — the individual parcel decides.
How the county’s soil area splits between drainage classes
| USDA drainage class | Share of mapped area | |
|---|---|---|
| excessively drained | 3% | |
| somewhat excessively drained | 14% | |
| well drained | 31% | |
| moderately well drained | 17% | |
| somewhat poorly drained | 14% | |
| poorly drained | 14% | |
| very poorly drained | 6% |
Drainage class definitions: USDA NRCS SSURGO. Highlighted row is the dominant condition (drclassdcd). Wettest class present in the county: poorly drained.
Key soil values for New Castle County
| Dominant drainage class | well drained — water leaves readily; the profile is saturated only briefly after rain |
|---|---|
| Wettest class present | poorly drained |
| Area needing artificial drainage | 34% |
| Linear extensibility (shrink-swell) | 1.9% — low modelled |
| Shallowest annual water table | 125 cm (4.1 ft) |
| Hydrologic soil group | A/D |
| Physiographic region | Atlantic coastal plain |
| Expected radon zone | Zone 3 (lowest) — predicted indoor average below 2 pCi/L expected, not the official designation |
| Basements in this state | a minority of homes have one |
What the three likely repairs cost in Delaware
| Reference job | Modelled range in DE |
|---|---|
| Interior drain along two walls + sump pump | $5,300–$11,400 |
| Exterior excavation of one 40 ft wall | $4,000–$11,350 |
| Underpinning on 10 piers | $15,750–$33,600 |
Reference basement 30 × 40 ft. Price book 2026.08, updated 2026-08-11, regional factor for DE: ×1.05. Run your own dimensions.
Given this soil, the order of operations here
- Get the second and third quote before you sign anything. Same scope, in writing, from firms that are not owned by the same parent. How to do it without paying twice.
Questions about New Castle County soil
Does “well drained” soil mean my basement will flood?
No. The class describes how long the soil profile stays saturated in an average year across mapped areas of the county. It raises or lowers the statistical odds of hydrostatic pressure against a wall. It says nothing about your grading, your footing drain or your downspouts — which is usually what decides whether water actually gets in.
Which number should I care about most?
Whichever is highest, because they point at different contractors. High moisture and water table risk is a drainage and pump problem. High crack risk with low moisture risk — common on the Colorado Front Range and in the Flint Hills — is a structural problem, and a waterproofing salesman is the wrong person to call about it.
A contractor told me my county has “the worst soil in the state”. Is that true?
Check it here and on the USDA source we link. It is a specific, checkable claim, and in our experience of the sales scripts it is used loosely. New Castle County scores 35 out of 100 overall on our combined index, which is moderate for the counties we cover.
Will my homeowners insurance pay for this?
Almost certainly not, if the cause is groundwater seeping in gradually. That is excluded from standard US homeowners policies, and the exclusion is usually the reason people find this site. What is and is not covered.
Does “well drained” soil mean my basement will flood?
No. The class describes how long the soil profile stays saturated in an average year across mapped areas of the county. It raises or lowers the statistical odds of hydrostatic pressure against a wall. It says nothing about your grading, your footing drain or your downspouts — which is usually what decides whether water actually gets in.
Which number should I care about most?
Whichever is highest, because they point at different contractors. High moisture and water table risk is a drainage and pump problem. High crack risk with low moisture risk — common on the Colorado Front Range and in the Flint Hills — is a structural problem, and a waterproofing salesman is the wrong person to call about it.
A contractor told me my county has “the worst soil in the state”. Is that true?
Check it here and on the USDA source we link. It is a specific, checkable claim, and in our experience of the sales scripts it is used loosely. New Castle County scores 35 out of 100 overall on our combined index, which is moderate for the counties we cover.
Will my homeowners insurance pay for this?
Almost certainly not, if the cause is groundwater seeping in gradually. That is excluded from standard US homeowners policies, and the exclusion is usually the reason people find this site. What is and is not covered.
Nearby counties
Neighbours in the same physiographic region behave similarly. Different region on the other side of the county line means genuinely different ground.
All 3 counties in Delaware · More about “well drained” soil
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