Soil series profile
Blocktown soil series
Blocktown is a well drained soil with a channery silt loam surface, mapped on 59,935 acres in 19 counties across 5 states. Hydrologic group D.
- Drainage class
- Well drained >99% of mapped acres
- Hydrologic group
- D 95% of mapped acres
- Typical topsoil pH
- 5.2 strongly acidic · range 5.2–6.5
- Mapped area
- 60k acres in 19 counties, 5 states
Typical Blocktown profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–6 in (Ap) | Channery silt loam | 5.2 | 18% | 27% | 2.5% |
| 6–17 in (Bt) | Extremely channery silt loam | 5.2 | 23% | 22% | 0.2% |
| 17–21 in (Cr) | Bedrock | Not reported | Not reported | Not reported | Not reported |
| 21–25 in (R) | Bedrock | Not reported | Not reported | Not reported | Not reported |
What this means
What Blocktown soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Blocktown soils is strongly acidic: pH 5.2 (most land between 5.2 and 6.5). Most vegetables and lawn grasses do best around 6.0 to 7.0, so lime is often needed; blueberries, azaleas and rhododendrons like it as it is.
Loamy topsoil (loam, silt loam and similar) covers >99% of mapped Blocktown acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is channery silt loam (68% of mapped Blocktown acres).
>99% of mapped Blocktown acres is moderately well to excessively drained, which suits most garden plants.
For lawns and yards
On 96% of mapped acres, rain soaks in slowly (hydrologic groups C and D, including dual groups that are D until drained). Expect runoff and puddles after heavy rain: core-aerate compacted lawns and keep ground sloping away from foundations.
For a septic system
For conventional septic absorption fields, NRCS rates 95% of the acres in mapped Blocktown soils very limited, 0% somewhat limited and 4% not limited.
Where the soil is very limited (slow permeability, a high water table, flooding, shallow bedrock or steep slopes), alternative systems such as mound or sand-filter designs are common and cost more.
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Where Blocktown soil is found
Mapped acres
Blocktown is mapped in Maryland, Pennsylvania, Virginia, Delaware and District of Columbia.
| County | Acres | Share of county land |
|---|---|---|
| Montgomery County, MD | 28,589 | 9.0% |
| Frederick County, MD | 10,520 | 2.5% |
| Baltimore County, MD | 6,203 | 1.7% |
| Carroll County, MD | 5,068 | 1.8% |
| Chester County, PA | 1,910 | 0.4% |
| Culpeper County, VA | 1,764 | 0.9% |
| Harford County, MD | 1,564 | 0.6% |
| Howard County, MD | 1,489 | 0.9% |
| York County, PA | 874 | 0.2% |
| New Castle County, DE | 780 | 0.3% |
| Cecil County, MD | 648 | 0.3% |
| Adams County, PA | 183 | 0.1% |
| Montgomery County, PA | 111 | 0.0% |
| Philadelphia County, PA | 94 | 0.1% |
| Prince George's County, MD | 67 | 0.0% |
| Bucks County, PA | 37 | 0.0% |
| District of Columbia, DC | 18 | 0.0% |
| Delaware County, PA | 10 | 0.0% |
| Baltimore city, MD | 7 | 0.0% |
Septic absorption fields
NRCS rating, share of Blocktown acres
Show as a table
| Category | Share of acres |
|---|---|
| Not limited | 4.4% |
| Somewhat limited | 0.0% |
| Very limited | 95.3% |
| Not rated | 0.3% |
Drainage, water table and flooding
Share of Blocktown acres
- Depth to seasonal high water table
- None reported within about 6.5 feet (median where reported).
- Flooding
- Not mapped as flooding on most acres.
- Slope
- Typically 6–35% (median 20%).
- Topsoil organic matter
- Median 2.5%.
Drainage class
Show as a table
| Category | Share of acres |
|---|---|
| Excessively drained | 0.0% |
| Somewhat excessively drained | 0.0% |
| Well drained | 99.7% |
| Moderately well drained | 0.0% |
| Somewhat poorly drained | 0.0% |
| Poorly drained | 0.0% |
| Very poorly drained | 0.0% |
| Not rated | 0.3% |
Hydrologic soil group
Show as a table
| Category | Share of acres |
|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 0.0% |
| B: moderate infiltration | 0.0% |
| C: slow infiltration | 0.4% |
| D: very slow infiltration (clayey, shallow or wet) | 94.8% |
| A/D: D as is, A if drained | 0.0% |
| B/D: D as is, B if drained | 0.0% |
| C/D: D as is, C if drained | 0.9% |
| Not rated | 4.0% |
Sources & data dates
- Source
- USDA NRCS Soil Survey Geographic Database (SSURGO), queried through Soil Data Access. Public domain.
- Data date
- SSURGO as published on November 3, 2026 (most recent survey area update October 26, 2026). NRCS refreshes SSURGO each October.
- Scope
- All map unit components named Blocktown (component kind "Series") in SSURGO: 59,935 acres.
- Method
- Shares are by mapped acres of Blocktown components. The profile comes from the single largest Blocktown component. Full methodology.