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Soil Survey Manual - Table 6-1

Interpretive soil properties and limitation classes for septic tank suitability

Interpretive Soil Property Limitation Class
Slight Moderate Severe
Total Subsidence (cm) -- -- > 60
Flooding None Rare Common
Bedrock Depth (m) > 1.8 1-1.8 < 1
Cemented Pan Depth (m) > 1.8 1-1.8 < 1
Free Water Occurrence (m) > 1.8 1-1.8 < 1
Saturated Hydraulic Conductivity (µm/s)      
Minimum 0.6 to 1.5 m a 10-40 4-10 < 4
Maximum 0.6 to 1 m a     > 40
Slope (Pct) < 8 8-15 > 15
Fragments > 75 mm b < 25 25-50 > 50
Downslope Movement     c
Ice Melt Pitting     c
Permafrost     d
a. 0.6 to 1.5 m pertains to percolation rate; 0.6 to 1 m pertains to filtration capacity
b. Weighted average to 1 m.
c. Rate severe if occurs.
d. Rate severe if occurs above a variable critical depth (see discussion of the interpretive soil property).