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2.3 Soil Absorption Areas

The soil absorption area is an integral component of any conventional and some alternative on-lot wastewater disposal systems in Pennsylvania. The soil absorption system typically receives effluent from a septic or aerobic tank and treats the effluent before the water recharges to the groundwater.   For conventional septic soil absorption systems in Pennsylvania, a minimum of 4 feet of suitable material below the system aggregate is needed to properly treat the recharging wastewater. In addition, the key to the long-term success of the system is the proper distribution and pretreatment of the wastewater. Therefore, uneven distribution of the wastewater can cause one area of the system to become overload and ultimately fail. The types of distribution systems include: a distribution box used to split flow equally to individual laterals, distribution loop were the laterals are connected at the end by unperforated piping, and pressurized distribution using a dosing pump or siphon system.

With the exception of a spray irrigation system, the minimum depth to a limiting zone is 20 inches. The actual depth to the limiting zone determines the general suitability of the site and systems that might be permitted in Pennsylvania. A limiting zone is defined as a soil horizon or condition in the soil profile or underlying strata which includes one of the following:

1)A seasonal high water table, whether perched or regional, determined by direct observation of the water table or indicated by soil mottling or redoximorphic features.

2) Rock with open joints, fractures or solution channels, or masses of loose rock fragments, including gravel, with insufficient fine soil to fill the voids between the fragments.

3)A rock formation, other stratum or soil condition which is so slowly permeable that it effectively limits downward passage of effluent.  This may include fragipan, duripan or other restrictive horizons.

 


Shallow Bedrock, Fracture Rock,
Rock Pinnacles,
Open Voids


Redoximorphic
Conditions,
Perched / Seasonal Water and/or
Fragipan Horizon

Structures Soil
Sand and Gravel
Pockets without
sufficient fine material

In Pennsylvania, the four main types of conventional individual septic systems include: