SITE ASSESSMENT

The Site Assessment is aimed at identifying the most appropriate application area and the most appropriate On-Site Sewage System to be used. Assessment criteria entails features such as:

FLOOD POTENTIAL
A 1 in 20 years flood probability contour may be used as limit for a land application area.

CLIMATE
Influences the hydraulic load for all types of land application systems.

EXPOSURE
Sun and wind exposure on land application areas should be maximized to enhance evaporation.

SLOPE
Excessive slope might pose problems for installing Systems and for even distribution of the effluent into the soil.

BUFFER DISTANCE
Zones must be kept between an On-Site System and sensitive environments (creeks/dams).

These and various other factors have to be taken in account to design an On-Site System. However, one of the most important features of all is the Soil and its ability to deal with effluent.

Therefore a Soil Assessment has to be undertaken.

SOIL ASSESSMENT

Soil is a complex arrangement of mineral and organic particles that vary horizontally and vertically in space, and vary with time. Having an understanding of the soil on a site will assist in choosing and sizing an On-Site Sewage Management System that will perform to expectations.

Soil Assessments involve observing and measuring attributes within a soil profile. A soil profile is a vertical section of soil consisting of various soil horizons. A soil horizon is layer of soil that may differ from adjacent layers in physical, chemical and biological properties. In general, soil characteristics can be assessed from auger boring, soil pits, soil cores or existing vertical exposures, like roadside cuttings.

Soil features to be investigated:

DEPTH OF SOIL
A soil depth of less than 0.6m to bedrock might not have enough capacity to filter nutrients and pathogens.

DEPTH TO EPISODIC/SEASONAL WATER TABLE
Attention must be given to ground water protection.

SOIL PERMEABILITY
Saturated hydraulic conductivity (permeability) is the measure of the soil ability to transmit water.

COURSE FRAGMENTS
Fragments larger than 2mm can pose limitations on root growth and lower the soil capacity to supply water and nutrients to vegetation.

BULK DENSITY
The measure of the soils porosity and structure.

PH
The PH value indicates the soils condition for vegetation growth and solubility. Soils with PH 4.5 - 8.5 should pose no constraints for land application area.

SODICITY
Sodic soil tend to have low infiltration capacity, low hydraulic conductivity and are susceptible to erosion.

CATION EXCHANGE CAPACITY
This process is referred to as Adsorption.

PHOSPHOROUS SORPTION CAPACITY
The capacity of soil to absorb phosphorus.

DISPERSIVENESS
Dispersive soils pose limitations to On-Site Sewage Management because of the potential loss of soil structure when effluent is applied. Soil pores can become smaller or completely block, which can lead to System failure.

The most limiting feature of a Site and Soil Assessment will be what determines the Site capability for a land application system or On-Site Sewage Management System.