Soil Suitability Mapping: A New Tool in Septic System Management 
It's an all too common scenario in communities across the country: failing septic systems from older camps and homes dump gallons of inadequately treated wastewater into lakes, rivers, and oceans. The wastewater, chock full of nutrients and bacteria, fuels excessive algae and weed growth and can lead to beach closings and unsafe drinking water. The problem can be difficult to solve since it isn't always obvious which systems are failing. Even if a failure is detected, it can be difficult to find a suitable replacement system design, especially if the soils were inadequate for an on-site soil-based disposal system in the first place. Soil suitability mapping can help identify which areas in a watershed or township may be susceptible to septic system failures and can even help determine what types of system designs would be appropriate for replacement.

Soil suitability mapping is conducted using Geographic Information Systems (GIS) technology to analyze soil types throughout the study area. The soils, slopes, geology, and groundwater resources maps in the study area are layered on top of each other and compared to the current State regulations for on-site disposal system design standards. Many areas that are not suitable for conventional on-lot soil-based wastewater disposal systems may be adequate for alternative systems, including raised sand mounds, drip irrigation, and spray irrigation systems. These alternative designs typically require less soil depth for installation than conventional systems and are becoming more and more common across the country.

The end result of the suitability mapping study is a set of maps depicting specific areas within the township where conventional septic fields, raised sand mounds, drip irrigation systems, or spray irrigation systems could be used. Areas where no soil-based wastewater disposal facilities should be constructed are also identified. These maps can then be compared to the known septic system uses in each area to determine likely failures. When failing systems are found, the proper type of system upgrade can be recommended based on the suitability mapping. Field site visits may be required in order to confirm the assumptions of the mapping project. A septic system upgrade program should then be developed in order to assist residents in addressing their septic system problems. If upgrading septic systems to sand mounds, drip irrigation, or other alternative systems is not feasible, especially when multiple failing systems exist in a neighborhood, decentralized wastewater systems should be considered.

Next month: A Review of Alternative On-Site Wastewater Technology


Example of a GIS layer showing soil suitability for alternative and conventional systems with regards to slopes in the Lake Carey Watershed Assessment

F. X. Browne, Inc. conducts soil suitability mapping, watershed inventories, and watershed restoration measures for all sizes of watersheds as well as designing wastewater systems and conducting lake and watershed studies. Please contact us at info@fxbrowne.com or 215-362-3878 for more information.