Risk = Hazard x Exposure
The public health risk from undocumented onsite wastewater systems (OWS) arises from a number of key risk factors. Adequate treatment of wastewater is dependent on the soil, type of treatment system, and characteristics of the wastewater.
The key risk factors identified by Boulder County Public Health (BCPH) were:
- Density: High density (greater than 1 dwelling per acre) of systems increases concentrations of pollutants in a given area.
- Age: The ability of a system to effectively treat effluent decreases over time.
- Undocumented Systems: It is probable that undocumented systems do not meet current regulations and are likely impacting water quality in Boulder County.
- Distance to Groundwater: The greater the distance between groundwater and a septic system, the less chance of groundwater contamination.
- Private Drinking Water Systems: Private drinking water sources can be negatively impacted by a septic system.
- Soil: Inadequate soils do not provide effective treatment of effluent.
- Slope: The steeper the slope, the greater the risk of system failure. If the ground slope is in excess of 30% the system must be designed by a registered professional engineer (RPE). Having engineering oversight does not guarantee longevity or adequacy of a system on steep slopes.
- Distance to Surface Water: The greater the distance between surface water and septic system, the less chance of surface water contamination.
Please Note: This information is intended to provide a better understanding of the functions of onsite wastewater treatment and the need for proper design, installation, and maintenance. Always consult a licensed professional or public health official with questions regarding engineering, installation, and servicing of onsite wastewater systems.