Last summer, some regions of the United States saw excessive rainfall and others excessive drought. Both conditions are attributed in part to changing climate. Models predict rainfall and storm events will intensify and increase in parts of the Midwest and East while in other areas, particularly the Southwest, the climate will become more arid.

Globally, warming is melting polar ice at alarming rates leading to sea water rise along the coasts. Evidence of rising seas is seen in the presence of “ghost forests” where the vegetation is dying because salt water is intruding inland as the ocean rise is killing the trees. This saltwater intrusion is also affecting groundwater levels and water quality. For residents near the coast this can render their well and septic system unusable.

We in the Great Lakes Region and middle of the country might have a tendency to say, “Wow, I sure am glad I live here and do not have to deal with that!” We may not have to deal with saltwater intrusion, but we will have to deal with similar impacts to our septic systems due to increased temperature and rainfall intensity.

ONSITE AND FLOODPLAINS

What are some of the problems we face due to increased rain events? There is the potential for the flooded systems, reduced treatment efficiencies and reduced ability to accept effluent to the point of system hydraulic failure. 

Flooding is one of the most obvious impacts with increased precipitation. Areas previously prone to flooding or ponding may see those flooding periods increase in number, length of time and levels. Most states have standards or requirements for systems installed in floodplains. 

In general, they call for not using the system during flood periods and require specific action after the waters recede before the system can be used. The longer the flood persists, the more time the homeowner must deal with not being able to use the system. Standards include pumping tanks and distribution boxes to remove solids and sediment and inspecting system components to determine they remain structurally sound and operating the way they are supposed to. 

From a soil treatment area perspective, the field was required to be installed so the bottom of the infiltrative surface was a minimum of 6 inches above the 100-year flood level to ensure sediment did not impact the treatment area. With increased flood levels and frequency, this may not be enough protection. Floodplain codes and standards may need to be revised to the point of not allowing residences in the area.

Increased precipitation also results in rising inland lake levels and corresponding groundwater connected with the lakes. Any lakeshore owner will tell you they have to deal with numerous issues when water levels rise in the lake. The immediate ones they see are loss of shoreline area from their lot and increased bank erosion affecting lake water clarity. What they often do not realize is the impact it may have on their in-ground septic system.

When groundwater rises, the separation distance to the infiltrative surface of the soil treatment unit narrows. This distance may be reduced to the point where there is not enough unsaturated soil, with enough oxygen to provide adequate treatment. This can result in greater transport of pathogens, nutrients and biochemical oxygen demand to the groundwater. 

BIOMAT ISSUES 

The nutrients and pathogens can move directly to the groundwater and the lake. The nutrients can contribute to increased algal blooms and provide the potential to have public health impacts by direct body contact through swimming or by contaminating nearby wells.

In addition to lack of treatment as the separation distance decreases and oxygen becomes less available in the soil, biomat development will increase. This causes a more resistant biomat, reducing the ability of the system to accept the amount of water delivered from the residence. That leads to hydraulic failure with effluent surfacing in the yard. 

Areas away from lakeshores are similarly affected due to rising groundwater levels and an increase in level and length of time periodic saturated zones exist in soils. The longer the soil is saturated and the closer it is to the bottom of a soil treatment system, the more it impacts the soil’s ability to treat and accept sewage effluent. 

Present standards call for minimum separation distances from periodic or perched groundwater areas. Typically, these standards require from two to five feet of separation. These requirements are designed to ensure treatment and to take into account biomat development when determining the size of the system. 

As periods of increased temperature and precipitation persist, there may be a need to adjust the standards and recommendations to incorporate anticipated groundwater rise. Permitting authorities could then begin to apply the standards to new or replacement installation of systems to prepare a gradual transition to what will be a new normal. If we do not anticipate some of these changes, we run the risk of future system failures so numerous they overwhelm our capacity to address them. 

WORKING TOGETHER

As a final note, one aspect of codes or rules should include the ability to modify and change them as conditions and technology change. This is the time states and other permitting authorities should be consulting with the industry about changes that may be needed to address problems due to climate uncertainty. Fortunately, professional organizations and associations are actively involved in obtaining funding to address the need for improved onsite sewage infrastructure.