On-site wastewater systems is another descriptive word for septic system. Most people don’t like to think about this subject. As long as the toilet flushes and waste matter disappears, everything is working properly. Don’t get me wrong. The septic system design used in early and present health codes did an amazing job of treatment. Older systems with tank and field designs worked their magic for many years. Problems occur after many years of operation and little or no maintenance. Let’s look at the what happens in the tank and then in the field.
In a septic tank, anaerobic bacteria do a good job of breaking down the organic, biodegradable materials into a liquefied inorganic chemical and bacteria laden solution. The separation within the tank prevents solids from carryover into the treatment field. Floating solids, heavier than water, are trapped at the surface. so unless you have an excess of floating solids (cap) or an excess of settled solids (sludge), the septic tank does a pretty good job of separation. Pumping the tank on a regular basis is the best way to head off serious (an expensive) problems.
The septic leach field receives liquefied wastewater either by gravity flow from the septic tank or by pump from the pump tank. The field distributes the liquefied waste over the full area of the field. Here aerobic bacteria in the soil work their magic on further converting pathogens and inorganic chemicals to less harmful content. A bio mass forms at the interface where there is aerated soil. This zone is called the vadose zone where aerobic breakdown takes place. The bio mass provides an important treatment zone for preventing pathogens and nutrients from entering the disposal zone. It is in the disposal zone where treated effluent from your system enters ground water.
What happens over time? Let’s assume the tank is pumped on a regular 3-5 year frequency. The leach field ages. If the soil in the leach field treatment zone gradually losses capacity to treat or becomes saturated, untreated or partially untreated wastewater is allowed to enter ground water. As a result, nutrients and pathogens can migrate into the ground water. This condition is a hidden failure condition and one that exists with many older septic systems.
As the ground water containing partially treated wastewater migrates through the soil, depending on the type of soils it comes in contact with, additional treatment and breakdown can occur. In this case, a plume of partially treated waste water moves through the soil. over time, THIS PLUME CAN TRAVEL CONSIDERABLE DISTANCES UNDER GROUND as the ground water migrates toward a water body. If the leach field is placed close to a body of water, septic influenced nutrients will eventually reach the water and cause problems. Homes that have leach fields within 300 feet of a body of water can eventually become a source of nutrients. Homes closer to the shoreline can have a much greater influence.
Nitrates are the most mobile nutrients that come from wastewater. Phosphorus, a less mobile nutrient will react quickly with soil until the soil no longer can attract more phosphate molecules. More phosphorus will migrate in the ground water using up the ground’s capacity to adsorb it until it too reaches the surface water. generally, it takes much smaller amounts of phosphates to drive the productivity of aquatic plants and algae. Rate of aquatic plant including algal growth can depend on the greater or less amounts of phosphorus present. Reducing phosphorus levels in lakes is a successful lake management strategy to improve the aesthetic value of the water.
Some lake communities were settled very early in the 20th century. Summer homes – bungalows, cabins, non-year-round houses- were built for vacationing and summer enjoyment. Many only had pit type wastewater systems called cesspools. Some had early design seepage pits. Separate tank and leach field type septic’s appeared much later after local building codes were established. I have known of instances where a drilled well was installed almost adjacent to a seepage pit because locations of these early installed systems became unknown to subsequent owner’s of the property. There are instances where the early pits are still in use. Do they still “handle” the wastewater demand? From a hydraulic perspective, yes because they do not flood out. Do they treat the wastewater? Only minimally if at all. Lake water receives much of it’s water from ground water. Ground water influenced by septics that are minimally functioning will cause problems in the lake. Currently in NJ, a house having a cesspool cannot undergo a real property transfer without the system being upgraded.