- Dec. 4, 2018
- 7 min read
Lake Phosphorus Loading from Septic Ground Water Contamination
There are reportedly 25 million septic systems in operation throughout the country. These systems are still being installed in rural developed areas of the country. Urban sprawl has fueled a tremendous increase in the number of septic systems in most states throughout the Country. This report focuses on those systems located within lake communities. Lake communities with septic systems are a part of a sensitive watershed that affects the overall quality of the water bodies.
What about septic systems? Their proper name is on-site waste water disposal systems. They are designed to treat the wastewater before it reaches ground water. A properly designed disposal field will successfully treat bacterial and inorganic compounds with perhaps one exception – nitrates for many years. There is no set age limit on septic systems. Phosphorus that is produced within the household that passes through the septic tank is captured in the disposal field soil elements, by chemical precipitation, and/or adsorption to soil particles. The soil fill must have an aerobic environment for these reactions to work and prevent phosphorus release. Bacteria from the household waste is also effectively treated in an aerobic zone close to the infiltration of wastewater just below the infiltration pipes.
The present day design requirements for septic systems are relatively recent regulations when compared to the decade’s long time frame that septic systems have been around. So it is valid to say a modern septic system that is properly installed is effective in removing phosphorus – for quite some time, but not forever.
What lake communities are dealing with in regards to groundwater contamination to the lake has slowly developed to be a major problem to the ecology of the water system. For example, at a lake in Northern New Jersey, a naturally formed lake with over 500 houses in its watershed, was developed in the early 20th century with small summer cottages on very small lots. The water remained pristine while most homes were used 3-4 months of the year. The water supported trout and had a clarity of over 12 feet in the 1950’s. This clarity was measured by the State in early July.
But as urban migration to lake country began in the 60’s to present, more and more homes were winterized and lived in 12 months of the year. As the lake community transitioned into year round living, the lake water quality began to become eutrophic with increased algae and weed productivity.
A lake study in 1990 estimated that 42% of the phosphorus loading came from failing systems.
Or more specifically, from septic systems that failed to treat effectively. This is known as anthropologic pollution. In addition to septic system influence, storm water systems were modernized, which resulted in additional nutrient loading. Phosphorus attaches to soil particles carried by storm water as it travels over the surface of decaying organic material and lawns. Storm drains can transport the nutrients via pipes to the lake.
In getting back to septic systems, realize they are accumulators of household phosphorus. Over the life of a septic system (something that is not defined), the soil fill continues to collect and treat organic and inorganic materials discharged from the septic tank.
Early septic fields were placed in the ground without proper regard for the type of fill, the type of soil and level of ground water or more importantly the proximity to water bodies. It wasn’t until the 1970’s that septic codes were developed for new systems to improve health standards in communities served by septic systems. These standards regulated design, placement, and construction of new systems. Functioning older system designs were grandfathered in. Early focus was more on improving treatment of wastewater to prevent the threat of disease. Less attention was focused on inorganic component treatment like nitrates and phosphorus. In NJ there was little to no regulatory function before the 1970s. These early septic systems remain in operation 50+ years later. The accumulated wastewater products, specifically phosphorus, have moved outside the soil fill area by ground water and the phosphorus has found its way to the lake.
The movement of phosphorus is a complex subject because of the variety of conditions that affect soil capacity to hold phosphorus. In one study in Ontario Canada documented by W. Roberts 2008, a 16 year study of one septic system demonstrated that the phosphorus did not reabsorb as it traveled 50 feet from the soil fill area to the lake. Close proximity of the septic field to the body of water lessens the time it takes for phosphorus migration to affect the water.
Groundwater monitoring wells are the only way to determine whether there is groundwater containing phosphorus levels that indicate the septic field is leaching.
Multiple wells and multiple depths would be needed. This represents a lot of time and effort. There needs to be an encompassing fix to reverse this situation within a lake community. Certainly, any proposal to replace all old fields would not win the day among lake residents. But, continuing to push pollutants into a tired field and into the ground water isn’t acceptable if we are ever going to reduce this impact.
The normal response from a typical homeowner, when questioned about their septic system’s effectiveness, is usually one of denial or simply that of being unaware. More often, the cost of field replacement causes alarm bells to ring and this results in nothing being done. Bottom line is that owners of old septic systems are unaware of their impact on the lake. This means that septic fields will not be replaced until there is some obvious sign; such as, untreated wastewater running over the ground or a noxious smell. With old systems operating beyond their functional life, this underlines the value of an alum augmented system that lessens the discharge of products into the field – particularly phosphorus and coliform.
