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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 effects 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 to 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 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 drain scan 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 grand fathered to continue.  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 or no regulatory function before 1970s. These early septic systems remain in operation 50 years or more 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 distance 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 either 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.

North American Lake Management Society (NALMS) Presentation 2018

I recently had the opportunity to present at the NALMS 2018 Symposium in Cincinnati this November.  It was a great opportunity to express my thoughts and research regarding Lake Management and Restoration, specifically with ways to reduce Septic System Impact on the Lakes in rural communities.

Attached you can find a PDF copy of my presentation. Please enjoy, and let me know if you have any questions, or if you are interested in learning more.

How Septic Tank Baseline Samples Were Obtained

There are two ways to obtain a sample from the septic tank.  The preferred method was to use a Sludge Judge.  This unique device obtains a liquid sample as it is immersed.  There is a check valve at the end of the sampler that holds the sample when the probe is raised.  The sample is released by depressing the check valve button into the bottom of suitable sample container. We found the easiest and most desired location for obtaining a septic tank liquid sample is to insert the sampler tube down through the tank outlet clean-out inspection pipe.  On septic tanks that are newer systems, the inspection pipe is seen as a 4″ PVC cap at grade level.  If there are two caps, it would be the cap furthermost from the house.  The sample that is obtained through the inspection pipe is very indicative of the effluent leaving the tank. Alternately, without an inspection pipe, the septic man way must be opened to obtain a sample.  See picture below.  In using the Sludge Judge, care was taken that the sample did not contain scum or cap and that the sampled is taken about 10 inches from the top of the liquid level. This improved the chances of obtaining a clarified sample.   The tank sample was taken only when wastewater was not being discharged into the tank – less disturbance resulted in less Total Suspended Solids (TSS).

Sampling Septic Tank with Sludge Judge
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Septic Influence in a Lake Community

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.