Leaking Septic Tank & Environmental Concerns

Environmental Concerns for a Leaking Septic Tank

The area directly underlying a leaking septic tank is a biologically active zone known as the “Infiltration Zone,” and is approximately 1 to 3 inches thick.  Usually, some oxygen is present at this depth, causing a process called “Nitrification.” Nitrification basically means ammonium nitrogen is being converted to nitrate.

An article about Nitrate and Nitrite, by Azad Kaligi, PG.

Nitrate from a Leaking Septic Tank – Into the Soil

Nitrate is a form of nitrogen that is found in the soil underlying septic systems. Other sources of nitrate are agricultural areas where fertilizers and animal manure are stockpiled.

High levels of nitrate and chloride in the soil surrounding a septic system indicate contamination of soil from leaking septic tanks.  A known fact about the California water resources industry is that more groundwater production wells have been shut-down due to high nitrate concentrations than any other chemical constituent.

Nitrate From a Leaking Septic Tank – Into the Groundwater

A Property with a Leaking Septic Tank can Include Nitrate and Nitrite Concentrations in Soil and Groundwater

Nitrate & Nitrite

Nitrates can fall through soil, and form a contamination plume in groundwater. Natural concentrations of nitrate in groundwater range from 0.1 milligrams per liter (mg/L) to 10 mg/L. Nitrate is soluble in groundwater, and has a high rate of mobility through aquifers. Nitrate has also been known to accumulate at specific portions of aquifers, depending on the geology and soil characteristics.

Since high-nitrate water  can cause fatal diseases affecting infants, drinking water standards are set at 10 mg/L.

After “Nitrification” – Nitrate Can Become Nitrite

After a some percolation time, nitrate changes to become nitrite with the help of bacteria in the subsurface. The bacterial count pre-existing within the septic system is usually an aid to this process.

Nitrite From a Leaking Septic Tank – Into to Soil and Groundwater

Through the underlying soil horizons, nitrite goes through a sorbtion process.  During seepage phosphorus and pathogens are removed along with all other septic tank matter. However nitrite (along with nitrate) typically fall through these zones and contaminate groundwater.

Environmental Evaluation of a Leaking Septic Tank

The Federal EPA developed Maximum Contaminant Levels (MCLs) as a health-based protective drinking water standard.  Nitrate and nitrite are included in the list of MCLs.  When conducting an Phase I Environmental Site Assessment or a Phase II Subsurface Investigation related to a potential septic tank release, it is important to consider the depth to groundwater, the regional geology & hydrogeology, and the findings of the percolation test prior to installation.

Leaking Septic Tank in Industrial or Commercial Properties 

At industrial sites, nitrate and nitrite may not be the only chemicals of concern potentially released to the subsurface.  Historical land use of industrial properties usually include dumping hazardous chemical waste into the onsite sewage system.  In such cases, a leaking septic tank serves as a pathway for various contaminants to reach soil and groundwater once dumped onsite.

For more information about leaking septic tanks and the environmental concerns for soil and groundwater contamination, call Geo Forward, Inc. at (888) 930-6887 and speak with a licensed professional geologist or engineer.

For information about environmental risk assessments and soil and/or groundwater sampling, check out Geo Forward’s Phase I ESA and Phase II ESA pages.


U.S. Environmental Protection Agency, office of Ground Water & Drinking Water, July 2002, List of Drinking Water Contaminants & MCLs: http://www.epa.gov.safewater/mcl.html#organic