4 Ways Contaminants Penetrate a Building’s Water Supply
In North America, the benzene, toluene, ethylbenzene and xylene (BTEX) hydrocarbon group represents a main source of groundwater contamination. Its ability to permeate many common piping materials makes it especially difficult to protect against, which can be concerning considering BTEX is an established carcinogen. The Environmental Protection Agency has regulated benzene in drinking water to 5 parts-per-billion because of its link to cancer.
What Materials are Affected?
Many common, plastic piping materials are at risk of permeation by BTEX and other chemicals. These materials should not be installed in areas where permeation is a possibility.
Piping systems made from metal are impervious to permeation. These materials are well suited for use in all ground installations, from water mains to the distribution lines that connect buildings to distribution network.
Transportation and Permeation Methods
Since BTEX is a primary components of petroleum products, it often spreads through accidental spills and when storm runoff passes over gas stations, roads and highways, parking lots, and other locations. Once BTEX is introduced, there are four primary ways it can move around an environment, potentially setting the stage for permeation events.
Volatilization
When BTEX compounds spill directly onto impermeable surfaces (such as concrete or roads), it does not fully evaporate. Instead, BTEX accumulates until rain or human activity washes it into vegetation, soil or bodies of water. Once BTEX is present in an environment it may permeate vulnerable piping materials, contaminating potable water in route to a building.
Dissolution
BTEX can dissolve in aqueous environments due to its high solubility. Of the four chemicals, the highly carcinogenic benzene has the highest solubility in groundwater. When present in the environment, natural, hydraulic gradients can move contaminated groundwater through an environment, placing it in contact with piping installations.
Sorption
If there is a low level of groundwater saturation, BTEX and other organic contaminants will be absorbed by unsaturated soil, which is the earth between the water table and the surface. Thankfully, this can actually help mitigate the spread of contaminants. However, the majority of distribution mains and service lines are installed in the unsaturated soil zone (two feet down or more), which may expose them to BTEX permeation.
Biodegradation
Like many other organic compounds, natural microbial activity can cause BTEX to biodegrade and disperse through an area, spreading its components around the environment. The rate of degradation is highly affected by several factors, such as oxygen levels, bacteria type, and soil size, properties and saturation, among others. Due to its complexity, it’s extremely difficult to calculate the level of damage BTEX’s degradation can permit during a permeation event or calculation.
What Can I Do?
For buildings in a high traffic, heavy commercial or industrial areas where contaminants may be present in the soil or groundwater, carefully consider the material type for the piping system. If the system includes vulnerable materials, those within the building could be exposed to harmful –possibly cancer causing– chemicals. For more information about the presence of contaminants in water, click here.
This summary makes use of the study “Assessment and Calculation of BTEX Permeation Through HDPE Water Pipe,” which was prepared for the HPDE Municipal Advisory Board and the Plastic Pipe Institute® or the PPI. To read the full study, click here.