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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

Onsite Treatment and Disposal of Domestic Wastewater:
Magnitude and Impact

Crop and Soil Environmental News, July 1998

R. B. Reneau, Jr., Professor, Waste Management and Water Quality
Charles Hagedorn, Biotechnology Specialist

Over the next few months we would like to present various options available for onsite treatment and disposal of domestic wastewater and evaluation of these options. However, this month we will acquaint you with the numbers of onsite systems that serve citizens of Virginia and the United States, the quantity of wastewater produced by these systems, and the potential problems that can be encountered with these systems.

Number of Households Served by Onsite Systems
In the United States and Virginia, the number of houses being served by onsite systems is increasing while the percentage of the total housing units served by onsite systems is decreasing (Table 1). With the reduction in federal funds for public sewer development, the percentage of housing units served by onsite systems in the future is expected to increase.

Table 1. Number of households served by public sewer and onsite systems.

Year Number, in millions, of households (percentage) served by public sewer Number, in millions, of households (percentage) served by onsite systems
United StatesVirginiaUnited StatesVirginia
197048.2 (71.2%)0.91 (61%)19.5 (28.8%)0.58 (39%)
198064.2 (74%)1.32 (65.8%)22.5 (26%)0.68 (34.2%)
199583.3 (74.8%)1.74 (69.7%)25.8 (25.2%)0.76 (30.3%)

Quantity of Effluent
Virginiaís population is approximately 6.2 million people, which means that the average residence has 2.5 occupants. Approximately 95 million gallons of wastewater are applied daily and 34 billion gallons annually to Virginia soils by onsite systems. The wastewater applied yearly to Virginia soils, if stacked on Interstates 81 and 64 from Blacksburg to Richmond (220 miles) would be approximately 30 ft wide and 130 ft high.

Potential Problems
When onsite systems are not properly sited or installed, they can be a potential risk to public health and a source of environmental degradation. The most common reason for onsite systems to fail, and become a potential threat to public health or the environment, is placement of systems in soils that do not have adequate capacity for wastewater renovation. A second common reason for system failure is installing a system in such a manner that only a small percentage of the soil available for renovation is actually used. Onsite system failure can result in problems that include direct exposure to improperly treated sewage, ground and surface water pollution, and contamination of shellfish beds.

The potential impact on public health and the environment come into focus when you consider that onsite systems apply the largest volume of wastewater to soils overlying ground waters and as such are the most frequently reported source of groundwater contamination. This contamination results in increased health risks to persons exposed to polluted waters, degradation of recreational and drinking water quality, movement of nutrients such as nitrogen and phosphorus into ground and surface waters, and contamination of shellfish beds in the Chesapeake Bay. Diseases that can be spread by exposure to improperly treated wastewater include salmonellosis, viral hepatitis A, viral gastroenteritis, and amoebic dysentery. From 1970 to 1995, 31% of all waterborne disease outbreaks were caused by contamination of surface or groundwater from the overflow or seepage of sewage from septic systems and cesspools.

The potential problems associated with onsite systems should not be interpreted to mean that domestic wastewater cannot be renovated when applied to soil. In fact, onsite wastewater is applied to many soils in an acceptable manner that has served the waste disposal and treatment needs of millions of people without putting these people at risk or polluting ground and surface waters. In the next several articles we will describe both current and future options for addressing these problems.

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