MODULE-5 Wastewater Management

Introduction
On-Site Sewage Systems
Large On-Site Sewage Systems
Small Sewage Treatment Plants
Innovative and Alternative (I/A) Wastewater Technologies
Water Reclamation and Reuse
Regulatory Jurisdiction for On-Site Wastewater Systems

On-site sewage (OSS) systems typically consist of a septic tank and a drainfield. The septic tank provides for the settling out of solids and some biological treatment of the wastes. The drainfield disposes of the liquid wastes into the subsurface environment. Soil provides additional treatment.

If tanks are not properly maintained (pumping once every three years is recommended for single family homes), solids may pass out of the tank and clog the drainfield. This can cause hydraulic failure of the system resulting in the possible backing up of wastewater into the building or effluent breaking out onto the land surface. The latter case may provide a direct route of transport to surface water.

Conventional on-site sewage systems (OSS) are designed to control pathogenic bacteria and are less effective in treating other pollutants such as nutrients. Drainfield effluents contain approximately 40 to 60 milligrams per liter (mg/l) nitrogen and 8-38 mg/l phosphorus (Hall, 1975). Nitrogen compounds generally move through the groundwater system relatively intact, ultimately reaching receiving waters or wells. Viruses, being much smaller than bacteria, also move easily through soils at the speed of groundwater. Because their inactivation times in groundwater are approximately 120-200 days, they have been documented to move distances greater than 300 feet in soils; if a septic system is located too close to a well, viruses could threaten the drinking water source. To summarize, in areas where nitrogen and/or viruses are a concern, conventional septic systems may not provide adequate treatment.

There are other wastewater contaminants that can endanger the drinking water supply. Conventional OSS can send hazardous wastes into the groundwater if the homeowner uses septic cleaners or improperly disposes of household hazardous wastes. Minute quantities of pharmaceutical chemicals have also been found in wastewater. For more information regarding OSS and their maintenance, please see the U.S. EPA's A Homeowner's Guide to Septic Systems.

The cumulative effects of many single family OSS on nutrient, pathogen, or hazardous waste levels in down-gradient waters can be significant. These impacts are dependent upon treatment system location and density relative to receiving water bodies. Many of these considerations have been accounted for in the State of Washington's On-site Sewage System Rules & Regulations (Chapter 246-272A WAC). These regulations, which were updated on July 1, 2007, are specific to systems with design flows of less than 3,500 gpd.

The regulations also require written wastewater management plans from the local health agency for OSS within the twelve counties that border Puget Sound. Each plan must specify how the local health jurisdiction will perform specified development and management activities, such as maintaining an inventory of OSS, identifying areas where OSS could pose an increased public health risk, and identifying operation, maintenance and monitoring requirements. The Washington State Department of Health (DOH) has provided guidance to support local health jurisdictions in writing management plans on their website.

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