MODULE-3 Susceptibility and Vulnerability

Potential Contamination Sources in Washington

Contamination to drinking water supplies comes in the form of both point source pollution (direct discharges from industrial and sewage treatment plants) and nonpoint source pollution (pollutants carried in stormwater runoff or wastewater effluent). In 2005, the Washington State Department of Ecology (DOE) produced a report, Washington's Water Quality Management Plan to Control Nonpoint Sources of Pollution. The two primary categories of nonpoint source pollution discussed here are those from rural development and agriculture.

Stormwater outfall pipe

Conventional rural development methods pose a significant risk to drinking water supplies. Increased impervious surfaces, such as roads, rooftops, and parking lots, combined with inadequate stormwater treatment, results in concentrated pollutants in runoff. Where untreated stormwater runoff is infiltrated, it can carry oil, metals, pesticides, and other harmful contaminants directly to the groundwater system.

Rural development also leads to increases in wastewater discharges. Conventional development typically involves traditional septic systems, which provide limited treatment of wastewater. Increased nitrogen loading is the primary concern with respect to increased septic flow; however, other pollutants, such as pharmaceuticals, also pose a risk. Nitrogen in septic system effluent is typically present in concentrations well above the 10 milligrams per liter (mg/L) Federal Drinking Water Standard. Effluent from a properly operating septic system may contain as much as 40 mg/L nitrogen. Drinking water from a private well that contains nitrogen at or near the 10-mg/L standard, may contain as much as 25% recycled wastewater effluent.

Elevated levels of nitrate in drinking water can cause serious problems for infants, who could develop methemoglobinemia, or blue baby syndrome. It is also recognized as a potential carcinogen for adults and is an indicator of other sewage-derived contaminants such as pathogens and pharmaceuticals. Nitrate-nitrogen in septic system effluent does not precipitate on or absorb into the soil materials through which it travels and reductions in concentration are caused only by mixing and dilution with native groundwater. Other potential sources of contaminants in rural areas include leaking underground fuel storage tanks, junkyards, automobile service stations, and landfills.

Agriculture, a major industry in Washington, can have considerable adverse impacts on surface water and groundwater quality. Typical sources of agricultural contamination are fertilizers and pesticides used to grow crops. Animal waste (such as from feedlots) can also have significant impacts on water resources in the form of increased nutrient loading (primarily nitrogen).

Rural agricultural lands in Washington

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