Groundwater Monitoring Objectives of Monitoring

A Valued Resource
Groundwater Contamination
Groundwater Management Areas

Monitoring Land Use Practices
Ensuring Safe Drinking Water
Groundwater Basin Reports

A Valued Resource

Groundwater is essential to the economic viability and livability of many Oregon communities. groundwater is used for irrigation, drinking water, municipal water supplies, and other uses. It serves as the water supply for over 70 percent of residents in Oregon. More than 600,000 Oregonians get their drinking water from individual private water wells.
Groundwater also influences the quality of many Oregon rivers and streams. Especially during the dry summer months, groundwater inflows affect stream flow, chemistry and temperature which in turn determine the quality of surface waters used for drinking water, irrigation and recreation. High quality inflows of groundwater are essential for maintaining cold-water fisheries in many streams.

Groundwater Contamination

Groundwater contamination is a serious issue in some areas of Oregon. Many agencies study the quantity and quality of Oregon’s groundwater resources. Ambient groundwater quality studies over the past 20 years and routine monitoring of public water supplies found 35 of 45 study areas show some impairment or reason for concern. Nitrate is the most commonly detected contaminant, followed by pesticides, volatile organic compounds, and bacteria. Data collected show that twenty-four percent of 1156 wells sampled statewide exceed the drinking water standard for arsenic. Sixteen percent of 2187 wells sampled exceed the drinking water standard for nitrate. Thirty-three percent of Willamette Valley rural wells contain at least one pesticide. In all, the program produces over 5,000 data points each year.

Groundwater Management Areas

The DEQ LEAD staff collects over 500 domestic well water samples each year from three groundwater management areas (GWMAs) in Oregon. Over 90 wells, including many rural home domestic wells, are sampled on a routine basis. Area-wide contamination in these areas is associated with nonpoint sources such as agricultural practices and rural residential septic systems. DEQ staff monitor wells in the Northern Malheur County, Lower Umatilla Basin and Southern Willamette Valley GWMAs several times each year to gather nitrate and other water quality information.

This chart shows a well in the Northern Malheur County GWMA with decreasing nitrate concentrations in the groundwater. The federal drinking water standard for nitrate is 10 mg/L.

Data are produced by the DEQ Groundwater Monitoring Program and are used by internal and external stakeholders to help them understand the complex interactions affecting the quality of the groundwater in these areas. With such data, local committees are able to implement best management practices in cooperation with DEQ and other state, federal and local agencies. Over the long term, these practices are expected to result in measurable reductions in the groundwater contamination within the GWMAs. DEQ also provides well owners involved in the long term studies a copy of the analytical results for their wells on a regular basis.

Monitoring Land Use Practices

DEQ also protects groundwater resources through a number of water quality and land quality permit programs. Each year monitoring staff visit approximately fifteen of more than 75 statewide solid waste landfill sites.

Samples are analyzed for a broad range of contaminants such as organic pollutants, metals and other contaminants of concern. Many landfills were initially monitored by DEQ staff. Now, the primary role of DEQ groundwater monitoring is to provide oversight and perform routine audits on various contractors that complete this valuable monitoring work at these facilities. Monitoring data from landfills are used by regional DEQ hydrogeologists, engineers and permit staff to evaluate compliance with solid waste permit requirements.

Ensuring Safe Drinking Water

DEQ staff worked with Department of Human Services (DHS) to evaluate source water quality at several public water supply systems located throughout Oregon. DEQ chemists assessed samples collected from these aquifers for a broad spectrum of contaminants including pesticides, pharmaceuticals and personal care products, many of which have no federal drinking water standards. In another effort, DEQ staff worked collaboratively with DHS to quickly assess water quality at more than 100 domestic wells in Douglas County. These efforts yielded important information on the quality of drinking water supplies for Oregonians living in rural communities.

Groundwater Basin Reports

For more detailed information on the groundwater quality in Oregon, see the links below.