Overview

Since late summer of 2023, DEQ has been coordinating with Governor Kotek's office, Department of Geological and Mining Industry, Oregon Health Authority, Oregon and Oregon Water Resources Department to address groundwater issues in Crook County.

Private well owners north of the city of Prineville have submitted complaints to multiple state agencies about their well water quality, including concerns for potential impacts on human health. The reports include concerns about drinking water quality and its impact on their health, household pipes, appliances and suitability for use by livestock and animals.  

DEQ's Top Priorities

To adequately investigate groundwater issues in Crook County, DEQ's priorities are to sample domestic wells, and to develop and fund a regional sampling and analysis plan. 

Domestic Well Sampling

Sampling domestic drinking water wells is an important first step in addressing water quality issues. The purpose of the domestic well water sampling is not to identify the source of any contaminants found, but to provide homeowners with drinking water quality information, and to provide the OHA with initial data to develop an area-wide public health consultation. OHA's public health consultation will be published in fall 2025.

Fall 2024 Domestic Well Sampling

A contractor, Maul Foster & Alongi, collected samples from 55 private wells over a two-week period. Results demonstrated:

• 28 (51%) wells had manganese levels at or above EPA's secondary drinking water standards of 50 micrograms per liter (µg/L), with a high of 409  µg/L. EPA's secondary drinking water standards provide guidelines for aesthetic considerations, such as taste, color, and odor and are not considered to present a risk to human health. EPA has not set a primary drinking water standard for manganese. A lifetime exposure Health Advisory for manganese is set at 300 µg/L. Five (9%) of the 55 wells had manganese levels above 300 µg/L.
• Nitrate concentrations were detected in 10 wells (18%) slightly above the primary MCL of 10 milligrams per liter (mg/L), with a high of 13.75 mg/L. Nitrate contamination of groundwater is an indication that groundwater is being impacted from surface activities such as fertilizer use, septic systems, or farm animals.
• 13 wells (24%) had positive detections for Total Coliform but were negative for E.Coli. Total Coliform is not necessarily a human health concern, but is not naturally present in groundwater and indicates that a source of bacteria has contaminated the well water.
• Arsenic, which is naturally occurring in groundwater in several parts of Oregon, was detected above the primary MCL of 10 µg/L in 19 (35%) of the 55 wells tested.

Read the full Preliminary Domestic Well Sampling letter report.

Spring 2025 Domestic Well Sampling

The Spring 2025 domestic well sampling effort is currently ongoing. Results are expected in July, 2025. DEQ and OHA recommend that private well users test their wells regularly (every one to two years) to ensure well water is safe for drinking. Find more information about these recommendations on OHA's website. 

Regional Sampling and Analysis Plan

DEQ requires more data to understand what is causing elevated manganese concentrations in groundwater in the region. In collaboration with EPA, DOGAMI, OHA, and OWRD, DEQ is developing a larger Comprehensive Sampling and Analysis Plan. If funded, this plan would provide further information about manganese distribution and groundwater flow patterns in the area, while also gathering information to evaluate potential sources of any contamination found in the groundwater.

The sampling and analysis plan is currently under review and will be made available soon.

Knife River Woodward Mine

DEQ and DOGAMI compelled Knife River Corporation to conduct a Groundwater Investigation in October 2024, due to observed water quality impacts in nearby domestic wells. Agencies directed Knife River to conduct a groundwater assessment to evaluate whether mining operations are causing or contributing to groundwater contamination. A plan for the Knife River groundwater investigation is nearing completion. Water quality and water level monitoring will begin immediately after plan implementation.

Read the letter from DOGAMI requiring that Knife River conduct a groundwater investigation.