Polk County reports mostly low nitrate in voluntary well-water testing; coliform positives prompt retests

Polk County Land & Water staff told the Environmental Services Committee on Oct. 1 that the county’s voluntary well‑water testing program collected 108 samples in two targeted watersheds and remains an active, grant‑supported effort to track groundwater conditions.

"We were lucky enough to get $11,500 towards this program," the presenter said, and added the county budgets roughly $10,000 annually to expand coverage. Staff said they mailed 836 invitations and exceeded their annual sampling goal of about 50 samples, receiving 108 voluntary submissions.

Staff focused results reporting on two chemical indicators: nitrate and chloride, and on bacteriological screening for coliform bacteria. On nitrate, about 24% of samples were below detection and many clustered near 2 parts per million, which the presenter described as a commonly occurring background level. Only a small share of samples exceeded the state public‑health threshold: "Happy to to see that only 7% of these nitrate tests were above the public health threshold of 10 parts per million," staff said; staff reported eight samples above that threshold in one watershed and noted overall percentages vary when both watersheds are combined.

On bacteriology, staff reported elevated coliform positives in this round: 16 positives out of 80 samples in the Cedar Lake/Horse Creek area and 10 positives out of 28 in the south branch of Beaver Creek, for an overall positive rate of roughly 24% in the sample set. Staff emphasized that coliform positivity is not itself an E. coli finding, and that retesting and diagnostic work are advised: "If someone has a positive coliform test, we recommend a retest and consultation with a well driller or pump installer to identify possible sample‑collection errors or breaches in the well casing or nearby septic systems." No E. coli positives were reported in these samples.

Chloride results were generally low: staff reported about 56% of samples under 10 ppm, 41% between 11–50 ppm, and only 4% between 51–100 ppm — well below levels typically associated with taste or health concerns. Staff acknowledged an on‑screen mapping error during the presentation and committed to providing corrected maps in the meeting packet.

Staff outlined next steps: participants will receive informational packets, a webinar is scheduled for Oct. 10 for follow‑up questions, and the program will continue next year with a planned expansion to additional watersheds and ongoing use of the Stevens Point Water and Environmental Analysis Lab to contribute data to the statewide groundwater viewer.

The committee did not take formal action on the report; staff said cost‑share funds and grant awards will support planting roughly 350 acres of cover crops in the targeted watersheds as a preventive practice tied to the program’s outreach.