What Wisconsin's wash water permit will not cover
Which pressure washing jobs fall outside Wisconsin's low-impact discharge permit?
Degreasing more than one oily engine a month
The permit covers degreasing of engines or oily equipment only in small volume. Past an average of one engine or oily piece a month at a site, the water needs another permit.
The limit is measured at one site over any six-month period. A fleet yard that sends you six trucks a week is well beyond it.
Below the limit, the permit adds its own steps. Wash on an impermeable surface, then treat the water with an oil and water separator or absorbent, or divert it to a holding tank or sanitary system. Or remove all oil and grease and dispose of it as solid waste first.
1 per monthThe permit excludes degreasing of more than one engine or oily piece of equipment per month at a site over any six-month period. — Wisconsin DNR, Low-Impact Discharge general permit WI-0066575-01-0, retrieved 2026-09-29
Degreasers with halogenated hydrocarbons
Discharges from degreasing that uses halogenated hydrocarbons are excluded. The permit also bars adding degreasing chemicals with halogenated hydrocarbons to washing solutions.
Read the safety data sheet for every degreaser on the truck. If the product lists a halogenated solvent, its water cannot go under this permit, and it should not be in the tank at all when the plan says otherwise.
Switching to a different degreaser is usually simpler than finding another permit. Note the product change in the plan so the crew sees it.
The permit excludes degreasing with agents containing halogenated hydrocarbons and bars them from washing solutions. — Wisconsin DNR, Low-Impact Discharge general permit WI-0066575-01-0, retrieved 2026-09-29
Spills, leaks and petroleum-contaminated water
The permit does not authorize an accidental or unplanned release, spill, leak or overflow to a water of the state. It also excludes petroleum-contaminated water.
A hose that splits, a tank that overflows or a pump that leaks is a release, not a permitted discharge. The permit expects a contingency plan for line breaks, leaks and overflows, and training for employees on it.
Carry absorbent and a plug for storm inlets. A plan that lists both gives the crew something concrete to reach for.
The permit does not authorize discharges from any accidental or unplanned release, spill, leak or overflow. — Wisconsin DNR, Low-Impact Discharge general permit WI-0066575-01-0, retrieved 2026-09-29
Impaired, outstanding and exceptional waters
Location can rule a job out. Discharges that contribute a measurable pollutant to a 303(d) impaired water or break a total maximum daily load are not covered.
Discharges directly to an outstanding resource water or an exceptional resource water are also excluded, and so are those that would lower water quality downstream of one. The permit expects the plan to include procedures for spotting these waters.
A lakefront dock cleaning is the usual trap. Check the DNR's impaired waters lists before you quote a shoreline job, and ask whether the runoff can reach the water at all.
Discharges directly to an outstanding or exceptional resource water are excluded from the permit. — Wisconsin DNR, Low-Impact Discharge general permit WI-0066575-01-0, retrieved 2026-09-29
Toxics, tribal land, historic property and wildlife
Several other limits sit in the same list. Discharges holding toxic or hazardous pollutants reportable under ch. NR 706, such as metals, solvents, biocides and pesticides, are not covered.
Discharges from properties within tribal lands are outside the permit, because the Tribe or EPA regulates them. Discharges that harm listed historic property, or endangered and threatened species, are excluded unless the department finds compliance.
Two other lines matter to this trade. Automatic car washes and noncommercial washing at individual residences are not applicable. The building washing page covers paint and other solids.
The permit excludes discharges from properties within tribal lands, where the Tribe or EPA regulates them. — Wisconsin DNR, Low-Impact Discharge general permit WI-0066575-01-0, retrieved 2026-09-29
Discharges containing toxic or hazardous pollutants reportable under ch. NR 706 are not covered. — Wisconsin DNR, Low-Impact Discharge general permit WI-0066575-01-0, retrieved 2026-09-29
Questions
What happens if a job is excluded from this permit?
The permit says a discharge that is excluded may still need coverage under another general or individual WPDES permit. If the DNR finds a discharge ineligible but still needing coverage, you apply for and obtain that coverage before discharging.
Can I still take an oily fleet job if I hold coverage?
Only if you keep the water out of the permit's scope, for example by hauling it to a treatment works or a sanitary sewer the utility approves. Above the one-per-month threshold the low-impact permit does not fit.
Where do I find whether a lake is impaired?
The permit points to the DNR's impaired waters pages for the list of 303(d) waters and approved total maximum daily loads. Look up the waterbody nearest the job before you quote shoreline work.