Wastewater Lagoon Leak Testing
A lagoon is only as good as its seal. A leak test tells you, in numbers, whether a cell is holding water or losing it to the ground.
We run lagoon leak tests for Oregon municipalities following the Oregon Department of Environmental Quality (DEQ) Guidelines for Estimating Leakage from Existing Sewage Lagoons, and we hand you a report you can send to DEQ.
When You Need a Leak Test
Your permit calls for it. Some National Pollutant Discharge Elimination System (NPDES) and Water Pollution Control Facilities (WPCF) permits require a leak test on a schedule or at renewal.
DEQ asks for it. A seepage evaluation can come out of an inspection, a permit renewal review, or a compliance action.
You are planning an upgrade. Before facilities planning, relining, or sludge removal, it pays to know the condition of the seal.
You suspect seepage. The water balance does not close, the level drops faster than evaporation explains, or there is a concern about groundwater or a nearby well.
How We Test
The test is a water balance. We measure how fast the lagoon level drops, then account for everything that is not seepage: evaporation, rainfall, and any flow in or out.
Level. A pressure logger set in the cell records the water level every 10 minutes for the length of the test.
Evaporation. A Class A evaporation pan with a hook gauge is set up at the lagoon and read daily. A lagoon evaporates less than a pan does, so we report seepage across the range of pan correction factors DEQ describes. We do not pick the one that looks best.
Rainfall. A rain gauge at the site is read daily, and the level record is checked for any rise that rain would cause.
Duration. Each cell is tested for about 10 to 15 days. We schedule tests in July and August, the window DEQ prefers because rainfall is at its lowest.
Cells that can be isolated. Inflow and outflow are shut off, and seepage is what remains of the drawdown after evaporation and rain are accounted for.
Cells that cannot be isolated. A lead cell that has to keep taking flow can still be tested. We run a full water balance using metered influent.
Your staff. Your operators can take the daily pan and rain gauge readings. We provide a written procedure and field log so the readings are taken the same way every day.
DEQ's guidelines treat seepage of 1/8 inch per day or less as normal. Seepage above 1/4 inch per day indicates the seal has failed or was never adequate.
What You Receive
A written report for each cell tested, with:
A summary of findings in plain language
The method and equipment used
The level record and the measured drawdown rate
Evaporation and rainfall data
The water balance, shown line by line
How the result changes across the range of pan correction factors
A comparison against DEQ's criteria
A review of nearby drinking-water wells using Oregon Water Resources Department (OWRD) well logs
A signed certification
When more than one cell is tested, you also get a summary report covering all of them, plus the field logs.
Lagoons We Have Tested
We have completed multiple successful lagoon leak tests in Oregon, including isolated cells and a lead cell that stayed in service during the test.
Tests run in July and August, so the time to plan is spring. Get in touch and we will lay out a schedule.