Parking Lot Not Draining? Retention Basin Drainage in Phoenix

Because the water was never the problem. It was a symptom. A pump-out drops the water level today. The reason the lot or basin held water is still there: a plugged catch basin, a storm line packed with silt, or a drywell sealed with sludge. The next hard storm brings the same water to the same blocked path, and you are back to calling someone. Pumping is useless the next time it rains.

A drainage fix goes after the path. Water takes the same route every time: grate, catch basin, storm line, retention area, drywell, ground. If any link is blocked, the water waits where it is. We find the blocked link and clear it.

We start at the grate and work toward the ground. We hold an Arizona A-12 license, which covers storm drain pipe and dry wells, so the whole path is work we are licensed to do.

1. 1Catch basins. Take the debris out of each basin so nothing gets pushed down the pipe. See catch basin cleaning and jetting.
2. 2The storm line. Jet the line all the way to the retention area and flush it out. That is the step that gets a parking lot to drain.
3. 3Drywells. Clean the sludge off the top of the leach rock so the well drains down again. See commercial drywell cleaning.

Then we check how the basin drains. If water still stands after the path is clear, we say so, because the next step is not ours.

The Valley's standard for how long retained stormwater may stand. Phoenix designs basins to empty within 36 hours. Maricopa County's zoning ordinance says retained runoff must be disposed of within 36 hours by percolation, drywells or an approved drainage way. Chandler's code goes further and makes it unlawful to let water stand in a retention basin longer than that.

The reason is mosquitoes. County Environmental Services says they breed in water that stands at least 72 hours. A basin that drains on schedule never gets there. A basin that holds water for three days is a public health problem as well as a flooded lot. See our FAQ on how long water can stand in a retention basin.

The owner, in the first instance. Phoenix City Code 32C-103 puts upkeep of retention basins and drywells on whoever controls the property, and the county's standards say retention basins are privately maintained. A lease can hand the work to a tenant, but the city looks to the owner first. If the property is an HOA or a multi-tenant center, that usually means the association or the property manager. Our FAQ on parking lot drainage responsibility goes through the lease question.

Keep the paperwork. Phoenix wants five years of maintenance records, and ADEQ recommends keeping inspection and maintenance records.

Look at how long water stands, then where.

If the whole path is clear and the basin still will not empty, the soil has stopped taking water or the system was undersized for the site. That is an engineering question: percolation tests, new drywells or regrading. A civil engineer designs that. We will tell you when the problem has moved past what cleaning can do.

And a flooded lot is not always a drainage failure. A storm bigger than the design storm can overwhelm a healthy system. Check what rain you got before you assume the basin is broken. Our parking lot flooding FAQ covers that, and the retention basin FAQ covers the checklist.

Tell us the address, how long water stands after rain, how many grates the lot has and when the basins and drywells were last cleaned. We give free estimates, and you get the price upfront before work starts. HQ is licensed and insured, and we take emergency calls 24/7.