Stormwater on a commercial site: a working week

Before the week: the plan and the people

The site disturbs about four acres, well over the one-acre point at which, according to the EPA guide, nearly all construction operators need NPDES permit coverage. The owner controls the plans and specifications and the general contractor runs the site day to day, so both are operators in this invented case and share one SWPPP. The plan names the superintendent as the person responsible for inspections and maintenance, and the subcontracts bind the earthwork, utility and concrete subs to it.

The basics behind the plan, including erosion control versus sediment control, are in SWPPP basics for builders.

Monday: the walk

The routine inspection the permit requires falls on Monday. The superintendent walks the whole site with the SWPPP site map and the inspection form:

• Perimeter silt fence along the low side of the site.
• Inlet protection on the two storm drain inlets in the street.
• The stabilized construction exit, the rock pad that knocks mud off tires before trucks reach the road. The street gets a look too.
• The concrete washout, which should hold washout water, not let it run.
• Stockpiles, covered or protected.
• Disturbed areas not being worked, checked for stabilization under the permit's timing.

Every finding goes on the inspection report, with who will fix it and by when.

Tuesday: fixing the silt fence

The EPA guide's silt fence advice, in our words: use it at the low edge of disturbed areas, trench it in on the uphill side, stake it on the downhill side, curve the ends uphill, and do not put it across ditches or concentrated flow or run it up and down a slope. It also says not to rely on silt fence alone where more than a quarter acre drains to each 100 feet of fence, and to remove sediment when it reaches one-third of the fence height.

Two checks with invented numbers.

The fence stands 24 inches above ground. Cleanout height: 24 / 3 = 8 inches of sediment. Monday's walk found 9 inches at the low corner, so it was due. Check: 8 x 3 = 24.

A 450-foot run of fence: the most area that should drain to it under the guide's quarter-acre per 100 feet is 450 / 100 x 0.25 = 1.125 acres. Check: 1.125 / 0.25 = 4.5, and 4.5 x 100 = 450 feet. If the grading sends two acres toward that fence, it needs help from another control, such as a sediment trap.

Thursday: the storm

The rain gauge on site reads 0.6 inches after an overnight storm. The guide says permits typically require an inspection after each rainfall of more than one-half inch, and 0.6 is more than 0.5, so in this invented case the superintendent does a second documented inspection. The guide also suggests inspecting before forecast storms, so a quick check on Wednesday afternoon had already found a torn section of inlet protection and replaced it.

After the storm, the walk finds:

• a small washout on the slope above the perimeter fence, needing a blanket and reseeding
• mud tracked onto the street at the exit, swept the same day
• the sediment trap about half full, scheduled for cleanout

Friday: the paperwork

• Both inspection reports signed and filed in the SWPPP.
• Corrective actions logged with dates completed.
• The site map updated, because a new stockpile moved.
• The SWPPP amended to add the slope blanket.

The guide says EPA's regulations require keeping the SWPPP and permit records for at least three years from the end of coverage or the expiration of the permit, and states may require longer. Treat the binder as a closeout document.

At the end of the job

Coverage runs until the site reaches final stabilization and the operator ends coverage, often by a Notice of Termination. The guide describes final stabilization as uniform perennial vegetation at 70% of the native background cover on unpaved areas, with some states asking more. If native cover nearby is 60%, the target is 0.70 x 0.60 = 42% uniform cover. Check: 42 / 60 = 0.70. That can lag the building's substantial completion by weeks or months, so plan the seeding season.

Where this sits for the exam

The bulletin lists subject areas only. Our reading puts stormwater under Site Construction, 15 of 115 questions, and the EPA guide is the listed reference whose title fits. It is free, so you can tab it early; the reference books guide has the list. NASCLA site construction covers the rest of the area.

Test your site knowledge

Take the free 10-question check. It needs no signup and explains every answer. For a Site Construction lesson and timed 115-question practice exams on the 330-minute clock, see the plans.

Sources

• Developing Your Stormwater Pollution Prevention Plan: A Guide for Construction Sites, U.S. EPA, 2007, document 833R06004. Free from the EPA, per the PSI bulletin.
• PSI Candidate Information Bulletin 1458, content outline and reference list, updated 7 Jul 2026. Retrieved 5 Nov 2026.
• The site, the week and all numbers are invented.

FAQ

When should sediment be removed from silt fence?

The EPA guide says when it reaches one-third of the fence height. Your permit or plan may set its own trigger.

How often are SWPPP inspections done?

The permit sets the minimum. The EPA guide says it is typically weekly or bi-weekly and after each rainfall of more than one-half inch.

Who is responsible for the SWPPP?

The operator or operators, as the permit defines them. Often that is the owner, the general contractor, or both, with subs bound by their subcontracts.