CPESC common mistakes
CPESC · Understand the traps and how to avoid them.
On scenario items, selecting a downslope sediment barrier such as silt fence or a sediment trap as the primary control for a steep, denuded slope.
Candidates memorize BMP names as a list and skip the erosion-to-sediment hierarchy; sediment controls only capture soil that has already detached and moved.
What to do instead
Before choosing a BMP, classify the problem as detachment or transport. Treat the source first with cover, matting, diversion, or stabilization, and use sediment controls only as a last line of defense.
Specifying silt fence across a concentrated-flow channel, swale, or ditch.
Silt fence is a ponding and filtration practice intended for sheet flow; concentrated flow overtops, undermines, or breaches it, and the failure is often accepted as normal.
What to do instead
Use ditch checks, check dams, lined channels, or sediment basins for concentrated flow. Verify contributing area, slope, and the applicable state or local design standard before selecting the practice.
Sizing a sediment basin or sediment trap by peak inflow capacity alone and ignoring required settling volume, surface area, or residence time.
Hydraulic conveyance and treatment are separate functions; a basin can pass the design storm without providing enough detention to settle fine particles.
What to do instead
Compute both conveyance capacity and treatment storage. Check the governing state or local criteria for volume, surface area, dewatering method, and drawdown time, and show both calculations.
Using the Rational Method with mixed units or outside its valid range, such as applying it to a large or complex watershed without checking assumptions.
The formula Q = CiA requires rainfall intensity in inches per hour and area in acres with a unit conversion factor; candidates mix SI and English units or ignore method limitations.
What to do instead
Write units beside every term and apply the conversion factor deliberately. For large, complex, or unusual watersheds, use an approved method such as TR-55 or the jurisdiction's required procedure.
Inferring permeability, infiltration, or erodibility from soil texture alone after a hand-texture test.
Texture is only one soil property; structure, compaction, organic matter, layering, and moisture condition control infiltration and detachment, so a sandy-looking soil can still behave poorly.
What to do instead
Combine texture with structure, compaction or bulk density, and field or laboratory infiltration data. State assumptions explicitly when site data are unavailable.
Assuming the federal Construction General Permit automatically covers every construction site.
NPDES authority may be delegated to states, local ordinances can be stricter, and some sites fall below disturbance thresholds or are covered by a different general or individual permit.
What to do instead
Check the state's delegated program, acreage and disturbance thresholds, common-plan aggregation rules, and local requirements before citing the CGP or any permit.
Producing a SWPPP that is a generic BMP list with no site map, no inspection schedule, and no named responsible person.
Templates are easy to copy, but reviewers look for site-specific pollutant sources, BMP locations, inspection frequency, and clear accountability.
What to do instead
Map each disturbance area to specific BMPs, include inspection frequency and corrective-action triggers, and name the roles and individuals responsible, with signatures.
Recording inspection results only as 'BMPs in place' without condition, location, photograph, deficiency, or corrective-action date.
Checklist habits focus on presence rather than performance, and vague records cannot demonstrate compliance or support maintenance decisions.
What to do instead
For each BMP record its location, condition or percent functional, deficiency, corrective action, responsible party, and close-out date. Attach dated photographs and note weather and recent rainfall.
Installing silt fence without a keyed trench, proper setback from the toe of slope, or J-hooks on long runs.
Crews treat silt fence as a fence line rather than a water-retaining structure, so flow goes under, around, or through the fabric.
What to do instead
Key the fabric into compacted ground per the specification, maintain the required setback, install J-hooks or returns on long runs, and inspect after every significant storm.
Signing, sealing, or certifying a plan, inspection, or report outside your competence or after the fact.
Schedule pressure and unclear scope lead to rubber-stamping, and ethical rules require both technical competence and truthful records.
What to do instead
Sign only work you personally reviewed and are qualified to perform. Record dates and times truthfully, disclose limitations, and decline or refer work that exceeds your expertise.