Installation runs in a fixed order: test the soil, protect the areas that have to stay undisturbed, put erosion controls in before anything else moves, excavate and build the facility, stabilize the site, then prove it works and close the permit.
That order is not a preference. Several steps are written into Pennsylvania’s Chapter 102 rules, including a requirement that a licensed professional be physically on site during critical stages, and a final certification signed under criminal penalty confirming the site was built to the approved plan.
The single decision that determines whether the finished system performs is made on day one and never appears in the design. It is keeping equipment off the ground the facility will infiltrate through.
Here is the sequence, start to finish.
Before Anything Moves
Work begins well before an excavator arrives.
- Soil and infiltration testing. The design depends on how fast the ground actually accepts water, verified in the field rather than assumed from a soil map. Where testing shows infiltration is not feasible, DEP’s Managed Release Concept provides an alternative strategy using a vegetated control measure with a controlled release through an underdrain.
- Survey and layout. Existing grades, the receiving point, and the exact footprint of every facility.
- PNDI review for species of special concern.
- Utility location through Pennsylvania 811, not less than three and not more than ten business days before excavation.
- Preconstruction meeting with the conservation district, the engineer, and the contractor to walk the sequence.
The preconstruction meeting is worth taking seriously. It is where the sequence gets agreed and where the inspector tells you what they will be looking at. Getting this stage right is most of what separates smooth stormwater management installations from ones that stall.
Controls Go In First, Then Everything Else
The first thing built on the site is the thing that protects everything downstream of it.
Erosion and sediment controls are installed before any earth is disturbed. That typically includes:
- Perimeter silt fence or compost filter sock
- A stabilized construction entrance to keep mud off the road
- Inlet protection on any existing structures
- Sediment traps or basins sized for the drainage area
- Diversions routing clean water around the work area
Alongside those, the infiltration areas get fenced. Pennsylvania review practice expects erosion and sediment plans to show, in plan view, the orange construction fence or silt fence that marks and protects infiltration areas. That fence is not decoration and it does not come down until the facility is built.
The One Rule That Decides Whether the System Works
Compaction destroys infiltration, and construction compacts everything it touches.
Pennsylvania review requirements are explicit on this point. Construction sequence notes must address the sequence for infiltration and water quality BMPs and must protect those areas from compaction during construction. Plans have to describe how soil compaction will be avoided at each infiltration location, following the protocol in the Stormwater BMP Manual. Design guidance is equally blunt about the excavation itself: the existing subgrade is not to be compacted or subjected to excessive construction equipment, and the bottom of an infiltration bed is to be at level grade with the surface manually graded and scarified.
There is a second half to the rule. Plans must include measures preventing stormwater runoff from unstabilized areas of the site from entering the infiltration systems during construction. Sediment-laden water reaching a clean stone bed seals it just as effectively as a loaded truck.
In practice that means:
- Fence the footprint before work starts
- Route construction traffic around it, never across it
- Excavate the final lift with the bucket working from outside the footprint where possible
- Keep sediment-carrying runoff diverted away until upstream areas are stabilized
- Scarify the subgrade before placing stone or media
Getting this right is a sequencing and excavation and grading discipline rather than a design question, and it is the most common reason a correctly designed infiltration facility never performs.
Clearing, Stripping, and Earthwork
With controls in place, the site work begins.
Topsoil is stripped and stockpiled separately, because it goes back on at the end and because subsoil at the surface will not grow the vegetation the plan requires. Stockpiles get their own perimeter controls and temporary seeding if they will sit for any length of time.
Rough grading establishes the shape of the site and the drainage pattern that feeds the facility. Cut and fill quantities rarely balance exactly on paper, since soil swells when loosened and shrinks when compacted, so imported fill or export of surplus is a normal part of the schedule. Different site conditions call for different methods, and our article on the types of excavation covers what changes when rock, wet ground, or deep cuts are involved.
Excavation of the facility itself follows, cut to the design elevations. For a basin that means the bottom, the side slopes, and the embankment footprint. For an infiltration bed it means reaching the design depth without over-excavating and without working the subgrade.
Structures, Piping, and the Outlet
The controls that make a basin a basin get installed next.
| Component | Function |
|---|---|
| Inflow points and forebay | Deliver runoff and drop out coarse sediment before the main cell |
| Outlet control structure or riser | Meters the release rate the design promised |
| Low-flow orifice | Controls the small frequent storms |
| Trash rack | Keeps debris off the orifice |
| Anti-seep collars or filter diaphragm | Stops water tracking along the outside of the barrel through the embankment |
| Barrel and outfall | Carries flow through the embankment to a protected discharge |
| Emergency spillway | Passes extreme events without overtopping the embankment |
| Outfall protection | Prevents scour where the water lands |
The outlet structure is where the design’s numbers live. Orifice sizes, weir elevations, and riser heights are what convert a hole in the ground into a facility that releases at an approved rate, and small deviations during installation change the performance. Conveyance to and from the facility is ordinary drainage solutions work, but the control structure itself gets built to the plan dimensions exactly.
Media, Stone, and the Embankment
Here the project does two opposite things at once, which is why it confuses crews unfamiliar with stormwater work.
Where compaction is forbidden. The infiltration subgrade, the bed bottom, and the soil beneath bioretention media. These get scarified, not rolled.
Where compaction is mandatory. The embankment. A dam holding water back is built in controlled lifts, each compacted to specification, with the fill material and moisture content checked. An embankment that settles or seeps is a safety problem rather than a maintenance one.
Between them sits the separation layer. Non-woven geotextile keeps fines out of the stone so the void space stays open, and it goes in with generous overlaps and no punctures.
Stone for storage beds is clean, washed, open-graded material. Bioretention and rain garden media are engineered mixes placed to specified depths. Substituting a cheaper material at this stage undoes the design quietly.
Where the Engineer Has to Be On Site
Pennsylvania does not leave this to the contractor’s judgment.
Under 25 Pa. Code Chapter 102, a licensed professional or a designee must be present on site and responsible during critical stages of implementing the approved post-construction stormwater plan. The regulation identifies those critical stages as potentially including installation of underground treatment or storage facilities, structurally engineered facilities, and anything else DEP or the conservation district considers appropriate.
The permit application itself has to identify those stages in advance, so both sides know when the engineer is expected on site. If your schedule has an underground storage bed going in on a Saturday with nobody notified, that is a compliance problem before it is a scheduling one.
Stabilization and Vegetation
Bare soil is the largest pollutant source on any construction site, so stabilization is not a finishing touch.
Areas are stabilized as they reach final grade rather than at the end of the project. Topsoil goes back, then seed and mulch, an erosion control blanket on slopes, or sod where conditions demand it. Basin bottoms and side slopes usually have their own seed specification, and vegetated facilities have planting plans that are part of the approved design.
Timing matters in Central Pennsylvania. Seeding in late autumn leaves bare ground through winter with no germination, which is why stabilization deadlines and temporary cover requirements exist in the plan.
Temporary erosion controls stay in place until the areas they protect are permanently stabilized, and then come out.
Closing the Permit Out
Construction ending and the permit ending are two different events.
Confirmation testing. DEP has moved toward requiring post-construction testing on infiltration facilities to determine actual as-built ponding or drawdown time and confirm it falls within the design tolerance, with results submitted as part of construction certification. In other words, you demonstrate the facility infiltrates rather than asserting it.
Record drawings and final certification. Chapter 102 requires the permittee to submit record drawings with the notice of termination, carrying a certification statement from a licensed professional. That statement is made pursuant to the penalties of 18 Pa.C.S.A. § 4904, and it certifies that the drawings accurately reflect as-built conditions and that the site was constructed in accordance with the approved plan.
Recorded instrument. Permittees must record a legal instrument identifying the post-construction stormwater control measures on the property. Under the 2019 version of PAG-02 that recording was required within 45 days of permit issuance, and DEP has been revising the timing and submission requirements, so confirm the current rule with your conservation district.
Notice of Termination. Only once the facilities are complete, the site is stabilized, and the paperwork is accepted does permit coverage end.
Owner notification on sale. DEP has been adding a requirement that a permittee selling property containing a stormwater control measure during the permit term provide the new owner with a notification form, the record drawings, and the long-term operation and maintenance plan.
Handing over a complete document package is the last construction task, and it is what keeps future owners out of trouble. Building the facility correctly is only half of a finished stormwater management installation.
How Long It Takes and What Delays It
The build itself is often the shortest part.
| Stage | Typical Duration |
|---|---|
| Testing, design, and permitting | Several months, longer for individual permits |
| Site preparation and controls | Days to a couple of weeks |
| Earthwork and facility excavation | One to several weeks by size |
| Structures and piping | Days to weeks |
| Stabilization | Days, plus a growing season to establish |
| Closeout and termination | Weeks to months |
Common delays: wet weather stopping earthwork in clay soils, infiltration testing coming back worse than assumed and forcing a redesign, utility conflicts found during excavation, seasonal seeding windows, and waiting on an engineer for a critical stage inspection.
Local conditions shape most of that. Clay soils and seasonal rainfall across Adams County and the surrounding counties mean earthwork windows matter, and building the schedule around them beats fighting them.
Final Thoughts
Stormwater installation is a sequence, and the sequence is the product. Controls before disturbance. Infiltration areas fenced and kept clear of equipment from the first day. Compaction forbidden in one place and mandatory a few feet away. Stabilization as areas finish rather than at the end. Testing, record drawings, and certification before the permit closes.
If there is one thing to take from it, it is that the most consequential moment on a stormwater job involves no construction at all. It is the decision to route a truck around the infiltration footprint rather than across it, made repeatedly, by people who understand why the fence is there.
JDI Site Solutions designs and installs stormwater systems for developers, businesses, farms, and municipalities across Adams County and Central Pennsylvania, including erosion control, facility construction, and closeout documentation. Call JDI Site Solutions to talk through what your project involves.