Stormwater Management Plan Comments in Fairfax County

When Fairfax County evaluates a stormwater management plan, it checks the plan against a comprehensive, watershed-based compliance framework built on federal Clean Water Act obligations, the county's MS4 permit, and Chesapeake Bay TMDL targets. The county organizes its stormwater program across six areas: Regulatory Compliance, Dam Safety and Facility Rehabilitation, Stream and Water Quality Improvements, Emergency and Flood Control, Conveyance System Rehabilitation, and Operational Support. Plan review comments are the front line of the Regulatory Compliance component, the point where the county's broader permit obligations meet an individual applicant's design.

The county's MS4 permit requires it to demonstrate a comprehensive stormwater management program, so a reviewer issuing a comment is defending the county's own permit compliance, not applying a preference. The sections that follow walk through the instruments reviewers use to enforce this framework, so start with the gate every plan must clear before a reviewer looks at a single calculation.

How the completeness determination works before technical review even begins

Before any technical evaluation occurs, Fairfax County Land Development Services runs every submission through a completeness checklist, and if a plan fails it, the county rejects it without a substantive review. The operative document is the Stormwater Management Plan Completeness Checklist, revised March 14, 2025. SWMO §124.1-2-5(C) requires the county to notify you within 15 calendar days whether it deems the plan complete. Compliance with the checklist does not ensure approval; it only secures acceptance for review, a distinction the checklist draws explicitly and one that shapes everything that follows.

The checklist runs through five functional groups, and each one maps to a section reviewers will later examine on technical merit. The first group covers outfall analysis and narrative, lines 1 through 10, and requires a description of each outfall, the downstream receiving water bodies and drainage facilities, a drainage area map per outfall, a downstream review divided into reaches under PFM §6-0203, cross-section information supporting channel adequacy claims, and a written opinion on downstream adequacy that must be certified, signed, and sealed by the submitting licensed professional. That seal requirement, line 10, is a frequent source of incompleteness findings on its own: a narrative description of adequacy is not a substitute for a certified, signed, and sealed opinion, and plans are routinely rejected at the gate for this gap alone.

The second group, stormwater facility narrative, lines 13 through 17, asks for contact information including the property owner's tax map number, a narrative on pre- and post-development stormwater conditions and any proffers or conditions attached to the site, a general description of proposed SWM facilities with type, location, geographic coordinates, and acres treated, a description of the receiving surface waters, and the mechanism for post-construction operation and maintenance. The third group covers hydraulic and hydrologic computations, lines 18 through 21: pre- and post-development runoff, inlet computations, storm drain computations, and open channel computations. The fourth group addresses water quality, quantity, and detention compliance, lines 22 through 25, covering water quality computations under SWMO Article 4 and PFM 6-0402.8, channel protection, flood protection, and detention computations under §124-4-4.D. The fifth group, site maps, lines 26 and beyond, requires drainage areas covering the entire site and limit of disturbance, existing streams, ponds, culverts, ditches, wetlands, RPAs, and floodplains, soil types and vegetative cover, existing land use and structures, sufficient offsite topography to assess downstream impacts, clearing and grading limits, proposed drainage patterns, and proposed land use with a surface area tabulation.

Completeness is a structural determination, not a technical one. The checklist tells a reviewer whether the plan contains the pieces needed to conduct a technical review at all, and it is only once that threshold is cleared that the substance of the engineering gets evaluated against the standards the next two sections describe.

What the VESMP checklist adds on top of the county's completeness requirements

Running parallel to the county's own completeness gate is the Virginia Erosion and Stormwater Management Program checklist, a state-level instrument that explains why comment letters often cite both county ordinance and state regulation in the same paragraph. The 2025 edition of the VESMP checklist organizes its requirements into narrative, site information, hydrologic analysis, hydraulic analysis, BMPs, piped systems, open channel systems, Chesapeake Bay regulations, SWPPP contents, and Pollution Prevention Plan contents, a broader scope than the county's completeness checklist alone.

Two VESMP items generate the most substantive comments when a site sits anywhere near a regulated water body. The first is the impaired-waters identification requirement: the narrative must state whether the receiving water body is classified as impaired in the Virginia DEQ 305(b)/303(d) Water Quality Assessment Integrated Report, and whether it is identified as an exceptional water under 9VAC25-260-30 A 3. The narrative must also address any additional control measures required under an approved local TMDL with a wasteload allocated for sediment, sediment-related parameters, nutrients, or PCBs. The second is the Virginia Runoff Reduction Method spreadsheet, which you need to document pollution load and reduction calculations. BMP entries on the VESMP checklist must use SWM Handbook names for each BMP type, report geographic coordinates to six decimal places, and separately specify total acres treated, acres impervious treated, and acres pervious treated.

The checklist's piped system and open channel standards are largely reference tables rather than interpretive judgment calls: primary road crossings are designed for 25-year flows, secondary roads and other locations for 10-year flows, culverts are checked against 100-year storm effects, hydraulic grade lines must sit 1 foot below inlets, and gutter spread is capped at 10 feet from the face of curb. You analyze open channel systems for the pre-development 10-year storm, you design them against erosion for the 2-year storm, and you size them for bank-fill liner design at the 10-year storm, with an overlot grading plan and 100-year overland relief assuming pipe failure. A missing or incomplete SWPPP is a VESMP deficiency independent of anything the county's own completeness checklist requires.

How the county's watershed-based framework shapes review comments

Fairfax County administers stormwater management on a watershed basis across its 30 completed watershed management plans, and a project's location within a specific watershed determines which stream health targets and impervious-cover thresholds the reviewer applies. That is why a technically correct plan, read against a narrow interpretation of the checklist, can still draw comments that appear site-specific. The watershed management plans supply targeted strategies for stream health based on current and future land use and the relative condition of the stream in question, so the same BMP is weighted differently depending on which drainage basin it is in.

The thresholds reviewers are protecting against are well established in the stormwater literature: biological and physical degradation becomes apparent as impervious cover approaches 10 percent, and severe degradation sets in above 20 percent. If a project pushes a watershed closer to either threshold, it draws closer scrutiny on runoff volume and quality calculations than an identical project sited in a watershed already well past those thresholds. The county's own 2023 monitoring data shows that most of its 40 monitored stream sites already sit above the 20 percent impervious threshold, and most streams are rated in poor or very poor biological health. Reviewers are managing a baseline that is already degraded, and comments on nutrient and sediment load reduction reflect that condition.

The downstream review requirements embedded in the completeness checklist, lines 5 through 9, are the procedural expression of this watershed framework. Reaches must be analyzed individually, channel adequacy must be demonstrated with cross-sections, and 100-year flood impacts on existing dwellings must be addressed. These items generate comments whenever the downstream analysis stops at the property line instead of extending to a point of demonstrably adequate capacity, because a property-line analysis cannot show what the watershed framework requires the reviewer to confirm. Sites within the county's Water Supply Protection Overlay District carry an additional layer of ordinance requirements on top of the standard VESMP and SWMO framework, a further illustration of how location, not just design quality, shapes what a reviewer is checking.

The ordinance amendments that changed what reviewers are checking as of 2025

If your firm calibrated its SWM plan templates and calculation workflows before mid-2025, you are submitting against a standard that has since moved, because both the state regulation and the county ordinance changed during the year. On December 9, 2025, the Board of Supervisors adopted amendments to Chapter 124.1, the Erosion and Stormwater Management Ordinance, to implement changes to the Virginia Erosion and Stormwater Management Regulation and to clarify existing requirements.

The water quality control requirements tied to the state regulation change took effect earlier than that. The two dates do the two different jobs: July 1 changed what reviewers check, and December 9 changed what the ordinance itself says. It reflects the July 1 implementation date, and any plan moving through review now should be checked against the standard in force since that date rather than the standard in force when an earlier, similar project was approved.

The categories of comments that appear most predictably

Most comments issued by Fairfax County Land Development Services fall into a small number of recurring categories, each tied directly to the completeness checklist or the VESMP checklist, and each one is a request for a specific type of information.

Outfall and downstream adequacy comments are the most common substantive category. They arise when the downstream analysis fails to reach a point of adequate capacity, when cross-sections are missing or insufficient to support a channel adequacy claim, or when the licensed professional's opinion, checklist line 10, is unsigned, unsealed, or not tied specifically to a PFM §6-0203 adequacy finding. Closing this comment requires extending the reach analysis to a demonstrably adequate receiving point, providing cross-sections with supporting computations for each reach, and making sure the PE opinion letter certifies adequacy under PFM §6-0203.3 directly.

The fix is maps that show contributing areas for the entire site and entire LOD under checklist line 26, with enough offsite topography and drainage divides, upstream, downstream, or adjacent, to assess impacts to downstream structures as required under line 30.

Closing this one means submitting a completed VRRM spreadsheet with inputs traceable to the site plan's land cover tabulation, using exact SWM Handbook BMP names, and documenting total acres treated, acres impervious treated, and acres pervious treated separately for each BMP, with coordinates to six decimal places.

The reviewer needs a direct lookup in the DEQ Integrated Report and a written narrative statement addressing each criterion, not a blank field or an unsupported "not applicable."

RPA and Chesapeake Bay regulation comments arise on any site where the county's preservation area map shows RPA components, when site-specific RPA boundaries haven't been delineated on the plan, when a required water quality impact assessment hasn't been submitted, or when a USACE jurisdictional determination letter is absent. Closing it requires submitting the RPA site-specific study application through the Zoning Division before the SWM plan resubmittal and coordinating the USACE JD or verification letter timeline with the plan review schedule, the most common schedule driver in this category.

Piped system and open channel design comments occur when pipe sizing computations don't demonstrate the required storm frequency, when hydraulic grade lines aren't shown at 1 foot below inlets, when road crossing storm frequencies don't match the primary or secondary road classification, or when open channel liner design isn't documented separately for the 2-year and 10-year storms.

You'll see operation and maintenance documentation comments when the post-construction O&M mechanism is described in general terms instead of naming the responsible party, the inspection schedule, and the agreement instrument. Checklist line 16 requires the mechanism for post-construction operation and maintenance, and the VESMP checklist adds a BMP maintenance plan with an inspection schedule and a signed maintenance agreement on top of that.

Approaching a resubmittal without generating new comments

A resubmittal that answers each comment in isolation, without auditing the rest of the plan for consistency, tends to produce a second round of comments on the downstream effects of the very fix that was meant to resolve the first round. This is the most avoidable comment cycle in the entire process, and it starts with treating the completeness checklist as an audit tool even after the plan has already been accepted for review. Walking each line item against the revised plan catches the chain reaction a single change can trigger: revising a drainage area map changes the pre- and post-development runoff computations, which changes BMP sizing, which in turn changes the VRRM spreadsheet.

Response letters organized by checklist line number and VESMP checklist section, rather than by reviewer comment number alone, let the reviewer verify a fix against the same framework used to raise the original comment, which cuts down on back-and-forth over whether a revision actually responded to what was asked. For downstream adequacy and outfall comments, you need a revised PE opinion letter with updated certification language, not just revised exhibits. The signed and sealed opinion has to reflect the revised analysis itself. For RPA and Chesapeake Bay regulation comments, the Zoning Division application or USACE coordination should be complete before the SWM plan is resubmitted; submitting the plan without that prerequisite documentation in hand restarts the comment cycle. For water quality and VRRM comments, send a revised spreadsheet with a change log identifying which input cells changed and why, since reviewers working through multiple resubmittals can verify that far more easily than a replaced spreadsheet with no record of what moved.

The July 1, 2025 implementation of the updated water quality control requirements sets a specific trap if your plan is already in cycle. If your firm is resubmitting a plan originally submitted before that date, audit all water quality computations against the current standard before resubmittal, even if you've already addressed the original water quality comment. A plan now in its second or third review cycle may still be carrying open items dated to before the standard changed, and those items will appear in the next round of comments whether or not they were ever raised before.