Market Intelligence
Stormwater ponds and basins per county (estimate)
County inventory estimates for wet ponds and dry detention basins, with public inputs, maintenance responsibility, research benchmarks and a worked service territory.
Direct answer
Anvilfield research puts ponds and dry detention basins in the Fairfax County inventory footprint at 2,320, with a range of 2,200 to 2,550; Loudoun's footprint at 1,160, ranging from 1,100 to 1,280; and Montgomery County's DEP footprint at 1,100, ranging from 1,050 to 1,210. The combined Anvilfield estimate is 4,580 facilities, ranging from 4,350 to 5,040, in the 2026 inventory snapshot.
On this page
What does a county pond count tell a service company?Anvilfield estimatesWhich ponds and basins belong in the count?Why does population miss the pond market?What turns a mapped basin into a serviceable account?How do leading teams measure a pond service territory?Benchmarks for a usable county inventoryWorked example: a regional stormwater service company in Fairfax CountyWho buys maintenance for these facilities?How does the asset count become inspection and maintenance demand?County inventory release checklistHow do you keep the county count useful?MethodologyOpen the related tool for the calculation, checklist, or packet.
Key takeaways
- Anvilfield estimates about 4,580 wet ponds and dry basins across the selected county inventory footprints.
- Count stable facility IDs and retain county coverage, asset class and status with every record.
- Qualify maintenance responsibility and access before estimating recurring workload.
What does a county pond count tell a service company?
A county pond count gives you a physical starting point for vegetation service, inspections, outlet maintenance and sediment projects. It helps decide where to research owners, build routes and develop specialist capacity. Keep the facility count attached to its geographic coverage and asset definition. A countywide stormwater database includes many controls that need completely different equipment and maintenance skills.
Targeted market intelligence means sizing and locating demand at the building level rather than the ZIP level. For stormwater work, that means connecting a basin to the development it serves, its maintenance documents and the organization that pays for the work. The location of a pond is useful even when its purchasing office sits outside the county.
Installed-base mapping means locating every unit of a product class in the field, across brands. Here the class is permanent wet ponds and dry detention basins recorded in county inventories. Keep each facility attached to a stable identifier so a later inspection, ownership change or revised classification updates the same record.
Targeted market intelligence explainedInstalled-base mapping explainedStormwater detention pond managementAnvilfield estimates
Anvilfield estimates about 2,320 ponds and dry detention basins in the Fairfax County inventory footprint, based on its active facility records. Anvilfield estimates about 1,980 dry detention basins in that Fairfax inventory. Anvilfield estimates about 340 wet ponds in the same Fairfax footprint.
Anvilfield estimates about 1,160 ponds and dry detention basins in the Loudoun County inventory footprint, after consolidating repeated facility IDs. Anvilfield estimates about 670 dry detention basins in that Loudoun inventory. Anvilfield estimates about 500 wet ponds in the same Loudoun footprint.
Anvilfield estimates about 1,100 ponds and dry detention basins in Montgomery County's Department of Environmental Protection, or DEP, inventory footprint, using completed records with the selected status. Anvilfield estimates about 860 dry detention basins in that DEP inventory. Anvilfield estimates about 240 wet ponds in the same DEP footprint.
Anvilfield estimates a combined mapped base of about 4,580 ponds and dry detention basins across these county inventory footprints, with a planning range of 4,350 to 5,040. Anvilfield estimates about 860 Fairfax ponds and dry basins marked for private maintenance. Anvilfield estimates about 1,460 Fairfax ponds and dry basins marked for public maintenance.
The maintenance categories divide the Fairfax total. Wet and dry categories divide each county total. The combined row joins the county totals. Read each row as a different view of the same asset register; add only categories that do not overlap. Source numbers point to the linked inputs in Methodology.
Methodology records the inventory dates, status filters, duplicate removal and range settings. Keep the named inventory footprint attached to every county result.
Methodology: inputs and research settings| Anvilfield estimate | Low | Central | High |
|---|---|---|---|
| Fairfax County, VA: All ponds and dry basins | 2,200 | 2,320 | 2,550 |
| Fairfax County, VA: Dry detention basins | 1,880 | 1,980 | 2,180 |
| Fairfax County, VA: Wet ponds | 320 | 340 | 370 |
| Loudoun County, VA: All ponds and dry basins | 1,100 | 1,160 | 1,280 |
| Loudoun County, VA: Dry detention basins | 630 | 670 | 730 |
| Loudoun County, VA: Wet ponds | 470 | 500 | 550 |
| Montgomery County, MD, DEP footprint: All ponds and dry basins | 1,050 | 1,100 | 1,210 |
| Montgomery County, MD, DEP footprint: Dry detention basins | 810 | 860 | 940 |
| Montgomery County, MD, DEP footprint: Wet ponds | 230 | 240 | 270 |
| Combined inventory footprints: all ponds and dry basins | 4,350 | 4,580 | 5,040 |
| Fairfax County: private maintenance | 820 | 860 | 950 |
| Fairfax County: public maintenance | 1,380 | 1,460 | 1,600 |
How to cite this estimate: Anvilfield, Stormwater ponds and basins per county (estimate), 2026, https://anvilfield.com/field-guides/market-intelligence/stormwater-ponds-and-basins-per-county-estimate/
Which ponds and basins belong in the count?
Use the facility's documented purpose and class. A wet pond maintains a permanent pool; a dry detention basin stores runoff temporarily and generally lacks a large permanent pool. The EPA dry detention fact sheet explains that small inlet or outlet pools can remain in a dry basin. A photograph of standing water therefore needs context before it becomes a wet-pond classification. [5]
Keep pretreatment forebays, outlet structures and connected pipes attached to their parent facility. A forebay can create a separate patch of visible water within a pond system. A point layer showing its outlet and a polygon layer showing its footprint can describe the same asset. Count the facility and retain the components as service quantities within its record.
The scope here excludes farm ponds, ornamental water features, underground detention, constructed wetlands, swales, rain gardens and infiltration-only practices. Some of those features require excellent recurring service, but they are separate asset classes. A broad search for anything with water or a depression would mix incompatible tasks and give the crew an unreliable equipment plan.
A dry basin deserves explicit search attention because maintained grass can hide its function. Review its grading, inlet, outlet and approved plan together. Use the bioretention and drainage guides when a candidate has planted media, a drain system or an uncertain flow path. Preserve an unresolved classification until the supporting record settles it.
Bioretention and rain garden identificationSubsurface drainage and catch basinsEPA dry detention definition [5]Why does population miss the pond market?
Population describes residents. A stormwater inventory describes built drainage assets associated with development patterns, roads and runoff management choices. A commercial district serves people who live elsewhere, while a residential development can share a basin across many properties. A per-resident ratio loses both relationships and gives an unhelpful basis for assigning service routes.
Anvilfield analysis finds that dry basins account for about 85% of the selected Fairfax pond inventory, 57% in Loudoun and 78% in the Montgomery DEP footprint. That mix changes the research task. A search concentrated on open water misses much of the dry-basin inventory, especially in Fairfax.
Building-first prospecting starts from the building and what is visible on it, then finds the decision maker. For pond work, extend the building record to the basin serving the property and trace shared facilities back to their maintenance agreement. The nearest building is a location clue; the agreement establishes the obligation.
Visible-asset data consists of facts read from aerial and satellite imagery and checked against records. Preserve the observation date, basin outline and visible access alongside the county classification. These evidence tracks answer different questions: imagery describes visible conditions, while the approved records describe the intended facility and its responsibilities.
Building-first prospectingVisible-asset dataDrainage, grading and slopeWhat turns a mapped basin into a serviceable account?
Fit-first lists are lists filtered to the buildings that fit a company's work. For stormwater maintenance, those criteria include asset class, maintenance responsibility, safe access, required qualifications and workable travel. Put the acceptance rules in writing before the research starts so every reviewer applies the same scope.
The county count is the top of this process. Move a record forward when the facility exists, the responsible organization is established, the work fits the crew and the buyer has a reason to discuss it. Keep reasons for exclusion. An inaccessible basin, an existing long-term contract and a specialist structural problem require different follow-up decisions.
Separate vegetation and litter work from hydraulic performance, sediment excavation and engineered repairs. EPA's wet pond management guide treats inspection, vegetation, sediment, access and mechanical components as distinct work areas. That separation makes the account useful to both a landscape service manager and a specialist contractor who handles the larger interventions. [6]
Confirm the maintenance area during an authorized visit. Water area, parcel area and mowed area answer different estimating questions. Document gates, approved equipment routes, designated vegetation, outlet access, disposal arrangements and reporting expectations. Use those observations to prepare a defined scope and schedule before a county market estimate becomes an annual revenue forecast.
Fit-first listsFind detention pond maintenance accountsPrice pond maintenance from a site scopeHow do leading teams measure a pond service territory?
Leading manufacturers, distributors and service companies measure the physical territory directly, linking the asset register to the work they sell. A vegetation contractor needs serviceable banks and access; an outlet supplier needs the installed component and replacement scope; a sediment specialist needs measured quantities and disposal requirements. The same county inventory supports each business when the qualification fields reflect its actual work.
For custom territory measurement, PorchRocket's Asset Search finds assets visible from above, including stormwater ponds, and returns the owner of record with reviewed findings. Give the search a written wet-pond and dry-basin definition, then reconcile the returned locations against county facility IDs and maintenance records.
Keep an asset table, a site table and an organization table linked together. Several basins can sit within a development, and a management organization can oversee facilities in different counties. A change in management should update the organization relationship without destroying inspection history or creating a second copy of the basin.
For the surrounding commercial-property research, PorchRocket's Ground Control filters buildings by business type, size, parking and other physical attributes, at $10 to $20 per building with delivery within 48 hours after payment. Use that building context to organize commercial sites, while specifying the pond inventory as a custom asset search.
A useful handoff gives the salesperson the facility identity, reason for fit, maintenance evidence and next unresolved question. The estimator then adds measured task quantities and access conditions. Reviewers should be able to follow that chain without searching the entire county map again whenever an owner replies.
Benchmarks for a usable county inventory
Use these operating rules to keep the research consistent across counties. They are Anvilfield workflow targets and inventory findings. Record whether a row is ready for sales research, ready for an authorized visit or ready for pricing; those stages require different evidence.
The dry-basin shares below use the selected, deduplicated public records. The workflow rules govern how to handle those records. Keep the measured ratios distinct from the targets your own research team adopts.
| Field rule or ratio | Benchmark | Practical use |
|---|---|---|
| Count each facility once under its stable county-qualified ID. | 1 asset ID per basin | Merge repeated source rows; retain related components. |
| Pair the mapped observation with a facility record. | 2 evidence tracks | Keep imagery dates and record dates in separate fields. |
| Expect dry basins to dominate the selected Fairfax inventory. | 85% dry | Include graded grass basins in the search rules. |
| Keep wet and dry searches equally visible in the Loudoun review. | 57% dry | Avoid a search based only on open water. |
| Treat dry detention as the larger Montgomery DEP pond class. | 78% dry | Carry the DEP coverage boundary into comparisons. |
| Resolve ownership, maintenance and purchasing separately. | 3 responsibility fields | Attach the agreement and the buying contact. |
| Separate routine service, sediment projects and structural repairs. | 3 scope buckets | Price each from its own quantities and approval path. |
| Finish a bounded research batch before expanding the territory. | 40 candidate facilities | Measure rejection reasons and reviewer effort. |
Worked example: a regional stormwater service company in Fairfax County
A regional stormwater service company in Fairfax County reviews 40 privately maintained facilities near its existing routes. Anvilfield estimates 30 responsibility-qualified facilities, 24 with workable access and travel, and 6 facilities with awarded routine-service agreements in this operating case.
The research funnel retains 75% of the initial batch at the responsibility screen and 80% of that group at the route screen. Agreements cover 25% of the route-qualified group. Keep the denominator beside each percentage so the sales team can see where records leave the process and what evidence would move them forward.
Anvilfield estimates 72 facility visits and 306 worker-hours annually for the service package. The visit workload is 4.25 worker-hours, including on-site work, travel and reporting. The crew plan follows the agreed routine scope and the visit inputs recorded in Methodology.
Price that measured workload with the company's loaded labor, equipment, materials and overhead. Add the agreed emergency response arrangements and keep sediment removal and structural repairs on separately defined scopes. The county asset total helps find the next research batch; the visit calendar establishes the workload the company has actually agreed to deliver.
Keep facilities and customers separate in the account record. A manager can authorize work across several basins, and a basin can involve shared responsibility. Count service visits against the facility schedule and invoices against the contractual customer. That avoids treating a portfolio agreement as an unexplained jump in asset count or a reduction in crew workload.
Landscape estimating and biddingCommercial landscape maintenance programsWho buys maintenance for these facilities?
Start with the recorded maintenance obligation. Fairfax County explains that privately maintained facilities remain the owner's responsibility even though the county inspects them. Its maintenance agreements are recorded with the land, and its inspection documents identify required work. Match those records to the specific facility before choosing a contact or drafting a proposal. [7]
For a homeowners association, identify the management contact, spending approver and authorized signatory. For a commercial property, establish whether the owner, operator or manager controls the relevant scope. Keep a public agency's inspection role separate from the purchasing responsibility for a privately maintained site. Each role belongs in the record with its evidence.
Public maintenance records describe a different route to work. Read the agency's solicitation, asset schedule and scope boundaries before counting it as an opportunity. A contract covering many stormwater practices can include ponds, pipes, treatment devices and vegetation areas with different pricing units. Match the eligible pond IDs to the bid schedule instead of importing the entire contract quantity into the pond market.
Treat equipment access and reporting as part of buyer qualification. A manager who can authorize mowing still needs a separate approval path for dewatering, excavation or engineered repairs. Ask who receives inspection findings and who releases additional work. Preserve that answer alongside the facility's approved maintenance documents.
Retention and detention pond maintenance bidsOwner, operator and decision makerFairfax private maintenance responsibilities [7]How does the asset count become inspection and maintenance demand?
Attach the approved operation and maintenance plan to the facility record, then build the task calendar from that plan and the applicable local requirements. Routine service, formal inspections and condition-triggered work have different triggers. A county's oversight inspection cycle does not establish the mowing calendar or the owner's contractual inspection duties.
Record the quantities that create paid work: designated vegetation area, accessible structures, litter handling, inspection time, travel, reporting and disposal. Carry measured sediment accumulation into a separate project scope. EPA's management guide emphasizes those maintenance components, giving the estimator a better structure than an annual charge based only on a pond's apparent area. [6]
Use the approved plans to understand the intended water level and flow path before classifying a visible condition as a defect. A vegetation change calls for review of the planting and maintenance requirements. A bare bank calls for a documented erosion assessment. A changed outlet needs a qualified review against the design before the sales team promises a repair.
Track demand using documented tasks and owner decisions. An inventory expansion increases the research universe; a confirmed deficiency, renewal date or capital plan creates a more specific sales action. Maintain both records so a larger county total does not automatically become a larger annual service commitment.
Erosion control and stormwater best management practicesEPA pond inspection and maintenance guide [6]County inventory release checklist
Before assigning research or calling owners, release the inventory with its definition, coverage and revision date attached. Have a reviewer inspect ambiguous classes and repeated IDs. A clear rejection reason is useful evidence for improving the next search and for keeping unsuitable work out of the estimator's queue.
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
How do you keep the county count useful?
Asset monitoring means dated change detection of new, removed or altered assets. Keep the earlier observation, the later observation and the reason for the classification change attached to the same facility ID. Distinguish a new record entering the county database from evidence that the physical basin has just been built.
A defensible visible change starts with 2 dated views and a comparison of the same feature. Reconcile new outlines, altered vegetation and changed structures with permits and facility records. Use the resulting change to assign a review task, such as checking a completion status or obtaining the revised maintenance plan.
For a territory that needs repeated observation, PorchRocket's Asset Search supports custom monitoring of visible assets with a cadence agreed for the search area. Keep those dated findings beside the county record so a physical change and an administrative update remain distinguishable in the service file.
Refresh the buyer relationship when ownership or management changes, and refresh the work scope when the approved facility changes. Carry existing inspection records forward. A clean history lets an account manager explain why a site entered the territory, what was verified and which task is now waiting for the owner.
Asset monitoring and dated change detectionMethodology
Anvilfield downloaded the public GIS inputs with curl for the 2026-11-05 edition, retrieved every selected object ID in complete batches and counted unique facility IDs. The input year is the 2026 retrieval snapshot, not a claim that every facility was inspected that year. The source table records each input, its vintage and its use; linked sources and HTTP records are retained with the calculation.
Fairfax retains In Service records classified Dry Pond or Wet Pond: 2,386 downloaded rows less 67 excluded-status rows gives 2,319 unique FACILITY_ID values. Loudoun selects Pnd_Dry and Pnd_Wet and consolidates the repeated FCTID DP0036: 1,162 rows become 1,161 facilities. Loudoun supplies no operational status field and describes coverage concentrated in its eastern urbanized area.
Montgomery retains STATUS I with DA_Status Complete: dry codes PDQN, PDQNED and PDQNSF; wet codes PDWT, PDWTCMAC and PDWTED. This selects 1,100 unique ASSET values from 1,210 rows. Wetland and infiltration-only classes are excluded. The DEP program excludes Rockville, Gaithersburg and Takoma Park; the model makes no municipal expansion or national extrapolation. [4]
Research setting A applies analyst-selected multipliers of 0.95, 1.00 and 1.10 to each eligible count. The low case removes 5% for residual ineligibility, the central case retains the inventory, and the high case adds 10% for uncatalogued facilities within the same footprint. These are sensitivity choices, not measured error rates or confidence intervals. Counts round independently to the nearest 10; dry shares use unrounded counts and round to whole percentages. Facility IDs are the counting unit, and different IDs remain distinct until records establish otherwise.
The worked company case uses Anvilfield operating inputs: 40 candidates, 30 responsibility-qualified, 24 route-qualified and 6 awarded facilities. Its 12-visit calendar, 2-person crew, 1.5 on-site crew-hours, 0.5 travel crew-hours and 0.25 report worker-hours produce the stated workload. Workflow targets and sales conversions are Anvilfield research settings. The routine service package is defined for this case; approved facility plans establish the actual maintenance calendar.
Public county records supply every inventory count in this article. For a custom inventory using the same class rules, PorchRocket's Asset Search provides a written search and monitoring scope with a scope-based quote. Carry that scope into the research notes so the delivered asset definition can be compared with the public-data baseline.
[1] Fairfax County: StormNet Facilities GIS layer[2] Loudoun County: Stormwater BMPs GIS layer[3] Montgomery County DEP: SWFAC GIS layer[4] Montgomery County DEP: Fall and Winter Stormwater Inspection and Maintenance Recommendations[5] US EPA: Dry Detention Ponds[6] US EPA: Stormwater Wet Pond and Wetland Management Guidebook[7] Fairfax County: Private Facility Maintenance| Public input | Year or vintage | Value or role used |
|---|---|---|
| [1] Fairfax StormNet Facilities | 2026 snapshot; metadata revised 2025 | 1,980 dry; 339 wet; maintenance split 862 private / 1,457 public |
| [2] Loudoun Stormwater BMPs | 2026 snapshot; no fixed inventory year | 665 dry; 496 wet, after ID consolidation |
| [3] Montgomery DEP SWFAC | 2026 snapshot; no fixed inventory year | 856 dry; 244 wet, selected completed records |
| [4] Montgomery DEP program bulletin | 2025 | Program boundary and municipal exclusions |
| [5] EPA Dry Detention Ponds | 2021 | Dry-basin definition and permanent-pool distinction |
| [6] EPA pond management guidebook | 2009 | Maintenance components; no cost input |
| [7] Fairfax Private Facility Maintenance | Undated guidance, accessed 2026 | Maintenance agreement, buyer responsibility and records workflow |
FAQ
How many stormwater ponds are there in a county?
Anvilfield's central inventory-based estimates are about 2,320 wet ponds and dry detention basins in Fairfax County, 1,160 in Loudoun County and 1,100 in Montgomery County's DEP footprint. Use the county inventory definition and coverage in Methodology when comparing those totals.
Do dry detention basins count even when they look like grass?
Yes. The included dry detention classes generally lack a large permanent pool. Use the facility record, approved plan, grading and visible structures to distinguish a dry basin from ordinary open space.
Does the estimate include every stormwater best management practice?
The estimate covers the specified wet-pond and dry-detention classes. Bioretention, swales, underground detention, constructed wetlands, infiltration-only practices and farm ponds are outside its asset definition.
Does a publicly mapped pond belong to the county?
Public mapping identifies a facility. Ownership and maintenance responsibility require their own records. Fairfax explicitly distinguishes privately maintained facilities from the county inspection role; use the recorded agreement to identify the party responsible for the proposed work.
Why is Montgomery described as a DEP footprint?
The Department of Environmental Protection program excludes the municipal programs of Rockville, Gaithersburg and Takoma Park. The estimate retains the selected county DEP records and makes no addition for those separate municipal inventories.
Are the low and high values measured inventory error rates?
They are Anvilfield planning sensitivity cases. The central value uses filtered unique facility IDs; the low and high values apply the eligibility and missing-record allowances documented in Methodology. The allowances are model inputs.
How should a contractor price the service market?
Qualify the responsible buyer, approved scope and access, then measure task quantities and price the required calendar. Keep vegetation and litter service, formal inspections, sediment removal and structural repairs tied to their own workload and approval requirements.
Can these county counts be multiplied into a national total?
Build a national estimate from compatible inventories and a documented coverage model. These county footprints support local comparison; their mix of facility classes, development patterns and program coverage does not establish a national average.
People also ask
Sources checked
- [1] Fairfax County: StormNet Facilities GIS layer 2026 live inventory snapshot, retrieved with curl on 2026-11-05, HTTP 200. Metadata revised 2025-02-03 and describes weekly updates. All typed pond records downloaded by object ID; FACILITY_ID is the counting key. Class, status and maintenance responsibility are retained.
- [2] Loudoun County: Stormwater BMPs GIS layer 2026 live inventory snapshot, retrieved with curl on 2026-11-05, HTTP 200. Metadata gives no single inventory vintage, describes primarily eastern urbanized Loudoun coverage and biannual updates. Pnd_Dry and Pnd_Wet records downloaded; FCTID is the counting key. No operational status field is supplied.
- [3] Montgomery County DEP: SWFAC GIS layer 2026 live inventory snapshot, retrieved with curl on 2026-11-05, HTTP 200. No fixed publication year is stated for the live layer. ASSET is the counting key. Six dry and wet pond codes selected, then restricted to STATUS I and DA_Status Complete. Program coverage is described by source [4].
- [4] Montgomery County DEP: Fall and Winter Stormwater Inspection and Maintenance Recommendations County bulletin issued 2025-11-26; opened with curl on 2026-11-05, HTTP 200. Describes the SWIM program and excludes the municipal programs of Rockville, Gaithersburg and Takoma Park.
- [5] US EPA: Dry Detention Ponds December 2021 fact sheet, opened with curl and extracted with pdftotext on 2026-11-05, HTTP 200. Supports dry detention identification and the distinction from a permanent wet pool. No historical cost is used.
- [6] US EPA: Stormwater Wet Pond and Wetland Management Guidebook Revised February 2009, opened with curl and extracted with pdftotext on 2026-11-05, HTTP 200. Supports separate inspection, vegetation, sediment, access and structural work categories. Its cost appendix is not an input.
- [7] Fairfax County: Private Facility Maintenance Undated live county guidance, accessed 2026-11-05 with curl, HTTP 200. Supports the distinction between county inspection and private maintenance, recorded maintenance agreements, facility identifiers and documented closeout.
- [8] PorchRocket Asset Search: stormwater search scope Live product page, accessed 2026-11-05 with curl using the full referral URL, HTTP 200. Supports custom visible-asset finding and monitoring, owner of record and scope-based quotations. No commercial data enters the public inventory estimates.
- [9] PorchRocket Ground Control Live product page, accessed 2026-11-05 with curl using the full referral URL, HTTP 200. Confirms commercial building filters, $10 to $20 per building and delivery within 48 hours after payment. These are building-list terms, not a custom pond-search price.