Dry Well¶

Dry wells are covered by BMP Manual Chapter 9.2 in the live source corpus. This page now stays with the source-backed core: what the BMP does, when it remains viable, and which chapter-level constraints still control design use.

Structured citation evidence for this page lives in the sibling claim manifest.

Overview¶

In the enrolled source set, a dry well is a compact infiltration BMP used to receive runoff from limited clean-roof tributary areas such as roof leaders. It is useful when the project needs distributed source control but does not have room for a larger surface BMP.

Chapter 9.2 is narrower than some of the older dry-well summaries. A dry well is only used to collect and temporarily store stormwater runoff generated by a clean roof; treatment of runoff from any other surface is prohibited. The chapter also requires an overflow for larger storms.

Source Mapping¶

The live citations layer resolves this route directly to the following canonical source bundles.

Route type: canonical
2023 source bundle: Chapter 9.2 (2023_BMP_9_2) - Dry Wells
2026 source bundle: Chapter 9.2 (2026_BMP_9_2) - Dry Wells

Key verified claims already tied to this page manifest: - Dry wells are source-control infiltration BMPs for limited tributary areas under Chapter 9.2. - Dry-well permeability and SHWT separation remain 0.5 in/hr and 2 ft across both eras. - Dry wells keep the 72-hour drawdown limit. - Dry-well viability stays tied to Chapter 12 and Chapter 13.

Design Criteria¶

The reconciled design criteria below come from the live crosswalk and page-level claim set, not from the older narrative snapshot.

Parameter	2023 source value	2026 source value	Change
Minimum Ksat (field-measured)	>= 0.5 in/hr	>= 0.5 in/hr	unchanged
SHWT separation	2 ft below dry well bottom - measured from static SHWT	2 ft below dry well bottom - measured from static SHWT	unchanged
Drawdown time	<= 72 hours	<= 72 hours	unchanged
Foundation setback	>= 10 ft	>= 10 ft	unchanged
Septic system setback	>= 10 ft	>= 10 ft	unchanged
Required infiltration test method	Primary: percolation test, tube permeameter, single ring infiltration test, basin flooding test. Additional: ASTM D3385 (Double-Ring Infiltrometer), USBR 7300-89, or other recognized methods	Primary: percolation test, tube permeameter, single ring infiltration test, basin flooding test. Additional: ASTM D3385 (Double-Ring Infiltrometer), USBR 7300-89, or other recognized methods	unchanged
K_design calculation	K_design = K_field / 2.0 (factor of safety = 2.0)	K_design = K_field / 2.0 (factor of safety = 2.0)	unchanged

Source-backed criteria that still control this route: - Dry wells are source-control infiltration BMPs for limited tributary areas under Chapter 9.2. - Dry-well permeability and SHWT separation remain 0.5 in/hr and 2 ft across both eras. - Dry wells keep the 72-hour drawdown limit. - Dry-well viability stays tied to Chapter 12 and Chapter 13.

Siting Constraints¶

The current source-backed siting review should focus on:

whether the contributing runoff source is appropriate for a Chapter 9.2 dry-well application
whether field testing supports the credited infiltration rate
whether SHWT separation and nearby structures allow infiltration safely
whether the project needs hydraulic-impact review under the Chapter 13 framework

If those checks fail, the design should move to a different BMP rather than stretching the dry-well chapter beyond its supported use.

Inflow and Pretreatment¶

Chapter 9.2 adds a more specific inflow screen than the current short summary implies:

roof runoff routed to a dry well must be pretreated by leaf screens, first flush diverters, or roof washers
the review agency may waive that pretreatment only where the building has no realistic potential for debris or vegetative material in the roof runoff
rooftop pollutant conditions still matter, so the chapter cautions against siting dry wells where roofs are likely to carry unusually high pollutant loads

Maintenance¶

Dry-well maintenance is still about preserving infiltration performance:

keep inlets and pretreatment features free of sediment and roof debris
watch for slow drainage or persistent surface ponding after storm events
inspect overflow and access points where the design includes them
treat clogging as a core performance issue, not just a housekeeping issue
keep the as-built testing record with the maintenance plan so the confirmed design permeability and design drain time remain documented for later inspections

Source Bundles¶

Use these source bundles when checking the live extracted text or paired OCR evidence:

2023 bundle: Chapter 9.2 (2023_BMP_9_2) - Dry Wells
2026 bundle: Chapter 9.2 (2026_BMP_9_2) - Dry Wells