Dry Wells
Description
Dry wells are small excavated pits, backfilled with aggregate, and used to infiltrate uncontaminated runoff from non-metal roofs or metal roofs located outside the Zone II or Interim Wellhead Protection Area of a public water supply and outside an industrial site. Do not use dry wells to infiltrate any runoff that could be significantly contaminated with sediment and other pollutants. Never use dry wells to infiltrate runoff from land uses with higher potential pollutant loads, including parking lot runoff.
Ability to Meet Massachusetts Stormwater Management Standards
| Standard | Description |
| 2 - Peak Flow | N/A |
| 3 - Recharge | Provides groundwater recharge. |
| 4 - TSS Removal | 80% TSS removal for runoff from non-metal roofs and runoff from metal roofs that are located outside the Zone II or Interim Wellhead Protection Area of a public water supply and outside an industrial site. |
| 5 - Higher Pollutant Loading | May not be used for runoff from land uses with higher potential pollutant loads, May not be used for runoff from metal roofs located at industrial sites. |
| 6 - Discharges near or to Critical Areas | Within a Zone II or IWPAmay be used only for runoff from nonmetal roofs. Outside a Zone II or Interim Wellhead Protection Area, may be used for both metal and nonmetal roofs provided the roof is not located on an industrial site. |
| 7 - Redevelopment | For rooftop runoff from non-metal roofs and from metal roofs located outside a Zone II or IWPA and outside industrial sites. |
Advantages/Benefits
- Applicable for runoff from non-metal roofs and metal roofs located outside of the Zone IIs or IWPA of a public water supply, and outside industrial sites
- Can reduce the size and cost of downstream BMPs and/or storm drains.
- Feasible for new development and retrofit areas
- Provides groundwater recharge
Disadvantages/Limitations
- Clogging likely when used for runoff other than that from residential rooftops.
- May experience high failure rate due to clogging.
- Only applicable in small drainage areas of one acre or less.
- When located near buildings, potential issues with water seeping into cellars or inducing cracking or heaving in slabs
- Overflow from roof leader must be directed away from sidewalks or driveways
Pollutant Removal Efficiencies
- Total Suspended Solids (TSS) 80%
- Nutrients (Nitrogen, phosphorus) Insufficient data
- Metals (copper, lead, zinc, cadmium) Insufficient data
- Pathogens (coliform, e coli) Insufficient data
Maintenance
| Activity | Frequency |
| Inspect dry wells. | After every major storm in the first few months after construction to ensure proper stabilization and function. Thereafter, inspect annually. |
| Measure the water depth in the observation well at 24- and 48-hour intervals after a storm. | Calculate clearance rates by dividing the drop in water level (inches) by the time elapsed (hr). See activity |
Special Features
For uncontaminated runoff from non-metal roofs. May be used for runoff from metal roofs located outside the Zone II or Interim Wellhead Protection Area of a public water supply and outside an industrial site. A metal roof is a roof made of galvanized steel or copper.
LID Alternative
Take advantage of LID site design credit and direct runoff from non-metal roofs to a qualifying pervious area. See Volume 3 of the Massachusetts Stormwater Handbook for information on disconnecting roof runoff.