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Dry Wells

Graphic of a dry well.

 

A dry well collects stormwater from rooftops or hard surfaces such as your driveway. An underground pipe directs runoff from roof downspouts into the dry well. 

A dry well is an underground area that is filled with stone or gravel. Once water enters the dry well, it passes through the stone or gravel and then seeps into the underlying soil.  Dry wells reduce stormwater runoff, promote infiltration and groundwater recharge, and filter pollutants. Sometimes a proprietary storage device is used to increase storage efficiency and decrease the footprint of the dry well.

 

 

Why Should I Install a Dry Well?

Directing roof or driveway runoff to a dry well is an effective way to reduce stormwater runoff from your property, because you are capturing the stormwater and allowing it to soak into the ground. Dry wells are underground features that work well in areas where space is limited. Dry wells generally do not impact the visual appeal of your property as they are located along your driveway or underground and may be covered with soil and sod or other shallow-rooted plants.

However, the most important reason to install a dry well may be that you are doing your part to help the environment and protect your local streams and the Chesapeake Bay. 

Dry wells can be installed under voluntary programs like the DEP Rainscapes program, or may be permitted under your building's construction.

 

 

 

Is a Dry Well Right for Me?

Not all properties are suitable for a dry well. 

Image of the front of the RainScapes Dry Well Guide
Want Help with Assessing Your Property for a Dry Well?  Download the Guide. (PDF, 1.8MB)

 
  • They are a good option when space is limited because they are built underground.

  • They require soils that drain well.

  • They are more expensive than other RainScapes techniques.

 

How to Assess Your Property

Assess your roof gutter and downspout system by walking around your property. Make your observations when it is raining, so you can see where the rain lands on your property and where it flows. Follow these basic steps to identify your site’s drainage conditions: 

To Collect Roof Runoff

  1. Locate each downspout and determine where each downspout directs the rainwater. You may find that your downspouts are directed to your grassy lawn, a landscaped area, a storm drain, or your driveway. If a downspout currently discharges to a grassy or landscaped area, you may not need a dry well because some of the water is already soaking back into the ground. Dry wells should not be placed in poorly draining soil or placed perpendicular to steep slopes. The best place for a dry well is where downspouts discharge on or near a hard surface where the water cannot be easily absorbed (i.e., driveway, sidewalk, patio, poorly draining soils, etc.), or where the neighbor’s yard is close and drainage is an issue.

  2. Once you have identified downspouts for a dry well, you need to estimate the size of the roof area that contributes water to each downspout (see diagram). Based on your observations in Step 2 of where the rainwater flows, estimate the drainage area (square feet) to the particular downspout. Then estimate what percentage of the building’s total roof area this amount represents. The drainage area and percentage of the building’s roof area are required for the RainScapes Rewards Rebate application.

To Collect Driveway Runoff

  1. Linear dry wells (infiltration trenches) can be added along driveways to collect and infiltrate runoff. You can capture runoff from part of your driveway using a trench drain or capture runoff from the entire driveway by relying on the slope of the driveway to send water to a dry well that runs along the side of the driveway.

Calculating Percentage of Building's Roof Area for Drainage. Total drainage area divided by total roof area.

 

Installing Your Dry Well

Ready to move ahead with installing a dry well?  

There are a lot of decisions that need to be made with your dry well after the assessment is complete.

  • Location

  • Size

  • Whether to collect roof runoff or driveway runoff 

  • Whether you want to do the project yourself (The Montgomery County Department of Permitting Services recommends that a dry well that is deeper than 2 feet be dug by a qualified professional. Linear dry wells are a good do-it-yourself option.)

The RainScapes Dry Well Guide (below) has suggestions and useful information on how to best make the necessary decisions. The RainScapes program has knowledgeable and helpful staff who can help you through the process as well as the RainScapes Rebates program with great financial incentives for installing the dry well.  

 

Download the RainScapes Dry Well Guide (PDF, 1.8MB)

 
 

Maintaining Dry Wells

As the property owner, you are responsible for all maintenance of your dry well unless a shared maintenance agreement has been made with the DEP Stormwater Facility Maintenance Program.

An un-maintained dry well may:

  • Cause flooding on other areas of your property if the stormwater is not able to flow into the dry well

  • Cause rainwater to pool on the surface and become a breeding place for insects

  • Require a complete replacement of the dry well, which can be very expensive

 

Actions You Can Take to Maintain Your Dry Well
Monthly Actions Seasonal Actions As Needed Actions

✔ Inspect your gutters after storms to make sure that rain water properly drains to the dry well.

✔ Remove leaves and tree debris from roof gutters from April through November.
✔ Inform contractors working on your property of the dry well’s location, to prevent accidentally damaging it.
✔ Ensure caps on observation wells are fastened. ✔ To prevent damage to your mower or to the observation
well cap, do not mow over the caps.
✔ Place gutter guards or screens on top of roof downspouts to filter
out leaves and sediment before the rainwater reaches the dry well.
  ✔ Repair any damage to gutters/downspouts from winter snow or ice.  

 


Actions You Shouldn't Take to Maintain Your Dry Well
Don't...
✘ Do not remove a dry well or reconfigure your downspouts to direct water somewhere else.
✘ Don’t place decks, sheds, or other structures on top of a dry well
✘ Don’t let children remove the observation well caps.
 

 

DEP can answer your questions and provide additional guidance about maintaining your dry well. Please email askdep@montgomerycountymd.gov or call the Montgomery County Customer Service Center at 3-1-1.

 

Image of the front of the Dry Well Maintenance Fact Sheet.
Want Help with Maintenance, Troubleshooting and Timelines?  
Download the Fact Sheet
(PDF, 1.33MB)

Dry Wells in the Stormwater Facilities Maintenance Program

The Stormwater Facilities Maintenance Program is responsible for maintaining all public stormwater facilities as well as all private facilities that transferred their maintenance to the County.  The program also maintains facilities that were required as part of the Department of Planning permits.

Not sure if your dry well is part of the Stormwater Facilities Maintenance Program?  Check out online Facilities Map or email askdep@montgomerycountymd.gov.

 

Can I remove my dry well after installation?

No, you cannot remove any facilities that were part of your building installation - these are permitted structures and DEP maintains a database of thesefacility locations as part of the Stormwater Facility Maintenance Program. DEP may perform a maintenance inspection of your practice if it is a permitted structure.  Property owners must contact DEP before any major changes can be performed to the structure. 

 

 

 

 

Rebates, Resources and Financial Incentives

Interested in installing a dry wellf?  The County offers incentives to help make the decision a little easier.

 

Logo of the RainScapes programThe RainScapes Rewards Rebates Program

The County offers technical and financial assistance (in the form of rebates) to encourage property owners to implement RainScapes techniques on their property, including dry wells. 

  • Residential properties are eligible for up to a $2,500 rebate

  • Commercial, multi-family or institutional properties are eligible for up to a $10,000 rebates.

To participate, your property must be located in Montgomery County, outside of the municipal limits of the City of Rockville, City of Takoma Park, or City of Gaithersburg. Projects are not eligible if they are associated with permit approval requirements for new building construction, additions, or renovations. 

​The program is funded each fiscal year (The FY begins July 1 and ends June 30).  Annual funds for the programs are limited, so rebates will be awarded on a first-come-first-served basis.

The RainScapes program also provides technical assistance to help with the installation of your dry well.  They have a wealth of information, expertise and want to help!

Learn more on the RainScape Rewards Rebates webpage. 

 

Image of a green roof.

 

 

The Water Quality Protection Charge Credit Program

After you have installed your dry well, you are now eligible to receive a credit off your annual Water Quality Protection Charge (found on your yearly property tax bill).  The credit provides an incentive for maintaining your dry well and other stormwater management practices.

You must apply for the WQPC credit separately – the credit will not be provided to you automatically.

Residential property owners can receive up to 50% off their WQPC depending on the type and size of stormwater management practices on the property.

Non-residential and multi-family properties can receive up to 50-60% off their WQPC depending on the type and size of the stormwater management practices on the property.

Learn more on the WQPC Credit webpage.