Stormwater management prevents flooding and erosion that can cause expensive damage to your home and property. Dry wells are a great solution. They redirect rainfall and runoff from non-absorbent surfaces into underground storage systems where the water can slowly seep into the surrounding soil.
This article covers how dry wells work and how to install one of your own. In the video above, This Old House landscape contractor Roger Cook demonstrates the installation of an impressively engineered dry well trench designed to manage stormwater and additional runoff at a renovation project.
What Are Dry Wells?
Dry wells, also known as concrete galleys, work by collecting water from downspouts, drains, and other sources of runoff. The collected water is then stored in perforated concrete units buried underground. These units allow water to gradually seep into the surrounding soil, effectively managing excess water and preventing flooding. They’re particularly useful in areas where natural drainage is insufficient or where new construction has reduced the amount of permeable ground surface.
Components of a Dry Well System
A typical dry well system is made up of several key components:
- Clean-outs: These are access points for maintenance and removal of debris that may accumulate in the dry well system. They help ensure the system remains clear and functions over time.
- Connecting pipes: These pipes channel water from downspouts or other drainage sources into the dry well.
- Landscape fabric: This material is placed over the stone foundation to prevent soil and debris from clogging the drainage system. It allows water to flow through while keeping the system clean.
- Perforated concrete galleys: These are the main storage units that collect and drain water. The perforations allow water to seep out and be absorbed into the surrounding stone foundation.
- Stone foundation: This layer surrounds the perforated galleys and provides additional water storage capacity. It provides stability and supports the structure of the dry well system.
Dry Well Benefits
By effectively managing excess water, dry wells help maintain the integrity of your property and contribute to overall environmental health. Installing a dry well provides several benefits:
- Improves landscape drainage: A dry well helps to manage excess water effectively, reducing surface pooling and preventing waterlogged areas in your landscape.
- Prevents flooding and erosion: By directing excess water away from vulnerable areas, a dry well reduces the risk of flooding and erosion, protecting both your property and the surrounding environment.
- Protects foundations from water damage: Properly managing water runoff helps prevent water from accumulating around the foundation, reducing the risk of structural damage and issues like mold or mildew.
- Reduces strain on municipal stormwater systems: By managing runoff on-site, a dry well alleviates pressure on local stormwater infrastructure.
- Recharges groundwater: As water seeps into the ground through the dry well, it replenishes the local groundwater supply, supporting ecosystems and maintaining natural water cycles.
Dry Well Installation Process
Installing a dry well is a complex process that requires careful planning and execution. Roger Cook guides us through the installation of a large-scale dry well system. Here’s a breakdown of the key steps.
- Site preparation and excavation: The first step in installing a dry well is preparing the site and excavating the area where the system will be placed. For the project shown in the video, this involved removing 100 yards of material to create a trench 36 feet long, 8 feet wide, and 7 feet deep.
- Laying landscape fabric: Once the hole is excavated, landscape fabric is laid on the bottom and sides. This step prevents debris, soil, and fine particles from entering and clogging the dry well system over time.
- Adding stone foundation: A 12-inch layer of stone is added to the bottom of the excavated area. This stone foundation serves two purposes: It provides a stable base for the concrete galleys and offers additional water storage capacity.
- Placing concrete galleys: The concrete galleys, or dry wells, are then placed on top of the stone foundation. In the project demonstrated, eight galleys were used, each capable of holding 300 gallons of water. This configuration provides a total storage capacity of 2,400 gallons.
- Backfilling with gravel: Once the galleys are in place, the surrounding area is backfilled with gravel. This process helps set the dry wells and provides even more water storage capacity. Approximately 12 inches of gravel is laid on top of the galleys to complete the system.
- Installing clean-outs and connecting pipes: The final steps are to install the clean-outs and connecting pipes. Clean-outs provide easy access points for maintenance. Connecting pipes tie the dry well system to other drainage features, such as downspouts and trench drains.
Factors Affecting Dry Well Design and Installation
There are a few things that can affect the design and installation of your dry well system. Here’s what you need to know.
Percolation Test Results
A percolation test, or “perc test,” determines how quickly water drains into the soil at the installation site. The results of this test help engineers decide on the appropriate size and configuration of the dry well system.
Impervious Surface Calculations
The amount of non-absorbent surface area on a property, such as roofs and driveways, directly impacts the size of the dry well system required. More impervious surfaces mean more runoff to manage, which means you need a larger system.
Local Building Codes and Regulations
Many municipalities have specific requirements for stormwater management, especially when new construction reduces the amount of permeable ground surface. These regulations often dictate the need for and specifications of dry well systems.
Worst-Case Scenario Planning
Engineers design dry well systems to handle extreme weather events. For example, the system shown in the video is capable of managing runoff from a 100-year storm, which can drop 9 inches of rain in 24 hours.
Examples of Large-Scale Dry Well Projects
Complex dry well systems can be extremely effective for large properties or areas with significant runoff. Here are some examples of successful large-scale installations:
- Commercial properties: Large retail centers often experience substantial runoff due to large amounts of impervious surfaces like parking lots and roofs. Engineers design massive dry well systems to handle peak flows during heavy precipitation.
- Schools and campuses: Educational institutions, such as universities and high schools, benefit from dry wells to manage runoff from multiple buildings and extensive landscaped areas. Stormwater management ensures safe and usable outdoor and recreational areas.
- Urban settings: In densely populated cities, dry wells integrated into the urban landscape help reduce the strain on municipal drainage systems while providing subsurface water management.
Cost Considerations When Installing a Dry Well
Installing a dry well system can be a significant investment. The project in the video cost the homeowners about $25,000. However, this was a large system designed for a specific construction project. Most homeowners can expect to pay between $1,300 and $4,600, according to cost data from Angi.
A project of the size shown in the video is better left to the professionals, but if there’s an area of your home or yard that pools and floods during rainstorms, it’s possible to build and install a simple dry well for your home. This can often be installed as a DIY project for a fraction of the cost of larger, engineered systems. The costs will vary depending on several factors:
- Labor: Professional installation ensures reliability but increases expenses.
- Materials used: The quality of materials, from the concrete galleys to the gravel and landscape fabric, affects overall costs.
- System size: Larger systems with more galleys and additional features increase the cost.
Dry Well Maintenance and Longevity
To maintain the longevity and effectiveness of a dry well system, perform a few maintenance tasks regularly. Routine care and inspection of the dry well system help aid early detection of potential issues and maintain the system’s efficiency. Inspect the clean-outs annually and monitor the area around the dry well for signs of pooling water. Have the system professionally inspected every few years.
Integration With Other Stormwater Management Practices
Integrating dry wells with other stormwater management practices can maximize their effectiveness. Here are a few strategies to consider:
- Green roofs: Installing green roofs on buildings can absorb rainfall, reducing runoff volumes that dry wells need to manage.
- Permeable pavements: Using permeable materials for driveways and walkways reduces runoff and allows water to percolate into the soil, working in tandem with dry wells.
- Rain gardens: Creating rain gardens around the property helps filter runoff and allows water to seep into the ground naturally, which complements the function of dry wells.
