Stormwater infiltration testing is about assessing a sites potential to drain stormwater into the soil subsurface. It involves exploring the subsurface conditions and conducting field testing to measure the rate of water infiltration. Soils investigations are conducted to evaluate the subsurface stratigraphy for limiting zones for infiltration to aide in the site planning process and design of stormwater management systems.
These tests are used to determine the percolation rate of rain water within the soil at the location tested. The percolation or infiltration rate is a measure of how fast water flows through the soil.
The results of the soil infiltration test will determine whether or not the site is suitable for the required stormwater management in that particular area.
What are some different types of infiltration tests?
- Double Ring Infiltrometer Testing
- Percolation Testing
- Basin Flood Tests
- Cased Borehole Infiltration Testing
Why are Infiltration tests performed?
- To satisfy the NPDES Stormwater requirements
- Provides More Stable Groundwater Table
- Maintains Base Flow to Streams and wells during Droughts
- Improves Quality of Streams (Drinking Water) for Wells, Natural Springs and Wetlands
- Supports Aquatic Communities and Fisheries
- Reduces Non-Point Sources of Pollution
Double ring Infiltration testing is the preferred method of testing soils for infiltration rates. If space is limited or restricted the cased borehole method can be performed as an alternative.
Double Ring Infiltrometer Test
Double Ring Infiltration (DRI) Testing is typically conducted in open areas or within shallow test pit excavation. DRI testing utilizes concentric outer and inner rings that are forced or driven into the soil at shallow depths. The rings are filled with water to test the infiltration rate of the soil at a particular location and depth. The outer ring, is to prevent or limit the water from the inner ring from flowing laterally. The infiltration rate is then calculated after a stabilized water reading in the inner ring is established. The DRI method measures more of a vertical infiltration rate rather than a horizontal rate which is more representative of vertical stormwater flow at the bottom of an infiltration area.
Cased Borehole Infiltration Test
Cased Borehole infiltration tests involves drilling a series of boreholes at the required test locations to the infiltration test depth. A pipe is then firmly seated and sealed into the boreholes. Soil and bentonite is filled around the pipe annulus and hydrated to seal the pipe in place. Water is then place inside the pipe and the water level drop is monitored to determine the infiltration rate of the soils. The infiltration rate is then calculated after a stabilized reading is established. Cased borehole infiltration testing is typically used when space is limited at a site or minimal disturbance is required in areas such as parking lots.
Earth Engineering conducts infiltration / percolation investigations and testing in PA, NJ, and Delaware. Contact one of our directors or project managers at any of our 4 locations to discuss your subsurface investigation needs and how Earth Engineering Inc. can help.