FACT SHEET

WHAT IS SOIL INFILTRATION TESTING?Soil Infiltration Testing is a type of field test conducted by an engineer, geologist, or soils scientist to determine the infiltration rate of a particular area’s soils and explore the subsurface conditions underneath the soil or pavement surface. The “infiltration rate” refers to the speed at which water enters into the soil.

WHY IS SOIL INFILTRATION TESTING IMPORTANT?Soil Infiltration Testing is typically conducted early in the planning and design process to determine if an infiltration-based design is suitable for a specific site and at what locations within the site.

Testing enables a successful and effective stormwater management design that incorporates a suitable infiltration rate for design calculations. Soil Testing also helps investigate the subsurface conditions below existing surfaces/pavement, and identifies existing soil horizons (layers), as well as any limiting features, historic conditions, etc.

HOW DOES SOIL INFILTRATION TESTING WORK? Boreholes (test holes), typically 6-10 inches in diameter and 5-10’ deep, are drilled using an auger into the area of the proposed design. This boring (drilling) method is used to minimize disturbance and maintain pedestrian/ vehicular traffic. After the test holes are presoaked, each test hole is filled with 6-12 inches of water. As this water slowly sinks (infiltrates) down into the ground, measurements of the water level are made inside the hole. A minimum of 8 readings are necessary to complevte the testing process. The change in the water level that occurs in the test hole during the final testing interval, expressed in inches per hour, represents the percolation rate for that test location.

Overview of Soil Infiltration Testing

City Of Lancaster Green Infrastructure Plan

As part of the Green Infrastructure Plan, the City of Lancaster is implementing a variety of Green Infrastructure projects to reduce the volume of stormwater runoff entering the City’s sewer system.

Green infrastructure uses the processes of infiltration (water slowly sinks into the soil to recharge existing groundwater supplies), evaporation/transpiration, and rainwater capture/re-use. For designs that rely on infiltration (porous pavement, rain gardens, infiltration trenches), soil infiltration testing is a crucial step to a successful stormwater management design.

Soil infiltration testing in progress(Photo: CH2M HILL)

Example diagram of soil infiltration testing(Image: Soil & Water Conservation District)

YOUR WATER. YOUR MONEY. YOUR CITY.

WHAT SHOULD I KNOW AS A PROPERTY OWNER?

• Soil Infiltration Testing can only be conducted by an engineer, geologist, or soils scientist.

• As with all field work and testing, attention must be given to all applicable OSHA safety regulations and local guidelines related to earthwork and excavation. Digging and excavation must never be conducted without adequate notification through Pennsylvania’s “One-Call” utility marking system.

• Locations of private underground utilities must be disclosed in advance by property owners to avoid damage during subsurface exploration.

• At no time shall a deep hole be left unattended unless secured and marked.

• Typically there will be 1-4 borings/test holes per project site, with one hole being 10’ deep and the others 5’ deep. A depth of 10’ is recommended to document the presence of any seasonal high groundwater table, bedrock, or other potential limiting conditions.

• The overall duration of the test is at least 3 hours, and most project sites are tested within 8-10 hours.

• Upon completion of the testing, the boreholes (test holes) will be backfilled with soil and capped with concrete (if in a paved area).

For more information about the Green Infrastructure program please contact: Fritz SchroederFritz@livegreenlancaster.org(717) 392-7891 ext. 207

• Narrative of testing procedure, including any abnormalities, difficulties, or obstructions encountered during borings and excavation

• Boring/test location plan

• Copies of boring logs and photographs

• Results of the infiltration tests with final rate for each location

Soil boring in progress (Photo: ALW)

A SUMMARY REPORT SHALL BE PREPARED BY THE TESTING CONTRACTOR AND SUBMITTED TO THE PROPERTY OWNER THAT WILL INCLUDE: