FACT SHEET
Overview of Soil Infiltration Testing
YOUR WATER. YOUR MONEY. YOUR CITY.
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.
Soil infiltration testing in progress
(Photo: CH2M HILL)
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.
Example diagram of soil infiltration testing
(Image: Soil & Water Conservation District)
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.
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 Schroeder
[email protected]
(717) 392-7891 ext. 207
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:
• N
arrative 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