Soil Testing Topics:
Percolation
Test
Deep
Observation
Pit (s)
Soil
Testing Application
Environmental
Concerns:
Septic
system installation
Septic
system
repairs
Building
Conversions, Additions & Accessory Structures
Water Quality
Applications
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Soil Testing
Installation details for a
septic system such as size, location, depth and configuration are
determined by soil testing. Percolation tests and deep observation pits
are required by the Health Code for both new and repaired septic
installations. Site testing for existing homes is generally conducted by a
TAHD sanitarian and by a Professional Engineer for new home construction.
A brief explanation of the percolation test and observation pit is noted
below:
Percolation
Test
The percolation test
consists of a hole 6-12 inches in diameter dug in the area of the proposed
septic system. The depth of this hole varies depending on the soils
encountered but it is generally not greater than 24 inches. The hole is
initially filled with water (presoak) in an attempt to saturate the soil,
allowed to drain away and than refilled with approximately 12 inches of
water. The rate at which the water drops in the hole is measured at
intervals over a period of time ranging from 30-60 minutes. The uniform
slowest rate of drop of the water level over a measured time interval is
converted to minutes per inch and used as a basis of design in determining
the septic system size. For example, if the water dropped uniformly 1\4
inch every five minutes the rate would be 20 minutes per inch. The Health
Code provides a simple table that determines the size of the system based
on the measured perk rate and the number of bedrooms in the home. The
greater the number of bedrooms and the slower the percolation rate, the
larger the system required. Commercial systems are sized using the perk
rate and projected estimates of water usage in gallons per day.
Deep
Observation Pit (s)
Observation pits are dug
in the proposed septic area in order to be able to see the various soil
layers. These holes are dug with a backhoe machine generally to a depth of
7ft and observations are made of the soil layers, color and texture and
recorded by the sanitarian or engineer. Particular attention is given to
the depth to ledge rock or ground water since both are specifically
addressed in the Health Code. The bottom of the leaching system must be
maintained a minimum of 18 inches above ground water or impervious soil
and 4 feet above ledge rock. The deep test pit information is used to
determine the depth of the system in the original ground. In this part of
Connecticut the soils encountered are such that a majority of septic
systems will require fill to comply with the separating distances to
ground water or ledge. Fill used in the installation of a septic system is
sandy in consistency and must meet minimum specifications set forth in the
Health Code. This type of material is in limited supply and as a result
the cost of a septic system is influenced greatly by the amount of fill
required.
The percolation test
results, observation pit data and the slope of the property in the septic
system area are used to determine the Minimum Lateral System Spread (MLSS).
In simple terms, MLSS is the length of leaching system spread along the
contours of the land that is necessary to allow the liquid waste to seep
naturally into the ground without surfacing. For example, a single 100ft
long leaching trench is more efficient than two 50 foot long trenches set
one below the other. MLSS was incorporated into the Health Code in 1995,
and all new septic systems must comply with this requirement.
Please view the TAHD
Map for
contact information. Click within your town boundary to receive
the name and contact information of the Sanitarian providing services for
your town.
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