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Septic Tank Drainfield Site Suitability and Evaluation Workshop Montana State University Extension S

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... interviews with local engineers, installers, pumpers, and ... hydraulic failure. ... Very low hydraulic conductivity; inaccurately distinguishing soil ... – PowerPoint PPT presentation

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Title: Septic Tank Drainfield Site Suitability and Evaluation Workshop Montana State University Extension S


1
Septic Tank Drainfield Site Suitability and
Evaluation WorkshopMontana State University
Extension Service, Department of Land
Resourcesan Environmental Sciences, in
cooperation with Montana Department of
Environmental Quality
1-Introduction DEQ Septic.ppt
2
Analysis of Septic System Failure Karen Deal MSU
Extension Service MSU Graduate Studies May 1998
3
Goal identify correlations between septic system
failures and improper site evaluation, improper
installation, or insufficient system
maintenance Conducted interviews with local
engineers, installers, pumpers, and homeowners to
determine what factors contribute to septic
system failure In general, septic system failure
occurs when the soil within the absorption field
(leach bed, drain field) no longer accepts
effluent from the septic tank at the same rate at
which it is generated. This is called hydraulic
failure. As long as sewage is not backing up into
the house, the system is working. However,
failure of treatment could be occurring while the
system is mechanically functioning. This would be
the case if insufficiently-treated wastewater
were discharged to a shallow aquifer, and reached
nearby wells or surface waters.
4
The main factors associated with septic system
failure are or construction, tight soils,
inappropriate drain field location, system age,
improper maintenance, drainfields unlevel or too
deep. Collectively, these circumstances leading
to system failure, hydraulic failure, and those
leading to treatment failure, are often a
consequence of inadequate site characterizations
being performed by site evaluators who are
unaware of such factors as soil structure,
structural discontinuities, and correct soil
characteristic assessments. When evaluating the
drainfield location, landscape positions, slope
positions and evidence of seasonal saturation by
groundwater are sometimes overlooked, not
recognized, or disregarded.
5
Improper Site Evaluation Since site evaluations
create the foundation for the completion of a
working septic system, these evaluations should
be as correct and thorough. For permitters, the
abililty to interpret data, recognize
limitations, and properly assess is
critical Examples Incorrectly performing site
evaluations such as altering and/or incorrectly
completing and reporting percolation test
results, where required. Very low hydraulic
conductivity inaccurately distinguishing soil
textural differences Inexperienced people
evaluating soils and the hydraulic capacity of
the soil is not being calculated correctly or
taken into account properly in the design
phase Surface drainage was not diverted from the
drainfield Slope and landscape positions were
disregarded, leading to surface drainage and
direct infiltration of the trenches Conventional
systems installed in saturated and/or poorly
drained clay soils where traditional systems
should not be constructed
6
Specific Locations of Concern Site
characteristics that must be looked for when
determining a sites suitability for a particular
septic system the most frequent causes of
failure related to site evaluations Reported by
soil scientists and inspectors include 1)
gravelly soils, 2) clay soils, and 3) high
(shallow, close to the land surface or trench
bottom) groundwater, contributing to saturated
soil conditions in the lower portion of the soil
profile of drain fields. Additionally, steep
slopes require appropriate designs and
percolation rates of the soil must be considered
(either from texture or measurement). Failure of
treatment in areas that have gravelly soils which
constitute a poor filter media or a conduit to
shallow groundwater. Soils with low percolation
rates particularly soils which are dominated by
clay, have obvious textural discontinuities, or
are consolidated Collectively. 1) seasonal high
groundwater infiltrating the trenches, 2) the
soils are not adequately permeable, or 3) the
trenches and/or pipes are not sloped to produce
appropriate distribution of effluent or proper
infrastructure is not provided
7
(No Transcript)
8
Will this site work properly?
Landscape
X
X
X
X
9
Changing Technology
10
What we plan to coverBasic soil scienceThe
soil formation processVariability of soil across
the landscapeAssessing and evaluating soil
propertiesLandscape effects on drain field
conditionsWater movement and behavior in
soilChemical movement and behavior in soilUsing
soil survey for site evaluationInformation
managementField site visit
11
Montana DEQ Septic Tank Drain Field - Wastewater
Treatment Site Evaluation FormEvaluator
_______________________________________________
Phone _______________________ Fax_______________
________Email __________________________________
_______________________________Mailing
address__________________________________________
_______________
__________________________________________________
_______Property owner or entity for whom
evaluation being completed ______________________
_______________________________________Site
location (physical location or address)__________
__________________________________________________
__________________Site location (GPS lat/long
coordinates or legal description)________________
________________________________________________E
xcavation method (circle appropriate option)
backhoe pit hand dug pit auger hole
exposed construction pit other
noneDate on-site evaluation completed
__________________________________________________
Weather and lighting at time of evaluation
____________________________________________Avera
ge annual rainfall at site vicinity (inches)
__________________________________________________
___General vegetation/land use in site vicinity
(circle appropriate option) grassland
sage/grass prairie timbered forest
suburban/pasture irrigated agriculture
dryland farming sedges/reedsSite Overview
and Preliminary Assessment Checklistwithin
floodplain YN evidence of past flooding
(distance from proposed site
feet)YN evidence of recent alluvial/ colluvial
deposition (distance from proposed site
feet)YNslope ( or feet/100 feet) at
proposed siteavailable suitable area for proposed
drain field (acres, L x W (in feet))coarse
gravel, cobble, boulders on surface (if
present, percent cover
)YNproposed drain field location within landscape
12
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