HomeMy WebLinkAbout1992 - septic system failure & replacement TO: File - 2095 Webber Hills Road
FROM: Stephen Weckman, On-site Systems Manager
DATE: November 18, 1992
RE: Septic System Failure and Replacement
The purpose of this letter is to provide additional information
regarding the septic system failure and subsequent replacement. For
additional information see memo to file dated September 21, 1992.
The old septic system was installed by Widmer Brothers in 1966 under
permit #1228. The septic system includes two concrete block tanks
with capacities of 1 , 000 and 500 gallons respectively and
approximately 500 sq. ft. of drainfield trenches. The owner of the
property requested a septic system inspection which was completed on
July 9, 1992 at which time the system was observed visibly discharging
untreated effluent to the surface requiring repair within ninety days
of the inspection date. Prior to this inspection there is no
indication from previous inspections that the septic system was likely
to fail in the near future.
The original septic system was presumably inspected when installed and
met the code requirements as they were administered at the time. The
City's inspection report dated July 11, 1978 indicated the system was
substandard under the new 1978 code based on the information
available. A fully conforming system would have needed two sealed
1,000 gallon tanks and an amount of drainfield based on the number of
bedrooms and the soil capabilities as determined from percolation
rate, water table depth, and other site factors. The drainfield at
2095 Webber Hills Road appeared to be too small for the house given
the probable soil conditions and was potentially too near the water
table. The septic tanks were also noted to be undersized and of
concrete block construction and may not be watertight. The system
was functional at the time and remained classified as a substandard
system until it was observed surfacing on July 9, 1992 at which time
it was considered non-conforming and requiring repair.
The exact cause for the system failure is unknown. Failure can occur
due to the proximity of the system to the seasonally high water table
and annual fluctuations of the water table, system maintenance, soil
or site limitations, or increases in water usage. Of the 31 homes
built between 1965 and 1975 on Webber Hills and Shevlin Roads, 12
systems have been replaced or repaired as of 1992. The high
percentage of repairs/replacements in this neighborhood suggests that
many of the original systems had a useful life of 15-20 years. In
theory a system designed and constructed according to current codes
could function indefinitely.
L
Memo
November 18 , 1992
Page 2
As of today a replacement septic system has been completed which is
classified as a conforming system which has been granted variances for
construction on fill soils and a 10' lot line setback. Soil testing
for this system identified a seasonally high water table between 18"
and 40" requiring a mound type system. Fill soils were identified
over one corner of the proposed treatment area requiring a variance to
the state and local ordinances. As the underlying soils appeared to
be suitable for sewage treatment and no other options were available,
the variance was granted. The City requires a 20' lot line setback
but, a 10' variance was also granted due to site limitations. As this
system meets the required 3' vertical separation from the seasonally
high water table, this system is considered to be a conforming system.
This has been confirmed by Mark Westpetal of the Minnesota Pollution
Control Agency.
The new septic system although requiring variances is considered more
conforming than the original system for several reasons. The old
septic system was constructed using concrete block septic tanks which
are not considered to be sealed tanks and are undersized by today's
standards. Also the drainfield of the old system did not meet the
required 3' vertical separation from the seasonally high water table
which is one criteria for classifying the old system as being non-
conforming. The current system however, was constructed using precast
concrete tanks which have no seams and the mound system does meet the
3' vertical separation from the seasonally high water table and is of
adequate size for the four bedroom residence based on state and local
codes.
ch
TO: File - 2095 Webber Hills Road
FROM: Stephen Weckman, On-Site Systems Manager
DATE: September 21, 1992
RE: Septic System Failure
The septic system was installed on August 5, 1966 by Widmer Brothers
under Permit No. 1228. The septic system includes two concrete block
tanks with capacities of 1, 000 and 500 gallons respectively. The
drainfield consists of three trenches 2' wide and between 75' and 100'
long.
The City of Orono has an inspection program for on-site septic
systems. Each septic system is inspected every other year in order to
determine the system conformity, tank condition, drainfield condition,
limiting site factors, and potential for system failure. The
inspection report includes a determination of the system's conformity
based on current Minnesota Pollution Control Agency (MPCA) Regulations
and City of Orono Municipal Codes, request maintenance, if necessary,
or require septic system repair or replacement when the system is not
functioning properly. As the inspections are infrequent, they only
provide a sampling of the system condition. Occasional septic
problems may not be evident at the time an inspection is performed.
Prior to the July 9, 1992 inspection, there is no indication from
previous inspection reports or the septic system inventory card that
the system was likely to fail. The four most recent on-site sewage
treatment inspection reports for the property in question have been
examined. Three inspection reports dated August 1, 1988, July 26,
1990, and April 29, 1991 all indicate that septic pumping is not
required and the drainfield is dry with no evidence of surfacing. The
septic system is classified as a substandard system not up to current
codes but appears to be designed in accordance with previous codes and
seems to be functioning properly. These reports also note no limiting
site factors. The potential for system failure is between low and
medium and the site capabilities for future expansion are fair. The
July 9, 1992 inspection indicates that tank maintenance is not
required but the drainfield is saturated and visibly discharging
untreated effluent to the surface making the system non-conforming
thus requiring repair within ninety days of the inspection date.
ch