HomeMy WebLinkAbout1992-10-15 Septic System Reviewit s 79 3 /'`1, ��ewb4t-o
To: Michael P. Gaffron, Asst Planning & Zoning Administrator
From: Stephen Weckman, On -Site Systems Manager
Date: October 15, 1992
Subject: Subdivision #1762, Paul Boyke - Septic Review
I have reviewed the proposed septic system testing and
design for this property and would make the following comments.
LOT 1, BLOCK 1 - EAST ONE-HALF 71 3 N - .-OWc- C, fir.
This lot has an existing residence with an on -site sewage
treatment system. The system is a conforming system according to
MPCA Rules Chapter 7080 and City of Orono Code. The system
includes two 1,000 gallon pre -cast concrete septic tanks and
approximately 1,000 s.f. of shallow drainfield trenches. The
septic system was installed in 1987 at which time soil testing
indicated a three foot separation between the trench bottom and
the seasonally high water table as indicated by mottling and is
presumed to be installed as designed.
The existing drainfield is approximately ten feet from the
proposed driveway for the west lot. Due to the elevation of the
existing driveway, the proposed driveway for the west lot would
likely require fill to be constructed which would impede the
natural drainage and could adversely effect the function of the
drainfield. Driveway specifications should be provided
including a topographic map detail so the impact of any) may be
noted.
Soil testing has been provided indicating an alternate
drainfield site fora 4-bedroom home to the east and north of the
existing drainfield. This area would also be suitable for a
shallow trench system. Drainage from the existing driveway would
flow directly across the alternate drainfield site, therefore a
drain tile or other method for redirecting the drainage must be
incorporated at the time the future site is to be used. Specific
alternate site details are included below:
- Depth of seasonal saturation (mottling) is 4' to 4'2",
requiring shallow trenches.
- Slope is 4%.
- The percolation rate averages 7.9 minutes per inch at
12 inches.
- Drainage must be directed away from drainfield site.
Subdivision #1762, Septic Review
October 15, 1992
Page 2
LOT 1, BLOCK 1 - WEST ONE-HALF
Soil testing and septic system design has been provided for
a 5-bedroom home including primary and alternate drainfield
sites. Both sites meet MPCA Rules Chapter 7080, however a 25'
section of the alternate drainfield site encroaches within the
20' setback required for driveways. The proximity of the
driveway to the alternate site cannot be avoided due to site
limitations. Driveway specifications should be provided to show
that drainage will not adversely effect this site.
Due to the proximity of the access road to the septic sites,
snow fencing will be required around both drainfield sites prior
to the issuance of final plat approval. Specific septic system
details are included below:
- Depth of seasonal saturation (mottling) is 1' 2" to 3'
6", requiring a mound.
- Slope at the primary and alternate drainfield sites is
up to 5%.
- Percolation rates average 6.2 minutes per inch at 12".
- A 10' driveway setback variance will be required for
the alternate site.
SUMMARY
The site inspection revealed several concerns regarding
drainage around the drainfield sites due to the existing driveway
for he east lot as well as the proposed driveway for the west
lot. Additional information will be required regarding the
proposed driveway to ar a that a 10' setback from both the
existing system for the lost lot and the proposed alternate
system for the west lot is feasible as well as to assure that it
is possible to drain the driveway away from both of these septic
sites. The alternate drainfield site for the existing residence
will also be required to assure that drainage can be directed
around this site from the existing driveway.
Provided that acceptable information can be provided
regarding these drainage questions, staff is comfortable with the
septic plans provided. One condition of the subdivision must be
that both the existing and proposed drainfield sites must be
staked using snow fencing to prohibit any traffic from compacting
these sites. The fencing must be installed prior to the granting
of a final plat approval and any motorized travel across these
areas.
lsv