HomeMy WebLinkAboutCU-18-12 - Supplemental - 0030 Myers Court (18)CATAMOUNT
consulting engineers, plic
PO Box 65067 1 Burlington, VT 05406 1 (802) 598-8081 1 www.cceAcom
February 20, 2019
Marla Keene
Development Review Planner
City of South Burlington
575 Dorset St.
South Burlington, VT 05403
Re: Sewer Service Evaluation for CU-18-12
30 Myers Ct.
South Burlington, VT 05403
Dear Marla.
At the City's request, Catamount Consulting Engineers, PLLC (CCE) performed a brief
site survey and evaluation of the existing sewer line serving the recently constructed
accessory structure located at 30 Myers Ct. in South Burlington, VT. The site visit was
conducted on February 18, 2019. The intent of the evaluation was to assess the existing
gravity sewer service that runs from the accessory structure to the primary structure to
assist in the City's review of application CU-18-12.
The results of this exercise provided us with the following information —
• The invert of the existing 4" PVC sewer service exiting the primary structure to
the accessory structure is approximately 3.63' below existing grade. This was
calculated through surveyed measurement of the invert in the basement of the
primary structure out to the existing exterior grade at the primary structure
foundation face along the sewer alignment location.
• This yields an estimated amount of cover of 3.30' (3.63' — 0.331) at the sewer
service alignment adjacent to the primary structure.
• Based on a local datum established for the survey, we assigned an invert elevation
of 91.39' to this existing sewer service where it exits the primary structure.
• Given the distance between the primary and accessory structures (f57.5'), and
working with the assumption that the minimum slope for a 4" gravity sewer
service should be approximately 2.0% (1/4 in. per 1 ft. per State regulations), we
calculated a minimum sewer invert at the accessory structure foundation face of
92.54' (91.39' + [0.02 x 57.5']).
• Working off the same local datum, we estimate the existing grade at the accessory
structure foundation face where the existing service enters to be 95.48'.
• This yields an estimated amount of cover of 2.61' (95.48' — [95.54' + 0.33']) at
the sewer service alignment adjacent to the accessory structure.
• Given the topography of the property and generally straight alignment of the
sewer service, the amount of cover over the sewer service between the structures
most likely ranges between the two values we calculated at the foundation faces
(3.30' to 2.61').
Although the State regulations recommend a minimum of 4' of cover be
maintained, and at least 5' in areas to be plowed in the winter, allowance for less
cover can be made if added measures are taken to protect against freezing.
Typically in the form of rigid insulation being installed over the pipe.
In talking with the property owner, it appears rigid insulation was installed over
the sewer service in question to maintain minimum burial depths and keep the
height of the accessory structure as low as possible.
In summary, based on the results of our field survey and investigation, as well as the
testimony provided to us by the applicant, it appears that all practical measures were
taken to keep the 4" PVC gravity sewer service from the primary to accessory structure
as low as possible. This includes installing a sewer service from the primary structure as
low as the existing service would allow, maintaining a minimum allowed pitch between
the two structures and installing rigid insulation over the sewer service to reduce cover
requirements.
It should be noted that alternative measures could have been evaluated that may have
provided solutions that did not involve raising the accessory structure building elevation.
These include providing thermal wraps around the gravity sewer service or installing a
pump station to service the accessory structure so that gravity service was not required.
However, these type of solutions may be considered cost prohibitive under certain
circumstances.
We hope this report helps the City's review of application CU-18-12. If you have any
additional questions or concerns, please feel free to contact me. Thank you for the
opportunity to assist you in the evaluation of this application.
Sincerely,
Jeffre O1 sky, P.E.
Attachments: 2/18/19 CCE Field Notes
Cc: CCE file 18033
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