HomeMy WebLinkAbout04-04-2017 Item 2, MattinglyCOUNCIL MEETING: RECCE
ITEM NO.: .Z
'" Council Memorandum APR 04 2017
SLC CITY CLERK
April 4, 2017
TO: City Council
FROM: Came Matting[ ,Utilities Director t'
t�
VIA: Katie Lic.htig, ty Manager
SUBJECT: April 4, 2017 City Council Meeting; Item 2; Study Session; Inflow and Infiltration,
including a Private Sewer Lateral Program Study Session
The study session identifies the contribution of Inflow and Infiltration (I/I) from private sewer
laterals as a major contributor of the overall City I/I issue. While public sewer mains do contribute
to the problem, private sewer laterals have been identified as a significant source. Several studies
performed over the past 25 years, numerous visual inspections and study of the flows in the
wastewater collection system and at the Water Resources Recovery Facility (WRRF) show
confirm laterals are a major source of I/I. The most recent study, performed by wastewater flow
specialists V&A, took 2 years and looked at the entire City during dry and wet weather. Its results
have helped better inform infrastructure replacement and wastewater programs.
Private sewer laterals make up more than half the public and private sewer system that flows to
the WRRF. Most of these laterals have not been replaced since the home or business was
constructed, many are well over 50 years old and have not been inspected or maintained. Because
many of these laterals were built using materials that have cracked, corroded or broken, have root
intrusion and lay beneath permeable surfaces such as landscaping, they have become a significant
contributor to UI.
Staff has visually observed both the sewer main and laterals during wet weather and have observed
I/I from both the City mainline and laterals. While areas of the City mainline do have I/1 issues,
laterals have been observed to contribute a significant portion. When discovered, severe observed
1/1 or deficiencies that would contribute to UI in the City system are addressed as a repair or
replacement. Only on rare occasions does the City have an opportunity to make these types of
corrections on private systems.
The City has actively revised engineering standards and our building code to ensure that best
possible pipe materials are installed on both the public and private side to reduce or eliminate I/I
and maintenance issues. These newer materials are fused at the connections and have demonstrated
long life spans. Many experts in the engineering field estimate a service life to be conservatively
70-100 years. All of the City's new or replaced mainlines and laterals in the past 20 years are made
of this new material.
As an example, the City recently replaced a large portion of public mainline in an area that
experienced significant wet weather flows; a flow study prior to the replacement confirmed I/I.
After replacement of the public system, staff returned to measure and monitor wet weather flows.
April 4, 2017, 1/1 Study Session Page 2
The flow monitoring showed that after the mainline replacement high wet weather flows
continued. No private sewer laterals were replaced with the public mainline. The replacement of
the public mainline without improvements of the private sewer laterals demonstrates the
significant contribution of UI made by laterals. This is consistent with very low level wet weather
flow monitoring results in newer areas of the City that have public and private systems installed
with newer materials.
Please feel free to contact David Hix at 781-7039 or at dhix@sloeity.org if there any questions.