PRESIDENT’S CORNER
FROM THE ADMINISTRATOR
COMMITTEE NEWS
FALL 2013
THE OFFICIAL PUBLICATION OF THE VIRGINIA WATER ENVIRONMENT ASSOCIATION, INC.
Address service requested PO Box 2324, Glen Allen, VA 23058-2324
SANITARY SEWER SYSTEMS:
Private Property Infiltration
and Inflow Abatement
INSIDE
•WaterJAM Review
•Good Lab Practices Committee Activities
•Strategic Plan Metrics
Our Vision: The Virginia Water Environment Association (VWEA) will preserve
and enhance Virginia’s Water Environment, now and for future generations.
SANITARY SEWER SYSTEMS:
Private Property Infiltration
VWEA Collection Systems Committee: Jeffrey Griffiths1 and Chris Wilson2
A sanitary sewer system consists of both
a public and private portion. The public portion includes
sanitary sewer lines and manholes, located in the public rightof-way, which collect and transport wastewater to wastewatertreatment plants. The private portion consists of laterals from
homes, businesses and industrial complexes which collect local
wastewater and connect to the public sewer. Sanitary sewer
systems are designed to collect and convey wastewater only,
not storm water or ground water. However, many of the country’s
aging sanitary sewer systems have been faced with excessive
flows from the infiltration of ground water and inflow of stormwater.
High levels of infiltration and inflow (I/I) can overload the sanitary
sewer system in a significant way. These excess flows lead to
sewer backups into homes and businesses, manhole overflows,
and increased wastewater treatment and conveyance costs.
Many localities and municipalities have been addressing
I/I in the public portion of the sewer system through various
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The Conduit – Fall 2013
maintenance, rehabilitation and repair methods. Although the
intention of rehabilitation is to make significant reductions in I/I, in
most cases comprehensive I/I abatement cannot be completed
without addressing the private portion as well. Often, rehabilitation
of the public portion effectively raises the local ground water table
and the I/I still flows, via the path of least resistance, to the private
side and enters the sewer system.
The age-old questions remain:
• How do you cost-effectively address the problems?
• Do you simply rehabilitate 100% of the laterals in areas with
significant I/I?
• Do you select laterals for rehabilitation based on mainline
inspection observations?
• Do you conduct pre-rehab lateral inspections to identify the
laterals with I/I or structural problems?
What does a comprehensive private property program look like?
Throughout the United States, authorities estimate that up to 50%
and Inflow Abatement
of a sanitary sewer collection system’s footage is comprised
of public-private laterals. Inflow and infiltration can originate
from a variety of sources within a collection system; however,
many of these sources are located on private property and/or
not maintained by the local sewer authority. Based on surveys
from many communities across the country, I/I derived from
private sources ranges between 20-80% of the total system I/I.
Though the percentage of I/I is highly dependent on factors
such as the type of system, the existence of gutter and sump
pump connections to the sanitary system, the system age, etc.,
the common conclusion throughout the industry is that private
property I/I sources are significant.
Many utilities are now finding it cost-effective to address
some of the private side I/I problems which can consequently
reduce capital expenditures and operating costs. In many cases,
municipalities and utilities look at the up-front cost and time to
conduct lateral inspections as purely an added cost and an
additional step in the maintenance process. Wholesale replacement
of laterals in an area may seem like the responsible solution given
system age alone. Another option is rehabilitating any lateral that
“appears” to have infiltration during a conventional CCTV inspection.
However, a risk-based replacement program founded on thorough
inspections can pay for itself several times over.
Historically, laterals have been neglected and rarely inspected,
largely due to often-complex public/private ownership issues,
limited access, and unreliable inspection technologies. While
quantitative assessment tools have largely been unavailable,
several investigative techniques have been used over the years.
Such methods include smoke, dye, and air testing to identify
sources of infiltration. Hydrostatic testing can be used to identify
exfiltration sources. However, the most common investigative
method is a visual inspection using a closed-circuit television
(CCTV) camera. Pushrod CCTV systems have been on the
market for decades and while they are necessary tools, they
Fall 2013 – The Conduit
33
Smoke testing private sewer lateral.
Wet weather simulation test of private sewer lateral.
require lateral cleanouts and/or right of entry to private property
access points (e.g., downspouts, roof vents, toilets, etc.). The
least invasive and most cost-effective investigative method
is a CCTV inspection from the mainline sewer using a robotic
crawler. Mainline lateral systems have been on the market for
about a decade, but recent technological improvements make
them the preferred method of inspection. Not only are more
laterals accessible with improved technology, but laterals can
be located with global positioning system (GPS) to update
mapping and geographic information system (GIS) records.
To supplement the lateral CCTV inspection, utilities such as
the Hampton Roads Sanitation District (HRSD) have been using
wet weather simulation during the inspection to better identify I/I
sources. This is conducted with a sprinkler/soaker system over
the lateral to induce a 1.5-inch rainfall event that creates inflow
sources and raises the groundwater to activate infiltration points.
With the advent of the National Association of Sewer Service
Companies (NASSCO’s) Lateral Assessment Certification
Program (LACP), CCTV lateral inspections can be coded and
are the only industry-wide quantitative assessment method. The
LACP program is an evolution of the Pipeline Assessment and
Certification Program (PACP) program, an industry standard that
offers a more quantitative assessment of underground piping
systems. Defect coding in PACP and LACP is similar, although
LACP has an additional focus on fittings and access points that
are unique to laterals.
Although still an evolving aspect of sewer system
maintenance and peak flow reduction, the incorporation of a
private property I/I abatement program just may be the missing
piece necessary to solve many utilities wet weather peak flow
issues. WEF has compiled a significant amount of information
at http://www.wef.org/privateproperty/ which you may also find
useful.
Jeffrey Griffiths, Regional Director
Hydromax USA, Newport News, VA
O: 757.353.1521, E: [email protected]
1
Chris Wilson, Associate
Brown and Caldwell, Virginia Beach, VA
O: 757.518.2404, E: [email protected]
VWEA Collection Systems Committee Chair
2
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The Conduit – Fall 2013
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Lynchburg, VA
VA
434-525-7929
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[email protected]
[email protected]