HomeMy WebLinkAbout07/00/1989, 1-A - BUDGET SUPPLEMENT - INFILTRATION AND INFLOW REVIEW AND ALTERNATIVES _ MEETWG DATE:
a .y Of San LUIS OBISPO July 24, 1989
COUNCIL AGENDA REPORT 'TEKA NUMBER:
FROM William T. Hetland, Utilities Director
SUBJECT: Budget Supplement - Infiltration and Inflow Review and Alternatives
RECOMMENDATION:
Staff recomends that the Council support the alternative approach to correction of
the infiltration and inflow problem through a combination of treatment plant
expansion, relief sewer construction and infiltration and inflow source
correction.
PURPOSE
During the City Council's budget review, concerns were expressed that an increased effort
was needed in correcting infiltration and inflow (I/I) problems in the collection system.
This report will provide some background on I/I and an alternative approach to increased
level of correction of the I/I sources.
SUMMARY
The City's wastewater collection system have significant deficiencies which have resulted
in major problems to the City. The system does not meet the current Regional Water
Quality Control Board standards nor does it meet the high ideals of this environmentally
sensitive community.
The City has done extensive study and analysis through the City's Wastewater Management
Plan over the last few years. This has resulted in development of a program of treatment
plant improvements and relief sewer construction to address the City's immediate
wastewater problems. Long term approaches to infiltration and inflow plus capacity for
growth are also included. This program is expensive and will take a number of years to
accomplish but it is the most realistic alternative for the City to meet our current
standards and correct the I/I problem.
BACKGROUND
The City's wastewater collection system consists of 150 miles of sewers ranging from 6 to
30 inches in diameter and 8 lift stations. The City has experienced problems with high
flows due to infiltration and inflow. Most of the infiltration and inflow is the result
of old clay pipe with cement mortar joints that have failed and deteriorating service
laterals composed of bitumimous fiber pipe (Orangeburg).
As part of the Wastewater Management Plan a detailed computer program of the collection
system was developed to better analyze the hydraulics of the system and determine needed
improvements. In addition, winter flow monitoring of the fourteen basins within the
collection system was done to measure the level of infiltration and inflow. These
measurements showed four to five of the basins were peak I/1 areas.
=� I CI O� San LWS OBISPO
page 2
Infiltration and Inflow Alternates
TRADITIONAL INFILTRATION AND INFLOW CORRECTION METHODS
Traditionally, infiltration and inflow is handled in two ways. The source of the I/I, the
collection system and laterals can be rehabilitated to eliminate the I/I or the treatment
plant capacity can be increased to treat the I/I. A cost benefit analysis to determine
which I/I correction option is the most cost effective can be performed. Extensive
studies required for the construction grants program showed that handling the I/I at the
treatment plant was usually the most cost effective option.
The City's flow monitoring work shows four or five basins with high I/I that may lend
themselves to rehabilitation. Other basins showed I/I but at lower levels. The
difficulty with rehabilitation work is the high cost and the uncertainty as to the level
of success that can be achieved. This is because it is difficult to clearly identify the
exact location of the I/I source and to make corrective repairs. Monitoring work required
to identify specific sources of I/1 is also very expensive. There is also a tendency that
as one section of pipe is repaired it simply moves the groundwater to the next section
where it finds new areas to infiltrate the sewer.
A key source of I/I is private sewer laterals, especially those involving bituminous fiber
pipe (Orangeburg). Bituminous fiber pipe was used in San Luis Obispo between 1940 to
1964. The subdivisions developed during that timeframe show some correlation to the
basins where high I/I exists, but not completely. It is estimated there are 4000 service -
laterals in the subdivision identified as having bituminous fiber pipe. If the average
cost for replacement of the laterals averaged $2500 per lateral, the total cost of a
replacement program would be $10,000,000.
These costs do not include any rehabilitation work for the collection system which are
another source of I/I. It has been estimated that an additional $4,000,000 to $6,000,000
would be needed for the rehabilitation of the collection system in the four basins with
the highest I/I. This approach of lateral replacement and collection system
rehabilitation would then total over $16,000,000 for only a partial solution and little
assurances that I/I problems would be resolved.
PREVIOUS COUNCIL DIRECTION
On July 5, 1988, Council provided direction to staff to approach the I/I problem in a
multifaceted manner. The general. philosophy was to handle the I/I at the treatment plant
(including relief sewers) in the short term, but also address the source of the I/I
(collection system and sewer laterals) over the long term. By following this approach the
City would be in compliance with the Regional Board and by reducing the sources of I/I
would provide an additional safety factor or insurance policy from future violations of
the City's waste discharge requirements. The program included the following specific
items:
1. Develop a relief sewer program and increase the treatment plant capacity to handle _i
the I/I problem. The treatment plant design has been completed at a cost of over
$1.0 million. The first phase of relief sewers are being designed by the City
staff and are 75% completed. It is anticipated to bid this work this summer and
fall.
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city Of san�LUIS OBIspo
Mi;% COUNCIL AGENDA REPORT
page 3
Infiltration and Inflow Alternates
2. Have staff develop an ordinance requiring the inspection and testing of sewer
laterals at time of saleof property. Inspection and testing of the laterals at
the time of any building permit issuance, issuance of special use permit for
changing residential to commerical residential, sidewalk reconstruction and street
resurfacing are also being considered. A draft ordinance has been prepared and
the agenda report completed. This will be placed on the Council agenda very
shortly.
3. Direct staff to develop a lateral replacement and loan financing program.
Alternative programs, cost estimates and funding options are currently being
investigated. With the competion of the budget, the Finance and Utilities
Director will work together to develop program options to present to Council in a
few months.
CONSENT DECREE IMPACT
The City is currently negotiating a consent decree with the Regional Board which has a
major impact on the City's Wastewater Management Program. The decree is basically a time
schedule which the City agrees to follow in order to comply with our established waste
discharge requirements. Interim discharge requirements are also in the decree. The
decree includes stipulated penalties the City would pay if it does not meet the time
schedule or violates other provisions of the decree. All the negotiations to date have
been based on the City handling I/I at the treatment plant and installing the necessary
relief sewers. To change that strategy significantly at this date may be very difficult,
if not close to impossible. If the City were to change its program we would not be able
to meet the standards and time schedule of the consent decree and could face the prospect
of losing to fines and penalties monies which could be better used to correct deficiencies
of the existing system.
CURRENT I/I ACTIVITIES
There are currently budgeted capital improvement projects and operations expenditures
which directly and indirectly help to correct I/I problems. There are two capital
projects that will address I/I. The first is the relief sewer project itself. As part of
that project it is estimated that over 1000 laterals will be tested and repaired if
necessary. In addition, our annual sewer main replacement program replaces those sewers
which are undersized or damaged and therefore a potential source of 1/1. Also it will
include the testing and repair of laterals associated with those projects. The City is
proposing to spend about $200,000 per year on these projects.
On the operations side of the budget nearly 20% ($50,000) of the collection system
operating budget is spent each year on I/I elimination tasks. These include manhole
repair, sewerline repair, and sewer lateral wye installation and repair. In addition I/I
detection involving smoke testing and televising of sewer lines is done. Also
approximately 5% ($3,000) of the Pretreatment Program operating budget is spent on the
detection and elimination of inflow sources as industrial waste inspections are performed.
��u��i�u��IIIII���Ini► J► City of San ling OBISpo
niis COUNCIL AGENDA REPORT
page 4
Infiltration and Inflow Alternates
1989-93 CAPITAL IMPROVEMENT PROGRAM ALTERNATIVE
The proposed 1989-93 Capital Improvement Program includes the two major projects which
relate to I/I; the expansion of the wastewater treatment plant and the relief sewers. It
is proposed that the relief sewers project be modified to better address the issue of 1/1
source correction. The first year project is the largest section of relief sewers which
will extend from the treatment plant north to above our major problem area at Chorro and
the freeway for a cost of $5.20 million. Over the next three years it was then proposed
to construct the balance of the relief sewers at a total cost of $3.77 million.
An alternative to this approach would be to construct the initial section of the relief
sewers to above Chorro and the freeway as initially prposed. Thi's section is currently
estimated at $5.20 million but may be less depending where the project is terminated.
This project would resolve our immediate problem of surcharging the system and popping
manhole covers in this area during peak storms. The balance of the relief sewer budget,
$3.77 to $4.50 million, could be used to follow a three part program. The first part
would be to analyze the upstream I/I and determine the feasibility of rehabilitation work
on the system and laterals. An extensive lateral repair/replacement program could be
implemented with the City providing the money up front and then require the homeowner to
repay the money over a set period of time. The third part of the program would be to
build additional relief sewers as may be needed with the proceeds of the repayment funds.
This alternative will require some additional study to determine its feasibility and
cost. This study may include additional computer modeling, flow monitoring, and
collection system and lateral inspection and testing. There may also be a slight increase
in the risk of spilling sewage following this approach. The program has the advantage of
solving the short term problem while correcting I/I over the long term. It also allows
the double use of money in correcting the 1/1 problem.
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1"* '=:uenp:es acion by Lead Person
July 24, 1989 Respond by:
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MEMORANDUM (j4m,Atty.
[[ �lerk•orig.
To: City Council 7.1% �r �
From: JohnDu BILE
Subject: Newsp er i erest - Inflow and Infiltration
For your information, Bill Hetland will be meeting with Winston Caine to
talk about "I and I" and related sewer issues.
JD:mp
RECEIVED
JUL 2 4 1989
/L:QTA
CITY CLERK
SAN LUIS OBISPO,CA