ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF ENFORCEMENT
EPA 330/9-74-003
't'niL crhi" Evaluation
^ o
of the
}\'cttLT Ointl/t} Control Plant
Stockton. California
NATIONAL FIELD INVESTIGATIONS CENTERS
DENVER. COLORADO AND CINCINNATI. OHIO
£
DECEMBER1974
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ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF ENFORCEMENT
ENGINEERING EVALUATION
OF THE
MAIN WATER QUALITY CONTROL PLANT
STOCKTON, CALIFORNIA
NATIONAL FIELD INVESTIGATIONS CENTERS
DENVER, COLORADO AND CINCINNATI, OHIO
DECEMBER 1974'
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CONTENTS
Page
INTRODUCTION 1
SUMMARY AND CONCLUSIONS 3
Sludge Lagoons 3
Trickling Filter Modifications 4
Building Additions and Modifications 6
METHODS OF INVESTIGATION 8
ENGINEERING EVALUATIONS , 9
A. Construction of Sludge Lagoons .... 9
B. Trickling Filter Modifications 24
C. Building Additions and Modifications ... 45
APPENDIX 50
Memo: Request for Technical Assistance
Construction Drawings
1. Sludge Lagoon, G5
2. Sludge Pumping Station, M2
3. Sludge Pumping Station, Ml
4. Sludge Lagoons, G3
C f 1 t. j J « _ I -. M n A » /"* A
iiuage Lagoons, tad
Sludge Lagoon, G4
6. Trickling Filters, S7
7. Trickling Filters, M2
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ENGINEERING EVALUATION OF THE
MAIN WATER QUALITY CONTROL PLANT
STOCKTON, CALIFORNIA
INTRODUCTION
On October 30, 1974, Region IX, USEPA, requested technical assis-
tance from the National Field Investigations Center-Denver (NFIC-D) in
the interim audit of the Stockton, California Main Water Quality Control
Plant. An engineering evaluation of the design and construction methods
was requested in a memorandum to the Regional Administrator, October 18,
1974, from the Manager, Western Area Audit Group (See Appendix).
EPA Grant No. C060695, the subject of the audit, covers the
enlargement and modifications of existing treatment facilities. The
total cost of the project was $15.2 million ($8.3 million Federal funds),
Six contracts were awarded under this grant; three contracts have been
completed and three are in the active status. The areas where technical
assistance was requested and the contractors involved include:
Project Constructipn Contractor
Sludge Lagoons C. N. Peterson Co.
Trickling Filter Modifications Caputo-COAC
Building Additions and C. S. Plumb
Modifications
The City of Stockton retained the consulting engineering firm of
Brown and Caldwell to provide (1) design services, (2) inspection and
construction, (3) preparation of O&M Manuals, and (4) miscellaneous
assistance. The engineering firm was given the responsibility for
managing the project.
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This report represents the results of the engineering investigations
conducted by NFIC-Cincinnati and NFIC-Denver personnel, the conclusions
herein represent our best engineering judgement. The report deals
specifically with the questions listed in the memo of October 18.
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SUMMARY AND CONCLUSIONS
The Western Area Audit Group asked specific questions concerning
construction practices, design errors, plant operating problems, structural
integrity, validity of change orders, and whether approved plans and
specifications were followed. The detailed discussions of the specific
questions are contained in ENGINEERING EVALUATIONS; the conclusions from
the investigations are summarized below.
+
A. Sludge Lagoons
The construction of the lagoons was accomplished according to
specifications. The telescoping weirs do not function as designed and
leak excessively. The consultant engineering firm specified an allowable
clearance between the weir and the riser unit; the contractor did not
fabricate the weirs to these specifications. The City will have to
correct the problem at their expense.
The existing sludge drawoff suction line cleanouts were installed
according to specifications, however the lagoons must be drained before
they can be used. Draining the lagoon in order to utilize a cleanout does
not constitute a good design, and a safety hazard remotely exists since
isolation valves were not included upstream of the cleanouts. There is
also a potential for back siphonage of lagoon contents into the City
water supply through the sludge piping system (Detail J/G3, contract
drawing G3)..
The sump pump in the sludge pumping station should be capable of
pumping 60 gpm against a head of 20 feet as required in the specifications,
based on our calculations. A pressure test on the pump discharge piping
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should be conducted to verify if the pump is capable of discharging at
the specified 20 feet of head at 60 gpm. The most cost effective original
design should have had the sump pump discharge back into the lagoon
rather than into the supernatant withdrawal piping.
Coning occurs when the sludge is pumped from the lagoon. No
instrumentation or visual aids such as a sludge density meter or sight
glasses were included to permit the operator to know when coning occurs.
Dredging is the most effective method of removing sludge from the
lagoons since the suction port can be moved to the solids, thus eliminating
the coning effect. However, operating and capital costs for such systems
are higher.
The seven change orders for the sludge lagoons and the 43 change
orders for trickling filter modifications are currently being evaluated
by the California State Water Resources Control Board and a report will
be issued to the audit group. A parallel investigation by NFIC personnel
would be redundant at this time. It is proposed that NFIC review the
completed report and submit comments to the audit group.
B. Trickling Filter Modifications
With the exception of specific items discussed below, it is our
conclusion that the construction work was accomplished in accordance
with approved plans and specifications.
The leakage experienced in the walls of trickling filter No. 4 was
the result of basic design error complicated by "hurry up" construction
techniques to make the filter operational for the 1973 canning season.
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There is no reason to believe that trickling filters Nos. 5 and 6
cannot be operated to full capacity. The filters may not be operated at
maximum capacity at all times due to energy costs required to lift the
wastewater to the top of the filters; a portion of the wastewater is
treated in the three 6-foot depth trickling filters. It would appear
that the leakage now experienced in the walls of filters Nos. 5 and 6
will not be as great as in filter No. 4.
The effluent leakage through the filter walls could have the effect
of attacking and leaching the mortar joint to the point where only
the silicon remains. The wetting and drying of the rebars exposed to
oxygen would accelerate corrosion of the bars and weaken adherence between
concrete grout and the rebars. However, this could take a number of years
before it would significantly affect the structure. The existing founda-
tion will withstand the additional weight of the concrete blocks
resulting from the effluent leakage.
Concrete blocks as specified in this contract are not noted for their
ability to withstand absorption. At the time of the original design,
the concrete block construction was probably the least costly alternative.
The "thudding" noise occurs in the two 30-inch check valves installed
on the discharge pipes from recirculation pumps. The possible causes for
the noise and vibration problems include improper installation, insufficient
spring tension, and improper design of the structure. The problem
should be corrected before structure fatigue occurs.
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Pump operational problems and the determination of who will correct
the problems are currently being negotiated by the pump suppliers and
the consulting engineers. The consultants suspect that the pumps were
supplied with the wrong pitched impellers. Pump No. 5 draws approximately
15 amperes more than pump No. 6. If the current drawn exceeds the rated
amperage, the circuit breaker will disengage. Any modification to the
circuit breaker to increase the amperage above the rated amperage will
decrease the motor life. If the problem is not corrected soon, the
increased amperage will break down the insulation in the motor and it
will have to be replaced.
If the doors of the main electrical substation are left open and
access to unauthorized personnel is not controlled, then both State and
Federal safety requirements are being violated. Equipment deterioration
due to dust and moisture will occur.
The walls of filter No. 4 did have numerous open mortar joints.
Corrective action has been delayed until a decision is reached on the
wall leakage problem. The exterior wall surfaces of filters Nos. 5
and 6 had full joints. The interior walls below the filter media could
not be inspected.
C. Building Additions and Modifications
After review of the concrete specimen data, those that failed and
those that passed specified criteria, it is concluded that the poured
concrete now meets the strength requirements. The maintenance building
will not be structurally affected by retention of the manhole adjacent
to the building.
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An 80% compaction vs a 95% compaction on the sandy material underneath
the sewer pipe should have relatively little effect on the pipe.
The brick veneer on the operations building is for aesthetic purposes.
Since the cavity between the brick and existing wall is grouted to a
height of 8 feet, it should prevent any movement if a vehicle hits it.
The reduced grouting above the 8 ft. height should present no safety
hazard.
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METHODS OF INVESTIGATION
An on-site inspection of the treatment facilities was made on
November 21, 1974 by Victor Oelen, NFIC-Cincinnati, David Brooman,
NFIC-Denver, and Barrett Benson, NFIC-Denver. Treatment plant
personnel were interviewed on November 22 from 8:30 am to 11:30 am
to ascertain the exact nature of operating problems experienced with
the sludge lagoons and trickling filters. Representatives of the
City and Brown and Caldwell were interviewed and construction records
examined from 11:30 to 6:30 pm on November 22. Personnel present included:
Mr. Thomas J. Dosh, Director of Public Works, Stockton;
Mr. Art Vieira, Superintendent, MWQCP, Stockton;
Dr. David Caldwell, President, Brown & Caldwell;
Mr. Albert R. Huff, Area Supervisor, Brown & Caldwell;
Mr. Paul J. Kramer, Resident Engineer, Brown & Caldwell;
Mr. Frank Wilson, Assistant Resident-Engineer, Brown & Caldwell;
Mr. Victor Jelen, NFIC-C;
Mr. David Brooman, NFIC-D;
Mr. Barrett Benson, NFIC-D.
Two inspectors, Mr. Jose Casillas and Mr. Mike Pooley, were also inter-
viewed by NFIC personnel, from 7 pm to 10 pm on November 22.
In all interviews, the discussions were limited to the areas
listed in the October 18 memo.
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ENGINEERING EVALUATIONS
The evaluations are divided into three sections, Sludge Lagoons,
Trickling Filter Modifications, and Building Additions and Modifications.
Each specific question raised by the auditors is stated and is followed
by the discussion.
A. Construction of Sludge Lagoons
Question No. A-l
"During the course of our audit, several operational problems
concerning the sludge lagoons have been brought to our attention.
We therefore would appreciate an independent technical determination
as to whether the construction work completed on the sludge lagoons is
acceptable and has been accomplished in accordance with the approved
plans and specifications."
Discussion
With the exception of the difficulties with the telescopic weirs
(Question A-2), the capacity of the pump station sump pump and the
repair of malfunctioning variable speed drive controls on the sludge
pumps (Question A-4), the construction work completed on the sludge
lagoons was accomplished in accordance with the approved plans and
specifications.
The major operational problems encountered to date with these
lagoons are attributable to poor quality control in the construction
of the telescopic weir assemblies and inherent problems with the
removal of thickened sludge from the lagoon bottom. The weir assemblies
may possibly be remedied in the field by the City. If these remedies do
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not solve the problem, a redesign may be required. The sludge removal
problems are more complex.
Sludge removal, pumping, and transport is a major engineering
challenge. Digested sewage sludge, if allowed to settle for a sufficient
period of time, will separate into two distinct phases, a liquid or
supernatant layer, and a concentrated solids layer. Influent digested
sludge from the digester to the lagoons would normally have a solids
concentration in the range of 3.5 to 4.5%. Although no data was
available for review, it could be expected that the solids concentration
at the lagoon bottom and in the sludge drawn off through the sludge
suction piping would be in the range of 8-10%. The increased solids
concentration causes the concentrated sludge to act like a viscous
mass rather than a fluid. It is more difficult to pump, has thioxotropic
properties which cause it to react like a gel, and will assume a natural
angle of repose under water. The latter property causes it to deposit
in banks under the supernatant surface rather than to flow evenly in
the lagoon to form a layer of equal thickness. It also causes coning
at submerged suction lines (discussed in Question A-4).
To overcome the sludge property of natural angle of repose, sludge
containment vessels (e.g., digesters) are often constructed with conical
bottoms with drawoff piping near the cone apex. In the interviews with
the consulting engineers, the use of steep lagoon sides was discussed.
The consultants said that this sort of design was considered, but
rejected due to excessive ground water contamination problems, a
reasonable explanation considering the proximity of the San Joaquin
River to the plant site. They designed multiple withdrawal pipes
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(four per lagoon) to offset the coning problems. It is questionable
whether this approach is totally satisfactory since the coning effect
is localized near the suction pipe opening. New sludge added to the
lagoon will fill in these coned areas and be removed during the next
pumping cycle. The old, established sludge will not reach the cone
influence area. The effective sludge residence time in the lagoon is
thus effectively reduced.
To overcome these problems some municipalities utilize actual
mobile dredging equipment for removal of concentrated sludge from
lagoons. The Metropolitan Sanitary District of Greater Chicago has
over 200 acres of sludge lagoons in Fulton County, Illinois. A
commercial river channel dredge is used to remove the concentrated
solids from the lagoons. Dredging is the most effective method of
removing the concentrated sludge from lagoons because the suction port
can be moved to the solids rather than attempting to make the solids
flow to the suction port. The operating and capital costs for such
systems are, of course, higher.
Question No. A-2
"Visual observations and discussions have indicated that the
telescopic weir in one of the sludge lagoons was not operating properly.
We would like to have the extent of this problem reviewed. If possible,
we would also like technical comments as to the cause of the problem and
a determination as to who has the responsibility to correct it."
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Diicussion
1. There are two digested sludge holding lagoons. The west
lagoon is designated Lagoon No. 1 by plant personnel, the east lagoon,
Lagoon No. 2. Each lagoon has two digested sludge inlet pipes, four
digested sludge drawoff pipes, and two supernatant drawoff pipes.
The telescopic weirs in question {four total) are located on the
supernatant drawoff piping systems.
Detail A/G5, Contract Drawing G5, (Appendix) illustrates the design
of the four telescopic weir units. The discharge weir unit has a
specified outside diameter of 29-7/8 inches and is to fit inside a riser
pipe with an inside diameter of 30 inches. A fabrication note on
Section 1/G5 specifies that the weir and riser pipe should be "Fabricated
for uniform clearance of 1/16" plus or minus 1/32" over the entire circum-
ference." This tolerance is apparently specified to permit the weir to
move within the riser pipe without binding and yet minimize the leakage
between the two components when the weir unit is positioned above the
minimum adjustable height.
The function of all of the telescopic weir units is to maintain
the water surface elevation within the lagoons at any level between
El.94.0 and El,98.0. During normal plant operating periods, the lagoons
may be operated at a reduced level (e.g., near El.94.0) to provide
additional volume for digester upsets, increased digested sludge
volumes from seasonal loads, etc. as they occur. As the sludge blanket
in the lagoons increases,.for instance during the rainy season when the
sludge drying beds cannot be loaded heavily or frequently, the lagoons
may be operated at higher elevations to maintain the desired sludge
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solids/supernatant layer separation. Also, by positioning the two weirs
in a given lagoon at different elevations, the flow pattern through the
lagoon can be changed, withdrawing supernatant from either the northeast
or southeast corner of the lagoon.
This operational flexibility is dependent on the weirs not leaking
appreciable quantities of water through the annular space between
the weir unit and the riser pipe. When such leakage does occur, and
the leakage rate exceeds the lagoon influent rate, it becomes impossible
to maintain the lagoon surface elevation above El.94.0, the top of the
riser pipe, by use of the telescopic weirs.
During the site inspection, the tops of the telescopic weirs in
Lagoon No. 1 were at elevations approximately 3" (NE weir) and 9"
{SE weir) above the lagoon water surface. If at least one of these weirs
was leaking, then this weir/lagoon surface elevation discrepancy would
exist. Conversely, if both weirs were watertight, then the lagoon level
should have been at the elevation of the NE weir provided that (!)
evaporation and concentrated sludge drawoff rates did not exceed digested
sludge influent rates and {2} the weirs were not raised to higher
elevations just prior to the inspection.
Both weir assemblies in Lagoon No. 2 were totally submerged during
the site inspection. This situation results when both valves are closed
on the 8" supernatant drawoff lines downstream from the telescopic
weirs. Since the weirs were submerged, visual examination of their
leakage potential could not be made. Discussions with plant operating
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personnel have verified that all four telescopic weirs leak excessively
and that it was necessary to install the above-mentioned valves to
control the lagoon elevations and discharge flow rates.
The cause of the problem appears to be one of poor fabrication of
the weir units and/or the riser pipe units. The 1/16" ;* 1/32" allowable
clearance between the weir and riser units was apparently not met.
The contractor (C. N. Peterson Company) tried to correct the weir
leakage problem with gaskets previous to the installation (by the City)
of the valves. These gaskets failed and caused operational problems
due to binding. The City plans to weld a stainless steel cap ring
onto the riser pipe. This ring will have an inside diameter 1/8 inch
larger than the field measured outside diameter of the corresponding
weir unit. Post modification testing of the individual weirs will
determine if the leakage problem is sufficiently reduced to eliminate
further design modifications. It is our understanding that the City
will bear the expense of the cap ring modification since the contractor
paid the City for the installation of the valves. In our opinion, if
the modifications achieve the specified 1/16" +_ 1/32" clearance between
the ring cap and weir, the contract requirements will be satisfied.
In the design of a similar telescopic weir assembly for the trickling
filter modification contract at Stockton, the consulting engineer called
.for three 0-ring gaskets on the riser pipe unit (Section 2/M2, Contract
Drawing M2). These gaskets form a seal between the weir and riser units.
The detailer did not specify clearance tolerances for this telescopic
weir unit, nor did-he even specify the weir outer diameter or length.
Gasket composition and method of attachment are also not specified.
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If the ring cap modifications for the lagoon telescopic weirs do
not solve the leakage problem, the.consul ting engineer should be brought
to task for improper design and required to change the weir design to
solve the problem.
Question No. A-3
"It was observed that the clean-out valves for the sludge lagoons
were located in the pump station which were considerably below the
lagoon water level. It was explained that the pumping station would be
flooded if the clean-out valves were uncapped. In addition, it was
suggested that the cleanouts served no useful purpose since the
lagoon would have to be drained before any clean-out work could be
performed. We would like a technical determination as to whether
clean-out valves are usable without creating a safety hazard to personnel
in the pumping station. If this is a .problem, we would appreciate a
determination as to whether it was attributable to a design error or
to the quality of construction and how it can be corrected".
Discussion
The plan view and section I/Ml of the sludge pumping station are
from Sheet Ml of the contract plans and specifications (Appendix). The
eight 8-inch diameter pipes pass through the east and west walls of the
pump station (four pipes through each wall) at a center!ine (c) elevation
of 85.00. These eight pipes are the sludge drawoff pipes from lagoons
1 and 2. Just inside the station walls, each pipe is connected to an
8-inch diameter pipe Y with a victaulic cap and coupling on the Y leg.
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*
These Y's were designed for use as clean-out ports in case the sludge
drawoff pipes should become severely clogged. The existing sludge suction
line cleanouts were installed according to specifications.
Shut-off (isolation) valves were not specified between the clean-out
Y's and the incoming sludge piping. Rather the shut-off valves were
specified downstream from the cleanouts. Since the normal operating
surface level of the lagoons is El.94.0 to El.98.0, the static pressure
head which exists at the victaulic caps is computed as follows:
minimum static head = 94.0'-85.0'-1.5' (Sin 45°)
= 7.9 ft = 3.4 psig
maximum static head = 98.0'-85.0'-1.5 (Sin 45°)
= 11.9 ft = 5.2 psig
The column of water formed by the lagoon contents exerts a constant
pressure (assuming the pipe is not plugged) of between 3.4 and 5.2
pounds per square inch on the clean-out caps. Since there are no
isolation valves between the lagoons and the clean-out points, it is
not possible to open the cleanouts once the lagoons are filled without
the lagoon contents entering the pump station structure. However,
if the particular pipe is clogged, lagoon material cannot flow in the
pipe. If the pipe is severely clogged and a rodding tool is used to
clean out the line via the clean-out port, once the obstruction is
removed, the pressure head would force the lagoon contents through the
pipe into the station.
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As designed and installed, the clean-out ports cannot serve a
useful purpose unless the particular lagoon is drained. Each of the
victrauliccaps has been stenciled with" a warning "DRAIN POND BEFORE
REMOVING". Although the warning may deter an unfortunate mishap, it
does not constitute a fail-safe situation. To drain the lagoon, it
would be necessary to isolate it from service and transfer its
contents via the station pumps to either the drying beds or the other
lagoon. Alternately, the lagoon contents could be drained by portable
pump to the other lagoon or to a landfill. The consulting engineers
stated that the Y connections were only to be used for cleanouts
once the lagoon was drained. The Y's would allow the operator to clean
the pipe from either the station end or lagoon end without having to
break into the pipe in the pump station. In our opinion, draining a
lagoon to be able to utilize a cleanout does not constitute a good design
and a safety hazard remotely exists since isolation valves were not
included in the design.
Provisions were made by the design engineers to bring City water
and compressed air to the pumping station structure. A two-inch water
line is tapped into the lagoon sludge drawoff piping. It is common
practice at treatment plants to use compressed air and/or water pressure
to blow out sludge lines which are not excessively clogged. Plant
personnel report that this technique has been already utilized with
success on this piping. However, pressure gages should be installed
on the backflush piping so that the operators can evaluate the back
pressure being applied to the clogged pipe.
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t
For a fail-safe design, the cleanouts should have been routed
above the surface elevation of the lagoons or valved upstream. Due
to the structural configuration of the pump station, it would be difficult
to revise the existing piping to accomplish this. Also, since there
are no isolation valves on the cleanouts, it would be difficult to
connect extensions to the existing cleanouts without flooding the
structure.
As a possible solution, a special cap and isolation valve could be
installed on the leg of the Y and eliminating the vitraulic cap. The
special cap would require packing around the cleanout port to allow use
of a cleaning rod. However, since the cleanouts would only be used in
rare instances, modifications are not warranted at this time.
Three items of concern about the air and water piping systems are
listed below. One, no connection to'an air supply is indicated on the
drawings. Rather, the terminus of this pipe is indicated as a cap
located near the existing City water hydrant (Detail J/G3, Contract
Drawing G3). Two, a hose bib or coupling is not specified on the sludge
suction piping which could be used for connection from the existing air
line to the clogged sludge suction line. Three, a vacuum breaker in
the 2" water line connection to the sludge piping is not indicated between
the sludge-piping connection and the City water hydrant. A cross
connection is thus developed by this design and the potential for back
siphonage of lagoon contents into the City water supply does exist.
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Question No. A-4
"Plant operating personnel commented that they were unhappy with
operations of the sludge lagoon from several standpoints. One of these
was that the sump pump was not able to effectively remove sludge.
Another was that the pumping station was causing problems since it had
a greater capacity than could actually be used. We would appreciate a
technical evaluation of the validity of the above problems and how they
can be corrected."
Discussion
Sump PumjJ - The sump pump referred to is located in the southwest
corner of the sludge pumping station (Contract Drawing Ml). Its function
is JlQt to pump sludge, but to remove from the station any spills,
wash-up water, foundation leakage, etc. which may be collected by the
floor drain system.
The discharge piping from this sump pump (pipe 3"SD) is routed overhead
in the station, through the south station wall, under the berm roadway
between the two lagoons, and tied in the 8" supernatant line from lagoon
No. 1's southeast telescopic weir (Detail M/G3 on Drawing G4). The
sump pump is thus supposed to discharge the station sump contents through
this line to the 8" supernatant line which was originally designed for
gravity flow.
The City has installed two 8" shut-off valves on the two 8" supernatant
"gravity" lines. When these valves are closed, supernatant completely
fills these 8" lines and the telescopic weir riser pipes up to the
elevation of the lagoon surfaces (El 94.0 to 98.0). Therefore the
sump pump must pump against a static head between 13.5 and 17.5 feet
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with the current operational mode. In the gravity mode, it would have
had to pump against a static lift of approximately 11.5 feet. On page
C38 of the actual contract specifications, the sump pump is specified
as follows:
"(2) Pump
Sump pump shall be of the submersible motor-driven, non-clog
type. Pump shall be capable of discharging 60 gpm against a total
head of 20 feet when driven by a 4-pole motor of at least 2 horse-
power. . ."
The specified pump, if operating correctly, should be capable of
pumping against the maximum static head of 17.5 ft discussed above.
Calculations for dynamic head (i.e., pipe and fittings resistance to
60 gpm flow) indicate a maximum dynamic head of approximately 2.5
ft. Therefore, if the sump pump was pumptig 60 gpm against the static
head of Lagoon No. 1 at maximum surface elevation of 98.0, the total
pumping head should be approximately 20.0 ft., the specified pump head.
Based on these calculations, the sump pump should be capable of dis-
charging the sump contents (if the contents don't exceed 60 gpm) through
the existing piping to Lagoon No. 1 via the southeast telescopic weir.
A pressure test on the pump should be conducted to verify if the pump is
capable of discharging against the specified 20 ft of head at 60 gpm.
A suggested alternate to the existing piping scheme is to run the
discharge line to a discharge point above the surface of Lagoon No. 1
near the pump station. There is no reason that the sump contents
cannot be returned directly to the lagoon. The discharge point should
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be at a point higher than the maximum lagoon surface elevation of El 98.0.
If the pump is capable cf discharging 60 gpm against 20 ft of total head,
a static lift of 17.5 ft plus a dynamic head of < 2.5 ft (reduced from
existing value because of reduced equivalent pipe length) should be no
problem. Had the design engineer anticipated the non-gravity flow
situation with the 8" supernatant line, he probably would have preferred
to discharge the sump back to the lagoon in the original design. A
question could be asked as to whether this alternate should not have been
the most cost effective original design.
Capacity of Pumping Station - Direct questioning of plant operating
personnel revealed no "pumping capacity" problems with the sludge
pumping equipment. The pumping problems which were mentioned are as
follows:
1) A vernier adjustment on the sludge pump motors was broken
and hence the variable speed pumps were not variable. This item
is on the contractors punch list and will be corrected before he is
issued final payment.
2) The sludge pumps must be turned up to maximum speed before
they will pump jludge from the basins. Digested sludge forms a dense,
thixotropic mass when it is allowed to settle for a period of time.
This mass would tend to form in and over the sludge suction piping
after each pumping cycle. It is conceivable that the pumps must be
turned up to maximum speed initially in order to free this obstruction
and refluidize the sludge solids. This fact should be included in the
plant operations manual. Once the sludge begins to flow however, it
should be possible to reduce the speed of the pump to obtain the desired
flow rate.
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3} The sludge pumps will pump dense solids when first activated
but soon the solids density falls off and eventually only supernatant
can be pumped. This is not an uncommon occurrence when sludge is pumped
from a containment via a fixed suction pipe. The phenomenon is called
"coning". As the sludge over the pipe is pumped away, the sludge
remaining in the vicinity of the pipe opening assumes its natural angle
of repose instead of flowing as a liquid into the pipe. The result
is an inverted cone of sludge with its apex at the pipe opening. When
this occurs, supernatant breaks through and is drawn into the suction
pipe diluting the sludge solids.
Each of the lagoons was designed with four drawoff pipes at different
locations in the lagoon. When coning is detected with one drawoff pipe,
the operator should switch to an alternate pipe location. No instrumentation
or visual aids are included in the design to permit the operator to
know when coning is occurring at a particular sludge drawoff pipe. Radio
communication between men positioned at the sludge pump discharge at
the sludge drying beds and the pump station operator could be established.
However, this would tie up two men during the pumping operation. A
sludge density meter and/or sightglasses could be provided to facilitate
the detection of sludge coning.
Question No. A-5
"A total of seven change orders have been initiated under the C.
Norman Peterson contract and approved by the resident engineer and
the City. These change orders were not submitted to the California
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State Water Resources Control Board (SWRCB) for approval until
September 4, 1974, although some of the change orders pertained to
work performed in later 1973. We would appreciate a technical deter-
mination of the acceptability of these change orders and a determination
as to whether the work included on the change orders has actually been
performed. In this regard, it should be noted that the SWRCB has assigned
a civil engineer, Mr. Joe Rodriquez, to review the validity of the change
orders."
Discussion
As noted in the question, the seven change orders on this contract
plus those pertaining to other contract work at this plant site are
being evaluated by Mr. Rodriquez. Mr. Rodriquez is to submit a report
on his findings, including recommendations as to approval or disapproval
of the change orders, to the Western Area Audit Office.
NFIC personnel met with Mr. Rodriquez on November 15, 1974 and
again on November 21, 1974 to discuss these change orders. He is still
attempting to obtain from the City of Stockton all required back-up
information which pertains to the change orders. Mr. Rodriquez'
expertise and method of approach appear compatible with the NFIC
investigation. Any additional parallel investigation by NFIC personnel
would be redundant at this time. It is proposed that NFIC personnel
review the completed report prepared by Mr. Rodriquez and submit comments
on it to audit personnel.
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B. Trickling Filter Modifications
Question No. B-1
"During our review, several operating problems concerning the trickling
filters were quite evident. In order to ascertain the full extent of
these problems, we would like a technical evaluation as to whether the
construction work completed on the trickling filters is acceptable and
has been accomplished in accordance with the approved plans and
specifications."
Discussion
Certain inaccessible details could not be evaluated. Examples
of such items include electrical conduit, the filter underdrain system,
interior filter wall surfaces below the media level, construction details
inside the filter recirculation distribution structure, etc. Likewise,
time was not available to fully evaluate all possible operating modes of
the systems* nor was it appropriate for NFIC personnel to dictate the
plant operating modes. However, with the exception of the specific
items discussed in Question Nos. B-2 through B-10 which follow, the
overall conclusion reached after NFIC's site inspection and review of
the facilities operating history is that the contractor has made a
conscientious attempt to construct the filters and attendant systems
according to the contract plans and specifications.
The filter wall leakage problems discussed in Question Nos. B-2
through B-6 and the check valve/recirculation pump problems discussed
in Question No. B-7 are the most significant areas where contractor
arid/or equipment supplier error may have been committed.
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Question No. B-2
"There is substantial effluent leakage and green algae growth on
the outside wall of trickling filter No. 4. Although this situation
has existed for almost one year, the leakage has not been eliminated.
In view of the substantial problem, we would appreciate a technical
determination as to whether the problem was the result of poor construction
or basic design errors."
Discussion
After inspection of the filter in question and having had discussions
with the job inspectors, the consulting engineers, and the wall coating
material suppliers, it is the opinion of NFIC that the leakage experienced
is the result of basic design error complicated by "hurry up" construction
techniques in order to place the filter in operation by the beginning
of the 1973 food processing season. The problem essentially comes down
to the original choice of the interior wall sealing material and, once
this choice was made, improperly defining in the specifications the
method of wall surface preparation which would be compatible with this
choice.
The following sequence of quotes from the contract specifications
must be followed in order to unravel the painting requirements for
the interior surfaces of the filter walls: Page C60; SECTION C8-PAINTING
"(2) Concrete and Masonry Surfaces
Concrete and masonry surfaces of trickling filter distribution
structure No. 1 and trickling filters Nos. 4, 5 and 6 shall be painted
as specified in Section C8.06."
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Page C66, Subsection C8.06 Finish Schedule
"(2) Trickling Filters
(b) Modified Filters Nos. 4, 5 and 6 Paint System
Walls, existing and new
Outside and top ring beam D
Inside B"
The inside walls of the modified filters are thus to recieve Paint
System B.
Page C63, Subsection C8.05 Paint Systems
"(3) Coal Tar Epoxy (System B)
(a) Surface. Concrete or masonry, interior or exterior
corrosive hydrogen sulfide atmosphere, black.
(b) Surface Preparation. As specified in sub-article
. (8.04(1)(c).
(c) Coatings
1. Amercoat Alternate. Prime coat shall consist of
one coat of coal tar epoxy resin coating, Amercoat
No. 78 resin. Finish coats shall consist of two coats
of coal tar epoxy resin coating, Amercoat No. 78
alternating red and black colors.
2. Engard Alternate. . .
3. Koppers A1ternatg. . .
(d) Notes:
1. All surfaces shall have aged 60 days and dried to
a maximum moisture content of 14 percent prior to
application of any paint.
2. Prime coat shall be thinned and applied at the rate
of approximately 200-300 square feet per gallon
depending on surface condition. Finish coats shall
be applied at the rate of 100 square feet per gallon.
3. Drying time shall be as recommended by the paint
manufacturer."
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Note: The Engard and Koppers alternates were not quoted verbatim
for the sake of brevity and since the Amercoat alternate was the one
used on Filter No. 4. These alternates were essentially the same as
the Amercoat alternate, the Engard alternate using Engard 463 Black
and the Koppers alternate using Koppers 300-M Black.
Page C61. C8.04 Construction
"(c) Preparation of Concrete and Masonry Surfaces^ All concrete and
masonry surfaces which require coating or painting shall be
dry and shall be prepared by light 'brush-off sandblasting.
Sandblasting shall be sufficient to remove all dirt, dust,
efflorescence, oil and grease stains and other foreign substances
and shall provide adequate surface roughening for good adhesion
between the concrete and coating or paint. All cavities and
voids shall be repaired and all surfaces troweled to finish
required."
In the specification quote above, m> specific surface finish material
is detailed for the interior walls of Filter No. 4, said surface finish
coat to be applied prior to the Amercoat prime and finish coats. NFIC
personnel contacted the technical development personnel at the manufacturers
of Amercoat (Ameron Products) in Brea, California to determine if this
was a proper application of Amercoat No. 78. The following information
was obtained:
1} Amercoat No. 78 can be used as a water resistant coating on
concrete block walls. It is not intended to be a waterproofing seal
where water pressure against a surface is anticipated. It will however
form a "water barrier" against droplets, vapors, etc., when applied
correctly and on a surface which has been correctly prepared.
2} Amercoat No. 78 becomes non-flexible as it cures. Although it
can withstand minor tension and compression strains, it will crack under
substantial stress.
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3) .The most significant point discussed is that Amercoat No. 78
must be applied only to surfaces which have been completely prepared
to remove all major ajid pinhole void spaces. For major cracks, gouges,
holes, etc., troweling of Ameron New Clad 109 epoxy paste filler material
is recommended. For minor or pinhole voids a squeegee application of
Ameron New Clad No. 1871 is recommended.
4) A thinned primer coat of Amercoat No. 78 coal tar epoxy will
not adequately seal all pinhole voids such as those which comprise the
interstitial matrix of a concrete block. In many cases the visible
pinhole is only the minor diameter of an interior void. Insufficient
sealing material gets through the pinhole to coat the interior surface
of the void.
From the above discussions, it can be concluded that the interior
wall surface preparation specified in the contract documents was
incorrect and/or incomplete. All surface voids were riot required to
be filled by squeegee application of New Clad No. 1871 (or equal). In
fact, the question may be raised as to whether the pointed grout joints
between the masonry blocks do indeed form "large voids" which should
have been filled with New Clad No. 109.
The choice of Amercoat No. 78 or any other coal tar epoxy resin
for this application is debatable. Considering that this material cures
to a relatively inflexible coating subject to cracking under stress and
impact, a better choice would have been an epoxy vinyl coating with a
silicone-based sealant. However, had the brick surface been properly
prepared to eliminate voids, the Amercoat No. 78 coating would have
provided an adequate seal.
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NFIC personnel discussed the Amercoat No. 78 application procedures
with both the job inspectors and the consulting engineers. Several
contract specification omissions committed by the contractor were noted
as follows:
1) Alternating colors of black-red-black were not utilized with
the prime and two finish coats of Amercoat No. 78.
. 2) The block wall surface was not light sandblasted prior to
coating application.
3) The mortar block wall and concrete cap beams were not allowed
to age for 60 days before the Amercoat No. 78 was applied. Similarly
adequate tests were not conducted to determine if the moisture content
of the walls was less than 14 percent before the coating was applied.
Excess moisture inhibits bond between coating and surface.
4) Adequate drying time was not allotted between coats of Amercoat
No. 78. The inspector reported that the two finish coats were applied
during the same day.
These contractor omissions would have contributed significantly
to an unsatisfactory coating application had the surface been properly
prepared initially. However, the surface void problem overshadows these
considerations.
A last item evaluated by NFIC personnel regarding the Amercoat No.
78 coating concerns the final inspection techniques employed by the
inspectors and consulting engineers. The consulting engineers maintain
that the inspector was told to perform a low voltage holiday check on
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the completed coating prior to final acceptance. The inspector stated
that though such equipment was available on site, he was never instructed
to use it on the masonry walls. When the consulting engineer's representative
was questioned as to the technique involved with the low voltage
holiday detection system on masonry or concrete, he stated that one pole
of the detector is connected to a reinforcing rod in the structure and
the opposite pole to the wet sponge used to scan the coating surface.
Sufficient moisture exists in the concrete block or concrete structure
to complete the electrical circuit should a coating imperfection be
detected.
NFIC personnel discussed this procedure with the technical development
personnel at Ameron Products. They stated that low voltage holiday
detectors are not recommended for inspection of Amercoat No. 78 coatings
on any material surface. Only high voltage (15,000 volt) spark test
equipment is recommended for such testing.
Question No. B-3 :
"It has been suggested that the modified trickling filters (Nos. 4,
5, and 6} will not operate at their designed capacity. We would like
a determination as to whether the filters can operate at their full
capacity. If filters Nos. 5 and 6 can operate at full capacity for
any length of time, could the effect on the outside walls of these filters
be the same as on filter No. 4?"
Discussion
The plant operating personnel were specifically questioned by NFIC
personnel on repeated occasions as to whether the filter units Nos. 4, 5
and 6 have operated and will operate at their design capacity (it was
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assumed that design capacity means the maximum hydraulic capacity of
24 MGD per filter). The plant personnel repeatedly answered that the
units could perform at rated hydraulic capacity and that acceptable BOD
removals of 65-70% through the filters were routine occurrences. In
general, these personnel appeared satisfied with the wastewater treatment
being obtained by the units. They also stated that at no time were
filters Nos. 5 and 6 run at reduced flow rates to "cover" for any
leakage problems with the filter walls. The filters are operated to
meet the treatment demand on plant.
During the site visit, only filters Nos. 5 and 6 were operating.
Filter No. 4 was down due to repairs to the structural members of the
rotating distribution arms. The sewage flow rates through the plant
were quite low, in the range of 10-16 MGD. The speed reducers on the
variable speed pumps which supply filters Nos. 5 and 6 were adjusted
to a setting of approximately 1300 rpm which corresponds to a pumping
rate of approximately 13 MGD. Visual observation of the spray distri-
bution patterns atop both filters indicated that an even pattern of liquid
was being applied to the filter media, all distribution pipe ports
were open and spraying wastewater, and the spray pattern was reaching
the inner wall surface. Visual examination of the exterior wall surfaces
revealed several leakage spots on these walls also. The leakage was
by no means as severe as that exhibited by filter No. 4.
It is logical that during the canning season, when plant flow rates
are at a maximum and all filters must be run at higher application rates,
more wastewater per unit time will be splashed against the interior wall
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surfaces of the filters. Wall leakage which exists under low flow
conditions will be magnified by increased flow rates, but it was not
possible to ascertain to what degree. The Sikaflex lining material
utilized on the interior walls of filters Nos. 5 and 6 appears to have
significantly reduced the leakage problem. Although filters Nos. 5
and 6 have been in operation one year less than filter No. 4, it would
appear that leakage will not be as great as on filter No. 4.
The design for these trickling filters and recirculation pumps
systems did not include any flow measuring devices. After the primary
effluent flow meters, there are no downstream flow measuring devices
for the secondary treatment system. Without such devices it is not
possible to accurately determine the flows being applied to each trickling
filter, the recirculation rates, or the relative flow split between
the old and new trickling filters. It was not possible during the time
available for this evaluation for NFIC personnel to accurately determine
if the specified hydraulic capacities can be achieved by the filters
themselves and/or their attendant pumping units. However, there was no
reason to believe that the filters could not be operated to full capacity.
The filters may not be operated at maximum capacity at all times due to
the cost of the energy required to lift the wastewater to the top of the
filters. A portion of the wastewater is currently treated in the three
6-foot depth trickling filters.
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Question No. B-4
"We would also like a determination as to what effect the effluent
leakage will have on the structural strength of the outside concrete
block walls of filter No. 4."
Discussion
The organic acids contained or generated in the leaking sewage could
have the effect of attacking and leaching the mortar joint to the point
where only the silicon remains. The wetting and drying of the rebars
exposed to oxygen would accelerate corrosion of the bars and weaken
adherence between the concrete grout and rebars. However, this could take
a number of years before it would significantly affect the structure.
A review of the construction details shows vertical rebars every
4 ft. around the perimeter of the filter and the holes in the block
filled with concrete grout. This in effect constitutes a reinforced
concrete pillar running the height of the wall every 4 ft. This pillar
is tied into the existing foundation wall by drilling and grouting at
the bottom and given support at the top by a reinforced concrete cap
beam that runs around the entire filter, tying it together at the top.
Details of the wall construction are shown by Drawing Sheet No. S 7
trickling filters Nos. 4, 5, 6 sections.
As determined by a review of the drawing and construction pictures
and questions of inspectors and the resident engineer, the walls were
constructed as per specs and drawings. However, as previously discussed
in Question B-2, the leakage is a result of design error.
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Question No. B-5
"In connection with B.4 above, we would appreciate a determination
of the ability of the existing concrete wall and foundation of filter
No. 4 to withstand the additional weight resulting from the effluent
leakage. This is important since the concrete block walls were built
on the old filter foundation."
Discussion
A maximum additional weight due to absorption of the leakage was
computed to be about 200# per lineal ft. or 16.67 #/lineal in. or
2.08 #/sq. in. on the old concrete foundation.
This would increase the loading from 13.02 #/sq. in. to 15.1 #/sq. in.
A review of the "Soils Investigations Report" by J. H. Kleinfelder
and Associates, indicates the soil bearing capacity will easily with-
stand the additional loading.
It is our opinion that there is sufficient design safety factor to
absorb this additional loading without significant impact.
Inspection of the foundation walls of filter No. 4 that is already
loaded with the additional weight shows no sign of weakening.
Question No. B-6
"In view of the leakage of the concrete block walls, we would
appreciate knowing whether cement blocks are generally noted for their
ability to withstand absorption. In addition, we would appreciate any
comments which you may have as to whether there is a less costly and
more effective way to construct high trickling filter towers."
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Discussion
Part A - Concrete blocks of the expanded shale type specified for
this contract are not noted for their ability to withstand absorption.
To verify the extent of absorption which can be expected from a typical
block, portions of a sample block from the job site were obtained during
the NFIC site visit. These samples were returned to the NFIC-Cincinnati
laboratories and subjected to the ASTM testing procedures for water
aborption. ,The additional weight due to absorption is discussed in
Question No. B-5.
Part B - An alternate to the masonry brick for constructing a high
trickling filter tower wall is to utilize a structural steel support
skeleton with corregated fiberglass panels for wall sheeting. The
advantages of such an installation include relatively low weight, ease
and speed of construction, and relatively low cost. The disadvantages
include poor aesthetics, leakage at joints, and the potential for cracking
of the fiberglass due to ultraviolet radiation exposure.
To overcome the ultraviolet and aesthetics problems, a sandwich
wall construction has been utilized on some filters. The interior wall
surface is constructed of regular fiberglass below the filter media
surface and special ultraviolet resistant fiberglass above the media.
The exterior wall surface can be pebble board, rough hewn plywood, etc.
These walls are light-weight but considerably more expensive.
Another alternate method is to pour monolithic reinforced concrete
walls. Advantages of this method include aesthetics and durability.
Disadvantages include increased weight, forming costs and labor time,
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and overall cost. However, since there is little horizontal load,
the method is not justifiable.
A high wall trickling filter was built in Ontario, Oregon using
double T prestressed reinforced concrete sections. There are no leaks
and the cost was equivalent to fiberglass plus steel framed walls.
This type of construction may not have been compatible with the Stockton
plant due to the weight limitations of the existing foundation.
The masonry brick alternate chosen for this particular contract
combines low wall weight with high aesthetic value. Its major dis-
advantages are time of construction and the obvious leakage problems
encountered. The latter problem can be minimized with the appropriate
choice and/or application of wall sealing compound.
Of the four possible methods of wall construction discussed, the
concrete block alternative was probably the least costly at the time of
the original design.
Question No. B-7
"We observed that the recirculation pumps for the trickling filters
make a tremendous thudding noise when they are turned off. In addition,
it was stated that the pumps were continually going out of operation.
One of the reasons given was that the motors on the trickling filter
recirculation pumps were operating at a higher amperage than they were
designed. We would appreciate an evaluation of the significance of the
pump problems and a determination of the effect the high amperage will
have on the pump motors." -
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Discussion
Part A - The "thudding" noise was heard by the NFIC personnel.
Not only is the noise very loud, but the entire filter distribution
structure and surrounding ground surface tremble when the noise occurs.
The problem can be traced to the two 30-inch check valves installed
on the discharge pipes from recirculation pumps Nos. 5 and 6 (Section 1/M2,
Contract Drawing M2). When the recirculating pumps shut off, back
pressure against the valve leaf plates forces the plates against the
valve seats with the resulting noise and vibration.
The following contract specification details all check valves used
in this contract: Page C56, Section C7-Piping and Pipelines,
Subsection C7.02 Materials
"(8) Valves
(b) Check Valves. Check valves shall be double-leaf, swing
type valves with flat faces for mounting between two pipe flanges.
Leafs shall be spring loaded. Valve body shall bear on flange faces
of adjacent piping and not on cement-mortar lining. Valve shall
have cast-iron bodies with aluminum-bronze plates. Trim including
stops, pins, and springs shall be 316 stainless steel. Resilient
seal shall be Buna N synthetic rubber. Valves shall be Mission Duo-
Check or equal".
The actual installed 30" check valves at this location are MB-12-5081-SF
units produced by Gulf Valve Company of Houston, Texas. NFIC personnel
discussed the installation and apparent problems with company representatives.
They offered the following possible causes for the noise and vibration
problems:
1) Valve installed improperly
2) Insufficient spring tension
3} Improper design of structure
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Each is discussed herein.
1) The leaf check valve must be installed in the horizontal pipe
with the leaf shaft in a vertical position. If the shaft is horizontal,
the lower leaf tends to fall by gravity to its seat position, whereas the
upper leaf is retarded by both gravity and the spring tension. Unequal
seating of the leaves occurs.
2) In some installations, the normal tension springs supplied
with the valve units are insufficient to retard the leaf closing under
backflow conditions and the leaves close with substantial force against
their seats. Gulf Valve Company personnel said they would be agreeable
to send the contractor heavy duty springs to replace the existing springs
if these will remedy the problem. They have made similar modifications
before.
3) In this particular structure configuration, recirculation pumps
Nos. 5 and 6 directly oppose each other. It is conceivable that in
addition to the static water pressure head acting on the check valves,
the discharge pressure of the opposing pump is being transmitted at
least in part, across the structure to act against the opposing check
valve. This additional pressure would tend to counteract the retarding
springs of the valves. However, the design engineers have equipped the
pump's discharge piping with 60° downturned fittings, apparently in an
attempt to minimize this effect.
It would be possible to evaluate the effect of opposing pumps on
the check valves by-operating only one of the pumps at a time, switching
it on and off, and monitoring the noise and vibration level at the
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corresponding check valve. Both pumps would then be operated, alternating
their on-off cycles, and the noise/vibration levels re-evaluated. The
static water level in the structure should be maintained constant in
both test phases by operating the original recirculation pumps Nos. 1, 2,
3 and 4. If a substantially higher noise/vibration level was obtained
with the pumps in the alternating operation mode, then it could be concluded
that the check valves are being influenced by the discharge pressure of
the opposing pump. Additional discharge baffling and structural changes
would be necessary at that point.
Whatever the cause of the check valve malfunction, it is imperative
that it be remedied quickly. Both structural damage and damage to the
vertical pumps and attendant piping will occur if this problem is left
unattended.
Part B - The pump operational problems alluded to in this question
pertain to the new recirculation pumps Nos. 5 and 6. In discussions with
the plant operating personnel, the consulting engineers, and the inspectors,
it was mutually agreed that pump No. 5 has repeatedly thrown the circuit
breakers on its electrical system requiring manual restart of the pump by
the plant operators. This situation occurs several times per day,
especially during the warm weather periods.
The consulting engineers mentioned that they have this problem
under consideration and are currently negotiating with pump suppliers,
Johnston Pump Company of Glendora, California for correction of the
situation. The consultants suspect that the pump{s) were supplied with
the wrong pitched impellers. Johnston counters with the suspicion
that the trickling filter distribution structure was designed incorrectly,
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the resulting effect being flow patterns which create vortexing at the
suction of the pump. The consultants did acknowlege that pump No. 5
draws approximately 15 amperes more than pump No. 6 under theoretically
similar pumping conditions.
Each of the above-mentioned conditions, i.e., the possibility of
improper impeller pitch and that of suction vortexing could result in
excessive current being drawn by the pump motors. If the current drawn
exceeds the rated amperage of the motor, the circuit breaker will throw
out. Any modification to the circuit breaker to increase its amperage
above that of the rated amperage of the pump motor so as to minimize
the pump shut down problem would only disguise the operational problem
and lead to a decreased motor life. NFIC personnel were assured by
plant operating personnel that no such modification has been made.
Continued operation of the pumps at the higher amperage levels will
cause a breakdown in the motor winding and insulation. When this
occurs, the unit will have to be replaced.
It was not within the scope of this evaluation for NFIC personnel
to determine the cause of the pump malfunction, only that the problem
existed. It does exist and all parties questioned acknowledged it.
It is recommended that the current discussions between the consulting
engineer and pump supplier be accelerated and remedial action initiated.
In addition to the incorrect pump impeller pitch and suction vortexing
possibilities currently being considered, the hydraulic profile for the
overall trickling filter distribution structure/dual 60" conduit line/
secondary sedimentation tank distribution structure configuration should
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X1
also be re-evaluated over the wide range of flow conditions which exist
at this plant. Extremes in raw sewage flow rate range from 35-40 MGD
during the three-month summer canning season down to 10-15 MGD during
the non-canning season. Recirculation ratios can also be varied over a
wide range. These hydraulic load changes will affect the flow paths
within the recirculation distribution structure and the operating character-
istics of the recirculation pumps.
The pump motor cut-out problem discussed herein, will accentuate
the valve noise/vibration problem discussed in Part A above.
Question No. B-8
"The doors to the main electrical substation which carry over 12,000
volts are continually left open. We would like to know whether this
situation violates any State or Federal safety requirements and what
effect, if any, this would have on the equipment located in the
substation."
Discussion
The Federal requirements for electrical safety are regulated by
the National Electric Code; the State requirements are specified in
Title 8 of the California Administrative Code. The CAL-OSHA program is
enforced by the California Division of Industrial Safety. Both Codes
are violated if access to unauthorized personnel is not controlled by
means of locked doors, walls, screens, fences, or other approved means.
If access is controlled, the fact that the doors are left open does not
in itself constitute a hazard or safety violation.
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The plant site is fenced, however access to the site is not
controlled, as the gate is left open. The electrical substation is not
fenced or isolated from personnel on the plant grounds. Since access
is not controlled, if the doors are continually left open, then both
Codes are violated in our opinion.
Equipment deterioration will occur due to dust and moisture.
If the doors are left open, this deterioration may be accelerated.
Question No. B-9
"A total of 43 change orders have been initiated by the contractor,
Caputo-COAC, in the modification of the trickling filters. These change
orders have been approved by the resident engineer and the City, but
they have been only recently submitted to the SWRCB for approval. We
would appreciate a technical determination of the acceptability of these
change orders and a determination as to whether the work included on
the change orders has actually been performed. In this regard, it should
be noted that the SWRCB has assigned a civil engineer, Mr. Joe Rodriquez,
to review the validity of the change orders."
Discussion
As previously discussed under Question No. A-5, Mr. Rodriquez of
the California State Water Resources Control Board is conducting an
extensive review of all change orders submitted by the City of Stockton
on this project. Any parallel investigation of them by NFIC personnel
would be redundant. NFIC review of Mr. Rodriquez's report to the Western
Area Audit Group upon completion of same is desirable.
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Question No. B-10
"An early inspection of the trickling filter walls indicated that
"the walls of subject filters reveals there, are joints that are not 'full
joints.1 It was also found that the incidence of voids in the walls is
high." The contractor promised to correct the deficiencies, however,
plant personnel indicated that these corrections were not fully accomplished.
In view of the leakage which has occurred on filter No. 4, we would like
a verification as to whether the above deficiencies were corrected."
Discussion
NFIC personnel conducted visual inspections of the exterior walls of
trickling filters Nos. 4, 5, and 6. These inspections revealed that the
walls of filters Nos. 5 and 6 were essentially free of open mortar joints
between the masonry bricks. The walls of filter No. 4 did have numerous
open mortar joints, the cause of which could not be accurately determined
due to the fact that the filter had been in operation for over a year.
Possible explanations of the open joints include:
1) The joints were not completely mortared during construction.
2} The mortar grout has washed out of the joints due to leaching
of the cement binder by leaking wastewater.
3) On the portion of the wall of filter No. 4 where the Xypex
waterproofing compound test patch was applied, it appears that the mortar
has been chiseled in several locations. City personnel stated that on
severe leak spots the Xypex material is applied in crystalline form and
physically driven into the area. This technique may account for the open
grout joints observed in this particular wall area.
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NFIC personnel also visually inspected the visible portions of the
interior wall surfaces for filters Nos. 4, 5 and 6. Since the trickling
filter plastic media was completely installed in these filters at the
time of site visit, the inspection was limited to the upper 3.5 feet of
the wall surface. No open joints were noted during this inspection on
filters Nos. 5 and 6; open joints were found in filter No. 4.
The open joints noted on the exterior wall of filter No. 4 were
discussed with Mr. Paul Prout of the City of Stockton, Department of
Public Works. He acknowledged the existence of the open joints and
stated that any corrective action to them was being delayed until a
decision could be reached on the entire filter wall leakage problem.
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C. Building Additions and Modifications
Question No. C-1
"The contractor has continually failed to follow approved plans
and specifications in the placement of his concrete. For example, the
contractor has cured his concrete with a curing compound rather than
the water cure method required by the specifications. It was also
noted that some of the poured concrete did not meet the minimum com-
pressive strength of 3,000 pounds per square inch at the end of 28 days
as required by the specifications. Additionally, the concrete used in
the project has failed to meet the 0.04 percent maximum allowable shrinkage
>
requirement included in the specifications. Further, the contractor has
not obtained advance approval for his rebar layout prior to the pouring
of concrete as required by the specifications. We would like an opinion
of the acceptability of the poured concrete in light of the contractor's
failure to follow the approved plans and specifications."
Discussion
A review of the concrete specimen data, those that failed and those
that passed specified criteria, leads the writer to express the opinion
that the poured concrete is acceptable and meets strength requirements.
The use of a curing compound is an acceptable method in curing the concrete
and can be used in place of the water cure method after 72 hours, if
approved by the resident engineer.
Pertaining to the item of advanced approval by the engineer of reinforcing
steel (rebar) layout drawings submitted by the contractor, all persons
interviewed agreed that it was not uncommon on this project for the con-
tractor to place rebars and pour concrete without having received prior
approval of submitted drawings.
-------
46
The following excerpts from the contract specifications state the
conditions of pre-approval of rebar placement drawings:
Pages C 24-25, Section C-3 - Concrete Work, Subsection C3.02 Material
"(3) Reinforcing Steel
Reinforcing steel shall consist of deformed bars of the size
called for on the drawings. Steel shall conform to ASTM 615-40.
Deformations shall conform to ASTM A305, A408. Mill certificates
showing conformity with these requirements shall be furnished to the
engineer for each melt. Wire reinforcements shall conform to
ASTM A!85.
Placing drawings and bending schedules shall be submitted to
the engineer for review. Reinforcement shall be carefully formed
as indicated on the drawings. Stirrups and tie bars shall be bent
around a pin having a diameter of not less than three times the
diameter of the bar. Except where specifically indicated otherwise on
the drawings, bends for other bars shall be made around a pin having
a diameter of not less than 8 bar diameters. All bars shall be bent
cold."
Pages B 10-11, Section B3 - Specifications and Drawings
"B3.04 Information to be Furnished by Contractor
The contractor shall furnish all drawings, specifications,
descriptive data, certificates, samples, tests, methods, schedules
and manufacturer's instructions as specifically required in the
specifications, and all other information as reasonably may be
required to demonstrate fully that the materials and equipment to
be furnished and the manner of performing the work comply with the
provisions and intent of the specifications and drawings. If the
information shows any deviation from the contract requirements, the
. contractor shall, by a statement in writing accompanying the informa-
tion, advise the engineer of the deviation and state the reason therefor.
B3.05 Review of Contractor's Information
When review and checking for acceptability is required of
any drawings, method of work, or of any information regarding materials
and equipment, the contractor shall prepare or secure, and submit
for review at least 5 copies thereof. If the information thus
submitted indicates the material and equipment is acceptable,
the engineer will return 2 copies marked acceptable, otherwise 2
copies will be returned with an explanation of why the material
-------
'47
or equipment is unacceptable and the contractor shall resubmit the
information until it is acceptable. If the contractor wishes more
than 2 copies returned, he may submit additional copies of the
information for review, but in no event shall the contractor submit
more than 7 copies of each item."
Page B 2, Section Bl - Definitions
"B1.15 Submi tted
'Submitted'Jwherever and in whatever manner used, means sub-
mitted to the engineer for his acceptance."
It may be argued that nowhere in the quoted specifications is it
stated that approval of rebar placement drawings is required prior to
or in advance of a concrete pour. This is an error in the preparation
of the specifications. However, prior approval of rebar placement drawings
is a common construction requirement. Advanced approval permits the
design engineer to insure that the steel to be placed truly conforms
with the intent of the design drawings and calculations. It is not uncommon
to find that the steel supplier and/or contractor misinterpreted said
intent.
The approved steel placement drawings also provide a valuable aide
to the field inspector. More detail is usually provided on these drawings
than on the original contract drawings * especially where irregular forming
and/or steel placement are required.
Finally, these drawings are a requirement of the specifications.
Their submittal with ample lead time for approval by the engineer is
the responsibility of the contractor. Contract specifications often
specify the advanced lead time required for submittal of approval
drawings by the contractor and the allowable turn around time for
approval/disapproval by the engineer. These specificaitons do not state
this and as a consequence may be negligent.
-------
48
Question No. C-2
"In constructing an auxiliary maintenance building, a large manhole
was discovered. The soils engineer for the project recommended that
the manhole be filled with concrete or pea gravel to insure that it
would not affect the loading of the building foundation. Since the
recommendation has not been followed, we would like an independent
opinion as to whether the building foundation has been adversely affected."
Discussion
The manhole referred to is poured concrete. Inspection shows no
cracks or movement of any sort. The maintenance building foundation is
about 8 ft. away at the closest point. It is of slab foundation
construction and is not likely to be affected if manhole is retained in
present condition.
Mr. Vieira, STP Superintendent, stated that since the manhole has
an existing pipe connection that leads back to the head of the plant,
they propose a future use for recirculation.
It is the writer's opinion that the maintenance building will not
be structurally affected by retention of the manhole.
Question No. C-3
"Although the degree of soils compaction included in the specifica-
tions was not always being met by the contractor, the resident engineer
has accepted the lesser degree of compaction. For example, the resident
engineer approved an 80 percent compaction on the bedding material
underneath a vitrified clay pipe although the specification called for
a 95 percent compaction. We would like a technical opinion as to whether
-------
49
this can result in any structural deficiencies and also the Region's
position in instances such as this where the contractor has not met the
approved plans and specifications."
Discussion
To answer the general question, failure to meet compaction specs
could result in structural failures depending on the situation. However,
in the case cited under the sewer bedding an 80 percent compaction vs.
a 95 percent compaction on the sandy material, we would not expect
structural difficulties as a result of the reduced compaction of the
soil. If movement of the pipe occurs, it could be detected by examining
the pipe run in question between manholes.
Question No. O4
"The resident engineer authorized the contractor to grout behind
the brick veneer around the operations building to a height of 8 feet,
instead of the full height of the brick veneer of 20 feet as required .
in the specifications. We would like an evaluation as to whether the
reduced grouting will create any safety problems."
Discussion
The brick veneer on the existing operations building is for aesthetic
purposes. The veneer is tied to the existing walls by drilling and
placement of ties. Since the cavity is grouted to a height of 8 ft.,
it should prevent any movement should a truck accidently back into it.
The reduced grouting above 8 ft. height should present no safety
hazard.
Sheet No. A205 - Typical wall section on the maintenance building
next to the operations building shows the design to be hollow backed.
-------
APPENDIX
-------
. October
TO: . _ Hr. Paul Da Falco, Jr.
Regional Administrator
. EPA, Region IX
,
FROM:. . Manager \
Western Area Audit Group .
* *
SUBJECT: : Reqtrest for Technical Assistance - . '
Interim- Audit of Stockton i>!ain Watar Quality
' Control Plant - EPA Project No. CG5DS95
* ' ' * " "
, , f "
* * *
' k'e are in tha final stages of completing our- interim audit of the .-
City. of Stockton's financial and rr.anages)ent controls over tha subject ...
EPA grant. In tMs regard, we are currently 1n tha process of re^ie^lng :
the consulting engineering flm's (Brown and Ca1d\7ell) financial records"
supporting its billings for engineering services. In addition, W3 ara
s un^arizirrg the results of our review at the City of Stockton. Upon cca-
pletion of this efforts, we will provide you with an overall briefing of
pur audit results prior to the issuance of our written report.
As discussed with you previously., it was Indicated that scsa engineering
assistance *.fould b^ required at a later date. Ha have noi-J reached the point
where this 'assistance is required,. The areas where the technical support is
required are listed on th^ attached
'.* He vfould appreciate 1t if tha assistance can b& provided and a
report of tha results furnished to us by Hovsr^bar 15., 1974. I believe that
the wori: can be expedited if the engineer or engineers assigned will initially
coordinate with rir. Gear^ Per,a of tny staff. "
' If the above tins frtuT>e3 are not acceptable or if you have qny questions
concerning this request, pi eass do not hesitate to contact me. .
TRUH4N ROHAU) BEELER
Enclosures
-------
LIST OF AREAS WHERE TECHNICAL ASSISTANCE
IS REQUIRED UNDER CITY OF STOCKTON PROJECT MO. COG0595
A. Construction of Sludqs Lagoons_
The contractor,'C. Norman Peterson Col', has completed construction of
"the sludga lagoons and the Brown-and Caldv;ell resident engineer accepted
the contractor's work'as "essentially coniplete" In April 1974. .
1.- During the course of our audit, several operational problems con- -
; .' cernlng.the sludge lagoons have been brought to our attention. V'a
.. therefore would appreciate an independent technical determination
,. as to whether the construction work completed on the sludga .lagoons
-' is acceptable and has been accomplished in accordance with-the
. approved plans and specifications. . . ... ";..'
2. -. Visual observations and discussions have Indicated that ths tels-
-. " .scopic weir in one of the sludga lagoons v;as not operating properly,
We would like to have the extent of this problem reviev^ed. If
possible, we would also like technical comments as to the.cause
of the problem and a determination as to who hau,the responsibility
to correct 1t. . ' ' - . - . .. '.-,
It was- observed that the cleanout .valves for the- sludge lagoons v?ere
.located in the pump station which- were considerably belcv? the lagoon
v;aten level. It was explained that the pumping station v.xmld-ba .-'
flooded if the cleanout valves were uncapped. In addition, .it was
suggested that the cleanouts served no useful purpose since the .
lagoon would have to be drained before any cleanout work 'could ba . .
performed. VJe would 11 ka a technical determination as to whether-
cleano'Jt valves are usable without creating a safety hazard to
personnel in the pumping, station. If this is a problem, v/a would.
appreciate a detenui nation as to whether it v/as attributable to
a design error or to the quality of construction and' how it can ba
corrected. . - '...'[ --""'.-;
4., Plant operating personnel ccjnmanfed that they were unhappy .with
. . operations of tha sludga lagoon from several standpoints. Cna of
these was that the sump 'pump was not abla to effectively rernova - " .
' sludge. Another was that the pumping station vras causing problems ..-
since 1t had a greater capacity than could actually ba used. VJa
would appreciate a technical evaluation of tho validity of" the above
probletDS and how they can be corrected. . ' .
"
5. A total of seven change orders have been initiated under the ".
C. Morgan Peterson contract and approved by the resident engineer
-------
end the city. These change orders were not submitted to the
- California State Hatsr Resources Control'Board (SU2CB) for approval
until September 4, 1974, altiib/jgh soi?4jpf^th2 char.ge orders per-
tained to worh performed in later 1973. We ivOtild appreciate a
*" technical determination of the acceptability of these change orders
and a determination as to whether the work Included on tha change
orders has actually been performed. In this regard, it should be
. noted that the 5URCB has assigned a civil engineer, Mr.-Joe Rodriguez,
. to-review the validity of the change orders. . .
*'.*-.
B- Trickl i ng Fi1 ter Hodifica.t1 ens .
The contractor, Caputo-- COAC, has completed^ all modification work on
.three trickling filters with, the exception of work applicable to five
change orders. The Brown and Caldwell resident engineer 1n a letter
.dated April 5, 1974, indicated "all Items of work required in the. .
' basic contract,..v^ere essentially complete on February. 20, 7974." '
IV. During our review, several operating problems concerning the trickling
' .filters were quite evident. In order to ascertain the full extent
of.these problems, we would like a technical evaluation as .to whether
the construction.work co/nnleted on the trickling filters is acceptable
' .'' end has been accomplished in accordance vrtth the approved plans aria
; ' specifications. > ' . ., - .,..-. . ". . j-'-
" !.''. " ' * ,..""' : "" *'"
2. There.is substantial effluent leakage and green algae .growth'on the - .
"_. . outside walk of trickling filter Mo. 4. Although this situation has
. .'".' existed for alirost one year* the leakage has not been eliminated..
. ' In'view of tha substantial problem, v:e would appreciate 2 tachninal
; datarmination as i,Q whether the problsa was tha result of poor .
construction or basic design errors. .-."'.. . -
3.- It has bean suggested that the modified trickling filters («05. 4,
/ 5, ?,nd 6) mil not operate at their designed capacity. He would
. . like a determination as to whether the filters can operate at their
full capacity. If filters Mos. 5 and 6 can operate at full capacity
for any Tength cf tirre, could the effect on tke outsida walls of
thass filters be.the sarae as on filter No, 4? ;. ;: ;\.;v ; > .' '
V ., V
4^ He would alsq liks a deterniination a$ to vvhat effect tha effluent
leakage \-ri11 hava on the structural strength of the outside concrete
block walls of fUtGr Ho. 4. - ; .;.,.'.
* "" ' * "
. 5.,- In connection v;ith B.4. above, we v~culd apprsciate a determination
of the ability of tha existing concrete v;aT1 end foundation of filter
- Mo. 4 to withstand the additional weight resulting frcra the effluent
leakage. This is Important since the concrete block walls were built
on the old filter foundation.
-------
6, In view of the leakage of the concrete block walls, we would
appreciate knowing whether cement blocks are generally noted for
their ability to withstand absorption. In addition, v?e would
appreciate any comments which you may have as to whether there
1s a less costly and inore effective way to construct high trickling
filter.tovvers. .
. ' - *
7. We observed that the recirculation pumps for ths trickling filters
nake a tremendous thudding noiss when they are turned off. In
. addition, it &as stated that the punrps were continually going out
of operation. One of the reasons given was that tha rotors on the
trickling filter rs circulation pumps were operating at a higher .
amperage than they were designed, k'a would appreciate an evaluation
. . -of the significance of the pursp problems and a dstsralaatloa'of the
" . effect tha high amperage v/1 11 have on tha punp rrotors, . ,
3, -The doors to the main electrical substation which carryover 72,000.
.'.. volts are continually, left open. We ivould like to kno« whether this
. ^ situation violates any State or Federal safety requirements and' what
effect, if any, this would have on the equiprr^nt located in tha.
. substaittdoq . . . . . . .... '.'."
9.
A total' of 43 changa orders have been Initiated by th? contractor,
Caputo - COAC, in the iTiOdification of the trickling-filters. These -.'~
"'. " change. ordei?s have been approved by .tha resident engineer and the
, .- -City, but they have been only recently submitted to tha SHRCB for '
approval.. Vie would appreciate a technical determination of tha - -
acceptability "of these change.orders and a determination as.to .whether
" " the v/ork included on tha change orders has actually been perforTned.-.-
- : In this regard* it should be noted that the SSfRCB has assigned a
.'civil engineer, Mr, Joe Rodriguez, to review the validity of tha . -
change.orders. . . . ; -. , . ...."
10... An early inspection of the trickling filter walls indicated that -
"ths walls of subject filters reveals these are joints that are not
"full joints,' It v;as also found that the incidences of voids in the
} walls is hight"** Tne contractor promised to correct the dgficlsncies,,.
hov>;ever, plant personnel indicated that these corrections wars not
fully acccsiplished. In vie1.-; of the leakage which has occurred on :
filter »io. 4, we would like a verification as to whether the above
deficiencies wara corrected, .... ;
C, Building Additions and Modifications . :./' ' ; -
The construction contract concerning the building'additions and modifi-
cations v-ork is still in process. The construction contractor is
C. S. Plumb Co. - *
-------
h
7." ihe contractor has continually ^failed 4? fallow approver! plons and
specifications in the placement of his c.o'n'cr&te. For example, the
contractor has cured his concrete with a curing compound rather them
the water cure method required by the spscifications. It was! also
noted that s.cire of the poured concrete did not rceet the minimum
cctnprrasive strength of 3,000 pounds per square inch at the end of
28 days as required by tha specifications. Additionally, the con-
crete used 1n the project has failed to m-eet the 0.04 percent maximum
allowable shrinkage requirement included In.the specifications*
. Furthers the contractor has not obtained advance approval for his
**'. ".-rebar layout prior to the pouring of concrete as required by tha
.-; specifications. He vxiuld like an opinion of tha acceptability'of -
" -. the poured concrete 1n.Tight of the contractor's failure to follow
'" the approved plans and spadfications* ; .
*** ' - * " "**"*.»
2; ."In constructing an auxiliary maintenance building, a large rcanhole ".'.
, '. was discovered. The soils engineer for tha project-recorrrrrended that
the inanhole be filled with concrete or psa gravel to insure that 1t
-.. '. v;ould not affect the loading.of the building foundation. Since the ".
". -. recofrm-sndatior. has not been followed, v/e would like an Independent .
; ' opinion-as to whether the building foundation has been, adversely
." ' affected.
3*;. Although the degree of soils compaction included 1h th-3 .specification
. .was not-always baing met: by the contractor, the resident engineer has
. . accepted the lesser degree of compaction. For example,.the resident
engineer approved an 80 percent compaction on the bedding notarial .
'., ' .underneath e vitrified clay pipe although the specification called ".
fora 95 percent conpactfon. .He would like a technical opinion es .-
': ' to-.whether this can-result in any structural deficiencies and also .
* . tha region's position 1n Instances such as this where the contractor.
has. not met the approved plans and specifications. '.".... - - .. ,'
4;'The resident engineer authorized the contractor to grout behind the
brick veneer around the operations building to a height of 8 feet,
.,: ..Instead of the full height of the brick veneer of 20 feet as required
in the specifications. Ha ivould like an evaluation as to whether
. the-reduced grouting will create any safety problems. .
-------
ear
feanua it.'ff SLOPS
li FLtTTEZ TTJV
SECTION^
SCALE: I "IOI
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SlUQQE LAGOOKS flFJO
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SLUDGE LAGOOM
SECTIONS AND DETAILS
COIL- MC CREOSOTE M^CCOKOMQS n'
WOOD P&SSZvaZS ASSGCMTICM SfEO
OF PUBLIC
CfTYOF STOCKTON. CALi
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-------
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SLUOSE LtOOONS iNO PUMP'KG STATION
SLUDGE PUMPING STATION
HEATING AND VENTILATION
DEPARTMENT OF PUBLIC WORKS
CITY OF STOCKTON, CALIFORNIA
-------
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DEPARTMENT OF PUBLIC rtOI
CfTY OF STOCKTON. C*L1FORS
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DEPARTMENT Of PUBLIC WORKS
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