HomeMy WebLinkAbout1987 CH2M Report - Rehabilitation of Well No. 5.pdfREPORT NO. 1 OF FOUR
REHABILITATION OF CITY OF RENTON WELL NO. 5
February 19, 1987
City Project CAG-070-86
'Is B.
S^ic;^r
Prepared by
CH2M HILL NORTHWEST, INC.
Bellevue, Washington
822077.AO
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REPORT NO. 1 OF FOUR
REHABILITATION OF CITY OF RENTON WELL NO.
February 19, 1987
(City Project CAG-070-86)
INTRODUCTION
Under an agreement for engineering services dated Novem
ber 25, 1986, between the City of Renton and CH2M HILL
NORTHWEST, INC., the consultant undertook to perform seven
basic tasks, which are all enumerated in Exhibit A to the
agreement. This first project report addresses Task 1, Sub-
tasks "a" through "d," Well Rehabilitation Study.
Well No. 5 has been previously evaluated by R. W. Beck and
Associates and their subconsultant. Converse Consultants.
R. W. Beck submitted a report to the City dated November
1983 (Task 1—Summary) with a November 16, 1983, report by
Converse Consultants as an appendix. A second undated re
port by R. W. Beck (Task 2—Summary Report) with a March 30,
1984, report by Converse Consultants as an appendix was also
submitted to the City.
Well No. 5 consists of an existing production casing and
screen assembly from which the pumping equipment has been
removed. The well was taken out of service in the 1960's
because it pumped sand and the water contained unacceptable
levels of H-S and manganese. The goal is to rehabilitate
the well to deliver a minimum of 1,000 gallons per minute
(gpm) of water with a quality that, after cost-effective
treatment and/or blending with water derived from other city
sources, will be suitable for delivery to water customers.
The City has provided copies of the Beck reports and field
survey data. It is agreed in the engineering contract that
CH2M HILL can rely upon the accuracy and adequacy of the
items provided to the consultant. A well inspection video
tape also has been made available. As-constructed details
of the well are shown in Converse Consultant's Drawing No. 1
included as an appendix to this report.
In the course of our work we have reviewed the Beck reports,
viewed the video tape, and held telephone conversations with
local well drillers to discuss possible rehabilitation
methods and order-of-magnitude costs. Three rehabilitation
alternatives have been developed. We have been directed by
the City that the alternative of drilling a completely new
well is not to be considered. The following sections dis
cuss the alternatives.
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REHABILITATION ALTERNATIVES
WELL REDEVELOPMENT
We recommend that the well be redeveloped. This is strongly
favored over other alternatives because the risk of damaging
the well is very low. There also are no available data to
confirm that an intensive development program has ever been
attempted. Development procedures should include surging or
hydraulic jetting, and chemical treatment.
Item
WELL REDEVELOPMENT
Estimated
Unit Cost
($)
Cable-Tool Rig and Crew
Chemicals (polyphosphate)
100/hour
600
Estimated Estimated
Number
of Units
115
1
TOTAL
Cost
($)
11,500
600
12,100
Note: All costs quoted in this report are order-of-magnitude
and primarily for comparing alternatives. They do not
include engineering, administration, or other charges.
The well development work would be primarily to reduce the
sand content to acceptable levels. It would not include
test pumping to determine the reliable capacity of the well.
If well development fails to reduce sand content to accept
able levels, then structural changes to the well must be
considered.
REMOVAL OF EXISTING SCREEN AND RISER AND REDRILLIN6 LOWER
SECTION OF WELL
Removing the existing, apparently improperly sized screen
sections and/or sand pack and replacing them with more
appropriate ones is an excellent rehabilitation alternative
if it can be achieved.
Removal of the 12-inch screen and riser could be attempted
by pulling with a pipe smaller than 12 inches in diameter,
sand locked inside the 12-inch screen assembly. Angular
sand particles placed in the screen assembly form the struc
tural connection between the two pipes. A rubber packer or
strips of burlap attached to the lower end of the pulling
pipe holds the sand in place. Two or three slots are cut
near the end of the pulling pipe so that the sand joint can
be loosened by backwashing if the attempt is not successful.
After removing the existing screens, the well bore below the
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20-inch production casing would be redrilled, geophysically
logged, and properly sized screens and gravel pack (if re
quired) installed.
There are two advantages to this method: (1) if successful,
the chances of constructing a sand-free well of the desired
yield are good; (2) the cost of an unsuccessful attempt is
relatively low (approximately $6,500).
There is a risk, however, that if the 12-inch screen assembly
begins to move it could become lodged at a higher elevation.
If this occurs, the well could be damaged beyond repair.
REMOVAL OF EXISTING SCREENS
Item
Removing screen
Redrilling borehole
Mob-demob
Twelve-inch stainless steel
continuous-slot screen
Twelve-inch steel riser
12 X 20 neoprene packer
assembly
Sand pack
Bentonite pellets
Miscellaneous
Development
Geophysical logging
Estimated
Unit Cost
($)
100/liour
iOO/hour
1,500
175/foot
17/foot
500
5/foot
30/bucket
100/hour
2,500
Estimated
Number of
Units
50 hours
50 hours
1
40 feet
70 feet
100 feet
2 buckets
40 hours
1
TOTAL
Estimated
Cost
($)
5,000
5,000
1,500
7,000
1,190
500
500
60
1,000
4,000
2,500
28,250
Unsuccessful Attempt
Removing screen
Mob-demob
100/hour
1,500
50 hours
1
5,000
1,500
TOTAL 6,500
INSTALLATION OF 8-INCH SCREEN ASSEMBLY INSIDE EXISTING
12-INCH SCREENS AND RISER
Setting a new 8-inch screen and riser assembly inside the
existing 12-inch screens and riser pipe has been suggested
as a rehabilitation alternative by R. W. Beck/Converse Con
sultants. Converse Drawing No. 4 is attached as an appendix
to this report. We agree that this is a legitimate alterna
tive. The screen and sand pack should be sized only after
obtaining a sample of the sand entering the well bore. This
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sample would be available if the well redevelopment alterna
tive was attempted first. If the well redevelopment alter
native is not considered, then the well should be pumped to
obtain a sand sample for grain size analysis.
Every effort to redevelop the lower screened section should
be made prior to installation of the 8-inch screen assembly
because it reportedly contributes 55 percent of the well
yield (R. W. Beck/Converse). Results presented in the pre
vious investigations indicate that the fine sand bed from
359 to 365 feet below land surface (reported) is a likely
source of sand for the lower screen located between 366 and
376 feet below surface. Converse Consultants report the
lower 5 feet of the deeper screen is also plugged and could
not be developed.
The 1984 Converse report contains (pages 10 through 14) a
discussion of the factors to be considered and the risks to
be assessed in installing a new 8-inch screen within the
existing 12-inch screen. Their discussion should be re
viewed by the City before this alternative is attempted.
Item
NEW 8-INCH SCREEN
Estimated
Unit Cost
($)
Setting screen
Mob-demob
Eight-inch Stainless steel
continuous-slot screen
Sand pack
Bentonite pellets
Development
Miscellaneous
8 X 20 neoprene packer assembly
100/hour
1,500
90/foot
5/foot
30/bucket
100/hour
500
Estimated
Number of
Units
50 hours
1
30 feet
100 feet
2 buckets
40 hours
Estimated
Cost
($)
5,000
1,500
2,700
500
60
4,000
1,000
500
TOTAL 15,260
WATER QUALITY OTHER THAN SAND CONTENT
Samples of well water obtained by Converse Consultants in
November 1983 and tested by Lauck's Testing Laboratories
showed high iron, manganese, and turbidity. The possibility
of a reduction in each by more continuous pumping is men
tioned in the R. W. Beck Task 1 report. Further review of
the well water under actual pumping conditions was recom
mended by Beck. The Task 2 report on pages 2 through 10
contains a detailed discussion of water quality, other than
sand content, and possible treatment methods. This section
should be reviewed by the City prior to selection of treat
ment alternatives.
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No further water samples have been taken since those of
February 1984 Which are the basis of the above-mentioned
discussion^ Under these circumstances we are unable to make
treatment recommendations and suggest that this element of
work be postponed until the well is rehabilitated and tested.
At that time more water samples can be obtained for
examination.
SUMMARY
This report describes rehabilitation alternatives to reduce
the sand content of water produced from Well No. 5. The
dilemma faced in well rehabilitation design is the uncer
tainty of the exact elevations and grain sizes of geologic
materials recorded on the well log. This problem is not
uncommon in water well construction and is caused by mixing
of materials downhole and uncertainty of elevation datum.
There is no guarantee that the the alternatives presented
will lower the sand content of the discharge water to
acceptable levels and/or achieve the minimum desired pumping
rate of 1,000 gpm. The first step of the rehabilitation
effort should be an earnest attempt at removing sand from
the formation by surging or hydraulic jetting and chemical
treatment. If development fails to lower the sand produc
tion to acceptable levels, either the existing 12-inch
screen and riser assembly must be removed and replaced or a
new 8-inch screen and riser assembly must be installed
inside the existing 12-inch assembly. The relative merits
of these alternatives and their order-of-magnitude costs are
summarized below.
Alternatives
Chances of
Successfully
Completing
Alternative
Chances
of Lowering
Sand Content
and Maintaining
Yield of
IfOOP gpm
Chances of
Damaging
Well
Approximate Cost
($)
(a) Redevelopment
(b) Remove existing
screen and install
12-inch screen and
riser
High
Moderate
Moderate Very Low 12,000
High Moderate (unsuccessful) 6/500
(if successful) (successful) 28/250
(c) Eight-inch liner
screen and riser High Moderate Low 15/000
Note: Costs are order-of-magnitude and do not include engineering/ administration/ or
other charges.
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RECOMMENDATIONS
We recommend that the well be redeveloped (Alternative 1).
If this is unsuccessful, then the existing 12-inch screen
and riser pipe should be pulled and a new 12-inch screen
assembly installed (Alternative 2). We recommend Alterna
tive 2 because the moderate risk of failure of Alternative 2
is offset by the higher probability of successfully reducing
sand and maintaining yield.
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