HomeMy WebLinkAboutRAM 001 00 - Dewatering Plan - ResponseRequest for Approval of Material
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Catalog Cut Approved Yes No
CAG-15-134 STPUL-1131(002)
Logan Ave N - Airport Way to N 6th Street - Project King
Johansen Excavating, Inc.
7-08SPDesigned Groundwater Services
10/13/2015
Designed Groundwater Services
001.00
B10 Dewatering Plan Designed Groundwater Services 7-08SP
C6 Dewatering Plan Designed Groundwater Services 7-08SP
Dewatering PlanA47
Please see the below remarks.
Widener & Associates reviewed RAM #1 and made the following comments:
Based on ground water test results, ground water cannot be discharged to waters of the state and must be discharged to
the sanitary sewer system. This will require a tank to filter settleable solids. The dewatering operation will be adapted to
project conditions as needed to stay within the flow limits of the discharge permit. W&A will periodically sample the ground
water during dewatering operations and advise if the sample results indicate changes may be made to the dewatering
system. The dewatering system shall be shut off when it is no longer needed.
8
8
8
Justin Sencer
11/23/15
1109 First Avenue, Suite 501, Seattle, Washington 98101 Phone: (206) 588.8200 Fax: (206) 588.8201
13Oct15
#MJA 4222.73
To: Gary Fors, Designed Groundwater Services LLC
CC: Jamie Mitchell, Designed Groundwater Services LLC
From: Frank Pita, PE, LHG
RE: Submittal for Temporary External Dewatering of a Portion of the Logan
Ave. N. Project, Renton, WA
Background & Conclusions
At the request of Designed Groundwater Services (DGS) management, McMillen Jacobs
Associates (MJA) is preparing this dewatering submittal to externally dewater specific
portions of the pipeline project in Logan Ave. N.
To arrive at this design of the external dewatering system; both DGS and MJA used the
drawing profiles on contract sheets and the geotechnical data in the project’s geotechnical
report #2013-063-21 Task 200 by HWA GeoSciences, Inc. (HWA). The report was
dated 8Jan15. The investigation advanced seven borings over the project site; all to a
depth of 21.5 feet each. Two of the borings were completed as monitoring wells.
The geotechnical data used for the dewatering system design, obtained from the report is
as follows;
The upper 2.5 to 7.5 feet of the soil column is FILL consisting of clean to slighty
silt SAND with occasional gravel, and
The remainder of the soil column is interbedded layers of clean or silty SAND
and organic or elastic SILT.
From a dewatering design standpoint; the boring logs indicate that the dominate soil
material that will produce water flow to the trench is an SP to SM type material. The
groundwater level in Figure 4 of the geotechnical report starting in October and going
through May is about the level of 4.5 to 6.5 feet. Therefore, a depth of 5 feet will be used
in the design model.
The pipe depths that require external groundwater control are between 7 and 10 feet in
depth and discussions between the General Contractor and DGS have estimated that
approximately,
800 lineal feet of stormwater pipe and
500 lineal feet of waterline fits this case.
1109 First Avenue, Suite 501, Seattle, Washington 98101 Phone: (206) 588.8200 Fax: (206) 588.8201
The approximate location of this external dewatering is shown on the marked up contract
drawings shown in Appendix A. Other portions of the trenches that are only 2 feet or less
below the water table will control the water using sumps if necessary.
As a result, DGS and MJA have concluded that a vacuum well dewatering system is the
proper external groundwater control approach for these variable soil conditions. As a
note, DGS has previously installed and operated vacuum dewatering systems in this area
for Boeing, the new Hotel near the Lake, and for the Renton Landing development with
good success, so therefore this system is proven to perform well in this area.
Vacuum System Discussion
A vacuum dewatering system uses a combination of gravity and the vacuum to move or
lower the water to the closest suction well. Typically each well can remove up to 35
gallons per minute (gpm) depending on diameter, length and setup. The amount of water
per well is dependent on the soil type and the nearness of the recharge source. From
MJA’s experience in this type of soil, the vacuum wells need to be 10 horizontal feet
apart or less and extend approximately 8 to 10 feet below the bottom of the excavation at
this spacing. If the wells are closer, then the well can be less than 8 feet below the
proposed construction. The key to the design is the slope of drawdown curve in the
aquifer material. The finer the material the steeper and more localized the curve.
The vacuum level that can be generated by the pump and the head loss in the system that
the water is moving through controls the vertical distance a vacuum pump can lift. Most
existing older textbooks indicate that approximately 16 feet vertical is the maximum
vertical draw of water due to the majority of the pumps available on the market at the
time the book was written. This vertical lift was and is true until the Thompson Pump
Company began to market their high air handling, large water volume and high vacuum
capability pump that can move up to 2,000 gallons per minute (gpm) of water while
generating up to 29 inches of Mercury (Hg) vacuum. McMillen Jacobs Associates (MJA)
has measured water being lifted over 24 feet on projects in the Seattle area. Other pumps
will not do this. Therefore, this design requires that a properly functioning Thompson
pump be generating the vacuum.
On this project, it is recommended that the suction wells be installed by jetting them into
place. The jet water washes the fines from the area where the screen is to be placed and
therefore improves the well characteristics by developing the filter pack around the
screen. If a void is present around the jetted hole, then Colorado Round sand is poured in
to seal the area and to create a filter above the screen. The well screen slot size is 20,
which matches the package filter sand material exactly. The top of the hole is sealed with
bentonite. The State of Washington (WAC 173-160) regulations require that all suction
wells be installed and abandoned by a licensed water well driller. Therefore, a licensed
water well driller must be onsite to oversee or perform the work at installation and
abandonment.
1109 First Avenue, Suite 501, Seattle, Washington 98101 Phone: (206) 588.8200 Fax: (206) 588.8201
Model Analyses
To further evaluate the spacing and depth of the wells, MJA used a European developed
computer program that allows the modeling of a vacuum system (please note that all units
are in metric). Details about the program are presented just after the model results.
MJA’s approach is to assume the entire soil column is this higher permeability soil and to
design for this highest probable permeability at the deepest portion of the trench (most
drawdown and vertical lift needed). The amount of water removed per point is fixed at a
safe level for a typically installed point.
From the HWA geotechnical and hydrological data available, MJA concluded that the
worst case hydrologic profile to be analyzed will be a system consisting mostly of SP
material. Therefore, we use the highest typical value for the range. Then, other less
permeable material, like SM & GM, should also be dewatered as well.
Therefore, from the following table, MJA obtained the permeability range for an SP type
material, which has the highest rate of 2x10-3 meters / second (m/sec).
Hydrogeology Model Case / A Portion of the Trench
The modelled case is for a fine clean SAND (SP). The parameters entered are as follows;
Spacing = 10 feet (3 meters),
Well depth = 22 feet (7.0 meters) (note: a well point set up is a 2” (50mm)
diameter point that is 3 foot long (1 meter) and attached to a 1.5” diameter riser
pipe to surface. The 3 foot long section has the slots in it that let in the water into
the system. The design has the bottom of the point at approximately 20 feet
below surface. The maximum drawdown that can occur at the point is almost 20
feet, (the bottom of the point because it has drawtube to the bottom of the slotted
point.)
Well diameter = 2 inches (50.0 mm)
Pumping rate = 9 gpm (0.25 liters/sec.)
Groundwater level = 5 feet (1.67 meters)
Max Trench depth = 15 feet max (4.6 meters)
From Powers etal / 2007
1109 First Avenue, Suite 501, Seattle, Washington 98101 Phone: (206) 588.8200 Fax: (206) 588.8201
Permeability (assumed) for variable soils = 2 x 10-3 m/sec, which is at the upper
range given in the table above. This builds in a factor of safety due to some of the
soil being an SM material.
Model Results: the analysis results show that the drawdown contours are below the level
of the bottom of a hypothetical 15 foot deep trench while each well is pumped at 9 gpm.
If the wells are pumped at 12 gpm, the water drops an additional 3 feet at the trench, so
the system, as designed, has the enough capacity to account for variability in the aquifer
parameters. Because of the layering of the soils, there still may be seepage into the
excavation from the perched layer of SP material that is above the SM material even with
the dewatering, especially if one side is left open for access. Therefore, the contractor
should be prepared for some sumping.
Also, if the soil is more permeable, than the pumping rate from each point will be a little
more, but in the current design the points have more capacity, so this approach should be
satisfactory. If the soils are not this permeable or if the water table is lower, then the
drawdown away from the point will be greater and the amount of water from each point
can be reduced so that drawdown at the point is less and the screen stays submerged.
Because of the layering of the soils, there still may be seepage into the excavation from
these layers even with the dewatering, especially if it is only done on one side.
MJA prefers vacuum systems because the closeness of the spacing and the adjustment of
the pumping rate from each well allows for more variability in the soil.
Conclusions / Recommendations
Since we have limited hydrogeologic data on the subsurface conditions, it may become
apparent during the installation and early operation that some modifications could be
made to the layout to improve its performance, but this is our first approach based on the
data we have available. This design is designed such that it has enough vacuum power to
remove the water down to bottom level of the wells and if they pump for several days
they will remove all the nearby water faster than in can seep back into the area.
The following is our recommended approach with the locations shown on the marked up
figures at the end.
The suction wells shall be 2.0-inch diameter, 3 feet long, 20 slot screen and jetted
on approximately 10-foot centers, so the bottom of the point is approximately 21
to 22 feet below the header elevation.
Some water entering the excavation can be removed by vacuuming the water
through a filtering technique (fabric, gravel around a bucket) into the vacuum
system. Note that the tip of the vacuum system must be submerged so that the
system does not allow air to enter. This can be accomplished by valving down the
sumping system.
No filter material will be used because of the jetting into place of the suction
wells, so no certifications will be provided. Colorado Round should be poured
1109 First Avenue, Suite 501, Seattle, Washington 98101 Phone: (206) 588.8200 Fax: (206) 588.8201
around the jetted in suction wells to fill the void and allow the upper lenses to be
dewatered.
The dewatering will generally proceed as follows:
1. Hubs or paint marks will be laid out on approximately 10 centers after the
general contractor lays out the excavation.
2. A jet pipe, water truck and a means to extend and hold it up in the air
(crane or track excavator) will be used to advance a hole into the ground to
the proper depth.
3. The jet pipe will run for up to a minute after depth is achieved to wash out
the fines. Then the metal pipe is removed.
4. The slotted well point(s) attached to plastic riser pipes is pushed into the
hole immediately.
5. Typically the hole caves, however some sand may be placed to fill the
void. Bentonite is placed at the top to seal the intake from air is done
before the end of the day.
6. Then the process is repeated many times.
7. After numerous points are in place, the header pipe is laid out and the
points are attached to the headed collection pipe using a plastic flexible
hose.
8. The single vacuum pump is placed at the end of the header and turned on.
9. Some points, where little water is present in the ground, will have the
water removed quickly and could allow air to enter the system, so ‘tuning’
will have to take place by turning off the valve to each well point. The
key is to have the well pump its maximum water without letting air in.
10. Wells will be abandoned per the WAC regulations. They will each be
filled with bentonite grout and cut off below the surface grade at the
direction of a licensed water well driller.
Each vacuum well pumping rate will vary because the soils vary within each site and
between sites. Therefore, the quantity at each site is variable but, from MJA’s experience
in these types of soils, each well will probably start at about 12 gallons per minute (gpm)
and then will lower down to 6 gpm max. The total pumping quantity will be relatively
low, in general unless a unique aquifer is found.
Closure
As a note, because of the variable nature of lake-bottom and City fill deposits, the suction
wells could easily pump different amounts of water. Therefore, if one well performs
better than another it does not mean that it was installed incorrectly, but instead it means
that the formation hydrologic parameters change quickly and vary horizontally and
vertically.
Also, this design is NOT a guarantee that the entire excavation will be dewatered as
predicted. The design is based on limited to no hydrogeologic data. Some water in the
excavation may require additional sumping and/or addition suction wells may be
required.
1109 First Avenue, Suite 501, Seattle, Washington 98101 Phone: (206) 588.8200 Fax: (206) 588.8201
Please contact me if you have any questions.
______________________________________________________________
Frank Pita, PE, PG (LHG), FASCE, DAGP
WA Professional Engineer (#17522) / Licensed WA Hydrogeologist (#1170)
Attachments: Groundwater Model Layout & Results
Appendix A: Marked up Contract Drawings showing Dewatering Locations
Appendix B: Pump & Component Data for Vacuum System
Appendix C: Example Surface Layout from Other Projects
1109 First Avenue, Suite 501, Seattle, Washington 98101 Phone: (206) 588.8200 Fax: (206) 588.8201
Model Case / System Layout for Pipeline (6 points on 3 meter (approx10 foot) centers
next to an excavation)
Case 1 Results / portion of Pipeline Trench (trench bottom at 15 ft, points to 22 ft)
This contour is below the trench bottom of
4.6 m = 15 feet.
DC-SOFTWARE
Analysis of ground-water lowering
DC-Dewatering
42
Graphic of the
water level with
color areas
Foundation pit
sectors of
different depth
German, English, French,
Romanian language
Arbitrary number and shape of
the pits, with different depths
Free number, diameter and
position of wells, several series
are possible
Soil layer definition with different
permeability
Unconfined, semi-confined or
confined aquifer
Adaptation of the lowering depth
to different pit depths is possible
Calculation with gravity or
vacuum wells
Analysis with required, prede-
fined pump-water rate or single
well quantities
QImproved formulae for the use
of Q > Q req
Output of the capacity of all wells
Calculation of the required
number of wells
Lowering and wetted filter height
of the wells
Consideration of the mutual
influence
Calculation of the range acc.
to Sichardt, acc. to Weyrauch
2004 for large foundation pits or
time-depending
Waterproof enclosure, calcula-
tion of the trough construction
method
Residual water quantities from
the wall and the base, inflow
from precipitation
Graphic of the lowering with
elevation lines or color areas
Determination of the critical
point
Free section draw with
water-level course
Interactive display of the
lowering at any point
Optimization: distribution of the
wells with arbitrary pit shapes
and depths
Optimization of the well depths
in accordance to the pumped
quantity
1109 First Avenue, Suite 501, Seattle, Washington 98101 Phone: (206) 588.8200 Fax: (206) 588.8201
Appendix A
Marked Up of Drawings
showing where
External Dewatering is Located
1109 First Avenue, Suite 501, Seattle, Washington 98101 Phone: (206) 588.8200 Fax: (206) 588.8201
Appendix B
Recommended Pump
&
Component Data for Vacuum System
Page 1 of 2
Double row
spherical ball
bearings
Carbon steel
inserts
Hardened drive
gears
* Some features
not available on
all models
Polyurethane
coated rotors
for abrasion
resistance
Drive shaft for
multiple drive
options
Lightweight
aluminum
castings and
housing
Top quality oil lubricated
mechanical seals with shaft
sleeves
Replaceable stainless steel wear
plates
• Wellpoint and underdrain sock dewatering
• Trench dewatering
• Filtered water transfer
• Remediation
• Sewer pipelines
• Lift stations
• Head walls
• Coffer dams
• Elevator pits
• Foundation structures
• Dams
• Borrow pits
Features
The Thompson Rotary Wellpoint Pump is the “original” rotary wellpoint pump trusted by
contractors worldwide for more than 30 years. The state-of-the-art 12R-DJDS-4045T-MC is
specifically designed and engineered for wellpoint and sock dewatering with high air handling,
large water volume and high vacuum capability. Pump unit includes a sound attenuation
enclosure covering both the engine and pump for noise abatement.
12” Rotary Wellpoint Pump
12R-DJDS-4045T-MC
• Standard Engine: John Deere 4045TF275
• Removable drop-on Silent Knight® sound
enclosure, constructed of 18 gauge solid
galvaneel shell and 2” thick, 8lb density mineral
wool, complete with 7 lockable doors.
• Sound levels less than 72 dBA @ 7 meters
• Unassisted priming and automatic re-priming
• Maximum flows to 2,500 gpm
• High vacuum of up to 29” Hg capacity
• High displacement volume of up to 500-cfm
• Engine speed can be lowered without losing
Working Principle
The Thompson Rotary Wellpoint Pump produces
constant suction as the rotors separate. The water is
directed over and under the rotors and out the
discharge.
Clearances are not a factor due to the use of suction
and discharge priming tanks. The polyurethane rotors
and the stainless steel wear plates offer abrasion and
corrosion resistance while the steel inserts provide
strength and durability.
Applications
In the interest of product improvement, Thompson Pump & Manufacturing reserves the
right to change specifications without incurring any obligation for equipment previously or subsequently sold.
Capacity, Head and Pump Curve are for comparative purposes. Consult engineering data for exact capabilities.
4620 City Center Drive, Port Orange, FL, 32129, USA (800) 767-7310 Fax (386) 761-0362
Email: sales@thompsonpump.com www.thompsonpump.com
Page 2 of 2 December 2005
12” Rotary Wellpoint Pump
12R-DJDS-4045T-MC
12R-DJDS-40405T-MC Dimensions
Canopy adds approximately 800 lbs to unit.
Materials of Construction
Engine: John Deere 4045T, 87 hp @ 1,800 rpm
Type: 4-cylinder, in-line, 4-cycle, water-cooled, turbo
charged, direct-injected, Tier II diesel
Standard Equipment: Alternator, radiator, muffler, and
exhaust stack with rain protection
Displacement: 275 cubic inches
Fuel Economy: .381 lb/hp-hr @ 1,800 rpm
Safety Shutdowns: High coolant temperature; Low oil
pressure
Fuel Tank Capacity: 127 US gallons
Fuel Consumption: 3.54 gallons per hour
Maximum Operating Speed: 500 rpm (pump)
Maximum Operating Temperature: 212°F
Maximum Operating Pressure: 65 psi
Maximum Suction Lift: 29 in Hg
Maximum Casing Pressure: 65 psi
Type: Positive displacement, low-pulsation, self-priming,
rotary lobe
Rotor: Four-lobe, single piece design with carbon steel
shaft and welded carbon steel fins with polyurethane
coating
Rotor Housing: Rugged, heavy-duty cast aluminum
Mechanical Seal: Oil lubricated with bronze rotating and
steel stationary seal faces. Single inside mounted, non-
pusher type with self-adjusting elastomeric bellows.
Suction Tank: A36 steel with permanent solids screen,
1-1/2” drain port, adjustable vacuum breaker valve and
vacuum gauge for system diagnostics
Discharge Tank: A36 steel with canvas reinforced
neoprene weighted flapper style check valve; built-in oil
reservoir with pressure relief and 1-1/2” drain port
Wear Plate: Replaceable, 304 stainless steel
Bearings: Heavy-duty, oil bath-pressure lubricated,
cylindrical roller type
Bearing Housing: Heavy-duty cast aluminum
12R-DJDS-4045T-MC
Performance Curve
Engine Specifications
Unit Specifications
Wellpoint Components
1109 First Avenue, Suite 501, Seattle, Washington 98101 Phone: (206) 588.8200 Fax: (206) 588.8201
Appendix C
Example Surface Setup
&
Layout from Other Projects
Dewatering Examples of Surface Layout
Photos of header & discharge piping / wells & connection to header/crossing / pump placed
in excavation so intake is at the level of header
14Aug07 15Aug07