A22c_Arkabutla Emergency Repairs - Pre-bid Slides and Notes.pdf

Arkabutla Emergency Repairs

Pre-Bid Meeting

10 January 2023

During the pre-bid meeting site visit, the following topics were noted and required additional information.

1) Grouting the voids beneath the stilling basin during installation of the stilling basin piezometers.

After additional discussion, the Government has determined to remove the flowable fill grouting requirement. If voids are found during drilling and installation of the stilling basin piezometers, the piezometer shall be cased as described in the amended plans and specifications. Please see Amendment 0002.

2) Power source for the outlet works pumps.

The contractor shall provide the power source for the contractor provided pumps. The existing power supply at the outlet works is not reliable. Please refer to Section 33 26 00.00 09 paragraph 3.8.1.1.

3) Pump size for the outlet works pumps.

The contractor shall size the pumps such that groundwater can be lowered to or below 163 ft to effectively perform the work without exceeding the pump rates described in Section 31 23 19.01 09 paragraph 1.7 and Section 33 26 00.00 09 paragraph 3.5. As stated in Section 33 26 00.00 09, additional well points may be required to lower the ground water as required.

4) Maximum pump capacity of the new wells during dewatering operations.

The maximum pump capacity is 500 GPM. Please see Amendment 0002.

5) Control of water during construction.

Please refer to Section 01 00 00.00 09 paragraph 1.30.1(b). The Government will lower/close the gate, provide chinking material to minimize gate leakage, and construct a sandbag cofferdam at the gate to conduit transition to collect gate leakage. The Government will pump and pipe this pool of water so that it discharges beyond the end sill of the stilling basin. The Government will coordinate with the Contractor to place the discharge piping such that it minimizes conflicts with the Contractor’s stilling basin operations as possible. The Contractor shall be responsible for minimum leakage not captured at the gates by the Government’s sandbag cofferdam and sump pump.

U.S. ARMY CORPS OF ENGINEERS,

VICKSBURG DISTRICT

PRE-BID MEETING

DeSoto County, Mississippi Arkabutla Dam Emergency Repairs FC/MR&T, Yazoo River Basin Coldwater River, Arkabutla Lake

Solicitation No. W912EE24B0001

10 JAN 2024

Drone picture – July 2020

Aug 2020 Jun 2023

AGENDA

• Opening Remarks

• Welcome and Introductions

• Technical Briefing

• Contract Administration

• Questions

• Site Visit

• Bid opening is Tuesday, 23 January 2024 at 2:00 PM.

• The successful low bidder will be required to provide a written response to the Definitive Responsibility Criteria listed in the solicitation.

• Bidders are required to enter questions asked during the pre-bid meeting into ProjNet for the official Government response.

• One amendment has been issued setting the pre-bid conference date. A second amendment is forthcoming in response to bidder inquiries. This amendment will include the slide deck and sign-in sheet from the pre-bid conference.

OPENING REMARKS

INTRODUCTIONS

TECHNICAL BRIEFING

Arkabutla Dam (MS01496) - Coldwater River Sardis Dam (MS01493) – Little Tallahatchie River Enid Dam (MS01495) – Yocona River Grenada Dam (MS01494) – Yalobusha River

Yazoo River Drainage Basin

Construction started in 1940 ($5.1M / $109.3M) Placed into operation in 1943

Authorization: 1928 FCA (1936 and 1938)

Annual Benefits (2018 price level)

• Flood Control $12.3M

• Recreation $4.1M

• Water Supply $0

PROJECT OVERVIEW

Arkabutla DamArkabutla Dam

Then Now

Main Components

• Earthen Embankment

• Closure Dikes

• Emergency Spillway

• Outlet Works

PROJECT OVERVIEW

North

Arkabutla Dam

Outlet Works

Spillway

Current Pool Restriction Current Outflow Restriction

Maintain Pool Elevation at 204ft Not to exceed 4,500 cfs

Dam Type Zoned Earth Fill Height 85 ft Length 7,300 ft

PROJECT OVERVIEW- EMBANKMENT

Spillway

Outlet Works

• Gate-Controlled Intake Structure

• 16 ft x 18.25 ft Ovoid Conduit

– 355 ft long

– 10,000 cfs capacity at EL 238.3 ft

• Stilling Basin

• Outlet Channel

PROJECT OVERVIEW- CONDUIT

Designed with no waterstops in the shaded area

PROJECT OVERVIEW- STILLING BASIN

RECENT DEVELOPMENTS-2020 SINKHOLE

1 32

RECENT DEVELOPMENTS- INITIAL INVESTIGATION

RECENT DEVELOPMENTS- INITIAL INVESTIGATION

HYDRAULIC JUMP LOCATION

• PFM 08: BEP into outlet works drainage system

RISK ASSESSMENT

SCOPE OF WORK

New Pressure Relief System

Piezometer Installation and Automation

Stilling Basin Work

Piezometer Installation and Automation

• Embankment - New

– 9 boreholes, 22 piezometers

– 10-in diameter boreholes

– 1.25-in diameter, sch. 40 PVC open standpipe

– Drilled through embankment from dam slope

– Some nested in the same borehole, screened at varying depths

– Automated with Vibrating Wire Piezometers (VWP)

– Some shallow trenching along dam slope required for wires

• Stilling Basin - New

– 2 boreholes, 2 piezometers

– 4-in diameter core through 6-ft thick concrete floor

– 1.25-in diameter, stainless steel open standpipe

– Only accessible once stilling basin is dewatered (order of work)

– Riser will be trenched across floor and up wall. VWP will need to be installed with the riser.

– Unknown conditions may exist beneath the concrete slab. See plans and specifications for information regarding casing to address possible voids.

– Automated with VWP

• Existing Piezometers

– 21, 1.25-in diameter, open standpipe

– PVC and steel

– Automated with VWP

Piezometer Automation

• Satellite

- Binary Format

- Compatible with GOES

- ID and time slot will be provided by MVK-Water Control and Geotech

Personnel (1ID for every 9 sensors)

• Wireless Cellular

- Web-Based Service

- 5 years cellular service

- Web-Interface must be intuitive and user friendly

• Training

- 3 Session of 4 hours to include but not limited to the following:

- Instrumentation Plan

- Installation and Automation

- Monitoring Data and Operation and Maintenance

New Pressure Relief System

• 6 Relief Wells and Discharge Laterals

– 12-inch x 70 ft, stainless steel

– Outlet works backfill

– Reverse circulation, temporary casing

– #30 screen slot size and Red Flint #30 filter pack

– Discharge laterals through concrete wall

• Long-term use

– Gravity operated foundation pressure relief

• Short-term use

– Pumped to drawdown groundwater level below stilling basin

– 6 pumps required on-site

• Acceptable

– Fully developed

– Minimal sanding

– Plumbness and alignment

• Pump Test

– Step-drawdown

– Minimum of 4 steps

– Wells must be accepted before pump tests are performed

– Not required to be performed prior to stilling basin work

Stilling Basin Work

• Misc. Requirements

– All relief wells will have to be installed and satisfactorily operational before work can occur in the stilling basin

– No work can be performed anywhere when lake levels exceed 220 ft

– 24-hr notice will be given to evacuate stilling basin if lake is forecasted to exceed 220 ft

– NWS link will be provided to access daily published QPF’s

– On-going work will have to be completed or acceptably paused

• Discharge Laterals

– Drilled through concrete walls to intercept relief wells

– Newly installed wells will have to be pumped to keep groundwater drawn down

– Freedom to adjust discharge lateral angle for ease of construction

• Piezometers in Chute

– Due to location and riser bends, VWP instrumentation will have to be installed while riser is trenched and installed

– Existing voids could be present between slab and foundation. If encountered, piezometer shall be cased to the top of the sand.

• Abandon Existing Drainage System

– Last order of work (must be done after laterals and piezometers)

– Install drain covers over existing underslab drainage system to positively plug off discharges

– Pumping relief wells will be required to shut-off flow from this system

ORDER OF WORK

1. Mobilize to the site

2. Install all piezometers except stilling basin

– Automation can occur concurrently with installation/drilling

– Collect piezometric data manually or through automation during remaining work activities

3. Install relief wells

4. Install stilling basin piezometers and relief well discharge laterals

5. Install underslab drain covers

6. Complete punch list items and cleanup work site

7. Demobilize

LAKE OPERATIONS

The conduit gates will be operated to maintain lake elevations at elevation 204 ft.

Work will be halted at the project when lake levels exceed elevation 220 ft.

When work is performed in the stilling basin, conduit discharges will be halted, and the lake will be allowed to rise above elevation 204 ft. Once forecasts indicate that lake levels will exceed elevation 220 ft, the contractor will be given 24-hr notice to evacuate the stilling basin and bring work to an acceptable stopping point such that conduit discharges won’t damage the work.

After a required evacuation of the stilling basin, USACE will allow the lake get back down to and remain at 204 ft for a forecasted 5-day interval before permitting the contractor to re-enter the stilling basin

LAKE OPERATIONS

DRILLING OPERATIONS

1. To mitigate risks, all drilling and sampling will be conducted in accordance with EM 1110-1-1804, Geotechnical Investigations (January 2001); ER 1110-1-1807, Drilling in Earth Embankment Dams and Levees (June 2023); and the appropriate ASTM standards.

2. No weighted drilling fluids or pressurized mediums will be allowed during borehole advancement through the embankment.

3. The drilling contractor will have a valid and up to date water well driller’s license applicable to the state of Mississippi and shall have a resume showing experience with drilling on at least 2 USACE dams or levees.

4. The contractor may propose different drilling methodologies not listed in this contract that are safer and conform more readily to ER-1110-1807. Any drilling method must be approved by USACE before operation can begin and methods must be validated by district staff with RMC approval.

DRILLING OPERATIONS

5. Preferred relief well drilling methodology is Reverse Circulation (RC)

6. Preferred embankment drilling is Hollow Stem Auger (HSA)

7. All drilling will be conducted under the supervision of a competent, experienced, and licensed water well operator with sufficient experience operating RC, HSA, or additional submitted methods.

8. Contractor will provide a licensed professional engineer or professional geologist with at least 5-years of experience to provide onsite oversight during the project.

9. Vibratory or percussion drilling are prohibited.

10.Oscillated casing or impact driven sheetpiles for installation of lateral drains is allowed provided it does not violate other provisions of the contract specifications and plans.

11. The contractor will anticipate steep slopes and provide means and methods for constructing drill pads (if needed), access roads, etc.

Dewatering Requirements

• Dewatering system must be able to maintain foundation pressures to an elevation of 163 ft, NGVD 29, which is 5 feet below the stilling basin floor, while working in the stilling basin. Nearby foundation piezometers and newly installed wells will be utilized to measure foundation pressures.

• The dewatering system must have the capacity to restrict any upward or horizontal flows into any necessary excavated areas.

• Dewatering system can include pumping existing outlet works relief wells and newly installed outlet works relief wells.

• Contractor must provide 6 temporary pumps and associate piping which must remain on site at all times.

• Maximum pump rates for existing outlet work relief wells South Outlet and North Outlet are 350 gpm.

• Relief well screens are much deeper than the backfill. Additional well points may be necessary to control shallow backfill water levels.

• Government is responsible for dewatering the conduit, closing and sealing off gates, and transporting any gate leakage beyond and out of the work area. Contractor will be responsible for any minor leakage.

Existing Wells, Drains, and Piezometers

Drain or Well Name Drain Diameter Max Pumping Capacities

South Outlet Relief Well 12 inches 350 gpm

North Outlet Relief Well 12 Inches 350 gpm

North Horizontal Backfill Drain 1 8 inches 0 gpm- gravity discharge

North Horizontal Backfill Drain 2 8 inches 0 gpm- gravity discharge

South Horizontal Backfill Drain 1 8 Inches 0 gpm- gravity discharge

South Horizontal Backfill Drain 2 8 Inches 0 gpm- gravity discharge

Final Site Plan with New Instrumentation and Relief Wells

New Relief Wells

Existing Horizontal Backfill Drains

Existing Horizontal Backfill Drains

Drain or Well Name Drain Diameter Design Capacities

SO-1, SO-2, SO-3 12 inches 500 gpm

NO-1, NO-2, NO-3 12 Inches 500 gpm

Groundwater Restriction

163 ft NGVD 29

CONTRACT ADMINISTRATION BRIEFING

CONTRACT ADMINISTRATION - DURATION

Total duration for the project is 180 days.

NTP will be issued immediately after verification of bonds.

Work in the stilling basin including installation of relief well lateral drains, underslab piezometers, and capping the existing underslab drainage system:

• Commencement of work in the stilling basin requires coordination between the Government and the Contractor.

• Once the Government has completed its unwatering responsibilities, the Contractor has 20 days to complete all work in the stilling basin. (Revised from 30 days to 20 days in forthcoming amendment.)

• Contractor is required to work 24 hours, 7 days per week until work in the stilling basin is complete. (Added in forthcoming amendment.)

• Contractor is encouraged to work diligently, adjust work schedules, work procedures, etc. to overcome any delays.

• The Government will accommodate the Contractor’s work schedule.

• If work is suspended due to lake stages, contractor has 10 days to return to work once the Government gives notice to resume work.

• This duration is subject to a separate assessment of liquidated damages.

If Options 1 and/or 2 are exercised, no additional performance time will be added to the contract.

CONTRACT ADMINISTRATION – OPTION ITEMS

Option 1: Suspension of Work in the Stilling Basin

• Consists of payment of all costs associated with suspension of work activities in the stilling basin including evacuation of materials and equipment and securing of permanent work for discharges as well as resumption of work.

Note: Contractor is required to provide an Evacuation Plan for Government Approval prior to start of work in the stilling basin in accordance with Section 01 00 00.00 09 paragraph 1.31.

• Suspension and resumption of work is closely coordinated with the Government.

• Contract time will stop during suspension of work.

• No payment will be made for suspensions of work to activities outside of the stilling basin due to lake stages.

Option 2: Additional Relief Well Pumping

• Consists of payment for all costs associated with furnishing all plant, labor, and equipment required for operation of the relief well pumps when directed by the Contracting Officer.

• Measured in pump days which is based upon 24-hour operation per relief well being pumped in operation.

Example: 4 pumps operating for 10 days = 40 pump days

• Pumping could occur concurrently with other activities or during a suspension of work.

• Does not include pumping required to complete work in the stilling basin, installation of the relief wells, or other required contractor dewatering efforts as required in the base scope of work.

CONTRACT ADMINISTRATION – DRC

Definitive Responsibility Criteria (DRC)

1. List of features of work self-performed by the prime contractor. List of subcontracted features of work and subcontractor intended to perform that feature.

2. Provide a narrative describing similar projects the Contractor and/or subcontractors have experience constructing that demonstrate the Contractor and/or subcontractors capabilities to successfully perform this contract. The narrative shall demonstrate experience:

a. drilling into dams and/or levees,

b. installation of relief wells,

c. installation of piezometers,

d. installation and automation of vibrating wire instrumentation,

e. control of subsurface water during drilling and excavation, and

f. management of piezometric pressures during drilling and excavation.

Identify if the provided projects were self-performed by the prime contractor, or if completed by a subcontractor, the subcontractor’s name and role on the project.

3. Provide the following information for all proposed drill rig operators.

a. Licenses or other evidence the personnel operating the drill rig(s) are licensed by the State of Mississippi.

b. Narrative demonstrating at least three (3) years of experience drilling with the type of equipment proposed.

c. Narrative demonstrating experience drilling on at least two dam and/or levee projects using the drilling methods prescribed in Sections 33 26 00.00 09 Relief Wells and 33 51 43 Instrumentation and Performance Monitoring of Structures.

d. Provide a list of equipment proposed to use for drilling the piezometers and relief wells in accordance with the approved drilling methods listed in Sections 33 26 00.00 09 Relief Wells and 33 51 43 Instrumentation and Performance Monitoring of Structures.

CONTRACT ADMINISTRATION – DRC

Definitive Responsibility Criteria (DRC) continued.

4. Provide license or other evidence of the Contractor’s proposed on-site licensed Professional Engineer (PE) or Professional Geologist (PG). Identify the employer of the PE or PG, i.e. is he employed by the prime contractor, a subcontractor, or an independent firm. Provide a narrative or resume demonstrating a minimum of 5 years of relevant experience.

5. Provide a narrative describing the Contractor’s proposed plan for installation of the lateral drains. The narrative shall consider restricted installation methods described in the contract and shall include, at a minimum, the order of work for this activity, the installation method, and equipment.

Submission of the information above does not replace the full submittal requirements for these items in accordance with the contract requirements.

QUESTIONS