31 23 19 – DEWATERING

Herbert, Rowland & Grubic, Inc. 31 23 19 - 1 009280.0426

SECTION 31 23 19 – DEWATERING

PART 1 - GENERAL

1.1 SUMMARY

A. Section Includes:

1. Dewatering system.

2. Surface water control system.

3. Monitoring wells.

4. System operation and maintenance.

B. Related Sections:

1. Section 31 23 33 – Trenching and Backfilling for Utilities

2. Section 31 25 00 – Erosion and Sedimentation Controls

1.2 REFERENCES

A. ASTM International:

1. ASTM C33 - Standard Specification for Concrete Aggregates.

1.3 DEFINITIONS

A. Dewatering includes the following:

1. Lowering of ground water table and intercepting horizontal water seepage to prevent ground water from entering excavations and trenches.

2. Reducing piezometric pressure within strata to prevent failure or heaving of excavations and trenches.

3. Disposing of removed water.

B. Surface Water Control: Removal of surface water within open excavations.

1.4 SYSTEM DESCRIPTION

A. Provide dewatering and surface water control systems to permit Work to be completed on dry and stable subgrade.

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B. Provide monitoring wells and monitoring equipment to obtain meaningful observations of conditions affecting excavation.

C. Furnish standby equipment stored at Project site and ready for immediate use upon failure of dewatering equipment.

1.5 PERFORMANCE REQUIREMENTS

A. Design dewatering systems to:

1. Lower water table within areas of excavation to minimum 2 feet below bottom of excavation to permit Work to be completed on dry and stable subgrade.

2. Relieve hydrostatic pressures in confined water bearing strata below excavation to eliminate risk of uplift or other instability of excavation.

3. Prevent damage to adjacent properties, buildings, structures, utilities, and facilities from construction operations.

4. Prevent loss of fines, quick condition, or softening of foundation subgrade.

5. Maintain stability of sides and bottoms of excavations and trenches.

B. Design surface water control systems to:

1. Collect and remove surface water and seepage entering excavation.

1.6 SUBMITTALS

A. Section 01 33 00 – Submittal Procedures: Requirements for submittals.

B. Shop Drawings:

1. Indicate dewatering system layout, well depths, well screen lengths, dewatering pump locations, pipe sizes and capacities, grades, filter sand gradations, surface water control devices, valves, and water disposal method and location.

2. Indicate primary power system location and capacity.

3. Indicate layout and depth of monitoring wells, piezometers and flow measuring devices for system performance measurement.

4. Include detailed description of dewatering and monitoring system installation procedures and maintenance of equipment.

5. Include description of emergency procedures to follow when problems arise.

C. Product Data: Submit data for each of the following:

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1. Dewatering Pumps: Indicate sizes, capacities, priming method, engine characteristics.

2. Pumping equipment for control of surface water within excavation.

D. Field Reports: Test and monitoring reports as specified in Field Quality Control article.

1.7 CLOSEOUT SUBMITTALS

A. Section 01 77 00 – Closeout Procedures: Requirements for submittals.

B. Project Record Documents: Record actual locations and depths of capped wells and piping abandoned in place.

1.8 QUALITY ASSURANCE

A. Comply with authorities having jurisdiction for the following:

1. Drilling and abandoning of wells used for dewatering systems.

2. Water discharge and disposal from pumping operations.

1.9 SEQUENCING

A. Section 01 10 00 – Project Summary: Requirements for sequencing.

B. Sequence work to obtain required permits before start of dewatering operations.

C. Sequence work to install and test monitoring systems minimum 7 days before testing and operating dewatering systems.

D. Sequence work to install and test dewatering and surface water control systems minimum 7 days before starting excavation and trenching.

1.10 COORDINATION

A. Coordinate work to permit the following construction operations to be completed on dry stable substrate.

1. Trenching in Section 31 23 33 – Trenching and Backfilling for Utilities.

PART 2 - PRODUCTS

2.1 DEWATERING EQUIPMENT

A. Select dewatering equipment to meet specified performance requirements.

Herbert, Rowland & Grubic, Inc. 31 23 19 - 4 009280.0426

2.2 MONITORING EQUIPMENT

A. Piezometers: Standpipe or Pneumatic type for sand filter or push in installation to monitor water elevation.

2.3 ACCESSORIES

A. Valves and Fittings: Furnish valves and fittings to isolate each well from header pipe and to prevent loss of pump prime.

B. Filter Sand: ASTM C33; natural river or bank sand; washed; free of silt, clay, loam, friable or soluble materials, and organic matter; graded to suit well screen.

C. Grout: Mixture of portland cement and bentonite clay or sand suitable for sealing abandoned wells and piping.

PART 3 - EXECUTION

3.1 EXAMINATION

A. Section 01 73 00 – Execution Requirements: Verification of existing conditions before starting work.

B. Conduct additional borings and investigations to supplement subsurface investigations as required to complete dewatering system design.

C. Call Pennsylvania One Call System, Inc. at 1-800-242-1776 not less than three working days before performing Work.

1. Request underground utilities to be located and marked within and surrounding construction areas.

D. Employ licensed land surveyor to provide following documentation:

1. Survey existing adjacent buildings, structures, and improvements for position and elevation of principal elements before and after completion of dewatering operations.

3.2 PREPARATION

A. Protect existing adjacent buildings, structures, and improvements from damage caused by dewatering operations.

3.3 MONITORING WELLS

A. Install monitoring wells at locations indicated on shop drawings as specified for dewatering wells.

B. Test each monitoring well point to verify installation is performing properly.

C. Install piezometers, calibrate, and test for proper operation.

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D. Protect monitoring well standpipes from damage by construction operations.

E. Maintain accessibility to monitoring wells continuously during construction operations.

F. Maintain monitoring wells until groundwater is allowed to return to normal level.

3.4 DEWATERING SYSTEM

A. Install dewatering system in accordance with shop drawings.

B. Locate system components to allow continuous dewatering operations without interfering with installation of permanent Work and existing public rights-of-way, sidewalks, and adjacent buildings, structures, and improvements.

C. Drill wells in sizes and to depth indicated. Provide temporary surface casing when required to stabilize soil while advancing well.

D. While drilling and installing well keep bore hole filled with natural or organic drilling fluid.

Bentonite clay drilling fluid is not permitted.

E. Attach well screen to riser pipe. Attach centralizers to riser pipe at maximum 20 feet spacing to keep screen and riser centered in bore hole. Insert well screen and riser pipe into well to elevation indicated.

F. Install sand filter surrounding well screen

G. Develop wells by over pumping, or air/water jetting to remove clay, silt, and sand from well screen and immediate vicinity of bore hole.

H. Test well for proper water flow through well screen and pumping rate for dewatering system operation. Repeat development until well meets performance requirements.

I. Cover and seal top of well until pump is installed.

J. Install pumps in accordance with manufacturer's instructions.

K. Connect pumps to discharge header. Install valves to permit pump isolation.

3.5 SURFACE WATER CONTROL SYSTEM

A. Provide ditches, berms, and other devices to divert and drain surface water from excavation area as specified in Section 31 25 00 – Erosion and Sedimentation Controls.

B. Divert surface water and seepage water within excavation areas into sumps and pump water into settling basins in accordance with requirements of agencies having jurisdiction.

C. Control and remove unanticipated water seepage into excavation.

Herbert, Rowland & Grubic, Inc. 31 23 19 - 6 009280.0426

3.6 SYSTEM OPERATION AND MAINTENANCE

A. Operate dewatering system continuously until backfill is minimum 2 feet above normal ground water table elevation.

B. Provide 24-hour supervision of dewatering system by personnel skilled in operation, maintenance, and replacement of system components.

C. Conduct daily observation of dewatering system and monitoring system. Make required repairs and perform scheduled maintenance.

D. Fill fuel tanks before tanks reach 25 percent capacity.

E. Start emergency generators at least twice each week to check operating condition.

F. When dewatering system cannot control water within excavation, notify Engineer and stop excavation work.

1. Supplement or modify dewatering system and provide other remedial measures to control water within excavation.

2. Demonstrate dewatering system operation complies with performance requirements before resuming excavation operations.

G. Modify dewatering and surface water control systems when operation causes or threatens to cause damage to new construction, existing site improvements, adjacent property, or adjacent water wells.

H. Correct unanticipated pressure conditions affecting dewatering system performance.

I. Do not discontinue dewatering operations without Engineer's approval.

3.7 SYSTEM REMOVAL

A. Remove dewatering and surface water control systems after dewatering operations are discontinued.

B. Remove piezometers and monitoring wells.

C. Fill abandoned wells with sand or grout.

D. Fill abandoned piping with grout.

E. Repair damage caused by dewatering and surface water control systems or resulting from failure of systems to protect property.

3.8 FIELD QUALITY CONTROL

A. Section 01 40 00 – Quality Requirements: Field inspecting, testing, adjusting, and balancing.

Herbert, Rowland & Grubic, Inc. 31 23 19 - 7 009280.0426

B. After dewatering system is installed, perform pumping test to determine when selected pumping rate lowers water level in well below pump intake. Adjust pump speed, discharge volume, or both to ensure proper operation of each pump.

C. Monitor and record the following, daily, until steady state conditions occur. Then monitor and record conditions twice each week.

1. Average discharge flow rate for each deep well, eductor header, and well point.

D. Monitor and record the following, daily, until dewatering system is discontinued.

1. Ground water elevation.

E. Monitor ground water discharge for sand content. Sample and test water from each well weekly for sand content. Maximum permitted sand content 5 parts per million.

F. Monitor ground water discharge for contamination while performing pumping in vicinity of potentially contaminated sites. Sample and test water weekly for contaminates.

G. Survey existing adjacent buildings, structures, and improvements weekly to detect movement in comparison to original elevations during dewatering operations.

1. Notify Architect/Engineer immediately of measured movement.

H. Submit initial installation reports including the following:

1. Installation and development reports for well points and pumps.

2. Installation and baseline reports for monitoring wells and piezometers.

3. Test reports of monitoring well water analysis.

4. Initial dewatering flow rates.

I. Submit weekly monitoring reports including the following:

1. Dewatering flow rates.

2. Piezometer readings.

3. Test reports of discharge water analysis.

4. Maintenance records for dewatering and surface water control systems.

END OF SECTION 31 23 19