906.1Description.
This work consists of dewatering work sites.
906.2Materials.
A.Portable Sediment Tank. Provide materials for portable sediment tanks as follows:
1.Wire Mesh - 23-gauge wire steel or galvanized welded wire reinforcement with openings 1/4-
inch by 1/4-inch.
2.Corrugated Metal Pipe
3.Geotextile Section 1060
4.Fasteners ASTM F541, Type 1 or Type 2
5.Metal Plate - 1/2-inch thick
B.Approved equal sediment tank
C.Dewatering Bag.
Use in accordance with the manufacture’s recommendations with a performance requirement retaining soil particles on a #80 sieve, 177 microns.
D.Sump Pit.
1.Coarse Aggregate, No. 57 Stone Section 1004
2.Corrugated Metal Pipe
3.Geotextile Section 1060
4.Wire Mesh – 23-gauge steel or galvanized welded wire reinforcement with openings 1/4-inch by
1/4-inch.
5.Approved equal sump pit
E.Skimmer dewatering device
1.Coarse Aggregate, No. 57 Stone Section 1004
2.Pipe Culverts, PVC Section 1031
3.Reinforcing Steel Section 1037
F.Well Point System
1.Coarse Aggregate Section 1004
2.Pipe Culverts Section 1031
3.Reinforcing Steel Section 1037
906.3Construction
A.Trap and filter water produced by dewatering activities. Pump to a suitable discharge area. Trap
and retain sediment before discharging water into drainage ways, adjoining properties, and rights- of-way below a project site.
B.Use dewatering practices shown in the contract. If the contract or the engineer do not specify a
specific dewatering practice, use a dewatering practice listed below that is appropriate for the specific situation. The engineer’s approval is needed to use dewatering practices not included in this list.
C.Inspect weekly and immediately after every rainfall to maintain and make repairs as needed.
D.Portable Sediment Tank
1.Construction
a.Construct the portable sediment tank according to the Standard Construction Details.
Construct an approved equal portable sediment tank in accordance with the manufacturer’s instructions.
i.The maximum allowable pump discharge of the typical portable sediment tank is 125
gallons per minute.
b.Locate the tank on a level surface and in an area where the tank will cause minimal
interference with construction activities, and vehicular and pedestrian traffic.
c.Obtain the engineer’s approval to locate the portable sediment tank at a different location,
within the LOC, than what is shown in the contract.
d.Construct watertight welds.
e.Fasten the wire mesh and geotextile to the pipe.
2.Maintenance
a.Remove sediment when it accumulates to a depth of 1/3 of the portable sediment tank
height.
b.Remove and replace the filter geotextile when:
i.It allows the portable sediment tank to exceed the maximum allowable discharge flow rate
of 125 gallons per minute; ii. when there is a tear; and iii. when directed by the engineer.
c.Dispose of all sediment collected in the portable sediment tank in an approved disposal area.
3.Removal
a.After removal, grade the area to match the contours shown in the contract. If no contours are
shown, match the grades that existed before construction of the tank.
b.Stabilize areas affected by the portable sediment tank in accordance with Section 908. E.Dewatering Bag
1.Construction
a.Place dewatering bags at locations designated in the contract in accordance with the
manufacture’s recommendations, or as approved by the engineer.
b.Maintain a water-tight connection.
c.Secure in place.
d.Do not exceed the manufacturer's recommended flow rate or capacity.
e.Discharge the dewatering effluent without causing erosion. The engineer will approve the
types of erosion control measures if needed.
2.Maintenance
Provide and place a new dewatering bag in accordance with the manufacture’s recommendations or as determined by the engineer.
3.Dewatering Bag Removal
a.Remove and dispose of a dewatering bag when replaced or when no longer needed.
b.Regrade the area to match the contours shown in the contract. If no contours are shown,
match the grades that existed before dewatering bag construction.
c.Stabilize areas affected by the dewatering bag in accordance with Section 908. F.Sump Pit.
1.Construction
a.Excavate the sump pit according to the dimensions in the Standard Construction Details or in
accordance with the manufacture’s recommendations.
b.Place the layer of stone in the bottom of the sump pit in accordance with the Standard
Construction Details. Place the stationary pipe with a bottom cap on top of the bottom layer of stone.
c.Place the removable pipe inside of the stationary pipe in accordance with the Standard
Construction Details. Extend both pipes to the same height and a minimum of 12 inches above the lip of the sump pit.
d.Backfill the sump pit with stone.
e.Slope the stone to meet the height of the pipes.
2.Maintenance
When clogged with sediment, replace the geotextile and, if applicable, the wire mesh on the removable pipe and bottom cap.
3.Removal
a.Remove the sump pit and regrade the area to match the contours shown in the contract. If the
contract does not show contours, match the grades that existed before construction of the sump pit.
b.Stabilize all areas affected by the sump pit, if needed, in accordance with Section 908. G.Skimmer Dewatering Device
1.Construction
Construct skimmer dewatering devices in accordance with the dimensions in the Standard Construction Details and place at the locations shown in the contract.
2.Maintenance
Maintain the skimmer dewatering device in proper operational condition while required on the project.
3.Removal
Remove the skimmer dewatering device from the project site when directed by the engineer.
H.Well Point System
A typical well point system consists of a series of small diameter wells connected via a header pipe to the suction side of a suitable well point pump.
1.Construction
a.Design a well point system capable of controlling groundwater in order to install proposed
structures on a dry and stable sub-base. Select a location for installing the well point system that will not interfere with construction of the proposed structure until removal is appropriate. If inclusion of the well point system in the work area requires modifications to construction phasing, include the modifications in the shop drawings.
b.Obtain and comply with all necessary permits in accordance with Section 902. Obtain permits and provide copies to the engineer before beginning excavation.
c.Install and test the well point system in accordance with the approved design to demonstrate
the system's effectiveness to the engineer’s satisfaction before continuing with the excavation.
d.Modify the well point system if it cannot maintain the groundwater elevation required to
provide a dry and stable sub-base.
2.Maintenance
Maintain the well point system to ensure working order and continuous drawdown throughout the dewatering process.
3.Removal
a.Remove the well point system after placement of all proposed structures and backfill affected
by groundwater conditions, or as directed by the engineer.
b.Stabilize areas affected by the well point system, if needed, in accordance with Section 908. 906.4Method of Measurement.
A.The Department will measure the quantity of dewatering work completed and accepted as
follows:
1.Portable sediment tanks by each placed and accepted.
2.Dewatering bag by each placed and accepted.
3.Sump pit by each placed and accepted.
4.Skimmer dewatering device by each constructed, placed and accepted.
B.The Department will not measure the well point system.
906.5Basis of Payment.
A.The Department will pay the quantities of dewatering practices at the contract unit prices for each
acceptably placed. The Department will pay for new dewatering bags using the unit cost of item 906002, dewatering bag. Price and payment constitute full compensation for:
1.Providing all materials;
2.fabricating;
3.excavating, backfill, and backfilling;
4.installing;
5.maintaining and sediment removal;
6.temporary stabilization;
7.relocating within project limits;
8.removal;
9.restoring the site; and
10.permanent stabilization.
B.The Department will pay the quantity of well point system as a lump sum. Price and payment will
constitute full compensation for:
1.Design;
2.Permits;
3.Installation;
4.Operation;
5.maintenance;
6.removal;
7.restoring the site; and
8.permanent stabilization.
C.The Department will consider re-design or modification of the well point system as incidental to
this item; ITEM DESCRIPTION UNIT 906001 PORTABLE SEDIMENT TANK EACH 906002 DEWATERING BAG EACH 906003 SUMP PIT EACH 906004 SKIMMER DEWATERING DEVICE EACH 906006 WELL POINT SYSTEM LS
Referenced in this section
Sections that cite this one
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Source: Delaware Standard Specifications for Road and Bridge Construction, 2026 Edition. Pages 597–0 of 786.
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