Department of EnergyAlbuquerque Operations Office

P.O. Box 5400Albuquerque, New Mexico 87115

NOV 21

Mr. Ramon F. HallDirector, Uranium Recovery Field OfficeU.S. Nuclear Regulatory CommissionRegion IVBox 25325Denver, CO 80225

Dear Mr. Hall:

Enclosed for review and concurrence is Project Interface Document (PID)#03-S-22 which concerns the addition of a toe trench at theDurango, Colorado disposal cell. Please note, the action is a "Class I"change to the Remedial Action Plan since this trench will be a permanentfeature of the cell.

The Uranium Mill Tailings Remedial Action Project Office requests yourreview of the enclosed PID as soon as possible. If you have anyquestions, please contact Elizabeth Damler or Steve Hamp of my staff at845-5654.

Sincerely,

Mark L. MatthewsActing Project ManagerUranium Mill Tailings Project Office

Enclosure

cc w/o enclosure:D. Gillen, NRC-H2J. Oldham, MK-FM. Kearney, TACM. Abrams, UMTRA

MORRISON UMTRA PROJECT OFFICEKNUDSEN PROJECT INTERFACE DOCUMENT[COULD NOT BE CONVERTED TO SEARCHABLE TEXT]

SECTION 02142

TAILINGS EMBANKMENT TOE DEWATERING

PART 1 - GENERAL

1.1 SCOPE

A. This Specification Section covers the requirements forconstruction of a permanent dewatering trench at the toeof the tailings embankment. The work includes thefurnishing of all labor, material, transportation, tools,fuel, lubricants, plant and other equipment necessary toconstruct the dewatering trench. A dewatering specialistwill install and operate a temporary dewatering system tolower the water level until construction of the trench iscomplete.

B. The permanent dewatering trench shall be constructed andready for use within 5 weeks of the receipt of the Noticeto Proceed. An additional week will be allowed for remo-val of the temporary dewatering system and demobilization.

C. The drainage filter and perforated drain pipe shall beconstructed to the line and grade shown on the SubcontractDrawings.

D. A temporary dewatering system of wellpoints installedseparately is shown on the Subcontract Drawings.

E. Excess porewater pressures exist in the tailings underportions of the existing clay cover at the work site.Trench excavation methods likely to create stabilityproblems or cause compaction concerns will not bepermitted.

1.2 RELATED WORK

A. Special Conditions:

1. Section SC-7: Construction Health and Safety

2. Section SC-8: Health Physics

B. Section 02200: Earthwork

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1.3 SUBMITTALS

For general submittal requirements see Section 01300.

1.4 DELIVERY, STORAGE, AND HANDLING

Filter material may be delivered to the site in bags or inbulk. The material shall be placed on a protective sheetto prevent contact between it and the ground and shall beprotected by impermeable covering.

PART 2 - PRODUCTS

2.1 MATERIALS FOR PERMANENT DEWATERING TRENCH

A. Gravel Filter: Filter material shall be sound and durablegravel particles from locally available river run gravelpreviously specified for Type A riprap. It shall begraded from a maximum size of 3-1/2-inch diameter to aminimum size of no more than 0-15 percent passing the1-inch sieve.

B. Sand Filter: Washed concrete sand shall be used as back-fill in the toe drain trench. It shall be as specified bythe State of Colorado, Department of highways for fineaggregate and for concrete or similar material as approvedby the Contractor.

C. Drain Pipe: Drain pipe shall be 6-inch diameter, rigid,perforated, approximately 330 feet long with a cap at oneend. The perforated pipe shall have two rows of 1/2-inchholes spaced at 5-inch centers. The rows shall be 120apart on the circumference of the pipe. Non-perforateddrain pipe shall be rigid, 6-inch diameter, and approxi-mately 215 feet long with appropriate connectors.

D. Vent Pipe: Vent pipe shall be rigid, non-perforated, 6inches in diameter, and 10 feet long.

E. Drain Valve: Drain valve shall be the blade or ball typeand shall be fabricated with an extension so as to operatefrom tne ground surface some 10 feet above the valve.

F. Plastic Lining: The plastic lining to be used for theholding pond bottom shall be similar to the 40 mil HDPEbeing used for the original subcontract.

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G. Filter Fabric: Prior to placing the pipe or filter mate-rial in tne excavated trench, the filter section shall belined with a filter fabric as specified below. The fabricmay be purchased in 360-foot long x 15-foot wide pieces.The fabric shall be a Geotextile product, No. 140N asmanufactured by Mirafi, Inc., and distributed by Big "R"Manufacturing, P.O. Box 1290, Greeley, Colorado 80632, orapproved equal.

H. Spillway Pipe: An automatic one way valve shall be in-stalled in the spillway pipe to preclude entry of waterinto the holding pond from the treatment pond.

I. Drainage Net: The drainage net, shall be placed betweenthe two layers of HDPE liner and shall be Polynet PN2000or approved equal.

PART 3 - EXECUTION

3.1 TRENCH CONSTRUCTION

A. General:

1. Construction of the permanent toe dewatering trench,the discharge trench and the holding pond shallconform to the requirements of this Specification andthe details shown on the Subcontract Drawings.

2. The sequence to be followed shall consist of grading abench across the top of the toe drain trench tofacilitate the installation of wellpoints. When thewater level has been drawn down sufficiently, the toedrain trench and the trench for the discharge pipe,shall be constructed.

3. No surcharge, such as vehicles, will be allowed on thebench above the excavated slope for the dewateringtrench.

4. Grading of the 2:1 slope and bench to install thewellpoints will require working around the fourexisting wells and piezometer located on the "A"line. These installations are to remain and shall notbe damaged during slope excavation.

5. A trench box shall be available at all times duringexcavation of the toe trench.

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6. Water levels shall be lowered at least 1 foot belowthe bottom of trench elevation prior to the start ofexcavation of the trench. These levels shall bedetermined by the Subcontractor with a method approvedby the Contractor.

7. Frost prevention will be necessary during constructionof the trenches and holding pond. The work in pro-gress shall be adequately covered to prevent anyoccurrence of frost damage.

8. The Subcontractor will be required to excavate to thelow permeability liner in a minimum of three locationsas directed by the Contractor. Samples of the claylining and other materials will be taken by the Con-tractor. It is estimated that approximately fourhours will be required for sampling at each location.

9. Materials excavated from the trench shall be removedto another area of the cell, as directed by the Con-tractor.

10. Filter fabric shall be placed around the gravelapproximately to the shape shown on the SubcontractDrawings and the ends shall overlap at least 24inches. Filter material shall be placed with care toprevent damage to the filter fabric.

11. Gravel filter materials shall be laced over thefilter fabric to a depth of 6 inches prior coinstalling and burying the perforated drain pipe.

12. Filter materials shall be uncompacted.

13. Backfill materials and compaction specifications forconstruction of the trenches and holding pond shallconform to the applicable requirements of Section02200.

14. A concrete waterstop shall be constructed around thedrain pipe where it enters the clay cover of theexisting dike as shown on the Subcontract Drawings.

15. Materials placed adjacent to the drain pipe, theconcrete cutoff and the vent pipe shall be compactedby hand compactor.

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16. The temporary dewatering system shall not be removeduntil after the trench and holding pond are installedand operational.

B. Holding Pond:

1. The holding pond is described below and is shown onthe Subcontract Drawings.

2. The holding pond is founded partly in cut section andpartly on fill as shown on the Subcontract Drawings.

3. The pond shall be totally lined with 2 feet of claylining similar to the low permeability material asspecified in Section 02200, compacted to a minimum of90 percent of maximum dry density in accordance withASTM D698 and shall be free of any material that maydamage the liner.

4. The HDPE liner shall be laid directly on the compactedclay.

5. A 6-inch diameter monitor pipe perforated for thelower 6 inches shall be installed in the northeastcorner of the holding pond to monitor any leakage.

6. A 6-inch diameter spillway pipe with appropriatewaterstops shall be installed at El. 7047.5 or 1/2foot below top of holding pond dike as shown on theSubcontract Drawings.

7. The HDPE liner shall be sealed around the dischargepipe, the monitor pipe and the spillway pipe wherethey penetrate the liner to prevent leakage. Sealingshall be done in accordance with the liner manufac-turer's published instructions.

C. Temporary Dewatering Plan:

1. The temporary dewatering plan, to be installedseparately, is described below for information onlyand is shown on the Subcontract Drawings.

2. The wellpoint system shall be designed to lower thewater level in the uranium tailings to El. 7046 orlower in the region of the toe trench. It will beoperating at more than 7000 feet above sea level.

3. Uranium tailings to be dewatered have a grain sizedistribution similar to a medium to fine sand with 13

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to 40 percent minus 200 mesh. They were compacted tomore than 90 percent standard proctor maximum. drydensity when placed.

4. Slotted PVC wellpoints, 1-1/2-inch diameter, will belocated on 4-foot centers on the upslope side of thetrench. A 12-inch screen length is recommended. Adrawdown tube shall extend to within 1 inch of thebottom of the wellpoint.

5. Holes will be predrilled by auger or rotary method,minimum 8-inch diameter. Fifty-six of the wellpointsshall penetrate to El. 7043, 1 foot above the top ofthe clay liner beneath the tailings. Care shall beused to avoid penetrating the liner when drilling.The remaining 28 wellpoint tips are at varying higherelevations corresponding to elevations shown on theSubcontract Drawings but also terminate near the celllining.

6. Holes are to be thoroughly flushed with clear waterbefore installation of filter sand. A separate jetpipe is recommended. A wash valve in the bottom ofthe wellpoint is not recommended, because of thelimited distance between the bottom of the drilledhole (El. 7043) and the required predrained waterlevel (El. 7046).

7. Flushing water shall be controlled in a closed loop,using dikes, ditches, pits and/or tanks. The waterwill be contaminated and shall be disposed of in theexisting treatment system. A fresh water holdingsystem and a settling tank will also be necessary inwellpoint construction.

8. Filter sand shall be washed concrete sand, ColoradoState Department of Highways Specifications for fineaggregate and for concrete or equal. It shall beplaced in a continuous stream to avoid bridging andreduce segregation, and shall extend up to 6 inchesbelow the header elevation. The top 6 inches of thehole shall be filled with clay or bentonite to providea seal.

9. Header elevation, and elevation of the wellpoint pumpsuction, shall be 7055 or lower along the 220-footsection of the trench and 12 feet above the wellpointtip along the remainder of the trench. The existingIndicated Phreatic Surface (IPS) in the area of thetoe drain may be at or slightly above this elevation.It may be advisable to predrill for the wellpoints and

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install them from a berm a foot or more higher than7055. A trench can then be excavated for the header,and a pit for the pump. It may be necessary to make ashort temporary installation of header and pump tolower the water for the final elevation.

10. The wellpoint system shall be designed such thatfreezing temperatures will not hamper operations.

11. The wellpoint pump shall be by diesel-generated power,with an air capacity of at least 200 ACFM, and a watercapacity of 25 gpm at a discharge head of 50 feet.Maximum horsepower of the motor shall be 30 MPthree-phase.

12. The wellpoint system shall tie into the existing 17-well dewatering manifold to transport the pumped waterto the storage tanks near DS-4 retention basin.

3.2 DISPOSAL OF MATERIALS

Debris, rubbish, and other materials resulting from trenchconstruction operations shall be removed from the site, ordisposed of in an approved area within the site and thesite shall be left in a neat presentable condition.

PART 4 - MEASUREMENT AND PAYMENT

4.1 MEASUREMENT

A. Measurement for payment for the following will be by thelineal feet of toe trench excavated, excavation andbackfill for discharge pipe, perforated drain pipeinstalled, and discharge pipe installed as shown on theSubcontract Drawings and as specified and approved by theContractor:

1. Excavate Toe Trench, Backfill Afterward

2. Excavate and Backfill for Discharge Pipe Installation

3. Install Perforated Pipe, Gravel Filter, and FilterFabric,

4. install Concrete Waterstop, Discharge Pipe with VentPipe and Valve

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B. Measurement for payment for the following will be by thenumber of units, as specified and approved by theContractor:

1. Sample Clay Liner, Repair Afterward

C. The following will not be measured for payment. Paymentwill be by lump sum for the work specified and approved bythe Contractor.

1. Cut or Fill for Holding Pond, Install Clay Liner andSpillway

2. Line Pond with Plastic and Install Monitor Pipe

4.2 PAYMENT

A. Payment for the items of Article 4.1 above will be bytheir applicable lineal foot, unit, lump sum prices quotedtherefor in the Bid Schedule.

B. No separate payment will be made for incidentals which arenot specifically listed as payment items in the BidSchedule.

END OF SECTION 02142

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ATTACHMENT TO SECTION 02142

TOE TRENCH AND HOLDING POND

BID SCHEDULE

Name of Bidder Date:

Following are the prices bid for completion of the Work asrequired by Section 02142:

Item Approx. UnitNo. Description Unit Quantity Price Amount

1. Excavate Toe Trench,Backfill Afterward L.F. 330

2. Excavate and Backfill forDischarge Pipe Installation L.F. 215

3. Sample Clay Liner,Repair Afterward Each 6

4. Install Perforated Pipe,Gravel Filter and FilterFabric L.F. 330

5. Install Concrete Waterstop,Discharge Pipe with Ventand Valve L.F. 215

6. Cut or Fill for HoldingPond, install Clay Linerand Spillway L.S. 100%

7. Line Pond with Plasticand Install Monitor Pipe L.S. 100% N/A

TOTAL PRICE

* For complete description of a bid item and measurement andpayment provisions, see Part 4 of Specification Section 02142.

END OF ATTACHMENT TO SECTION 02142

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