DRAFT TECHNICAL MEMORANDUM - WordPress.com Rau, PE DRAFT January 6, 2016 Paragon Consulting Group,...

DRAFT TECHNICAL MEMORANDUM

Date: January 6, 2016 Document No.: 1524433 005 TM03 RevA

To: Dave Rau, PE Company: Paragon Consulting Group, Inc.

From: Stephen W. Rogers, PE Email: [email protected]

cc: Scott Hummer (NPIC)

RE: BOXELDER B-2 AND B-3 WATERSHED DAMS ALTERNATIVES ASSESSMENT

1.0 INTRODUCTION This memorandum summarizes the preliminary evaluation of alternatives for Boxelder Watershed Dams

B-2 and B-3 to meet current State of Colorado and NRCS Dam Safety Requirements. The State of

Colorado Department of Water Resources has designated both dams as High Hazard structures based

on hypothetical dam breach evaluations and inundation mapping. Hydrologic evaluations and a

preliminary Incremental Damage Assessment (IDA) completed by Golder Associates Inc. (Golder)

indicate that the appropriate Inflow Design Flood (IDF) for Watershed Dam B-2 should be the full

Probable Maximum Flood (PMF) event and the IDF for Watershed Dam B-3 should be the 75-percent

PMF event. While both the embankment and emergency spillway structures are in good condition,

modifications are required to safely pas the IDF without overtopping the embankment.

This memorandum presents design criteria adopted by Golder, preliminary alternatives under

consideration, estimated implementation costs, and preliminary recommendations. Golder has completed

the preliminary engineering evaluations to support the work, which is included in the Phase 1 Summary

Report (Golder 2015).

2.0 DESIGN CRITERIA Design criteria that will be used to evaluate and compare alternatives are based on current NRCS and

State of Colorado Division of Water Resources requirements. Table 1 summarizes the design criteria that

will be used to evaluate and compare alternatives.

I:\15\1524433\0100\0122\005 TM03 RevA\1524433 005 TM03 RevA DRAFT BoxelderAlternatives 06JAN16.docx Golder Associates Inc.

44 Union Boulevard, Suite 300 Lakewood, CO 80228 USA

Tel: (303) 980-0540 Fax: (303) 985-2080 www.golder.com

Golder Associates: Operations in Africa, Asia, Australasia, Europe, North America and South America

Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation

mailto:[email protected]

Dave Rau, PE DRAFT January 6, 2016 Paragon Consulting Group, Inc. 2 1524433 005 TM03 RevA Table 1: Watershed Dams B-2 and B-3 Design Criteria

Criteria B-2 B-3 Source

Embankment Min. Design Crest Elevation (feet amsl) 5,574.4 5,489.0 As-built survey Min. Design Crest Width (feet) 17 17 Colorado DWR regulations Max. Side Slope 2½H:1V 2½H:1V Stability analysis Max. RCC Overtopping Velocity (fps) 30 30 USBR guidelines Max. ACB Overtopping Velocity (fps) 30 30 Manufacturer’s recommendation Max. Reinforced Vegetation Overtopping Velocity (fps) 30 30 Manufacturer’s recommendation Static Embankment Stability Factor of Safety 1.5 1.5 Colorado DWR/NRCS regulations Rapid Drawdown Factor of Safety 1.2 1.2 Colorado DWR/NRCS regulations Pseudo-static Embankment Stability Factor of Safety 1.0 1.0 Colorado DWR/NRCS regulations Hydrology 6-hour Duration PMP (Local Storm) (inches) 8.85 10.01 HMR 55A 6-hour Duration PMP (General Storm) (inches) 16.87 16.87 HMR 55A 24-hour Duration PMP (General Storm) (inches) 24.00 24.00 HMR 55A 72-hour Duration PMP (General Storm) (inches) 29.93 29.93 HMR 55A Spillway Capacity Min. Design Crest Elevation (feet amsl) (100-year WSEL) 5,564.4 5,477.0 FEMA FIS IDF Peak Inflow Discharge (cfs) 147,200 58,400 Golder hydrologic analysis IDF Peak Outflow Design Discharge (cfs) 146,500 58,100 Golder hydrologic analysis Max. Velocity through Existing Spillway (fps) 30.0 6.5 Published literature

3.0 PRELIMINARY ALTERNATIVES The proposed improvements will be designed to meet current State of Colorado and NRCS dam safety

requirements and will likely require modifications to the dam and/or spillway structures. Preliminary

alternatives that have been identified for further evaluation include the following:

Future without Project (No Action Alternative) The No Action Alternative is required to be evaluated as an alternative by NRCS. For dams that pose a potential safety hazard from failure, the future-without-project (FWOP) plan or no-action alternative is based on the course of action that the sponsors are most likely to take in the event that no federally financed rehabilitation work were to be undertaken. This includes a deliberate breach. A deliberate breach would be likely to reduce safety risks as compared to a sudden, catastrophic dam failure.

No action is not considered to be a viable alternative as the dams would not meet the Purpose and Need, because downgradient residences would no longer have flood protection. However, NRCS requires that it be carried through the analysis as a baseline to compare the action alternatives listed below.

Decommissioning Decommissioning would involve reducing the embankment height and storage volume to a level where the dams are not considered to be jurisdictional structures (less than 10 feet high and 100 acre-feet of storage volume) by either State of Colorado or NRCS standards. Decommissioning would greatly reduce the flood attenuation benefit of the facilities and result in higher peak discharges and flooding downstream for lower

I:\15\1524433\0100\0122\005 TM03 RevA\1524433 005 TM03 RevA DRAFT BoxelderAlternatives 06JAN16.docx

Dave Rau, PE DRAFT January 6, 2016 Paragon Consulting Group, Inc. 3 1524433 005 TM03 RevA

magnitude flooding events. The decommissioning alternative differs from the future without project, in that it would use federal funds and, thus, be required to meet NRCS standards.

Modifications to Existing Spillways

Modifications to the existing spillways could be undertaken to increase the conveyance capacity and reduce the potential for overtopping of the embankments. These alternatives include:

Installation of hydraulically efficient crest structures (ogee, labyrinth)

Crest lowering and installation of fuseplugs/fusegates

Widening/lowering of the existing spillway

Increased Freeboard (Embankment Crest Raise) The embankments could be raised to increase spillway conveyance discharges and minimize the potential for overtopping. The embankments would be raised using either downstream, centerline, or upstream construction methods.

Overtopping Protection

Overtopping protection of the embankments (or a section of the embankments) could be implemented to protect the embankment from erosion and potential failure. Overtopping protection alternatives include:

Roller-compacted concrete (RCC)

Articulated concrete blocks (ACB)

Geosynthetics or other turf reinforcement mats (TRM)

Secondary Emergency Spillway

A secondary spillway could be constructed on the abutments or on the embankment to provide additional flood conveyance capacity. The secondary spillway could include the installation of fuseplugs constructed within the embankment that would serve as a controlled release from the dam.

These alternatives are discussed in more detail in the sections below.

3.1 No Action (Future without Project) Under this alternative, the embankment would be breached and armored to protect from erosion. This

would likely be the minimum action required to meet Colorado Dam Safety Criteria without any

modifications to increase spillway capacity. Since the dam would be breached, minimal flood attenuation

would occur and the flood control benefit of the dam would be greatly reduced. The breach was sized

based on flood routing calculations to pass the appropriate IDF for each structure assuming maintaining a

maximum 9-foot flow depth (assuming 1 foot of freeboard). The remainder of the embankment would be

left in its existing condition. The breach would be trapezoidal in shape (with a 3H:1V side slope) and

unlined. As such, erosion of the channel through the breach during larger flood events would be likely.

The calculated breach width to meet the above criteria is 1,300 feet for B-2 and 700 feet for B-3. The

maximum velocity during the IDF through the breach is estimated to be approximately 12 fps. Figures 1


Dave Rau, PE DRAFT January 6, 2016 Paragon Consulting Group, Inc. 4 1524433 005 TM03 RevA and 2 provide sections of the proposed conceptual breach configuration of this alternative for B-2 and

B-3, respectively. Figure 3 shows a concept view of the treatment required through the breached section.

Advantages and disadvantages of this alternative are summarized in the table below:

Advantages Disadvantages

Minimizes construction costs Reduces flood control benefits in downstream areas

Changes use of structure; Environmental Assessment (EA) likely required

Minimizes water quality and sediment deposition benefits

3.2 Decommissioning This alternative is similar to the No Action alternative with the exception that a meandering low-flow

channel would be re-established through the breach and the floodplain bench would be vegetated with

riparian vegetation. The side slopes would be armored with riprap to minimize the potential for lateral

erosion. In the case of Watershed Dam B-3, the low-flow channel would also be used to deliver irrigation

water to the downstream diversion structure located below the dam. Figure 3 provides a section of the

proposed conceptual design of this alternative through the breached section.



Minimizes construction costs Re-establishes natural channel system

Reduces flood control benefits in downstream areas

Changes use of structure; EA likely required Minimizes water quality and sediment

deposition benefits

3.3 Overtopping Protection For this alternative, the embankment would be protected from overtopping flows during the IDF using

either Roller Compacted Concrete (RCC), Turf Reinforcement Mats (TRM), or Geosynthetics or

Articulated Concrete Blocks (ACB). The maximum overtopping flows for both Watershed Dams B-2 and

B-3 are approximately 3 feet across the entire embankment crest, and the associated anticipated

velocities on the face of the dam would be acceptable for the use of these materials. Excavation of the

crest and downstream face would be required to maintain the existing geometry of the slope after

installation of the overtopping protection. Topsoil and vegetation could be used to cover the erosion

resistant overtopping protection to maintain the aesthetics of the embankments. A 30-foot wide RCC or

ACB apron and end sill wall are also required at the toe of the dam to minimize the potential for scour at


Dave Rau, PE DRAFT January 6, 2016 Paragon Consulting Group, Inc. 5 1524433 005 TM03 RevA the toe of the embankment. Figure 5 provides a cross section of the proposed conceptual design of these

alternatives.



Prevents the potential of an overtopping failure during the IDF; meets regulatory requirements

Maintains flood control benefit of structure Maintains existing spillway function

Relatively high construction costs

3.4 Modifications to Existing Spillway Structures The B-2 spillway could be widened by approximately 1,070 feet (to a total width of 1,250 feet) by

excavating the embankment, demolishing one of the reinforced concrete walls of the existing spillway,

and constructing a new reinforced concrete spillway extension of the existing spillway, which would

convey the required IDF without overtopping the dam. The dam crest would be raised by 1 foot (using

some of the excavated embankment material) to increase the freeboard. Total flow through the spillway is

estimated to be approximately 146,500 cubic feet per second (cfs).

The B-3 spillway could be widened by 200 feet and lowered approximately 3 feet by excavating the

earthen spillway channel and removing the separator berm between the two existing spillway channels.

Two (2) concrete cutoff walls would be installed to direct flows through the spillway, and the dam crest

would be raised by 1 foot using the some of the excavated material from the spillway. The total estimated

flow through the proposed modified spillway is approximately 69,800 cfs, which would convey the

required IDF without overtopping the embankment. Figures 6 and 7 provide a plan view and cross

section of the proposed conceptual design of these alternatives for Watershed Dams B-2 and B-3,

respectively.



Prevents the potential of an overtopping failure during the IDF; meets regulatory requirements


Relatively high construction costs

3.5 Auxiliary Fuseplug Spillway This alternative consists of installing an auxiliary fuseplug spillway in the embankments by excavating a

new spillway channel and installing one or more fuseplugs (or fusegates). A fuseplug is essentially a

section within a spillway or embankment that is designed to fail in a controlled fashion so that additional


Dave Rau, PE DRAFT January 6, 2016 Paragon Consulting Group, Inc. 6 1524433 005 TM03 RevA flood conveyance can occur without uncontrolled failure of the dam. This would allow for a controlled

release of water from the dam during an extreme flooding event. The existing emergency spillways would

continue to operate as originally designed until overtopping of the fuseplug structures occurred, allowing

for a controlled release of water from the reservoir. The fuseplugs would be constructed with reinforced

concrete splitter walls with pilot channels at various elevations to allow for a gradual release of water from

the auxiliary spillway during an extreme flooding event. A reinforced concrete floor would minimize

additional erosion of materials from the embankment below the existing auxiliary spillway crest elevation.

The B-2 auxiliary fuseplug spillway would be 1,200 feet wide, and the B-3 auxiliary spillway would be

500 feet wide, each with a minimum of three (3) fuseplug cells. Figures 8 and 9 provide a plan view and

cross section of the proposed conceptual design of these alternatives for Watershed Dams B-2 and B-3,

respectively.



Reduces the potential of an overtopping failure of the embankment during an extreme flooding event; meets regulatory requirements


Requires excavation of embankment and specialized construction

Fuseplug requires regular maintenance and inspection

4.0 COMPARATIVE ESTIMATED IMPLEMENTATION COSTS Implementation costs for the alternatives presented above were estimated based on unit rates of similar

projects in Northern Colorado and preliminary unit rates from vendors. Tables 2 and 3 below provide a

summary of the estimated implementation costs for the alternatives for Watershed Dams B-2 and B-3,

respectively. The costs were estimated for comparative purposes only and include 25-percent

contingency. Attachment 1 provides a breakdown of the quantities and unit rates used to determine the

implementation costs.

Table 2: Boxelder Watershed Dam B-2 Estimated Implementation Costs

Alternative Estimated Cost Rank

No Action (Future Without Project) $3,600,000 1 Decommissioning $3,800,000 2 RCC Overtopping $27,600,000 6 TRM Overtopping $15,200,000 5 ACB Overtopping $28,100,000 7 Spillway Widening $8,600,000 4 Auxiliary Fuseplug Spillway $6,100,000 3


Dave Rau, PE DRAFT January 6, 2016 Paragon Consulting Group, Inc. 7 1524433 005 TM03 RevA Table 3: Boxelder Watershed Dam B-3 Estimated Implementation Costs

Alternative Estimated Cost Rank

No Action (Future Without Project) $1,600,000 1 Decommissioning $1,700,000 2 RCC Overtopping $11,600,000 6 TRM Overtopping $7,200,000 5 ACB Overtopping $12,700,000 7 Spillway Widening $2,400,000 3 Auxiliary Fuseplug Spillway $2,400,000 3

5.0 SUMMARY AND RECOMMENDATIONS Based on the alternatives evaluations completed, the most cost-effective alternative would involve

decommissioning of the dams by breaching the embankment and restoring a low flow channel through

the breach. However, decommissioning of the dams would change the beneficial use of the structures

and increase flood hazards downstream during more frequent runoff events (100- to 500-year frequency

events). The most cost effective alternatives that would adequately convey the IDF without overtopping

the dam embankment involve widening the existing spillway structures to accommodate a larger flood

event or installation of an auxiliary fuseplug spillway within the embankment that would not compromise

the existing spillway structures and would allow for a controlled release form the reservoir during extreme

flooding events that would not increase flooding impacts downstream.


DRAFT

FIGURES

Figure 1 Boxelder B-2 Breach Alternative Figure 2 Boxelder B-3 Breach Alternative Figure 3 Cross Section – No Action Breach Alternative Figure 4 Cross Section – Decommissioning Alternative Figure 5 Cross Section – Dam Overtopping Alternatives Figure 6 Boxelder B-2 Existing Spillway Modifications Alternative Figure 7 Boxelder B-3 Existing Spillway Modifications Alternative Figure 8 Boxelder B-2 Auxiliary Fuseplug Spillway Alternative Figure 9 Boxelder B-3 Auxiliary Fuseplug Spillway Alternative

ELEV

ATIO

N (F

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5480

5490

5500

5510

5520

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5550

5560

5570

5580

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5600

5480

5490

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5570

5580

5590

5600

0+00 2+00 4+00 6+00 8+00 10+00 12+00 14+00 16+00 18+00 20+00 22+00 24+00 26+00 28+00 30+00 32+00 34+00 36+00 38+00 40+00 42+00 44+00 46+00 48+00 50+00 52+00 54+00 55+00

178 ft

BREACH WIDTH ~1300 ft

EXISTING SPILLWAY

EXISTING DAM CRESTELEVATION 5,574.4 ft

ORIGINAL GROUNDSURFACE

STATION (ft)

3H

1V

3H

1V

C EXISTINGSERVICE

SPILLWAY

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EXCAVATE EMBANKMENTAND DEMOLISH EXISTINGSPILLWAY STRUCTURE

REMOVE EXISTINGSPILLWAY STRUCTURE

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BOXELDER DAMB-2 AND B-3 WATERSHED PLANNING STUDY

NORTH POUDRE IRRIGATION COMPANY

BOXELDER B-2BREACH ALTERNATIVE

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PLAN VIEW

PROFILE

DRAFTNOT FOR CONSTRUCTION

ELEV

ATIO

N (F

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ELEV

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N (F

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B3

5430

5440

5450

5460

5470

5480

5490

5500

5510

5520

5430

5440

5450

5460

5470

5480

5490

5500

5510

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0+00 2+00 4+00 6+00 8+00 10+00 12+00 14+00 16+00 18+00 20+00 22+00 24+00 26+00 28+00 30+00 32+00 34+00 36+00 38+00 39+00

EXISTING DAM CRESTELEVATION 5,489 ft

ORIGINALGROUNDSURFACE

ELEVATION 5,481 ft

EXISTING SPILLWAY

BREACH WIDTH ~700 ft

3H

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EXCAVATE EMBANKMENTAND DEMOLISH EXISTING

SPILLWAY STRUCTURE

STATION (ft)

C EXISTINGSERVICE

SPILLWAY

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BOXELDER B-3BREACH ALTERNATIVE

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PLAN VIEW

PROFILEDRAFT

NOT FOR CONSTRUCTION

EXISTING EMBANKMENT CREST

10 ft

RIPRAP KEYED IN A MINIMUM OF 3 ftBREACH WIDTH

B2 ~ 1300 ftB3 ~ 700 ft

3 ft MIN.1V1V

NATURAL GROUND SURFACE

3H3HRIPRAP KEYED IN A MINIMUM OF 3 ft

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CROSS SECTIONNO ACTION BREACH ALTERNATIVE

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EXISTING EMBANKMENT CREST

10 ft

RIPRAP (KEYED AT TOE)

BREACH WIDTHB2 ~ 1300 ftB3 ~ 700 ft

2 ft MIN.

3H1V

3H1V

NATURAL GROUND SURFACE10 ft

C MEANDERING LOW FLOW CHANNELL

WETLANDS/NATIVE VEGETATIONBANK BOULDERS

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CROSS SECTIONDECOMMISSIONING ALERNATIVE

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ELEV

ATIO

N (F

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SL)

ELEV

ATIO

N (F

T.-M

SL)

5500

5520

5540

5560

5580

5600

5500

5520

5540

5560

5580

5600

180 160 140 120 100 80 60 40 20 0 20 40 60 80 100 120 140 160 180

4.16 ft1 ft10 ft

4.71 ft1 ft

10 ft

3H (OVERALL)1V

1H (LIFT FACE)1V

2.5H (OVERALL)1V

17 ft

30 ft 15 ft

GRADE BREAK

MATCHEXISTING

STEEL SHEET PILE ORCONCRETE CUTOFF WALL

ORIGINAL GROUND

CREST EL. 5574.4 ft

BENCH EL. 5554.4 ft

STATION (FT.-MSL)

CONCRETE CUTOFFWALL

1H:1V(TYP.)

COMPACT 1H:1V EDGE OF LIFT(TYP. EVERY LIFT)

COMPACT EXPOSED HORIZONTALFACE OF RCC LIFT (TYP. EVERY LIFT)

10 ft RCCSTEP WIDTH (TYP.)

1 ft LIFT THICKNESS AFTER COMPACTION (TYP.)

PREPAREDSUBGRADE

2.5H:1V

1.0 ft COMPACTED SUBGRADE

ACB

0%

CHANNEL FILL (COMPACTED)

GEOSYNTHETICS AND GRANULAR BEDDINGPER MANUFACTURER'S RECOMMENDATIONS

2 ft

HYDROBINDER INFILL

ENGINEERED SYNTHETIC TURF

WOVEN GEOTEXTILE

STRUCTURED MEMBRANE

PREPARED SUBGRADE

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CROSS SECTIONDAM OVERTOPPING ALTERNATIVES

TITLE

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SCALE 1'' = 30' SECTION - RCC OVERTOPPING (B-2)

0

FEET

15 30

1'' = 30'

15

SCALE N.T.S. RCC DETAIL 25

SCALE N.T.S. ACB DETAIL 35

SCALE N.T.S. TRM DETAIL


ELEV

ATIO

N (F

T)

ELEV

ATIO

N (F

T)

5480

5490

5500

5510

5520

5530

5540

5550

5560

5570

5580

5590

5600

5480

5490

5500

5510

5520

5530

5540

5550

5560

5570

5580

5590

5600

0+00 2+00 4+00 6+00 8+00 10+00 12+00 14+00 16+00 18+00 20+00 22+00 24+00 26+00 28+00 30+00 32+00 34+00 36+00 38+00 40+00 42+00 44+00 46+00 48+00 50+00 52+00 54+00 55+00

178 ft

MODIFIED SPILLWAY WIDTH ~ 1250 ft

EXISTING SPILLWAY

DAM CRESTELEVATION 5,575.4 ft

ORIGINAL GROUND SURFACE

STATION (ft)

C EXISTINGSERVICE

SPILLWAY

L

ELEVATION 5,465.4 ft

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DAM CRESTELEVATION 5,490 ft


ELEVATION 5,481 ft

STATION (ft)

MODIFIED SPILLWAY WIDTH ~ 600 ft

C EXISTINGSERVICE

SPILLWAY

L

ELEVATION 5,478 ft

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FIGURE

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ELEV

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AL - (1)

5480

5490

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AUXILIARY FUSE PLUG SPILLWAY WIDTH ~ 1200 ft

ELEVATION 5,574.4 ftELEVATION 5,573.4 ft

ELEVATION 5,572.4 ftELEVATION 5,571.4 ft

DAM CRESTELEVATION 5,575.4 ft


STATION (ft)

178 ft

EXISTING SPILLWAY

C EXISTINGSERVICE

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FIGURE

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DAM CRESTELEVATION 5,490 ft


AUXILIARY FUSE PLUG SPILLWAYWIDTH ~ 500 ft

ELEVATION 5,486 ftELEVATION 5,487 ft

ELEVATION 5,488 ftELEVATION 5,489 ft

STATION (ft)

200 ft 200 ft

ELEVATION 5,481 ft

EXISTINGEMERGENCYSPILLWAY

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FIGURE

9A

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DRAFT

ATTACHMENT 1A B-2 COST ESTIMATE INFORMATION

January 2016 Alternatives Cost Estimate SummaryBoxelder Watershed Dam B-2

1524433 005 TM03 RevADRAFT

AlternativeEstimated Cost Rank

No Action (Future Without Project) 3,600,000$ 1Decommissioning 3,800,000$ 2RCC Overtopping 27,600,000$ 6TRM Overtopping 15,200,000$ 5ACB Overtopping 28,100,000$ 7Spillway Widening 8,600,000$ 4Auxiliary Fuseplug Spillway 6,100,000$ 3

I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1A Boxelder B-2 AlternativeCosts.xlsx\Summary

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COST ESTIMATEPROJECT: Boxelder B-2 Watershed Planning Study DESIGN

LEVEL:Conceptual PROJECT NO: 1524433

ITEM: No Action (Future without Project) Alternative ESTIMATED BY:

S. Rogers DATE: 12/15/2015

NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 100,000$ 100,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 40,000$ 40,000$ 4 Erosion Control 1 lump sum 5,000$ 5,000$ 5 Earthwork5a Excavation (Embankment) 541,900 cubic yards 4$ 2,167,600$ 5b Riprap 1,600 cubic yards 65$ 104,000$ 5c Outlet Works Demolition 1 lump sum 25,000$ 25,000$ 6 Reclamation and Seeding 2 acres 8,500$ 17,000$ 7 Instrumentation and Monitoring 1 lump sum 6,000$ 6,000$ 8 Unlisted Items (10%) 232,000$

Construction Cost Subtotal 2,711,600$ Contingency (25%) 677,900$ Engineering (5%) 135,600$ Constr. Oversight, QA/QC Testing, As-builts (5%) 135,600$ Permitting 60,000$ Legal 20,000$ Total Estimated Costs 3,605,100$

Notes: 1. Preliminary cost estimate developed using unit rates from other similar projects in the Northern Colorado. Final cost estimate will be updated based on final design.2. Dewatering/diversion assumes that irrigation flows will need to be maintained during construction.3. Construction Oversight, QA/QC Testing, as-built documentation, permitting and legal fees are estimated.

I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1A Boxelder B-2 AlternativeCosts.xlsx\No Action

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ITEM: Decommissioning Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 150,000$ 150,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 40,000$ 40,000$ 4 Erosion Control 1 lump sum 10,000$ 10,000$ 5 Earthwork5a Excavation (Embankment) 541,900 cubic yards 4$ 2,167,600$ 5b Riprap 2,000 cubic yards 65$ 130,000$ 5c Outlet Works Demolition 1 lump sum 25,000$ 25,000$ 6a Reclamation and Seeding (Wetlands) 2 acres 15,000$ 30,000$ 6b Reclamation and Seeding (Grasses) 2 acres 6,500$ 13,000$ 7 Instrumentation and Monitoring 1 lump sum 10,000$ 10,000$ 8 Unlisted Items (10%) 238,000$



I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1A Boxelder B-2 AlternativeCosts.xlsx\Decomissioning

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ITEM: RCC Overtopping Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 250,000$ 250,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 25,000$ 25,000$ 4 Erosion Control 1 lump sum 10,000$ 10,000$ 5 Earthwork5a Excavation (Embankment) 59,800 cubic yards 4$ 239,200$ 5b RCC Overtopping 98,700 cubic yards 150$ 14,805,000$ 5c RCC Apron 12,000 cubic yards 150$ 1,800,000$ 5d Reinforced Concrete Cutoff Walls 2,000 cubic yards 450$ 900,000$ 5e Riprap 8,000 cubic yards 65$ 520,000$ 6 Reclamation and Seeding 3 acres 6,500$ 19,500$ 7 Instrumentation and Monitoring 1 lump sum 10,000$ 10,000$ 8 Unlisted Items (10%) 1,829,000$

Construction Cost Subtotal 20,422,700$ Contingency (25%) 5,105,700$ Engineering (5%) 1,021,100$ Constr. Oversight, QA/QC Testing, As-builts (10%) 2,042,300$ Permitting 40,000$ Legal 20,000$ Total Estimated Costs 27,630,700$


I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1A Boxelder B-2 AlternativeCosts.xlsx\RCC Overtopping

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ITEM: TRM Overtopping Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 150,000$ 150,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 25,000$ 25,000$ 4 Erosion Control 1 lump sum 10,000$ 10,000$ 5 Earthwork5a Excavation (Embankment) 29,900 cubic yards 4$ 119,600$ 5b TRM Overtopping 807,600 square feet 7$ 5,653,200$ 5c ACB Apron 162,000 square feet 18$ 2,916,000$ 5d Reinforced Concrete Cutoff Walls 2,000 lump sum 450$ 900,000$ 5e Riprap 8,000 cubic yards 65$ 520,000$ 5f Topsoil 29,900 cubic yards 8$ 239,200$ 6 Reclamation and Seeding 4 acres 6,500$ 26,000$ 7 Instrumentation and Monitoring 1 lump sum 10,000$ 10,000$ 8 Unlisted Items (10%) 1,038,000$

Construction Cost Subtotal 11,622,000$ Contingency (25%) 2,905,500$ Engineering (5%) 581,100$ Constr. Oversight, QA/QC Testing, As-builts (5%) 581,100$ Permitting 40,000$ Legal 50,000$ Total Estimated Costs 15,198,600$


I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1A Boxelder B-2 AlternativeCosts.xlsx\TRM Overtopping

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ITEM: ACB Overtopping Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 200,000$ 200,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 25,000$ 25,000$ 4 Erosion Control 1 lump sum 10,000$ 10,000$ 5 Earthwork5a Excavation (Embankment) 59,800 cubic yards 4$ 239,200$ 5b ACB Overtopping 807,600 square feet 18$ 14,536,800$ 5c ACB Apron 162,000 square feet 18$ 2,916,000$ 5d Reinforced Concrete Cutoff Walls 2,000 lump sum 450$ 900,000$ 5e Riprap 8,000 cubic yards 65$ 520,000$ 5f Topsoil 29,900 cubic yards 8$ 239,200$ 6 Reclamation and Seeding 4 acres 6,500$ 26,000$ 7 Instrumentation and Monitoring 1 lump sum 10,000$ 10,000$ 8 Unlisted Items (10%) 1,939,000$

Construction Cost Subtotal 21,576,200$ Contingency (25%) 5,394,100$ Engineering (5%) 1,078,800$ Constr. Oversight, QA/QC Testing, As-builts (5%) 1,078,800$ Permitting 40,000$ Legal 50,000$ Total Estimated Costs 28,139,100$


I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1A Boxelder B-2 AlternativeCosts.xlsx\ACB Overtopping

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ITEM: Emergency Spillway Widening Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 150,000$ 150,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 10,000$ 10,000$ 4 Erosion Control 1 lump sum 10,000$ 10,000$ 5 Earthwork5a Excavation (Embankment) 64,500 cubic yards 4$ 258,000$ 5b Excavation (Stilling Basin) 39,600 cubic yards 4$ 158,400$ 5c Riprap 7,900 cubic yards 65$ 513,500$ 6 Emergency Spillway6a Concrete Chute (1250 feet wide) 10,600 cubic yards 450$ 4,770,000$ 6b Concrete Walls 180 cubic yards 450$ 81,000$ 7 Reclamation and Seeding 2 acres 6,500$ 13,000$ 8 Instrumentation and Monitoring 1 lump sum 10,000$ 10,000$ 9 Unlisted Items (10%) 580,000$



I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1A Boxelder B-2 AlternativeCosts.xlsx\Spillway Widening

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ITEM: Auxiliary Fuseplug Spillway Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 150,000$ 150,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 10,000$ 10,000$ 4 Erosion Control 1 lump sum 10,000$ 10,000$ 5 Earthwork5a Excavation (Embankment) 23,000 cubic yards 4$ 92,000$ 5b Riprap 13,970 cubic yards 65$ 908,050$ 6 Fuseplug Construction6a Concrete Apron 5,130 cubic yards 450$ 2,308,500$ 6b Concrete Walls 210 cubic yards 450$ 94,500$ 6c Fuseplug Materials 18,400 cubic yards 32$ 588,800$ 7 Reclamation and Seeding 2 acres 6,500$ 13,000$ 8 Instrumentation and Monitoring 1 lump sum 15,000$ 15,000$ 9 Unlisted Items (10%) 402,000$



I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1A Boxelder B-2 AlternativeCosts.xlsx\Auxillary Fuseplug Spillway

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Boxelder B-2 Estimated Quantities

Crest Length 5400 feet Breach AlternativeCrest Width 17 feet Width 1300 feetCrest El. 5574.4 feet Breach Sideslope (XH:1V) 3Auxiliary Spillway Crest El. 5564.4 feet Length 331 feetService Spillway Crest El. 5546.6 feet Average Length 174 feetLow Point 5522 feet Excavation Volume 492646 cyMax. Height 52.4 feet Breach Flow Depth 10 feetAvg. Height 42 feet Riprap Thickness 2 feetDownstream Slope (XH:1V) 3 Riprap Volume 1553 cyAvg. Slope Length 133 feet Side Slopes Riprap 1553 cySpillway Width 180 feet Low Flow Channel Depth 3 feetSpillway Freeboard 10 feet Low Flow Channel Width 10 feetApron Width 30 feet Low Flow Channel Riprap 471 cyRiprap Width 20 feet

Overtopping Area 807638 sq ft Spillway WideningApron Area 162000 sq ft Total Width 1250 feetRiprap Area 108000 sq ft Increase 1070 feet1 ft Excavation 29913 cy Bottom Length 77 feet2 ft Excavation 59825 cy Average Length 47 feet3 ft Excavation 89738 cy Slope Length 101 feet

Excavation (Embankment) 58628 cy1 foot crest raise 3400 cy Excavation (Stilling Basin) 39630 cyCutoff Walls 1000 cy Riprap 7926 cy

Concrete Thickness 1.5 feetIDF Discharge 146,500 cfs Concrete Floor Volume 10578 cy

Concrete Wall Volume 178 cyExisting Spillway Discharge 17,100 cfsModified Spillway Discharge 150,500 cfsAuxiliary Fuseplug Discharge 131,300 cfs Fuseplug AlternativeTotal Flow w/ Auxiliary Fuseplug 151,000 cfs Total Width 1200 feet

Spacing between Cells 400 feetNo. of Splitter Walls 4Excavation 22978 cyConcrete Floor Volume 5133 cyConcrete Wall Volume 205 cyRiprap Volume 13967 cy

I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1A Boxelder B-2 AlternativeCosts.xlsx\Quantities

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DRAFT

ATTACHMENT 1B B-3 COST ESTIMATE INFORMATION

January 2016 Alternative Cost Estimate SummaryBoxelder Watershed Dam B-3


AlternativeEstimated Cost Rank

No Action (Future Without Project) 1,600,000$ 1Decommissioning 1,700,000$ 2RCC Overtopping 11,600,000$ 6TRM Overtopping 7,200,000$ 5ACB Overtopping 12,700,000$ 7Spillway Widening 2,400,000$ 3Auxiliary Fuseplug Spillway 2,400,000$ 3

I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1B Boxelder B-3 AlternativeCosts.xlsx\Summary

Page 1 of 9



PROJECT: Boxelder B-3 Watershed Planning Study DESIGN LEVEL:

Conceptual PROJECT NO: 1524433

ITEM: No Action (Future without Project) Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 100,000$ 100,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 25,000$ 25,000$ 4 Erosion Control 1 lump sum 5,000$ 5,000$ 5 Earthwork5a Excavation (Embankment) 202,000 cubic yards 4$ 808,000$ 5b Riprap 1,300 cubic yards 65$ 84,500$ 5c Outlet Works Demolition 1 lump sum 25,000$ 25,000$ 6 Reclamation and Seeding 2 acres 8,500$ 17,000$ 7 Instrumentation and Monitoring 1 lump sum 6,000$ 6,000$ 8 Unlisted Items (10%) 94,000$


Notes: 1. Preliminary cost estimate developed using unit rates from other similar projects in the Northern Colorado. Final cost estimate will be updated based on final design.2. Construction Oversight, QA/QC Testing, as-built documentation, permitting and legal fees are estimated.

COST ESTIMATE

I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1B Boxelder B-3 AlternativeCosts.xlsx\No Action

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ITEM: Decommissioning Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 150,000$ 150,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 25,000$ 25,000$ 4 Erosion Control 1 lump sum 10,000$ 10,000$ 5 Earthwork5a Excavation (Embankment) 202,000 cubic yards 4$ 808,000$ 5b Riprap 1,700 cubic yards 65$ 110,500$ 5c Outlet Works Demolition 1 lump sum 25,000$ 25,000$ 6a Reclamation and Seeding (Wetlands) 2 acres 15,000$ 30,000$ 6b Reclamation and Seeding (Grasses) 2 acres 6,500$ 13,000$ 7 Instrumentation and Monitoring 1 lump sum 10,000$ 10,000$ 8 Unlisted Items (10%) 100,000$



COST ESTIMATE

I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1B Boxelder B-3 AlternativeCosts.xlsx\Decomissioning

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ITEM: RCC Overtopping Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 250,000$ 250,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 25,000$ 25,000$ 4 Erosion Control 1 lump sum 10,000$ 10,000$ 5 Earthwork5a Excavation (Embankment) 25,700 cubic yards 4$ 102,800$ 5b RCC Overtopping 38,500 cubic yards 150$ 5,775,000$ 5c RCC Apron 6,000 cubic yards 150$ 900,000$ 5d Reinforced Concrete Cutoff Walls 1,000 lump sum 450$ 450,000$ 5e Riprap 4,000 cubic yards 65$ 260,000$ 6 Reclamation and Seeding 3 acres 6,500$ 19,500$ 7 Instrumentation and Monitoring 1 lump sum 10,000$ 10,000$ 8 Unlisted Items (10%) 752,000$



COST ESTIMATE

I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1B Boxelder B-3 AlternativeCosts.xlsx\RCC Overtopping

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ITEM: TRM Overtopping Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 150,000$ 150,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 25,000$ 25,000$ 4 Erosion Control 1 lump sum 10,000$ 10,000$ 5 Earthwork5a Excavation (Embankment) 12,800 cubic yards 4$ 51,200$ 5b TRM Overtopping 346,400 square feet 7$ 2,424,800$ 5c ACB Apron 81,000 square feet 18$ 1,458,000$ 5d Reinforced Concrete Cutoff Walls 1,000 lump sum 450$ 450,000$ 5e Riprap 4,000 cubic yards 65$ 260,000$ 5f Topsoil 12,800 cubic yards 8$ 102,400$ 6 Reclamation and Seeding 4 acres 6,500$ 26,000$ 7 Instrumentation and Monitoring 1 lump sum 10,000$ 10,000$ 8 Unlisted Items (10%) 478,000$



COST ESTIMATE

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ITEM: ACB Overtopping Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 150,000$ 150,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 25,000$ 25,000$ 4 Erosion Control 1 lump sum 10,000$ 10,000$ 5 Earthwork5a Excavation (Embankment) 25,700 cubic yards 4$ 102,800$ 5b ACB Overtopping 346,400 square feet 18$ 6,235,200$ 5c ACB Apron 81,000 square feet 18$ 1,458,000$ 5d Reinforced Concrete Cutoff Walls 1,000 lump sum 450$ 450,000$ 5e Riprap 4,000 cubic yards 65$ 260,000$ 5f Topsoil 12,800 cubic yards 8$ 102,400$ 6 Reclamation and Seeding 4 acres 6,500$ 26,000$ 7 Instrumentation and Monitoring 1 lump sum 10,000$ 10,000$ 8 Unlisted Items (10%) 864,000$



COST ESTIMATE

I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1B Boxelder B-3 AlternativeCosts.xlsx\ACB Overtopping

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ITEM: Emergency Spillway Widening/Deepening Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 150,000$ 150,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 10,000$ 10,000$ 4 Erosion Control 1 lump sum 10,000$ 10,000$ 5 Earthwork5a Excavation (Spillway) 160,000 cubic yards 4$ 640,000$ 5b Embankment Fill (Crest) 1,700 cubic yards 12$ 20,400$ 5b Riprap 1,800 cubic yards 65$ 117,000$ 6 Spillway Cutoff Walls 800 cubic yards 450$ 360,000$ 7 Reclamation and Seeding 17 acres 6,500$ 107,438$ 8 Road Re-location 1 lump sum 125,000$ 125,000$ 9 Instrumentation and Monitoring 1 lump sum 10,000$ 10,000$ 10 Unlisted Items (10%) 138,000$



COST ESTIMATE

I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1B Boxelder B-3 AlternativeCosts.xlsx\Spillway Widening

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ITEM: Auxiliary Fuseplug Spillway Alternative ESTIMATED BY:


NO DESCRIPTION QUANTITY UNIT UNIT COST TOTAL COST1 Mobilization/De-mobilization 1 lump sum 150,000$ 150,000$ 2 Erosion Control Plan and Construction Permits 1 lump sum 15,000$ 15,000$ 3 Dewatering/Diversion 1 lump sum 10,000$ 10,000$ 4 Erosion Control 1 lump sum 10,000$ 10,000$ 5 Earthwork5a Excavation (Embankment) 6,680 cubic yards 4$ 26,720$ 5b Riprap 5,330 cubic yards 65$ 346,450$ 6 Fuseplug Construction6a Concrete Apron 1,810 cubic yards 450$ 814,500$ 6b Concrete Walls 170 cubic yards 450$ 76,500$ 6c Fuseplug Materials 5,300 cubic yards 32$ 169,600$ 7 Reclamation and Seeding 2 acres 6,500$ 13,000$ 8 Instrumentation and Monitoring 1 lump sum 15,000$ 15,000$ 9 Unlisted Items (10%) 146,000$



COST ESTIMATE

I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1B Boxelder B-3 AlternativeCosts.xlsx\Auxillary Fuseplug Spillway

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Boxelder B-3 Estimated QuantitiesEstimated Cost

Crest Length 2700 feet Breach AlternativeCrest Width 17 feet Width 700 feetCrest El. 5489 feet Breach Sideslope (XH:1V) 3Auxiliary Spillway Crest El. 5481 feet Length 281 feetService Spillway Crest El. 5467.8 feet Average Length 149 feetLow Point 5445 feet Excavation Volume 202022 cyMax. Height 44 feet Breach Flow Depth 10 feetAvg. Height 35 feet Riprap Thickness 2 feetDownstream Slope (XH:1V) 3 Riprap Volume 1316 cyAvg. Slope Length 111 feet Side Slopes Riprap 1316 cySpillway Width 400 feet Low Flow Channel Depth 3 feetSpillway Freeboard 8 feet Low Flow Channel Width 10 feetApron Width 30 feet Low Flow Channel Riprap 400 cyRiprap Width 20 feet

Overtopping Area 346443 sq ft Spillway WideningApron Area 81000 sq ft Total Width 600 feetRiprap Area 54000 sq ft Increase 200 feet1 ft Excavation 12831 cy Total Depth 12 feet2 ft Excavation 25662 cy Bottom Length 1200 feet3 ft Excavation 38494 cy Embankment Crest Raise 1 foot

Excavation 160000 cy1 foot crest raise 1700 cy Riprap Volume 1778Cutoff Walls 500 cy Concrete Thickness 1.5 feet

Concrete Wall Volume 800 cyIDF Discharge 69,800 cfs

Existing Spillway Discharge 25,300 cfs Fuseplug AlternativeModified Spillway Discharge 69,800 cfs Total Width 500 feetAuxiliary Fuseplug Discharge 40,500 cfs Spacing between Cells 125 feetTotal Flow w/ Auxiliary Fuseplug 70,700 cfs No. of Splitter Walls 5

Bottom Length 65 feetAverage Length 41 feetExcavation 6681 cyConcrete Floor Volume 1806 cyConcrete Wall Volume 173 cyRiprap Volume 5333 cy

I:\15\1524433\0100\0122\005 TM03 RevA\Attachment 1B Boxelder B-3 AlternativeCosts.xlsx\Quantities

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DRAFT TECHNICAL MEMORANDUM - WordPress.com Rau, PE DRAFT January 6, 2016 Paragon Consulting Group,...

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