October 27, 2026 Project No. 226-026

Neil Ogden, P.E.

HDR Engineering, Inc.

1670 Broadway Suite 3400 Denver, Colorado 80202-4824

Re: Revised Aggregate Surfacing Recommendations Steve Thompson Wildlife Drive Laguna Atascosa National Wildlife Refuge

TX FW LGA 10(5)

This project is proposed to upgrade the existing condition of Steve Thompson Wildlife Drive (STWD) in Laguna Atascosa National Wildlife Refuge (NWR) to a durable aggregate surfaced road. Currently, much of the road surfacing consists of badly deteriorated chip seal over aggregate base. The proposed treatment of the road is to process the top three inches of surfacing using full depth reclamation (FDR) in conformance with the Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects (FP-24, Section 304). The FDR treatment will be followed by the application of additional surfacing aggregate to provide the minimum required aggregate surfacing thickness. Bidding options in the plans will provide alternatives for additional aggregate for the road to address loss of aggregate due to traffic and provide a longer service life for sections of STWD.

Traffic and soils data from the Geotechnical Engineering Report, Steve Thompson Wildlife Drive, Laguna Atascosa National Wildlife Refuge, Yeh and Associates, Project 220-065, January 8, 2021 (Report) were used to evaluate the required aggregate surfacing thickness. The Report includes traffic and soils data along the north loop of STWD and very limited data along the south loop of STWD. Additional investigation of soils along the south loop of STWD is beyond the scope of this work.

The Central Federal Lands Highway Division (CFLHD) Supplement 11.14.2-1 for Aggregate Surfacing Design (Supplement) was used to evaluate the minimum required aggregate surfacing thickness.

Table 1 summarizes data from the Report and the associated classification from the Supplement used in evaluating the minimum aggregate surfacing thickness.

Table 1 – Aggregate Surfacing Design Values

Property Value Supplement Classification

20-Year 18-kip ESAL 3,126 Low Volume

Subgrade R-values 8 to 22 Very Poor – Poor

Subgrade Resilient Modulus, psi 5,400 Poor

Climatic Region IV Dry -No Freeze

Amendment A001 10/28/2026

Re: Aggregate Surfacing Recommendations Project No. 226-026 Steve Thompson Wildlife Drive, Laguna Atascosa NWR, TX FW LGA 10(5) October 27, 2026

Based the Supplement and the data provided in the Report, STWD will require a minimum aggregate thickness of 8 inches to address future traffic loading.

The attached Aggregate Thickness Following FDR Treatment table presents the existing chip seal and aggregate base thicknesses based on data provided in the Report and the anticipated aggregate thicknesses for the roadway following FDR treatment. The anticipated aggregate thickness following FDR treatment varies from 5.75 inches to 18.5 inches with an average of 8.9 inches for the north loop and from 8 inches to 12.75 inches with an average of 10.8 inches for the south loop. The available data for the south loop is very limited with only three borings in the general vicinity of the south loop start and end points.

To achieve the minimum aggregate surfacing thickness in the areas with the least anticipated aggregate thickness following FDR treatment, the north loop will need to receive an additional 2 inches of new aggregate following the FDR treatment. Following the FDR treatment, the south loop is anticipated to achieve the minimum 8-inch thickness without the additional 2 inches of new aggregate. Grading and compaction of the FDR and new aggregate is recommended to provide drainage and improved durability.

CFL personnel supplied the attached Special Contract Revision (SCR) for surfacing aggregate to allow the project to use locally available aggregate materials and still provide a durable aggregate surfacing.

This SCR will help local contractors in accurately bidding the project and should save confusion and costs compared to the FP-24 standard material specifications.

If you have any questions, please contact me at (303) 781-9590.

Sincerely, YEH AND ASSOCIATES, INC.

Prepared by: Reviewed by:

Robert F. LaForce, P.E. (CO) Brett Arpin, P.E. (TX) Senior Project Manager Project Manager

Attachments

Aggregate Thickness Following FDR Treatment

Section 703. - Aggregate

10/27/2026

Steve Thompson Wildlife Drive Yeh Project No. 226-026

STEVE THOMPSON WILDLIFE DRIVE

AGGREGATE THICKNESS

FOLLOWING FDR TREATMENT

North Loop - North of Renee's Overlook

Total

Aggregate

Boring After FDR

Number Chip Base Inches

P-2 1 6 7

P-3 0.5 8 8.5

P-4 0.5 8 8.5

P-5 0.5 6 6.5

P-6 0.75 7 7.75

P-7 0.5 7 7.5

P-8 0.5 18 18.5

P-9 0.75 5 5.75

P-10 1 6 7

P-11 1.5 6 7.5

P-12 1 8 9

P-13 1 7 8

P-14 1 7 8

P-15 1 8 9

P-16 0.75 10 10.75

P-19 1.5 8 9.5

P-20 1 12 13

Average 8.9

South Loop - South of Renee's Overlook and Bayside Drive

Total

Aggregate

Boring After FDR

Number Chip Base Inches

P-1 2 6 8

P-17 0.75 12 12.75

P-18 0.75 11 11.75

Average 10.8

Source: Geotechnical Engineering Report, Steve Thompson Wildlife Drive

Laguna Atascosa National Wildlife Refuge, Yeh and Associates, Project No. 220-065, January 8, 2021

Section 703. — AGGREGATE

703.05(a) General. Delete the paragraph and substitute the following:

703.05(a) General. Provide hard, durable particles or fragments of crushed stone, crushed slag, crushed gravel, caliche, or iron ore conforming to the following:

(1) Los Angeles abrasion, AASHTO T 96 50 percent maximum

(2) Soundness of aggregate using sodium sulfate, AASHTO T 104, 5 cycles

(a) Coarse aggregate 12 percent loss maximum

(b) Fine aggregate 12 percent loss maximum

(3) Fractured faces, AASHTO T 335 (one or more) 70 percent minimum

(4) Without organic matter or lumps or balls of clay.

703.05(b) Subbase or base course aggregate. Delete Subsections (1) and (2) and substitute the following:

(1) Gradation Table 703-1

(2) Liquid limit, AASHTO R 58 and AASHTO T 89 40 maximum

703.05(b) Subbase or base course aggregate. Delete Table 703-1 and substitute the following:

Table 703-1

Target Value Ranges for Subbase, Base, and Surface Course Gradation

Sieve size

Percent by Mass Passing Designated Sieve (AASHTO T 27 & T 11)

Grading Designation(1)

Subbase Base Surface

A B C D E Texas Special G H

2½ in 100(2) – – – – – – –

2 in 97 to 100 100(2) 100(2) – – 100(2) – –

1½ in – 97 to 100 – – – – – –

1 in 65 to 79 – 80 to 100 100(2) – – 100(2) –

⅞ in – – – – 65 to 95 – –

¾ in – – 64 to 94 86 to 100 100(2) – – 100(2)

½ in 45 to 59 – – – – – 70 to 80 –

⅜ in – – 40 to 69 51 to 82 62 to 90 50 to 75 – –

No. 4 28 to 42 40 to 60 31 to 54 36 to 64 36 to 74 40 to 70 40 to 50 41 to 71

No. 10 – – – – – – 25 to 40 –

No. 40 9 to 17 – – 12 to 26 12 to 26 10 to 35 15 to 25 12 to 28

No. 200 4.0 to 8.0 4.0 to 12.0 4.0 to 7.0 4.0 to 7.0 4.0 to 10.0 5.0 to 20 8.0 to 14 9.0 to 16

(1) Contractor specified target values. See Table 703-2 for allowable deviations.

(2) Statistical procedures do not apply.