TX FW LGA 10 Aggregate Surfacing Recommendations

June 18, 2026

Project No. 226-026

Neil Ogden, P.E.
HDR Engineering, Inc.
1670 Broadway
Suite 3400
Denver, Colorado 80202-4824
Re:

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

20-Year 18-kip ESAL
Subgrade R-values
Subgrade Resilient Modulus, psi
Climatic Region

3,126

8 to 22

5,400
IV

Supplement
Classification
Low Volume
Very Poor – Poor
Poor
Dry -No Freeze

Re: Aggregate Surfacing Recommendations
Steve Thompson Wildlife Drive, Laguna Atascosa NWR, TX FW LGA 10(5)

Project No. 226-026
June 18, 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.