Report Cover Page

Brennaaleen Cedar Drainage Improvements Geotechnical Engineering Report

June 15, 2023 | Terracon Project No. 88235025

Prepared for:

City of Edinburg 415 W. University Drive Edinburg, TX 78539

1506 Mid Cities Drive

Pharr, Texas 78577 P (956) 283 8254

Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

June 15, 2023

City of Edinburg 415 W. University Drive Edinburg, TX 78539

Attn: Ms. Alicia Carmona, P.E., CFM P: (956) 388 8211 E: acarmona@cityofedinburg.com

Re: Geotechnical Engineering Report Brennaaleen Cedar Drainage Improvements W. Freddy Gonzalez Drive and Sugar Road (NEQ) Edinburg, Texas Terracon Project No. 88235025

Dear Ms. Carmona:

We have completed the scope of Geotechnical Engineering services for the above referenced project in general accordance with Terracon Proposal No. P88235025 dated February 21, 2023. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork for the proposed project.

We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report or if we may be of further service, please contact us.

Sincerely, Terracon (Texas Firm Registration No. F-3272)

Martin Reyes Alfonso A. Soto, P.E., D.GE Group Manager Senior Principal

6/15/23

Brennaaleen Cedar Drainage Improvements | Edinburg, Texas

Facilities | Environmental | Geotechnical | Materials i

Table of Contents Report Summary .............................................................................................. i Introduction Project Description Site Conditions Geotechnical Characterization

Groundwater Conditions Geology

Geotechnical Overview Earthwork

Site Preparation Excavation Fill Material Types Fill Placement and Compaction Requirements Wet Weather/Soft Subgrade Considerations Earthwork Construction Considerations

Detention Pond Detention Pond and Embankment Preparation

Gravel-Surfaced Drives Subgrade Preparation Design Recommendations Maintenance

Slope Stability General Comments

Figures GeoModel

Attachments

Exploration and Testing Procedures Site Location and Exploration Plans Exploration and Laboratory Results Supporting Information

Note: This report was originally delivered in a web-based format. Blue Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com. Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

Facilities | Environmental | Geotechnical | Materials i

Report Summary

Topic 1 Overview Statement 2

Project Description

The project will consist of design and construction of a detention pond facility in Edinburg, Texas.

Geotechnical Characterization

Lean Clay (CL), and Fat Clay (CH) soils were encountered to termination of borings.

Groundwater was not observed in the borings either during or upon completion of the drilling operations.

Below Grade Areas

The on-site soils appear to be suitable to construct earthen berms and subgrade of the proposed detention facility.

Roadways We anticipate that traffic loads may consist of maintenance vehicles and occasional heavy equipment.

Earthwork Existing on-site soils may be used for general fill.

General Comments

This section contains important information about the limitations of this geotechnical engineering report.

1. If the reader is reviewing this report as a pdf, the topics above can be used to access the appropriate section of the report by simply clicking on the topic itself.

2. This summary is for convenience only. It should be used in conjunction with the entire report for design purposes.

Facilities | Environmental | Geotechnical | Materials 1

Introduction

This report presents the results of our subsurface exploration and Geotechnical Engineering services performed for the proposed Brennaaleen Cedar Drainage Improvements project in Edinburg, Texas. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions

■ Groundwater conditions

■ Site preparation and earthwork

■ Excavation considerations

■ Groundwater control

■ Slope stability

The geotechnical engineering Scope of Services for this project included the advancement of test borings, laboratory testing, engineering analysis, and preparation of this report.

Drawings showing the site and boring locations are shown on the Site Location and Exploration Plan, respectively. The results of the laboratory testing performed on soil samples obtained from the site during our field exploration are included on the boring logs in the Exploration and Laboratory Results section.

Project Description

Our initial understanding of the project was provided in our proposal and was discussed during project planning. A period of collaboration has transpired since the project was initiated, and our final understanding of the project conditions is as follows:

Item Description

Information Provided

By Ms. Alicia Carmona, P.E. on February 1, 2023.

Detention Pond Facility

The proposed development will include the design and construction of an earthen detention facility of approximately 3 acres in total area. The detention area may have berms of up to 10 feet in height. The crest width (top of berm) may be used as maintenance vehicle path across its length. The emergency spillway will be located on a strategic location as indicated by the civil engineer, if any.

Facilities | Environmental | Geotechnical | Materials 2

Item Description

Construction Type We anticipate that embankments and toe elevation of the detention facility may be constructed with on-site soils as the primary option.

Roadways The proposed maintenance roads should consist of a typical aggregate surface road.

Terracon should be notified if any of the above information is inconsistent with the planned construction, especially the grading limits, as modifications to our recommendations may be necessary.

Site Conditions

The following description of site conditions is derived from our site visit in association with the field exploration and our review of publicly available geologic and topographic maps.

Item Description

Parcel Information

The proposed Brennaaleen Cedar Drainage Improvements project is located in the northeast quadrant of W. Freddy Gonzalez Drive and S. Sugar Road in Edinburg, Texas.

Approx. GPS coordinates of boring B-1:

Latitude: 26.291938° N Longitude: 98.175651° W.

See Site Location

Existing Improvements

Undeveloped land

Current Ground Cover

Bare soils, native grass, and midsize trees

Existing Topography

Relatively flat and level

Geotechnical Characterization

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of the site. Conditions observed at each exploration point are indicated on the individual logs. The individual logs can be found in the Exploration and Laboratory Results and the GeoModel can be found in the Figures attachment of this report.

Facilities | Environmental | Geotechnical | Materials 3

As part of our analyses, we identified the following model layers within the subsurface profile. For a more detailed view of the model layer depths at each boring location, refer to the GeoModel.

Model Layer

Layer Name General Description

1 Clay Lean Clay (CL) / Fat Clay (CH); medium stiff to hard

Groundwater Conditions

The borings were advanced in the dry using a dry-auger drilling technique that allows short term groundwater observations while drilling. Groundwater seepage was not encountered within the maximum drilling depth at the time of our field exploration.

Groundwater conditions may be different at the time of construction. Groundwater conditions may change because of seasonal variations in rainfall, runoff, and other conditions not apparent at the time of drilling. Long-term groundwater monitoring was outside the scope of services for this project. The boreholes were backfilled with on-site soil cuttings upon completion of the drilling operations.

Geology

The Geologic Atlas of Texas (1976), McAllen - Brownsville Sheet has mapped the Lissie Formation (Ql) of the Pleistocene Period of the Quaternary age at or near this site. The Lissie Formation (Ql) soils are mostly composed of clay, silt, sand, gravel and caliche. The soils are gray to brown to pale yellow in color. The gravel is mainly siliceous and locally cemented by and inter-bedded with sandy caliche. The caliche is massive to nodular. The surface is characterized by many undrained circular to irregular depressions, by relic clay dunes, and by stabilized northwest-trending longitudinal dunes.

Geotechnical Overview

The site appears suitable for the proposed construction based upon geotechnical conditions encountered in the test borings, provided that the recommendations in this report are implemented in the design and construction phases of this project. The subsurface materials generally consisted of Lean Clay (CL) and Fat Clay (CH). These soils will form the subgrade for the bottom of the detention facility.

Groundwater was not encountered in the test borings but may be encountered in deep cut areas during construction operations. Given the potential for perched water or seepage conditions, drains may be incorporated at strategic locations during or after construction.

Provisions should be made to incorporate appropriate surface or subsurface drain systems and direct it off the site. The recommendations contained in this report are based upon

Facilities | Environmental | Geotechnical | Materials 4 the results of data presented herein, engineering analyses and our current understanding of the proposed project.

The recommendations contained in this report are based upon the results of field and laboratory testing (presented in the Exploration and Laboratory Results), engineering analyses, and our current understanding of the proposed project. The General Comments section provides an understanding of the report limitations.

Earthwork

Prior to placing any fill, all vegetation, topsoil, possible fill material and any otherwise unsuitable material should be removed from the construction areas. Wet or dry material should either be removed, or moisture conditioned and recompacted. After stripping and grubbing, the subgrade should be proof-rolled where possible to aid in locating loose or soft areas. Proof-rolling can be performed with a loaded tandem axle dump truck. Soft, dry and low-density soil should be removed or compacted in place prior to placing fill.

Where fill is placed on slopes steeper than 4H:1V, benches should be cut into the existing slopes prior to fill placement. The benches should have the minimum vertical face height the maximum vertical face height and should be cut wide enough to accommodate the compaction equipment. This benching will help provide a positive bond between the fill and natural soils and reduce the possibility of failure along the fill/natural soil interface.

Furthermore, we recommend that fill slopes be over filled and then cut back to develop an adequately compacted slope face.

Site Preparation

Construction area should be stripped of all vegetation, topsoil and other unsuitable material. Additional excavation as recommended in this report or as needed should be performed within the proposed development area. Proper site drainage should be maintained during construction, so that ponding of surface runoff does not occur and cause construction delays or inhibit site access.

Excavation

We anticipate that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. The bottom of excavations should be thoroughly cleaned of loose soils and disturbed materials prior to backfill placement and/or construction.

Facilities | Environmental | Geotechnical | Materials 5

Fill Material Types

Engineered fill should consist of approved materials, free of organic material, debris and particles larger than about 2 inches. The maximum particle size criteria may be relaxed by the geotechnical engineer of record depending on construction techniques, material gradation, allowable lift thickness and observations during fill placement.

Material property requirements for on-site soil for use as general fill and structural fill are noted in the table below:

Property General Fill Structural Fill

Composition Free of deleterious material Free of deleterious material

Maximum particle size 6 inches

(or 2/3 of the lift thickness)

2 inches

Fines content Not limited Less than 85% Passing No. 200

Sieve

Plasticity Index Not limited Not applicable

GeoModel Layer Expected to be Suitable1

1 1

1. Based on subsurface exploration. Actual material suitability should be determined in the field at time of construction.

Imported Fill Materials: Imported fill materials should meet the following material property requirements. Regardless of its source, compacted fill should consist of approved materials that are free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade, if applicable.

Soil Type 1, 2, 3, 4

USCS

Classification Acceptable Parameters (for Structural

Fill)

Low Plasticity Cohesive

CL and/or SC Liquid Limit minimum of 40

Plasticity Index (PI) minimum of 20 Less than 85% Passing No. 200 Sieve

Granular

SC, GC, Caliche, Crushed Limestone and Crushed Concrete

Less than 50% Passing No. 200 Sieve

Flowable Fill --- Confined areas and backfill for utility trenches

Facilities | Environmental | Geotechnical | Materials 6

Soil Type 1, 2, 3, 4

USCS

Classification Acceptable Parameters (for Structural

Fill)

Cement-Stabilized Backfill

Used for backfilling of utility trenches in accordance with local standards or TxDOT

Item 400 Excavation and Backfill for Structures

1. Structural and general fill should consist of approved materials free of organic matter and debris. A sample of each material type should be submitted to the Geotechnical Engineer for evaluation prior to use on this site. Additional geotechnical consultation should be provided prior to use of uniformly graded gravel on the site.

2. Crushed limestone and crushed concrete material should meet the requirements of 2014 TxDOT Item 247, Type A, or D, Grade 1-2 or 3. The structural fill materials should be free of organic material and debris and should not contain stones larger than 2 inches in the maximum dimension. The clayey gravel and caliche materials should meet the gradation requirements of Item 247, Type B, Grade 1-2 or 3 as specified in the 2014 TxDOT Standard Specifications Manual and a Plasticity Index between 7 and 20.

3. Flowable fill should have a 28-day strength between 80 and 200 psi and meet the requirements for 2014 TXDOT Item 401. Although usually more costly, flowable fill does not require placement in lifts or mechanical compaction.

4. Cement-Stabilized Backfill should consist of a non-plastic sand or caliche as aggregate with a minimum of 2 sacks of Type I Portland cement per cubic yard based on the dry weight of the aggregate or as indicated by local standards. No mixing will be allowed on the project site.

Fill Placement and Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Item Structural Fill General Fill

Maximum Lift Thickness

8 inches in loose thickness when heavy, self-propelled compaction equipment is used 4 to 6 inches in loose thickness when hand-guided equipment (i.e. jumping jack or plate compactor) is used

Same as structural fill

Minimum Compaction

Requirements 1,2,3

95% of MDD below foundations and within 1 foot of finished subgrade 95% of MDD above foundations, below concrete slabs, and more than 1 foot below finished subgrade

92% of MDD

Facilities | Environmental | Geotechnical | Materials 7

Item Structural Fill General Fill

Water Content

Range 1

Low plasticity cohesive: -2% to +2% of optimum High plasticity cohesive: 0 to +4% of optimum Granular: -2% to +2% of optimum

As required to achieve minimum compaction requirements

1. Maximum Dry Density (MDD) and optimum water content as determined by the Standard Proctor test (ASTM D 698).

2. High plasticity cohesive fill should not be compacted to more than 100% of Standard Proctor maximum dry density.

3. If the granular material is a coarse sand or gravel, or of a uniform size, or has a low fines content, compaction comparison to relative density may be more appropriate. In this case, granular materials should be compacted to at least 70% relative density (ASTM D 4253 and D 4254). The caliche, crushed limestone and crushed concrete should be compacted to at least 95% of the Standard Proctor test (ASTM D 698). Materials not amenable to density testing should be placed and compacted to a stable condition observed by the Geotechnical Engineer or representative.

Wet Weather/Soft Subgrade Considerations

Construction operations may encounter difficulties due to the wet or soft surface soils becoming a general hindrance to equipment due to rutting and pumping of the soil surface, especially during and soon after periods of wet weather.

If the subgrade cannot be adequately compacted to minimum densities as described above, one of the following measures will be required:

■ Removal and replacement with dry on-site soils,

■ Chemical treatment of the soil to dry and increase the stability of the subgrade,

■ Drying by natural means if the schedule allows.

In our experience with similar soils in this area, chemical treatment is an efficient and effective method to increase the supporting value of wet and weak subgrade. Terracon should be contacted for additional recommendations if chemical treatment of the soils is needed.

Prior to placing any fill, all surface vegetation, topsoil, possible fill material and any otherwise unsuitable materials should be removed from the construction areas. Wet or dry material should either be removed, or moisture conditioned and recompacted.

Facilities | Environmental | Geotechnical | Materials 8

Groundwater/Dewatering Control

Groundwater seepage and water flow is not anticipated during construction excavation, However, an effective and/or permanent groundwater/dewatering control system may be needed at this site.

The design, operation, and maintenance of dewatering systems and groundwater control should be the responsibility of the contractor. This is appropriate since water control affects construction operations, e.g. excavation and scheduling. We anticipate the system would likely consist of a vacuum well point or jet eductor system. Well points should be installed with suitable screen and filters so that pumping of fines does not occur. Discharge should be arranged to facilitate sampling by the engineer.

Earthwork Construction Considerations

Shallow excavations, for the proposed detention pond, are anticipated to be accomplished with conventional construction equipment. The site should also be graded to prevent ponding of surface water on the prepared subgrade or in excavations. Water collecting over, or adjacent to construction areas should be removed.

For vertical cut excavations greater than 5 feet in depth, excavations will require the use of a trench box or shoring and bracing to prevent sloughing and caving of the soil into the excavation. The contractor should use a trench box or shoring and bracing as necessary to maintain a safe and clean excavation which meets Occupational Safety and Health Administration (OSHA) requirements.

Excavations must be performed and evaluated under the supervision of the contractor’s designated Competent Person. The Competent Person (as defined by the OSHA Standard, 29 CFR Part 1926.650 to .652, Subpart P - Excavations) must evaluate the excavations at the time of construction activity to safeguard workers.

Bracing for vertical excavation walls should be designed to resist a uniform lateral earth pressure of at least 36H psf, where H is the depth of the excavation in feet. Additional lateral pressure, due to surcharge loads along the trench, should be considered by adding a lateral pressure of 50 percent of the surcharge pressure.

In lieu of shoring, bracing, or trench boxes for excavations greater than 5 feet, OSHA standards provide recommendations for the design of temporary sloped excavations with a depth less than 20 feet. The OSHA standards provide maximum allowable slopes contingent on three designated soil types: Type A, Type B, or Type C. The surface slopes should be protected from deterioration and weathering if they are left open for significant periods of time.

Facilities | Environmental | Geotechnical | Materials 9

We recommend that no equipment should be operated within a horizontal distance equal to the excavation depth from the edge of the excavation and no materials should be stockpiled within this distance. Excavations should not approach closer than a horizontal distance equivalent to the excavation depth from existing structures or buried utilities without some form of protection for the facilities. Proper berming or ditching should be done to divert any surface runoff away from the excavations.

Excavations should be performed with equipment capable of providing a relatively clean bearing area. Excavating equipment should not disturb the soil beneath the design excavation bottom and should not leave loose soil in the excavation.

The bearing surface should be protected against disturbance and deterioration by completing the utility installation and backfilling operations as quickly as possible. The excavation bottom should be properly sloped to allow water infiltrating into the excavation to be collected at a convenient location along the edge of the excavation. Water should not be allowed to stand within the bearing area.

Construction Observation and Testing

The earthwork efforts should be monitored under the direction of the Geotechnical Engineer. Monitoring should include documentation of adequate removal of vegetation and top soil, proof-rolling and mitigation of areas delineated by the proof-roll to require mitigation.

Each lift of compacted fill should be tested, evaluated, and reworked as necessary until approved by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content at a frequency of at least one test for every 5,000 square feet in subgrade areas. One density and water content test for every 50 linear feet of compacted utility trench backfill. In the event unanticipated conditions are encountered, the Geotechnical Engineer should prescribe mitigation options.

In addition to the documentation of the essential parameters necessary for construction, the continuation of the Geotechnical Engineer into the construction phase of the project provides the continuity to maintain the Geotechnical Engineer’s evaluation of subsurface conditions, including assessing variations and associated design changes.

Detention Pond

We understand that a detention pond is being considered for the proposed development.

This type of ponds is typically constructed of earthen materials. The earthen materials will either be designed to allow water seepage or to retain water.

Facilities | Environmental | Geotechnical | Materials 10

We anticipate that the bottom of the pond will be at about 8 feet below top of berm elevation. This will require a cut operation across the proposed pond area to bring the site to construction grade.

If the pond needs to retain water, then a geosynthetic material may be used to reduce the permeability surface. A coefficient of permeability, k, of about 1 x 10-7 cm/sec or lower would generally be suitable for soils used as a clay liner.

The upper on-site Lean Clay (CL) soils due to their sandy properties may not be suitable for this purpose. The estimated order of magnitude soil permeability values based on published data and our experience for Lean Clay (CL) soils is approximately greater than 5 x 10-8 cm/sec. Hydraulic conductivity (permeability) laboratory test results indicate the upper 10 feet of on-site soils have a coefficient of permeability (k) in the order of 1.7 x 10-8 and 4.8 x 10-8 cm/sec. The on-site Fat Clay (CH) soils may be suitable for this purpose.

In addition to permeability, the berms of the pond must be stable. Considerations should be given to vegetating the berms and base of the pond to limit erosion. Additionally, consideration should be given to protecting the berms from drying by providing a minimum 12 inches of protective soil cover or using a pond liner material. The liner materials selected to construct the pond should be placed in 8-inch loose lifts. The materials should be moisture conditioned between optimum and 4 percentage points above of optimum moisture content and compacted to 95 percent of ASTM D 698. Care should be taken to limit dry clods and provide a relatively homogenous mixture of cohesive material for the pond’s base.

Detention Pond and Embankment Preparation

The pond construction will require flattening of the interior of the area, construction of embankments, providing wave action protection and construction of the emergency spillway, if applicable. We have provided the following subgrade preparation recommendations which are intended to result in berms that will provide support for the liner.

■ Strip all existing vegetation, loose topsoil and any deleterious material from the pond area. The pond area is defined as the area that extends at least 5 feet beyond the perimeter of the embankment. The removed topsoil may be stockpiled for later re-use over the new embankment. Excavate 2 feet of on-site soils below the proposed pond subgrade and interior side slopes to create a moisture conditioned and compacted soil liner, remove and stockpile for reuse.

■ The exposed subgrade in the pond area should be proofrolled with at least a 15-ton roller, or equivalent equipment, to evidence any weak yielding zones.

Facilities | Environmental | Geotechnical | Materials 11

■ Over excavate any confirmed weak yielding zones, both vertically and horizontally, to expose competent soil. The excavated soil maybe used to restore grade provided that the material is relatively free and clean of deleterious material or materials exceeding 3 inches in maximum dimension. The soil should be placed in loose lifts of no more than 6 inches compacted; moisture conditioned within 2 percentage points of the optimum moisture content and compacted to at least 95 percent of the maximum dry density determined in accordance with ASTM D 698.

■ After proofrolling and the replacement of weak yielding zones, scarify and moisture condition the top 8 inches of subgrade within 2 percentage points of the optimum moisture content. Compact the subgrade to at least 95 percent of the maximum dry density determined in accordance with ASTM D 698.

■ On-site soils with moderate plasticity in combination with soils of high plasticity may be mechanically blended or mixed to produce a uniform soil matrix or imported fill may be needed to achieve the desired pond bottom (liner) and Top of Berm Elevation (TBE). Lift thickness should not exceed 8 inches loose measure or 6 inches compacted measure. Each lift of on-site soils or imported fill should be moisture conditioned within 4 percentage points above of optimum moisture content and compacted to at least 98 percent of the maximum dry density determined in accordance with ASTM D 698. Recommendations for fill are included in the Fill Material Types section of this report. We recommend that fill slopes be over built and then cut back to develop an adequately compacted slope face.

■ Finished subgrade and slope areas should be free from sharp objects and foreign materials that may inhibit proper placement of designated liner on the subgrade.

The top 6 inches of subgrade should be free of materials exceeding 1 inch in maximum dimension. The subgrade surface should have a smooth finished surface.

■ Finished subgrade preparation should not precede the liner installation by more than 48 hours, to minimize potential damage due to wind, rain and other elements.

If blended soils are used as pond liner, we recommend that additional samples of the blended soils, as well as the clay clods, be obtained prior to and during earthwork operations to evaluate if the blended soils can be used for that purpose. It is recommended to perform several permeability tests on the blended or imported clay soils.

As an alternate to the soils (clay) liner, a 3-foot-thick soil-cement compacted to high density may be used to construct the pond bottom and spillways. The required soil-cement thickness facing is typically determined based on analysis and possible loss of surface materials during service life of the pond. The analysis should include, but not limited to hydrostatic uplift due rapid drawdown and wave action.

Facilities | Environmental | Geotechnical | Materials 12

Gravel-Surfaced Drives

Subgrade Preparation

On most project sites, the site grading is accomplished relatively early in the construction phase. Fills are typically placed and compacted in a uniform manner. However, as construction proceeds, the subgrade may be disturbed due to utility excavations, construction traffic, desiccation, or rainfall/snow melt. As a result, the aggregate-surfaced roadway may not be suitable for construction and corrective action will be required. The subgrade should be carefully evaluated at the time of construction for signs of disturbance or instability. We recommend the subgrade be thoroughly proofrolled with a loaded tandem-axle dump truck prior to final grading. The top 8 inches of the exposed subgrade should be scarified, moisture conditioned, and recompacted to at least 95 percent of the Maximum Dry Density (MDD) as determined by ASTM D698 before any new fill or aggregate is placed.

Design Recommendations

Design of aggregate-surfaced roadways for the project has been based in general accordance with the “Aggregate-Surfaced Road Design Catalog” subsection of the 1993 AASHTO “Guide for the Design of Pavement Structures” and based on subsurface conditions observed at the site and laboratory test results.

Our analysis has assumed a “low” traffic volume which is appropriate for 10,000 to 30,000 equivalent single axle loads (ESALs) over the life of the gravel surfacing. This traffic volume should be confirmed by the design team; additional geotechnical consultation and revision of recommendations could be necessary with higher traffic volumes.

Recommended minimum aggregate surfacing thickness is provided in the table below.

Recommended Gravel Surface Thickness 1

Granular Base Material 8 10

Treated Subgrade 8 ---

Moisture Conditioned Subgrade --- 8

1. Treated subgrade consists of an 8-inch thick modified and compacted subgrade layer. A geogrid may be used instead of the 8-inch treated subgrade layer. If used, the geogrid may be Tensar InterAx or equivalent material and should be placed on top of the moisture conditioned and compacted subgrade.

Quality roadway surfacing materials should consist of a blend of gravel, sand, and fines (clay and silt). We believe the maximum size particle should not exceed 1 inch in diameter

Facilities | Environmental | Geotechnical | Materials 13 and the gravel should be crushed with angular edges (not rounded). The blend of materials should be selected to allow for easy compaction resulting in a firm, low permeable surface promoting surface drainage off the roadway surface. Materials meeting TxDOT Item 247 specifications can be used for aggregate surfacing material. Aggregate surfacing material should be placed in lifts not exceeding 8 inches and compacted to a minimum of 95 percent of the maximum dry unit weight as determined by ASTM D1557.

A quality roadway surfacing material should also contain approximately 10 to 25 percent fines (silt and clay-sized particles passing the No. 200 sieve). The fines should exhibit low to moderate plasticity (plastic index less than 15) and will act as a binder to help reduce risk for wash boarding. If the fines content of a roadway surfacing material is comprised mostly of silt, the fines will be non-plastic and the surfacing materials will not have the benefit of the binder or cohesive aspects.

Aggregate-surfaced roadways performance is affected by its surroundings. In addition to providing preventive maintenance, the civil engineer should consider the following recommendations in the design and layout of aggregate-surfaced roadways:

■ Site grades should slope a minimum of 10 percent away from the roadways;

■ The subgrade and the aggregate-surfaced roadways have a minimum 10 percent slope to promote proper surface drainage;

■ Consider appropriate edge drainage; and

■ Install pavement drainage in surrounding areas anticipated for frequent wetting.

Presented below are our recommended material requirements for the unsurfaced gravel sections.

Granular Base Material: Granular base material should be composed of crushed limestone or crushed concrete meeting the requirements of 2014 TxDOT Standard Specifications Item 247, Type A or D, Grade 1-2 or 3.

As an alternate to the Type A base, treated “caliche” material meeting the requirements of 2014 TxDOT Standard Specification Manual Item 247, Type B, Grade 1-2 or 3 may be used. The granular base material (caliche) may be treated with about 2 percent by dry weight of cement (modifier).

The granular base material should be compacted to at least 95 percent of the maximum dry density as determined by the modified moisture-density relationship (ASTM D 1557) at moisture contents within 2 percentage points of optimum moisture. If it is necessary to use additives to the material to meet these criteria, the amount of additive should be limited so as not to create a rigid base layer that tends to dry, shrink, and crack.

Treated Subgrade: The subgrade may be treated with lime (modifier) in accordance with 2014 TxDOT Standard Specifications Item 260. The recommended percentage of modifier)

Facilities | Environmental | Geotechnical | Materials 14 is for estimating and planning. The actual quantity of modifier required should be determined at the time of construction by laboratory tests on bulk samples of the subgrade soils.

If chemical treatment of the subgrade is chosen, we anticipate that the on-site surficial soils be treated with about 3 percent of lime. This percentage is given as application by dry weight and is typically equivalent to about 22 pounds of modifier per square yard per 8-inch thick layer.

The subgrade should be compacted to a minimum of 95 percent of the Standard Effort (ASTM D 698) maximum dry density within 2 percent of the optimum moisture content.

Preferably, traffic, should be kept off the treated subgrade for about 3 to 5 days to facilitate curing of the soil - chemical mixture.

Post-construction subgrade movements and some cracking of the unsurfaced gravel are not uncommon for subgrade conditions such as those observed at this site. Although chemical treatment of the subgrade will help to reduce such movement/cracking, this movement/cracking cannot be economically eliminated.

Moisture Conditioned Subgrade: The subgrade should be scarified to a depth of 10 inches and moisture conditioned within 2 percent of the optimum moisture content. The subgrade should then be compacted to at least 95 percent of the maximum dry density determined in accordance with ASTM D 698. This should result in a compacted, moisture conditioned layer about 8 inches thick.

Related civil design factors such as subgrade drainage, shoulder support, cross-sectional configurations, surface elevations and environmental factors which will significantly affect the service life must be included in the preparation of the construction drawings and specifications. Normal periodic maintenance will be required.

Long-term pavement performance will be dependent upon several factors, including maintaining subgrade moisture levels and providing for preventative maintenance.

Prior to implementing any maintenance, additional engineering observations are recommended to determine the type and extent of preventative maintenance.

Maintenance

Periodic maintenance extends the service life of the aggregate-surfaced roadways and should include re-grading and replacement of aggregate base course in any deteriorated areas. Thicker aggregate base course sections could be used to reduce the required maintenance and extend the service life of the aggregate-surfaced roadways. Design alternatives which could reduce the risk of subgrade saturation and improve long-term performance include installing surface drains next to any areas where surface water could

Facilities | Environmental | Geotechnical | Materials 15 pond. Properly designed and constructed subsurface drainage will reduce the time subgrade soils are saturated and can also improve subgrade strength and performance.

Slope Stability

The Scope of Services for this project included a review of global slope stability of the planned detention pond berms along one cross-section.

Analysis Conditions

The following conditions were considered in our analyses:

■ A surcharge load of 250 psf was applied to planned drive area around the proposed pond embankment to account for vehicular traffic.

■ New Structural Fill placed to construct the pond embankments is considered to have similar density and strength properties as the surficial native clays.

■ Minimum Factor of Safety for global slope stability o 1.3 under short-term (total stress) conditions o 1.5 under long-term (effective stress) conditions

Cross-Section A-A

Geometry

Min. Global Slope Stability

FOS

Global Slope Stability Results

FOS

Short-Term Long-Term Short-Term Long-Term

Section A-A 1.3 1.5 4.6 1.7

Cross-Section A-A plus Surcharge (250 psf)

Geometry

Min. Global Slope Stability

FOS

Global Slope Stability Results

FOS

Short-Term Long-Term Short-Term Long-Term

Section A-A 1.3 1.5 3.9 1.6

Analysis Model Geometry

The cross-section geometry used in our analyses are based on the Brennaaleen Cedar Drainage Improvements Proposed Pond Typical Sections sheet prepared by KCI Technologies, dated June 8, 2023.

Facilities | Environmental | Geotechnical | Materials 16

Analysis Methodologies

Global slope stability runs were completed using the computer software “SLOPE/W” developed by GEOSLOPE International Ltd. This program is a finite element software product that calculates the Factors of Safety (FOS) against slope failure along multiple hypothetical (user-defined) circular failure planes, and then ‘optimizes’ the critical circular failure plane resulting in a composite slip surface (i.e., parts of the critical failure plane are circular while other parts are linear). The FOS results were determined using the Morgenstern-Price methodology (i.e., satisfies both moment equilibrium and force equilibrium).

Analysis Results

Based on our analyses, the detention pond berms along the one cross-section reviewed, have an adequate Factor of Safety against global slope instability issues under both short-term (total stress) and long-term (effective stress) conditions.

General Comments

Our analysis and opinions are based upon our understanding of the project, the geotechnical conditions in the area, and the data obtained from our site exploration.

Variations will occur between exploration point locations or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. Terracon should be retained as the Geotechnical Engineer, where noted in this report, to provide observation and testing services during pertinent construction phases. If variations appear, we can provide further evaluation and supplemental recommendations. If variations are noted in the absence of our observation and testing services on-site, we should be immediately notified so that we can provide evaluation and supplemental recommendations.

Our Scope of Services does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

Our services and any correspondence are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third-party beneficiaries intended. Any third-party access to services or correspondence is solely for information purposes to support the services provided by Terracon to our client. Reliance upon the services and any work product is limited to our client and is not intended for

Facilities | Environmental | Geotechnical | Materials 17 third parties. Any use or reliance of the provided information by third parties is done solely at their own risk. No warranties, either express or implied, are intended or made.

Site characteristics as provided are for design purposes and not to estimate excavation cost. Any use of our report in that regard is done at the sole risk of the excavating cost estimator as there may be variations on the site that are not apparent in the data that could significantly effect excavation cost. Any parties charged with estimating excavation costs should seek their own site characterization for specific purposes to obtain the specific level of detail necessary for costing. Site safety and cost estimating including excavation support and dewatering requirements/design are the responsibility of others. Construction and site development have the potential to affect adjacent properties. Such impacts can include damages due to vibration, modification of groundwater/surface water flow during construction, foundation movement due to undermining or subsidence from excavation, as well as noise or air quality concerns. Evaluation of these items on nearby properties are commonly associated with contractor means and methods and are not addressed in this report. The owner and contractor should consider a preconstruction/precondition survey of surrounding development. If changes in the nature, design, or location of the project are planned, our conclusions and recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

Figures

Contents:

GeoModel

E le va ti o n

M

S L

(f ee t)

Layering shown on this figure has been developed by the geotechnical engineer for purposes of modeling the subsurface conditions as required for the subsequent geotechnical engineering for this project.

Numbers adjacent to soil column indicate depth below ground surface.

NOTES:

B-1 B-2

This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

1506 Mid Cities Dr

Brennaaleen Cedar Drainage Improvements

W. Freddy Gonzalez Drive | Edinburg, Texas

Pharr, TX

Terracon Project No. 88235025

GeoModel

LEGEND

Lean Clay

Fat Clay

Model Layer General DescriptionLayer Name

Lean Clay (CL) / Fat Clay (CH); medium stiff to hard1 CLAY

Attachments

Exploration and Testing Procedures

Field Exploration

Number of Borings Approximate Boring

Depth (feet) Location

2 25 Proposed detention pond area

Boring Layout and Elevations: Terracon personnel provided the boring layout using handheld GPS equipment (estimated horizontal accuracy of about ±10 feet) and referencing existing site features. If elevations and a more precise boring layout are desired, we recommend borings be surveyed.

Subsurface Exploration Procedures: We advanced the borings with a truck-mounted, drill rig using continuous flight augers (solid stem and/or hollow stem, as necessary, depending on soil conditions). Five samples were obtained in the upper 10 feet of each boring and at intervals of 5 feet thereafter. In the thin-walled tube sampling procedure, a thin-walled, seamless steel tube with a sharp cutting edge was pushed hydraulically into the soil to obtain a relatively undisturbed sample. In the split-barrel sampling procedure, a standard 2-inch outer diameter split-barrel sampling spoon was driven into the ground by a 140-pound automatic hammer falling a distance of 30 inches. The number of blows required to advance the sampling spoon the last 12 inches of a normal 18-inch penetration is recorded as the Standard Penetration Test (SPT) resistance value. The SPT resistance values, also referred to as N-values, are indicated on the boring logs at the test depths.

A 3-inch O.D. split-barrel sampling spoon with 2.5-inch I.D. ring lined sampler was used for soil sampling. For safety purposes, all borings were backfilled with auger cuttings after the groundwater observations were completed.

The sampling depths, penetration distances, and other sampling information was recorded on the field boring logs. The samples were placed in appropriate containers and taken to our soil laboratory for testing and classification by a Geotechnical Engineer. Our exploration team prepared field boring logs as part of the drilling operations. These field logs included visual classifications of the materials observed during drilling and our interpretation of the subsurface conditions between samples. Final boring logs were prepared from the field logs. The final boring logs represent the Geotechnical Engineer's interpretation of the field logs and include modifications based on observations and tests of the samples in our laboratory.

Laboratory Testing

The project engineer reviewed the field data and assigned laboratory tests. The laboratory testing program included the following types of tests:

■ Water Content ■ Unconfined Compression

■ Atterberg Limits ■ Consolidated Undrained (CU)

■ Grain Size Analysis ■ Hydraulic Conductivity (Permeability)

■ Unit Dry Weight ■ Hydrometer

The laboratory testing program often included examination of soil samples by an engineer.

Based on the results of our field and laboratory programs, we described and classified the soil samples in accordance with the Unified Soil Classification System.

Site Location and Exploration Plans

Site Location Plan Exploration Plan

SITE LOCATION

Brennaaleen Cedar Drainage Improvements ■ Edinburg, Texas June 15, 2023 ■ Terracon Project No. 88235025

TOPOGRAPHIC MAP IMAGE COURTESY OF THE U.S. GEOLOGICAL SURVEY

QUADRANGLES INCLUDE: EDINBURG, TX (1/1/2002).

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS

NOT INTENDED FOR CONSTRUCTION PURPOSES

SITE

EXPLORATION PLAN

Brennaaleen Cedar Drainage Improvements ■ Edinburg, Texas June 15, 2023 ■ Terracon Project No. 88235025

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS

NOT INTENDED FOR CONSTRUCTION PURPOSES

AERIAL PHOTOGRAPHY PROVIDED

BY MICROSOFT BING MAPS

Exploration and Laboratory Results

Boring Logs

LEAN CLAY (CL), with sand, brown, medium stiff

FAT CLAY (CH), light brown, stiff to hard

- light olive brown at 13½ feet

Boring Terminated at 25 Feet

Boring Log No. B-1

W at er L ev el

O bs er va tio ns

D ep th

Ft

Facilities | Environmental | Geotechnical | Materials

G ra p h ic

L o g

M o d el

L ay er

17.0

18.9

18.0

18.4

18.2

19.5

19.9

20.4

CU

CU

38-14-24

58-16-42

57-20-37

4.0

25.0

2-2-4 N=6

3-3-5 N=8

4.5 (HP)

6-13-15 N=28

4.5 (HP)

4-6-8 N=14

4.5 (HP)

7-10-15 N=25

Abandonment Method Boring backfilled with auger cuttings upon completion.

Advancement Method Dry augered from 0 to 25 feet

Hammer Type Automatic

Driller

SWD

Logged by

JG

Boring Started 05-11-2023

Boring Completed 05-11-2023

1506 Mid Cities Dr

Drill Rig

CME 55

Brennaaleen Cedar Drainage Improvements

Pharr, TX

W. Freddy Gonzalez Drive | Edinburg, Texas

Terracon Project No. 88235025

See Exploration and Testing Procedures for a description of field and laboratory procedures used and additional data (If any).

See Supporting Information for explanation of symbols and abbreviations.

Notes

Ground elevation was obtained from the Google Earth aerial image.

Water Level Observations Groundwater was not observed

S am pl e

T yp e

Pe rc en t

Fi n es

W at er C o n te n t

D ry

U n it

W ei g h t

(p cf

S tr ai n

C om p re ss iv e S tr e n g th

(t sf

T es t T y p e

Elevation.: 98 (Ft.)

Atterberg Limits

LL-PL-PI

See Exploration PlanLocation:

Latitude: 26.291938° Longitude: -98.175651°

Depth (Ft.)

Strength Test

Fi el d T es t

R es u lt s

91.5

LEAN CLAY (CL), with sand, brown, medium stiff to very stiff

- light brown at 4 feet

FAT CLAY (CH), light olive brown, stiff to hard

Boring Terminated at 25 Feet

Boring Log No. B-2

W at er L ev el

O bs er va tio ns

D ep th

Ft

M o d el

L ay er

Facilities | Environmental | Geotechnical | Materials

G ra p h ic

L o g

6.5

25.0

2-3-4 N=7

3-4-5 N=9

3.0 (HP)

4-6-7 N=13

4.0 (HP)

4-8-12 N=20

9-11-14 N=25

14-15-20 N=35

19.9

22.2

21.2

19.9

20.5

19.8

22.6

22.4

CU

46-16-30

56-21-35

73-22-51

65-24-41

Abandonment Method Boring backfilled with auger cuttings upon completion.

Advancement Method Dry augered from 0 to 25 feet

Hammer Type Automatic

Driller

SWD

Logged by

JG

Boring Started 05-11-2023

Boring Completed 05-11-2023

1506 Mid Cities Dr

Drill Rig

CME 55

Brennaaleen Cedar Drainage Improvements

Pharr, TX

W. Freddy Gonzalez Drive | Edinburg, Texas

Terracon Project No. 88235025

See Exploration and Testing Procedures for a description of field and laboratory procedures used and additional data (If any).

See Supporting Information for explanation of symbols and abbreviations.

Notes

Ground elevation was obtained from the Google Earth aerial image.

Water Level Observations Groundwater was not observed

S am pl e

T yp e

Pe rc en t

Fi n es

Depth (Ft.)

Strength Test

Fi el d T es t

R es u lt s

W at er C o n te n t

D ry

U n it

W ei g h t

(p cf

S tr ai n

C om p re ss iv e S tr e n g th

(t sf

T es t T y p e

Elevation.: 98 (Ft.)

Atterberg Limits

LL-PL-PI

See Exploration PlanLocation:

Latitude: 26.291177° Longitude: -98.176224°

Supporting Information

General Notes Unified Soil Classification…