UNITED CONSULTING625 Holcomb Bridge Road | Norcross, GA 30071 | (770) 209-0029www.unitedconsulting.com

REPORT

Subsurface Exploration Randall Hall Road

Sewer Extension Task Order - #2013-002

Fulton County Atlanta, Georgia

Project Number 2013.3244.01

July 19, 2013 Revised

December 3, 2013

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625 HOLCOMB BRIDGE ROAD ♦ NORCROSS, GEORGIA 30071Tel: 770/209-0029 ♦ Fax: 770/582-2900 ♦ Client Services: 800/266-0990http://www.unitedconsulting.com ♦ E-mail: united@unitedconsulting.com

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July 19, 2013 Revised December 3, 2013 Ms. Nicole Wilson Watershed Project Manager City of Atlanta Bureau of Engineering Services Project Management Office 55 Trinity Avenue Suite 5400 South Building Atlanta, Georgia 30303 Via Email: nwilson@atlantaga.gov PROJECT: Subsurface Exploration

Randall Hall Road Sewer Extension FC-4918B; Task Order #2013-002 Randall Hall Road to Foxcroft Road Atlanta, Fulton County, Georgia Project No.: 2013.3244.01.Rev

Dear Ms. Wilson: United Consulting is pleased to submit this report of our Subsurface Exploration. This document was revised based on the provided surveyed boring location and elevation performed and provided by City of Atlanta. This document addresses field conditions encountered during our subsurface exploration, reviews our field procedures, presents our findings, and presents recommendations for difficult excavation conditions.

SITE AND PROJECT INFORMATION The project site consisted of a proposed sewer pipeline from Sta. 0+00 to Sta. 8+28 for the Randall Hall Road sewer extension. The proposed sewer line begins adjacent to Pipe ID 24200306501 and extends to near the existing Pipe ID 24200306401. The proposed alignment will traverse through properties located at 3655 Randall Hall Road, 3651 and 3652 Rembrandt Road, and 1003 Foxcroft Road. The new sewer line will connect to the existing line located on Foxcroft Road.

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SCOPE The scope of our Geotechnical Services has included the following items:

1. Drilling three (3) standard penetration test borings to assess the general nature and condition of the subsurface soils along the proposed sewer line;

2. A visual evaluation of soil samples obtained during our field exploration;

3. Evaluating the existing soil conditions with respect to the proposed construction; and

4. Preparing this letter report to document the results of our field program.

EXPLORATION PROCEDURES Three (3) Standard Penetration Test (SPT) borings (designated as borings B-1 to B-3) were drilled at the approximate locations shown on the attached Boring Location Plan & Profile Figures (Figure 1). Boring B-1 was drilled to auger refusal depth of 38 feet along the right of way of Foxcroft Road approximately 30 feet north of the proposed manhole #6 at Station 8+28. Boring B-2 was drilled to 40 feet along the right of way of Rembrandt Road approximately 20 feet east of manhole #3 at Station 3+49. Boring B-3 was drilled to 20 feet at approximately 10 feet northwest of existing manhole #24200306501 at station 0+00. The locations of the borings are shown on the attached boring location plan and profile (Figure 1). Soil test borings were performed in general accordance with ASTM D 1586. A narrative of field operations, soil classification information and a legend for symbols used on the Boring Logs are included on the Appendix tab page of this report. Soil samples obtained were visually evaluated by a Geotechnical Engineer and classified generally following the visual-manual procedure in ASTM D 2488. A narrative of field operations is included in the Appendix. Boring locations were determined in the field by our engineering representative from the provided plans and existing site features using measuring tape/wheel. Therefore, the boring locations shown on the attached figures (Fig. 1) should be considered approximate.

SUBSURFACE CONDITIONS Below the existing ground cover and topsoil, borings B-1, B-2, and B-3 encountered fill to depths of about 8, 3, and 18 feet, respectively. The fill soils encountered generally consisted of very loose to medium dense sand with some clay and varying amounts of silt, or soft to firm silt with some clay and clay and trace amounts of sand. The standard penetration test resistances (N-values) in the fill generally ranged from 3 to 24 blows per foot (bpf). The low consistency (N-

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values ≤ 6) fill were encountered in borings B-2 from 0 to 3 feet and borings B-1 and B-3 from 0 to 5 feet or so. Below the fill, typical residual soils of the Piedmont Physiographic Province were encountered. The residual soils encountered consisted of medium dense to very dense sand with varying amounts of clay and silt. The residual soils also consisted of stiff to hard silt with varying amounts of clay and sand. The N-values in the residual soils encountered ranged from 12 to 86 bpf. Lens of partially weathered rock (PWR) were encountered in boring B-1 at depths of 23 to 33 feet and in boring B-2 from 28 to 33 feet. PWR was also encountered in boring B-2 at a depth 38 to boring termination depth of 40 feet. PWR is a term for the residuum that can be penetrated by soil drilling techniques and has standard penetration test resistance values in excess of 100 blows per foot. The PWR encountered generally consisted of very dense sand with varying amounts of silt, clay, and rock fragments. Auger refusal occurred in boring B-1 at a depth of 38 feet. Auger refusal indicates the depth at which the boring cannot be drilled further using soil drillings tools and techniques. Auger refusal levels may represent the top of massive bedrock, a boulder or seams of rock. Groundwater was encountered at the time of drilling in borings B-1, B-2, and B-3 depths of 31, 27, and 18.5 feet, respectively. Groundwater levels should be anticipated to fluctuate with the change of seasons, during periods of very low or high precipitation, or due to changes in the floodplain or watershed upstream from the area. A more precise description of the subsurface conditions encountered is provided in the boring logs included in the Appendix. The borings were backfilled with auger cuttings immediately after completion of the drilling.

DISCUSSION Groundwater was encountered at the time of drilling in borings B-1, B-2, and B-3 at depths of 31, 27, and 18.5 feet below existing grade. Due to the presence of lenses of silt and PWR, the site is susceptible to formation of perched water. Perched water is surface water that infiltrates the higher permeability fill and sand residual soils and is trapped above the less permeable silt/clay residual soils, PWR, and rock. Also, groundwater tends to run on top of the underlying rock. Therefore, the contractor should be prepared to lower the groundwater as needed. For trench excavation, we recommend a performance criterion that groundwater levels be maintained at least 2 feet below the bottom of excavations, for the duration of the excavations. Borings B-1 encountered lens of PWR above the proposed pipe invert elevation. Also, boring B-1 encountered auger refusal near the pipe invert elevation. Depth of rock can vary significantly over short horizontal distances, Therefore, difficult excavation conditions requiring ripping or blasting is anticipated particularly in the vicinity of Station 9+02. If micro tunneling, use of rock bits may be required around this approximate area.

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General Some of the soil encountered in the borings contained a significant amount of silt. These soils should be placed within a narrow range of their optimum moisture to achieve proper compaction. We recommend that the Geotechnical Engineer of record be consulted during trench backfill to verify that the backfill is placed and compacted in accordance with the project specification. Conventional scrapers and loaders can generally excavate soils. Lower consistency PWR (50/5” and 50/4”) typically requires loosening by ripping with large dozers pulling single tooth rippers in mass and trench excavation. Denser PWR (50/3”, 50/1” or denser) may be removed by ripping using large dozer pulling single tooth ripper in mass excavation but generally requires blasting in confined (trench) excavation. Relatively sound, massive, rock typically requires blasting for removal in mass or trench excavation. Excavation techniques will vary based on the weathering of the materials, fracturing and jointing in the rock, and the overall stratigraphy of the feature. Actual field conditions usually display a gradual weathering progression with poorly defined and uneven boundaries between layers of different materials. We recommend that the following definitions for rock in earthwork excavation be included in bid documents: In Mass Excavation: Any material occupying an original volume of more than 1 cubic

yard which cannot be excavated with a single-toothed ripper drawn by a crawler tractor having a minimum draw bar pull rating of not less than 80,000 pounds usable pull (Caterpillar D-8 or larger).

In Trench Excavation: Any material occupying an original volume of more than 1/2 cubic

yard which cannot be excavated with a backhoe having a bucket curling rate of not less than 40,000 pounds, using a rock bucket and rock teeth (a John Deere 790 or larger).

Removal of rock by blasting can be very expensive. The costs of excavation vary with the type of material encountered and the quantities to be excavated. Hence, control of quantities is important. You may consider exposing the rock surface prior to blasting so the rock quantities can be more accurately estimated using surveying methods. Leaving soil overburden in place during blasting may result in difficulties in determination of blast rock quantities resulting in greater rock excavation costs. Also, residual soil overburden may increase the confining pressure of the rock and reduce the effectiveness of blast charges. Loose fill or blasting mats can be placed over the blast area to control fly-rock. We recommend that the surrounding structures be surveyed prior to and upon completion of blasting to document the current conditions of these structures, in order to reduce potential lawsuits. United Consulting recommends that pipe invert to be “set” as high as possible to reduce potential excavation difficulties resulting from shallow PWR and/or rocks.

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Ripped PWR and/or blasted rock fragments may be reused and mixed into engineered fill provided that they are pulverized to less than 6 inches in any dimension and fully choked with soil to fill voids between the rock pieces. PWR or rock greater than 12 inches in any dimension may be used in deep fill areas and should be well choked with a geotextile fabric or a minimum 6-inch layer of crusher-run or GAB. A minimum of 4 feet of clean fill is recommended over the soil/rock fill.

LIMITATIONS This report is for the exclusive use of the City of Atlanta, and the designers of this project, and may only be applied to this specific project. Our conclusions and recommendations have been prepared using generally accepted standards of Geotechnical Engineering practice in the State of Georgia. No other warranty is expressed or implied. Our firm is not responsible for conclusions, opinions or recommendations of others. The right to rely upon this report and the data within may not be assigned without UNITED CONSULTING’S written permission. The scope of this evaluation was limited to an evaluation of the load-carrying capabilities and stability of the subsoils. Oil, hazardous waste, radioactivity, irritants, pollutants, molds, or other dangerous substance and conditions were not the subject of this study. Their presence and/or absence are not implied or suggested by this report, and should not be inferred.

CLOSURE We appreciate the opportunity to work with you on this project. If you have any questions or if we can be of further assistance, please feel free to contact us. We look forward to working with you on future projects. Sincerely, UNITED CONSULTING

Mehdi Moazzami, P.E. Senior Geotechnical Engineer

Chris L. Roberds, P.G. Senior Executive Vice President

CC/MM/CLR/nj

APPENDIX General Notes/Narrative of Drilling Operations Figure 1 – Boring Location Plan & Profile Boring Logs (B-1 through B-3) http://ucblade10/sites/Geotechenv/7811/2013.3244.01/Geotechnical Documents/2013.3244.01.geo Ext.REV.doc

APPENDIX

General Notes/Narrative of Drilling Operations

Figure 1 – Boring Location Plan & Profile Boring Logs (B-1 through B-3)

FIG. 1