Soil_Borings_Information_-_Topock_Marsh_2010_0001.pdf

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To:

Cc:

Robert Baca, P.E.

U.S. Fish and Wildlife Service

From:

Office:

Date:

Greg Glunz, P.E.

Denver

March 15, 2010

Subject: Geotechnical Investigation, Topock Marsh Infrastructure Improvement Project, Havasu National Wildlife Refuge, Mohave County, Arizona, IDIQ Contract 98210-5-D001, Task Order 20181RY006, URS Project 22241402

1.0 INTRODUCTION

A geotechnical investigation was completed for the Topock Marsh Infrastructure Improvement Project, located approximately 2 miles southwest of Needles, CA in Mohave County, AZ. The purpose of the geotechnical investigation was to collect geotechnical data to support assumptions used in the final design of the Topock Marsh Infrastructure Improvement Project.

In general, the scope of the geotechnical investigation included the following:

• Develop and complete the drilling program;

• Complete laboratory testing of selected samples collected during the investigation;

and

• Develop this technical memorandum to summarize the results of the field investigation.

• Prepare a technical memorandum to summarize the laboratory testing program results.

2.0 SUMMARY OF FIELD INVESTIGATION

Four test holes were drilled between March 4 and 5, 2010 by Eagle Drilling, Las Vegas, Nevada under subcontract to URS. Test hole TH-1 was drilled in the vicinity of the proposed location of the inlet canal control structure, test hole TH-2 was drilled near the proposed outlet of the fire break canal gravity diversion structure conduit, test hole TH-3 was drilled near the proposed location of the fire break canal maintenance road control structure, and test hole TH-4 was drilled near the existing Farm Ditch inlet structure. The approximate test hole locations are shown on Figure 1-1 in Attachment 1. The test hole locations shown on Figure 1-1 were located based on aerial photos. The ground surface elevation at each test hole was approximated based on the survey data provided by the U.S. Fish and Wildlife Service (USFWS) used for the Topock Marsh Infrastructure Improvement Project.

Topock Marsh Geotechnical Investigation Technical Memorandum

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Drilling was completed using a truck-mounted Diedrich D120 drill rig. Test holes were advanced using continuous flight hollow stem augers. A URS field geologist observed the drill crew, logged the test holes, collected soil samples, and recorded groundwater levels.

Disturbed soil samples were collected from the test holes using a 2.5-inch outside diameter (OD) split-spoon sampler and a 3-inch OD Dames & Moore sampler. Relatively undisturbed soil samples were collected using a 3-inch OD thin-walled sampler (Shelby tube). Spilt-spoon and Dames & Moore sampling were performed in general conformance with Standard Penetration Test (SPT) procedures (American Society of Testing and Materials [ASTM] D1586), by driving the sampler 18 inches using a 140-pound hammer falling 30 inches.

Spilt-spoon samples were placed in zip-lock bags and Dames & Moore samples (which were collected in brass rings) were capped and placed in zip-lock bags. The number of blows for each 6-inch increment of penetration was recorded, unless the sampler encountered refusal, which was defined as more than 50 blows for 6 inches or less of penetration. The standard penetration resistance (N value) was determined as the number of blows required to penetrate the final 12 inches. Split-spoon or Dames & Moore samples were collected approximately every 5 feet in the test holes. Shelby tube sampling consisted of pushing the tubes 2 feet with the drill rig under constant pressure with drill rods. Shelby tubes were sealed with expandable o-ring caps and the ends were sealed with plastic end caps and duct tape.

Preliminary test hole summary logs are shown on Figure 1-2 in Attachment 1. Final test hole summary logs will be prepared after laboratory testing has been completed.

After completion of the drilling operation, the test holes were backfilled to the ground surface with auger cuttings and bentonite chips.

2.1 Inlet Canal Control Structure (Test Hole TH-1)

Test hole TH-1 was sampled to a depth of 51.5 feet below ground surface (bgs). Sand was encountered the full depth of the test hole. Based on field observations, the sand (SP)1 is fine to coarse grained, dry to wet, and tan to light brown. The consistency is loose to medium dense, with N values ranging from 5 to 21.

No bedrock was encountered in test hole TH-1.

Groundwater was encountered at a depth of 14.5 feet bgs during drilling.

2.2 Fire Break Gravity Structure (Test Hole TH-2)

Test hole TH-2 was sampled to a depth of 51.5 feet bgs. Sand was encountered the full depth of the test hole. Based on field observations, the sand (SP) is fine to coarse grained, dry to

1 Letters in parentheses are the estimated soil classification based on the Unified Soil Classification System, based on field observations.

N:\Projects\22241402_Topock_Marsh\Sub_00\6.0_Deliverables\Geotech Investigation\Geotechnical Investigation_Topock Marsh_031210.doc wet, and tan to light brown. The consistency is medium dense, with N values ranging from 10 to 28.

No bedrock was encountered in test hole TH-2.

Groundwater was encountered at a depth of 20 feet bgs during drilling.

2.3 Fire Break Maintenance Road Structure (Test Hole TH-3)

Test hole TH-3 was sampled to a depth of 51.5 feet bgs. Sand and clay were encountered in the test hole. The sand was encountered from the ground surface to about 10 feet bgs and from about 33 feet bgs to 51.5 feet bgs. The clay layer has a thickness of about 23 feet and was encountered from about 10 feet bgs to about 33 feet bgs. Based on field observations, the sand (SP) is fine to coarse grained, dry to wet, and tan to light brown. The consistency of the sand is loose to medium dense, with N values ranging from 7 to 21. The clay (CL) is slightly sandy, slightly organic, moist to wet, and brown to dark brown. The consistency of the clay is soft to medium stiff, with N values ranging from 3 to 8.

No bedrock was encountered in test hole TH-3.

Groundwater was encountered at a depth of 9 feet bgs during drilling.

2.4 Farm Ditch Inlet Structure (Test Hole TH-4)

Test hole TH-4 was sampled to a depth of 51.5 feet bgs. Sand was encountered the full depth of the test hole. Based on field observations, the sand (SP) is fine to coarse grained, dry to wet, and tan to light brown. The consistency is loose to medium dense, with N values ranging from 6 to 16.

No bedrock was encountered in test hole TH-4.

Groundwater was encountered at a depth of 15 feet bgs during drilling.

3.0 LABORATORY TESTING

Selected soil samples obtained from the geotechnical investigation have been submitted for laboratory testing to confirm field characterizations. Kumar & Associates of Denver, Colorado, under subcontract to URS, will be performing the laboratory testing. Samples were delivered to Kumar & Associates on March 12, 2010. The results of the laboratory testing will be summarized in a separate technical memorandum. The Shelby tube samples and samples not submitted for testing are being retained by URS for a period of 6 months in case the client would like to perform additional laboratory tests (i.e., strength, consolidation, etc.) in the future.

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4.0 CONCLUSION AND RECOMMENDATIONS

The results of the geotechnical investigation conducted for the Topock Marsh Infrastructure Improvement Project indicate the site is generally underlain by sand and a discontinuous clay layer. The consistency of the sand is loose to medium dense and the clay is soft to medium stiff. No bedrock was encountered during the investigation. Groundwater depths at the time of drilling ranged between 10 and 20 feet bgs.

Based on the results of this geotechnical investigation, the site appears to be suitable for the construction of the project features included as part of the final design of the Topock Marsh Infrastructure Improvement Project, transmitted to the USFWS on February 19, 2010.

However, the following should be noted;

• The groundwater depths encountered during this investigation may not represent groundwater depths encountered during construction. Based on discussions with Refuge personnel, the groundwater level in this area is highly variable; and

• Special care should be taken to ensure temporary excavation slopes meet OHSA requirements based on the soil types encountered.

5.0 LIMITATIONS

Professional judgments on subsurface conditions are presented in this technical memorandum. They are based partially on the evaluation of the technical information gathered from this investigation, partially on our understanding of the characteristics of the site, and partially on our experience with subsurface conditions in the surrounding area. We do not guarantee the performance of the project in any respect, only that our engineering work and judgments rendered meet the standard of care of our profession.

The number and locations of the test holes for this investigation were selected to obtain a reasonable understanding of subsurface conditions for the intended purposes of this investigation. Variations from the conditions portrayed, which are not indicated by the test explorations, should be expected to occur. Judgments made should consider this potential variability. If different conditions are encountered during construction, it is necessary that URS be contacted so that our recommendations can be reviewed.

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Attachments

Memorandum

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Attachment 1

Test Hole Location Figure Test Hole Summary Logs