7.4 PO-133-Mag Survey_Report.pdf

Survey Report Page i LaBranche Central Marsh Creation June, 2013

LABRANCHE CENTRAL

MARSH CREATION PROJECT

PROJECT NO. PO-133

SURVEY REPORT

PREPARED FOR:

JUNE 20, 2013

SUBMITTED BY:

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LABRANCHE CENTRAL

MARSH CREATION PROJECT

PROJECT NO. PO-133

SURVEY REPORT

Prepared for: U.S.D.A.

Natural Resources Conservation Service 3737 Government St.

Alexandria, LA 71302

Submitted By: T. Baker Smith, LLC 412 S. Van Ave.

Houma, LA 70363

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LABRANCHE CENTRAL MARSH CREATION PROJECT

PROJECT NO. PO-133

SURVEY REPORT

TABLE OF CONTENTS

1.0 INTRODUCTION

2.0 PROJECT OVERVIEW

3.0 DATA COLLECTION SUMMARY

3.1 GEOTECHNICAL BORING LOCATION SURVEYS

3.2 MAGNETOMETER SURVEYS

3.3 PIPELINE INVESTIGATION SURVEYS

4.0 METHODOLOGY

4.1 SURVEY CONTROL AND DATUM INFORMATION

4.2 GEOPHYSICAL SURVEYS

4.3 PIPELINE INVESTIGATION SURVEYS

LIST OF APPENDICES

APPENDIX 1 --- Survey Benchmark Datasheet

Digital Appendix

Project drawings (PDF & DWG format) Survey point data (CSV format) Survey Field Notes (PDF Format)

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SURVEY REPORT

LABRANCHE CENTRAL

MARSH CREATION PROJECT

PROJECT NO. PO-133

1.0 INTRODUCTION

The purpose of the data collection tasks summarized in this report is to provide critical support information for planning and design of the LaBranche Central Marsh

Creation Project (PO-133). The services provided under this task order involved geophysical field data collection and pipeline investigations, related data processing, and the organization of all data into a workable format for design purposes.

2.0 PROJECT OVERVIEW

The LaBrache Central Marsh Creation Project is an authorized Project Priority

List 21 Coastal Wetlands Planning, Protection, and Restoration Act (CWPPRA) Project.

The project is sponsored by the Natural Resources Conservation Service (NRCS), in cooperation with the Louisiana Coastal Protection and Restoration Authority (CPRA).

The primary objective of this project is to dredge sediment from Lake Pontchartrain and create approximately 762 acres of marsh and nourish approximately 140 acres of existing marsh. The site is located in Region 1 of the Pontchartrain Basin in St. Charles Parish. It is bounded to the north by the railroad running parallel to Interstate 10, to the west by

Bayou LaBranche, to the east by a pipeline canal and to the south by Bayou Traverse.

3.0 DATA COLLECTION SUMMARY

During the period of May 13 through June 3, 2013, T. Baker Smith, LLC (TBS) collected field data throughout the project area. This data collection task consisted of geotechnical boring location surveys, geophysical surveys and pipeline investigations throughout the marsh creation project area. All surveys and data collection were completed by a three-man survey crew aboard an airboat.

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3.1 GEOTECHNICAL BORING LOCATION SURVEYS

Proposed geotechnical boring locations were staked out with cane poles and flagging in the marsh creation area for the geotechnical contractor. A magnetometer survey was conducted at each boring location to clear the location of any pipelines or metallic objects. A minimum of two circles were run with a gradiometer around each location, one with a 25’ radius and the other with a 50’ radius.

3.2 MAGNETOMETER SURVEY

Magnetometer surveys were performed in the proposed marsh creation area to determine the location of any possible oil and gas pipelines and other metallic obstructions. The survey was performed using a 15’ airboat and a proton magnetometer.

The magnetometer transects running north-south were spaced at approximately 500’ intervals throughout the project area while the transects running east-west were spaced at approximately 1000’ intervals. A total of 97 magnetic anomalies were detected during this survey. Upon investigation of each anomaly, only 17 were found to represent a total of 2 pipelines in the project area. All other anomalies were either inconclusive or were found to represent trash or debris. Some areas within the project area were unable to be run with the proton magnetometer due to the railroad tracks, levees, high spoil banks and very thick vegetation. These particular sections were investigated by the field crew with a gradiometer in order to detect any metallic obstructions.

3.3 PIPELINE INVESTIGATION SURVEY

All magnetic anomalies were investigated using a gradiometer and water jet probe to determine the possible existence of pipelines. A minimum of two circles were run with the gradiometer around each target, one with a 25’ radius and the other with a 50’ radius. Two pipelines were located within the project area. An 8” Shell pipeline runs parallel to the railroad tracks just south of the lower guide levee road on the east side of the project area until it breaks to a southwest direction and follows the pipeline canal to the west side of the project area. The Shell pipeline breaks out of the pipeline canal and

Survey Report Page 3 then runs south. A Gulf South pipeline runs along the pipeline canal on the very east side of the project area.

4.0 METHODOLOGY

4.1 SURVEY CONTROL AND DATUM INFORMATION

The primary horizontal and vertical survey control used for all data collection on this project was Benchmark “876 2372 F TIDAL”. The benchmark is part of LDNR’s secondary GPS network. The horizontal datum for all survey data collected is Louisiana

State Plane, South Zone (1702), NAD 83, in U.S. Survey feet. The vertical datum for all data is NAVD 88 (Geoid 03), in U.S. Survey feet. Published data for the benchmark can be seen in Appendix 1.

A temporary benchmark “TBM 1” was established at an accessible location near the boat launch. This point was established using Static GPS observations from the primary control monument “876 2372 F TIDAL”. Horizontal and vertical data for “TBM

1” is shown on Sheet 1 “Overall Site Plan” of the PO-133 LaBranche Central

Magnetometer Survey drawings.

4.2 GEOPHYSICAL SURVEYS

Geophysical instruments used during this survey consisted of a Marine Magnetics

SeaSPY marine proton magnetometer. Horizontal positioning of the survey vessel was accomplished using HyPack® navigation software with a Trimble R8 GNSS (RTK) global positioning receiver. Horizontal accuracy of this positioning as stated by the manufacturer is 2-3 centimeters. The magnetometer sensor was deployed 50 feet behind the positioning antenna. The magnetometer sensor was attached to a buoyant PVC sled and towed behind the Airboat (see Figure 1). This method allows the operator to survey continuously through both open water and low-elevation marsh. The magnetometer sensor was set at .1sec/gamma.

All magnetometer data was digitally recorded by an onboard laptop computer using the SeaSPY interface linked with the HYPACK MAX survey navigation software

Survey Report Page 4 mentioned above. The magnetic data was processed in Hypack to obtain the exact position, signature type, and strength of each anomaly. The Hypack processing software allows the user to view the magnetic data as actual magnetic field values along a continuous line. The user is able to easily pinpoint anomalies as deflections from the normal magnetic field of 47,700 and note the position based on the center of the signature. Each magnetic anomaly is interpreted based on its size, signature type, and actual field observations.

Figure 1. Proton magnetometer sensor and PVC sled being towed behind Airboat.

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4.3 PIPELINE INVESTIGATION SURVEYS

Pipeline investigation surveys were performed using a standard three-man survey crew, accessing the survey area by airboat. A Trimble model R8 GNSS GPS RTK unit was used to collect the topographic field data. The manufacturer’s stated accuracy of this unit is 2-3 cm horizontal, and 3-4 cm vertical. All RTK GPS Survey information was stored digitally using a Trimble TSC-2 Data Collector.

Topographic survey data was downloaded from the Trimble TSC-2 Data

Collector into the Trimble Business Center software for processing. This software allows for QA/QC of GPS data, and was used to check for instrument setup errors, antenna height errors, and other errors. These points were then exported and entered into

AutoCAD Civil 3D for further processing. The processed survey data was also exported to one complete digital text file containing point numbers, X, Y, Z coordinates, and point descriptions using the DOTD survey feature code list.

Survey Report

APPENDIX 1

Survey Benchmark Data Sheet