Marine Archaeological Survey for the Webster to Seadrift Pipeline Project in Calhoun and Jackson Counties, Texas
Authors: Rawls John , Tuttle Michael , Hughey Jim , Quennoz Michael 
Published: July 2020

Under contract to BIO-WEST, Inc., Gray & Pape, Inc., of Houston, Texas, conducted a Phase I marine archaeological survey for the proposed Webster to Seadrift Pipeline Project in Calhoun and Jackson counties, Texas. Enterprise Products Operating LLC sponsored the archaeological survey. All marine fieldwork and reporting activities were completed with reference to state law (Antiquities Code of Texas [Title 9, Chapter 191 of the Texas Natural Resources Code] and Texas State rules found in the Texas Administrative Code [Title 13, part 2, Chapters 26 and 28]) for cultural resources investigations. Work was completed under Texas Antiquities Permit Number 9004. The United States Army Corps of Engineers, Galveston District has been identified as the lead federal agency. All project records are curated at the Center for Archaeological Studies at Texas State University in San Marcos, Texas.

The Phase I underwater archaeological investigation assessed the number, locations, cultural affiliations, components, spatial distribution, data potential, and other salient characteristics of potential submerged cultural resources within the proposed project area. The linear project area includes approximately 391 hectares (967 acres) of submerged land in Calhoun and Jackson counties, Texas. The investigation included a comprehensive magnetic and acoustic remote sensing survey and target analysis designed to determine the presence or absence of potentially significant remote sensing targets that might be affected by proposed project activity.

Background research revealed that there are no previously recorded sites within the Area of Potential Effects and that there have been two previous cultural resource surveys (Pearson et al. 1993; Gearhart 2016), conducted between 1993 and 2016, partially within the project Area of Potential Effects. Research also revealed that the 50-meter (164-foot) avoidance areas, as mandated by Texas Administrative Code, Title 13, Part 2, Chapter 26, for three previously recorded magnetic anomalies (Mag 7–Mag 9) identified by Gearhart (2016) are partially located within the survey area. These three magnetic anomalies were recommended for avoidance as they represent potential cultural resources.

The grid for the remote sensing survey within the open waters of Lavaca Bay consisted of a total of 19 track lines (Lines 1–16, 18,19, 37, and 38) at 20-meter (65.6-foot) line spacing oriented parallel to an existing pipeline right-of-way. The remaining portions of the project area within Lavaca River and Catfish Bayou were surveyed at 20-meter (65.6-foot) line spacing (Lines 0, 17, 22–35, and 39–43) oriented perpendicular to the survey corridor. The marine field investigations consisted of a magnetometer and side-scanning sonar investigation of the proposed project area in safely navigable waters between July 29 and 30, 2019, and required approximately 60-person hours to complete.

A total of 284.6 kilometers (176.9 linear survey miles) were transected utilizing the magnetometer and side-scan sonar. Comprehensive analysis of the magnetic and acoustic data recorded for this project resulted in the identification of 127 discrete magnetic anomalies, with 80 meeting or exceeding the Pearson and Linden (2014) 50-gamma/65-foot criteria. A total of 43 of the 80 anomalies that meet or exceed the 50-gamma/65-foot criteria are associated with existing pipelines. While the remaining 37 anomalies, consisting of 22 magnetic targets, meet and/or exceed the 50-gamma/65-foot criteria, they do not meet Gearhart’s 2011 magnetic orientation and spatial criteria to be considered potentially significant. They are interpreted as relic oils wells, ferrous debris scatters associated with the oil and natural gas industries and recreational and commercial fishing activities, and miscellaneous debris from previous tropical storms and hurricanes. Review of the sonar record revealed two distinct acoustic targets (SST-1 and SST-2) consisting of the remnants of a subsequent exploratory oil well and a subsided pipeline trench. Based on the applied criteria, these magnetic and acoustic targets do not exhibit any characteristics associated with historic shipwrecks and/or other significant submerged cultural resources. As such, the recommended management action for magnetic targets, Numbers 1–22, as well as acoustic targets, SST-1 and SST-2, is no further archaeological investigations.

One magnetic target, Number 23, situated outside of the Area of Potential Effects, is associated with previously recorded anomaly Mag 8, which was deemed as potential historic shipwreck remains. While it is located outside of the Area of Potential Effects, it was recorded within the 50-meter (164 foot) avoidance buffer of previously recorded anomaly Mag 8. No magnetic signatures were recorded within the portion of the avoidance buffer that is within the Area of Potential Effects. The lack of any residual magnetic signatures of the anomaly within the Area of Potential Effects indicate that no portions of the ferrous source objects for Mag 8 extend into the current survey area or the construction footprint; and therefore, the submerged target or its avoidance buffer will not be impacted by the proposed activities.

Additionally, no magnetic signatures associated with previously recorded anomalies Mag 7 and Mag 9 were identified in the 50-meter (164-foot) avoidance buffers within the Area of Potential Effects. The lack of any residual magnetic signatures of anomalies (Mag 7 and Mag 9) within the Area of Potential Effects indicate that no portions of the ferrous source objects for these two magnetic anomalies extend into the current survey area or the construction footprint; and therefore, the submerged targets or their avoidance buffers will not impacted by the proposed activities.

The recommended management action for the portions of the 50-meter (164-foot) avoidance buffers for Mag 7, Mag 8, and Mag 9 that extend partially into the current survey area is avoidance from any bottom disturbing activities. If bottom disturbing activities within the buffer buffers cannot be avoided, additional marine archaeological investigations in the form of diver-ground-truthing will be required to determine the nature and historical significance of the source magnetic objects.