Diver Evaluation of
Unidentified Magnetic Anomalies and/or Side-Scan Sonar Targets: Search and Methodological
Requirements
MISSION
Magnetic anomalies are localized disturbances in the earth's magnetic field. The goal
of the following test procedures is twofold:
- to determine if the magnetic anomaly and/or side-scan target is modern debris or a
historic archaeological resource; and
- to determine if the magnetic anomaly and/or side-scan target possesses qualities
that makes it a significant and unique archaeological property as defined by Federal law.
Not all shipwrecks are considered "significant."
TESTING PROCEDURES
Unidentified Magnetic Anomalies
A professional marine archaeologist must be present to direct, observe and monitor the
diving investigations and must contact the Minerals Management Service (MMS)
archaeologists to coordinate the operation prior to going offshore. The following
procedures must be followed:
- a Differential Global Positioning System (DGPS) must be used to relocate the
unidentified magnetic anomalies listed in the Minerals Management Service archaeological
analysis for this project;
- a marker buoy must be dropped at the precise location of each magnetic anomaly to be
tested;
- at each marker buoy location, the diver will perform a series of 10 radial search sweeps
around the position of the marker buoy. These search sweeps will be in 5-ft increments
(i.e., 5 ft, 10 ft, 15 ft, etc.) out to a maximum radius of 50 ft; and
- anomalies detected by the diver shall be probed minimally to a depth of 5 feet to
determine the depth of burial, approximate size of the target, and association with other
features.
This methodology will provide a 100-ft diameter circle of investigation around each
unidentified magnetic anomaly location. Each radial search sweep shall be conducted with a
hand-held gradiometer, magnetometer, or metal detector to locate the anomalies on the
seafloor. An alternate search strategy (e.g., linear grid, radials, etc.) may be employed
with the approval of the field archaeologist.
If recorded anomalies on or near the pipeline centerline can not be located using the
above search methodology, additional magnetometer surveying may be required to determine
the precise location and limits of the anomaly or anomaly cluster. The specific survey
methodology will be determined by the field archaeologist.
If the source of the anomaly is encountered by the probe, the anomaly must either be
buoyed for avoidance by the proposed operations or evaluated by the field archaeologist to
determine its historical significance. A determination of the anomaly's historical
significance shall be made using the criteria specified in 36 CFR Part 60.4, "Determination
of Eligibility for Inclusion in the National Register of Historic Places," and
National Register Bulletin No. 20, Nominating Historic Vessels and Shipwrecks to the
National Register of Historic Places."
If the anomaly can not be physically (i.e., hands-on) located by the 5-ft-probe testing
procedure, it may be assumed that the source of the anomaly is buried deeper than 5 feet.
Consequently, this anomaly location will not be affected by pipeline centerline
construction. The effects of the proposed method of construction (i.e., lay-barge
anchoring, jack-ups, etc.) on anomalies off the centerline also must be considered. The
anomaly location is cleared when, in the opinion of the field archaeologist, construction
will not adversely affect a potentially significant archaeological resource. Testing must
extend to the depth of impact to the seafloor where possible. These search procedures
shall continue until all anomalies either are cleared or evaluated by the field
archaeologist.
Side-Scan Sonar Contacts
The diver must be able to conduct a hands-on assessment and evaluation of each sonar
contact listed in the MMS archaeological analysis. This assessment must include an
analysis of the age, physical composition, and structural integrity of the object (i.e.,
wood or metal, intact or dispersed). Next, an evaluation shall be undertaken to determine
if the object is of historical significance using the criteria specified in 36 CFR Part
60.4. Measured drawings and/or underwater video or still photographs of the sonar
feature shall be made for documentation and submitted with the final "Report of
Finding".
REQUIRED COORDINATION WITH MMS
A "Report of Findings" prepared in accordance with the report writing
standards specified in MMS Notice To Lessees (NTL)
2005-G07, Enclosure No. 2, must be
submitted to the MMS for approval within ten work days of the completion of fieldwork. MMS
archaeologists must concur with the findings of the field archaeologist prior to the start
of construction.
Alternatively, if the field archaeologist determines that the magnetic targets are
caused by modern marine debris, or that the source of the anomalies can not be located by
any of the means specified above, and that the proposed construction will have no effect
on potentially significant archaeological properties, notice to proceed can be given by
the MMS Field Operations Pipeline Unit upon receipt of a telefaxed notification of these
results signed by the field archaeologist. The proposed construction may proceed pending
the mandatory 48-hour notification to the Pipeline Unit and fulfillment of any other
permit requirements. A "Report of Findings" still must be submitted as indicated
above.
If diving investigations discover a potentially significant archaeological property,
the Field Operations Pipeline Unit must be notified immediately. Further operational
measures will be developed in accordance with MMS
NTL 2005-G07, Enclosure No. 3, in
consultation with the lessee or right-of-way holder, the field archaeologist, and the MMS.
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