Introduction
The Massachusetts Board of Underwater Archaeological Resources (BUAR) is the state agency charged with the identification, preservation and protection of the Commonwealth’s underwater archaeological resources. The purpose of archaeological investigations is: (1) to determine the presence or absence of culturally related materials and resources within an area or region of interest; (2) interpret these resources for the benefit of the public; and (3) assess their eligibility for listing in the State and National Register of Historic Places (National Register). Such work is undertaken pursuant to the applicable laws and regulations pertaining to the cultural resources of Massachusetts. Generally, these archaeological investigations are conducted to comply with the National Environmental Policy Act of 1969 (NEPA) and Section 106 of the National Historic Preservation Act of 1966 (NHPA), as amended (36 CFR 800), and implementing regulations of the Advisory Council on Historic Preservation (Advisory Council), as well as pursuant to Massachusetts General Laws concerning the BUAR and the Massachusetts Historical Commission (MHC), the Massachusetts State Archaeologist, and the Massachusetts State Historic Preservation Office (SHPO).
As our knowledge of the natural and cultural resources in our region has developed, it has become necessary to establish a set of survey standards and parameters to which those who choose to work within Massachusetts waters must adhere. Given the high variability of the marine environment and the diverse nature of submerged cultural deposits, alterations may be made to these standards on a case-by-case basis, such as in instances where adherence may not be safe or feasible. However, barring any such alterations, adherence to the procedures laid out in this document is required of any permittee and project proponent’s technical service consultant (i.e., archaeologist).
Past experiences have proven the cost-effectiveness and efficiency of having a project archaeologist be directly involved as early as possible in project planning, especially during geophysical survey planning and data acquisition. This participation should ensure that the concerns of the BUAR and review agencies will be addressed adequately.
Standards for Archaeological Investigations
The methodology for archaeological investigations described herein is intended to establish the minimally acceptable standards for the discovery of underwater archaeological resources in the waters of the Commonwealth of Massachusetts. BUAR and other state or federal review and compliance agencies may set more (or less) stringent standards depending on location, sensitivity, and potential impacts. Furthermore, this guidance is not intended to supersede the techniques and methods employed by other bodies in the course of archaeological investigations, only to ensure that the minimum standards required by BUAR are met.
Coordination and consultation with BUAR and other state or federal review and compliance agencies is an integral component of project planning. For those projects subject to Section 106 of the NHPA (36 CFR 800), project proponents are directed to consult with, provide their proposed research design and methodology to, and obtain the approval of the SHPO/MHC/State Archaeologist and the lead federal agency, in accordance with 36 CFR 800.4, prior to conducting archaeological field investigations. Additionally, for intertidal survey activities above mean low water, coordination with MHC is also necessary, as a State Archaeologist’s permit may be required, in addition to a BUAR permit.
All archaeological survey and data collection activities should be undertaken in consultation with and/or under the supervision of a qualified archaeologist (see Appendix A).
1. Desk-Based Assessment:
Background research and pre-survey archaeological sensitivity evaluation
The purpose for undertaking background research is to determine general locations within the permit or study area where there is a likelihood, or archaeological sensitivity, for encountering cultural materials. This information also provides the environmental and cultural contextual framework informing the archaeological identification and evaluation of those resources.
i. Consult with the Massachusetts State Archives and perform a comprehensive literature review of textual sources, documents, photographs, maps and charts, histories, site reports, and files that pertain to the environmental and cultural histories within the area of interest with special reference to known or potential sites within the project area.
ii. Consult with the MHC and BUAR to determine if there are any inventoried sites within or near the proposed work area, or those that are currently under review for addition to, the National Register of Historic Places (NR). BUAR maintains an inventory and permit files. MHC maintains NR nominations, an inventory, a cultural resource management (CRM) report bibliography and collector files.
iii. Consult with local experts and persons possessing expert knowledge about the environmental history and precontact and postcontact period cultural histories of the area of interest.
iv. Perform an artifact and material culture review. This can be a detailed analysis of previously recovered cultural materials from within, or within the immediate vicinity of, the project area. Artifacts can be found in private or museum collections. Knowledge of previously recovered materials will provide insight into the cultural affiliation, possible function, and significant characteristics of the area.
v. Review environmental reports so as to describe the nature of the site in terms of past and present geological, ecological, climatic, and other environmental conditions encompassing the project area. This information is necessary for understanding the function and condition of the site and expected remains.
vi. Provide pre-survey archaeological sensitivity evaluation and predictive models concerning anticipated site locations and find types. The criteria and justifications set forth in establishing these predictions should be a clear summary of the results of each phase of the desk-based assessments.
2. Field Survey:
a) Remote-Sensing/Geophysical Survey:
A remote-sensing/geophysical field survey is required following the Desk-Based Assessment. This allows for a non-invasive inspection of the project area focused on characterizing the nature of the site and locating objects, vessels, or sites of potential precontact and/or postcontact period historic significance. There is a suite of tools and technologies available for use in archaeological investigations, each providing a different function with their own operational costs and constraints.
The following is a list of remote-sensing/geophysical survey techniques required (i.e., magnetometer, side-scan sonar, sub-bottom profiler) and recommended (swath/multi-beam bathymetry) by the BUAR:
- Magnetometer: Magnetometers work by measuring the Earth’s ambient magnetic field. Deposits of ferrous rock or ferrous cultural materials can produce anomalous readings in the measured magnetic field. Magnetometers have the ability to sense even those ferrous cultural materials that are buried under multiple sediment layers and not visible on the seafloor’s surface. The utility of magnetometers in archaeology is constrained by the size and condition of the ferrous cultural materials and theirdistance from the magnetometer’s sensor, as well as by nearby sources of electro-magnetic noise from electrical power infrastructure, ferrous rock in local geology, and high concentrations of ferrous metal debris in a survey area.
Requirements:
i. Use of a cesium-vapor, Overhauser, or other type of high-sensitivity magnetometer capable of fast sampling rates and outputting data digitally.
ii. Trackline intervals should be spaced at 15 m (50 ft) above the 30 m (100 ft) water depth contour, and may not exceed 30 m (100 ft) below the 30 m (100 ft) depth contour.
iii. The magnetometer should be towed at a height above the seafloor of 6 m (± 1 m) (18-23 ft) and far enough away from the survey vessel to minimize interference from its hull.
iv. Magnetometer sensitivity should be one gamma (γ)/one nanoTesla (nT) or less.
v. The data sampling interval may not exceed one (1) second. - Side-Scan Sonar:
Side-scan sonar refers to a category of sonar employed to acoustically image in plan-view the surface of the seafloor. These systems work by emitting high-frequency sound pulses through the water column that are directed towards and reflect off of the seafloor and then plotting the returning signals based on the time and intensity of the return. The resulting monochromatic imagery allows for the discernment of different features on the surface of the seafloor as viewed in plan (e.g., bed forms, surface geology, natural or human-made obstructions, and the extent of a site), based on the varying densities and types of materials encountered. Harder materials (e.g., wood, rock, or metal) are more acoustically reflective than are softer materials (e.g., mud or organics).
Requirements:
i. A dual-channel 100/500 kHz side scan sonar that records data digitally.
ii. Survey trackline spacing should be such so as to provide a minimum of 100% coverage of the project area (ideally a 30 m [100 ft] interval at a 50 m [164 ft] range scale), with 200% being the desired coverage.
iii. Surveys should be conducted in a manner that allows for the detection of objects on the seafloor with minimum dimensions 1-x-1-x-1 m (3.3-x-3.3-x-3.3 ft) (obtained from acoustic shadow-length measurements), regardless of depth.
iv. Towfish height above the seafloor should be 10% to 20% of the range scale in use.
v. Survey speed should be sufficient to adequately ensonify all features. - Sub-Bottom Profilers:
Sub-bottom profilers are marine survey instruments that utilize lower-frequency (as compared the frequencies of side-scan sonar) sound pulses sent through the water column and into the seafloor for the purpose of imaging buried stratigraphic layers and sub-surface features. Penetrative power and resolution depend on the system used (i.e., "chirp” or “boomer”) and the composition of the seafloor. In terms of archaeological applications, higher or swept-frequency chirp subbottom profilers may be used to directly survey buried sites (submerged landscapes or anthropogenic materials) or to study the geological and sedimentological nature of a site.
Requirements:
i. A high-frequency system with an operational bandwidth between 1.5 and 4.5 kHz must be used to provide high-resolution digital images on near-surface features.
ii. The profiler must be capable of achieving a vertical resolution of 30 cm (1 ft) in the upper 15 m (50 ft) of sediment.
iii. Sediment penetration must exceed the depth of the feature being surveyed. - Swath/Multi-Beam Bathymetry: (Recommended but not required)
Multi-beam bathymetric surveys use a fan-shaped swath of numerous directed sound pulses or multiple beams of sound to ensonify and map the submerged topography, or bathymetry, of the seafloor. Unlike side-scan sonar, which produces imagery based on processed acoustic reflective intensity plots, bathymetric surveys provide depth and position data derived from the two-way travel time of the sound emitted. The acquired depth and position data can be used to create high-resolution digital bathymetric models of the sea floor. While side-scan sonar towfishes are equipped with two transducers that ensonify the areas left and right of the towfish as it moves horizontally through the water along a survey trackline, multi-beam bathymetry systems survey a fan-shaped swath directly beneath the sonar transducer that extends outwards at a predetermined angle with the least reliable data being collected at the outer edges of the multi-beam sonar swath. The use of swath bathymetry systems requires highly-skilled operators, careful measurements of the properties of the water that the system is being used in, and extensive data processing and interpretation.
Requirements:
i. Any multi-beam swath bathymetric survey conducted for the purpose of archaeological investigation must be capable of distinguishing an object with the dimensions of 1-x-1-x-1 m (3.3-x-3.3-x-3.3 ft) on seafloor in waters less than 20 m (66 ft) in depth.
ii. In waters 20 m (66 ft) in depth or greater, the survey must be conducted in a manner capable of detecting a cube measuring 5% of the depth with finer resolutions desirable.
iii. Line spacing must be such so as to provide 100% seafloor coverage (less than 100% coverage is acceptable if paired with 200% side-scan sonar coverage).
iv. Grid resolution must be 0.5 m (1.6 ft) or less at depths above 20 m (66 ft), and not less than 5% of the water depth in waters 20 m (66 ft) and deeper.
v. CTD (conductivity, temperature, depth) casts should be made at the start and end of the survey day, and every 2 hours during the survey day to adjust for variations in the speed of sound through the water column.
vi. The use of heave, pitch, and roll sensors is desired to mitigate errors caused by the survey vessel's movements.
vii. Data should be tide-corrected before being submitted (recommended).
General requirements for all Geophysical Field Surveys:
In addition to the instrument-specific requirements listed above, the following represents the requirements for all geophysical field surveys regardless of method:
i. All survey data is to be positioned by the use of a differentially-corrected Global Positioning System (DGPS) with a precision error not to exceed ±5 m (16 ft) in water depths less than 200 m (656 ft) and ±15 m (49 ft) in waters 200 m (656 ft) and deeper.
ii. Depths are to be tracked digitally using a single-beam or multi-beam echosounder.
iii. Surveys should be conducted in Universal, or Zulu, Time.
iv. Data sets must all correlate and be referenced to the North American Datum of 1983 (NAD 83). Coring samples must match sub-bottom profiling data.
v. All equipment must be operated, and data interpreted, by a qualified and experienced geophysical survey technician. Final interpretation and report preparation is to be handled by a qualified marine archaeologist.
vi. In the event that a sonar contact or magnetic anomaly is located in the project area, a sufficient number of lines are to be run to ensure that the contact or anomaly is fully defined, with lines to be spaced at intervals not to exceed 10 m (33 ft).
vii. All sonar contacts (including any feature or object producing a stronger return than that of the surrounding area) should be targeted digitally within the survey data directly (where applicable) and positions noted on a separate document in X/Y format with accompanying screen grabs, descriptions, and locations charted at an appropriate scale. Seafloor features that represent either identified or potential archaeological remains, should likewise be plotted on a map and listed in a table that includes elevation above the seafloor, central X/Y coordinates, a screen-grab image, and narrative description of the feature.
viii. The position of any shore features, such as landmarks, anomalies, and/or GPS-base stations, should also be included on a separate document with accompanying descriptions.
ix. Locations of any natural geomorphic features having sediment traps (i.e., submerged river, stream, and/or creek channels, sinkholes, etc.) that are identified through the evaluation of sub-bottom profiler data should be mapped to show their extent. Cross-section plots showing definable strata should also be prepared for each of these geomorphic features.
x. For cultural resource management (CRM)/environmental review and permitting compliance surveys, the BUAR typically requires that a magnetometer, side-scan sonar, and sub-bottom profiler, which meet the specifications set forth previously in this section, comprise the remote-sensing suite to be utilized.
b) Visual Survey:
The visual survey and documentation of the project area provides in situ inspections to characterize conditions, validate assessments, and identify potential cultural objects, features, and/or sites. As with remote-sensing/geophysical surveys, the steps outlined here are intended to be non-invasive.
- Walkover/Swimover: A quick inspection from the surface of the project area to characterize conditions and assess either potential hazards to the survey or any potential archaeological remains.
- Diving: In cases where the site is subtidal and it is safe to do so, SCUBA may be employed, so that the site may be subjected to a direct visual inspection and the conditions of the site and any materials within it may be characterized.
- Remotely Operated Vehicle (ROV)/Autonomous Underwater Vehicle (AUV): Under the supervision of an archaeologist and operation of a qualified ROV/AUV Pilot, visual inspections using ROVs and AUVs may be used to provide an effective remote-sensing alternative to a direct visual inspection done on SCUBA for the purpose of identifying, characterizing, and assessing potential cultural features or sites in the project's remote-sensing data.
Requirements:
i. Digital video and photography is required for collection and submittal during ROV/AUV surveys.
ii. Submitted media must be of sufficient resolution/quality to enable reviewers to draw conclusions about the project area.
iii. Media must include, date, time, orientation, and GPS coordinates for reference to survey tracklines, field maps, and plans. - Submarine:
Under the supervision of an archaeologist, visual inspections using submarines can provide an effective alternative means to SCUBA diving for the purpose of identifying, characterizing, and assessing potential cultural features or sites in the project's remote-sensing data, especially in deep water.
General requirements for all Visual Field Surveys:
While (with the exception of ROV/AUV surveys) there are no specific requirements for the individual methods of visually surveying an area of interest, the following represents general requirements and recommendations:
i. Visual inspections must be conducted in a systematic and safe and effective manner, especially those in which divers or other individuals are in the water.
ii. Visual inspections must be conducted during times of optimum visibility and the inspecting/reviewing body should be able to draw reasonable conclusions about the site based on those inspections.
iii. Visual surveys are non-invasive and tampering with or damaging any archaeological materials is to be avoided.
iv. Digital video or other photographic evidence is required for submittal in the case of ROV/AUV surveys, and is desirable in all other cases, but not required.
c) Potentially Intrusive and Direct Data Collection Activities:
A number of invasive data collection techniques have valuable application to archaeological assessments and investigations when used appropriately.
- Grab-Sample Survey:
Grab-samples (bottom samples) are collected to characterize surficial seafloor sediments. This method should not be used for direct archaeological data collection, but, instead, as a means to characterize the surface of the seafloor encompassing a site. However, under certain conditions, it is possible for recovered samples to (unintentionally) contain archaeological materials.
Requirements:
i. A sufficient number of diffuse samples should be recovered to accurately characterize the surface of the sea floor within the project area.
ii. Samples must be described based on visual inspection, noting such elements as color, texture, inclusions, and general grain size.
iii. Samples should be photographed for submission with final reports. - Vibracore/Borehole Survey:
Vibracore/borehole surveys are undertaken to provide a detailed profile of the local stratigraphy. Acquired sediment samples provide direct evidence for the analysis and ground-truthing of conditions documented in side-scan sonar and sub-bottom profiling data. Vibracores/borings give insight into the past and present geological, sedimentological, and climatological conditions of the project area, and provide data that may be useful in determining the presence and integrity of preserved submerged ancient landscapes that may have archaeological sensitivity. Samples may contain archaeological materials, though steps should be taken to avoid vibracoring/boring directly through cultural remains.
Requirements:
i. Vibracores/borings should be collected in conjunction with sub-bottom profiling data to assist in identifying and characterizing distinct acoustic reflectors in the seafloor's subsurface strata.
ii. Vibracore/boring locations should be distributed throughout the survey area ideally in a pattern that crosses the prevailing trend of the offshore geology.
iii. Cores should be spaced no more than 300 m (1,000 ft) apart.
iv. The minimum accepted recovery of each vibracore is 80% with at least three attempts made to do so at each sampled location (recommended).
v. Vibracores should be split in half lengthwise with one half archived while the other is submitted for analysis and sampling. Each half must be labeled with the collection location and date of collection.
vi. Individual vibracore/boring samples may be substituted for individual bottom samples where applicable. - Benthic Survey:
Benthic surveys allow for the characterization of marine flora and fauna within the project area. This information is relevant as it may affect the manner in which latter stages of the investigation are conducted, as well as give insight into the condition of materials and dynamics of the site. As with coring and grab sampling, steps should be taken to avoid damaging any archaeological remains.
General requirements for all Potentially Intrusive and Direct Data Collection Activities:
i. All survey results should be reviewed by a qualified archaeologist.
ii. All surveys must be conducted in a safe and effective manner.
iii. Care must be taken not to damage any cultural remains within the survey area.
iv. Photographic evidence is to be included in reports discussing survey results.
v. Sampling location areas should be depicted on plans and/or survey maps at appropriate scales.
vi. Care must be taken to cause no unnecessary harm to the marine life within or adjacent to the survey area.
3) Artifact Recovery, Excavation, Preservation
The results gathered from the non-invasive and sediment sampling surveys must be reported to the BUAR prior to moving forward on the initial project. Only on the basis of those reports will decisions be made regarding artifact retrieval, site excavation, conservation, and material preservation, if any cultural materials are present. Artifacts should not be collected during the survey phase of the investigation. Decisions regarding object recovery and/or excavations will be made through consultations with the BUAR. Methods and approach will be established at that time.
In the event of an unexpected recovery, see the BUAR’s see the BUAR's Policy Guidance on the Unanticipated Discovery of Underwater Archaeological Resources.
4) Summary and Additional Recommendations
The goal of these surveys is to identify underwater archaeological resources and areas of archaeological sensitivity based on reasonable expectations of site occurrence, frequency, and preservation within the region. Prior to the start of any field work, desk-based assessments should have provided the basis for any expectations for encountering cultural deposits in the project area. In addition to evaluating the possibility of locating underwater archaeological resources, the impacts of the proposed activity (e.g., dredging) on those resources need to be considered. The nature of the proposed activity may be taken into consideration for the alteration of the survey guidelines.
In regions with such a high degree of human activity as Massachusetts State waters, contemporary/modern debris will likely be encountered during the course of an archaeological survey. By identifying such objects during the initial survey using high-resolution survey methods, cost and effort will be reduced as those objects deemed archaeologically insignificant will not require further (and costly) investigation.
By instituting these survey standards, it is hoped that the maritime cultural history and Indigenous precontact period cultural history preserved in the underwater archaeological record of Massachusetts will best be served. Archaeologically significant materials can be identified, avoided, and preserved. Through experience and review of accepted archaeological survey protocols, we have found the criteria established in this document should in many cases ensure the adequate resolution and coverage allowing for the detection of surficial and buried underwater archaeological resources in the waters of the Commonwealth.
Applicable State and Federal Laws
MGL Chapter 9, § 26-27C - MHC review of state projects, State Archaeologist’s Permits
MGL Chapter 91, §63 – Underwater Archaeological Resources Permits
312 CMR 2.00: Board of Underwater Archaeological Resources
950 CMR 70.00: Massachusetts Historical Commission
Section 106 of the National Historic Preservation Act of 1966 (16 USC 470f), as amended