Reburial in the context of development: Approaches to reburial in the English planning process

Abstract

Rescue archaeology in England is now firmly embedded in the planning process, following the introduction by the UK government of Planning Policy Guidance Note 16 in 1990 (PPG 16; Departmentof the Environment. Planning Policy Guidance Note 16 — Archaeology and Planning. HMSO, London (1990)). The basic premise of PPG 16 is a strong preference for in situ preservation of nationally important archaeological remains. This often includes reburial of archaeology prior to construction activity, once it has been exposed in test-pitting (‘evaluations’) or full excavation. Reburial strategies are often prepared by civil engineers and there appears to be an overemphasis on consideration of the potential physical impacts on the archaeology. These strategies usually include the use of geotextiles and sand, or other graded material, chosen for its particular particle size/shape characteristics. A greater awareness of the chemical and physical characteristics of a burial environment is now required to ensure that reburial is effective. Archaeologists and conservators are beginning to consider both the natural and, increasingly, the ‘man-made’ (industrial, domestic and agricultural) changes to the soil chemistry of an archaeological site. More use needs to be made of the potential information ‘locked up’ in the artefactual material retrieved from evaluations and excavation nearby. An assessment of the degree of preservation of material should be an integral component for the design of a reburial strategy.     

Monitoring the burial environment of terrestrial wet archaeological sites in The Netherlands

Abstract

Monitoring the burial environment of archaeological sites is necessary to assess the success of their preservation in situ. Also, monitoring the state of preservation of actual archaeological remains together with that of their burial environment will further our understanding of the degradation processes acting on archaeological remains in situ. These remains consist not only of objects made from wood, metal, stone, etc., but also of pollen, soil features and even micromorphological features. Although, to date, the precise degradation mechanisms of archaeological remains in situ are not yet fully understood, general agreement exists on which parameters should be monitored in wet terrestrial environments. Also, it has been established that in situ measurements are preferable to laboratory analyses of soil (water) samples. In practice, it is difficult to find suitable monitoring equipment for in situ measurement as it must meet many requirements: an in situ measuring principle; stable for a period of at least several months; robust for use in the field; and equipped with a datalogger. A suitable principle exists for measuring the redox potential, however a simple, robust field instrument with datalogger is not yet available. Monitoring of the water table level, temperature and oxygen content is possible with recently developed, commercially available instruments. Monitoring of acidity is less complex as it does not vary as rapidly as, for example, the redox potential; however, the recommended method is still based on analysing soil samples, which is not acceptable in the long term at archaeological sites.     

A Qualitative Approach for Assessment of the Burial Environment by Interpreting Soil Characteristics; A Necessity for Archaeological Monitoring

Abstract

Modern-day archaeological monitoring is often hampered by lack of money, lack of time, inadequate measuring equipment, and lack of insight in the conservation potential of a site.

Although in modern archaeological excavations soil characteristics are noted (colour, texture, groundwater level, and sometimes mineralogy), these characteristics are mainly used for the interpretation of a site. However, by looking to these characteristics from a conservational view eventually combined with the conservation status of the archaeological objects, much can be learned about the burial environment. This is essential for optimizing archaeological monitoring.

Degradation processes result from the change of reactive phases in the soil or the site. Reactive phases are soil components such as organic matter, sulfides, iron(hydr)oxides and carbonates (chalk, shells), and, if present, components in the ground or interstitial water such as hydrogen ions and sulphate. The presence of these phases can easily be established by the archaeologist or soil scientist in the field. We propose a simple field-based method for assessing degradation processes essential for in situ preservation and monitoring.     

Do geotextiles affect soil biological activity in the ‘reburial’ environment?

Abstract

The effect of five different proprietary geotextiles on the activity of soil micro-organisms (respiration as measured by CO₂ production) has been investigated in model laboratory chambers. The aim was to determine whether geotextiles, used to ‘protect’ archaeological materials during conservation by reburial, influence microbial processes that may promote biodegradation of organic archaeological materials by altering the physical properties of the soil. Four of the geotextiles were composed of either polythene or polypropylene and did not provide substrates for microorganisms. These four geotextiles had no significant effect on microbial activity over a short-term (56 days) burial period. By contrast, one of the geotextiles had a core of wheat straw and coconut fibre bonded in a polypropylene mesh. This geotextile led to increased microbial activity as a result of biodegradation of the straw and fibre core. From a practical point of view, these data suggest that geotextiles that are not themselves readily biodegradable did not enhance biodegradation of other organic material in the short term in the burial environment. If the use of geotextiles offers other advantages, such as providing a marker in the soil or back-fill, or because they facilitate subsequent cleaning and preservation operations, then their use is warranted.     

Reburial and Analyses of Archaeological Remains in the Marine Environment — Investigations into the Effects on Metals

Abstract

The treatment and long-term storage of recovered cultural material from underwater heritage sites is becoming less cost effective, and reburial of archaeological sites and the associated artefacts in the marine environment is becoming increasingly common practice in managing the submerged cultural resource. Following recent large-scale underwater archaeological excavations in Marstrand harbour, Sweden, the majority of recovered finds were reburied in defined trenches in the harbour sediment. Subsequently, the Studio of the Western Sweden Conservators in conjunction with the Bohus County Museum initiated a fifty-year research project to evaluate reburial as an appropriate method of preserving waterlogged archaeological artefacts in the long term. The research project, entitled ‘Reburial and Analyses of Archaeological Remains’, was launched in 2002 and consists of six sub-projects. The main aims of these sub-projects are to analyse the extent of deterioration of the most common material types found on underwater archaeological sites, assess the stability of packing and marking materials used in archaeological documentation, and monitor the reburial environment.

The aim of the metals sub-project is to investigate the short- to long-term corrosion behaviour of metals buried in the marine environment by examining the deterioration of reburied and exposed modern metal coupons and eventually compare these results to the analysis of actual shipwreck artefacts. The environmental monitoring sub-project is designed to complement the other sub-projects by assessing the physico-chemical changes occurring in the reburial environment over time and the effect on the deterioration of the different reburied material types. In comparing the results obtained over the past seven years from both the metals and monitoring sub-projects, it should be possible to more accurately evaluate the effectiveness of reburial as a long-term in situ preservation strategy for metallic archaeological remains.     

The Never-Ending Story? The Lessons of Fifteen Years of Archaeological Monitoring at the Former Island of Schokland

Abstract

The former island of Schokland became part of the mainland of the Netherlands when the Noord-Oost polder was drained in the 1940s. Mesolithic camp sites, Neolithic and Bronze age settlements, and medieval dwelling mounds (terps) on Schokland and in its immediate surroundings now form a UNESCO World Heritage site.

The main threat to the former island and the archaeology is drying out of the soil profiles, causing degradation of organic remains. Because of this, on the island and in its immediate surroundings the groundwater table is kept high in a specially created hydrological zone.

Schokland was one of the first sites in the Netherlands to be monitored in order to assess threats to the archaeological record and ongoing degradation processes. Monitoring started in 1999, and subsequent measurements were taken in 2001, 2006, and 2009/10. This included measurements of groundwater tables, water composition, redox, soil moisture and soil chemistry, micromorphology, and the degradation of botanical remains and bone. This time series of measurements makes it possible — first and foremost — to study long-term effects and changes in the Schokland burial environment, and their effects on the archaeology. In addition, the development of monitoring techniques around Schokland illustrates how the field of archaeological monitoring has evolved over the years.

Since the first monitoring round in 1999, developments in monitoring have included (1) technological developments enabling monitoring of high-frequency variations in groundwater, redox, and moisture contents, for example; (2) growing knowledge of degradation processes and the relevant characteristics of the burial environment; and (3) an increase in easily accessible datasets from third parties. Worries have arisen about the long-term storage and availability of monitoring data.

For future monitoring rounds, the value of the various monitoring techniques need to be critically evaluated, and the purpose of monitoring specific sites need to be reconsidered.     

Making Better Use of Monitoring Data

This paper addresses the knowledge gap that exists in relation to understanding and quantifying the sensitivity of organic-rich archaeological deposits with respect to changes in the soil environment. Based on two case studies we demonstrate that it is possible to quantify the current decay rate in unsaturated archaeological deposits by combining decay rates measured in the laboratory with on-site monitoring data in a simple decay model. The decay of organic archaeological deposits is highly sensitive to variations in soil temperatures and soil water content. Measurements of soil water content cannot always stand alone as a representative measurement of oxygen availability; which suggests that in situ measurements of oxygen content or redox potential are needed in order to understand the preservation conditions at a site. The results of this study emphasize the advantage of combining monitoring data with laboratory studies, in order to document in more detail where and when degradation takes place.     

Relevance of soil biology and fertility research to archaeological preservation by reburial

Abstract

This paper discusses how soil biological information can help to improve understanding of, and possibly inform decisions about, preservation of organic archaeological remains by reburial. A brief summary of the properties of the soil biological community is followed by an outline of results from recent biological investigations following the recovery of archaeologically relevant materials that had been buried for thirty-three years in one of the experimental earthworks in England UK. Examples from the soil biology and fertility literature are discussed to illustrate the effects of fluctuations in soil wetness and aeration, and of nitrogen availability on decomposition. Finally, the impact of soil handling and physical disruption on biological processes in soil are discussed, as they influence whether soil functions can be restored at a reburial site once the archaeological resources have been ‘protected’ beneath.     

The RAAR Project — Heritage Management Aspects on Reburial After Ten Years of Work

Abstract

The general purpose of the international reburial project, Reburial and Analyses of Archaeological Remains (RAAR), is to evaluate reburial as a method for the long-term storage and preservation of waterlogged archaeological remains. Since 2001 material samples have been buried, retrieved, analysed systematically, and the results reported.

RAAR has mainly focused on the degradation of materials commonly encountered on archaeological sites, and on environmental monitoring techniques in order to determine what type of material can be reburied and for how long. The project has concluded that a heritage institution could provide short- or long-term curation for its archaeological archive by using reburial depots provided they are set up according to guidelines and restrictions stipulated by the RAAR project.

However, there are management and legal aspects that need to be discussed and resolved before each reburial project. Actual reburials that have been carried out so far are often a solution to emergency situations and lack collection and management policies. The questions ‘what’, ‘why’, and ‘for how long’ have been forgotten and need to be addressed. The legal protection of a reburial site is also important. This paper discusses these aspects and their consequences and highlights possible differences in approaches between the countries involved in the RAAR project.     

Southwest Scottish Crannogs: using in situ studies to assess preservation in wetland archaeological contexts

This paper presents the results of in situ monitoring of waterlogged burial contexts in southwest Scotland. The sites investigated are Iron Age crannogs (lake dwellings) which have a proven waterlogged archaeological component, and which are being assessed as part of a national program of study by the Scottish Wetland Archaeology Programme (SWAP) team. A monthly monitoring program commenced in July of 2004. To date, monitoring of water levels, pH, and redox potential, has been undertaken for a period of 17 months in order to encompass any seasonal variability at the sites studied. The results have proven robust in that an ‘ideal’ site for in situ preservation has been identified from the five sites investigated, and the monitoring has highlighted external variables and seasonal impacts that have the potential to influence the long-term in situ preservation at the remaining sites studied. In general, these results have expanded upon our knowledge of the potential for the preservation of existing archaeological remains within such contexts. This study represents the first stage of monitoring aimed at developing a holistic understanding of in situ conditions at the crannog sites studied in southwest Scotland.     

Reburial research: preliminary field experiments at Fort Selden

Abstract

Preservation through reburial is an effective strategy for cultural sites, and information exists that identifies broad categories of fill type, materials and the below-ground physico-chemical and biological conditions that favour survival of cultural artefacts. This apart, relatively little systematic research and testing has been undertaken on the reburial of archaeological materials under alternating wet—dry conditions, which pertain in many areas of the world where rich archaeological resources exist that are also a focus of excavation. Preliminary field research and testing was undertaken at the site of Port Selden, New Mexico, over an approximate eighteen-month period in 1995–1996 as a precursor to intended longer-term experiments. The ultimate objective was to determine optimal conditions for designed reburial interventions of archaeological materials. Testing was done in pits and on the ground and utilized a standard artefact comprised of adobe and lime as well as several indicator materials (wood, textile, brass). The problems associated with the design of the experiment, instruments and monitoring are discussed, as well as findings relevant to current practice and future testing. The eighteen-month preliminary testing itself followed an earlier (1988) reburial test at Fort Selden in which adobe walls were buried. The results of this test wall experiment are also included here, as they are pertinent to an understanding of the behaviour of earthen architectural materials in the reburial environment.     

Reburial and protective covering of ancient mosaic pavements: The experience of the conservation department of the Israel Antiquities Authority

Abstract

Four case studies are presented illustrating different attempts to protect excavated ancient mosaics by reburial or protective covering, with varying degrees of success, at three archaeological sites in Israel: Tel Itztaba, a site excavated between 1991 and 1994 where planning for reburial at the outset of the excavation could have prevented considerable losses; Khirbet Minya (Horvat Minim), a site excavated in the 1930s, reassessed after four years of reburial; the Promontory Palace at Caesarea Maritima, a site excavated in 1978, partially destroyed by the sea, reburied and regularly monitored since 1994; and an experimental test site at Caesarea Maritima. These examples demonstrate the importance of planning, monitoring and maintenance for successful reburial, and allow an assessment of which materials and methods performed better than others.     

Quantification and Visualization of In Situ Degradation at the World Heritage Site Bryggen in Bergen,Norway

Abstract

Environmental monitoring at the World Heritage Site of Bryggen in Bergen, Norway, has shown damaging settling rates caused by degradation of underlying archaeological deposits. Measurements of piezometric head, oxygen, and soil moisture content, as well as chemical analyses of water and soil samples are key elements of the environmental monitoring.

Groundwater monitoring and geochemical analyses reveal a complex and dynamic flow through the natural and anthropogenic stratigraphy. The preservation conditions within the organic archaeological deposits are strongly correlated with oxygen and soil moisture content, that are controlled by the groundwater flow conditions at the site. To quantify decay rates, it is thus essential to understand the wider hydrogeological context of the site. This paper presents recent advancements in quantifying decay rates in the saturated zone at Bryggen. The paper also shows that 3D geo-archaeological modelling can contribute to preservation management by visually combining results of geological, archaeological, geochemical, and hydrological investigations. This opens up for improved multidisciplinary understanding of preservation potential, thereby contributing to an improved protection of archaeological deposits in situ.     

Chaco Canyon reburial programme

Abstract

Chaco Culture National Historical Park in northwestern New Mexico contains a wealth of archaeological resources, including 150 large earth and masonry structures under active management and preservation. In response to loss of original fabric from exposure over the last 100 years and more, as well as from continuous cycles of maintenance and repair, an extensive and long-term reburial programme was embarked upon in the late 1980s. The overall context of the site and the decision to undertake reburial as a principal conservation strategy is described in Part I of this paper. Part II provides a summary of the results of partial reburial at Chetro Ked, one of the ‘great houses’ of the canyon, in which protection of original timber was the main objective. Most of the wood at Chetro Ked could be covered only by a shallow overburden of soil, necessitating a specialized reburial design and materials to exclude moisture. Recent evaluation of the efficacy of the wood reburial was undertaken. Problems and shortcomings that were identified have led to re-design of part of the reburial and more careful attention to quality control during the intervention, as well as to selection of more appropriate geosynthetic materials. Additional monitoring techniques have been developed to allow direct withdrawal of samples of wood for assessment of deterioration.     

The reburial of mosaics: an overview of materials and practice

Abstract

A significant proportion of the literature on the reburial of archaeological sites concerns mosaics. These publications reveal that a variety of materials have been used for mosaic reburial, including specialized fill and separation layers, from the early 1980s onwards. Although reburial practice often demonstrates an ad hoc and indiscriminate use of fill and separation materials, or the following of trends and anecdotal information favouring certain materials, knowledge of their characteristics is very important in developing an appropriate technical design for reburial of mosaics. The materials most commonly employed in mosaic reburial practice, including geotextiles, are reviewed and an assessment of their positive and negative characteristics within a reburial design is provided. Recent but limited laboratory and field testing, monitoring and evaluation of reburial interventions have begun to provide preliminary evidence about the behaviour of these materials, indicating which ones are most appropriate and how they should be utilized to best advantage. However, their selection and use remains uneven, and positive results continue to be as much a function of adequate maintenance as proper design and execution.     

Monitoring and Modelling Saturation as a Proxy Indicator for in situ Preservation in Wetlands—a GIS-based Approach

The unifying nature of water on the preservation of organic archaeological and palaeoenvironmental source material within wet deposits is well recognized. It is also understood that, while the preservation of such deposits is fundamental towards our understanding of the past, in many areas de-watering through agricultural drainage and water abstraction is degrading them. Within the framework of preservation in situ such environments present considerable challenges. Fundamentally, the environmental dynamics of wetlands, not least of water, mean that they must be monitored carefully in order to understand the condition of the burial environment and thereby the likely preservation potential. This paper presents an approach to monitoring the saturation of the burial environment and modelling this data using a geographical information system (GIS). It demonstrates a method aimed at modelling the conditions of current preservation, and predictively modelling the conditions for long-term, in situ preservation in order to provide a baseline for resource management. It is shown that the quantification of saturation is possible and advantageous in the management of dynamic wetland environments.     

In Situ Preservation of Wetland Heritage: Hydrological and Chemical Change in the Burial Environment of the Somerset Levels,UK

Abstract

In situ preservation is a core strategy for the conservation and management of waterlogged remains at wetland sites. Inorganic and organic remains can, however, quickly become degraded, or lost entirely, as a result of chemical or hydrological changes. Monitoring is therefore crucial in identifying baseline data for a site, the extent of spatial and or temporal variability, and in evaluating the potential impacts of these variables on current and future in situ preservation potential.

Since August 2009, monthly monitoring has taken place at the internationally important Iron Age site of Glastonbury Lake Village in the Somerset Levels, UK. A spatial, stratigraphic, and analytical approach to the analysis of sediment horizons and monitoring of groundwater chemistry, redox potential, water table depth and soil moisture (using TDR) was used to characterize the site.

Significant spatial and temporal variability has been identified, with results from water-table monitoring and some initial chemical analysis from Glastonbury presented here. It appears that during dry periods parts of this site are at risk from desiccation. Analysis of the chemical data, in addition to integrating the results from the other parameters, is ongoing, with the aim of clarifying the risk to the entire site.     

The use of geosynthetics for archaeological site reburial

Abstract

Applications of geosynthetic materials in reburial practice include geotextiles for separation, filtration and protection (cushioning); geomembranes and geosynthetic clay liners for infiltration control; geonets and geocomposites for sub-surface drainage; and geocells for erosion control. Mechanically stabilized earth reinforcement using geocells, geogrids and geotextiles can also provide substantial benefits for reburial projects by reducing lateral earth pressure against backfilled structures. Other aspects of modern geotechnology that may be useful for reburial projects include micro-piles and soil nailing for foundation and excavation support and evapotranspirative capping technology to establish the depth of soil cover required to isolate a structure or artefact from moisture and temperature fluctuations. Optimal application of these geotechnologies requires an understanding of the basic engineering principles associated with their implementation, as well as knowledge of the factors influencing archaeological site preservation.     

The Use and Deployment of Modern Wood Samples as a Proxy Indicator for Biogeochemical Processes on Archaeological Sites Preserved in situ in a Variety of Environments of Differing Saturation Level

Abstract

In situ preservation of archaeological sites is becoming an ever increasing trend as a means of preserving our cultural heritage. In connection with this the environmental conditions, such as water level, dissolved oxygen, temperature, pH and water chemistry, of a site are often monitored. It is generally agreed that a waterlogged and anoxic environment is essential for optimal preservation conditions but the set-up and maintenance of an environmental monitoring programme can be costly.

This paper discusses the design and use of a system whereby modern samples of wood can, with a minimal disturbance of the soil, easily be deployed and retrieved from archaeological sites. The system was deployed in an unsaturated environment, an environment with fluctuating water levels and a fully saturated peat bog. The samples were assessed after two years using microscopic, physical and molecular biological methods, and the types of wood-degrading organisms seen were compared with the results of environmental measurements. Modern wood samples were used, as the microbial ecology of wood-degrading organisms in these different types of environments is relatively well documented. Preliminary conclusions show that the deterioration processes of modern wood samples in these environments act as a good proxy indicator of the environmental conditions and biogeochemical processes ongoing at a site.