St. Paul's Catacombs Complex: Environmental Impact Study

ST. PAUL’S CATACOMBS COMPLEX RABAT, MALTA

ENVIRONMENTAL IMPACT STUDY UCL INSTITUTE FOR SUSTAINABLE HERITAGE MSc SUSTAINABLE HERITAGE 2016-2017 REPORT, APRIL 2017 RASA AKELYTE | SALLY EL SABBAHY | ZHANG JIAYING | XANDER LACSON | BIANCA MADDEN AIDAN MISSELBROOK | COSMO PHILLIPPS | CARLA PIANESE | ANDREW ROWSON | LEI SHUYU | SIDIE XU | JIN YE | WANG YINI

Acknowledgements The authors would like to acknowledge the generous support and warm hospitality of Heritage Malta in Rabat, including staff at the St. Paul’s Catacombs Complex, the Board Members and Senior Management, in particular: David Cardona, Romina Ferry, Mario Galea, Kenneth Gambin, Janice Sammut, and Godwin Vella.

We would also like to thank our external lecturers: Konrad Buhagiar, Professor JoAnn Cassar, and Dr. David Mifsud, whose expertise was invaluable during the project.

Professor May Cassar, Dr. Katherine Curran, and Dr. Kalliopi Fouseki of the Institute for Sustainable Heritage, University College London, deserve our special thanks for their feedback and guidance on the project and encouragement throughout.

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Table of Contents 0 1 2 3 4 5

1.1 1.2 1.3 1.4 2.1 2.2 3.1 3.2 3.3 3.4 4.1 4.2 4.3 4.4 5.1 5.2 5.3 5.4 5.5

6 7 APPENDIX A: APPENDIX B: APPENDIX C: APPENDIX D: APPENDIX E:

EXECUTIVE SUMMARY

3

INTRODUCTION

5

Background and Objectives Historic Significance Climate of Malta and Rabat Site Description

5 6 6 7

METHODOLOGY

10

Methods Limitations

10 11

REPORT FINDINGS

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Catacombs Visitor Centre Underneath the Visitor Centre Garage

12 19 26 29

REPORT RECOMMENDATIONS

32

Catacombs Visitor Centre Underneath the Visitor Centre Garage

32 35 38 40

CONCLUSION

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St. Paul’s Catacombs Complex Catacombs Visitor Centre Underneath the Visitor Centre Garage

42 42 43 43 43

BIBLIOGRAPHY

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LIST OF FIGURES & TABLES

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Project Brief Action Plan Risk Assessment Condition Surveys & Mapping Underneath the Visitor Centre R2 Graphs

49 52 58 68 72

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Executive Summary

ERDF 32: Archaeological Heritage Conservation Project involved extensive surveys of St. Paul’s Catacombs Complex; building a new Visitor Centre; and walkway, lighting and landscaping works to increase site accessibility and visitor appeal. The project’s over-arching aim was to achieve sustainable use and enjoyment of the site, balancing preservation and accessibility. This report aims to assess the impact of the above project on the site, especially on the archaeology and displayed collections.

This study required monitoring environmental conditions in two Catacombs (12 & 17), the Visitor Centre, the tombs underneath the Visitor Centre, and the garage used for collection storage to determine if they had changed from before the project started; and if these changes were detrimental to the in-situ archaeology and artefacts. Broader concerns of long-term site sustainability in the face of economic and environmental pressures were also considered.

Temperature and relative humidity (RH) were recorded using data loggers at each study location for 11 months in 2016-2017. Spot readings taken in November 2016 of visible light and UV levels, temperature and RH supplemented this data. Pollutant and pest data was also collected. Risk assessments were carried out for each study location and condition assessments undertaken for representative samples of collections kept in the Visitor Centre and garage. Condition mapping was performed in Catacombs 12 & 17 and under the Visitor Centre. The site’s Curator of Phoenician, Roman and Medieval Sites was interviewed and many site visits undertaken for observation. Desktop study of relevant literature, and a series of lectures on related topics, complemented the primary data collection.

Data analysis highlighted the following main themes: In the Catacombs, there is a stable internal environment with very high RH which, coupled with light, is causing extensive biological growth that may damage the archaeology. Visitor damage (both intentional and inadvertent) is also a problem. In the Visitor Centre, the building does not buffer the external environment to a significant degree, with consequently high RH levels being potentially detrimental to the collections displayed there. The area underneath the Visitor Centre was found to have a fairly stable environment closely mirroring external conditions without causing immediate concern.

The garage has an unsuitable environment for long-term archaeological collection storage due to high RH. These findings have led to a series of recommendations to improve the sustainability and resilience of the site over the short, medium, and long-term. For the Catacombs, it is suggested regular environmental monitoring and condition mapping is undertaken to better determine if (and how) any damage might be occurring. Concurrently, visitors should be comprehensively briefed and their movements monitored to reduce their impact on this sensitive environment.

Over the longer-term, depending on prevailing conditions, systems to control visitor entry to particular Catacombs or to rotate Catacomb opening to reduce visitor impacts are proposed.

In the Visitor Centre, it is advised that continuous environmental monitoring and regular condition surveys of collections should be carried out in order to closely track current conditions

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Executive Summary

and any resulting deterioration. Other core recommendations are to lower high RH levels by improving the buffering capacity of the building (by creating a transition from the exit door, and potentially shutting the underfloor void space during more humid months), and through a programme of using silica gel in display cases. Long-term, suggested strategies include exploring a switch to a greener energy source for the current HVAC system and engaging conservation volunteers and/or students to assist in monitoring and preserving the collections, thus improving economic sustainability.

For the area underneath the Visitor Centre, a regular programme of maintenance inspections is recommended to minimize flood risk and the risk of associated damage. Frequent condition surveys and further environmental monitoring to track deterioration of the tombs and inform future management would complement this approach. Regarding the collections housed in the garage, it is suggested that these be relocated to the more stable environment of the Natural History Museum in Mdina or the National Museum of Archaeology in Valletta. If unfeasible, measures are proposed to improve the garage’s capacity to buffer the external environment and to better protect the collections from damage and dissociation through modified storage and cataloguing practices.

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Introduction

1.1 Background and Objectives The preservation and development of St. Paul’s Catacombs Complex were key objectives of the European Regional Development Fund’s Archaeological Heritage Conservation Project 32. To achieve these objectives, the project sought to make St. Paul’s Catacombs Complex a prime tourist attraction in Malta by creating a new on-site Visitor Centre for the display of archaeological artefacts, and by providing public accessibility to the Catacombs to promote education and awareness of the burial complex and its rich history (ERDF 32 n.d.).

St. Paul’s Catacombs Complex was officially opened to the public on October 4, 2015 (Heritage Malta 2015), and an on-site visit for the purposes of this report was conducted between November 21 and December 1, 2016. Following Heritage Malta’s brief, key areas of the St. Paul’s Catacombs Complex were investigated to assess the impact of the site’s recent development on its archaeology, with the wider purpose of informing future practices within the site [see Appendix A].

Aims, objectives and structure of the report: • To study the suitability of environmental conditions within the new Visitor Centre which is modern in design and constructed from lightweight materials.

• To assess any impact of the new construction on the exposed archaeological remains underneath (the Visitor Centre rests on raised foundations above some open tombs).

• To assess internal environmental conditions in Catacombs that have recently been opened to the public.

• To assess the suitability of the on-site garage as a storage facility for archaeological artefacts not displayed in the Visitor Centre.

The report will first present an overview of the site’s wider significance, macroclimate, physical properties and layout, followed by the project methodology.

The main body of this report contains the findings from the four primary study areas of the St. Paul’s Catacombs Complex [see 1.4: Site Description]. These findings are composed of environmental data, mapping and condition survey results, and risk assessment conclusions [see 3: Report Findings]. These are followed by a series of recommendations designed to mitigate any identified risks to the different site areas within short, medium, and long-term time frames [see 4: Report Recommendations, and Appendix B: Action Plan].

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Introduction

1.2 Historic Significance The St. Paul’s Catacombs Complex is the largest late-Roman underground cemetery in Malta (Heritage Malta 2015). The tombs were carved from globigerina limestone and developed in phases over centuries of use, eventually covering an area of more than 2,000m2. They are the earliest and largest archaeological evidence of Christianity in Malta, however the site also functioned as a burial ground for all faiths and social classes, with peoples of pagan, Christian and Jewish beliefs buried there side-by-side. The archaeological, historical and cultural significance of the site is so great that it is being considered for inscription as a World Heritage Site (ERDF 32 n.d.), hence the recent developments aimed at preserving it and providing visitor accessibility and interpretation.

ERDF 32 acknowledges the multiple significances that the site holds and emphasizes the value of not only preserving the site, but developing the burial complex into a fully-fledged tourist destination, capable of improving awareness of, and providing education about, the unique multi-cultural and multi-religious history of the Catacombs (ERDF 32 n.d.). This is a key characteristic that makes the site universally significant as it reveals that the inclusive practice of multi-culturalism is not solely a modern notion, but one that has existed for millennia as part of the fabric of Maltese society.

The new Visitor Centre showcases some of the archaeological objects that the site contained prior to excavation including imported gold and bronze jewellery, glass perfume bottles, pottery cookware and the remains of a funerary meal of roasted pig. Imagery in the Centre depicts a Roman funerary procession, reminding visitors of the broader societal functions of the Catacombs as well as the long and culturally rich history of the Maltese islands.

1.3

Climate of Malta and Rabat

The climate of Malta is a typical southern Mediterranean seasonal climate, with dry summers and wet winters. Humidity is high all year due to the island location. Rabat is located inland, near the Western coast of the main island of Malta, and it experiences weather that is characteristic of the country as a whole. RH never drops below 60% [see Table 1], and most days are sunny, with temperatures in the range of 10 – 30 °C [see Table 2]. This general climate is reflected in the external environmental data collected at the St. Paul’s Catacombs Complex.

Table 1: Average RH in Malta. Source: www.weather-and-climate.com (2017)

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1

Introduction Table 2: Average Minimum and Maximum Temperature in Malta. Source: www.weather-and-climate.com (2017)

1.4 Site Description The St. Paul’s Catacombs Complex is located in the suburbs of the town of Rabat. The surrounding neighbourhood is densely populated and there are homes, restaurants, and shops on the site boundary. The site is bisected above ground by a road that separates the largest Catacomb and new Visitor Centre from the rest of the Catacomb entrances [see Figure 1] although the Catacombs underneath remain interconnected. The site was divided into four study areas for data collection [see Figure 2], with collection undertaken by three separate teams.

The teams and their assigned tasks were as follows: Visitor Centre: The Visitor Centre team evaluated the internal environment in the Centre and its suitability for the display of collection objects.

Underneath Visitor Centre and Garage Storage: The garage team assessed the suitability of the garage building for the storage of archaeological artefacts and also evaluated the environment and condition of the exposed archaeology beneath the Visitor Centre.

Catacombs: The Catacombs team assessed the internal environments of Catacombs 12 and 17, with special attention paid to the Catacomb 17 fresco and the possible impacts caused by opening these Catacombs to the public.

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Introduction

Figure 1: St. Paul’s Catacombs Complex site (in colour) within the local context. Source: Google Earth (2017)

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Introduction

Figure 2: Site plan of St. Paul’s Catacombs Complex, showing the report study areas. Source: Heritage Malta (2015)

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Methodology

2.1 Methods The methodology combined both desktop review and on-site data collection, divided into the following methods of data gathering and analysis: o Qualitative Data:        



Historical and climatic research; Staff interviews and walk-through onsite; Follow-up questions posed to the site’s Curator; Values Assessment of site and specific archaeological contents; Risk Assessment using a bespoke template - drawing on Waller (1994), Brokerhof & Bulow (2016); Strengths, Weaknesses, Opportunities and Threats (SWOT) Analysis; Visual analysis and condition assessments of the collections in the Visitor Centre and garage using our own frameworks - adapted from Keene (1996), refined following Taylor & Stevenson (1999) and lecturer consultation; Condition mapping and visual analysis of Catacombs 12 & 17, and the tombs underneath the Visitor Centre, using a system based on consultation with Professor JoAnn Cassar and work by CNR-ICR (1988), Fitzner, Heinrichs & La Bouchardiere (2000), Fitzner & Heinrichs (2004) and ICOMOS-ISCS (2008); Analysis and benchmarking of environmental data against a variety of relevant, reputable, and widely accepted industry standards (including BSI publications, US National Parks Service materials)

o Quantitative Data: 

Monitoring and analysis of environmental data for the inclusive periods of 17 February – 27 October 2016 and 22 November 2016 – 23 February 2017: - Temperature and RH readings taken using standalone EasyLog EL-USB2+ data loggers (Lascar Electronics) with an accuracy/overall error of ±0.45 °C and ±2.05%RH;  Monitoring of pollutants (Nitrogen Dioxide, Sulphur Dioxide, Ozone) for the inclusive period of 26 August 2016 – 23 September 2016 at four locations – inside the Visitor Centre, in an outdoor area, inside Catacomb 12 and in the Natural History Museum in Mdina: - Diffusion tubes used to collect gases, contents analysed using ion chromatography by Gradko Environmental based on in-house methods (GLM2 for Ozone, GLM3 for other gases);  Spot readings taken during site visits from 21 – 30 November 2016 for: - Temperature and RH using Pocket Humidity/Temperature Pen: 44550 (Extech Instruments) with an accuracy/overall error of ±1 °C and ±5%RH; 10

2

Methodology -



UV and Light Intensity using:  UV Light Meter UVA/B – 850009 (Sper Scientific) Accuracy: ±4% + 1 digit;  Pocket Digital Light Meter LX1010BS (Sinometer) Accuracy: ±4.0% + 0.5%f.s.;  Light Meter: EasyView Extech EA31 (Extech Instruments) Accuracy: ±3%rdg + 0.5%FS.; Pest surveys (using Museum Trap Standard Triangular Blunder Traps)

2.2 Limitations Additional data that would have strengthened this report’s conclusions include: o o o

o o o

A full 12 months of environmental data; Environmental data for the garage for the inclusive period of 22 November 2016 – 23 February 2017 for comparative purposes; Environmental data from within the display cases of the Natural History Museum in Mdina and the National Museum of Archaeology in Valetta for comparative purposes; Energy survey of the Visitor Centre to determine the building’s performance and buffering capabilities; Data logger monitoring of additional Catacombs; More in-depth, semi-structured interviews with staff and decision makers from different departments working on the project to enable more specific recommendations to be made.

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Report Findings

3.1 Catacombs The aim of collecting data on the Catacombs was to assess their internal environmental conditions following their opening to the public. The focus was on Catacombs 12 and 17 with special attention paid to the fresco located in Catacomb 17. The subsequent findings concentrated on two main areas of interest: the internal environment of the Catacombs (particularly in regards to biological growth) and visitor effects.

Internal Environment The internal environmental findings for the Catacombs are partly based on RH and temperature data collected from February 2016 – February 2017. This data was compared against previous data collected over a period of 18 months during 2010 – 2011 before the opening of the St. Paul’s Catacombs Complex to the public (Curteis 2011). Similar patterns were evidenced in both data sets with RH within the Catacombs measuring between 94 – 100% and ambient temperature ranging from 12 – 23oC. Analysed data is primarily drawn from Catacomb 12 as the site Curator identified this Catacomb as representative of the majority of Catacombs located on-site. Readings from Catacomb 17 had to be discounted as the data loggers malfunctioned due to surface condensation caused by the high RH. However, given the unique nature of the fresco in Catacomb 17 and its stated importance in the project brief, this report also covers its analysis.

Both temperature [see Table 3] and RH were found to be fairly constant, in particular the RH which remained at, or close to, saturation at all times [see Table 4]. In comparison with the external environmental data [see Tables 5 and 6], the rock-hewn structure of the Catacomb provides a high level of thermal buffering between the internal and external environments.

12

T (°C)

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Report Findings

40 35 30 25 20 15 10 5 0

22.5 0C 11 0C

Date

RH (%)

Table 3: Internal temperature from Catacomb 12

120 100 80 60 40 20 0

106 % 94 %

Date

T (°C)

Table 4: Internal RH from Catacomb 12

40 35 30 25 20 15 10 5 0

34.5 0C

3.5 0C

Date Table 5: External temperature at the St. Paul’s Catacombs Complex

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RH (%)

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Report Findings

120 100 80 60 40 20 0

98 %

18 %

Date Table 6: External RH at the St. Paul’s Catacombs Complex

These environmental conditions are ideal for microbiological growth, as observed on the majority of surfaces in both Catacombs. This primarily took the form of white deposits composed of salt efflorescence and actinobacteria growing between the salt crystals (Universitat de Barcelona 2012). Green microbiological growth that is associated with light sources – both natural and artificial – was also found, particularly along the track lighting the walkways [see Figure 3].

However, no adverse effects from the spotlighting were observed in relation to these growths.

Black microbiological growth, likely cyanobacteria (Universitat de Barcelona 2012), was only observed in Catacomb 17 and was found primarily on plastered surfaces and the fresco [see Figure 4].

Figure 3: In the image on the left: green mould growth associated with natural light sources in Catacomb doorways.

In the image on the right: green growth associated to the installed track lighting

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Report Findings

Figure 4: Cyanobacteria and mould growth on the fresco in Catacomb 17

Environmental monitoring results to date have not shown significant effects on the internal environment of Catacomb 12 since its opening to visitors, with new data comparable to that presented previously by Curteis (2011). Data collected between June – September 2011 [see Table 7] shows a stable temperature of 23oC and RH that fluctuates slightly but remains mostly between 90 – 100%.

Table 7: Historic temperature and RH data for Catacomb 12. Source: Curteis (2011)

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Report Findings

Visitor Effects Visitor effects present two potential risks: 1. Physical risk to the Catacombs due to inadvertent or intentional physical contact with the rock surfaces and due to the installation of the necessary infrastructure to enable visitor entry and exploration (walkways, lighting); 2. Risk to the visitors’ health and safety, including trip and fall hazards or lack of air circulation. According to the site Curator there are between 50,000 – 60,000 visitors per year so the potential for accidents is not insignificant.

Based on limited observation of visitor behaviour, a number of visitor actions that could be deleterious to the Catacombs were identified.

Each Catacomb has an information panel situated near the entrance providing a general indication of the Catacomb layout / contents, maximum capacity and potential hazards. Most visitors ignored or pay minimal attention to these panels; some visitor groups were in excess of the stated maximum capacity for some Catacombs, while other visitors were observed running down the Catacomb entrance stairs, which are characteristically steep and narrow.

Additionally, within the Catacombs evidence of abrasions, scratch marks and graffiti was identified, demonstrating active visitor contact with archaeological surfaces [see Figures 5 and 6].

Figure 5: Evidence of abrasions on unprotected surfaces, likely due to inadvertent visitor damage

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Figure 6: Evidence of abrasions on unprotected surfaces, likely due to inadvertent visitor damage

Lighting As has already been stated above, the introduction of lighting systems has led to an increased presence of some microbiological species along the runs of floor lighting. Any increases in temperature and RH, combined with the increased CO2 levels due to human respiration, are likely to encourage further microbiological growth, while any increase in fluctuations in RH and temperature due to visitors is likely to increase the rate of salt efflorescence and therefore of potential impact on the archaeological stone surfaces.

The lighting systems within the Catacombs are UV and IR filtered LED spotlights and floor lights, controlled by motion sensor timers. The timers are set to allow visits of 10 minutes, with the track lighting staying on an additional 5 minutes to allow time for safe visitor exit from the Catacombs. According to the site Curator, there had been earlier problems with the lighting timers, with lighting systems remaining on for longer that intended. This is likely to have contributed to the microbiological growth observed around the track lighting.

Pests Pest surveys were conducted in the Catacombs using eight blunder traps strategically placed throughout Catacombs 12 and 17. The majority of traps were collected empty (although showing signs of structural collapse due to the high RH levels within the Catacombs). Those that had trapped pests contained benign species such as woodlice, spiders and houseflies.

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Report Findings

Concluding Key Findings In summary, assessments of the environments in Catacombs 12 and 17 have recorded high internal RH and temperature, conditions that are ideal for microbiological growth. However, despite RH being close to or at saturation, both RH and the temperature are stable due to the rock hewn Catacombs providing a good level of thermal buffering between the internal and external environments. The environmental monitoring to date has not revealed any major negative effects on the internal environment due to visitor numbers; confirmation of this will require further monitoring. There is an element of risk posed to the Catacombs due to visitor contact, with evidence of visitor damage proving that there is a level of physical risk to the Catacombs from increased visitor numbers.

The findings from the Catacombs suggest that the key impacts of opening to visitors are: the risks of intentional or inadvertent visitor damage; risks both to visitors and Catacombs from overcrowding and the risk of increased microbiological growth and salt efflorescence within the Catacombs. This increased risk will be caused by changes to the equilibrium of the internal environment (which is likely to be caused by increased humidity and CO2 levels due to large visitor groups); daylight from any openings; and impacts of the electrical lighting system.

Furthermore, while opening up the Catacombs has unarguably improved the on-site archaeological interpretation and educational experience, there is scope to build on this success.

Visitor understanding of the Catacombs could be enhanced by use of further interpretative material within the Catacombs themselves, to improve visitor understanding of their original use and function. The environmental conditions are likely to prove inappropriate for the display of delicate original artefacts or sensitive technology / equipment, but replicas could be employed to provide relevant in-situ information; such as scene setting or developing scenarios related to the Catacombs’ original use.

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Report Findings

3.2 Visitor Centre Environmental Data Over an 11-month period, from 17 February – 27 October 2016 and 22 November 2016 – 23 February 2017, four data loggers recorded the environmental conditions within two showcases containing human remains and copper clasps, and within the open display space of the Visitor Centre [see Figure 7]. Spot readings of light, UV, RH and temperature were taken on November 22, 2016 and risk assessments and condition surveys [see Appendices C and D] were conducted on the Centre's displayed objects. The purpose of this data collection and observation period was to assess the suitability of the Centre’s interior environment and determine if it is providing museum grade conditions for the archaeological objects that are presently on display.

Figure 7: Floorplan of the visitor centre indicating the location of displays, data loggers, and other environmental data collection tools

The average temperature inside the Visitor Centre is 21°C, which fluctuates within a range of 10.5 – 29.5°C [see Table 8]. RH inside the Visitor Centre also fluctuates, with an average RH of 65% and a range of 28 – 88% [see Table 9]. Both RH and temperature inside the Centre appear to be highly influenced by the exterior climate, given that there are regular fluctuations in both despite the consistent use of air conditioning in an attempt to regulate internal conditions.

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T (%)

The internal environment could present a risk for mould germination and growth, as the interior conditions regularly exceed 20°C and 65% RH simultaneously (Michalski 1992; BSI 2012), however to confirm this risk the air movement near the surfaces of the objects would have to be measured. Three exposed tomb markers [see Figure 7] may be at risk for mould growth on their surfaces due to the RH (NPS 2001). There is also a comfort issue for visitors given that the recommended range for human comfort is 18 – 25 °C (BSI 2012), and the Visitor Centre regularly exceeds the upper limit, primarily in the summer months.

40 30 20 10 0

Date

RH (%)

Table 8: Temperature data collected by an internal logger located at the Northern wall (louvers) of the Visitor Centre

120 100 80 60 40 20 0

Date Table 9: RH data collected by an internal logger located at the Northern wall (louvers) of the Visitor Centre

Two showcases containing very vulnerable objects were monitored – one holding organic remains including human bone and the other inorganics including copper.

During the monitoring period, temperature in the case containing human bone ranged between 10 – 28.5°C with moderate diurnal and seasonal fluctuations, and averaged 20.3 °C [see Table 10]. The RH inside the case ranged between 54 – 73%, averaging 62% [see Table 11]. Ideally, to prevent deterioration of objects such as bone, temperature should never exceed 24°C, and RH should be maintained within a band of 45 – 55% (NPS 2001). This may account for why the bones were observed to be flaking [see Figure 8].

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3 T (%)

Report Findings 40 35 30 25 20 15 10 5 0

Date

RH (%)

Table 10: Temperature inside the bone showcase

120 100 80 60 40 20 0

Date Table 11: RH inside the bone showcase

Figure 8: Female skeleton with evidence of flaking highlighted

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Data for the showcase containing copper objects were similar, with temperature ranging from 10 – 28 °C, and an average temperature of 20.2 °C [see Table 12]. RH ranged between 45 – 83%, with an average of 64% [see Table 13]. Given that copper is a sensitive inorganic material, it should ideally be kept in an environment with RH under 30%, and a temperature range of 15 – 22 °C, with as little fluctuation as possible to reduce the risk of deterioration from corrosion and bronze disease (NPS 2001). Information on previous damage caused by corrosion to one of the clasps [see Figure 9] was provided by James Licari, a conservator at Heritage Malta, who noted that the clasp was treated in 2014 and again in 2016.

T (%)

40 30 20 10 0

Date

RH (%)

Table 12: Temperature inside the copper showcase

120 100 80 60 40 20 0

Date Table 13: RH inside the copper showcase

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Report Findings

Figure 9: Circled areas show corrosion damage to a copper clasp

Additional Findings Seven blunder traps were distributed around the Visitor Centre, including inside three showcases. Only one caught any pests. This trap, located near the external door of the Centre, captured harmless pests including garden ants and flies.

Spot readings of UVA/UVB inside the Visitor Centre measured maximum readings of 4 uW/cm2 by the exposed tomb markers, and 0 uW/cm2 by the bone and copper showcases. Given that the tomb markers are of inorganic materials, UVA exposure is generally not a concern (BSI 2012) and in the case of the Visitor Centre, the internal UVA readings were low. In comparison, the spot readings taken at the exterior front entrance of the Centre measured 1,000 uW/cm2.

Spot readings of electric light levels by the bone and copper showcases were 90 lux and 40 lux, respectively, which are within a suitable range (under 150 lux) to prevent problems such as fading and flaking (BSI 2012).

Readings for pollutants show that Ozone measured 9.5 ppb, which falls within the Getty Conservation Institute’s guidelines for maximum levels of Ozone (25 ppb) for museum collections (Grzywacz 2006). 9.5 ppb also falls well within the safe range for human health, the maximum recommended exposure being 100 ppb (ibid.).

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The Mdina Natural History Museum: Environmental Comparisons To assist with understanding the Visitor Centre’s ability to buffer external environmental conditions, internal temperature and RH data was collected at the Natural History Museum, located 4.5 kilometres away nearby in Mdina.

The temperature at the Natural History Museum ranged between 11.5 – 31.5°C, with an average temperature of 21°C [see Table 14]. This is the same average and largely the same range as the Visitor Centre. RH in the Natural History Museum ranged between 33 – 81%, with an average of 55% [see Table 15]. While still quite high compared to recommended standards, this is lower than the Visitor Centre’s average RH of 65% and is also lower than the Centre’s peak RH of 88%.

T (%)

Fluctuations in the Visitor Centre are also more extreme than those in the Natural History Museum, often spanning 20% - 30% [see Table 9]. This difference in internal RH and temperature absolute values and fluctuations between the two sites may be attributed to the limestone construction of the Natural History Museum, with the stone acting as a partial buffer to the external environment. During the on-site visit, it was observed that the Visitor Centre is, in addition to being of lightweight construction, a structure that is permeable to air, given that the entrance/exit door opens directly to the outside (without any lobby or overhead shade) and the opening (or void) in the Centre’s glass floor that allows visitors to directly view the tombs underneath (which in turn, are open to the external environment). Without first resolving these issues with air permeability, it will be difficult to determine if the modern lightweight construction of the Centre is a suitable substitute for a traditional masonry structure like the Natural History Museum [see Appendix A].

40 30 20 10 0

Date Table 14: Temperature data from the Natural History Museum

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RH (%)

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120 100 80 60 40 20 0

Date Table 15: RH data from the Natural History Museum

Concluding Key Findings The key findings are that the Visitor Centre experiences regular fluctuations in both temperature and RH and does not meet museum recommended standards for either. This poses potential problems with visitor comfort and enjoyment, but also raises concerns about the long-term future of the Centre’s more vulnerable archaeological objects on display. The average RH of the centre is 65% and the average temperature is 21°C, with considerable diurnal and seasonal fluctuations in both over the data logging period, which could contribute towards accelerated deterioration of the display objects (due to the fluctuations); and there is a possibility of mould growth (due to the high RH coupled with the moderate to high temperature), although the likelihood of this depends on existing air movement patterns and rates within the building.

Without first improving the buffering abilities of the Centre, it cannot be determined if the building can provide museum grade conditions for its collection. The employment of an airtightness test would assist in identifying the most porous areas of the building and would aid in deciding whether making the Centre more airtight is both possible and advisable. In this respect, it is still too early to say if a traditional masonry building would be able to provide more suitable environmental conditions for the archaeological objects at the Visitor Centre. It is apparent from the collected environmental data that the more heavyweight construction of the Natural History Museum does provide better buffering of the external environment compared to the Visitor Centre, but issues of possible location, costs, and site archaeology amongst others might make use of more heavyweight construction at the St. Paul’s Catacombs Complex impractical. The current Visitor Centre achieves its goal of providing improved interpretation of the St. Paul’s Catacombs Complex, as required by the ERDF 32 project; however, its goal to provide a suitable environment for the conservation of the site’s archaeological objects still needs to be proven.

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3.3 Underneath the Visitor Centre A risk assessment identified that the main risks to the rock-cut tombs underneath the Visitor Centre are flooding from exceptionally heavy rain or leaking pipes, fluctuations in RH that may lead to salt crystallization cycles and dissociation of the tombs from their context and information about them [see Appendix C].

Water-related risks, such as flooding, can cause biological growth to develop on rock surfaces, salt efflorescence and possible saturation of rock, all of which may damage the surface layers of the tombs.

Condition mapping of the tombs [see Appendix D] highlighted some green biological growth on surfaces exposed to high levels of natural light, areas of salt efflorescence, areas of surface cracking and some surface friability. However, overall the tombs appeared to be in a reasonably stable condition.

Pest monitoring collected flies, spiders, lice, woodlice, midges, wasps, and lizards. None of these pose a risk to the rock-cut tombs or collections inside the Visitor Centre. However, pest monitoring taken outside the museum context can harm wildlife and needs to be applied with caution and possibly after an evaluation of the natural habitat.

Environmental data (RH and temperature) collected from three data loggers in the tomb area underneath the Visitor Centre [see Figure 10] indicates that the data provides strong evidence of environmental conditions underneath the Visitor Centre.

Figure 10: Locations of data loggers underneath the Visitor Centre

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Report Findings

This conclusion was reached using the R2 measure, also called the ‘coefficient of determination’, which provides an indication of how strongly one set of variables predicts another set of variables. R2 values fall between 0 and 1. The closer the R2 value is to 1, the more changes in one variable (the ‘predictor’) ‘explain’ variations in the other variable (the ‘dependent’) (PSU 2017).

However, it should be noted that technically this is a measure of the strength of association between the variables, rather than a strict indicator of causation (ibid.).

With a mean average R2 of 0.8 for RH, and a mean average R2 of 0.92 for temperature for the three data logger locations [see Figure 11, sample R2 graphs in Table 16, full selection of graphs in Appendix E], it could be concluded that the Visitor Centre building only provides minimal buffering of the environmental conditions in the tomb area. Visual comparison of the raw data for RH underneath the Visitor Centre and in the external environment further supports this view [see Tables 17 and 18].

R2 Values of external environmental conditions vs. those underneath the Visitor Centre (RH: External Env. vs. Museum Underfloor) R2 = 0.92786 (RH: External Env. vs. Foyer Underground) R2 = 0.67354 (RH: External Env. vs. Truncated Access Area) R2 = 0.8013 (T: External Env. vs. Museum Underfloor) R2 = 0.97685 (T: External Env. vs. Foyer Underground) R2 = 0.86728 (T: External Env. vs. Truncated Access Area) R2 = 0.93174 Figure 11: R2 values comparing external environmental data to data logger locations underneath the Visitor Centre

T Correlation Graph

RH Correlation Graph 40 R² = 0.9279

100

External Environemnt T (C)

External Environemnt RH (%)

120

80 60 40 20

R² = 0.9769

30

20

10

0

0 0

20

40

60

80

100

Museum Underfloor RH (%)

120

0

10

20

30

40

Museum Underfloor T (C)

Table 16: R2 plots of RH and temperature for a data logger located underneath the Visitor Centre

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Report Findings

RH (%)

Underneath Visitor Centre RH 120 100 80 60 40 20 0

98 %

19%

Date Table 17: RH underneath the Visitor Centre

RH (%)

External Environment RH 120 100 80 60 40 20 0

99%

18%

Date Table 18: RH of the External Environment

In summation, there are no severe risks to the rock cut tombs at the present time, but in the longer-term, the effects of water ingress and high and fluctuating RH will need to be closely monitored. Furthermore, it is advisable that the causes of water ingress are dealt with as a priority in order to better conserve the tombs.

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Report Findings

3.4 Garage The risk assessment found that the main potential risks to the collections were dissociation from the information about them and a lack of maintenance of the garage fabric leading to damage to the stored objects [see Appendix C].

The garage collections primarily consist of pottery sherds and some animal bones. A condition survey of a representative sample of stored objects established that they were in a stable condition [see Appendix D], although the presence of soil around some objects prevented a complete condition assessment.

Pest monitoring collected bagworm moth larvae, springtails, silverfish, woodlice, spiders, and small flies. None of these species pose a risk to the garage collections.

Garage environmental data [see Tables 19 and 20] was compared with that for the Visitor Centre as a store with similar archaeological objects. Garage environmental data was strongly correlated with that from the Visitor Centre, both in terms of annual temperature and RH ranges and fluctuations. This environment is broadly acceptable for the storage of inorganic stone/pottery.

Table 19: RH of garage

RH (%)

Garage RH 120 100 80 60 40 20 0

87 %

30%

Date

Table 20: Temperature of garage

T (%)

Garage T 40 35 30 25 20 15 10 5 0

31 0C

11 0C

Date

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Report Findings

Figure 12: Garage used for collection storage

However, the garage [see Figure 12] is not deemed suitable for long-term collection storage of organic materials. This conclusion is supported by the environmental data [see Tables 21 & 22 comparing garage RH and temperature to the US National Parks Service’s (2001) recommended standards for the storage of bone]. Nevertheless, it should be noted that the garage is viewed as a temporary storage space by the site Curator.

Garage RH / T 40 35

Temperature (°C)

30 25 20 15 10 30

40

50

60

70

80

90

100

110

120

Relative Humidity (%) Table 21: Relative Humidity/Temperature of garage YELLOW BOX = US National Park Service’s standards for bone

BONE (GARAGE)

NPS’ Lower Limit

NPS’ Upper Limit

T (°C) Range

10

23.89

47.6

%

RH (%) Range

40

55

13.4

%

% of time within NPS Specifications for BONE

Table 22: Percentage of time garage temperature and RH are within the NPS’s standards for bone

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Report Findings

In summary, there are no major risks to the collections stored in the garage at the present time, but in the longer-term the objects may benefit from a more environmentally suitable storage environment; improved labels and cataloguing to reduce the risk of dissociation.

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Report Recommendations

4.1

Catacombs

Overview Key impacts of opening the Catacombs to visitors include: 1. The potential for intentional and inadvertent visitor damage; 2. Risks to both visitors and Catacombs from over-crowding; 3. An increase in microbiological growth and salt efflorescence within the Catacombs, associated with: the internal environmental conditions, light from the doorways, and the electric lighting system Despite high RH and temperature levels in Catacomb 12 [see 3.1: Catacomb Findings], thus far the data has not shown a noticeable increase in fluctuations or absolute levels since it was opened to visitors. However, it is important to continue to monitor the environmental conditions while a thorough parallel assessment of the visitor impact is carried out.

In order to assess the rate of microbiological growth and the levels of visitor damage, it is recommended that a regular programme of condition mapping is carried out to build up a body of evidence to inform appropriate future preventive action. A simple survey method would involve mapping deteriorations over photographs of selected areas at regular intervals. The project would require the expertise of a conservation professional to carry out the following tasks: 1. Identify specific representative areas to illustrate particular vulnerabilities or deterioration, to photograph and monitor (e.g. the fresco in Catacomb 17, green biological growth along lighting tracks, areas vulnerable to inadvertent visitor contact); 2. Recommend the frequency of monitoring; 3. Either train existing staff members in the use of monitoring data, or work with conservation students; 4. Interpret the results of the monitoring data; 5. Implement easily-accessible storage for condition mapping records and comparisons over time Ideally, this monitoring would be carried out in comparison with an equivalent survey in a closed ‘control’ Catacomb to better assess visitor impact(s).

Observation of visitor behaviour is also recommended, to establish which Catacombs are the most frequently visited, which routes visitors take and in general how many Catacombs are visited. Once the effects of visitation and the conditions of the Catacombs and visitor behaviour have been understood, a suitable management plan can then be devised.

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Report Recommendations

Visitor understanding of the Catacombs could be enhanced by the inclusion of some interpretative material within individual Catacombs to demonstrate their original use. While the environmental conditions and security within the Catacombs are not appropriate for the display of original objects, replicas could be used to provide a clear and accessible idea of their original use.

Short term (0-1 years) Research  Set up a regular programme of condition mapping to monitor the rate of microbiological growth and levels of visitor damage – ideally in tandem with monitoring a closed ‘control’ Catacomb  Continue RH and temperature data monitoring to help inform the condition mapping.

Ideally also set up RH and temperature monitoring in the closed ‘control’ Catacomb  Visitor monitoring: routes taken, behaviour, number of Catacombs visited Action/Management/Training  Set up condition mapping procedure with the help of a conservation professional  Train either existing staff or external conservation students in the mapping procedure  Start condition mapping programme  Brief visitors when purchasing tickets regarding visitor advisory panels outside Catacombs, permitted numbers per Catacomb, health and safely within the Catacombs Medium term (2-5 years) Research  Early on in the medium term, start environmental monitoring in specific areas to understand the impact of air flow on growth of microbiological organisms and salt buildup  Continue with condition mapping and environmental monitoring. This is required until data patterns have been established clearly enough to devise and implement an appropriate management strategy to mitigate deterioration, and for a year after the implementation of any strategy, to ensure it is effective  Professional interpretation of the first year’s results of condition mapping and environmental monitoring  Interpret visitor monitoring results and use these to inform visitor management

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Report Recommendations

Long term (beyond 5 years) Research (dependent on earlier findings)  Continual visitor information regarding number limits and other health and safety considerations in the Catacombs  Continual observation of the conditions inside the Catacombs to remain alert for signs of deterioration Action/Management/Training Future medium and long-term actions and management are dependent on the results from the above research, but could include:  Staff training, and regular staff briefing, on management system  Rotating the number of Catacombs open at any one time to manage environmental impact, light exposure and physical damage to the more visited Catacombs  Opening neighbouring Catacomb groups together to enable easier visitor observation by site custodians  Once the conditions within Catacomb 17 have been understood and stabilised it is suggested that conservation treatment work could be undertaken on the fresco to remove/reduce the microbiological growth from the surface and spot stabilisation work undertaken as necessary to prevent further degradation  The addition of some interpretative material within the Catacombs in the form of replica objects to give a clearer understanding to the visitor of the site’s original use

34

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Report Recommendations

4.2

Visitor Centre

Overview Interpretation and understanding of the site is greatly enhanced by the display of excavated artefacts within the Visitor Centre, but the building’s current environmental conditions pose challenges for some of these objects. Conditions in both the main space and the show cases containing copper and human remains, need to be altered so that they lie within an acceptable range for the preservation of these collections.

More fundamentally, the opening in the floor between the Visitor Centre and the void beneath needs to be sealed. Acceptable temperature and RH ranges cannot be maintained in a space that is partially open to the external environment and air-conditioning cannot control temperatures in this situation (though a lot of energy may be wasted trying). Localised measures to stop external air entering the building so easily via the entrance/exit door may also help to control internal conditions, while at the same time improving visitor comfort and enjoyment.

Improvements to the existing practices for silica gel use could also enable greater reductions in RH to be achieved locally, within the show cases.

All of these measures should be combined with ongoing monitoring of the environment and the condition of objects. This will demonstrate whether these interventions are having the desired effect. Finally, management procedures should be put in place to provide for the long-term care of the building and its artefacts. These should include a regular maintenance schedule, measures to reduce energy use and a targeted plan for future research.

Short term (0-1 years) Research  Survey visitors to better understand their experience of the Visitor Centre in terms of comfort and enjoyment  Assess options for better buffering external environment at entrance/exit door (assess merits of a draught lobby, localised air-conditioning, using the door as fire escape only etc.)  Research properties and suitability of different types of silica gel for control of RH within Visitor Centre showcases Action/Management/Training  Close up void to tombs underneath (possibly with glass panel similar to other areas of floor in the Visitor Centre)  Based upon outcome of research, install suitable silica gel in bone and copper showcases to try to reduce RH levels to between 40% - 65% (bone) and under 30% (copper)

35

4    

Report Recommendations Implement a procedure for the installation, replacement and monitoring of silica gel (i.e. mandate how often gel is changed, amount of gel to be used, how long cases are open every time gel is changed, when gel should be replenished) Given that this lightweight building needs air-conditioning to regulate internal temperature, review the set-points for the HVAC system and assess whether it is achieving desired aims by comparing with temperature recordings from data loggers Continue RH and temperature data monitoring to collect data to assess impact of above measures Carry out condition survey of vulnerable bone and copper objects regularly (every month) to aid in noting any changes and to inform actions that can mitigate risks

Medium term (2-5 years) Research  Professional interpretation of the results of condition surveying and environmental monitoring data from the first year following closure of the void to the tombs underneath Action/Management/Training  Continue to monitor environmental conditions within the Visitor Centre main space, the show cases and underneath the Visitor Centre  Develop a maintenance plan for the site with periodic surveys and recurrent maintenance works scheduled  Develop an emergency action plan to safeguard the collections  Plan for possible future changes to the displayed collection. Schedule the types of artefacts that can be safely displayed in the Visitor Centre, given the recorded environmental conditions and the conditions that Standards define as acceptable for different types of objects Based upon results of the environmental data collection and condition surveys, additional actions could include:  

Provide climatic buffer to Visitor Centre entrance/exit door (based upon preferred option from earlier research). This action would be required if temperature and RH in the Visitor Centre continued to fall outside acceptable levels as a result of the enabling works Carry out conservation works to any deteriorating artefacts and produce an action plan to improve the environment conditions for these objects should deterioration continue to be occur in the future

36

4

Report Recommendations

Long term (beyond 5 years) Research  Review more sustainable sources of powering the air conditioning system, if providing a suitable internal environment is dependent upon this system. For example, photovoltaic cells on the roof, an air source heat pump could perhaps be investigated Action/Management/Training  Draw up a list of conservation / research needs and advertise for voluntary university intern positions to help fill these roles, if the budget does not allow for paid positions  Continue to monitor environmental conditions, but on a less frequent basis if conditions have been shown to have stabilised at acceptable levels  Install more sustainable air conditioning system  If sensitive artefacts continue to decay at an unacceptable rate, implement mitigation measures (these may include climate controlled cases, or zoned spaces such as display rooms, or as a last resort relocating elsewhere on-site or moving off-site completely)

37

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Report Recommendations

4.3

Underneath the Visitor Centre

Overview The main areas of concern are water ingress, salt efflorescence and biological growth. Our recommendations focus on two objectives: firstly, the monitoring of these conditions to observe any changes and impacts on the rock-cut tombs and secondly, preventive maintenance strategies to reduce the likelihood of more serious problems developing in the future.

There is also potential to introduce easier and more convenient access to underneath the Visitor Centre by installing stairs connecting to the Visitor Centre side walkway. This might attract more visitors to the site and bring additional revenue. However, detailed initial assessment of potential benefits/costs is required given the possibility of increased wear and tear of the tombs, as well as health and safety ramifications.

Short term (0-1 year) Research & Action/Management/Training  Regular inspection of pipes underneath the Visitor Centre (ideally every 2 weeks) to limit likelihood of future leaks, and prevent significant water ingress  Conduct research (perhaps in collaboration with the University of Malta) into how different cleaning regimes/specific methods might affect biological growth, salt efflorescence and the rock-cut tomb surfaces. If findings suggest regular cleaning would be beneficial, trained professionals could be engaged to implement a cleaning cycle and closely monitor the results  Monitor light levels using telemetric data loggers - to assess potential for damage to areas of rock exposed to natural light due to thermal stress caused by heating/cooling cycles, links between light exposure and biological growth  Mapping exercises should be carried out approximately every 6 months to record conditions in the tomb area, with results compared to previous data, to ascertain if conditions are stable or further intervention is required  Consult Heritage Malta staff at the Hypogeum, and faculty expert in stone deterioration at the University of Malta, to better understand the main environmental threats to the rock-cut tombs and what experience indicates is the best course of action to mitigate these effects Medium term (2-5 years) Action/Management/Training  Early on in the medium term, consider the use of microclimatic modelling to assess the impact of partial or complete closing of external access to the area underneath the Visitor

38

4 



Report Recommendations Centre on the air flow beneath the Centre, and associated effects on RH levels. This is subject to budgetary and expertise constraints Carry out further monitoring of the different sections of the rock-cut tombs underneath the Visitor Centre using telemetric temperature and RH data loggers. Compare data over time to determine if those areas that are relatively less ‘exposed’ to external conditions would benefit from a more stable environment and especially lower RH with reduced fluctuations Further Possibility: If the decision is supported by data, partial or total sealing of the external access underneath the Visitor Centre may be undertaken to confirm if this lowers high levels of RH and appreciably reduces biological growth. Monitoring of conditions after any works to gauge success is essential (via telemetric temperature and RH data loggers)

Long term (beyond 5 years) Research & Action/Management/Training  Monitor the climate change impacts to the rock-cut tombs, such as consequences of extreme weather events (e.g. heavy storms, heat waves). Use the findings from monitoring to prepare and implement a climate change mitigation/adaptation strategic plan  Continue to regularly inspect the area and assess its condition to ensure minimal deterioration of tomb surfaces

39

4

Report Recommendations

4.4

Garage

Overview The primary areas of concern regarding the garage collections are firstly that the internal environment may damage certain items and secondly that as long as the items remain un-cleaned and un-catalogued in the garage, this is a missed opportunity for learning and education about the Catacombs, as well as improving the visitor experience. Our recommendations therefore focus on improving the storage environment of the collection and aiming for the collection to be brought up to a suitable condition for long-term conservation and/or display.

Short term (0-1 years) Action/Management/Training  Move collections stored in the garage to a facility with more suitable environmental conditions for all objects. This could be the Natural History Museum in Mdina for convenience, or the National Museum of Archaeology in Valetta, which as a national centre of archaeological expertise is well-equipped to house such collections If manpower or budgetary constraints do not permit this, then: Medium term (2-5 years) Action/Management/Training  Mesh-over the existing air vent in the garage wall to prevent accidental entry by animals  Install mohair weather strips under doors to prevent insect ingress and increase the buffering capacity of the garage space versus external environmental conditions  Cover plastic storage boxes with lids to prevent water ingress, pest entry and dust accumulation on collection objects  Secure tags to plastic bags containing items to minimise the risk of dissociation of objects and related information  Replace current paper tags with plastic coated tags to proof against water ingress and potential data loss from tags  Properly catalogue, survey and record all garage collection objects to identify priorities for movement/conservation work/display  Clean all collection items of debris so their condition can be properly assessed and potentially important details revealed  Conserve items in need of preventive or remedial works as necessary, with the aim of stabilising all items in the collection ready for storage or display  Items of most significant historical interest and/or which best complement the existing collections on display should be displayed in the Visitor Centre

40

4 

Report Recommendations Explore the possibility of using the garage as an additional on-site display area – either for more robust collection items (primarily pottery sherds); or as an additional interpretive/educational facility for displays on Catacomb use and history (complementing the modern display structure nearby), potentially featuring replica objects

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5

Conclusion

5.1 St. Paul’s Catacombs Complex ERDF 32 sought not only to develop the St. Paul’s Catacombs Complex in order to increase cultural tourism to Malta, but also to preserve the ancient burial site, ensure its accessibility, and provide “a renewed, sensitive and educational approach to Malta’s heritage for the general public” (ERDF 32 n.d.).

The findings of this report largely indicate that interpretation of the site has progressed appropriately via the newly-built Visitor Centre and through the provision of visitor access to many of the Catacombs. The uses, history, and cultural significance of the site are successfully emphasized through this engaging visitor experience which allows exploration of the Catacombs and access to archaeological objects and related information in the Visitor Centre.

However, due to the humid Southern Mediterranean climate that is characteristic of Malta as a whole [see 1.3: Climate of Malta and Rabat], preservation of the site faces some crucial challenges. The primary challenge is the need to mitigate negative impacts caused by fluctuating and relatively high temperature and RH. Given the scale and intricacy of the St. Paul’s Catacombs Complex, this is a complicated task. Recommendations based on the findings provided by this report are designed to clarify, and assist in, decision-making about key areas of the St. Paul’s Catacombs Complex.

5.2 Catacombs The findings from the Catacombs indicated the following risks: intentional or inadvertent visitor damage; safety of both visitors and the Catacombs due to over-crowding and increased microbiological growth and salt efflorescence within the Catacombs. In order to understand the impact of opening the Catacombs to visitors, and to inform an appropriate future management plan, a period of further research should be undertaken.

This would take the form of condition surveying – with initial set up and later interpretation carried out by a conservation professional. Regular condition surveying over the course of a year would collect a body of information on mould growth, salts, and visitor damage. This surveying should be carried out in tandem with continued environmental (RH and temperature) monitoring, in both a visited Catacomb and, ideally, a closed ‘control’ Catacomb, to assess visitor impact. It is also recommended that a study of visitor behaviour is undertaken to understand which are the most regularly visited Catacombs, the average duration of visits to each Catacomb, which routes are the most often taken, and how many Catacombs are viewed on average per visit.

It is further suggested that at the point of ticket sale visitors are briefed about health and safety within the Catacombs and that their attention is drawn to the information boards outside each Catacomb which show the maximum numbers allowed per Catacomb.

42

5

Conclusion

5.3 Visitor Centre Due to the lightweight and permeable construction of the Visitor Centre, there are some challenges in managing its internal environment, especially when faced with the generally high temperature and RH externally, which appear to be impacting the internal conditions of the Centre (as evidenced by the fluctuating temperature and RH within). At present, the Centre is not providing the necessary conditions to effectively preserve the more sensitive display objects such as human bone and copper.

One of the key challenges in adequately controlling the internal environmental conditions of the Centre is that the building is open to the external environment (via the void in the floor). If the building were fully enclosed, it would be easier to assess whether the lightweight construction is able to provide adequate museum grade environmental conditions. Hence, further internal monitoring and increasing the Centre’s capacity to buffer the external environment are priorities.

It is also worth noting that in a building of this type, mechanical heating, cooling, and ventilation equipment is required to regulate internal conditions. Therefore, if Heritage Malta does move towards commissioning more buildings of this type at other sites, they should consider the energy consumption of these mechanical systems and actively explore more environmentally friendly (and more cost efficient) ways of providing temperature regulation, through either mechanical or passive means.

5.4 Underneath the Visitor Centre Environmental conditions in the area underneath the Visitor Centre are similar to those found externally, with high RH and direct light causing some deterioration of the rock-cut tomb surfaces. It is likely that the Visitor Centre has restricted air flow, exacerbating the impact of Malta's naturally high RH levels, but the primary concern from a conservation perspective is water leaks from the Visitor Centre pipework. Overall, we would recommend that regular pipework maintenance and tomb inspections are carried out to monitor conditions and caution that the under-floor area is not suitable for any in-situ display of original collection objects (replicas being excepted) due to the environmental conditions and potential for water leaks.

5.5 Garage The garage environmental conditions are inadequate to ensure the safe storage and preservation of any collection items excepting those of an inorganic and durable nature (pottery sherds and stone objects). Even then, caution is necessary as the generally high RH and fluctuating RH levels may cause damage over the long term. We would recommend that the garage collection items are not stored or displayed there longer than absolutely necessary and are moved to a more suitable environment, in addition to being cleaned and catalogued to promote longevity and contribute to future education.

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Bibliography

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ICOMOS-ISCS (2008) Illustrated glossary on stone deterioration patterns [online]. Monuments and Sites XV. Available at: https://www.icomos.org/publications/monuments_and_sites/15/pdf/Monuments_and_Sites_ 15_ISCS_Glossary_Stone.pdf (Accessed 14 April 2017) Keene S. (1996) Managing Conservation in Museums. Oxford: Butterworth-Heinemann.

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Universitat de Barcelona (2012) Study of Biological Communities at St Paul’s Catacombs. MSc Sustainable Heritage, BEVGSH2, Heritage Materials and Assemblies [online]. Available at: https://moodle.ucl.ac.uk/course/view.php?id=40067 (Accessed 29 Dec 2016).

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List of Figures & Tables

Figures Page

8 9 14 15 16 17 19 21 23 26 27 30 58 59 60 61 62 63 64 65 66 67 70 71

Figure 1: Figure 2: Figure 3: Figure 4 : Figure 5: Figure 6: Figure 7: Figure 8: Figure 9: Figure 10: Figure 11: Figure 12: Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24

St. Paul’s Catacombs Complex site within the local context Site Plan of St. Paul’s Catacombs Complex Mould / Green growth Cyanobacteria and mould growth on the fresco in Catacomb 17 Evidence of Abrasions Evidence of Abrasions Visitor Centre Floor Plan Female Skeleton Corrosion Damage on Copper Clasp Data Logger Location underneath the Visitor Centre R2 Values of External Environment versus Data Logger Locations Garage used for Collection Storage Risk Assessment Legend Interior of Catacomb 17 Risk Assessment of Catacombs 12 & 17 Bone objects in display case, Risk Assessment of bone objects Wooden objects in display case, Risk Assessment of wooden objects Stone objects on open display, Risk Assessment of stone objects Glass objects, Risk Assessment of glass objects Copper objects in showcase, Risk Assessment of metal objects Photographs and Risk Assessment of area underneath the Visitor Centre Photographs and Risk Assessment of Garage Archaeological Collection Condition Mapping of Truncated Access Area underneath the Visitor Centre Condition Mapping of Rock-cut Tombs Interior underneath the Visitor Centre

7 7 13 13 13 14 15 20 20 21 21 22 22 24 25 27 28 28 29 29 30 30 68 69 72

Table 1: Table 2: Table 3: Table 4: Table 5: Table 6: Table 7: Table 8: Table 9: Table 10: Table 11: Table 12: Table 13: Table 14: Table 15: Table 16: Table 17: Table 18: Table 19: Table 20: Table 21: Table 22: Table 23 Table 24 Table 25

Average RH in Malta Average Minimum and Maximum Temperature in Malta Internal Temperature from Catacomb 12 Internal RH from Catacomb 12 External Temperature at the St. Paul’s Catacombs Complex External RH at the St. Paul’s Catacombs Complex Historic Temperature and RH data for Catacomb 12 Temperature at Northern Wall of Visitor Centre RH at Northern Wall of Visitor Centre Temperature inside Bone Showcase RH inside Bone Showcase Temperature inside Copper Showcase RH inside Copper Showcase Temperature from Natural History Museum RH from Natural History Museum R2 Plots: RH and Temperature for Data Logger underneath the Visitor Centre RH underneath the Visitor Centre RH of the External Environment RH of Garage Temperature of Garage Scatter Plot of RH and Temperature of Garage Percentage of Time Garage Temperature & RH within NPS’s Specs (Bone) Condition Survey of representative sample of Visitor Centre Collection Items Condition Survey of representative sample of Garage Archaeological Collection R2 Values for data at three locations underneath Visitor Centre

Tables Page

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7

List of Figures & Tables

APPENDICES

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Appendix A: Project Brief Context Following completion of the ‘Archaeological Heritage Conservation Project’ (ERDF 32) and the inauguration of the St. Paul’s Catacombs project in October 2015, Heritage Malta wishes to review certain aspects of the project with particular focus on the new main visitor centre 12 months after its opening. The study will inform Heritage Malta’s future decision-making around the protection and presentation of cultural heritage in its care to national and international visitors.

Significance The underground caverns and spaces under the fields known as Tad-Dlam (translation: of the dark) in the area of Ħal Bajjada in Rabat have attracted the attention of people from all social classes for centuries. Until the first archaeological survey of the site in 1894, many traditional stories had developed around the site among the local population.

One of the most outstanding features of the St. Paul’s Catacomb Complex is its size. The main catacomb alone covers an area of more than 2000 m2, much larger than any other in Malta. This is however just one of at least twenty-four Catacombs in the fields of Tad-Dlam. Therefore, what makes this site significant is that visitors can experience a vast cemetery with many Catacombs in close proximity. Another significant feature of this Complex is that people of different cultures and religions including pagan, Jewish and Christian lived together on Malta; they were also buried next to each other in the same grounds.

The cultural importance of the St. Paul’s Catacomb Complex is multi-faceted. The Complex values of the site have been revealed as scholarly research has enhanced knowledge of the site. This has uncovered a Complex stratigraphy of phases which shed light on a ‘new’ story of the site before the Catacombs. While the archaeological value is among the highest-ranking element, the social values attached to the site are also increasing in importance. The St. Paul’s Catacombs Complex of underground cemeteries provides an insight into the social and cultural way of life of the people that made use of this cemetery through the various centuries of its use.

Aim of the study The aim of this study is to understand the impact that the ERDF-funded project (including the Visitor Centre) has had on the St. Paul’s Catacomb Complex after one year. This will include: 1. Understanding the impact that the introduction of a modern building (the Visitor Centre) in close proximity to an archaeological site can have, including the suitability of the internal environment for the display of objects on open display and within showcases, and for human comfort.

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Appendix A: Project Brief 2. Understanding the impact that the opening of Catacombs to the public that have previously been closed is having on their internal environment.

3. Understanding the quality of the garage location for the storage of archaeological artefacts.

Research questions The specific questions that Heritage Malta wishes to be addressed are: 1. The main Visitor Centre is of lightweight construction supported by a heating, cooling and ventilation system. To what extent can it provide museum grade environmental conditions for the type of objects on display and visitors alike? To what extent can Heritage Malta sustainably replace traditional masonry construction with modern construction? How do the environmental conditions within the modern Visitor Centre compare to data collected in the Natural History Museum in Mdina? Given the nature of the climatic conditions, what types of heritage materials can be safely displayed within the Centre, with the building alone providing year-round protection and/or with conditions designed to be created using the heating, cooling and ventilation system?

2. The main visitor centre stands on foundation piles above the surface of a proportion of the site in order to reduce the impact on the site. However, pooling of rainwater and algae growth is visible on the exposed rock beneath the main visitor centre. Part of the archaeology underneath the visitor centre has been protected by a boundary wall, and part of it has not. What are the environmental conditions within the “protected” and “unprotected” areas? How do these environments compare to each other and to the environment within the Visitor Centre and within the Catacombs? Are these conditions suitable for potential future display of objects insitu?

3. A proportion of the excavated finds from the site are stored in a local garage. What are the environmental conditions within this building and are they adequate for the storage of heritage materials?

4. How do the climate and environmental conditions within Catacombs 12 and 17 compare with the data captured as part of the ERDF project? Have these changed since the Catacombs were opened to the public in October 2015? What are the principle differences in these conditions and those of the other locations of the study? Is there evidence of deterioration on the fresco in Catacomb 17? Is this related to the environmental conditions and/or to the visitors?

5. Given the environmental conditions within the Visitor Centre, the Catacombs and the archaeology underneath the Visitor Centre, what are the costs/benefits of keeping the artefacts on site, within the context of the St. Paul’s Catacomb Complex, compared to moving them to another museum e.g. the National Museum of Archaeology?

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Appendix A: Project Brief Supporting documents and data The following documents and data will be provided by Heritage Malta: -

Main Visitor Centre specification Heating, cooling and ventilation system specification Energy bills On site weather monitoring data for 2010-11 Report on the biological growth on the site Remote sensing data, maps and report

Heritage Malta will engage with the development of this brief through David Cardona and Godwin Vella. Environmental monitoring for the study commenced in February 2016 using data loggers in each of the following locations (unless otherwise advised): -

Visitor Centre: in gallery, in a typical case, in the skeleton case Outside: under with building within ‘sealed’ area and in ‘unsealed’ area Sample Catacombs: Catacombs 12 and 17 Storage: within garage Comparison museum: Natural History Museum

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Appendix B: Action Plan Catacombs Goal

Tasks to be completed

Measure of Success

Short Term (0-1 years)

Further research

Management and Training

 Set up regular condition surveying programme, in open and closed ‘control’ Catacombs  Continue environmental (RH and temperature) monitoring in open and closed ‘control’ Catacombs  Monitor visitor behaviour  Train staff in condition mapping, aided by conservation professionals  Start condition mapping  Brief visitors on health and safely within the Catacombs when tickets purchase

Capture body of data detailing impact of opening to visitors on environmental conditions of Catacombs, to inform future management plan.  Staff informed and able to conduct and implement condition mapping programme.  Increased visitor awareness regarding health and safety and Catacomb vulnerabilities.

Medium Term (2-5 years)

Further Research

Management and Training

 Continue condition mapping and environmental monitoring  Professional interpretation of first year’s results of condition mapping and monitoring  Interpret visitor monitoring data  Depending on findings from the above, possibly start environmental monitoring to understand the impact of air flow on growth of microbiological organisms and salt efflorescence  Start to form management plan based on data collected  Staff training in the new management system  Continue to brief visitors at point of ticket purchase regarding health and safety, and Catacomb vulnerabilities Further strategies are dependent on the findings from the above research, suggested examples:  Limit number of Catacombs open at a time/open them on a

Results and interpretation of surveying will help to inform a future management plan.

 Staff are informed and able to carry out management tasks effectively.  Visitor awareness regarding health and safety and Catacomb vulnerabilities is increased  Catacomb environments more stable and less vulnerable to visitor damage.

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Appendix B: Action Plan rotational basis, to limit environmental impact, light exposure and physical damage on the more visited Catacombs  Open neighbouring Catacomb groups to enable easier visitor observation by site custodians Long Term (beyond 5 years) After understanding and stabilising of environmental conditions within Catacombs, undertake conservation of fresco in Catacomb 17 Dependent on the findings of the research but requires: Action, Management & Training

 Regular staff training in management practices  Continue to brief visitors regarding health and safety and Catacomb vulnerabilities  Continual observation of conditions in the Catacombs to watch for signs of deterioration

 Stable environmental conditions within Catacombs without evidence of visitor damage.  Stable and conserved fresco in Catacomb 17.

Visitor Centre Goal

Tasks to be completed

Measure of Success

Short Term (0-1 years)

Reduce RH in copper and bone show cases

 Conduct desktop analysis and on-site research on efficacy of using silica gel as a dehumidification solution in Visitor Centre showcases, to determine optimum amounts, placement, composition  Establish a timetable and procedure for regular monitoring and replacement of silica gel in cases  Review conditions of bone and copper objects on a consistent and regular basis (e.g. every month)

 Data loggers indicate that fluctuations in RH are minimized to less than +/- 5 from the set standard.  Condition of objects is stabilized. Further incidents of bronze disease are prevented, and skeletons stop flaking and chipping.  RH in the copper show case is maintained below 30%.  RH in the bone show cases is maintained within a band of 45% - 55%, per the National Parks Service’s guidelines.

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Appendix B: Action Plan

Moderate temperature and RH inside the Visitor Centre

 Create a buffer/transition space from the exit door to the exterior  Conduct visitor surveys to assess the degree of human comfort in the Visitor Centre  Assess air conditioning set points to judge whether they are in line with visitor comfort expectations, and adjust accordingly  Introduce a dehumidifier to the main space inside the Visitor Centre to help control RH  If time and budget permit, seal void with tomb opening to Centre to improve environmental stability

 Temperature and RH fluctuations are eliminated.  Temperature and RH stay within the set standard range for a minimum of 90% of the year, as indicated by data loggers.  Visitor comfort is improved, particularly in the summer months.

Medium Term (2-5 years)

Develop an effective maintenance and environmental monitoring plan for the Visitor Centre

 Conduct periodic surveys of the physical and environmental condition of the Visitor Centre, as well as the objects (in show cases and exposed), to assess the effectiveness of the Centre’s climate control system  Monitor the environmental conditions underneath the Centre following the sealing of the void, in order to assess any potential environmental impacts on the Centre itself

Better understand the impact of the external environment on the Centre, and make appropriate changes to mitigate or adapt to any negative impacts (such as high or fluctuating RH and temperature).

Long Term (beyond 5 years)

Create and promote internship positions for conservators-intraining

 Create a rolling internship program targeting conservation and heritage students from the University of Malta  Engage with students and create awareness of the program through social media and strategic relationships with the University of Malta  Develop specific expectations/roles for interns to fulfil

 Workforce for the Visitor Centre is increased without concurrent financial outlay.  Existing conservators are provided with support in their current positions.  Future conservators are engaged with their heritage and given practical, professional skills.  Workforce strain at the Centre is reduced.

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Appendix B: Action Plan

Explore and initiate the introduction of more sustainable, long-term climate control methods for the Visitor Centre

 Assess the potential cost savings, feasibility, and environmental impact of installing sustainable, renewable energy infrastructure at the Centre  Explore recommended options such as: air source heat pump; solar panelling  Apply for EU grants or other potential financial support systems to assist in the installation of the chosen system, as well as staff training and maintenance

 Running costs of the Centre’s climate control are significantly reduced in the long-term  A steady stream of energy is supplied indefinitely for the Centre’s climate control system

Tasks to be completed

Measure of Success

Underneath the Visitor Centre Goal

Short Term (0-1 years)  Clean biological growth with appropriate biocides Prevent deposit damage to rock Remove salt efflorescence via cut tombs scraping (without damaging rock surface)  Inspect pipes underneath Visitor Centre on a regular basis Prevent water damage to rock-cut to detect leaks tombs  Any leaks discovered to be quickly sealed, water supply to affected sections isolated as necessary

Assess effects of light on rock-cut tombs

 Set up telemetric light loggers at locations prone to biological growth  Set up telemetric temperature sensors in same locations, measuring rock surface temperatures  Monitor light levels over time to determine impacts on biological growth, rock heating/cooling cycles

No significant biological growth or salt deposits remain.

No flooding of area under the Visitor Centre, leaks kept to a minimum and quickly repaired.

Better understanding of relationship between light levels, biological growth, and temperature of rock surface.

Potential to inform future conservation of tomb area.

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Appendix B: Action Plan Medium Term (2-5 years)

Monitor RH and temperature underneath Visitor Centre to determine correlation with external conditions, specific areas of greatest concern

Improve access to area underneath the Visitor Centre

 Install and maintain telemetric RH and temperature loggers  Compare findings over time with external conditions, and between areas of the tombs, to determine correlations between internal and external conditions, and areas with the most stable environment (especially RH)  Could be external for easy monitoring and maintenance of location; or potentially internal via tomb void inside Visitor Centre

Better understanding of RH and temperature correlation with external conditions in different areas underneath the Visitor Centre. Results of this will inform decisions relating to possible sealing off of different sections of the tombs.

Access faster and safer than at present, for site workers and visitors.

Long Term (beyond 5 years)

Assess impacts of climatic change, adapt to or mitigate these impacts

 Carry out annual inspections to assess condition of rock-cut tombs  Specific inspections to take place after heavy storms, heat waves or other extreme weather events to assess any damage

Understanding impacts of climate change on the rock-cut tombs.

Possibility of limiting impacts of climatic change in the future.

Tasks to be completed

Measure of Success

Garage Goal

Short Term (0-1 years)

Understand priorities for object conservation

Reduce risk of dissociation of information from garage collection items

 Catalogue and survey all items in garage collection storage – to identify priorities for conservation, items of least concern  If time and budget permit, make records available in digital format for easy access, updating, sharing within Heritage Malta as necessary  Replace existing paper object tags with laminated or plastic tags to reduce potential data

Complete inventory and condition survey of garage collection items is prepared and made available to Heritage Malta and other interested parties.

All items are kept in a bag with a securely attached waterproof plastic label.

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Appendix B: Action Plan

Improve garage internal environment to protect collections and reduce maintenance requirements

Improve storage box environment for garage collections

loss from water ingress, paper degradation over time  Secure tags to individual plastic bags containing items  Mesh air vent in side-wall to prevent animal ingress  Install mohair weathering strips under garage doors to better buffer internal environment and reduce insect/small animal ingress  Fit lids to storage boxes for collection items – to prevent dust build-up, pest/animal ingress, and buffer against external environmental fluctuations (particularly RH)  Add silica gel to storage boxes containing more sensitive organic items to prevent damage from high RH

Lack of animal ingress, number of pests trapped reduced over time.

All storage boxes are fitted with tight-fitting lids, silica gel present in boxes with organic items and gel is checked and replaced as required.

Medium Term (2-5 years)

Move collections to storage in Mdina Natural History Museum or the National Museum of Archaeology in Valetta

Clean and conserve all collection items, research history of and display most significant materials in the Visitor Centre

Move collections to storage in Mdina Natural History Museum or the National Museum of Archaeology– for a more stable internal environment with better buffering of external conditions

Collections are all stored in Mdina Natural History Museum or National Museum of Archaeology, no collection items remain in the garage.

 Clean all collection items stored in garage to assess significance and signs of damage  Conserve items as necessary, especially consolidation of organics to prevent further degradation  Select items of greatest interest in explaining site history and providing contextual information to be displayed in the Visitor Centre, complementing existing display collections

All items cleaned and cared for as necessary, items deemed most significant put on public display in the Visitor Centre for educational purposes.

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Appendix C: Risk Assessment Introduction Risk assessments were conducted on four different areas of the St. Paul’s Catacombs Complex: 1. Catacombs 12 and 17; 2. The Visitor Centre; 3. Underneath the Visitor Centre 4. The garage The risk assessments assisted in identifying what security and preservation measures are required, and helped to determine the main priorities in the conservation decision-making process. An adaptation of Michalski’s (1990) quantitative method - calculating the probability of damage affecting the four areas - was utilised.

The risk score represents the sum of both the frequency and severity of a risk [see Figure 13], and the change of value indicates the ‘sense of loss’, which results from a change in the value of the objects. Priority for action is then determined by the combined sum of the risk score and any change in value.

Risk assessments conducted in the Visitor Centre, underneath the Visitor Centre, and on the garage collections shared the same format, as outlined above. Those conducted for the Catacombs followed a simplified format.

Figure 13: Risk Assessment Legend

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Appendix C: Risk Assessment Catacombs 12 & 17 Catacomb risk assessments were divided into two distinct sub-assessments – the first undertaken to identify potential risks affecting the visitors to the Catacombs, the second to identify risks to the Catacombs from the visitors. The two assessments followed the same format with the priorities determined by simple addition of the frequency and severity of risk in both cases.

The risk assessment in Catacomb 17 [see Figure 14] identified high RH levels as the greatest risk to the fresco [see Figure 15]. In both Catacombs, the high and fluctuating levels of RH observed in the environmental data could also affect the general stone condition, in terms of mould growth and re-crystallization of salts.

As for human damage, visitor behaviour and overcrowding in a small space may result in scratching and disfiguring of the surface of the fresco. Moreover, increasing numbers of visitors to the Catacombs will increase heat and humidity. Maintenance is identified as a further risk in terms of managing visitor flows, and monitoring time spent and on-site behaviour.

Figure 14: Interior of Catacomb 17, fresco can be seen in right hand picture at bottom

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Appendix C: Risk Assessment

Figure 15: Risk Assessment of Catacombs 12 & 17

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Appendix C: Risk Assessment Visitor Centre Risk assessments were conducted on the archaeological collection on display (within showcases and exposed) and were divided by material category: bone, wood, stone, glass, and metal.

Visitor Centre: Bone Objects

Figure 16: Bone objects in display case, risk assessment of bone objects

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Appendix C: Risk Assessment The bone collection is particularly susceptible to damage from RH fluctuations and extremes, and frequent temperature changes [see Figure 16], despite most of the collection being housed within showcases. Additionally, while disasters such as floods, earthquakes and fires are expected to occur extremely rarely, they obtained a high overall score because the effects may result in a significant or total loss of the collection involved. Similarly, dissociation is likely to be infrequent, but lack of available object information may represent a significant risk if occurring.

Visitor Centre: Wood

Figure 17: Wooden objects in display case, risk assessment of wooden objects

Overall, the wood collection is moderately vulnerable to high RH, because it may lead to mechanical deterioration (rapid expansion and contraction of the material) on the wooden objects which were previously treated. Although fires are likely to be extremely infrequent, the consequences may include total loss of the material/objects, hence the high overall risk result [see Figure 17].

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Appendix C: Risk Assessment Visitor Centre: Stone

Figure 18: Stone objects on open display, risk assessment of stone objects

Inorganic materials like stone that are kept on open display (such as the tomb markers in the Visitor Centre) are generally stable under a wide range of environmental conditions, being less susceptible to environmental changes than organic objects or metals. They are mainly susceptible to risks such as vandalism, visitor over-crowding, and high levels of pollution, all of which are deemed broadly unlikely within the Visitor Centre [see Figure 18].

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Appendix C: Risk Assessment Visitor Centre: Glass

Figure 19: Glass objects, risk assessment of glass objects

The glass collection is kept entirely within showcases and therefore is unlikely to be at risk from the main hazard types considered in the risk assessment [see Figure 19].

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Appendix C: Risk Assessment Visitor Centre: Metal

Figure 20: Copper objects in showcase, risk assessment of metal objects

Frequent moderate fluctuations of RH recorded in the environmental data may affect the stability of metal objects, especially the ones kept within showcases which are particularly susceptible to changes due to previous conservation treatments. Fluctuations may also speed up the degradation processes caused by oxygen, water vapour, or gaseous pollutants [see Figure 20].

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Appendix C: Risk Assessment Underneath the Visitor Centre

Figure 21: Photographs of area underneath the Visitor Centre, risk assessment of area underneath the Visitor Centre

Flooding, RH fluctuations, and dissociation are considered to be three most significant risks posed to the area underneath the Visitor Centre [see Figure 21]. Pipes from the Visitor Centre may leak directly into the tombs (as has previously occurred), making the area highly susceptible to flooding. Exposure to external environmental conditions leads to high RH levels and persistent fluctuations, with the potential to cause mechanical damage to the tombs’ stone surfaces, whilst the moisture content may result in salt dissolution and recrystallization and biological growth. As for dissociation, if any part of the information in the above Visitor Centre relating to the tombs is lost or moved, this will render the appreciation and interpretation of the tombs difficult.

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Appendix C: Risk Assessment Garage Archaeological Collection

Figure 22: Garage and representative collection items, risk assessment of garage archaeological collection

Dissociation was evaluated as the greatest risk posed to the archaeological collection stored inside the garage [see Figure 22]. The general outcomes of dissociation from any cause are loss of objects, of whole collections, of their associated data, or of their associated values. ‘Loss’ in this context means ‘becoming unable to retrieve on demand that which is wanted’ (Waller & Paisely 2017). In the case of data loss, objects or collections lose context and information-related values, which is a real concern for the garage collections since they are labelled with paper labels in un-sealed boxes.

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Appendix D: Condition Surveys & Mapping Visitor Centre: Condition Survey A condition survey was used to assess the condition of objects in the display cases at the Visitor Centre [see Table 23], specifically to determine their overall physical condition, stability, and to make note of any observable degradation or deterioration. The condition survey was conducted on selected objects including pottery, stone tomb markers, bronze pieces, and human bone, these being representative of the full collection at the Visitor Centre. Most of the surveyed objects appear to be in a reasonably stable condition, however they bear some obvious signs of deterioration, including minor discolouration, cracking, corrosion, and powdering. The objects of most concern consisted of wood, copper, bronze, and human bone.

Table 23: Condition Survey of representative sample of Visitor Centre Collection Items

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Appendix D: Condition Surveys & Mapping Garage: Condition Survey A second condition survey was performed on a representative sample of the objects stored in the garage [see Table 24]. These objects mainly consisted of pottery sherds, animal bones, and globigerina limestone fragments. The majority of the objects appeared to be in a stable condition.

However, determining their precise condition was not always possible as the objects had not been cleaned of soil and other debris after excavation.

Table 24: Condition Survey of representative sample of Garage Archaeological Collection

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Appendix D: Condition Surveys & Mapping Underneath the Visitor Centre: Condition Mapping – Truncated Access Area Condition mapping was performed to assess the general condition of the rock-cut tombs in the truncated access area underneath the Visitor Centre. The most noticeable damages identified were erosion, and white deposits (likely salt efflorescence caused by high and fluctuating RH levels) [see Figure 23].

Figure 23: Condition Mapping of Truncated Access Area underneath the Visitor Centre

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Appendix D: Condition Surveys & Mapping Underneath the Visitor Centre: Condition Mapping – Rock-cut Tombs Interior Further condition mapping of the rock-cut tombs underneath the main museum display room floor was undertaken. This highlighted some discolouration of the rock, areas of white deposits, and green growth (likely caused by exposure to light) [see Figure 24].

Figure 24: Condition Mapping of Rock-cut Tombs Interior underneath the Visitor Centre

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Appendix E: Underneath the Visitor Centre R2 Graphs Underneath the Visitor Centre: R2 Values for three data logger locations

Table 25: R2 Values comparing external and underneath Visitor Centre data for three data logger locations

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