Determining where potentially contaminated land is can be tricky as the source of contamination may no longer exist. Devoid of the advent of time-travel, gaining insight into the past can only really be achieved through the analysis of historical data or, of course, personal knowledge. It is well accepted that most contamination arises from past land use and only a reliable and consistent historical record of the land use is of any value for investigations.
This article explores how, by combining disparate historical map data, the environmental and residential housing market is provided with reliable spatial data resources and solutions, enabling home buyers or purchasers of land to make informed decisions relating to land which is potentially contaminated. In the UK, the Landmark Information Group (LIG) [1] national digital historical map archive is one source of information that achieves these requirements.
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We currently find ourselves in the aftermath of the ‘Credit Crunch’. Although a temporary situation, this phenomenon has reduced financial risk-taking, especially with regards to speculative purchases by developers of land. Because of this, it is has never been so important for people to understand the need for Environmental due diligence and avoid the prospect of litigation resulting from the transfer of potentially contaminated land.
Conscientious developers will, before committing to a purchase attempt to avoid costly remediation expenditure by first determining whether a site is likely to be contaminated.
{sidebar id=322 align=right} Conscientious or not, whether you are buying a new residential property or developing the Olympic Village, the process is always abundant with legislative pitfalls and risks relating to the purchase. Thankfully for all concerned, under the provisions of the UK Environmental Protection Act (1990) and the UK Environmental Act (1995) the responsibilities and subsequent liabilities for the owner or occupier of a contaminated site have become clearer.
The purchaser of land or property needs to recognise liabilities for contamination that may be based solely upon ownership of contaminated land, regardless of whether or not the new owner actually created the contamination; whereas liability for remediation may lie with the original polluter. Environmental due diligence (usually involving Phase 1 Risk Assessments (P1RA)) and residential enquiries therefore form a basic, yet important element in reducing financial or legislative risk for the purchaser/developer of land.
Unlike some other desktop studies (such as noise modelling), P1RAs relating to contaminated land can only be based on ‘real’ historical data.
P1RA’s comprise the collation of desk-based research together with the understanding gained from a site walkover. The P1RA typically includes a review of historical maps and aerial photographs. Thought is given to past land uses on a site using published sources and contact with regulatory authorities and retrieval of ground information from database resources. Consideration of these resources is now routinely required by regulatory bodies as part of the planning process when development is proposed.
{sidebar id=289 align=right} After considering the requirements of P1RAs, LIG identified the need for a national digital source of historical mapping and formed a joint venture with the Ordnance Survey (OS) [2] to create a digital historic map archive of mainland United Kingdom (UK). LIG’s historical map archive now includes 1:500, 1:1250, 1:2500, 1:10,000 and 1:10,560 scale OS maps starting in the 1840’s (Fig. 1).
The historical archive starts with Lancashire, which was first surveyed in 1841, with the rest of the UK surveyed in subsequent years. Each county was then revised between three and five times prior to 1945. These maps form LIG’s Historic Map Pack, a product which includes all available LIG historic maps centred on the user’s required location and provided in either .PDF or paper format.
The process undertaken to create the digital archive was incredibly labour intensive. One of the main challenges was to correctly geo-reference the images from different historical epochs into one comprehensive, consistent and accurate digital map archive. Individual maps did not only use different projections, but had also been created using a variety of survey techniques spanning over 100 years.
Significant hurdles had to be overcome during the archive creation, one of which is the differences between historic and current mapping and the projection system used during the survey. Known to most as County Series Mapping, the historical archive was originally created using the now obsolete ‘Cassini’ projection. Each county had a separate Cassini projection, often using different origins. Re-projecting the mapping into the OSGB36 projection enables the mapping to be used within modern GIS, together with existing data.
One of the characteristics of the Cassini system is that distortions are increased the further East or West you travel from the point of origin, particularly at the county boundaries.
1944-45 saw the projection origins for Great Britain standardised and transferred to the British National Grid system (OSGB36) on the Transverse Mercator projection. This system employs a single point of origin at latitude 49° north at the south of the British Isles. Figure 2 illustrates how a Cassini projected map appears alongside the British National Grid system.
For over a decade many environmental practitioners have been comparing LIG’s historical map layers (usually in the form of hard copy mapping) against a light box or even a window in an attempt to identify and follow potentially contaminated features through the years, a slow and laborious task when undertaking P1RA assessments or enquiries regularly.
This problem has been remedied through the development of an online GIS tool called Envirocheck Analysis (EC Analysis), which was developed based on feedback from consultants and practitioners involved in this type of work.
{sidebar id=323 align=right} LIG’s historical mapping archive is at the heart of EC Analysis. The EC Analysis tool brings together LIG’s full range of current and geo-referenced stack of historical mapping into one online facility, allowing users to overlay and ‘toggle’ between maps to easily analyse points of interest from all layers.
EC Analysis was created in response to a demand for something which would streamline the process of P1RAs, and has provided a new perspective to this already old practice. The system allows the user to trace historical land use through the ages determining where, and more crucially when, the change(s) to features occur. It could be said that EC Analysis is a data and software hybrid; a user driven analysis solution.
The online system allows the user to: extract customised images, compare two or more maps at a time by adjusting the opacity of each layer and measure and create polygon, line and point feature types. The user defined features can then be attributed information relevant to their customer’s requirements.
Figure 3 shows a series of screenshots of EC Analysis in action; the historical map archive is shown on the left of each image together with a variety of digitising and map annotation tools above. The red point feature in the map window (created by the user) shows the extent of the area of interest (optionally buffered to 50m, 100m and 250m).
Surrounding the point of interest are green (polygon) features illustrating where potentially contaminated features have been identified by the user. The user can attribute these features with ‘from and to’ dates allowing for powerful analysis of historical features through time.
So what is the value of this data? Using the UK’s Department of Environment guidelines, EC Analysis can be used to systematically analyse the archive to identify various industrial and potentially contaminative land uses. Another advantage of EC Analysis is that it enables users to view both the Cassini maps (now re-projected into OSGB36) and native British National Grid mapsets (OS historical mapping) together as seamless layers. Also, features of interest can be digitised by the user to create a comprehensive study of historical land use dating from the 1840s to near-present day.
As previously mentioned, a variety of potentially contaminated features can be identified that include (but are not limited to): Areas of in-filled land; water features that have since disappeared; former marshes; land that may be liable to flood; abattoirs; fuel depots; and gas works to name but a few.
Of course, the UK was not just mapped by its own mapping agency. Past enemies have always been interested in knowing where strategic and military sites are located. World War 2 Germany is one such example; they took a lot of aerial reconnaissance photographs, used to create maps or in their own right. Another example is the Russian mapping Great Britain archive now owned by LIG. The Soviet Military of the time, realising the military, economic and political benefits of topographic information, set about mapping the whole world – a colossal task (Fig. 4).
{sidebar id=324} Today, very little is known about how the organisation was structured and how such high quality results were achieved. Certainly the capture process was secret and militarily driven, very well controlled, often capturing politically sensitive features that were deliberately excluded from even the UK’s own national mapping.
In addition to the problems posed by geo-referencing a completely alien projection system, the maps had to be translated from Russian in order for them to be useful to a predominantly English speaking audience.
The Russian commissioners’ efforts were ultimately ineffective of course, if the reason was world domination, but for environmental professionals these historical maps provide an enthralling and invaluable insight into the structure of our towns and use of land during this period.
Historic map analysis is far from being a new phenomenon; the value of historical maps has long been appreciated. But, whilst the environmental market has continued to progress and adapt to new business demands, historical mapping has become increasingly important not least driven by legislative requirements.
Looking forward, the future is very exciting; with the advent of tools like EC Analysis new user driven perspectives will continue to allow the historical data to come back from the past enabling historical maps to be viewed, analysed and disseminated in ways that only GIS professionals, up until now, have been able to achieve.
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Darren Lamble – (MSc FRGS) is GIS Analyst at the Landmark Information Group, UK.
[1] Landmark Information Group is a Daily Mail and General Trust company, and a supplier of digital mapping, property and environmental risk information since 1995.
[2] Britain’s National Mapping Agency
