It is no secret that contamination taints the environment. But, for environmental professionals, it can also corrupt the processes used to identify sites suspected to have contamination. Traditional identification methods, such as reviewing historic aerial photographs, fire insurance company maps, industrial directories, title and deed records, tax maps and facility records, as well as performing onsite geophysical surveys, often do not provide the degree of accuracy required by regulatory bodies. Inaccuracies can occur when one converts between different map scales, when working from a copy of a map rather than the original, when maps are based on estimated distances rather than measurements, and when there are general deficiencies in the historical site information. Whatever the reason, it is not uncommon for environmental regulators, aware of the limitations of traditional location methods, to require subsequent investigations to validate data. Often, environmental professionals find themselves having to prove a negative, that is, assure regulators of the absence of contamination, at great expense of time and money.
When we at Schoor DePalma, a leading New Jersey-based engineering and design firm, were faced with the task of determining the presence of contamination for a site that had spent nearly 100 years manufacturing gas for local distribution and use, and years after that as a grass-covered corporate campus, we quickly exhausted traditional channels and were forced to find new methods to determine the locations of areas of concern (AOCs).
The site, located in central New Jersey, began with coal gas manufacturing operations around 1851, which were expanded over the next few decades. Around the turn of the century, operations shifted from coal to carbureted water as the source of the manufactured gas. In 1912, operations were reduced to emergency production only. Over the next four decades, the site operations were continually reduced. The last gasholder retired from service and moved from the site in 1957. At the peak of operations, the site held more than 20 facilities devoted to gas manufacturing.
During the 1950s, the parcels comprising the site were sold in three separate transactions and redeveloped for public and private use. A portion of the site is traversed by a major highway access ramp, while the rest makes up a corporate campus and is mostly grass-covered. It was certainly not an ordinary site to evaluate.
A Means to an EndWe led the team with a thorough search of all existing records, including site plans, facility maps, tax maps, Sanborn maps, USGS Topographic Quadrangle maps and aerial photographs. Each document was carefully examined for any evidence of former site uses. The Sanborn maps offered a promising start by providing the locations of various physical features and potential AOCs, which included buildings, processing areas, storage areas and gasholders. Unfortunately, this information was presented relative to roadways, buildings and other structures that had long been vacated, demolished or otherwise removed. There was no hard physical evidence remaining at the site and, therefore, no way to accurately locate former facilities.
The next strategy was a field expedition, which required an accurate base map of the site’s existing physical conditions. To achieve an accurate base map, the team first obtained new photography of the site through aerial photogrammetry. Then, ground control points were established within the state plane coordinate system and the North American Vertical Datum of 1988 by using the state database to find nearby first-order monumentation.
We used Trimble (Sunnyvale, Calif.) 4800 global positioning receivers capable of centimeter accuracy to provide the northings, eastings and elevations of points identifiable on the newly obtained aerial photographs. Elevation accuracy is of utmost importance since regulators require that samples be taken from the elevations that existed at the time of contamination. Once control points were established, they were used to control the stereo models, allowing an accurate base map of the area to be compiled. Upon completion, a field edit, using conventional surveying instrumentation, was performed to determine existing elevations of structures in the vicinity of the suspected AOCs.
While compiling the base map, it became apparent that, because many of the physical features had changed over the years, further research was necessary to determine precise locations for subsurface exploration and analysis, and the search for historical documents would have to be expanded. Several aerial photography firms were contacted to find the oldest available stereo image photography of the area and, soon, photography from 1940 was located. Here, another problem presented itself: to be useful, the 1940 photography would have to be subject to the same horizontal and vertical control system that was used to control the 2000 photography so that it could be plotted photogrammetrically.
There were now two photogrammetric maps to work with, one from 2000 showing the corporate facility and conditions at present, and one depicting site conditions from 1940. Since both maps were controlled through the same GPS coordinates, work could shift from the field to the office for analysis and manipulation of the two maps through AutoCAD computer mapping software.
The two maps were systematically overlaid in the computer using the established control points. The maps became one composite photogrammetric map showing the 1940 conditions on top of the existing 2000 conditions. By using geometric modules in AutoCAD, we were able to precisely determine the coordinates of 20 AOCs at the site, using information from the historical records to determine their dimensions. Site investigation protocols for selecting sampling locations and frequencies (as set forth in the New Jersey Department of Environmental Protection’s Technical Requirements for Site Remediation, N.J.A.C. 7:26E), were then applied to determine the number of samples and locations necessary for an adequate evaluation. A written sampling matrix was prepared and plotted onto the AutoCAD maps, and, using this combined information, the outlines of the AOCs and over 60 proposed sampling points were superimposed onto the AutoCAD maps. The coordinate data for the AOCs were then uploaded to the electronic data collectors and GPS hardware.
The real test came when it was time for survey crews to stake out the AOCs as well as each proposed sampling point. Although the current surface features were mostly grassy, our GPS survey crew was able to navigate to the uploaded coordinate points and precisely stake out what had been determined to be the locations of the former gas plant structures.
Saving the SiteUsing these combined technologies, Schoor DePalma Site Assessment and Remediation professionals were able to present an accurate picture of the environmental health of the site. It was determined that all, save one, of the gas plant structures had been removed. The one remaining structure, the concrete base of a gasholder, was analyzed and results indicated that the base was cleaned during demolition.
Site topographic elevation differences between 1940 and 2000 showed slight changes and highlighted areas where fill had been used as part of the corporate campus and nearby highway construction.
The primary constituents affecting the soil at the site are likely attributable to the past gas operations, but may also be the result of runoff from the highway or from fill imported from an unknown source. Several of the AOCs did not have concentrations of hazardous substances that would cause concern. However, a handful of the AOCs had levels that exceed regulatory standards.
The combined methods employed for this project significantly increased the degree of accuracy of both the horizontal and vertical components of sampling point location selection. Ultimately, this will translate into a higher degree of confidence on the part of regulators that we have provided more complete confirmation of the absence of contamination at certain AOCs, reducing the number of further, costly investigative iterations.
The Benefits of GIS and CADDMost municipal engineering and planning information is being developed in CADD or GIS formats, which are readily integrated into a GIS software package such as ESRI’s ArcView GIS software (Redlands, Calif.). In ArcView, layers from the AutoCAD files that contain specific information appropriate for the project can be selected and incorporated. For this project, which utilized AutoCAD 14 files, we used the CADD data to identify roads and buildings, and chose a distinct color scheme to show their location in relation to the base map features.
The software was also used to assign labels to the locations of the rock core and borings, based on the attribute data collected on the project site using a Trimble 4800 GPS receiver for quick reference. The labels were easily placed on the layout as part of the basic functionality of GIS and ArcView. The firm also created current features in a CADD environment, including tree lines and roads, and overlaid them on the modern aerial photo with the core and boring samples locations. ArcView was then used to assemble the various data sources together in one map to efficiently present the project information visually. ArcView was also used to assist with the development of comprehensive plans and reports.
This software not only allows mappers to easily manipulate data to find solutions to tough problems like determining the accurate location of AOCs, but also allows complicated information to be presented visually and shared with organizations using the same or similar software for future applications.
In the end, we were able to complete our task of proving the negative of contamination on the New Jersey site—and the positive of technology advancements.