High-Tech Siting

Julia O. Domingue

Hounded by legal and technical criteria, finding a suitable landfill site is becoming increasingly difficult. However, geographic information systems (GIS), which are de-signed to analyze and evaluate data based on geographic locations, have become the principal tool for wading through the myriad of concerns in siting a landfill of any size.

A GIS is a computerized system that integrates digital maps with a variety of databases for analysis. A complete GIS hardware and software system allows users to view, update, query, analyze, combine and manipulate data from a wide variety of sources to create new maps and tables.

While a sophisticated technology, GIS is a viable alternative for siting even small landfills, as one New York community learned. Having decided to build a new landfill, Eagle, N.Y., a small town approximately 40 miles southwest of Rochester invited several large waste management companies to explore the feasibility of building and operating the facility.

GIS was used by New York, N.Y.-based TAMS Consultants to select suitable sites by ranking technical criteria and analyzing legal and administrative information.

First, all of the study's data was digitized for GIS use. A 1:2400 scale was selected as the accuracy level because many of the sources for the project were mapped at that scale and no sources were mapped at a less accurate scale.

Primary Stage The legal/administrative criteria included:

* primary water supply and principal aquifers;

* public water supply wellhead areas;

* state- and federally-regulated wet-lands;

* endangered species locations, and/or critical habitat; and

* floodplains, airport locations and parks.

Aquifers and public water supply wellhead areas were mapped from state or municipal sources. State wetlands were digitized from the New York State Department of Environ-mental Conservation (NYSDEC) wetland maps while the federal wetlands were digitized from National Wetlands Inventory (NWI) maps. The town tax parcel maps also were digitized, and parks were identified.

Floodplains were noted using the Federal Emergency Management Agency flood hazard area maps. All of these categories were eliminated from consideration.

Airports within three miles of the town were mapped using Federal Aviation Authority navigational charts. The state requires a buffer between landfills and airport runways to prevent birds from becoming hazards to aircraft. No buffers overlapped the town, eliminating airport safety as a consideration.

A terrestrial biologist reviewed the endangered species and critical habitats within the town and then made a windshield survey to verify the findings. All habitats of endangered species were mapped. Since biological species are not fixed in specific locations and because the habitats were generally small, these locations were not used to eliminate sites. Instead, they became part of the ranking system in the secondary stage.

Finally, using a map of all elimination criteria, overlain with tax parcels, nine potential sites within four parcels were identified.

Secondary Stage The technical criteria included legal issues, slope, soil type and thickness, groundwater depth, proximity to seismic faults and geologic stability or monitorability. However, the feasibility study also had to consider access to both rail and truck transportation as well as land use compatibility. In addition, each site was mapped by an ecologist for existing wetlands not on NYSDEC or NWI maps.

The nine sites then were ranked on each of the criteria.

Slopes for each of the sites were mapped according to U.S. Geological Survey (USGS) contour information. One site measured a 5 to 10 percent average slope, while all others fell between 5 to 15 percent.

The Soil Conservation Service soils map was digitized, and each site was ranked based on the predominant soil characteristics. Rankings ranged from soils high in pervious sands and gravels to those with deep clays, fine tills, and sands and gravels. Five sites scored a top rating.

Soil thickness was considered along with geology, based upon geologic maps, with sites ranked according to stability and depth to bedrock. The lowest ranking was for unmonitorable or unstable land areas, while the highest was for depth to bedrock greater than 50 feet. One site had shallow bedrock (less than 10 feet); the others ranged from 10 to 50 feet.

Proximity to faults also was taken into account. Buffers of 200 feet, a half-mile and one mile were generated in the GIS for faults.

The sites surveyed fell into all three rankings. Five classes of depth to groundwater also were developed, based upon geologic maps and well data. All sites fell into ranges from 10 to 35 feet and from 35 to 50 feet.

Proximity to transportation was determined based on USGS topographic maps and identifies road class and railroad locations. Of the nine sites, five had direct access to rail on the property. Truck access was based on proximity to state highways and on the degree of new road construction that would be needed.

Five sites offered direct access to a state highway, with the remaining sites requiring use or rebuilding of town or country roads for distances greater than three miles.

Only one of the sites had wetlands within the landfill itself; one other required building the access road through the wetlands. The other seven had substantial buffer areas around the landfill cell in wetlands, but no construction would take place in the wetlands. All sites contained wetlands.

Finally, compatibility with nearby land uses was ranked. Sensitive receptors, such as schools and hospitals, were mapped, but none was adjacent to the sites. All sites were isolated; however, all but two had high visibility.

After comparing the data and ranking all nine sites, one was chosen.

In this case, using GIS proved to be efficient and cost effective. Even though hard copy maps for most of the data were available, they existed in several different scales which would have made it difficult to compare.

Further, because the town was small, it didn't take much time to digitize the maps and prepare the database.

Properly applied, GIS allows for flexibility in measuring a myriad of factors and permits each site to be ranked accurately and objectively.