Environmental Progress - Fall 2000

Modern Technology Aids Environmental Investigations

Cleanups speed up with long range -- very long range -- help

Once upon a time, investigations at environmental sites began with careful measurements of the property, followed by creating a map of the site, to scale. On the map were locations of soil samples, monitoring wells, structures, terrain and landscape features. Computer aided drawing programs were immensely helpful in ensuring accuracy of information and scale. Of course, measurements still had to be done by hand and mistakes were sometimes still made.

In recent years, environmental professionals have looked more and more to technological advances to increase the accuracy of their work product. One of the tools is the GPS, or global positioning system. Twenty-five GPS satellites orbit the earth twice a day, 11,000 miles above the earth, transmitting their precise position and elevation. Four to six are in view at any one time. The GPS receiver acquires the signal, then measures the interval between transmission and receipt of the signal to determine the distance between the receiver and the satellite. Once the receiver has calculated the data for at least three satellites, its location on the earth's surface can be determined.

GPS is a technology that was originally developed by the Department of Defense as a military system. Today, sailors, aviators, well drillers and a wide variety of industries use GPS to locate underwater hazards, landing sites, drill sites and pinpoint geographic positions. On May 1 of this year, the U.S. military removed a built-in error factor, called selective availability, that limited positional accuracy. Now, a point can be located within a centimeter, depending on the equipment used. (For the metric-challenged, a centimeter is approximately half an inch.)

In environmental work, GPS- derived data points are entered into a geographic information system (GIS) data maintenance system. This computer program will then construct geographically accurate maps, which can be easily updated and allows the investigator to easily return to the same points for continued study.

The Illinois EPA and similar agencies use GPS for a variety of functions to accurately locate site-related features that have no reference points from which to measure, such as sample locations in open fields and sediment or water samples in rivers and lakes. GPS can also be used to provide reference points to "rectify" aerial photography, by giving the map real world coordinates. Then, the aerial photo can be accurately compared to a site map and specific structures. Using historic aerial photography, areas of concern that are no longer present, such as tank farms, drum fields and buildings, are located. Using GPS and waypoint navigation, the inspector can return to previously identified locations that may have been altered over time. Future environmental uses include using survey grade GPS, mapping groundwater flows and plumes of selected sites and creating perimeter features, as well as mapping groundwater recharge areas, overlain on sub-surface bedrock features. This information helps state and local planners to evaluate where to best plan industrial parks, for example, to avoid contaminating a crucial recharge area for a community water supply.

Case Study: Demolition work began in 1998 at the Texaco Refinery Site, in Lawrenceville, to prepare for remedial investigation. Before demolishing the surface structures, the locations of all surface facilities (tanks, buildings, pipelines, spill areas etc.) needed to be mapped for later identification during the clean up. GPS crews from Region 5 and the Illinois EPA mapped the facility and generated maps for later identification. With the locations of spill sites and other source areas mapped, GPS can be used later to more easily navigate back for clean up.