ABSTRACT
The Finnish National Road Administration, in cooperation with the Technical Research Centre – VTT and the National Board of Water and Environment, has drawn up new guidelines for groundwater protection in the area of highway projects. The slope seal is intended to function as a construction measure in the protective area of water supply facilities or groundwater reservoirs, primarily in the case of accidents, e.g., with oil or chemical transporters. The construction measures stipulated for slope areas are intended to keep pollutants from penetrating the groundwater area for at least 12 hours, a period which must suffice for emergency services to take the requisite corrective measures.
The use of deicing salt in winter also means a significant potential danger for groundwater contamination. Sodium and calcium chloride, because of their greater density in a hydrous solution than water, tend to concentrate in depressions where groundwater is present. In the long term, salt has a contaminating effect and its penetration in the groundwater area is therefore to take priority over accident risk as a planning factor.
Because of the depth of frost experienced in Finland, and the flat nature of the country, the cross section of the road is generally carried out as an embankment. The slope inclination varies, depending on the importance of the road, and in the case of new construction, is generally made flat (e.g., 1 : 5), for safety reasons and to simplify maintenance work.
In planning protective measures, it is necessary to contend with a number of unknown factors. Because of the variety of environmentally-dangerous loads carried on the road, the contaminating medium is unknown in the case of an accident. The season and the weather constantly affect the condition of the slope and the area that the road influences. There are innumerable variations of current conditions, from a solid blanket of snow to saturated, baseless soil layers, or desiccated, cracked earth crust and other possible situations.
There are comprehensive investigations on the territorial extension of the area to be protected beside the roadway. One third of the vehicles coming off the roadway continue their path over the area of the facing slope, that is to say, beyond the drainage ditch.
The main routes for chemical transporters representing an environmental risk have been statistically registered. However, as there is no rigorous obligation to report, deviations from customary routes are always to be reckoned with, and are also to be expected, particularly in the case of traffic jams.
