Water Quality

	Environmental engineers try to ensure the protection of the natural habitats during construction. Many things must be considered in the removal and replacement of even a small bridge in the country. A rare breed of trout is known to inhabit this particular creek and had to be protected.   The small rural bridge was made of creosote treated beams and timber. Insects had severely damaged several of the wooden supports which had not been treated with creosote. The insects along with weather and normal traffic wear had caused the bridge to become structurally unsound. When the bridge was removed, it was found that creosote (oily liquid obtained by distillation of coal tar and used as a wood preservative) had leached into the surrounding soil. The contaminated soil had to be removed and replaced. (creosote can be recovered from the soil as it is heavier than water and then reused. Unfortunately it is harder to recover from the beams and poles. They should not be disposed of in landfills. The best disposal method is high temperature incineration.) The top soil from the construction site was removed and stock-piled. If the soil is correctly removed and replaced, it is not necessary to replant the site at the finish of construction. A small fence lined with filter cloth was place along one side to prevent the soil from contaminating the creek flowing on the right. The water downstream of the construction site was protected from silting by the placement of filter cloth along the sides of the creek. At one point early in construction, the environmental engineers stopped the project because the water downstream was becoming cloudy. A small culvert was placed under the temporary road to allow the continuous flow of water in Whiskey Creek. The grass filter was placed around the sides of the opening to prevent silt from falling into the creek. Grass filters were placed along the edges of the creek, where the new culvert was to be placed, to prevent soil from rolling down the sides of the excavated trench and contaminating the creek. It was decided to replace the timber bridge with a large culvert which would allow for the possibility of spring flooding of the creek. Baffles are attached to the bottom of the culvert to slow the water flow and ease the passage of the fish in the creek. Finished bridge. "Water quality in lakes, reservoirs and estuaries is a vital concern, particularly where growing populations and intensive farming methods put pressure on resources. Excessive inflows of nutrients, for example, can result in weed overgrowth and algal blooms."