Cost-Effectiveness of the The U.S. Geological Survey began a na- by methods other than operating a The final step is used to determine the best allocation of money and manpower among the stations that remain in the program after the two screening steps. Because there are so many uses made of streamflow data, minimization of the standard error of streamflow data, expressed as percentages, is chosen as the general measure of the program's effectiveness. This part of the analysis defines the uncertainty function for each station in the program, develops the necesary cost information, and determines the number of visits necessary to each station to minimize the uncertainty. The uncertainty function relates the standard error of streamflow data to the number of visits and measurements made per year or season. Examples of typical uncertainty functions from the Maine study are given in figure 1. These uncertainty functions are computed using a statistical technique that evaluates the accuracy of the streamflow rating curve, the accuracy of transferring flows from nearby stations, and the variability of historical flows at the station. The rating curve at each station is the relationship that enables the hydrologist to convert the recorded water-surface elevation (gage height or stage) to streamflow. At some sites, additional correlative data are necessary to determine the flow, such as the fall in water surface between sites. When the recorder at the station fails to record the water-surface elevation (or other correlative data), the rating curve cannot be used, and daily flows must be estimated from flows at nearby sites or from historical flows at the station. The uncertainty function includes the variability or standard error of flows estimated in these various ways. Once the uncertainty functions for each station are known, various costs associated with stream gaging can be determined. Feasible routes are defined for servicing the stations, and each station is assigned to one or more routes. The cost of servicing each station, route costs, and the minimum number of times each station should be visited are determined. The fixed costs of operating each station, including the cost of computing records and their storage and publication, are also determined. This information and the uncertainty functions are input to a computer program that determines the number of times each route is used. The routes selected are those with the largest reduction in uncertainty per dollar of expenditure. By varying the total budget and repeatedly running the program, an uncertainty or average standard error relationship with the budget can be developed. Figure 2 is an example of an uncertainty-cost relationship for Maine. The original Maine stream-gaging program, consisting of 51 stations, operated with an annual budget of $211,000. As a result of the data-use analysis, it was recommended that 6 of the original 51 stations in the Maine stream-gaging program be discontinued. The stream-gaging program analyzed for cost-effectiveness consisted of 45 stations. The current criteria for operating the 45-station program require a budget of $180,300. This is the circle in figure 2 marked "Current Practice." The average standard error of the streamflow records was 17.7 percent. As can be seen in figure 2, this overall level of accuracy could be maintained with a budget of about $170,000 if allocation of resources among the gages was altered. The recommendation was to modify the operation of the program and to use the residual $10,300 to increase receipt of data from the interior of the State. The relationship in figure 2 indicates the reduction in uncertainty that can be achieved by increasing the total budget. Studies like the one in Maine are scheduled for completion in 17 States during fiscal year 1983. The entire stream-gaging program will be analyzed over the next 5 years as part of the continuing effort of the Geological Survey to evaluate the Na Figure 1. Typical uncertainty functions for three gaging Section showing major processes controlling the transport through ground water and fate of coal-tar derivatives, St. Louis Park area, Minnesota. Contamination of Ground Water by Coal-Tar Operation of a coal-tar distillation and The problem of most immediate concern The Prairie du Chien-Jordan aquifer is Vertical movement of coal-tar fluids Flow of uncontaminated 900 surface and is overlain by glacial drift, two Contaminants in the Prairie du ChienJordan aquifer have moved at least 2 miles northeast and southeast of the plant site. The direction and rate of contaminant movement changes with time because the bedrock ground-water flow system continually adjusts to hydraulic stresses caused by water withdrawals and flow through multiaquifer wells. Contaminants move rapidly through the Prairie du ChienJordan aquifer because the upper part is a carbonate rock with fractures and solution channels. Consequently, the concentration and composition of contaminants in water pumped from the Prairie du Chien-Jordan aquifer through individual industrial and municipal wells fluctuates with time. Contaminants entered the uppermost bedrock aquifer, the Platteville, directly from the drift and moved at least 4,000 feet from the plant site. Locally, the conDegradation of phenolic compounds by bacteria Retardation of movement Dissolution of taminants have reached the St. Peter aquifer through the Glenwood confining bed and (or) through bedrock valleys where the confining bed has been removed by erosion. The greatest mass of contaminants is in the drift near the plant site. Coal-tar derivatives reached the water table by percolation through the unsaturated zone and through ponds that received surface runoff and process water from the plant. Parts of the drift contain an undissolved liquid mixture of many individual coal-tar compounds. Chemical analyses of organic fluid and water from a monitoring well completed in the drift 50 feet below the water table identified more than 200 individual organic substances. The viscous organic fluid is denser than water and has moved slowly downward independent of the direction of ground-water flow. Ground water entering the area of the plant site through the drift is contaminated by partial solution of the organic fluids and by release of compounds sorbed on the drift materials. The contaminated water moves laterally to the east and southeast and downward into the Platteville aquifer. Water in the drift 4,000 feet from the site contains less than 10 milligrams per liter of disolved organic carbon but has a distinct chemical odor and contains a large proportion of coal-tar compounds highly soluble in water. One major group of coal-tar compounds (phenolic compounds) is being degraded to methane and carbon dioxide by bacteria that metabolize phenolic compounds in the anaerobic (oxygen-free) environment that exists in the aquifer. This finding is of |