Groundwater and Surface Water Contamination from Resource ...

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230 III. Introduction to Water Resources and ContaminationQUESTIONS 15, PART A1. Using the data in Table 15.1, construct a water-table map(Figure 15.1). Begin by transferring the water-table elevationsfrom Table 15.1 to the appropriate test hole locations inFigure 15.1. Then contour the water-surface elevations usinga contour interval of 2 feet. The contours should roughlyparallel the 864-feet contour already drawn.2. Draw several flow lines originating at the brine holdingponds to the most likely area of groundwater discharge.Remember that during dry weather streams flow onlybecause groundwater discharges into them.3. What is the gradient from pond C to the Olentangy River?ft/ft.4. What is the gradient from pond C to Saunders Creek? ft/ft.5. Calculate the velocity of groundwater moving from pondC to the Olentangy River and from pond C to SaundersCreek using the following formula and the data given earlierin this exercise on the hydraulic characteristics of the unconsolidatedmaterial.v = {KI)/(n e)where v = velocity (ft/day), K = hydraulic conductivity(ft/day) I = gradient, (ft/ft), and n e= effective porosity(% as a decimal)a. The velocity of groundwater from pond C to the OlentangyRiver is about ft/day.TABLE 15.1 Chloride Content of Wells and Water-Table Elevation in the Delaware AreaWell No. Water-Table Elevation (March 1969) Chloride Content (mg/L)Nov. 1965 Oct. 1966 March 19691 867 4,500 288 242 871 — 875 363 866 12 12 124 869 — 12,000 2005 862 — 8,000 4006 868 18,000 8,875 4077 868 — 26,250 6628 865 — 1,000 4909 870 — 14 1610 868 25,500 9,850 91711 868 31,000 7,500 55012 864 — 8,750 74013 865 — 6,875 1,35514 864 — 3,125 29215 864 — 1,725 30216 864 22,750 15,500 1,23017 868 — 10,000 1,30018 864 5,600 1,500 60019 869 27 25 30020 862 15,000 1,40021 865 9,000 1,10022 862 4,800 4,800 11723 859 5,250 6,625 77924 861 33 235 2725 860 95 — 40W-1 880 20 320
Exercise 15 • Groundwater and Surface Water Contamination from Resource Extraction 231b. The velocity of groundwater from pond C to SaundersCreek is about ft/day.11. What techniques might be used to increase the rate of flushingof the high-chloride water in the areas of contaminatedsoil?6. If we divide the distance of travel (measured along a flowline) by the rate of flow of groundwater, we obtain the traveltime. What are the travel times for water from pond C toa. Olentangy River:b. Saunders Creek:7. On another map (Figure 15.2) construct contours representinglines of equal chloride concentrations (isochlors).Use the data for October 1966 (Table 15.1) and a contourinterval of 5,000 mg/L. Consider the direction of groundwaterflow when drawing these contours. Thus isochlors aregiven in Figure 15.2.8. Should the Olentangy River and Saunders and NorthCreeks contain higher than normal concentrations of chloridein the vicinity of the contaminated area? Why?12. A second isochlor map, based on the March 1969 data, isshown in Figure 15.3. A contour interval of 300 mg/L wasused. This map is useful in determining the change in contaminationwith time. Compare Figures 15.2 and 15.3 anddescribe the changes that have occurred.13. The shallow farm well (12 ft deep) at W-l increased inchloride concentration between 1966 and 1969 (Table 15.1).Has this contamination resulted from brine disposal intoponds A, B, C, or D? Explain your answer with the aid of thecross-section sketch (Figure 15.4), which goes from points Xto X' in Figure 15.1. Complete the water table and indicategroundwater flow by arrows in Figure 15.4.9. Wells 23 and 24 (Table 15.1) contain higher concentrationsof chloride in October 1966 than in November 1965, whilethe other wells contained less. Consider your answer toquestion 6b in your explanation of why this is happened.10. What do you think the chloride concentration of thegroundwater was before brine-pit disposal began (i.e., whatwas the background concentration)?PART B. SURFACE WATER CONTAMINATIONFROM OIL FIELD BRINES IN CENTRAL OHIOIn this part of the exercise river pollution can be tracedto techniques for disposing of saltwater (brine) that ispumped with oil. Regulations in most areas nowrequire subsurface disposal of oil field brines and havesignificantly reduced groundwater and surface-waterpollution.Surface waters can be contaminated directlythrough effluent discharge and surface runoff or indirectlythrough discharge of contaminated groundwater.This exercise illustrates the effects on a drainagebasin of poor waste-disposal practices of oil fieldFIGURE 15.4 Cross section from points X to X' in Figure 15.1.
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