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Ozone Remediation Pilot Test Work Plan San Joaquin County Public Works, Stockton, CA June 15,2015 Page Mass flux is the average mass movement of contamination in groundwater across a defined boundary. The average linear velocity of groundwater as it moves through interconnected pores in the aquifer material can be calculated using the following equation: V = (K./10(dh/d1) Where V is the average linear velocity, K is the hydraulic conductivity, tie is the effective porosity of the aquifer material, and dh/dl is the groundwater gradient. Published hydraulic conductivity values for silt range from 106 to 10 4 centimeters per second (cm/sec), and for fine sand range from 10 -5 to le cm/sec. Published porosity values for silt range from 35 to 50 percent, and for sand range from 25 to 35 percent. Shallow groundwater gradients at the site has averaged 0.0040 since 1999. The hydraulic conductivity of 10'3 cm/sec, a porosity of 25 percent, and a groundwater gradient of 0.004 were used to calculate the average linear velocity because the use of these values would result in the highest average linear velocity. Historically gradients have been as low as 0.0012. The calculated average linear velocity is 1.6 x 10 -5 cm/sec. The average linear velocity for groundwater calculated in this manner is 1.38 centimeters per day, or 0.045 feet per day, 505 centimeters per year, or 17 feet per year. The mass flux of petroleum hydrocarbons from the source area across the site in the downgradient direction, which varies, can be calculated as follows: Mass flux = (average linear velocity) x (cross-sectional area of aquifer containing petroleum hydrocarbons) x (concentration of petroleum hydrocarbons within the cross-sectional area). The isoconcentration contours for TPH-G and MTBE in groundwater shown on Figures 3 and 5, respectively (Appendix A), were used in calculating the mass flux across the site. The distance between isoconcentration contours near the dispensers were used to calculate the width of the plume between each contour. The average of the upper and lower isoconcentration contour values that bound each area were used to calculate the mass within each area. For areas within a single isoconcentration contour, the laboratory analytical results for the groundwater sample collected from the nearest well during the first quarter 2015 groundwater monitoring event were used to calculate the mass flux. An example calculation of the mass flux of TPH-G between the 100 micrograms per liter (pig/L) and 1,000 1.tg/L isoconcentration contours is shown below. V= 0.045 Aquifer thickness = 15 1 ft l = 28.32 Area between 100 pig/L and 1,000 1.1g/L Distance between contours on west = 20 Distance between contours on east — 40 Area = 900 Discharge = V x area = 41 Discharge = 1,147 Average concentration [(100 + 1,000)/2]= 5,050 Mass flux = 5,792,148 Mass flux = 5.79 ft/day ft liters ft ft ft2 cubic feet per day (ft3 /day) liters/day pig,/L micrograms per day (jig/day) grams/day Similar calculations were used to calculate the mass flux of MTBE in the downgradient direction to the west of the dispenser area. The mass flux calculations are presented in Appendix B. The estimated mass 4t5 COND014