NAME GROUP CEE 330 Spring 2014 Exam 2 Use PEN to write the answers for your exam If you use pencil you CANNOT request a regrade Closed book closed notes no cheat sheets nothing from class or book stored on calculators A list of relevant formulas and equations is given after the exam questions on pages 8 9 EPIWIN data are available at the end This exam has 6 questions Question 1 5 Question 2 5 Question 3 35 Question 4 10 Question 5 5 Question 6 40 Question 1 5 points The retardation factor of a contaminant in an aquifer is 5 Therefore A Four fifth of the contaminant is absorbed onto the solids B Four fifths of the contaminant is dissolved in the groundwater C The groundwater travels at five times the speed at which the contaminant travels D The contaminant is equally distributed between the solids and the groundwater Solution C Question 2 5 points The bioconcentration factor BCF for benzo a pyrene in daphnia is approximately 10000 The concentration of benzo a pyrene in daphnia living in water that has a benzo a yrene concentration of 2 ppb mass is most nearly A 20 mg L B 200 mg L C 2000 mg L D 20000 mg L Hint 1 mg L 1ppm Do show your work Solution A BCF L kg biota Cbiota mg kg biota Cw mg L Cbiota BCF Cw 20000 ppb 20000 ppb 1 ppm mg L 1 20mg L 1000 ppb ppm 1 Question 3 35 points You were hired by an environmental consulting firm Your first task was to assist a toxicologist to test the toxicity of toluene in fish For this test small fish are placed in a fish tank containing various concentrations of toluene As an engineer you made an assumption that these fish can be modeled as bags of 1 L containing by volume 5 fatty tissue that is similar to octanol in its affinity for toluene 3 air in a swim bladder and 85 water The remaining 7 is non sorptive for toluene i e does not sorb toluene At equilibrium when concentration of toluene in air inside the fish i e bladder is 1 g L 1 what is concentration of toluene in water inside the fish 10 points 2 what is the mass of toluene in water inside the fish 5 points 3 what is the mass of toluene in the bladder 5 points 4 what is the mass of toluene in the fish fatty tissue 5 points 5 what mass fractions of toluene in the fish will reside in fatty tissue 10 points Temperature is 298K Data from EPIwin are at the end of this exam Hint convert Henry s law constant from atm m3 mole to Lwater Lair Solution atm m3 atm m3 1000 L atm L K H 6 64 10 3 6 64 10 3 6 64 3 mole mole m mole atm L 6 64 LH 2O K H C mole H 0 27 air CW Lair RT 0 08205 L atm K mol 298K Cw Cair 0 27 1 g L 0 27 3 7 g L Mass of toluene in water of fish Vfish 0 85 Cw 3 13 g Mass of toluene in swim bladder Vfish 0 03 Cair 0 03 g Mass of toluene in fatty tissue Vfish 0 05 Kow Cw 0 05 102 73 Vfish Cw 98 88 g Total mass 3 13 g 0 03 g 98 88 g 102 g Fraction in fatty tissue 98 88 g 102 g 100 96 9 Question 4 10 points An environmental lab gives you the following results for soil sorption in water The aqueous phase concentration of DDT is 0 05 g kg and the soil concentration of DDT is 0 06 g kg Assume that the fraction of organic carbon in this soil is 0 15 The organic carbon partition coefficient Koc is most nearly A 0 12 kg water kg organic carbon B 0 60 kg water kg organic carbon C 4 0 kg water kg organic carbon D 8 0 kg water kg organic carbon Do show your work Solution D C 0 06 gDDT kgsoil K totalsoil K oc f oc 1 2kgwater kgsoil Cw 0 05 gDDT kgwater K oc K f oc 1 2kgwater kgsoil 0 15kgOC kgsoil 8kgwater kgOC 2 Question 5 5 points Both the Henry s constant and vapor pressure of a chemical are measures of volatility i e the tendency of the chemical to partition into the vapor phase Explain the difference between what the Henry s constant measures and what the vapor pressure measures 5 points Solution Vapor pressure is for equilibrium between pure liquid chemical and air 2 5 points Henry s law constant is for equilibrium between water and air 2 5 points Question 6 40 points An underground storage tank leaks toluene at a rate of 100 mL day This continues for a year before the leak is discovered and stopped The tank lies at the water table so all of the toluene released enters the sand aquifer but is not necessarily immediately dissolved in the groundwater The aquifer is 4 0 m deep and composed of sand with fraction of organic carbon foc 0 1 The actual groundwater velocity is 0 09 m day and the hydraulic gradient is 0 0005 The bulk density of the sand is 1600 kg m3 The porosity is 34 Density of toluene is 0 8786 g mL a What is the hydraulic conductivity of the aquifer 5 points b What is the retardation factor R 5 points c How far would you expect the toluene to have traveled down gradient during the oneyear period 10 points d If a non sorbing non degrading pollutant is released into the same sand aquifer compare the spreading speed of this pollutant with toluene Explain your answer 10 points e Find concentration of toluene in the groundwater if the concentration of toluene in soil is 1 g kg soil 10 points Data from EPIWIN are at the end of the exam Solution a v 0 09m day 0 34 hydraulic conductivity K act 61 2m day dh dL 0 0005 b Experimental Log K oc 2 07 R 1 Kd B 1 K oc f oc B 10 L kg OC 0 001 kg OC kg soil 1 6 kg soil L 1 1 55 0 34 c vact v 0 09m day R vconta min ant act 0 058m day vconta min ant R 1 55 2 07 distance 0 058m day 365day 21 19m d Non sorbing compound will travel faster because sorption does not slow it down e Find water concentration K Ctotalsoil C 1 g kg soil Koc f oc Cw totalsoil 2 07 8 51 g L Cw Koc f oc 10 L kg OC 0 001 kg OC kg soil 3 4 K H atm M Pair Cw Csoil K K oc L kg f oc Cw BCF Cbiota Cw K OW Co mole m3 Cw mole m3 log 1 LC50 0 871logKow 4 87 LC50 is the concentration that is …