ENVE 2310 Environmental Engineering Fundamentals Problem Set 4 1. Take a look at this USGS site: https://www.usgs.gov/special-topic/water-science school/science/contamination-groundwater?qt-science center objects=0#qt science center objects and search elsewhere as needed (a) What are some typical uses and sources of the following compounds at a contaminated site: i. Chromium ii. Benzene, toluene, xylene, ethylbenzene (BTEX) iii. Perchloroethylene and Trichloroethylene iv. Dieldrine 2. Draw a vertical profile of soil and groundwater below our feet, including a small stream. Include and label all major components: groundwater table, confining layers, unconfined aquifer, confined aquifer, saturated zone, unsaturated zone, the direction of groundwater flow. Be sure to show how the stream water level connects to the groundwater table. What if you spilled a DNAPL (a dense non-aqueous phase liquid) on the soil surface? Where would it migrate to in the subsurface? What if you spilled a LNAPL (a light non-aqueous phase liquid) on the soil surface? Where would it migrate to in the subsurface? 3. Calculate the volumetric flow rate through a compacted clay liner at the bottom of a landfill, if the area of the landfill is 15 ha and the liner thickness is 1 m. The hydraulic conductivity of the clay is 7.5 X 10-10 m/s. Assume that the head difference of water is 0.6 m across the liner thickness. 4. Often mixtures of organic contaminants are spilled into the subsurface where they can contaminate groundwater. An aquifer with bulk density of 2.3 g/cm³ and porosity 0.3 becomes contaminated with a mixture of trichloroethylene (TCE, Kd= 5 L/kg), hexachlorobenzene (HCB, Kd = 104 L/kg) and dichloromethane (DCM, Kd = 20 L/kg). (a) Calculate the retardation factor for each of these compounds. (b) Rank the compounds in terms of their travel time, from fastest to slowest. 5. A new municipal well is installed in an alluvial aquifer having a hydraulic conductivity of 5 X 103 m/s, a porosity of 0.25 and a bulk density of 1.7 kg/L. The aquifer is 20 m thick. A municipal water supply well is put into operation pumping 2 ML/d through a capture zone that is effectively 70 m wide. Unfortunately, a spill of gasoline 150 m upgradient of the well has contaminated the groundwater with benzene. Assuming that the sorption coefficient for benzene is 10 L/kg, calculate how long that the municipal water is safe to drink (i.e. no benzene contamination).