Question

A mixture of benzene, Napthalene, trichloroethylene and chlorobenzene were found in a groundwater plume.   Consider the partitioning of these four compounds in a contaminated soil. Assume that the hydrocarbon mixture has contaminated the soil at an average of 0.09 liters of the mixture per cubic meter of soil. Considering the soil above and below the water table (ie. each cubic meter is 60% saturated with water by volume). The soil contains 0.75% organic carbon and has a porosity of 30% and a bulk density of 1600 kg/m^3. The mole fraction for each component is as follows: benzene = 0.035, Naphthalene = 0.032; trichloroethylene = 0.020 and chlorobenzene = 0.018. Where needed use the average Molecular weight of the chemical mixture and the average density (SG) of the mixture. Make sure the work is presented in a memo form – all hand calculations can be place in the appendix, but all equations used and assumptions made must be included in the memo. Include schematics as needed and there should be summary tables and figures showing the results of the portioning analysis.

1. Complete the table below with the chemical characteristics of each compound and provide a paragraph on each compound: what are its industrial uses, what are its hazardous characteristics, Toxicity characteristics (IRIS or other courses – MCL, RfD, Slope factor, NOAEL, LOAEL etc. as available). You will need to so a good internet search to get all of the info. Make sure unit so parameters are correct. Koc may need to be estimated from Kow as discussed in class.
2. What is the total mass of each compound in each partitioning phase (air, soil, water, NAPL). (Use a final table and pie charts to illustrate).
3. If there are 200,000 cubic meters of soil that have been contaminated in this manner, how much oxygen will be needed to aerobically degrade the contaminant mixture (need to make some assumptions here and use some redox chemistry)? Include complete redox equations for the oxidation of each compound.
4. How many pore volumes of groundwater would be needed to treat the contaminant plume if the groundwater D.O. was 4.0 mg/l?
5. What levels of contamination would have to be met for the site to be considered “safe” by regulators?
6. How long would it take to remediate the site if you relied on natural biological process and the length of the plume along the groundwater flow path is 1200 meters, the hydraulic gradient of 0.009 m/m and a hydraulic conductivity of 55 m/d?
7. Why is this partitioning theory important with respect to bioremediation and the treatment of contaminated sites?

Compound	MW (g/mole)	Specific Gravity	Henry's Law (L-atm/mole)	Solubility (mg/l)	Kow	Koc (L/kg)
Benzene	78.1	0.88	5.6	1750	135	63
Naphthalene	128.2	1.16	0.45	33	1995	820
TCE	131.4	1.46	9.1	1250	410	101
chlorobenzene	112.6	1.11	3.0	500	690	280

Answer 1

A typical light stick contains a hydrogen peroxide solution, a solution containing a phenyl oxalate ester and a fluorescent dye. The hydrogen peroxide oxidizes the phenyl oxalate ester, resulting in a chemical called phenol and an unstable peroxyacid ester. Subsequently an unstable peroxyacid ester compound decomposes, resulting in additional phenol and a cyclic peroxy compound. The cyclic peroxy compound decomposes to carbon dioxide.

This decomposition releases energy to an added dye. The particular dye used in the chemical solution gives the light a distinctive colour for instance ‘9, 10-diphenylanthracene’ emitting blue light (450nm) and ‘16, 17-(1, 2-ethylenedioxy) violanthrone’ emitting red light (680nm) (Galland, 2011). The electrons in the dye atoms jump to a higher state and then fall back down releasing energy in the form of light.