**Q. Can contaminants be transported by rain?  If so, what transport media would that be classified under, water or air? 
A. Many “air pollutants” are transported by rain, but not too many “toxic chemicals.”  Plain dust, PM10 or PM2.5, is transported by rain, but the dust particles are generally inert substances.  Generally one would focus on the transport by air, and the possibility of rain influencing the exposure would be minor. 

*Q. Is that person who brought me (transported) a Ziploc bag smelling like dry cleaning chemical now a Potentially Responsible Party under CERCLA? 
A. Not if you eat the dirt – then it’s a pure food and drug issue.  Anyhow, you bring up a surprisingly relevant practical matter.  When there is a CERCLA waste on a site, say in the backyard of CleanCo Chemical Company, and CleanCo hires a contractor to remediate the waste.  Now the contractor excavates the waste, does the contractor become responsible?  Rest assured that CleanCo is responsible – forever – but how about if CleanCo goes bankrupt, or the contractor is a large economic entity than CleanCo?  Yes, the contractor is also responsible now for the waste.  I worked for the Corps of Engineers remediating old sites and we were constantly taking dirty soil from its resting place and making a hazardous waste out of it.  Now might that be a RCRA issue?  No, it would remain CERCLA. 

*Q. In the Fox River RI document they are concerned that the emission of PCBs from the sediment to the water column. As well they do write that the PCBs will be stuck in the solid and will therefore not be of concern for the air pollutant. But isn’t PCBs actually able to evaporate from the solids and would therefore be of concern for inhaling? I thought I read somewhere that today people are afraid of old building containing PCBs because when tearing  them down it will course exposure through inhaling. I know it will only be the PCBs with low degree of attached chlorides but shouldn’t it have been included?
A. There are about 216 PCB congeners, that is different numbers and arrangements of chlorines on the basic biphenyl.  The volatility and toxicity varies with the congener.  However, it is impossible to manage each congener, so the regulatory agencies often work to “total PCB.”  PCBs were used in many things, including fire retardant paints.  There is some concern when demolishing an old building that there will be PCB exposure, but it is usually assumed to be in the dust, which the chemical PCB is part of a paint or other matrix - not from its volatilization.  In general, a PCB molecule would prefer to stay bound to the organic carbon in the sediment, or the water for that matter, and its evaporation would be very slow and thus, probably, not detectible.  Some of the lighter PCB congeners might evaporate more quickly, however. 

***Q.I had a problem in the quiz 2 question 4; “Since there is only one "exposure point," it is important to choose it carefully”. I which kind of situation would we be able to choose the exposure point? I’m not sure I understand the question.
A. Think of the cartoon of the waste site with the drums buried.  There are several humans shown, each could be an exposure point.  You could choose to evaluate the exposure at any or all of points.  For example, you might choose the worker at the site, because his exposure will be the highest, or you might decide to not evaluate the worker because he will only be there a short time.  In general, the exposure will be different at each of the exposure points, and consequently the risk will be different.  However you would state the risk for each receptor and exposure point.

**Q.   Beyond policy, can I quantifiable state that 100kg of benzene from a chemical plant should be handled differently than 100 kg of fresh benzene? 
A. If it is a waste, yes.  Say you have barrel of benzene in the back of your garage.  It is a useful chemical.  The fire marshal might worry, but it is not an EPA or DEC issue, not an “environmental issue.”  Now if one day you look inside the barrel and see it has some rust and crud floating and decide that you cannot use the benzene any more.  At the moment, the barrel of useful chemical becomes a “waste” and thus (possibly) a RCRA issue.  Transporting the barrel would be different, before and after you noticed it was contaminated. 

* Q. Sub-module 2B—I have two liquid chemicals with identical LD50; overall risk concentrations for exposures are identical.  The only difference is their transport characteristics.  Chemical A is water soluble and water is its transport media (indicating risk of water table contamination).  Chemical B bonds tightly with a mineral in soil and is less likely to transport into a water table. Question:  How does transport factor into the “threshold equation?”  Generally speaking, would I be permitted to release more Chemical B due to the fact that it is less likely to interact with groundwater?  
A. “Release” is the word.  If you are actively disposing of a chemical (and everything is a chemical, right?), you need to determine if it is a “hazardous waste” under  RCRA.  We go over that in ENVE 649 and often ENVE 644.  That hazardous waste determination is based on regulations which in turn supposed to be based on risk. In this course, we are concerned with risk evaluation.  So we are very concerned with the fate and transport.  But for your question, as a practical matter, can the chemical be cleaned up?  Many can’t.  If the PRP can demonstrate that the chemical is unlikely to move AND if it degrades with time, the PRP may be allowed to use “natural attenuation.”  On the other hand, if the chemical moves very quickly, the PRP may be able to persuade the regulators that it will be gone before he can clean it up.