Too bad MW-1 was dry.
The site with the highest concentration shows 360 ug/L benzene adjacent to the tank pit and then the wells up-gradient approximately 100 feet are non-detect. This is the site that when sampled four years later 80 ug/L benzene was detected. Unfortunately no data for the down-gradient wells was provided for that sampling event. Figure attached
Are the downgradient wells below the standard? Is there a significant decrease in concentrations between the tank and DG wells? This is important data to consider.
It depends on your experience in the area, soil types, natural attenuation over 10 years, etc. If you feel that it's likely that the TP has been impacted then don't be afraid to call it like it is. Just because you identify a REC doesn't mean the client has to do anything about it. Talk it through and they can decide if a Phase II is worthwhile or not.
And there are wells down-gradient of the tank pits.... just not at a significant distance.
Actually yea I think it is a sewer pump station so never mind that. Typically, would you call these sites RECs based on this information? From what I've read most petroleum products do not migrate more than 1,200 feet. These sites are 1,000 feet away. At one site, benzene was reported at 360 ug/L in 2000, in 2004 benzene was reported at 80 ug/L. This is by far the highest reported concentration out of the LUST sites... but still not very significant. Tough call... might have to go conservative and say the presence of four LUST sites 1,000 feet away and up-gradient constitutes a REC. Just not very confident on my dissolved petroleum product migration knowledge.
No wells down gradient of the tanks? That's too bad.
Is this a sewer pump station? It could draw down the GW if there's an infiltration issue I suppose.
Ahh I see what you mean. The regulatory limit (drinking water standard) for benzene is 5 ug/L in GA. The well data for the LUST sites appear to have elevated concentrations in the vicinity of the tank pits but the up-gradient wells (not adjacent to tank pits) are non-detect. However, only one site has wells up-gradient a significant distance from the tank pit, the others only samples onsite and in close proximity to the tank pits. The highest concentration of benzene reported was 80 ug/L and that was immediately up-gradient of the tank pit.
Regarding the pump station on the Property.... in your experience is that considered something that can effect groundwater? Potentially "pulling" groundwater toward the pump station which in other circumstances may not occur?
Even if the plume wasn't delineated do you have data from the most downgradient wells at each LUST site? Are the concentrations above/below the regulatory limit for your TP?
Also look at how much the concentrations decrease between wells on the LUST site. This will give you a rough idea of the extent of the plume.
No plume delineation data found during file review. I'm not sure what you mean by groundwater limit.
Were the plumes delineated? What's your groundwater limit?
Just curious... I mentioned the benzene concentration was 27 ug/L... which I agree is low, but I'm wondering at what concentration do you begin to get concerned?
Hey JG. Thanks for your input. Based on the inferred plume based on the well data I concluded the the subject property was not within the CD.
Thanks for the link to that document. Much appreciated!
EPA vapor intrusion guidance documents are final as of a few days ago. Figure 4 and Table 2 provide some good information on this topic. An adjacent closed petroleum LUST site would not be a REC unless very unusual circumstances, such as source directly beneath a building on the subject property or free product has migrated in shallow groundwater beneath a building on the subject property. Both of these scenarios are unlikely for off-site closed LUST releases. This matches up what I've seen from most states.
EPA and states don't care about VECs. Seems to be a lot of consultants that think every VEC is a REC, which is not true.