Understanding the “why” of pesticides appearing in wells
The initial issue is dieldren and chlordane’s persistence in the environment.
Chlordane does degrade, but obvious takes many years to do so, but dieldren seems to last longer.
Both pesticides are considered water insoluble, with the solubility of dieldrin being 0.186 ppm and chlordane’s being 0.032 ppm.
The first thing to consider; dieldrin is slightly more soluble that chlordane and would move a bit better in ground water.
More to consider; a study performed in 1992 indicated that chlordane would become more soluble, significantly (> 400 ppm) more soluble in ground water with a high organic carbon content (such as septic systems).
Does dieldrin do the same thing? There are no studies that I found.
What I do have is the information of the quarterly tests done on wells with Connecticut Department of Energy & Environmental Protection showing 2 cases where chlordane shows up in the well water test after 30 days of heavy rains. This does not occur with dieldrin.
Chlordane also becomes undetectable when the rainfall amounts are not great.
The second issue is presence of chlordane in sediment from Long Island Sound (LIS) presented in a study from 2007. The end discussion is that there is continued chlordane input into LIS, even though it is decreasing. This means that most of the chlordane has “washed out” of the soils where it might influence well water. There was no references to dieldrin.
Now this secind bit of information might have implications for the Lobster die off?
No - it clear says that levels have not changed since 1977 - chlordane is not the problem...
 Environmental Science & Technology, 1992, 26, 2234-2239, Partitioning Behavior and the Mobility of Chlordane in Groundwater.
 Environmental Science & Technology, 2007, 41, 7723-7729, Persistent Chlordane Concentrations in Long island Sound Sediment: Implications from Chlordane, 210Pb, and 137Cs Profiles