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Been doing some more reading and google searches and from what I can tell we are spraying what amounts to normal household bleach concentrations.

What I mean is that according to the Wikipedia article on SH "Household bleach sold for use in laundering clothes is a 3-6% solution of sodium hypochlorite at the time of manufacture." And that it decreases with time. That is why you should use the freshest mix possible.

http://en.wikipedia.org/wiki/Sodium_hypochlorite

Now with our mix being at 4% that puts it right in line with normal household bleach in strength. The only difference being is that we apply it at full strength and add some other chemicals to the mix. Maybe this is something that can be pointed out if objections to bleach arise during the sales process. The home owner uses the same strength stuff just diluted in the washer.

If you take 30 gallons of 12.5% SH and multiply by .125 you come out with 3.75 gallons of 100% SH. This means you only have 3.75 gallons of 100% SH per 100 gallons of mix. If I did the math right which is how I think the 4% figure was calculated. 40 gallons of 12.5% to a 100 gallon mix comes out to be 5% mix.

In all we are not using anything that the home owner is not already putting into the ground. Maybe put their minds at ease.