Now, Im looking to close on my new property and am considering of just paying the $4000 for mold removal....but this really hurts my bottom line and adds a huge expense to what was thought of as a good deal.Any feedback on what to do is greatly appreciated.

Whatever decision you make, think about how it improves your personal bottom line now, and how that decision could potentially prove out in the future.

Liabilities: massive differed capital cost as sludge accumulates in lagoon and then must be removed every 20 or 30 years, potential groundwater contamination from partially treated wastewater leaking out bottom of lagoon, huge amount of land required for lagoons (1 to 3 acres for 50 space park), inability of lagoons to remove nutrients (nitrates under new regulations), irradict / poor treatment during winter.

Bottom like, we want to resolve the water issue ASAP.

But people in LA have no reason to go up the hill while the weather is perfect at the bottom I guess. 

It says nothing about the bottom line and gives a distored  picture when comparing returns across different markets since operating expenses can vary greatly by market.

Brief background, I own a top/bottom duplex in Pittsburgh and am looking to get two, separate air condensers installed for the top and bottom unit.

I think if prices start to subside investors will swoop into buy, the bottom is 5-6% CAP rate at worst.

Bottom line, cost seg and 1031 are great partners.

I'd say 75% of my offers are accepted and I've never hit something, some critical hidden issue, that significantly affected my expected bottom line.Lastly, I do this for custom-built duplexes and single-family -- I don't have the technical expertise to try this on something like a 40-unit complex.