Here is the solution I implemented to fix this issue and ultimately brought the humidity level to a stable 58%:
-First and foremost the first thing I did was get a Meade Instruments TM005X-M so I could measure the humidity levels in my crawl space and get a baseline. My starting humidity levels were 75%-88%, most likely hitting 100% over the summer.
-I Had a contractor come out and replace gutters, adding two downspouts to the front of the house. In addition I will be digging trenches to send the water at least 10 feet away from the house. This was necessary because there were no downspouts on the front of the house and the water would pour over the sides of the gutters.
-I then laid out 6mil black plastic on about 75% of the dirt in the crawl space. This alone lowered the humidity from 88% to around 75%. I did not remove all of the rocks, and even after crawling on it with kneepads it did not break or tear the plastic. We did remove some of the obnoxiously large Ozark rocks. The 6mil plastic (recycled even) ($75.00) is very strong. I did a 12"-24" overlap and did not seal the seams. We did not go up the wall. We staked it down with garden stakes ($8). It is by no means perfectly sealed, but is covered.
-I sealed up all of the crawl space vents (6) with 1.5" foam, and used expanding foam to make sure the seal was good. ($30.00)
-I installed the humidifier and set it to run in continuous mode. The humidifier model I ended up getting was the FFAD7033R1 which can run in continuous mode by hooking a hose up to it. This hose drains to the sump pump. The sump pump did not have a lid, so I purchased a standard 5gal bucket lid and used waterproof duct tape to seal the lid onto the sump pump, then drilled a hole in it for the hose to come through. This put us around 65% humidity. Later I will set this to a specific humidity to hold at, and it will only run when needed. ($250.00)
-Finally, we covered the final 25% of the crawl space with the same 6mil plastic. During this time we discovered standing water, a couple 1/4" deep small puddles near the front of the house (north, the bad spot). At this time I inspected the area thoroughly and found that the sewer line going through the foundation and out had no sealer around it. This left a 1/2" gap around the entire pipe, going directly to the dirt. Under the pipe there was mud-like residue, so I was now certain this was the root issue. We used expanding foam sealer around the pipe, and laid the 6mil plastic over the puddles. This final step brought us to 58%, and I am confident it will continue to drop.
All in all, I was quoted $10,000.00 to fix this problem with a CleanSpace® system, and ended up spending around $450.00 max plus my time, about 20 hours to fix it myself. Note I don't count the gutters as included in the price since they were old and failing already. Also, the solution from the contractor did not include solving outside water problems, which in my opinion is where you should start.
Additional note about sealed vs unsealed crawl spaces. There is tons of conflicting information on this subject so I decided to test for myself. On a day when the humidity was around 55% outside, and the humidity was around 70% in the crawl space, I setup box fans to suck the 55% humidity air from the outside into the crawl space for around 12 hours straight. Doing this lowered the humidity only by 1-2%, so I knew sealing my vents was the answer.
It may seem counter-intuitive, but when dealing with crawl space issues START OUTSIDE.
Concrete is pretty hygroscopic, meaning it attracts water - to a degree in my experience. Capillary action is the classic way concrete attracts water, but if it is cooler than the air it can and will condense moisture from the air. And concrete holds water in and under pretty well: if you were to dig under it, probably not dry.
If accumulation only happens in some spots, are they depressions, or lower than other adjacent areas? That would be why it accumulates there. Another thing to check is whether those specific spots are cooler than other areas so you have local action going on (sounds crazy, but you've exhausted a lot of other ideas, now it's time for outta the box thinking.) Use a pretty sensitive digital thermometer (measuring portions of a degree) to check.
Which brings up another point: is the air in your basement somehow a bit moist? Have you checked the humidity level, esp. in various places (dry here, moister there). Is there any possible air-current that could move air over specific spots, or around them so they don't dry?
Best Answer
The humidifier works well in the basement. Two ideas:
Otherwise, get a second dehumidifier for the upper level. I see isherwood commented a similar idea while I was writing this. If you can set the dehumidifier on a counter next to a sink, you're in business, just like the basement. If you don't have convenient counter space, you could set up some type of surface next to the sink that is higher than the sink and run a discharge hose into the sink. If that isn't a good option (sink height is typically higher than normal table height), you can still do it using a condensate pump.
You don't describe the exact setup for getting the water into the drain in the basement. Dehumidifiers typically have the ability to connect a hose to the collection tray. Use adapters to connect a piece of vinyl tubing to that tray drain.
Run that tubing into a condensate pump (http://www.homedepot.com/b/Plumbing-Pumps-Utility-Pumps-Condensate-Removal-Pumps/N-5yc1vZbqoh). You will need to raise the dehumidifier so the collection tray drain is higher than the input hole in the condensate pump and keep the tubing short enough so it is a straight shot and doesn't dip a lot lower (set the dehumidifier on a small stand or table). Run the condensate pump discharge to a sink.
I've done that in an enclosed crawl space connected to a basement and it works well for unattended, long-term use.