Sealing crawl space vents in Pacific Northwest

Obviously, the soil needs to be graded away from the house (in the back yard). If that means you need a retaining wall, then you need a retaining wall.

Regarding the swale, improved drainage sounds helpful. The real question is, why isn't water shedding (what is the real issue)? I've had swale issues, and the problem in those cases, was not with my swale, but the neighbors'... so water backed up in my yard. In such a circumstance, you can talk to the neighbors about the issue, ask them to fix it, offer to help, and/or sue them for damages.

But if the neighbors aren't to be blamed, then another alternative to keep the grass cut very short (grass slows drainage). Or you could check into a trench drain (concrete ditch). This is just another option that I didn't see mentioned, although it may not be your best option. As Tester101 pointed out, being there to see the issue is probably necessary.

Regarding power outages, gasoline or propane generators are the most reliable answer. A moderate generator should be enough for a sump pump, the fridge, and should keep the toilet flushing too. As you know, the drawback with a battery bank is that once it discharges, then you don't have a simple solution, like getting more gas.

Edit- Here's a possible way to use a retaining wall to increase the grade away from the house.

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.