I'm 20 years old. This summer, two friends from high school an I (all 20) will be exploring the drains underneath our city. We are all students at the local university and I'm a graphic design minor so I will be taking photographs. One of the three of us uses marijuana but we will have no drugs/substances of any sort on us. The day of, we will all be clean shaven and try to look as non-menacing as possible in case anyone sees us. If we meet anyone, the cover story we will tell will be that we are doing hands-on research for a university course. (This is not untrue.)

In terms of safety, first aid and equipment we are all set, but I am a little worried about potential run-ins with law enforcement. If I have any criminal arrest history at all I will be pretty much fucked over in terms of employment in my preferred career fields so this still worries me a little.

Information about my city:
>in Oregon, originally founded in 1870s
>city population: 157,000
>metro population: 270,000
>violent crime is very low
>most abundant crime is meth possession and homeless people trespassing in areas
>local politics very liberal
>in my city, 85% caucasian, 8% hispanic/latino, 7% other
>no underground transit of any sort; no public train transit system of any sort
>not a single 'ghetto' or slum neighborhood in the entire area
>police and populace get along well

And so my main questions are:
1) what is the likelihood that the pipes will be monitored to any degree? The entrance we are going to use is at the edge of a city park, there are no security cameras in the area, there are no 'entrance forbidden' signs of any sort and there is absolutely nothing blocking anyone from entering.
2) in the event of a run-in with an officer of the law, how likely is it that they would arrest us rather than just make us leave?

If this goes off without a hitch, I will report back with OC photos.