ARUNDEL — Jim McMahon stepped away from a full-time career as a radiologist at York Hospital in January. And McMahon, 67, decided to spend the start of his retirement helping outdoor organizations, becoming one of the many volunteer trail crew members who cover the state.

The problem was choosing which outdoor group to help.

McMahon’s lifelong interest in trains led him to the Seashore Trolley Museum in Arundel, not far from his Kennebunkport home. He put his name on the museum’s list to receive more information. And when he got a call for a volunteer workday, his new career began.

How did you get involved with the Seashore Trolley Museum’s mountain biking trails?

I signed up to get information and saw they needed volunteers. It turns out it was helping men with shovels and picks work on the tracks. The tracks in one building started to tilt and were in jeopardy of sliding into the side of the building. During that work day (museum executive director) Sally Bates came over to thank me and I said, “What other things do you need done?”

She asked if I knew how to work a chainsaw and I said I had one. So that led to clearing some brush by the entrance driveway around the pine trees. She wanted it to look a bit more tidy.

It turns out I’m pretty good at clearing brush. That led to another clearing job before their Speakeasy (fundraiser). I asked what the next job was and Sally told me about the mountain bike trail out here, that connects to Kennebunkport Conservation Trust trails.

I always wanted to explore by bike. It’s fabulous. I’m in the woods. I get to bike. You don’t have to go far here to be in a quiet place.

You said while riding the trolley here that you grew up in Boston around trolleys?

I grew up in Quincy with a grandfather who worked for the Eastern Massachusetts Railroad Company. He was a trolley man. Then I lived in Weymouth and I lived near a train station. I was down at the tracks as a kid all the time. It was unbelievable what we could do as kids. There were big rocky cliffs next to the tracks. As kids we would climb them, and we got pretty good at it. I had just enough sense not to kill myself.

There were trolleys in Quincy. Then every little town had trolleys. They were in Arundel, Biddeford and around Portland.

It’s the people at this museum that keep the trolleys alive now. One thing I noticed when I started as a volunteer, there is a huge number of wonderful organizations in Maine. I also volunteer for the Saco River Salmon Club and the Kennebunkport Conservation Trust.

What work are you doing?

I helped scout out a stream for the Saco River Salmon Club. They wanted to see the tributaries of the Saco, to know what they looked like, if salmon could get up the river to these places to spawn. The Swan Pond Creek is one tributary. The salmon club wanted someone to check it out. So I went with waders. Every part of this was fun. There was brush on the sides, but I could see the brook. I put my waders on and walked down the center of the stream, until I got to a beaver dam that had obstructed the flow of the creek. I walked the creek and brought a GPS and plotted where the dam was.

When did you retire as a radiologist and get into all this?

In January I semi-retired. There was an opportunity to share a shift with another radiologist, so he works most of the week and I work one-fourth of the week. I have a fabulous setup. In Maine there is no limit to the things we can learn. I find simple things to help people. I want to be outdoors. And I try to stay out of the politics and the policy. I don’t want to fundraise. I like clearing brush, being in the woods. And every little town has a small cemetery, I realized. These are forgotten places in the woods.

We have a camp in Winthrop near Maranacook Lake. When I was driving around the hills I noticed these new American flags. They’re for veterans who were in the Revolutionary War, or Spanish American War, or the War of 1812. There was this whole other thing. And I promised myself I would find who put in those flags and see if I could help maintain the grave sites. I’m also interested in history.

These places you want to volunteer, the trolley museum, cemeteries, they’re all very quiet. Is that why you want to volunteer at these places?

Yes. The week I was wading in that creek, I could have been in a stream in central Africa. You couldn’t hear a sound. All you could hear was the brook. It’s perfect. The trolley museum’s (trails) are fabulously quiet.

Did you come up with a list of things you wanted to do as a volunteer, or did these opportunities just come to you?

They were in my mind. I was careful not to get involved in the PR or the politics of things. I’m the elder statesman at the radiology lab, so my life has been pretty busy. It wasn’t until the spring that I started to get good at how I would spend my time (in retirement). I wanted to be outside. I knew that.

I helped the salmon club and Trout Unlimited freeing a stream where there were brook trout, to make it free-flowing habitat. This stream was impounded by (debris) and was 4 feet higher. We spent four hours pulling out logs, making it free-flowing. It was a fabulous scene in nature. I don’t know why more people are not helping. There were eight of us. It could have been done differently with grants instead of local people.

With volunteers, when the scale is right, it is better. It’s so much simpler. Decisions are made on the ground, not by committee.