Saturday, May 29, 2010

A Patch Over Bellingham's Void

Pavement patch on East Holly Street

Coal was discovered adjacent to Bellingham Bay in the early 1850s. The discoveries were very fortuitous as the coal could be loaded directly onto ships for transit to centers of demand. Bellingham had at least three coal mines adjacent to the bay. If there ever was any documentation of the first mine it has remained undiscovered and for many years it was assumed the mine entailed simply a minor amount of surface mining. However, the old mine was rediscovered during a construction project near the shore in south Bellingham in the early 1990s. The shaft was filled with gravel after discovery and was described to me as being a steep audit that was approximately 80 feet deep. The second mine had a longer life with workings extending beneath what was then the small town of Sehome. The mine operated from the 1850s through the early 1870s.

Schooner and coal loading facility, Bellingham Bay.

Coal loading facility on Bellingham Bay

This second mine has presented a bit of a problem because of the risk of collapse. The downtown area of Bellingham later developed over a portion of the area mined. Several collapses of portions of the mine were reported in the 1880s and very early 1900s along Railroad Avenue and there were reports of holes between North State Street and Railroad Avenue as recently as the 1970s. A hole was reportedly filled at the corner of Railroad Avenue and Holly Street in 1888.

In the early 1990s the Mason Building, one of the largest buildings in downtown Bellingham burned. The entire interior burned leaving a precarious skeleton of steel and masonry. The structure was torn down and a chain link fence enclosed the basement foundation. This blight on Bellingham’s downtown landscape was referred to as The Pit. The Pit gained considerable notoriety in Bellingham. The Pit stood at the most important downtown intersection in the city. After no apparent action from the land owner to do anything with the site the City of Bellingham began condemnation proceedings ultimately buying the property.

This is where the patch in the pavement comes in. The company I worked for at the time was hired to assess the property for potential contamination and geotechnical issues. We were aware of the possibility of a mine under the site but various maps had the mine located at different places. Tim Walsh and Robert Logan (1989) had estimated the mine location based on old mine reports and an assumed shaft entrance. The structural engineering company we were working with had a map that was similar to Walsh and Logan but with a sharper turn to the trend of the mine as I recall it. Tetra Tech (1984) had the mine under the site at a depth of 300 feet. We proposed using an auger drill rig to drill to bedrock and then switch to mud rotary with a few change outs to obtain rock cores. I had the pleasure of overseeing this operation and really enjoyed the reaction of people had to mud drilling at the busiest intersection in Bellingham.

Walsh and Logan (1989) showing two of the mines underlying
Bellingham with the downtown area on the lower right. 
A much bigger mine underlies the northwest portion of the city. 

One of the best parts was that we did rock coring at a few intervals. This entailed pulling out the rotary drill bit and then stringing the core tool down the boring. I did not have a lot to do while the drillers did the work of changing out the drill tool so I crossed the street and had eggs, hash browns, and coffee while watching the drillers from through the window. After a couple of rock coring runs we did continuous mud drilling with a goal of reaching the coal seam. The returning mud was light brown but at 110 feet it suddenly turned black and just as suddenly all drained down the bore hole. We had found the void! The next day we preformed the same operation around the corner on Railroad Avenue. This time the same thing happened at 88 feet.

Ultimately we did lots of research to come up with an approach to estimate the potential settlement if the void collapsed and the collapse worked its way to the surface; not very good news for the structural engineers. Additional drilling was done using continuous rock coring methods, but by then I had left the company. The continuous coring was done to the south and west and found the coal seam but no voids. This means that retreat mining was not done and the scale of collapses and risks posed are significantly less than if all the coal had been taken. All said it appears that Walsh and Logan (1989) had very closely located the mine and mine orientation on their map though very good research.

Today the building that replaced The Pit is at the center of an area that has seen redevelopment. Other development has taken place over the mine in the past few years and it has been interesting to see how seriously various geotechnical consultants and for that matter the City of Bellingham take the issue. I am aware that drilling has taken place on some of the sites but not on others and I am also aware of one building that was redeveloped that likely had been impacted by mine subsidence.
The former Pit, now offices and Starbucks

An additional segment of The Pit is worth mentioning. Once the City began moving towards funding the building project, a number of citizens demanded that The Pit be turned into a park versus being developed. Lots of passionate protesting ensued including at the City Council meetings. Protesters were arrested, but one the most infamous protester who went by the name Raptor was never arrested. He was never identified and from all appearances drove the police nuts. Three arrested protesters were tried at least in part because they wouldn’t give up Raptor’s true identity. One of the joys of living in a small city is that one can get to know a lot of the personalities involved. The defense attorney was a friend of mine, and I knew a couple of the protesters, the lead detective and a couple of the jurors as well as numerous witnesses. There was a three day trial that ended with a hung jury.

So every time I see the fading patches in the pavement of Holly Street and Railroad Avenue it brings back fond memories of a mud rig on one of Bellingham’s busiest street, a great breakfast at the Little Cheerful and finding the void under downtown Bellingham. But unknowns still remain; I never did find out the identity of Raptor.

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