Over the last several years, I have made many trips on or around Beaver Lake. I have not, however, been under the surface of Beaver for more than a few seconds. This is unfortunate because all the action, limnologically speaking, is under the water. Beaver Water District’s plant engineer, Bill HagenBurger, is on the other hand an avid scuba diver. It turns out that Bill is also an excellent writer. The following is an article that Bill wrote for the Fall 2015 issue of the Southwest Water Works Journal, the official publication of the Southwest Section of the American Water Works Association. It describes a diving trip that he and his daughter made on Beaver late this last summer. Enjoy! – Bob
By Bill HagenBurger, P.E.
Plant Engineer, Beaver Water District
I was suffering from a bad case of writer’s block when trying to figure out what to write about for this journal article. I had planned on going for a dive at Beaver Lake and thought, “What better place to think about an idea for an article about water than 40 feet underwater at Beaver Lake, the raw water source for Northwest Arkansas?”
So, we packed the Jeep and my daughter’s boyfriend’s truck up with scuba gear and kayaks and headed to the lake. The scuba gear was for my oldest daughter and myself and the three kayaks for my wife, youngest daughter and her boyfriend. We got to the lake at the Dam site north park. The water level on Beaver Lake was so high that we were able to park within 10 feet of the water. My wife, daughter and her boyfriend unloaded the kayaks while my other daughter and I went to the local dive shop to pick up two full tanks of compressed air. When we got back to the lake, my wife, daughter and her boyfriend were out on the kayaks paddling around, my daughter was getting some sun, her boyfriend was fishing and my wife was enjoying being on the lake. So my daughter and I got on our gear, swam out about 50 feet and headed under the water. Next thing you know, I am about 30 feet down and it gets cold. I had hit the thermocline. My daughter will not get into the cold water, so we stayed right at the 30 foot mark. I did get down to 36 feet deep, but not the 40 foot mark as planned.
There I was, underwater just waiting for something to hit me for this article. Nothing. So we swam along and found a string line. We followed it to a sunken car that a dive shop had placed there. We found about a dozen fish swimming around it, mostly small perch, but what looked like some larger bass. We found another string line and followed it to the dive platform that was placed there for certification dives. I looked at my dive computer while standing on the platform and it said we were 26 feet deep. We swam down to the bottom of the platform and it started getting cold. I was at 34 feet deep. I thought the dive platform would be deeper since the lake was so high. The lake was only about a half foot below the top of the flood pool, so it could not get much higher than that.
Then I thought, “I guess they really want to keep the platform above the thermocline.” As I swam around the bottom of the platform, I saw the rope they had tied to it and it hit me, “They move the platform up and down, depending on the lake level.” A look at my pressure gauge and it was right about 600 psi (pounds per square inch), so it was time to ascend to about 15 feet for a safety stop to decompress a little and then head up. When we got to the shore, I realized I had gone through a full tank of compressed air and my daughter still had a little over a half of tank.
We ran to the dive shop to get a refill, headed back, got our gear on and went under again. I started thinking about what an unusual summer it has been for our raw water quality. We had some late spring rainfalls, and then some early summer rainfalls. Those rains managed to fill the lake up enough that the floodgates had to be opened twice, once after the 4th of July! That has never happened on Beaver Lake. The good thing about these late rains was that the spring foliage was already grown and not much sediment was washed into the lake, so we did not see the high turbidity that we normally see if the floodgates were opened in the early spring. So I was thinking, “This is a good thing… the lake is full early in the summer and no turbidity.” Then we started seeing some of our THM1, TOC2 and DOC3 numbers and, well, they were pretty high. It seems that with the spring foliage fully grown, the runoff coming into the lake did not bring a lot of sediment. But what it did bring was a lot of carbon, and to make it worse, it was a lot of dissolved carbon, which is very difficult to settle out. So now, we are struggling to remove as much dissolved carbon as we can and keep our THM numbers down. Just goes to show you — that’s the thing about water treatment – if it is not one thing it’s another.
1 trihalomethanes (THMs) A group of disinfection-by-products consisting of four separate compounds.
2 total organic carbon (TOC) A measure of the amount of carbon in a sample that originates from organic matter only.
3 dissolved organic carbon (DOC) A general description of the organic material dissolved in water.