Back in the day, there was controversy over thermal pollution from electric power plants (notably nuclear plants) that used lake or river water to cool their turbines. Today, attention is turning to thermal contributions from wastewater treatment plants, notably in areas with cold-water streams that harbor salmon and trout.
One plant dealing with that issue is the Medford Regional Wastewater Reclamation Facility in Central Point, Ore. It faces a state Department of Environmental Quality requirement to reduce thermal loading to its receiving stream, the Rogue River. Rather than actually cool its effluent, the facility is looking to reduce heat load to the river by planting trees along the banks to create cooling shade.
Medford’s story is of interest not just because of the thermal issue itself but because it represents another case of looking beyond the treatment plant for reductions in pollutants of various kinds.
For example, the State of Wisconsin has a phosphorus rule that says treatment plants can deal with phosphorus permit levels not just by changing their own processes but by undertaking watershed-based activities, like encouraging farmers to adopt cropping practices that reduce runoff into receiving streams.
And in the eastern states, where nitrogen is a huge issue (notably around the Chesapeake Bay), there is activity on trading of nitrogen credits in addition to better nitrogen-removal treatment processes.
Dennis Baker, manager of the Water Reclamation Division for the City of Medford, talked about his organization’s river shading program in an interview with Treatment Plant Operator.
TPO: Please tell us about Medford and its surroundings.
Baker: Medford is in south central Oregon, about 30 miles north of the California border. It has a population of about 70,000. The Rogue River runs just outside the city, and it supports a lot of sporting and outdoor activities. The timber industry used to be huge here; it has dwindled quite a bit, although it is still a significant employer.
Agriculture is growing. Pears are a big crop in the river valley, and our wine industry is getting larger every year. The Rogue River has a lot of salmon in it. It’s a good-sized river and is classified as a Wild and Scenic River. It has some rapids and is a pretty spectacular waterway. Fishing is huge in the area.
TPO: How would you describe your treatment plant and its process?
Baker: We are a regional plant that takes wastewater from the City of Medford as well as Central Point, Jacksonville, Phoenix, Talent, Eagle Point, and unincorporated areas of Jackson County. We have an average design dry-weather flow of 20 mgd and currently average about 17 mgd. The existing plant was built in the late 1960s and has been through a lot of changes, but the core of it is still pretty much intact.
We have preliminary treatment with bar screens, followed by aerated grit basins and primary sedimentation. Then we send the flow to a biotower, after which it goes into activated sludge with fine-bubble aeration. That’s followed by secondary settling, disinfection and discharge to the river.
We have two permit cycles. The winter cycle is 30 mg/l BOD and TSS, and our summer cycle is 10 mg/l BOD and 20 mg/l TSS, with an ammonia limit of 13 mg/l.
TPO: What is the history of the thermal loading issue?
Baker: It goes back about five years to when the DEQ first looked at TMDLs (total maximum daily loadings) on the rivers and at fish habitats in general across the state. For the major rivers, they came up with TMDLs for several constituents, but the main one concerning us on the Rogue was temperature.
TPO: Why the concern about your plant? Does your effluent account for a large share of the river’s flow at the outfall?
Baker: Not really. According to DEQ requirements, there are only a couple of weeks out of the year where we would currently be discharging any excess thermal load, and then it’s only about one-third of a degree Fahrenheit that we’re above the limit. The time of year of note is in October, if the river flow is in the Q7-10 stage — which means the lowest-flow seven consecutive days in a 10-year period — we would be over our limit by about one-third of a degree. We’re not a massive thermal load, but we are in fact a load, and the goal is to mitigate all loads if possible. Being over is being over.
As the population increases over time, our thermal impact will increase, and that is factored into our load compliance schedule.
TPO: Do you have salmon spawning in the river at those times of year?
Baker: Yes, that time of year is during the spawning season for the salmon, and is the driving concern.
TPO: What is the timetable for complying with this permit provision?
Baker: We have a 10-year compliance schedule in our new permit to get to a minimum of 177 million kilocalories per day (or thermal credits), with an end goal of about 300 million thermal credits over 20 years.
TPO: What options were explored before you chose the shading program?
Baker: We looked at a cooling tower, but the trouble was that during the time of year in question, there isn’t enough differential between the air temperature and the water temperature to get any kind of cooling that way. Then we thought about mechanical chillers, which would definitely work, but when we costed that out, it was in the neighborhood of $15 million.
Then there are some old lagoons next door to us that belong to our sister organization, Rogue Valley Sewer Services. The thought was that we could excavate those out. The engineering work showed they would need to be dug from their current depth of about 12 feet to about 30 feet. Then we could send a certain amount of effluent over there, allow it to cool, and discharge it from the bottom — essentially taking advantage of geothermal cooling. However, that again would cost some $15 million, not counting upkeep on the transfer and discharge pumping systems we would have needed.
TPO: How did the idea of shading the river come up?
Baker: Temperature trading was actually the option favored by the DEQ. We’re partnering with a group called The Freshwater Trust to implement the program. They’ve been around for about 30 years doing environmental projects. When all is said and done, the cost of the temperature trading program is about $8 million.
TPO: How will this project actually work?
Baker: It’s a 20-year program. We have a 10-year contract with The Freshwater Trust with a 10-year renewal. They will go out and determine the areas on the Rogue River and its tributaries where geographically it would be worthwhile to add shading. Then they have to negotiate with the landowners to get easements. There will be payments to the landowners for the use of the land. Then they will have to clear off whatever brush is there and plant native tree species that over time will grow tall enough to offer enough shading to provide mitigation credits.
The choice of trees will be a mix of cottonwood, alder, willow and maple. The varieties planted will be dictated by site-specific conditions.
TPO: How is it possible to measure the impact of this shading on river temperature?
Baker: There is a computer program called Shade-A-Lator where you plug in various data and it will give back the amount of heat mitigation you can generate from a given tree planting program.
TPO: Do you have a feel for the scope of the planting program that will be required to reach the goal?
Baker: It’s estimated we will have to add shading to about 25 to 30 miles of river. It’s a pretty daunting task. All the field work will be done by The Freshwater Trust, since we don’t have the staff or expertise in-house to undertake a project like that. The area where we can operate starts at River Mile 62, which is 62 miles upstream from where the Rogue discharges to the ocean, and extends about 100 miles upstream from that point to our location.
In addition, we can do work on about 300 miles of tributaries to the Rogue, although these offer a much lower kilocalorie yield. We’re going to look at the highest-yield areas first and try to work on those that give us the most kilocalories of mitigation per individual project.
TPO: How soon will work begin?
Baker: We’ve got approval from our city council and we have a contract signed with The Freshwater Trust. So now that we have our new NPDES permit, which was issued in mid-December, we’ll be able to get started.
TPO: How will this effort be paid for?
Baker: We’ll pay as we go. We have worked very diligently to avoid incurring debt, so our projects are solely based on the resources we have. Our rates are among the lowest in the state. We’re pretty frugal, and with a conservative financial approach we have been able to maintain a surplus of project money. So we’re able to do this without having to go out for bonds or loans.
TPO: Is there any precedent for this type of project in Oregon?
Baker: Clean Water Services, which takes care of Washington County, one of the state’s most populous areas, has done a program similar to this to meet their temperature requirements. We are the first agency in the state to do this with a partner and only the second agency (after Clean Water Services) to have a trading program. It’s a big trial for us and a big trial for The Freshwater Trust, which was the only organization that responded when we issued our request for proposals.
We have had a pretty good level of support and interest from the community at large. The program is looked on very favorably, in part because I think it does make sense, the landowners will receive improvements to their property with the clearing of invasive brush and the planting of native trees, plus a certain level of financial support for participating. So we feel we have a pretty good chance of getting this done.
