Editor’s note: This commentary is by Jeff Wennberg, who is commissioner of the City of Rutland Department of Public Works.
[L]ake Champlain International has adopted an agenda to address the issue of “combined sewer overflows.” While this is commendable, LCI has not fairly represented the facts. If policymakers react to LCI’s hyperbole serious harm to Vermont’s waters may result.
Combined sewer overflows (CSOs) happen when sewer systems that carry both stormwater and wastewater are overwhelmed by rainfall events. Because the capacity of collection systems and treatment plants are limited, too much stormwater can back up in the system and surface on streets and into buildings. To prevent this from happening CSO structures within the collection system allow the excess water to bypass the treatment plant and release it directly to receiving waters.
There are multiple ways to minimize and control CSOs, but the only way to eliminate them is to separate all the sewers so that wastewater and stormwater do not use the same pipes.
But combined sewer systems also capture and treat large volumes of urban stormwater runoff, protecting streams from untreated runoff from roads, parking lots, roofs and other impervious surfaces. Collecting and treating stormwater in this fashion is the most effective means known to protect water quality. Put another way, if the combined sewers were separated and all CSOs were stopped, streams would receive dramatically more pollution than is currently the case – even with the CSOs.
In any CSO the vast majority of the reported overflow volume is stormwater, which would be released to receiving waters without treatment (or public notice) if the sewers were not combined. Only a fraction of the volume is wastewater. And even when a CSO is underway, a much greater volume of stormwater is treated at the wastewater treatment plant than is released without treatment.
The state reporting system requires utilities to report the total volume of the overflow, not just the wastewater portion. Separated storm sewer systems are not required to report stormwater discharge volumes, even though the environmental impact is essentially the same.
The state reporting system treats every CSO outfall as a separate event. So a community with a single outfall will report one event and a community with four outfalls will report four events for the same storm. The city of Rutland has four outfalls, so the actual number of CSO storm events is about one-quarter the number reported to the state.
The state does not require actual monitoring or measurement of CSOs. The state allows “tell-tale blocks” – blocks of wood on a rope – as a CSO monitoring system. This approach requires utility workers to visually inspect the CSO structure to see if the block has moved after a rain event. Reporting to the state is required one hour after the CSO is “discovered,” so if the structure is not visually inspected no report is required. And when structures are inspected it is usually after the storm has passed, sometimes a day or more later. There is no way to measure the actual volume of a CSO with a tell-tale block.
Rutland has real-time telemetry at every CSO location, so if an overflow is underway utility workers are immediately alerted. These sensors track the overflow level and duration at five-minute intervals allowing a precise calculation of overflow duration and volume at each site. Rutland has over-complied with the statute and CSO notification rule from their beginning.
In a typical year, Rutland treats one billion gallons of wastewater and 500 million gallons of stormwater at the wastewater treatment plant, whose effluent is cleaner than the river into which it flows. The cost to separate Rutland’s combined sewers is estimated at $150 million which is beyond the ability of Rutland (and arguably the state of Vermont) to afford. But assuming the funding could be found, if 500 million gallons of stormwater was diverted from the treatment plant to the streams, phosphorus loading to Otter Creek and Lake Champlain would increase dramatically. Spending money we do not have to increase pollution makes no sense.
Sixty years ago wastewater treatment did not exist. Since then water quality has steadily improved and is generally better now than at any time in memory, with notable exceptions. No one has accomplished more in this regard than wastewater treatment engineers and operators. CSOs remain a challenge and need to be addressed but we will make the right decisions only if we understand the whole picture.
