A 3.75-million-gallon manure biodigester was built without several crucial pollution prevention features, any one of which would have prevented a nearly 400,000-gallon spill in November and a smaller breach in January, a newly released report shows.
Operators of the Clear Horizons facility near Waunakee are meeting next week with Wisconsin Department of Natural Resources officials who cited the company with five violations of state water pollution laws.
The DNR and company officials said Wednesday that they couldn’t immediately explain why contractors and engineers for the Milwaukee-based Clear Horizons and state engineers approved plans without the safety features.
“Prior to this happening, we had no idea we were at risk, so shame on us for that,” said Clear Horizons chief executive officer Jim Ditter. “It’s not like we made a consistent decision that we were going to save $10 to take on all these risks. It’s a mechanical plant and you are going to have things that will break.”
The report by the Brookfield engineering company Applied Technologies recommends relatively simple changes in pipe fittings, alarm systems and shutoff valves that could have been installed when the $12 million plant was built in 2010.
Report details flaws
Biodigesters generate electricity and remove excess phosphorus from manure before it is spread on farm fields as fertilizer.
Reducing the phosphorus level is important because farm runoff is a major cause of the unnatural tangles of foul smelling algae and weeds that mar Madison’s chain of lakes.
Both spills at the Clear Horizons plant started when a short section of above-ground pipe burst. The first spill was much larger because it happened at night when no workers were on duty, allowing sludge to spew for 6½ hours and spread more than a mile over ground and through ditches that eventually drain into Lake Mendota. The second spill released only 22,000 gallons because employees were on duty and stopped it within minutes.
But the consulting company report indicates there are better ways to prevent spills that could harm water quality. The consultants found that Clear Horizons engineers and company contractors:
• Neglected to install flexible pipe sections designed to bend very slightly instead of breaking when pumps cause adjoining lines to vibrate or when connected underground pipe moves because the soil shifted.
• Failed to document whether soil was compacted sufficiently during construction or that mechanical devices were installed to prevent underground pipes from shifting and breaking connected pipes above the ground — even after finding in early 2013 that another below-ground line had become misaligned.
• Didn’t install sensors, alarms and automatic shutoff valves that would have greatly reduced spillage from the pipe failures.
• Set existing sensors so that they didn’t sound alarms even when a digester tank lost one-third of its load.
• Never equipped stormwater drains with a shutoff valve to prevent a spill from sluicing outside of the containment berms.
Ditter said it isn’t a high priority to determine why the safety measures were omitted. “Our focus has really been on implementing changes to make sure we can prevent this from happening in the future,” he said. After the second spill, he said, the company installed flexible pipe in the place where both spills originated and in nine other potentially vulnerable junctures.
Each piece costs $650. The company has indicated it planned to follow the consultant’s other recommendations, but on Wednesday Ditter said adding alarms and automatic shutoff valves could prove costly. Changing the stormwater system could mean a burdensome state approval process, he said.
Other problems cited
The DNR cited the company for the spills and also alleged that it has at times failed to remove enough phosphorus from manure before it is spread on farm fields, bypassed the phosphorus removal system and filed reports late, said Mark Cain, a wastewater engineer for the agency who helps write the rules, issue permits and oversee cleanups.
Ditter said he was disappointed in the citations because the company has cooperated with the DNR from the beginning, even going back to construction of the plant.
Dane County Executive Joe Parisi wants to be sure adequate alarm systems are placed at the biodigester to prevent another large spill, said chief of staff Josh Wescott.
Wescott and others emphasized that the biodigester has removed far more phosphorus from the watershed than the small amount that in November entered Six Mile Creek, which empties into Lake Mendota.
The consultant’s report and an attached narrative written by Clear Horizons disclosed that the spill was 380,000 gallons, nearly 30 percent more volume than the 300,000 gallons the company reported to the public previously.