PH control plan
With either the spreading or pickup operation, the contractor will monitor and control the pH of the slurry. The slurry pH should be below 12.5 and greater than 2.
When operations start, the contractor will test the pH at least once per hour to ensure it is within acceptable limits. The test equipment will be calibrated daily and approved by the engineer. Once the pH control plan is operational and producing consistent results, the testing frequency may be reduced to four tests per day.
The contractor shall log all test results and deliver a signed copy to the engineer weekly. At no time shall slurry containing a pH outside the above limits be deposited on the ground. The contractor shall determine the procedure to be used to maintain the slurry within the acceptable range. The engineer shall approve this procedure.
Best practices: A case study
In the 1980s, the Minnesota Department of Transportation allowed slurry to be deposited in roadside ditches and slopes. However, in the late 2000s contractors were required to vacuum all slurry and dispose it off site, adding significantly to project costs.
The goal was to control pollution, but because concrete slurry is very similar to the lime-treated water farmers use on crops the policy seemed unnecessary.
The Concrete Paving Association of Minnesota (CPAM) worked with state regulators for two to three years to alter the requirements. CPAM provided information from North Dakota State University, which had tested the slurry and its effects on the soils, as well as a California water quality study that reported no slurry-related impacts to groundwater. Procedures from other states were also presented.
After encountering an impasse, CPAM looked to state legislators for a ruling. During the process, Terry Kraemer, president of Diamond Surface Inc., Rogers, Minn., testified on behalf of the industry, outlining the best practices currently used throughout the nation. CPAM educated legislators on slurry and cited many studies that had been conducted on slurry management.
After weighing the facts, Minnesota’s legislature exempted slurry from being considered a regulated solid waste and therefore not subject to the same pollution controls. The new wording states that the definition of solid waste “does not include … concrete diamond grinding and saw slurry associated with the construction, improvement, or repair of a road when deposited on the road project site in a manner that is in compliance with best management practices and under rules of the agency.” Contractors could return to roadside disposal where conditions allow.
In response, Minnesota DOT developed the nation’s first best-practice guidelines for roadside disposal. Contractors may not dump slurry into fresh water and may treat the material to bring it within the correct pH range.
“This initiative has been very successful,” says CPAM Executive Director Matthew Zeller. “We spent a lot of time early in the process bringing legislators up to speed and making them familiar with the current research related to slurry disposal. We wanted to familiarize them with the slurry product and the disposal options that are available. The result now allows us to use slurry management methods that research has proven to be non-harmful to the environment while costing the DOTs, and ultimately the taxpayers, less for the project.”
By using IGGA’s best management procedures as a model, CPAM brought Minnesota’s slurry disposal procedures in line with those used throughout the nation.
“Unnecessary regulations add to project costs,” says IGGA executive director John Roberts. “Eliminating them in appropriate situations benefits agencies and taxpayers alike by reducing costs while providing a safe, smooth, and quiet roadway.”
For more information on best practices, visit here. To learn more about CGR, visit here.
Kari Moosmann is AEC senior editorial eirector, Constructive Communication Inc., Dublin, Ohio.