8/23/99

Contacts:
Stewart Melvin, agricultural engineering, research leader, (515) 294-1434
Mike Burkart, National Soil Tilth Laboratory, geology of sites, (515) 294-5809
William Simpkins, geology, geology of sites, (515) 294-7814
Jim Baker, agricultural engineering, soil analysis (515) 294-4025
Tom Glanville, agricultural engineering, seepage losses (515) 294-0463
Tom Richard, agricultural engineering, management of structures/history of site (515) 294-0465
Karen Bolluyt, Agriculture Information, (515) 294-3701

ISU STUDY OF EARTHEN WASTE-STORAGE STRUCTURES RELEASED

AMES, Iowa -- Most earthen waste-storage structures built in compliance with 1987 Iowa Department of Natural Resources (IDNR) regulations have seepage loss rates near or below the performance standards they were designed to meet, according to Iowa State University researchers.

The study was done in four parts: geological characterization of structure sites, surveys of the management of the structures and historical use of the sites, measurements of seepage, and soil analyses. Stewart Melvin, ISU agricultural engineer and research leader, said he believes this is the most extensive and comprehensive such study performed in the United States.

Project geologists characterized five major Iowa aquifers in terms of their vulnerability to contamination, and researchers analyzed the performance of earthen waste-storage structures within these areas, testing whether they met the 1987 IDNR seepage standard for agricultural wastes. This standard was the same as the standard required for municipal and industrial earthen structures. It permits a seepage rate of no more than 1/16th of an inch per day when structures are filled to a depth of 6 feet.

Melvin said the challenge of measuring very small seepage rates from an entire earthen structure was met when one team member developed a new procedure to measure water losses.

Melvin said that the team explored numerous ways to separate evaporation losses from total losses but could not do so. "The seepage losses we reported probably are slightly higher than actual seepage because evaporation losses weren't subtracted," he said.

Melvin added that most of the final measurements were taken at night, during low-wind conditions, with no rainfall and 95% humidity to minimize evaporation losses.

Statistical analyses of the research data yielded the following findings: Twelve of 28 sites had seepage rates below the 1987 IDNR standard; one had a higher rate than the standard and the remaining 15 sites were not significantly different than the standard.

"Our data indicate that most structures are meeting the standards to which they were built. We find that very encouraging," Melvin said.

Analyses of eight soil cores taken from outside each structure berm were compared with a background average obtained from soil cores taken away and upslope from each site. Elevated levels of ammonium and chloride in some soil cores (typically one or two per site) usually occurred in locations where historic uses of the land or more recent events such as spillage during manure handling might have influenced the measurements.

At four sites, elevated levels of ammonium were not associated with previous use of the land. At three of those sites, elevated levels were found in only one sample.

In other analyses, researchers noted little correlation between contaminant levels and seepage rates, and there was no difference in seepage rates from slurry pits, which hold undiluted manure, and lagoons.

"The majority of soil cores indicated no significant increase in contamination levels compared with background levels. There was some localized contamination but no evidence of general contamination," Melvin said.

The report also outlines management practices important to the maintenance of the structures. "We are emphasizing these practices in education and training programs," said Tom Richard, agricultural engineer who led the management portion of the study.

Recommendations from geologists on the project included that hydrogeologic criteria should be taken into account in siting the storage structures. For example, stream setbacks might vary depending on hydrologic and soil characteristics at a site.

The Iowa Legislature requested and funded the research. The report is available on the Internet at http://www.ag.iastate.edu/iaexp/reports/.

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