Manure Management to Protect Water
by Matthew A. Culp and Greg D. Fuhrmann
|Source: Iowa State University Extension
Methods of raising livestock in Iowa have changed dramatically in recent years.
Today, increasing numbers of livestock are raised in concentrated populations within
confined environments (see maps above). These operations produce large volumes of
manure that are temporarily stored in nearby earthen lagoons or basins (aerial image,
below) until applied to farmland as a nutrient source. As a result of this trend in
livestock production, animal confinement operators are now required to submit a Manure
Management Plan to the Iowa Department of Natural Resources (DNR) for approval.
Each plan estimates the volume of manure generated at a particular facility, and proposes
how and where the manure will be applied to agricultural land.
|Storage of manure in lagoons adjoining large, confined-animal feeding
operations, and subsequent application of manure to the land, are environmental concerns
in geologically vulnerable areas of the state. (Simulated photo image)
The concentrated populations of livestock, the large volumes of stored manure, and the
application of manure to farmland have increased concerns for safeguarding Iowa's water
resources from the chemical nutrients and pathogens found in animal manure. These
include nitrate, ammonia, and fecal bacteria. Environmental concerns involve the
potential for excessive seepage of these contaminants from the lagoons and basins in
geologically vulnerable areas. The same concerns apply to excessive concentrations
of manure being applied to the land. Geologic vulnerability occurs where porous
earth materials allow fluids and water-borne contaminants to move into an aquifer,
potentially affecting private and public water wells in the area. Contaminants can
also drain into a nearby stream or river. To address these potential contamination
problems, site assessments are conducted by the DNR. Geologists review the known
hydrologic and geologic conditions at each permitted manure storage structure, as well as
the geologic deposits underlying the areas identified for manure application.
A vital tool used for these assessments is Geographic Information System (GIS) technology.
State-of-the-art computer applications utilize a wide range of geologic and
cultural data layered together in map form, which allows for comparison and analysis at
any location. Bringing together accurate, up-to-date information from numerous data
sources is an efficient and effective method for evaluating a sites potential for
To conduct a site assessment for a proposed (or existing) manure storage structure, or for
land designated for manure application, requires compilation of the sites GIS
"coverages." This is done by combining layers of data such as rivers,
state highways, and urban area outlines. Information is initially compiled at a
county-wide scale, and later the viewer can "zoom in" on the smaller geographic
area of interest.
Once common geographic reference features are compiled into a base map, other relevant
data layers, such as sinkholes and public and private wells, are added until the final
site coverage is constructed (see map below). Using this site coverage, an
assessment can be made on groundwater vulnerability, and on whether other environmentally
sensitive areas are located near the manure storage structure or the land application area
|GIS MAP OF THE DECORAH AREA (Winneshiek County)
Used to Evaluate Groundwater Protection
|Horizontal map distance = 24 miles
Groundwater vulnerability is determined by several factors that can be evaluated using
GIS technology. One important variable is the type and depth of groundwater aquifers
that underlie a site. There are several types of aquifers in Iowa, and one or more
could be present beneath a proposed manure storage structure or manure application area.
Two of the most vulnerable geologic settings in Iowa are alluvial and shallow
bedrock aquifers. Alluvial aquifers are composed of porous sand and gravel deposits
that occur at or near the lands surface along streams and rivers. They are
particularly vulnerable to seepage or spills from manure storage structures, or from
land-applied manure because they have little if any natural protection.
Other aquifers that are particularly vulnerable are shallow bedrock aquifers, which are
found in several counties in northeast Iowa and at scattered locations elsewhere in the
state. These aquifers are composed of fractured limestone and dolomite, carbonate
rocks that are subject to dissolution by infiltrating groundwater. Associated
sinkholes and springs seen at the land surface are vivid expressions of their shallow,
fractured, and easily infiltrated nature. Like alluvial aquifers, shallow bedrock
aquifers have little or no protection from surface contaminant sources.
The vulnerability of Iowas deeper bedrock or buried alluvial aquifers is dependent
on the type and thickness of glacial age materials that overlie them. These glacial
materials may be sand, gravel, silt, or pebbly clay, and their horizontal and vertical
distribution varies greatly across the state. Understanding the porosity and
thickness of these materials is essential to assessing how well protected an underlying
aquifer might be.
Another significant factor in evaluating a site involves the location, type, and depth of
any nearby drinking water wells that tap a specific aquifer. Physical
characteristics of these wells will determine the potential risk to human health posed by
a proposed manure management site. Ecologically sensitive areas can also be
identified on a site coverage. These may include communities of threatened, rare, or
endangered plant or animal species, as well as state and county parks and preserves.
Based on the information found during the site assessment process, recommendations are
made regarding needed modifications to the Manure Management Plan, the general suitability
of a site for placement of a manure storage structure, or use of the land for manure
application. his process is designed to protect Iowas valuable water resources
through the application of knowledge derived from on-going geologic research in the state.
Adapted from Iowa Geology 1999, Iowa Department of Natural