IATP Hog Report - Institute for Agriculture and Trade Policy

Section 3
Hog Factory Impacts on Groundwater
Groundwater Pollution
When earthen manure basins or lagoons are constructed, they are thickly
lined with clay, which, theoretically, provides a protective liner against
manure leaching from the lagoon into the soil or groundwater. In this case,
theory does not conform to reality. Groundwater pollution can occur when
manure leaks into the soils beneath and surrounding manure
lagoons. 24,25 , 26 Cracks in lagoon sidewalls develop when the lagoon has
been emptied for spreading. 27 The sidewalls are exposed to air and dry
out, forming cracks in the clay lining. As the lagoon fills, manure fills the
cracks and leaks into the surrounding medium before the manure seals
them. Pollutants travel through the soil to shallow groundwater tables. 28
Both soil and groundwater can be contaminated in this way. Repeated
emptying and refilling of the lagoon degrades the sidewalls over time so
that eventually the clay liners are no longer effective at preventing seepage.
In many cases, storage pits are constructed under barns and made of
concrete. Pits of concrete construction do not offer greater groundwater
protection automatically. 29 Joints leak and concrete cracks. If concrete is
laid in sand or gravel, leaking manure can migrate to water tables.
Particular specifications related to suitability of the soils and structural
reinforcement must be followed to prevent cracks in the concrete and
leakage. However, there are no rules requiring that these specifications be
used.
Overapplication of waste occurs because handling and transportation costs
are less when liquid wastes are applied near the waste source rather than
where nutrients are needed. Factory farms may have little or no associated
cropland, but must rely on neighboring farmers to apply the manure onto
their land.
Groundwater pollution can also occur when manure is spread or sprayed
onto land, particularly around abandoned, uncapped wells, or if heavily
incorporated into shallow or well-drained soils. 30 In karst areas, there is
not only danger of seepage, but there is danger that sinkholes will form
and swallow lagoons. (Karst refers to land that is underlain by limestone
or dolomite bedrock, where erosion has resulted in fissures, cracks,
sinkholes, caverns, and underground streams.) Areas with karst or faults
are extremely vulnerable to lagoon leaks because sinkholes and cracks are
preferential pathways through the soil to groundwater. 31
Scientists are learning that even seemingly invulnerable areas can be
vulnerable to groundwater pollution, however. In the Oklahoma
http://www.iatp.org/hogreport/sec3.html (4 of 23)2/27/2006 3:50:08 AM