 Introduction
Most people living in rural areas of Manitoba rely on groundwater as their primary
source of water. To protect and preserve the quality of below-ground water sources, it is
important that agricultural producers operate in a responsible manner as stewards not only
of the land but also of the water under the land.
What is Groundwater?
Groundwater is defined as "all water below the
surface of the ground." This
includes water found in the unsaturated zone above the water table and water in the
saturated zone beneath the water table. Rain or snow melt enters the subsurface in
recharge areas, then migrates to discharge areas where it comes out of the ground as
springs or seepage or is used by plants.
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Groundwater in the saturated zone can be found in aquifers or
aquitards. An aquifer is an area of sand, gravel or bedrock that can provide sufficient
water to wells or springs to supply at least a single family dwelling.
In contrast,
groundwater can move only very slowly through aquitards. The heavy clay (gumbo) found in
the Red River valley is a good example of an aquitard.
The rate of groundwater movement is generally slow except in coarse sand, sand and
gravel, or bedrock aquifers which contain fractures, such as the Carbonate Rock aquifer.
Because of the very slow rate of water movement through aquitards, they protect
underlying aquifers from surface contaminants. |
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Protecting Groundwater
Livestock operations produce either liquid or solid manure. Manure contains nutrients,
salts and micro-organisms so it is important to protect groundwater from being impacted by
seepage from areas where manure is stored or applied to fields.
The following are potential seepage sources:
- manure storage structures;
- solid manure piles;
- outdoor pens or exercise areas;
- runoff retention ponds; and
- fields where manure is applied.
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Manure
Storage Structures
Where possible, manure storage structures should be located in areas that are underlain
by thick deposits of clay materials. Since the rate of water movement through these
materials is very slow, they provide natural protection for underlying aquifers. In other
areas, earthen manure storage structures must be adequately lined with compacted clay
and/or synthetic liners to reduce or eliminate seepage. Additional protection can be
provided by installing a collection system that will intercept seepage and return it to
the storage structure. In some locations groundwater monitoring may also be required by
Manitoba Conservation under the permitting process. Above-ground steel or concrete
structures are other options. |
Provincial regulations require a permit for construction, modification or expansion of
any manure storage structure. The permitting process requires test drilling at the site to
evaluate geological conditions, and appropriate engineering design. Manitoba Conservation
conducts site inspections during construction to ensure the storage structure is properly
built. Livestock producers are responsible for regular inspections and maintenance to
ensure the integrity of their storage facility. Manitoba Conservation also carries out an
annual inspection program.
Storage of Solid Manure
Solid manure should be stored in areas where thick clay deposits overlie any aquifers.
Solid manure should not be stored in areas underlain by coarse sand, sand and gravel or
shallow bedrock aquifers. In sensitive groundwater areas, solid manure piles should be
stored on a concrete pad or other impermeable base. A properly constructed retention pond
may be required to gather runoff for later land application.
Locations where solid manure is temporarily stored in the field prior to spreading
should be rotated annually, with crops allowed to grow at older sites to utilize nutrients
left in the soil.
Outdoor
Pens and Exercise
Areas
Outdoor areas where livestock are confined in high densities should be located where
the subsurface contains a considerable thickness of clay materials overlying any aquifer.
Areas where the subsurface materials consist of sand, sand and gravel, or where bedrock
aquifers are found close to ground surface, should be avoided.
Producers who propose to construct certain types of confined
areas such as feedlots that are capable of housing 300 or more
animal units, must obtain a permit from Manitoba Conservation
before construction begins.
To minimize seepage, pens should be sloped to promote runoff. Runoff should be directed
to a properly constructed runoff retention pond or area with deep-rooted grasses or
legumes. As well, the use of bedding materials should be maximized, and annual cleaning of
the pens should be carried out. In sensitive groundwater areas, compacted clay or
artificial liners should be installed beneath pens. |
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Land Application of
Manure
Liquid or solid manure and runoff from pens or storage sites for solid manure must be
applied to fields as a fertilizer. The rate of application must not exceed the crop’s
requirement for nitrogen.
Particular caution must be exercised in sandy soils and areas with shallow bedrock
aquifers. In these areas, leaching to the water table may occur quite rapidly.
To minimize the potential for groundwater impacts in these areas, operators should:
- sample the soil beyond 60 cm (2 feet) to determine if rapid downward movement of
nutrients is occurring below the root zone;
- apply manure in the spring or summer rather than fall, and avoid manure applications
prior to expected significant rainfall;
- develop and follow an appropriate manure management plan.
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Summary
Livestock operations are a potential source of groundwater contamination. The risk of
impacts on potable groundwater supplies can be minimized by:
- locating manure structures, outdoor pens and field manure storage in areas underlain by
thick clay materials
- minimizing the duration of field manure storage before spreading
- applying manure at proper agronomic rates as a fertilizer with due consideration for
crop requirements, soil texture and sensitivity of underlying aquifers.
Other titles in the series: "Living with Livestock Production" are
available from Manitoba Agriculture, Food and Rural Initiatives
offices.
- Health Issues and Livestock Production
- Livestock Odours - Sources, Concerns & Solutions
- Surface Water Issues
- Nitrates in Soil and Water
- Land Application of Manure
- Siting Livestock Production Operations
- Understanding Anti-Microbial Resistance
- Food Safety on the Farm
- Livestock Operations and Groundwater Quality
- Livestock Pathogens- A Natural Occurrence
- Managing Livestock Mortalities
- Livestock Manure Storage
- Confinement of Livestock
- Phosphorus in Soil and Water
More detailed information can be found on the Internet at www.gov.mb.ca/agriculture/livestock. Copies of
the Farm Practices Guidelines for Hog Producers in Manitoba and Poultry
Producers are available from Manitoba Agriculture,
Food and Rural Initiatives offices in rural
Manitoba and from Agriculture Publications at 8th Floor, 401 York Avenue, Winnipeg MB
R3C 0P8 (FAX: 204-948-2498)
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