Livestock waste management requires sizing, design, construction and management of the appropriate facilities. These guidelines specifically address the construction requirements and procedures for the liquids storage facility. Although many of these guidelines also apply to solids storage facilities, they are not specifically addressed herein. The Idaho Waste Management Guidelines for Confined Feeding Operations (IWMG) is the main source of information for the sizing and design of livestock waste facilities. The University of Idaho Cooperative Extension System (U of I), USDA Natural Resources Conservation Service (NRCS) (NRCS) and Idaho State Department of Agriculture (ISDA) are available to assist with planning and designing livestock waste containment facilities.
The primary requirements for construction of the waste storage pond are that it must be sealed to prevent contamination of the ground water and must not allow a surface discharge. Many different materials may be used for the construction of the liquid waste containment facility, including soil, synthetic liners, concrete, asphalt, steel, plastic and fiberglass.
During construction of sites one acre or larger, operators are required to obtain authorization to discharge stormwater under an NPDES construction stormwater permit from the EPA.
Initial cost, site construction constraints, and long term maintenance are all important criteria to consider before choosing a construction material. The advantages and disadvantages of each material type are discussed below, however, it is important to remember that the best option may be a combination of materials, such as a concrete bottom with earthen side.
The existing onsite soil or imported soil may be used to construct the storage facility if it meets the requirements of SNTC-716 (Revision 1), Design and Construction Guidelines for Considering Seepage from Agricultural Waste Storage Ponds and Treatment Lagoons, prepared by NRCS. Specifically, the soil must have a 15% or higher clay content and 20-100% passing the #200 sieve. Alternatively, the in-place soil specific discharge may be lab tested to meet 1x10-5 cm/sec or 0.34 in/day. If the existing onsite soil meets this criteria, an earthen lagoon is typically the most economical solution initially. However, the annual cleaning and maintenance of this type of facility is a disadvantage. Earthen ponds must be constructed 2 ft. above highest ground water level, rock or gravel which may be a limiting factor at some sites.
Figure 1: Completed Earthen Lagoon in N. Idaho (Photo by Les Boian)
These liners include PVC, polyethylene and rubber products which are used as an impermeable barrier for the construction of the storage pond. Most of these products require a well prepared soil layer below the liner and a cover of at least 6" of soil or gravel. These materials are expensive to install (typ. $0.40 to $1.20 per square foot). Synthetic liners are also very fragile, increasing the annual cleaning and long term maintenance costs. Synthetic liners should be located a minimum 6" above highest ground water level, rock or gravel.
Concrete containment facilities can consist of precast tanks (similar to septic tanks), concrete/asphalt lined ponds and above ground concrete vaults. Facilities constructed of reinforced concrete are the longest lasting and have the lowest maintenance costs of all systems. The primary disadvantage of concrete storage facilities is the initial cost. Asphalt lined ponds are slightly cheaper than concrete lined ponds, however, they require a greater attention to detail during the preliminary construction phases. Concrete/asphalt ponds may be located slightly below the ground water level but because of possible "floating", an engineer should review the project prior to construction.
Steel, plastic, fiberglass and other manufactured containment facilities are available, typically in the vertical silo configuration. The operation and maintenance of these types of facilities is the primary advantage, with the high initial cost being the main disadvantage.