Locating enough suitable land may make irrigating treated wastewater difficult for some communities. Adverse soil conditions, topography, and land use can increase the land area needed to irrigate wastewater to ensure the protection of public health and the environment.
Three land ownership arrangements are typical of irrigation systems: 1) the wastewater treatment authority purchases and manages the land used for irrigation; 2) the wastewater treatment authority purchases the land and leases it to farmers; 3) the wastewater treatment authority contracts with land owners to provide irrigation as a long-term management plan.
Very low soil permeabilities dramatically affect the amount of land needed for a wastewater reuse system. Soil surveys developed for each of Ohio's counties provide an estimate of the soil permeabilities at a potential reuse site. If more detail is needed, field evaluations can be conducted by certified soil scientists.
Excess soil water limits the amount of additional water that can be applied through wastewater irrigation. Subsurface drainage systems are needed to remove excess soil water from agricultural fields in Ohio. A subsurface drainage system may also help minimize runoff and erosion, wet conditions in the plant root zone, or unfavorable field working conditions in the spring and autumn.
A useful tool for evaluating the impact of subsurface drainage systems is the computer model DRAINMOD. This model estimates the drainage system design requirements necessary to obtain the optimal irrigation frequency for the proposed site. The model simultaneously provides information on irrigation and storm events that produce runoff, allowing the designer to put runoff control measures in place.
Over the years, operator training and experience has been directed toward mechanical treatment plants with stream discharge. Operating a wastewater treatment/irrigation system requires specialized operator skills.
Provisions for adverse conditions can sometimes add to the cost and complexity of a treatment/irrigation system. A variety of options need to be considered for winter conditions, including storage through winter months, protection from freezing and draindown for winter operation, or treatment for permitted stream discharge during the winter months.
Irrigation system components, such as irrigation pipe, emitters, and pumps, are an added expense to a wastewater treatment system. These added costs need to be accounted for when measuring cost savings that result from reduced treatment requirements for irrigated wastewater.