62-610.625. Design Influences

(1) Due to the objective of overland flow systems, the design will provide for runoff of applied effluents, and limited infiltration. Most suited to this type of system are areas with soils of relatively low infiltration and vertical hydraulic conductivity with an acquitard in the soil profile.

(2) A continuous acquitard (natural or artificial) shall be present in the unconsolidated medium under the proposed land application site such that effluent percolating through the soil system above the acquitard is under operational control (for further treatment if necessary). Operational control exists when the percolate flows to the surface drainage system (as opposed to vertical leakage through the aquitard or lateral movement beyond the influence of the drain system).

(a) The confining zone shall be present at relatively shallow depths; shall have a representative hydraulic conductivity no greater than 10% of the average hydraulic conductivity of the unconsolidated medium overlying the acquitard; and shall be of such permeability and thickness to provide reasonable assurance that downward percolation of waters will be minimized.

(b) The permittee shall establish the number of soil samples required to determine representative hydraulic conductivity values and to affirmatively demonstrate that a natural acquitard is continuous at a particular site. Samples shall be distributed throughout the project site. An estimate of sample size required shall be determined through statistical techniques which, based on the size and variance of an initial number of partially-distributed samples, predict the minimum number of samples required to assure that the population and sample means are within a 95 percent confidence interval.

(c) Other methods (e.g., geophysical techniques) to establish the extent and continuity of a natural acquitard shall be approved by the Department upon justification by the permittee.

(3) Design land surface slopes, slope lengths, and detention times required for the system will be governed by preapplication treatment levels and by final effluent limitations required as a result of receiving water conditions. Land surface slopes of 2-8 percent shall be applicable, with slope lengths of 100-300 feet involved.

(4) A maximum annual average hydraulic loading rate of seven inches (or 4.4 GAL/FT2) per week as applied to the entire area receiving overland flow is required. Rates higher than seven inches per week shall be accepted where rates are substantiated in the engineering report on the basis of the renovative ability of the system or other considerations and demonstration that Department rules will be met. Application cycles of wetting and drying the system shall be developed so as to maintain the presence and activity of microorganisms on the soil surface and shall be described in the engineering report.

Rulemaking Authority 403.051, 403.061, 403.087 FS. Law Implemented 403.021, 403.051, 403.061, 403.062, 403.085, 403.086, 403.087, 403.088 FS. History–New 4-4-89, Formerly 17-610.625, Amended 1-9-96.