7 Del. Admin. Code § 7103-77.0
Current through Reigster Vol. 28, No. 6, December 1, 2024
Section 7103-77.0 - Distribution Systems and Construction77.1 General 77.1.1 The Department recommends Section 15 of the USDA Soil Conservation Service National Engineering Handbook" and the 1983 publication Irrigation by the Irrigation Association as references for the design of slow rate wastewater distribution systems. Also recommended are material and installation standards of the American Society of Agricultural Engineers. Note that these publications were written for the design of supplemental irrigation systems. herefore not all material contained in these publications will be appropriate for systems intended to treat wastewater through spray irrigation.77.1.2 Spray field pressure variation due to friction loss and static head for solid set, uniformly spaced systems should not exceed plus or minus 10 percent of the design spray nozzle pressure. If this criterion cannot be met, sprinkler head spacing and spray nozzle diameters should be adjusted or flow control valves be used to insure a uniform application depth. The use of pressure reducing or throttling valves to balance the distribution system should be avoided.77.1.3 The use of secondary mist nozzles on impact sprinklers is not recommended. These nozzles tend to cause more frequent sprinkler freeze-up in winter.77.2 Access, Flow Measurement, and Controls 77.2.1 The layout of spray fields and spray field roads should provide easy access for inspection and maintenance of the distribution system. Spray field access roads must be designed for all-weather use. Steep grades must be avoided. Irrigation on access roads is prohibited.77.2.2 A flow recorder, in conjunction with chart recorder and totalizer, is required on the discharge of each irrigation pump station to measure the total volume of wastewater applied to the spray fields. If an automated system is chosen, it must include use of chart recorders to monitor system operation. Influent flow monitoring devices may be required for domestic facilities in order to evaluate treatment facility performance.77.2.3 A low pressure detection system to automatically shut down irrigation pumps in the event of force main, submain or lateral blowout is required. A high pressure shut-off at the irrigation pump station should also be provided.77.3 Freeze Protection 77.3.1 The Department requires that above ground piping systems drain when depressurized. Pipe drains shall discharge either to the spray fields or to the storage pond(s) and must not produce a runoff.77.4 Construction Disturbance, System Start-up and Testing 77.4.1 Construction activities associated with distribution systems can greatly alter the infiltration rate of spray field soils. Construction disturbance within spray fields must be minimized.Excessive compaction of surface soils by construction equipment must be avoided.Regrading of pipeline trenches must match original contours.Subsidence of trench backfill must be repaired, as this promotes channelization of runoff and erosion.77.4.2 In forested systems, it is necessary to grub only the pipe centerline. Excessive clearing and grubbing should be avoided. Clearing for above ground piping systems should involve only vegetation that will interfere with operation of the system. All areas disturbed by construction must be revegetated immediately. Sloped areas may require protection from erosion.77.4.3 "The Manual for Erosion and Sediment Control in Delaware" published by the Division of Soil and Water Conservation should be used as a guide for erosion and sediment control during construction of slow rate land treatment systems.77.4.4 Pressure testing of the irrigation force mains and laterals shall be conducted during installation to avoid damage to spray fields from reexcavation and repair. Extensive flushing is usually necessary to clear distribution system pipes of construction debris which will clog sprinkler nozzles. Care should be exercised to prevent erosion or flooding of the spray fields during pipeline flushing. Every effort should be made to keep trash and debris out of the distribution systems. Sprinklers and drain valves shall be checked for proper operation prior to installation.77.4.5 Bare soil resulting from construction can tolerate only short periods of wastewater application before producing runoff. Irrigation of bare soil compacts the soil surface, reduces the infiltration rate, promotes erosion, and hinders the establishment of vegetation. In addition, the treatment capacity of bare soil is poor. Wastewater irrigation on bare soil is not allowed beyond what is necessary to establish a vegetative cover. Wastewater application at the design rate can begin only when a uniform vegetative cover has been established. Specifications for spray field construction must include a revegetation performance standard and this standard must be enforced.77.4.6 The Department recommends that spray fields be constructed early in the project so a vegetative cover can be reestablished on disturbed areas before wastewater irrigation begins. Potable, ground or surface water may be used for distribution system testing and irrigation to establish vegetation. At least one growing season may be necessary before newly constructed spray fields can accept the design wastewater loading. This start-up period must be considered in the design and operation of slow rate land treatment systems.7 Del. Admin. Code § 7103-77.0