CONVERSION TO A NO-DISCHARGE IRRIGATION SYSTEM FROM A DISCHARGING LAGOON SYSTEM
|Water Protection Program fact sheet||
|Division of Environmental Quality Acting Director: Steve Feeler||
The conditions and requirements for many Missouri State Operating Permits have changed in recent years, with new permit limits for ammonia and for E. coli bacteria. In addition, on Aug. 22, 2013, the U.S. Environmental Protection Agency finalized new water quality criteria for ammonia based on toxicity to mussels and gill-bearing snails. Missouri’s current ammonia criteria do not take these species into account, and it is anticipated that ammonia limits will become more stringent in the future. Further, the Missouri Use Designation Dataset (MUDD) was approved by the Missouri Clean Water Commission on Nov. 6, 2013, and became effective under state law Feb. 28, 2014. This dataset assigns designated uses to approximately 90,000 miles of previously unclassified waters. The effect of this designation is that many streams now have a presumed designated use for whole body contact recreation, which has a corresponding water quality standard for E. coli. So, if a facility does not currently have final permit limits for E. coli bacteria, the next issuance of the operating permit will most likely include them. Unfortunately, many discharging lagoon systems cannot meet the upcoming effluent limitations for ammonia or E. coli.
If a facility cannot meet the required final limits, their wastewater treatment system must be upgraded. This will likely include the requirement to submit an engineering report and obtain a construction permit for upgrades. While there are many alternatives that a facility may choose when upgrading their system, Missouri Regulation 10 CSR 20-6.010(4)(D) requires that the submitted engineering report include consideration of the feasibility of constructing and operating a facility which will have no discharge to waters of the state. One such consideration is to convert the lagoon to a no-discharge storage basin followed by the land application or irrigation of wastewater. One of the primary reasons for considering a no-discharge alternative is that existing standards, such as ammonia, may become more stringent or standards for new pollutants, such as phosphorous and nitrogen, could be adopted in light of new scientific data. Therefore, eliminating the discharge to waters of the state minimizes, if not eliminates, the need to further upgrade the facility for the foreseeable future.
While an irrigation system is recommended if feasible, there are several items a facility must be aware of when converting their discharging system to a no-discharge system. First and foremost, wastewater irrigation should be occurring whenever weather and soil conditions are suitable, while adhering to the application rates listed by the operating permit. These application events must occur during daylight hours unless a nighttime irrigation plan is approved by the department. The facility is still required to maintain the earthen storage basins in good operational condition, including mowing, removing any woody vegetation, sludge monitoring and removal, and maintaining any security features such as fences and gates. Rodents, such as muskrats, will need to be removed, and any damage sustained to the berms will need to be repaired as necessary. Also, the operational control monitoring requirements of Missouri regulation 10 CSR 20-9, where applicable, as well as any permit specific monitoring, including wastewater and soil sampling, could also be required.
An irrigation system must be properly operated to avoid damaging the equipment. Moreover, the operator will be required to periodically inspect the irrigation field for equipment malfunctions and to ensure that irrigated wastewater does not flow off the field. Any erosion in the field will need to be repaired, and the vegetation needs to be maintained (including harvesting and reseeding as necessary). Additionally, the irrigation equipment will need to be maintained. Winterization of the equipment should also be considered as irrigation is not typically allowed on frozen, snow covered, or saturated ground and any water left in piping and irrigation equipment could cause severe damage during freezing conditions. However, irrigation may continue as long as the weather permits, up to the design application rates listed in the operating permit.
When upgrading to a no-discharge system, the facility must obtain or create an operation and maintenance (O&M) manual. The operator must become familiar with the O&M manual and follow it. When unforeseen difficulties arise, it is recommended that the owner or operator communicate with the department as soon as possible and obtain assistance. Also, the storage basin must be adequately sized to store the design flow plus the wettest-year-in-10 rainfall minus evaporation for a design storage period. The minimum total days’ required storage period ranges from 120 days in northern Missouri to 60 days in southern Missouri. Additional storage provides for operational flexibility such as planting of the irrigation field. The effective storage volume of the basin is usually from the two-foot depth above the bottom to two feet below the top of the berm (assuming the lagoon has a one-foot safety volume below a one-foot-deep overflow spillway).
The facility must still be vigilant in maintaining and repairing their collection system, since any inflow and infiltration (I&I) flowing into the collection system will need to either be stored or irrigated. The city should have a regular program for periodic smoke testing and televising of sewer pipes, as well as visual inspection of manholes for any deterioration, cracks, or staining. The department offers a template for a collection-system maintenance and repair program. It is noted that this activity has an added cost for the facility regardless of the type of treatment system used.
It is to be noted that a no-discharge system is allowed to discharge in an emergency. Although these discharges are considered to be bypasses, they are authorized only when the facility can demonstrate that they received precipitation in excess of the wettest year in 10 during the previous 12 months or the design storage period, and/or in excess of the 25-year, 24-hour catastrophic storm event. They also must ensure that they have met the pump-down requirement (having pumped the storage basins down to the two-foot level) as required by the permit. However, the operating permit for the facility will likely require that the city sample when discharging. Discharging without documenting the emergency conditions noted above or without sampling, as required in the operating permit, would be a violation of the permit.
Depending on the type, size, and complexity previous treatment system and the type and size of the proposed no-discharge system, any facility thinking about converting to a no-discharge system must understand that these expectations may require more operation and maintenance time and expertise from the operator to ensure the functionality and longevity of the system.
Best Management Practices
Before a facility converts to a no-discharge land application system, there are several best management practices that should be considered. Many of these practices are required by regulation and/or by the subsequent operating permit issued to the city; others are optional.
The required practices include but are not limited to: 1) Wastewater shall be applied uniformly over the entire application area; 2) No irrigation on frozen, saturated, or snow covered ground; 3) Set-backs prohibiting irrigation within 300 feet of losing streams and sink holes, 300 feet from existing potable water supply, 150 feet of a dwelling or public use area, 100 feet from gaining, perennial or intermittent streams or their tributaries (a 35 foot vegetative buffer can be a compliance substitute), and 50 feet from a property line or public road; 4) Prohibition of public access during irrigation activities; 5) Prohibition of nighttime irrigation unless otherwise approved by the department; and 6) Wastewater irrigation shall not exceed agronomic rates (which are typically listed in the operating permit).
Some best management practices that are not necessarily required include but are not limited to: 1) Establishment of permanently vegetated buffers around water features or tile inlets, 2) Structural protection of tile inlets such as a cap or bucket, and 3) Construction of swales or terraces.
As mentioned earlier in this fact sheet, one main benefit of the conversion to a land application system is that the need to upgrade to meet new standards in the future is minimal. Other benefits include no longer being required to sample and analyze the effluent as the facility must be operated in a no-discharge manner. However, if a permittee must discharge (e.g. due to rainfall exceeding the chronic or catastrophic rainfall totals), they will still be required to sample on a daily basis unless otherwise prescribed by the department. One reason for sampling is to determine the extent of environmental damage being caused as well as to ascertain what mitigation efforts may be required. Sampling can also provide incentive for the city to properly operate and maintain their no-discharge system.
Another benefit is the salvage value of the land (if owned by the facility) and any potential profit from selling the harvest. Normally a hay crop is recommended, such as a tall fescue, Bermuda grass, or brome grass, as well as other mixtures including wheat and red clover. While it is also possible for land to be leased from a nearby farmer, it is important for the facility to maintain sufficient control over the irrigation process. Difficulty occurs when the farmer partner refuses to irrigate during certain times of the year, especially during pre-planting or pre-harvest activities.
See the following documents:
- Wastewater Irrigation Frequently Asked Questions--PUB2668
- Ammonia Criteria: New EPA Recommended Criteria, Fact Sheet--PUB2481
- Capacity, Management, Operations and Maintenance Plan Model Guidance--PUB2574
- Small Community Engineering Assistance Program--PUB2485
- Wastewater Engineering - Construction Permitting Manual for Facilities with a Design Flow of 22,500 gpd or Greater--PUB2445
- Missouri Clean Water Commission Regulation 10 CSR 20-6
- Missouri Clean Water Commission Regulation 10 CSR 20-8