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Planning for IRSIS or Small Flow-SIS

Slow Rate Application Technology

Total Nitrogen Removal via Shallow Soil Processes

Introduction

After years of use in Pennsylvania, Individual Residence Spray Irrigation Systems were codified for permitting by local agency Sewage Enforcement Officers. Loading is extremely light in comparison with Large Volume Spray Irrigation Systems. Total nitrogen uptake by Large Volume Spray Irrigation Systems from plant nutrient uptake, crop harvesting, and removal from the spray area is well documented. Failure to remove the crop will eventually result in pollution of the groundwater beneath the spray field. The crop in this case is the grass clippings.

With Large Volume Spray Irrigation Systems spraying in adverse conditions such as during rainstorms and while the ground is frozen can lead to surface runoff of the effluent. By spraying lightly over a relatively large area the IRSIS is allowed to spray during these periods.

Turf managers recommend fertilization at levels that create the greenest, healthiest lawns. Studies indicate there is over-fertilization of suburban lawns.

Calculations indicate that the two smallest IRSIS spray field sizes for a three-bedroom home, 10,000 ft² and 15,000 ft², would experience some breakthrough of effluent over 10 mg/L to the groundwater during the winter. A spray field of 20,000 ft² should not experience any breakthrough of effluent with nitrogen over 10 mg/l even during the winter months. Leaching of nitrogen stored in the soil column to the groundwater may still continue.

A minimum 15,000 ft² spray field is required for a three-bedroom home to insure nitrogen removal unless soil and slope criteria as listed in Chapter 73, Section 73.16 (e) require a larger spray field.

The most common source of nitrogen is years of over application of manure, fertilizer, and sewage sludge. Studies have shown that bacteria will act upon easy sources of nitrogen (chemical fertilizers) first and save harder to breakdown sources (manure, plant roots, leaf litter, grass clippings or other plant debris) for later. As increasing amounts of nitrogen accumulate as more complex organic-nitrogen materials, more time (years or decades) is required to flush the nitrogen from the soil.

Specific planning requirements for using individual or small flow spray irrigation for nitrogen removal:

Normal planning requirements for the use of an IRSIS system. That is, feasibility for placement of the system.

See Section 73.163 for restrictions on the placement of spray fields, and construction requirements.

See Section 73.14(b) for soil testing requirements.

See Section 73.13(d) for minimum isolation distances.

Determine that the spray field area is a minimum of 15,000 ft² or larger if soil and slope conditions warrant. See Section 73.16(e) and Table B.

Replacement area is not required.

A revision for new land development, adopted by the municipality, is required. An exception to the requirement to revise the official plan for new land development (Section 71.55) may not be used.

A request from the applicant to require the use of denitrification units rather than conducting a preliminary or detailed hydrogeologic study.

The narrative should state that the proposed revision includes the required use of a spray irrigation system for removal of nitrogen.

A note on the final subdivision plan that will be recorded that all of the proposed lots are required to be served by a spray irrigation system for the removal of nitrogen.

A note on the final subdivision plan that all grass cuttings or other acceptable cover crops will be removed from the spray field and disposed of off site.

At no time will the spray field have commercial nitrogen fertilizer, lawn fertilizer, lawn service solutions, manure, sludge, plant debris, mushroom compost, or other nitrogen containing material placed upon it.

The spray field will not contain clover, legumes or nitrogen fixing plants.

All manure or stores of fertilizers will be stored or piled a minimum of 50 feet and downhill from the spray field. No transport of manure or fertilizer materials will occur across the spray field.

A signed three-party agreement assuring proper operation and maintenance of the system. The requirements of Section 73.167 should be included. The agreement should also include assurances that the applicant will remove grass clippings for off-site disposal and that the municipality will inspect the site to make sure that the grass clippings or other acceptable cover crops will be removed from the spray field. The municipality will keep inspection records, which will be available to the DEP on request.

An acknowledgement that an application for a spray system permit will be made to the DEP by the lot owner or designated chartered association or trust.

With the exception of spray field sizing as described above, the design of the system and spray field shall, as a minimum, meet the criteria in Chapter 73 for an individual residence spray irrigation system.

Systems sized up to 2000 gallons per day may be considered if the documented strength of the influent is characteristic of residential sewage. The spray field size shall be sized proportionately per EDU.

No reduction in spray field area may be considered.

The applicant must agree to allow the DEP to require or install sampling equipment in addition to the normal sampling required for an IRSIS. Suction lysimeters may be installed during the construction of the system. The DEP must be informed of the proposed start of construction at least one week in advance.

(Information Courtesy of the Pennsylvania Department of Environmental Protection)

32 Mount Joy Street - P.O. Box 128 - Mount Joy, PA 17552-0128 - (717) 653-5308

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Last Updated: 10/10/2008