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At this critical time of reducing nutrient loading to the Bay, Maryland continuously seeks economical ways to protect our environment. Spray irrigation of treated wastewater onto land surfaces is one of the alternatives for wastewater disposal. With this alternative comes several benefits, such as purifying the wastewater through soil and crops and reuse and recycling of the water and nutrients. While wastewater moves through the soil profile, advanced wastewater treatment also takes place. Treatment mechanisms such as soil filtration of solids and microorganisms, soil adsorption of trace elements and crop uptake of nutrients remove pollutants from wastewater prior to entering the groundwater system.
Crop uptake of nutrients (nitrogen and phosphorus) reduces their input to ground and surface waters. A spray irrigation system is comparable to a nutrient removal process installed in an advanced wastewater treatment plant. It reduces nitrogen load to surface water and ultimately the Chesapeake Bay. Crop removal of nitrogen varies with season of year and type of crop. According to the publication EPA Land Treatment of Municipal Wastewater, nitrogen uptake rates vary for selected crops, ranging from"
- Cotton: 67 pounds per acre/per year
- Coastal Bermuda grass: 600 pounds per acre/per year,
- Corn: 170 pounds per acre/per year.
For a system irrigating an annual average rate of 2 inches per week of treated wastewater onto a cornfield, wastewater must be pretreated to 8 milligrams per liter of nitrogen for the corn to remove the remaining nitrogen in the wastewater. A storage pond is required for a spray irrigation system to store wastewater during rainy days and any freezing period. Irrigation in the winter season is feasible if the ground is not frozen and the spray field is planted with cover crops. Irrigation rates in the winter should be lower since the nitrogen uptake rate is low. In the summer, irrigation rates can be as high as 4-5 inches per week to meet the crop consumptive demand depending on crop type.
There are a total of 33 existing spray irrigation systems in Maryland: 9 systems on golf courses and 24 systems on agricultural irrigation of crops or grass. Spray irrigation systems can be installed in wooded areas, open fields or farmland. Spray irrigation of treated wastewater is regulated under Annotated Code of Maryland § 9-303.1 and COMAR 26.08.02.09 and requires a State Groundwater Discharge Permit. For more regulatory information, visit
www.dsd.state.md.us.
Guidelines Available
Sites approved for spray irrigation must meet the soil and groundwater table requirements specified in the Maryland Department of the Environment Guidelines for Land Treatment of Municipal Wastewaters, which are available at
www.mde.state.md.us/programs/ResearchCenter/ ReportsandPublications/Documents/
www.mde.state.md.us/assets/document/MDE-WMA-001-Land-Treatment-Guidelines.pdf . Wastewater must be pretreated to meet effluent limitations prior to spray irrigation. To minimize aerosol effects caused by spray irrigation, two tiers of buffer zone requirements are applicable depending on effluent quality. Groundwater monitoring wells are required to be installed around the spray field to assess impact of spray irrigation on groundwater quality.
Impact of nitrogen to groundwater quality caused by spray irrigation must be evaluated thoroughly prior to system approval. This includes nitrogen balance evaluation to ensure no adverse impact to groundwater, surface water and the Chesapeake Bay. Spray irrigation is a viable alternative for wastewater disposal. The feasibility of a spray irrigation system is judged by land and soil characteristics. However, the merits of the system including water reuse, nutrient recycle to crops and nitrogen reduction to the Bay warrant a favorable consideration in evaluating wastewater treatment and disposal processes. In 2003, MDE amended its Guidelines for Land Treatment of Municipal Wastewaters. These Guidelines are posted on MDE’s website (www.mde.state.md.us/programs/ResearchCenter/ ReportsandPublications/Documents/
www.mde.state.md.us/assets/document/MDE-WMA-001-Land-Treatment-Guidelines.pdf) to expedite spray irrigation and other land treatment system implementation, where appropriate while safeguarding the integrity of surface and groundwater of the State. Spray irrigation plays an important role in enhancing nutrient reductions to the Bay and its tributaries.
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