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AUG- 9-99 MON 9:37 AM 7-H TECHNICAL SVC GRP FAX NO, 5302732290 P, 4 Drip irrigation systems(also known as Drip system emitters are designed toto groundwater.(Refer to page 6 for a list -trickle"systems)are another efficient ensure that the wastewater is always of some advantages and disadrarrrages of and proven technology many small con' released at the same slow rate at atmos- subsurface drip systems.) munities can chose to recycle and dispose pheric pressure,even though the water of wastewater.Drip irrigation technology pressure inside the tubes can range from 5 1 0MV SySISM D98%n Elements using treated wastewater is used in Israel to 70 pounds per square inch(psi)during As with spray irrigation systems,waste- and throughout the world as a way to con- a dosing cycle.However,most systems water must p pretreated priorrotect public hes[t drip serve Water resources.These systems are engineered to maintain relatively con- irriation to pgh and the require less water than spray systems to sistent pressure inside the tubes.usually environment and to prevent systems from irrigate plants.and the technology has been about 20 psi.The pressure-compensating clogging-Settleable and floatable solids are used for more than 30 years for various feature of emitters allows drip irrigation removed by primary treatment,which may agricultural and landscape applications. lines to be installed at different elevations take place in a community treatment plant at a site while maintaining uniform flow. or lagoon or on individual home lots in a Because subsurface drip systems release septic tank or home aerobic treatment unit. Subsurface Drip Systemswastewater below-ground directly to plant Ptimary treatment always is followed by Deliver Effluent to Plant RaotS roots,they irrigate more efficiently`and'Y- filtration in a particle-size filter to protect With drip s sterns.treated wastewater is have advantages different from those of the tubing from clogging- applied to soil slowly and uniformly from surface irrigation systems.For example. In most systems.effluent flows to a tank a network of narrow'tubing(0.5-to 0.75- the soil surface tends to stay dry.which or pump chamber equipped with controls. inch diameter[.usually plastic or polyeth- means there is less water lost to evapora- where it is stored until a predetermined ylene,placed either on the ground surface tion and there is almost no opportunity for dosing volume is reached.All drip systems or below ground at shallow depths of 6 to the wastewater to come in contact with are equipped with a filtration system before 12 inches in the plant root zone.The plant foliage,humans.or animals,Also. the distribution system,such as a series of wastewater is pumped through the tubes percolation losses are reduced because the disc filters or mesh screen filter membranes. under pressure.but drips out slowly from wastewater is applied to a wide area of to remove small suspended solid materials a series of evenly-spaced openings.The soil at a slow rate directly to plant roots. from the wastewater that can clog tubes openings may be simple holes or,as is In addition,in drip systems the waste- and emitters.Sortie systems also include the case in most subsurface systems.they water is delivered to the most biologically a disinfection step to protect public health. may be fitted with turbulent flow or Pres- active part of the soil.which enhances The U.S.Environmental Protection sure-compensating emitter devices.These treatment and minimizes the possibility of Agency approves the use of the chemical emitter design,are proprietary and vary groundwater contamination.The constant trifluralin to prevent root intrusion into depending on the manufacturer of the moisture in the to zone also may emitters.although some states may not permit it. One manufacturer of drip system system.(The graphic below is meant increase the availability of nutrients to rrier to to illustrate a generic subsurface drip plants.reducing the delivery of nitrogen Bing incorporates root ion directly into the ltuhing mate- tube design.) tial itself-However,the consistently wet conditions in the soil and the pressure Example drip tubing :--'�"l compensating emitter design discourages root growth into the distribution lines. -�--'" The distribution system in subsurface drip systems usually includes a mainline. submain,and narrow drip laterals with emitters.The total length of drip tubing will depend on the restrictiveness of the i site.the area needing irrigation,and the amount of storage space available.The latcrals normally are installed in narrow (approximately 10 centimeters trenches(app y _} '•} wide)dug with a vibratory plow.Because k" :1?tL9t!x '`a�iA` r:FP't t- ;'?•'{:�.?.�.";'!J- w.- v,4j^yR, of the flexibility of the laterals and their shallow placement,drip lines can be laid oe ! around trees and other topographic features •*D z• with little disturbance to the site. o•e .n: •.�`<r, ` • � rontirrrrcd on pu,Sc•b National Small Flows Clearinghouse 1-800.824 8301 Winter 1999;Vol.10,No.1