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Predicting Ground-Water Nitrate-Nitrogen Impacts by Norman N.Hantache'and E.John F'innemisrc° Abatratel The buildup ofnitraln in upper ground-water,cost=is.polrnlladcumulative effect ofon-aii sewage disposal pr actices which k not addressed by standard siting and dare criteria.I hrnlurc concerning the contribution and fair of nitrogen bennth seplic lank disposal fields is nykwrd.From these findings,ron—kni.simplified methods an dr-eloped for tattmaling long-term pound-water nitrale Increases on an area-wide bask,The methods are presented in•ma—useful lir englneen,Planers,and ngulalory agencies for routine—duailion of misting and pnMused land developments and for design of tarp,common disposal systerm.Typical sluthms are shown graphically to illustrate the relative importance of tubus Wines,including developneal demMy,rainfall recharge,and soil denitrife.tion.Predicted n Wes are compared with sid-]monitoring data for three C'.lifomis cominunitin verify ify tht e reasorublevi ,of the soggrslyd reetSe—tilracl,Se—til poesdble regulatory applications are+uggasted. Introduction have worked to develop rmdelmes and rnh•t is In impuve The use of on-sue whsudace sewage duposal ya=m, on-ate sewage disposal p,a—'1 he aim hm bun m mmi- inpanicularsepbetantdigsonad(Ids,hos long leen recug- mac potential health and water quality probknu associated nined m one of the oust effective means of dealing with with the siting,design,ron5iru lion,and mmnlena a of domestic waste-woo problems to rural settings.Many soils such systems The main concent as the proleetion of water have a high capacity to ac'apt,filter,and assimilate sewage ,.ppli.and general public health from the standpoint of effluent.Nw,in sparsely populated arras,the availabtltly d bacterial contamination and desease aammusion.Prwec- Ingeamounuofopen land tendsbominimuepoasible*ata lion of ground-watcl quaiuY.for example,u aehicwd by quality or public health cdduos associated with such sewage requiring a specified vertical separation distantt between disposal praaiees.Icon n now,however,a growing Vend the dup ial system and the highest expected rose of the to make permanent lax of on-site sy+tems for large-soak water ubk.This provides an unsaturated it one wherein urban fringe,rural resdentud.and recreational develop- high degrees of physical,biological,and chemical treatment mens Small,unuwered cummunincs are also tending occur.Surf—waten an similarly protected by the esub. n w mannmse more and more and coue with the uof I.Men of lateral tieback nyuirortcnu. septic tanks ruler than embarking on major sewerage con- An important water quality issue that p--ly hat struction proyacts. not been arktmsed in guidelines and ngula0om o that of During the past several yeast.water quality and public the persistent or increasing dleet of large numben of sys- health agencies and researchers throughout the country tema:n concentrated areas.For example,many subctmnecs contained in sewage arc soluble and may stow-niativcly unaffected through the sod lir acwmulate in underlying pound ton=s nr drseharge to adlaan wrfue wsam Also, -- under certain conditions,the total volume of selvage du. 'Questa E.pracri-I Cwporatwn, 122n Roickyvd Cove charged from many systems nuY all=Local pound-water Rod.Susie 92o6,Rihmonil.Cahf.-.Wail. le-Istothe pant nfeff-unglhc prformunceofutdivdual 'Depart rmm o1 C-1 Fna:ocrong.Sam.Clan l:nwenny psysicros or the degree of treatment prorvded by the sol Soma t Crrrnia 9 o system IFmnenwre and H-1—he.1983 Recenld Anl 19911,.rn'iseJ Slplemllen 1991,xupted d' Setsumlwo 1991. The buildup of nitrate in ground water is pnentiahy Doc.—or..nand Jams..1,190 one of the most significant lung-term cnnsequenees of on. 490 Vol.10.No.i GROUND WAI F'R July August 1992