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-,...tdy estimating the quantity of recharge wal—is — ckarlyevident,partowlarly incases of higher nitrogen lual- �•� r..,awa s.a mg and lower denitrification rates. _ • c .n In Figure 2,the critical minimum gross acreage per lot. A.is plotted against the annual talc of rainfall recharge.R. 2 for a select.l range of values for n.and d,with na=1.0 mg;'I as before.In this instance she long-term waste-water 7 I"I",W.is assumed equal to ISO gal;day per DU,on the - basu of an average egpccted occupancy ofthme persons per _ - residence and SO gal;personlday.[be U.S.EPA(19W),nr- _ - a5 galMay as the typical per capita flow for residential dwellings.The influence of climate and the water belacs nis Y seen to he significant,panicularl-v for lower ranges of R.i.e., .. drier limates Thus,in desert area,very large lots may be rteoosary. e • u u s u w In typical new developrtrenu of single family resi- dences,practical lot sirs limits exist because of minimum Fig.2.tell uenre of effluent q.atity,deaitdriouji n,and nlnhll space requirements for lite development,disposal fields, nrharge on Mtlra]lot is., roadways,open spas,etc.These limit%maybe on the order of 0.25 to 1.0 gross acre%per dwelling unit,depending on local codes and specific development plans. As men io - Figure 2,such practical or+tamn.y hmds may often be more stringent than the critic%)minimum gross acreage per - -- lot,A,determined From equation(2). Ibis is particularly - n Irur av R salute increase. Case Study Examples r It,dealt—rate and lest their validity,the preceding methods for assessiryl nitrate impacts wen cntnpared against the acloj ground-water quality data for three cote. %a." California communities.All three ofthese commumtres rely vasa o on individual on-site systems for—age disposal In each caseground-water eomammationby nitrates hu hecuducti - ti maned by extensive monitoring programs.Ibe three com- umtrn reviewed here as cue stsdv examples are:I I)the j "mars Mesa area in Marin County.(2)the Chico area in •avw000- J oaoa Rune County;and(J)the Ba)wod-1.n(lens%sea in San o, - pr• , J Luis Obispo County(5gue J) , Oesafpffon of Study Mesa The general physical characteristics of the three study ••• •^ °•• areas arc summarved in-fable 1.Background on the study ides is dueu%W below. Fig.J.I.—Ists,of llun Fav study romm.nirir,i.caWoleW Table 1.hA*a ChaneduitYs M M CM Seedy Areas c'hwxrerwa Aodrae Mane am Chico nee _ Asy.o.dfIns Ow IaMlorm Masfea(oras Valley flea Coastal dope f upogsaphy 0005% O to 2% 3'o 5% S,ol. Seedy Inas pad Sandy Fran+ Loamy ..it. ur47 do?g— and..it I,rah to g,—.d water(11) lead, 15 so 20 15 to 10 Avenge'archil(-.:yl 30.9 22.5 20.0 Burrawd rainl.11—targe lot'VI) 14.4 169 12.0__ S_-fee less - — Wf