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cvalernz of close cormspo.1—between actual..it pe- puate.However.even in such cases,the vesical recharge
<br /> dieted values confirms the validity of this method for esti- from wear water and rainfall will tend to acumulMe and
<br /> mating the ama-wde nitrate effects on ground water from rcmaus in a layer at the water table,largely unaffected by
<br /> onsite sewage disposal systems. lateral inflow.This a due to the slow venical mixing that
<br /> With rapal to the upgradient group of wells for ocounm horizontal ground-water flow.Uscofthe methods
<br /> ll"ood-Los Osis,one would expect the nurale•mfrogen in this paper will protect against nitrate-nitrogen concenin-
<br /> noicertralion to be considerably less than that predicted by tions in such upper layer,exceeding safe limits
<br /> equation(1),because these wells arc not afleeted by the 2.Th,nllrate-nitrogemm�nlrmionspredictMbythe
<br /> ma)oriiyof thedevelopment in thcstudy area.This is brnror netbods of this paper are long-term values. Font,the
<br /> our by the results in Table 1 and Figure%,which show that development of an area to its ultimate density and wutc-
<br /> the mean nitrate-nitrogen concentration in the upgradient water loading rates may take many yeas.Second,deperd-
<br /> well%is 43 percent of that Dhvrwd in the downgradsmi Ing upon the thickness and nature of the unsaturated zone,
<br /> wells the travel time of effluent to the water table could vary from
<br /> days to yeas.I•mally,where the vesical recharge of waste
<br /> DbeUulon water and rainfall adds to ground water in dap aquifers
<br /> having little lateral flow,deep mixing will be a long-term
<br /> Fa,-tors to be considered when using]be simplified process.Such deep mixing could he caused by deep pump-
<br /> mass balance method presented in this paper include the ing wells,leakage to even deeper aquifen,and ground-water
<br /> fo0owing: nuill".
<br /> 1.The metbod oicorporates only the vertical compo- 3 The predictive equations are intended to he used to
<br /> rent o(ground-water recharge,ignoring anydilu(ion effects evaluate average,arca-wide ground-water conditions.Thcq
<br /> of lateral ground-water inflow from opgradiem areas.From do not yield result%(hat can be applied to a single point,such
<br /> a planning and regulatory perspective,this is an appto- as,might he required for siting or protecting an individual
<br /> priale,conservative(wont cmc)approach.One most con- well.1 his would entail a more detailed analytic of the areal
<br /> sdcr that the nitrate-nitrogen concrntrations in pound and veztocal distribution of nitrate-nitrogen in the ground
<br /> water inflow from upgradoem areas may also iricrease over water
<br /> time to response to waste-water loading or other land ise a.The amplified methods here do nee explicitly amount
<br /> aclnstier in those areas,thus making u miaMc any esti- for other identifiable sources of nitrate-nitrogen,such as
<br /> mates of the degree of diluntm due to lateral ground-water animal wastes and feruluci appleatin—I uveatoek wages
<br /> inflow.In circum tan,%where lateral ground-warer inflow contain very high kvcls of nitrogen which may he a vignifi-
<br /> isdetermmedtobesignificant and can beassigned areliable cant contributor to ground-wafer nitrate-niungeneoreen-
<br /> couslanllong-teen nitrate-nlrogen concem,anun,then the tr inim,depending upon livestock densities.soilcondiraons,
<br /> use of a mass balance model which includes such a lateral and waste handling practices.Wastes produced by a single
<br /> flow component,a g.,Webrmann(19113),muy be appro- horselot example.contain twice as much nitrogen 2 that
<br /> It..a typical household.psis potential source should be
<br /> added to the mus balance analysis when considering areas
<br /> where significant livestock populations exist or can le
<br /> expected within the development area.
<br /> - — Lawn fertihzen contribute much less nitrate-nitrogen
<br /> is .a.ra..n � than do livestock.For typical residential subdivisions and
<br /> ruralcommunities,a m,—,bk usump.n I,","about 10
<br /> R percent of the gross area is landscaped with turf that h
<br /> r• ' Issifugc
<br /> tad.The mtron fertr ¢hrcr u (owe
<br /> r ll-bepl lawns is
<br /> i °•...a s`• n•sa estimated by nurtefia to he about 30 to 65 lbs per year per
<br /> e :°•::•,• ••�• z%I acre of turf. Typically.50 to 75 percent of the applied
<br /> �.•s. t_____ _ __ •.-�f—=r—. nitrogen can la expected In be cwwwted by plant uptake
<br /> and wit c1cmirifeation(WI'CF.19901 The resultant load
<br /> Ing to ground water is fen approximalcly in the range of I
<br /> to 311%s per Year per developed acre.For an assumed r.nfaf
<br /> _ recharge rate of 12 iMhcs.'year, the rdunam nitrite-
<br /> a, ..aa a+. - 1 91 mgnsgenw nrrariom OomtlwkachingolYmilser would
<br /> .. n+r c.,.os+r:.r,.s•. be about 0.37 to 1.1 mg!1 In the%implied methods of the
<br /> paper, 6 considered tulle substantially accounted for in
<br /> o...«ass+.—.aaraa, •c..°..« the usumplrun of a background nitrate nitrogen corimmurt.
<br /> •..r...............„ a«,•,•,+„^••• non.to 510 l 0mgrl Where substantial petmm of t he srtc
<br /> �i,..... o.• •”" _ are devoted to turf.special aeeuuntitg may teed to be made
<br /> c:: «.°° °" vw«•� for fertilizer nitrate-miroWn contributions.Mass balance
<br /> Iia t.c—p.risoo or swl.rrd padicted rourvo M-w. models by Tinker(1991)and the Center for Environmental
<br /> concem'.6—M ground at. Research(1965)incorporate a turf fertilizer component.
<br /> 497
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<br /> C�L.NC
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