The depth (cm) of wastewater applied and
peratures. Gamble et al. (1977) found that of 95
the concentration (mg/L) of NH4-N and
denitrifying isolates collected from diverse tem-
perate soils, 65 were capable of growth and activ-
NO3-N are listed for each simulation cycle.
ity at 4C, and 10 were capable of growth at 41C.
The output obtained from the model included:
Most evidence indicates that, as a result of the di-
The predicted NO3-N concentrations for the
verse genera of bacteria involved, denitrifying or-
entire profile to a depth of 150 cm at 2-cm
ganisms have adapted to a wide range of tempera-
increments;
tures. Consequently, essentially all soils subjected
The amount of groundwater outflow dur-
to a range of temperatures demonstrate denitrifi-
ing the cycle (cm); and
cation activity over that range.
The amount of NO3-N leached below the un-
saturated zone.
The concentration of N entering groundwater from
the soil profile can be calculated from the water
METHODS
outflow and the amount of NO3-N leached. Since
the model output uses a 1000-cm2 area, the mean
CRREL assisted the Philadelphia District of the
Corps of Engineers by providing WASTEN simu-
concentration of N in water entering the saturated
lations for conditions appropriate for a proposed
zone is:
treatment facility at Fort Dix. Both short-term and
(
)
total N leached (mg N) 1000cm3
long-term steady-state simulations were run.
mg N
=
.
(
)
total water outflow (cm) area 1000cm2 L
L
Initial short-term simulations
Results
Input
Initially two simulations were run. Simulation
The initial WASTEN simulations were based on
1 (App. B) represented 21 cm of 4 mg NO3-N/L
conservative input data estimates, representing
applied once, with the output listed every day for
worse-than-expected conditions:
four days following application. The mean con-
The soil depth from the surface to the water
centration of the output N was 0.97 mg N/L, which
table was set at 150 cm (4 ft).
included and was "diluted" with the water initially
The soil was assumed to have three layers
in the profile. At day 4 the NO3-N "bulge" is at
within the profile.
approximately 35 cm. Also, the average total out-
The soil-water characteristics for the simu-
put, about 0.097 mg N/L, is less than the initial N
lation were described using an equation de-
concentration in the profile (0.1 mg N/L). That is,
veloped by Green and Corey (1971), and the
the leading edge of the incoming wastewater is
coefficients used were from Windsor sandy
being denitrified sufficiently so that it dilutes the
loam soil, B horizon, which has physical pro-
already low N concentrations in the profile.
perties similar to the soil at the Fort Dix site.
Simulation 2 (App. C) represented 21 cm of 4
The plant uptake and evapotranspiration
mg NO3-N/L water applied daily for four consecu-
were set to zero.
tive days, with the output given daily. This simu-
The loading rate for nitrogen was based on
lates repeated applications of all the wastewater
4 mg NO3-N/L in wastewater and approxi-
on half the total acreage. Following the fourth day
mately 21 cm of wastewater applied per
of N application, the output was continued for
cycle. This application was determined from
several more days of leaching. The final output
the 5.6 million gallons/day (mgd) on a 25-
estimated the NO3-N concentrations in the lower
acre surface.
profile to be 1.105 mg N/L, and the mean cumula-
The initial conditions for the soil profile were
tive N concentration entering the groundwater was
(a) saturation throughout to provide maxi-
predicted to be 1.6 mg N/L.
mal NO3-N transport rates, and (b) negli-
gible NO3-N and NH4-N concentrations.
Long-term steady-state simulations
Denitrification was based on first-order ki-
netics and moisture content. The relatively
Input
conservative denitrification rate used was
0.01 hr1. Since no NHx-N was applied, ni-
Based on the results of the first two simulations,
further model simulations were conducted to pro-
trification rates are not active in this simula-
vide insight into longer-term effects of land treat-
tion.
5
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