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5369                                                     001R79102
                                      DESIGN EXAMPLE
                                     HIGH RATE SYSTEMS
                                        Prepared by

                                      Dr.  Al Wallace
                                    University of Idaho
                                       Moscow, Idaho
                                       Prepared for
                          Environmental Research Information Center
                                        Seminar on
                      Land Treatment of Municipal Wastewater Effluents
                                         June 1979
                          ENVIRONMENTAL RESEARCH INFORMATION CENTER
                            OFFICE OF RESEARCH AND DEVELOPMENT
                            U.S. ENVIRONMENTAL PROTECTION AGENCY
                                   CINCINNATI, OHIO  45268

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                  DESIGN EXAMPLE - HIGH RATE SYSTEMS


Introductory Note

     The input data for this example represent a composite of conditions

encountered during the preparation of several  facilities  plans.   Although

that makes the example somewhat artificial,  the intent is to touch as

many bases as possible in the demonstration  of the process of site selec-

tion and process design.  The site selection and design illustrated herein

closely parallels that for an actual system.



General Design Conditions

     The City of Jason has an existing trickling filter plant located

near the south city limits.  Effluent discharge is to a small stream which

flows south and discharges to the Rush River about one-half mile west of

the village of Belson.  The existing plant,  constructed in 1930, is grossly

overloaded and structurally, in rather bad shape.  In addition,  the draft

NPDES permit for continued discharge to the  stream  will  call for ammonia

limitations and dechlorination in addition to a high level of secondary

treatment.  As development is continuing in  areas south of the plant, it

has been decided to locate a new plant about 3 to 3 1/2 miles south of the

present plant site.

     Pertinent design data are listed below.

                                             1978            2000

Population                                   6,400           12',500
Average sewage flow                           1.54 mgd        3.0 mgd

Draft NPDES permit for discharge to the stream [period:  May 1 to Oct. 14 -
monthly averages.j               BQD _ 2Q mg/L            ^^  daW ,  *>

                                 SS  - 20 mg/L                    \>*.  7_
                              NH3-N  - 6 mg/L    150 Ib/d           

                              residual C12 - < .02 mg/L, combined

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            period:   Oct.  15 -  April  30.  -  monthly  averages
                       BOD - 30 mg/L
                       SS   - 30 mg/L
                  NH3-N -  10 mg/L,  250 Ib/d
                  residual CK  - <  .05 mg/L,  combined.
     Land treatment with eventual  recharge  of the  Rush  River is  seen  as  the
most cost-effective way of meeting  the effluent limitations  while meeting
the highly restrictive environmental  requirements  of the area and avoiding
heavy commitments of energy and chemicals.   In addition, slow-rate land
treatment options are not  acceptable  for two  reasons; the unavailability
of large enough tracts of  land  and  the very cold climate and short growing
season in the area.   For example, there are normally only 100 days between
the last and first 32F temperatures.
     There are, however, four sites,  shown  on figure 1, which are available
from local landowners and  which may be adequate for development  of a  high-
rate land treatment system.  Pertinent field  data  for a preliminary screen-
ing of these sites were gathered during the early stages of the  facilities
planning.

Si! te_ Screening Process
     Groundwater table elevations are highest in the area during late May
and through June and lowest from September through most of the winter.  By
installing 15 observation wells and utilizing 10 shallow private wells and
one public well, enough data were gathered to construct a rough water table
contour map for the period of maximum water table height.  The results are
shown on  figure 2.  The groundwater flow is seen to be generally south,
turning southeast at the  point where the valley necks down with a gradient
of from 4 to 5.5 ft. per  1000 ft.

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     A backhoe was used to dig several  pits  in  order to  inspect the  soil

profile on each site.   Then a series of double-ring  infiltrometer tests

were run to get a preliminary estimate  of the intake rates  of the soils

on each site.  Three depths in the profile at site 1 were tested, two

were tested on site 2 and only the surface soils were tested on sites 3

and 4.  The decisions concerning which  parts of each profile to test were

determined entirely by the preliminary  inspections.



                               Soils Data

Note:  All profiles are to approximately 12  ft.

A. Site 1

         0' - I1   Sand topsoil, some silt
         I1 - 4'   Sand, medium and clean
         4' - 12'  Gravelly sand, trace of silt, scattered  large
                   cobbles to 10 in.


         Infiltration Tests (2 in each  profile)
            Surface
            3'
            5'
 8.4,  12.1  in/h
15.0,  21.2  in/h
 6.6,   7.1  in/h
B.  Site 2
         0' - 1.5'   Sandy top soil, trace of clay
       1.5' - 4.5'   Gravelly sand, trace of clay
       4.5  - 5.5"   Gravelly, sandy clay
       5.5' - 8.0'   Sandy clay, appears dense
       8.0  -12.0    Sandy gravel, trace of clay

       Infiltration Tests (2 in each profile tested)

            Surface  :   6.2, 7.4 in/h
            6'       :   0.2, 0.6 in/h
C.  Site 3
       1.   East end
            O1 - 2.5'    Silty topsoil
          2.5' - 6.0'    Silty sand,  many 4 in.  cobbles
          6.0' -12.0'    Sand, trace of silt, many 4-10 in.  cobbles

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          Infiltration  Tests
               Surface:   1.1,  2.3  in/h

       2.   West end
            0'  - 2.0'   Sandy  silt  topsoil
          2.0'  - 3.5'   Silty  sand,  some  4  in.  cobbles
          3.5'  -12.0'   Silty  sand,  lots  of 4-6 in.  cobbles

           Infiltration Tests
                Surface:   2.8, 3.1  in/h
D.   Site 4
       1.  East end

            0'  - 2.0'
          2.0'  - 5.0'
          5.0'  -12.0'
Fine sand topsoil
Sand and gravel, poorly graded
Sandy gravel, many large 4-8 in.  cobbles
           Infiltration Tests
                Surface:  4.7,  4.7 in/h



           West end

            0'  - 2.0'   Sandy topsoil
          2.0'  - 4.5'   Sand gravel, some 4 in.  cobbles
          4.5'  -12.0'   Fine gravel and sand, poorly graded, large cobbles

           Infiltration Tests
                Surface:  5.9,  8.1 in/h
A.  Log


    Surface
                        Bel son Village Well  Data
                  Elev.
Bottom of grout pack
Top of gravel pack


Perforations
    3020-2995
                  3056
                  3054
                  3051
                  3036

                  3027

                  3020
 0' - 2'   Topsoil
 2' - 5'   Sand, trace of silt
 5' -20'   Gravelly fine sand,
            some silt

20' -66'   Gravel, sand
Water

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Pump suction pt.        _        3000
Bottom of bore hole                      2990  Hard  limestone
Bottom of casing
                                            v(,T
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B.  Production
     Tested at 400 gpm with 5.5 ft.  of drawdown.   Present pump produces
               175 gpm
     Based upon these preliminary data, sites 1  and 2 are dropped from
further consideration.   Site 1  was dropped because there is  no easy way
to ensure that the percolate would not impact the shallow village well which
completely penetrates the same  aquifer and is directly down-gradient from
the point of wastewater application.   Site 2 was dropped because of the
underlying layer of restricted  permeability which would create a perched
water table and a reduction in  the available zone of aeration.
     Between sites 3 and 4, site 3 is superior in many respects.  It has
finer grained surface soils, affording more renovation capacity; more depth
to the water table and is closer to the highway, requiring less access road
construction and decreasing the environmental impact of sewer construction
to the site.  On the other hand, its  percolate would discharge, at least in
part, to Slater creek which has a far smaller flow than Rush River.  This
site would also have a greater  visual impact from the highway.  Another
factor is price.  Site 3 is valued much higher than site 4 by their owner
due to its location near the highway, its fine stand of timber, and its
superior view should he choose  to develop it.
     Thus, even though site 4 is somewhat inferior to site 3 in some
respects, it is concluded that  additional planning should focus on this site.
This decision involved input from many quarters including the Jason and

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Belson city governments,  the county  commissioners,  the  state  environmental
agency, the EPA, the consulting firm and  the  landowner  (who also  owned
site 3).

Preliminary Design:   Site 4
     A.  Preapplication Treatment Considerations
              Something approaching, but  perhaps  not completely equivalent
         to, secondary treatment will  be  necessary  to ensure  that adequate
         levels of nitrification can be achieved.   In addition, it is
         desired to achieve the permit limitations  on fecal coliforms in
         the river without having to resort to continuous disinfection  and
         this result will be easier  to achieve as the level of "secondary"
         treatment is increased.  The two systems of preapplication treat-
         ment investigated were a three-cell  aerated lagoon  system and  an
         oxidation ditch.  The oxidation  ditch showed a slightly  higher
         cost than the aerated lagoon system and  would  also  prove to be
         harder to operate and have  a more troublesome  sludge disposal
         problem.  It was nevertheless recommended because of its smaller
         land requirement and ability to  produce  a warmer effluent during
         winter operation.  It was considered that the  heat balance across
         an infiltration basin might prove critical during the winter months.

     B.  Rapid  Infiltration Basin Sizing
              The surface soils which are not to be greatly disturbed during
         construction, represent the least permeable materials in the profile.
         In addition to the four tests already available, a total of ten
         more were run in these surface soils at random locations.  The geo-

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         metric mean value of all  14 infiltration  tests  was  found  as
         5.5 in/h.   A value of 5%  of this  figure,  equivalent to 0.55
         ft/d (200  ft/yr.) was selected as a reasonable  design figure.
         Thus, based on bottom area, about 17 acres  are  required.   This
         area will  be provided in  7 roughly equal  sized  basins, located
         at the east end of the site to avoid the  high groundwater table
         near the southwest corner.  With  access and flood protection
         dikes, the basins will occupy about 25 acres of the site. The
         oxidation  ditch, clarifiers and a storage pond  capable of holding
         three days flow will occupy about 8 acres.   This leaves roughly
         56 acres for future expansion of  the rapid  infiltration system, all
         on the west end of the site.  Future development of this  set-aside
         area will  require some attention  to interceptor drains around  the
         northwest  perimeter to divert some of the groundwater flow around,
         rather than under the site.  In addition, one or more lines  of  re-
         lief drains may be required under the site  to prevent mounding.
         These potential requirements can  be addressed much  more confidently
         after a few years of experience with the  system as  presently proposed
         and shown  as figure 3.

Design Check
     During the course of the planning and preliminary design, some additional
field work was performed at site 4.  In particular,  five more shallow wells
were installed to follow the groundwater table during a  full season of
fluctuation.  Well  locations are shown on  figure 4 which also shows ground-
water level contours during the period of  maximum  water table levels.  Table 1

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                                                                         11
gives the seasonal  depths to groundwater for the array of seven wells.


       Table 1.   Depth (ft.) to Groundwater at 7 Observation
                 Wells on Site 4.

                                              Well  No.
Week
4
4
2
4
2
2
3
Month
5
6
7
7
8
9
10
1
5.0
5.2
5.1
6.4
7.1
7.1
7.4
2
3.7
3.7
3.7
4.7
5.2
5.1
5.5
3
6.4
6.3
7.1
9.0
9.6
9.8
9.7
4
4.6
4.8
5.0
6.4
6.9
7.4
7.8
5
5.1
5.3
5.5
6.4
7.2
7.6
8.3
6
6.2
6.4
6.6
7.4
7.8
8.6
9.2
7
7.1
7.0
7.1
7.8
8.4
8.9
9.4
     Using the May water table depths and assuming design load conditions

on the site, some approximate calculations were performed to predict the

water table rise during the May-June period of operation.  The following

approximations and assumptions were used in making the mound growth

calculations using equation C-10 in the "Design Manual."

     1.  The infiltration area can be considered circular with an equiva-

         lent radius of 612 ft.

     2.  The "steady" application rate over the area is 0.34 ft.  per day.

     3.  The saturated depth over the barrier layer (limestone) is 30 ft.

         (estimated from stock watering well log).

     4.  The hydraulic conductivity is 760 ft/day (estimated from Belson

         Village well data).

     5.  The drainable voids average 0.3.

     6.  Average depth to water during June will be 5.7 ft. (average of

         observed levels in wells 4, 5, 6 and 7.)

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                                                            12
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                                                                         13
     The results of the calculations  are shown  on  figure  5  and  indicate
an almost certain mounding problem.   Thus,  a system of horizontal  drains
is indicated to ensure maintenance of a reasonable zone of  aeration.

Drainage Design
     To employ equation C-ll  of the "Design Manual" it is necessary to decide
how high you wish the maximum water table height to be.   Assuming  we  decide
to control  it to a depth of greater than 4.5 ft. and further,  that we de-
cide to install the drains in the water table,  at  a depth of 6  ft., we can
get the drain spacing by trial  and error.  Trial and error  is  necessary
only because of the correction which  must be made  to the  depth  from the
bottom of the drains to the impermeable layer.   See page  C-45  of the
"Design Manual" or references on drainage design.   In any event, a spacing
of 847 ft.  is computed as sufficient  to control  the water table depth.  This
could be accomplished with three lines of drains running  N-S and discharging
to a surface ditch which in turn discharges to  the Rush River.   Of course
this ditch  would have to be monitored when  the  drains were  flowing and
a NPDES permit written for this discharge.

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