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FACILITY PLAN
PHASE 1 REPORT
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SEPTEMBER 1976
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LOWER SOUTH PLATTE
FACILITY PLAN
PHASE I REPORT
for
Metropolitan Denver Sewage Disposal District No. 1
Prepared by
CH2M HILL, INC.
12000 East 47th Avenue
Denver, Colorado
September 1976 D9728.A0
CONTENTS
Page
SUMMARY i
INTRODUCTION 1
General 1
Planning Background and Considerations 2
Planning Area Description 3
EXISTING FACILITIES 7
Wastewater Treatment Plants 7
Pump Stations, Interceptors, and Force Main 10
POPULATION AND WASTEWATER FLOWS 15
Population Projections 15
Wastewater Flow Projections 15
EFFLUENT LIMITATIONS 19
Stream Classification 19
DRCOG Water Quality Management Plan 19
Proposed Effluent Qualities 22
ALTERNATIVE WASTEWATER MANAGEMENT SYSTEMS 25
EPA Guidelines 25
Development of Alternatives 28
EVALUATION OF ALTERNATIVES 37
Economic Considerations 39
Engineering Considerations 41
Implementation Considerations 45
Environmental Considerations 47
Miscellaneous Considerations 54
Alternative Comparison Summary 54
TABLES
Table Page
1 EXISTING WASTEWATER TREATMENT PLANTS 8
2 SUMMARY OF DESIGN VALUES FOR WASTEWATER FLOWS 16
3 STATE WATER QUALITY STANDARDS FOR B2 STREAM
CLASSIFICATION 20
4 PROPOSED EFFLUENT QUALITY FOR DISCHARGE
TO THE SOUTH PLATTE RIVER 23
5 DESCRIPTION OF ALTERNATIVES 32
6 SYSTEM COMPONENT DESCRIPTIONS 38
7 PRESENT WORTH COSTS OF ALTERNATIVES 37
8 PRESENT WORTH COSTS FOR SCREENED ALTERNATIVES 40
9 AVERAGE ANNUAL COSTS FOR SCREENED ALTERNATIVES 41
10 COMPARISON OF ALTERNATIVES 56
11 DESCRIPTION OF SCREENED ALTERNATIVES 57
FIGURES
Figure Page
1 PLANNING AREA MAP 5
2 LOWER SOUTH PLATTE BASIN 6
3 LOWER SOUTH PLATTE EXISTING FACILITIES 13
4 LOWER SOUTH PLATTE BASIN--
THORNTON/NORTH WASHINGTON INTERCEPTOR 14
5 LOWER SOUTH PLATTE BASIN SERVICE POPULATION 17
6 LOWER SOUTH PLATTE BASIN WASTEWATER
FLOW PROJECTION 18
7 PROPOSED FACILITIES LOCATIONS FOR
ALTERNATIVES 1 , 2, 3, 4, 7 AND 8 34
8 PROPOSED FACILITIES LOCATIONS FOR
ALTERNATIVES 5 AND 6 35
9 POSSIBLE FACILITIES LOCATIONS FOR
ALTERNATIVES 9, 10, 11, 12 AND 13 36
SUMMARY
Phase I of the Lower South Platte Basin Facility Plan includes study of
existing conditions and water quality requirements, development and evaluation
of alternative wastewater management systems, and the selection of the most
cost-effective alternative. The results of Phase I, up to the final alternative
selection, are presented in this report for review and comment by the public
and involved agencies. Phase II of the Facility Plan will be a predesign
study of the selected system.kOn the basis of the Lower South Platte Basin effluent limitations and projected _
wastewater flows t rouq the year 2000, 13 wastewer_ m ans ement alternatives,
' t were developed for consideration_ _The basic manasement concepts were�e_w.,
tr ment_ plants_;__new pu pstati
eaons, equalization_basi_ns, and land application
systems, including Infi:tration/perceil tion basins ancf high ate—f r T ati ri
Both regional anTlocarzed systems-were considered. The main components of
the 13 alternatives are outlined on Table 5, pages 32 and 33 in the text.
After a preliminary screening, based principally on a present worth cost
analysis, seven alternatives were identified as the more viable systems for
detailed comparison. A cost-effectiveness analysis was made of the screened
alternatives covering economic, engineering , implementation, environmental,
and other considerations. All the evaluation factors and the analysis
results are given on Table 10, page 56 of this report. The four alternatives
outline-d._bolo-w- ppear--,to=be--the_most1easi_ble at thistime. The different
areas mentioned are identified on Figure 2, page 6. Each alternative would
also include upgrading the existing plant treating the South Adams County
Water and Sanitation District flows and transporting the Upper Thornton and
North Washington Street Water and Sanitation District flows through the
i existing Thornton-North Washington Interceptor, Pump Station, and Force Main
to the Central Plant. These existing facilities are shown on Figure 3, page
{7{ 13.
kY
F. I R Alternative 14
New wastewater treatment plant (WWTP) in vicinity of 164th to treat
(,\ flows from Brighton; 1st, 2nd, and 3rd Creeks; and Lower Thornton.
f.. .\ Alternative 5
New WWTF in vicinity of 164th to treat flows from Brighton and 1st,
2nd, and 3rd Creeks.
New pump station in vicinity of 124th and new force main to the
Central Plant for flows from Lower Thornton.
/1j • Alternative 6
New WWTP in vicinity of 164th to treat flows from Brighton.
New pump station at 140th and new force main to the Central Plant
for flows from 1st, 2nd, and 3rd Creeks and Lower Thornton.
i
bc ■ Alternative 10
Infiltration/percolation basins approximately between 136th and
150th to treat flows from Brighton; 1st, 2nd, and 3rd Creeks; and
Lower Thornton.
All the alternatives were evaluated without the benefit of public or agency
input. The public involvement meetings and agency reviews may indicate that
some of the other alternatives should be reconsidered or perhaps new alternatives
should be evaluated.
Details of the existing facilities, all the proposed alternatives, and the
method used in the comparative evaluation are all described in this report.
Commentary from both the public and agencies affected by these wastewater
management systems will be solicited and will be an important part of the
final selection process. Interested parties, therefore, are encouraged to
4 read this Phase I report and to provide input that will aid in the spin --\
of a management plan that_wUJI best_meet the goals ofthe_va_rkous communities
within the Lower South Platte Basin and will minimize total resource commitments.
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LOWER SOUTH PLATTE FACILITY PLAN
PHASE 1 REPORT
INTRODUCTION
GENERAL
As defined by the Federal Water Pollution Control Act Amendments of 1972, a
Facility Plan is a document comprising text and maps that present a systematic
economic,en ineering a� nd environmental evaluation of feasible alternatives
tor was er treatment and dis_po. or given geograp, ica�at , The
wastewater management alternative finally selected must meet the required
effluent limitations, be cost effective, provide flexibility for future t
changes, be environmentally sound, and satisfy the personal and community, a *+ 3 6 pi
concerns oft eo hip ple affected. The facility planningeprocedure assures the
public and all levels of government that are "J
soundly made and take into consideration all relevant fa�tor_s. a -.
X11• The Facility Plan study scope includes the following activities: (lLinvesti- b*41 ✓
gation of existing conditions, j2_1. review of State and Federal water quality
l��` regulations, (development of alternative wastewater management systems,
�� (4) preliminary screening of the alternatives, 5Lcomparative examination of
Vv 01‘, tie remaining alternatives, (6�,gelection of one management system, and (7) a
,� detailed description of the selected alternative. The fac_iLi_t4;�i?nning,,,
process must also provid f_ar_early and continuous involveme.at_of e,.public
,U sum advertised public meetir�_s__a ackw er-e-ci-tizens ran_exprg,,ssJocaL
concerns, interests, and_.prerer es.
jOrjli
EPA regulations require that the planning period for evaluating various
wastewater management alternatives be 20 years from the date the system is
expected to be operational . In the case of the Lower South Platte Basin, the
earliest date for implementation of an alte 1 .
Therefore, the 20-year p arming period for the basin is through the year
2000. A different length planning period can be used if reasons for changing
the planning period are sufficiently documented.
The Facility Plan for the Lower South Platte Basin has been divided into two
phases. Phase I covers the study activities up through the selection of the
most cost-effective alternative, including a public involvement program.
Phase II is a predesign study of the selected alternative that refines the
costs, treatment methods, and other details.
This report presents the study results up through the comparative evaluation.
It is intended to provide all interested parties sufficient information for
—evaluating the alternatives and making meaningful commentary. It is designed
to be a handout for various public meetings to stimulate citizen input.
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r
PLANNING BACKGROUND AND CONSIDERATIONS
The Lower South Platte Basin was originally included in the Metro District's
service area as the Northeast Service Area in the April 1972 predesign study
for the Central Plant expansion. That study recommended that a plant be
constructed in the Lower South Platte Basin in the vicinity of Branter Gulch
(East 124th Avenue) and the South Platte River and that another study be
undertaken to investigate construction of this proposed plant in more detail .
As a result of this initial study, two additional studies of the Lower South
Platte Basin were undertaken by Metro to define the boundaries of the basin.
This study indicated that a plant in the general vicinity of 136th Avenue and
the South Platte River would be the optimum management plan. Meanwhile, the
Facility Plan requirements were instituted and the Region VIII EPA required
that the Lower South Platte Basin be studied under those guidelines. Hence,
the planning which was originally started in 1971 for this basin is now being
completed under the new EPA guidelines.
The majority of the wastewater from the metropolita ives
secondary treat nLar_th a a C.en.tr_a.l Plant, includinq its own on ary
treated flows and those from the Denver North_Side-P_Iant.s This wastewater
-s2 comes from four_basins=serveQ he_.D_yJstrict--Clear Creek Basin, Lower South
Pltte_gas.in,._Sand Creek_ Basin and CentraL Denver-B _asin. Figure 1 s-hows the
boundaries of these four basins and the locations of the Central and North
Side Plants. Facility Plans are presently underway for all but the Central
(7
,, ,/ ume
Denver Basin. Reports similar to this docnt have been prepared for tho
� Clear Creek and Sand Creek Facility Plans. For the purpose of this study,
all wastewater from the Central Denver Basin is assumed to flow by gravity to
both the Denver North Side and the Metro Central Plants for treatment and
discharge.
Varying amounts of wastewater flow to the Central Plant are associated with
the different alternative management systems being considered for the Clear
Creek, Lower South Platte, and Sand Creek Basins. The volume of wart ester
that will finally be conveyed to the Central Plant will depend on which of
th-e various combinations o wastewater mana ement alternatives for these
basins is im e ___ is in er-re ationship among_thebasinswiltaffea,
how large the_Central Plant expansion-wiU_bedw a� _ hat_pr-oporti.on oL the
tota
l flows treated_at- Cent-ra-I-P_la- t_i-s attnibu_tahle-to_each-basin.
Furthermore, the cost to each basin for treatment of its wastes at th-e_Centi l
Plant is-determined by__=&hazt_.propor_tion its flows are of the total Central
Punt flows.,_,For example, if the flows from all four basins are-treaYetl-at
the Central Plant, costs to exgan_d_the_pJantand to treat the wastes would be
proportionately absorbed b the fo_ur_bas-ins u_s,__thecosts to_the Lower
South Platte Basin would be lower than_ifjust its flows were purrs e_d to the
Central Plant and_ other_b ins_.built=.separate_plan_ts ortrea_tment facilities.
As iscussed in the "Evaluation of Alternatives" section later, the interaction
of the various Facility Plans is accounted for in the cost comparison of the
Lower South Platte Basin alternatives.
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PLANNING AREA DESCRIPTION
The major portion of the Lower South Platte planning area occupies the western
part of Adams County and lies generally northeast of metropolitan Denver.
The boundaries of the service area are for the most part based on drainag
basin hound riec with sp a adjustment to conform to the piiticai hni�ndariec
of present District member_triunicipaLities.
The Lower South Platte Basin boundaries and the nine subareas delineated in
this study to calculate wastewater flows are shown on Figure 2. Within the
basin's boundaries is the`South Adams County Water and Sanitation District
(SACW nl . This District is conducting its own Facility Plan and, therefore,
is not within the Facility Plan study area for the Lower South Platte Basin.
However, for planning purposes, wastewater management for the total basin is
considered in this study. Thus, the SACWSD flows and treatment alternatives
are included in the development of management alternatives for the Lower
South Platte Basin.
One change has been made from the boundaries defined in the earlier Lower
South Platte Basin studies. For the ongoing facility planning, the Upper
First Creek area is included in the Sand Creek Basin rather than the Lower
South Platte Basin for several reasons. First, the E. 56th Avenue Interceptor,
which now serves the Upper First Creek area, crosses the northern end of the
Sand Creek Basin and joins the Sand Creek Interceptor. This existing E. 56th
sewer has sufficient capacity to handle the projected wastewater flows through
the planning year of 2000. To process the flows as part of the Lower South
Platte Basin instead would require a new and expensive interceptor along
First Creek. Also, the City of Denver has annexed a portion of the area.
Thus, the area's sewerage system could logically become part of the City's
other collection facilities in the Sand Creek Basin. Later studies for
planning beyond year 2000 should again evaluate which basin should serve the
Upper First Creek area, depending on its growth and sewer capacity at that
time. The Upper First Creek service area is shown on Figure 2.
The rnjorrt of Ha h I nwer nut lattP Racin_� ejop c and is charac-
terized by irrigated cro�landact _Land and_feedl_ots R�cidential dPVPlnn-
men is - reo�m nantLx in the Cities ThorntQ_r1,,-.Jtrthglenn. Federal
eights, Commerce City_and Br_ig.lzton--1 st k u apment-is-generally-
If�ii ed fo the"Commer_ee City a '-ea-and also-the-North-Wash-i-ngtan StrPef IMP tAr
and Sanitation The topography topography of the basin can be described as gently undulating with the
elevation falling to the north along the South Platte River. The basin
experiences a semi-arid, continental-type climate with cold dry winters and
warm, relatively dry summers. It has low average precipitation and humidity
rates, being 14.2 inches and 39 percent, respectively, and pronounced variations
in diurnal and seasonal temperatures.
Surficial soil deposits consist mostly of alluvial material, aeolian deposits
and Castle Rock Conglomerate. The alluvial deposits are found mostly in the
flood plains of the South Platte River and the First, Second and Third Creeks
and are as much as 60 feet deep. Aeolian deposits cover most of the eastern
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two-thirds of the basin and range from 0 to 40 feet deep. The Castle Rock
Conglomerate is found largely in the western portion of the basin and can be
described as gray, brown, tan and green-gray shale, clay and siltstone with
occasional sandstone and conglomerate.
Ground water in the Lower South Platte service area is found in the Laramie-Fox
Hills Formation and the Denver-Arapahoe- Dawson Formation with the former
being the more significant source of ground water. Depth to ground water is
about 1, 000 to 1, 500 feet for the Laramie-Fox Hills Formation and within
approximately 100 feet for the Denver-Arapahoe-Dawson Formation.
The water quality of the Lower South Platte River is affected_b_y dicchargAs
from industrial a_nd m_unicipaLtreatmer_t lants and storm_water_rt_noff rat
UT"B-an and ag,ricultural__Lands_in_the_Den_v_e.�are_a__Itese form the major sour,
"—� �--o ppollution of_the South Platte River and its two major tributaries, Sand
I i Creek and Clear Creek_�Because individual Facility Plans ��ii1 e � eted
for the Sand and Clear Creek Basins, water quality_ga_besg_s_zaa,5Jetall not
be discussed in thiss report. Existing water quality of the South Platte
River has been shown in the DRCOG 208 Water Quality Management Plan study to
be detrimental to the aesthetics and secondary recreational uses of the
river. Water quality of the South Platte River is discussed in more detail
in the section entitled "Effluent Limitations. "
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PLANNING AREA MAP
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DISTRICT no.,
EXISTING FACILITIES
The major existingasewater collection and treatment_arilities� the
basin are locAt _dro ur__ The main Clear Creek and Sand Creek Intercep-
tors are also shown to indicate the inter-relationships of those two basins
with the Lower South Platte Basin.
Wastewater flows from_.the City of Brighton, South Adams County Water and
Sanitation District ) >, Hazeltine Heights, Highland Acres, Eastwood
E'states, and Rocky Mountain Arsenal are all treated in separate facilities
which discharge either to the South Platte or First Creek or which have no
discharge. The rest of the basin's flows are eventually processed at the
Metro Central Plant for final discharge to the South Platte. Flows from the
North Washington Street Water and Sanitation District (NWSWSD) receive primary
treatment at the NWSWSD plant. The effluent is discharged to the Thornton-North
Washington Pump Station where it combines with the Thornton area wastes for
transport to the Central Plant. Flows from the two Lower Thornton service
areas, identified on Figure 2, are collected in the Thornton Outfall Sewer
and then enter the Thornton- North Washington Interceptor, which also collects
the Upper Thornton wastes, as shown on Figure 3. Just before entering the
Thornton-North Washington Pump Station, these flows are combined with the
Barr Trunk wastes. From the pump station, all the waste streams are pumped
through the Thornton-North Washington Force Main and into the Clear Creek
Interceptor and Inverted Siphon to flow by gravity to the Central Plant.
The following brief descriptions indicate the physical condition of the
face i ies, etr_resen. an�_pro ecFe capacities; 1-Te-r-abiMy-1(i-_meet
projected flows, and other information that maybe snificantfor.-pla_r3njng
purposes-The project wasfewa eT rte_o s used to evalu_ate so nee_aakle
-factlirres are is�c curse llii-tie neicl section entitled "P ulati-on_alid W__ast _:_-
water Flows. "
WASTEWATER TREATMENT PLANTS
There are present) nin astewater treatment plants in the Lower South
Platte Basin, including the SACWSD plant, which falls under a separate Facility
ij
Plan. The nine plants are listed on Table 1 . The SACWSD'plant and four
other lants in the basi tat are of si nificant size are brief) described
be ow. The remaining fur plants rnncist of three.thattrea residential
wastes and are redominantl nondischarging and one that is a lagoon system
1 or t e oc y-Mounta)n A sr Table 1 gives types of treatmerfirg,
average flow and discharge points for all nine plants.
It has been assumed that the smaller facilities will remain in operation
until the normal expansion of the sewer network reaches their location.
These plants could then be abandoned.
Metro District Central Plant
The Central Plant generally consists of primary and secondary treatment
facilities with disinfection and discharge into the South Platte River. The
plant is well maintained and is in good condition. The plant's primary
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Table 1
EXISTING WASTEWATER TREATMENT PLANTS
CAPACITY 1975 AVG. FLOW POINT OF
PLANT TYPE(1) (mgd) (mgd) DISCHARGE
Metro Central AS 170(2) 129 South Platte
Plant River
Denver North P 106 88 .r1 Metro Central
Side Plant
Brighton TF 1 .76 1 .4 ( South Platte
River
North Washington P,TF 1 . 5 1 . 5 '4etro Central
Street(3) Plant
South Adams TF 2. 5 1 .9 , fa outh Platte
County River
Hazeltine Heights AS, L - (4) - (4) Nondischarging
Highland Acres L - (4) - (4) Nondischarging
Eastwood Estates L - (4) - (4) Nondischarging
Rocky Mountain L - (4) - (4) First Creek
Arsenal
(1) AS = Activated Sludge F
TF = Trickling Filter
L = Lagoon
P = Primary Treatment Only
(2) Includes the 72-mgd expansion.
(3) Flow only receives preliminary treatment.
(4) Capacity and 1975 average flows unknown.
I
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- ez4,3\
treatment facilities have a theoretical existing capacity of 28 mgd. The
secondary treatment capacity through an activated sludge system is 98 mgd.
Presently, the primary and secondary facilities are being expanded by 42 mgd
and 72 mgd, respectively, so their total design capacity will be 70 mgd and
170 mgd, respectively. In this study, 170 mgd is considered the plant's
existing capacity.
The sludge generated in the plant is presently chemically treate �cacuum
filtered and hauled btruck to the Low.Bombi. g_Range where it is inc rpo-
rated into the soil On_com_p-letion of the expansion program, however, the
s u ge—wi b naerobically digested. It is proposed that the digested
sTia ge pumped through a pipeline to a land drying operation. The dried
sludge would then be mar keted_to t ie farming_communit_y__or_industria ce.rns
o as a fertilizer aid.
Denver North Side (DNS) Plant
The DNS Plant has a nominal capacity of 106 mgd and provides primary treatment
for wastewater from the Central Denver Basin. The plant's effluent is dis-
charged to the Metro Central Plant for further treatment. The sludge collected
in the primary sedimentation tanks is anaerobically digested and then pumped
to the Metro Central Plant for further processing and disposal . A report
prepared for the City and County of Denver indicates the plant is generally
in good condition and also identifies certain facility deficiencies which are
recommended for correction. Some of these deficiencies are now under contracts
for correction.
City of Brighton Plant
The existing plant in Brighton consists of primary clarification, secondary
treatment by high-rate trickling filters, effluent disinfection and discharge
to the South Platte River Sludge from the plant is anaerobically digested,
dried on sand beds., and then worked into the soil in nearby areas. The plant
has an estimated capacity of 1 .8 mgd. Historically, this facility has met
the State standards that were in effect at the time of its construction.
However, due to the more stringent standards currently being implemented,
this facility will have to be upgraded in the very near future. A report by
the City of Brighton's consulting engineers indicates that a new 4.0-mgd
treatment facility is the preferred way of meeting the more recent State
standards, due to the poor condition of the existing facilities.
North Washington Street Water and Sanitation District (NWSWSD) Plant
The NWSWSD plant consists of primary clarification followed by a high-rate
trickling filter with the effluent discharging to the Thornton-North Washington
Pump Statio f r ditional treatment at the Central Plant. It has an estimated
c_pacity c 1 ..5 mad with flows in excess of this amount being bypassed directly
to the pump station. In 1975, the average flow was 2. 1 mgd, with 0. 6 mgd
bypassed. Sludge is anaerobically digested, dewatered on open air drying
beds and marketesLas fert4l iz-er
-9-
The operation of this facility has been important for providing pretreatment
of the predominantly industrial wastewater from this District. However, the
plant is old and is currently experiencing mechanical and structural problems
associated with age. The NWSWSD is presently evaluating whether or not the
necessary repairs are economically justifiable. It is recommended that the
plant remain in service until such time as its operation becomes uneconomical .
South Adams County Water and Sanitation District (SACWSD) Plant
Although the SACWSD facility does not fall within the contractual requirements
of the Lower South Platte Facility Plan, a brief description is included to
provide a complete inventory of the existing facilities in the basin. The
plant provides treatment through primary clarification, trickling filtration,
final clarification, chlorination, and discharge to the South Platte River.
Sludge is anaerobically digested and dewatered on sand drying beds; the dried
sludge is disposed of on land. The facility has an es imated capacityCL2..9
mgd and is presently treating approximately:1 .9 mgd/of gd'of wastewater. A more
detailed description of this facility and its physical condition can be found
in the Facility Plan prepared for the SACWSD.
PUMP STATIONS, INTERCEPTORS, AND FORCE MAIN
Peaking Factor
When determining the estimated life of a pump station, interceptor, or force
main, consideration must be given to the peak wastewater flows, which are the
critical values in computing capacities. The peak flow is ob ain _d by multi-
plying the annual average daily wastewater flow by a peaking factor. This
peaking factor accounts for the diurnal flow increases due to living habits
a-§7.-iv-in as storm water WEI= rra+l�_indus_trla disch ges and otbe_�
extraaPouS wastewater sources which combine to increase the flow above the
average --_-- _-_=------ - ______________
The following peaking factor (PF) equation was derived for the Denver metro-
politan area:
PF = 3. 65/ (mgd)0. 166
The equation was developed by plotting the most recent peak flows in the
sewer system discharging to the Metro Central Plant and by drawing a curve to
fit the higher flows. The resulting curve was then checked against similar
curves for other metropolitan Denver areas and was found to be reliable in
projecting peak flows. The minimum peaking factor was found to be 2.0,
based on annual average flow in mgd.
Thornton-North Washington Pump Station
The Thornton-North Washington Pump Station is located near the confluence of
Clear Creek and the South Platte River. It was put into operation in 1967
and pumps wastewater from the Thornton service areas and the NWSWSD to the
Metro Central Plant. The maximum pumping capacity has recently been increased
to 30 mgd. This capacity could be increased to 35 mgd by increasing the size
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of the existing pump impellers. It has been estimated that the 30-mgd capacity
will be reached by approximately 1986, based on the flow projections determined
for the District members served by the pump station, as presented later in
this report. The pump station is in good condition and is well maintained.
It is expected to operate satisfactorily throughout the planning period with
some modification to the screening assemblies.
Miscellaneous Pump Stations in the Basin
The City of Thornton maintains and operates several small pumping stations in
their collection system. One of these pump stations, the Eastlake Pump
Station, is presently nearing capacity and does not have a standby pumping
system. The remaining pump stations appear to have the necessary capacity,
at least for the present. Dual power supply or standby generators have not
been included in these installations. Many of these pump stations will be
abandoned with the implementation of any one of the wastewater management
alternatives, and therefore additional capacity requirements have not been
determined. Because several of the pump stations were installed relatively
recently, they are still in good condition and no operational problems are
foreseen with the exception of the Eastlake Pump Station discussed above.
Thornton Outfall Sewer
Wastewater generated in the Thornton area generally north of 100th Avenue is
conveyed through the Thornton Outfall Sewer to the Thornton-North Washington
Interceptor. The outfall sewer has an approximate capacity of 15 mgd and a
diameter varying between 36 inches and 27 inches. Wastewater flow projections
indicate that the sewer has sufficient capacity until late in the planning
period. Figure 4 shows the capacity of this sewer based on gravity flows
only. The sewer was recently installed and is considered to be in good
condition with sufficient capacities to meet the requirements of all the
proposed alternatives.
Thornton-North Washington Interceptor
The Thornton-North Washington Interceptor sewer is approximately 12, 000 feet
long and has a diameter of 48 inches. It has an approximate capacity of
20 mgd, which is projected to be reached by about 1985. Some surcharging of
this line would extend the life of the interceptor by 1 or 2 years. Figure 4
shows the capacity of the interceptor based on gravity flow with no surcharging.
The grade of this sewer is adverse to the natural ground slope and is therefore
not very steep. This grade, combined with the gradual grades in the Thornton
collection system, has resulted in long detention times, low velocities and
consequently odors caused by anaerobic conditions. As a result, corrosion of
the Clear Creek Interceptor has occurred downstream of the Thornton-North
Washington Force Main junction. The Metro District is investigating reaeration
of the flows within the Thornton-North Washington Interceptor and anticipates
that this will alleviate the problem of anaerobic conditions. Damage to the
Clear Creek sewer has been repaired, and the sewer is again in good condition.
-11-
Barr Trunk
The Barr Trunk serves the southwest area of Thornton, Western Hills, small
sections of the NWSWSD and the North Pecos Sanitation District. Because the
area served by this trunk sewer is almost completely developed, it is antici-
pated that little additional wastewater flow will be generated and, therefore,
that the Barr Trunk should have sufficient capacity through the year 2000.
Little information is available on the condition of the sewer or its exact
location and size.
Thornton-North Washington Force Main
The force main is 42 inches in diameter and is approximately 6, 000 feet in
length. The force main discharges to the Clear Creek Interceptor. The main
has sufficient capacity to handle the anticipated year 2000 peak flow of 30
mgd from the Thornton-North Washington Pump Station. The main is in good
condition and is not expected to require any major maintenance work before
the end of the planning period.
Clear Creek Inverted Siphon
The Clear Creek Siphon conveys wastewater from both the Clear Creek and Lower
South Platte Basins under the South Platte River into the Central Plant. The
siphon consists of three barrels or pipes of 18 inches, 30 inches, and 54
inches diameter. The maximum allowable head loss through the siphon without
surcharging the system is approximately 4 feet. This allowable head loss is
based on the hydraulic design of the headworks into the Central Plant and
corresponds to a capacity of about 64 mgd. The siphon is regularly flushed
with water and is therefore maintained in relatively good condition. Depending
on possible corrosion problems, and the combination of alternatives selected,
the siphon could last through the year 2000.
The estimated peak flow from the Clear Creek Basin will be between 45. 6 and
74. 5 mgd, depending on what wastewater management alternative is selected as
the Clear Creek Facility Plan. Including the flow from the Lower South
Platte Basin, the range is increased to between 45. 6 and 93.7 mgd, depending
on the combination of alternatives selected for the two basins. The siphon
may therefore have to be increased in capacity, although with a 25-percent
surcharge, an extra 11 mgd of capacity can be obtained.
-12-
IV WA
/ v- /
• P-11 (011tAiL/(k1 MTIA4 VI~ �4 \ Gam'POPULATION AND WASTEWATER FLOWS
POPULATION PROJECTIONS
The population estimates used in this Facility Plan study were derived from
the areawide population projections developed by DRCOG for the ongoing 208
Water Quality Management Plan. The estimated future op pualations in the hasin
that will rec_e' 70
census o elation as a base and u dated those figures by standard demograp is
rocedures o a 1975 base tha as ee se or a llu re _o e
actual figures used for this study were taken from the computer run of
26 February„1976 which_has_.bbeen stated as giving the most accurate population)
figures fc%r aZ5 =Ihe_compu_ter model_used to derive the popula_tio rp�a�ts
includes approximately_16-different variables to describe_the future land use,
patterns and, therefore, the projected populations for the area,_
WASTEWATER FLOW PROJECTIONS
Unit wastewater flow values were calculated for the following land use types
as described by DRCOG:
■ Residential--Single Family and Multi-family, including mobile homes
• Industrial/Transportation, Communication and Utilities, including
the bulk storage of goods or materials and businesses that extract
their products from the natural environment
• Commercial--Retail and Service
• Public, excluding government administrative offices
• Parks and Recreation
All flows were established by using measured values in the greater Denver
metropolitan area and then comparing these values with those published in
literature. To determine the basin's residential unit flow, a per capita
flow was calculated for a predominantly bedroom community whose wastewater
volume is measured by the Metro District. This per capita flow was then
compared with two other residential flow figures-- one from a study performed
in Boulder on individual homes and the other from a study performed in the
midwest. Because the three values were very close, a weighted average of
these was selected for the residential unit value. Similar methods were used
for the other land use types.
The unit values calculated as discussed above were applied to the established
1975 population and land use types developed by DRCOG. The resulting flows
from each subarea were compared to the measured values and minor adjustments
were made to the unit values. The final selected 1975 wastewater unit flows
used in this study for the Lower South Platte Basin are shown below on Table
2 for each type of land use.
-15-
Table 2
SUMMARY OF DESIGN VALUES FOR WASTEWATER FLOWS
LAND USE FLOW UNITS (1) YEARS
1975 1980 1990 2000
Residential gpcd 62 65 70 75
I ndustr is I/TCU gpad 1000 1000 1100 1100
Commercial gpad 1000 1000 1000 1000
Public gpad 700 700 750 750
Parks/Recreation gpad 100 100 100 100
Infiltration/Inflow gpcd 11 11 11 11
(1) gpcd = gallons per capita day
gpad = gallons per acre day
The projected 1980, 1990, and 2000 unit flows on Table 2 are based on various
social and economic considerations. Some of the factors considered were the
national trend of increasing per capita wastewater flows, the present percentage
of water-consumptive industries in the basin, and the outlook for industrial
and commercial development. Table 2 also shows the infiltration/inflow rate of
11 gpcd that has been calculated for the basin.
j(77 To determine the total wastewater flows for the basin and its subareas, the
unit va ues ond-b. .ttae_QR� �r^� A ^n, L�+�^^� ^d
t e acres associatedh each Ian usP I the�resultng_figures were
added together to derive t_l�P.praj_eced_ra� �_s h�water fo o_a F..ig.ur_e,6.
As a check on these projections, an equation giving the estimated annual
average daily wastewater flows for Colorado was determined by statistical
analysis. This equation is given below:
Q = 120P1 .05
where Q = Total average daily wastewater flow in mgd
P = Population in millions
Applying this equation to the basin's estimated population for year 2000, for
example, yields a flow of 26 mgd. This flow is very close to the 27 mgd
shown for year 2000 on Figure 6.
-16-
60
LOWER TH RNT#
•
50
UP' R •T ORN ON •
V
• .
• •
.40
Q
• T
•
D •. T.WA .H/N6' ON ' W/
I0
SOU AD MS ••'
o •
.
COU TY W S .• I
Q 30
J .
oo
••
0 • • ' •
e•. ••
W ••
20 •r •
w •
cr ••• BR/ HTO
(f) •.
.
NO"THW STER ARIA ....•
10
I
•
.0.• F/ ST, ECO' 0 &
'•S �
I•
.
0 . •_•
1975 1980 1985 1990 1995 2000
YEARS
Figure 5
LOWER SOUTH PLATTE BASIN
SERVICE POPULATION
0
a
N
r-
AS) CH2M::HILL
30
•
25
0
o
20
-TOTAL BASIN
3 FLOW
0
J
L
} •
J 15
a
0
w •
0
a
re
w
a IO
5
0
1975 1980 1985 1990 1995 2000
YEARS
Figure 6
LOWER SOUTH PLATTE BASIN
a
WASTEWATER FLOW PROJECTION
03
N
N
,096)`R' ) CH2MHHILL
EFFLUENT LIMITATIONS
STREAM CLASSIFICATION
The Facility Plan must provide for the achievement of the effluent qualities
needed to meet the wate- quality standards established by the State. The
State of Colorado has adopted a system of stream classifications which correlates
the stream water quality with the anticipated use of that stream. Streams
have been divided into four basic classifications, which are described below.
However, not all streams in the State have been classified, including the
First, Second and Third Creeks of the study area. Streams not classified yet
fall under the Basic Standards, which require that the discharge to such
streams be free of any ruisance or objectionable substances and free of all
toxic pollutants.
The stream classifications can be generally described as primary body contact
(Class A) and nonprimary body contact (Class B) . These two classifications
are further divided into cold water fisheries (subscript 1) and warm water
fisheries (subscript 2) . Also, a Class C d@signation was recently adoptedLine
February 1976. A Class C desi natio e ' is
parame er__imitatior!s ti t— be��}uir_ed itncer the stream!s_A or B classi-
fication. It is assigned to astreagLor segment__whe_n_ac ievemetlt.of tbgAim
B standard would (11._be. beyond_the_ca.pabi=Lities of_present technology,,(2)
cause widespread economic_or_social hardship, or_L3J be precluded because of
sTrrie naturaF or irrever.sibl_e_man-induced conditions.
The South Platte River has been designated Class B2 for the reach through the
Lower South Platte Basin. The required stream standards for this reach of
the river are given on Table 3.
DRCOG WATER QUALITY MANAGEMENT PLAN
On the basis of the State classifications, the DRCOG 208 Water Quality Manage-
ment Plan study includes computer modeling of streams to identify what pollutants
are of concern for achieving the designated uses of the streams. The results
of the stream modeling are presented in Task Memorandum Nos. 6-3 and 6-4 (TM
#6-3 and #6-4) by the technical consultant on the 208 study. More detailed
information on the modeling may be obtained directly from DRCOG.
The modeling identifies three potential problems which impact the aesthetics
and secondary contact recreation of the South Platte River. The three parameters
of concern are phosphorus (P) , total nitrogen content (Total-N) , and fecal
coliforms (coli) . The effects of these and other commonly used parameters
are discussed in the fol owing paragraphs.
• Biochemical Oxygen Demand (BOD) is a measure of the oxygen demand
of organic matter in water. In itself, BOD is not a pollutant, has
no substance and exercises no direct harm. The BOD load can exert
enough oxygen demand to cause anaerobic conditions which can lead
to septicity. Therefore, maximum allowable values of BOD discharged
to receiving streams are established to minimize the oxygen demand.
-19-
Table 3
STATE WATER QUALITY STANDARDS FOR B2
STREAM CLASSIFICATION (1)
PARAMETER STANDARD
Settleable Solids Free From
Floating Solids Free From
Taste, Odor, Color Free From
Toxic Materials Free From
Oil and Grease Cause a film or
other discoloration
Radioactive Material Drinking Water Standards
Fecal Coliform Bacteria Geometric Mean of
<1000/100mI from five
samples in 30-day period
Turbidity No increase of more than
10 JTU
Dissolved Oxygen 5 mg/I minimum
Temperature Maximum 90° F.
Maximum Change:
Streams-5o F
Lakes-3° F
Fecal Streptococcus ---
(1) B2: Waters suitable for secondary contact recreation and a warm
water fishery.
-20-
A BOD level of less than 20 mg/I is considered to be a safe
average discharge for the South Platte River.
a Settleable and Suspended Solids (SS) are solid particles or clusters
of particles which will settle out in calm water. SS is detrimental
to a stream by causing turbidity (clouding) . SS from WWTP is
usually about 50 percent oxygen-demanding matter. The principal
danger of SS is its ability to harbor bacteria and virus. The SS
can surround these bacteria and virus, making the water difficult to
disinfect. A river bottom can become covered with settled solids
and act as a breeding ground for bacteria, virus and cysts. A
bottom blanket creates an oxygen demand and can lead to septicity
and odor. The blanketing effect on the stream bottoms also kills
eggs, young aquatic life and food organisms and destroys spawning
beds. An average discharge value of less than 20 mg/I is believed
to be a safe effluent limitation.
a Dissolved Oxygen (DO) concentration is the amount of oxygen in
solution in the water. This is probably the most important measure
of water quality. All water needs some DO to avoid septicity and
therefore avoid objectionable odors. In addition, to sustain fish
and other aquatic life, the minimum DO concentration generally
accepted is 5 mg/I .
■ Chlorine is a chemical used as a disinfectant for the inactivation
of bacteria and possibly virus. However, chlorine is toxic to fish
and other aquatic life. It is recommended that the total residual
chlorine not exceed 0.05 mg/I . As a result of the toxicity of
chlorine, dechlorination of the effluent is assumed as a future
requirement.
■ Fecal Coliform is a harmless bacteria measured as an indicator of
pathogenic (disease-causing) bacteria. All fecal coliform comes
from the intestinal tracts of warm-blooded animals. A count of
1 ,000 per 100 ml of water is generally accepted as indicating a
2 percent chance of the presence of a pathogenic organism. The
smaller the count, the smaller the chance of the presence of pathogens.
■ Nitrogen is a natural element found essentially everywhere. It is
present in wastewater in the form of ammonia, nitrite, nitrate, and
in organic forms.
Ammonia can be toxic to fish and cause an oxygen depletion in the
receiving waters. Based on several studies, it has been shown that
toxicity is attributable to the un-ionized ammonia form (NH.2) with
some very minor toxicity resulting from the ionized form (KO .
Ammonia toxicity is directly dependent upon pH and temperature,
with the toxicity increasing with increasing pH and temperature.
The recommended allowable concentration of un-ionized ammonia has
been set at 0.02 mg/I to avoid fish kills. This low value normally
requires that wastewater effluent be treated to remove the total
ammonia to less than 3 mg/I .
-21-
Ammonia can be biologically oxidized to nitrite and then to nitrate
in the receiving waters and can thereby add significantly to the
oxygen demand of the river. The biological conversion of ammonia
to nitrate requires approximately 4.6 pounds of oxygen for each
pound of ammonia converted. Therefore, it can be seen that a large
oxygen deficiency could result if significant quantities of ammonia
are discharged to the receiving streams. Domestic wastewater
usually contains about 125 pounds of ammonia per million gallons.
Nitrite can be hazardous to infants under 3 months as well as very
toxic to fish. Levels of nitrite-nitrogen in public water supplies
therefore are recommended at a maximum of 1 mg/I . It should be
noted that nitrite is readily converted to nitrate by biological
activity and is only found in rivers in trace amounts.
Nitrate concentrations in excess of 10 mg/I in drinking waters have
been shown to cause methemoglobinemia ("blue baby") in infants less
than 3 months old. High nitrates are frequently found in shallow
wells on farms and rural communities.
■ Phosphorus is a naturally occurring element and is found every-
where. It is considered in the forms of elemental phosphorus and
phosphates.
Elemental phosphorus is toxic and is subject to bioaccumulation.
The limit of elemental phosphorus has been recommended at 0. 10 mg/I
to avoid toxicity.
Phosphates are one of the major nutrients required for plant nutrition
and are essential for life. Investigations have indicated that
high phosphate concentrations tend to accelerate eutrophication of
waters and that aquatic plant problems occur in standing bodies of
water. However, because studies to date have been inconclusive,
phosphorus has not been considered for removal in this study.
Results of the DRCOG modeling program have been discussed both with the DRCOG
staff as well as the technical consultant to DRCOG in an effort to establish
the required effluent qualities for discharge to the South Platte River. The
effluent qualities finally selected are described below.
PROPOSED EFFLUENT QUALITIES
To achieve the standards set by the Colorado Water Quality Control Commission,
any proposed facility in the South Platte Basin will have to produce an
effluent with less than 20 milligrams per liter (mg/I) of BOD and suspended
solids and less than 3 mg/I of ammonia-nitrogen. These effluent limitations
and other required parameters are given on Table 4.
At present the State discharge control system does not account for the dilution
effect of the water in the receiving stream. As a result, the State is now
studying the stream classifications with the objective of establishing instream
water quality standards for municipal discharges. Also, areawide wasteload
-22-
Table 4
PROPOSED EFFLUENT QUALITY FOR DISCHARGE TO THE SOUTH PLATTE RIVER
WEEKLY MONTHLY
PARAMETER UNITS AVERAGE AVERAGE
Suspended Solids mg/I < 30 < 20
BOD5 mg/I < 30 < 20
Ammonia-Nitrogen mg/I < 3 < 3
Oil and Grease mg/I < 10 < 10
Dissolved Oxygen mg/I > 5 > 5
Color Units < 25 < 25
Turbidity JTU < 25 < 25
Fecal Coliforms Number/100mI <2000 <1000
Residual Chlorine mg/I < .05 < .05
pH - 6.0-9.0 6. 0-9.0
< Less than or equal to
> Greater than or equal to
-23-
allocations for each of the streams in the Denver metropolitan area will be
established at the conclusion of the 208 study being prepared by DRCOG.
The effects of these developments on this Facility Plan cannot be determined
yet. Meanwhile, the proposed effluent qualities for the South Platte River,
as shown on Table 4, have been transmitted to the State Health Department,
EPA and DRCOG for their concurrence. To date, no reply has been received
from these agencies.
-24-
ALTERNATIVE WASTEWATER MANAGEMENT SYSTEMS
EPA GUIDELINES
When establishing feasible wastewater management systems, certain basic EPA
requirements must be considered. These basic considerations are briefly
described below.
1 . Continued Operation of Existing Facilities - Existing facilities
within the Lower South Platte Basin should be evaluated to determine
if they can attain the proposed effluent qualities. In addition,
the optimized performance of the existing facilities should serve
as a baseline for planning additions and modifications to the
existing facilities.
2. Regional Solutions - Regional solutions may include the interconnec-
tion of facilities, the construction of one or more large facilities
to eliminate the need for several much smaller facilities, and
joint management of facilities to improve the operation and main-
tenance and to reduce costs.
3. The No-action Plan - A no-action alternative should be evaluated on
the basis of the effect it may have on surface and ground water
qualities, land use limitations, and socioeconomic factors such as
residential-industrial development and health hazards.
4. Effluent Handling - At a minimum, the following three methods for
effluent handling must be considered in order to meet the require-
ments for Best Practicable Wastewater Treatment TPchnnlnnv fBP nn"T)
established -Pollution Co tr�4-Ac+ A►rPndments
0 972: _
■ Treatment and discharge
a Treatment and reuse
a Land application
5. Miscellaneous - The selected alternatives should take into account
and allow for the inclusion of newer technology at a later date in
order to provide for the reclamation or recycling of wastewater
and, therefore, eliminate the discharge of pollutants.
The above five guidelines have been considered in developing the alternative
wastewater management systems for the Lower South Platte Basin. A brief
explanation of how each guideline was followed is given in the following
paragraphs. A more detailed account of these requirements will be provided
in the final Facility Plan report.
As discussed in a previous section, the conditions, capacities, and future
capabilities of existing facilities have been inventoried. Many of the
alternatives developed, as described later, incorporate existing facilities.
The modifications or additions needed for their continued use are indicated
as necessary in each alternative description.
-25-
Four of the management alternatives discussed in the next section are regional
approaches to wastewater handling in the basin. Attention has also been
given to other regional plans, such as the DRCOG Water Quality Management
Plan developed in 1972-74 and the ongoing DRCOG 208 areawide wastewater
management program. All regional plans under consideration for the basin
will be documented in the final Facility Plan.
A no-action plan is not considered a viable alternative for the Lower South
Platte Basin. Under a no-action plan, the existing pollution level would
continue and even increase, the effluent limitations would not be satisfied,
and public health hazards probably would develop.
ei
Consideration was also given to installing another Thornton-North Washington
interceptor, pump station, and force main paralleling the existing system
when the need arose to handle increased flows. However, this expansion of
the existing system was found to be economically unfeasible. Moreover, the
odor and corrosion problems associated with the gentle slopes of the Thornton-
North Washington collection facilities would be aggravated.
Each of the three effluent handling methods for meeting the BPWTT requirements
has been considered. The treatment and discharge and the land application
systems are covered in the description of the alternatives. The following
reuse possibilities were considered for inclusion in the Lower South Platte
Basin:
■ Urban irrigation (irrigation of golf courses, parks, schools, etc.
within an urbanized area during the summer months) .
• Industrial reuse (for industrial cooling water or process water) .
• Domestic reuse (for recycling water back to the raw water supply of
a municipality) .
• Agricultural reuse (for irrigation of existing farmlands by the
exchange of water rights and storage rights) .
Opportunities for industrial or domestic reuse could not be identified within
the planning period. If water rights limitations can be resolved, then urban
irrigation becomes a possible source for reuse. The Adams County golf course
and the parks and school grounds-+4-Brig.bton__are_.suggested.areas for__was1ewater
irriga ion. Based_o Lat. Qr er-area, urban reuse-was found
to be cost effective and has man Qndary environmental benefits.__These
bene i s inc_u r_ans_mouota_i_n di_yersion of water fes and` round.watex—_
depletions. '�_ j
Agricultural reuse of wastewater is_perhaps the.most_feasible reuse aiterlaatkke
for he Lower South Platte Basin because_of the many existing_irrigation
ditches-which serve thousands of_irrigated acres_of__lansf Uowever, to impleo�,ent
an agric`ultura I reuse=syst_e_m _various__structuraLand_noastrJactural_reqiiirerneffts
must be met. These requirements are discussed briefly below.
-26-
V'� u' e
y 11 1 • P 1 ii . ...o f V'_---
til 3(‘'d 3 L. ehfilWa 1 --- v6'
4, ,', N,A` Strus,)kpraI Factors
4d wr G\ ,�17°' ' One or more irrigation ditches should be close to the site of the
, ;
G'\, il treatment facility to avoid excessive delivery costs (pumping and
,) a� pipeline installation and maintenance) .
`'� ■ One or more irrigation ditches would be needed that have both the
capacity and water volume to match the projected wastewater flows.
- ■ There should be adequate storage downstream of the wastewater
introduction point to handle a minimum of 7 to 8 months of wastewater
flow.
■ The ditches suggested for use may have to be upgraded to increase
their reliability against possible rupture and loss of water.
■ The diversion structures and flow measuring devices may have to be
upgraded to provide more positive control of the system.
Nonstructural Factors
■ Better overall management of the water supply and storage would be
required.
\\ • The "operational spills" that are common to ditches in this area
would have to be controlled. This may result in a water rights
\ problem since frequently the spills form part of an adjacent farm's
water supply. If the spills are eliminated, then other water may
\4 have to be supplied to the adjacent farm.
General water rights and storage rights must be considered. Trans-
fer of water rights and storage rights may be required to implement
the system.
• Most importantly, the cooperation of the ditch companies and farmers
would be required. Without their cooperation, this type of system
4 " just cannot be implemented.
'' These are a few of the many factors that must be considered for the implementa-
tion of an'agricultural reuse system. Also, based on some preliminary work,
' the cost of implementing this type of system appears to be greater than the
cost of most of the alternatives that have been developed for consideration.
The high costs are associated with construction of storage, upgrading any
Ir existing ditches to the required levels of reliability, and the delivery
costs of introducing the wastewater to the ditch. In addition, an important
i time factor is involved in the transfer of water and stora e ri hts e
1 th em o e imp emente here ore because • ed
time cons rain s an a igh costs, an agricultural reuses s em_ has not,
een con -dered any--further in this Facility an.
-------— -
It should also be noted that most of the alternatives considered in this
study do not prec u e agricultural reuse in the basin. The only exceptions
-27-
would be th a utilize hi h-rate irri ation as the treatment method.
The possibility for agricultural reuse on th uaIityr of efflue
produced by the various alternatives.
All the alternatives are capable of being upgraded to include new technology
to varying degrees. The specific treatment processes and possible upgrading
methods associated with the selected management system will be specified in
its detailed description. Also, the ability to be upgraded is one of the
factors used to compare the alternatives, as discussed later.
DEVELOPMENT OF ALTERNATIVES
Based upon the EPA guidelines outlined above and meetings with Metro District
personnel, several alternatives for the Lower South Platte Basin were estab-
lished. The alternatives are conceptual management plans rather than specific
treatment process plans. The exact treatment processes will be determined
once the best way to manage the basin's wastewater is identified.
First, a preliminary set of 13 alternatives was developed and evaluated to
narrow down the feasible plans for a more detailed comparison. The 13 alterna-
tives, described below, centered around one or two of three basic concepts:
new treatment plants, new pump stations, equalization basins, or land application
systems. After an initial economic analysis, these alternatives were reduced
to seven for a closer comparison, as discussed later.
For comparison purposes, all the structural management systems are assumed to
include an air-activated sludge plant capable of providing ammonia removal
with sludge handling by anaerobic digestion and air drying with subsequent
marketing. An air-activated sludge plant was selected at this point because
it is a well-known system, it has well-documented operating and cost data,
and the capital and operation and maintenance costs tend to be at the median
by comparison to other biological treatment systems.
The flow equalization facility considered consists of an influent pumping
station, an earthen equalization basin, and the areation equipment required
to maintain adequate mixing and aerobic conditions. All components were
sized to accommodate flow in excess of the average.
In developing the alternatives, four basic land application techniques were
considered. These were (1) overland_flo , (�)z infilxratio�[ ercolation_,
basins, (3)_conventional irrigation, and (4) high-rate_ irrigation. A_prelirnirry
revCe�ir of the-planning area 1�owed that there were no areas suitable for_the
overland flow technique and that convention-al irrigation would require too
many acres of land and would be much more e-xpensive: The alternatives finally
developed, therefore, only include_ infiltration/percolation basins and,
high-rate irrigation systems.
Pretreatment by aerated lagoons was assumed for both these land treatment
methods. The first type of land application system requires alluvial sand
and gravels so that the effluent from a lagoon system can infiltrate and
percolate downward to an underdrain collection system from where it is pumped
to the South Platte River. A high-rate irrigation system requires normal
-28-
agricultural-type soils, but is also underlain with drains so the effluent
can be collected and returned to the South Platte River by means of a gravity
sewer. Also, for the_h gb-_ ale_ trig ion_sy_stem, the following features
were included: 5 months storage,_ center pivotrigs_fQr__irrigation and a
crop production return of $1.12__per nogd_of_wastewater.
The alternatives for study in the Lower South Platte Basin are briefly described
below. Because several alternatives are very similar except for what areas
are served by a particular proposed facility, the components of the alterna-
tives and the areas served have been outlined on Table 5 for easy reference.
This table immediately ol lows the alternative descriptions. The locations
of the various components are shown on Figures 7, 8, and 9. The land application
sites were selected for comparison purposes only and have not been evaluated
in detail . If a land application alternative is selected, the actual site
could be located elsewhere in the basin.
▪ Alternative 1 - Construction of an interceptor and a new wastewater
treatment plant (WWTP) at approximately 164th Avenue and the South
Platte Rive- to treat the flow from the entire basin, including
SACWSD.
■ Alternative 2 - Construction of an interceptor and a new WWTP at
approximately 164th Avenue and the South Platte River to treat the
flow from the entire basin, including SACWSD. An equalization
basin would also be constructed at approximately 100th Avenue and
west of the South Platte River to smooth the flow variation from
the Upper Thornton and NWSWSD areas.
■ Alternative 3 - Construction of an interceptor and a new WWTP at
approximately 164th Avenue and the South Platte River to treat the
flow from the entire basin except SACWSD. The existing WWTP at
SACWSD would be expanded and upgraded to treat and discharge the
flow from SACWSD.
■ Alternative 4 - Construction of an interceptor and a new WWTP at
approximately 164th Avenue and the South Platte River to treat the
flow from Brighton, Lower Thornton and First, Second and Third
Creeks. The existing WWTP at SACWSD would be expanded and upgraded
to treat and discharge the flow from the SACWSD. Flow from Upper
Thornton and the NWSWSD would be pumped by the existing Thornton-
North Washington Pump Station to the Central Plant for treatment
and discharge.
cm...) Alternative 5 - Construction of an interceptor and a new pump
station at approximately 124th Avenue and the South Platte River to
pump the flow from Lower Thornton directly to the Central Plant for
treatment and discharge. A new WWTP would be constructed at approxi-
mately 164th Avenue and the South Platte River to treat the flow
from Brighton and First, Second and Third Creeks. The existing
WWTP at SACWSD would be expanded and upgraded to treat and discharge
the flow from SACWSD. Flow from Upper Thornton and the NWSWSD
would be pumped by the existing Thornton-North Washington Pump
Station to the Central Plant for treatment and discharge.
-29-
A Alternative 6 - Construction of an interceptor and a new pump
station at approximately 140th Avenue and the South Platte River to
pump the flow from Lower Thornton and First, Second and Third
Creeks to the Central Plant for treatment and discharge. A new
WWTP would be constructed at approximately 164th Avenue and the
South Platte River to treat flow from Brighton. The existing WWTP
at SACWSD would be upgraded and expanded to treat and discharge the
flow from SACWSD. Flow from Upper Thornton and the NWSWSD would be
pumped by the existing Thornton-North Washington Pump Station to
the Central Plant for treatment and discharge.
a Alternative 7 - Construction of an interceptor and a new WWTP at
approximately 140th Avenue and the South Platte River to treat and
discharge flow from Lower Thornton and First, Second and Third
Creeks. A new WWTP would be constructed at approximately 164th
Avenue and the South Platte River to treat flow from Brighton. The
existing WWTP at SACWSD would be upgraded and expanded to treat and
discharge the flow from SACWSD. Flow from Upper Thornton and the
NWSWSD would be pumped by the existing Thornton-North Washington
Pump Station to the Central Plant for treatment and discharge.
■ Alternative 8 - Construction of an interceptor and a new WWTP at
approximately 140th Avenue and the South Platte River to treat and
discharge the flow from Brighton, Lower Thornton, and First, Second
and Third Creeks. Flow from Brighton would be pumped to 140th
Avenue from the existing Brighton WWTP site. The existing WWTP at
SACWSD would be upgraded and expanded to treat and discharge the
flow from SACWSD. Flow from Upper Thornton and the NWSWSD would be
pumped by the existing Thornton- North Washington Pump Station to
the Central Plant for treatment and discharge.
■ Alternative 9 - Construction of an interceptor and land application
system (infiltration/ percolation basins) approximately between
136th and 160th Avenues along the South Platte River to treat the
flow from the entire basin including SACWSD.
0 Alternative 10 - Construction of an interceptor and land application
system (infiltration/ percolation basins) approximately between
136th and 150th Avenues along the South Platte River to treat the
flow from Brighton, Lower Thornton and First, Second and Third
Creeks. Flow from Brighton would be pumped to 140th Avenue from
the existing Brighton WWTP site. The existing WWTP at SACWSD would
be upgraded and expanded to treat and discharge the flow from
SACWSD. Flow from Upper Thornton and the NWSWSD would be pumped by
the existing Thornton- North Washington Pump Station to the Central
Plant for treatment and discharge.
■ Alternative 11 - Construction of an interceptor and land application
system (infiltration/ percolation basins) approximately between
136th and 150th Avenues along the South Platte River to treat the
flow from Lower Thornton and First, Second and Third Creeks. A new
WWTP would be constructed at approximately 164th Avenue and the
-30-
South Platte River to treat flow from Brighton. The existing WWTP
at SACWSD would be upgraded and expanded to treat and discharge the
flow from SACWSD. Flow from the Upper Thornton and the NWSWSD
would be pumped by the existing Thornton-North Washington Pump
Station to the Central Plant for treatment and discharge.
■ Alternative 12 - Construction of an interceptor and a new pump
station at 140th Avenue and the South Platte River to pump to a
land application system (high-rate irrigation) . The system would
be located at a site north of Barr Lake and east of Brighton to
treat the flow from the entire basin. Flow from Brighton would be
pumped to 140th Avenue from the existing Brighton WWTP site.
■ Alternative 13 - Construction of an interceptor and a new pump
station at 140th Avenue and the South Platte River to pump to a
land application system (high-rate irrigation) . The system would
be located at a site north of Barr Lake and east of Brighton to
treat the flow from Brighton, Lower Thornton and First, Second and
Third Creeks. Flow from Brighton would be pumped to 140th Avenue
from the existing Brighton WWTP site. The existing WWTP at SACWSD
would be upgraded and expanded to treat and discharge the flow from
SACWSD. Flow from Upper Thornton and the NWSWSD would be pumped by
the existing Thornton-North Washington Pump Station to the Central
Plant for treatment and discharge.
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TABLE 5
DESCRIPTION OF ALTERNATIVES
ALT. AREA NO.
NO. FACILITY AREA SERVED ON FIG. 2
1 NEW WWTP AT 164TH & NEW INTERCEPTOR ENTIRE BASIN
2 NEW WWTP AT 164TH & NEW INTERCEPTOR ENTIRE BASIN
EQUALIZATION BASIN UPPER THORNTON 3,4
NWSWSD 5
3 NEW WWTP AT 164TH & NEW INTERCEPTOR BRIGHTON 7
1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,6
UPPER THORNTON 3,4
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
4 NEW WWTP AT 164TH & NEW INTERCEPTOR BRIGHTON 7
1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,6
EXISTING THORNTON-N. WASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
5 NEW WWTP AT 164TH BRIGHTON 7,PART OF 6
1ST,2ND,3RD CREEKS 8
NEW INTERCEPTOR TO NEW PUMP STATION AT
124TH TO NEW FORCE MAIN TO CENTRAL
PLANT LOWER THORNTON 1 ,2,PART OF 6
EXISTING THORNTON-N. WASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4,
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
6 NEW WWTP AT 164TH BRIGHTON 7,PART OF 6
NEW INTERCEPTOR TO NEW PUMP STATION AT
140TH TO NEW FORCE MAIN TO CENTRAL
PLANT 1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,PART OF 6
EXISTING THORNTON-N. WASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
7 NEW WWTP AT 164TH BRIGHTON 7,PART OF 6
NEW WWTP AT 140TH & NEW INTERCEPTOR 1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,PART OF 6
EXISTING THORNTON-N. WASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
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TABLE 5 CONT.
8 NEW WWTP AT 140TH & INTERCEPTOR BRIGHTON (NEW PUMP
STATION AT EXIST-
ING PLANT SITE) 7
1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,6
EXISTING THORNTON-N. WASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
9 INFILTRATION/PERCOLA-ION BASINS
BETWEEN 136TH AND .60TH
& NEW INTERCEPTOR ENTIRE BASIN
10 INFILTRATION/PERCOLA-ION BASINS
BETWEEN 136TH AND :50TH
& NEW INTERCEPTOR BRIGHTON (NEW PUMP
STATION AT EXIST-
ING PLANT SITE) 7
1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,6
EXISTING THORNTON-N. WASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
11 INFILTRATION/PERCOLATION BASINS
BETWEEN 136TH AND 150TH
AND NEW INTERCEPTOR 1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,PART OF 6
NEW WWTP AT 164TH BRIGHTON 7,PART OF 6
EXISTING THORNTON-N. NASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3 ,4
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
12 HIGH-RATE IRRIGATION SYSTEM NORTH OF
BARR LAKE WITH NEW INTERCEPTOR TO
NEW PUMP STATION AT 140TH ENTIRE BASIN
INCLUDING BRIGHTON
(NEW PUMP STATION
AT EXISTING PLANT
SITE)
13 HIGH-RATE IRRIGATION SYSTEM NORTH OF
BARR LAKE WITH NEW :NTERCEPTOR TO
NEW PUMP STATION AT 140TH BRIGHTON (NEW PUMP
STATION AT EXIST-
ING PLANT SITE) 7
1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,6
EXISTING THORNTON-N. "ASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
-33-
EVALUATION OF ALTERNATIVES
A cost-effectiveness analysis was made to compare the wastewater management
systems discussed in the previous section in accordance with EPA regulations.
A cost-effectiveness analysis is the evaluation of various alternatives based
on economic, engineering, implementation and environmental factors. The
specific factors used in the comparative analysis are presented and described
in detail in this section. The purpose of the comparison is to select that
alternative which achieves the desired wastewater management goals while
minimizing the total resource cost.
The alternative wastewater management systems first were given a preliminary
screening to reduce the total number of alternatives for more detailed analysis.
The sizings of the principal component facilities of the management alternatives
used for screening are given on Table 6. For this Facility Plan, the preliminary
screening process was based on the present worth costs presented on Table 7
and, to a less extent, on the information presented on Table 6 and on major
environmental impacts.
Table 7
PRESENT WORTH COSTS OF ALTERNATIVES
ALTERNATIVE PRESENT WORTH
NUMBER(1) (Millions of Dollars)
9 $16. 5
10 20.4
11 24.0
5 24.9
6 26.2
8 26. 5
4 26.6
7 28.6
1 30. 8
2 30.8
3 32. 1
13 32. 1
12 44.4
(1) For descriptions of a ternatives, see Table 5.
This screening eliminated six of the wastewater management systems from
further examination. The seven alternatives remaining after the preliminary
screening were each critically reviewed to more closely approximate the
-37-
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-38-
projected timing of facility construction. Also, the many subtleties present
in the remaining seven alternatives were considered in modifying the input
data for a more accurate cost comparison. These refined cost estimates are
discussed further in the comparison of alternatives.
The seven alternatives were evaluated on the basis of the following five
general areas:
a Economic considerations
a Engineering considerations
a Implementation considerations
a Environmental considerations
a Miscellaneous considerations
Several descriptive factors were used to identify the more important aspects
under each of these areas of comparison to evaluate the alternatives. The
evaluation procedure is described in more detail at the end of this section.
ECONOMIC CONSIDERATIONS
The inter-relationship between the four basins in the Metro service area was
discussed in the "Introduction" section of this report. There was a total of
832 possible combinations of the alternatives for the four basins prior to
the screening process and 168 after the alternatives were screened. Because
of this large number, a computer program was developed to determine the
present worths of all the combinations, as well as an estimate of the range
of annual costs.
Initially, the basic assumptions for the cost computations were that secondary
treatment will be operational by 1981; ammonia removal facilities, by 1983;
and an expansion of both these processes, by 1991 . The selection of a 10-year
phasing period was based upon an analysis of the estimated inflation rate,
the interest rate, the learning curve effect, and the economy of scale factor.
The learning curve effect relates the reduction in construction costs to the
recent refinement in designs as well as newer technology, and the economy of
scale factor is determined by the type of facilities to be constructed.
These four factors have different effects on the phasing period. Generally,
the lower the interest rate and the economy of scale factor, the longer the
phasing period. Conversely, the lower the inflation rate and the learning
curve effect, the shorter the phasing period.
To determine the costs for each of the al - --tives, equations for both
capital and o.eration and maintenanc- (O&M osts of various treatment processes
were developed and the results checke .ainst the capital and O&M costs of
installed facilities. These equations, as well as the wastewater flows
established for use in the various alternatives, formed the principal input
data to the computer program. Other required data for input are period of
operation, dates of phased construction, the number of years over which the
facility is constructed, and the relationship between O&M cost as a function
of the percent design flow. The resulting curve provides an estimate of the
O&M costs for any year based on the estimated wastewater flow for that year
as a percentage of the flow in the design year.
-39-
The cost equations were all updated to reflect costs in January 1976 dollars,
using either the EPA plant index of 2143.7 or the Engineering News Record
(ENR) construction cost index of 1898. Capital and O&M costs are not increased
due to inflation. Also, the costs developed herein do not include any existing
debt service nor the administrative costs for operating a special service
district such as Metro Denver. However, the estimates do indicate the relative
cost differences among the alternatives. The cost estimates may be increased
to future cost levels by taking the index used in this report as a ratio to
the projected index in the year of interest.
Present Worth Costs
The economic analysis that discounts all expenditures to the present is
called a present worth analysis. Present wortht ,y he rlafina as the amoi,nt
of money that would_have=to_be invested at the beginning_ofre_pa_Kment
period, at a_certain_ interest_rate,_to_provi e th_e exact am u.at f�!n o
ma�Ce all the necessary expenditures wi-tin tiat period.
The screened alternatives were reviewed and the input data refined to more
closely approximate the projected timing of construction and to include the
many nuances inherent in each alternative. The average life of the facility
was assumed to be Jyea s, hiie the period o� f analvsis extende t near
2000. e salvaae value was computed l using straight line deprec�ation aid
the interest Th rate was 6-1 8 ercent. The results of this analysis are included ,
on Table 8
Table 8
PRESENT WORTH COSTS FOR SCREENED ALTERNATIVES
ALTERNATIVE PRESENT WORTH
NUMBER (Millions of Dollars)
9 $16.7
10 19.4
11 214.6
4 24.6
6 24.9
5 25.8
8 27.9
Annual Costs
Economic cost-effectiveness requires that the estimated annual expenditures
also be considered. These costs include both O&M and the amortized costs of
the capital investments. The capital costs are converted to an equivalent
annual cost basis by assuming 75 percent Federal funding and a 7 percent
interest rate over 30 years. The range of annual costs, amortized capital
plus O&M expenditures, was computed and is shown on Table 9. Also included
on Table 9 are estimates of the average cost per million gallons for the
entire basin.
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Table 9
AVERAGE ANNUAL COSTS FOR SCREENED ALTERNATIVES
ALTERNATIVE RANGE OF ANNUAL COSTS TREATMENT COST
NUMBER (Thous. of Dollars) (Avg. $/MG (1))
Low High
4 $1, 039 $2, 111 $217. 5
5 1 ,053 2,222 224. 5
6 1 ,093 2, 279 231 . 2
8 1,096 2, 120 224. 2
9 722 931 124. 8
10 9143 1, 068 18. 23
11 1 ,093 1, 909 213. 5
(1) MG = Millions of gallons
ENGINEERING CONSIDERATIONS
Net Energy Consumption
The net energy consumption is determined by subtracting the usable energy
generated onsite from the energy required to operate and maintain the facility.
The usable, onsite energy is derived from converting methane gas into electrical
power. The methane gas is generated in the anaerobic digestion process used
to stabilize the sludges produced in wastewater treatment. The conversion of
methane gas to electrical power is inefficient at 30 percent. Therefore,
designers are tending to crive natural gas engines directly from the methane.
This increases efficiency to about 50 percent. However, an economic analysis
should be made to determine whether or not onsite generation of energy is an
economic operation. Generally, onsite generation is not economical in very
cold areas but is in hot climates. The Denver area tends to be between the
two extremes.
The quantity of energy consumed, usually fossil fuels, in conventional waste-
water treatment is directly related to the level of pollutant removal . The
greater the level of pollutant removal, the greater the energy consumed. The
extraction and processing of these resources constitutes an environmental
impact, although usually in other areas. Transporting the finished product
such as electricity, coal or natural gas also causes an impact on the environment.
Finally, the depletion of unrenewable resources should be considered.
-41-
All seven screened alternatives require a significant amount of energy for
operation, although the absolute amounts would vary for each alternative.
The land application alternatives would not provide any onsite power generation
because anaerobic digestion is not included as part of the treatment process.
However, because they include aerated lagoons, their operating energy require-
ments are lower than for conventional plants. Power requirements for pumping
stations are directly related to the total height to which the water is
pumped and are therefore difficult to assess prior to a detailed predesign
study. However, for the alternatives that require pumping the wastewater
across the basin, the total power consumption would be higher than for the
other alternatives. Finally, due to economies of scale and efficiencies of
operation, one large conventional plant would tend to use less energy than
would multiple smaller plants treating the same total volume of wastewater.
Chemical Consumption
As with energy consumption, chemical consumption by wastewater treatment
systems is also directly proportional to the amount of pollutant removal.
However, depending on the chemical being considered and its function, the
consumption can decrease or increase as the pollutant removal increases.
Those chemicals required for pollutant removal would increase while disinfection
costs would decrease with improved effluent quality.
In addition to the consumption of chemicals, there are several other consider-
ations regarding the use of chemicals. First, production of the chemical
requires energy while at the same time causes resource depletions. Second,
the cost of chemicals has risen sharply as a result of the energy crisis and
is expected to continue an upward spiral . Third, production of chemicals
results in significant secondary impacts at their source.
In the systems under consideration, the only chemicals used are chlorine for
disinfection and sulphur dioxide (SO2) for dechlorination. The aerated
lagoon effluents would require approximately twice the chlorine dose than
would the effluents from any of the mechanical plants, although dechlorination
would not be required. For the treatment and discharge alternatives, de-
chlorination by SO2 would follow chlorination, and the required dose would be
approximately equal to the chlorine dose. Finally, a single large facility
would tend to consume less chemicals than would multiple facilities due to
efficiencies of scale and the greater automation of larger installations.
Utilization of Existing Facilities
Usually, large investments have already been made in existing facilities
which are quite capable of continued reliable service. These facilities
should therefore be utilized to the fullest practical extent.
All the screened alternatives under consideration, except the regional approach
in Alternative 9, utilize existing facilities in the Lower South Platte
Basin. Alternatives 6 and 5 utilize the existing Central Plant to a greater
extent than do any of the other alternatives. In addition, many of the
alternatives include the upgrading of the SACWSD plant, as recommended in the
SACWSD Facility Plan.
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Reliability of Operation
The reliability of a wastewater treatment system can be defined as the con-
sistency of its treatment as well as its treatment (or removal) capability.
Treatment consistency is the ability to produce a desired effluent on a
continuous basis and can be measured by the frequency of plant failure.
Therefore, reliability can be evaluated against the system's susceptibility
to process failures.
The ability of a treatment system to produce a desired effluent quality
consistently depends upon (1) the wastewater characteristics, (2) drastic or
abrupt changes in the facility influent, (3) the type of treatment technology,
and (4) the operation and management of the system. The first three variables
can be overcome by good design, but the fourth variable is totally dependent
on the ability and process understanding of the operating staff. The fourth
variable is also a very important function of the overall dependability of
the facility.
Infiltration/percolation basins can be considered the most reliable system
because they have a relatively simple treatment process. The process is
similar to a slow sand filtration of the effluent, but is actually using the
soil profile as the filtering and biological medium. However, the operation
and management of the system requires that the effluent be discharged into
various basins on a predetermined rotating schedule. If the schedule is
altered for some reason or the basins become flooded for too long a period,
significant algae growth occurs and odor and unsightly visual problems arise.
Larger conventional installations, instead of many smaller facilities having
the same cumulative volume, are the next most reliable treatment method due
to the higher degree of automation that is normally incorporated into the
design. The automation maintains optimal plant operation, and thereby a high
quality of effluent is produced continuously. Finally, the least reliable of
the alternatives are those which include multiple plants and a major remote
pump station as one component. A remote pump station introduces other factors
into the overall process such as anaerobic wastewater and its associated
problems, which are more difficult to treat. Also, the pump station has
potential problems such as pump clogging and power failures, which are more
serious in outlying areas.
Ability to Upgrade to a Higher Level of Treatment
Because of the EPA's goal of zero discjiarge of pollutants by 1985, all_trreeat-
ment facilities should have tfle fLe i.bility_ta_be upgraded relatively easily.
For zero dischar a the remainin ercenta es_of R(lf� and suspender of d
the nutrients nitrogen val_ of these
po9Tfa`nts is acco d
s i s, which are eas• v . Hence arw prora_�s that m���cole et Imo,
converts the soL oudd-be-rnore--adakecteet--the--
fu ure disc�iar_ge s_ta arils.
The infiltration/percolation system would most closely approach the 1985 goal
and therefore have the greatest potential for being upgraded to meet any
future standards. This land application system removes most pollutants from
-43-
the waste streams and would only require minimal extra treatment to achieve
higher treatment levels. Again, a single large conventional facility would
be the next easiest to upgrade, followed by multiple conventional facilities.
Abi I ity to Expand
As wastewater flows increase, the treatment facilities must be expanded to
accommodate and treat these higher flows. The addition of individual unit
processes is considered the simplest means of expanding the capacity of a
facility. In turn, one large plant would be easier to expand than would
several smaller plants. Due to its land consumptiveness, the alternatives
involving infiltration/percolation basins would be the most difficult to
expand. Finally, expanding a pump station/force main system is relatively
easy if sufficient capacity and space are built into the system initially.
However, if the pump station/force main combination is very large, then the
risk of septicity, odor and corrosion is high. Conversely, if the pump
station/force main combination is undersized, then new construction may be
required for expansion. The tendency is therefore to design the pump station
structure sufficiently large to accommodate all anticipated flows and to
allow for paralleling the force main in the future.
Effluent Quality
The quality of the effluent from a treatment facility can be described by
many different parameters. However, for the purposes of this comparative
evaluation, BOD, suspended solids, and ammonia-nitrogen are considered the
critical parameters for designing a treatment system for the Lower South
Platte Basin. These parameters have already been discussed. Total dissolved
solids (TDS) is one other important parameter that should be briefly con-
sidered. TDS is objectionable because of physiological effects, mineral
taste and economic consequences. High TDS values result in a laxative effect
on humans, while values over 1 ,000 mg/I can have adverse effects on crops.
The accepted limit for drinking water is 500 mg/I . The TDS remains essentially
the same for conventional biological wastewater treatment but is increased by
about 10 percent in an infiltration/percolation system. TDS is normally
measured by the specific electrical conductance test.
Although land application systems are not designed to achieve a specific
effluent quality, these systems generally produce an effluent of better
quality than is required. Land application systems are designed on the basis
of the hydraulic and nutrient uptake capacities of the soil profile, while
conventional systems are designed on the quality of water required from the
system. However, because of the inherent nature of its treatment process,
which uses the soil as a natural filter, land application is usually graded
higher than conventional systems in the level of effluent quality achieved.
The alternatives employing infiltration/percolation basins would yield the
highest quality of effluent. For conventional systems, one large facility
would tend to produce a higher quality effluent than would several smaller
facilities due to the automation of the unit processes. However, multiple
discharge points would tend to take advantage of the assimilative capacity of
the receiving streams.
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IMPLEMENTATION CONS[DERATIONS
Institutional
The alternatives could all be implemented using existing units of government.
The wastewater treatment capability could be expanded and upgraded without
the creation of a new service district. Intergovernmental agreements will be
required to accommodate the transfer of responsibility for wastewater treatment
and to provide for longer term funding of operation and maintenance on an
equitable basis. The institutional basis will be established when a specific
alternative has been selected for further development.
A major wastewater treatment program is likely to be recommended as a result
of this Facility Plan. The preparation of a detailed predesign study will be
complemented by an analysis of the legal requirement to implement the plan.
Those alternatives which maintain the status quo in terms of agency respon-
sibilities would probably be easier to implement than would those which
require negotiations between two or more agencies. The units of local govern-
ment in the Lower South Platte service area have traditionally been capable
of performing the utility service functions on an individual basis. While
cooperative arrangements have been very effectively implemented, they can
contribute to delays in construction of the required facilities.
Possible methods of implementing a wastewater management system include
establishment of a new special district, an intergovernmental contract such
as the Englewood/Littleton arrangement, one direct contractual arrangement
with one of the existing c ties such as Brighton, or expansion of the existing
Metro District to manage any new systems.
Financial
The economics of the various alternatives are considered elsewhere in this
report. The question addressed here has to do with the means and the ability
of agencies responsible for wastewater treatment in the Lower South Platte to
accept the financial obligation of construction as well as operation and
maintenance.
As required by Section 39. 935-13 of CFR Title 40, the agencies implementing a
Facility Plan must as a condition of the grant develop a system of Users
Charges and an Industrial Cost Recovery Program for the construction of new
facilities or expansion and upgrading of existing facilities. Users Charges
and Industrial Cost Recovery systems are being used by wastewater treatment
agencies in the Lower South Platte at the present time. It is anticipated
that these systems would be adapted to meet the changed condition of expanded
wastewater treatment capability.
Capital debt service and operations costs associated with the Facility Plan
would be accounted for in the Users Charge system and in the Industrial Cost
Recovery system.
-45-
The capital cost to the local agency is the cost remaining after Federal and
state grants have been subtracted from the total . In Colorado, the local
share is 25 percent of construction. The local share can be generated in two
basic ways, through funds available in construction accounts or through the
issuance of bonds.
Legal
For new facility sites, a specific permit restriction is related to zoning.
Develo ment of most of the proposed sites would require zing ange and
conditiioona �s �Qrm't from Adams Coffin jam_This, it can be argued hat • is
4 more desirable to exp d_an_dupgrade existing faci lities_than to__davelop p_e,w
fac�ifities. While it is ossible=that change.o_f_zoning_or_coc�ditiona�u
pe mi s would be requ_ired_to_expandr_approval_by the_Plan_ni_r�_q_CommisSio d
Board of`-Commissioners could robably be acguired_with greater ear
expansion an for new=facilites_permit
The zoning for the proposed sites is Flood Control . The type of developments
allowed in this zone are those which can be flood proofed, either through the
elevation of structures or the construction of berms to contain the flood
waters. These provisions can be complied with in the design of the proposed
alternatives. However, any alternatives that require significant land area
may, if perimeter berms are used, reduce the flood holding capacity of the
flood plain. This will create a higher elevation backwater area upstream of
the embankment and will contribute to increased flood velocity past the flood
protection structure. Downstream this will have the effect of reducing the
elevation of flood water and increasing the duration of flooding. However,
n none of the screened alternatives is expected to cause any problems with the
l backwater elevations or an increased flood duration downstream of the site.
° In addition, mitigating measures will be taken to minimize the effect of
locating a facility in the flood plain. In addition to the zoning provision_
of Adams County, the Federal Government requires that aii fa e.aU. ==cictarl
projects be flood p- n--�- or c_nstrlgtec__ou,ts_ide_at flood_plains,
Another legal consideration is the filing of a grant request with Federal and
State agencies. A grant by any Federal agency requires compliance with the
provision of the National Environmental Policy Act (NEPA) . The Federal
agency involved in implementing this Facility Plan and ensuring compliance
with NEPA is the EPA. To comply with NEPA, the Region VIII Division of the
EPA has elected to write an overall EIS of the Denver metropolitan area
covering the secondary impacts of growth patterns on land use, the economy
and the environment as related to the implementation of a wastewater management
system. Site specific impacts of the selected alternative will also be an
input to the EIS.
The alternatives being evaluated have been developed to include both new
facilities and existing facilities. This acknowledges the realization that
the technical and environmental merits must be weighed against the feasibility
of implementation. A treatment system that is not optional in all considera-
tions may be better than no solution at all .
-46-
Finally, construction of all new facilities requires a Site Approval that is
issued by the Water Quality Control Commission (WQCC) . To obtain this Site
Approval, a special procedure is followed in which various agencies are
requested to approve the application. The WQCC then evaluates the comments
received from the various agencies and votes on whether or not to issue the
Site Approval . Adams County is also investigating wastewater facilities and
is considering imposing a separate Site Approval for construction of facilities
in Adams County.
Public Sentiment
Wastewater treatment is generally perceived by the public to be of social
value in terms of public health, safety and aesthetics. However, individuals
often tend to resist financing public utility programs or, more often, resist
having the physical facility located in their vicinity. If a generalization
can be made about universal public attitude, the generalization most applicable
to wastewater is "out of sight, out of mind."
The alternatives having the lowest cost and making the greatest possible use
of existing facilities are being suggested for review by the public and
agencies prior to selection of a specific system. After this initial round
of public involvement, ar alternative will be selected. When the predesign
program produces definitive information, a second round of public involvement
will be initiated to foster good communication with the residents of the area
to be affected and to incorporate their concerns into the predesign process.
Agency Sentiment
The alternatives will be reviewed by the pertinent regulatory agencies, as
well as any others that may have an interest. These agencies will be asked
to submit written comments and present oral comments as may be needed.
Following selection of a specific project, these agencies will be recontacted
for input into the predesign process. This communication will reduce the
possibility of unforeseen conflicts and allow for early resolution of public
agency objectives.
ENVIRONMENTAL CONSIDERATIONS
Climatological Effects
The climatological changes associated with wastewater treatment facilities
have to do with modification of microclimates in the immediate vicinity of
the facility. The microclimates are in areas usually less than 1 square
mile.
Increased atmospheric moisture in the form of either fog or humidity is the
primary concern. TR a limi Cl PXteni tem na :r _ WPVPt ,
temperature chap a is ore a function of changes in humidit becau. se-a-,higher
h i i y retainsJieat longer., In ad Lf�o r asteaaua#� t eatrx�eczt facIIties,
d6 not te=s:raficar _ u tities_of waste t kt.
-47-
The development of wastewater treatment facilities in the Lower South Platte
Basin would have virtually no effect on the general climate of the basin or
metropolitan Denver. Any effect in the immediate vicinity of the potential
treatment sites would be too small to distinguish between the alternatives.
Air Quality
Short-term considerations of air quality are related to dust and vehicular
emissions during construction. None of the alternatives should create signifi-
cant air quality problems at any of the presently identified sites.
Vehicular emissions would contribute to the atmospheric pollution loading.
Increased traffic is anticipated while the treatment facility is under con-
struction. The mechanical treatment plants, because they are more labor
intensive during both construction and operation, would contribute more
vehicular pollutants. However, the number of vehicles and their impact on
air quality would be relatively minor regardless of the alternative chosen.
The impact related to dust during construction would be highly dependent upon
the location chosen for facility construction. The potential impact is
limited in that most of the dust usually settles out in the immediate vicinity
of the construction. Adequate construction safeguards can substantially
reduce both the frequency and severity of this problem.
Land consumptive alternatives, because they involve more extensive earth-moving
during construction, would have the greatest short-term impact on air quality
during construction. Multiple plants would disperse the air quality disturbances
among several sites rather than create a larger disturbance at one site.
However, multiple plants would also expose several sites rather than one site
to construction activities. From the perspective of air quality control, a
single site would be easier to regulate.
Ground Water
The proposed alternatives possess the potential for degradation of ground
water in the event of failure of the treatment facility or if proper precautions
are not followed in the construction of the land application systems. Restric-
tions related to site location, soil, geologic and topographic considerations,
application rates, and allowable loadings have not been developed. However,
it can be assumed that design standards would provide a high degree of certainty
that ground water would not be degraded. Those alternatives which allow for
relatively complete control over sludges and effluent would have less potential
for contaminating the ground water.
In the event of treatment plant failure, surface water would temporarily be
degraded. This could lead to slight ground water quality impairment as well
through interaction between surface and shallow ground water in the Lower
South Platte Basin.
The land application system may contribute to pollution of the ground water
unless extremely stringent operational procedures are implemented. The
potential buildup of heavy metals and salts in the soil profile of the infil-
-48-
tration/percolation basins presents the possibility of leaching to the ground
water. The soil's uptake capacity and the assimilative capacity of the
ground water are unknown but are assumed to be limited. Thus, the ground
water could be degraded if these capacities are exceeded.
Ground water quality would be enhanced by multiple discharge points because
the ground water profile would be enriched in several areas rather than at a
single point.
Soils and Geology
None of the alternatives would affect the geologic base of either the treatment
sites or the Lower South Platte area. The treatment plant alternatives
require disturbance of the soil profile. During construction, soil erosion
would occur in areas exposed to the construction activities. The land
application systems would also cause disturbance, although it appears the
land application sites have previously been disturbed by agricultural pursuits.
The soils of an individual site would be examined for their suitability or
adaptability for use as a wastewater treatment site. For the land application
sites, in addition to engineering characteristics, soils would be evaluated
with regard to their ability to assimilate nutrients and heavy metals. The
infiltration/percolation system is site specific and requires sands and/or
gravels through which the effluent can percolate. The alluvial materials
should be 10 to 15 feet deep and be underlain with bedrock.
No environmental effects are anticipated with relation to soils or geology
offsite, and limited effects are expected relative to onsite soil degradation.
It can be anticipated that soil weathering would be accelerated as water
quantities are increased. Thus, the land application alternatives would have
the greatest impact, although the impact cannot be considered to be significant.
None of the alternatives would constitute a major disturbance to the soil or
geology of the Lower South Platte and hence should not greatly affect alternative
selection.
Vegetation/Wi Idl ife
The identified alternatives would not significantly reduce flora in the Lower
South Platte Basin. None of the alternative sites supports native plant
communities. Rather, each of the sites proposed for wastewater treatment
facilities is typified by various introduced flora. Pasturage and agri-
cultural crops are the most typical . The study area has supported intensive
agricultural activity for approximately 100 years.
The infiltration/percolation basins and the treatment plants would remove
vegetation and substitute instead a semi-aquatic environment or impervious
building surfaces. The losses cannot be considered to be substantial since
the vegetation that would be displaced is common throughout the Lower South
Platte service area, and indeed throughout the front range of the Rocky
Mountains. The sole differentiation regarding impacts on vegetation which
can be made between the alternatives is related to the size of the facilities
and subsequently the amount of vegetation that would be removed.
-49-
The effects of the alternatives on plant life all seem to be directly related
to the area of disturbance and too insignificant to be a factor in choosing a
system to expand and upgrade wastewater treatment facilities. The alternative
requiring the least land area would be the most favorable in terms of minimizing
impacts on vegetation.
Wildlife would not be substantially affected. The reduction of ground cover,
as discussed above, would be concentrated in areas of introduced plant species.
There would be some reduction of habitat for some small animals. Principal
cover adjacent to the South Platte River would remain relatively unaffected.
The river and sand islands would not be affected, thus the primary vegetation
and wildlife habitats would remain intact. While site specific studies have
not been conducted, it can be anticipated that loss of highly productive
habitat or rare and endangered animal species would not occur.
All of the alternatives are proposed to improve the quality of water in the
South Platte River. This improvement to water quality would enhance productivity
of the aquatic environment and through the food chain would also enhance
productivity of the terrestrial environment. The resulting greater carrying
capacity of these ecosystems could increase the number of individuals supported
in the area. The potential for establishing species not presently supported
in this reach of the South Platte is probably insignificant.
The alternatives that include multiple discharge points would have the greatest
benefit to wildlife through enhancement of the flood plain. However, multiple
plants would also require the greatest disturbance and removal of habitat.
Hydrology/Water Quality
The greatest discharge of treated wastewater would ultimately return approxi-
mately 28 mgd to the South Platte River, which constitutes 11 percent of the
average annual South Platte River flow. Continued monitoring of the area's
water regime by EPA, Metro Denver, the Corps of Engineers, and the State of
Colorado Department of Natural Resources along with U.S.G.S. monitoring
programs would allow close surveillance of hydrologic impacts. Changes in
water flow conditions will provide the information needed to document future
impacts on area water resources in general and stream hydrology in particular.
An important water quality management program of concern in the Denver area
is the Denver Regional Council of Government's 208 areawide study currently
being prepared. That study includes the investigation of various operational
and administrative alternatives which are available and will determine the
most practicable program for ensuring protection of the surface and ground
water resources.
The alternatives with multiple discharge points would be most desirable in
terms of establishing a relatively steady-state hydrologic regime and improving
the water quality of the streams. It should also be noted that the existing
average annual flow of the South Platte River is approximately 55 percent
Metro Denver effluent, as measured at Henderson.
-50-
Aquatic Environment
All of the alternatives would improve the aquatic environment of the South
Platte River in that fewer pollutants would be discharged for assimilation by
the river. The continuing improvement in water quality of the South Platte
River would tend to promote the return of previous species to a greater level
and may encourage the establishment of new species.
Some short-term impacts on the South Platte aquatic life are probably unavoid-
able during construction, even with special construction practices and pro-
cedures. Increased turbidity and sedimentation could temporarily eliminate
some bottom habitat, kill fish, and lower water quality.
All of the alternatives would enrich the aquatic environment. However, it
can be assumed that multiple discharges of effluent offer the opportunity for
an increased number of habitat areas, although of smaller scale than those
provided by a single discharge of treated wastewater. The higher quality
effluent from the infiltration/percolation basins has more potential for new
habitats than does effluent from conventional plants.
Vectors
The proposed alternatives do not present significant environmental concern
relative to vectors. Rodents are uncommon among adequately operated treatment
facilities. Normal operation of the infiltration/percolation basins includes
both wet and dry cycles, which should preclude the hatching of mosquito
larva. The other alternatives should not provide the environment required
for the propagation of insect species either.
Vectors which may inadvertently occur can be controlled by judicious application
of State- and Federal-approved pesticides and insecticides or by specific
biological control techniques such as predator introduction.
Vectors do not appear to be a significant factor for selection of an alternative
since any potential problem that may occur could be controlled. However, the
land consumptive alternatives would have the greatest potential for attracting
vectors.
Land Use
Present privately held land used for wastewater treatment would be under the
control of a special government district and hence would be removed from the
tax rolls of the Adams County government and, in addition, would be removed
from the private enterprise system. In order to acquire an adequate amount
of land for any of the alternatives, it would be necessary for the District
or another agency to negotiate a fee. If the landowner does not wish to sell
his land, then condemnation proceedings are instituted and the court sets a
fair market value on the land. The owner and the agency then negotiate a
final price. Those alternatives that are highly land consumptive may tend to
create objections to the project and thus significantly delay its development.
-51-
The infiltration/percolation system would not be capable of producing agricul-
tural products. Thus, this system would serve to reduce consumable production
for a considerable area within the Lower South Platte drainage by removing it
from agricultural use.
The proposed mechanical treatment plants would require significantly less
total land area and would not have the implications on the agricultural
economy that the infiltration/percolation system appears to have at this
time. Of the two primary plant sites, the one that seems to be the most
desirable is in the vicinity of 140th Avenue near an existing sand and gravel
operation. This site would offer the opportunity to reclaim part of the
mined area for the construction of a treatment facility. The area has no
value for agricultural production because of the severe disturbance associated
with the sand and gravel operations. The area around the sand and gravel
mine has historically been disturbed through other activities, and therefore
the treatment plant should not create a negative impact in the area. The
site near 164th Avenue on the west side of the South Platte River opposite
Brighton is presently used for pasturage and hay crops. A plant at that site
would create an intrusion of urban Brighton across the geographic barrier of
the South Platte River and would tend to reduce the amenities associated with
the rural lifestyle west of Brighton in the valley bottom of the South Platte
River. However, the 164th Avenue plant site has already been proposed for a
new WWTP to serve the City of Brighton and therefore is assumed to be acceptable
to the City.
Those alternatives that offer an opportunity to reclaim an area previously
used for development would create the least noticeable impact on land use
patterns in the study area.
Health and Safety
There are two basic purposes for the proposed expansion of treatment capability.
One objective is to protect public health through disinfection of wastewater.
The second purpose is to reduce pollution loadings to promote the retention
or restoration of an environment that is beneficial to all organisms and that
does not endanger humans.
The nature of present-day wastewater treatment technology is to aggregate the
wastewater into a single series of facilities. This also aggregates the
pathogenic organisms at a single source. However, the likelihood of disease
being contracted via any of the alternatives is very remote. Nevertheless,
while treatment processes are designed to remove or destroy these health
hazards, all pathogens are not eliminated and thus the possibility exists of
transmission to either facility employees or the public.
If reasonable caution is exercised in the design and operation, threats to
health and safety would be reduced to a minimum. Because the same positive
and negative health considerations are associated with all the alternatives
utilizing plants, these factors cannot be used to distinguish between these
different systems. However, due to the increased acreage of the infiltration/
percolation basin system, security of the site becomes more difficult and the
probability of unauthorized personnel entering the site increases. This
-52-
causes a greater potential for health and safety problems. In addition, some
rather insignificant risk is associated with the facility operators being
exposed to greater areas of wastewater in the treatment lagoons, compared to
a conventional plant.
Aesthetics
While the structural treatment systems would be the least land intensive,
they are also the systems which would tend to have an odor, noise, and visual
impact on the study area. The construction of a treatment plant would certainly
be intrusive and would tend to alter the visual character of the area. The
land application systems, on the other hand, would probably not be noticeable
as a distinct and separate land use within the agricultural community.
Although the odor and noise associated with a treatment plant may be more
noticeable, they also tend to be more localized than the odor and, to some
extent, the noise problems associated with an infiltration/percolation system.
Those alternatives which would create the greatest disturbance would be those
closest to residential or commercial developments. However, all alternatives
are located in areas which are not heavily developed.
Socioeconomic Considerations
The Lower South Platte River Basin is basically a water-short area. Thus,
the agricultural sector ma be si nificantly disru ted by changes in the
existing pattern of watercansumption or water diversion an -y t ie use
signincant land areas for wastew tPc_Ar t e_nt as world occur i t}�ea f�J-_�
tration/per elat�oC S stems o„a.n.egative impact on the irrigated farmin_.
operations could have a ripple effect and also reduce_thev_itality of the
nonirrigated_srops_andLor_bee_ef cattle_ and dairy cattle operations within and,
around the study area,
Another effect on the basin's rural areas is a possible increase in urbanization
once basinwide wastewater management is implemented. Those individuals who
presently reside in the rural areas of the Lower South Platte Basin may do so
because of the quality of life associated with undeveloped land holdings
and/or because of small nonintensive livestock-raising activities. An increasing
rate of urbanization would reduce the values historically associated with a
bucolic setting. However, these rural landowners would derive a steady and
considerable increase in the value of their holdings and could, if they
strongly desire the rural setting, move to the urban fringe.
The two main socioeconomic impacts for distinguishing between the alternatives
are changes in lifestyles and modification of water availab_Wly. Those
alternatives centering around use of the Central Plant would have the least
potential for these two impacts.
-53-
MISCELLANEOUS CONSIDERATIONS
Conformance With 1972-74 Water Quality Management Plan (WQMP) Goals
The WQMP prepared for DRCOG between 1972 and 1974, although not having a
legal base, still indicates general attitudes toward wastewater treatment and
some of the findings are therefore of value in this analysis. The more
important findings are summarized below.
■ That an overall system utilizing multiple plants be implemented,
including treatment facilities on Clear Creek, Sand Creek and the
South Platte River in addition to the Central Plant.
■ That the wastewater management systems minimize inter-basin pumping
and maximize gravity flow systems.
■ That the wastewater management systems be phased to defer capital
expenditures and utilize existing facilities to their maximum
extent.
■ That existing "package plants" or other small separate treatment
facilities be phased out and connected to the regional system as
the sewers are extended to these plants during the normal course of
growth.
■ That the selected wastewater management system be sufficiently
flexible to allow changes in general configurations based on differing
population and land use projections.
In terms of meeting these goals, the alternatives proposed in this report
that include all or some of these principles are preferred over those that do
not. The goal opposing inter-basin pumping is one major factor for distinguish-
ing between the alternatives.
ALTERNATIVE COMPARISON SUMMARY
To further reduce the number of alternatives, the seven screened wastewater
management systems were compared on the basis of the factors presented in
this section, with the exception of public and agency sentiment. A weighted
numerical ranking was used as described in this paragraph to identify the
preferred alternatives. Each alternative is assigned a number that is an
index of the relative impact of that alternative for the factor under considera-
tion. If two or more alternatives have an equal impact for a particular
factor, then each is assigned an identical score. The lower the score, the
less is the impact associated with that alternative for the particular factor.
Also, a "weight" is assigned to each factor to indicate its importance with
respect to the other factors in the opinion of the evaluators. The "weight"
for each factor is then multiplied by the relative impact score to yield a
weighted numerical ranking. When the weighted impacts are summed, the lowest
total score indicates the preferred alternative.
-54-
The results of this numerical evaluation are shown on Table 10. The indicated
preferred alternatives at this time are 4, 5, 6, and 10. However, this
detailed analysis was performed without the benefit of either public or
agency input. The results of the public meetings and agency reviews may
yield somewhat different results, and the public is invited to study the
alternatives dropped from contention. A shortened version of Table 5 with
only the screened alternatives has been included in this section for conven-
ience in evaluating these alternatives. It can be used in conjunction with
Table 10.
-55-
Table 10
COMPARISON OF ALTERNATIVES (1)
WEIGHT
EVALUATION FACTORS FACTOR ALT. 4 ALT. 5 ALT. 6 ALT 8 ALT 9 ALT 10 ALT 11
ECONOMIC CONSIDERATIONS S(2) R(3) S R S R S R S R S R S R
Present Worth Cost 10 3 30 4 40 4 40 4 40 1 10 2 20 3 30
Annual Cos-is 7 3 21 4 28 4 28 4 28 1 7 2 14 3 21
ENGINEERING CONSIDERATIONS
Net Energy Consumption 7 3 21 4 28 4 28 4 28 1 7 2 14 3 21
Chemical Consumption 7 3 21 3 21 3 21 3 21 1 7 2 14 3 21
Utilization of Existing Facilities 6 2 12 1 6 1 6 2 12 3 18 2 12 2 12
Reliability of Operation 7 3 21 4 28 4 28 4 28 1 7 2 14 4 28
Ability to Uograde 5 3 15 3 15 3 15 3 15 1 5 2 10 3 15
Ability to Expand 5 1 5 1 5 1 5 1 5 3 15 2 10 2 10
Effluent Qu4lity 7 3 21 3 21 3 21 3 21 1 7 2 14 ,3 21
IMPLEMENTATION CONSIDERATIONS
Institutional 7 3 21 1 7 1 7 4 28 5 35 3 21 2 14
Financial 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2
Legal 10 2 20 1 10 1 10 3 30 5 50 4 40 4 40
Public Sentiment — — — — — — — — — — — — — — —
Agency Sentiment — — — — — — — — — — — — — — —
ENVIRONMENTAL CONSIDERATIONS
Climatological Effects 2 1 2 1 2 1 2 1 2 3 6 2 4 2 4
Air Quality_ 2 1 2 1 2 1 2 1 2 2 4 1 2 1 2
Grourd Water 9 1 9 1 9 1 9 1 9 3 27 2 18 2 18
Soil and Geology 7 1 7 1 7 1 7 1 7 3 21 2 14 2 14
Vegetation 2 1 2 1 2 1 2 1 2 3 6 2 4 2 4
Wildlife 2 1 2 1 2 1 2 1 2 3 6 2 4 2 4
Hydrology/Water Quality 7 3 21 3 21 3 21 3 21 2 14 2 to 1 7
Aquatic Environment 6 4 24 4 24 4 24 4 24 1 6 3 18 2 12
Vectors 5 1 5 1 5 1 5 1 5 3 15 2 10 2 10
Land Use 9 2 18 1 9 1 9 2 18 3 27 3 27 3 27
Health and Safety 5 1 5 1 5 1 5 1 5 3 15 2 10 2 10
Odor 8 2 16 2 16 2 16 2 16 1 8 1 8 1 8
Visual Impacts 4 2 8 1 4 1 4 2 8 2 8 2 8 2 8
Noise 5 2 10 2 10 2 10 2 10 1 5 1 5 2 10
Socioeconomics 8 3 24 1 8 1 8 3 24 4 32 3 24 2 16
MISCELLANEOUS CONSIDERATIONS
Conformance with WQMP Goals 2 1 2 2 4 2 4 1 2 1 2 1 2 1 2
TOTALS 367 341 341 415 372 357 391
(1) For description of alternatives, see Table 5
(2) 5=Score
(3) R=Weighted rank where R=Score x weight factor
1
TABLE 11
DESCRIPTION OF SCREENED ALTERNATIVES
ALT. AREA NO.
NO. FACILITY AREA SERVED ON FIG. 2
4 NEW WWTP AT 164TH & NEW INTERCEPTOR BRIGHTON 7
1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,6
EXISTING THORNTON-N. WASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4
NWSWSD 5
UPGRADED EXISTING PLANT---- SACWSD 9
5 NEW WWTP AT 164TH BRIGHTON 7,PART OF 6
1ST,2ND,3RD CREEKS 8
NEW INTERCEPTOR TO NEW PUMP STATION AT
124TH TO NEW FORCE MAIN TO CENTRAL
PLANT LOWER THORNTON 1 ,2,PART OF 6
EXISTING THORNTON-N. WASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
6 NEW WWTP AT 164TH BRIGHTON 7,PART OF 6
NEW INTERCEPTOR TO NEW PUMP STATION AT
140TH TO NEW FORCE MAIN TO CENTRAL
PLANT 1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,PART OF 6
EXISTING THORNTON-N. WASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4,
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
8 NEW WWTP AT 140TH & INTERCEPTOR BRIGHTON (NEW PUMP
STATION AT EXIST-
ING PLANT SITE) 7
1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,6
EXISTING THORNTON-N. WASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
-57-
TABLE 11 CONT.
9 INFILTRATION/PERCOLATION BASINS
BETWEEN 136TH AND 160TH
& NEW INTERCEPTOR ENTIRE BASIN
10 INFILTRATION/PERCOLATION BASINS
BETWEEN 136TH AND 150TH
& NEW INTERCEPTOR BRIGHTON (NEW PUMP
STATION AT EXIST-
ING PLANT SITE) 7
1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,6
EXISTING THORNTON-N. WASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
11 INFILTRATION/PERCOLATION BASINS
BETWEEN 136TH AND 150TH
AND NEW INTERCEPTOR 1ST,2ND,3RD CREEKS 8
LOWER THORNTON 1 ,2,PART OF 6
NEW WWTP AT 164TH BRIGHTON 7,PART OF 6
EXISTING THORNTON-N. WASH. INTERCEPTOR
& PUMP STATION TO CENTRAL PLANT UPPER THORNTON 3,4
NWSWSD 5
UPGRADED EXISTING PLANT SACWSD 9
-58-
Hello