**USDA-Rural Development**

MN 1780 Guide 6

(Rev 12/04)

**MINNESOTA PRELIMINARY ENGINEERING REPORT SUPPLEMENT**

**FOR**

**WATER, WASTEWATER, STORM WATER AND SOLID WASTE PROJECTS**

I.  GENERAL

    A.  This supplement is to be used in addition to USDA RUS Bulletins
        1780-2, 1780-3, 1780-4 and 1780-5, Preliminary Engineering
        Reports.

    B.  Type of report to prepare: Projects that do not include funding
        from MPCA (i.e., ISTS, Petrol-Fund, etc.) or the Sate Revolving
        Loan Fund only require the preparation of a Preliminary
        Engineering Report (PER). In addition to the below requirements
        for preparing a PER, a Facility Plan (FP) should include all of
        the requirements listed in Exhibit B as well as any other
        information requested by MPCA.

    C.  Modesty: Rural Utilities Service (RUS) projects must be modest
        in design, size and cost, simple to operate, and constructed and
        operated in an environmentally responsible manner.

    D.  Minnesota RUS policies:

        1.  Contingency funds: The items that are needed for the project
            must be included in the beginning scope of the project.
            Contingency Funding is for unforeseen conditions or bids
            that exceed the engineer's cost estimates. The Contingency
            Fund is not intended to be a slush fund or a "want list
            fund". The Contingency Fund will be administered in
            accordance with RUS Instruction 1780.45(f).

        2.  Growth: Applicants in growth areas are to design systems
            that will accommodate growth as it is realized. However,
            Rural Development will allow a system to be 20% larger than
            currently needed for the residential and business users in
            those areas that have a history of growth when determining
            grant and loan amounts. If the Rural Development engineer
            determines that the system is being proposed for more than
            20% growth, the application will be returned to the Area
            Office for a more in depth determination of the availability
            of other credit. When such condition exists, Rural
            Development will only consider grant eligibility based on
            120% of the flows that should actually be generated by
            residential and business users. Any additional capacity will
            be considered for loan only. When there are phased systems
            or growth included, the areas of growth must be determined
            and included in both the determination of median household
            income and in the environmental review process.

        3.  Operation and maintenance (O&M) costs: O&M costs vary by
            type of system; therefore it is difficult to provide exact
            cost guidelines. However, we suggest that if the operating
            and maintenance costs of a sewer system are substantially
            higher or lower than \$17.50 per EDU that additional
            information be obtained to justify the proposed costs.
            Likewise, if a water system has operating and maintenance
            costs substantially higher or lower than \$15/EDU that
            additional information be obtained to justify the proposed
            costs.

II. Water

    A.  All water projects must follow Minnesota Department of Health
        requirements and guidelines.

    B.  Fire protection: A primary goal of the RUS Water and Waste
        program is to develop and maintain reliable, safe drinking water
        systems. It is the policy of RUS to include reasonable fire
        protection where economically feasible. However, providing full
        fire protection in a system financed by Water and Waste would
        quickly deplete program funds. Therefore, determining reasonable
        and practicable fire protection is a challenge for both rural
        communities and RUS and will require creative solutions.

III. Wastewater

     A.  Collection and treatment alternatives shall be considered in
         the following order:

         1.  New Individual Sewage Treatment Systems (ISTS) with
             centralized management to provide assured monitoring,
             operation and maintenance.

         2.  Decentralized wastewater systems that combine localized
             failed ISTS into a multiple-household, soil-based system
             with centralized management.

         3.  Connect the failed unsewered area to an existing wastewater
             treatment facility with available capacity.

         4.  Connect the failed unsewered area to an existing wastewater
             treatment facility, which requires additional capacity
             through an expansion.

         5.  Development of a new wastewater collection and treatment
             facility.

     B.  Infiltration and inflow (I&I): Our policy is that I&I will be
         corrected to the extent that it is economically practical.
         There will be times when regulatory agencies, Rural Development
         and other funding agencies determine that it is economically
         more practical to provide larger treatment capacity rather than
         correct all I & I. When such condition exists, Rural
         Development will only consider grant eligibility for treatment
         based on 120% of the flows that should actually be generated by
         residential and business users including normal I & I. Any
         additional capacity needed because of I & I will be considered
         for loan only.

     C.  See Exhibit A Minnesota Pollution Control Agency Design Flow
         and Loading Determination Guidelines.

IV. Solid Waste

    A.  No additional Minnesota RD requirements or clarifications.

V.  Storm Water

    A.  No additional Minnesota RD requirements or clarifications.

**EXHIBIT A**

**MINNESOTA POLLUTION CONTROL AGENCY**

**DESIGN FLOW AND LOADING DETERMINATION GUIDELINES**

These guidelines are recommended procedures for estimating design flow
and loading conditions. It is expected that the engineer will use good
engineering judgment in selecting the design conditions and will give
due consideration to unique aspects of the contributors, to the type of
treatment, to the return wastewater flows and return sludge, etc.

INTRODUCTION

The flow monitoring period for any particular project must record flow
data during critical peak wet weather flow events which have occurred
during a sustained wet weather flow period. Data collected during this
flow period are used to estimate the four (4) flow conditions that are
critical to the design and operation of wastewater treatment plants (see
Table 1): average dry weather (ADW), average wet weather (AWW), peak
hourly wet weather (PHWW), and peak instantaneous wet weather (PIWW).

The average dry weather flow is the daily average flow when the ground
water is at or near normal and a runoff condition is not occurring.
Average wet weather flow is the daily average flow for the wettest
thirty (30) consecutive days for mechanical plants or for the wettest
180 consecutive days for controlled discharge pond systems. The 180
consecutive days for pond systems should be based on either the storage
period from approximately November 15 through May 15 or the storage
period from approximately May 15 through November 15. The treatment
plant must meet the calendar month average NPDES permit requirements at
average dry weather and average wet weather flow conditions.

The peak hourly wet weather flow is the peak flow during the peak hour
of the day at a time when the ground water is high and a five-year
one-hour storm event is occurring. To determine this five-year one-hour
storm event for the specific project, please refer to the attached Map
Number 1. The peak instantaneous wet weather flow is the peak
instantaneous flow during the day at a time when the ground water is
high and a twenty-five year one-hour storm event is occurring. To
determine the appropriate twenty-five year one-hour storm event, please
refer to Map Number 2. No separate permit limitations are associated
with either peak hourly wet weather flow or peak instantaneous wet
weather flow.

Clarifiers must be designed to meet the appropriate surface settling
rate and weir overflow rate at peak hourly wet weather flow. The
disinfection unit must be designed to provide adequate detention at peak
hourly wet weather flow. At the treatment facility, all preliminary
units, screens, filters, piping and pumping must be designed for peak
instantaneous wet weather flow. The collection system must be capable of
transporting all flows to the treatment facility. All other units should
be designed to allow this flow to pass through the units.

Where the Minnesota Pollution Control Agency (MPCA) determines that the
above design flow considerations will not provide adequate protection to
the receiving waters, facility capacity in excess of peak instantaneous
wet weather flow may be required.

In cases where flow studies are over five years old, or where the
consultant designing the treatment or transmission facility did not
perform the flow study, a verification of the acceptability of the flow
data should be performed.

**TABLE 1**

**DESIGN FLOW CONDITION SUMMARY**

  ------------- --------------------------- ------------------------------
  Item          Description                 Purpose

  ADW           Average dry weather flow    Facility designed to meet the
                assumes normal ground water calendar month average permit
                with no runoff.             limitations and to determine
                                            if flow equalization should be
                                            evaluated.

  AWW           Average wet weather flow    Facility designed to meet the
                (wettest 30-day average for calendar month average permit
                mechanical plant and        limitations and to determine
                wettest 180-day average of  if flow equalization should be
                controlled discharge pond   evaluated.
                systems). Assume high       
                ground water with inflow    

  PHWW          Peak hourly wet weather     Clarifier and disinfection
                flow. Assumes high ground   sizing and to determine if
                water with inflow due to a  flow equalization should be
                five-year one-hour storm    evaluated.
                event.                      

  PIWW          Peak instantaneous wet      Hydraulic design sizing for
                weather flow. Assumes high  preliminary units, screens,
                ground water with inflow    filters, piping and pumping at
                due to a twenty-five year   the treatment facility.
                one-hour storm event.       
  ------------- --------------------------- ------------------------------

BYPASS/OVERFLOW

All bypass/overflow structures shall be manually controlled and kept
locked at all times. All bypassing is prohibited unless:

1\. Bypass was unavoidable to prevent loss of life, personal injury or
severe property damage;

2\. There was no feasible alternative to the bypass;

3\. The Permittee gives previous notice of an anticipated bypass.

Any bypassing must be reported to the MPCA in a report consistent with
permit requirements. This report shall include, but not be limited to,
the bypass duration, estimated volume and associated meteorological
conditions. Periodic bypassing at any discharge point under flow

conditions less than PIWW may precipitate the need for a corrective
action plan to upgrade the system.

The following design flow consideration shall be incorporated into new
or existing treatment facilities in order to reduce frequency as well as
degree of adverse environmental impact associated with bypassing:

1.  The treatment facility shall provide pretreatment for the removal of
    coarse floatable and/or settle-able solids during flows in excess of
    peak instantaneous wet weather. In additions, the pretreated waste
    shall then be blended with the fully treated effluent, where
    practical, and discharge samples collected for the purpose of
    determining NPDES/SDS permit compliance of the blended effluent.

2.  Flow equalization for mechanical plants may be necessary in order to
    effectively operate treatment plants. Please refer to the section
    entitled Flow Equalization.

TREATMENT SYSTEMS WITH NEW SANITARY SEWER COLLECTION SYSTEMS

If a new collection system is being constructed and no inflow sources
will be connected, the average wet weather flow for this treatment plant
shall be based on a minimum of 100 gallon per capita day (GPCD) for the
residential flow plus 20 GPCD for out of town students plus the average
commercial and industrial flow. The average wet weather flow for
seasonal residents shall be based on a minimum of 20 GPCD for day
visitors and 80 GPCD for seasonal visitors.

For mechanical plants, if the industrial flow varies during the day or
week, the design flow should be based on the average flow on the peak
day during the period when the industry or industries are operating.
This condition is called "rated flow." For example, if the industry
discharges 10,000 gallons over eight of the twenty-four hours, the rated
flow is 30,000 gallons per day. For controlled discharge pond systems,
if the industrial flow varies during the day or week, the average design
flow may be based on a weekly average.

The peak hourly wet weather design flow and peak instantaneous wet
weather design flow are the peak hourly industrial flow plus 2.5 times
the sum of the average wet weather design flow for residential
(full-time and seasonal), commercial and out of town students.
Individual circumstances may dictate higher values than the above
minimum requirements.

The MPCA may approve of an alternate flow design with appropriate
justification.

For determining the design of the collection system (including design
flow), refer to Chapter 20 Design of Sewers from the "Recommended
Standards for Sewage Works" (Ten State Standards).

MECHANICAL TREATMENT PLANTS WITH EXISTING SANITARY SEWER SYSTEMS

For mechanical plant, if a separate sanitary sewer system exists, Table
2 should be used to determine the peak hourly wet weather flow, the peak
instantaneous wet weather flow, the average dry weather flow and the
average wet weather flow.

Part A of Table 2 along with Figure 1 are used to determine the peak
hourly wet weather flow. The measured flow should be plotted for a
twenty-four hour period when ground water is at or near normal and a
runoff condition is not occurring (Curve X on figure 1). The ground
water elevation in relation to the sewer elevation should be noted. The
present peak hourly dry weather flow\[(1) on figure 1 and Table 2\] is
peak hourly flow during the twenty-four hour period when he ground water
is at or near normal and a runoff condition is not occurring. The
measured flow should be plotted for a twenty-four hour period when
ground water is high and a runoff condition is not occurring (Curve Y).
The ground water elevation in relation to the sewer elevation should be
noted. Number (2) on Figure 1 and Table 2 is the peak hourly flow during
a high ground water period for that specific area and system when a
runoff condition is not occurring. This flow (2) minus the present peak
hourly dry weather flow (1) is the peak hourly infiltration.

The measured flow should be plotted for a twenty-four hour period when
the ground water is high and a runoff condition is occurring (Curve Z).
This should include overflow, bypasses and emergency pumping. The amount
of rainfall and its duration should be plotted on the same graph. The
peak inflow is represented by the greatest distance between Curve Y and
Curve Z. The present hourly flow at the point of greatest distance
between Curve Y and Z \[(5) on Figure 1 and Table 2\] minus the present
hourly flow during high ground water at the same time of day \[(6) on
Figure 1 and Table 2\] is the peak hourly inflow.

It may be necessary to adjust the measured flow based on a relationship
between the data attained during a major storm event and the five-year
one-hour designed storm event. Items (10) and (13) are determined
through a cost effectiveness evaluation. The GPCD contribution for
population increase in Item 15 (also in 25, 33 and 41) should be 100
GPCD.

Part B of the Table determines the peak instantaneous wet weather flow.
The present peak hourly inflow adjusted for a five-year one-hour
rainfall event (see part A line 8) is subtracted from the peak hourly
wet weather flow (see Part A line 19). To this number, add the present
peak hourly inflow adjusted for a twenty-five year one-hour storm event.
The resulting number is the peak instantaneous wet weather flow.

Part C of the Table determines the average dry weather flow. The present
dry weather flow (24) is the average flow received over a twenty-four
hour period when the ground water is at or near normal and a runoff
condition is not occurring. If the industrial flow varies during the day
or week, the present average dry weather flow should be based on the
average flow of the peak day during the period when the industry or
industries are operating (rated flow). This also applies to the average
flow from industrial increases.

Part D of the Table determines the thirty day average wet weather design
flow. The average infiltration and inflow after rehabilitation (where
rehabilitation is cost effective) is the wettest thirty-day average. The
amount of infiltration after rehabilitation averaged over the thirty
wettest days should be the same or nearly the same as the peak
infiltration after rehabilitation. This is due to the fact that ground
water could stay high for a fairly extended period of time. The amount
of inflow after rehabilitation averaged over the thirty wettest days
depends on the type of sources, their location, the amount of rainfall
that affects the source, etc.

Part E of the Table correlates all related information which can impact
the degree of accuracy of the determination of design flows. It is
recommended that a minimum of six months of accurate data be recorded.
Minn. R. 7077.0150, subp. 2B requires a minimum of 30 consecutive days
of actual flow monitoring. Data associated with the critical peak wet
weather flow events for a sustained wet weather period are essential for
accurate estimation of design flows. Critical peak wet weather flow
events typically occur in the spring (March-June) and must be include
the condition of high ground water with inflow.

CONTROLLED DISCHARGE POND SYSTEMS WITH EXISTING SANITARY SEWER SYSTEMS

The peak hourly wet weather and the peak instantaneous wet weather
design flows to a pond system with an existing sanitary sewer system are
arrived at in the same manner as in Parts A and B of the previous
section. If the present industrial flow varies during the day or week,
the present average dry weather flow (24) and (30) may be based on a
weekly average. When computing the average wet weather flow, the average
infiltration after rehabilitation (31), and the average inflow after
rehabilitation (32) are averages over the wettest 180 consecutive days.

FLOW EQUALIZATION

This section applies to all treatment facilities except pond systems.
During a period of high ground water for that area and system, if the
ratio of peak hourly wet weather design flow to average wet weather
design flow \[which is (19)/(37)\] is three or more, flow equalization
shall be evaluated. When the ratio is three or more and flow
equalization is not employed, an explanation must be included outlining
how the plant will handle this transition from average wet weather
design flow to peak hourly wet weather design flow.

During a normal ground water period, if the ratio of the peak hourly
design flow during the five-year one-hour storm event (1 + 14 + 15 +
17 + 18) to the average dry weather design flow (29) is three or more,
flow equalization shall be evaluated. When the ratio is three or more
and flow equalization is not employed, an explanation must be included
outlining how the plant will handle this flow transition.

WASTEWATER TREATMENT PLANT DESIGN LOADING

Table 3 should be used to determine the design loadings for the upgraded
wastewater treatment plant.

**TABLE 2**

**DETERMINATION OF DESIGN FLOWS**

\(A\) For determination of peak hourly wet weather design flow (PHWW):
gpd

\(1\) Present peak hourly dry weather flow \_\_\_\_\_\_\_

\(2\) Present peak hourly flow during high ground water period (no
runoff) \_\_\_\_\_\_\_

\(3\) Present peak hourly dry weather flow \[Same as (1)\] -
\_\_\_\_\_\_\_

\(4\) Present peak hourly infiltration = \_\_\_\_\_\_\_

\(5\) Present hourly flow during high ground water period and runoff at
a point of

greatest distance between Curves Y & Z \_\_\_\_\_\_\_

\(6\) Present hourly flow during high ground water (no runoff) at

same time of day as (5) measurement - \_\_\_\_\_\_\_

\(7\) Present peak hourly inflow = \_\_\_\_\_\_\_

\(8\) Present peak hourly inflow adjusted for a 5-year 1-hour rainfall
event \_\_\_\_\_\_\_

\(9\) Present peak hourly infiltration \[Same as (4)\] \_\_\_\_\_\_\_

\(10\) Peak hourly infiltration cost effective to eliminate -
\_\_\_\_\_\_\_

\(11\) Peak hourly infiltration after rehab (where rehab is cost
effective) = \_\_\_\_\_\_\_

\(12\) Present peak hourly adjusted inflow \[Same as (8)\]
\_\_\_\_\_\_\_

\(13\) Peak hourly inflow cost effective to eliminate - \_\_\_\_\_\_\_

\(14\) Peak hourly inflow after rehab (where rehab is cost effective) =
\_\_\_\_\_\_\_

\(15\) Population increase \_\_\_\_@\_\_\_\_ gpcd times 2.5 (peaking
factor) \_\_\_\_\_\_\_

\(16\) Peak hourly flow from planned industrial increase \_\_\_\_\_\_\_

\(17\) Estimated peak hourly flow from future unidentified industries
\_\_\_\_\_\_\_

\(18\) Peak hourly flow from other future increases \_\_\_\_\_\_\_

\(19\) Peak hourly wet weather design flow (1 + 11 + 14 + 15 + 16 + 17 +
18) \_\_\_\_\_\_\_

\(B\) For determination of peak instantaneous wet weather design flow
(PIWW):

\(20\) Peak hourly wet weather design flow \[same as (19)\]
\_\_\_\_\_\_\_

\(21\) Present peak hourly inflow adjusted for a 5-year 1-hour rainfall
event \[same as (8)\] - \_\_\_\_\_\_\_

\(22\) Present peak inflow adjusted for a 25-year 1-hour rainfall
event + \_\_\_\_\_\_\_

\(23\) Peak instantaneous wet weather design flow = \_\_\_\_\_\_\_

\(C\) For determination of average dry weather design flow (ADW):

\(24\) Present average dry weather flow \_\_\_\_\_\_\_

\(25\) Population increase \_\_\_\_@\_\_\_\_gpcd + \_\_\_\_\_\_\_

\(26\) Average flow from planned industrial increase + \_\_\_\_\_\_\_

\(27\) Estimated average flow from other future unidentified
industries + \_\_\_\_\_\_\_

\(28\) Average flow from other future increases + \_\_\_\_\_\_\_

\(29\) Average dry weather design flow (24 + 25 + 26 + 27 + 28) =
\_\_\_\_\_\_\_

\(D\) For determination of average wet weather design flow (30-day
average for

mechanical plant and 180-day average for controlled discharge ponds):
(AWW)

\(30\) Present average dry weather flow \_\_\_\_\_\_\_

\(31\) Average infiltration after rehab (where rehab cost effective) +
\_\_\_\_\_\_\_

\(32\) Average inflow after rehab (where rehab cost effective) +
\_\_\_\_\_\_\_

\(33\) Population increase \_\_\_\_@\_\_\_\_gpcd + \_\_\_\_\_\_\_

\(34\) Average flow from planned industrial increase + \_\_\_\_\_\_\_

\(35\) Estimated average flow from other future unidentified
industries + \_\_\_\_\_\_\_

\(36\) Average flow from other future increases + \_\_\_\_\_\_\_

\(37\) Average wet weather design flow (30 + 31 + 32 + 33 + 34 + 35 +
36) = \_\_\_\_\_\_\_

\(E\) Critical data (including a graphical display similar to Figure 1),
methodology, and a discussion on the following

items shall be included with the above calculations:

\(38\) Dates during which actual flow data was recorded and its probable
degree of accuracy.

\(39\) Ground water elevation data relative to the collection system,
during the time period when flow data was recorded.

\(40\) Rainfall data during the time period when flow data was recorded
and how the amount of rainfall compares to normal

seasons.

\(41\) Probable degree of accuracy of flow reduction due to proposed or
completed I/I correction or elimination of bypasses.

**TABLE 3**

**DETERMINATION OF DESIGN LOADINGS**

![](media/image1.emf)

\* It may be necessary to also test for TKN for certain industrial
contributors

**EXHIBIT B**

# FACILITY PLAN REQUIREMENTS

# 

# 

# GENERAL: 

A.  Before adopting, municipality must hold at least one public hearing
    to discuss the proposed project.

B.  Must be prepared and signed by a professional engineer registered in
    the state of Minnesota.

C.  Facility plans for individual sewage treatment systems (ISTS)
    designed to treat 5000 gallons or less per day must be prepared and
    signed by either a professional engineer or an evaluator/designer.

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I.  CONTENT:

    A.  Description and evaluation of existing system which must
        consider:

        1.  Age;

        2.  Condition;

        3.  Design Capacity Treatment capacity;

        4.  Treatment capabilities of each treatment unit;

        5.  The system\'s ability to meet current of proposed permit
            requirements; and

        6.  For existing ISTSs, a survey must also be prepared which
            identifies whether or not each ISTS project in the project
            area conforms to Minn. Rules ch.7080.

    B.  Data describing existing residential and non-residential
        wastewater flows and loadings reported on a form provided by the
        MPCA.

    C.  Data describing future residential and nonresidential wastewater
        flows and loadings with the next 20 year period, using Exhibit A
        and associated forms, based on;

        1.  Projected residential growth;

        2.  Projected nonresidential growth; and,

        3.  Signed letters of intent from significant industrial users.

    D.  A discussion of treatment alternative\'s that were considered
        during the facility selection process and are capable of meeting
        the applicable effluent, water quality and public health
        requirements for 20 years. The discussion must include:

        1.  A cost-effective comparison of the alternatives that were
            considered;

        2.  A site assessment of the existing soil and ground water
            conditions conducted and signed by a professional engineer;

        3.  For ISTSs designed to treat less than 5,000 gallons per day,
            a site assessment must be done by either a professional
            engineer or a certified evaluator/designer;

        4.  An evaluation of the impact of the alternatives on all
            existing wastewater treatment systems, including sewers and
            lift stations; and,

        5.  A comparison of the potential environmental impacts.

    E.  A description of the selected treatment alternatives and the
        complete wastewater treatment system of which it is a part,
        including:

        1.  The specific design parameters of all individual treatment
            units and the complete treatment system;

        2.  Estimated construction, annual operation and maintenance,
            and equipment replacement costs;

        3.  Estimated annual sewer service charges;

        4.  A determination of whether pretreatment of any industrial
            wastes is needed in order to avoid disruption of the proper
            operation of the proposed system; and,

        5.  An evaluation of how and where sludge or septage resulting
            from the treatment process will be disposed.

    F.  An analysis of the 25- and 100- year flood elevations in
        relation to the proposed project site or sites, showing that the
        project will be operable during a 25-year flood and protected
        during a 100-year flood.

    G.  An analysis of how interim treatment will be accomplished during
        construction to meet permit requirements.