SULTAN CITY COUNCIL

AGENDA ITEM COVER SHEET

ITEM NO: Action A 3

RECOMMENDED

February 14, 2002

 C. H. Rowe, Mayor
City of Sultan
P.O. Box 1199
Sultan, WA 98294

RE: Task Order 2002-05 to Professional Services Agreement dated March 1, 1999 for City Engineer Services

Phases I & II for Inflow and Infiltration (I&I) Reduction Program

Dear Mayor. Rowe:

We have completed the attached memo dated February 14, 2002 regarding the I&I impacts on the sewage treatment plant in accordance with the City’s Task Order 2002-03. A schedule and budget for Phases I and II of the I&I reduction program developed in the memo are attached.

In accordance with the Professional Services Agreement between the City of Sultan (City) and Berryman and Henigar (B&H) dated March 1, 1999, we have been asked to continue our services as acting City Engineer to initiate the I&I reduction program.

This work of preparing the I&I Reduction Program will include the following services:

PHASE I

• Develop a list and preliminary description of recommended improvements to the sanitary sewer or storm drainage system to reduce I&I into the sanitary sewer system. Prepare a preliminary cost estimate of these repairs.
• Prioritize the list of possible repairs with input from the City staff. Prepare construction budget and schedule and review with City Council.
• Prepare construction drawings and specifications in configurations allowing the Public Works Director to utilize the small works roster.
• Assist the City in soliciting bids for construction of the improvements.
• Provide engineering oversight during construction.

PHASE II

• Prepare applications for Public Works Trust Fund and State Revolving Fund loans to fund Phase II.
• Perform field investigation and perform field measurements to determine I&I quantities. Develop other storm drainage facilities that may be necessary. Prepare preliminary cost estimates of proposed repairs/additions to the system.
• Prioritize projects along with input from City Staff, prepare budget and schedule for approval by the City Council.
• Prepare construction drawings and specifications.
• Assist the City in soliciting bids for construction of the improvements.
• Provide construction services as requested.

We anticipate completing engineering in Phase I and the loan applications in Phase II for the Inflow and Infiltration (I&I) Reduction Program and have it ready for a staff presentation to the City Council in May 2002. The estimated budget for this work is $27,000.

Sincerely,

Gary Bourne, Regional Manager C. H. Rowe, Mayor

Berryman & Henigar

Connie Dunn, Public Works Director

City Staff has been preparing to initiate the work necessary for the removal of excess inflow and infiltration (I&I) from the City’s sewer system. From 1991 to 1997 there were a number of studies and reports that documented sources of I & I in the City’s sewer system. Although City staff has eliminated a number of these I & I sources over the last few years, numerous problem locations remain. In addition, there will be new sources of I & I that have not been identified.

Removal of excess I&I from the City sewer system has become more important in the last couple of years as excess water in the system will begin to reduce the treatment capacity of the City’s wastewater treatment plant. This was recently demonstrated during the heavy rains in November that caused the peak flows to tax the capacity of the Wastewater Treatment Plant (WWTP).

However, the ability of the WWTP to treat flows is not measured on peak flows, rather on average flows. The average flows during the summer months of 2001 were in the range of 250,000 gallons per day (0.25 mgd). During the month of November the average flows were in the range of 0.35 mgd. The capacity of the WWTP to treat average flows is in the range of 0.78 mgd. Present average flows indicate a current population of approximately 2,500 people connected to the sewer system.. The design population of the WWTP is about 4,800 people connected. All of this indicates that the size and capacity of treatment plant is not the problem.

Industry and treatment design standards would normally consider I&I to be a problem when the peak flows exceed average design flows by a factor of five or greater. Recent peak flows at the WWTP exceeded 2.2 mgd which results in an I&I peak flow factor of 8, indicating a significant I&I problem. An I&I problem that is reducing the use of the WWTP for treating new customers.

This memorandum will discuss the I&I issue and identify recommended actions. Although an I&I reduction project will require an extracted effort over an extended period of time, it is recommended that the most significant sources of inflow be eliminated as soon as possible.

The 1997 Comprehensive Wastewater Plan established an estimated budget for this I&I removal work of $240,000. The City’s current sewer rate structure includes those costs as part of the utilities capital budget.

Infiltration and inflow (I&I) is storm and/or ground water that enters the sewer system through cracked pipes, leaky manholes, or improperly connected storm drains, down spouts and sump pumps. Most inflow comes from stormwater and most infiltration comes from ground water. I&I affects the size of Sultan’s sewer pipes and treatment plant, and ultimately the costs of operating those systems.

Infiltration quantities typically exhibit seasonal variation in response to groundwater levels. Storm events can trigger a rise in groundwater levels and increase infiltration flows. The highest infiltration flows are observed following significant storm events or following prolonged periods of precipitation. Infiltration is related to the total amount of piping and appurtenances in the ground and not to any specified water use component.

Inflow is surface water which enters the wastewater system from yard, roof and footing drains, from cross-connections with storm drains, downspouts, and through holes in manhole covers. Inflow occurs as a result of storm events such as rain and snowfall, springs or snow melt that contribute to excessive sewer flows. Peak inflow can occur during heavy storm events when storm sewer systems are surcharged, resulting in hydraulic backups and local ponding.

Comprehensive planning for the sanitary sewer system has recognized that the City’s system has an I&I problem for at least the past ten years. Those plans and I&I highlights are listed below:

• "Sewer Comprehensive Plan ", 1991, HDR Engineering – This plan included an I&I study accomplished by Ott Engineering that was completed in 1989. At that time the peak daily flow was 362 gpm and I&I was 214 gpm . Three serious cross-connections on 4^th street, Manholes B8, B9 and B9.1 were identified.
• Engineering Report, "Treatment Plant Expansion", January 1993, Horton-Dennis Engineering – On page 3-1 of this report several known major points of inflow were identified. "Manholes along 4^th Street at the intersections of Bell and Fir Avenues were constructed with both sanitary and storm waters separated by a wall that would allow flow from one to the other depending on the flows in each system. Table 3.1, Gravity System Deficiencies (attached), identified ten pipes that are laid flatter then minimum grade. This can cause solids settling with a reduction in pipeline flow capacities. Table 3.2, Areas of Highest Inflow, identified peak inflows into the sanitary sewer system at 53% of peak sewage flow rates.
• Capital Facilities Plan, 1995, Grey & Osborne – Page 4-1 again identified three serious cross-connections at Manholes on 4^th Street, labeled B8, B9 and B9.1. Page 7-1.8 described three manholes in the flood-plain, Cl, E3-1 and E4 that should have water-tight lids.
• Comprehensive Plan Amendment, 1997, Earth Tech – Table 4-6 "Inflow Sources" and Table 7-2 Six Year CIP, Items 9 and 10 attached).

The constant theme of all of these past reports is that the sewer system has substantial I&I contribution to its flows. Sewage flows to the treatment plant have increased in the past ten years due to growth in the number of customers and increasing I&I has caused flows at the plant that exceed its hydraulic capacity.

The Federal Clean Water Act prohibits anyone from discharging pollutants through a point-source into a water of the United States unless they have an NPDES Permit. The permit will contain limits on what can be discharged, monitoring and reporting requirements, and other provisions to ensure that the discharge does not hurt water quality or people’s health.

The City has a National Pollutant Discharge Elimination System Permit issued on April 29,1999, by the Washington State Department of Ecology. This permit contains discharge limitations, monitoring requirements, record keeping requirements, facility loading, operation and maintenance, and pretreatment requirements. In general, this is the operating document for the treatment plant. It also contains a description of the penalties for violating the permit.

Recent flows from the treatment plant to the river outfall have lifted lids on some of the manholes and created negative publicity for the City, even though these flows have already passed through the treatment plant. These flow conditions reflect the heavy I&I flows the plant is experiencing.

It is very important to address the inflow portion by separating the storm water from the sewage lines. The costs of this work and funding for it has been planned for by the City when the last rate study was completed in 1998 and appropriate rates were adopted. This revenue has accumulated in the Utility and Cumulative Reserve Accounts. The Public Works staff and consultants are recommending that the I & I Reduction Program be undertaken in two Phases.

• Engineer to prepare a map of the city locating the known inflow locations based on existing information. Add to this map information from the City maintenance staff and field investigations to develop as complete an information base as possible.
• Engineer to develop list and preliminary description of recommended improvements along with preliminary cost estimates.
• City staff and Engineer to prioritize list and prepare budget and schedule for approval by City Council.
• Engineer to prepare construction drawings and specifications in project sizes to utilize the small works roster and limit the amount of construction disruption to the residents of the City.
• City to solicit bids from its public works roster for construction of the improvements.
• Complete the work before fall season of 2002.

Phase II – Second Level of I & I Removal

• Apply for PWTR and DOESRF loans to fund Phase II.
• Information gained in Phase I will be incorporated into the development of priorities for Phase II.
• Items of work that will be considered to develop these priorities may include:
• Information from Surface Water Quality Plan including cross connections to sanitary sewers.
• Include information from previous I&I studies and staff.
• Flow measurement in spring and fall of 2002 to determine problem areas (or Step III).
• City staff and Engineer will prioritize list and prepare budget and schedule for approval by the City Council.
• Construction contract to be awarded by public bid and/or small works roster.

Table 4-6, (included below), Inflow Sources, taken from the l997 Amendment to the Wastewater Plan is an excellent place to start this process. The Six-Year CIP Improvements, also taken from the 1997 Comp Plan show preliminary budget of $240,000 for this work in 1997 dollars.