2-WEF 2014 Abstract - Pierce County (20140501)(O)

PREDL Systems North America Inc.—WEF Abstract 2014 Submittal—Pierce County Wins a 35-Year Battle with RDII

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Water Environment Foundation (WEF) 2014 Abstract Submittal Pierce County Wins a 35-Year Battle with RDII

By Peter Keefe, M.Sc., Robin Ordonez, P.E., Kip Julin, and Terry Soden, P.E.

Problem: While hundreds of WEF papers have been de-voted to identifying and reducing I/I, few have addressed what it takes to build a city sized sewer system that is tight.

Goals and Objectives: To publicize steps taken over the past 35 years to build an extremely tight 691 mile sewer system in Pierce County, WA that stands out not only for lack of I/I but also because of low maintenance and excep-tional performance. The story is compelling and enlight-ening.

Pierce County didn’t set out to build the tightest sewer system that they could, just the best one. They learned best practices from design consultants, the Washington State Department of Ecology and from colleagues. The result is a sewer system that has never had a plant bypass, never had an NPDES violation, rarely has sanitary sewer overflows (SSOs), rarely has basement flooding and sees just a 2.1 to 1 peaking factor in trunk sewers near the treatment plant. 2.1 to 1 isn’t a daily dry weather peaking factor, but rather the ratio of peak flows from a 2-year storm divided by average daily dry flow, (see Figure 1, be-low). Every monitored sewer site can transport flows from a 10-year storm without overflowing. Obviously this is no ordinary sewer system. For those of us who have been chasing I/I for many years this kind of performance

is unheard of. What, in the world, did Pierce County do right?

Pierce County is situated just south of King County (Seattle) and contains the city of Tacoma, though Tacoma owns and operates its own sewer system. County sewer construction started in 1978 and by 2013 contained 691 miles of public sewers serving eleven cities, towns and unincorporated county areas. Sewers flow westerly from the Cascades to the Chambers Creek Regional WWTP which is a 28.6 mgd advanced secondary facility that dis-charges into Puget Sound. Plant bio-solids are refined into a 100% natural, organic fertilizer named SoundGRO™ which meets EPA Class A ‘Exceptional Quality’ standards and Washington State Department of Agriculture stand-ards for commercial fertilizer. SoundGRO™ is selling at a rate of 2,500 tons per year. The plant received the 2012 Outstanding Treatment Plant Award from the Washington State Department of Ecology.

Building Watertight Sewers: Starting in the late 1970s, Pierce County started building a sewer system and treat-ment plant. Learning quickly the county switched away from concrete pipe toward PVC and HDPE depending on pipe size. Certain unusual applications are reserved for ductile iron or fiberglass. Vitrified clay and concrete were disallowed. The collection system ranges in size from 8

Figure 1.



inches to 84 inches in size. They found a source of unu-sual corrosion-proof, water-tight manhole bases, lined on the inside with yellow fiber-reinforced plastic in-cluding flow channels, (see Figure 2). Anecdotal maintenance reductions achieved by the manhole bases created the incentive to write this abstract. County inspectors exam-ined every bit of the new

construction, preventing many “errors and omissions” from being installed underground. To pre-vent infiltration from migrating across low drainage di-vides the county start-ed installing trench dams as early as 1991. So, by that time nearly all public sewerage ap-purtenances were not only water-tight, but trench water migration was also inadvertently controlled through a groundwater initiative generated by water districts.

On private property, all sewer laterals were built using PVC and all lateral connections were tested and in-spected thoroughly. The result was a sewer system that in 2011 had the lowest I/I rates that the au-thor had ever seen, (see Figure 3). I/I rates were 66% to 71% lower than the next best performing system that the author has encountered.

How Tight Are the Sewers? Pierce County sewers are not completely devoid of I/I; there’s just very little of it. Fig-ure 4, from the October 20, 2013 RDII report to the coun-ty is a schematic that shows Basin PC18 (red) had worst case RDII in excess of 10% and PC01 (yellow) had worst case RDII in excess of 5%. The green basins had worst case RDII rates below 5%. The white dots represent un-monitored areas. Worst case RDII is defined as the high-est runoff coefficient measured in any of the 21 significant storms during the monitoring period. Worst cases are used in RDII analyses, because EPA regulations prohibit SSOs under any conditions.

Six of the monitored storms exceeded the intensity of a 1-year storm in one or more rain gauges. Only the Novem-ber 21, 2011 storm exceeded the intensity of a 1-year storm in all seven rain gauges.

Normally more than 10% rainfall ingress is considered to be excessive RDII and more than 5%, is considered to be possibly excessive RDII. This was not the case in Pierce County because both of those two monitoring locations were able to pass a 10-year storm without overflowing. This meant that they did not need relief sewers. Relief sewers are expensive and they drive most of the econom-ic need to reduce RDII. Since relief sewers were not need-ed, the economic incentive to remove RDII was eliminat-ed. All monitored sites in the county were able to pass a 10-year storm without overflowing.

Table 1 on page 3 gives the numbers ranked from leakiest at the top and tightest at the bottom. Rankings were based on the maximum measured percent rainfall ingress in any storm in 2011, (see column three). WIB in column 5 stands for “water in basement”.

SSO and Basement Flooding Performance: Pierce County’s SSO goal is to have less than 1 SSO per 100 miles of sewer per year and that goal is 4 times tighter than the national SSO goal which is less than 4 SSOs per 100 miles of sewer per year. Since 2002, the county has responded to 56 SSOs. With 691 miles of pipe, this works out to 0.67 SSOs per 100 miles per year – well within the county’s goal. Further, as a result of quick re-sponses, only 4 of the SSOs have reached the

waters of the state. There have also been 29 flooded basements in Pierce County in the past 11 years. That works out to 2.6 flooded basements per year or 0.38 flooded basements per 100 miles of sewer per year.

Figure 2.

Figure 4.

Figure 3.



Table 1: Maximum Percent RDII Results

Basin Linear

Footage

Max Per-

cent RDII

Num.

SSOs

Num.

WIBs Excessive? Rank

PC18 21,315 15.07 0 0 Non-excessive 1

PC01 21,090 5.31 0 0 Non-excessive 2

PC17 16,094 4.19 0 0 Non-excessive 3

PC21 22,343 4.15 0 0 Non-excessive 4

PC06 35,114 2.52 0 0 Non-excessive 5

PC16 46,443 2.52 0 0 Non-excessive 6

PC08 10,769 2.51 0 0 Non-excessive 7

PC Tunnel 19,360 2.10 0 0 Non-excessive 8

PC05 21,472 1.81 0 0 Non-excessive 9

PC02 35,746 1.75 0 0 Non-excessive 10

PC04 16,645 1.32 0 0 Non-excessive 11

PC22 20,838 0.26 0 0 Non-excessive 12

PC03 16,288 0.00 0 0 Non-excessive 13

PC19 20,669 0.00 0 0 Non-excessive 14

PC20 14,640 0.00 0 0 Non-excessive 15

PC25 26,041 0.00 0 0 Non-excessive 16

Cleaning those 29 basement backups cost the county $378,000 providing ongoing incentives to reduce sewer flooding. Though not perfect, the county’s record on SSOs and flooded basements is excellent compared to na-tional standards.

Reducing Maintenance Costs through High Quality: Mod-elers are aware that standard concrete manhole channels can create 15% to 40% head losses.1, 2. Clogged manholes often required lots of expensive maintenance including cleaning, corrosion repair and rechanneling so county per-sonnel started looking for solutions. After a few months of asking and searching, some manholes with fiberglass reinforced plastic bases and troughs showed up on the radar screen. The County tried them on an interceptor project and they worked. From that point they were spec-ified and installed on all new construction projects. The County now has more than 10,000 such manholes and manhole trough maintenance costs have dropped signifi-cantly. Taking a page from the Southwest Airlines mainte-nance manual, the county standardized on the best brand of pumps that they could find. By 2013 they had specified

that brand of pumps for 99 pump stations countywide. Just as every Southwest Airlines mechanic knows how to fix a Boeing 737, every Pierce County pump mechanic knows how to fix every pump. Sole sourcing 737s does not seem to have increased Southwest ticket prices and despite some sole sourcing Pierce County has been able to pay for its entire collection system without raising bonds.

High Quality through Tight Specifications: Pierce County has not been afraid to specify exactly what it needed to accomplish its goals of high quality and low maintenance. While a few products have been sole sourced, scores of other product choices have been rigorously restricted to the “good stuff” through tight specifications. The link be-low leads to the county’s Sanitary Sewer Development Specifications:

www.co.pierce.wa.us/DocumentCenter/View/1106

Also available online from the Pierce County Document Center are the Sewer Design Checklist and Standard De-tails among other, continuously improved documents.

http://www.co.pierce.wa.us/DocumentCenter/View/1106



As one can see in the Sanitary Sewer Development Speci-fications only two products are currently sole sourced while 74 others are named as quality standards with “Approved Equal” products allowed if accepted by the sewer utility engineering manager. As one would expect in a free marketplace, sole sourcing occupies very few niches.

Many of us remember when Insituform was the only source for inversion lining. After their patent expired in 1995 dozens of competitors entered the marketplace. Prices dropped and inversion lining became common-place. Good for the marketplace and good for rate pay-ers, right? For a while yes, it was good, however, Jim Shelton recently observed3 that inversion lining has be-come so intensely price-competitive that many providers have thinned their liner walls to the point where they’ve sprung multiple leaks within their first year. Is that what the marketplace wants? It’s actually a predictable part of any natural market cycle. When competition drives profit out of an industry the most common response is to cut corners and cheapen the product. Until there is another technical breakthrough in the sewer liner business, knowl-edgeable engineers like Mr. Shelton should specify wall thickness for inversion liners. Engineers must be the keepers of municipal quality; the purchasing department won’t do it. So we can now line pipes inexpensively, but is that what we really need?

High Quality through Rigid Inspection: The County’s in-spection staff has been professionally trained to coordi-nate their work with engineering and maintenance staff for acceptance and approval of all construction projects. Sewer lines are air tested and televised and manholes are vacuum-tested prior to acceptance. Following NASSCO inspection standards has resulted in an extremely well-constructed sewer system.

So, What Does Pre-treatment Have To Do With It?: Without a vigilant, observant, successful pre-treatment program, levels of selenium and molybdenum might be too high to refine SoundGRO™ to its Class A, Exceptional Quality standard. By paying close attention to details, Pierce County, in cooperation with a building siding manu-facturer, has discovered that the manufacturer should not mine sand from one particular corner of its open sand pits because of high concentrations of selenium and molyb-denum at that end of the pit. That discovery and others have helped protect the exceptional quality standards of SoundGRO™. Why is this important?

SoundGRO™ generates $134,000 per year in sales to the public. The county’s SoundGRO™ manufacturing facility opened in 2006 and was the first such facility in Washing-ton State. It won the Governor’s Award for Sustainability in 2007.

A Government that Actually Works? While Washington D.C. has sunk into stalemate, Pierce County has actively promoted internal education and cooperation through bi-weekly staff meetings that included six divisions of the utilities department: 1) Engineering & Planning, 2) Inspec-tions, 3) Wastewater Treatment Plant Operations, 4) Pre-treatment, 5) Collection Systems Maintenance and 6) Ad-ministration. Sharing information eventually led to broad cooperation across the utility. Administrators knew they had succeeded when Engineering began asking for input from other departments on all facets of design and con-struction. That doesn’t happen in many municipalities.

All staff impacted by new capital projects were included in design, review and equipment selection. Collection sys-tems maintenance staff also reviewed developer-built sewer extensions and pump stations. During construc-tion, maintenance and operations staff inspected, tested and accepted or rejected new construction elements in accordance with county standards.

Conclusions: Extremely low RDII and SSO rates, low maintenance costs, high collection system and treatment plant performance and award winning fertilizer produc-tion in Pierce County were achieved through an unusual culture of excellence, service and cooperation in county government. The many technical, engineering, operations and maintenance lessons discussed herein are largely a result of a government that works. An abstract journey that started over interesting, water-tight manholes ends with the realization that they were an important piece of a much bigger picture.

References:

1. Marsalek, J., Grek, B.J., “Head Losses at Manholes with a 90o Bend” Canadian Journal of Civil Engineering, 1988 2. Mrowiec, M., “Head Loss at Two-Way Circular Manholes in Drainage Systems Under Surcharge Conditions” Częstochowa University of Tech-nology, Institute of Environmental Engineering 3. Shelton, J., “Cured in Place Liner Defects” WEFTEC, Collection Sys-tems Committee Presentation, 2013.



Appendix:

Acceptance by the Water Environment Foundation (WEF) of 2014 Abstract Submittal by Pierce County, WA and PREDL Systems North America, Inc. for publication by WEF and presentation by the co-authors at WEFtec 2014 on Wednesday, October 01, 2014, New Orleans, LA.

2-WEF 2014 Abstract - Pierce County (20140501)(O)

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