Precast Solutions - January/February 2008 - (Page 24)

Public water supply Y Consumption yard watering, drinking, washing car, etc. H2O Meter (M1 ) Septic I& no reinforcement; inferior, permeable, low-strength concrete; or the total lack of a high-quality sealant in the joint line. A combination of these problems would require replacing the entire tank with a watertight design that had a plant certification program behind it. A review of the specifications for the two systems revealed only one difference in the tank requirements: the specification for sealing the inlet access port lid. System 1 did not require the concrete inlet access port lid to be sealed prior to installation, while System 2 did. After a brief discussion and consultation with the tank manufacturer, engineer and field personnel, it was decided that the first place to check in the collection system would be the tanks. The access ports that were not sealed would be uncovered and inspected first. If the access ports had not shown any signs of I&I, the inspection would be expanded, which would require uncovering and visually inspecting any and all seams and joints on the tanks, risers and inspection ports. However, when the first tank was uncovered, it was immediately apparent that the inlet side access port lid (see Figure 1), which measured 18 inches in diameter, was allowing surface water to enter the tank. All of the tanks showed varying degrees of I&I during the Table 3 inspection. THE FIX The next step was to seal each of the inlet access port lids on each tank in System 1 with a high-quality butyl sealant to ensure a watertight seal. Fortunately, the unsealed lid was close to ground level, allowing an easy fix. System 1 and System 2 tank specifications were now identical to each other and should perform equally well against I&I into the collection system. After evaluating the following month’s meter readings, the success of applying the butyl sealant on the inlet access port lids became evident as System 1 showed a dramatic decrease in treated sewage. Sixty percent of the total purchased water was now entering the sewage treatment facility, cutting the treated wastewater by more than half. This validated that the I&I problem originated from the unsealed access port lids. Table 3 shows the purchased water and treated effluent comparisons. CONCLUSION Sewer collection systems are only as good as the weakest component. In this case, failure of the utility to specify proper sealing of the tank totally negated the tank’s watertight design and construction and resulted in the tank being the weakest component in the entire system. Overlooking such a simple precaution to both specify and properly seal a watertight tank can be SYSTEM 1 — TROUBLE SYSTEM (POST-FIX) Six-month Period After Fix Total water purchased Total sewer treated Percent of purchased water treated 254,600 gallons 147,300 gallons 60% (good) catastrophic for all sewage collection systems, resulting in system overloads and significantly increased operating costs. In addition, breakdown in system performances such 24 PRECAST SOLUTIONS | JAN/FEB 2008

Table of Contents Feed for the Digital Edition of Precast Solutions - January/February 2008

Precast Solutions - January/February 2008 Contents Precast Concrete Short-Span Bridges Precast Micro-Reinforced Concrete A Winning Edge The Creative Edge TMI: Too Much Infiltration! Architectural Details Cast in Stone

Precast Solutions - January/February 2008

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