I&I - When it Rains it Pours
Inflow and Infiltration (I&I) describes stormwater (inflow) and groundwater (infiltration) entering a sewer system. As a wastewater collection system ages, the ground beneath sewer lines and other infrastructure can shift, pipe gaskets degrade, and manholes lose water-tightness. In some communities, residential and commercial sump pumps, gutter down spouts and foundation drains are connected directly to the sewer system. This combination of problems can allow thousands of gallons of clear water to enter a sewer system and overwhelm treatment facilities and sewer utility budgets.
Counting the Cost
The costs associated with traditional wastewater treatment are significant. There are several large initial expenses such as engineering design, permitting and major construction. Ongoing expenses must then be budgeted for power, chemicals, labor, monitoring equipment, sludge disposal and other Operations and Maintenance (O&M) activities. It’s difficult to calculate a true industry average for the cost to treat a unit of wastewater due to differences in treatment processes and other factors. However, a ScienceDirect article published in 2018 determined the cost to treat wastewater starts around $5.00 per gallon when you factor in the myriad of upfront and ongoing expenses and depreciation of a wastewater system throughout its useful life. Unfortunately, the smallest wastewater facilities (often small towns) are hit the hardest as treatment costs tend to increase as the size of the treatment plant decreases. “For facilities with flows less than 100,000 GPD, the treatment cost per 1000 gallons was nearly 15 times greater than that incurred by the largest facilities.” Given the potential for such significant cost savings, the challenging goal is to minimize clear water in a sewer collection system that does not need to be treated.
The costs of I&I are also not limited solely to financial ones. In an age of smartphone cameras and social media sharing, community residents can and do take to the social-sphere to highlight issues and assign blame. When public sewer backups cause private damage, there certainly can be cost implications, but equally concerning are the blows to public trust and increased scrutiny from state and local regulators.
The right tool for the job
At Ziptility, we advocate for using simple, field-first software to plan and execute a strategic I&I initiative. Our mobile, map-based system allows you to organize inspection tasks with automatic reminders, document findings in a central place, and pull actionable reports to keep leadership informed and proactive in their decision making. Having a structured plan with tasks assigned over a set timeframe also communicates a powerful message to regulatory agencies. This demonstration of commitment can make the difference in satisfying Enforcement Actions and Orders requirements.
The procedural outline below serves as a starting point for our conversations with wastewater teams struggling with I&I problems. As discussions progress, these steps are customized and a project timeline can be developed. The Ziptility Customer Success team partners closely with operators and management throughout this process. We can help flesh out the specific data that should be captured, build the digital inspection forms personnel will complete in the field, and demonstrate how to easily pull reports that will allow leadership to evaluate the situation analytically and plan next steps based upon real data. Depending on system size, significant progress on the initial 7 steps of this plan can be accomplished in 6-12 weeks. The final 3 steps take place over several months as budget and other limiting factors must be considered.
Making a plan
- Identify and add all manholes (we help you do this!) to your Ziptility map.
- Complete inspections of each lift station on a set schedule. Log pump drawdown data and keep a running pump run time log in Ziptility.
- Perform baseline manhole inspections and document findings in the field using a pre-created form in Ziptility.
- During a rain event, document channel flow and any evidence of infiltration in each manhole. Take photos with a smartphone and add to each manhole in Ziptility.
- Compare average pump run times after rain event compared to pump run times during dry periods.
- Use steps #4 and #5 to determine biggest problem sections in the system.
- Televise and smoke test problem sections and document findings in Ziptility.
- Prioritize repair or replacement of problem sections.
- Update your infrastructure assets in Ziptility as repairs are made.
- Continue collecting data and evaluate improvements based upon pump run times and WWTP flows after rain events compared to previous data.
Let's Connect
Contact us anytime to discuss the unique challenges your utility is facing. We would welcome the opportunity to brainstorm solutions and connect you with other water and wastewater teams who are using Ziptility to address similar problems. You can email Josh Hawley at Josh@ziptility.com or call 812-324-1345. You can also connect with us anytime on Facebook or LinkedIn.
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