Coastal View Article

Raindrops keep falling on Carpinteria, and the sewer collection, pumping and treatment systems that serve the community have been put to the test over the past couple months with sharply increased flow rates. On Feb. 19 the Carpinteria Sanitary District’s wastewater treatment facility processed a record amount of water – 3.52 million gallons in a single day, over three times the amount we normally treat.

Obviously, the rain is good for our local water supply, but it can be a real problem for wastewater agencies when too much comes down in a short period of time. Sewer collection systems – the network of buried pipes that transports wastewater from homes and businesses to the treatment plant – are not designed to handle stormwater.

It is a common misconception that public storm drains combine with sewer collection pipes: they don’t! When we see excessive flows during and following rainfall events in the sewer system, we attribute it to infiltration and inflow, or I & I in industry speak. Infiltration is when shallow groundwater and subsurface rainwater enter the system through cracks or defects in buried pipes. Inflow, which poses a much bigger challenge for operators, is when stormwater directly enters the sanitary sewer system.

Fortunately, so far we have been able to manage the spiking flows caused by I & I without serious impacts. But when the hydraulic capacity of a sewer system is exceeded due to stormwater inflow, it can lead to sewer spills and overflows that threaten public health and the environment. Spills that enter waterways can result in beach closures, fines and other ratepayer impacts. Even when we avoid spills, the excessive flows caused by I&I increase costs for pumping, treatment and staff labor. We provide award-winning service, but like all agencies, we are not immune to I & I.

Common causes of sewer infiltration and inflow 

We know the common causes of I & I. Street flooding can allow inflow through vents in cast-iron manhole covers. When soils are saturated, stormwater can infiltrate the sewer system through cracks in underground manholes, sewer mains and sewer laterals. These issues arise  as infrastructure ages. We work hard to maintain and rehabilitate our network of underground collection pipes. In Carpinteria, we have over 45 miles of underground pipes. Sewer laterals add about that same amount of buried pipe to the system.

Unfortunately, inadvertent and sometimes illicit actions can be major contributors to I & I. Roof drains and yard drains should never be connected to the sanitary sewer system. District ordinances strictly prohibit this, but we have found many stormwater drain connections over the years, both intentional and accidental. Missing or broken cleanout caps can also allow large volumes of surface water to enter the sewer system. Another culprit is defective sewer laterals. A lateral is the privately owned section of buried pipe between your home and the sewer main in the street. Cracks and other defects in sewer laterals can be a big source of infiltration, and wastewater agencies across California are encouraging or requiring their customers to repair defects or replace laterals entirely.

Preparation and prevention techniques to reduce I & I 

Carpinteria Sanitary District always takes preventative measures ahead of storm events, and we work throughout the year to maintain and rehabilitate the collection system. But when our daily flow triples due to rainfall-related I & I, we know we still have work to do addressing the sources.

In low-lying areas where we know manholes tend to get inundated – like Padaro Lane – we have historically put corks in the pick holes to minimize inflow. Now we are planning to install new watertight manhole lids in these areas to prevent inflow completely. We are doing focused CCTV inspection of sewer mains immediately following rain events to locate defects allowing infiltration and identify connections with higher-than-expected flow rates. We will also strategically perform smoke testing in the near future to target problem areas with tests that use harmless, colored smoke pumped into sewer mains and laterals to reveal spots where the system isn’t watertight.

For residential and commercial customers, please call Carpinteria Sanitary District at (805) 684-7214 if you believe your sewer lateral is vulnerable to infiltration or is performing sub-optimally. Depending on the signs and symptoms, we can check or refer a plumbing specialist to assist with your private lateral and cleanout. If you are aware of any unauthorized drain connections or open cleanouts that allow stormwater to enter the system, we will gladly work with you to remedy that situation. As a smaller agency, we have been able to be proactive, helping our customers dial in their laterals so they perform as they should and don’t add stormwater stress to the system. Carpinteria Sanitary District is first and foremost an agency providing environmental solutions. We handle and treat wastewater to protect local water supplies and the environment. We welcome the rain and groundwater recharge, while working diligently to prevent spills caused by I & I. We all can work harder to get educated and take appropriate action to reduce Infiltration and Inflow and protect our wastewater system.  

By Craig Murray, General Manager, Carpinteria Sanitary District