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Heavy downpours cause I&I issues for Carpinteria Sanitary District

By Craig Murray, General Manager Carpinteria Sanitary District, for CoastalView.com

As they say, when it rains it pours. On Friday, Feb. 17 it poured in Carpinteria. Nearly 4.5 inches of rain fell during a 24-hour period, more than I’ve seen in any single day since my job made me start paying attention to such things.

Of course, with the prolonged drought, we need the rain badly and this deluge allowed our local water purveyors to breathe a small sigh of relief. For wastewater agencies, however, intense rainfall events like this one can end up in the category of “too much of a good thing.”

Infiltration and inflow, or I&I, is an industry term that refers to storm water or shallow groundwater that enters the sewer collection system during and immediately following a rain event. In the wastewater business, I&I is bad.

There are several ways that rainwater gets into the sewer system. Surface flooding can inundate sewer manholes allowing water to enter the system through vent holes in cast iron manhole lids. When soils are saturated, rainwater can infiltrate the sewer system through cracks in underground manholes, sewer mains and sewer laterals. Finally, and most significantly, storm water can enter the sewer system through the illicit connection of roof drains, yard drains and other surface drains.

No doubt all of these sources of I&I came into play on Feb. 17. Flows into the wastewater treatment plant were over three times higher than normal—we treated 3.4 million gallons as compared to just over a million gallons on a normal day. Fortunately, the treatment facility has the hydraulic capacity to handle these abnormal events, but pumping and treatment costs are dramatically affected by I&I.

Read the full article here.