Using TOC to Protect Water Quality During Storm Water Season

It’s that time of year again across the country. Some refer to it as stormwater season, runoff season or simply sampling season. Regardless of what we call it, it’s raining. In some parts of the Nation, such as California, rain and snow totals are at record levels. A series of winter storms this season has brought record-breaking rainfall and dropped snow levels dramatically across the state, bringing snow to L.A. and other areas that rarely see any. In early February, snow fell in Malibu, Pasadena, West Hollywood, Northridge, San Bernardino, and Thousand Oaks, and dusted Saddleback Mountain in Orange County. The consistent rainfall provided an 18-trillion gallon soaking of the state and has reached nearly half the volume of Lake Tahoe. California is not alone at this time of year. Late winter and early spring storms bring rain across nearly all regions of the country.

Urbanization has fundamentally altered the way water moves through the landscape. When rainwater can’t soak into the ground, it runs along streets and parking lots and picks up pollutants.  This polluted runoff can flow into our rivers and streams, or overwhelm local infrastructure to cause sewage overflows.

This time of year can be particularly challenging for operators of water treatment plants (WTP’s) and wastewater treatment plants (WWTP’s). Other industries that can be affected include refineries, chemical plants, and construction sites. Products, such as refined fuels or other petroleum-based products, which are contained within the plant or construction site, are now washed out to the surrounding watershed.

The Clean Water Act (CWA) establishes a comprehensive program to restore and maintain the chemical, physical, and biological integrity of the Nation’s waters. The CWA also includes the objective of attaining water quality which provides for the protection and propagation of fish, shellfish and wildlife, and recreation in and on the water. To achieve these goals, the CWA requires EPA to control discharges of pollutants from point sources through the issuance of the National Pollution Discharge Elimination System (NPDES) permits. The Water Quality Act of 1987 (WQA) added section 402(p) to the CWA, which directed EPA to develop a phased approach to regulate stormwater discharges under the NPDES program.  EPA published a final regulation in the Federal Register, often called the Phase I Rule on November 16, 1990, establishing permit application requirements for, among other things, stormwater discharges associated with industrial activity.

In most cases, the source waters for water treatment plants, whether these are groundwater or surface water sources, are generally stable and well-characterized in regard to their chemical content. This includes TOC. However, naturally occurring events such as heavy rains and flooding, algal blooms, or greater-than-average snow melts can alter the chemical composition of the source water. This is particularly true for surface water sources.

When rain falls on the ground, it can do one of two things: flow into the ground and become groundwater, or flow on top of the ground and become runoff. As water flows into the ground, the soil acts as a “filter,” catching and holding most anything the rainwater brought with it. Trees and other plant life also capture the nutrients the water brings. However, when the water has no way to enter the ground, like when it falls on a parking lot, it will keep traveling above ground until it hits the nearest river, lake, or sea.

As it flows over the land surface, stormwater picks up potential pollutants that may include sediment, nutrients (from lawn fertilizers), bacteria (from animal and human waste), pesticides (from lawn and garden chemicals), metals (from rooftops and roadways), and petroleum by-products (from leaking vehicles).

Pollution originating over a large land area without a single point of origin, and generally carried by stormwater, is considered non-point pollution. In contrast, point sources of pollution originate from a single point, such as a municipal or industrial discharge pipe. Polluted stormwater runoff can be harmful to plants, animals, and people.

Since this water had no opportunity to deposit whatever it grabbed along the way, it deposits that matter into the water body where it can begin to have negative effects on the WTP that is pulling that water into the plant for treatment and distribution to the community it serves.

Total Organic Carbon (TOC) is an important water quality parameter, as contamination is generally comprised of carbon-containing compounds. Whether the contamination is naturally-occurring material (NOM), such as decomposing plants or fumic acid from soils, or anthropogenic, such as industrial wastewater, the accurate assessment of TOC in water is critical to detecting environmental pollution and ensuring clean water supplies. It is also an important parameter in the study of carbon cycles in ocean waters.

TOC is often used as a non-specific indicator of water quality. In the natural process of our environment and the man-made processes of industry, the ubiquitous nature of carbon provides a screening tool to determine the status of water quality.  Water and wastewater treatment plant operators, and operators of plants that hold NPDES permits, need a reliable TOC system that can determine contamination from natural-occurring compounds, man-made compounds, viruses, bacteria or biological growth during stormwater runoff events.

About the author: John Welsh, earned his Ph.D. in Analytical Chemistry from Texas A&M University and has 25+ years of experience in analytical instrumentation. Five of those years have been specifically dedicated to TOC analysis research, so you can trust he is an expert on all things TOC.

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