Depth Studies for Municipal Wastewater Plants

Environmental Business Specialists (EBS) has performed numerous depth surveys at industrial manufacturing plants over the years. These depth surveys are used to determine basin retention time and how it may have changed over the years. Sampling for items such as pH and dissolved oxygen can also occur during a study. Knowing how a pond’s depth has changed over time communicates changes in its ability to remove Biochemical Oxygen Demand (BOD), mimimize total suspended solids (TSS) carryover, and other elements that affect its overall efficiency.

Recently, EBS was contracted by a dredging company to perform a depth survey on a Storm Cell Basin at a municipal wastewater treatment plant. Since, the basin had recently been dredged, the main objective was to determine if enough solids had been removed to increase retention time and gain overall volume.

Basins accumulate solids resulting in a slow, but steady reduction in system capacity. Over time, sludge and other inorganic compounds that cannot be degraded settle out in areas throughout the basin, reducing its volume. It is important to ensure that any system does not reach the point where it is no longer capable of providing the desired treatment. A depth survey on a treatment pond provides valuable information regarding the current volume and how much volume has been lost from the original design volume.

The use of Global Positioning System (GPS) and sonar provides an accurate method of mapping the floor of a wastewater treatment basin. Because water depths vary throughout a basin, it is important to have as many data points as possible. This method allows EBS to obtain several thousand depth measurements, which helps us determine where pockets of sludge are building up and areas of the treatment basin that need to be dredged. Each GPS coordinate recorded corresponds with the depth giving a three-dimensional graph of the bottom topography of the basin. Below are graphs taken from depth surveys detailing areas of sludge build up.

Depth Studies GPS Sonar

Figure 1

Depth Studies GPS Sonar

Figure 2

Figure 1 shows a depth profile before dredging has occurred and Figure 2 shows the same section after dredging. The maroon color essentially indicates zero feet of water in many areas of the basin. After dredging, there is less maroon and more orange and yellow, indicating that sludge was removed resulting in an increase in basin retention time and more effective BOD removal.

For more information on depth and tracer surveys, how they might provide your plant with valuable information, or to just discuss your plant’s needs, contact EBS at or 985-674-0660.

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