Terrieu Creek

Figure 1. Location of the Terrieu Creek study site.

The assumed source of fecal coliform contamination is a wastewater treatment plant located 400 m upstream of the well field. Primary-treated wastewater is collected in a basin during rain storms, the retention basin sometimes overflows and the treated wastewater flows into Terrieu Creek. Previous research by Malard et al. (1994) at this... 

Rainfall at the site sufficient to cause Terrieu Creek to flow resulted in marked temporal changes in TSS and bacterial content in both surface and ground water. Both wells P7 and P8 responded quickly to elevated TSS concentrations and bacteria in Terrieu Creek. Temporal changes in TSS and concentrations of free and sediment-associated bacteria continued over several days. 

Fecal coliform density reached extremely high levels in Terrieu Creek and both wells directly after the creek began to flow and again several days later (Fig. 3b). The first peak in bacteria in Terrieu Creek coincided with the TSS peak in the first flush of streamflow. The second increase occurred when creek flow slowed and the water began to pond, peaking just before the creek ceased to flow. Samples of ponded water were not collected after cessation of flow. 

Fecal coliform density in both P7 and P8 increased more than an order of magnitude within 10 hours after flow began in Terrieu Creek. The bacteria then decreased for about 60 hours, before increasing again, peaking 120 hours after rainfall at 30,000 and 25,000 CFU/100 mL, respectively. 

Figure 3. Concentrations of TSS (a) and fecal coliform density (b) in wells P7 and P8 and Terrieu Creek in response to a storm.

Figure 4. Percent fecal ooliform associated with particulates in wells P7 and P8 and Terrieu Creek (a) and comparison of fecal ooliform densities in whole water (b) and on suspended sediment (o) in each of the two wells to that in surface water. Ratios are calculated as CFU/L in each well divided by CFU/L in Terrieu Creek for whole water, and CFU/g in each well divided by CFU/g in Terrieu Creek for suspended sediment.

At the well field adjacent to Terrieu Creek in southern France, a large proportion of fecal coliform bacteria was associated with suspended sediment, at times up to 90%. Bacterial concentrations associated with sediment in surface water and in the subsurface were very similar, indicating a close connection between the two. The association of bacteria with sediment has important implications for public health. The bacteria may be protected from predation, may be able to use the substrate as a food source, and are less susceptible to standard methods of disinfection. 

---