2004 Progress Report: Riverbank Filtration Effectiveness in an Arid EnvironmentEPA Grant Number: R829009
Title: Riverbank Filtration Effectiveness in an Arid Environment
Investigators: Langford, Richard P. , Pillai, Surresh , Schulze-Makuch, Dirk
Institution: The University of Texas at El Paso , Texas A & M University
EPA Project Officer: Page, Angela
Project Period: September 1, 2001 through August 31, 2004 (Extended to August 28, 2005)
Project Period Covered by this Report: September 1, 2003 through August 31, 2004
Project Amount: $437,418
RFA: Drinking Water (2000) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
The objective of this research is to determine whether bank filtration in an arid environment is effective at removing microbial pathogens. The field site for the proposed studies is unique because it is located in an arid region and utilizes the Rio Grande River system that exhibits significant fluctuations in both water quantity and quality. The results from these studies can be significant for this region because the region relies almost exclusively on aquifers for its municipal drinking water.
This year we completed our data collection. The geochemical analysis is completed, and analysis of microbial concentrations is almost complete. The three dimensional model has been constructed and has been adjusted for steady-state conditions. Tests and various pumping stages are now being completed.
Because of the drought in the Rio Grande headwaters, there was no flow through the Rio Bosque. We obtained some samples from December 2003 through January 2004 and were able to complete our geochemical and microbial sampling. Four sampling episodes were completed during this time.
Geochemical parameters at the field site remained relatively constant during the 3-year sampling period. No significant change was observed during the sampling events. The main solutes in the groundwater are sodium chloride and calcium sulfate with a total dissolved solid content slightly above 1000 mg/L. Biological content in well water is present, but typically low in biomass and not the result of fecal contamination. Nutrients are scarce in the groundwater. The channel is, however, a source of high Kjeldahl nitrogen and elevated phosphorus when channel water is drawn into the groundwater.
Four pump tests were conducted, one at a low pumping rate (0.005 m3/sec, 79 gal/min) and three at a high pumping rate (0.0025 m3/sec, 40 gal/min). The background samples from the canal contained detectable concentrations of the target indicator organisms and selected pathogens (Giardia spp.). We postulated that we could monitor the presence of these organisms in the different sampling wells during pumping to determine the movement of organisms under the varying pumping flow rates.
The results from these tests suggest that riverbank filtration appears to be an effective tool to prevent the migration of protozoan cysts. Riverbank filtration, however, does not totally remove or retard the migration of bacteria. Bacteria migrated at nearly the same rate at both low and high flow rates. We monitored the migration of two bacterial indicator organisms, Escherichia coli and Enterococci, which appeared in reduced numbers in the pumping well as compared to the canal, suggesting that bacterial pathogens could break through the barriers during riverbank filtration.
Figure 1. An Example of the Results of Pumping Test 1. Notice the variability of indicator species in both the channel and pumping well.
The project almost is complete. We now are concentrating on writing and publishing our results.