Sioux City Riverbank Filtration Study
Abstract
The City of Sioux City (City) obtains a large percentage of their drinking water supply from both a horizontal collector well system and vertical wells located adjacent to the Missouri River. These wells are set in either the Missouri Alluvium or the Dakota Sandstone aquifer. Several of the collector well laterals extend out beneath the Missouri River, with the laterals being over twenty feet below the river channel bottom. Due to concerns regarding ground water under direct surface water influence, the Iowa Department of Natural Resources (IDNR) required the City to expand their water treatment process to deal with potential surface water contaminant issues. With the extensive cost of these plant upgrades, the City and Olsson Associates (OA) approached the IDNR requesting approval for assessing the degree of natural riverbank filtration for water treatment. If this natural process could be ascertained, the level of treatment from the plant could be reduced. The objective of this study was to quantify the degree of surface water (i.e. Missouri River) filtration due to the underlying Missouri River sediments. Several series of microscopic particulate analysis where conducted, along with tracking of turbidity, temperature, bacteria and a full scale particle count study. Six particle sizes from six sampling points were assessed over a nine-month period that spanned summer, fall and spring weather periods. The project was set up in two phases and utilized industry accepted statistical analyses to identify particle data trends. The first phase consisted of twice daily sample collection from the Missouri River and the collector well system for a one-month period. Statistical analysis of the data indicated reducing the sampling frequency and sampling locations would yield justifiable data while significantly reducing sampling and analysis costs. The IDNR approved this modification, and phase II included sampling and analysis under this reduced plant for an eight-month period. Final statistical analyses of the nine months of data indicate up to a four-log particle reduction occurs through river bank filtration. Consequently, Missouri River sediments within the City's well field are very effective in water filtration. This information was submitted to the IDNR for review and approval. Subsequently, the IDNR approved 4.0 log removal for Giardia and 3.5 log removal for Cryptosporidium through the riverbank and treatment plant. The City and IDNR have agreed on subrogate parameters for monitoring purposes.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....12102M