A water district in Southern California supplies drinking water with a combination of
local shallow well groundwater and imported raw and treated water. The well is located
120 ft away from a seasonal creek. Based on limited temperature data, the California
Department of Health Services (DHS) determined that the groundwater was under direct
influence from the creek. In 2000, DHS required the district to install a water filtration
plant. Before expending upwards of $1 million on a new treatment plant, the district
elected to set up a sampling and testing protocol to determine more conclusively whether
or not groundwater was under direct influence of surface water, and if so, what treatment
credit could be given to river bank filtration. This paper reports a natural filtration study
conducted in 2003 and 2005 for the district. The study, supported on well and creek
monitoring, was devised to establish how rapidly well water quality responds to surface
water quality changes, and to quantify river bank effectiveness in removing turbidity,
total and fecal coliform (TC and FC), Giardia and Cryptosporidium.
Devising a meaningful well and creek monitoring program presented challenges because
of the seasonal nature of creek flow and well production (i.e. the wells start production
early in the rainy season before creek flow starts, and well production continues for a
period after the creek stops flowing). The monitoring program included different
sampling intervals, tests and procedures for the various flow conditions. The monitoring
program captured several significant rain events that resulted in high creek flows and
associated increased creek water turbidity.
Tracer test data showed a 30-hour groundwater travel time from the creek to the
production wells. Based on creek and well sample data, natural filtration provides
removals as high as 3-log turbidity, 4.4-log TC, and 2-log FC. The highest creek
Cryptosporidium concentration during the sampling program was 0.4 organisms/L and
Giardia 0.03 organisms/L. Well samples showed none detected for both organisms. Data
evaluated included turbidity, coliform bacteria, protozoa, temperature, pH, electro-conductivity, and particle counts.
Based on the results, well water is under the influence of creek water; however, natural
filtration provides removal of turbidity, bacteria and protozoa. Particle count data show
that 5 to 15 micron particles, the size of pathogenic protozoa, although partially removed
in the creek bank, still appear in product water. Includes tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 1.1 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 11 |
| Published : | 06/17/2005 |
