Extremely impaired water sources represent a significant resource to Southern California. With
treatment, these sources can produce potable water that is equal or superior to other available
supplies. Water currently pumped from the I-105 dewatering wells near the Southern limits of
Downey (City) are an example of a source that may be put to beneficial use. Steps taken to
achieve this begin with extensive analysis of water quality, treatment options and risk assessment
in compliance with Department of Health Service (DHS) requirements.
The I-105 freeway was constructed by Caltrans and placed into service in 1993. A portion of the
freeway system between the Los Angeles and San Gabriel Rivers was constructed approximately
35 to 40 feet below existing grade to mitigate noise concerns. However, groundwater recharge
activity to the north, resulted in increasing groundwater levels negatively impacting the freeway.
To resolve the high groundwater problems, Caltrans implemented a groundwater control and
dewatering system in 1996. The system includes a series of wells installed to depths ranging
from 80 to 110 feet. The wells were constructed for the purposes of dewatering and were
therefore not constructed to potable water standards. The water removed by the dewatering
wells is pumped through granular activated carbon (GAC) filters prior to discharge to the Los
Angeles River. The system has performed adequately and has lowered the groundwater table
preventing damage to the freeway.
There are several issues associated with the existing Caltrans groundwater dewatering system
that make an alternative solution desirable:
the system operates under a National Pollutant Discharge Elimination System (NPDES)
permit allowing discharge into the Los Angeles or San Gabriel Rivers;
high total dissolved solids (TDS) content, mineral constituents, and levels of volatile
organic compounds (VOCs) require GAC treatment prior to River discharge;
a pump tax is imposed for water extracted from the Central Basin; and,
negative public perception is associated with groundwater discharge without beneficial
use.
Caltrans partnered with the City of Downey to investigate utilizing the groundwater for potable
water use, as a win-win solution for both agencies. The proposed plan consists of 5 new
drinking water wells (in addition to the test well 1D6A), a 3.6 mile pipeline, and a 6.5 MGD
treatment plant.
To meet DHS requirements and public expectations, the water quality needs to meet or exceed
the quality of existing sources of supply. To meet these expectations, some of the treatment
alternatives under consideration include reverse osmosis, packed tower aeration and granular
activated carbon.
In addition, an extensive source water assessment, including groundwater modeling
(MODFLOW), was undertaken to delineate capture zones and determine well capacity to keep
the freeway dry, identify the sources of contamination, and develop a protection plan. This paper
outlines the considerations necessary to evaluate the innovative project to expand beneficial
use of local water resources by replacing dewatering wells with drinking water wells. Includes tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 3.5 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 13 |
| Published : | 06/15/2003 |
