Challenge

The California Department of Water Resources (DWR) regards groundwater in the Rialto-Colton Basin (RCB) as being severely impaired by perchlorate and volatile organic compounds (VOCs) contamination, and by overpumping. Both of these issues have affected the City of Rialto, preventing the City from obtaining sufficient, clean water sources and leading the DWR to require a replacement water system for the City.

Solutions

GLA was originally contracted by San Bernardino County in 1997 to assist in the evaluation of perchlorate in the RCB. In response to our evaluation that found perchlorate and VOC impacts, the County Solid Waste Management Division (SWMD) contracted GLA to assist in designing a response to the groundwater impacts at and near the planned Unit 5 expansion area of the Mid-Valley Sanitary Landfill.

GLA’s original evaluation had led to the discovery of the Western Plume, which posed a threat to municipal production wells in the area. After contracting with SWMD, GLA installed 18 groundwater monitoring wells to characterize the nature and extent of perchlorate and VOC impacts to the groundwater within the Western Plume. Hydrogeologic and chemistry data from these wells were used to develop a three-dimensional numerical groundwater flow model to assess plume transport and potential contaminant measures.  The model results supported development of a Remedial Investigation/Feasibility Study (RI/FS) report, which detailed alternative mitigation measures, and concluded that impacts could best be remedied by intercepting and containing the plume, treating the collected water to potable standards, and distributing the treated water to the City of Rialto.

Our team then designed a groundwater treatment system (GWTS) at Rialto Well No. 3 based on the RI/FS report. We worked closely with the County and the City of Rialto to provide all required permitting, regulatory, and other documentation to the DWR, then for the GWTS. After, we proceeded with constructing the GWTS. We have continued to assist in the operation of the GWTS, which has expanded to include two additional groundwater production wells, a 125,000-gallon influent reservoir, an ultra-violet treatment unit to address bacteria in the pumping wells, two ion exchange vessels, and four granular activated carbon (GAC) treatment vessels.The GWTS now includes treatment of both the Western Plume and the Eastern Plume (Combined Remedy). GLA provides litigation support through comments to County Counsel and SWMD to verify that the County’s treatment responsibilities will not be negatively affected by the Combined Remedy.

Results

Our work on this project has provided water to an area in critical need of reliable water resources. We have provided the County with an effective and cost-efficient system that has successfully reduced the threat posed by the Western Plume and delivers clean water to the City of Rialto.