Water Expansion Project Resolves Pollution Issues, Leads to Scientific Breakthrough

By:
Sarah L. Raker, PG, CHG
Principal Geologist
MACTEC, Inc.

A plume of toxic groundwater discovered in a small neighborhood in Chico, CA (pop. 88,000; about 90 miles north of Sacramento) more than six years ago has not only been successfully addressed, but has also resulted in a significant breakthrough in better understanding the region’s geological history – core samples taken from drilling groundwater monitoring wells in the Skyway Homes Subdivision area are providing important information for scientists.

Zurich, Switzerland-based ABB (www.abb.com) provides power and automation technologies for utility and industry customers. The ABB Group of companies currently operates in more than100 countries and employs about 120,000 people. ABB purchased a tract of land that unknown to them, had been the site of groundwater contamination by a previous owner. The site was also owned in the 1970s by a company that manufactured aluminum shower enclosures and windows. A solvent, trichloroethylene (TCE), was detected in water supply wells located at the former manufacturing facility and in nearby domestic and irrigation wells.

Although ABB had no role in polluting the groundwater, the California Department of Toxic Substances Control (DTSC) determined that they were still legally bound to clean up the site. ABB reimbursed the state for nearly $1 million already spent on cleanup and another $2 million to put in water lines that supplied residents with clean water provided by the California Water Service Co.

MACTEC was retained by ABB to assist with the cleanup, providing environmental consulting and construction oversight for investigating and remediating elevated levels of TCE in the groundwater.

Existing water mains were extended into the impacted neighborhood and private homes were connected to the public water supply.A total of 3,400 feet of 12-inch pipe; 4,700 feet of 8-inch pipe, 350 feet of 6-inch pipe, 21 fire hydrants, and 68 connections were made.

Key Tasks

There were a number of tasks undertaken to implement the Remedial Investigation/Feasibility Study (RI/FS) required by DTSC. Some of these included:

Community Relations – Providing technical support in preparing fact sheets, public notices for public meetings; providing updates on the investigations progress and potential impacts to the community.

Remedial Investigation Implementation – Included monitoring well installation, developing, sampling and collecting groundwater samples from domestic and irrigation wells near the Skyway Subdivision Groundwater Plume. Also consisted of installing, developing and surveying two replacement wells; installing three nested monitoring well locations and one shallow well using sonic drilling methods.

Annual Wellhead Treatment System Sampling – ABB offered 73 residents connections to the local water supply; four property owners declined. The four property owners will continue to use the wellhead treatment system to filter their groundwater for potable use.

Public Water Expansion Project – Involved coordinating with ABB, California Water Service Co. and West Valley Construction for installing the public water supply connections to subdivision residents.

Quarterly Groundwater Monitoring – Duties include preparing and submitting Butte County Encroachment permits for access to a monitoring well; collecting groundwater samples from 43 monitoring wells using dedicated passive samplers; and procuring an analytical lab for volatile organic compounds (VOCs).

Ancient Ground Formations

During monitoring well installation, sonic drilling technology was used to obtain the core samples (these went down 250 feet) – a continuous core is recovered intact from a bore hole as it was formed over thousands of years, layer upon layer. ABB offered the rock cores to Chico State University, DTSC, the California Department of Water Resources and the California Regional Water Quality Control Board.

The samples may help geologists determine the relationship between the 3.3 million-year-old Tuscan Formation that holds the Sacramento Valley’s groundwater (which includes Chico), and local aquifer systems to identify potential drought-related implications.

Todd Greene, an assistant professor of geology and environmental sciences at Chico State University, noted that this marks the first time rock data for the Chico area has been made available in such pristine condition. Greene is also involving his students – the samples are helping to educate them about the Tuscan Formation aquifer, its flow paths and the changes in volume of groundwater.

And the bottom line? Top priority was a permanent remedy for the water problem – potential exposure to chlorinated solvents in drinking water has been resolved. The core rock samples also promise to contribute to a greater understanding of geologic formations underlying the Sacramento Valley.

WORD COUNT: 723

Editor’s Note: Sarah L. Raker, PG, CHG is Senior Principal Geologist for MACTEC and is based in the firm’s Petaluma, CA office. Contact her at slraker@mactec.com. MACTEC (www.mactec.com), based in Alpharetta, GA, is a leading infrastructure engineering firm focused on five strategic business lines: Industrial/Commercial, Transportation, Municipal, Energy, and Federal. With annual revenues over $490 million, MACTEC’s 3,000-plus employees work from over 80 offices nationwide. MACTEC consistently ranks in the top 10% of Engineering News-Record’s Top 500 Design Firms.