The Sacramento Branch is pleased to present:
William E. Motzer, PhD, PG, CHG
Geology and Geochemistry of Chromium Sources in California’s Groundwater
Chromium (Cr) including Cr(VI) species occur in California’s groundwater from both anthropogenic and geogenic (natural sources). Past investigations largely focused on anthropogenic sources (e.g., added to water as a biocide) popularized by the 2000 movie Erin Brokovitch. More recently, groundwater investigations have considered geogenic sources with California having a unique geologic framework, including numerous areas of ultrabasic and serpentinized ultrabasic rocks. These contain abundant Cr and Cr minerals, which when weathered, can undergo transformation in the critical zone to Cr(VI) complex oxyanions.
The San Francisco Bay Area has several areas where ultrabasic and serpentinized rocks can be observed, including areas on Mt. Diablo in Contra Costa County and the Ring Mountain Open Space Preserve (RMOSP) in Marin County. In the critical zone, many RMOSP soil types derived from the underlying serpentine and ultramafic rocks are serpentine soils, with unusually high concentrations of iron, chromium, nickel, and cobalt. However, these often are deficient in calcium and have low water holding capacities. Such soils can be very stressful for plant growth, consequently forming serpentine barrens commonly consisting of open grassland or savannas where the climate would normally result in forest growth. Serpentine barrens also result in unique eco- or model-systems for evolution, ecology, and conservation studies of rare plant communities. On RMOSP serpentine soils cover about 225 acres.
Groundwater in alluvial aquifers derived from ultrabasic and serpentinized terrain can contain Cr(VI) oxyanions, particularly chromate (CrO42–) and dichromate (Cr2O72–), generally forming under alkaline pH and oxidizing (+Eh) conditions. In other areas, Cr(VI) oxyanions can sorb to hydrous ferrous oxide (HFO) coatings on quartz grains. For projects in which recycled water (RW) is introduced to replenish depleted groundwater supplies, changes in pH and Eh have the potential for liberating Cr(VI), arsenic, and lead. Leaching tests with stabilized RW and geochemical modeling, using USGS PHREEQC and PHAST models can be used to assess possible impacts to groundwater by these constituents.
William E. (Bill) Motzer is a registered California Professional Geologist (PG) and Certified Hydrogeologist (CHG), with PG registrations in five other states. Bill has extensive experience in conducting surface and subsurface water quality chemistry and environmental forensic investigations. Bill is a recognized expert in water quality and forensic geochemistry, with particular expertise in stable and other isotopic “fingerprinting” and age dating techniques, water quality/contaminants, and emerging contaminant geochemistry. He has conducted numerous environmental projects, throughout California and other western states. He is a past President of the San Francisco Bay Branch of the Groundwater Resources Association of California (GRA), past Vice President for the International Society of Geochemistry and Health, and contributing editor to the California Section of the American Chemical Society’s (ACS) newsletter – the Vortex (www.calacs.org).
ANNOUNCING SCHOLASTIC SPONSORSHIP OPPORTUNITIES:
All Proceeds to Benefit Science Students
The GRA Sacramento Branch has a history of supporting university-level science students. Our Scholastic Sponsorship Program is an opportunity to publicize your business while contributing toward a good cause. The cost is minimal; if interested, please contact Ellen Pyatt at (916) 852-9118 x 512 or firstname.lastname@example.org.
THIS MONTH'S SPONSOR:
ASC Tech Services (ASC) is a professional environmental field services company founded in 1996 by a Geologist with over 25 years of environmental consulting experience. ASC specializes in the implementation of High-Resolution Site Characterization (HRSC) technologies to assist consultants and clients in the understanding of subsurface lithology/hydrogeology and/or contaminant distribution in real-time. ASC can acquire HRSC data to determine lithologic/hydrogeologic changes and track contaminants by taking a snapshot of the subsurface with minimal disturbance of the subsurface and without generating soil or groundwater wastes. With innovative HRSC technologies, ASC can assist consultants and clients to evaluate a site in one visit, allowing the infield professionals to make real-time decisions. Our services are provided with geoscientists in the field in order to assist consultant and client personnel in the interpretation of HRSC data.
ASC provides professional, cost-effective services globally.
- (MIP) Membrane Interface Probe;
- (HPT) Hydrologic Profiling Tool;
- (OIP) Optical Image Profiler;
- (UVOST®) Ultra-Violet Optical Screening Tool;
- (EC) Soil Conductivity Testing;
- (MiHpt) Combined MIP/HPT;
- (MIP-CPT) Combined MIP/CPT;
- Combined MiHpt/CPT;
- (PST) Pneumatic Slug Testing;
- Geothermal & In-Situ Pressure Profiling/Monitoring;
- Hydrostratigraphic & Hydrogeologic Characterization & Modeling;
- Multi-Variant Modeling & GIS Integration.
ASC is a State of California Certified Small Business (SB/MB) and Minority Business Enterprise (MBE).
Social Hour 5:30-6:30 p.m.
Announcements & Dinner 6:30-7:30 pm
Presentation 7:30-8:30 pm
Usual great food, including two meat entrées, salad, rice, potatoes, vegetable and Iced Tea. A No-host beer and wine bar will be available.
- If you register after Noon on Monday, May 8th, or walk-in, a $3.00 surcharge will be added to the meeting cost.
- Cancellations must be made by Noon on Monday, May 8th.
Questions about the meeting, please telephone Rodney Fricke at (916) 407-8539 or email him at email@example.com. Questions about the Sacramento Branch in general, including submittal of your ideas and/or desires for future presentations, please telephone Linda Bond at (530) 757-1500 or email her at Linda.Bond@water.ca.gov
UPCOMING MEETINGS & EVENTS:
June 14th: Barry Hecht with Balance Hydrologics, Inc., Post-Fire Effects on Channels and Recharge