Naturally Occurring Compounds of Regulatory Concern

SYMPOSIUM DETAILS: 
Recent groundwater research and monitoring shows that many regulated chemical compounds occur naturally in California groundwater.  Metals such as chromium, arsenic, and uranium are naturally occurring and are commonly detected in groundwater at problematic concentrations.  Recent studies also show that nitrate and perchlorate accumulate naturally in arid climates such as the American Southwest.  Even many organic compounds such as benzene, methane, and tert butyl ether (TBA; a gasoline oxygenate) are naturally occurring in California groundwater. 
 
While these compounds are naturally occurring, the compounds may become mobilized or exhibit increased concentrations as a result of human activities.  For example, naturally occurring dissolved salts, once largely sequestered in fine-grained sediment in the San Joaquin Valley, have been mobilized by changes in vertical hydraulic gradients brought on by decades of irrigation and groundwater pumping.  Exposure of stable trivalent chromium to oxidizing agents converts trivalent chromium to more mobile, toxic hexavalent chromium, which is also naturally occurring.  Injection of oxygenated recharge water in Aquifer Storage and Recovery (ASR) projects can dissolve arsenic-bearing minerals, thereby increasing dissolved arsenic concentrations in the recovered groundwater.   
 
Some of these compounds may pose health risks, while other naturally-occurring compounds are objectionable due to taste and odor.  Naturally occurring substances such as dissolved iron and manganese, TDS, calcium and magnesium (hardness), sulfate, algae, dissolved organic matter, and hydrogen polysulfide (from chlorination of sulfide-bearing water) can impart objectionable taste or odor to water supplies. Aesthetic impacts such as these can be particularly troublesome for water purveyors who strive to provide drinking water at the lowest possible cost. 
 
This symposium will focus on the occurrence, forensic evaluation, toxicology and regulation of naturally occurring chemical compounds in California groundwater.  Particular attention will be focused on sustainable management practices that help ensure that these constituents remain below evolving threshold concentration limits.
 
Session 1:  Dissolved metals and radionuclides (e.g., chromium, arsenic, uranium, selenium)
Session 2:  Other inorganics (e.g., TDS, nitrate, perchlorate)
Session 3:  Organic compounds (e.g., benzene, methane, TBA)
Session 4:  Aesthetic impacts/exceedance of secondary MCLs (e.g., color and odor issues)
 
The two day symposium will end with a panel discussion.