Langan Engineering & Environmental Services, Inc.
Bob Bond, P.G. is a consulting senior hydrogeologist with Langan in Doylestown, PA. He has over 30 years of environmental assessment and remediation experience and holds a B.S. Degree in Geology from Allegheny College and an M.S. Degree in Geology from Lehigh University. Mr. Bond's practice focuses on the hydrogeologic assessment and remediation of aquifers impacted by suites of chlorinated solvents, geochemical forensic methods, commingled plume issues, as well as environmental litigation support and expert witness testimony. Bob has served on three Interstate Technology and Regulatory Council (ITRC) teams, and has a history of yearly involvement and responsibilities with national conferences, including Battelle, National Ground Water Association (NGWA), and the Geological Society of America (GSA). He has taught university short courses and spoken at local and national conferences on environmental forensics, data analysis, fractured bedrock assessments, and the fate and transport of contaminants.
Remedial Evaluations of 1,4-Dioxane Source Areas Using 1,1,1-TCA Degradation Rates
The compound 1,1,1-TCA is unique among chlorinated volatile organics as the only major solvent that can be completely transformed abiotically by hydrolysis in 20 years to 1,1-DCE. The abiotic degradation rate to 1,1-DCE, as well as the combined abiotic/biotic degradation rate to 1,1-DCE and 1,1-DCA, can be quantified in a reasonable investigation timeframe typical of chlorinated volatile organic groundwater sites. The degradation rates can also be used to back-calculate the date of the discharge of 1,1,1-TCA to groundwater, as we have done in the majority of cases that we have reviewed. TCA has been identified as the primary source of 1,4-dioxane in groundwater plumes. We have combined our previous work on the evaluation of the forensic 1,1,1-TCA ratio age-dating method from twenty cases with the remedial evaluation of collocated 1,4-dioxane plumes and source areas. Estimated TCA/1,4-dioxane discharge dates in our recent study span approximately 26 years and range from 1971 to 1997.
We will present the results of our work from multiple sites located in various geologic and geochemical settings, including coastal plain aquifers and fractured bedrock aquifers. Plume lengths for 1,4-dioxane in our case studies range from 800 feet to 2,500 feet. Two cases involve distal plume discharges and impacts to surface water. Components of the study that will be presented include the geometry and stability of commingled plumes of 1,4-dioxane, TCA, 1,1-DCE and 1,2-DCA, discharge dates, first order rate constants for TCA loss and daughter products, and 1,4-dioxane attenuation rates. Our findings will be put in context with site-specific conditions, such as commingled chlorinated ethenes and methanes, natural attenuation conditions, various source area remedial actions performed, and geologic and geochemical conditions.