Cooperative Studies: Arsenic in Groundwater 2009 & Kate Muldoon Watershed Monitoring February 2011

Transcription

1 Cooperative Studies: Arsenic in Groundwater 2009 & 2011 Kate Muldoon Watershed Monitoring February 2011

2 Arsenic Studies 2009 & 2011 A. Background B. Purpose C. Goals of studies D. Scope and extent E. Participants F. Analysis schedule

3 N Arsenic exceedances in Hillsborough County, by location and magnitude

4 Background Problem: arsenic found in high levels in groundwater in 4-county area Potential anthropogenic sources: citrus groves cattle dipping vats golf courses wells, ASR, overpumping Potential natural sources: Pyrite & Powellite -contains arsenic & molybdenum, released by disturbance

5 Questions & Goals Questions: Do the following significantly affect arsenic concentrations in groundwater (GW)? water levels (seasonality) aquifer lithology land use (urban, rural, land use changes) interactions among the three factors significantly affect arsenic concentrations in GW? Goals of study: Answer questions Create model to differentiate anthropogenic vs. natural sources of arsenic in GW

6 Extent and Scope 4 counties 4 years Obtain representative lithologic cores Sample different aquifers (surficial, intermediate, Floridan) Sample wells with low & high arsenic levels Sample wet & dry season groundwater Obtain current & historical land use data Compare lithologic & geochemical data Cooperatively-funded and executed effort of SWFWMD & DEP s FGS, WMS, and GWPS

7 Phase II Arsenic sampling in 48 randomly-selected wells in grid of area 18 Water Supply Restoration program (WSRP) wells 30 Status wells

8 Analytes & Schedule Field measurements ph, DO, ORP, conductance, temperature, turbidity Lab samples: cations and trace metals, anions and alkalinity SWFWMD and Tampa WMS staff sampled 48 wells in dry season of April, May, June, and again in wet season of August, September, October Preliminary analysis found that 15% wells had high arsenic readings in dry season vs. 11% in wet season. Rick Copeland conducting further analyses...

9 [As] (ug/l) 2011 Focus: Arsenic Concentration Fluctuations over Time AAI4200 AAK4240 AAL

10 TV Study Background Problem: arsenic concentrations can fluctuate dramatically in groundwater Potential sources/sinks: oxidative dissolution of pyrites & powellite reductive dissolution of hydrous iron oxides Potential precipitators: drought flooding human activities (dams, wellfields, etc.)

11 Implications & Purpose Implications: Many potable water wells that show Arsenic levels below the current standard of 10ug/L may, in fact, have occasional exceedances that have human health consequences. Purpose: Identify geochemical & geophysical processes in temporal variability of arsenic concentrations Understand the natural and anthropogenic causes of arsenic mobilization.

12 Specific Objectives of 2011 Study Examine the correlation of key redox indicators with arsenic and other trace metal concentrations in the well water over time. Investigate the presence of the mineral powellite in targeted core samples Identify mineral associations (pyrite, powellite, hydrous ferrous oxides) of arsenic and other trace metals. Develop a geochemical model to represent temporal variations and/or verify results found in the FAS

13 Analytes Field measurements ph, DO, ORP, conductance, temperature, turbidity Unfiltered Lab samples: sulfides, total arsenic. Filtered Lab samples: total dissolved arsenic, nutrients, nutrients & anions, cations and trace metals, anions and alkalinity (initially) Total dissolved arsenic sample to be pushed through SPE cartridge for arsenic speciation (As III, As V) in field, preserved for lab analysis. Portable spectrophotometer used for confirming iron and sulfide concentrations.

14 Extent and Scope 2 sampling sites: Sample Floridan aquifer Sample DEP monitoring wells and homeowners wells in known areas of high arsenic levels

15 Extent and Scope Merritt s Mill Pond Lithia/Dover

16 Extent and Scope 18 months duration IF Compare representative lithologic cores (Powellite?) and geochemical data Cooperatively-funded and executed effort of DEP s FGS, WMS, SIS

17 Quality Assurance Regional sampling by different sampling staff: ensure we all follow the same protocol. QA Officer oversees training and follows up with field audits of samplers throughout the state. All samples analyzed at NELAP-certified laboratories: DEP Central Lab, Tallahassee Activation Labs, Ancaster, Ontario, Canada

18 Questions???