2011 Maine Water Conference
Wednesday, March 16, 2011
Augusta Civic Center, Augusta, Maine

SESSION 9
Groundwater Geochemistry: Natural and Human Influences

Chair: Bruce Hunter, Hydrogeologist, Maine Department of Environmental Protection

Chair Bio:
Bruce Hunter, CG #242, Environmental Hydrogeology Manager, has been working as a hydrogeologist in the environmental sector since 1988.  His work has included soil and groundwater transport modeling to develop soil cleanup standards, database development, regional groundwater contamination studies and site characterization and remediation.  He is currently supervising a group of 20 hydrogeologists and support staff who work in the remediation of soil and groundwater.  Early in his career he worked for 8 years in the oil industry in Texas, off-shore New Jersey and Alaska.  Bruce has a B.S. in Geology from Haverford College, a Masters degree in Geology from University of Missouri and a PhD from Texas Tech University.

Description: Groundwater is the drinking water of choice for more than half the people in Maine. It is also used as process water for some industries. The taste, odor, usability and appearance of the water depend on its chemistry, which is determined by the geochemical processes in the groundwater from which it comes. Talks in this session will discuss aspects of groundwater geochemistry. Topics may include, but are not limited to:

• Natural contaminants such as arsenic, manganese, uranium or other radiological elements;
• Mobilization of natural contaminants by human activity, such as mobilization of arsenic by de-oxygenated groundwater;
• Non-toxic chemistry such as high iron, sulfates and calcium;
• Landfill generated changes in groundwater geochemistry; and,
• Seawater intrusion.

PM SESSION

Biological Controls on Groundwater Chemistry
Richard S. Behr, Richard H. Heath; Maine Department of Environmental Protection, Bureau of Remediation and Waste Management, Augusta, ME

Micro-organisms catalyze an amazing number of important biogeochemical reactions which significantly influence groundwater chemistry.

The role of micro-organisms is particularly important whenever humans alter the natural environment.  The introduction of degradable organic carbon often rapidly depletes the available dissolved oxygen.  Once dissolved oxygen is significantly reduced or completely exhausted, anaerobic micro-organisms continue to oxidize available carbon using alternative terminal electron acceptors.  We will briefly describe how micro-organisms metabolize organic compounds using alternative electron acceptors including nitrate, manganese, iron and sulfate.  Using data from several Maine sites we will demonstrate how rapidly introduced organic carbon exhausts available oxygen.

We will present examples illustrating how the use of alternative electron acceptors may significantly alter groundwater chemistry.  Topics will include how the reduction of Fe (III) dramatically increases the concentration of the more soluble Fe (II).   Increased arsenic concentrations often result, in part, from the microbial mediated reduction of iron.  Other examples will demonstrate the importance of micro-organisms capable of using manganese and sulfate as terminal electron acceptors.

The affect micro-organisms have on groundwater chemistry is not limited to the use of alternative electron acceptors.  While their ability to metabolism complex organic compounds is largely responsible for limiting the size of petroleum contaminant plumes, many micro-organisms satisfy their energy requirements by capturing the energy in the reduced iron, manganese and sulfur compounds produced by other microbes.  We will conclude with data illustrating how the biologically mediated oxidation of reduced metallic species limits the solubility of iron, manganese and arsenic.

Detecting and Delineating Groundwater Contamination at a Leaking Waste Disposal Site using Microbial Community Profiles
Paula J. Mouser; Civil and Environmental Engineering, University of Maine, Orono, ME

Detecting subsurface contamination from leaking waste disposal sites can be challenging when using a limited network of groundwater monitoring wells that are sampled for multiple hydrochemical parameters over discrete temporal intervals. Microbial communities are sensitive to changes in nutrient resources and therefore represent a unique source of information for detecting contamination and tracking long-term changes in contaminated aquifers. To test the ability to detect groundwater contamination using biotechnology tools, the microbial community was sampled from groundwater wells surrounding a leaking landfill, and community profiles for bacteria and archaea were created using terminal restriction fragment length polymorphism (T-RFLP) fragments and primers targeting the 16S rRNA gene. Bacterial profiles were correlated to known gradients of leachate and effectively detected changes along plume fringes that were not detected using hydrochemical data. Microbial community profiles were correlated at considerable spatial distances, and could be used in a similar capacity as hydrochemistry data for mapping the extent of landfill-leachate contamination in the subsurface. This work demonstrates how molecular-genetic tools targeting in situ microbiological communities combined with multivariate statistical techniques may be used for identifying and further delineating the extent of groundwater contamination at leaking waste disposal sites.

Groundwater Quality of New England Crystalline Bedrock Aquifers
Sarah M. Flanagan¹, Joseph D. Ayotte¹, Gilpin R. Robinson, Jr.²
1 U.S. Geological Survey, New Hampshire/Vermont Water Science Ctr., Penbroke, NH
2 U.S. Geological Survey, Reston, VA

A regional-scale characterization of water quality in crystalline rock aquifers in New England and northern New Jersey was done using data from untreated groundwater samples collected from 117 domestic-supply bedrock wells sampled by the U.S. Geological Survey and from 4,775 public-supply bedrock wells sampled for the state Safe Drinking Water Programs. About 13.3 percent of 2,054 wells had concentrations of arsenic greater than the MCL of 10 micrograms per liter, but exceeded 22.8 percent in wells in calcareous metasedimentary bedrock in eastern New England.  Of 556 uranium samples, 14.2 percent had concentrations of uranium greater than the MCL of 30 micrograms per liter, however, the rate for the domestic wells was lower (4.3 percent). Of 4,781 nitrate-N samples, only 5 samples had nitrate-N concentrations greater than the MCL of 10 milligrams per liter. Deethylatrazine (18 percent) and atrazine (8 percent) were the most frequently detected pesticides in 114 domestic well samples. Methy tert Butyl Ether (36 percent) and chloroform (32.9 percent) were the most frequently detected VOCs in 86 domestic well samples. Elevated fluoride concentrations (> 2 milligrams per liter) generally occurred in older, high pH (>8) sodium-bicarbonate waters in granitic bedrock. Chloride to bromide ratios indicate that the groundwater was affected by at least three halogen sources: local precipitation and recharge, seawater and connate waters evolved from seawater, and recharge waters affected by road de-icing salts. Collectively, the frequent detection of man-made organic and inorganic compounds in domestic wells indicates that wells in these aquifers are vulnerable to anthropogenic contaminants.

Effect of Proximity, Slope, Soil and Overburden on Transport of Road Salt
Mark Holden, John Hopeck; Bureau of Land and Water Quality, Maine Department of Environmental Protection, Augusta, ME

This study assesses the effect of road salt on residential well water quality in eight areas in Maine. Using spatial raster analysis, a risk model was developed based on lab chloride dataand spatial coordinates from 360 Maine DOT pre-construction sampling locations. ArcMap spatial analysis tools were used to consider the effects of source proximity, slope, flow direction, soil character and surficial geology. It was found that, in general, with any degree of slope, and any soil or overburden, the risk is greatest in the down-slope direction, on the lower side of the road, with risk decreasing away from the road in either direction. This risk is higher by approximately a factor of two or higher on the down-slope side. This is most clearly the case in areas of low slope (less than 3 degrees) and any kind of soils or overburden. There are significant variations to this model if the slope is greater than three degrees. Overall, the dominant factor appears to be drainage-controlled residence time of salt-laden storm water over an area of infiltration.