Hydrogeology with TOR Resident, Dan Davis

CONVERSATION CORNER

With ECC member, Amy Fradon
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Topic: Hydrogeology with Town Of Rochester resident, Dan Davis

 

Underneath the grass and soil that we walk on, play on, garden in and build upon is a whole world and network of rock layers and waterways. They are not only there to hold us up as we walk through life, but they play a vital role in providing, cleaning and managing our water supplies. How we interact with this complex network will affect us and future generations for ever.
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We are lucky to have local resident, Dan Davis, to help us figure out how to preserve the integrity of our geology through his work in hydrogeology. He is a great resource for the Town Of Rochester.

 

Where do you live and what is it you do?
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Dan: I live in Accord and work as a geologist for New York City Department of Environmental Protection. ~My wife (Terri Ritter) and I and our four kids moved here from Fairbanks, Alaska in 1987. ~We have lived on the Shawangunk Ridge ever since. ~For most of the 1990’s I worked as a consulting hydro geologist working on projects all over the US. ~I’ve been working for NYCDEP since 1997and am a member of the Stream Management Program. ~We work with communities and other stakeholders on developing plans to live wisely along a stream corridor. ~We do stream geology research too. ~Right now I am working with Cornell Cooperative Extension and other partners to study and develop a plan for the upper Esopus Creek in the Town of Shandaken.

 

What is hydrogeology?

 

Dan: Hydrogeology is the study of groundwater and its interaction with the earth. ~Groundwater is the water that flows through the sub-surface in rocks, sand and gravel, or even as underground streams in cave systems. ~The groundwater that most of us in Rochester get our water supply from flows through the pores and fractures in the underlying bedrock. .As a hydro geologist I am interested in collecting information that will help me understand how the local or regional groundwater flows through aquifers and is impacted by minerals and natural or contaminating chemicals

 

What exactly is the study of geology?
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Dan: Geology is the study of the earth – its processes and products. ~Geologists are interested in everything from the forces that form our planet’s interior (rock formation) and exterior (erosion and landscape formation) to the forms those forces create. ~We look at rocks and infer their history.
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Why is it important for us to know about geology?
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Dan: Geology has grown into such an important science in the modern world for several reasons. ~First, by understanding and exploring geologic resources like minerals and fuels (coal, oil, and gas) it has made so much of our advancements possible. ~Then because the exploration and use of the material removed from the earth can cause environmental contamination we need to understand how contaminants move through the water and soils. ~Understanding earthquakes and volcanoes helps us to plan for living in their active presence – so geology also helps us with predicting and surviving hazards.
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Two examples of local importance relate to groundwater. ~Back in the late 1980’s and early 1990’s I participated in a study to characterize the groundwater flow system through the Shawangunk bedrock. ~We were able the identify areas where water supply is ~not expected to be a problem, areas where there is very limited water supply and very importantly where and how the groundwater system gets recharged with new water. ~Soon after completion of this study, in High Falls the groundwater that many residents tap with wells for their drinking water was found to be contaminated by chlorinated solvents. ~These heavy solvents, called “sinkers”, entered the fractured bedrock aquifer at an important recharge zone and made their way to over 50 wells.
(A sinker is a nick-name for dense non-aqueous phase liquid (DNAPL), so it’s a lot easier to say “sinker”. ~Essentially solvents (typically chlorinated hydrocarbon compounds) that are heavier than water “sink” to a low point. ~When we pump water to remove the contaminant the water is easily extracted but the heavier, denser chemical tends to remain behind. ~That is a pretty gross simplification of a very complex situation. A recharge zone is the area where the water (as rain or melting snow) enters into the subsurface, becoming groundwater. Typically recharge areas are areas where the amount of water entering the ground exceeds the amount necessary to supply plant life or streams. ~Obviously these are important areas to protect.)

 

The first mystery to solve was: why did two wells adjacent to each other have very different levels of contamination? If this aquifer was uniform like a sand and gravel aquifer you would expect the contamination plume to be predictable and uniform. ~However, in a fractured bedrock aquifer the contaminants form a very irregular plume that can be nearly impossible to accurately characterize. ~The other problem with “sinkers” in fractured bedrock is that they are practicably impossible to remove by pumping and treating the water. ~There will be some of these chlorinated solvents in the aquifer for generations. That’s why High Falls will have a municipal water supply tapping into the Catskill Aqueduct.
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Can you tell us about some of our local geological history?
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Dan: The problem for me is I could go on and on there is so much to tell. ~This is also where I can’t help but get geeky and use geologic terms. ~Maybe we could save the bulk of that answer to this question for another time. The thing about geologic history of an area is to know when to start. ~The geology of an area goes back to the formation of the planet – it’s just changed so much over the last 4.5 billion years or so that the geologic record is continuously recycled. ~That is a very cool thing about geology by the way: knowing that the earth is always recycling its crust through the rock cycle driven by plate tectonics. So in our chunk of the planet we have parts of the last 450 million years (or so) to piece together the history. ~This is a very simplified account of our local geology.
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The oldest (or earliest) bedrock in the area are the shales, siltstones and sandstones of the Martinsburg formation. ~This ~10,000 ft thick sequence of rocks was deposited in a deep inland ocean basin around 450-435 million years ago in the geologic time period called the Ordovician. ~The dark, very fractured Martinsburg rocks outcrop in parts of the Shawangunk Ridge.
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The next rocks to be deposited are the Shawangunk sandstones and conglomerates which were deposited in broad braided rivers and beaches between a mountain range to the east (the ancestral Taconics) and an inland ocean to the west. ~This was during the Silurian time period around 430 million years ago. ~These white rocks are almost pure quartz and very resistant to erosion forming the “capstone” of the Shawangunk Ridge.
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As the ancient Taconic Mountains wore down to nubs, the inland ocean moved east laying down the next sequence of rocks which are Devonian in age (418 – 360 million years ago): these include the fossil rich limestones of the Rondout formation (mined for Portland cement) through to the Onandaga limestone to the very black Esopus shales that were deposited in a deep ocean basin that did not host any life. ~
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Another mountain building event happened to the south and east and the inland ocean moved west. ~The Devonian Catskill formations (sandstones, shales and conglomerates) were deposited by an ancient river system that flowed from mountains to the inland sea. ~~~~~
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We are missing big chunks of time since then. ~What was going on for the last 360 million years? ~We know the material previously deposited was buried, cooked and pressed into rock and then uplifted back to the surface where we see it today. ~But we can’t say based on rocks we see what kind of environment was here after the Catskill rocks were deposited. ~Whatever was going on locally its geologic record was eroded away.
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The next geologic evidence we have to interpret is the material on top of the rocks. ~Most of what we see was left during and just after the ice ages. ~This was a dramatically different landscape and climate 10,000 – 25,000 years or so ago. ~At its thickest, a mile of continental-scale ice was flowing over the landscape covering all of the Catskills and the Shawangunk Ridge. This was the period of the most recent ice ages (the Pleistocene). ~There is plenty of evidence for this passage of ice. ~Thick deposits of glacial till (an unsorted mix of sediment of all sizes from clay to boulders) are found throughout the area. ~The thick deposits of sand and gravel in the Rondout valley between the Catskills and the Ridge were formed from rivers that drained the melting ice. ~Several places have thick layers of clay deposited at the base of Glacial Lake Wawarsing that once filled the valley as the ice retreated out of the valley and up the Hudson ~River valley. ~The polished and striated surface of the Shawangunk rock is famous for its remarkable recording of the passage of ice.
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What are the prominent rock types that we have in the Catskills? Are there any geological occurrences that are specific to our immediate area?
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Dan: All bedrock in our Town is sedimentary rock – that is, the rock is made up of some kind of sediment left by ancient water or air. ~There are no igneous (formed from magma like granite or basalt) or metamorphic (formed from high temperatures and/or pressures like mica schist or marble) rocks native to this area. ~If you see any they are likely to have been brought along by the continental glacier or by people (I’ve been known to let some of my exotic rocks go free). ~I find beautiful stones of Adirondack garnet gneiss in many places around here. ~As the glacial till erodes its foreign rocks are set free to add spice to the often bland sandstones and limestones we see. Though that is not quite fair to the sandstones and limestones. ~Some of the limestones are loaded with fossils and some of the sandstones and conglomerates have interesting sedimentary features.
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There are many interesting geological occurrences around here that merit more attention than I can give here. ~Two examples – one for the Shawangunks and one for the Catskills:
The ice caves and crevice networks of the Shawangunks are fascinating to experience. ~The interconnected fracture system along cliff and ravine boundaries hold cold air, and snow that has fallen or drifted into place can remain well into the summer months. ~The Shingle Gully and “Grand Canyon” ice cave system above Ellenville is remarkable. ~In the Catskills the unique circular drainage of Esopus Creek and Woodland Valley creek around the base of Panther Mountain stands out even in satellite photographs. ~All other streams in the Catskills have a dendritic (tree-like) pattern of tributaries. ~It has been hypothesized that the circular drainage around Panther Mountain is related to the imprint of an ancient impact crater from a small asteroid-like body back when the Catskill rock was still sediment. ~This hasn’t been proven but is an interesting idea.

 

What functions do the rocks play in the ecosystem as a whole?
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Dan: Great question. ~Rocks serve many functions in an ecosystem: they form the substrate (In geology substrate typically refers to soil or rock. ~It has different meanings in different sciences.) and provide nutrients for life. Different rocks make different kinds of soil which support unique plant communities and the animals that live among them. ~~Limestone yields a soil that has a relatively high pH (base) and certain plants prefer that soil; the quartz-rich Shawangunk conglomerate yields a high pH soil (acidic) that supports the unique dwarf pitch pine ecosystem of the ridge. Similarly the bedrock controls the pH of the lake water. ~The Shawangunk sky lakes are all to acidic to support much aquatic life (no fish) with the exception of Mohonk Lake which is the only lake on the ridge to have shale and not the Shawangunk conglomerate line the lake bottom. The result is a neutral water body that supports a healthy aquatic ecosystem (lots of fish).
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Are there any environmental impacts from quarrying or mining a particular spot?
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Dan: There can be environmental impacts from quarrying sand and gravel or rock like bluestone, however, the impact is limited to the size and manner of the operation. ~Quarrying is necessary if we want to get sand and gravel for road building. ~During the first 200 years of the settlement of this area quarrying bedrock for building stone and millstone was an important part of the economy. ~The environmental impact of that quarrying is not very evident now. ~We see the quarries and they can have a strong local visual impact but seem to not have a significant impact. ~Very large sand and gravel quarries certainly can impact the area quarried and may modify the water table if the quarry has to be dewatered.
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Mining for minerals or coal can have a significant impact on not only the mined area but also large areas impacted by contaminated water leaving the site. ~I believe there has been no mineral mining in Rochester though there was some along the Shawangunk ridge further to the south (Ellenville to Wurtsburo.)

 

Tell us about the effects of mining in a watershed area.

 

Dan: Well, that depends on the kind of mining. ~If you are mining for copper or gold or any other precious mineral or element that is embedded in rock (called ore) the process typically involves leaching the mineral element out of the rock and often the groundwater or surface water (streams, ponds, and lakes) is contaminated. ~~There are many examples of this out west (and I have worked on a few projects trying to clean the water up after the mining). ~If you are talking about sand and gravel quarries, it is unlikely (in my opinion) that there is a large impact on the watershed. ~I am fairly ignorant of the process so I may be quite wrong, but the biggest impact may be a local lowering of the water table.

 

You mention contaminants in groundwater. Are there any in our Rochester groundwater and where can we find out about it and how to prevent more from occurring?
Dan: There probably are. ~Wherever there are old underground gas tanks you tend to have leaks and components of gasoline getting into the groundwater. ~~I have to say I haven’t looked into it in the last few years. ~You can check with NYSDEC to see if there are any reported cases. ~The best way to prevent contamination is to have good regulations: federal, state, county and local.

 

What’s the difference (if any) between a rock and a semi-precious or precious stone or crystal? ~
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Dan: Rocks are composed of minerals. ~They can be made up of one mineral, like quartz for instance in some of the Shawangunk conglomerate, or several minerals as often found in some igneous and metamorphic rocks. ~Crystals are the free growth form of minerals. ~By free growth I mean that the mineral formed without having its boundaries constrained by other minerals. ~All minerals have their unique crystal forms. ~The most common crystals we find around here are quartz crystals in the Shawangunk formation. ~Crystals of pyrite and calcite are also common in some of the rocks around here. I really don’t know much about gemology and the difference between semi-precious or precious stones.
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What drew you to the study of geology? ~Were you particularly drawn to this area because of its geological content? Have you worked elsewhere and if so, what are the geological differences? ~
Dan: I have always been curious about nature and science was my favorite subject in high school. ~I first studied anthropology and archaeology at the University of Alaska at Fairbanks. I came pretty close to completing my studies in anthropology before I switched to geology. ~I continued studying geology and hydrogeology at SUNY New Paltz. ~But to answer your question: what drew me to study geology were glaciers. ~Living in Alaska and doing lots of ski mountaineering I spent a lot of time in the glaciated Alaska Range and fell for their beauty and power. ~After moving here I had lots of fun studying the record of the glaciers that once occupied our Town. It wasn’t the geology that brought me here but it sure has been nice to be in a place that has such interesting geology. ~~
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I have worked as a hydrogeologist in lots of places in the US, mostly in the west developing groundwater flow models and studying contaminant transport in groundwater. ~The coolest place I worked in was Greenland where I spent two months (practically the whole summer there) working with my close friend Jonathan Caine on his Ph.D. research. ~That was a rare opportunity to live briefly in a raw part of the planet with glaciers all around, soaring 10,000 foot high mountains along an iceberg-filled fjord, musk ox roaming the narrow shore between fjord and kilometer high cliffs. ~Very fascinating and humbling. ~It was the scariest place I ever camped. ~Soon after we were dropped off by helicopter with our two month supply of food, tents and other gear we were bombarded by rock fall off the cliffs. I slept with my hardhat on (!) for the first two nights until I got used to hearing the rocks cascading down the cliff face. ~

 

Is there anything about this subject that you feel passionately about and would like to share?

 

Dan: Maybe just that for me geology is never boring. Much has been discovered and explained that we can use to interpret what we find in the geology around us. It is that interpretation – solving the mystery that geology presents – that continues to engage me 20 years after I started studying geology. ~I can’t imagine an end to that fascination.