Lewes professor talks groundwater
Dr. William Ullman treated coastal Sussex residents to a primer on hydrology at the University of Delaware’s College of Marine Studies (CMS) on Aug. 18, with a topic perhaps especially relevant to officials moving toward final draft on sweeping new statewide water pollution regulations.
The Department of Natural Resources and Environmental Control (DNREC) is pushing for a serious reduction in the excessive amount of nutrients (specifically, nitrogen and phosphorus) washing from the uplands into the region’s Inland Bays watershed.
DNREC has created a set of regulations called the Pollution Control Strategy (PCS), indirectly as a result of pressure from the Sierra Club, which had challenged the Environmental Protection Agency on widespread “non-attainment” of nutrient reduction goals at the state level.
Either the federal governments, or the states if they proved willing to act first, were court-ordered to expedite, and DNREC Secretary John Hughes is hoping to enact Delaware’s PCS by sometime in December.
However, as Ullman explained, the PCS was based entirely on surface water runoff – and for many areas, even on Sussex County’s flat, porous Coastal Plain, that was fine.
But there were areas where groundwater became a significant factor, as well. How much of a factor — or, at any rate, how much groundwater wasn’t being accounted for — Ullman and his colleagues (and grad students, and research assistants) set out to find.
Looking at total water in versus total water out, he explained how hydrologists could solve for the groundwater variable. Precipitation stands on one side of the equation — rain gauges and meteorological data give scientists an accurate measure there. On the other side of the equal sign, there’s evaporation (from the ocean, standing water, etc.), transpiration (absorbed by trees) and surface runoff (this includes groundwater that makes it to a stream before entering an actual Inland Bays estuary).
These are all pretty well measurable — “evapotranspiration” had been the focus of much study, Ullman pointed out, and scientists had a handle on that, and like precipitation, runoff could be measured with relative accuracy at clearly identified points (for instance, the gauge at the Millsboro Pond spillway — the single largest input into the Inland Bays, Ullman noted).
Plugging in the known numbers, the scientists solved for the final, unknown variable — groundwater (in this case, recharge). And recharge had to be pretty close to groundwater discharge, Ullman continued.
“Anything that enters must leave, or basically, we’d fill up,” he said. “We’d have no more land surfaces.”
He went back to five main areas where surface runoff entered the Inland Bays, to determine how much groundwater they were missing. Locally, he noted Blackwater Creek and Beaverdam Ditch — but soils were more impermeable there, so surface runoff did indeed account for nearly all the total flow into the watershed.
And while he was unaware of any major underground streams feeding the Little Assawoman Bay, he suggested the same would hold true there — impermeable soils would confine groundwater below that water body, although it might escape into the ocean further offshore.
However, at the other areas (Swan Creek, Bundicks Branch and Munchy Branch, on the Delaware Bay), Ullman said the equation didn’t come close to balancing. “We were missing 40 to 50 percent of the water — and that water may be much more nutrient-rich than surface runoff,” he pointed out.
Impermeable soils here and there notwithstanding, Ullman equated the main Coastal Plain area to a big sand pile. And while everyone was measuring the success of nutrient (pollution) control programs in surface runoff, rainfall didn’t typically run very far before soaking in, when the highest point in the county was at the 124-foot mound of trash at the garbage dump near Georgetown, he noted.
(On a more cheerful note, the highest natural point in Sussex stands at a close-second 110 feet, Ullman pointed out — the Great Dune at Cape Henlopen State Park.)
“So, groundwater recharge and discharge are likely to be very significant,” he said. “A lot of places, where there are rocks or muddy soils, you can ignore groundwater. You can’t do that here.”
So, Ullman and company set out to find where the groundwater was entering the rivers and bays — at “beachfaces.”
He said they’d have to readdress areas where underground streams trickle into the marshlands, but at the beach and along the riverbanks, he said they’d had some luck pinpointing interchanges.
Groundwater remains at a more or less constant temperature all year round, so they set up an experiment using infrared photograph.
Along the Indian River, he noted additional aerial infrared photos pinpointing underground streams at Love Creek, Oak Orchard and across the river from the (Delmarva Power) plant.
In retrospect, Ullman said they probably could have acquired the same data by asking local watermen where they harbored their boats for the winter. With groundwater welling up all year long, there were plenty of people who could have told him those spots never froze over.
He also described a trip to the beach, in the middle of the night to avoid confusing reflections from shiny water surfaces, and with grad students marking the low tide line with little charcoal braziers to orient for the pilot.
Those photographs clearly showed areas where fresh water was pouring off the beach — and, as later experimentation revealed, at a prodigious rate (one quart per minute, per yard).
However, there was evidence that even the porous sands were retaining some water, Ullman pointed out. “The sands are not just a through-put — there’s reactivity,” he said.
He compared the beaches to the sand filter system used at many wastewater treatment plants — and offered parallel concerns for what might happen if those filters went too long without being changed.
The flows were relatively constant, although in dry years, the ratio of groundwater to runoff increased (and vice versa in wet years).
For that reason, he suggested it would be especially important to measure groundwater in dry years, to determine how successfully nutrient management programs were really performing.
How his work would tie into the PCS, Ullman wasn’t sure. However, he noted “volatized” nutrients (passed into the air as vapor) from contained animal feeding operations (CAFOs) that weren’t being measured yet, either.
He expected the state would continue to refine the PCS over time, and would eventually give these secondary pollution sources more attention.
There’s one more Ocean Currents lecture scheduled for this summer – Center for the Inland Bays (CIB) Director Ed Lewandowski will present “Delaware’s Inland Bays: An Estuary of National Significance” on Sept. 15 at 7 p.m., at the CMS in Lewes.
For more information, call (302) 645-4279.