WATER RESOURCE CONCERNS | 6.21.25
Water Resource Protection Area map for New Castle County, Delaware
Yorklyn and Hockessin rely on water pumped from underground aquifers — and therefore on the continued health and careful consideration of the Cockeysville Water Resource Protection Area (WRPA), which runs from Yorklyn to Lantana Square
Because the parcels contained by Auburn Valley Master Plan are not under control of the county, they are also not governed by the Unified Development Code — which has safeguards in place for Delaware’s aquifers.
In the zoom meeting held between DNREC and Yorklyn Community members on Monday, June 16th, Secretary Patterson said that he was unaware of a WRPA in Yorklyn. In his follow up email on Thursday, June 19th, he wrote: “I have shared your questions about the Cockeysville provisions with our Water Division and we will be back to you to discuss.”
Below is an abridged version of the memo we prepared for Secretary Patterson, Senator Sturgeon, and Representative Griffith regarding our concerns surrounding the WRPA.
This memo was prepared with assistance from Dr. Mary Ann Levan, a soil scientist and educator who lives in Hockessin’s Sharpless Road area. After completing her Ph.D. at Cornell University, Dr. Levan took additional coursework in groundwater at the University of Delaware and worked at the Delaware Geologic Survey. Dr. Levan worked with geologists at the Geologic Survey when John Talley was developing the water protection maps for vulnerable areas of the state of Delaware.
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The approved subdivisions—Quarry Walk, Mill’s Edge, and Mill 6—sit atop the Cockeysville Water Resource Protection Area, which is carefully regulated by the New Castle County UDC in accordance with Delaware law regarding Source Water Protection. However, because the Auburn Valley Master Plan is exempt from the UDC, it appears that those regulations have not been enforced. To protect the quantity and quality of water in the Cockeysville aquifer, we urge DNREC to enforce those regulations before construction proceeds.
Why any AVMP construction should be paused until water resource protection regulations are enforced and until an AVMP water budget is analyzed:
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The premise of the Auburn Valley Master Plan was that remediation, redevelopment, and conservation in Yorklyn required special coordination and oversight, given the area’s complexity and uniqueness. For the same reason, we have insisted that impact studies must also be coordinated, taking into account the Master Plan as a whole—not just individual parcels on an ad hoc basis. This principle should apply whether it is DNREC or New Castle County that oversees the AVMP.
In concrete terms, this means that both parcel-specific and whole-project impact studies should be conducted before any construction proceeds on the approved sub-divisions with signed redevelopment agreements: Quarry Walk, Mill’s Edge, and Mill 6 (the Cattermole and Carpenter properties).
The most urgent of these relate to Quarry Walk, where DNREC allowed construction to begin.
Our basic stance remains that Quarry Walk is an illegitimate development that would not have been allowed under New Castle County authority—or perhaps even under Secretary Patterson and Director Matt Ritter. The parcel was added to the AVMP without community input, and the justification was flimsy. The 10 acres of mature trees were cut down without community input or notice, and in contradiction to DNREC’s mission. Clearcutting a forested area to remediate century-old arsenic and build upscale townhomes only makes sense as an action taken for the developer’s benefit, not the community’s.
If DNREC is proceeding as if the Quarry Walk development is legitimate, and if DNREC is mirroring New Castle County in its role as the land use authority, then construction must be paused until the following questions are answered, requirements met, and studies conducted. This is especially true if DNREC’s goal, as stated to our group, is to promote a smooth transition back to the County.
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The valley that extends from Yorklyn through Hockessin to Limestone Road has long been the subject of interest and concern to water resource interests in Delaware. This small valley is comprised of weathered and pitted marble bedrock. This makes the rock an exceptionally good aquifer, providing an extraordinary amount of drinking water for such a small acreage. But the underground pitting makes it vulnerable to contamination and susceptible to sinkholes.
As the area has developed, concerns grew over developing farmland into residential and commercial properties. As early as 1989, the county commissioned local scientists to study this valley—the “Cockeysville marble” and the impact of development on the underground water supply. The authors conducted mapping and groundwater studies for two years and made recommendations for land use planning. [1]
The authors cautioned that excessive impervious cover would prevent water from soaking into the ground and recharging the aquifer and that chemical spills or leakage could contaminate the groundwater.
In line with this research and the state’s own groundwater protection law (DE code Title 7, Chapter 60, Subchapter VI), the county added regulations to its Unified Development Code concerning land within “water resource protection areas” (WRPAs) and to the Cockeysville WRPA specifically. These regulations are found in Article 10 of the UDC. Their purpose is:
“…to protect the quality and quantity of surface water and groundwater supplies through the protection of environmentally sensitive areas important to the state’s water supply. Under the UDC, all developments within recharge, wellhead, Cockeysville and reservoir water resource protection areas are required to meet maximum impervious cover thresholds and may require groundwater recharge facilities, water monitoring, and water management facilities.” [2]
Below, we have identified several applicable UDC requirements that should apply to Quarry Walk, Mill 6, and Mill’s Edge given their location in the Cockeysville Water Resource Protection Area. We are asking DNREC for evidence of enforcement in order to ensure that our community’s water supply is being protected. And we are asking DNREC and the legislature to commit to protecting this water resource in this year’s epilogue language.
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Part A: Given its location in the Cockeysville WRPA, has the Quarry Walk project followed all applicable UDC requirements “to protect the County's water resources from contamination and pollution and to insure adequate water quantity for future needs”?
Part B: Was Quarry Walk’s environmental impact assessment report “certified by a State-registered professional geologist or professional engineer with technical expertise in hydrogeology”?
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Did the Quarry Walk plan include WRPA lines and the parcel’s location within those lines?
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Did Quarry Walk LLC submit a subsurface investigation report on the stability of the rock formation and likely contamination risks?
Is surface drainage designed to prevent erosion of underlying rock (and thus to prevent sinkholes and contamination risks)?
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Part A: Does Quarry Walk’s plan include more than 20 percent impervious cover? If so, did Quarry Walk LLC demonstrate that the quality of stormwater run-off will be the same as before or better, and that quantity will be the same as, or less than, before development?
Part B: Does Quarry Walk’s plan include partial reforesting of open space? (“For open space that is not currently forested, 25% of the area must be reforested pursuant to 40.10.351.”)
Additional Background
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To ensure water resource protection as Hockessin faced new development, the County commissioned the “Annual Water Budget for the Cockeysville Formation for the Hockessin Village Plan,” published in 2004 by the University of Delaware’s Water Resources Agency (UDWRA).
The annual water budget for the Cockeysville Formation was designed for the 2004 Hockessin Village Plan—but not the 2011 Auburn Valley Master Plan nor the subsequent expanded versions of the AVMP.
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Did DNREC consult the 2004 Annual Water Budget for the Cockeysville Formation when developing the Auburn Valley Master Plan?
Did DNREC prepare any revised water budget analysis for the Cockeysville Formation when developing and updating the AVMP? If so, was that water budget followed when Quarry Walk was approved?
Is DNREC monitoring the Cockesyville aquifer and its ability to recharge given all the development in the Cockeysville WRPA since 2004? If monitoring has been left to Artesian, has DNREC verified Artesian’s reports and water supply models?
Can the Cockeysville WRPA support all of the recent and planned development within its bounds, from Yorklyn to Lantana Square in Hockessin? What evidence is there?
For residents on well water, what assurances do we have that we will have sufficient water quantity and quality in the future?
What about residents who depend on well water along Sharpless Road, which is just outside the Cockeysville WRPA?
Until legislators and the community have answers to these questions—and until all applicable UDC Water Resource Protection requirements are followed—construction should not proceed on any AVMP parcels. This is the rationale behind our proposed Section 80 language regarding a construction pause.
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Delaware’s drinking water comes from underground storage—referred to simply as “the groundwater,” and more technically as “an aquifer.” Through the water cycle, precipitation feeds water into the ground, it is naturally filtered and stored, and can be removed by residential or public well systems.
The Yorklyn-Hockessin Valley sits atop a special source of water: the Cockeysville aquifer, which runs from the village of Yorklyn to Limestone Road (State Route 7). See image below.
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The clearest explanation comes from geologists Margaret Plank and William Schenck and their booklet “Delaware Piedmont Geology including a guide to the rocks of the Red Clay Valley” (published in 1998 by the Delaware Geological Survey, University of Delaware).
North of the [Wilmington & Western Railroad] track is a long, flat valley that begins at Yorklyn, extends through Hockessin, and ends abruptly along Limestone Road.This valley is underlain by the bright, blue-white marble of the Cockeysville Marble. Because the marble is easily eroded and dissolved by acidic water, it is rarely seen at the surface. Indeed, the lack of outcrop and float (loose rock) in low flat valleys is usually taken as evidence for underlying marble. Marble is dissolved by groundwater to form what hydrologists call solution channels, but what the rest of us call caves. These solution channels act as reservoirs for ground water, and, indeed, in the Hockessin area commercial wells drilled into the Cockeysville pump 1.5 to 2 million gallons of water per day. The marble aquifer is an important source of water for the residents of northern New Castle County.
Recharge of ground water to the marble is primarily from rainwater and by leakage from the steams that flow over the marble. Developers, attracted to the broad flat valleys underlain by the marble, have recently built a series of office complexes, shopping centers and high-density communities in the Yorklyn-Hockessin valley. These buildings with their asphalt driveways and parking lots restrict recharge and change the pattern of ground water flow. Alarmed by the loss of ground water, New Castle County has recently declared the marble a resource protection area and applied land use restrictions. In some places the loss of ground water in the solution channels has caused the ground overlying the channels to collapse and form sinkholes.
In summary, the Cockeysville Marble is a special aquifer—a ready source of fresh water but one that is vulnerable to contamination and collapse. It therefore needs special care in relation to land use and development.