Vulnerabilities & Threats to Our Aquifer

An aquifer is an underground formation of rock, sand, or gravel that stores water and allows it to move through the spaces between particles or along fractures in the rock. In our area, the aquifer lies beneath layers of soil and sediment shaped over millions of years by geologic processes. When rain or melting snow seeps into the ground, it filters downward through the soil and into the aquifer, where it fills the open spaces between rock and sediment. This stored groundwater is what our wells draw from to supply every home and business in Mount Gretna Borough.

The aquifer system serving Mount Gretna is a fractured bedrock aquifer with both unconfined and confined zones. Shallow wells may draw from unconfined layers that have no protective clay or dense rock sealing them off from the surface, while deeper wells may draw from confined layers that offer more protection. In other words, the same geologic features that allow our aquifer to provide clean water also make it vulnerable to contamination if the land above it is not carefully managed.

Our aquifer is part of the larger Conewago Creek watershed and is fed primarily by local recharge—meaning most of the water entering it comes from precipitation that falls within or near our community. Because the aquifer is recharged so close to home, what happens on the land here can directly affect the quality of the water we pump from our wells.

The Mount Gretna Region Source Water Protection Plan defines three wellhead protection zones to help visualize this connection:

• • Zone I – The immediate area around a well (100–400 feet in radius), where land use can directly and quickly influence water quality.

  • Zone II – The “capture zone” where groundwater flows toward a well over about 10 years. Activities here have a higher chance of eventually affecting what comes out of the tap.

  • Zone III – The broader contributing area that recharges the aquifer feeding Zones I and II. This includes the entire Pennsylvania Chautauqua/Mount Gretna Borough.

View Groundwater Protection map →

In our case, essentially the entire Borough lies within Zone III (see map), and some areas overlap Zones I and II for the three wells that serve us. That means forest health, stormwater management, road maintenance, and even individual property care all influence the water beneath us.

How much of town is in the recharge area?

Approximately 90% of Mount Gretna Borough lies within Zone III, the broad contributing area that recharges the aquifer feeding our wells. Short sections of Yale and Lancaster toward State Avenue, and all of State Avenue, fall outside Zone III. Some parts of town also lie within Zones I and II, where the connection to the wells is even more direct.

Being inside a recharge area means that rainfall or melting snow on your property may eventually make its way into the aquifer—and possibly into our wells—sometimes traveling underground for years or even decades. In fractured bedrock aquifers like ours, groundwater doesn’t always move in a straight line. In certain cases, it may flow in a different direction and discharge into a stream, spring, or even another water system entirely. This means that what happens on your land could affect not just Mount Gretna’s drinking water, but potentially the water supply for other communities as well.

Understanding whether your property lies within Zones I, II, or III helps reveal how land use—whether forested, paved, or landscaped—affects the amount and quality of water reaching the aquifer. Actions that protect recharge areas today can safeguard clean drinking water for years, even generations, to come.

Why forest location matters (not just size)

Forests protect water quality by slowing runoff, filtering pollutants, and allowing water to soak into the ground. In source-water systems, the location of forest cover often matters more than its size.

For example, the Southern Chautauqua Woodland sits directly beside Pennsylvania State Game Lands #145. Around 2009, a large swath of the Game Lands next to this woodland was clear-cut—reportedly due to gypsy moth damage. Since then, some residents along Temple Avenue near the boundary have noted stormwater drainage problems, even as the cleared area slowly regrows. This illustrates how large-scale canopy loss can alter runoff patterns for many years. The lesson is not just about past damage, but about how intentional management today can avoid similar problems in the future.

Within our borough, forested parcels near wells or in recharge-critical areas play an outsized role in protecting groundwater. If forest health declines and trees are removed without planning, runoff can increase, carrying more sediment and pollutants into the aquifer. Science-based forest stewardship—including retaining certain downed trees in strategic locations—can slow stormwater, maintain filtration, and allow healthy regrowth while minimizing invasive plant takeover.

Current gap

The Pennsylvania Chautauqua–owned lands do not yet have a formal forest stewardship plan. Without one, decisions about tree work, invasive control, trail placement, and stormwater handling happen piecemeal. True stewardship goes beyond simply cutting down dead or hazardous trees — it requires coordinated, science-based practices that sustain forest health, biodiversity, and water protection over the long term. Without this level of guidance, even well-intentioned actions can unintentionally reduce the land’s ability to slow, filter, and absorb water—especially in recharge areas. Over time, unmanaged sites are likely to see invasive plant takeover, which can reduce biodiversity and weaken the natural systems that protect water quality. (See the Forest Stewardship page for more detail.)

Common local threats

These are common threats to groundwater generally. Listing them here does not mean they are all present in Mount Gretna, though tree removal has been observed locally.

• Road salt and de-icing chemicals that infiltrate groundwater.

• Stormwater runoff from roofs, roads, and driveways carrying sediment, oils, and nutrients.

• Septic system issues introducing microbes and nutrients.

• Spills or leaks from fuel tanks, vehicles, or equipment.

• Tree removal or soil disturbance—especially in Zones I, II, and III—that reduces natural filtration and increases runoff.

The Source Water Protection Plan maps potential sources of contamination and uses this to help prioritize management and education efforts. This mapping helps identify where small improvements in land management—like better stormwater control, reduced chemical use, or added vegetation buffers—can have the biggest impact on protecting water quality.

Prevention beats cleanup

Once contaminants enter groundwater, they can persist for decades in a fractured rock aquifer because water moves slowly and cleanup is complex and expensive. Some pollutants—like certain solvents, fuels, or road salts—are highly mobile in groundwater and can travel long distances before diluting or breaking down. Others, like nutrients from septic systems, may contribute to algae blooms in connected streams and lakes, harming aquatic life.

Preventing contamination is far more effective than trying to fix it after the fact. Proactive, science-based land stewardship—such as maintaining forest buffers, managing invasive plants, minimizing soil disturbance, and controlling runoff—protects our aquifer and ensures safe drinking water for generations to come.

How the plan helps

The DEP-approved Source Water Protection Plan identifies local vulnerabilities and outlines strategies for reducing risks. Many are non-regulatory and voluntary, such as:

• • Educating property owners about best practices.

  • Coordinating with emergency responders for spill prevention and cleanup.

  • Protecting sensitive recharge areas through land management agreements or easements.

  • Installing or maintaining signage to raise public awareness.

These strategies only work if residents and local leaders take them up and make them part of daily care.