Most streams in Easttown Township are part of the Darby Creek Watershed which flows south through Delaware County to the John Heinz National Wildlife Refuge and under I-95 into the Delaware River.  The Darby and Cobbs Creek Community Science Program (“DCCCS”) is a partnership between Willistown Conservation Trust (“WCT”) and Darby Creek Valley Association (“DCVA”) established in 2021.  Over 40 volunteers monitor the water quality by measuring water temperature, conductivity, sodium chloride, and nitrogen every four weeks at 38 sites throughout the Darby and Cobbs Creek Watershed.

During the height of the Fall 2024 drought, from which the area still has not recovered, as of early January 2025 many DCCCS volunteers across the Darby and Cobbs Creek Watershed noticed the chloride levels at their sites were skyrocketing, while other sites remained stable or even saw a reduction in chloride levels.  That raised a lot of questions – starting with “Why?”

Lauren McGrath, Director of the Watershed Protection Program at WCT, explains: “While some chloride is present in the geology of Chester and Delaware Counties, the majority of chloride is introduced into local watersheds through the application of road salts (usually sodium chloride, NaCl) to melt snow and ice in the winter.  As the snow and ice melt, the salt flushes into local waterways directly or through stormwater drainage systems.  In areas where salt is applied frequently and in abundance, the chloride can build up in the soils, leading to salty groundwater and high levels of chloride year-round – instead of just after winter storms.  Chloride, including the form road salt, is known to be harmful to sensitive fish and invertebrates, including the recently discovered Darby Creek mussels, in freshwater systems.  When salt buildup in soils meets drought conditions, it leads to salty streams.  Less rainfall (or in the case of October 2024 no rainfall) leads to little to no dilution of groundwater entering the stream, increasing the concentration of chloride in local waterways.  When these dry conditions are paired with unseasonably warm temperatures, it is a recipe for rapid evaporation of surface waters.  Evaporation leaves chloride behind, causing even higher concentrations of chloride.  During a severe drought, stream systems are almost entirely fed by groundwater, which means the potential for higher concentrations of chloride.”

In the Easttown Township Darby Creek headwaters, there are currently six testing sites, with more to be added soon, monitored by DCCCS volunteers (see map).  Of these six sites, one small tributary on South Leopard Road saw a marked increase in chloride levels, while chloride levels at other sites remained stable or even saw a decrease (see scatter graph).  Why?  Lauren continues: “Reasons for this are complicated - these sites with stable chloride levels may have less salt contamination in groundwater sources or there may be more surface flow.  Many of the sites most highly impacted by the drought are small tributary streams.   Interactions between surface water and groundwater are complex and remain poorly understood across the entirety of the watershed.”  

However, there is no question that what we do on land impacts the water quality of the Darby Creek headwaters and our groundwater year-round: there is too much sodium chloride (salt) in our waterways and groundwater.  In all six Darby Creek testing sites in Easttown Township, chloride levels are consistently above the stress threshold all year long, especially in areas of Darby Creek nearer to dense impervious surfaces where water cannot pass through (roads, parking lots, etc.).  Further, because chloride is corrosive, high chloride levels in the creek and groundwater can contribute to costly infrastructure and property damage.

Simple Acts of Kindness to Care for Darby Creek and Our Groundwater – the cumulative impact can make a big difference!

There are two fundamental ways to reduce chloride in Darby Creek and in our groundwater:  (1) minimize the use of road salt while ensuring safety; and (2) encourage infiltration and filtering of stormwater which removes salts and pollutants before stormwater gets into the groundwater or Darby Creek.

You can minimize the use of road salt while ensuring safety by:

• using less – it goes further than you think!  Shovel first and then apply road salt to targeted areas.  Only use what is needed: a 12 oz cup of salt clears 20 feet of driveway or 10 sidewalk squares.
• reusing your salt!  Sweep it up after the snow melts to reuse at the next snowfall.
• using calcium chloride or magnesium chloride instead of sodium chloride.  Both are safer for the environment but are more expensive than sodium chloride.
• avoiding using any products containing urea, kitty litter, or ashes.
• making sure your road salt is stored in a dry, covered area that prevents any inadvertent contact with land or water.

You can encourage filtration (cleaning) of stormwater by:

• letting your grass grow a couple of inches, which will increase the root system and facilitate some stormwater filtration.  Grass roots grow half the length of the grass blade: short grass and lawns can be impervious!  Or, where permissible, convert a portion of your lawn to a meadow.
• choosing native plants for your yard.  Native plants have more extensive root systems that maximize stormwater absorption and filtration, while offering habitat and food for native wildlife, birds, and pollinators.
• If your property borders a waterway (creek, tributary), planting and/or protecting a riparian buffer of native shrubs and trees to filter stormwater and protect the waterway banks.
• considering a rain garden for infiltration and filtration or a downspout planter to intercept stormwater from your gutters before it becomes runoff.

If you have substantive stormwater or flooding issues, consider a bioswale (consult with a professional engineer on design, soil and plant analysis, and impact to neighboring properties).  Easttown’s Stormwater Management Advisory Committee (SMAC) is also a resource: 

Source:  Darby and Cobbs Creek Community Science Program

On the left, the six DCCCS testing sites in Easttown Township identified by blue dots.  On the right, the scatter graph shows chloride levels generally above the stress threshold year-round at all sites in the Darby Creek headwaters in Easttown Township.

Source: Stroud Water Research Center and Lauren McGrath, Willistown Conservation Trust

Developed areas with impervious surfaces of 50-80% (red) or 80-100% (maroon) are most concentrated along Lancaster Avenue, suggesting higher chloride levels in Darby Creek in or near those areas, which then flows downstream throughout the watershed.

Source: Lauren McGrath, Willistown Conservation Trust

The extensive root systems of native plants are far superior to turf grass for infiltrating and filtering stormwater, removing salt and other pollutants before the water reaches the groundwater aquifer or Darby Creek.