Pennsylvania Water Science Center



Andrew Reif


Bacteria Monitoring Stations in Chester County, Pennsylvania

Stations in the Bacteria Monitoring Network (view site map)

The Chester County Water Resources Authority, Chester County Health Department and the U.S. Geological Survey are cooperating on a monitoring project to measure fecal coliform bacteria at three sites in the Brandywine Creek Watershed, one site in the French Creek Watershed, and one site in the White Clay Creek Watershed. Currently, these five sites typically are sampled approximately once every month during the spring, summer and early fall months when the streams are most frequently used for recreation.

Due to the 24-hour incubation period required for analysis of bacteria in water samples, results from the sampling were typically published on this website within 2 to 3 days of the actual sampling date. The Pennsylvania Department of Environmental Protection 's standard for fecal coliform bacteria in recreational waters is 200 colonies per 100 milliliters (mL)*.

* - During the swimming season, (May 1 through September 30), the maximum fecal coliform level shall be a geometric mean of 200 colonies per 100 milliliters (ml) based on a minimum of five consecutive samples, each sample collected on different days during a 30-day period. No more than 10% of the total samples taken during a 30-day period may exceed 400 per 100 ml. For the remainder of the year, the maximum fecal coliform level shall be a geometric mean of 2,000 per 100 milliliters (ml) based on a minimum of five consecutive samples collected on different days during a 30-day period. (Commonwealth of Pennsylvania, Pennsylvania Code, Title 25, Chapter 93, Water Quality Standards, December 15, 2001)

New Study (2017):

Estimating fecal coliform bacteria concentrations using near real-time continuous turbidity data at five stream sites in Chester County, Pennsylvania (USGS Report SIR 2017-5075)

Real-time estimates of bacteria concentrations

The availability of near real-time continuous stream discharge, turbidity, and other water-quality data at five gaging stations on streams in Chester County, Pennsylvania presents an opportunity to use surrogates to estimate near real-time concentrations of fecal coliform (FC) bacteria, a type of bacteria used to indicate the potential presence of fecally related pathogens that may pose health risks to humans exposed through water contact. The U.S. Geological Survey, in cooperation with the Chester County Health Department and the Chester County Water Resources Authority, developed regression equations to estimate fecal coliform (FC) bacteria concentrations by using 1) FC concentrations in discrete samples collected during March– October annually at or near five gaging stations with near real-time continuous data for the period 2007-15 (2012-15 at two of the five stations), and 2) explanatory variables of near real-time continuous data for stream turbidity and seasonal factors calculated using Julian Day. The five gaging station sites are on streams used for recreational activities (fishing, swimming, and boating) and known to have periodic elevated concentrations of FC bacteria. The regression models were validated on the basis of FC and turbidity data collected in 2016.

During summer months, the estimated and measured FC concentrations commonly were greater than the Pennsylvania Department of Protection established standards of 200 and 400 colonies per 100 milliliters for water contact from May through September at the five stream sites, with FC concentrations typically more elevated at two sites (White Clay Creek and West Branch Brandywine Creek at Modena) than at the other three sites (East Branch Brandywine Creek below Downingtown; Brandywine Creek at Chadds Ford, French Creek near Phoenixville). The estimated concentrations of FC bacteria during the summer months commonly were higher than measured concentrations and therefore could be considered cautious estimates of potential human-health risk. The near-real time estimates of FC concentrations provide timely information about associated potential health risks during recreational use of streams and will be available to the public through web sites.

Continuous Water-Quality Monitoring Stations in Chester County, Pennsylvania

Streamflow is sampled hourly for basic water-quality parameters such as pH, specific conductance, temperature, dissolved oxygen, and turbidity by automated water-quality monitors. Monitoring streamflow is an important part of protecting and maintaining surface-water supplies and aquatic habitats. Water resource authorities and county health departments use these data to monitor for threats to surface-water supplies and fish. If dissolved oxygen drops below 5 milligrams per liter, which may occur in the warmer months, fish kills could result. Data from the stream-water-quality monitors also are used to:

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