Conodoguinet Creek Watershed Study-Program Information

  Program Description

The Conodoguinet Creek Watershed Study was a 24-month (September 1991 ­ August 1993) field study designed to monitor nutrients, major ions, and triazine herbicide concentrations in precipitation falling on agricultural, forested, and urban areas within or adjacent to the watershed. The Conodoguinet Creek watershed is located in south-central Pennsylvania, stretching from Harrisburg in the east to Shippensburg in the west. The major objective of the study was to better understand the relationship of measured contaminants to prevailing land use and their potential pathways to the Chesapeake Bay. Eleven monitoring stations (at 8 different monitoring sites) were employed. One of these sites was co-located with an existing Pennsylvania Atmospheric Deposition Monitoring Program (PADMP) site in order to assess comparability of analytical results. This study was a cooperative effort between the Alliance for the Chesapeake Bay, the Pennsylvania Department of Environmental Protection (DEP), and the U.S. Geological Survey (USGS). A unique aspect of this study was the utilization of trained citizen volunteers to collect precipitation samples immediately after cessation of rainfall events.

Precipitation/Air Sampling and Analysis

Precipitation samples were collected during spring, summer, and fall at the following sites:

Winter samples were not collected because rainfall froze in the collection apparatus and because samplers were not designed to sample snowfall.

A precipitation collector consisted of a PVC cylinder housing a sample bottle. A glass funnel whose stem extended through the sealed top of the PVC cylinder into the mouth of the sample bottle was used to actually collect the precipitation.

Citizen volunteers were recruited and trained to collect samples of significant rainfall events (>0.1 inches). Glass collection funnels were exposed to the atmosphere no longer than 8 hours prior to and 12 hours after a rainfall event. A "project coordinator" provided the citizen volunteers with an Atmospheric Deposition Citizen Monitoring Instruction Manual, as well as training. The project coordinator also maintained equipment and supplies, supervised quality assurance, performed field measurements, and monitored weather forecasts to coordinate sampling of "significant" rainfall events at multiple locations.

The chemical parameters measured in precipitation samples were dissolved calcium, magnesium, potassium, fluoride, silica, iron, manganese, bromide, sodium, sulfate, chloride, orthophosphate, ammonia, ammonium, nitrate (dissolved and total), and nitrate+nitrite; triazines; pH, total alkalinity, specific conductance, and total hardness. Chemical "field analyses" for pH, alkalinity, and specific conductance were performed at the nearby USGS laboratory in Lemoyne. Samples were analyzed for triazines using immunoassays. In addition, samples were analyzed for specific herbicides and metabolites using solid-phase extractions. A small volume of each sample was shipped to the USGS laboratory in Denver for further analysis.

Project Quality Assurance (QA)/Quality Control (QC)

Over the 24-month study period, over 50 samples were collected from the 11 monitoring stations and analyzed for major ions for project quality control. Fifteen samples were found to have analytical results complete enough to allow for ion balance calculations. Eight of the 15 samples showed ion balances with less than a 20 percent difference, and 13 of 15 samples were within 30 percent. Where field conductivity measurements were available, comparisons between those values and conductivity calculated from the sum of major ions were acceptable (within 20 percent) 88 percent of the time. Comparisons to laboratory conductivity measurements were acceptable 73 percent of the time.

Further QA/QC for sample collection was provided by co-locating a collector at an existing PADMP site north of the watershed (Little Buffalo State Park near Newport) and by analyzing replicate storm samples from a second collector located at the Lemoyne site.

Comparisons were made between results from samples collected at the Newport site and the PADMP monitoring site. Although the two methods of monitoring differ and the sites were not precisely co-located (about 400 yards apart), the data showed reasonable agreement with major ion concentrations for 51 of 76 data pairs falling within approximately 25 percent of each other. Agreement between data sets was best for pH, specific conductance, sulfate, nitrate, ammonium, and magnesium and worst for calcium, potassium, and chlorides.

A comparison between the true replicate samples collected at Lemoyne was performed. These data show very minimal variation with 95 percent of the paired results falling within the 25 percent range for acceptability.

Related Report

The following report on the Conodoguinet Creek Watershed Study is available from the Pennsylvania DEP, Bureau of Watershed Conservation:

• The Relationship of Prevailing Land Uses to Precipitation Quality in a Southcentral Pennsylvania Watershed -- Conodoguinet Creek Watershed, Prepared by the Pennsylvania Department of Environmental Protection, Bureau of Watershed Conservation, Harrisburg, Pennsylvania, December 29, 1995.

As found on: http://www.dep.state.pa.us/dep/deputate/watermgt/Wqp/WQStandards/wqstandards.htm

Go to the Conodoguinet Creek Watershed Study Data Page

For more information, e-mail Dr. John Sherwell at the PPRP, or call him at 410-260-8660