Previous Findings about Pesticides in Pennsylvania Groundwaters

2015 to 2020—Sampling to determine changes in pesticide concentrations in hydrogeologic settings

2019 to 2020—Sampling to determine changes in pesticide concentrations in non-carbonate settings - Selected wells in two non-carbonate settings that had been previously sampled are being resampled in 2019-2020 to determine if concentrations of pesticides in groundwater have changed or stayed the same.

2015 to 2018—Sampling to determine changes in pesticide concentrations in carbonate settings - Selected wells in four carbonate settings that had been previously sampled twice (once in the 1990’s and once in the 2000’s) were resampled in 2015-2018 to determine if concentrations of pesticides in groundwater have changed or stayed the same.

2003 to 2014—Sampling to complete a statewide assessment and determine changes in pesticide concentrations in hydrogeologic settings

2010 to 2014—Sampling to determine changes in pesticide concentrations in non-carbonate settings - To determine if concentrations of pesticides in groundwater had changed or stayed the same, USGS resampled three non-carbonate hydrogeologic settings in 2010 and 2012-2013. Also, to continue filling in gaps in the statewide assessment, a non-carbonate setting was sampled for the first time in 2014.

2008 to 2009—Sampling to determine changes in pesticide concentrations in carbonate settings - Selected wells in carbonate settings that had been sampled in 1993-1995 were resampled in 2008-2009 to determine if concentrations of pesticides in groundwater had changed or stayed the same (Zimmerman and Breen, 2012).

2003 to 2007—Sampling to complete a statewide assessment - To fill gaps in the statewide assessment, USGS sampled five hydrogeologic settings in 2003-2007 to characterize pesticide occurrence. See USGS Report Sir 2009-5139.

1993 to 2002—First cycle of USGS National Water-Quality Assessment (NAWQA) studies, statewide study design for assessing pesticide occurrence, and quality-assurance design

Lower Susquehanna River Basin - Pesticide occurrence and distribution was based on results for 169 wells sampled in 1993-95. See USGS Report WRIR 01-4012.

Allegheny and Monongahela River Basins - Pesticide occurrence and distribution in groundwater was based on results for 58 wells sampled in 1996-98. See USGS Report C-1202.

Delaware River Basin - Pesticide occurrence and distribution in groundwater was based on results for 76 wells sampled in 1999-2001. See USGS Report C-1227.

Potomac River Basin - Pesticide occurrence and distribution was based on results for 105 wells sampled in 1993-95. See USGS Report OFR 97-666.

Study design for statewide assessment of pesticide occurrence - A hydrogeologic framework was created to be used as a basis for sampling for pesticides in Pennsylvania, and a prioritized plan for sampling groundwater in areas of the state that had not been adequately characterized for the occurrence of pesticides was presented. Initially, the USGS NAWQA program design laid the foundation for regional assessments of pesticides in Pennsylvania groundwaters. An example of NAWQA design is found in USGS Report OFR 97-583. The statewide design for Pennsylvania is documented in USGS Report 99-4076 and establishes settings for assessment based on physiography (Pennsylvania Bureau of Topographic and Geologic Survey, 1995; digital data in figures below based on Pennsylvania Bureau of Topographic and Geologic Survey, 1998) and major aquifer material types (Miles and Whitfield, 2001) documented by the Pennsylvania Department of Conservation and Natural Resources and glacial data (Soller and Packard, 1998) documented in USGS Data Series 38. Carbonate aquifers are made up of limestone and dolomite, and when at or near the land surface, carbonate aquifers are the most vulnerable to contamination. The noncarbonate aquifers are crystalline, siliciclastic, and surficial. Crystalline aquifers are typically schists or other metamorphic or igneous rocks. Siliciclastic aquifers are commonly sandstones, siltstones, and shale. Surficial aquifers are often comprised of unconsolidated sands and gravels.

Quality-assurance design for statewide assessment of pesticide occurrence - An assessment of pesticides in groundwater from carbonate aquifers in the Delaware River Basin illustrated how quality-control samples are used to assure quality of pesticide results. See USGS Report WRIR 00-4104.

Before 1993—Earliest work that led the way in understanding pesticide occurrence in groundwater and illustrated that limestone (carbonate-rock) areas are vulnerable to pesticides

Pioneering research on pesticide occurrence in the Piedmont Physiographic Province, Lancaster County - This USGS study established the importance of aquifer material type in explaining the occurrence of pesticides in groundwater.  Carbonate aquifers were more vulnerable to contamination than noncarbonate aquifers. See USGS Report WSP 2493.

Regional reconnaissance assessment of pesticide occurrence in the Valley and Ridge Physiographic Province - One of the earliest regional reconnaissance assessments of pesticide occurrence was done by USGS in 1980-85 across Bedford, Blair, Centre, Clinton, Huntingdon, and Mifflin Counties.  The carbonate aquifers of Cambrian and Ordovician age were assessed by sampling 20 wells and springs.  This assessment discovered exceptionally large concentrations of herbicides in water from well BA 437 and identified this well as a hot-spot location in a limestone area. See USGS Report OFR 90-109.

Pesticide occurrence in the Pequea and Mill Creek watersheds, Lancaster County - A groundwater assessment of 167 wells conducted by USGS in 1991 discovered exceptionally large concentrations of herbicides in water from well LN 1842 and identified this well as a hot-spot location in a limestone area. See USGS Report AWDR 1992, volume 2, p279 to access data from the assessment.