Surface Water Monitoring
Surface water monitoring projects generally fall into one of the following three categories:
Edge-of-Field Runoff Studies
The objective of these studies is to assess the runoff potential (measured as water concentration or mass transport) of pesticide products under actual use conditions from a single farm field or study plot. In selecting sites for a runoff study, we identify regions with high product sales. Stone staff meet with growers in these regions and characterize potential sites by determining catchment area, treatment area, soils, field slope, cropping practices, and other factors that influence runoff generation and chemical transport. We establish sampling points proximal to existing channels and culverts that collect and convey runoff. Our sampling methods range from inexpensive, low-tech approaches involving grab sampling, siphon-type runoff samplers, and non-recording rain gauges to higher-tech installation of weather stations, flumes, flow meters, stage recorders, and autosamplers.
Watershed Scale Monitoring
Between the edge of a farm field and a downstream water treatment plant is a network of drainage ditches and streams. We monitor the water and biota in these perennial streams to assess the potential impact of pesticides on aquatic animals and plants. We conduct stream sampling at this intermediate scale, where environmental concentrations of a pesticide need to be measured for comparison with ecotoxicological levels of concern.
Stone conducts probabilistic assessments to identify stream reaches where pesticide concentrations are predicted to exceed regulatory levels of concern. We use several models (SWAT, WARP, PRZM/EXAMS) in combination with GIS to target certain reaches for monitoring on the basis of product use, crop, meteorological, soils, and other data. We instrument sampling stations with autosamplers and flow monitoring equipment, or rely on a schedule of grab sampling, with flow data derived from public sources. No standard exists in the pesticide fate field for surface water monitoring studies; therefore, Stone is particularly interested in working creatively with registrants to formulate solid experiment designs.
Community Drinking Water Monitoring
We have led the industry in conducting community drinking water monitoring studies since 1994. These studies have involved several hundred community water systems (CWSs) across the US. We have worked with the Acetochlor Registration Partnership on the largest such study yet conducted, which involved almost 200 CWSs and spanned a period of seven years. Our smallest study involved just five systems sampled over the course of a year to address a product registration issue in a specific region.
Over the last 20+ years, we have developed and refined efficient procedures to select and characterize vulnerable CWSs, train sampling personnel, and manage sampling at participating CWSs. Integral to the system selection process is the use of a Geographic Information System (GIS) to locate the CWSs in each state, to delineate watersheds for the source waters used by these systems, and to characterize land use, product use, runoff potential, and other spatial factors that contribute to vulnerability. Stone has created custom tools for use with ArcGIS that efficiently query, map, and summarize crop data, soils data, land use, and historical precipitation records. The objective is to winnow, through an orderly and defensible process, the approximately 10,000 community water systems relying on surface water sources in the US to a representative number of potentially vulnerable systems.
Since surface drinking water monitoring studies rely heavily on the cooperation of the employees of the CWSs, we place a great deal of emphasis on engaging CWS personnel and supporting them with supplies and logistical help throughout the study period. We make sure these employees are well trained in the sampling procedures and relevant aspects of GLPs. We provide a toll-free number so they can call Stone for assistance at any time and speak with a project scientist. We prepare field notebooks customized for each CWS containing sampling/chain-of-custody forms, bottle labels, prepaid shipping airbills, and sampling instructions. We use customized FedEx tracking software to ensure that samples are taken on time and delivered directly to the lab. If there is a problem anywhere in the system, we identify it quickly and make arrangements to correct it. We recently completed a successful study in which more than 2,400 samples were collected and shipped to an independent laboratory over a three-year period.