Closed sign for herbicide treatment of hydrilla

Water Monitoring Post-Herbicide

NYS Department of Environmental Conservation (DEC), and Tompkins County Health Department (TCHD), developed monitoring protocols for endothall and fluridone, which are part of the DEC permits for herbicide use. This monitoring is required. Additional monitoring was conducted during fluridone treatment to ensure adequate herbicide levels are maintained throughout treatment. Maps of the monitoring sites and results of the sampling are available year-to-year. 

Monitoring of herbicide concentrations is designed to fulfill three purposes:

  • Drinking Water Safety (TCHD sites)
  • Environmental Protection (DEC sites)
  • Maintenance of adequate herbicide levels for effective treatment (monitored by the Hydrilla Task Force after endothall application and by the Task Force and SePRO, the manufacturer of Sonar, during fluridone treatment)

Endothall Treatment Monitoring

TCHD requires water monitoring at 4 locations, in addition to Bolton Point to protect drinking water. NYS law requires that endothall levels in drinking water be below 50 parts per billion (ppb). This is referred to as the Maximum Contaminant Level (MCL) and may be commonly referred to as the drinking water standard. Water samples are collected on days 1, 3, 5, 7, 10, 14, 17 and 21 in the treatment area and/or at the Bolton Point water supply intake. 

To comply with the DEC pesticide permits, Tompkins County Soil and Water Conservation District (TCSWCD), collected water samples from the shore at five locations outside the herbicide treatment area. These are required by DEC and focus on environmental protection. The DEC sample sites are upstream and downstream of the treatment areas as well as 1/2 mile beyond the end of the treatment area. Water samples for DEC are collected 24 hours after treatment and days 2, 3, 4, 7 and 14 to ensure that the herbicide is not spreading beyond the treatment area . See the product labels that explain legal use of the herbicides. 

Fluridone Treatment Monitoring

Water monitoring for fluridone starts 24 hours after the first treatment  and continues until after treatment had stopped and fluridone is below measurable levels. Prior to the fluridone treatment, a background sample is collected at the Bolton Point intake.

The NYSDOH Maximum Contaminant Level (MCL) is 50 ppb for fluridone in drinking water. Fluridone is never expected to exceed this because the concentration of fluridone required for effective treatment is only three to eight (3-8) ppb, much less than the MCL. As a precaution, TCHD tracks drinking water safety through duplicates at sampling locations CI-1, CI-4, CI-9, and the Bolton Point intake. These water samples are split and used by TCHD and SePRO. One portion of the sample is sent to CSI ( Community Science Institute Laboratory) for analysis on behalf of TCHD in order to obtain results as soon as possible. In addition, the splits serve to confirm the accuracy of the analysis.

Fluridone sampling required by DEC is done at the same DEC sites used for endothall, plus one additional site. DEC samples are taken 24, 48 and 72 hours after the fluridone treatment starts, weekly for a month, and then monthly. This is to verify that the chemical is not spreading outside the treatment area. CSI analyzes these samples.

Analysis Methods

Most of the analysis is done using ELISA (Enzyme-Linked Immunosorbent Assay). Several of the samples are split and a portion of the water samples are analyzed using Gas Chromatography/Mass Spectrometry (GC/MS) (both explained below). This is referred to as a duplicate or a split. When a sample is split, both results are shown.

For endothall and fluridone at DEC and TCHD sites, CSI uses the ELISA method, which has been used for analysis of the samples since 2011. It is chosen because it renders analytical results comparatively quickly, thereby enabling rapid reporting to the public. This test method can detect herbicide concentrations as low as 7 parts per billion (ppb). Anything below 7ppb is referred to as "nd" for "non-detect". This information is used to guide adjustments in dosing levels.

ELISA is not currently certifiable in NYS. Therefore, for endothall monitoring, samples taken at the Bolton Point water system intake are "split," and a portion of selected samples sent to Benchmark Labs. Benchmark is certified by NYS Dept. of Health (NYSDOH) Environmental Laboratory Approval Program (ELAP) to conduct EPA method 548.1. This analysis method employs Gas Chromatography/Mass Spectrometry (GC/MS) to quantify endothall levels in drinking water. GC/MS detection limit is 5 ppb. Benchmark reports a non-detect as less than 5 ppb. When samples are split, both sets of results are reported.

The SePRO lab uses HPLC (High Performance Liquid Chromatography), which can detect fluridone concentrations as low as 1 ppb. Any levels below 1 ppb are referred to as "nd" for "non-detect". Some of the SePRO samples are split and a portion sent to CSI so that TCHD can receive early reporting of the herbicide levels in order to assure  drinking water protection.

Last updated January 15, 2020