drinking water exposure, while raw water better reflects watershed and usage characteristics allowing better risk management decisions.
Given the analytical costs for paired raw and finished water samples and the lack of comprehensive information on water treatment effects on the removal and transformation of most pesticides, does the panel have alternative recommendations on assessing raw and finished water?
Preliminary analyses by EFED indicates pesticide fate properties, sampling frequency, and
hydrologic residence time impact the accuracy of calculated annual mean concentrations.
Does the SAP have recommendations on balancing the characteristics of the pesticides and the water body being sampled with the number of samples needed to adequately measure the annual mean at different CWSs?
7.) Annual mean pesticide concentrations occurring at any CWS vary from year to year. A multi-year study would help to quantify year-to-year variability but is more costly.
Does the SAP have any suggestions for assessing annual variability given the financial constraints of the survey?
Would drawing out the survey over three years (with the same number of samples per CWS) improve it?
8.) EFED recognizes that pesticide concentrations in drinking water are dependent on factors including watershed characteristics, pesticide use, pesticide fate properties, surface water hydrology, and water treatment processes. Interpretation of the monitoring data will be dependent on the collection of such related ancillary data.
What types of ancillary information does the SAP believe would assist in the interpretation
of the monitoring data, and application of the data to model development and validation?
9.) We have defined our population as CWSs with pesticide use in their watersheds, based on the assumption that runoff and near field spray drift are the major routes of loading to the water supply.
Is this a reasonable assumption and should we monitor facilities that do not have pesticide
use in the watershed?
10.) One option proposed in the design framework is a census of the facilities serving the largest cities. These facilities are believed to have little agriculture in their watersheds, but reflect the drinking water for a large percentage of the population.
Does the SAP believe sampling CWSs serving very large populations is useful even if they
are expected to be of low vulnerability?
11.) Modeling should allow the Agency to reduce the extent of future drinking water surveys, and help to better identify areas at higher risk.