Document ID: EPA-HQ-OPP-2007-1163-0007
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2008-10-15T04:00Z

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

MEMORANDUM	Date:  August 25, 2008

SUBJECT:	Response to public comments on the Guidance for Conducting
Prospective Ground-Water Studies 

FROM:	Amy McKinnon, Environmental Scientist

		Environmental Risk Branch IV

Environmental Fate and Effects Division (7507P)

		Office of Pesticide Programs (OPP)		

		

THROUGH:	Elizabeth Behl, Branch Chief

		Environmental Risk Branch IV

		Environmental Fate and Effects Division (7507P)

		Office of Pesticide Programs

		

TO:		Docket #  HYPERLINK
"http://www.regulations.gov/fdmspublic/component/main?main=DocumentDetai
l&o=090000648039b8ef" EPA-HQ-OPP-2007-1163 

	

	This memo addresses the public comments on the Guidance for Conducting
Prospective Ground-Water (PGW) Studies from FR notice
EPA-HQ-OPP-2007-1163; FRL-8347-5.  The public comment period for the
guidance document ended on March 15, 2008.  All of the comments received
during the public comment period are posted to the docket for the
Guidance Document for PGW Studies ( HYPERLINK
"http://www.regulations.gov/fdmspublic/component/main?main=DocumentDetai
l&o=090000648039b8ef" EPA-HQ-OPP-2007-1163 ).  Only two sets of comments
were received from: the California Department of Pesticide Regulation
(CA DPR) ( HYPERLINK
"http://www.regulations.gov/fdmspublic/component/main?main=DocumentDetai
l&o=09000064803fb9a0" EPA-HQ-OPP-2007-1163-0004.1 ) and the Florida
Department of Agriculture & Consumer Services (FDACS) ( HYPERLINK
"http://www.regulations.gov/fdmspublic/component/main?main=DocumentDetai
l&o=09000064803fb864" EPA-HQ-OPP-2007-1163-0003.1 ).  EFED held
conference calls with both groups to discuss proposed revisions in
response to their comments.

	Comments from the CA DPR focused on ensuring that enough irrigation
water would be applied to test plots to allow recharge to the ground
water table during the study.  In Section 4.12 of the guidance
(Irrigation), the recommended irrigation target is described as 120% of
crop demand or 120% of historic rainfall, whichever is greater.  CA DPR
was concerned that this irrigation guidance would not be sufficient for
all growing regions in the United States.  This section has been
modified and now reads “Estimate target water requirement by month
(for example:  120% of crop water demand or 120% of historical rainfall
data, whichever is greater).  However, it should be noted that the
estimated target water requirement for a specific study site may be much
greater than 120% of crop water demand or 120% of historical rainfall
data.  State agricultural agents should be consulted to determine an
appropriate target irrigation rate in order to ensure recharge of
irrigation water to ground water.  For example, historical irrigation
efficiencies in the San Joaquin Valley of California are estimated at
60% for surface (flood) irrigation and 70% for sprinkler irrigation
(DWR, 1983; Snyder et al., 1986; California Agricultural Technology
Institute, 1988).  These efficiencies translate to water application
rates of 167% and 143% of plant demand, respectively.  In addition,
extensive agricultural areas in California have been identified as
vulnerable to ground water contamination due to the presence of coarse
soils and shallow ground water.  CA DRP has calibrated the LEACHM
transport and fate model to these conditions and has estimated
concentrations of pesticides in ground water from simulated water
application of 167% of plant demand.  These values agree well with
measured well water concentrations (Spurlock, et al., 2006).  California
indicated they have limited water applications to 125% of plant demand
to mitigate ground water contamination for some contaminants.  Attached
as a reference are two example spreadsheets that were developed by the
California Department of Pesticide Regulation, Environmental Monitoring
Branch to estimate drainage from a prospective ground water study.” 
In addition, CA DPR noted that in Section 7.46 of the guidance (Weather
Data), “pan evaporation” was missing from the list of site-specific
weather data that is collected during PGW studies; this has been added
to the document.

FDACS had several specific comments that have been addressed by making
the following revisions:  

In regard to Section 4.48 of the guidance (Sampling Frequency),  FDACS
objected to  compositing of lysimeter samples.  The language has been
clarified and now reads “Samples should be drawn from lysimeters at
each sampling period and analyzed individually.  In the event that an
insufficient volume of water is collected from a lysimeter, samples from
two lysimeters located at the same depth increment may be composited;
however the practice of sample compositing should be avoided if at all
possible.”

In regard to Section 4.53 (Number and Location of Monitoring Well
Clusters) FDACS stated that the guidance document mentions down-gradient
wells, but provides little guidance on the required number and location,
and if shallow and deep monitoring wells would be required.  The
guidance has been modified and now reads “The placement of a
monitoring well down gradient of the treated field is not critical for 
PGW study, but may be useful for the purposes of assessing impacts to
nearby off-site water quality.  State agricultural agents should be
consulted during the planning stage in order to determine if a down
gradient well is beneficial to the study being conducted (in addition to
on-site wells) or even required by the state.  The depth of the well
should be determined based on local hydrology to ensure that water
recharged on the treated field is intercepted by the well.  State and
local requirements for ground-water monitoring should be included in
planning.”  

In regard to Section 6.53 (Decontamination) FDACS indicated that use of
spectrographic water is an unnecessary excessive cost.  The reference to
spectrographic water has been removed and that section now reads “If
non-dedicated pumps are used for sample collection, deionized water
should be pumped through equipment after decontamination and a sample
collected for analysis.”

In regard to Section 6.54 (Sample Collection) FDACS pointed out that the
guidance only allowed for use of a bladder pump for collecting volatile
pesticides.  This section has been changed to “Peristaltic pumps,
low-flow submersible pumps and bladder pumps are suitable for sampling
for volatile pesticides.” 

 In regard to Section 6.6 (Sample Handling and Tracking) the guidance
states that pH, temperature, and specific conductance be placed on
sample labels.  FDACS indicated that including these parameters on the
labels of small containers would be difficult.  The guidance document
reads “In general, sample labels should be placed in duplicate on the
sample container and should include:  Date and time of collection, pH,
temperature, and specific conductance, Identification of sample
location, Analytes, and Signature of field technician.”  The guidance
document continues to request that all sample parameters are written on
the label.

In regard to Section 7.34 (Quality Assurance) FDACS indicated that there
is no mention of annual and final GLP field and facility audits.  The
guidance document states that “Field studies should be conducted in
compliance with good laboratory practices (GLPs) and should be properly
documented.”  

In regard to Section 7.44 (Soil Properties) FDACS requested
clarification on whether undisturbed or disturbed bulk density should be
measured.  This has been clarified to request the measurement of
undisturbed bulk density.  In addition, FDACS pointed out a spelling
error where “matrix potential” was incorrectly listed and is now
correctly listed as “matric potential.”  

In regard to Section 7.46 (Weather Data) FDACS indicated that there is
no mention of the location of the weather station and recommended that
the guidance state that the weather data be gathered from a location
close to the test plot and in an open, exposed area.  The language has
been changed to “The following site-specific weather data collected
during the PGW study is requested from a weather station located close
to the test plot in an open, exposed area without trees.”  

In regard to Section 7.48 (Chemical Monitoring Results) FDACS indicated
that an x-y graph would be just as easily or more easily visualized than
a bar-graph.  The paragraph has been modified to “At a minimum,
provide analytical results for each monitoring well in x-y graph format
so a trend in increase and/or decrease will be easily visualized.  Graph
results for each monitoring well separately for entire sampling period
(i.e. 24 months).”

FDACS requested that the guidance document only use English units. 
Previously comments have been received to use only metric units in the
guidance document.  Because some parameters are typically reported in
English units and others in metric units, the guidance document has not
been modified.

OPP appreciates the willingness of the public to provide constructive
comments on the  Guidance for Conducting Prospective Ground Water
Studies.  As indicated above, the guidance document will be revised to
reflect relevant comments received during the public comment period.  

   HYPERLINK "http://www.regulations.gov/"  http://www.regulations.gov/ 

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