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Golf Course Adjustment Factors for Modifying Estimated Drinking Water Concentrations and Estimated Environmental Concentrations Generated by Tier I (FIRST) and Tier II (PRZM/EXAMS) Models

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Golf Course Adjustment Factors for Modifying Estimated Drinking Water Concentrations and Estimated Environmental Concentrations Generated by Tier I (FIRST) and Tier II (PRZM/EXAMS) Models (6 pp, 128K, About PDF)

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Memorandum

December 7, 2005

SUBJECT: Golf Course Adjustment Factors for Simulated Aquatic Exposure Concentrations

FROM: Steven Bradbury, Ph.D., Director /s/, Environmental Fate and Effects Division (7507C), Office of Pesticide Programs

TO: Environmental Fate and Effects Division (7507C), Office of Pesticide Programs

The Water Quality Technology Team has developed golf course adjustment factors (GCAFs) for modifying Estimated Drinking Water Concentrations (EDWCs) and Estimated Environmental Concentrations (EECs) that are generated by EFED's aquatic exposure models for golf course turf use scenarios. Rather than assuming that an entire golf course is treated, modelers can use these adjustment factors to account for the percent acreage of a golf course that is labeled for treatment with an individual pesticide.

The attached document provides guidance on how to quantitatively discount for the percentage of the golf course acreage that is not treated with an individual pesticide. These factors should only be used to refine EDWCs and EECs for turf in a golf course use scenario. In the future when additional data are available, adjustment factors will be developed for turf in other types of use scenarios (e.g., sod farms, residential, right-of-way, other recreational uses, etc.).

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Need for Golf Course Adjustment Factor Guidance

Golf course adjustment factors are needed to account for the percent acreage of a golf course that is treated with an individual pesticide. These factors would be used to refine surface water Estimated Drinking Water Concentrations (EDWCs) and Estimated Environmental Concentrations (EECs) generated by EFED's aquatic exposure models for golf course turf use scenarios.

Golf course facilities consist of separate playing areas that are classified as tees, greens, practice greens, fairways, driving ranges, and roughs, in addition to "unmanaged grounds" where lakes, ponds, out-of-play areas, conservation areas, and buildings are located. Depending on the playing area, management practices and intensity can vary in these facilities. When an individual pesticide is used, for example, only on tees and greens, or tees and greens plus fairways, it is assumed in the model scenario, that the entire golf course is treated. This assumption can lead to an overestimation of the EDWCs/EECs. The use of an adjustment factor (GCAF) to refine those values can correct this problem by quantitatively discounting the percentage of managed land area on a golf course that is not treated with a pesticide.

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Background Information

Based on the World Golf Foundation's "The Golf 20/20 Industry Report for 2002," there were about 15,827 golf courses in the United States as of March 2003. Golf course characteristics information provided by the Golf Course Superintendents Association of America Exit EPA Disclaimer indicates that an 18-hole golf facility averages about 150-200 acres of total land, including water bodies, hard structures, and out-of-play areas. A typical urban golf course is only 110-120 acres, and courses in resort areas may be 170-190 acres (G. Lyman, GCSAA; personal communication 11/19/04). Generally, pesticides are not applied to entire golf courses, but rather to some holes and some parts of the course (e.g., tees, greens, and/or fairways). They may be applied as a spot treatment or to an entire portion of the course although pesticide labels are rarely specific on the usage details. Tees and greens are typically the most intensely managed areas and tend to receive higher inputs compared with fairways and roughs.

In determining EDWCs for a drinking water assessment, EFED utilizes a standard EXAMS scenario referred to as the "index reservoir" in Tier II modeling with PRZM/EXAMS. The Tier I model FIRST also uses the index reservoir scenario, which simulates a 172.8-ha field (watershed) draining into a 5.3-ha reservoir. For agricultural crops, a percentage cropped area factor (PCA) is used to adjust the EDWCs to account for the portion of a drinking water watershed that contains fields planted with a specific crop. PCAs have been developed for only a few agricultural crops to date, largely limited by availability of data at the required scale. At the present time, data are not available at the scale needed to develop the non-agricultural equivalent of a PCA for golf course uses.

For agricultural and non-agricultural crops, it is assumed that the entire field is cropped and treated. While this is the case for agricultural crops, it is not always the case for golf courses. Thus, for the drinking water exposure assessment, the GCAF will adjust the EDWCs to account for the percentage of the field that is not treated. This, in effect, makes the GCAF a "percentage land area treated" adjustment, characteristic of land use on a golf course. This adjustment will be applied to both Tier I and Tier II modeling outputs for use in the drinking water assessment.

In determining EECs for ecological exposure assessment, EFED uses a standard EXAMS scenario referred to as the "standard pond" in Tier II modeling with PRZM/EXAMS. Scenarios simulate a 10-hectare field draining into a 1-hectare static pond that is 2-meters deep and does not have an outlet. The pond serves as a surrogate for a variety of small water bodies that can be found at the top of a watershed. It is assumed that runoff is equally likely to flow into the pond from all areas of the treated field, and that the entire field is cropped and treated. With the standard pond and turf scenarios, EFED concluded that EECs are representative of a subset of ponds that occur on golf courses, given their configuration, the size of the ponds, and their drainage area. Thus, a GCAF is not used with Tier I EECs from GENEEC2. It is only used after Tier II (unadjusted) EECs result in relevant Levels of Concern (LOC) exceedences. If there are no exceedences, then only the RQ's derived from non-modified EECs are reported in the risk assessment. For ecological exposure modeling, a GCAF will only be used to refine the Tier II EECs. In this case, both the adjusted and unadjusted Tier II EECs are reported in the ecological risk assessment. This approach differs from that used in estimating drinking water exposure because, for drinking water, effects are integrated over a watershed of larger spatial scale and estimated concentrations are generally accepted as reasonably conservative.

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Supporting Data for Recommended GCAF Values

In developing this GCAF guidance, two independent sources of data were reviewed. Additional information/data searching was conducted by personal communication and by consulting research reported on golf organization Web sites (e.g., Golf Course Superintendents Association of America Exit EPA Disclaimer and the United States Golf Association Exit EPA Disclaimer). The data obtained from the GCSAA, presented in Table 1, were used to develop the recommended GCAFs. The data from a USGA survey (which was an internal survey for use by pesticide registrants) were not used to develop the GCAFs, as the results were based on information for a smaller sample of golf courses and percentages were calculated based on total facility acreage, including non-turf grass areas.

The survey data provided by the Golf Course Superintendent Association of America (GCSAA) is based on the survey responses from 741 GCSAA members submitted over two years. Responses represented multiple course types, including private, semi-private, daily fee, municipal, resort, and other. The majority of the courses were 18-hole facilities (572); others that were represented included 9-hole (79) and ≥19-hole (90) facilities. Respondents were from eight (USGA) regions of the country: Northeast (90), Mid-Atlantic (58), Southeast (73), Florida (45), Mid-Continent (150), North Central (163), Northwest (36) and Southwest (122). The distribution of responses matched the distribution of GCSAA members by course type, size and USGA region.

Table 1
Golf Course Superintendent Association of America
golf course acreage survey data
Use TypeAverage number of acres1 Percentage of Course (%)2
Tees2.72.4
Greens2.92.6
Fairways31.928.6
Roughs66.860
Practice Green30.20.018
Driving Range47.16.4

1 From the Golf Course Superintendent Assoc. of America's Performance Measurement Survey, 1999-2000 Preliminary Results, February 2001. Based on personal communication with Greg Lyman, GCSAA, 11/19/2004, these data represent the final results of the survey for golf course size.

2 Percentage represents course subtype divided by total maintained turf acreage of 111.5 acres. Acreage in lakes, ponds, out-of-play areas and hard structure acreage is not included; when included, the average size of a golf course is closer to 150 acres.

3 Practice green acreage is managed similar to greens and is accounted for in the recommended GCAF for tees and greens.

4 Driving range acreage is managed similar to roughs and is accounted for in the recommended GCAF for roughs.

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Procedure for Use of Adjustment Factors Specific to Golf Course Turf on Tees, Greens, Fairways, and Roughs

Calculations

This procedure describes how to adjust EDWCs (drinking water assessment; both Tier I and Tier II) and to refine EECs (ecological exposure assessment; Tier II only), resulting from pesticide use on golf course turf. The modification of estimated concentrations, using EFED aquatic exposure models, accounts for the percentage of the total golf course acreage that actually receives pesticide treatment.

For pesticides applied only to tees and greens, the FIRST or PRZM/EXAMS output values should be multiplied by 0.05 to modify the EDWCs (surface water only) and Tier II EECs, and the resulting values should be reported as the adjusted EDWCs or EECs. For applications to fairways only, the output values should be multiplied by 0.29. When tees, greens, and fairways are all treated, the output values should be multiplied by 0.34. If tees, greens, fairways, and roughs are all treated, a GCAF should not be used, as the output values are multiplied by a factor of 1. For EECs, both adjusted and unadjusted EECs should be reported. These GCAFs are summarized in Table 2.

Table 2
Recommended golf course adjustment factors by turf type
Treated Areas of Course (Turf Type)GCAF
Tees and Greens (includes practice greens) (0.024 + 0.026) = 0.05
Fairways 0.29
Roughs (includes driving range)0.66
Tees and Greens and Fairways(0.05 + 0.29) = 0.34
Tees and Greens and Fairways and Roughs (0.05 + 0.29 + 0.66 ) = 1.0

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Use Guidance/Restrictions

The assumption that the entire watershed of a drinking water system is comprised of a golf course and that it will be 100% treated is unlikely and is highly conservative. However, with approximately 15,827 golf courses in the United States, the co-occurrence of golf courses and other crops treated with the same pesticide cannot be disregarded. Still, EFED's default PCA of 0.87 (for agricultural crops) should not be used to refine EDWCs for golf course or other turf uses. The current default PCA is based on the highest percentage of agricultural land in any USGS 8-digit Hydrologic Unit Code (HUC) in the conterminous United States. More data at a relevant spatial scale are necessary before the division can develop PCAs for turf grass or other non-agricultural uses, including golf courses.

The GCAF is different from the Percentage Crop Area (PCA) factor, which is applicable only to agricultural crops and refers to the fraction of a watershed that is planted with a particular crop. Instead it is a correction factor used to account for the partial land area treated relative to the total golf course acreage. The GCAF should always be applied to model estimates for drinking water assessments. For ecological exposure modeling, the GCAF will only be used to refine the Tier II EECs if Tier II (unadjusted) EECs result in exceedences of relevant Levels of Concern (LOCs). The GCAF should not be used for Tier I EECs from GENEEC2. If there are no LOC exceedences in Tier II modeling, then only the RQ's derived from non-modified EECs should be reported in the risk assessment. If there are exeedences in Tier II modeling, both the adjusted and unadjusted Tier II EECs should be reported in the ecological risk assessment, and the differences described in the risk characterization.

The GCAF should not be applied to groundwater values determined by the Tier 1 model SCI-GROW, which is based on a treated field rather than a watershed.

The adjustment factor is only applicable to golf course use scenarios, and should not be used for other turf use scenarios, such as sod farm, residential, right-of-ways, (other) recreational, or any other turf uses. If other uses are allowed on the label, the adjustment factor should be used only to modify, as appropriate, the values reported for golf course turf use. If there are any turf uses on the label other than golf course turf (for example, if the use is for "undifferentiated turf" or "sod farms"), the unadjusted values should be reported to represent those uses, in addition to the adjusted values representing the golf course use. Additionally, when used for modifying EECs, both the initial Tier II EEC and adjusted/refined Tier II EEC values should be reported in the risk assessment.

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Remaining Uncertainties

While a GCAF will allow the user to modify the EDWCs and EECs determined by aquatic exposure models for a golf course turf use scenario, it does not take into account all uncertainties involved in estimating surface water concentrations associated with the use of a pesticide on a golf course.

There are several aspects of pesticide use on golf course turf that may result in the model scenario underestimating surface water concentrations. Golf courses are commonly built near water; many are near wetlands. Golf courses are typically designed to drain water, incorporating a mix of areas with higher slopes, depressions, and tile drainage systems. These drains rapidly transport water that infiltrate to discharge points in nearby surface water bodies. Currently, neither the Tier I nor the Tier II aquatic exposure models used by EFED can account for subsurface drainage on golf courses. Also, the turf standard scenario used in the Tier II model is a general one that is not specific to golf courses.

The GCAF takes into account that not all of the turf is treated; thus, it only allows for a "percentage land area treated" adjustment. The GCAF does not account for the fact that, for drinking water, it is highly unlikely that an entire drinking water watershed would be comprised of golf course turf. Additional data, analogous to the data used to develop Percentage Crop Area factors, are needed, but are beyond the scope of this guidance.

The values used to develop the GCAF represent average values, not the 90th percentile values, as data were not available. Also, the use of the GCAF assumes that the estimated surface water concentrations will be reduced in equal proportion to the reduced level of acreage treated; supporting data for this assumption are not available.

Future research needs to help address some of these uncertainties include review of reliable pesticide monitoring data for golf courses with adequate ancillary data to allow comparison with initial and refined EECs. The results of this research and additional data may lead to revised scenarios in the future.

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Implications for Existing Scenarios in PRZM/EXAMS

The current "Pennsylvania Turf" and "Florida Turf" standard scenarios for PRZM/EXAMS state that for pesticides applied to golf courses, the fraction of the total course area, which is composed of greens, tees, and fairways, may be used to modify the modeling results. The scenarios then state that the fractions are 23% for fairways, and 2% each for tees and greens. These values will need to be amended to reflect information from this guidance document.

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