Department of Pesticide Regulation Environmental Monitoring Branch 1001 I Street, P.O. Box 4015 Sacramento, California 95812

September 2017

STUDY #300: PROTOCOL FOR GROUNDWATER MONITORING OF DCPA AND ITS DEGRADATES (MTP AND TPA)

I. INTRODUCTION

The Pesticide Contamination Prevention Act (PCPA) is defined in Sections 13141-13152 of the California Food and Agricultural Code (FAC). Currently, Section 13149 mandates that when a pesticide active ingredient or other specified ingredient or degradation product of a pesticide is detected and confirmed in groundwater and the contamination is found to be due to legal agricultural use, then the California Department of Pesticide Regulation (DPR) is required to conduct a formal review (Detection Response Process) to determine if use of the pesticide should continue and, if so, under what conditions.

Chlorthal-dimethyl (DCPA or Dacthal) is the active ingredient of a number of herbicide products with historic or current use in California. DCPA has two major degradation products: monomethyl tetrachloroterephthalate (MTP) and 2,3,5,6-tetrachloroterephthalic acid (TPA). DPR conducted groundwater sampling studies between 1990 and 1997 in different areas of the state where DCPA had been legally used, looking specifically for DCPA, MTP, and TPA. None of the laboratory analyses of the collected samples from those studies yielded a confirmed detection of DCPA or MTP. However, the laboratory analyses did confirm detections of TPA in samples collected in several counties.

The PCPA was originally enacted in 1985 under Assembly Bill 2021 and was significantly revised in 2014 under Senate Bill 1117. Under the 1985 version of the PCPA (i.e., that includes the period from 1990 to 1997 when DPRs DCPA sampling studies were conducted), an active ingredient was entered into the Detection Response Process when one of its degradation products was found in groundwater only when the measured levels of that degradation product were determined to be high enough to pose a threat to public health. Although confirmed detections of TPA were found between 1990 and 1997, the DPR Medical Toxicology Branch reviewed the toxicological data for TPA submitted by the registrant at the time and concluded that the levels found in groundwater did not pose a threat to public health (CDPR, 1991). Consequently, it was recommended then to not enter DCPA into the Detection Response Process (CDPR, 1992). A health reference level (HRL) of 70 g/L was subsequently calculated for both DCPA and TPA by the United States Environmental Protection Agency (USEPA) (USEPA, 2008) and adopted

by DPR for its monitoring of these constituents in groundwater (CDPR, 2012). Since 1997, several agencies have reported detected levels of TPA in water wells located throughout the state but the measured TPA concentrations were all well below the established HRL.

The revision of the PCPA in 2014 lifted the requirement to demonstrate a threat to public health of degradation products found in groundwater. Consequently, an active ingredient is now entered into the Detection Response Process simply when its degradation product is found in groundwater and determined to have originated from legal agricultural use. Given the recent changes to the PCPA and the previous detections of TPA throughout the state, DCPA will be entered into the Decision Response Process. Current groundwater concentrations of DCPA, MTP, and TPA in areas of the state where DCPA use has been relatively high will be needed to inform the Detection Response Process in its determination of whether current use of DCPA pollutes, or threatens to pollute, groundwater in California.

II. OBJECTIVE

The purpose of this study is to assess current concentrations of DCPA, MTP, and TPA in groundwater samples collected in regions where recent agricultural use of DCPA has been relatively high and where detections of TPA have been found in previous studies. Assessment of current concentrations of DCPA, MTP, and TPA will be used to inform the Detection Response Process.

III. PERSONNEL

Well sampling will be conducted by the Environmental Monitoring Branch of DPR under the general direction of Joy Dias. Project personnel include:

Project Leader: Nels Ruud Field Coordinator: Craig Nordmark Senior Scientist: Murray Clayton Laboratory Liaison: Sue Peoples Analytical Chemistry: Center for Analytical Chemistry, California Department of Food

and Agriculture (CDFA)

Please direct questions regarding this study to Nels Ruud at (916) 324-4167, e-mail: .

IV. AGRICULTURAL USE OF DCPA

The DPR Pesticide Use Report database contains reported agricultural use of DCPA (in pounds) on a township-range-section basis from 1990 to present (CDPR, 2015a). Total annual use of DCPA in California from 1990 to 2014 is shown on Figure 1. Annual use declined steadily during the 1990s from a high of 849,074 pounds (lbs) in 1992 to a low of 133,688 lbs in 2000

mailto:Nels.Ruud@cdpr.ca.gov

(Figure 1). Annual use from 2001 to 2014 leveled off somewhat with an average rate of 192,771 lbs per year. Total use during 2014 was 172,054 lbs.

Annual DCPA use by county from 2000 to 2010 is given in Table 1. The top users of DCPA were Monterey and Imperial counties with average annual usages of 75,526 and 45,731 lbs, respectively. Lesser amounts of DCPA (

public water supply wells in Monterey County (CDPR, 2015b). Although these detections have not been confirmed by DPR using its monitoring standards, their reported occurrence provides useful information in planning the sampling for this study.

VI. GROUNDWATER SAMPLING IN THE SALINAS VALLEY

Monterey County has the highest current and historic use of DCPA among all counties in the state (Table 1). DCPA use in Monterey County occurs primarily in the Salinas Valley, where five confirmed detections of TPA have been found (see Figure 2 and Table 3). Therefore, initial groundwater sampling in this study for DCPA, MTP, and TPA will be planned in the Salinas Valley approximately between the cities of Salinas and King City where use has historically been the highest (Figure 2). After sampling has been conducted in the Salinas Valley and the follow-up laboratory analyses of the samples has been completed, additional sampling may be planned in other counties with relatively high DCPA use (i.e., Imperial, Fresno, Ventura, Riverside, San Luis Obispo, and Santa Barbara).

The Salinas Valley Groundwater Basin is the source of groundwater for the urban, rural-domestic, and agricultural water users in the Salinas Valley. The Salinas Valley Groundwater Basin is divided into eight sub-basins. Sections between Salinas and King City with the highest DCPA use in Monterey County are located in four of the eight sub-basins: 1) Pressure Sub-basin (sometimes referred to as the 180/400-Foot Aquifer Sub-basin) (CDWR, 2004a), 2) Eastside Sub-basin (CDWR, 2004b), 3) Forebay Sub-basin (CDWR, 2004c), and 4) Upper Valley Sub-basin (CDWR, 2004d) (see Figure 2 for locations of sub-basin boundaries). The four sub-basins are not hydraulically isolated from one another but instead exchange horizontal groundwater flows across their common boundaries. The four sub-basins are distinguished from one another by differences in hydrostratigraphy, water levels, and groundwater recharge characteristics.

In this section, we describe an approach for selecting potential sampling sites in the four sub-basins as a function of local hydrogeology, locations of wells with previous confirmed detections, and sections with relatively high DCPA use.

Pressure Sub-basin

The Pressure Sub-basin (Figure 2) is conceptualized as consisting of three semi-confined to confined aquifer units: 180-foot aquifer, 400-foot aquifer, and deep aquifer. The three aquifers are so-named with respect to the approximate depths beneath the ground surface at which they occur. The 180-foot aquifer is overlain by a confining layer called the Salinas Valley Aquitard (SVA). Vertical recharge from irrigation return flows, rainfall, and seepage from the Salinas River is known to create a perched water table condition above the SVA in areas of the Pressure Sub-basin. Horizontal recharge into the Pressure Sub-basin from the southeastern (upgradient) direction occurs across its boundary with the Forebay Sub-basin. Horizontal recharge from the northwestern (downgradient) direction occurs as seawater intrusion from the Monterey Bay. Although the SVA is generally thought to be relatively continuous across the Pressure Sub-basin,

some amount of groundwater from the perched water table is likely recharging the 180-foot aquifer via vertical leakage through the SVA (Fogg et al., 1999).

Wells in the Pressure Sub-basin between Salinas and Gonzales that have been previously sampled by various agencies have completed depths from 50 to 700 feet beneath the ground surface (ft bgs) (CDPR, 2015b). Wells that are considered shallow in the Pressure Sub-basin are screened in the perched aquifer with completed depths in a range of about 50 to 200 feet bgs. Wells that are considered deep are screened in the 180-foot, 400-foot, and Deep aquifers and have top-of-screen locations generally greater than 200 feet bgs. For this study, sampling in the Pressure Sub-basin should be conducted in wells with completed depths less than 200 ft bgs.

An ordering of the township-range-sections in the Salinas Valley from the highest to lowest total DCPA use (i.e., minimum of 6,000 lbs per section) from 2000 to 2010 and the sub-basins in which they are respectively located is given in Table 4. The section (M16S04E10) with the highest total DCPA use in the Salinas Valley (18,569 lbs), for example, is located in the Pressure Sub-basin (Table 4). The regional direction of groundwater flow in the Pressure Sub-basin is northwest along the valley axis and northeast into the Eastside Sub-basin. For this study, sampling should be conducted in shallow wells located within, north, or east of the high use sections in the Pressure Sub-basin identified in Table 4 and displayed on Figure 2.

Three wells with confirmed detections of TPA are located in the Pressure Sub-basin (Figure 2). Re-sampling of those three wells will also be attempted for this study.

Eastside Sub-basin

The SVA present in the Pressure Sub-basin is thought to diminish in thickness at or near the boundary separating the Pressure and Eastside sub-basins (Figure 2). Groundwater in the Eastside Sub-basin is not otherwise subjected to confined conditions and the sub-basin is therefore conceptualized as an unconfined to semi-confined aquifer. Vertical recharge in the Eastside Sub-basin is only from irrigation return flows and rainfall since the Salinas River does not intersect that sub-basin. Horizontal recharge into the Eastside Sub-basin from the western direction occurs across its boundary with the Pressure Sub-basin; from the southeastern direction across its boundary with the Forebay Sub-basin; and from the northwestern direction as seawater intrusion from the Monterey Bay (CDWR, 2004b).

Pumping along the eastern side of Salinas has created a significant groundwater depression in that region of the Eastside Sub-basin (MCWRA, 2015). In general, groundwater levels in the Eastside Sub-basin are lower than those in the adjacent Pressure Sub-basin and upgradient Forebay Sub-basin. For example, during the 2014 Water Year (WY) the average depth to groundwater (DGW) for eleven monitoring wells in the Eastside Sub-basin ranged from about 125 feet bgs in February 2014 to 158 feet bgs in August 2014 (MCWRA, 2015). By comparison, the average DGW for five monitoring wells in the 180-foot Aquifer in the Pressure Sub-basin ranged from about 45 feet bgs in February 2014 to 65 feet bgs in August 2014. The average

DGW in the Eastside Aquifer in November 2014 was about 139 feet bgs in comparison to about 130 feet bgs in November 2013. Given a lack of perched water conditions in the Eastside Sub-basin and the significant pumping impacts on groundwater levels east of Salinas, sampling in this study should be conducted in wells with completed depths of 300 feet bgs or less.

Sections in the Eastside Sub-basin with the highest total DCPA use from 2000 to 2010 are listed in Table 4 and displayed on Figure 2. The regional direction of groundwater flow in the Eastside Sub-basin is northwest along the valley axis towards the groundwater depression east of Salinas. For this study, sampling should be conducted in the shallowest wells located within or northwest of the high use sections in the Eastside Sub-basin identified in Table 4 and displayed on Figure 2.

One well with a confirmed detection of TPA is located in the Eastside Sub-basin (Figure 2). Re-sampling of that well will also be attempted in this study.

Forebay Sub-basin

The Forebay Sub-basin (Figure 2) is conceptualized as an unconfined to semi-confined aquifer. Vertical recharge in the Forebay Sub-basin is from irrigation return flows, rainfall, and seepage from the Salinas River. Horizontal recharge into the Forebay Sub-basin occurs from the upgradient Upper Valley Sub-basin and horizontal discharge occurs from the Forebay Sub-basin into the downgradient Pressure and Eastside sub-basins. Wells in the Forebay Sub-basin generally tend to be shallower (

downgradient Forebay Sub-basin (CDWR, 2004d). During the 2014 WY, the average DGW for nine monitoring wells in the Upper Valley Sub-basin ranged from about 46 feet bgs in February 2014 to 55 feet bgs in September 2014 (MCWRA, 2015). The average DGW in the Upper Valley Aquifer in November 2014 was about 58 feet bgs compared to about 46 feet bgs in November 2013. For this study, sampling in the Upper Valley Sub-basin should be conducted in wells with completed depths of 200 feet bgs or less.

Sections in the Upper Valley Sub-basin with the highest total DCPA use from 2000 to 2010 are listed in Table 4 and displayed on Figure 2. In general, total DCPA use from 2000 to 2010 in the Upper Valley Sub-basin between King City and the boundary with the downgradient Forebay Sub-basin is low to moderate and southeast of King City is low. For this study, sampling should be conducted in the shallowest wells located within or northwest of the high use sections in the Upper Valley Sub-basin identified in Table 4 and displayed on Figure 2.

No wells with previous confirmed detections of TPA are located in the Upper Valley Sub-basin for re-sampling.

VII. SAMPLING AND ANALYTICAL METHODS

Wells for sampling will be chosen in the areas described in the previous section following the guidelines described in the standard operating procedure (SOP) Number FSWA006.02 (Nordmark and Wong, 2013). Domestic wells are preferred for sampling since they tend to be shallower than municipal and agricultural wells and are more accessible. Samples will be collected from the wells using the methods described in SOP Number FSWA001.01 (Nordmark and Herrig, 2011). Quality assurance samples will be collected in the field following the guidelines described in SOP QAQC001.00 (Segawa, 1995).

Chemical analysis will be performed by the CDFA Center for Analytical Chemistry. CDFA will analyze for DCPA, MTP, and TPA using method EMON-SM-05-040 (CDFA, 2016). The method detection limits for DCPA, MTP, and TPA are 0.00629, 0.0155, and 0.0313 g/L, respectively (Table 5). The DPR reporting limit for all three chemicals is 0.05 g/L (Table 5). Analytical laboratory quality control will be conducted following the guidelines described in SOP QAQC001.00 (Segawa, 1995).

VIII. DATA ANALYSIS

Results obtained from the CDFA Center for Analytical Chemistry will be used to assess current levels of DCPA, MTP, and TPA in the sampled aquifers in the Salinas Valley in order to inform the Detection Response Process. A report of the results will be prepared. A letter report describing the results will be provided to participating property owners.

http:QAQC001.00http:QAQC001.00http:FSWA001.01http:FSWA006.02

IX. TIMETABLE

January through June 2017: Conduct sampling August 2017: Obtain and review analytical results from CDFA laboratory September 2017: Review laboratory results and determine if additional sampling in other counties is necessary.

December 2017: Prepare report of findings. Communication

o Provide notice to the County Agricultural Commissioner, DPR Enforcement Branch Regional Office, and the local Farm Bureau two weeks prior to initiating monitoring in a county. Additional notice will be provided if there is a six-month lapse in monitoring within a county.

o Provide results to property owners within 30 days of receipt. o Provide results to state and local agencies when sampling is concluded and results have been reviewed and approved by the project team.

X. BUDGET

Budget Component Units Expense per Unit Total Component Cost Primary sample analysis

50 $840 $42,000

Backup sample analysis

25 $840 $21,000

Control sample analysis

25 $840 $21,000

Travel 45 $130 $5,850 Person Years 1 $100,000 $100,000 Total $189,850

IX. References

CDFA. 1992. Report EH 92-01: Survey of Chlorthal-Dimethyl Residues in Well Water of Seven California Counties. Available at: http://www.cdpr.ca.gov/docs/emon/pubs/ehapreps/eh9201.pdf (verified June 30, 2015) California Department of Pesticide Regulation, Sacramento, California.

CDFA. 2016. EMON-SM-05-040. Analysis of Dacthal, Dacthal Monoacid, and Dacthal Diacid in Well Water using Gas Chromatography/MSD. California Department of Pesticide Regulation, Sacramento, California.

CDPR. 1991. Memorandum from Larry Nelson to Ron Oshima: Toxicological significance of a degradation product of Dacthal (chlorthal-dimethyl). Dated: October 11, 1991. California Department of Pesticide Regulation, Sacramento, California.

CDPR. 1992. Memorandum to John Sanders from Kean Goh: Z060: Determination whether residues of a degradation product of chlorthal-dimethyl pose a threat to public health, and whether residues of the active ingredient, chlorthal-dimethyl, were also present in ground water in Los Angeles County. Dated: August 28, 1992. California Department of Pesticide Regulation, Sacramento, California.

CDPR. 2012. Memorandum from Jay Schreider to Lisa Ross: Toxicological Significance of Degradation Product of Dacthal. Dated: January 31, 2012. California Department of Pesticide Regulation, Sacramento, California.

CDPR. 2015a. Pesticide Use Reporting. Available at: http://www.cdpr.ca.gov/docs/pur/purmain.htm (verified June 30, 2015) California Department of Pesticide Regulation, Sacramento, California.

CDPR. 2015b. Well Inventory Database. Available at: http://www.cdpr.ca.gov/docs/emon/grndwtr/wellinv/wirmain.htm (verified June 30, 2015) California Department of Pesticide Regulation, Sacramento, California.

CDWR. 2004a. Salinas Valley Groundwater Basin, 180/400 Foot Aquifer Subbasin. Californias Groundwater Bulletin 118.

CDWR. 2004b. Salinas Valley Groundwater Basin, Eastside Aquifer Subbasin. Californias Groundwater Bulletin 118.

CDWR. 2004c. Salinas Valley Groundwater Basin, Forebay Aquifer Subbasin. Californias Groundwater Bulletin 118.

CDWR. 2004d. Salinas Valley Groundwater Basin, Upper Valley Aquifer Subbasin. Californias Groundwater Bulletin 118.

http://www.cdpr.ca.gov/docs/emon/pubs/ehapreps/eh9201.pdfhttp://www.cdpr.ca.gov/docs/pur/purmain.htmhttp://www.cdpr.ca.gov/docs/pur/purmain.htmhttp://www.cdpr.ca.gov/docs/emon/grndwtr/wellinv/wirmain.htm

Fogg, G.E., LaBolle, E.M., and G.S. Weissmann, 1999. Groundwater Vulnerability Assessment: Hydrogeologic Perspective and Example from Salinas Valley, California. In book: Application of GIS, Remote Sensing, Geostatistical, and Solute Transport Modeling to the Assessment of Non-point Source Pollution in the Vadose Zone, AGU Monograph Series 108, Publisher: AGU, pp.45-61

MCWRA, 2015. Monterey County Water Resources Agency Groundwater Level Monitoring Program. Available at: http://www.mcwra.co.monterey.ca.us/groundwater_level_monitoring/groundwater_level _monitoring_overview.php (verified June 30, 2015)

Nordmark, C. and J. M. Herrig, 2011. SOP FSWA001.02. Obtaining and Preserving Well Water Samples. Available at: http://www.cdpr.ca.gov/docs/emon/pubs/sops/fswa00102.pdf (verified June 30, 2015) California Department of Pesticide Regulation, Sacramento, California.

Nordmark, C. and M. Wong, 2013. SOP FSWA006.02. Planning, Conducting, and Documenting Small-Scale Ground Water Monitoring Studies. Available at: http://www.cdpr.ca.gov/docs/emon/pubs/sops/fswa00602.pdf (verified July 13, 2015) California Department of Pesticide Regulation, Sacramento, California.

Segawa, R. 1995. SOP QAQC001.00. Chemistry Laboratory Quality Control. Available at: http://www.cdpr.ca.gov/docs/emon/pubs/sops/qaqc001.pdf (verified June 30, 2015) California Department of Pesticide Regulation, Sacramento, California.

USEPA. 2008. Regulatory Determinations Support document for Selected Contaminants from the Second Drinking Water Contaminant Candidate list (CCL 2), Chapter 4: DCPA Mono- and Di-Acid Degradates. EPA Report 815-R-08-012.

http://www.cdpr.ca.gov/docs/emon/pubs/sops/fswa00102.pdfhttp://www.cdpr.ca.gov/docs/emon/pubs/sops/fswa00602.pdfhttp://www.cdpr.ca.gov/docs/emon/pubs/sops/qaqc001.pdfhttp:QAQC001.00http:FSWA006.02http:FSWA001.02http://www.mcwra.co.monterey.ca.us/groundwater_level_monitoring/groundwater_level

Table 1. Annual DCPA use (pounds) by county from 2000 to 2010 (CDPR, 2015a).

County 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Total Average Monterey 77,704 78,985 74,270 77,743 94,815 73,347 75,683 77,692 74,900 66,731 58,921 830,790 75,526 Imperial 17,056 38,811 48,616 60,166 53,111 64,055 58,885 54,303 36,743 27,709 43,584 503,039 45,731 Ventura 8,267 12,358 22,475 27,094 16,828 15,139 9,185 5,000 6,294 6,629 8,578 137,847 12,532 Fresno 2,820 1,660 7,763 2,072 2,154 23,328 29,252 7,000 3,731 20,999 10,978 111,757 10,160 Riverside 9,610 9,160 8,225 11,586 9,852 9,308 24,279 19,433 16,039 5,523 2,225 125,239 11,385

Santa Barbara 4,888 11,658 11,132 10,312 16,013 12,396 10,464 7,401 8,607 4,799 4,497 102,167 9,288 San Luis Obispo 1,187 6,424 6,510 10,273 7,154 6,977 8,173 5,958 3,902 4,255 5,092 65,904 5,991 San Benito 5,540 5,254 7,011 7,890 7,341 6,794 8,298 5,046 5,059 3,463 5,699 67,394 6,127

San Bernardino 824 3,325 8,259 9,704 3,774 3,920 4,984 6,120 5,704 8,151 5,036 59,802 5,437 Kern 2,400 1,920 732 756 324 1,853 4,612 7,871 7,084 4,920 3,681 36,153 3,287

Santa Clara 148 1,498 3,012 2,355 4,667 5,191 3,543 4,358 3,083 1,511 1,549 30,915 2,810 Stanislaus 3 521 738 569 1,578 3,886 1,827 2,215 1,548 3,512 1,036 17,431 1,585 San Joaquin 0 180 374 1,730 159 889 1,488 1,726 2,145 768 951 10,409 946 Los Angeles 948 1,440 1,157 184 137 44 1,023 144 9 40 25 5,150 468

Tulare 221 74 209 1,711 953 703 278 4,148 593 Merced 27 12 659 405 843 1,947 389

Santa Cruz 410 182 366 336 372 110 241 179 78 5 11 2,290 208 Shasta 420 626 407 585 2,037 509 Yolo 64 104 84 317 209 91 133 108 117 330 55 1,611 146

Siskiyou 330 330 330 Madera 223 3 1,013 392 1,630 408 Colusa 1,310 34 133 8 1,485 371 Kings 166 647 544 1,357 452 Modoc 0 0

Sacramento 24 390 24 60 25 523 105 Glenn 420 420 420 Sonoma 18 15 23 23 26 34 38 38 36 249 28 San Diego 23 21 9 38 91 23 Sutter 147 147 147

Contra Costa 0 35 16 15 23 89 18 San Mateo 35 12 16 11 11 6 5 95 14 Orange 3 1 0 12 1 2 1 20 3 Solano 18 18 18 Butte 18 18 18 Placer 0 1 2 2 2 1 8 1

Calaveras 6 1 7 3

Table 2. Total DCPA use (pounds) by crop from 2000 to 2010 (CDPR, 2015a).

Crop DCPA Use (pounds)

BROCCOLI 967,953 ONION (DRY, SPANISH, WHITE, YELLOW, RED, ETC.) 469,723 CAULIFLOWER 152,078 CABBAGE 89,986 BROCCOLI RAAB (RAPA, ITALIAN TURNIP, RAPINI) 69,877 CHINESE CABBAGE (NAPPA, WON BOK, CELERY CABBAGE) 56,554 ONIONS (GREEN) 51,744 BOK CHOY (WONG BOK) 41,187 RADISH 38,166 NOUTDR GRWN CUT FLWRS OR GREENS 32,235 ORNAMENTAL TURF (ALL OR UNSPEC) 32,197 PEPPERS (FRUITING VEGETABLE), (BELL,CHILI, ETC.) 22,273 GAI LON 18,465 KALE 13,999 TURNIP, GENERAL 8,177 MUSTARD, GENERAL 7,073 COLLARDS 5,693 CHINESE GREENS, CHINESE LEAFY VEGETABLES 5,461 GARLIC 5,264 LEEK 4,726 RAPE (ALL OR UNSPEC) 3,613 BRUSSELS SPROUTS 3,105 NOUTDR CONTAINER/FLD GRWN PLANTS 3,087 KOHLRABI 2,553 LEAFY VEGETABLES (ALL OR UNSPEC) 1,811 PEPPERS (CHILI TYPE) (FLAVORING AND SPICE CROP) 1,551 TOMATOES, FOR PROCESSING/CANNING 1,307 NOUTDR GRWN TRNSPLNT/PRPGTV MTRL 1,160 GAI CHOY (LOOSE LEAF) 1,004 WATERMELONS 998 CANTALOUPE 942 BEANS, SUCCULENT (OTHER THAN LIMA) 830 CHINESE RADISH/DAIKON (LOBOK, JAPANESE RADISH) 599 LETTUCE, HEAD (ALL OR UNSPEC) 498 STRAWBERRY (ALL OR UNSPEC) 496 RIGHTS OF WAY 492 UNCULTIVATED AGRICULTURAL AREAS (ALL OR UNSPEC) 483 EGGPLANT (ORIENTAL EGGPLANT) 432 SOIL APPLICATION, PREPLANTOUTDOOR (SEEDBEDS,ETC.) 425 LANDSCAPE MAINTENANCE 416 MELONS 364 CUCUMBER (PICKLING, CHINESE, ETC.) 351 SQUASH (ALL OR UNSPEC) 326 SHALLOT, ONIONS (SHALLOT) 321 SQUASH (SUMMER) 300 CHERRY 300 LETTUCE, LEAF (ALL OR UNSPEC) 257 NGRNHS GRWN PLANTS IN CONTAINERS 227 COTTON, GENERAL 166 OATS, GENERAL 158 RESEARCH COMMODITY 152 COLE CROPS (ALL OR UNSPEC) 138 GARBANZOS (INCLUDING CHICK PEAS) 102 TOMATO 91 NGRNHS GRWN CUT FLWRS OR GREENS 84 PIMENTO (PIMIENTO TYPE PEPPER) 66 BEANS (ALL OR UNSPEC) 56 PEAS, GENERAL 48 UNCULTIVATED NONAG AREAS (ALL OR UNSPEC) 44 VERTEBRATE PEST CONTROL 32 BEETS, GENERAL 32 YAMS, TRUE (LISBON & WHITE YAM) 30 GRAPES, WINE 30 CILANTRO (CHINESE PARSLEY, CORIANDER LEAVES) 21 STRUCTURAL PEST CONTROL 18 SPINACH 15 FLAVORING AND SPICE CROPS (ALL OR UNSPEC) 8 CHIVE (SIBERICUM) 8 DILL 5 MINT (ALL OR UNSPEC) 5 PECAN 4 CHICORY (ALL OR UNSPEC) 3 CORN, HUMAN CONSUMPTION 3 VEGETABLES (ALL OR UNSPEC) 1 NGRNHS GRWN TRNSPLNT/PRPGTV MTRL 1 ENDIVE (ESCAROLE) 1

Table 3. Summary of previous confirmed detections of TPA by CDPR (CDPR, 2015b).

County Sampling Date Range

Reporting Year

Unique Wells

Sampled

Confirmed TPA

Detections Los Angeles 5/9/1990 1991 1 1 Santa Clara 5/9/1990 1991 1 1 Los Angeles 7/10/1990 1991 5 2 Santa Clara 7/11/19907/12/1990 1991 7 5 Monterey 8/6/19908/8/1990 1991 15 5 Fresno 8/13/19908/23/1990 1991 15 2 San Luis Obispo 8/14/1990 1991 3 1 Santa Barbara 8/14/19908/16/1990 1991 7 4 Kern 8/21/19908/22/1990 1991 10 5 Los Angeles 8/21/1990 1991 4 0 Tulare 8/21/19908/22/1990 1991 6 0 Monterey 7/8/19917/11/1991 1992 2 0 San Luis Obispo 5/19/19925/20/1992 1993 6 1 Colusa 4/19/19944/28/1994 1994 8 0 Fresno 4/19/19946/9/1994 1995 147 2 Tulare 5/11/19946/8/1994 1995 31 0 Madera 7/16/19961/16/1997 1997 6 3

Total 274 32

Table 4. Total DCPA use (pounds) from 2000 to 2010 by townshiprangesection number in Monterey County (CDPR, 2015a)

TownshipRangeSection DCPA Use (lbs)

Subbasin Location

27M16S04E10 18,569 Pressure 27M16S05E06 15,612 Eastside 27M18S06E02 15,551 Forebay 27M15S04E15 15,124 Eastside 27M15S04E32 14,698 Pressure 27M15S04E26 11,771 Eastside 27M19S07E17 10,772 Forebay 27M16S04E14 10,001 Pressure 27M18S06E33 9,605 Forebay 27M17S05E26 9,554 Forebay 27M19S07E22 9,512 Upper Valley 27M17S06E31 9,465 Forebay 27M19S07E13 9,458 Upper Valley 27M15S03E15 9,315 Pressure 27M16S05E28 9,233 Eastside 27M18S06E27 8,924 Forebay 27M16S05E21 8,530 Eastside 27M14S03E31 8,515 Pressure 27M17S05E36 8,385 Forebay 27M15S04E36 8,375 Eastside 27M15S04E21 8,110 Eastside 27M15S04E20 8,002 Eastside 27M15S03E10 7,813 Pressure 27M19S07E12 7,404 Upper Valley 27M18S06E04 7,382 Forebay 27M18S07E19 7,361 Forebay 27M18S06E23 7,025 Forebay 27M14S03E19 7,022 Pressure 27M17S05E09 6,997 Forebay 27M15S04E28 6,899 Eastside 27M21S09E24 6,640 Upper Valley 27M19S07E03 6,406 Forebay 27M19S07E04 6,285 Forebay 27M19S07E25 6,264 Upper Valley 27M15S04E08 6,165 Eastside 27M19S07E10 6,097 Forebay 27M16S05E32 6,015 Pressure

Table 5. Method detection and reporting limits for DCPA, MTP, and TPA (CDFA, 2016).

Chemical Method Detection Limit (ug/L)

Reporting Limit (ug/L)

DCPA 0.00629 0.05 MTP 0.0155 0.05 TPA 0.0313 0.05

Figure 1. Annual DCPA use in California from 1990 to 2014 (CDPR, 2015a).

0

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San Benito County

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E

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M14S07E M14S09E

M16S09E M16S11

Figure 2. Total DCPA use (lbs per section) from 2000 to 2010 and locations of confirmed and unconfirmed detections of TPA in Salinas Valley area of Monterey County(CDPR, 2015a; 2015b).

!A

!A

!A

!A!A

!A

!A

!A

!A

!A

!A

!A

!A!A !A!A!A

!A

!A!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

Chualar Spence

Monterey County

Salinas

Gonzales

Soledad

Greenfield

King City

Eastside Sub-basin

Pressure Sub-basin

Forebay Sub-basin

Upper Valley Sub-basin

M17S10E

M18S05E

M17S05EM17S02E

M15S0

M21S06E

M18S04E

M12S05E

M14S0M14S03E

M18S03E

M17S06M17S03E

M15S03E

M18S10E

M22S06E

M15S05E

M12S03E

M15S04E

M13S05EM13S04E

M21S09E

M12S0

M18S09E

M21S08E

M13S03E

M19S08E

M20S04E

M16S05E

M19S06E

M22S09E

M20S10E

M15S02E

M12S02E

M17S04E

M21S10E

M14S02E

M13S0

M20S09E

M19S10EM19S09E

M18S07E

M16S04E

M21S04E

M12S04E

M22S05E M22S08E

M20S08E

M17S09E

M16S06

M22S07E

M19S07E

M22S10E

M18S08EM18S06E

M19S05E

M17S08E

M20S05E

M18S02E

M21S07E

M19S03E

M13S02E

M21S05E

M19S04E

M20S03E

M19S02E

M22S04E

M23S05E M23S06E M23S07E M23S08E

M21S03E

M23S09E M23S10E

M20S02E

M11S10EM11S09EM11S08EM11S07EM11S06EM11S05EM11S04EM11S03EM11S02E

M14S05E

M14S04E

M16S03E

M20S07E

M16S02E

M20S06E

M22S11E

M21S11E

M20S11E

M19S11E

M18S11E

M17S11E

E

M23S11E

M11S01E

M23S04E

M22S03E

M13S01E

Monterey County !A Confirmed Detections of TPA !A Unconfirmed Detections of TPA

Sub-basins of Salinas Valley Groundwater BasinDCPA Use (2000 to 2010)(lbs per section)

20,000

S14S10E

S16S11ES16S10E

S15S11E

S14S11E

S17S10E

S15S10E

S17S11E

S16S09E

S15S09E

17S09E

14S09E

Figure 3. Total DCPA use (lbs per section) from 2000 to 2010 and locations of confirmed detections of TPA in Imperial County (CDPR, 2015a).

Brawley

El Centro

Salton Sea

Imperial County

Imperial

Calexico

SALTONS

S13S13E S13S15E S13S14E S13S16E

S13S10E

S10S16E

S11S16E

S16S12E

S12S16E

S10S14E S10S15E

S11S10E

S09S16E S09S15E

S13S11E

S09S14E

S11S15E S11S14E

S09S13E

S13S12E

S12S15E

S15S12E

S12S14E

S16S15E

S14S12E

S12S10E

S16S14E S16S16E

S15S14E

S16S13E

S15S13E

S14S15E

S15S15E S15S16E

S14S13E S14S16E S14S14E

S12S13E S12S11E

S09S12E

S17S12E

S08S12E S08S13E

S13S17E

S08S11E S08S14E

S10S10E

S17S13E

S09S17E

S08S15E

S10S17E

S08S16E

S14S17E

S11S17E

S10S13E

S17S14E

S15S17E

S12S17E

S16S17E

S12S09E

S08S17E

S17S15E

S11S09E S11S13E

S17S16E

S12S12E

S09S11E

S17S17E

S10S09E

S

S

S13S09E

S11S11E

S09S09E

S08S10E

S09S10E

S18S09E

S10S11E

S10S12E

Imperial CountyDCPA Use (2000 to 2010)(lbs per section)

20,000

S02S24W

Figure 4. Total DCPA use (lbs per section) from 2000 to 2010 and locations of confirmed detections of TPA in Ventura County (CDPR, 2015a).

Santa Paula

Ventura

Oxnard Camarillo

Ventura County S05N22W S05N23W S05N20W S05N21W S05N19W

S02N22W

S05N18W S05N24W

S04N23W S04N19W S04N22W

S03N22W

S04N20W

S03N20W

S01N20W

S03N19W

S01S18W

S04N18W

S03N23W

S01N19W

S02N19W

S01N18W

S03N21W

S02N18W S02N20W

S03N18W

S04N24W S04N21W

S01S19W

S01N21W

S02N21W

S05N17W

S01N22W

S04N17W

S01S20W

S03N17W

S02N17W

S01N17W

S01S17W

S06N23W

S03N24W

S06N22W S06N18W S06N21W S06N20W S06N19W S06N24W

S05N25W

S04N25W

S06N17W

S02N23W

S06N25W

S01S21W

S02S18W S02S19W

S03N25W

S01N23W

S01S22W

S02S17W

S02N24W

Ventura CountyDCPA Use (2000 to 2010)(lbs per section)

20,000

!A!A!A

M21S21EM22S21E

19E M20S22E

M19S21E

19E M18S22E

M23S21E

M18S21E

19E

M20S21E

M21S20E

M20S20E

M19S22E

M23S22E

M21S22E

M18S20E

M22S22E

9E

M23S20E9E

M22S20E

M19S20E

9E

M23S23E

M21S23E

M22S23E

M18S23E

M20S23

M19S23

M24S22EM24S21E9E M24S20E M24S23E

Figure 5. Total DCPA use (lbs per section) from 2000 to 2010 and locations of confirmed detections of TPA in Fresno County (CDPR, 2015a; 2015b).

!A !A

!A

!A

San Joaquin

Mendota Fresno

Huron

Fresno County

M19S14E

M20S14E

M23S16E

M22S16E

M20S17E

M17S12E M17S17E

M19S17E

M18S17E

M11S21E M11S17E

M18S12E

M21S15E

M19S15E

M14S16E

M22S13E

M11S20E M11S12E

M15S16E

M20S18E

M21S14E

M11S18E M11S22E

M10S22E

M12S12E

M11S14E M11S15E

M16S16E

M22S14E

M18S15E

M11S13E M11S19E

M17S15E

M20S

M17S21E

M11S16E

M10S14E

M15S15E

M13S16E

M10S17E

M23S14E

M18S

M16S15E

M19S18E

M17S14E

M19S

M23S15E

M20S12E

M13S15E

M14S15E

M18S18E

M13S14E

M14S17E

M17S18E

M12S17E

M14S14E

M12S15E

M16S17E M16S21E M16S22E

M17S22E

M21S12E

M16S20E

M15S17E M15S19E M15S21E

M13S17E

M12S13E

M23S18E

M21S18E

M13S18E

M14S20E

M15S20E

M10S15E

M13S13E

M16S19E

M21S1

M15S13E

M12S14E

M15S14E

M20S15E

M10S18E

M12S16E

M17S19E

M21S16E

M10S20E

M22S18E

M13S22E

M16S18E

M14S21E

M15S18E

M10S16E

M23S1 M23S13E

M18S14E

M15S22E

M14S19E

M10S13E

M13S21E

M16S14E

M21S17E

M12S21E M12S22E M12S20E

M20S16E

M14S18E

M12S18E

M13S19E

M10S19E

M13S20E

M16S13E

M13S12E

M14S22E

M22S1

M14S13E

M23S17E

M17S20E

M10S12E

M22S17E

M12S19E

M10S21E

M23S12E

M14S12E

M19S16E

M18S16E

M17S16E

M22S15E

M15S12E

M20S13E

M21S13E

M22S12E

M16S12E

M19S13E

M17S13E

M18S13E

M09S18E M09S17E M09S20E M09S19E M09S16E M09S22E M09S14E M09S21E M09S15E

M19S12E

M09S13E M09S12E

M17S23E

E

E

M13S23E

M15S23E

M14S23E

M16S23E

M10S23E

M12S23E

M11S23E

M09S23E M09S11E

M24S12E M24S16E M24S13E M24S14E M24S15E M24S17E M24S18E M24S1

M10S11E

M11S11E

M12S11E

M17S11E

M14S11E

M15S11E

M13S11E

M16S11E

M18S11E

Fresno County !A Confirmed Detections of TPA DCPA Use (2000 to 2010)

(lbs per section)20,000

ea

S09S03E

S11S01E S11S02E

S07S03E

S12S01E S12S02E S12S03E

S0

S10S02E

S07S01E S07S02E

S10S01E

S08S01E

S11S03E01W

S09S01E

S08S02E

S09S02E

S08S03E

01W

S

S0

1W

S

S10S03E

1W

1W

W S07

S13S03ES13S02ES13S01E01W

Figure 6. Total DCPA use (lbs per section) from 2000 to 2010 and locations of confirmed detections of TPA in Riverside County (CDPR, 2015a).

Salton S

Riverside County

Coachella

Temecula

Hemet

Rancho Mirage

San Bernardino County

San Diego County SALTONS

S11S05E

S12S07E

S11S08E

S12S06E

S10S05E

S07S06E

S12S05E

S09S07E S09S05E

S11S09E

S03S02E S03S01E

S08S06E

S10S08E

S03S08E

S02S08E

S09S08E

S11S07E S11S06E

S01S05E

S12S04E

S01S08E

S03S03E

S06S02E

S10S09E

S02N04E

S02S09E

9S04E

S04S07E

S05S07E

S02S07E

S05S06E

S01S06E

S04S06E

S02N05E

S05S05E

S09S06E

S06S07E

S04S04E

S07S02W

S06S03E

S05S08E

S11S02W

S01S09E

S03S04E

S05S03E

S03S06E

S06S08E

S12S09E

S04S05E

S03S05E

S01N05E

S02S02E

S12S08E

S05S01E

S03S07E

S04S08E

S02S01E

S06S06E

S07S08E

S04S09E

S01S03E

S03S09E

S01N09E

S06S05E S06S09E

S07S07E

S02N06E S02N09E

S01N03E S01N02E

S01S02E

S01N08E S01N07E

S02S04E

S01N06E

S05S09E

S06S01E

S01S07E

S08S05E

S02S03E

S04S03E

S05S02E

S02N01E S02N07E

S02S05E

S10S07E

S02N02E

S11S

S01N01E

S02S06E

S02N08E S02N03E

S06S04E

S05S04E

S01S01E

S10S02W

S12S02W

S04S02E

S01S04E

S07S05E

S09S02W

S04S01E

S12S

S10S06E

S01N01W

10S04E

S08S07E

S04S02W

8S04E

S06S02W

S10S0

S08S08E

S02S01W

11S04E

S04S01W

S03S02W

S05S01W

S01N04E

S03S01W

S02N01W

S06S01W

S01S02W

S05S02W

S02S02W

S01S01W

S08S0

S07S09E

S09S0

S01N02W

S02N02W

S07S01 S04E

S08S02W

S13S09E S13S07E S13S08E

S09S09E

S02N10E

S01N10E

S13S06E S13S05E

S01S10E

S13S04E S13S S13S02W

S03N02W S03N01W S03N01E S03N02E S03N03E

S13S03W

S03N04E S03N05E

S02S10E

S12S03W

S11S03W

S04S10E

S03S10E

S05S10E

S10S03W

S09S03W

S06S10E

S07S03W

S08S03W

S07S10E

S08S09E

S03N06E S03N07E S03N08E

S09S10E

S03N09E

Riverside CountyDCPA Use (2000 to 2010)(lbs per section)

20,000

S

Figure 7. Total DCPA use (lbs per section) from 2000 to 2010 and locations of confirmed detections of TPA in San Luis Obispo and Santa Barbara counties (CDPR, 2015a; 2015b).

!A

!A

!A

!A!A !A

San Luis Obispo County

Santa Barbara County

Lompoc

Arroyo Grande

San Luis Obispo

Santa Maria

M30S15E M30S16E M30S14E

M32S16E

M30S11E M30S12E

M31S13E M31S17E

M30S17E M30S13E

M32S13E

M31S12E M31S16E

S11N35W

S08N35W

S10N34W

S11N34W S11N33W

M32S14E

S08N34W

M32S15E

S09N34W S09N33W

S10N35W S10N33W

S08N33W

S07N34W S07N33W

S06N31W

M31S14E

S09N35W

S11N32W

S06N34W S06N33W

S09N31W

M31S11E

S07N31W

S09N32W

S11N31W

S07N32W

S10N31W

M31S15E

S08N31W

S06N32W

M29S15E

S06N35W

S08N32W

M32S17E

S07N35W

S10N32W

M29S17E M29S16E M29S14E M29S11E M29S12E M29S13E

S05N34W S05N33W S05N31W S05N32W

M32S18E

10N36W

S12N32W S12N31W S12N33W

M31S10E

M32S12E

S12N34W S12N35W

S05N35W

M31S18E

M30S18E

S11N30W

S09N30W

M29S18E

S10N30W

S07N30W

S08N30W

S06N30W

M30S10E

S06N36W

S11N36W

M29S10E

S12N30W

S08N36W

S09N36W

M32S11E

S12N36W

S07N36W

San Luis Obispo CountySanta Barbara County !A Confirmed Detections of TPA DCPA Use (2000 to 2010)

(lbs per section)20,000

Figure 8. Locations of previous confirmed detections of TPA in California from samplingconducted between 1990 and 1997 (CDPR, 2015b).

!H!H!H

!H

!H!H!H !H

!H

!H!H!H!H

!H!H!H

!H !H!H!H

!H

!H !H

!H

!H!H!H

!H!H!H!H!H

Kern

InyoFresno

Tulare

Mono

Monterey

Los Angeles

MaderaMerced

Kings

Ventura

Tuolumne

San Luis Obispo

Santa Barbara

MariposaStanislaus

Solano

Orange

Calaveras Napa

Alameda

Alpine

San Bernardino

San Benito

San Joaquin

Santa Clara

Amador Yolo Sacramento

Contra Costa

San Diego

San Mateo

Santa Cruz

Marin

El Dorado

San Francisco

!H Confirmed Detections of TPA County Boundaries

Tables_Figures_finalized.pdfTables_finalTable1_finalTable2_finalTable3_finalTable4_finalTable5

Figures_1_8_finalFig1_CA_DCPA_use_finalFig2_Monterey_DCPA_use_finalFig3_Imperial_DCPA_use_finalFig4_Ventura_DCPA_use_finalFig5_Fresno_DCPA_use_finalFig6_Riverside_DCPA_use_finalFig7_SLO_SB_DCPA_use_finalFig8_confirmed_detects_final