Air Quality Water & California Rice Pesticides Rice Straw Wildlife

Environmental & Conservation Balance Sheet for The California Rice Industry

Chapter 3: Water Quality in Relation to Rice Farming

The purpose of this chapter is to document the water quality issues associated with rice production in California. The background material for this chapter was the white paper Water Use for Rice Farming in California (CH2M HILL, 1992). New information pertaining to recent initiatives, regulations, monitoring results, and other water quality issues are also reviewed and documented in this chapter.

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Rice Farming's Influence on Water Quality

Because rice is farmed in standing water, the importance of good farming practice to water quality is evident. However, water quality problems associated with other crops and locales, such as soil erosion and sediment transport, saline drainage waters, and high concentrations of trace elements (e.g., selenium, molybdenum, arsenic) in subsurface drainage, are typically not a problem with rice farming. The generally slow rate of flow through rice fields and the controlled rate of water release tend to avoid significant soil erosion. Also, because much of the water used to irrigate rice fields initially has a low salt concentration, and there is little possibility for salt accumulation in a continuously flooded system, salt concentrations in return flows are usually relatively low. Trace element concentrations in return flows are also low for the same reasons, and perhaps because Sacramento Valley basin soils do not contain elevated concentrations of trace elements.

The major potential water quality challenge for rice farmers is the need to achieve acceptably low pesticide concentrations in return flow, which is a problem shared with other sectors of agriculture. Therefore, this chapter discusses the following:

• Pest management by rice farmers, including water management to achieve water quality goals
• Criteria and performance goal development
• Water quality management and compliance with performance goals

Pest Management by Rice Farmers

Virtually all agricultural crops require the farmer to control weeds, diseases, and insects, as well as other animal pests. Rice is no exception. When alternative methods are available, farmers choose among control methods according to available information, crop loss potential, regulatory controls, level of effectiveness, cost, and environmental impact. The effectiveness of chemical methods of pest control in rice allow for profitable production with the help of relatively few registered pesticides.

Insecticides and herbicides are commonly applied at some phase of rice production to manage pests. The use of these chemicals is intended to control damaging pests and competing plant species. However, if not properly managed, they can cause deleterious effects to nontarget animals and plants and jeopardize human health. For these reasons, environmental regulatory agencies such as the United States Environmental Protection Agency (U.S. EPA) and the California State Water Resources Control Board (SWRCB) through the Central Valley Regional Water Quality Control Board (RWQCB) formulate water quality criteria, river basin plans, and goals for the protection of aquatic life and human health. The California Department of Pesticide Regulation (DPR) is the lead agency for pesticide regulation in California. DPR is required by California law to register and regulate the use of pesticides and protect public health and safety by providing environ mentally sound pest management. These criteria, standards, goals, and regulations govern pesticide use by the rice farmer so as to meet the dual goals of effective pest management and environmental integrity.

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Animal Pest Management

The primary animal pests of rice in California are tadpole shrimp, crayfish, rice water weevil, leaf miner, midges, army worms, and leafhoppers. Several chemicals can be applied to control these pests and minimize damage. Common insecticides used on specific-target rice pests in California and their regulatory status are presented in Table 3-1.

Table 3-1: Insecticides Used in Rice Cultivation in California

Chemical Name	Target Pest	Status
Carbofuran	Rice water weevil	Registered, restricted use
Malathion	Midges	Registered, restricted by label
Methyl parathion	Tadpole shrimp, midges	Registered, restricted use
Copper sulfate	Tadpole shrimp	Registered, restricted by label

Malathion and copper sulfate are the only fully registered insecticides with no special restrictions for California rice. The DPR has placed restrictions on the other commonly used insecticides. Restrictions may include holding time limits for discharge water, a permit from the County Agricultural Commissioner to possess or use the pesticide, and limitation of the land area that can be treated. Carbofuran's registration has been extended through the 1996 growing season; however, it will not be renewed for 1997. Growers will nevertheless be able to use available stocks of carbofuran during 1997.

The most intense period of insect and invertebrate pest management is the period between sowing the rice seed and the stand establishment. Carbofuran, used for control of rice water weevil, is applied prior to field flooding or within the first 6 weeks of stand establishment. Other insecticides (malathion, methyl parathion, and copper sulfate) for controlling tadpole shrimp and rice seed midges are also applied in the initial stages of stand development to avoid economic losses of the crop.

Weed Pest Management

The most widely practiced form of weed control is cultural, which does not involve herbicides. Flooding of rice fields is universal in California, and it is the most effective way to control many weeds. Tillage before rice planting can also be helpful. Timely planting and rapid establishment of rice plants at the proper spacing suppresses weeds by eliminating the space and light that weeds need to grow. California rice farmers are proficient at these techniques of controlling weeds, having perfected efficient methods for planting rice directly onto flooded fields. However, several aquatic weeds can still grow under continuously flooded conditions, so further efforts by the farmer are necessary.

At a somewhat greater cost, other nonchemical control measures are available. A small market for organically grown rice has supported the efforts of some farmers in developing these methods to a great extent. Crop rotation with fallow or nonflooded crops, such as corn or beans, is helpful in some instances because it provides time for some of the seeds shed by the previous seasons' aquatic weeds to die off. This can be expensive because most good rice soils are difficult to farm economically with other crops, and the farmer must own or lease equipment to farm the other crops. Maintaining a deeper flood on the field helps suppress weeds, but requires higher levees as well as additional management and water.

At a relatively lower cost, farmers can control weeds with a variety of selective herbicides (chemicals that, at a prescribed concentration, kill weeds but not rice). A number of effective chemicals have been used by rice farmers over the years. Some have been found to harm other crop plants (MCPA and propanil), or are too mobile in groundwater and surface water (bentazon), and some have been or are being removed from use. Corresponding restrictions for use have been imposed. To avoid conflict with sensitive crops, propanil and MCPA use has been geographically restricted. Bentazon use has been forbidden. Other herbicides are organic compounds that break down over time, do not have mobility or toxicity problems, and have associated management practices that have been developed to ensure that they do not pollute water supplies.

The management practices minimizing the deleterious effects of rice herbicides are based on the following general approach:

• Define acceptable concentrations for the protection of human health and aquatic wildlife resources.
• Reduce concentrations in waterways to levels at or below acceptable concentrations by applying herbicides at appropriate rates or allowing time for their breakdown within the rice field before any water is released into waterways.

Herbicides used in California rice production and their regulatory status are presented in Table 3-2. Triclorpyr is a new herbicide available for use in the 1996 growing season.

Herbicides are applied during various stages of the growth cycle of the rice plant. Molinate can be applied from preflooding through initial tillering (sprouting of multiple stems from each plant). Thiobencarb can be applied at post- emergence through initial tillering. MCPA is applied from tiller initiation through panicle initiation (Flint, et al., 1992).

Figure 3-1 indicates the evolution of water quality criteria and performance goals for molinate and thiobencarb from 1981 through 1995. As knowledge has been gained about the sensitivity of fish species, the California Department of Fish and Game (CDFG) has required lower maximum levels of molinate and thiobencarb in agricultural drains. Research on rice water and weed management, as well as rapid adoption of the new technologies by rice farmers, are aimed at meeting this challenge of protecting water quality. The rice farmers' success in this regard is discussed in the Water Quality Monitoring and Compliance with Performance Goals section.

Table 3-2: Herbicides Used in Rice Cultivation in California

Chemical Name	Target Pest	Status
Bensulfuron methyl	Broadleaf, sedges	Registered, restricted by label
Molinate	Grass weeds	Registered, restricted use
Thiobencarb	Broadleaf, sedges, grass weeds	Registered, restricted use
MCPA	Broadleaf, sedges	Registered, restricted use
2,4,D	Broadleaf, sedges	Registered, restricted use
Fenoxaprop	Broadleaf	Registered, restricted by label
Propanil	Broadleaf, sedges, grass	Registered, restricted use
Triclorpyr	Boadleaf	Registration under public notice

Bensulfuron methyl and fenoxaprop are currently the only fully registered herbicides without any special restrictions for California rice. However, weed resistance to bensulfuron methyl has developed, and this has reduced its usefullness in California rice production. Use of MCPA and 2,4,D is limited to certain areas because these chemicals can damage other types of crops.

The pesticides used in rice production are broken down by natural mechanisms. A principal mechanism is biodegradation. When rice fields are flooded, oxygen flow into the soil is greatly reduced. Below the surface half-inch of soil, microbes rapidly deplete oxygen and begin to seek other compounds for respiration, including sulfur, nitrogen, iron, and manganese. This layering creates a wide range of chemical and microbial conditions that are ideal for breaking down organic compounds like rice herbicides. The extent of destruction depends on how fast these conditions are created and how long they exist. Microbes work well at high water temperatures that are favored by relatively little inflow of fresh, cool irrigation water. Reducing or eliminating flow out of the rice field keeps herbicide in the field where microbes in the soil and the water can degrade it over time. Figure 3-2 shows that after 7 to 10 days, herbicide concentrations are reduced by 80 to 90 percent for all but MCPA. Nevertheless, MCPA levels in return flow have not been a problem.

Several methods have been developed to retain water on flooded fields to aid in herbicide breakdown. Chapter 2 describes the closed and conventional systems and presents a breakdown of the percentage of rice acreage using each system within the rice producing counties.

Prior to 1980, water retention by the closed or conventional systems was rare. Installation of recirculation systems for substantial acreage is an indication of the commitment of rice farmers' resources to water quality (see Chapter 2). For example, the increase in holding times for tailwaters containing molinate from 4 days (post-application) in 1983 to the current (1996) practice of 28 days and the encouragement of tailwater recycling practices have contributed to the reduction in molinate loadings to receiving waters in the Sacramento River Basin. A provision of the rice pesticide control program allows emergency releases of pesticide-treated tailwaters prior to the standard holding times (with authorization from the county agricultural commissioner). This program provision has resulted in concerns about the impacts of these releases on surface-water quality downstream of these discharges. A study conducted by the RWQCB in 1991 determined that only 0.8 percent of total rice acreage was granted emergency releases in 1991. However, the RWQCB calculated that these releases accounted for approximately 15 percent of the molinate measured at the Colusa Basin Drain. These findings resulted in restriction of emergency release authorizations unless no other options are available (RWQCB, 1992).

In 1992, the RWQCB requested that the DPR conduct a program to reduce the drift of rice pesticides during aerial application, which contributes to rice pesticides in surface waters adjacent to rice fields. The 1994 program has specific provisions for reducing the effects of aerial drift on water quality. These provisions are based on drift control measures outlined in Section 6460 of Title 3 of the California Code of Regulations, and include additional measures to prevent drift by increasing the average size of spray droplets. The provisions also prohibited application to sites immediately upwind of waterways and to all sites when wind speeds are greater than 5 miles per hour (DPR, 1994). Drift provisions for 1995 were the same as in 1994; however, special attention was given to prevent aerial deposition to sweat ditches during application. Aerial drift provisions for 1996 will remain the same (DPR, 1995).

Other 1992 RWQCB pesticide management recommendations requested DPR to incorporate the practice of sealing weir boxes and field drain structures with canvas to minimize leakage of rice field water during holding periods (RWQCB, 1992). These management recommendations should provide additional benefits in limiting pesticide concentrations in drains and ultimately in the Sacramento River. In 1994, pesticide users were required to prevent seepage of field water through the field's weir box by securing the box with plastic and mounding soil in front of each weir box (DPR, 1994). Field inspectors noted that the new 1994 provision requiring mounding of soil in front of each field's drain box was a valuable enforcement tool.

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Criteria and Performance Goal Development

Beginning in May 1980, and on a yearly basis through 1983, over 65,000 carp, catfish, black bass, and crappie died in rice field drain waters in the Sacramento Valley (Hill et al., 1991). At approximately the same time, monitoring studies found that thiobencarb concentrations as low as 1 g/L resulted in increases in water taste complaints from people whose drinking water originated in the Sacramento River downstream of the rice field agricultural drains.

As a result of the fish loss events in the early 1980s, CDFG conducted investigations that indicated that the fish losses resulted from molinate poisoning (SWRCB, 1990). By implementation of increased holding times for irrigation waters containing molinate, no additional fish losses have been documented since June 1983.

Monitoring studies in the early 1980s by the RWQCB determined that molinate, carbofuran, malathion, and methyl parathion were present in rice field drains in concentrations that could cause a threat to aquatic life. As a result of the fish losses and the monitoring results through the early 1980s, the DPR initiated the Rice Pesticide Control Program in 1984 to manage and regulate the discharge of pesticides from rice fields.

Findings by CDFG and RWQCB further moved the SWRCB to contract for scientific studies to develop a toxicity database and to suggest limits for pesticide levels in the Valley's rivers and agricultural drains.

A review of information on toxicity of molinate and thiobencarb was conducted by the SWRCB (1990). This review was used to develop specific water quality criteria and performance goals for those herbicides. The CDFG has also recently completed hazard assessments for the insecticides carbofuran, malathion, and methyl parathion. The results of these investigations support the RWQCB recommended performance goals on the basis of studies by the CDFG laboratory and a review of the toxicity literature (Finlayson, pers. comm., 1992). Presently, the performance goals for the five rice pesticides are only targets and are not enforceable.

In 1990, the RWQCB amended The Water Quality Control Plan (Basin Plan) for the Central Valley Region. The Basin Plan prohibited the discharge of irrigation return flows containing molinate, thiobencarb, carbofuran, malathion, and methyl parathion unless a RWQCB-approved management practice is followed. Proposed management practices are intended to control pesticide concentrations in return flows from rice fields so that specific performance goals are met. The RWQCB is currently working on amendments to the existing Basin Plan that would establish enforceable water quality objectives by 1997.

The DPR continues to submit yearly rice pesticide control program results and proposed management practices for these pesticides to meet the RWQCB performance goals. Irrigation water-holding times, guidelines for emergency releases, and voluntary limits on acreage treated are examples of current rice pesticide management practices.

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Water Quality Monitoring and Compliance with Performance Goals

Since the early 1980s, major accomplishments have been made in reducing the pesticide and herbicide concentrations in rice field drains. Through voluntary and regulatory programs, the Sacramento Valley rice growers have been successful in significantly reducing the total pesticide loadings into the major drains and the Sacramento River. As a result of these reductions in rice pesticide loadings, residuals are well below public health criteria (no known instances of a threat to human health have been experienced). Potential threats to aquatic life should be further minimized by ongoing efforts to improve water quality.

The RWQCB is charged with protection of water quality in California's rice growing region. This has included enforcement of primary water quality criteria for protection of public health and secondary criteria for water quality, and taste and odor. These criteria are established by the U.S. EPA and the California Department of Health Services (DHS). The CDFG is similarly responsible for protection of fish and wildlife resources. These agencies define safe levels of pollutants, including pesticides, in California's waters and also monitor these pollutants to ensure compliance.

As a result of fish kills in the early 1980s, the DPR (formerly a part of the California Department of Food and Agriculture), the City of Sacramento, RWQCB, and CDFG began intensive monitoring of rice pesticides in the Sacramento Valley. These studies included sampling of agricultural drains, the Sacramento River, and fish tissues in both the drains and the river. These monitoring activities have resulted in the establishment of the current water quality objectives and performance goals for maximum concentrations of pesticides in the surface waters of the Sacramento River Basin. The 1996 performance goals for carbofuran, malathion, molinate, methyl parathion, and thiobencarb are 0.4 g/L, 0.1 g/L 10.0 g/L, 0.13 g/L, and 1.5 g/L, respectively (RWQCB, 1994). Seven water quality objectives for pesticides have been defined in the 1994 Basin Plan. Following is a summary of these objectives:

• Pesticides shall not be present in concentrations that adversely affect beneficial uses.
• Discharges shall not result in pesticide concentrations in bottom sediments or aquatic life that adversely affect beneficial uses.
• Total identifiable persistent chlorinated hydrocarbon pesticides shall not be present in the water column at concentrations detectable within the accuracy of analytical methods.
• Pesticide concentrations shall not exceed the lowest levels technically and economically achievable.
• Waters designated for use as domestic or municipal supply shall not contain concentrations of pesticides in excess of maximum contaminant levels set by the California Code of Regulations.
• Waters designated for use as domestic or municipal supply shall not contain concentrations of thiobencarb in excess of 1.0 g/L.

Since the early 1980s, rice pesticide and herbicide concentrations have been significantly reduced in both the Sacramento River and the Basin agricultural drains. These reductions have been achieved through continued monitoring of study results, setting of performance goals and water quality objectives, research into rice tailwater management practices, and innovations in rice cultivation practices.

The total herbicide load (molinate and thiobencarb) carried by the Sacramento River dropped from approximately 40,000 pounds in 1982 to less than 125 pounds in 1992 (California Environmental Protection Agency, 1992). In 1993, the molinate load (thiobencarb was not detected in the Sacramento River) carried by the Sacramento River increased to approximately 4,200 pounds, but then decreased again in 1994 to approximately 240 pounds. Figure 3-3 shows the mass loading to the Sacramento River from 1982 to 1995. Weather conditions may explain some of the variations in the peak concentrations and mass loadings. For example, the dissipation rate of some pesticides increases with increasing temperature. Warm weather in May of 1987 and 1992 may explain the low molinate concentrations and mass loading to the Sacramento River during those years. On the other hand, the cool, wet conditions in May of 1990 and June of 1993 may explain the higher levels occurring during those years.

Seasonal peak levels of two herbicides over the past 15 years are shown in Figure 3-1. Water and weed management systems have changed greatly during this period. Resulting levels of molinate and thiobencarb in the Sacramento River have been below limits established to protect water quality and public health and have generally declined throughout the monitored period (1982 to 1995). Levels of thiobencarb have been below the secondary public health level (taste) since 1986.

Peak levels in the Colusa Basin Drain have also declined (to less than 10 percent of pre-1985 levels). This water is virtually all return flow, mostly from rice fields. Relevant RWQCB goals in this drain are for the protection of fish.

Since 1982, the molinate concentrations in the Colusa Basin Drain at Highway 20 have decreased from a peak of 357 g/L in 1981 to 25 g/L in 1995 (Figure 3-1). This has resulted in the reduction of molinate concentrations at the City of Sacramento's water intake from a high of 16 g/L in 1982 to 0.16 g/L in 1995, a decrease in concentration of approximately 99 percent (UC Coop. Ext., 1991, DPR, 1995). Drought during the early 1990s resulted in low flows, increasing concentrations of herbicides (Figure 3-1). No Ordram has been detected in the City's drinking water (Cal EPA, 1992). Molinate goals were met between 1986 and 1989, and in 1991.

Molinate goals were exceeded in 1990 as a result of significant reductions in performance goals (from 90 g/L in 1989 to 30 g/L in 1990) and drought-related low flows in the drains and rivers.

Thiobencarb goals were met between 1983 and 1991; however, peak levels were above the performance goals between 1992 and 1995. Performance goals have become significantly more stringent, from 24 g/L in 1989 to 1.5 g/L in 1991. Thiobencarb concentrations at the City of Sacramento's water intake from 1982 to 1995 have also declined. From peak concentrations of 3 to 4 g/L in 1985, the concentration of thiobencarb at the City's intake was less than 1.0 g/L from 1986 to 1995.

The water-holding requirements in the Sacramento Valley in 1995 were adequate to meet performance goals during 1995 and will not be adjusted in 1996. (DPR, 1995).

In lab tests associated with monitoring of rice field drainwater by the CDFG Pesticide Investigations Unit, pesticide levels in the Colusa Basin Drain have not been shown to be toxic. Evidence and experimental data suggest that declines in the striped bass populations in the San Francisco Bay-Delta Estuary since the mid-1970s are probably not a result of rice pesticide use in the Sacramento Valley (Finlayson, pers. comm., 1992).

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Conclusions

The California rice industry continues to invest in crop, land, and water management practices that result in reliably high water quality. Their sensitive location in California's water supply network has obliged rice growers to take a proactive approach to water quality. The results demonstrate to other irrigators and industries the potential value of this approach.

The significant reduction in pesticide inputs into the Sacramento River is, "...one of the most successful water pollution control programs in the United States. It has taken concerted effort by numerous state and local agencies and creative implementation by the rice industry to make this happen." (William Crooks, RWQCB's Executive Officer)

The following sections present the justification for ratings of the rice industry's performance relative to the environmental value of water quality.

Overall performance of rice relative to water quality values is good. This positive performance is primarily due to irrigation methods that control return flow (surface water flow back to rivers) and limit subsurface drainage discharge, to the capability of rice fields to degrade pesticides, to rice fields' capability to retain plant nutrients, and to low sediment delivery from rice fields. Alternative land uses influence water quality by land drainage, nutrient and pesticide application, machinery spills, home maintenance, and municipal and industrial water use.

Fertilization

Fertilization associated with alternative land uses (including other crops and urban development) generally results in higher levels of nutrients being discharged to waterways than rice farming. Nitrogen use by rice can be extremely efficient since nitrogen remains primarily in the ammoniac form in flooded fields. (This form is far less mobile in soil than the nitrate form dominating non-flooded soils.) Also, phosphorus moves primarily with eroding soil, which is minimal under rice cultivation. Runoff from urban and commercial developments, another alternative land use, can contain significant amounts of nitrogen from lawn over-fertilization, and phosphorus attached to eroding soil (from building sites and the like).

Topdressing of nitrogen in rice, while not shown to cause significant nitrogen loading of surface waters, is nevertheless less efficient than application before planting. Topdressing is not practiced on all fields and is used to supply only a portion of the annual nitrogen requirement where it is practiced. Because rice can require mid-season fertiliza tion, the practice is expected to continue.

Irrigation

Holding water within rice fields for herbicide breakdown is positive relative to the limited drainage management options available with other crops. This level of protection is difficult to achieve with other, non-flooded crops.

Flood maintenance of rice is compared with surface irrigation of other crops on similar lands, and to municipal and industrial water use by urban developments. The influence of irrigation on surface-water and groundwater quality is considered.

Water percolating to groundwater beneath upland (non-flooded) crops can have substantially higher salinity than the irrigation water. This is less pronounced for flood irrigated rice. Also, there is less mobile nitrate nitrogen in the rooted soil of a rice field is lower than in the rooted layer of upland crops. This is a direct result of flooding. Therefore, groundwater recharged through rice fields is of high quality relative to recharge through upland crop fields.

Surface-water quality is generally degraded by higher temperatures and concentrations of salinity, trace elements, nutrients, and organic pollutants. Water returning to the river from any irrigated crop or wastewater treatment plant is commonly warmer than the water in the river, warming the river where this flow reenters. To irrigate other crops on this land, much of the land would probably require artificial subsurface drainage that is not required for rice. Since much of the existing acreage devoted to rice production has saline, shallow groundwater, the salinity of this drainage would greatly exceed that of surface drainage currently found in the Sacramento Valley. Trace element and nutrient concentrations in such drainage would be higher than in return flow from rice fields, and could also degrade water quality. The wetland chemistry of a rice field is also an ideal environment for degradation of organic compounds, such as herbicides and pesticides. These conditions are exclusively present in continuously flooded fields. Flood irrigation avoids environmental degradation associated with warm, saline, nutrient-rich drainage, yet does contribute warm, relatively non-saline return flow. The influence of rice irrigation on water quality therefore compares favorably with irrigation of alternative crops.

Pest Control

Animal (including insect) pest control requires less intensive effort in rice than in many alternative crops. The amount applied, and the resulting levels in the drainage, are significantly lower than for alternative crops.

In most rice fields, a combination of cultural (non-chemical) and chemical weed control is employed. Tillage and flood irrigation are clean technologies in the sense that no pesticides are required. Herbicides are also employed to control weeds, which can otherwise significantly depress crop yields. The focus of regulatory attention on herbicides has made water quality at times the "Achilles heel" of rice farming, and at other times their greatest success. Under current water management systems, herbicide impacts on surface- water quality are minimal, less than or comparable to those associated with alternative crops or urbanization. Continued investment in environmentally acceptable means of weed control should lead to continuing improvement.

Rice farmers can take advantage of naturally rapid herbicide degradation in flooded rice fields: from 80 to 90 percent in 7 to 10 days for most of the registered herbicides. This is due partly to innovations by rice farmers that enable them to retain water in their rice fields after herbicide application. Water retention provides sufficient time for herbicide degrada tion to affect most of the applied chemical, so that released water is of acceptable quality. Performance goals for rice herbicides in the Sacramento River and the Colusa Basin Drain (an agricultural water conveyance facility) have gradually been lowered to extremely low levels. Nevertheless, since 1985, no peformance goals for a rice herbicide has been exceeded for the Sacramento River, and a significant reduction in concentrations in the Colusa Basin Drain has been achieved. These achievements have resulted from extensive and costly research by the rice industry and its collaborators.

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References

California Environmental Protection Agency (Cal EPA). 1992. Rice Pesticides Virtually Eliminated from Sacramento Drinking Water Supply. Release Date: 26 February 1992. Sacramento, California.

California Department of Pesticide Regulation (DPR). 1995 . Information on Rice Pesticides. Submitted to the California Regional Water Quality Control Board, Central Valley Region. December 28.

Crooks, W. Personal communication. Regional Water Quality Control Board, Executive Officer.

DPR. 1994. Information on Rice Pesticides. Submitted to the Central Valley Regional Water Quality Control Board. December 28.

DPR. 1995. 1995 Rice Season Update. October 13.

California Rice Industry Association (CRIA). 1991. Chemicals Generally Available for Use on Rice in California.

Central Valley Region-Regional Water Quality Control Board (RWQCB). 1992. Staff Report: Consideration of Approving Department of Pesticide Regulation's 1992 Management Practices for River Pesticides.

Finlayson, B. 1992. Personal Communication. California Department of Fish and Game, Region 2, Rancho Cordova.

Flint, et al. 1992. Integrated Pest Management for Rice, second edition. University of California, Division of Agricultural Sciences. 101 pages.

Hill, J. E. et al. 1991. Abstract to Poster of Rice Herbicide Monitoring Program.

Kleinfelder, Inc. 1995. 1995 Pesticide Monitoring Program, Kleinfelder Field Sampling Three Locations Sacramento River Drainage Basin. September 19.

Regional Water Quality Control Board. (date unknown). Staff Report: Consideration of Approving Department of Pesticide Regulation's 1994 Management Practices for Rice Pesticides.

Regional Water Quality Control Board. (date unknown). Staff Report: Review of the Results of the 1992 Rice Pesticide Control Program and Consideration of Recommendations Regarding the 1993 Program.

Regional Water Quality Control Board. (date unknown). Staff Report: Consideration of Approving Department of Pesticide Regulation's 1992 Management Practices for Rice Pesticides.

Regional Water Quality Control Board. 1994. Water Quality Control Plan (Basin Plan), Central Valley Region, Sacramento and San Joaquin River Basins.

State Water Resources Control Board. SWRCB. 1990. Sacramento River Toxic Chemical Risk Assessment Project. Final Project Report 90-11WQ. October 1990. Water Resources Control Board, State of California.

University of California Cooperative Extension. 1991. Reducing Pesticide Levels from Rice Field Drain Waters of the Sacramento Valley, 1990 Progress Report.

University of California Cooperative Extension . 1991. Cereal Briefs, Rice, Wheat, Barley, Oats. August 16.