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HAZARDS, PUBLIC HEALTH AND SAFETY
Public Health and Safety for District activities include management of risk of wildland fires, flooding, hazardous and/or toxic materials released from sediments into water or air, and risk of accidents to the public from the work.
Sediment removal, and to a lesser degree, bank protection and vegetation management, has a potential to suspend sediment in streams. The increased turbidity in streams and canals would have short term impacts and can be minimized by the use of BMPs listed in this section; sediments in the projected work areas are generally not toxic and do not have long term water quality effects.
The maintenance areas and equipment used in these areas are secured or under the constant supervision of the District maintenance personnel who are required to follow safe construction practices and keep the public away from the work area.
Pesticides, primarily herbicides used for vegetation management, are subject to extensive regulation and are used under closely controlled circumstances. A review of pesticides to be used by the District in the SMP shows minimal risk to public safety. Infrequent application (once or twice per year) results in low potential exposure and the innate toxicity of the products used is low.
1. Water Quality
a. Setting
1) Beneficial Uses of Water
The water quality issues associated with routine maintenance activities within the District are directly related to actions taken during and after the maintenance work. Water pollution sources associated with District activities in general are described in the Santa Clara Valley Nonpoint Source Pollution Program (NPS), the subject of a separate Nonpoint Source Discharge Elimination System (NPDES) permit issued June, 1995, and the Total Daily Maximum Load (TMDL) program.
Water quality objectives have been developed by the Regional Water Quality Control Board (RWQCB) for the protection of existing or potentially designated beneficial uses of a water body. For most watercourses in the District, designated beneficial uses include aquatic habitat, recreational water uses, and local water supply. Within the District, urban runoff is indirectly recharged to the groundwater but is not considered a municipal drinking water supply. For this reason, concentrations of pollutants in urban runoff are not compared to Water Quality Objectives for the protection of human health for drinking water supplies (Santa Clara Valley NPS Program, District Project No.007902).
As stated in the SMP, the NPS Program is comprised of: (1) "area wide" activities performed collaboratively with 14 other agencies in northern Santa Clara County under the Santa Clara Valley Urban Runoff Pollution Prevention Program and (2) "District-specific" activities performed uniquely by the District for its own operations and within its own jurisdiction.
2) Implications of Elevated Mercury Levels in Guadalupe River Watershed
The Guadalupe River, its tributaries, and South San Francisco Bay are classified as impaired with regard to mercury contamination under Section 303 (d) of the Clean Water Act. The TMDL program and implementation plan for San Francisco Bay calls for a 90 percent reduction in the amount of mercury loading that is entering the bay from the Guadalupe River watershed. Because mercury is largely associated with sediment, transport of mercury in the Guadalupe River watershed is of concern in relation to SMP activities (Guadalupe River Project, Downtown San Jose Draft Report for Proposed Project Modifications, June 2000).
Elevated mercury levels in the Guadalupe Watershed are in large part a legacy of the California gold mining era, when mercury was used in the gold refining process. Mines such as the New Almaden Mine, which operated for many years in the upper watershed extracting the mercury ore cinnabar, are known to be a source of mercury in the Guadalupe River system. Leaching of mine tailings and overland transport of mercury-bearing sediments have resulted in the downstream accumulation of mercury in the watershed (Guadalupe Creek Restoration Project, November 2000).
Previous studies have shown that mercury concentrations in sediments from different parts of the Guadalupe Watershed vary widely. For example, sediment sampling efforts conducted in the mid-1990s found that mercury concentrations in approximately 70 channel sediment samples from sites within the watershed ranged from 0.05 to 49 milligrams per kilogram (mg/kg or ppm, parts per million) (CH2M Hill 1994, CH2M Hill 1995). The majority of these samples had mercury concentrations below 10 mg/kg, and one of the samples contained no detectable mercury. However, two samples had mercury concentrations of 22 mg/kg and 49 mg/kg, respectively. More recent sampling on the Lower Guadalupe River between Highway 237 and Blossom Hill Road (below Almaden Expressway) documented mercury concentrations ranging from 0.05 to 0.46 mg/kg in a suite of ten samples (Tetra Tech 2000). Most mercury in the freshwater environment is chemically bound to suspended particles of soil or sediment; a smaller fraction is bound to dissolved organic carbon. Sediment-bound mercury may still be available to aquatic organisms and thus remains a pollutant of concern. The potential for adverse environmental effects from sediment-bound mercury depends primarily on transport and depositional characteristics (e.g., particle size), and the physical and chemical properties of the sediment.
The greatest concern with regard to the accumulation and transport of mercury in the watershed is the potential for mercury methylation. Methyl mercury is readily adsorbed by aquatic plants, fish, and wildlife, and has been demonstrated to accumulate in their tissues. Factors conducive to methylation of mercury include: low flow or stagnant waters, hypoxic or anoxic conditions in the water column, low pH (< 6), and high concentrations of dissolved carbon. Most of these factors are in turn affected by biological processes such as metabolism, growth, and decay.
Because methylation is affected by changes in physical and biological conditions, it is likely that the rate and quantity of methyl mercury formation changes seasonally; seasonal variation in flow velocity and volume probably also contribute to variation in methylation rates. During the winter rainy season and subsequent spring flushing period, streamflow is high and rapid and even in the deepest pools turbulent overturn of the water column likely keeps the water well oxygenated. Because oxygen is more soluble in water at lower temperatures, cooler winter water temperatures are also expected to foster oxygenation throughout the water column. By contrast, during the warm, dry summer months, flow volumes drop significantly and the creek's deep pools may approach a stagnant condition, decreasing oxygenation of bottom waters; warmer summer water temperatures may also reduce oxygenation. These conditions typically intensify throughout the course of the summer and fall dry season. During the late summer and fall, methylation may thus occur in deep, slow-moving pools in the creek's main channel and possibly also in pools that form when minor channels become isolated and stagnant.
b. Significance Criteria
A project would be normally considered to have a significant effect on water quality if one or more of the following factors were met:
Criterion WQ-1 Substantially degrade water quality;
Criterion WQ-2 Contaminate a public water supply;
Criterion WQ-3 Substantially degrade or deplete groundwater;
Criterion WQ-4 Interfere substantially with groundwater recharge;
Criterion WQ-5 Involve an activity or process that would result in a point source discharge to a receiving body that exceeds state water quality or discharge requirements, standards or objectives (e.g. RWQCB Basin Plan Objectives and State maximum contaminant levels, where applicable, WDR or NPDES discharge requirements, or Water Quality Control Plan standards for the receiving water body) or result in substantial non-point source contaminants; or
Criterion WQ-5 Resuspension of sediments which may cause substantial and prolonged increased turbidity or resuspension of toxic pollutants.
c. Impacts and Mitigation <>1) Overview
Increased turbidity and resuspension of heavy metals could result from removing sediment and vegetation below the water line and by excavating toes of slopes for bank protection. Pollutants that have been buried can be resuspended as a result of excavation of sediment during sediment removal and the excavation of the toe of slopes during bank protection projects.
Bypassing streamflow around the work site prevents resuspension of any pollutants that might occur in the sediment that is removed. These sediments are tested and disposed of properly if they contain any pollutants of concern. However, when streamflow is reintroduced to the site after sediment removal work is completed, any pollutants in the newly exposed channel bottom may become resuspended in the water column. Studies have shown that heavy metals of potential concern in District streams will not become chemically active as a result of routine stream maintenance activities.
BMPs which reduce or avoid all significant Water Quality impacts from Sediment Removal projects:
| 1.1 | Conduct Work During Low Flow Periods |
| 1.2 | Tidal Work Areas |
| 1.3 | Dewater/ Bypass Water at Non-tidal Sites |
| 1.4 | Avoid Erosion When Restoring Flows |
| 1.5 | Erosion and Sediment Control Measures |
| 1.6 | Use of Wheel and Track Mounted Vehicles in Stream Bottoms |
| 1.7 | Pump/
Generator Set Operations and Maintenance |
| 1.8 | Handle Sediments So As to Minimize Water Quality Impacts |
| 1.9 | Soil Stockpiles |
| 1.13 | Prevent Scour Downstream of Sediment Removal |
| 2.7 | Seeding |
| 4.4 | Sanitary/Septic Waste Management |
| 4.5 | Vehicle and Equipment Cleaning |
| 6.1 | Spill Prevention |
| 6.2 | Spill Kit Location |
| 6.3 | Hazardous Waste Management |
| 6.4 | Vehicle and Equipment Fueling |
| 6.5 | Vehicle and Equipment Maintenance |
BMPs which reduce or avoid all significant Water Quality impacts from Vegetation Management projects:
| 1.14 | Minimize Sediment Transport Downstream from In-channel Herbicide Sites |
BMPs which reduce or avoid all significant Water Quality impacts from Bank Protection projects:
| 1.6 | Use of Wheel and Track Mounted Vehicles in Stream Bottoms |
| 1.11 | Concrete use near waterways |
| 1.12 | Groundwater Management |
| 1.15 | Prevent Erosion Downstream of Bank Protection Sites |
| 2.6 | Mulching |
2) Increased Turbidity and Resuspension of Heavy Metals
Resuspension of Sediment
Sediment in channels comprises bedload and suspended load. Bedload is that portion of the total sediment load of a river which is transported by sliding, rolling and bouncing over the bed, and includes the coarsest portion of the river load. The bedload ranges in size from large cobbles to gravels and coarse sand that cannot pass through a #20 sieve (0.18 mm or 180). Particles that are within the #20 sieve size are further classified as coarse sand. If mechanically disturbed and lifted into the water column, coarse sediment will drop to the bottom of the channel within a few hundred feet and rejoin the bedload.
Suspended load is sediment retained in the column of water by turbulence and velocity of flow. Suspended load includes the finer portion of the bed material which is only intermittently suspended. Depending on velocity, suspended load ranges in size from less than a # 20 sieve size (coarse sand) to #200, (fine sand, or 35-115), to clay, which ranges in size from 0.1 to 35 . Gravity will settle particles that have settling velocities (a function of the particle diameter and density) large enough to overcome upward impelling forces caused by fluid motion. While gravity tends to settle particles, turbulence tends to resuspend particles (Woodward-Clyde, 1992). Depending on size, most suspended load will not fall out within 1,000 feet of origination, and the very fine washload will not settle until the water is still (California Department of Conservation, Division of Mines and Geology, 1990).
Sediments that are smaller than 1 contain clay and/or organic carbon and play an important role as both a source or sink for metals and hydrophobic (which exhibit an adversity to water) organic pollutants. Because of the sediment adsorptive capacity for such constituents, sediments may act as a sink for pollutants released into the stream water. Conversely, the pollutant-rich sediments may also serve as a source during high streamflows in the wet-weather season when the sediment material (particularly the fine silt and clay fraction) is resuspended into the water phase, and during construction excavation associated with routine maintenance during the dry-weather season (Santa Clara Valley Nonpoint Source Study [Woodward-Clyde], 1991).
Resuspension of Heavy Metals
Resuspension of heavy metals (zinc, copper, and lead) would not occur because these particles will not unbind from sediment during routine maintenance activities. Heavy metals are most likely to be adsorbed to clay dissolved-sized particles since they have the largest collective surfaces (Harter 1982). Since metals tend to be associated with sediments, correlations between metal concentrations and other sediment properties such as grain size distribution were investigated for the Loads Assessment Report (see Table IV-D-1, Mean Metal Concentration (Mg/kg) and Grain Size Distribution of Sediment Samples from Stream Stations).
The amount of fine-grain-size material from the sediment sample was obtained by summing the silt and clay fractions. For the three metals (zinc, copper, and lead), the amount of silt and clay in the stream sediment was highly correlated with these metal concentrations. This means that the higher concentrations of zinc, copper, and lead observed in sediment samples can be mostly explained by the larger proportions of fine sediment material (silt and clay) present, and therefore, these metals will not be resuspended or become chemically active during sediment removal since they are tightly bound to the small particles. Therefore, this is not a significant impact.
Mercury is known to be present in portions of the Guadalupe watershed due to historical mining. Mercury is toxic in its inorganic form, but is more toxic in its organic form as methyl mercury because it is more rapidly adsorbed, it accumulates in animal tissue, and it is concentrated at higher levels of the food chain (see also discussion of mercury in the Toxics section of this chapter). The District's overall goal is to minimize downstream transport of mercury to minimize methyl mercury formation in the Bay (Refer to the Guadalupe River Project, Downtown San Jose Draft Report for Proposed Project Modifications for further explanation on the mercury levels in the Guadalupe River and effective methods for treating soils with mercury during construction activities along streams in the Guadalupe watershed. These methods have been approved by the RWQCB). Mercury is also tightly bound to small soil particles, so for those sites that have less than 1 part per million (ppm)mercury, there is not a significant impact. For higher concentrations there is a greater concern. This is dealt with by preventing erosion of contaminated soil - either by protecting it in place, or by removing it altogether.
Table IV-D-1
Mean Metal Concentration (Mg/kg) and Grain Size
Distribution of Sediment Samples from Stream Stations
| Station | S1 | S2 | S3 | S4 | # of samples per station | Total of naturally
occurring amounts in soils (Means and Ranges)† |
| % Silt | 9.3 | 11.4 | 64.3 | 26.0 | ||
| % Clay | 0.0 | 1.1 | 9.3 | 6.9 | ||
| Station | S1 | S2 | S3 | S4 | # of samples per station | Total
of naturally occurring amounts in soils (Means and Ranges)† |
| % Silt | 9.3 | 11.4 | 64.3 | 26.0 | ||
| % Clay | 0.0 | 1.1 | 9.3 | 6.9 | ||
| % Sand | 90.7 | |||||
| 87.5 | 26.4 | 67.1 | ||||
| Arsenic | 4.1 | 3.6 | 5.4 | 7.3 | 2 | 5 1-50 |
| Cadmium | 0.1 | 1.3 | 0.8 | 0.7 | 2 | 0.06 0.01-0.70 |
| Chromium | 78 | 81 | 125 | 90 | 2 | 100 1-1,000 |
| Copper | 35 | 49 | 69 | 50 | 4 | 30 2-100 |
| Lead | 29 | 66 | 100 | 58 | 4 | 10 2-200 |
| Nickel | 62 | 64 | 120 | 116 | 3 | 40 5-500 |
| Mercury | 0.1* | 0.1* | 3.1 | 0.3 | 4 | 0.03 0.01-0.3 |
| Selenium | 0.2* | 1.4* | 0.9* | 0.5 | 4 | 0.30 0.1-2 |
| Silver | 0.6* | 1.0* | 1.2* | 1.0* | 4 | 0.05 0.01-5 |
| Zinc | 101 | 115 | 211 | 167 | 4 | 50 10-300 |
Source: Santa Clara Valley Nonpoint Source Study,
Volume 1: Loads Assessment Report, February 22, 1991.
* At least one value in the sampling was below the
detection limit.
† Lindsay, WL., 1979. Chemical Equilibria in Soils.
With respect to mercury, the goal of the RWQCB is to reduce the load of mercury
discharged to San Francisco Bay from the watershed and to address conditions
within the watershed that promote the transformation of mercury in sediment
into bioavailable forms. As indicated above, mercury is known to be present
in portions of the Guadalupe Watershed due to historical mining. The SMP
would not change the quantity or patterns of mercury
that enter Upper Guadalupe River from the upper watershed. Consistent with the
RWQCB's goal, the District's overall goal with respect to mercury is to minimize
downstream transport of mercury when conducting routine stream maintenance activities
(refer to the Guadalupe River Project, Downtown San Jose Draft Report for Proposed
Project Modifications for further explanation on the mercury levels in the Guadalupe
River and effective methods for treating soils with mercury during construction
activities along streams in the Guadalupe Watershed. These methods have been approved
by the RWQCB).
In addition, the District proposes under the program to periodically remove
bedload sediment to maintain channel capacity for conveying flood waters between
Trimble Road and Montague Expressway. The Lower Guadalupe River Sedimentation
Study (Northwest Hydraulic Consultants, 2000) indicates that over 90 percent
of the bedload will continue to be deposited in the reach between Trimble Road
and Montague Expressway when all flood protection projects are operational.
Removal of sediment that contains excessive levels of mercury would be considered
beneficial to the overall goal of the San Francisco Bay RWQCB's TMDL Program
for mercury, which is to reduce mercury contamination in the watershed.
The geomorphic conditions present at sediment removal sites are clearly depositional.
Following sediment removal operations, exposed surfaces potentially contaminat4ed
with mercury will not be eroded, rather they will be covered with new sediment.
For bank protection, there is a risk of further exposure and erosion of contaminated
sediments. This can be mitigated by application of a specific BMP.
Impact WQ-1 Erosion of mercury containing sediment.
Application of this BMP will reduce downstream mercury transport to levels
below current regulatory concern.
3) Water Supply and Groundwater Resources
Many of the creeks subject to maintenance are used for groundwater recharge,
but are not directly used for water supply. Because the areas of streams and
canals subject to routine maintenance do not directly contribute to the municipal
drinking water supplies, routine maintenance in the channels will have no impact
of public water supplies.
Groundwater recharge is accomplished two ways: 1) instream retention using
gravel dams or flashboard dams, and 2) percolation ponds, where water is diverted
from the channels to large, flat basins that have permeable beds. The instream
recharge program is the focus of a separate Corps permit (#21227S98), and the
effects of instream recharge impacts are identified in that report (instream
recharge is not part of the SMP).
In the past, certain widely used pre-emergent herbicides such as atrazine
and hexazinone have been found as contaminants in ground water. These herbicides
have been placed on so-called "list A" by the California Department of Pesticide
Regulation (CDPR) to restrict their use in certain areas. List "A" compounds
are chemicals or their breakdown products that have been detected in ground
water due to legal agricultural use and have the potential to pollute ground
water. The District does not use "list A" herbicides.
Other herbicides with physical and chemical characteristics that create a
potential to impact ground water were placed on "list B"; their use is not restricted.
CDPR has recently proposed new restrictions on use of "list B" pre-emergent
herbicides including several which the District uses:
chlorsulfuron (Telar)
isoxaben (Gallery)
oryzalin (Surflan)
sulfometuron methyl (Oust)
These proposed restrictions are intended to minimize potential ground and
surface water contamination.
Although the District does not apply these herbicides in actual areas of ground
water recharge, the application is along channels that convey water that may
contribute to recharge. Application on impervious surface poses a potential
risk of waterborne runoff carrying the herbicide into the channel before it
is incorporated into the soil at the application site. Pre-emergent herbicides
act in the near subsurface of the soil in the shallow zone where weed seeds
germinate. To reach this zone, the applied herbicide must be leached into the
soil at the application site by irrigation or by rainfall. The period between
application and soil incorporation presents the risk of runoff.
The District is currently reviewing the recent CDPR proposal and will determine
whether its herbicide program will need to be adjusted by the time that the
EIR is finalized.
Bank protection may add impervious hardscape over short reaches of banks,
but not to channel bottoms. The degree to which infiltration would be impaired
is insignificant.
2. Fire Safety
a. Setting
The District controls combustible weeds and grasses in the following areas:
1) Vacant District parcels 2) Top of bank areas along creeks and canals, 3)
Roadways and access roads. In narrow right-of-way areas (less than 10 feet),
control needs to extend down the channel slope to provide adequate defensible
space. The methods the District uses to meet fire code requirements are described
below.
1) Regulation
The District is responsible for control of weeds and grasses on its property
in order to meet local fire codes. Fire code requirements for local cities and
Santa Clara County are taken from the State of California Uniform Fire Code.
Though the code for each municipality may be worded differently, each basically
states that "a property owner is responsible to maintain a property in such
a manner that no weeds will be left standing by July 1st of each calendar year".
The exceptions to this requirement mentioned below provide adequate protection
while preserving habitat.
2) Existing Control
Discing
Many of the District's outer banks of levees and upland areas are comprised
of weedy, nonnative grasses and forbs. The outer banks of levees are mowed for
fire protection, and the other upland areas maintained by the District are usually
disced using the following criteria:
Other methods
In top of bank areas which are too narrow for vehicular access, it is necessary
to maintain a firebreak between the adjacent property line and the top of bank
or down the slope to provide defensible space. In most areas this is performed
by applying pre and post-emergent herbicides with a controlled droplet applicator
which the vegetation technician carries as a back pack. In addition, hand labor
crews are used at various times.
The District has many vacant parcels which serve various purposes. As a general
rule, parcels less than one hundred feet in width and less than one-quarter
acre are treated with pre and post-emergent herbicides to control weeds on most
of the District's facilities. In areas greater than one hundred feet in width
and more than one-half acre, a herbicide application is made around the perimeter
of the parcel and around any structures or utility poles, and the remainder
of the area is disced to bury the weeds and grasses, or mowed or hand cleared
to abate hazard.
b. Significance Criterion
A project would be normally considered to have a significant effect on fire
safety if the following factors are not met:
Criterion FS-1 Maintaining a clear defensible space in areas with flammable
brush, grass or trees where maintenance activities will occur.
For the SMP, increased fire hazard could occur either from increased use of
maintenance vehicles in areas of flammable vegetation, from increased maintenance
operations in areas currently subject to maintenance, or from maintenance operations
in areas not currently maintained in the capacity described in the SMP.
c. Impacts and Mitigation
1) Increased Fire Hazard from Maintenance Vehicles
The use of fuels and lubricants for heavy equipment is subject to standard
District practices and other environmental controls to prevent pollution of
stream channels. Use of fuels and spark arresting devices are part of the standard
District practices; the use of vehicles as part of the maintenance program will
not increase the risk of fire in flammable areas. Therefore, this is not a significant
impact.
2) Increased Fire Hazard from Maintenance Operations
Sediment Removal
Areas typically slated for sediment removal do not pose fire safety risks
other than the use of heavy equipment in dry areas mentioned above. While there
may be dry vegetation on areas where sediment is to be removed, much of this
vegetation would typically be removed along with the sediment. There will not
be an increased risk of fire hazard from sediment removal operations. Therefore,
this is not a significant impact.
Vegetation management
Pre and post-emergent herbicides are currently used on roadways and firebreaks
to control weeds and grasses on all District stream channels in the Santa Clara
Basin and canals to allow access and reduce fire hazards. Many of the District's
canals parallel residential areas where a firebreak clear space is required
by local fire codes between the District's facility and private property. Herbicide
use is proposed in the Pajaro River Basin under the SMP. This is considered
a beneficial effect.
Bank Protection
Bank protection activities are usually performed on slopes without woody vegetation.
Bank protection incorporating plant material could add an additional fuel load.
Maintenance of defensible space in these areas would offset these impacts. Other
than risks posed by the use of heavy equipment in dry areas, bank protection
activities would not increase the risk of fires. As mentioned above, use of
fuels and spark arresting devices are part of the standard District practices;
the use of vehicles in bank protection activities will not increase the risk
of fire in flammable areas. Therefore, this is not a significant impact.
3. Flood Protection
a. Setting
1) Flood Protection
As stated in the SMP, "the Stream Maintenance Program is designed to provide
long-term guidance to the District to effectively implement routine stream maintenance
projects. Stream maintenance is required to meet the District's flood protection
and water supply mandates. This authority is provided by the SCVWD Act, as amended."
The mandate for new projects is to provide flood protection from 1% floods for
sediment removal and vegetation management projects, and from the 2% floods
for bank protection projects. This level of flood protection is based upon the
frequency of major flooding events. These events are expressed by a percentage
of the chance that a flood of a certain magnitude will occur in any given year.
For example, a one hundred year flood event has a one percent chance of occurrence
in any one year period. Due to the fact that this frequency is based on an average
over hundreds of years, a one hundred year event may happen two years in a row
or twice in the same year. Fifty year flood protection is known as two percent;
ten year, ten percent etc. Some existing projects provide 10 or 25 year protection.
Maintenance on those facilities would restore that level of protection.
2) Regulation of Federal Flood Protection Projects
Many District flood protection projects have been designed and constructed
by Federal agencies such as the Natural Resource Conservation Service (formerly
Soil Conservation Service) and the U.S. Army Corps of Engineers. Once these
projects are completed, they are turned over to the District for maintenance
under the general direction of the sponsoring agency. The following maintenance
requirements are mandated by federal law, and annual inspections are performed
to ensure they are met.
(a) Maintenance of Hydraulic Design
(b) Maintenance of Revegetation Mitigation Areas
Maintenance of revegetation areas becomes the responsibility of the District
once the project is turned over by the sponsoring agency. Predetermined survival
rates are set and annual plant counts are made, at least for the first two years,
to determine that these criteria are met. Control of weeds and undesirable plants
is necessary to reduce competition and help the native plants become established.
The SMP must comply with the Federal Emergency Management Agency's (FEMA) flood
insurance program requirements if the District wishes to remain in the national
flood insurance program. Maintenance Guidelines are prepared for each flood
control project, generally during project planning, to ensure each facility
is maintained at the level of flood protection for which it was constructed.
These guidelines are the basis for determining when sediment removal or other
stream maintenance activities that affect flood capacity should be scheduled.
See SMP Appendix B, Maintenance Guidelines
. These efforts protect the public's investment and
help to comply with regulations of the federal flood insurance program (Flood
Damage Reduction Objective 6, District Policies and Procedures 0-105).
3) District Maintenance Guidelines
As stated in the SMP, District Maintenance Guidelines are based on two concepts:
(1) the maintenance standard, and (2) the acceptable maintenance condition.
The maintenance standard is defined as the design facility condition, where
the modified stream has full design capacity and freeboard. The acceptable maintenance
condition is the condition to which a channel can be allowed to deteriorate
before capacity is determined to be compromised and maintenance work becomes
essential. The focus of the hydraulic analysis is related to sediment accumulation
and vegetation management since these two factors typically affect capacity.
By conducting these routine maintenance activities, the District ensures that
facilities continue to provide the level of flood protection for which they
were constructed.
The Maintenance Guidelines detail information for
each creek to the extent it is available. This information includes whether or
not the Guidelines are existing (based upon construction documentation) or new
(based upon new engineering calculations), background information (e.g., available
studies, facility engineering reports, and applicable permits), average frequency
of maintenance activities (history), and any additional supporting data and calculations.
4) Significance Criteria
A project would be normally considered to have a significant effect related
to flooding if one or more of the following factors were met:
Criterion FL-1 Cause substantial flooding, erosion, or siltation;
Criterion FL-2 Result in a significant reduction of the temporary storage capacity
of a 100-year floodplain;
Criterion FL-3 Construct permanent habitable structures within a 100-year floodplain,
which would expose people or structures to a significant risk of loss, injury
or death due to flooding;
Criterion FL-4 Substantially restrict flow capacities of a 100-year storm event
due to placement of obstructions in the floodplain; or
Criterion FL-5 Increase the risk or severity of flooding in downstream areas.
b. Impacts and Mitigation
One of the main objectives of the maintenance program is to continue to provide
flood protection. The effects of maintenance on the risk of substantial flooding
would result in a beneficial impact, as the risk of flooding would be reduced.
Maintenance activities seek to maintain the design flood capacity (flow) in
creeks and the temporary storage capacity of the floodplains (where applicable),
not restrict it. There are no significant impacts to flood control and flood
storage capacity as a result of the maintenance activities; the maintenance
activities improve flood capacity, and therefore have a beneficial impact.
The program does not include the addition of impervious structures
or surfaces which would increase runoff or contribute additional surface water
to any body of water. Because of the District's existing BMPs for construction
in areas below the OHW, which is to provide water diversion techniques by using
temporary barriers both upstream and downstream of any maintenance site, the
routine maintenance activities would not be the source of additional flooding,
erosion or siltation.
4. Hazardous Materials
a. Setting
Hazardous materials broadly include substances that may cause injury or death
through their action as poisons, corrosive or irritants, or flammable or explosive
substances. For the most part, the concern for maintenance is for fuels. However,
within the Guadalupe Watershed, there is also concern over the potential to
expose soils contaminated with mercury.
b. Significance Criteria
A project would be normally considered to have a significant effect related
to hazardous materials if one or more of the following factors were met:
Criterion Haz-1 Creation of any known or potential human health
or safety hazard;
Criterion Haz-2 Application, use, disposal, or risk of explosion or the release
of toxic or hazardous materials;
Criterion Haz-3 Create a significant hazard to the public or environment through
the unregulated transport, use or disposal of hazardous materials or release
of hazardous materials in the environment due to accident;
Criterion Haz-4 Be located on a site listed by the State pursuant to Government
Code Section 65962.5 as a hazardous material site and would create a significant
hazard to the public or the environment;
Criterion Haz-5 Emit hazardous emissions or handle hazardous or acutely hazardous
materials, substances or waste within one-quarter mile of an existing or proposed
school and there is a substantial likelihood of exposure of the occupants of
the school;
Criterion Haz-6 Impair implementation of or physically interfere with an adopted
emergency response plan or emergency evacuation plan;
Criterion Haz-7 For projects located within an airport safety zone as designated
in local airport land use plans or within 2 miles of a public airstrip where
no local airport land use plans exist, result in a safety hazard to persons
working or residing within this area;
Criterion Haz-8 Pose a hazard or public health risk due to exposure to onsite
soils or water that are contaminated by hazardous materials and encountered
during project construction activities; or
Criterion Haz-9 Result in migration of contaminants into waterways or drinking
water supplies due to exposure of subsurface contamination during construction.
c. Impacts and Mitigation
1) There are potential hazards to human health associated with exposure of
newly excavated bank materials with elevated mercury concentrations. Construction
activities associated with the proposed bank protection activities (e.g., excavation
and grading to create surfaces suitable for planting riparian vegetation, ripping
to prepare surfaces for filling and planting, and installation of bed and bank
stabilization) may result in the exposure of soils with higher mercury concentrations
than those found at the pre-excavation surface level. Exposure of newly excavated
soils with elevated mercury concentrations has the potential to result in adverse
effects on the health of construction workers and residents of nearby areas.
Based on the results of the sampling programs conducted for the Guadalupe
Creek Restoration Project and the Upper Guadalupe River Flood Control Project,
mercury concentrations vary in the Guadalupe Watershed. For example, the sampling
programs for the Guadalupe Creek Restoration Project showed that mercury concentrations
in the project area are estimated to be on the order of 10 mg/kg at the surface
(average of average values from June-July 2000 and September 2000 analysis),
19 mg/kg at the 6-inch sample depth, 19 mg/kg at the 2-foot sample depth, 24
mg/kg at the 5-foot sample depth, and 13 mg-kg at the 10-foot sample depth.
Thus, materials exposed by grading and/or ripping on newly created surfaces
may have mercury concentrations in excess of the 20 mg/kg hazardous materials
threshold or the 23 mg/kg Preliminary Remediation Goal (PRG) for total mercury
established by EPA. (Guadalupe Creek Restoration Project, November 2000)
The potential for human health effects as a result of exposure to toxic substances
depends on the existence of an exposure pathway and on the toxicity of the compound
via the pathway. For example, the toxicity of mercury is strongly dependent
on the form in which it occurs. The forms of mercury most toxic to humans are:
elemental mercury in pure liquid form (usually referred to as metallic mercury);
and organic mercury compounds such as methyl mercury. Analysis of samples collected
in September 2000 indicates that although the total mercury concentration in
bank materials locally exceeds 20 mg/kg, most of the mercury is inorganic. No
liquid elemental mercury deposits were found in the sediments or bank soils
within the project reach, and no mercury-rich particles were identified by scanning
electron microscopy in four sediment samples (Tetra Tech personal communication).
Sequential leaching tests on selected sediment samples showed that more than
64% of the total mercury consists of the mercury sulfide mineral cinnabar, which
is less bioavailable and less toxic than the organic forms of mercury, including
methyl mercury. In addition, concentrations of methyl mercury recorded in water
and sediment samples collected from the project site in September 2000 ranged
from 0.32 nanogram per liter (ng/l) to 0.93 ng/l, and from 0.0004 micrograms
per gram (~tg/g) to 0.042 gg/g, respectively. These soil concentrations are
well below the 6.1 mg/kg PRG for methyl mercury in soils established by EPA
(Tetra Tech personnel communication).
Although average mercury concentrations in newly exposed soils are not expected
to exceed the 20 mg/kg hazardous materials threshold or the 23 mg/kg PRG, construction
activities may expose localized areas with mercury concentrations above these
thresholds. This impact is considered significant. Implementation of the following
mitigation measure together with the implementation of BMP Impact WQ-1 will
reduce potential postconstruction health hazards to nearby residents associated
with exposure of soils with elevated mercury levels to a less-than-significant
level.
To ensure that worker safety is protected during bank protection projects,
the District, inc conjunction with the RWQCB, will develop and implement a program
to test soils exposed by excavation or grading or otherwise disturbed by project
construction to determine mercury concentrations in the exposed surfaces. Soils
with mercury concentrations exceeding 20 mg/kg will be removed and disposed
of in a Class I landfill following established work practices and hazard control
measures. Personal protective equipment will be required during project construction
to maintain exposure below levels established by the Occupational Safety and
Health Agency (OSHA).
2) No hazardous chemicals are used in sediment removal since the overlying
vegetation that may have to be removed for either sediment removal work or erosion
repair is removed by mechanical means, not with herbicides. The use of fuels
and lubricants for heavy equipment is subject to standard District practices
and other environmental controls to prevent pollution of stream channels. Use
of fuels and spark arresting devices are part of the standard District practices;
the maintenance program will not increase the risk of fire in flammable areas.
The work crews and equipment at the work sites do not pose hazards to the
general public because standard construction practices limit access by the public
into construction zones. The proposed project will not increase the risk of
injury to the public in construction areas (Ron Whipp, personal communication).
5. Toxic Substances
a. Setting
Under routine maintenance, District use of pesticides is primarily
use of herbicides for Vegetation Management and limited use of rodenticides
for canal, levee and dam protection from burrowing animals. District staff applies
herbicides and a contractor with a specialized training in vertebrate pest control
applies rodenticides.
Herbicides
Herbicides are generically termed pre-emergent, intended to inhibit germination
of plants, and post-emergent, intended to kill plants already growing. In practice,
some herbicides have both actions and the District commonly mixes a pre-emergent
and a post-emergent herbicide so that one application can kill existing vegetation
and also inhibit regrowth.
Current District herbicide use is summarized in Project Description Table
II-5. The products listed in the table are termed "District use herbicides"
in the EIR. The range of available herbicide products changes over time. The
District will continue to evaluate these products and may discontinue use of
some, and similarly, may adopt different products. The public safety review
in Appendix H of the SMP describes the kind of information that is available
to the District in making its selection of what products should be applied to
vegetation management.
Most in-channel vegetation control is use of the post-emergent herbicide glyphosate,
formulated as Aquamaster® (formerly Rodeo®).
Rodenticides
Rodenticides are directed primarily at ground squirrels and occasionally gophers
whose burrows threaten the integrity of levees, dams, or canal banks intended
to retain water. The District specifies the area to be treated and the contractor
selects the methods from those permissible by law and the County Agricultural
Commissioner.
In the past, fumigants such as aluminum phosphide have been used; these are
placed down a burrow and the burrow plugged with newspaper to allow moisture
to generate highly toxic phosphine gas. In practice, the operator is present
during the dangerous period of use and this provides a reasonable margin of
public safety.
Currently, the majority of ground squirrel control is by a grain bait treated
with chlorophacinone. The bait is scattered near the burrows and is attractive
to rodents. Other animals, such as domestic pets, are not able to ingest enough
bait in quantities that would cause harm, or, in the case of birds, are not
very susceptible to the poison. Children would not be practically capable of
collecting sufficient grain to be injured. Gophers are controlled by depositing
strychnine treated bait in burrows underground where they are not accessible
to other animals.
b. Regulatory Setting and Significance Criteria
1) State and Federal Regulation
All pesticides used by the District are subject to regulation by federal and
state agencies. Federal regulation takes place under the Federal Insecticide,
Fungicide and Rodenticide Act (FIFRA),amended by the Federal Environmental Pesticide
Control Act (FEPCA). FIFRA/FEPCA covers herbicides, and in the terminology of
law, undesirable vegetation is a "pest". The US Environmental Protection Agency
implements these laws. Key provisions of law 1) prohibit use of a pesticide
inconsistent with the label; 2) classifies pesticides as a) general use or b)
restricted use; 3) allows states to licence and certify applicators and to enforce
the law; 4) requires all products to be registered with EPA.
EPA registration requires that the manufacturer submit information that the
product when used as directed will a) effectively control the pests listed on
the label, b) not injure humans, crops, livestock, wildlife, or damage the total
environment, and c) not result in illegal residues in food or feed.
The State of California, through the Department of Food and Agriculture, further
restricts pesticide use and the label will carry these California-specific limitations.
The State sets different training and licencing requirements for personnel applying
or supervising application. A key requirement is that a pesticide recommendation
be prepared by a State licensed Pest Control Advisor (PCA). The PCA must evaluate
the pest control needs and determine the appropriate pesticide to be used, if
any, the rate and method of application and in general, assure that the use
is consistent with the label. Actual use is reported monthly to the County Agricultural
Commissioner.
All pesticide use by the District is in compliance with the applicable state
and federal law. The District employs several Pest Control Advisors who write
recommendations for individual vegetation control work. PCA and qualified applicators
undergo mandatory ongoing training.
2) CEQA
A project would be normally considered to have a significant effect related
to hazardous materials if one or more of the following factors were met:
Criterion Tox-1 Creation of any known or potential human health
or safety hazard.
Criterion Tox-2 Application, use, disposal, or risk of explosion or the release
of toxic or hazardous materials.
c. Impacts and Mitigation
Toxicity levels were tested as part of Santa Clara Valley Nonpoint Source
Loads Assessment Report, and is discussed in the Water Quality section of this
chapter. While there is mercury in several reservoir sediment samples, no samples
from the areas subject to work projected under this Program EIR have mercury
that would categorize the sediment as hazardous waste or affect its disposal.
1) Sediment Removal
The sediments that are removed from the creeks are not toxic. The levels of
heavy metals measured at representative sampling stations throughout the District
subject to urban runoff from residential, commercial and industrial areas were
usually within the range of natural occurrence of these trace elements in sediments
and are within the range acceptable for disposal of at a suitable site or in
an approved landfill (See Project Description).
2) Vegetation Management
Pesticides have long been under intense regulatory scrutiny and are subject
to a variety of potential public health and safety screening studies. There
is also controversy surrounding most widely used pesticides and non-governmental
information sources provide alternative health information and interpretation
of the scientific literature. Most of the publicly debated pesticide issues
involve pesticide contamination of food and materials found in insecticides
and fungicides rather than herbicides. Herbicides are formulated to kill plants
and have a mode of action that does not have a counterpart in human (animal)
physiology. Herbicides are generally very low toxicity to humans. The District
does not use insecticides and fungicides in its routine stream maintenance activities.
As part of the District's environmental review process, the SMP contains a
literature summary of official and non-official health information on District
use pesticides presented in Appendix H.
The Literature Review in Appendix H includes a wide range of information,
but several key points emerge. These are listed here and discussed below.
Acute toxicity is injury or death resulting from a single, relatively brief
exposure. The estimates of acute toxicity are usually derived from animal testing
studies, supplemented by occasional instances of human exposure. The response
of test animals to poison is represented by the LD50, meaning the dose proving
to be lethal in 50% of the animals exposed. Dose is usually expressed as milligrams
(mg) of chemical per kilogram (kg) of body mass, reflecting the general phenomenon
that larger amounts of poison are needed to kill larger animals. Most pesticides
can be harmful if ingested or if absorbed through the skin, so LD50 may be reported
for both oral and dermal exposure.
Since herbicides are formulated to kill plants, most herbicides are in the
low toxicity category, with LD50 greater than 5,000 mg/kg. By reference, a 50
kg human (110 pounds) would need to ingest 250 grams (over ½ pound) of a substance
to receive a dose of 5,000 mg/kg. While such quantities are present in the concentrated
product as supplied to the District, in use, the herbicide is greatly diluted
and the potential for exposure is significantly reduced. The District reduces
potential for exposure by scheduling application when treatment areas are not
likely to be have people or pets present and by ceasing application if persons
enter the treatment area.
Table IVD-2a lists the District use herbicides and their typical rate of application
according to the label. In the second part, Table IVD-2b compares the acute
toxicity with several scenarios of public exposure. One of these is a small
herbivore consuming a large amount of treated vegetation, the second is a child
absorbing spray material through the skin, the third is an adult receiving a
skin dose. In some cases, the herbivore could consume a toxic dose, although
the LD50 is actually not reported for compounds with LD50 demonstrated to be
greater than 5,000mg/kg. The high herbivore exposure reaches potentially toxic
exposure. In the exposed human scenario, the dose received is a small fraction
of the LD50. Thus, the potential for acute toxicity effects is not significant.
Table IVD-2a
acre
g/L
Table IVD-2b
(rat)
0.5 kg animal,10m2 exposure
11 kg person, 0.6m2 exposure
50 kg person, 2m2 exposure
methyl
Source: Thomas Reid Associates, 3/01
Much of the controversy expressed in opposition to pesticides is based on
selective reporting of scientific studies, often emphasizing results that are
not accurate in the context of actual pesticide use. The selective reporting
is not necessarily intended to support an objective review of pesticides and
is often held up in direct opposition to information provided by the manufacturers.
Nonetheless, areas of controversy need to be considered carefully, particularly
in the light of numerous past examples of chemical use once thought safe, but
now known to be harmful.
Some of the concern expressed for acute or chronic toxicity is based on circumstances
(quantity of dose, length of exposure, physical or physiological limitations
on exposure) that are not relevant to public health. For example, the triclopyr
herbicide formulation, Garlon, includes ethanol which is the form of alcohol
in wine and beer. Ethanol is reported as a suspected carcinogen. As a practical
matter, the public will not be drinking undiluted Garlon and will not be getting
a significant exposure to this potential carcinogen. Thus, literature citation
of toxicity by itself is not an indicator that the pesticide is not safe to
use.
Chronic toxicity, including cancer and reproductive effects, result from exposure
to lower levels than are needed to produce acute effects, but the exposure must
also be over a much longer time period. Because any exposure along the routine
maintenance work areas is brief and infrequent, the conditions for chronic effects
are absent. Therefore, this is not a significant impact. The Literature Review
in Appendix H of the SMP describes studies of the District use herbicides; they
have been found to have no detectible risk, or a very low risk of chronic toxicity,
including cancer and reproductive effects. While there is controversy over some
of these findings, the most important factor in determining no significant chronic
effects is the infrequent potential exposure.
1.10
Avoid Exposing Soils with High Mercury Levels
District Use Herbicide Application Rates
Herbicide
Product
% active
ingredient
Application
Rates for Active Ingredient
pounds/
mg/m2
solution
isoxaben
Gallery
75
0.75
84.06
0.45-8.99
triclopyr
Garlon 3A
44.4
1.5
168.13
1.81-9.22
triclopyr
Garlon 4
61.6
1.0
112.19
1.198
sulfometuron methyl
Oust
75
0.23
26.27
0.70-1.87
pendimethalin
Pendulum
60
3.0
336.26
< 8.99
glyphosate
Aquamaster
53.8
2.7
302.63
2.02
glyphosate
RoundUp Pro
41
2.5
280.21
-
oryzalin
Surflan
40.4
4.0
448.34
-
chlorsulfuron
Telar
75
0.09
10.54
0.056
clopyralid
Transline
40.9
0.25
28.02
3.99
District Use Herbicide Acute Toxicity and Exposure Scenarios
Herbicide
Product
LD50 mg/kg
Exposure
scenario mg/kg
Oral
Dermal
(rabbit)
Herbivore
Child
Adult
isoxaben
Gallery
>10,000
>2000
1680
4.58
3.36
triclopyr
Garlon 3A
1847
>5000
3360
9.17
6.73
triclopyr
Garlon 4
1338
>2000
2240
6.12
4.49
sulfometuron
Oust
>5000
>2000
525
1.43
1.05
pendimethalin
Pendulum
>5000
>2000
6730
18.3
13.5
glyphosate
Rodeo
>5000
>5000
6050
16.5
12.1
glyphosate
RoundUp Pro
5600
>5000
5600
15.3
11.2
oryzalin
Surflan
>10,000
>2000
8970
24.5
17.9
chlorsulfuron
Telar
5545
3400
211
0.57
0.42
clopyralid
Transline
>5000
>5000
560
1.53
1.12