Current through Register Vol. 41, No. 3, September 23, 2024
A. Site
specific information shall be submitted with the preliminary proposal in
accordance with this chapter and standards contained in this chapter.
Land treatment systems shall have adequate land for
pretreatment facilities, storage reservoirs, administrative and laboratory
buildings, and buffer zones, as well as the application sites (field area). The
availability of this land should be determined prior to any detailed site
evaluation. Site availability information should be obtained concerning:
1. Availability for acquisition or acceptable
control.
2. Present and future land
use.
3. Public
acceptance.
B. Site
design. Conformance to local land use zoning and planning should be resolved
between the local government and the owner. Adjacent owners should be contacted
by the applicant to establish whether significant opposition to the proposed
location, or locations, exists. Concerns of adjacent landowners will be
considered in the evaluation of site suitability. Public meetings may be
scheduled either during or after the evaluation of final design documents so
that the department can discuss the technical issues concerning the system
design through public participation procedures. Public hearings may be held as
part of the certificate/permit issuance procedures.
1. The estimated established site size should
be calculated using a typical maximum annual loading depth of 36 inches for
slow rate systems and a maximum depth of 72 inches per year for high rate
systems to compute the field area size. In addition, the buffer zone area
should be estimated using a typical distance of 200 feet from the extremities
of the field areas to adjacent property lines. This total estimated site area
should be available and permission obtained to gain access to the site for
field investigations.
2. When
investigating a potential site for application of wastewater, there are some
limiting factors, including topography, soils, and vegetative growth (crop),
which shall be evaluated early to determine site suitability for a land
treatment system. This evaluation should be made in two phases: a preliminary
phase and a field investigation phase.
3. The preliminary phase of site evaluations
should include the identification of the proposed location of the land
treatment system on a recent U.S.G.S. topographic map (7.5 minute quadrangle)
or acceptable reproduction or facsimile thereof. A property line survey map
should also be available for use in identifying the site location or
locations.
4. The 100-year flood
elevation should be identified and the proposed pretreatment unit processes
should be roughly located in relation to elevation.
5. Preliminary soils information should
include a soil site suitability map and include information to identify soil
textures, grades, drainage, erosion potential, suitability for certain crops,
etc. Information on soil characteristics may be available from either the
National Resources Conservation Service (NRS) Office, the local Cooperative
Extension Service Agent, or the Soil and Water Conservation Nutrient Management
Specialist.
6. The field area
available for effluent application may be estimated using typical criteria
based on topography and soil characteristics. Field areas should be delineated
on topographic maps of the proposed land treatment site.
7. The land treatment system design
consultant should arrange a Preliminary Engineering Conference (PEC), as
described in this chapter, as a final step in the preliminary phase of the site
evaluation. The requirements for soil borings and backhoe pits as needed to
study soils should be established at the PEC. A site visit should be scheduled
at the PEC that involves the appropriate regulatory personnel and the owner and
design consultant.
8. The land
treatment system design consultant may not wish to conduct detailed field
investigations of site topography, hydrology and soil characteristics prior to
the site visit by regulatory personnel and their advisors. However, the
proposed locations of field areas and pretreatment units should be established
and identified during the site visit. The location of any existing soil
borings, backhoe pits, springs, wells, etc., should also be identified during
the site visit. Soil borings and backhoe pits may be excavated prior to, during
and following the site visit as required. The requirements for soil
permeability and hydraulic conductivity testing should be developed either
during or shortly after the site visit.
9. Applicants for development of all land
treatment systems shall be required to submit at least the minimum required
information as required for the appropriate certificate/permit to be
issued.
C. Site
features. The soil at a potential site should be identified in terms of its
absorption capacity and crop production classification, which is a function of
physical and chemical characteristics. Important physical characteristics
include texture, structure and soil depth. Chemical characteristics that may be
important include pH, ion exchange capacity, nutrient levels, and organic
fraction. The absorption capacity of a soil may be directly related to soil
texture and structure. Soil color may provide an indication of the movement of
moisture through soil. Hydraulic conductivity may be estimated from in-field
tests using acceptable infiltrometer devices. In addition, the absorption
characteristics of a soil may be related to its hydraulic conductivity as
measured by both in situ and laboratory tests using acceptable procedures
(Table 9). The conductivity tests should be conducted in the most restrictive
layer within the depth affected by the land application system. Soil
productivity and nutrient management characteristics are discussed in the
Virginia Pollution Abatement Permit Regulation (9VAC25-32).
1. Soil evaluation for a land treatment
system should follow a systematic approach of selecting proper locations for
borings or excavations based on topographic position, slopes and drainage. The
physical characteristics of site soils should then be verified by an acceptable
number of recorded observations that include soil depth to horizon changes,
restrictive layers and parent material, color, texture and structure, for
borings or excavations to a minimum depth of five feet.
2. If the soil characteristics differ
substantially between borings or excavations, without a logical technical
reason for the variation, then additional boring and excavation locations
should be studied to identify the nature and extent of the changes in soil
patterns throughout the proposed site.
3. The soil characteristics of the proposed
site should be described by a qualified technical specialist knowledgeable in
the principles of soil science, agronomy, and nutrient management. The
long-term impact of land application of the treated effluent on site soils and
vegetation or crops must be evaluated by the land treatment system design
consultant. Certain minimum soil depths are required for approval of a land
application site. The minimum required depth for field areas will depend on the
type of land application system as well as the soil characteristics.
4. Representative soil samples shall be
collected for each major soil type identified by the field investigation and
analyzed for certain parameters in accordance with this chapter.
5. Detailed information on the geologic
conditions of the proposed site shall be provided by a geologist or other
technical specialist, or specialists, knowledgeable in geohydrologic
principles.
a. Detailed information on the
site hydrology and groundwater shall be provided by a geologist, hydrologist or
other technical specialist, or specialists, knowledgeable in hydrologic
principles and ground water hydrology.
b. The depth to the permanent ground water
table below the site shall be determined. The location, depth and extent of
perched water tables as well as the estimated seasonal fluctuations shall be
established. The effect of the permanent and seasonal water tables on
performance of the particular land treatment system shall be evaluated by the
design consultant.
c. The
characteristics of ground water movement under the proposed site should be
established and evaluated using piezometer installations or other acceptable
methods. The potential impact of the land treatment system on aquifer
hydraulics and water quality shall be predicted through the use of modeling and
appropriate monitoring devices.
d.
The present and planned uses of the aquifer(s) identified as affected by the
land treatment system should be determined by the consultant.
D. Land treatment
methods. The following methods, or combinations thereof, as regulated by the
appropriate permit or certificate, are considered conventional technology in
accordance with this chapter:
1. Irrigation -
slow rate. Wastewater may be applied by spraying, flooding, or ridge and furrow
methods. Irrigation methods are designed not to discharge to surface
waters.
2. Rapid infiltration.
Wastewater may be applied by spreading and spraying. The system shall be
designed to meet all certificate/permit requirements and groundwater
standards.
3. Overland flow. This
method of wastewater renovation is best suited for soils with low permeability.
Generally, a permit or certificate for a discharge to surface waters must be
issued.
E. Other
alternatives. Natural treatment systems such as aquatic ponds, constructed
wetlands and biological/plant filters and other aquatic plant systems are
somewhat related to land treatment technology. Natural treatment involves the
use of plants in a constructed but relatively natural environment for the
purpose of achieving treatment objectives. The major difference between
nonconventional natural and conventional treatment systems is that conventional
systems typically use a highly managed and controlled environment for the rapid
treatment of the wastewater. In contrast, nonconventional natural systems use a
comparatively unmanaged environment in which treatment occurs at a slower rate.
1. The use of natural treatment as a part of
a land treatment system may take several forms including ponds called "Aquatic
Processing Units" (APU). Floating plants such as water hyacinths and duckweed
are often used in APU treatment.
2.
Constructed wetlands are defined as areas where the wastewater surface is
controlled near (subsurface flow) or above (free water surface) a soil or media
surface for long enough each year to maintain saturated conditions and the
growth of related vegetation such as cattails, rushes, and reeds.
3. Constructed wetlands must provide for
groundwater protection and may be used to provide additional treatment to
primary, secondary, or highly treated effluents prior to final
discharge.
4. Natural (existing)
wetlands are considered as state waters and any discharge to them shall be
regulated in accordance with an issued discharge permit or
certificate.
F.
Features. Biological treatment that will produce an effluent either with a
maximum BOD5 of 60 mg/l or less, or be of such quality
that can be adequately disinfected, if necessary, shall be provided prior to
natural treatment, including use of conventional unit operations prior to the
land application of treated effluent and advanced treatment prior to reuse.
Disinfection may be required following or prior to land
application and other natural treatment. If spray irrigation equipment is
utilized, adequate aerosol management including pre-disinfection shall be
provided.
Buffer zones around field areas shall be provided in
accordance with the monitored maximum microbiological content of the applied
effluent as follows, with no reduction in required minimum distances to water
sources and channels:
|
Fecal Coliform Count(1)
(No./100 mls)
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Minimum Buffer Distance, Feet
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200 or less
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200(2)
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23 or less
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50(3)
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2.2 or less
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None, but no application during occupation of
field area(3)
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Notes:
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(1)Exceeded by no more
than 10% or less of samples tested.
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(2)No public use of
field areas.
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(3)Transient public
use may occur after a three-hour drying period following application.
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1. The
owner shall provide sufficient holding time to store all flow during periods
either when crop nutrient uptake is limited or nonexistent, the ground is
frozen, surface saturation occurs during wet weather, the ground is covered
with snow, or the irrigation site or field areas cannot otherwise be operated.
The total volume of holding required shall be based on the storage necessary to
provide for climatic conditions and the nutrient management requirements of the
field area crop. Operational storage necessary for system maintenance shall be
provided. Climatic holding periods shall be based on the most adverse
conditions of freezing and precipitation, as taken from accurate recorded
historical data that are available for the local area (in no case less than 25
years). The storage volume shall be sufficient to prevent any unpermitted
discharges to state waters.
2. A
minimum holding period of 120 days shall be required when climatic data is not
available. System backup storage shall be determined by the complexity of the
entire treatment system. An increase or reduction of minimum storage may be
considered on a case-by-case basis based on adequate documentation of agronomic
crop production and nutrient utilization.
3. The depth of the volume containment for
total storage requirements shall be measured above any minimum depth
requirements for maintenance.
4.
The owner shall provide a minimum reserve area equivalent in size to 25% of the
design field area. Additional reserve area may be required as evaluated by the
division, if the general conditions of the field area are deemed marginal or in
proximity of critical areas or waters. The reserve area shall be capable of
being used as a functional area within 30 days of notice.
5. Some allowance for a reduced reserve shall
be allowed if additional storage is provided or if there is an alternate
treatment mode (e.g., discharge) that can be utilized by the
facility.
6. Design criteria for
treatment or storage ponds shall be in accordance with this chapter and
standards contained in this chapter. In addition, the following requirements
shall be met:
a. A minimum operational water
depth shall be maintained.
b.
Provisions shall be made to allow complete drainage of the pond for
maintenance.
c. Duplicate pumps
shall be provided if necessary to transport pond flows, with the capacity of
each pump sized to handle the maximum rate of flow plus an allowance to deplete
stored volumes.
d. Disinfection may
be provided either upstream from ponds, or the pond effluent may require
disinfection.
e. When chlorination
is utilized to disinfect pumped flows, the detention time of the holding pond
chlorination facilities shall provide a minimum of 30 minutes of contact time,
based on the maximum design pumping rate in accordance with this chapter and
standards contained in this chapter.
G. Design loadings. Loading rates shall be
based on the most critical value as determined by the liquid and nutrient
application rates, or total application amounts for other constituents (such as
boron, salts, pH-alkalinity, copper or sodium, etc.), present in such
concentrations as could produce pollution of either the soil, cover crop, or
water quality. Total weekly application (precipitation plus liquid loading
rate) shall not exceed two times the design loading rate. This higher than
conventional loading rate shall be used only to balance seasonal water
deficits, and groundwater quality standards shall not be exceeded unless a
variance to the violated standard has been approved by the department.
1. An overall water balance shall be
investigated in accordance with one of the following equations based on design
criteria:
a. Irrigation or infiltration
design precipitation + effluent applied =
evapotranspiration + hydraulic conductivity.
b. Overland flow
design precipitation + effluent applied =
evapotranspiration + hydraulic conductivity + runoff.
2. Design precipitation shall be
the wettest year for a 10-year period (return frequency of one year in 10).
Minimum time period for this analysis should be 25 years. Average monthly
distribution (average percentage of the total annual precipitation that occurs
in each month) shall be assumed.
3.
Design evapotranspiration (monthly) shall be 75% of average monthly pan
evaporation values collected at official weather stations within or contiguous
to the Commonwealth of Virginia and should be representative (similar
geographically and climatological) of the proposed site.
4. Design hydraulic conductivity shall be a
given percentage (see Table 9) of respective laboratory and field measurements
that yield the rate at which water passes through the soil under presoaked
conditions.
The test methodology should be in accordance with current
published procedures made available to the department.
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TABLE 9.
DESIGN HYDRAULIC
CONDUCTIVITY
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Type of Test
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Percent of minimum measured value to be used in
design
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i. Saturated Vertical Hydraulic
Conductivity
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7
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ii. Basin Infiltration
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12.5
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iii. Cylinder Infiltrometers
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3
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iv. Air Entry Permeameter
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3
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v. (Other--to be evaluated by the
department)
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5. During periods of application, the applied
nitrogen shall be accounted for through (i) crop uptake and harvest; (ii)
denitrification; (iii) addition to surface water and ground water, or storage
in soil. In winter, site loadings for slow rate systems shall not exceed the
hydraulic design for those particular months. Winter application of treated
effluent may be provided only (i) to cool season grasses (ii) following three
consecutive days of minimum daily temperatures in excess of 25°F and
maximum in excess of 40°F.
6.
The annual liquid loading depth for plant nitrogen requirements shall be
determined by the following equation:
L = N/2.7C
Where:
N = Crop nitrogen uptake, lb/acre/yr.
C = Total nitrogen concentration, mg/l
C = TKN + NO2-N + NO3-N
L = Annual liquid loadings depth, ft/yr.
TKN = Total KJELDAHL nitrogen = organic N +
NH3 - N
7. The monthly nitrogen loading rate design
should be distributed over the growth cycle of the particular crop, as much as
practicable.
8. If other nutrients,
organics, or trace elements are present in concentrations critical to either
crops, soil, or water quality, then a total mass balance similar to that for
nitrogen shall be investigated for each critical element or compound.
9. The land application design average rate
shall be determined by the climatic conditions, selected crops, and soil
characteristics. However, the maximum application rates in terms of depth of
effluent applied to the field area shall be as follows:
a. One-fourth inch per hour.
b. One inch per day.
c. Two inches per week (one inch per week in
forest field areas used for year round application).
H. Field area design. Field area
is defined as the area of land where renovation of wastewater takes place (area
under actual spray or distribution pattern). The field area shall be designed
to satisfy the most critical loading parameter (i.e., annual liquid loading
depth) according to the following equation:
Field Area (acres) = Q/D*365/(365-S)
Where:
Q = Wastewater flow in (acre-inches/week)
D = Applied depth in inches/week
S = Minimum required storage capacity + annual resting
periods during the application season when no waste can be land applied.
1. The minimum storage capacity shall be the
average design volume of flow accumulated over a period of 60 days, unless
other storage periods are justified by climatic data. It should be noted that
the field area equation does not take into consideration the area needed for
reserve capacity or future expansion (no less than 25% of design field
area).
2. The field area shall be
divided into smaller sections for application to allow for rotational use of
these sections. Rotational operation shall be designed to provide the maximum
resting periods for field areas. The distribution system shall be designed to
meet the requirement for alternating application to the field area sections.
Minimum resting periods shall be two days, one day and two weeks for
irrigation, overland flow and infiltration-percolation, respectively. Maximum
wetting period shall not exceed five days, one week, and one day respectively
for irrigation, infiltration-percolation, and overland flow, respectively.
Resting and wetting periods depend on soil types, climatic conditions,
harvesting requirements, etc.
3.
The field area or areas shall be adequately enclosed with suitable fencing to
prevent access to livestock and the public where necessary. Signs shall be
posted at sufficient intervals (100 to 300 feet) around the entire perimeter of
field areas to identify the land treatment operation and specify access
precautions.
4. A groundwater
monitoring system shall be provided in accordance with the permit or
certificate requirements. A minimum of one upgradient and two downgradient
monitoring wells shall be provided. The well locations, along with typical well
construction specifications, shall be submitted with the proposal. Upon
installation, the driller's log shall be submitted. Additional monitoring well
locations may be required if deemed necessary upon evaluation of monitoring
data. The results of any required sampling and testing of groundwater shall be
submitted to the department for evaluation in accordance with the operating
permit.
5. Representative
agriculturally related soil tests are required on crop dependent systems to
ensure adequate vegetative cover. The growing and maintaining of a vegetative
cover on application sites is a very integral part of the system. The plants
prevent soil erosion and utilize nutrients and water. The system design should
provide for a proper balance between applied amounts of water and nutrients.
The designer may wish to consult with both agronomic and nutrient management
specialists on these matters. The design shall address crop and nutrient
management.
6. The wastewater
application schedule should be worked around the plans for harvesting. A
minimum of 30 days shall be required between the last day of application and
utilization of all crops. Crops that will be consumed raw by man shall not be
grown in land application field areas.
7. Information on the proposed crops and
their intended use may be forwarded to the Virginia Department of Agriculture
and Consumer Services for evaluation.
I. Low intensity design. The low intensity
application or irrigation field area should be as flat as possible with maximum
slopes of 5.0% or less. The design of low intensity irrigation of treated
effluent shall provide for nutrient management control. When it is necessary to
locate field areas on slopes of eight to 12%, special precautions shall be
taken to prevent seepage or runoff of sewage effluent to nearby streams. Dikes
or terraces can be provided for field areas, together with runoff collection
and return pumping equipment. The maximum field area slope should be 12%. The
irrigation field area shall be located a minimum distance of 50 feet from all
surface waters.
1. Five feet of well-drained
loamy soils are preferred. The minimum soil depth to unconsolidated rock should
be three feet. The hydraulic conductivity should be between 0.2-6
inches/hour.
2. The minimum depth
to the permanent water table should be five feet. The minimum depth to the
seasonal water table should be three feet. Where the permanent water table is
less than five feet and the seasonal water table is less than three feet, the
field area application rate shall be designed to prevent surface saturation. In
addition, underdrain and groundwater pumping equipment may be
required.
3. The method of applying
the liquid to the field shall be designed to best suit prevailing topographic,
climatic, and soil conditions. Two methods of application are:
a. Sprinkler systems with low trajectory
nozzles or sprinkler heads to uniformly distribute the applied effluent across
a specified portion of the field area. Application is to be restricted in high
winds that adversely affect the efficiency of distribution and spread aerosol
mists beyond the field areas.
b.
Ditch irrigation systems that utilize gravity flow of effluent through ditches
or furrows, from which effluent percolates into the soil. For uniformity of
distribution, the slope of the field area is to be uniform and
constant.
4. The height
of spray nozzles, pressure at the spray nozzles and spacing of the laterals
shall be adequate to provide uniform distribution of the effluent over the
field area. The design height and pressure of the spray nozzles shall avoid
damage to vegetation and soil.
5.
Adequate provisions shall be made to prevent freezing and corrosion of spray
nozzles and distribution lines when the system or a section of the system is
not in operation.
6. Appropriate
vegetation shall be maintained uniformly on all field areas. Usually water
tolerant grasses with high nitrogen uptakes are used. Over seeding with cool
season grasses may be necessary during the fall season, prior to October 15 of
each year. Silviculture sites and reuse irrigation sites may also be used with
this type of land treatment.
J. Rapid infiltration. This form of treatment
requires the least amount of land. Renovation is achieved by natural, physical,
chemical, and biological processes as the applied effluent moves through the
soil. Effluent is allowed to infiltrate the soil at a relatively high rate,
requiring a field area with coarse grained soils. This system is designed for
three main purposes (i) ground water recharge; (ii) recovery of renovated water
using wells or underdrains with subsequent reuse, or (iii) discharge and
recharge of surface streams by interception of ground water.
1. Five feet of sand or loamy sand is
preferred. Soil grain size should be greater than.05 mm in size. The hydraulic
conductivity should be greater than two inches/hour.
2. The permanent ground water table shall be
a minimum of 15 feet below the land surface. With this method, a recharge mound
is not uncommon and shall be properly evaluated by the consultant. A minimum
distance of 10 feet should be maintained between the land surface and the apex
of the recharge mound (during a worse-case situation). Lesser depths may be
acceptable where under drainage is provided.
3. Spreading and spraying are the two main
application techniques that are suitable for
infiltration-percolation.
4. Design
application rates will vary according to the site area, soil, geology, and
hydrology characteristics.
5. The
buffer distances from extremities of field areas to private wells should be at
least 400 feet.
K.
Overland flow. Renovation of wastewater is accomplished by physical, chemical,
and biological means as applied effluent flows through vegetation on a
relatively impermeable sloped surface. Wastewater is sprayed or flooded over
the upper reaches of the slope and a percentage of the treated water is
collected as runoff at the bottom of the slope, with the remainder lost to
evapotranspiration and percolation. Overland systems should be capable of
producing effluent at or below secondary level; however, additional treatment
units may be needed to achieve the permitted effluent limitations.
1. Soils should have minimal infiltration
capacity, such as heavy clays, clay loams or soils underlain by impermeable
lenses. The restrictive layers in the soil should be between one to two feet
from the surface to maintain adequate vegetation. The hydraulic conductivity
should be less than 0.2 inches/hour. Field area slopes shall be less than 8.0%.
Monitoring wells shall be provided.
2. Renovated water shall be collected at the
toe of the slope in cut off ditches or by similar means and channeled to a
monitoring point and disinfected as required.
3. The effluent application method should
achieve a sheet flow pattern that will produce maximum contact between the
applied wastewater and the soil medium. This can be accomplished by lateral
distribution methods, low pressure sprays and moderate to high pressure impact
sprinklers discharging onto porous pads or aprons designed to distribute the
applied flow while preventing erosion. Maximum application rates in terms of
depth of effluent should be less than 10 inches per week.
4. Perennial field area vegetation shall be
required. Hydrophilic or water tolerant grasses are usually grown with this
type of system.
L.
Alternative design. Information submitted for approval of other natural
treatment systems and reuse alternatives shall include performance data
obtained from either full-scale systems similar to the proposed design, or
pilot studies conducted over a testing period exceeding one year, to a period
of two years, based on test results.
Special consideration should be given to the following
factors in planning and design of natural systems:
1. Many aquatic plants are sensitive to cold
temperatures and may require the use of a protected environment or operation on
a seasonal basis. Some plants may be considered unacceptable for use and their
growth must be controlled.
2.
Control of insects, particularly mosquitoes, is normally required for
constructed wetlands and aquatic plant systems. The use of mosquito-eating fish
and water depth adjustments are recommended.
3. Some constituents which may be present in
wastewaters, particularly those having high industrial loads, are toxic to many
aquatic plants. Therefore, tests should be conducted to identify possible
toxics prior to selection of the aquatic plant species.
4. Natural systems utilize a higher life form
of less diversity than found in more conventional biological treatment systems.
This lack of biological diversity may reduce treatment performance. Constructed
wetland and aquatic plant systems could be more susceptible to long term
process upsets. Therefore, the effects of fluctuations in climate and
wastewater characteristics is extremely important in the design of natural
systems.
5. Some aquatic plant and
animal species have the potential to create a nuisance condition if
inadvertently released to natural waterways. Federal, state and local
restrictions on the use of certain aquatic plants and animals shall be
considered.
6. Harvesting and the
use or disposal of aquatic plants should result in removal of organics, solids
and nutrients such as nitrogen and phosphorous from the APU effluent.
Management of residual matter shall be in accordance with this chapter and
standards contained in this chapter.
Statutory Authority: § 62.1-44.15 of the Code of
Virginia.
