(a) Types of Constructed Wetlands. A constructed wetland
may be either a free water surface system or subsurface flow system.
(b) Natural Wetlands. The use of natural wetlands
for wastewater treatment is prohibited. For the purposes of this
chapter, a natural wetland is an area which was not constructed for
wastewater treatment that meets the definition of wetlands in 40
Code of Federal Regulations, Part 230.
(c) Constructed Wetland Design.
(1) A constructed wetland must be preceded by primary
treatment or secondary treatment.
(2) A primary treatment system that precedes a constructed
wetland must be designed to control odor and algae.
(3) A primary treatment system must produce an effluent
quality with no more than 150 milligrams per liter of five-day biochemical
oxygen demand to discourage anaerobic conditions and stress on vegetative
communities in any subsequent wetland treatment unit.
(4) A wastewater treatment facility that uses a constructed
wetland as the means of complying with a permit effluent limit must
be sized and designed to ensure that the permit limitations will
be met even when any one wetland cell is out of service. The engineering
report must include water balance calculations and the potential
effect of evaporation on the predicted effluent concentrations.
(d) Vegetation. A constructed wetland must have a
diverse vegetative community of emergent and floating plants to
minimize any adverse impact from potential disease, insect pests,
or species-specific toxicity. A constructed wetland must include
a diversity of plants selected from the following categories of emergent
plants, floating plants, or both.
(1) Emergent plants for use in constructed wetlands
include:
(A) Schoenoplectus spp. (bulrush);
(B) Sagittaria spp. (arrowhead);
(C) Phragmites spp. (reeds);
(D) Juncus spp. (rushes);
(E) Eleocharis spp. (spikerush);
(F) Carex spp. (sedges);
(G) Caladium spp. (elephant ear);
(H) various aquatic grass species (e.g., wild rice);
and
(I) other appropriate emergent plant species approved
in writing by the executive director.
(2) Floating plants for use in constructed wetlands
include:
(A) Lemna spp. (duckweed);
(B) Hydrocotyle umbellata (water pennywort);
(C) Limnobium spongia (frogbit);
(D) Nymphaea spp. (water lily);
(E) Wolffia spp. (water meal); or
(F) other appropriate floating plant species approved
in writing by the executive director.
(3) The vegetation used in a constructed wetland must
be suitable for the local growing conditions. The use of indigenous
plants is recommended if the species have been demonstrated effective
in a constructed wetland wastewater environment. The engineering
report must identify the plants that will be used in each constructed
wetland.
(4) Plans for harvesting aquatic plants from water
in the state must be reviewed with the United States Army Corps of
Engineers to determine if regulatory coordination is required.
(5) Gathering seed plants from natural wetlands must
minimize any impact on the harvested plant community and the natural
wetlands.
(6) The use of any harmful or potentially harmful
wetland plant or organism is subject to review by the Texas Parks
and Wildlife Department, as required by 31 TAC §§57.111
- 57.118 and §§57.251 - 57.258 (relating to Definitions;
General Rules; Exceptions; Health Certification of Harmful or Potentially
Harmful Exotic Shellfish; Transportation of Harmful or Potentially
Harmful Exotic Species; Exotic Species Transport Invoice; Exotic
Species Permit: Application Requirements; Exotic Species Permit Issuance;
Definitions; General Provisions; Permit Application; Denial; Renewal;
Amendment; Reporting and Recordkeeping; and Prohibited Acts, respectively).
(e) Maintenance of a constructed wetland must not
result in a deterioration of effluent quality.
(1) The use of herbicides, insecticides, and fertilizers
in a constructed wetland is prohibited.
(2) Floating Material Removal.
(A) A constructed wetland must be designed to allow
the removal of an algal mat or other floating material prior to the
effluent entering each cell of the constructed wetland.
(B) A removal mechanism must be a screen, a submerged
adjustable inlet, a baffle, or another method approved in writing
by the executive director. The removal mechanism must be justified
in the engineering report.
(C) The removed floating material must be stored and
disposed of in a manner that minimizes odor and complies with the
requirements of Chapter 330 of this title (relating to Municipal
Solid Waste).
(3) The operation and maintenance manual for a wastewater
treatment facility that has a constructed wetland must include a
detailed description and schedule for maintaining the constructed
wetlands. The maintenance plan must include a schedule and procedure
for removing overabundant live plant material and dead plant material.
(f) A constructed wetland system must have an established
plant community and must be functioning properly before wastewater
effluent is processed. The engineering report must include a management
and oversight program that specifies construction scheduling, plant
species selection, planting practices, and start-up procedures.
(g) Liners.
(1) The liner for a constructed wetland system must
comply with the requirements of §217.203(d) and (e) of this
title (relating to Design Criteria for Natural Treatment Facilities).
(2) A layer of productive topsoil at least 6.0 inches
thick must be placed above a liner to encourage root propagation.
(h) Berms. A berm of a constructed wetland must comply
with the requirements of §217.203(f) of this title.
(i) Flood Hazard Analysis. A constructed wetland must
be protected from flooding according to the requirements of §217.35
of this title (relating to One Hundred-Year Flood Plain Requirements).
(j) Nitrification. A constructed wetland that provides
nitrification is an innovative and non-conforming technology and
is subject to the requirements of §217.7(b)(2) of this title
(relating to Types of Plans and Specification Approvals).
(k) Allowed Uses. A constructed wetland may be used
as a secondary treatment unit, as an advanced secondary treatment
unit, or for polishing wastewater effluent. A constructed wetland
may not be used for primary treatment.
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