Castroville Regional Park Constructed Wetlands Project

The Medina River is a vital source of water for domestic household use and agriculture along its 120-mile course from Medina Dam on the Medina-Bandera County line to its confluence with the San Antonio River in southern Bexar County. The river, which below the dam has a relatively consistent flow due to the discharge from Medina Lake, also serves as important habitat for aquatic and riparian species in a drought-prone region that has relatively few consistent surface water flows.

However, due to increased development and growth in the Medina River basin, the river’s water quality also faces increasing threats from wastewater treatment plant discharge, failing septic systems, stormwater runoff, and overuse of fertilizers that contain nitrogen and phosphorus. These increased threats can lead to increased algal blooms and reduced water quality across the Medina River basin. Currently, the Texas Commission on Environmental Quality (TCEQ) has flagged four of the five segments of the Medina River Below Medina Diversion Lake (1903_01 through 1903_04) for water quality concerns because of excess nutrients and bacteria levels in the water. In fact, TCEQ has listed three of the five segments (1903_01 through 1903_3) in the Texas 303(d) List, the state’s report of waterbodies that are not meeting applicable water quality standards.

The Medina River segment directly affected by this project, segment 1903_05, remains unimpaired and meets TCEQ standards for domestic use, swimming, agriculture, and aquatic life. However, this segment passes through the City of Castroville, whose population has increased from 2,860 in 2010 to 3,284 in 2020. As the City of Castroville’s growth continues to increase, effort needs to be taken today to protect and preserve the water quality within segment 1903_05.

To meet this goal, project efforts will focus on the design and installation of a constructed wetland to assist in keeping the Medina River segment unimpaired by employing passive wetland treatment to further clean the water discharged from the Castroville Waste Water Treatment Plant (WWTP) before it enters the Medina River. The wetland plants to be installed in the more-than-300-meter channel will remove many of the nutrients, bacteria, and other contaminants that remain in the treated wastewater discharged from the Castroville WWTP, resulting in a decreased pollution load to the Medina River.

In addition to providing improved water quality, the constructed wetland will serve as a wildlife habitat and a recreational amenity to Castroville Regional Park, the largest municipal park in Medina County. Rather than simply providing a concrete-line channel to convey the wastewater directly to the Medina River, this project would add a series of pools and riffles with native plantings that will enhance the park’s attractiveness and habitability for invertebrates, fish, reptiles, amphibians, and birds.

Since February 2020, the City of Castroville (the City) has been engaged in the design phase of an upgrade to its wastewater treatment plant, located at Castroville Regional Park, to ensure the facility continues to meet state standards. As part of this upgrade, the City has contemplated installing a drainage channel to convey treated wastewater from the plant’s discharge point to the Medina River. This channel would be linear, trapezoidal, and lined with concrete. However, in partnership with GEAA and Friends of Castroville Regional Park (FCRP), the City is considering formal approval of constructed wetlands as an alternative proposal that would better accommodate wildlife habitat, water quality, and recreation needs.

The U.S. Environmental Protection Agency defines “constructed wetlands” as “treatment systems that use natural processes involving wetland vegetation, soils, and their associated microbial assemblages to improve water quality” (EPA, 2004). The Castroville Constructed Wetlands Project will rely on native wetland vegetation and natural channel design to achieve an improvement in water quality, with an associated benefit for wildlife.

Many of Castroville Regional Park’s visitors come to the park to use the trails designed and maintained by FCRP, a 501c3 nonprofit organization. In 2012, FCRP and GEAA started work on the Botanical Garden Trail Project, which approximately parallels the route of the proposed wastewater treatment plant effluent. Prior to the trail’s construction, there was no safe way for park visitors to move from the upper parking lot, butterfly garden, and swimming pool to the main part of the park without walking in the street. In 2021, this project was renamed the Mary Irish Botanical Garden Trail (MIBGT).

The MIBGT functions much more than a simple sidewalk. This winding trail, through existing planting areas, provides visitors an opportunity to observe native plants, birds, and pollinators as they walk from the upper parking lot to the main areas of the park. Enhancing the trail with the adjacent Constructed Wetland Project improves the water quality discharge from the City wastewater plant into the Medina River while providing an attractive recreational and educational amenity.

The MIBGT project consists of four sections. Section One leads visitors from the upper parking lot through Planting Area 2. Section Two goes from Planting Area 2, past the main information kiosk for the park, to the Founder’s Garden. Section Three continues from the Founder’s Garden to the start/finish sign of the One Mile Walking Loop in the main portion of the park. Section Four incorporates a Constructed Wetland into the MIBGT, the One Mile Walking Loop, and the Garden of Roots.

The MIBGT project was approved by the City Council at a regularly scheduled meeting on July 22, 2014. Section One has been completed. Work on Sections Two-Four was suspended due to a Texas Commission of Environmental Quality (TCEQ) enforcement order for dam repairs at the wastewater plant.

GEAA has provided technical and financial assistance to FCRP since 2012 when downstream landowners complained about the City’s proposed discharge to the Medina River. GEAA staff felt that working to improve the quality of the effluent was a preferable solution than contesting the permit. GEAA hired Marita Roos (UrbanBiology), a landscape architect, to work with FCRP and develop a concept plan for a Constructed Wetlands Project in Castroville Regional Park.

FCRP, GEAA, and the City of Castroville have entered into a formal agreement to collaborate on the successful implementation of MIBGT, Section Four, the Constructed Wetland. This will consist of a series of native plant features that will improve the water quality discharged into the Medina River. These constructed wetland features will be interconnected with a universally accessible walking trail and create an outdoor environmental education classroom. Funding received from the Dudley T. Dougherty Foundation will directly assist in the administration and development of this stated project effort.