Elsevier

Ecological Engineering

Volume 73, December 2014, Pages 353-366
Ecological Engineering

Great swamp natural effluent management system – a summary of thirteen years of operations

https://doi.org/10.1016/j.ecoleng.2014.09.018Get rights and content

Abstract

Beaufort-Jasper Water & Sewer Authority has discharged reclaimed wastewater continuously for thirteen years to a 194 ha natural swamp forest in coastal South Carolina (USA). Wastewater inputs have increased from an average of 363 m3/d in 1999 to an average of 8823 m3/d in 2011. Natural inflows of rainfall and runoff to the swamp forest, averaging 9757 m3/d exceed anthropogenic inputs. Wastewater inputs have increased the swamp’s inundation frequency in the lowest areas from 43 to 100%. Reclaimed water receives advanced secondary pretreatment with concentrations averaging 2.9 mg/L five-day biochemical oxygen demand (BOD5), 2.8 mg/L total suspended solids (TSS), 0.5 mg/L ammonium nitrogen (NH4-N), 6.7 mg/L total nitrogen (TN), and 2.2 mg/L total phosphorus (TP). A variable percentage of these pollutants are assimilated within the swamp. Concentrations of chlorides, specific conductance, and TP are the only downstream water quality evidence of discharge. The dominant gum (Nyssa spp.) and baldcypress (Taxodium distichum) trees are thriving; however, red maple (Acer rubrum) trees have reduced dominance primarily due to increased hydroperiod. Macroinvertebrate and fish populations in the swamp forest have increasing biomass in response to increased wetted area. The Great Swamp Effluent Management System is an example of adaptive ecological engineering, protecting downstream recreational and shellfish waters by creating a productive interface between reclaimed wastewaters and natural wetlands.

Introduction

High seasonal rainfall, shallow groundwater, slow-flowing rivers, and sensitive coastal environments result in challenging issues for wastewater management in coastal South Carolina. These challenges are exacerbated as more and more people move into the area. Direct discharges of treated wastewaters to surface waters are severely limited by low flow conditions and the need to protect shellfish resources in the area’s coastal rivers. While land application of treated effluent is the preferred alternative for effluent reuse and ultimate disposal, application rates to area “uplands” are often limited by marginal soil drainage and inadequate unsaturated soil depth, especially during rainy periods.

Limited wastewater disposal capacity has led the area to a wastewater management solution that integrates urban development and the area’s abundant natural aquatic resources. Pioneered at the nearby Sea Pines Plantation Forest Preserve on Hilton Head Island beginning in 1983, wet weather backup wastewater disposal incorporates compatible natural freshwater wetlands into an overall effluent management system (Knight and Ferda, 1989). This solution to the area’s increasing need for wastewater management helps to conserve natural wetland habitat in public ownership and restore previously impacted wetlands while providing an environmental reuse option for recycling treated wastewater. Furthermore, the area’s coastal waterways remain attractive for recreation while wastewater is managed in a cost-effective manner.

Section snippets

Treatment system and operating permit

BJWSA owns and operates the 28390 cubic meters per day (m3/d) Cherry Point/Okatie Area Water Reclamation Facility (WRF) in southern Jasper County, South Carolina. This oxidation ditch/activated sludge/filtration facility provides a high level of treatment for five-day biochemical oxygen demand (BOD5), total suspended solids (TSS), and ammonium nitrogen (NH4-N), with long-term average permitted effluent concentrations less than 5,5, and 2 mg/L, respectively. Following UV disinfection, reclaimed

Methods

To evaluate the health of the wetland following the initiation of treated effluent discharge, permit conditions required baseline monitoring. Since discharge began in 1999, sampling has been completed to collect data for comparison to the baseline monitoring period. Collection of baseline data for comparison has both advantages and disadvantages. The advantages of this type of baseline monitoring are the collection of site-specific data that may be difficult or impossible to replicate in a

Hydrology

During the baseline period the primary input of water to the EMS was from direct rainfall and runoff. The dominance of natural water inputs has remained during the 13-year operational period with period-of-record average rainfall and runoff estimated at 2866 m3/d and 6892 m3/d, respectively. On average it was estimated that the 2011 reclaimed water inflow of 8823 m3/d was equivalent to about 40% of the combined inputs from rainfall and non-point source runoff.

Since project initiation in 1999,

Discussion

The NPDES permit for the Great Swamp EMS includes “biological criteria”, including allowable changes to canopy dominance in each vegetation quadrat as well as for the average over the entire wetland. Significant negative impacts are defined in the permit as a total decline in canopy basal area (dominance) of 20% or more averaged over the entire wetland site or a canopy decline of 40% or more at any individual station.

Overall average canopy basal area (quadrats) as well as groundcover

References (14)

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