ANNUAL REPORT FOR 2008
Wastewater Treatment Mitigation Site
New Hanover County
TIP No. U-92 A/B
Prepared By:
Natural Environment Unit & Roadside Environmental Unit
North Carolina Department of Transportation
September 2008
TABLE OF CONTENTS
Summary 1
1.0 Introduction 2
1.1 Project Description .................................................................................2
1.2 Purpose ..................................................................................................2
1.3 Project History ........................................................................................2
2.0 HYDROLOGY 5
2.1 Success Criteria .....................................................................................5
2.2 Hydrologic Description............................................................................5
2.3 Results of Hydrologic Monitoring............................................................5
2.4 Conclusions............................................................................................5
3.0 VEGETATION 6
3.1A Success Criteria (Bald Cypress Area) ....................................................6
3.1B Success Criteria (Marsh Grass Area) .....................................................6
3.2A&B Description of Planted Areas..............................................................7
3.3A Results of Vegetation Monitoring (Bald Cypress Area)...........................7
3.3B Results of Vegetation Monitoring (Marsh Grass Area)............................8
3.4A Conclusions (Bald Cypress Area)...........................................................9
3.4B Conclusions (Marsh Grass Area)............................................................9
4.0 OVERALL CONCLUSIONS/RECOMMENDATIONS 9
FIGURES
Figure 1. Vicinity Map .............................................................................................3
Figure 2. Site Location Map....................................................................................4
APPENDICES
Appendix A - Site Photos & Plot and Photo Locations Map
1
SUMMARY
The following report summarizes the monitoring activities that have occurred in 2008 at
the Wastewater Treatment Mitigation Site. The 2008-year represents the fifth year of
hydrology and vegetation monitoring following construction. The site must demonstrate
success for a minimum of five years or until the site is deemed successful. The site was
constructed to serve as mitigation for impacts associated with the construction of
U-92A/B for the Smith Creek Parkway.
A tidal gauge was installed at the Bridge Maintenance site in July 2000 and was used
as a reference for the Smith Creek, Wastewater Treatment, and County Sites. Tidal
data was collected from July 2000 to July 2004. These sites were graded to elevations
based on this tidal data.
Hydrologic monitoring utilizes four surface water gauges located on the adjacent County
Mitigation Site and a reference gauge located on the Bridge Maintenance Mitigation
Site. These gauges monitor the tidal regime to confirm the site’s flooding period.
An onsite agency meeting was held in July 2004. At this time, it was agreed to remove
the surface water gauge at the Bridge Maintenance Site since there was sufficient past
tidal data. The available tidal data for the Bridge Maintenance gauge revealed
inundation for 25.6% from February to July (2004). The four surface water gauges at
the County Site were compared to the reference gauge. Three of the four surface
gauges indicated that the site was inundated 100% of the growing season (hourly
readings), while one gauge revealed 94.8%. For the gauge data provided, all four
surface water gauges satisfied the inundation criteria determined by the reference
gauge.
Vegetation monitoring is required for five years. Vegetation monitoring of the
baldcypress area revealed an average tree density of 72 trees per acre. This average
is above the minimum success criteria of 50 trees per acre. For the marsh grass area,
the target species and scale values were 63% and 4.6, respectively; the marsh grass
area is on track for the fifth year of monitoring.
During the July 2004 onsite agency meeting, it was agreed that NCDOT could propose
to remove the four surface water gauges at the County Site if there was successful tidal
data during the 2004-monitoring season. During the 2004 annual monitoring meeting
on May 5, 2005, it was agreed that the County Mitigation Site had one year of
successful gauge data (tidal); therefore the four surface gauges were removed on June
22, 2005 and no hydrologic data has been presented in this report.
NCDOT proposes to discontinue all monitoring at the Wastewater Treatment Mitigation
Site.
2
1.0 INTRODUCTION
1.1 Project Description
The Wastewater Treatment Mitigation Site is located in New Hanover County, adjacent
to Bridge Maintenance and the U-92B project in Wilmington (Figure 1). Totaling 0.71
acre in size, the site provides tidal swamp forest creation mitigation for a portion of the
wetland impacts associated with U-92A/B (Figure 2).
1.2 Purpose
In order to demonstrate successful mitigation, hydrologic and vegetation monitoring
must be conducted for a minimum of five years or until the site is deemed successful.
The following report describes the results of both hydrologic and vegetation monitoring
for the 2008-year (the fifth year of monitoring).
1.3 Project History U-92 Wastewater Treatment Site
February 2004 Baldcypress Planted
April 2004 Marsh Grass Planted
March-November 2004 Hydrology Monitoring (1 yr.)
August 2004 Vegetation Monitoring (1 yr.)
September 2005 Vegetation Monitoring (2 yr.)
August 2006 Vegetation Monitoring (3 yr.)
August 2007 Vegetation Monitoring (4 yr.)
October 2007 Phragmites Treated
April 2008 Phragmites Treated
September 2008 Vegetation Monitoring (5 yr.)
October 2008 Kudzu Treated
3
Figure 1. Vicinity Map
4
Figure 2. Site Location Map
5
2.0 HYDROLOGY
2.1 Success Criteria
Hydrology monitoring for the Wastewater Mitigation Site is conducted at the adjacent
County Mitigation Site. Data from an offsite tide gauge located at the adjacent Bridge
Maintenance Site (collected 02-27-04 through 07-14-04) was used as a baseline to
estimate the percentage of time that the site should remain flooded, at specific
elevations. A target elevation of 2.5 feet above mean sea level was selected for the
Wastewater Mitigation Site. Using the baseline data and the proposed elevation, the
Wastewater Site will be considered hydrologically successful if the adjacent County Site
is inundated for 25.6% of the growing season, from February 27 to November 26 (271
days).
2.2 Hydrologic Description
The County Mitigation Site was equipped with four surface water gauges that were
installed in December 2003. Since the site is a tide-driven system, groundwater and
rain gauges were not installed. During the 2004 annual monitoring meeting on May 5,
2005, it was agreed that the County Mitigation Site had one year of successful gauge
data (tidal); therefore the four surface gauges were removed on June 22, 2005 and no
hydrologic data has been presented in this report.
2.3 Results of Hydrologic Monitoring
Hydrology monitoring has been discontinued at the County Mitigation Site.
2.4 Conclusions
During the 2004 annual monitoring meeting on May 5, 2005, it was agreed that the
County Mitigation Site had one year of successful gauge data (tidal); therefore the four
surface gauges were removed on June 22, 2005 and no hydrologic data has been
presented in this report.
6
3.0 VEGETATION: U-92 WASTEWATER TREATMENT SITE
(YEAR 5 MONITORING)
3.1A Success Criteria (Baldcypress Area)
One 50’ x 50’ plot has been set and will be counted as part of the vegetation monitoring
for the site.
The site will be considered a success for the baldcypress if there are 50 five-year
old trees per acre after the end of the fifth growing season….changes in
the hydrology of Smith Creek have caused the decline in natural baldcypress
populations, and it is uncertain if the planted baldcypress trees will survive. If
the baldcypress survivorship declines to below the success criteria, then the
Department of Transportation will consult with the Corps of Engineers to
determine appropriate action.
Establishment of cypress trees over the restoration area of the Wastewater
Treatment Site is proposed, although there is evidence that they may not
survive because of increases in salinity, tidal amplitude, and sea level
(Hackney and Yelverton, 1990). Consequently, if cypress mortality occurs
and the area develops into an emergent marsh community, the vegetational
success criteria will be based on emergent marsh vegetation.
3.1B Success Criteria (Marsh Grass Area)
The vegetative marsh success of the wetland site will be determined in accordance with
NMFS Guidelines. Monitoring plots found to be located within the open water channel
will not be evaluated, and will not count to the final count of plots. The vegetation
component of the wetland site will be deemed successful if the following criteria are
met.
1. At year five, the average of all plots should have a scale value of 5 (75%
vegetative cover) consisting of wetland herbaceous species, not including any
invasive species.
2. A minimum of 70% of the plots shall contain the target (planted) species.
7
3.2A & B Description of Planted Areas
The following plant communities were planted throughout the Wastewater Treatment
site (approximately 0.71 acres):
Spartina cynosuroides, Big Cordgrass
Cladium jamaicense, Sawgrass
Taxodium distichum, Baldcypress
3.3A Results of Vegetation Monitoring (Baldcypress Area)
Plot #
Baldcypress (5 Year)
Total (at planting)
Density (trees/acre)
1 6 9 72
AV G . DE NS ITY 72
8
3.3B Results of Vegetation Monitoring (Marsh Grass Area)
Site Notes: The following species were also noted in the monitoring plots. The number
of plots the species were found in is listed in parentheses (i.e. 28 of the plots contain
cattail) cattail (28), Sagittaria sp. (2), Scripus robustus (2), and phragmites (2). Some
small patches of phragmites were treated in October 2007 and April 2008. These spray
treatments have helped to minimize the amount of phragmites noted on site. There was
some kudzu noted encroaching from the fill slope out into the site during the 2008
monitoring evaluation. Division Roadside treated the kudzu on October 1, 2008.
ZONE
Plot #
Scale Factor
Spartina cynosuroides
Cladium jamaicense
Frequency
Notes
1 1 5.0     Cattail
2 4.0      
3 5.0 Cattail
4 4.0 Cattail
5 5.0     Cattail
6 4.0 Cattail
7 5.0       Cattail
8 5.0       Cattail
9 5.0     Cattail
10 5.0     Cattail
11 5.0     Cattail
12 5.0     Cattail
13 5.0    
14 5.0     Cattail
15 5.0     Cattail
16 3.0 Sagittaria sp. , Cat tail
17 2.0 Sagittaria sp. , Cat tail
18 5.0     Cattail
19 5.0     Cattail
20 3.0 Cattail, 1% Phra gmites
21 4.0 Cattail, 1% Phra gmites, Scirpus robustus
22 5.0 Cattail, Scirpus robustus
23 5.0 Cattail
24 5.0       Cattail
25 5.0 Cattail
26 5.0     Cattail
27 4.0     Cattail
28 5.0     Cattail
29 5.0     Cattail
30 5.0
Freqency (Percenta ge of
Plots with Desired Species) 63%
Sum Scale Value 138
Total Number of Plo ts Counted 30
Vegetative Cover (Scale Value) 4.6
9
3.4A Conclusions (Baldcypress Area)
Baldcypress trees were planted on 20’ centers throughout the approximately 0.71 acre
site. One 50’ x 50’ plot was established in the planting area. The vegetation monitoring
of the planted area revealed an average of 108 baldcypress trees per acre.
NCDOT proposes to discontinue monitoring the baldcypress area.
3.4B Conclusions (Marsh Grass Area)
· Percent Frequency of Target Species (Big Cordgrass and
Sawgrass) 63%
Frequency of 70% required.
· Vegetative Cover Scale Value 4.6
Scale Value of 5 required for year 5.
Approximately 0.71 acres of this site involved marsh grass plantings. There were 30
random plots established throughout the planting area. These plots were located with
GPS. The overall comparison of the percent frequency and the scale value for the
marsh grass area is on track for the fifth year of monitoring.
NCDOT proposes to discontinue monitoring the marsh grass area.
4.0 OVERALL CONCLUSIONS/ RECOMMENDATIONS
An onsite agency meeting was held in July 2004. At this time, it was agreed to remove
the surface water gauge at the Bridge Maintenance Site since there was sufficient past
tidal data. The available tidal data for the Bridge Maintenance gauge revealed
inundation for 25.6% from February to July (2004). The four surface water gauges at the
County Site were compared to the reference gauge. Three of the four surface gauges
indicated that the site was inundated 100% of the growing season (hourly readings),
while one gauge revealed 94.8%. For the gauge data provided, all four surface water
gauges satisfied the inundation criteria determined by the reference gauge.
Baldcypress trees were planted on 20’ centers throughout the approximately 0.71-acre
site. Vegetation monitoring of the baldcypress area revealed an average tree density of
72 trees per acre. This average is above the minimum success criteria of 50 trees per
acre. Approximately 0.71-acre of this site involved marsh grass plantings. For the
marsh grass area, the target species and scale values were 63% and 4.6, respectively;
the marsh grass area is on track for the fifth year of monitoring. NCDOT proposes to
discontinue monitoring the baldcypress and marsh grass areas.
10
During the 2004 annual monitoring meeting on May 5, 2005, it was agreed that the
County Mitigation Site had one year of successful gauge data (tidal); therefore the four
surface gauges were removed on June 22, 2005 and no hydrologic data has been
presented in this report.
NCDOT proposes to discontinue all monitoring at the Wastewater Treatment Mitigation
Site.
APPENDIX A
SITE PHOTOS
&
PLOT AND PHOTO LOCATIONS MAP
Wastewater Treatment
Photo 1 Photo 2
September 2008