1

Chapter One: Introduction

Figure 1.1: Villanova University Constructed Stormwater Wetland (View from Upstream/Inlet Looking Downstream/Outlet)

1.1 Introduction

The primary purpose of the present study is to analyze the pollutant removal efficiency o

the Villanova University Constructed Stormwater Wetland (CSW) during both times of baseflow

and storm events. This research analyzes the presence of a trend in the pollutant removal

efficiencies throughout the different seasons of the year as well as in the removal efficienci

between the different pollutants. Additionally, while not part of this present research, the data

collected and analyzed add to the body of nutrient data for this CSW. A secondary aspect of the

study is the investigation of plant effects on the removals. Factors that impact nutrient removal

include the flow path, retention time, plant density and plant type. The Villanova University

CSW has a Phragmites australis invasion problem. Although P. austra

f

es

lis is very efficient at

moving nutrients, control regimes are used to remove P. australis from the CSW in order to

ival of the native plants. This poses a question: If P. australis is

re

allow for the continued surv

2

effective at removing pollutants, why should it be removed from the CSW? A second

component of the present study, a plot study, aims to answer this question. The plot study is a

series of plots within the CSW with different plant types. As flow moves through each plot,

as surface water and groundwater, nutrients may be removed through physical, chemical and

biological action. Another question addressed in the plot study is: Are nutrients removed

through the plots? To answer these questions, the study will test the hypothesis of: A species

diverse CSW is more effective at removing pollutants than a P. australis dominated CSW. If th

studies show that native plants are just as or more effective at pollutant removal than P. austral

then P. australis control programs would be more substantiated, and the goal of maintaining a

species diverse CSW will receive an even larger desire for realization.

1.2 General Background

The objective o

both

e

is,

f the present study is to examine the nutrient removal efficiency of a

d Wetlands

rest

m

ars time will be analyzed in order to assess the functioning and seasonal performance

f a ma

ivil

rmwater

artnership (VUSP) in 2002. The mission of the VUSP is to foster the developing

omprehensive stormwater management field as well as aide the formation of public and private

partnerships through research on stormwater Best Management Practices (BMPs), directed

studies, technology transfer and education. The VUSP manages a collective research effort on a

functioning CSW. Constructed stormwater wetlands (CSWs) are designed to remove pollutants

from stormwater runoff via a variety of mechanisms: plant uptake, microbial breakdown of

pollutants, retention, settling and soil adsorption (Metropolitan Council, Constructe

Stormwater Wetlands, 2001). CSWs have low operating and maintenance costs, and they are

also aesthetically pleasing (EPA, Constructed Treatment Wetlands, 2004). The CSW of inte

is a green infrastructure located on the campus of Villanova University (Figure 1.1). Previous

studies have been performed on this CSW addressing the removal efficiencies during times of

storm events and baseflow (Rea, 2004; Woodruff, 2005). Both storm and baseflow events fro

over a ye

o ture CSW. The pollutants of interest in the removal studies are: total nitrogen, total

phosphorus, total orthophosphate, total chloride, total suspended solids, and total dissolved

solids.

The Pennsylvania Department of Environmental Protection and the Department of C

and Environmental Engineering of Villanova University created the Villanova Urban Sto

P

c

3

variety of stormwater BMPs both on and in the vicinity of Villanova Universitys campus in

Villanova, Pennsylvania (VUSP Mission, 2008); one such BMP is the Villanova University

CSW.

The Villanova University CSW was retrofitted from an existing dry detention basin

(Figure 1.2) in October of 1999 with an EPA 319 Program grant from the Pennsylvania DEP

(Stormwater Wetland Project Report, 2008). This detention basin acted more like a detention

pond, which treated stormwater flows from both the main and west campuses of Villanova

University, totaling an approximate total drainage area of 56.6 acres (Woodruff, 2005).

Figure 1.2: Original Dry Detention Basin (Rea, 2004; Stormwater Wetland Project Report, 2008)

Water quality considerations were not taken into account in the original design of the dry

detention basin (Figure 1.3). Th

e basin was designed with the intended purpose of reducing and

managing stormwater runoff flows from Villanovas campus. Runoff entered the basin from two

inlet pipes and sheet flow from a parking lot. (EPA, Section 319 Success Stories, 2007) The dry

detention basin was constructed with an outlet structure designed to pass the 25, 50 and 100-year

storms (Woodruff, 20 basin dry during

periods of non-storm events. However, it was discovered that even though the basin would

05). It was built with a 12 inch underdrain that kept the

4

remain dry, there was baseflow throughout the year in the underdrain, even during the summer

ce of the baseflow may be from a series of natural springs. The constant

baseflo ter

1999 drought; the sour

w made the site an ideal location for the creation of a stormwater wetland. (Stormwa

Wetland Project Report, 2008)

Figure 1.3: Plan of Original Dry Detention Basin (Stormwater Wetland Project Report, 2008; Woodruff, 2005)

1.3 Site Retrofitting

The design concepts presented in the Pennsylvania Handbook of Best Management

Practices for Developing Areas (Pennsylvania Association of Conservation Districts, 1998) were

used during the retrofitting of the dry detention basin into the CSW. The retrofit of the dry

detention basin concentrated on retaining small storms while simultaneously not violating the

original stormwater peak flow controls mandated by law (EPA, Section 319 Success Stories,

2007). The CSW maintained the basins ability to moderate the two to 100-year storms, but it

also became a water quality treatment facility (Woodruff, 2005). The underdrain of the basin

was removed in order to allow for baseflow, wh h is a critical part of the CSW, to flow

throughout the ba dering wetland

ic

sin. Earthen materials were shaped into berms to create a mean

5

channel in order to in bay was created in

order to allow for suspended particles to settle ou the water column. (Stormwater Wetland

In addition, the CSW was planted with a diverse selection of native

crease flow path distance (Figure 1.4). A sediment fore

t of

Project Report, 2008)

wetland plants (EPA, Section 319 Success Stories, 2007).

Figure 1.4: Design Plan for the Villanova University CSW (Stormwater Wetland Project Report, 2008; Woodruff, 2005)

1.4 Site Description

The Villanova University CSW receives stormwater runoff from a 57 acre watershed;

approximately 32 acres of impervious surfaces such as parking lots, dormitories, school

buildings, railroads, highways and housing areas; approximately 16 acres of semipervious

rfaces, such as lawns; approximately seven acres of the watershed is made of pervious surfaces

such as trees; approximately one acre of the watershed consists of the CSW itself (Jones, 2008).

The CSW consists of two inlets, a sediment forebay, a meandering channel and an outlet

structure.

su

6

ke up the inlet

tructure

nal to the

reten

lined with wetland plants, which help to increase roughness and promote friction between the

water flow and land, thus Wetland Project

Report, 2008) Low velocities allow

g Channel Flow Path 04; St Wetlan rt, 20

The inlet structure of the original dry detention basin was not altered during the

retrofitting of the site into the current CSW (Figure 1.4). Two main inlet pipes ma

structure of the CSW.

The sediment forebay was an addition during the retrofit of the dry detention basin

(Figure 1.4). The main purpose of the sediment forebay is to capture the sediment loads and

prevent them from exiting the CSW (Davis, 1995). It was placed offline from the outlet s

to aid in the prevention of resuspension.

The meandering channels were created during the retrofit of the dry detention basin

(Figure 1.5). The ability of a CSW to efficiently remove pollutants is directly proportio

tion time of the water. In order to increase the waters retention time, meandering channels

were created to extend the flow path of water through the CSW. The meandering channels were

constructed with a minimal channel slope to allow for low velocities. The channels were also

creating low water flow velocities. (Stormwater

an increase in the retention time of water in the CSW, which

increases the pollutant removal efficiency. (Kadlec, 1995)

Figure 1.5: Meanderin(Rea, 20 ormwater d Pr