Flynn, Thesis, Villanova

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Transcript of Flynn, Thesis, Villanova

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    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

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    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

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    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

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    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

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    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