Integrated Watershed Planning: A Case Study In Meeting TMDL/NDPES Permit Requirements

INTRODUCTION
In response to National Pollutant Discharge Elimination System (NPDES) MS4 permit requirements, counties are finding watershed assessments an integral tool for identifying high priority stormwater management projects within their jurisdiction. An NPDES MS4 permit was issued to Harford County that mandates restoration of pollutant laden streams from stormwater sources. The permit required Harford County to treat 20% of the impervious area by the end of the permitting period. Impervious area was treated through stream restoration, outfall stabilization, and BMP stormwater management facilities.
The Clean Water Act (CWA) requires states, territories, and authorized tribes to: develop water quality standards for all jurisdictional surface waters; monitor these surface waters; and identify and list impaired waters. States must also establish priority rankings and develop Total Maximum Daily Loads (TMDLs) for waters on the 303(d) list, which generally target pollutants including sediment, metals, bacteria, nutrients, and pesticides. According to the United States Environmental Protection Agency (USEPA), a TMDL is a calculation of the maximum amount of a pollutant that a water body can receive and still safely meet state water quality standards. The goals of the Harford County watershed studies were to assess the current physical conditions of the Lower Bynum Run watershed, including the current land use, soils, and impervious area; conduct a field survey of the streams, outfalls, and best management practices (BMPs) within the watershed, provide potential restoration projects to meet pollutant reduction requirements within the County, and clearly convey the results of the watershed study to residents within the watershed.
METHODOLOGY
A watershed-based approach was used to evaluate water quality conditions and improvement potential within the watershed. The first step in this process determines watershed drainage area. The Lower Bynum Run watershed is an urban watershed that covers portions of the Town of Bel Air and Harford County, Maryland and encompasses approximately 9,746 acres. It is contained within the Bush River sub-basin draining to the Chesapeake Bay and is located on the western side of the Bynum Run watershed. The Lower Bynum Run watershed includes the Upper Farnandis Branch watershed, which was assessed prior to the remaining Lower Bynum Run watershed. In addition to characterizing the entire watershed, analyses were conducted on a subwatershed scale to provide detailed information for smaller areas. WSP chose to analyze subwatersheds because it allows for easier monitoring of restoration efforts. Using ArcGIS, WSP performed a desktop analysis on a subwatershed scale to determine existing land use, soil types, and impervious area percentages within the watershed. The audience will learn how these conditions impact water quality and the in-stream and riparian habitat of the receiving water body. The results of the desktop analysis on existing conditions created a visual comparison between subwatersheds. Since the larger size of the watershed and the budget necessitated field assessing a subset of the watershed, this information assisted WSP and the County in deciding where field assessment efforts would be most beneficial. Field assessments for BMPS, streams, and outfalls were conducted throughout the Lower Bynum Run watershed to evaluate existing conditions within Lower Bynum Run, a portion of Bush River Branch, and their tributaries. The audience will learn how and what protocols the team set up for selecting subsets of streams, outfalls, and BMPs to assess. During the field assessments, GPS enabled tablets were used to collect field information, location data of outfalls, and stream characteristics as well as pictures that were taken at each location. Field maps were created for BMP sites as well as all surveyed stream channels to allow field notes and documentation during the assessment. The stream assessments were conducted based on Maryland DNR's Stream Corridor Assessment (SCA) Survey Protocols, which were developed as a tool for environmental managers to quickly identify environmental problems within a watershed's stream network (Yetman, 2001). The SCA is a rapid field survey used to identify Channel Alteration Sites, Erosion Sites, Exposed Pipes, Fish Migration Barriers, Inadequate Stream Buffers, Pipe Outfalls, and Trash Dumping along the surveyed stream channel. Outfalls were assessed, in conjunction with the SCA, using protocols developed by WSP to quickly assess the condition of the outfall and determine outfall stabilization opportunities. BMPs were assessed separately from the stream and outfall field assessments due to their locations throughout the watershed. Protocols for BMP assessments were developed by WSP to quickly assess the existing condition of the BMPs and determine potential retrofit opportunities.
FINDINGS
Land use, soils, and impervious area are three existing conditions that were assessed at the onset of this project. The majority of the soil within the watershed (nearly 60%) falls into hydrologic soil group B which has a moderate infiltration rate and a relatively low runoff potential. The predominant land use types present within the Lower Bynum Run watershed are low- and medium-density residential, forest, and agriculture. Due to the high percentage of residential land use within the watershed, the impervious area was a significant portion of the watershed. The total impervious area calculated is 1,322 acres or 14.3% of the watershed. Stream watersheds with 10% or more impervious area have a higher potential for negative impacts because of the high percentage of impervious area. This watershed study assessed 15.5 miles of stream, 79 outfalls, 65 existing BMPs, and 11 potential BMPs. Of the assessed features, 17 stream and outfall restoration projects, thirteen retrofit BMP projects, and two proposed BMP projects have been recommended within the Lower Bynum Run watershed. If implemented, these projects would provide 861 acres of impervious area treatment, 2,988 lbs of nitrogen reductions, 1,997 lbs of phosphorus reductions, and 1,310,395 lbs of sediment reductions.
PUBLIC OUTREACH
Harford County provides continual public outreach to keep the public informed of watershed assessments and restoration plans to reduce stormwater pollutants. The County created a website with information on the Lower Bynum Run watershed to inform the public. A story map, showing spatial data, was created using the ArcGIS Online application to share information in an easy to follow and systematic way. The public has the capability to view the story map at their own convenience and at their own pace. The story map provides a link to an online comments form at the Harford County website that allows the public to post questions, concerns, and comments. The audience will learn how a story map was created for the Lower Bynum Run watershed to show existing physical conditions within the watershed as well as potential restoration projects.