ACHIEVING STORM WATER SEDIMENT CONTROL

 By Alfred N. Kovalik, P.E., Associate,
Trumbull, CT office

According to the 1996 EPA National Water Quality Inventory, approximately 40% of U.S. water bodies are impaired by pollution and do not meet water quality standards. The EPA estimates that 45% of impaired estuaries are affected by urban/suburban storm water runoff. Earlier this year, Leggette, Brashears & Graham, Inc. (LBG) was retained by the Department of Public Works (DPW) for a highly urbanized municipality to begin a project aimed at addressing the sources of pollution included in the EPA survey.

The DPW has been experiencing excessive sedimentation in two very popular marinas. The marinas become filled with sediment and debris that flow from two storm water drainage networks. The first network drains a watershed of about 120 acres. There is approximately 15,000 linear feet of reinforced concrete pipe (RCP) ranging from 12 inches to 90 inches in diameter throughout the basin. The second basin is smaller, encompassing about 50 acres. This basin has approximately 5,000 linear feet of RCP that drains it.

As a result of the excessive sedimentation at the outfalls of the drainage networks, the depth of water available for boats to dock becomes too small and the marinas become unusable. To alleviate the problem, the DPW has the marinas dredged approximately every two years. In addition to the difficulty the DPW experiences in coordinating with the privately owned marina operators to complete the dredging activities, the agency must obtain United States Army Corps of Engineers (USACE) permits to dredge the sediments.

Of considerable consequence is the cost incurred to remove and dispose of the dredged materials. It is estimated this costs the town about a two hundred thousand dollars ($200,000) per event. To reduce the frequency of dredging, and therefore the cost to the DPW, LBG was asked to evaluate options for removing sediment from the system before it reaches the outfalls in the marinas.

Funding the Evaluation
While developing a scope for this project, the DPW consulted its state department of environmental protection and the EPA. In addition to showing regulators it is a proactive municipality; the DPW was successful in obtaining a grant to assist in the evaluation process.

To receive the grant, however, the DPW was asked to incorporate additional requirements of the National Pollutant Discharge Elimination System (NPDES) Storm Water Phase II Final Rule (Phase II Final Rule), scheduled for implementation next year, into the study. Phase II Final Rule refers to the EPA's latest efforts to "preserve, protect, and improve the nation's water resources from polluted storm water runoff."

Earlier and ongoing EPA efforts to improve water quality include implementation of Phase I of the storm water program, promulgated under the Clean Water Act (CWA) in 1990. Phase I utilizes NPDES permits to address polluted runoff from "medium" and "large" (based on population density) municipal separate storm sewer systems (MS4s), construction activities disturbing 5 acres of land or more, and industrial land falling within designated use categories. The NPDES permitting process allows effluent criteria to be set or treatment/management to be required and includes some form of monitoring and reporting.

Smaller Municipalities
The NPDES permitting authority has been told to issue general permits to small MS4s for Phase II by December 10, 2002. The EPA's Phase II Final Rule looks to incorporate smaller municipalities into the program along with construction projects encompassing between one and five acres of land. In addition to targeting specific water quality parameters (e.g., total suspended solids (sediments, etc.) and oil & grease), the Phase II program looks to improve water quality and awareness by requiring the following six minimum control measures in any storm water management program: 1.) construction site runoff control; 2.) post-construction runoff control; 3.) pollution prevention/god housekeeping; 4.) public education and outreach; 5.) public participation/involvement; and 6/)illicit discharge detection and elimination.

Conceptual Plan
With the goals for the project set (i.e., reduce sediment loading to the marinas and evaluate required components of Phase II Final Rule), LBG prepared a conceptual storm water management plan for the two watersheds. The plan was tailored so the DPW could install several storm water control structures and implement various non-structural activities in the watershed in order to evaluate the effectiveness of the different options available for full-scale implementation throughout the watershed and city.

The first part of the process included gathering the appropriate background data necessary to ensure the final storm water management plan is based on accurate information. Some data were readily available. For example, locations of new construction sites are extremely limited due the developed nature of the watersheds and therefore, did not warrant extensive review. The task of confirming the existing watershed characteristics and drainage network connections proved to be cumbersome since the system was constructed at various times starting in the early 1900s. As-built maps were scarce and many of the connections had to be field verified.

Pollution prevention/good housekeeping includes implementing best management practices (BMPs) to reduce pollution. The BMPs can be either structural (e.g., sedimentation chambers) or non-structural (e.g., increased frequency of street sweeping). For this project, several different BMPs were proposed so the DPW can install them or incorporate them into their existing maintenance program. For the two watersheds in this demonstration project, many of the conventional structural BMPs (i.e., retention basins, infiltration basins, etc.) were not considered practical for implementation since over 80% of the watersheds are developed and open space is simply not available. The different structural BMPs selected for evaluation included physical separators (e.g., swirl separators) and catch basin inserts. These structural BMPs and the proposed non-structural BMPs (e.g., increased frequency of street sweeping and catch basin cleaning) will be implemented so they can be evaluated to determine which are the most effective and practical for implementation throughout all of the municipalities entire drainage systems.

To address the public education and outreach/public participation and involvement minimum requirement, schools, community centers, religious centers and volunteer facilities within the watersheds were identified. The intention is to educate personnel in these locations and enlist their constituents in efforts to raise public awareness such as painting "no dumping" on catch basins or distributing informational material.

By completing conceptual storm water management plans for the two watersheds, key data are being identified and a monitoring plan developed. The monitoring plan will be implemented and the results used to verify placement and sizes of the various BMPs. After the BMPs are installed or implemented, their performance will be monitored for a year and then the most successful and cost effective BMP(s) throughout the remaining storm drainage networks within the municipality.

(This is the first of a three-part article on the demonstration project)