Stormwater Monitoring - Newington Solid Waste Facility

Editor's Notes

1. This discussion will focus on the development of a monitoring program for a large-scale sand filter at the Newington Solid Waste Facility. The program was designed to both determine the efficiency of this best management practice and provide insight on the maintenance needs of such a facility.
2. I’ll go through the steps from concept to results, along with some lessons learned regarding both sampling and future maintenance of such a facility.
3. This project was originally conceived in response to language in a draft MS4 permit. It stated that the County should identify facilities with greater than 2 acres of impervious surface with potential for stormwater retrofit opportunities. Based on a County-wide evaluation, the Newington Solid Waste facility had a high potential to discharge pollutants. In addition, the Director of Solid Waste was a very amenable partner and was willing to pilot new approached for managing stormwater.
4. The primary focus of the retrofit was the development of a large-scale sand filter designed to treat runoff originating from a parking lot for approximately 60 waste disposal vehicles. The schematic give a sense of the dimenisons and the capacity of the filter. Designed to treat 1” of rainfall Drawdown time of 40 hours One quick, big rain activates overflow pipe
5. Some photos to illustrate the scale of the project. ~$850,000 for construction of filter ~$85,00 for design costs
6. Stormwater Planning was brought in to develop a monitoring plan. We’ll go through the steps that lead to actual sampling: Objectives Site Specific Considerations Partnerships Targeted Parameters Sampling Design
7. An effective monitoring plan has to start with clearly defined objectives In this case, we wanted to: Evaluate BMP effectiveness at removing pollutants from stormwater runoff at an industrialized site Determine maintenance needs at such a facility – the County has experience with smaller-scale sand filters but this is the first we’ve installed at such an industrial facility at this size. We also need to take into account the location as we design the monitoring plan. - the filter has a defined input and output – targets for the autosamplers - safety considerations while sampling are important, as this is a high traffic facility with heavy equipment - BMP in a gated facility, so coordination is important
8. Successful programs rely on coordination between invested parties. In this case, buy-in from the facility managers was critical to success, as disruption to regular activity while under construction is significant. Coordination with County maintenance staff was important as we learned more about the function of the sand filter Consultants who designed the facility could lend insight to the monitoring crew- in this case they were one and the same. A certified lab able to carry out the comprehensive sample analysis And the Planning team to ensure oversight and facilitation, in addition to long term data analysis
9. To ensure we are capturing how efficient the BMP is, we developed a comprehensive parameter list for industrial sites. This includes flow, water chemistry, visiuals, metals, nutrients and hydrocarbons – the latter require a first flush grab sample, complicating sampling efforts.
10. The intent of the sampling design is to collect one sample per quarter from both the inflow and the outflow of the sand filter. These photos show the two locations, and also illustrate the challenge in setting up monitoring locations.
11. After setting up for a storm event, certain conditions need to be met to trigger a sample. Once the rain gauge measure > .1 inches of rain, the inflow autosampler will activate. As there is a lag for the water to travel through the filter, the outflow autosampler is triggered solely on level. As we are collecting hydrocarbons , they require a grab sample as well – this necessitates having staff on site during the event until both the infow and outflow samples are collected.
12. At this point in time, we have only one successful event from last summer. I’d like to point out a few encouraging finds from this limited dataset: Total flow was reduced by 52 percent from inflow to outflow, which illustrates the ability of the sand filter to both slow down and attenuate the stormwater from the site. There was also a significant reduction in temperature after coming off the parking lot. For both the diesel-based hydrocarbons and the oil and grease parameters – almost 90% reductions were found . As we found during maintenance, the filter sludge smelled strongly of hydrocarbons, which is most likely byproduct from the trucks such as leaking hydraulic couplings and motor oil.
13. EMCs decreased for all sampled parameters except for nitrate-nitrite. The literature shows that media filters tend to export this form of nitrogen, although the total N went down as a result of greater reduction of TKN.
14. The decrease in total pollutant loads ranged from 53% for total nitrogen to greater than 87% for BOD5. It should be noted that the percent reduction of pollutant loads was greater than the percent reduction in EMCs. This can be attributed to the reduction in total flow measured at the outflow. A larger storm may not provide the same results as storage in the sand filter would be decreased, increasing the flow coming out.
15. The influent flow was initially recorded at approximately 3:25 pm and measurable effluent flow began at approximately 5:05 pm resulting in a detention time of approximately 1 hour and 40 minutes. This variable increases the complexity for grab collection, necessitating staff remain on site during storm events for a long period of time.
16. The results so far, while encouraging, are very limited. We have one successful storm, which was relatively low intensity. Two other events that we mobilized for were not successful – once for not enough rain and another for a clogged intake tube. As we move forward, we are considering revising the sampling protocol to increase chances for collection. Shortening the dry period to 48 hours and utilizing a lab with extended weekend hours would put more storms into play. Facility access and working in a busy facility are limiting factors that need to be taken into account as well.
17. I also received some insight from maintenance staff – - an industrialized site such as this shortens the maintenance interval – scheduling for this type of facility will need to follow a different frequency than other sand filters in the County. It took about a year for the sand filter to fully clog after installation. Trash collection activities generate a higher than average amount of contaminated runoff. Maintenance could be cost prohibitive over the lifetime of the BMP Maintenance is specialized - The work must be conducted during a period or in such a manner where the extracted stone and sand will not be exposed to precipitation or runoff.