Opinion ID: 2068368
Heading Depth: 1
Heading Rank: 2

Heading: Storm Water Management

Text: The District government reviewed Dorchester's proposed storm water management plan. On November 7, 2005, James R. Collier, P.E., Bureau Chief of the Bureau of Environmental Quality, Environmental Health Administration, District of Columbia Department of Health (DOH), issued a memorandum which stated, in part: The site assessment ... shows that there is no immediate existing storm sewer system available in Chain Bridge Road to provide drainage connection for the entire site, thus making it imperative that a comprehensive on-site storm water management system is required to control the anticipated additional runoff from the proposed development in such a manner that there would be no adverse impact on the receiving creek. The conceptual storm water management plan that has been submitted by the developer and reviewed by the Watershed Protection Division, shows a broad range of best management practices [BMPs] which are intended to treat all the anticipated runoff from the impervious areas of the proposed development.... In general, it is our opinion that if the proposed system of BMPs which technically constitutes a treatment train is fully implemented, the proposed development would meet the District's storm water management requirements. However, DOH made two recommendations, one of which concerned the prevention of in-stream erosion and stream bank erosion. DOH concluded by indicating that its comments did not cover erosion and sediment control because no plans pertaining to this area have been submitted to the Bureau of Environmental Quality for review. A subsequent April 6, 2006 e-mail from DOH referenced revisions to the conceptual site plan, including relocation of some inlets and a section of the storm water piping system. In preparation for the July 18, 2006 continued BZA hearing on Dorchester's application, Mary K. Sears, a professional engineer and witness for intervenors, submitted a letter to the BZA, dated July 11, 2006, referencing Dorchester's Revised Storm Water Conceptual Plan, dated June 22, 2006. In her professional opinion, the plan appear[ed] to meet the storm water management technical parameters required by [DOH].... Nevertheless, she stated, the plan has various conflicts and areas of concern with regards to grading, limits of disturbance, storm water management device construction, maintenance, erosion and sediment control and design capacity. In addition, she maintained that [t]he overflow ... has not been addressed with respect to offsite runoff. There aren't any proposed measures to ensure that the overflow surface runoff will be non-erosive from the steep slopes.... Ms. Sears elaborated on her written comments during her rather extensive testimony at the BZA hearing and specifically stated: There has never been a[n] [erosion and sediment] plan ... submitted. [2] In addition, Maxine Brown-Roberts of the Office of Planning (OP) commented on the lack of erosion and sediment plans, stating: The [DOH] also noted that they did not review the plans for erosion and sediment control ..., as they were not provided. At the April 11, 2006 hearing, James Afful, a civil engineer and storm water management expert for Dorchester, responded to a BZA question about long-term sustainability and maintenance of the devices comprising the proposed storm water management system. Mr. Afful indicated that the devices are precast and Dorchester would follow the manufacturers' recommendations for maintenance and cleaning, and that the homeowners association, not the homeowners, would be responsible for maintenance. [3] Mr. Afful described the proposed system as follows: [W]e are looking at two tiers of design. One, we're going to infiltrate as much runoff as possible from the roofs. That's the area that we know we generate a lot of runoff. So we infiltrate that into the ... exfiltration system. That is a D[istrict of] C[olumbia] standard. So we're going to infiltrate that and then pipe it down underneath into the outflow structure. But before it gets to that outflow structure, we have installed a rain storm device that also is an exfiltration system.... It stays and retains the water and then it infiltrates a lot of the water into the ground. What is over and beyond that goes into the piping system into the outflow. We're trying to minimize the amount of water that goes out downstream. The outflow of water would be slowed by another device to avoid erosion velocities that will impact the adjacent property. The remaining water would flow into an existing inlet, that is an 18-inch terra cotta [pipe]. A test revealed that the remaining water comes out into an existing well-defined channel that was walked by [the District's] Watershed Protection Storm Water Management Department. Ms. Brown-Roberts of OP, who testified at the July 18, 2006 hearing, confirmed that [a] homeowners association would be created to handle ... the maintenance of the storm water management system for each individual lot.... Moreover, [f]ield percolation tests were ... conducted, and showed that the infiltration system, if fully implemented will meet the District's storm water management requirements. She asserted that [t]he conceptual Storm Water Management Plan that has been approved by DOH would prevent runoff from the site. She reiterated that DOH did not review the plans for erosion and sediment control ..., as they were not provided. During the September 19, 2006 hearing, the BZA asked James Afful to address Ms. Sears' assertion that the storm water management concept failed to take into account off-site flows. Mr. Afful replied that soil tests had been performed, and he explained that the system was designed to capture any runoff or to intercept as much water, if there's any at all, on [the] slopes. Dorchester would captur[e] water from the rooftop with the drywells[,] and then would provide[ ] an overflow system, ... in case the drywells get ... soggy, and the overflow system [would] funnel[] water through eight-inch pipes. The Chairman of the BZA responded, [s]o all that water you're anticipating comes down, you need to grab it before it leaves the property? Mr. Afful agreed that overflow water would be intercepted and any overflow would infiltrate into a storage tank that would seep into the ground; there would be a backup system or a rain storm device that would back[ ] up the water, and then it would allow[] [the runoff] to infiltrate. As he explained earlier, what we've tried to do is to capture any runoff that comes from the driveway, and then from the trench drains that are associated with them, and then funnel them right through the storm filters and then have them clean it before you go south. The backup tank storage areas would be oversized to allow for more water than anticipated. Mr. Afful maintained that Dorchester would reduce the outflow of water from the site by about 30 percent, which would bring the storm water that is leaving the site to 70 percent of its current volume. In his view, that would constitute an improvement over current conditions. In response to a BZA concern, articulated by Ms. Sears, about the viability of the terra cotta pipe, Mr. Afful reported that he had visited the site with Ms. Sears on January 27, 2006, to examine storm water flow at one point, measure[d] the invert of [a] terra cotta pipe and concluded that the pipe has more capacity than what [Dorchester would] release into it. He asserted that terra cotta pipe, which is basically hardened clay pipe, is durable, and despite the traffic loading, the existing pipe shows no evidence of destruction at all. When he returned for the October 31, 2006 hearing, Mr. Afful noted that percolation tests had been completed and the results submitted to the District. However, he admitted that a geotechnical report had not yet been submitted to the District, but Dorchester planned to obtain such a report. Mr. Afful sidestepped the question whether the District's regulations would preclude use of Dorchester's planned configuration of the infiltration system if the geotechnical report revealed fill soil.