February 26, 2025, Planning Board Special Meeting Transcript - WEHI

03/03/2025 06:36:47 AM Page 29 to 32 of 115 8 of 46 sheets 29 existing conditions. So in other words, the contour1 lines reflect where the water will move and Mr. Walsh2 has created the two drainage areas that he has discerned3 based on the contour lines on the site as they exist4 today.5 Is that correct?6 THE WITNESS: Yes.7 MAYOR McCARTNEY: Did he change anything?8 MR. AFRAN: He hasn't change any existing9 contour lines. Simply identified where on the document10 the two drainage areas exist.11 Correct. Let me, I think I -- so, no, let me12 A. explain. What they show on this map is the drainage13 area of the disturbed area. So what I did was I used14 the coloring to show what would feed the entire wetland.15 That's it. That's the difference.16 MR. KLEIN: Yours is existing, their's is17 proposed?18 THE WITNESS: This is existing.19 MR. AFRAN: I think I understand. What's20 happening is on the original version the drainage areas21 showed by the applicant was reflecting the area of22 disturbance and drainage from that area. Mr. Walsh has23 shown drainage areas more broadly as they exist on the24 site. So he's showed -- he's showing other drainage25 30 areas not just drainage from the area of proposed1 disturbance.2 Is that a fair summary or am I incorrect?3 Q. Yeah, that, I wanted to show you the original4 A. one, the original DA that they had here. They point5 out, they had this disturbed point. They're only6 concerned -- they show the drainage area in the7 disturbed area. I was showing what's in the entire8 wetland, that's why I had the color. That's why I used9 colorization.10 COUNCIL PERSON SCARPA: Is that because11 there's other wetlands to be affected, so he's showing12 all different --13 THE WITNESS: I want to show everything, not14 just what was disturbed.15 COUNCIL PERSON SCARPA: And how it would16 affect each other?17 THE WITNESS: Yeah, and how that interacts.18 Sorry for the confusion.19 MR. AFRAN: Let me note, I was attempting to20 answer the question but obviously Mr. Walsh's opinion is21 authoritative, not mine. So his description obviously22 governs. To the extent I differ, Mr. Walsh is correct.23 Now, the area on the left is about 32 acres and24 A. the area on right about 48.4 acres. Now, I'm going to25 31 show you one more figure for this.1 MR. AFRAN: What's on the screen now is a2 colorized version of DA-2 and Mr. Walsh will explain.3 All

4 A. the area on right about 48.4 acres. Now, I'm going to25 31 show you one more figure for this.1 MR. AFRAN: What's on the screen now is a2 colorized version of DA-2 and Mr. Walsh will explain.3 All right. Can you see here, now we're looking4 A. at a proposed drawing and what I did was I, once again,5 drew the drainage areas that would feed the wetlands and6 what is shown is how that would change. You can see how7 it's through the developed area, because those no longer8 contribute to wetlands over here, over here or down9 these areas, the flows being routed to basins at the10 bottom of the site. And what we wanted to show was that11 there was a reduction in the drainage area and the12 wetlands. On this side the drainage area was reduced by13 about 9 acres, a 20 percent reduction.14 You mean the left side, the darker green?15 Q. Left side, darker green. And on the right side,16 A. the lighter green, that was a reduction of 16 acres,17 which is a 33 percent reduction. Just wanted to point18 that out and there would be an impact to the wetlands.19 MS. MCGOVERN: Okay. This is another new20 exhibit. This is going to be O-9 and we'll have to get21 that one submitted.22 So it's colorized DA-2.23 All right. Next I would like to talk about time24 A. of concentration. Time of concentration is a bit of a25 32 technical term but a very important term. So time of1 concentration is the time it takes for a piece -- for2 water to go from say the highest point on the watershed3 down to the discharge point. It's the time -- and that4 time is very important. That time helps dictate the5 peak flow runoff, especially in existing conditions6 modeling. Once again, that's restraining. When we7 develop existing conditions we know what's flowing off8 the site in existing conditions and DEP will require you9 to meet reduction rates so you're not causing flooding10 further down stream.11 This is an old document, this is, this DA-1 from12 the report submitted by the applicant.13 So this is not a colorized version, this is the14 Q. original DA-1, is that correct?15 So the only difference is I put two scaled16 A. measurements on here just to show the difference, that I17 will get to in maybe ten minutes.18 MR. AFRAN: So since it's on the screen, Ms.19 McGovern, I think we probably should make it O-10, which20 is DA-1 with colorized red arrows. Would that be a fair21 description?22 MS.

ybe ten minutes.18 MR. AFRAN: So since it's on the screen, Ms.19 McGovern, I think we probably should make it O-10, which20 is DA-1 with colorized red arrows. Would that be a fair21 description?22 MS. MCGOVERN: Yeah. Just the red arrows?23 THE WITNESS: Just those are all I added and24 you'll see why in like maybe five minutes or something25

9 of 46 sheets Page 33 to 36 of 115 03/03/2025 06:36:47 AM 33 like that.1 MS. MCGOVERN: Okay.2 All right. Now, time of concentration is, as I3 A. said, how water flows through to get to the end4 discharge location. Water flows in different ways.5 This sheet flow is the shallow concentrated flow. Sheet6 flows is, as you can imagine, if there's a field and it7 starts to rain, kind of the water moves like a sheet8 along the ground. Now, as the water progresses and it9 builds up it will actually start to consolidate and it's10 called, something called shallow concentrated flow.11 Now, the DEP has rules on how you calculate that.12 That's all outlined out the Chapter 5 in the DEP manual.13 And what he found is when we looked at the rate the14 applicant calculated was, unfortunately it seemed like15 they had used an older version of how to calculate time16 of concentration. The rules and methods that we're17 supposed to use to calculate time of concentration has18 changed over time and unfortunately from what we can19 tell is that they used the older version. And this20 older version generated a lower time of concentration.21 So let me give you, I want to use the shallow22 concentrated flow as an example, and kind of a dead23 giveaway is you see here the shallow concentrated flow,24 unpaved. Now, it wasn't that long ago but there was an25 34 unpaved option where you would basically take the slope1 of the land and you'd say it was unpaved because it's2 forest and it would give you a flow rate. They don't do3 that now. Now they have a more complicated chart and4 like it tells you exactly which land it is. Is it a5 forest, is it grass, is it farm field. And based on the6 slope they will give you a specific flow rate.7 If I can ask you one question. So it's not a8 Q. generalized unpaved area flow rate. There's a specific9 flow rate based on the slope and the specific type of10 topography?11 Yes.12 A. Okay. Thank you.13 Q. Yes.14 A. All right. So what I did was I went back and I15 went to the manual and I decided to recalculate the16 shallow concentrated time. Their shallow concentrated17 time for this area was 7.2 minutes. I went back and I18 used the charts and I said, all right, this is a19 forested area with heavy litter, it's got the same20 slope, 5.4 percent, and using the chart that says it's21 got a velocity of 0.55 feet per second. And you divide22 1,625 feet

all right, this is a19 forested area with heavy litter, it's got the same20 slope, 5.4 percent, and using the chart that says it's21 got a velocity of 0.55 feet per second. And you divide22 1,625 feet by 0.55 feet per second, you get 2,95423 seconds, or 49 minutes. Now, what they're saying is24 that it's 7 minutes, but based on the new method it's25 35 taking 49 minutes. Which means it's about seven times1 longer than what they're saying.2 Now, I did this again for POA-2 -- sorry. Let me3 take a step back.4 There's this drainage area and then there's5 another drainage area over here. You can tell by the6 distinction of the two different blue lines which is7 your time of concentration. We also did it for POA-28 using the shallow concentrated flow.9 And that's on the right side of the chart?10 Q. That's on the right side of the chart. Of the11 A. plan.12 And so it's, they have 564 linear feet at unpaved13 9.2 -- 9.2 percent slope. According to their model and14 their calculation that takes 1.9 minutes. Again, I went15 back to the chart and the manual, I recalculated that16 velocity for a heavily forested area, add 9.2 percent17 slope and what I got was 12 and a half minutes. Again,18 that's about a seven fold increase in time of19 concentration.20 All right. Now, you're probably wondering why21 time of concentration is different. Now, what does --22 how does that impact the design. The shorter the time23 of concentration typically the higher the peak flow rate24 you have. The water is traveling a certain amount of25 36 time, so the longer it is, the lower your peak flow1 rates are. Now, it's really important to establish the2 correct peak flow rates of the existing conditions,3 because that's going to set the benchmark for what your4 designs going to be. Because the DEP will require you5 to reduce your runoff. Your peak flow rate from your6 design -- sorry. DEP is going to require two year peak,7 flow runoff rate is going to be 50 percent less than8 what is existing. For the 10-year storm it's going to9 be 25 percent less. For the 100-year storm it's going10 to have to be -- 10-year storm is 25 percent less.11 100-year storm is 20 percent less. So now, thing about12 peak flow rate it's easier to meet those reductions the13 higher your rates are, because it's just more water.14 You don't have to move much water, you don't have to15 have a big basin. I always

out12 peak flow rate it's easier to meet those reductions the13 higher your rates are, because it's just more water.14 You don't have to move much water, you don't have to15 have a big basin. I always hope, if you do the math16 right, the bigger the existing flow, it makes my life17 easier. But see here because they're miscalculating18 we're already getting miscalculation peak flows in19 existing conditions. So we're risking not reducing the20 flow as much as we should be.21 And what does that translate to in terms of22 Q. controlled outcome?23 It means more water is going to come off the site24 A. than it does and you can risk flooding further25

03/03/2025 06:36:47 AM Page 37 to 40 of 115 10 of 46 sheets 37 downstream. Because now the site isn't holding back1 water. It could actually be generating more runoff. So2 the issue with flooding downstream, now we're3 exacerbating that problem. If you develop this plan and4 now your producing even more runoff than less. The5 point of the regulation to reducing peak flow is that it6 should not impact further downstream. We don't want to7 -- in order to develop buildings you have to develop8 land sometimes, but you don't have to flood downstream9 areas.10 I'm going to be getting a little technical here,11 I just kind of want to use an analogy here to kind of12 make it simpler. Suppose -- I'm a basketball fan,13 suppose I saw someone dunk a basketball and say, yeah, I14 can dunk basketballs, then when you kind of went closer15 to the net and brought the tape measure to it you're16 like, wait a minute, this is an 8 foot tall net,17 basketball nets are 10 feet tall. And that's what's18 going to happen here. You're artificially shortening19 the time of concentration to meet these requirements,20 so.21 MR. KLEIN: Can I ask a question.22 I want to go a little further on --23 A. MR. KLEIN: One quick question. What year24 did that change? From using that general unpaved to --25 38 THE WITNESS: I don't know off the top of my1 head. I can get it for you. I don't know off the top2 of my head.3 MR. KLEIN: Do you know if, when they did4 the calculation that was correct at the time or you're5 sure it wasn't?6 THE WITNESS: No, I'm sure it wasn't.7 MR. KLEIN: Okay.8 MR. AFRAN: Mr. Chairman, I hate to burden9 to board, could I ask for a two-minute break.10 CHAIRMAN BAGOFF: You got it. Two-minute11 break.12 (Whereupon, a short recess is taken.)13 CHAIRMAN BAGOFF: Back on the record.14 Mr. Afran, Mr. Walsh.15 MR. AFRAN: Thank you, Mr. Chairman. I16 appreciate the break and we will continue with Mr.17 Walsh.18 All right. So we just finished talking about how19 A. the time of concentration was used with the current20 method. It's longer, which means the flow rates should21 be lower than originally calculated in the applicants22 submission.23 I want to point something out with POA-2 here.24 You can see the blue line here, this is where you show25 39 the flow path of POA-1. This is a path that goes from1 top of the drainage area down to the bottom.2 You're tracing a line that's

-2 here.24 You can see the blue line here, this is where you show25 39 the flow path of POA-1. This is a path that goes from1 top of the drainage area down to the bottom.2 You're tracing a line that's parallel to those3 Q. red arrows, is that correct?4 Yes, parallel to the red arrows.5 A. You'll see there, that path total is about 6716 feet long. What's unusual here is you compare it to the7 other model of the drainage area, the left POA-1, the8 blue line goes all the way to the discharge point, which9 is what it's supposed to do. But for some reason they10 stopped it short, it stops here, but the drainage -- the11 discharge point is here. The time of concentration is12 supposed to measure the entire flow event. This water13 should keep going down here, go around, keep going. At14 a minimum it's 700 feet short. So there's 700 feet of15 flow, this isn't accounting for the time of16 concentration calculation. And, again, this is just17 another example of how like a basketball rim gets18 artificially shortened, because now it's traveling less19 distance than it really is. So again, time of20 concentration will be, will be shorter. The peak flows21 will be higher and it will be easier --22 MR. AFRAN: For the record, the battery was23 running low on Mr. Walsh's computer and he's about to24 charge it.25 40 All right. Sorry about that.1 A. So once again, this is just another example how2 the time of concentration calculation, it's not even3 complete here. They use their own method and not using4 equal distance, so it just can't be trusted.5 So let me ask one question. Accepting what you6 Q. just said, what does this translate into in terms of7 practical outcomes that the board should be concerned8 about?9 So to demonstrate that what I did was, we used10 A. the information that was available from the applicants11 submission. We recalculated the existing conditions12 models using the HydroCAD, which is the model they used,13 to develop new peak flow runoff rates, and compare them14 to what they hd in the report to see how big a15 difference is, because this is their own methods. It's16 less than half the distance. We were concerned what the17 impacts of that's going to be.18 I got to go through my notes to make sure I get19 the numbers correct.20 So the applicant's submission shows that time of21 concentration is 16.8 minutes. Our calculation is22 closer to 60, at

o be.18 I got to go through my notes to make sure I get19 the numbers correct.20 So the applicant's submission shows that time of21 concentration is 16.8 minutes. Our calculation is22 closer to 60, at about 60.8 minutes. Four times longer23 more time during that time period.24 Now, for example, two-year storm we calculated25

11 of 46 sheets Page 41 to 44 of 115 03/03/2025 06:36:47 AM 41 that the peak flow runoff rate was 7.52, I'm going to go1 -- one second, I'm going to go to the report the2 applicant submitted.3 What was that figure you just said?4 Q. 7.52.5 A. All right. We're looking at Page 11 of the6 applicants stormwater drainage report, it summarizes the7 discharge rates they calculate for the proposed and8 existing conditions and I just want to compare them to9 our findings.10 So the existing, the two-year storm they have the11 existing flow rate of 17.5. Now, we calculated it as12 7.52, which is 10.2 feet per second more than what we13 have. So, again, this demonstrates how much higher it14 is.15 Now, if you're looking at this same table, it's16 stormwater, that means the storm size. This EX is17 existing. PER is permitted. So remember, I discussed18 the two-year storm, you have to reduce peek flow by 5019 percent. And then for the ten-year storm you have to20 reduce it by 25 percent. 100-year storm you have to21 reduce it by 20 percent, that's what's permitted. It's22 taking the existing flow they calculated and shows what23 they're allowed to permit.24 And this is shown from the applicants Page 11?25 Q. 42 This is applicants Page 11, yes.1 A. All right. Now, the T, the total, this is the2 last column. It totals all the other flows in this to3 give you the total flows. This is the target flow they4 need to meet. So they show the peak flow rate for a5 two-year storm is 7.24. Now, they meet it under their6 terms but if you take, remember we calculated the7 existing two-year storm as 7.5. You have to have that,8 which is about 3.76. So right now their peak flow is9 twice what it should be. So once again, they need to go10 back, look at their basins, look at their models, make11 everything bigger to hold more water back because12 they're discharging to much water right now. And I want13 to point out that on top -- this is on top of some of14 the other things we found where some of the basins are15 getting impacted by mounding, they're not going to hold16 as much and they're also impacted by the seasonal high17 water table. So we already know from earlier18 discussions that these peak, the peak flow rates that19 they're giving are artificially low and now we know20 that, you know, their bar is to high. Their bar needs21 to be lower. The sites going to generate more