Problems With Stormwater Infiltration And Easy Ways To Correct Them

Problems With Stormwater Infiltration And Easy Ways To Correct Them

Stormwater management is essentially the process of trying to mimic pre-development hydrology with post-development site planning and engineering. Early attempts focused on managing the rate of precipitation leaving a site, but now we take a more integrated approach that incorporates rate, volume, and water quality. It’s not surprising that a stormwater management approach that focuses on infiltrating water back into the soil has gained popularity. However, with all good things there can be the potential for problems, and stormwater infiltration is not immune to those problems. Listed below are 3 common problems that arise when infiltrating stormwater and some easy ways to correct them.

1. The Soils

When designing a site plan it’s tempting to immediately pencil in the stormwater BMPs in the low spots and to rely on the NRCS soil map and the hydrologic soil groups to assume that it will all work out when things get constructed. Unfortunately, although soil maps are a nice place to start, and it would make life so simple to send water to those low areas, believing in either or both of those assumptions is likely leading you to some future construction problems. Soils can change dramatically over a small extent and knowing what is there before you commit to a site layout will save you headaches further into the project.

You’ll want to get a look at the soil through a soil test pit to determine any limitations to stormwater renovation. Assuming the soil looks suitable, you’ll want to conduct an infiltration test. Most test procedures are based on measuring the saturated hydraulic conductivity. The point is to measure the rate of water moving into the soil. Once you know the soil is suitable for renovating stormwater and you have a measured rate at which it can infiltrate water, you can properly site and size your infiltration BMP.

2. Compaction

You have the perfect soil, in the exact location you want to place a BMP..… until you destroy the soil during construction. Now your perfect soil is the functional equivalent of concrete. The most frustrating thing about compaction is that it can be minimized or avoided with just some simple construction and project planning techniques.

First, limit vehicle and foot traffic in areas that will be used for infiltration. Second, excavate out most of the soil you need to remove, but leave 6 to 12 inches in place. Then, as you are ready to finalize the BMP, remove the remaining soil as you back the equipment out of the area.

3. Siltation

During any land development project, the use of erosion and sediment controls are common. How many times has there been a proposed infiltration BMP used as a sediment trap during construction, but when converted to an infiltration basin all the erosion controls are taken away? What you’re left with is a vulnerable BMP just waiting for a precipitation event to funnel all that upslope soil into the basin before vegetation has been established. If the silt and clay get into the basin before significant vegetation establishment occurs, the infiltration surface “silts over” and the infiltration rate plummets. Now you’ve effectively turned your infiltration basin into a stagnant retention pond. Stopping this from happening is easy, just make sure proper erosion and sediment control measures are in place around the BMP. Things like Silt Soxx or silt fence work great to accomplish this.

As discussed, fixing problems is always harder and more costly than avoiding them. Take the time upfront during planning to understand the soil conditions of your site. Think out construction sequences and equipment work flow and spend a little more time prepping the infiltration BMP to avoid compaction. Finally, protect the infiltration BMP like the valuable piece of infrastructure it is. Although they are often simple in regards to design and construction, infiltration BMPs need some attention during and post construction to assure their designed function is realized.

MAN WHO STAND ON TOILET IS HIGH ON POT

MAN WHO STAND ON TOILET IS HIGH ON POT

I get asked this question nearly every day. “Hey Den, how are you doing? You guys busy? ” I always give my stock answer ” yeh, we are hanging in there, things seem to be moving along”. I have answered this question about the same for the last 17.8333 years in business. But the follow up question is the one that has recently changed. “What are you busy with, mostly residential? commercial? ” No, I am busy with Pot! WHAT? Actually, I am not that busy with pot, but it is coming. Although Governor Wolf is cool (not Fonzie cool, but temperature cool) to the idea of legalized marijuana, he did sign a bill legalizing medical marijuana in the state nearly a year ago. We are already seeing municipalities scramble to change zoning ordinances to allow for the growing and processing of medical marijuana facilities. As well they should, so as not to be caught up in a “fair share” type challenge to their ordinances. Last week Aston Township voted unanimously to change their zoning ordinance to allow medical marijuana facilities in their limited industrial districts. To some residents surprise, many voiced support for a medical marijuana facility while critics fear allowing these facilities will simply lead to the legalization of recreational marijuana. Over the years we have watched municipalities scramble to re-write ordinances to convert Wawa convenience stores to allow gas, allow lighted bill board signs and none of us will ever forget the fun that was had with the cell towers. I was at a township, that shall remain nameless, until 2:30 am once listening to unhappy residents about a cell tower so I can only imagine how much fun pot stores will be. If they do actually happen though I have the perfect landscape architect to team up with, who also shall remain nameless! Anyway, by the time recreational marijuana is legalized in PA I will be too old for 2:30 am meetings, they will be something my son can enjoy!

Snow Easements, Who needs em?

Snow Easements, Who needs em?

As winter winds down with a whopping total of 7″ of snow this year, I can’t stop thinking about being required to provide snow storage easements on a recent subdivision plan. Obviously, the developer agreed to add these to the plan, as it wasn’t worth an argument a few weeks from getting approval, however as I sat there at my desk drafting them in, I couldn’t stop thinking, “Are these really necessary?” In today’s world, residential lots seem riddled with restrictions from easements. Stormwater BMP easements, sanitary sewer easements, access easements, walking trail easements, conservation easements, waterline easements, drainage easements, riparian buffer easements and NOW snow easements? I actually live on a cul-de-sac, and while I’ve lived there for only 5 years, I have been witness to what I would consider very large snowstorms for our area. Can you guess how many times I sat there thinking I wish these plows would stop pushing the snow off the road and onto my lawn? Zero. I could be wrong but I would like to think most, if not all people, would have no problem with plowed snow as long as the plow doesn’t tear up their grass or knock over their mailbox.

So considering I’ve never been a snowplow driver, even though it was my childhood dream to be one, I’m going to give the Township and their Public Works Department the benefit of the doubt on this one. Maybe just living on a cul-de-sac or driving through neighborhoods after major snowstorms doesn’t qualify me to decide if another set of easements is really necessary. I mean I can only imagine, we’re a couple days away from a snowstorm and the public works crew is sitting around the table planning where they are going to put all that snow. “Alright guys, I know for the past 40 years we’ve been struggling to clear the snow from all those cul-de-sacs out there, but I have great news for you. You know that new development off Main Street, all our problems have been solved, you have an extra 10 feet past the sidewalk where you can push all the snow. But make sure you bring that full set of land development plans to keep in your truck so you can find out exactly where that easement begins and ends.” “You got it, Boss!”

Ok, so I honestly can’t see that happening, but let’s assume that it does. As I said before I’ve never plowed snow, so maybe these easements will make things easier and cause fewer headaches. I can only imagine if we’re providing them here in Southeastern PA where we average something like 36″ a year, with statistical analysis showing that we can expect a single storm to exceed 20″ on average once every 10 years and snowstorms that exceed 10″, about every other year; places like Buffalo and Upstate New York must have snow storage easements all over the place. Right? I mean they get like at least three times the snow fall we get. Where do they put it all? Do they not allow cul-de-sacs? What do you think? Do we need more easements?

PS -If we do happen to get the big blizzard next week that is currently being predicted, send us your cul-de-sac snow pictures to dgibbons@dhowell.com

Non-Reportable Conditions for Stream Obstructions

Non-Reportable Conditions for Stream Obstructions

 

Did you recently buy a property with a significant erosion issue in your yard? If you did and you’re thinking about having it repaired, then it would be wise to contact DL Howell. The erosion issue could consist of a long eroded channel that may have been caused by a pipe upstream that is conveying a high velocity of water through your yard. This becomes a complicated situation because the eroded channel could be classified as a stream per The Pennsylvania Code. A stream is defined as a channel or conveyance of surface water having a defined bed and banks, whether natural or artificial, with a perennial or intermittent flow. If the eroded channel in your yard only conveys water during a storm event, it may still be classified as a stream per this definition.

An eroded channel in your yard can be a nuisance. It may be displeasing to look at and could pose major safety risks for children and even animals. If the channel has a defined bed and bank, then it will most likely be deemed as a stream. Typically, whenever earth disturbance is proposed within a stream as defined above, general permits are required. However, there is a stipulation that allows a water obstruction in a stream or floodway without having to be reported to the state as long as it satisfies the proper criteria. A water obstruction is defined as a dike, bridge, culvert, wall, wing wall, fill, pier, wharf, embankment, abutment or other structure located in, along or across or projecting into a watercourse, floodway or body of water. A permit for a water obstruction can be waived as long as the drainage area is 100 acres or less and no wetlands are located within the floodway. This waived activity is classified as a Waiver 2.

In addition to the waiver of permit requirements stipulated in the PA Code, the U.S. Army Corps of Engineers also requires that there be no more than 250 linear feet of stream disturbance and a Pennsylvania Natural Diversity Inventory (PNDI) search receipt dated May 4, 2015, or later, that states “No Known Impact, No Further Review Required” for the U.S. Fish and Wildlife Service (USFWS) for it to be a non-reporting activity. However, there are some exceptions to the PNDI requirement which would still allow the work to be a non-reporting activity. In addition, even if the project satisfies all of the above criteria, the local municipality will most likely require a plan review to ensure that the work complies with their code.

Please keep in mind that a water obstruction can still be constructed if any of the aforementioned requirements aren’t met. However, a general permit would then have to be applied for with the state and/or with the USACE. Please contact us if you need assistance or guidance in addressing your erosion issue.