Wednesday, November 3, 2010

Permeable Pavement Systems – Worthless Without Proper Maintenance

The concept is simple enough; create a pavement surface that will allow rainwater to simply pass downward through it and into a gravel reservoir where it has a chance to percolate back into the soil. Not only will these systems greatly reduce or eliminate storm water runoff volume from a paved area, but also greatly improve the quality of the water that enters the groundwater or storm drain system. With the inception of storm water quality design constraints for many sites, more projects are deploying permeable pavement systems, in the form of pervious concrete, pervious asphalt, gravel-filled plastic reinforcing grid systems, and the ever-popular permeable interlocking concrete pavers (PICPs).

If Not Maintained, Permeable Pavement Becomes Impermeable

When pervious pavement is first installed, its top layers can infiltrate more water than would ever be experienced in any rainstorm anywhere on the face of the earth; up to 500 inches per hour! This is simply because clean gravel, or anything highly porous, will pass a great amount of water through it vertically. Over time, surface sediments, mud, silt, debris, and organic material lodge themselves in the porous spaces. Additionally, the fill gravel used in the grout spaces of PICPs can become displaced by differential settling and high-speed surface traffic. In 2 years or less, without proper maintenance, a fully-functioning system can become completely clogged, and will function just like conventional concrete. Storm water may pond and go places never intended in the original design.

What Doesn’t Work

The following methods should not be employed to maintain permeable pavement systems:
  • Power Washing – This method displaces necessary fill gravel (in PICPs), and can drive clogging particles deeper into the porous top layer
  • Infrequent Sweeping – Displaces fill gravel (in PICPs), and is simply not adequate at removing embedded materials. Some types of frequent sweeping can offer some benefit so long as surface is monitored and lost fill gravel is replaced.
  • Pulling Large Weeds – If large weeds are growing in your pavement, then the system is being poorly maintained by definition. But pulling large weeds after they’ve grown will also exacerbate the problem, because dead root material will remain behind.
  • Waiting Too Long and/or Doing Nothing – Whatever maintenance methods are utilized, waiting too long between maintenance actions is one of the biggest contributors to failure of permeable pavement systems.

Complicating and Contributing Factors

Some site conditions exacerbate pavement clogging, and should be avoided. Where they cannot be avoided, an accelerated maintenance schedule is needed.

  • Lots of tree canopy – Overhanging trees that shed debris can quickly clog a permeable pavement system.
  • Systems that ‘accept flow’ from a nearby source – Pervious pavements should not be located next to a watershed (on a downward slope from a nearby area), or at the end of a drainage channel that will dump runoff into the edge of the pavement.
  • Windblown soil and debris – These systems will clog faster when constructed near bare or denuded areas with frequent or steady winds.
  • Landscape stockpiling – Site maintenance personnel should be trained not to stockpile any materials on top of permeable pavements, where the soil or landscape debris can directly clog the top layers of the system.
  • Unsuitable Traffic Conditions – Permeable pavement systems are not appropriate for frequent heavy vehicle traffic or high-speed traffic.

The Standard for Proper Maintenance

The best maintenance program for these pavement systems includes

  • Regular vacuuming (approximately every 6 months) and/or frequent and well-monitored sweeping
  • Spray or Flame Weed Abatement (when weeds are still very small)
  • Replacement of Fill Gravel (for PICPs), restoration of gravel back to surface (performed immediately after vacuuming)

Time is the enemy of any permeable pavement system. If regular vacuuming is not performed or the pavement is abandoned for a long time, a high-powered vacuum system should be able to restore the system. But be careful; special high-powered truck vacuums cannot reach confined spaces, and even where such a vacuum can reach and extract the clogging debris, it will also extract a good deal of joint gravel as well in PICPs (which must be immediately replaced). In pervious concrete and asphalt applications, wait too long to vacuum and the porosity can never be restored – the only solution is a complete pavement replacement.

Don’t waste the expense and efficiency of an otherwise excellent storm water device by not properly planning for regular maintenance. And make sure that a new owner or site manager understands the system they are inheriting, before they find out the hard way.

John S. Coffey, PE, PLS, is founder and President of Coffey Engineering, Inc. in San Diego. He’s contributed to over a thousand civil engineering, surveying, and planning projects in San Diego and surrounding communities over the past 15 years. 858-831-0111

Sunday, August 8, 2010

Who can do my Survey?

One question I’m frequently asked is: Where is the line drawn between the responsibilities of the Civil Engineer and the Land Surveyor when it comes to the survey or development of land?


There is some confusion over the authority of engineers and surveyors. Who can do what? From 1941 to 1982, licensed Civil Engineers were authorized to perform all of the duties reserved for licensed Land Surveyors, in addition to all of the design decisions traditionally attributed to engineering. The California Board of Professional Engineers and Land Surveyors (BPELS) decided in ’82 (a culmination of 15 years of lobbying from surveying interests) that important matters of real property, including surveying and interpretation of parcels, subdivisions of land, rights-of-way, and easements, were too specialized for Civil Engineers, who in most cases are not educated or experienced in such matters. BPELS did however, allow Civil Engineers to retain the authority to perform topographic surveys and construction staking, and Civil Engineers licensed prior to 1982 were ‘grandfathered’ and can still perform all of the duties of a Land Surveyor until their retirement.

Frequently Asked Questions / Frequent Comments

"I thought that Civil Engineers could do everything a Land Surveyor can do, and more."

That was the case prior to 1982 (and is still the case for all Civil Engineers licensed prior to that date). But since then, only surveyors can prepare subdivision maps and condominium plans, perform boundary surveys, draft legal descriptions, and the like.

“Can a Civil Engineer perform my topographic survey?”

Maybe. The laws do allow for this authority. However, if the topographic survey must include references or dimensions to property or easement lines, then only a Land Surveyor (or pre-’82 Civil) can prepare such a survey.

“Can a Civil Engineer perform construction staking for my project?”

Probably. But again, if there are critical dimensions to property lines or easements that are part of the construction staking/survey, then doing so may be overstepping the bounds of the engineering license.

“Should I hire a Land Surveyor or Civil Engineer to perform my construction staking?”

That depends. The Civil Engineer may say that they should handle the construction staking because they designed and laid out the grading or improvement plan, and therefore they know the project more intimately. The Land Surveyor may say that surveying is their customary profession, something they do all the time, and therefore it’s best to employ the best professional; or a boundary issue may come up as part of the survey, and they are the only ones able to handle the issues that arise out of such work. Both arguments have good merit and should be considered at the client’s discretion.

“My Civil Engineer performs boundary surveys for me all the time.”

If he/she does, then they were probably licensed prior to 1982 (license number is less than 33966), or they employ (or subcontract) a licensed Land Surveyor to perform these tasks on their projects. Otherwise, they could be violating the law to perform such work under their own license.

“So can my Land Surveyor prepare grading plans, improvement plans, retaining wall plans, water and sewer design, etc?”

No, an LS does not have the authority to design such features for construction. However, an LS may practice ‘land planning’, and if they are presenting these features in concept as part of a planning document, then they may have such authority.

“Who can prepare Tentative Maps?”

Good question. Tentative Maps often contain boundary information and proposed lines of subdivision, together with proposed roadways, storm drainage features, water and sewer facilities, etc. Some purists believe that such maps must be dually stamped (a Land Surveyor and a Civil Engineer), because they contain elements of both professions. Most agencies, however, interpret this as a planning document and therefore allow either a Surveyor or Engineer prepare Tentative Maps.

When in doubt, just think 'Boundary’

Ask yourself “does what I’m trying to do directly involve the boundary of ownership or other legal interest in real property?” If the answer is ‘yes’, then you probably need the services of a Professional Land Surveyor (or a Civil engineer licensed prior to 1982). Subdivision of land? PLS. Lot line adjustment? PLS. Legal description for a new easement? PLS. Survey my property boundary? PLS. You get the idea.

John S. Coffey, PE, PLS, is founder and President of Coffey Engineering, Inc. in San Diego. He’s contributed to over a thousand civil engineering, surveying, and planning projects in San Diego and surrounding communities over the past 15 years. 858-831-0111

Monday, March 29, 2010

A Primer on Post-Construction Storm Water Regulations

The Clean Water Act, passed in 1972, and amended in 1977 and 1987, is a Federal law regulating the discharge of pollutants into receiving waters of the US. Its enforcement is broadly overseen by the Environmental Protection Agency (EPA), but more directly controlled and interpreted by the Regional Storm Water Quality Control Board (RWQCB). The San Diego RWQCB is the 9th (out of 9) boards in California. The regulations require that local municipalities oversee, mitigate, or control storm water exiting from a site when reviewing or approving local development projects.

The Board regulates the water runoff from sites both (1) during construction and (2) post-construction. Although the ‘during construction’ requirements can be onerous and difficult in themselves, this discussion covers only the post-construction or permanent conditions.

Controlling Factors

The level of detail for water quality design solutions varies depending on a number of factors, but the 3 main controlling features are:

  • Location of the site: The proximity of your project to a sensitive water body (i.e. a major river, stream, or the Pacific Ocean) may affect what category of design solutions you need to have studied and mitigated.
  • Type of project proposed: A single-family residence will be much less likely to trigger a full water quality report than say, a manufacturing operation, large restaurant, or a 50-lot subdivision.
  • Existing terrain of project: Most municipalities have a special category for sites that lie on or adjacent to a steep natural slope.

Different Requirement Categories

Depending on the factors listed above, your site generally falls into 3 different categories of study and enforcement:

  1. Basic: If you’re fortunate, your site will trigger only an elementary level of study. May times, this consists only of a signed statement from the owner or developer and simple information on the site or drainage plan which demonstrates an effort to reduce storm water pollutants as much as practicable. In addition, the municipality may require that a standard checklist-based form be filled out describing the water quality-based design implementations for the project. More recently, the City of San Diego has been mandating a Water Quality Study (WQS) for this level, which requires a basic analysis of polluted waters downstream, a summary of potential pollutants to be generated from the site, and a description of mitigating design solutions (including scheduling and costs to maintain).

  2. Intermediate: If your project triggers one of the pollutant risks described in the ‘controlling factors’ above, a more advanced analysis will be required. This takes the form of a Water Quality Technical Report (WQTR), or a Storm Water Mitigation [Management] Plan (SWMP). This is a more advanced study that requires a more detailed analysis of downstream impacts. It requires that list of possible pollutants be matched to the found pollutants in a downstream water body, and a solution be specifically designed for any correlations. For example, if a downstream river has tested positive for bacteria, and your site use has been known to generate bacteria and send it downstream in storm water, then a specific solution must be designed to limit or eliminate bacteria from heading downstream.

  3. Advanced: This category is reserved for sites that are expected to generate specific levels of harmful pollutants. A WQTR or SWMP is needed, but in addition, a specific monitoring and testing program must be outlined to assure the municipality that the implemented solution is adequate to limit the pollutant. Monitoring is generally conducted at certain intervals, and the results of such testing are submitted to the municipality for their review over time, or in perpetuity.

Types of Solutions

Since the onset of more rigorous enforcement of the regulations, literally hundreds of methods, solutions, and products have been implemented to mitigate the effects of storm water pollutants from leaving the project site. But a few of the most popular solutions for the majority of projects include the use of one or more of the following:

  • Flow over planted surfaces (vegetated swales, strips, buffers)

  • Pervious Paving (open aggregate surfaces, ‘turf block’, ‘grasscrete’, open pavers)

  • Reinfiltration Pits or Trenches

  • Sediment or Retention Basins

  • No ‘directly-connected’ systems (downspouts dump to surface, paved surfaces lead first to vegetated areas before employing catch basins)

  • Filter systems (Manufactured, pre-fabricated systems designed to treat different pollutants).

Monitoring Enforcement

Although the responsibility to maintain the implemented systems lies with the land owner, most municipalities have not yet installed a specific inspection and enforcement program to track completed projects. But in recent years they have been collecting detailed information about treatment implementations, and have required storm water maintenance agreements, recorded with the County Recorder’s office. Word has it that regular inspections, long after the project has been completed, are not far behind. Stay tuned.

John S. Coffey, PE, is founder and President of Coffey Engineering, Inc. in San Diego. He’s contributed to over a thousand civil engineering, surveying, and planning projects in San Diego and surrounding communities over the past 15 years. 858-831-0111

Sunday, January 17, 2010

Plan for a Rainy Day

Wondering what you can do when heavy rains are forecast to hit your construction site? There are numerous erosion and sediment control methods, practices, and materials available to the contractor, but there are a few usual suspects when things go wrong when it’s raining (yes, sometimes it actually rains in San Diego). Here are the five biggest oversights or mistakes that we’ve witnessed on sites when it comes to construction BMPs. Avoiding them may mean the difference between an uneventful rainfall and a costly cleanup later.

1.) Silt fences that don’t have a chance of containing any silt:
If you can see daylight at the bottom of your silt fence, then the only purpose it serves is that of a flimsy 2-foot high perimeter construction fence; alerting neighbors where the edge of your construction site is. A properly-installed silt fence should be embedded at least 4 inches (6 inches is standard) into the soil below, and the base of the fabric below the soil should be ‘keyed-in’. To achieve this, cut a 6” x 6” trench at the base of your future fence, run the fabric along the bottom of your trench and then up the side, so that at least 8-12 inches of the fabric lies below grade once you fill your trench back in.

2.) Limited or No Monitoring of the Site:
Even with the best-laid protection devices on a construction site, without monitoring by a person delegated with the responsibility, a small breach or channel created by a single rainstorm can render the performance of your materials worthless. You may have constructed a fine desilting basin at the outflow point, and then the water carves its way around or beneath the gravel bags or earth berm, sending a deluge of silt downstream over the course of hours (or days). The site should be inspected after each significant rainfall. When the storm is particularly heavy, lasts a long time, or storms follow one after the other, put on your best boots and check out the storm while it is raining to survey the installed devices in action, and take action on the spot if need be.

3.) The Right Materials Installed at the Wrong Location:
Silt fences and straw wattles are very effective sediment control devices, but they are nearly worthless at points of concentrated flows. Any low points or other places where you expect a stream of water during a storm need heavy devices such as gravel bags, rock check dams, or earthen berms to keep from tracking sediments off site. And putting something intended for flatter areas (like loose mulch or straw) on steep slopes just creates more debris to wash downstream when it does finally rain.

4.) No Backup Plan:
A well-protected job can fall apart quickly in a bad storm if there are no materials stockpiled on site. Unless you have a really good relationship with your erosion control supplier, you’re not going to get them to show up with an hour’s notice in the middle of a stormy week. The best single item to keep at hand? Gravel bags, or at least a pile of gravel, bags to put it in, and the manpower to assemble them. Gravel bags can be used to create a strong desilting basin or barrier, as small checkdams in a drainage swale, and can also be used in place of a breached section of silt fence or straw wattle. Once things dry out, the gravel can be re-used in numerous other capacities on site.

5.) Size Matters:
Installing a small check dam or desilting basin on a postage-stamp size lot isn’t the same as controlling the flows from a 10-acre construction site. Larger sites need special attention to the size of the installed features. Temporary dams and basins may need to be excavated out. Their size should be calculated from expected flow rates and types of soil on the site.

Thankfully in the dry climate of San Diego, attention to erosion and sediment control on the construction site is usually not a problem. Some projects can be started and finished over the summer, or during a particularly dry winter. But we can’t let that lull us into a false sense of security when we get a bad storm or series of storms. The risks of damage to downstream properties and facilities, not to mention the fines and claims that may come with them, are too great to just ignore.

John S. Coffey, PE, is founder and President of Coffey Engineering, Inc. in San Diego. He’s contributed to over a thousand civil engineering, surveying, and planning projects in San Diego and surrounding communities over the past 14 years. 858-831-0111