Development of a Scoring System for Construction-Site BMP Assessment
A tool to rate the quality of implementation and maintenance
A scoring system to evaluate best management
practices (BMPs) implementation at construction sites was developed and
used in Lincoln and Omaha, NE. A simple metric tool was developed to
score the quality of implementation and maintenance of five types of
construction-site BMPs at 87 construction sites from the two
communities. The scoring system was developed to be simple to use,
employing a three-tiered rating system for each BMP type. This simple
system requires minimal training and allows for quick assessments that
are reproducible between evaluators. The scores were used to assess the
relative frequency at which construction-site BMPs were properly or
improperly implemented. The system could be used to monitor and document
BMP implementation improvement through time and to identify the BMP
types that are in need of improved implementation, increased monitoring,
or improved training. Results, using the inspection metric, showed that
implementation and maintenance of stormwater BMPs followed a uniform
distribution from excellent to very poor. That is, at least half of the
construction sites had BMP systems that were not implemented or
maintained well and were, therefore, likely providing little stormwater
protection. Because the effectiveness of various BMPs is typically
reported for properly implemented and well-maintained installations, the
actual in-the-field performance may be significantly less than the
reported effectiveness implies.
a result of the 1987 amendments to the Clean Water Act (Clean Water Act
1977), the USEPA established a comprehensive phased approach to
stormwater management under the existing National Pollutant Discharge
Elimination System (NPDES) program. NPDES Phase II lowered the threshold
on municipal separate storm sewer systems (MS4s) to populations greater
than 10,000 and construction activities to 1 acre (NDEQ 2004; USEPA
Nonpoint-source pollution from stormwater is difficult to
monitor and/or treat for a number of reasons, including the nondiscrete
location of the sources and transport routes of pollutants. Because of
this difficulty, nonpoint-source pollution is not regulated to a numeric
limit but is instead addressed through the use of BMPs, which are
techniques, measures, or structural controls that are used to manage the
quantity or quality of stormwater runoff (USEPA 1999, 2004).
have shown construction activities to be a major source of
nonpoint-source pollution (primarily sediments and nutrients) (Willett
1980; Yorke and Herb 1976; Owens et al. 2000; Novotny et al. 1979).
Construction-site runoff controls are typically focused on erosion
prevention and sediment control, due to the large amounts of uncovered
ground present during the construction process.
mid-1990s, when stormwater management became more common, the number of
available construction-site controls has significantly increased.
Accordingly, so has the research on these controls. Most available
research focuses on pollutant removal capabilities of BMPs and not on
their maintainability. Recently, many researchers are finding that
proper maintenance and inspection is a significant problem for BMP
programs. For example, Corish (1995) concluded that 67% of communities
encountered major problems with inadequate installation and maintenance
of BMPs. Similarly Patterson (1999) concluded that “poor implementation
remains a widespread obstacle [to effective BMP use.]” Shaver and Piorko
(1996) stated that “most ESC [erosion and sediment control] programs do
not have the resources to effectively inspect construction activity.”
Shaver and Piorko also noted that of surveyed inspectors, each inspector
is responsible for an average of 150 sites, which can significantly
limit the ability to properly inspect each site.
In addition, a
general lack of guidance on BMP inspection methods and requirements has
led to variability in the methods and quality of inspections. This is
apparent from a review of the inspection checklists commonly available
over the Internet. For example, some communities like Bellevue, WA, have
a number of detailed checklists (SCVURPP 2006), while others like
Overland Park, KS, have a simpler system (Overland Park 2006).
Additionally, in some communities like Lincoln, NE, a majority of the
inspections are conducted by a designated inspector who works for the
community, while in other communities like Omaha, NE, a majority of the
inspections are conducted by contractors for the developers who report
their findings to the community.
Lincoln and Omaha, NE, are
classified as large MS4s; therefore, they are regulated under the
stormwater provisions of the Clean Water Act. One of the six minimum
measures required for compliance for each of these communities is
construction-site runoff control. This is accomplished in both
communities through permitting and inspections of implemented BMPs.
study was conducted to evaluate the implementation and maintenance and,
therefore, the effectiveness of construction-site BMPs in two
Midwestern communities. During the study, it was found that a quick and
reproducible scoring method was needed for construction-site BMP
assessment. The purpose of this article is to describe the development
and use of this method.
Selection of Construction Sites
active construction sites (42 from Lincoln and 45 from Omaha) were
selected randomly from recently submitted and approved stormwater
pollution prevention plan (SWPPP) permits. Lincoln and Omaha are typical
small- to medium-sized Midwestern cities. Lincoln has a population of
about 240,000, and Omaha has a population of about 400,000 with an
immediate urban area population of about 800,000. In an effort not to
bias the site selection, information contained in the permit and
associated SWPPPs was not used for the selection or evaluation of the
sites. All sites were inspected during the growing season (i.e., April
through September). The Lincoln sites were inspected in September 2004
and April/May 2005. The Omaha sites were inspected during the summer of
2005. Inspections were done by two individuals. The Omaha inspector was
trained by the Lincoln inspector. The training included consistency
checking to ensure that the BMPs were evaluated the same way in both
communities. Because of the relatively simple assessment metric,
training and consistency checking were completed with only a few visits
to each BMP type.
Development of Metric for Assessment
evaluate construction sites objectively, a simple metric tool was
developed to rate the quality of construction-site BMP implementation
and maintenance. The metric was based on the “Ohio EPA Construction Site
Inspection Checklist” (Ohio EPA 2003). The metric included evaluation
of five BMP categories: stabilization, sediment tracking control, ponds,
linear controls, and inlet protection. These five BMP types were
selected because they are the primary BMP types used to reduce the
transport of soil and sediment from construction sites. The evaluated
categories of BMPs are similar to the list of the five common BMP types
discussed by Lee (2000). Wind erosion controls were not assessed, as
typical applications are temporary.
Scoring Metric for BMP Types
following sections describe the assessment matrix used for the five
construction-site BMP types that were evaluated in this study.
Stabilization refers to the
use of cover materials, typically vegetation, used to reduce erosion
potential. Most communities have standards for how long an area can
remain unstabilized during the construction process. Because one-time
visits were used to assess the construction sites, it was not possible
to evaluate how long areas remained unstabilized. Therefore, evaluation
of the need for stabilization was based on the state of the site at the
time of the visit. If construction on the facility or structure (i.e.,
homes or offices) had begun, stabilization was deemed required. Sites
were given a score of 1.0 if stabilization measures (e.g., seeding,
sodding, or artificial cover material) were actively being used over
two-thirds of the construction site. Only two-thirds of the site was
required to be stabilized to receive a score of 1.0 to allow for ongoing
construction activities on the other one-third of the site. A score of
0.5 was given where stabilization was present but inadequate (e.g., less
than two-thirds of the applicable area was properly stabilized). A
score of 0 was given where no stabilization was seen and construction
was ongoing. A score of not applicable (NA) was given where
stabilization was not present but was deemed not necessary due to site
conditions (e.g., where grading had been done and the soil was left
bare). Figure 1 shows the metric developed to assess stabilization practices.
Sediment Tracking Control Assessment
tracking control category was used to assess the use of measures (i.e.,
rocked construction-site entrances and wash stations) to prevent the
tracking of sediments onto streets or adjacent properties. A score of
1.0 was given where construction-site entrances were present and
constructed properly. A score of 0.5 was given where a construction
entrance was present but improperly designed or operated (e.g., where
rock sizes were less than the typically required 2-inch diameter [Ohio
EPA 2003]). A score of 0 was given where no sediment tracking control
was present. A score of NA was given where the use of construction
sediment tracking control was no longer necessary due to stabilization. Figure 2 shows the metric developed to assess sediment tracking practices.
Ponding Practices Assessment
The pond category was
used to assess the use of ponding facilities (i.e., sediment basins,
retention ponds, detention ponds). A score of 1.0 was given where
ponding facilities were necessary and present. Scores of 0.5 were not
given, because ponds are generally either present or not. A score of 0
was given where no ponding facility was present and the site was larger
than six residential lots (approximately 1 acre). A score of NA was
given where the use of ponding facilities was determined unnecessary
because the size of the construction site was less than six residential
lots. Figure 3 shows the metric developed to assess ponding practices.
Linear Controls Assessment
The linear controls
category was used to assess the use of linear sediment control devices
(e.g., silt fence). A score of 1.0 was given where controls were
present, properly installed (e.g., dug in), and maintained over at least
two-thirds of the construction site. The use of two-thirds of the
construction site was used to allow for areas of ongoing construction
activities that would prevent linear control installation and
maintenance on the other one-third of the site. A score of 0.5 was given
where controls were present but either not properly installed or not
properly maintained. A score of 0 was given where no controls were
present but were necessary. A score of NA was given where controls were
determined unnecessary because of stabilization. Figure 4 shows the metric developed to assess linear control practices.
Inlet Protection Assessment
The inlet protection
category was used to assess the installation and maintenance of storm
sewer inlet protection devices (e.g., fabric barriers, inlet blockages).
This category did not consider inlet marking or storm sewer stenciling.
A score of 1.0 was given where controls were present and properly
installed and maintained for two-thirds of the site. The use of
two-thirds of the construction site was used to allow for areas of
ongoing construction activities that would prevent inlet control
installation and maintenance on the other one-third of the site. A score
of 0.5 was given where controls were present but not properly installed
or maintained (e.g., didn’t cover the entire inlet, silt fence had
failed). A score of 0 was given where no controls were present. A score
of NA was given where controls were determined unnecessary because of
stabilization. Figure 5 shows the metric developed to assess inlet protection practices.
Results and Discussion
assessment method was applied to 42 construction sites in Lincoln (16
commercial, 12 general, 14 residential) and 45 construction sites in
Omaha (15 commercial, 15 general, 15 residential). Figure 6
shows the overall results of construction-site visits according to the
type of control and type of construction for the Lincoln sites. Figure 7
shows the overall results of construction-site visits according to the
type of control and type of construction for the Omaha sites.
was the most difficult BMP category to assess because of the
potentially transient nature of this BMP. However, it did receive some
of the highest scores. Of the 65 sites (Lincoln and Omaha combined)
where stabilization was deemed necessary, 33 (51%) received the highest
score of 1.0, while 14 (22%) received a score of 0 (showing no presence
of stabilization). Residential construction in Lincoln received the
lowest score for stabilization, with typical scores significantly lower
than for commercial and general construction. It was not uncommon to see
home sites completely finished that had not been stabilized. This may
be because, in part, of the perceived ambiguity in the construction-site
regulations. Because individual residential lots are typically smaller
than 1 acre, some builders may believe that the construction-site
regulations do not apply, even though the lot is part of a larger
development. In addition, because the lot is small, construction
activities typically involve most of the lot; therefore, it is difficult
to properly maintain BMPs such as stabilization.
Sediment Tracking Controls
tracking controls received the lowest scores as a group. Of the 72
sites where tracking controls were deemed necessary, only three (4%)
received the highest score of 1, while 38 (53%) received a score of 0
(showing no presence of tracking controls).
Low scoring in this
category also came as a result of improper rock size selection on
construction entrances. Most guidance stipulates that a construction
entrance should be constructed of rock with a mean diameter of 2 inches
(Ohio EPA 2003; Fifield 2004). Often entrances were constructed of much
Ponding facilities received
relatively high scores. This was also the category that produced the
best results for residential construction. Of the 46 sites where ponds
were deemed necessary, 35 (76%) received the highest score of 1, while
the remaining 11 (24%) received a score of 0. Note that only scores of
1.0 or 0.0 were given for this BMP category.
general construction likely received lower grades due to ambiguity of
the need for a facility, reluctance to construct ponding facilities on
high-value land, or difficulties in sequencing construction and removal
of a pond at a commercial site. Residential construction is typically of
the scale that there is no question of the need for such a facility.
Residential developments are typically amenable to the sequencing of
construction, and ponding facilities can often be left as green space
controls were present at most sites, and results in this category were
similar for all types of construction. Silt fence was the most common
BMP in this category and on construction sites in general. Of the 83
sites where linear controls were deemed necessary, 38 (46%) received the
highest score of 1, 20 (24%) received a score of 0 (showing no linear
controls onsite), and 58 (30%) received a score of 0.5 (showing that
linear controls were present but not properly installed or maintained).
Often, silt fence was located in areas with little function (e.g., as
perimeter control or near tops of hills). Maintenance and proper
installation of silt fence was a common problem at the visited sites.
protection was fairly common at the visited sites. However, of the 57
sites visited where inlet protection was deemed necessary, only 13 (23%)
received the high score of 1, while 30 (53%) received the low score of
Two main types of inlet protection were observed: silt fence
around an inlet and preconstructed, commercially available inlet
protection devices. In the silt fence inlet protection applications, a
number of well-constructed applications were found; often they were
backed with chicken wire and supported by a sturdy 2x4 frame. However,
many installations using silt fence for inlet protection simply
installed the silt fence like standard linear control silt fence. These
sites proved to have difficulty being maintained, likely because of the
presence of concentrated flows. This shows that although silt fence can
be used for inlet protection, it must be designed and installed as inlet
protection, not as linear control.
available devices showed few problems with maintenance. However, these
devices often received lower grades due to improper application.
Evaluation of Overall Site Scores
Figures 6 and 7
show that the sediment tracking and inlet protection (except for
general construction in Lincoln) BMPs scored the lowest in this study.
The results from this type of evaluation could be used to focus
inspection efforts and to improve training for construction contractors.
In addition, the results could be used to monitor and document
improvements in BMP implementation through time.
The data do not
follow a normal distribution; therefore, typical statistical analysis
cannot be conducted. However, analysis of the data was done using the
nonparametric sign test. This test allows the comparison of the mean of a
data set to some predetermined value at a specified confidence level.
For example, for the BMP assessment, one can determine if the mean score
for a BMP is statistically above some level (say 0.5) at the 95%
confidence level. The results of this analysis show that the mean scores
for the following BMPs were not above 0.5 at the 95% confidence level
in Lincoln: stabilization (residential); sediment tracking (all
construction types); linear controls (commercial/industrial); and inlet
protection (commercial/industrial and residential). The mean scores for
the following BMPs were not above 0.5 at the 95% confidence level in
Omaha: sediment tracking (all construction types); inlet protection
(general and residential). These statistical measures could be used to
assist evaluation and comparison of the BMP types (e.g., identifying
differences in implementation quality between BMP types or changes in
BMP implementation quality through time).
Figures 8 and 9
show the distributions of the overall average scores for each
construction site visited. These figures show fairly uniform
distributions of scores from 0.0 to 1.0, showing that a range of
implementation and maintenance quality is present in both communities.
The uniform distributions in Figures 8 and 9 show that the numbers of
construction sites with very good, very poor, and mediocre
implementation and maintenance of BMPs are roughly equal. However, the
scoring system used in this study is likely rather generous. That is,
typically sites were given the top score of 1.0 if only two-thirds of
the site’s BMPs were installed and maintained properly, and sites were
given a score of 0.5 if the BMPs were present but not properly
maintained. Under this scoring system, a site could have essentially
ineffectual BMPs and still receive a score of 0.5. Therefore, the
distributions showing half of the sites with overall scores below 0.5
likely indicates that more than half of the sites have largely
Considerable research has been done on the
removal efficiencies of various BMPs for controlling certain pollutants
(USEPA 2004). For example, silt fence has been reported to remove from
75% to 85% of sediments (USEPA 2004). However, these results are based
on properly installed and maintained BMPs. The actual removal
effectiveness of a BMP is a function of how well a BMP works if
installed properly and how well it is installed and maintained in the
field. Therefore, the overall effectiveness of a BMP program should
consider both the types of BMPs that are to be used and the quality of
implementation and maintenance of those BMPs.
Based on the results
of this study, proper installation and maintenance occurs on fewer than
50% of the sites studied. Therefore, it is likely that
construction-site BMP systems perform significantly below the optimal
levels. This result should be considered when planning and evaluating
BMP programs and when estimating the potential benefits (i.e., pollutant
removal efficiency) of proposed BMP programs.
Improvements to Construction-Site BMP Inspection Protocol
metrics developed for this study used a three-tiered grading system,
generally: 1.0 for sites with BMPs present and properly maintained over
two-thirds of the site, 0.5 for sites with BMPs present but not properly
installed and maintained over two-thirds of the site, and 0.0 for sites
lacking appropriate BMPs. The simple three-tier metric was selected to
reduce ambiguity between grading levels. Analysis of the results showed
that while the simple three-tier system was simple and reproducible, a
scoring system with more grading steps would likely make the results
more realistic. For example, sites with BMPs present but completely
ineffectual received scores of 0.5, implying that they were “half-good,”
while in reality they provided little to no pollutant removal
Recommendations for Further Study
is recommended that additional study be conducted to revise the
inspection scoring protocol to better describe the actual performance of
the BMPs. In conjunction with that study, methods to determine the
acceptable threshold for BMP quality should be evaluated.
assessments were conducted at 87 construction sites in Lincoln and
Omaha, NE. The results of these assessments showed:
of construction-site controls varied greatly and produced a uniform
distribution of scores, from very well-installed and -maintained sites
(score of 1) to those where no controls were witnessed (score of 0).
Therefore, at least half of the construction sites have significant
shortcomings regarding BMP implementation and maintenance and,
- Because construction-site BMPs are only
installed and maintained properly about 50% of the time, actual BMP
effectiveness may be only 50% of reported values for specific BMP types
(e.g., silt fences are reported to remove approximately 80% of
sediments, but if they are installed improperly 50% of the time, the
actual effectiveness is significantly less).
- Installation and
maintenance of BMPs on construction sites appears to be limiting the
effectiveness of construction-site controls.
- The scoring method
has proven to be a useful tool for identifying BMP types that may
require additional monitoring or contractor training and for identifying
changes through time of BMP installation quality.
Author's Bio: David Admiraal is an associate professor in the Department of Civil Engineering at the University of Nebraska in Omaha.
Author's Bio: Tony Krause is a research assistant in the Department of Civil Engineering at the University of Nebraska in Omaha.
Author's Bio: Bruce Dvorak is an associate professor in the Department of Civil Engineering at the University of Nebraska in Omaha.
Author's Bio: John Stansbury is an associate professor in the Department of Civil Engineering at the University of Nebraska in Omaha.
Author's Bio: Andrew Young is a research assistant in the Department of Civil Engineering at the University of Nebraska in Omaha.