D - 63
APPENDIX D
SITES IDENTIFIED USING THE XBAR PLOT
D.1 Description
The following appendix describe those sites described as unusual in other land uses besides residential.
D.2 Censored Data Descriptions
In this section is presented a brief description of the characteristics of each constituent. It includes the range of detected values in the database, the maximum and minimum values, the most frequent non-detected observation and the frequency at this level of censoring.
Conductivity is the ability of the water to carry electrical current. It depends of the available ions present in the sample. The database contains 685 samples collected in single land uses most of them in residential and industrial areas. Only 2 samples were collected in Open Space. All the samples collected were detected. Residential, industrial and the pooled dataset have almost the same range. Low conductivity values are around 10 mS/cm, whereas high values are close to 2000 mS/cm. A single observation of 5955 mS/cm was observed in the complete dataset. The BMP database has a range between 0.04 and 600 mS/cm included in their database. In the NSQD around five percent of the conductivity values are greater than 600 mS/cm.
Hardness indicates the presence of metallic cations (Ca, Mg, Sr, Fe and Mn) in the water. Concentrations lower than 75 mg/L CaCO3 are considered low. Concentrations between 150 and 300 mg/L CaCO3 are considered hard (Sawyer, et al, 2003). Hardness is highly correlated with the characteristic of the soil in the watershed. If there is an elevated presence of the metallic cations in the soil of the catchments it is expected a high hardness concentration. The range of the residential commercial and industrial land uses is very similar. It varies between 1.9 and 900 mg/L. Around 99% of the values found in the database are smaller than 400 mg/L. The BMP database has a range between 0.5 and 543 mg/L. There are six values higher than the maximum reported in the BMP database. There is only one detection limit (<10 mg/L) for this constituent in the database. Around 5% of the detected values in the NSQD were lower than this level.
Oil and Grease is related with discharges coming from parking lots, commercial areas and residential areas with failing septic tanks. It is important in stormwater discharges because oil and grease have low solubility and trend to float on water. Open space has the lower variability among land uses. It is not expected elevated concentrations in this land use. Freeways and commercial land uses have the higher percentage of detected values. The range of detected values varies between 0.2 and 11,000 mg/L. Only 1% of the total dataset has values above 400 mg/L and around 95% of the dataset has values smaller than 60 mg/L. The range in the BMP database is between 1.5 and 66.7 mg/L. The concentration at any percentile value was always higher in freeways than in any other land use. Around 50% of the non-detected values are located in <1 mg/L. This censoring level was also the most frequent in all the land uses except for freeways where <3 mg/L was the most frequent. The second most frequent level was <5 mg/L. About 2% of the detected values in all land uses were lower than 1 mg/L while 52% of the detected values were smaller than 5 mg/L.
Total Dissolved Solids calculates the fraction of solids that passes through a filter. It is important in stormwater because it can be associated with the concentration of dissolved metals in runoff samples. More than 97% of the collected samples were detected. The maximum percentage of non-detected values was observed in open space with 2.22%. For all the land uses only 0.2% of detected values were smaller than 5 mg/L. In the other hand, around 1.8% of the detected values were higher than 470 mg/L. The range between 5 mg/L and 300 mg/L contains around 95% of the total detected values. The BMP database contains a range of dissolved solids between 12.5 mg/L and 7100 mg/L. They assume a detection limit of 12.5 mg/L after corrections. The most frequent detection limit was 5 mg/L. This value is the most appropriate because even though the scale can detect variations around 1 mg/L, there are more factors associated with the variability during the measurement.
Total Suspended Solids calculates the fraction of solids that is retained in a 0.45 mm filter or smaller. The range of TSS was between 3 mg/L and 2500 mg/L approximately except for a single sample in a freeway land use. Around 95% of the detected concentrations were below 450 mg/L. Only 1.5 % of the detected samples were observed below 5 mg/L. The percentage of non-detected values in all land uses were below 2% except for open space that was close to 4.5%. The BMP database has a range of TDS between 38 and 11000 mg/L. In the NSQD 34% of the detected samples were located below 38 mg/L. Almost 80% of the non-detected values were located at <5 mg/L. The second most frequent detection limit was <1 mg/L, in samples collected in open space and industrial land uses.
Biochemical Oxygen Demand (BOD) represents the total amount of oxygen that bacteria require to decompose the organic material in a sample under aerobic conditions (Sawyer et al. 2003). More than 3000 samples are included in the database. More than 84% of the samples were detected. The range of commercial, residential and industrial land uses is very similar except for a single sample of 6920 mg/L in an industrial site. The lower range was observed in open land use with a maximum observed value of 20 mg/L. The BMP database has a maximum value of 230 mg/L. There were observed 10 detection limits varying between one mg/L and 100 mg/L. More than 80% of the non-detected values are between one and five mg/L. Detection limits larger than 20 mg/L are considered no relevant in the analysis. Around 7.5% of the non-detected samples were right censored.
Chemical Oxygen Demand calculates the total oxygen required for oxidation of a sample to carbon dioxide and water (Sawyer et al., 2003). The database contains 2,750 samples mostly collected in residential land use. The smallest range was observed in open space, and the largest was observed in industrial. The probability plot of the freeways was always the highest while the probability plot of the open space was always the smallest. The percentages of non-detected were lower than 2% except for open space that has 23.26%. The BMP database has a range of COD between <12.14 mg/L and 2,030 mg/L. All the samples collected in open space were lower than 100 mg/L except for an observation of 476 mg/L. The COD range varies between 1 mg/L and 1260 mg/L. The highest observation was observed in an industrial land use. Six detection limits were observed in the data set. The most frequent detection limit was <10 mg/L with 41% of the total non-detects. Around 80% of the non-detected samples in open space were lower than 20 mg/L while all the non-detected samples in freeways were less than 10 mg/L.
Fecal Coliform is an indicator of bacteria in water. The probability plot of the open space was always higher when compared with the other land uses. The BMP database has a range between <1,000,000 and 1,827,000,000 colonies /100 mL. Open space has smallest concentration of fecal coliform with 650 colonies per 100 mL. Open space also has the smallest range with a maximum detected concentration of 63,000 colonies/100 mL. Fecal coliform was detected in all the freeways samples. In open space around 8% of the samples were non-detects whereas in residential, commercial and industrial the percentage was close to 12%. The data set contains left and right-censored values. Around 39% of the non-detected values were left censored, the remaining were right censored. The highest frequency was observed in <1 col/100mL with 22% of the non-detected values. Close to 45% of the non-detected values in industrial land uses were lower than 1 col./100 mL. The censored values found in open space were larger than 160,000 colonies/100 mL. The second most frequent detection limit was >60,000 colonies/100 mL with a 15% of the total non-detected values. This was the most frequent censored value in commercial land use and the second most frequent in residential land use.
Fecal Streptococcus is indicator of fecal contamination. The probability plot of commercial and industrial land uses was always smaller when compared with the other land uses. The BMP database has a range between 2 and 1,500,000 colonies/100 mL. In this case the largest minimum detected was observed in freeways with 560 colonies/100 mL. The smallest range was observed in open space with a maximum of 101,000 colonies/100 mL. There was observed a single observation above 1,100,000 colonies/100 mL in an industrial site. All the freeways samples were detected. Less than 10 percent of the samples in each land use were non-detected. The most frequent non detected value was <1 colonies/100 mL. Around 50% of the industrial non-detected samples are in this group. The second most frequent detection limit was >60,000 colonies/100 mL, more than 45% of the non- detected values in commercial land used are in this group.
Ammonium ion NH4+ is produced by the interaction of ammonia gas (NH3) and water. The probability plot of freeways was always higher and the probability plot of open. The smallest ammonia concentration values were observed in residential land uses. The highest percentage of non-detected values was observed in open space. For the remaining land uses the percentage of non-detected was smaller than 20%. The range of ammonia in the BMP database is between <0.5 mg/L and 9 mg/L. Around 54% of the non-detected values were <0.2 mg/L. All the non-detected freeway observations were observed in this group. The second highest group was when the detection limit was not reported. The third group was <0.5 mg/L. About 70% of the non detected values in open space have censored observations at 0.5 mg/L.
Nitrite and nitrate (NO2 and NO3) are produced after the reduction or oxidation of NO2. NO2 can be formed during combustion process such as internal combustion of gasoline engines. NO3 can be formed also by oxidation of nitrogen or ammonia in the production of fertilizers. Nitrate can be reduced to nitrite inside a warm body. If nitrite reaches the bloodstream it can reduce the oxygen transport (Sawyer et al., 2003). The range was between 0.01 and 18 mg/L. The BMP database has a range between <0.01 and 9.09 mg/L. Only 1.5% of the dataset was greater than 3 mg/L. The probability plot indicates that the median nitrite-nitrate in industrial land uses was always lower than in other land uses. The percentage of non-detected values was smaller than 4% in any land use except for open space that has approximately 16% of non-detected values. The most frequent detection limit was <0.1 mg/L. All the non-detected values in open space and 50% of the commercial land use were found in this group. All the non-detected values in freeways were <0.3 mg/L. The second highest group was observed when the detection limit was not reported.
The total Kjeldahl nitrogen (TKN) method destroys all the organic nitrogen using sulfuric acid. The destruction releases the nitrogen as ammonia gas (Sawyer et al, 2003). TKN is the sum of organic nitrogen and ammonia. The range of TKN was between 0.05 mg/L and 36 mg/L. About 6.5% of the reported values were larger than 5 mg/L. The BMP database has a range for TKN between <0.025 mg/L and 18.31 mg/L. Less than 5% of the dataset was not-detected in any land use except for freeways where the percentage of non detected observations was close to 30% was non-detected. About 30% of the non-detected values were at <0.2 mg/L followed by <0.5 mg/L with 22%. All the non-detected values in open space were located at <0.5 mg/L. Half of the non-detected values in freeways were at <0.1 mg/L the other half was at <1 mg/L. Almost 40% of the non-detected at industrial land uses were <1 mg/L. In approximately 16% of the all non-detected values the detection limit was not reported.
Dissolved Phosphorus corresponds to the fraction of phosphorous able to pass a 0.45 mm filter. Phosphorous as nitrogen are associated with fertilizer and domestic wastewater. The observed range of dissolved phosphorous was between 0.01 mg/L and 7 mg/L. Concentrations higher than 2 were observed in industrial, mixed industrial and freeways land uses. The range in the BMP database is between 0.0022 mg/L and 8.42 mg/L. The probability plot of freeways indicated higher medians than the other single land uses. Less than five percent of the freeway observations were non-detected, for the remaining land uses the percentage of non-detected varies between 12 and 21%. The highest level of non-detected was observed in open space. In this case it is clear that the level of non-detected observed in freeways was lower than in the other land uses because more accurate equipment was used. In 34% of the non-detected cases the detection limit was not reported, when reported <0.02 mg/L, <0.05 mg/L, <0.1 mg/L and <0.5 mg/L were the most common detection limits. About 80% of the detected observations were smaller than 0.5 mg/L.
Total phosphorus is important for the growth of organisms. They are divided in three groups: orthophosphate, polyphosphate and organic phosphorus (Sawyer et al., 2003). Notice that in this case the highest value was observed in an open space. The probability plot indicates that the median total phosphorus concentration for open space was always smaller than in other land uses. Less than one percent of the observations in freeways were non-detected, in the other land uses it was around four percent except for open space where the percentage was 15%. The range in the BMP database was between <0.1 mg/L and 80.2 mg/L. All the non-detected observations in freeways were at 0.03 mg/L. The largest frequency of non-detected values was <0.5 mg/L followed by <0.1 mg/L. In around 14% of the non-detected values the detection limit was not reported.