**SAN FRANCISCO, CA IMPERVIOUS SURFACES**

This scenario is intended to be used to mimic hydrology of untreated
portions of the San Francisco Area, CA. The intention is to couple the
edge of field concentrations from this scenario with the edge of field
concentrations from the residential scenario for San Francisco to
generate weighted concentrations for areas of varying impervious cover.
Therefore, this scenario relies on a similar soil series as the
residential scenario; however the upper horizon has been adjusted to a
non-soil nature.

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Although this scenario has undergone basic testing, the scenario should
be used with caution since it has not been fully tested under a range of
conditions to ensure that PRZM is capable of simulating pesticide runoff
from impervious surfaces. For instance, during development, it was
impossible to force PRZM to convert all precipitation to surface runoff
(even with a curve number of 100). In addition, setting all soil
parameters to zero in the surface horizon caused errors in PRZM. For
example, soil moisture parameters cannot be set to zero, since PRZM
requires soil moisture for partitioning the chemical into the dissolved
phase for transport. Additionally, CAM selection appears to be somewhat
problematic. Since there are no crops in an impervious surface the
maximum interception storage of crop, rooting depth, and coverage has
been set to zero. However, the consequences for a foliar application
(CAM = 2) which may result from direct spraying of the surface, CAM may
not be pertinent. During testing, this scenario was run several times
using various CAM values. When setting CAM = 1 versus CAM = 2 the same
EECs were produced. When using CAM = 1, an application depth of 4 cm is
automatically used. When running PRZM/EXAMS with CAM = 4, depth = 1 EECs
were even higher than with CAM = 1 or 2. If the scenario is run with
depth = 0 the model produces no EECs. For this scenario, users may need
to set CAM = 4, depth = 0.1 cm. Furthermore, if this scenario is couple
with a residential scenario, the effects of irrigation in one scenario
versus no irrigation in another must be considered.

Metfile W23234 was selected for this scenario since it is the closest
metfile to San Francisco. Its data were collected in San Francisco, CA.
The station is located approximately 2 meters above mean seal level
(AMSL). San Francisco receives approximately 20 inches of rainfall
annually with nearly 60% of the annual precipitation occurring in
January, February, and March (NOAA, 2006). This station is the closest
available weather station that includes data required for PRZM.

[]{.mark}

Soil parameterization followed the methods used for a previous
endangered species assessment in Barton Springs, Texas. Beacause the
surface layer is the most important component of the scenario, values
used were obtained from the existing scenario to maintain consistency.

[]{.mark}

[Number range CHAPTER]{.mark}

+-----------------+----------+-----------------------------------------+
| **Table 1. PRZM |          |                                         |
| 3.12 Climate    |          |                                         |
| and Time        |          |                                         |
| Parameters for  |          |                                         |
| San Francisco,  |          |                                         |
| CA.**           |          |                                         |
+-----------------+----------+-----------------------------------------+
| **Parameter**   | *        | **Source/Comments**                     |
|                 | *Value** |                                         |
+-----------------+----------+-----------------------------------------+
| Starting Date   | Jan. 1,  | Meteorological File from San Francisco, |
|                 | 1961     | CA (W23234)                             |
+-----------------+----------+-----------------------------------------+
| Ending Date     | Dec. 31, | Meteorological File from San Francisco, |
|                 | 1990     | CA (W23234)                             |
+-----------------+----------+-----------------------------------------+
| Pan Evaporation | 0.77     | PRZM Manual Figure 5.1 (EPA 1998).      |
| Factor (PFAC)   |          | Value represents much of CA coastline.  |
+-----------------+----------+-----------------------------------------+
| Snowmelt Factor | 0        | Snow is not expected to occur in San    |
| (SFAC)          |          | Francisco.                              |
+-----------------+----------+-----------------------------------------+
| Minimum Depth   | 17.5     | Mid point of range (15-20), PRZM        |
| of              |          | Manual, Figure 5.2 (EPA 1998).          |
|                 |          |                                         |
| Evaporation     |          |                                         |
| (ANETD)         |          |                                         |
+-----------------+----------+-----------------------------------------+

[]{.mark}

[]{.mark}

  ----------------- ----------- ------------------------------------------
  **Table 2. PRZM               
  3.12 Erosion and              
  Landscape                     
  Parameters for                
  San Francisco --              
  impervious                    
  surfaces.**                   

  **Parameter**     **Value**   **Source/Comments**

  Method to         4 (MUSS)    Default value.
  Calculate Erosion             
  (ERFLAG)                      

  USLE K Factor     0           Set to zero, no erodibility for impervious
  (USLEK)                       surfaces.

  USLE LS Factor    0.37        Calculated according to Haan and Barfield
  (USLELS)                      (1978) equation: LS =
                                ((λ/72.6)^m^)((430x^2^ + 30x +
                                0.43)/6.613), where λ = slope length, x =
                                SLP/100 and m = constant. In this case, λ
                                = 400 m (default value) and m = 0.3 (EPA
                                2004).

  USLE P Factor     1           Contour plowing is not applicable (EPA
  (USLEP)                       2004).

  Field Area        172 ha      Area of Shipman Reservoir watershed (EPA,
  (AFIELD)                      1999)

  NRCS Hyetograph   2           PRZM Manual, Figure 5.12 (EPA, 1998).
  (IREG)                        

  Slope (SLP)       2.5%        Lawns are generally limited to slopes
                                where it is safe to operate mowers (0-5%).
                                Selected as midpoint of the range. Darren
                                Haver (USDA 2006a).

  Hydraulic Length  600 m       Shipman Reservoir (EPA, 1999)
  (HL)                          

  Irrigation Flag   0           Irrigation is not warranted for impervious
  (IRFLAG)                      surfaces.
  ----------------- ----------- ------------------------------------------

[]{.mark}

+-----------------+----------+-----------------------------------------+
| **Table 3. PRZM |          |                                         |
| 3.12 Crop       |          |                                         |
| Parameters for  |          |                                         |
| San Francisco   |          |                                         |
| -- impervious   |          |                                         |
| surfaces.**     |          |                                         |
+-----------------+----------+-----------------------------------------+
| **Parameter**   | *        | **Source/Comments**                     |
|                 | *Value** |                                         |
+-----------------+----------+-----------------------------------------+
| Initial Crop    | 1        | Default value                           |
| (INICRP)        |          |                                         |
+-----------------+----------+-----------------------------------------+
| Initial Surface | 1        | Scenario does not warrant crop          |
| Condition       |          | parameters. Set to 1 to allow PRZM to   |
|                 |          | execute.                                |
| (ISCOND)        |          |                                         |
+-----------------+----------+-----------------------------------------+
| Number of       | 1        | Scenario does not warrant modeling crop |
| Different Crops |          | cover. Set to 1 to allow PRZM to        |
| (NDC)           |          | execute.                                |
+-----------------+----------+-----------------------------------------+
| Number of       | 30       | Set to weather data in meteorological   |
| Cropping        |          | file: San Francisco, CA (W23234)        |
| Periods (NCPDS) |          |                                         |
+-----------------+----------+-----------------------------------------+
| Maximum         | 0        | No interception on impervious surfaces  |
| rainfall        |          | (Dunne and Leopold, 1978)               |
| interception    |          |                                         |
| storage of crop |          |                                         |
| (CINTCP)        |          |                                         |
+-----------------+----------+-----------------------------------------+
| Maximum Active  | 0 cm     | Crop parameters are not applicable to   |
| Root Depth      |          | this scenario.                          |
| (AMXDR)         |          |                                         |
+-----------------+----------+-----------------------------------------+
| Maximum Canopy  | 0        | Crop parameters are not applicable to   |
| Coverage        |          | this scenario.                          |
| (COVMAX)        |          |                                         |
+-----------------+----------+-----------------------------------------+
| Soil Surface    | 1        | Crop parameters are not applicable to   |
| Condition After |          | this scenario; however value was set to |
| Harvest (ICNAH) |          | 1 to allow PRZM to assign curve number. |
+-----------------+----------+-----------------------------------------+
| Date of Crop    | 1/1/61   | Crop parameters are not applicable to   |
| Emergence       |          | this scenario; however values were      |
|                 |          | assigned to prevent PRZM from crashing. |
| (EMD, EMM,      |          |                                         |
| IYREM)          |          |                                         |
+-----------------+----------+-----------------------------------------+
| Date of Crop    | 2/1/61   | Crop parameters are not applicable to   |
| Maturity        |          | this scenario; however values were      |
|                 |          | assigned to prevent PRZM from crashing. |
| (MAD, MAM,      |          |                                         |
| IYRMAT)         |          |                                         |
+-----------------+----------+-----------------------------------------+
| Date of Crop    | 31/12/61 | Crop parameters are not applicable to   |
| Harvest         |          | this scenario; however values were      |
|                 |          | assigned to prevent PRZM from crashing. |
| (HAD, HAM,      |          |                                         |
| IYRHAR)         |          |                                         |
+-----------------+----------+-----------------------------------------+
| Maximum Canopy  | 0        | Crop parameters are not applicable to   |
| Height (HTMAX)  |          | this scenario.                          |
+-----------------+----------+-----------------------------------------+
| Maximum Dry     | 0.0      | Crop parameters are not applicable to   |
| Weight (WFMAX)  |          | this scenario.                          |
+-----------------+----------+-----------------------------------------+
| SCS Curve       | 98, 98,  | TR-55 (Table 2-2a) CN for impervious    |
| Number (CN)     | 98       | areas (USDA 1986)                       |
+-----------------+----------+-----------------------------------------+
| Manning\'s N    | 0.011    | TR-55 (Table 3-1). Value for smooth     |
| Value (MNGN)    |          | surfaces (concrete, asphalt, gravel, or |
|                 |          | bare soil)                              |
+-----------------+----------+-----------------------------------------+
| USLE C Factor   | 0        | Set to zero. No cover and management    |
| (USLEC)         |          | fact or is applicable. Expected to      |
|                 |          | produce 100% less soil loss than a      |
|                 |          | similar continuously tilled area.       |
+-----------------+----------+-----------------------------------------+

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+---------+---------------------+-------------------------------------+
| **Table |                     |                                     |
| 4. PRZM |                     |                                     |
| 3.12    |                     |                                     |
| "Arti   |                     |                                     |
| ficial" |                     |                                     |
| Soil    |                     |                                     |
| Par     |                     |                                     |
| ameters |                     |                                     |
| for     |                     |                                     |
| Cal     |                     |                                     |
| ifornia |                     |                                     |
| --      |                     |                                     |
| imp     |                     |                                     |
| ervious |                     |                                     |
| surf    |                     |                                     |
| aces.** |                     |                                     |
+---------+---------------------+-------------------------------------+
| **Para  | **Value**           | **Source/Comments**                 |
| meter** |                     |                                     |
+---------+---------------------+-------------------------------------+
| Total   | 46 cm               | This scenario is intended to be     |
| Soil    |                     | coupled with the residential        |
| Depth   |                     | scenario. Scenario is manipulated   |
| (CORED) |                     | to simulate and impervious surface. |
|         |                     | Values were obtained from the       |
|         |                     | Barton Springs Endangered Species   |
|         |                     | Scenario, based on the              |
|         |                     | Brackett-Rock outcrop-complex,      |
|         |                     | Travis County, TX. Number range     |
|         |                     | CHAPTERNRCS Soil Data Mart Database |
|         |                     | (<ht                                |
|         |                     | tp://soildatamart.nrcs.usda.gov/>). |
|         |                     |                                     |
|         |                     | Additional data were listed for a   |
|         |                     | 4^th^ HORIZN. However, these were   |
|         |                     | not included in this soil profile   |
|         |                     | since the 4^th^ HORIZN is composed  |
|         |                     | of bedrock.                         |
|         |                     |                                     |
|         |                     | Set horizon 1 to high bulk density  |
|         |                     | to mimic impervious surface. The    |
|         |                     | actual density of asphalt is        |
|         |                     | actually quite low, around 1        |
|         |                     | (Conoco Philips MSDS) and the       |
|         |                     | density of concrete asphalt is 2.24 |
|         |                     | (http://ww                          |
|         |                     | w.simetric.co.uk/si_materials.htm). |
|         |                     | For this scenario, PRZM accepted BD |
|         |                     | as high as 1.9 before producing a   |
|         |                     | fatal error. []{.mark}              |
|         |                     |                                     |
|         |                     | Number range CHAPTERPRZM Scenario   |
|         |                     | Guidance (EPA 2004).                |
|         |                     |                                     |
|         |                     | THEFC for Horiz 1 is not            |
|         |                     | representative of impervious        |
|         |                     | surfaces, however PRZM requires     |
|         |                     | soil moisture content in Horiz 1 to |
|         |                     | allow partitioning of pesticide     |
|         |                     | into runoff water (Eq. 6-1, PRZM    |
|         |                     | Manual, EPA 1998).                  |
|         |                     |                                     |
|         |                     | THEWP for Horiz 1 set to THEFC to   |
|         |                     | prevent transpiration.              |
|         |                     |                                     |
|         |                     | Adjusted using the relationship %   |
|         |                     | OC = % Organic Matter/1.724         |
|         |                     | (Doucette 2000). Set to 0 in upper  |
|         |                     | horizon to mimic impervious         |
|         |                     | surface.                            |
+---------+---------------------+-------------------------------------+
| Number  | 3                   |                                     |
| of      |                     |                                     |
| H       |                     |                                     |
| orizons |                     |                                     |
| (       |                     |                                     |
| NHORIZ) |                     |                                     |
+---------+---------------------+-------------------------------------+
| Horizon | 10 cm (HORIZN =1)   |                                     |
| Th      |                     |                                     |
| ickness | 5 cm (HORIZN =2)    |                                     |
| (THKNS) |                     |                                     |
|         | 31 cm (HORIZN =3)   |                                     |
+---------+---------------------+-------------------------------------+
| Bulk    | 1.90 g/cm3 (HORIZN  |                                     |
| Density | =1)                 |                                     |
| (BD)    |                     |                                     |
|         | 1.40 g/cm3 (HORIZN  |                                     |
|         | =2)                 |                                     |
|         |                     |                                     |
|         | 1.43 g/cm3 (HORIZN  |                                     |
|         | =3)                 |                                     |
+---------+---------------------+-------------------------------------+
| Initial | 0.280 cm3/cm3       |                                     |
| Water   | (HORIZN =1)         |                                     |
| Content |                     |                                     |
| (THETO) | 0.280 cm3/cm3       |                                     |
|         | (HORIZN =2)         |                                     |
|         |                     |                                     |
|         | 0.252 cm3/cm3       |                                     |
|         | (HORIZN =3)         |                                     |
+---------+---------------------+-------------------------------------+
| Comp    | 0.1 cm (HORIZN = 1) |                                     |
| artment |                     |                                     |
| Th      | 5.0 cm (HORIZN = 2) |                                     |
| ickness |                     |                                     |
| (DPN)   | 1.0 cm (HORIZN = 3) |                                     |
+---------+---------------------+-------------------------------------+
| Field   | 0.280 cm3/cm3       |                                     |
| C       | (HORIZN =1)         |                                     |
| apacity |                     |                                     |
| (THEFC) | 0.280 cm3/cm3       |                                     |
|         | (HORIZN =2)         |                                     |
|         |                     |                                     |
|         | 0.252 cm3/cm3       |                                     |
|         | (HORIZN =3)         |                                     |
+---------+---------------------+-------------------------------------+
| Wilting | 0.280 cm3/cm3       |                                     |
| Point   | (HORIZN =1)         |                                     |
| (THEWP) |                     |                                     |
|         | 0.164 cm3/cm3       |                                     |
|         | (HORIZN =2)         |                                     |
|         |                     |                                     |
|         | 0.145 cm3/cm3       |                                     |
|         | (HORIZN =3)         |                                     |
+---------+---------------------+-------------------------------------+
| Organic | 0.00 % (HORIZN =1)  |                                     |
| Carbon  |                     |                                     |
| Content | 1.16 % (HORIZN =2)  |                                     |
| (OC)    |                     |                                     |
|         | 0.73 % (HORIZN =3)  |                                     |
+---------+---------------------+-------------------------------------+

[]{.mark}

[]{.mark}

[]{.mark}

[]{.mark}

**References**

Dunne, T., and L. Leopold. 1978. Water in Environmental Planning. W.H.
Freeman and Company, New York. 818 pp.

Number range CHAPTEREPA. 1998. Carsel, R.F., J.C. Imhoff, P.R. Hummel,
J.M. Cheplick, and A.S. Donigian, Jr. PRZM-3, A Model for Predicting
Pesticide and Nitrogen Fate in the Crop Root and Unsaturated Soil Zones:
Users Manual for Release 3.0. National Exposure Research Laboratory,
Office of Research and Development, U.S. Environmental Protection
Agency, Athens, GA.

EPA. 1999. Jones, R.D., J. Breithaupt, J. Carleton, L. Libelo, J. Lin,
R. Matzner, and R. Parker. Guidance for Use of the Index Reservoir in
Drinking Water Exposure Assessments. Environmental Fate and Effects
Division, Office of Pesticide Programs, U.S. Environmental Protection
Agency, Washington, DC.

Number range CHAPTEREPA. 2004. Pesticide Root Zone Model (PRZM) Field
and Orchard Crop Scenarios: Guidance for Selecting Field Crop and
Orchard Scenario Input Parameters. November 15, 2001; Revisions July
2004.

Haan, C.T. and B.J. Barfield. 1978. Hydrology and Sedimentology of
Surface Mined Lands. Office of Continuing Education and Extension,
College of Engineering, University of Kentucky, Lexington, Kentucky
40506. pp. 286.

NOAA. 2006. National Climatic Data Center. Climate Data Inventories --
Bakersfield, CA Station. Online at:
<http://www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwDI~StnSrch~StnID~10001177>.

USDA Soil Conservation Service. 1986. Urban Hydrology for Small
Watersheds. Technical Release 55, 2nd edition, June 1986.

USDA. 2006. Soil Survey Areas of the California Bay Area. U.S.
Department of Agriculture, Natural Resources Conservation Service
(NRCS), Soil Data Mart. March 1, 2006. Online at:
[http://soildatamart.nrcs.usda.gov](http://soildatamart.nrcs.usda.gov/).