USING ArcInfo TO COMPLY WITH NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM (NPDES) REGULATIONS

The first step in determining the zones was to establish a study areas. Study areas are polygons having common attributes which comprise the entire County and divide it into many parts. Each of these study areas are analyzed and rated for the three criteria (common attributes).

One could have formed study areas using townships or sections, however; parcels would be severed by the study area boundaries causing confusion in the final analyses when ascertaining which parcels belong to which zone. It was decided, therefore, that the study area boundaries should be derived from parcel lines.

In Riverside County, historically, the entire parcel layer was mapped by the Assessor's Office and placed in Assessor's Books. These Assessor's Books are stored in the Assessor's office for public record. The books consist of 11 by 17 inch pages and are about 3 inches thick on average. The area covered by an Assessor Book is contiguous.

The first three digits of the nine digit Assessor's Parcels Number (APN) indicates in which Assessor's Book the parcel can be found in. The nearly 7300 square miles in Riverside County are divided into 534 Assessor's Books. The books having more dense development cover a smaller area so the distinction of Assessors Book Boundaries is finer in the more urbanized areas. In the final analysis, it would take a table of only 534 records to determine which zone any parcel belongs to using the first three digits of the Assessor's Parcel Number. For these reasons the Assessor's Books were used as study areas.

The next step was to assign attributes in the Assessor's Book Coverage's PAT to store the values for population, parcels, and parcels with structures. The number of parcels and parcels with structures could be easily summed up with links to the assessor's database. Population values were a little harder to calculate. This method involved a polygon overlay with census block coverages. If a census block fell totally within an assessor's book polygon then the total population attributed to that block would be added to the population value of the Assessor's Book polygon. If a census block fell partially within an assessor's book polygon, then the ratio of that area, that fell within, over the total area of the census block would be multiplied times the population attributed to the census block and added to the population of the Assessor's Book. Once the totals for population, parcels, and parcels with structures were calculated in the Assessor's Book PAT, the Assessor's Book polygon area attribute was used to determine per-square mile statistics for the criteria. Statistics were run on population per square mile, parcels per square mile, and parcels with structures per square mile to determine minimums, maximums, means, averages, and totals. Using these statistics, cut-off values were established as such.

Any assessor's book which exceeded at least two of these categories would be considered a "more-urbanized" assessor's book and added to ZONE-A.

Next a study of the COST to service ZONE-A and ZONE-B was conducted. It was then necessary to summarize the total BAUS for each zone. (see formula for calculating BAUS mentioned previously.) Having the Total BAUS for each zone and knowing the COST to implement the program, the RATE was calculated with the previously mentioned formula.

Investigating Land Use Discrepancies

Although the Assessor assigns a land use designation to each new parcel created, in many cases, these values may have to be altered. For example, a parcel may be assigned an agriculture land use but since the owner has put up a fruit stand, the actual land use is commercial with regards to our assessment program.

Since we have a land use layer in one of our GIS libraries that concerns itself with "actual land use", as it was derived from areal photographs, we can draw this layer on the screen to help determine "actual land use" for the assessment, or we can perform polygon overlays, with background processes, to check new assessments for discrepancies between the "actual land use" and the land use assigned by the Assessor as part of an update to the Assessment Database.

Resolving Acreage Discrepancies

When a new Assessor's Parcel is created it's acreage, if available, is entered into the Assessor's database, which is linked to the GIS Parcel layer PAT by the Assessor's Parcel Number. (APN) Many times when Assessor's personnel enter the APN into the Assessor's Database, they do not have acreage information. Without a parcel's acreage it is impossible to determine the parcel's assessment. Since the parcel probably has been digitized into the GIS Parcel layer, the acreage information may be extracted from GIS, as part of the assessment database update process, while producing a report.

In many cases some of the area of a parcel may be actually undeveloped land, although the entire area of the parcel is classified by a land use code which generates BAUS. For some of the higher rated land use codes ( for example commercial codes ) undeveloped land may create a large unfair assessment. The Landuse Layer may give a good idea of how much a parcel's acreage is actually developed when intersected with the Parcel Layer.

Screening Unusually High Assessments

When calculating NPDES assessments an exception report is printed out for any assessment over 100 BAUS ( 100 times the RATE ). These exceptions are investigated. In many cases, new assessments may have to be equalized or given an alternative acreage or land use designation in the NPDES Assessment Database.

The Override NPDES Database

When assessments are unfair using assessor's land use or acreage data, override data elements are created in the exception data fields. Of course the actual Assessor's data is never altered. Therefore the Override Database continues to grow as parcels are reviewed because of exception reports, or inquires from the public. In all cases, if override data exists, it is used in the assessment calculation.

DETERMINING STREET SWEEPING ROUTES

Street sweeping is considered a Best Management Practice (BMP) towards compliance with the NPDES regulations. Many pollutants that wind up in our storm-drains can be found on the street, deposited by automobiles or dumped by residents of the neighborhood.

Considering limited fiscal resources, the task of determining which, of the thousands of streets, will be swept, is made possible by our Street Sweeping GIS application.

Structuring the Database

The following three factors were determined to be relevant in selecting prime street sweep candidates:

Certain land use codes, for example High Density Single Family Residential or Commercial Strip Development, are considered high priority land use's when selecting candidates for street sweeping.

The Riverside County GIS Land Use Layer has 129 unique land use classifications connected to the Landuse PAT related by a landuse code. Of these 129, we determined 58 to be the landuse types through which street primary sweeping candidates pass. An info key-file was created for selecting these land use codes by copying the Landuse Look-up Table and purging the unwanted records.

The road Centerline Layer in our GIS classifies our roads in terms of surface type, whether the road is owned by or maintained by the County, and the General Plan type. Selection key-files were created in the same way, as mentioned previously, with landuse designations. County maintained paved roads were (for example) the primary target for street sweeping in this regard. Of the 30 centerline classifications we have, 9 of them were used in our selection key-file.

The County maintains a separate database as part of the Pavement Management System, that may be linked to the GIS Centerline Layer AAT by a road number. The road number historically was created for record keeping including maintenance and cost accounting. This database allows us to determine whether a road has curb and gutter on one or both sides.

Next an identity is performed on the Centerline layer using the Land Use Layer as the identity coverage thereby adding land use attributes to the arc attributes of a county wide street sweeping coverage.

Establishing Selection Criteria

Now, having a county wide line coverage with attributes for the three criteria previously mentioned, and having created the info selection files identifying the attributes of the prime candidates, we are able to select arcs for street sweeping in Arcplot using the Reselect command with the Key- file option.

Creating Street Sweeping Zones

Obviously when selecting Road Candidates for street sweeping on a county wide basis (Riverside County is about 7300 square miles) you are attempting to create several different street sweeping routes, rather than one route.

When you select streets based on the previously mentioned criteria, you will have many different fragments of streets somewhat connected but more so connected in areas of dense development.

We will now want to form street sweeping zones which determine where a route will be created. When we created our street sweeping route study areas, we decided that if a street sweep candidate (SSP) fell within 1/2 mile of another SSP, the two candidates should be considered part of the same route. In other words, we are not willing to drive more than 1/2 miles over streets we do not target for sweeping to get to a street we target. In resolution, we buffered 1/4 mile (1320 feet) around our "prime targets" as the first step in creating our street sweep zones within which we created our routes.

This created a number of polygons greatly varying in area. The smaller polygons were zones where few "candidates" were in proximity to each other and the larger polygons indicated areas where many candidates were in proximity to each other. Using summary statistics, knowing the per-mile cost of street sweeping, we were able to estimate how much it would cost to implement street sweeping in each zone. Our intent is to implement street sweeping in as many of the largest zones as possible within budget limitations.

Adding Links

After selecting a zone, for implementation of the Street Sweeping Program, a refined study was made using GIS. A menu driven application was developed that enabled the analyst to add to or remove streets as candidates, interactively, for any zone, in an effort to create logical connected routes. The user is able to query all the attributes of any arc, or set of arcs, and generate statistics about landuse, surface type, mileage, and costs, while viewing the arcs graphically with various geographic features in the background. Finally, one may generate a statistical report accompanied with maps of each of many alternative routes. Finally, upon selecting an alternative, the maps and reports are used in the bidding process by various street sweeping services companies.

Funding

A GIS application is now being developed, for the County of Riverside, to determine those parcels which are benefited directly by street sweeping. The application will not only determine which parcels lie adjacent to a route, but also will calculate an assessment based on cost per-mile to sweep and the amount of frontage attributed to the parcel.

With the Parcel layer linked to the Assessor's database, tax assessments will be automatically generated and forwarded to the Auditor/Controller's Office to be added to the property tax bill.

THE STORM-DRAIN INVENTORY

NPDES regulations state specifically that an inventory of the Storm Drain System be created and maintained. We have chosen to create this inventory as a layer in our GIS library.

We also will produce the Storm Drain Facilities and Drainage Easement Map Book, as part of our compliance to these regulations. The Stormdrain layer is a line coverage with line and node attributes and the Drainage Easement layer is a polygon coverage with polygon attributes.

Stormdrain Line Attributes

SD-NUMBER is used by the County for accounting and maintenance history tracking purposes by the field crews. If there is a maintained road associated with the stormdrain line, then this field will be the same as the maintained road number.

WIDTH is width of the facility in inches. If the facility is a pipe (round) the width will be the diameter. If the width of the facility varies, then the average width will be the WIDTH.

DEPTH is the depth of the facility in inches, from the top, to the bottom. The depth is not measured from the surface of the ground to the top or bottom of the facility. If the facility is a pipe (round) the DEPTH will be the diameter. If the depth of the facility varies, then the average depth will be the DEPTH.

TYPE is the major classification of the facility distinguished by a code that relates to an info file that provides a symbol and a description in cross reference. This field is redefined into two categories, P-TYPE and R-TYPE.

CONTACT This field holds an associated record number to a related CONTACTS file. The CONTACTS file contains information concerning 'who to contact' for maintenance, access permission, reporting of emergencies, pre-excavation information (etc).

PLAN-NUMBER The improvement plan (design) file number as provided by the Survey Department.

P-TYPE The physical classification of the utility, or what type of construction it is. This code references a description in a related file having the following classifications:

R-TYPE The legal implications of responsibility and use. This code references a description in the related file having the following classifications:

Stormdrain Node Attributes

TYPE The type of in-line structure for the stormdrain layer. Each code is linked to a description and symbol in a related file. The descriptions are as follows:

CONTACT This field holds an associated record number to a related CONTACTS file.

FL-ELEVATION The elevation at the position of the node on the flow line of the storm drain utility.

GR-ELEVATION The elevation at ground level above the position of the node.

Drainage Easements Polygon Attributes

DATE-RECORDED The recordation date of the instrument or map that created the easement.

REFERENCE A reference to the document that created the easement.

Illicit Discharges

NPDES regulations state that illicit discharges should be tracked and action should be taken to legalize them. Our NPDES Stormdrain layer will allow us to locate and track proceedings against illicit discharges through our stormdrain maintenance record tracking system.

Pollutant tracing

Each stormdrain line is created or edited to have a direction of flow. (The to node is always downstream). In the future we will test water quality at sampling stations along the stormdrain. A sampling station test result file will be linked to the stormdrain node attribute table.

Our Parcel Layer Polygon Attribute Table will be linked to a Standard Industrial Code (SIC) Table by Assessor's Parcel Number. This table will indicate what types of industrial activities, take place on the parcel. Another table which associates pollutants with the (SIC) code will be created and linked to the SIC Table by SIC-CODE.

The Stormdrain nodes will be linked to the Parcel Layer Polygon Attribute Table by performing an identity process. Stormdrain nodes will also be related by Assessor's Parcel Number.

When a contamination is identified at any of the sampling stations, a tracing program will be executed which searches upstream, following a pattern of from-nodes and to-nodes, identifying all parcels of land which exist upstream from the sampling station that detected the pollutant. The parcels with SIC codes that are linked to the pollutant will be highlighted and listed in an exception report.

Contact Agencies

It has been determined that in the event of an emergency, for example, a broken or clogged storm drain line, when the County is reached one may locate a storm drain facility by an address, or by a parcel owner's name, or any other feature(s) in the GIS. The user may then point to the stormdrain and obtain the organization, phone number, and person responsible for the maintenance of the facility.

CONCLUSION

After the EPA had determined that non-point (from urban storm water run-off) pollution contributes as much pollutants as point source (industrial discharges), to our nations waterways, the Clean Water Act was amended to include non-point source pollutant controls. This amendment has been reviewed and interpreted by the EPA, who has published the NPDES regulations.

In following these regulations, Riverside County has made use of its GIS in several different aspects. Riverside County has piloted a GIS storm drain inventory and drainage easement layer. We believe these layers will prove to be much more effective than conventional tabular inventory systems as they will be used to create the Storm Drain and Drainage Easement Map Book. Furthermore, upstream contaminant tracing and hydrological flow modeling will be possible using these layers.

We have also been generating NPDES tax assessments to fund our program with our GIS. We have created and maintained assessment rate areas based on geographic "urbanization" criteria to more closely relate those assessed to those benefited. We have used our GIS to research and uncover assessments that need to be more closely examined and equalized.

Realizing that street sweeping is an important BMP to implement, we have, using our GIS, determined street sweeping routes while targeting county maintained roads having certain landuse, pavement type, and design characteristics to make the best use of the limited money available for street sweeping.